CN116914822A

CN116914822A - Multi-port converter circuit, device and control method for new energy storage integration grid connection

Info

Publication number: CN116914822A
Application number: CN202310747034.6A
Authority: CN
Inventors: 郭焕
Original assignee: Jinan University
Current assignee: Jinan University
Priority date: 2023-06-21
Filing date: 2023-06-21
Publication date: 2023-10-20
Anticipated expiration: 2043-06-21
Also published as: WO2024148889A1

Abstract

The invention provides a multiport converter circuit, a multiport converter device and a multiport converter control method for new energy storage integration grid connection, which comprise the following steps: at least 2 AC/DC converting units and at least 1 multi-winding transformer, wherein the 2 AC/DC converting units are connected in series at the DC side and then lead out 3 DC terminals, and a DC bus is connected with a distributed power generation device and a DC load; the multi-winding transformer leads out an alternating current terminal connected with the alternating current side of each converter unit and an alternating current port connected with an alternating current power grid; the three-port converter circuit comprises a lever effect of power conversion, multiplexing of devices of a 2 nd converter unit and direct conversion between alternating current and direct current ports; a multi-port current transformation circuit is formed by connecting one or more current transformation units in series on the direct current side based on the three-port current transformation circuit. The invention carries out the optimal design and configuration of key parameters based on the three-port or multi-port topology, thereby obviously reducing the cost of the converter and improving the conversion efficiency.

Description

Multi-port converter circuit, device and control method for new energy storage integration grid connection

Technical Field

The invention relates to the field of power transmission and distribution of power systems, in particular to a multi-port converter circuit, a device and a control method for new energy storage integration grid connection.

Background

In order to respond to the demands of global environment protection and low-carbon energy construction, more and more new energy sources are developed and applied, such as photovoltaics, wind power and the like. However, since the new energy power generation has the characteristics of randomness and intermittence, the peak valley of the power consumption in each field is inconsistent with the fluctuation power generation of the new energy, which will affect and impact the stable operation of the power system. The energy storage can relieve the influence of the intermittence and randomness of the new energy power generation on the power grid, relieve the unsynchronized characteristic of the new energy power generation and the power grid load demand, and utilize the peak clipping and valley filling, thereby ensuring the safety of the power grid, and improving the economic benefit of the power utilization side, so that the energy storage system has more value in the distribution of the distributed new energy.

Referring to fig. 1, the current new energy and energy storage grid-connected device generally adopts a two-stage cascade structure, and a photovoltaic, energy storage and direct current load is connected with a direct current bus and grid connection is realized through a grid-connected converter. The novel energy sources such as photovoltaic and the like are connected with a direct current bus through a DC/DC boost converter, and maximum power tracking is realized through the DC/DC boost converter, so that electric energy is output as much as possible. The energy storage is connected with the direct current bus through the bidirectional DC/DC converter, when new energy is full, the inexhaustible surplus power is stored, and when wind lack and light lack occur, the surplus power is released to meet the load, so that the fluctuation and randomness of the interactive power of the distributed power supply and the power grid are reduced.

However, at present, there are several aspects of new energy sources and energy storage grid-connected devices that can be optimized: firstly, the existing two-stage cascade structure can meet grid-connected requirements only by adopting a plurality of converters, and the converters are arranged among energy storage equipment, photovoltaic equipment and a direct current bus, so that the capacity of a converter device is large; secondly, the conversion efficiency between the existing energy storage equipment and the power grid and the DC bus is lower, so that the total loss of the device is higher, and the total efficiency is lower; the existing new energy and energy storage grid-connected device mainly adopts a two-stage cascade structure, indirect conversion is performed between a first-stage initial end port and a second-stage final end port, direct conversion between three ports cannot be realized, and flexible switching of an operation mode and functions is difficult to realize; fourth, the traditional devices such as each DC/DC converter, the AC/DC grid-connected converter, the transformer and the like rely on communication equipment to exchange data, the communication equipment among the distributed devices has higher cost and lower reliability, and an integrated multiport converter device capable of reducing the distributed communication dependence and cost is necessary to be designed.

Disclosure of Invention

The multi-port converter circuit, the device and the control method for the new energy storage integration grid connection are mainly used for solving the problems that the device and the unit capacity of the existing converter are large, the cost reduction of the grid connection device is not facilitated, the conversion efficiency is low, the flexible switching of the operation modes/functions cannot be realized, the converters are relatively dependent on communication equipment, and the like, so that the capacity and the cost of the converters are remarkably reduced, the conversion efficiency is improved, the flexible switching of the diversified operation modes is realized, and the communication requirements and the cost between the traditional DC/DC converters, the AC/DC grid connection converters and the equal-distributed equipment of the transformer are reduced.

The invention realizes the above purpose through the following technical scheme:

the multi-port converter circuit for integrating new energy storage and grid connection comprises at least one AC/DC converter unit and at least one multi-winding transformer, wherein three DC terminals are led out after the AC/DC converter units are connected in series on the DC side, the three DC terminals are a common terminal and two non-common DC terminals, the common terminal is the DC terminal with the lowest or highest potential, and the common terminal and the two non-common DC terminals form two DC ports with independent regulation and control functions through combination of two by two; the high potential current converting unit is a 1 st current converting unit, a 1 st direct current port of an external direct current bus is formed by a non-common terminal and the common terminal of the 1 st current converting unit, and the direct current bus is connected with a distributed power generation device and a direct current load; the lower potential current converting unit is a 2 nd current converting unit, and a non-public terminal and a public terminal of the 2 nd current converting unit form a 2 nd direct current port of an external energy storage device; the multi-winding transformer leads out an alternating current terminal connected with the alternating current side of each current converting unit and an alternating current port connected with an alternating current power grid to form a three-port current converting circuit with two direct current ports and one alternating current port.

The three-port converter circuit comprises a lever effect of power conversion, multiplexing of devices of a 2 nd converter unit and direct conversion between alternating current and direct current ports.

The three-port current converting circuit is further expanded to a plurality of current converting units which are connected in series on the direct current side to form the multi-port current converting circuit.

The three-port converter circuit and the multi-port converter circuit are suitable for integration grid connection of new energy and energy storage and a single-phase or three-phase alternating current system. When integrated with a single-phase alternating current system, the current converting unit adopts a single-phase direct current-alternating current circuit, and the multi-winding transformer adopts a single-phase multi-winding transformer; if the three-phase alternating current system is integrated with the grid connection, the current transformation unit adopts a three-phase direct current-alternating current transformation unit, and the multi-winding transformer adopts a three-phase multi-winding transformer.

The multi-winding transformer may be an integrated multi-winding transformer structure including a plurality of windings, or a distributed multi-winding transformer structure including a plurality of double-winding transformers.

Therefore, when the conversion power of the 2 nd converter unit is zero, the conversion power from the 1 st direct current port to the 2 nd direct current port and the alternating current port is larger than the actual power of the 1 st converter unit, so that the lever effect of completing the power conversion of the larger port by using the smaller power converter circuit is realized, the capacity of the required converter unit is reduced, the cost and the loss are reduced, and the efficiency is improved.

Therefore, the device multiplexing of the 2 nd converter unit included in the multi-port converter circuit is realized, the 2 nd converter unit is applied to the power conversion of the 1 st direct current port and the 2 nd direct current port, and can be used for the alternating current-direct current conversion between the port 2 and the alternating current port and the alternating current-direct current conversion between the port 1 and the alternating current port, and the power transmission directions of the port 1 and the port 2 are generally opposite, so that a part of equipment capacity can be saved, the equipment cost can be reduced, and the power density can be improved.

Therefore, the multi-port converter circuit comprises the alternating current/direct current ports, and the direct conversion between any two ports of the 1 st direct current port (direct current bus port), the 2 nd direct current port (energy storage port) and the alternating current port can be realized through the topology circuit, so that the conversion efficiency is improved; in addition, the conversion power of the third port can be further increased by the conversion capability of the second port, and the direct conversion is realized by a primary converter circuit (generally a converter unit such as a bridge circuit).

Therefore, the invention can simultaneously access the DC buses and the energy storage devices with different voltage grades by connecting the plurality of current converting units with the plurality of primary windings of the multi-winding transformer and expanding the DC ports of the current converting circuit through series connection, the energy storage devices realize independent grid connection control, the electric energy is converted among the DC buses, the energy storage devices and the AC side, the functions of converting alternating current into direct current and converting direct current into direct current are realized, the capacity of the current converting circuit is obviously reduced, and the capacity of the device is only equivalent to that of the grid-connected current converter with the current two-stage cascade structure according to the design method, thereby saving the energy storage DC/DC current converting units and greatly reducing the cost of the integrated grid-connected device.

The three-port converter circuit is based on the 1 st DC port rated voltage V _d1N Rated voltage V of 2 nd DC port _d2N The rated voltage V of the direct current side of the 1 st current converting unit and the 2 nd current converting unit can be obtained _u1N 、V _u2N The method comprises the following steps of:

determining rated voltage of each winding of the multi-winding transformer according to rated voltage of a direct current side and alternating current port voltage; determining the power of the converter unit according to the transmission power of the port, and according to the formula:

wherein P is _d1 、P _d2 Input power of direct current bus port and energy storage port respectively, P _u1 、P _u2 The direct-current side input power of the 1 st current converting unit and the 2 nd current converting unit respectively, V _u1 、V _u2 Direct-current side voltages of the 1 st current converting unit and the 2 nd current converting unit respectively, V _d1 、V _d2 The direct current bus port voltage and the energy storage port voltage are respectively.

The multiport converter circuit has three converter modes, including a direct current-to-alternating current (or alternating current-to-direct current) converter mode, a direct current-to-direct current direct converter mode and a direct current-to-direct current indirect converter mode; the working range of a current converting unit based on the three current converting modes three-port current converting circuit is divided into 8 sections; the power of each converter unit is obtained according to the formula (4) according to the power requirement of each port, and the three-port converter circuit can flexibly operate in the combination of different converter modes and different working intervals formed by the combination.

Wherein the DC-to-AC (or AC-to-DC) conversion mode is one or two of the power conversion between the DC ports and the AC ports, when the output power P of the AC ports _ac When the value is greater than 0, electric energy flows into the alternating current port from the direct current port; otherwise, electrical energy flows from the ac port to the dc port.

The direct conversion between two direct current ports is realized based on direct current coupling power exchange formed by direct current side series connection in the direct current-direct current conversion mode.

The direct current and direct current indirect conversion mode is based on direct current-to-alternating current conversion and alternating current-to-direct current conversion functions of the conversion unit, and combines power exchange of electromagnetic coupling of a transformer to realize indirect conversion between two direct current ports.

The three conversion modes, wherein the DC-AC conversion power is the AC port output power P _ac The method comprises the steps of carrying out a first treatment on the surface of the For the three-port converter circuit, when the input power directions of the 1 st direct current port and the 2 nd direct current port are consistent, the direct current-direct current direct conversion power and the direct current-direct current indirect conversion power are both zero; when the input power directions of the 1 st DC port and the 2 nd DC port are inconsistent, the direct conversion power P is converted from DC to DC _DD1 Direct current-to-direct current indirect conversion power P _DD1 Total power of DC-DC conversionP _DD The calculation can be performed as follows:

wherein P is _d1 For DC bus port power, P _u1 、P _u2 The direct current side input power of the 2 nd current converting unit and the direct current side input power of the 2 nd current converting unit are respectively, wherein:

working interval 1 electric energy flows in from the 1 st direct current port and flows out from the other two ports, wherein the power P is converted _DD1 And P _DD2 Are all greater than zero; in the working range 2, electric energy flows in from the 1 st direct current port and flows out from the other two ports, wherein the power P is converted _DD1 Greater than zero, P _DD2 Equal to zero; in the working space 3, the electric energy flows in from the 2 nd direct current port and flows out from the other two ports, wherein the power P is converted _DD1 And P _DD2 Are all less than zero; working interval 4 power flows from the ac port to two dc ports, P _DD1 And P _DD2 Are all equal to zero; the current and power flow paths in the working intervals 5, 6, 7, 8 are the same as the current and power flow paths in the working intervals 1, 2, 3, 4, respectively, but in opposite directions; four boundary lines, P, exist in the 8 working areas _u2 ＝-P _u1 Is the 1 st boundary line, P _u2 ＝P _u1 V _u2 /V _u1 For the 2 nd boundary line, P _u1 =0 is the third boundary line, P _u2 =0 is the fourth boundary line; wherein V is _u1 、V _u2 The direct-current side voltages of the 1 st and the 2 nd converter units are respectively.

When the converter circuit operates on the fourth boundary line, the port of the DC bus is switched to the AC port and the energy storage port according to k _V1 ∶(1-k _V1 ) Where k is the ratio of the power delivered _V1 For the 1 st variable current cell voltage V _u1 And the 1 st DC port voltage V _d1 Ratio of (a) and0<k _V1 <1, a step of; at the moment, the total power of the converter unit is P _u1 Multiport conversion power to P _d1 ＝P _u1 V _d1 /V _u1 ＝P _u1 /k _V1 >P _u1 The method comprises the steps of carrying out a first treatment on the surface of the And the power transmission between the ports is realized through the total power of the smaller converter units, so that the power conversion lever effect is realized.

At this time, the conversion efficiency η _b1 The method comprises the following steps:

η _b1 ＝1-k _V1 (1-η ₁ )-P _st /P _d1 (5)

wherein 0 is<k _V1 <1，P _st For the loss power, P, of the multi-winding transformer _d1 For the input power of the DC bus port, eta ₁ For the current transformation efficiency of the 1 st current transformation unit, due to the lever effect, when the transformer loss is not considered, the conveying efficiency of the multi-port current transformation circuit is higher than that of a single current transformation unit, the operation on the fourth boundary line is the optimal operation mode, and the obtained efficiency is the highest.

Further, in the operation process, the lowest voltage and the highest voltage of the 1 st direct current port are respectively V _d1min And V _d1max The lowest and highest operation voltages of the 2 nd DC port in the energy storage charging and discharging process are V respectively _d2min And V _d2max The lowest and highest dc operating voltages of the 1 st current converting unit are:

The conditions that the direct current side voltage of each converter unit stably operates within the allowable variation range are as follows:

wherein V is _ac1max 、V _ac2max The maximum value of the reasonable change range of the alternating current side line voltage of the 1 st current converting unit and the 2 nd current converting unit respectively,k _r margin coefficients for keeping stable operation of the converter unit are provided; v (V) _u1min For the lowest DC operating voltage of the 1 st current converting unit, V _d2min Is the lowest operating voltage of the energy storage port, and has:

wherein k is _T1 ，k _T2 V is the voltage ratio between the windings connected with the 1 st current converting unit and the 2 nd current converting unit and the network side winding respectively _acmax The maximum value of the reasonable variation range of the wire voltage of the winding at the wire side of the network;

the method can obtain:

by setting the higher voltage of the energy storage port, k is made _V1 The power is reduced, so that the lever effect is enhanced, and the conversion power and efficiency are improved; the energy storage port is charged and discharged to cause voltage change, and the minimum and maximum values of the port voltage are required to meet the formula (6-3); and high-efficiency operation is realized through matching of the direct-current side voltage and the alternating-current side voltage of the current converting unit in a reasonable variation range.

Further, the method is as follows:

wherein:

P _u1N 、P _u2N rated input power of direct current side of 1 st current converting unit and 2 nd current converting unit respectively, V _u1N 、V _u2N The rated voltage of the direct current side of the 1 st current converting unit and the rated voltage of the direct current side of the 2 nd current converting unit are respectively.

The maximum transmission power of the alternating current and direct current ports of the three-port converter circuit can be determined according to the formulas (4) and (5).

The maximum power of the 1 st direct current port, the 2 nd direct current port and the alternating current port is as follows:

the maximum power P of the 1 st direct current port _d1max Maximum power P of 2 nd DC port _d2max Maximum power P of ac port _acmax The condition of (1) being equal to or greater than its target value is:

thereby:

wherein P is _uN ＝P _u1N +P _u2N Superscript "×" denotes a design target value; and (3) designing rated power of the converter unit according to the formula (9), wherein the maximum transmission power of each port is greater than or equal to the design target value.

When the three-port converter cell power satisfies:

wherein The Suffix (TSC) represents a two-stage cascade structure (Two Stage Configuration), P _acmax ^(TSC) 、P _d1max ^(TSC) P and P _u1N ^(TSC) The maximum output power of the alternating current port, the maximum input power of the direct current bus port and the direct current side rated power of the 1 st converter unit of the two-stage cascade structure are respectively.

And (3) carrying out rated power design of the current converting unit according to the formula (9-1), wherein when the maximum transmission power of each port of the proposed topology is greater than or equal to the port power of the corresponding two-stage cascade structure, the total current converting unit capacity is only the capacity of the grid-connected current converting unit in the corresponding two-stage cascade structure, so that the energy storage DC-DC current converting unit is saved, and the cost is reduced.

Therefore, under the condition that the maximum output power of the alternating current and direct current ports is not smaller than the maximum power of the ports corresponding to the common two-stage cascade structure current converting device (namely, the cascade topology structure of the DC/DC converter and the grid-connected DC/AC converter), the total capacity of the three-port current converting unit is only the capacity of the 1 st current converting unit in the common two-stage cascade structure, so that the DC/DC converter in the two-stage cascade structure is saved, and the cost is obviously reduced.

Neglecting converter circuit losses, the maximum switching power between the ports of the three-port converter circuit:

wherein P is _12max For the maximum exchange power between the 1 st DC port and the 2 nd DC port, P _13max For maximum switching power between the 1 st DC port and the AC port (3 rd port), P _23max Is the maximum switching power between the 2 nd dc port and the ac port (3 rd port).

The condition that the maximum transmission power between the 1 st direct current port, the 2 nd direct current port and the alternating current port (3 rd port) is equal to or more than a target value is as follows:

k _V1 P _12max ^* /P _uN ≤P _u1N /P _uN ≤min[1-(1-k _V1 )P _13max ^* /P _uN ,1-P _23max ^* /P _uN ] (11)

the conditions that the maximum power of the ports and the maximum exchange power between the ports of the three-port converter circuit are larger than the target values according to the formulas (9) and (11) are as follows:

if the maximum exchange power between the two ports is unconditionally limited, the target value is zero, and the power calculation of each converter unit is carried out according to formulas (10) - (12), and the transmission power between the ports is greater than or equal to the design target value.

The multiport converter of new forms of energy storage integration grid-connected includes: the novel energy storage integrated grid-connected multi-port current converting circuit comprises a sampling module, a main control module and the novel energy storage integrated grid-connected multi-port current converting circuit, wherein the sampling module is used for respectively collecting three-phase/single-phase alternating current, three-phase/single-phase alternating voltage signals, direct-current side voltage and current signals and temperature signals and outputting sampling signals to the main control module, the main control module performs algorithm analysis according to the sampling signals and outputs PWM modulation wave signals to the multi-port current converting circuit, a direct-current bus port of the multi-port current converting circuit is connected with a direct-current bus, an energy storage port of the multi-port current converting circuit is connected with an energy storage device, an alternating-current port of the multi-port current converting circuit outputs alternating current, and the multi-port current converting circuit controls a switching device to be switched on or off according to the PWM modulation wave signals so that electric energy is converted among the direct-current bus, the energy storage device and the alternating-current side.

The main control module comprises a DSP, a PWM module and a communication module, wherein the DSP outputs PWM modulated wave signals to the multi-port converter circuit through the PWM module, and the DSP establishes communication with the power grid dispatching system through the communication module to exchange data.

Therefore, the multi-port structure of the converter device can be simultaneously connected with the direct current bus, the energy storage device and the alternating current side load, and centralized regulation and control of electric energy conversion are realized through the main control module of the converter device, so that the requirements of communication equipment among the traditional DC/DC converters, the alternating current-direct current grid-connected converters, transformers and other equipment are reduced, and the problems that the electromagnetic field of the converter device affects the communication line and protects the communication line are complicated in consideration of the strong electric line are avoided while the cost is reduced.

Therefore, the invention establishes communication with the power grid dispatching system through the communication module of the converter device, thereby being beneficial to the exchange of new energy, energy storage and power grid prediction and measurement information and the remote control and management of system integration.

The multi-port converter device supports two operation modes of grid connection and grid disconnection, is connected with an alternating current power grid in grid connection operation, can be matched with a power grid dispatching system, controls the energy storage device to participate in voltage regulation and frequency modulation of the power grid, and realizes peak clipping and valley filling of power grid load through charging/discharging; in off-grid operation, the multi-port converter device is disconnected from the alternating current power grid and operates in a direct current micro-grid mode, and the multi-port converter device controls the energy storage device to charge and discharge so as to realize continuous power supply to direct current load or (and) alternating current load.

In the grid-connected operation, if the energy storage device is cut off or the energy storage device is not installed, the 2 nd converter unit can be controlled to operate in a constant direct-current voltage mode, and the grid-connected operation of the new energy power generation device and a direct-current bus connected with the new energy power generation device is realized.

Therefore, the multi-port converter device can realize flexible switching of operation modes, can select whether an energy storage device is needed to be connected or not, and can work in an AC-DC conversion mode if the energy storage device is not externally connected, so that a new energy source and a grid-connected operation mode of a direct current bus connected with the new energy source are realized; if the energy storage device is externally connected, the novel energy storage device has the functions of AC-DC and DC-DC conversion, and flexible power conversion among three ports of a new energy source, a direct current bus, energy storage and an alternating current network connected with the novel energy source is realized.

The multi-port converter device can be used for a single-phase circuit and a three-phase circuit; when the single-phase power supply is used for a single-phase circuit, the current converting unit and the transformer respectively adopt a single-phase current converting unit and a single-phase transformer; when the three-phase current transformer is used for a three-phase circuit, the current transforming unit and the transformer can be a single-phase current transforming unit and a single-phase transformer respectively, and can also be a three-phase current transforming unit and a three-phase transformer respectively; the three-phase integrated converter circuit formed based on the single-phase converter unit and the single-phase transformer is equivalent to the superposition application of three groups of single-phase integrated converter circuits, so that more energy storage devices can be accessed; the three-phase integrated converter circuit formed by the three-phase converter unit and the single-phase transformer can be connected and combined into a three-phase transformer through three groups of single-phase transformers.

Under the condition of wider voltage change range of an energy storage port or a direct current port, the transformer can be loaded with an on-load tap-changer, so that higher modulation ratio and conversion efficiency are maintained, the voltage change of each winding of the transformer in a reasonable range is ensured, and the high-efficiency stable operation of the multi-port converter is ensured.

The multi-port converter device can be provided with a plurality of direct current bus ports and a plurality of energy storage ports, wherein the plurality of direct current bus ports are used for being connected with multiple paths of direct current buses with different voltage levels so as to match the voltages of different new energy power generation devices and direct current loads, and the plurality of energy storage ports are used for being connected with multiple energy storage devices with different capacities and voltage levels so as to match the direct currents with different voltage levels and output alternating currents with multiple paths of frequencies and different voltages.

Therefore, the ports of the multi-port converter device can be flexibly combined according to actual needs, and the multi-port converter device can be suitable for different power transmission and distribution occasions.

The multi-port current transformation control method for the new energy storage integration grid connection is applied to the multi-port current transformation device for the new energy storage integration grid connection, and comprises the following steps:

s1: establishing conversion relation between alternating current and direct current port current and power and current and power of a conversion unit;

S2: determining a maximum power target value of the ports, and if necessary, considering the maximum transmission power target value among the ports, and completing the rated power design of the converter unit according to the conversion relation between the alternating current and direct current port currents and the power, the current and the power of the converter unit, wherein the rated power design meets the requirements of the maximum power target value of the ports and the maximum transmission power target value among the ports;

s3: establishing a current, power or voltage control strategy of a direct current port and an alternating current port, and determining a corresponding control strategy and a control method of the current converting unit according to the conversion relation between the current and power of the alternating current port and the direct current port and the current and power of the current converting unit;

s4: setting priority of port current, voltage and power control, and sequentially meeting the control requirements of all ports from high to low according to the priority;

s6: according to the control priority of the AC and DC ports and the reference value of the controlled quantity, the control method is combined with the control method of the converter unit, and the controlled quantity reference value of each port and the converter unit is calculated and defined for control;

s7: and according to the controlled quantity reference values of each port and each converter unit, referring to an optimal operation mode, combining new energy power generation and load prediction, moderately optimizing the controlled quantity, and performing efficient optimized operation control and management.

Therefore, the invention can further realize current, power control and direct-current voltage control of the diversification of the direct-current ports through the current transformer by establishing the electrical parameter transformation relation between each alternating-current and direct-current port and the current transformer, can further form a current transformation expansion circuit with different connection relations based on different direct-current port control and different alternating-current port control strategies, improves the applicability of the current transformer, and realizes the efficient and stable operation of the current transformer under different control strategies by setting the priority of the current, voltage and power control of the ports.

Further, according to formula (2):

the conversion power of the 2 nd converter unit is V of the input power of the direct current port _d2 /V _d1 The sum of the multiple and the input power of the energy storage port, if the alternating voltage vector is positioned on the D axis by adopting vector control based on synchronous coordinates by the current converting unit

Wherein R is ₁ 、R ₂ Equivalent resistances of the 1 st current converting unit and the 2 nd current converting unit respectively, neglecting losses of the current converting units, and enabling the D-axis active current I of the 1 st current converting unit _D1 Active current I of D axis of 2 nd converter unit _D2 The method comprises the following steps:

wherein V is _D1 For the 1 st current converting unit D axis voltage, V _D2 For the D-axis voltage of the 2 nd current converting unit, V _d1 、V _d2 The 1 st DC port voltage and the 2 nd DC port voltage, I _D21 、I _D22 The D-axis current of the 2 nd converter unit corresponding to the 1 st direct current port and the 2 nd direct current port is input respectively;

the transfer functions of constant current control, constant power control or constant direct current voltage control of two direct current ports can be established on the basis of formulas (12-1) - (13);

when the control strategy is to control the ith direct current port (i is 1or 2) and the alternating current port, the controlled reference quantity of the other direct current port can be expressed as the corresponding controlled reference quantity of the alternating current port and the ith direct current port, and the corresponding control is performed; taking power control as an example, the reference power of another dc port (i.e., kth dc port) is:

P _dk ^* ＝P _ac ^* -P _di ^* ，k＝3-i，i＝1 or 2 (14)

wherein ". Times" represents a control reference amount, "1or 2" represents a 1 st DC port or a 2 nd DC port, P _dk Representing the power of DC port k, P _di Representing the power of the DC port i, P _ac Representing the power of the ac port;

and (3) performing power control on the kth direct current port according to the formula (14), and completing power control on the alternating current port, thereby realizing power control on the ith direct current port and the alternating current port.

Further, the 1 st DC port power P _d1 Varying between minimum and maximum values, the 2 nd DC port power P _d2 And ac port power P _ac The working interval of (2) is:

when the priority of the 1 st direct current port is highest, firstly, according to the power range requirement of the 1 st direct current port in the step (16), the transmission power requirement of the 1 st direct current port is firstly met; when the priority of the 2 nd direct current port is arranged in the 2 nd order, under the condition that the power requirement of the 1 st direct current port is met as much as possible, the transmission power requirement of the 2 nd direct current port is met as much as possible according to the formula 2 in the (16); when the alternating current ports are arranged in priority 2, the power reference value of the direct current port 2 is calculated according to the power reference values of the direct current port 1 and the alternating current port according to the formula (14), and under the condition that the power requirement of the direct current port 1 is met, the transmission power requirement of the direct current port 2 is met as far as possible according to the formula (16).

Correspondingly, when the priority of the 2 nd direct current port is highest, firstly, according to the power range requirement of the 2 nd in the (16), the transmission power requirement of the 2 nd direct current port is met as far as possible; when the priority of the 1 st direct current port is arranged in the 2 nd, under the condition that the power requirement of the 2 nd direct current port is met as much as possible, the transmission power requirement of the 2 nd direct current port is met as much as possible according to the formula 1 in the (16); when the priority of the alternating current ports is arranged in the 2 nd, the power reference value of the 1 st direct current port is obtained according to the power reference values of the 2 nd direct current ports and the alternating current ports according to the formula (14), and under the condition that the power requirement of the 2 nd direct current ports is met, the transmission power requirement of the 1 st direct current ports is met as far as possible according to the formula (16).

The term "as far as possible" in the above description is interpreted as that the reference power of the port satisfies the requirement in the transmission range, and the power transmission is performed outside the transmission range according to the maximum or minimum value closest to the reference power requirement in the transmission range; for other control modes such as constant direct current voltage control, constant alternating current voltage control and the like, the reference current or the reference power at the 1 st direct current port and the 2 st direct current port is obtained according to the control modes, and corresponding control is completed according to the priority control mode.

Further, the three-port converter operates in an optimal mode, i.e. on the boundary line near the fourth side, P _u2 ＝0，P _u1 Not equal to 0, thereby achieving higher efficiency; when the system operates on the fourth boundary, the new energy storage grid-connected operation mode comprises the following steps:

when P _u1 >0, corresponding to the situation that the power generated by the new energy power supply connected to the direct current bus is abundant and the generated power is larger than the connected direct current load, P _u2 At this time, the integrated converter device presses k from the dc bus port _V1 ∶(1-k _V1 ) The ratio of (2) is used for respectively transmitting redundant power to the alternating current port and the energy storage port.

When P _u1 <0, corresponding to the condition that the power generated by the new energy power supply connected to the direct current bus is insufficient and the generated power is smaller than the connected direct current load, P _u2 =0, at this time the integrated converter device is pressed by k _V1 ∶(1-k _V1 ) The ratio of (2) is to transmit surplus power from the ac port and the energy storage port to the dc bus port, respectively.

When the power ratio between the alternating current port and the energy storage needs to be adjusted, the P is adjusted _u2 The setting is realized, the closer to the optimal operation mode, the higher the efficiency, and near the optimal operation mode, there are:

when P _u1 >0,P _u2 Not equal to 0, the integrated converter device is connected with the direct current bus port according to (k) _V1 P _d1 +P _u2 )∶[(1-k _V1 )P _d1 -P _u2 ]Is used for respectively transmitting redundant power to the alternating current port and the energy storage port according to the proportion of P _u2 The smaller the absolute value, the higher the efficiency; when P _u2 >0 will deliver more power to the ac port than the optimal mode of operation, otherwise more power will be delivered to the energy storage port.

When P _u1 <0，P _u2 Not equal to 0, the integrated converter is respectively pressed from the alternating current port to the energy storage port (-k) _V1 P _d1 -P _u2 )∶[(1-k _V1 )P _d1 -P _u2 ]Power is supplied to the DC bus port in proportion to P _u2 The smaller the absolute value, the higher the efficiency; when P _u2 <0 will draw more power from the ac port than the optimal mode of operation, otherwise more power will be drawn from the tank port.

The invention is described in further detail below with reference to the drawings and the detailed description.

Drawings

Fig. 1 is a diagram of a photovoltaic energy storage system to which a current transformer with a two-stage cascade structure according to the prior art is applied.

Fig. 2 is a schematic diagram of a three-port converter circuit of the present invention, wherein: figure a) is a three-phase three-port converter circuit schematic diagram, and b) is a single-phase three-port converter circuit schematic diagram.

Figure 3 is a schematic diagram of a four port converter circuit of the present invention.

Figure 4 is a schematic diagram of a five port converter circuit of the present invention.

Fig. 5 shows the dc current and ac power flow directions of the three-port converter circuit of the present invention in different operation regions.

Fig. 6 is a schematic diagram of the operation range and the operation range of the three-port converter circuit according to the present invention.

FIG. 7 shows different power ratios P according to the present invention _u1N /P _uN And a maximum transmission power line diagram of each port in the case, wherein: figure a) is a multi-port structure current converting circuit of the invention, and figure b) is a two-stage cascade structure current converting circuit.

Fig. 8 is a transfer function diagram of the dc port current control of the present invention.

Fig. 9 is a transfer function diagram of the dc port power control of the present invention.

Fig. 10 is a transfer function diagram of the dc port voltage control of the present invention.

Fig. 11 is a dynamic diagram of the control of dc port voltage variation in accordance with the present invention.

Fig. 12 is a dynamic graph of control of power change of the tank port according to the present invention.

Fig. 13 is a dynamic diagram of the operation of the ac port voltage variation of the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. It will be apparent that the described embodiments are some, but not all, embodiments of the invention. All other embodiments, which can be made by a person skilled in the art without creative efforts, based on the described embodiments of the present invention fall within the protection scope of the present invention.

Multi-port converter circuit embodiment for new energy storage integration grid connection

Referring to fig. 2-4, the multi-port converter circuit of the new energy storage integration grid connection comprises at least one alternating current/direct current converter unit and at least one multi-winding transformer, wherein three direct current terminals are led out after the two alternating current/direct current converter units are connected in series on a direct current side, the three direct current terminals are a common terminal and two non-common direct current terminals, the common terminal is the direct current terminal with the lowest or highest potential, and the common terminal and the two non-common direct current terminals form two direct current ports with independent regulation and control functions through combination of each other; the high potential current converting unit is a 1 st current converting unit, a 1 st direct current port of an external direct current bus is formed by a non-common terminal and the common terminal of the 1 st current converting unit, and the direct current bus is connected with a distributed power generation device and a direct current load; the lower potential current converting unit is a 2 nd current converting unit, and a non-public terminal and a public terminal of the 2 nd current converting unit form a 2 nd direct current port of an external energy storage device; the multi-winding transformer leads out an alternating current terminal connected with the alternating current side of each current converting unit and an alternating current port connected with an alternating current power grid to form a three-port current converting circuit with two direct current ports and one alternating current port.

Specifically, the "lever" effect of the power conversion described in this embodiment is: when the conversion power of the 2 nd converter unit is zero, the conversion power from the 1 st direct current port to the 2 nd direct current port and the alternating current port is larger than the actual power of the 1 st converter unit, so that the lever effect of completing the power conversion of the larger port by using the smaller power converter circuit is realized, the capacity of the required converter unit is reduced, the cost and the loss are reduced, and the efficiency is improved.

Specifically, the multiplexing of the devices of the 2 nd current transformation unit in this embodiment is: the 2 nd converter unit is applied to the power conversion of the 1 st direct current port and the 2 nd direct current port, can be used for the alternating current-direct current conversion between the port 2 and the alternating current port and can also be used for the alternating current-direct current conversion between the port 1 and the alternating current port, and the power transmission directions of the port 1 and the port 2 are generally opposite, so that a part of equipment capacity can be saved, the equipment cost is reduced, and the power density is improved.

Specifically, the direct conversion between the ac/dc ports in this embodiment is as follows: direct conversion between any two ports of a 1 st direct current port (direct current bus port), a 2 nd direct current port (energy storage port) and an alternating current port can be realized through a topological circuit, so that conversion efficiency is improved; the conversion power of the third port can be further increased by the conversion capability of the second port, and the direct conversion is realized by a primary conversion circuit, which is generally a conversion unit such as a bridge circuit.

Specifically, in this embodiment, the current transforming unit is a three-phase ac/dc current transforming unit or a single-phase ac/dc current transforming unit, the multiple three-phase ac/dc current transforming units and the three-phase multi-winding transformer form a three-phase multi-port current transforming circuit, the three-phase multi-port current transforming circuit is formed by 3n single-phase ac/dc current transforming units and n three-phase multi-winding transformers, each single-phase current transforming unit is connected to one energy storage device, and the single-phase ac/dc current transforming units and the single-phase transformer form a single-phase multi-port current transforming circuit.

The three-phase alternating current-direct current conversion unit is a two-level voltage source conversion circuit, a three-level voltage source conversion circuit or a bridge type conversion circuit, and the single-phase alternating current-direct current conversion unit is an H-bridge alternating current-direct current conversion circuit or a single-phase alternating current-direct current conversion circuit.

Referring to fig. 2-4, the three-phase multiport converter circuit includes a plurality of two-level voltage source converter circuits and a multi-winding three-phase transformer, the two-level voltage source converter circuits include IGBT valves and capacitors, each phase of the two-level voltage source converter circuits is provided with two series IGBT valves, a common end of each phase of the IGBT valves after being connected in series is connected with a primary winding of the multi-winding three-phase transformer, two free ends of the IGBT valves are connected in parallel with the capacitors, one end of each capacitor is led out of the direct current input end, the other end of each capacitor is connected with a capacitor of the next two-level voltage source converter circuit, and the next direct current input end is led out.

Specifically, in this embodiment, fig. 2 is a three-port current converting topology formed by 2 current converting units and 1 multi-winding transformer, where the (d 1-d 3) ports are connected to a dc bus, and the (d 2-d 3) ports are connected to an energy storage device, and the integrated grid-connected current converting structure with more energy storage, dc and ac ports can be expanded based on a greater number of current converting unit topology circuits and different combination connection modes thereof. The topology structure of the four-port new energy storage integrated grid-connected device with 1 direct current bus port, 2 energy storage ports and 1 alternating current port is shown in fig. 3, wherein (d 1-d 3) ports are connected with the direct current bus, and (d 2-d 3) and (d 3-d 4) are double energy storage ports, so that two energy storage devices can be connected, more direct current ports can be expanded to be connected with direct current buses with more different voltage levels, the topology structure of the five-port new energy storage integrated grid-connected device with 2 direct current bus ports, 2 energy storage ports and 1 alternating current port is shown in fig. 4, wherein (d 1-d 5) and (d 3-d 5) are double direct current bus ports, two direct current buses with different voltage levels can be connected, and (d 2-d 3) and (d 4-d 5) are double energy storage ports, so that two energy storage devices can be connected.

Therefore, the invention can simultaneously access the DC buses and the energy storage devices with different voltage grades by connecting the plurality of current converting units with the plurality of primary windings of the multi-winding transformer and expanding the DC ports of the current converting circuit through series connection, the energy storage devices realize independent grid connection control, the electric energy is converted among the DC buses, the energy storage devices and the AC side, the functions of converting alternating current into direct current and converting direct current into direct current are realized, meanwhile, the capacity of the current converting circuit is obviously reduced, the capacity of the device is only equivalent to that of the grid-connected current converter with the current two-stage cascade structure, thereby saving the energy storage DC/DC current converting units and greatly reducing the cost of the integrated grid-connected device.

Specifically, the 1 st current converting unit and the 2 nd current converting unit of the topology in this embodiment are connected in series at the dc side and draw out 3 dc terminals, where the low voltage dc terminal d3 of the 2 nd current converting unit is a common low voltage dc terminal. The high-voltage direct-current terminal d1 and the common terminal d3 of the 1 st current converting unit form a direct-current port, and can be externally connected with a direct-current bus and further connected with a new energy power generation device such as a photovoltaic device and a direct-current load through the direct-current bus.

The high-voltage direct-current terminal d2 and the common terminal d3 of the 2 nd converter unit form an energy storage port, so that the energy storage port is connected with electrochemistry and the like for energy storage. The alternating current sides of the 1 st current converting unit and the 2 nd current converting unit are respectively connected with different windings on the primary side of a three-winding transformer, and three alternating current terminals are led out from the secondary side winding of the three-winding transformer to form an alternating current port, so that a three-port new energy storage integrated grid-connected current converting topology with 1 direct current bus port, 1 energy storage port and 1 alternating current port is formed.

Therefore, the serial circuit expansion structure of the current transformation unit designed by the invention can realize the current transformation application of the low-voltage switching device in a higher direct-current voltage circuit.

In this embodiment, the three-port current transformation circuit is configured to output a 1 st DC port rated voltage V _d1N Rated voltage V of 2 nd DC port _d2N The rated voltage V of the direct current side of the 1 st current converting unit and the 2 nd current converting unit can be obtained _u1N 、V _u2N The method comprises the following steps of:

The multiport converter circuit has three converter modes, including a direct current-to-alternating current (or alternating current-to-direct current) converter mode, a direct current-to-direct current direct converter mode and a direct current-to-direct current indirect converter mode; the working range of a current converting unit based on the three current converting modes three-port current converting circuit is divided into 8 sections; the power of each converter unit is obtained according to the formula (2) according to the power requirement of each port, and the three-port converter circuit can flexibly operate in the combination of different converter modes and different working intervals formed by the combination.

Wherein the DC-to-AC (or AC-to-DC) conversion mode is one or two of the power conversion between the DC ports and the AC ports, when the output power P of the AC ports _ac When the value is greater than 0, electric energy flows into the alternating current port from the direct current port; otherwise, electric energy flows from the alternating current port to the direct current port;

The three conversion modes, wherein the direct current-to-alternating current or alternating current-to-direct current conversion power is the output power P of an alternating current port _ac The method comprises the steps of carrying out a first treatment on the surface of the For the three-port converter circuit, when the input power directions of the 1 st direct current port and the 2 nd direct current port are consistent, the direct current-to-direct current direct conversion power and the direct current-to-direct current indirect conversion power are both zero; when the input power directions of the 1 st DC port and the 2 nd DC port are inconsistent, the direct conversion power P is converted from DC to DC _DD1 Direct current-to-direct current indirect conversion power P _DD1 DC-DC conversion total power P _DD The calculation can be performed as follows:

When the converter circuit operates on the fourth boundary line, the port of the DC bus is switched to the AC port and the energy storage port according to k _V1 ∶(1-k _V1 ) Where k is the ratio of the power delivered _V1 For the 1 st variable current cell voltage V _u1 And the 1 st DC port voltage V _d1 Ratio of 0<k _V1 <1, a step of; at the moment, the total power of the converter unit is P _u1 Multiple portsConverting power to P _d1 ＝P _u1 V _d1 /V _u1 ＝P _u1 /k _V1 >P _u1 The method comprises the steps of carrying out a first treatment on the surface of the And the power transmission between the ports is realized through the total power of the smaller converter units, so that the power conversion lever effect is realized.

η _b1 ＝1-k _V1 (1-η ₁ )-P _st /P _d1 (5)

Specifically, referring to fig. 5 and 6, in 8 working intervals of the current converting circuit of this embodiment, the working interval 1 applies a direct current-to-direct current converting mode and a direct current-to-direct current indirect current converting mode, and electric energy flows in from the 1 st direct current port and flows out from the other two ports, where the power P is converted _DD1 And P _DD2 Are all greater than zero; direct conversion from direct current to direct current is applied in the working interval 2; applying a direct current to direct current conversion mode and an indirect direct current to direct current conversion mode in a working interval 3, wherein electric energy flows in from the 2 nd direct current port and flows out from the other two ports, and power P is converted _DD1 And P _DD2 Are all less than zero; working interval 4 power flows from the ac port to two dc ports; the current and power flow paths in the working sections 5, 6, 7, 8 are the same as the current and power flow paths in the working sections 1, 2, 3, 4, respectively, but in opposite directions.

Referring to fig. 7, in particular, in this embodiment, if the total rated power of the current transforming units of the multi-port current transforming circuit is consistent and is 1p.u (i.e. a standard unit), the maximum transmission power P of the ports of the multi-port current transforming circuit is seen _dt1max 、P _dt2max And inter-port transmissionPower P _12max All along with the power ratio P _u1N /P _uN Increase and increase, and inter-port transmission power P _13max At P _u1N /P _uN Less than k _V1 As power ratio P _u1N /P _uN Increase and increase, at P _u1N /P _uN Greater than k _V1 As power ratio P _u1N /P _uN Increase and decrease, and P _13max With power ratio P _u1N /P _uN The number of the ports is increased and the number of the ports is decreased, so that the port parameters can be optimally set according to actual needs by referring to the change relation.

Therefore, the invention improves the efficiency of power conversion between the energy storage device and the power grid and improves the conversion efficiency between the direct current bus and the energy storage device by setting the electric energy transmission proportion and setting higher energy storage port voltage, thereby reducing the total loss of the converter circuit and improving the overall efficiency.

In the present embodiment, the minimum and maximum voltages of the 1 st DC port during operation are V _d1min And V _d1max The lowest and highest operation voltages of the 2 nd DC port in the energy storage charging and discharging process are V respectively _d2min And V _d2max The lowest and highest dc operating voltages of the 1 st current converting unit are:

wherein V is _ac1max 、V _ac2max The maximum value k of the reasonable change range of the alternating-current side line voltage of the 1 st current converting unit and the 2 nd current converting unit _r Margin coefficients for keeping stable operation of the converter unit are provided; v (V) _u1min For the lowest DC operating voltage of the 1 st current converting unit, V _d2min Is the lowest operating voltage of the energy storage port, and has:

the method can obtain:

Specifically, the voltage of the energy storage port in this embodiment changes within a certain range along with the charge and discharge of the energy storage device and the SOC, and the rated voltage and the change thereof need to consider the influence on the operation of the multi-port current converting circuit, especially the influence on the stable operation of the 1 st current converting unit, wherein the lowest dc operation voltage V of the 1 st current converting unit _u1min And a maximum DC operating voltage V _u1max The method comprises the following steps:

V _u1min ＝V _d1min -V _u2max ,V _u1max ＝V _d1max -V _u2min (6-4)

therefore, the multi-port converter circuit can maintain higher operation efficiency and stably operate within the allowable voltage variation range in the charge and discharge process of the energy storage device by controlling the magnitude relation between the lowest operation voltage of the direct current port of the converter circuit and the alternating current side voltage.

In this embodiment, it is obtainable by the formula (2):

wherein:

P _u1N 、P _u2N rated input power of direct current side of 1 st current converting unit and 2 nd current converting unit respectively, V _u1N 、V _u2N The rated voltage of the direct current side of the 1 st current converting unit and the rated voltage of the direct current side of the 2 nd current converting unit are respectively;

determining the maximum transmission power of an alternating current/direct current port of the three-port converter circuit according to formulas (2) and (7);

thereby:

When the three-port converter cell power satisfies:

wherein P is _12max For the maximum exchange power between the 1 st DC port and the 2 nd DC port, P _13max For maximum switching power between the 1 st DC port and the AC port (3 rd port), P _23max Maximum switching power between the 2 nd dc port and ac port (3 rd port);

Specifically, in this embodiment, the maximum transmission power of the ac/dc ports of the three-port converter circuit is determined according to formulas (2) and (7).

Specifically, the maximum transmission power of the dc port d2 of embodiment 2 is:

P _d2max ＝P _u1N V _u2N /V _u1N +P _u2N ＝P _u1N (1-k _V1 )/k _V1 +P _u2N ＝P _u1N (1/k _V1 -1)+P _u2N (7-1)

the maximum transmission power of the alternating current and direct current ports of the three-port topology and the common two-stage cascade topology provided by the invention is further calculated, and the embodiment is further obtained by (8-1):

specifically, the transmission power between the energy storage and the ac port of the cascade converter circuit of this embodiment is:

typically, the power ratio P of the cascaded converter circuits _u1N /P _uN 0.5 or more, and the power ratio P of the multi-port converter circuit _u1N /P _uN Greater than or equal to k _V1 Thus there are:

further obtainable by the formula (10-2):

in particular, the present embodiment is applicable to the power ratio P _u1N /P _uN Satisfying the formula (9), the maximum power of each port of the multi-port converter circuit is larger than or equal to a target value; when the power ratio P _u1N /P _uN Satisfies 11), the maximum transmission power between ports of the multi-port converter circuit is larger than or equal to the target value, and the maximum transmission power is integrated, and when the power ratio P _u1N /P _uN Satisfying the formula (12), the maximum power of each port and the maximum transmission power between ports of the multi-port converter circuit are both larger than the target reference value, and if the power ratio required by the formula (12) is not satisfied, the P is further improved _uN To calculate reasonable parameters.

It can be seen that the present invention designs a proper power ratio P according to the maximum transmission power requirement between ports _u1N /P _uN And the power ratio of the multi-port converter circuit are optimally set so as to improve the transmission power of the converter circuit.

Specifically, the conditions that the total power of the converter units of the multi-port converter circuit and the cascade converter circuit is consistent are as follows:

k _V1 ≤P _u1N /P _uN ≤min[1-(1-k _V1 )P _u1N ^(TSC) /P _uN ,1-P _u2N ^(TSC) /P _uN ] (12-1)

wherein the superscript "TSC" indicates the corresponding variable of the cascaded converter circuit.

From Table 1, it can be seen that the maximum transmission power P of the AC port of the cascade converter circuit _acmax From P _u1N And determining that when the power relation of the multi-port converter circuit and the cascade converter circuit meets the formula (12-1), the maximum transmission power of the alternating current ports of the multi-port converter circuit and the cascade converter circuit is equal.

Specifically, the conditions that the maximum transmission power of other ports of the multi-port converter circuit is greater than or equal to the maximum transmission power of the corresponding ports of the cascade converter circuit are as follows:

under the condition that the maximum output power of the alternating current and direct current ports is not smaller than the port voltage corresponding to a common two-stage cascade structure current converting circuit (namely, a cascade topological structure of a DC/DC converter and a grid-connected DC/AC converter), the total capacity of the three-port current converting unit is only the capacity of a 1 st current converting unit in the common two-stage cascade structure, so that the DC/DC converter in the two-stage cascade structure is saved, and the cost is obviously reduced; wherein P is _acmax ^(TSC) 、P _d1max ^(TSC) P and P _u1N ^(TSC) The maximum output power of the alternating current port, the maximum output power of the direct current bus port and the rated power of the 1 st converter unit of the two-stage cascade structure are respectively.

It can be seen that when the maximum transmission power of other ports of the multi-port converter circuit is greater than or equal to the maximum transmission power of the corresponding ports of the cascade converter circuit, the 2 nd converter unit of the cascade converter circuit can be omitted, so that the cost of the multi-port converter circuit is greatly reduced, and a proper power ratio P can be further set according to the maximum transmission power requirement among the ports on the basis of the formula (12-2) _u1N /P _uN And the power and power ratio design of the converter circuit is further optimized.

Multi-port converter embodiment for new energy storage integration grid connection

The invention relates to a multi-port converter device for new energy storage integration grid connection, which comprises a sampling module, a main control module and a multi-port converter circuit for new energy storage integration grid connection, wherein the sampling module is used for respectively collecting three-phase/single-phase alternating current, three-phase/single-phase alternating voltage signals, direct-current side voltage and current signals and temperature signals and outputting sampling signals to the main control module, the main control module performs algorithm analysis according to the sampling signals, the multi-port current converting circuit controls the switching device to be switched on or off according to the PWM modulation wave signals, so that electric energy is converted among the direct current bus, the energy storage device and the alternating current side, and the alternating current to direct current, direct current to alternating current and direct current to direct current conversion functions are realized.

Specifically, the sampling module of this embodiment includes a voltage, current sampling circuit, a temperature sensor, and the like.

Specifically, the communication module in this embodiment includes an RS485 communication circuit, and the RS485 communication circuit uploads data such as line electrical parameters, device running states, and temperatures collected by the main control module to the remote scheduling platform through an RS485 bus for RS485 bus communication.

In this embodiment, the multi-port current transformer may be used in a single-phase circuit or a three-phase circuit; when the single-phase power supply is used for a single-phase circuit, the current converting unit and the transformer respectively adopt a single-phase current converting unit and a single-phase transformer; when the three-phase current transformer is used for a three-phase circuit, the current transforming unit and the transformer can be a single-phase current transforming unit and a single-phase transformer respectively, and can also be a three-phase current transforming unit and a three-phase transformer respectively; the three-phase integrated converter circuit formed based on the single-phase converter unit and the single-phase transformer is equivalent to the superposition application of three groups of single-phase integrated converter circuits, so that more energy storage devices can be accessed; the three-phase integrated converter circuit formed by the three-phase converter unit and the single-phase transformer can be connected and combined into a three-phase transformer through three groups of single-phase transformers.

Multi-port variable-current control method embodiment for new energy storage integration grid connection

The invention relates to a multi-port converter control method for new energy storage integration grid connection, which is applied to the multi-port converter device for new energy storage integration grid connection, and comprises the following steps:

In this embodiment, it is obtainable according to formula (2):

wherein V is _D1 For the 1 st current converting unit D axis voltage, V _D2 For the D-axis voltage of the 2 nd current converting unit, V _d1 、V _d2 The 1 st DC port voltage and the 2 nd DC port voltage, I _D21 、I _D22 To be respectively connected with the 1 st direct current port and the 2 nd direct current portThe current port inputs the corresponding D-axis current of the 2 nd current converting unit;

when the control strategy is to control the ith direct current port (i is 1 or 2) and the alternating current port, the controlled reference quantity of the other direct current port can be expressed as the corresponding controlled reference quantity of the alternating current port and the ith direct current port, and the corresponding control is performed; taking power control as an example, the reference power of another dc port (i.e., kth dc port) is:

P _dk ^* ＝P _ac ^* -P _di ^* ，k＝3-i，i＝1 or 2 (14)

Wherein ". Times" represents a control reference amount, "1 or 2" represents a 1 st DC port or a 2 nd DC port, P _dk Representing the power of DC port k, P _di Representing the power of the DC port i, P _ac Representing the power of the ac port;

Specifically, the current control strategy in this embodiment is to control the current of one dc port i and the ac port, where the reference current of the other dc port k (the 1 st dc port or the 2 nd dc port) is:

wherein ". Times" represents a control reference amount, "1 or 2" represents a 1 st DC port or a 2 nd DC port, I _dk Representing the current at DC port k, I _di Representing the current at DC port i, V _ac Representing the voltage at the ac port, I _ac Representing the current at the ac port.

It can be seen that the conversion power of the 2 nd converter unit is V of the DC port input power _d2 /V _d1 The sum of the power and the input power of the energy storage port.

Specifically, the present embodiment is according to formula (13), wherein I _D21 、I _D22 The method comprises the following steps:

constant current control, constant power control and constant direct voltage control transfer functions of the direct current ports are established according to equation (13).

The constant current control, constant power control and constant direct voltage control transfer functions for establishing the direct current port according to equation (13) are shown in fig. 8, 9 and 10, respectively. Different combinations may be further formed based on the above different dc port controls and different ac port control strategies.

In the present embodiment, the 1 st DC port power P _d1 Varying between minimum and maximum values, the 2 nd DC port power P _d2 And ac port power P _ac The working interval of (2) is:

when the priority of the 1 st direct current port is highest, firstly, according to the power range requirement of the 1 st direct current port in the step (16), the transmission power requirement of the 1 st direct current port is firstly met; when the priority of the 2 nd direct current port is arranged in the 2 nd order, under the condition that the power requirement of the 1 st direct current port is met as much as possible, the transmission power requirement of the 2 nd direct current port is met as much as possible according to the formula 2 in the (16); when the priority of the alternating current ports is arranged in the 2 nd, calculating the power reference value of the 2 nd direct current port according to the power reference values of the 1 st direct current port and the alternating current port according to the formula (14), and under the condition that the power requirement of the 1 st direct current port is met, transmitting the power requirement of the 2 nd direct current port according to the formula (16) as far as possible;

correspondingly, when the priority of the 2 nd direct current port is highest, firstly, according to the power range requirement of the 2 nd in the (16), the transmission power requirement of the 2 nd direct current port is met as far as possible; when the priority of the 1 st direct current port is arranged in the 2 nd, under the condition that the power requirement of the 2 nd direct current port is met as much as possible, the transmission power requirement of the 2 nd direct current port is met as much as possible according to the formula 1 in the (16); when the priority of the alternating current ports is arranged in the 2 nd, obtaining a power reference value of the 1 st direct current port according to the 2 nd direct current port and the power reference value of the alternating current ports in the formula (14), and under the condition of meeting the power requirement of the 2 nd direct current port, according to the formula (16), the transmission power requirement of the 1 st direct current port is met as much as possible;

The term "as far as possible" in the above description is interpreted as that the reference power of the port satisfies the requirement in the transmission range, and the power transmission is performed outside the transmission range according to the maximum or minimum value closest to the reference power requirement in the transmission range; for other control modes such as constant direct current voltage control and constant alternating current voltage control, the reference current or reference power of the direct current ports 1 and 2 is obtained according to the control modes, and corresponding control is completed according to the priority control mode.

Specifically, the present embodiment is seen by formula (16), P _d2 And P _ac Is subject to P _d1 The influence of the size can be seen, so that once P _d1 Determining P _d2 And P _ac The minimum and maximum values of (2) are also determined accordingly.

Specifically, this embodiment is obtainable by the formula (5):

thereby obtaining P _d2 P when varying within the minimum and maximum ranges _d1 And P _ac The working interval of (2) is:

thereby obtaining P _ac P when varying within the minimum and maximum ranges _d1 And P _d2 The working interval of (2) is:

it can be seen that the maximum power output by each port of the converter is affected by the output power of other ports, so that priority needs to be set in power control, and the port power requirement with high priority is satisfied first in operation control of the converter.

Specifically, in this embodiment, when the priority of the 2 nd dc port is highest, the power range requirement of the 1 st dc port is first set to meet the transmission power requirement of the 1 st dc port as much as possible according to the power range requirement of the 1 st (16-2). When the priority of the 2 nd dc port is as high as possible, the transmission power requirement of the 2 nd dc port is as high as possible according to equation 2 in (16-2) while the power requirement of the 1 st dc port is as high as possible. When the priority of the AC port 2 is the same, the power reference value of the 2 nd DC port is calculated according to the power reference values of the 1 st DC port and the AC port according to the step (14), and under the condition that the power requirement of the 1 st DC port is met as much as possible, the calculated power requirement of the 2 nd DC port is met as much as possible according to the step (16-2) of the formula 2.

Specifically, in this embodiment, when the ac port priority is highest and the priority of the 1 st dc port is highest, the feasible ac port reference power requirement is calculated according to the power range of (16-3) in the formula 1, and then the feasible reference power of the 1 st dc port is calculated according to (16-3) in the formula 2. When the priority of the flow port is highest and the priority of the 2 nd direct current port is next, the feasible alternating current port reference power requirement is calculated according to the power range of the formula 1 in the step (16-3), and then the feasible alternating current port reference power of the 2 nd direct current port is calculated according to the formula 3 in the step (16-3).

Specifically, the control method of the port current, the port voltage and the like in this embodiment can also be based on the priority control principle, firstly, the port control requirement with high priority is completed, then, the port control requirement with the next priority is completed, and the current or the power of the remaining ports is correspondingly determined.

In this embodiment, the three-port converter operates in an optimal manner, i.e., on the boundary line near the fourth boundary line, P _u2 ＝0，P _u1 Not equal to 0, thereby achieving higher efficiency; when running on the fourth boundary, new energyThe source energy storage grid-connected operation mode comprises the following steps:

When P _u1 <0,P _u2 Not equal to 0, the integrated converter is respectively pressed from the alternating current port to the energy storage port (-k) _V1 P _d1 -P _u2 )∶[(1-k _V1 )P _d1 -P _u2 ]Power is supplied to the DC bus port in proportion to P _u2 The smaller the absolute value, the higher the efficiency; when P _u2 <0 will draw more power from the ac port than the optimal mode of operation, otherwise more power will be drawn from the tank port.

In particular, the primary function of the energy storage device (ESS) of the present embodiment is to absorb excess energy generated by renewable energy sources and release the energy when the power generation is deficientExternal energy. For a typical two-stage cascade structure, the capacity of the 2 nd dc port (i.e., the tank port) is typically a percentage of the capacity of the 1 st dc port (i.e., the dc bus port). Taking a two-stage cascade structure (TSC) converter device as an example, it is assumed that the voltages of the 1 st dc port and the 2 nd dc port are 750V and 480V, respectively, and the ac port voltage is 380V. Rated power P of grid-connected converter (1 st converter unit) _U1 Rated power P of 136kW energy storage bidirectional DC/DC converter (2 nd converting unit) _U2 64kW, total capacity P of current converting unit _U 200kW, the maximum transmission power of the 1 st direct current port, the energy storage port and the alternating current port is 200kW,64kW and 136kW respectively.

According to the method, when the total power of the current converting units of the multi-port current converting device is consistent with the power of the 1 st current converting unit of the cascade current converting device, the maximum transmission power of the alternating current ports is equal. If the maximum transmission power of other ports of the multi-port converter is greater than or equal to the maximum transmission power of the corresponding ports of the cascade converter, the 2 nd converter unit of the cascade converter can be omitted in different application scenes, so that the cost of the multi-port converter is greatly reduced. According to formula (12-2), there are:

according to (17), the power ratio P is taken _u1N /P _uN The power of each converter cell was calculated to be 0.53 as shown in table 3. From equation (8), the maximum transmission power of each port can be further calculated as shown in table 2.

The total power of the converter units of the multi-port converter device is 136kW, and the converter units are rated power of grid-connected converter units with a two-stage cascade structure. In addition, the capacity of the two transformers is equivalent, so that an energy storage converter unit with a two-stage cascade structure is omitted, and the cost of the device is greatly reduced.

Table 3 conversion unit and port power of new energy storage grid-connected device

The maximum power of the direct-current port and the alternating-current port of the novel multi-port converter is the same as that of the two-stage cascade structure, but the maximum transmission power of the energy storage port reaches 192kW, which is 3 times of the maximum power of the energy storage port of the two-stage cascade structure, so that the charging speed and the charging and discharging power of the energy storage device are greatly improved, and the novel multi-port converter is particularly suitable for grid-connected application of the power type energy storage converter.

The energy storage voltage changes along with the change of the state of charge SOC in the operation process, if the energy storage voltage is considered to change from 467V to 493V and the rated current is kept unchanged, the transmission power of each converter unit and each port is calculated as shown in table 2, and the power of each converter unit and each port has certain change around the rated value of the converter unit and the port, but the change is not obvious.

Specifically, table 4 is obtained through simulation and verification according to the above device design in this embodiment, and table 4 lists transmission power examples of the grid-connected converter device under the condition that the converter units in the above 8 working intervals have different reference power settings.

As can be seen from table 4, the reference set value and the simulation value of the transmission power of the converter unit are relatively identical, and the maximum rate deviation is 1.6kW, which is about 2% of the reference value. Port transmission power P _d1 、P _d2 、P _ac The simulation measurement results of (2) are also more consistent with the calculation results according to the formula (1-1). In addition, direct dc-direct conversion power and direct dc-direct conversion power were also calculated, which are consistent with the basic analysis and the calculation result of formula (1) in table 1.

Table 4 conversion power of novel multi-port converter device in different operation intervals

In the 1 st section example and the 4 th section example of table 4, the transmission power between the 1 st dc port and the 2 nd dc port is close to the maximum conversion power. Almost 96% of the power of the 1 st direct current port flows into or flows out of the 2 nd direct current port, is used for rapid charging or discharging, has the rapid charging and discharging capability far higher than that of a two-stage cascade topology, and is particularly suitable for a power converter.

In the examples of interval 2 and interval 6 in table 4, the conversion power between the dc and ac ports reaches the maximum, which represents the highest power exchange between the dc and ac ports, so that the stable operation of the dc bus or the dc power grid is supported. The functionality is comparable to the TSC topology. As can be seen from table 4, the maximum power of the ports in the above interval example is typically much higher than the power converter cell power rating. Therefore, the multi-port converter device can realize larger power transmission among ports through the converter units with smaller capacity. Conversely, the total converter unit capacity of the new energy storage grid-connected converter device is also much smaller than that of the cascade structure.

Specifically, fig. 11 of the present embodiment shows the dynamic changes of the voltage, current and power of the three ports when the dc reference voltage of the 1 st dc port is adjusted. Wherein the DC reference voltage V _d1 ^* Increase by 0.05p.u at t=1.0 s and decrease by 0.05p.u at t=1.2 s. During this process, the input power of the 1 st dc port was maintained at 200kW, the power reference of the 2 nd dc port was maintained at-96 kW, and the voltages of the energy storage and ac ports were maintained. Visible DC reference voltage V _d1 ^* The change in (c) causes a dynamic response of the port current and the dynamics end around 0.05 seconds. The dc port current Id1 decreases from 266.4A to 254.6a starting at 1.0s and returns to 266.4A starting at 1.2 s. Port current dynamics still further result in dynamic changes in port power. But the steady-state power of the 1 st direct current port, the 2 nd direct current port and the alternating current port is respectively controlled at 200kW, -96kW and 104kW, and the constant power operation is kept unchanged.

Fig. 12 shows the port voltage, current and power control dynamics that occur when the reference power of the tank port is adjusted. Wherein P is _d2 ^* Increasing from-96 kW to-76.8 kW at t=1.0 s and decreasing again to-96 kW at t=1.2 s. The input power of the 1 st direct current port in the whole process is kept unchanged by 200 kW. In addition, the voltage at the three ports and the current at the 1 st dc port remain unchanged. Visible P _d2 ^* The varying adjustment results in a fast dynamic variation of the 2 nd dc port current and the ac port current, because the bandwidth of the current control link is higher than the bandwidth of the dc voltage control. The 2 nd DC port current Id2 increases from-201A to-161A at 1.0s and decreases further from-201A at 1.2 s. It can be seen from fig. 12 that the rapid current dynamics in turn lead to rapid power dynamics.

Fig. 13 is a graph of the dynamic change in port voltage, current and power as the grid voltage amplitude changes. Wherein the grid voltage amplitude decreases from 1.0p.u to 0.9p.u starting at t=1.0 s and increases again to 1.0p.u at t=1.2 s. In the process, the input power of the 1 st direct current port is kept to be 160kW, the reference power of the 2 nd direct current port is kept to be 96kW, and the voltage of the 2 nd direct current port is kept to be constant. It can be seen that the change in the grid voltage amplitude causes a slight change in the 1 st dc port voltage, current, 2 nd dc port current, power. The ac port current amplitude increases from 342A to 380A after t=1.0 s, and again decreases to 342A after t=1.2 s. The ac port current dynamics can be seen to end at around 0.5 s.

Therefore, the simulation verifies that the variable flow control method of the patent realizes reasonable application, and the dynamic change generated in the control and operation adjustment process is controlled within a reasonable range.

The above embodiments are only preferred embodiments of the present invention, and the scope of the present invention is not limited thereto, but any insubstantial changes and substitutions made by those skilled in the art on the basis of the present invention are intended to be within the scope of the present invention as claimed.

Claims

1. The multi-port converter circuit for new energy storage integration grid connection is characterized by comprising:

the three direct current terminals are a public terminal and two non-public direct current terminals, the public terminal is the direct current terminal with the lowest or highest potential, and the public terminal and the two non-public direct current terminals form two direct current ports with independent regulation and control functions through combination of two by two; the high potential current converting unit is a 1 st current converting unit, a 1 st direct current port of an external direct current bus is formed by a non-common terminal and the common terminal of the 1 st current converting unit, and the direct current bus is connected with a distributed power generation device and a direct current load; the lower potential current converting unit is a 2 nd current converting unit, and a non-public terminal and a public terminal of the 2 nd current converting unit form a 2 nd direct current port of an external energy storage device; the multi-winding transformer leads out an alternating current terminal connected with the alternating current side of each converting unit and an alternating current port connected with an alternating current power grid to form a three-port converting circuit with two direct current ports and one alternating current port;

The three-port converter circuit comprises a lever effect of power conversion, multiplexing of devices of a 2 nd converter unit and direct conversion between alternating current and direct current ports;

2. The new energy storage integration grid-connected multi-port converter circuit according to claim 1, wherein:

wherein P is _d1 、P _d2 Input power of direct current bus port and energy storage port respectively, P _u1 、P _u2 The direct-current side input power of the 1 st current converting unit and the 2 nd current converting unit respectively, V _u1 、V _u2 Direct-current side voltages of the 1 st current converting unit and the 2 nd current converting unit respectively, V _d1 、V _d2 The direct current bus port voltage and the energy storage port voltage are respectively;

the multiport converter circuit has three converter modes, including a direct current-to-alternating current (or alternating current-to-direct current) converter mode, a direct current-to-direct current direct converter mode and a direct current-to-direct current indirect converter mode; the working range of a current converting unit based on the three current converting modes three-port current converting circuit is divided into 8 sections; according to the power requirements of each port, the power of each converter unit is obtained according to the formula (2), and the three-port converter circuit can flexibly operate in the combination of different converter modes and different working intervals formed by the combination;

the direct conversion between two direct current ports is realized based on direct current coupling power exchange formed by direct current side series connection in the direct current-direct current conversion mode;

the direct current and direct current indirect conversion mode is based on direct current-to-alternating current conversion and alternating current-to-direct current conversion functions of the conversion unit, and realizes indirect conversion between two direct current ports by combining power exchange of electromagnetic coupling of a transformer;

the three conversion modes, wherein the DC-AC conversion power is the AC port output power P _ac The method comprises the steps of carrying out a first treatment on the surface of the For the three-port converter circuit, when the input power directions of the 1 st DC port and the 2 nd DC port are consistent, the direct current-direct current direct conversion power and the direct current-direct current indirect conversion power are both zeroThe method comprises the steps of carrying out a first treatment on the surface of the When the input power directions of the 1 st DC port and the 2 nd DC port are inconsistent, the direct conversion power P is converted from DC to DC _DD1 Direct current-to-direct current indirect conversion power P _DD1 Total power P of DC-DC conversion _DD The calculation can be performed as follows:

working interval 1 electric energy flows in from the 1 st direct current port and flows out from the other two ports, wherein the power P is converted _DD1 And P _DD2 Are all greater than zero; in the working range 2, electric energy flows in from the 1 st direct current port and flows out from the other two ports, wherein the power P is converted _DD1 Greater than zero, P _DD2 Equal to zero; in the working space 3, the electric energy flows in from the 2 nd direct current port and flows out from the other two ports, wherein the power P is converted _DD1 And P _DD2 Are all less than zero; working interval 4 power flows from the ac port to two dc ports, P _DD1 And P _DD2 Are all equal to zero; the current and power flow paths in the working intervals 5, 6, 7, 8 are the same as the current and power flow paths in the working intervals 1, 2, 3, 4, respectively, but in opposite directions; four interval boundary lines, P, exist among the 8 working intervals _u2 ＝-P _u1 Is the 1 st boundary line, P _u2 ＝P _u1 V _u2 /V _u1 For the 2 nd boundary line, P _u1 =0 is the third boundary line, P _u2 =0 is the fourth boundary line; wherein V is _u1 、V _u2 The direct-current side voltages of the 1 st converter unit and the 2 nd converter unit are respectively;

When the converter circuit is at the fourth boundaryOn-line operation, the direct current bus port is switched to the alternating current port and the energy storage port according to k _V1 ∶(1-k _V1 ) Where k is the ratio of the power delivered _V1 For the 1 st variable current cell voltage V _u1 And the 1 st DC port voltage V _d1 Ratio of 0<k _V1 <1, a step of; at the moment, the total power of the converter unit is P _u1 Multiport conversion power to P _d1 ＝P _u1 V _d1 /V _u1 ＝P _u1 /k _V1 >P _u1 The method comprises the steps of carrying out a first treatment on the surface of the The power transmission between the ports is realized through the total power of the smaller converter units, so that the lever effect of power conversion is realized;

η _b1 ＝1-k _V1 (1-η ₁ )-P _st /P _d1 (5)

3. The new energy storage integrated grid-connected multiport converter circuit of claim 2, wherein:

the lowest voltage and the highest voltage of the 1 st direct current port are respectively V in the operation process _d1min And V _d1max The lowest and highest operation voltages of the 2 nd DC port in the energy storage charging and discharging process are V respectively _d2min And V _d2max The lowest and highest dc operating voltages of the 1 st current converting unit are:

the method can obtain:

by designing the energy storage port voltage to be higher, k is made _V1 The power is reduced, so that the lever effect is enhanced, and the conversion power and efficiency are improved; however, the energy storage port is charged and discharged to cause voltage change, and the minimum and maximum values of the port voltage need to meet the formula (6-3); and high-efficiency operation is realized through matching of the direct-current side voltage and the alternating-current side voltage of the current converting unit in a reasonable variation range.

4. A new energy storage integrated grid-connected multiport converter circuit according to any one of claims 1-3, wherein:

From formula (2):

wherein: subscript "N" represents the nominal value, I _u1N 、I _u2N The rated current of the direct current side of the 1 st current converting unit and the rated current of the direct current side of the 2 nd current converting unit are respectively,

determining the maximum transmission power of an alternating current/direct current port of the three-port converter circuit according to formulas (4) and (5);

thereby:

wherein P is _uN ＝P _u1N +P _u2N Superscript "×" denotes a design target value; rating the converter unit according to (9)The power design is carried out, and the maximum transmission power of each port is larger than or equal to the design target value;

when the three-port converter cell power satisfies:

wherein The Superscript (TSC) denotes a two-stage cascade structure (Two Stage Configuration), P _acmax ^(TSC) 、P _d1max ^(TSC) P and P _u1N ^(TSC) The maximum output power of the alternating current port, the maximum input power of the direct current bus port and the direct current side rated power of the 1 st converter unit of the two-stage cascade structure are respectively;

Carrying out rated power design of the current converting unit according to the formula (9-1), wherein when the maximum transmission power of each port of the extracted topology is greater than or equal to the port power of the corresponding two-stage cascade structure, the total current converting unit capacity is only the capacity of the grid-connected current converting unit in the corresponding two-stage cascade structure, so that the energy storage DC-DC current converting unit is saved, and the cost is reduced;

5. The multi-port converter device for new energy storage integration grid connection is characterized by comprising:

the multi-port converter circuit for integrating new energy storage and grid connection according to any one of claims 1 to 4, wherein the sampling module is used for respectively collecting three-phase/single-phase alternating current, three-phase/single-phase alternating voltage signals, direct-current side voltage and current signals and temperature signals and outputting sampling signals to the main control module, the main control module performs algorithm analysis according to the sampling signals and outputs PWM modulation wave signals to the multi-port converter circuit, the direct current bus port of the multi-port current converting circuit is connected with a direct current bus, the energy storage port of the multi-port current converting circuit is connected with an energy storage device, the alternating current port of the multi-port current converting circuit outputs alternating current, and the multi-port current converting circuit controls a switching device to be switched on or off according to PWM (pulse width modulation) wave signals, so that electric energy is converted among the direct current bus, the energy storage device and an alternating current side, and the alternating current-to-direct current, direct current-to-alternating current and direct current-to-direct current conversion functions are realized;

the main control module comprises a DSP, a PWM module and a communication module, wherein the DSP outputs the PWM modulated wave signal to the multi-port converter circuit through the PWM module, and the DSP establishes communication with a power grid dispatching system through the communication module to exchange data;

The multi-port converter device supports two operation modes of grid connection and grid disconnection, is connected with an alternating current power grid in grid connection operation, can be matched with a power grid dispatching system, controls the energy storage device to participate in voltage regulation and frequency modulation of the power grid, and realizes peak clipping and valley filling of power grid load through charging/discharging; in off-grid operation, the multi-port converter device is disconnected from an alternating current power grid and operates in a direct current micro-grid mode, and the multi-port converter device controls the energy storage device to charge and discharge so as to realize continuous power supply to a direct current load or (and) an alternating current load;

6. The new energy storage integration grid-connected multiport converter device according to claim 5, wherein:

the multi-port converter device can be used for a single-phase circuit and a three-phase circuit; when the single-phase power supply is used for a single-phase circuit, the current converting unit and the transformer respectively adopt a single-phase current converting unit and a single-phase transformer; when the three-phase current transformer is used for a three-phase circuit, the current transforming unit and the transformer can be a single-phase current transforming unit and a single-phase transformer respectively, and can also be a three-phase current transforming unit and a three-phase transformer respectively; the three-phase integrated converter circuit formed based on the single-phase converter unit and the single-phase transformer is equivalent to the superposition application of three groups of single-phase integrated converter circuits, so that more energy storage devices can be accessed; the three-phase integrated converter circuit formed on the basis of the three-phase converter unit and the single-phase transformer can be connected and combined into a three-phase transformer through three groups of single-phase transformers;

Under the condition of wider voltage change range of an energy storage port or a direct current port, the transformer can be loaded with an on-load tap-changer, so that higher modulation ratio and conversion efficiency are maintained, the voltage of each winding of the transformer is ensured to be changed within a reasonable range, and the high-efficiency stable operation of the multi-port converter is ensured;

7. The multi-port converter control method for new energy storage integration grid connection is characterized by being applied to the multi-port converter device for new energy storage integration grid connection as claimed in any one of claims 5 to 6, and comprising the following steps:

8. The multi-port variable current control method for new energy storage integration grid connection according to claim 6, wherein the method is characterized in that:

obtainable according to formula (2):

P _dk ^* ＝P _ac ^* -P _di ^* ，k＝3-i，i＝1 or 2 (14)

9. The multi-port variable current control method for new energy storage integration grid connection according to claim 7, wherein the method is characterized in that:

1 st DC port power P _d1 Varying between minimum and maximum values, the 2 nd DC port power P _d2 And ac port power P _ac The working interval of (2) is:

10. The multi-port variable current control method for new energy storage integration grid connection according to any one of claims 7 to 9, wherein the method comprises the following steps:

the three-port converter operates in optimal mode, i.e. on the boundary line near the fourth side, P _u2 ＝0，P _u1 Not equal to 0, thereby achieving higher efficiency; when the system operates on the fourth boundary, the new energy storage grid-connected operation mode comprises the following steps:

when P _u1 >0, corresponding to the situation that the power generated by the new energy power supply connected to the direct current bus is abundant and the generated power is larger than the connected direct current load, P _u2 At this time, the integrated converter device presses k from the dc bus port _V1 ∶(1-k _V1 ) The ratio of the power supply to the alternating current port and the energy storage port respectively;

when P _u1 <0, corresponding to the condition that the power generated by the new energy power supply connected to the direct current bus is insufficient and the generated power is smaller than the connected direct current load, P _u2 =0, at this time setThe current transformer is k _V1 ∶(1-k _V1 ) The ratio of the power supply system is that redundant power is respectively transmitted from an alternating current port and an energy storage port to a direct current bus port;

when P _u1 >0,P _u2 Not equal to 0, the integrated converter device is connected with the direct current bus port according to (k) _V1 P _d1 +P _u2 )∶[(1-k _V1 )P _d1 -P _u2 ]Is used for respectively transmitting redundant power to the alternating current port and the energy storage port according to the proportion of P _u2 The smaller the absolute value, the higher the efficiency; when P _u2 >0, comparing with the optimal operation mode, more power is transmitted to the alternating current port, otherwise, more power is transmitted to the energy storage port;