CN113572381B - Energy conversion device of micro-grid - Google Patents
Energy conversion device of micro-grid Download PDFInfo
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- CN113572381B CN113572381B CN202110811468.9A CN202110811468A CN113572381B CN 113572381 B CN113572381 B CN 113572381B CN 202110811468 A CN202110811468 A CN 202110811468A CN 113572381 B CN113572381 B CN 113572381B
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
- H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
- H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
- H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M7/483—Converters with outputs that each can have more than two voltages levels
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/28—Arrangements for balancing of the load in a network by storage of energy
- H02J3/32—Arrangements for balancing of the load in a network by storage of energy using batteries with converting means
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/28—Arrangements for balancing of the load in a network by storage of energy
- H02J3/32—Arrangements for balancing of the load in a network by storage of energy using batteries with converting means
- H02J3/322—Arrangements for balancing of the load in a network by storage of energy using batteries with converting means the battery being on-board an electric or hybrid vehicle, e.g. vehicle to grid arrangements [V2G], power aggregation, use of the battery for network load balancing, coordinated or cooperative battery charging
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
- H02J3/381—Dispersed generators
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
- H02J3/388—Islanding, i.e. disconnection of local power supply from the network
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M3/00—Conversion of dc power input into dc power output
- H02M3/02—Conversion of dc power input into dc power output without intermediate conversion into ac
- H02M3/04—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters
- H02M3/10—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M3/145—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
- H02M3/155—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
- H02M3/156—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of output voltage or current, e.g. switching regulators
- H02M3/158—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of output voltage or current, e.g. switching regulators including plural semiconductor devices as final control devices for a single load
- H02M3/1582—Buck-boost converters
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M3/00—Conversion of dc power input into dc power output
- H02M3/22—Conversion of dc power input into dc power output with intermediate conversion into ac
- H02M3/24—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters
- H02M3/28—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac
- H02M3/325—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal
- H02M3/335—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only
- H02M3/33507—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of the output voltage or current, e.g. flyback converters
- H02M3/33523—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of the output voltage or current, e.g. flyback converters with galvanic isolation between input and output of both the power stage and the feedback loop
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
- H02J2300/20—The dispersed energy generation being of renewable origin
- H02J2300/22—The renewable source being solar energy
- H02J2300/24—The renewable source being solar energy of photovoltaic origin
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J2310/00—The network for supplying or distributing electric power characterised by its spatial reach or by the load
- H02J2310/40—The network being an on-board power network, i.e. within a vehicle
- H02J2310/48—The network being an on-board power network, i.e. within a vehicle for electric vehicles [EV] or hybrid vehicles [HEV]
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E10/00—Energy generation through renewable energy sources
- Y02E10/50—Photovoltaic [PV] energy
- Y02E10/56—Power conversion systems, e.g. maximum power point trackers
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- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Inverter Devices (AREA)
Abstract
The invention relates to an energy conversion device of a microgrid, belonging to the technical field of power control of the power grid, and the device comprises an AC/DC power converter, a non-isolated DC/DC power converter and an isolated DC/DC power converter, wherein the AC/DC power converter adopts a T-shaped three-level inverter circuit structure, the AC side is connected with an AC power grid, the DC side is connected with the non-isolated DC/DC power converter and the isolated DC/DC power converter through a DC bus, and the conversion of a bidirectional transition process working mode between grid connection and off-grid connection can be completed; the main circuit of the non-isolated DC/DC power converter adopts a three-level bidirectional conversion circuit, the first port of the non-isolated DC/DC power converter is connected with a direct current bus, and the second port of the non-isolated DC/DC power converter is connected with an energy storage battery for realizing charging, discharging and voltage stabilizing effects; the isolated DC/DC power converter comprises a front-stage structure and a rear-stage structure, respectively corresponds to the BUCK-BOOST circuit and the bidirectional AC/DC power resonant converter, and is used for realizing charging and discharging of the load of the electric automobile. The invention can realize the flexible conversion of the operation mode of the microgrid.
Description
Technical Field
The invention belongs to the technical field of power grid energy control, and particularly relates to an energy conversion device of a micro-grid.
Background
The power supply in the micro-grid is a micro power supply, and a small unit (less than 100 kW) with a power electronic interface comprises a micro gas turbine, a fuel cell, a photovoltaic cell, a super capacitor, a flywheel, a storage battery and other energy storage units. The devices are installed on a user side, and have the characteristics of low cost, low voltage, low pollution and the like, but in the existing micro-grid, the micro-grid and a large power grid (alternating current grid) are generally connected through the arranged bidirectional AC/DC, and the conversion function efficiency of the device is low during the operation period due to the fact that the structure of the device is not properly matched with a control strategy.
Disclosure of Invention
The invention aims to provide an energy conversion device of a microgrid, which is used for solving the problem of low conversion efficiency of an AC/DC device of the existing microgrid.
Based on the purpose, the technical scheme of the energy conversion device of the microgrid is as follows:
the AC/DC power converter adopts a T-shaped three-level inverter circuit structure, and the alternating current side of the AC/DC power converter is used for connecting an alternating current power grid and exchanging power with the alternating current power grid; the direct current side of the AC/DC power converter is connected with the non-isolated DC/DC power converter and the isolated DC/DC power converter through a direct current bus, the working modes of the AC/DC power converter in the microgrid comprise off-grid and on-grid, and the AC/DC power converter can complete the conversion of the working modes in the bidirectional transition process between on-grid and off-grid;
a main circuit topology of the non-isolated DC/DC power converter adopts a three-level bidirectional conversion circuit, a first port DC1 of the non-isolated DC/DC power converter is connected with the direct-current bus, and a second port DC2 of the non-isolated DC/DC power converter is used for connecting an energy storage battery; when current control is carried out from the first port DC1 to the second port DC2, the main circuit works in a BUCK working mode; when current control is carried out from the second port DC2 to the first port DC1, the main circuit works in a BOOST working mode, bidirectional flow of energy is realized in a double-loop control mode of a voltage outer loop and a current inner loop, and when the micro-grid is connected to the power grid and works, the non-isolated DC/DC power converter is used for stabilizing disturbance of photovoltaic and direct-current loads, eliminating photovoltaic power generation, and carrying out peak clipping and valley filling by starting charging and discharging of an energy storage battery; when the micro-grid operates independently, the non-isolated DC/DC power converter is used for stabilizing the voltage of the direct-current bus;
a first port of the isolated DC/DC power converter is connected with the direct current bus, and a second port of the isolated DC/DC power converter is used for supplying power and connecting a charging load of the electric automobile; the isolated DC/DC power converter comprises a front-stage structure and a rear-stage structure, the output end of the front-stage structure is connected with the input end of the rear-stage structure, the front-stage structure adopts a BUCK-BOOST circuit with a voltage boosting and reducing function, the rear-stage structure adopts a bidirectional AC/DC power resonance converter, and when a micro-grid works, the isolated DC/DC power converter is used for receiving dispatching and achieving ordered operation of charging and discharging of electric automobile loads.
The beneficial effects of the above technical scheme are:
the invention provides an efficient energy conversion device, which is characterized in that an AC/DC power converter, a non-isolated DC/DC power converter and an isolated DC/DC power converter are arranged, each converter adopts a specific circuit structure, and a proper working mode is set for each power converter, and the three converters are matched with each other, so that the flexible conversion of the operation mode of a microgrid and the efficient conversion of power can be realized, and the application prospect is good.
Further, to solve the off-grid operation problem of the AC/DC power converter, when the AC/DC power converter is in the off-grid operation mode, the operation steps are as follows:
s1, when in off-grid working mode, AC/DC powerThe rate converter is in an independent inversion operating mode, and in the operating mode, the AC/DC power converter presents voltage source characteristics to the AC load according to a given AC effective value V * rms Is controlled by an output voltage V rms Feedback to generate amplitude V of AC voltage RMS With a given voltage value V ref Making a difference;
s2, amplitude (V) RMS -V ref ) And obtaining an instantaneous value at the moment through sinusoidal variation, then calculating direct current component feedback corresponding to the instantaneous value, eliminating the direct current component, obtaining a given value of a control current loop through PI operation of a voltage loop, and generating output through impedance conversion and driving.
Further, in order to solve the grid-connected operation problem of the AC/DC power converter, the AC/DC power converter is operated by two or more than two AC/DC modules in parallel, when the AC/DC power converter is in a grid-connected operation mode, a control mode of a voltage control outer loop and a current control inner loop is adopted, and the control mode specifically comprises the following working steps:
t1, each AC/DC module takes stable direct current bus voltage as a target, and voltage ring given values UDC + _ ref and UDC- _ ref are set as rated operation voltage of the direct current bus; the given value of the voltage loop is differenced with the corresponding output positive/negative voltage, and the difference is summed after PI regulation;
t2, when the generated power in the direct current bus is larger than the power consumption, the voltage of the bus is increased, and the voltage ring outputs and regulates given current Iref _ total which is transmitted to the bus;
t3, when the generated power in the direct current bus is smaller than the power consumption power, adjusting and increasing the transmission current Iref _ total to the direct current bus to be used as the maximum limiting current of the AC/DC module so as to limit the maximum output power of the module;
and T4, comparing the output given current value Iref _ mod with the set current limit value Iref _ rating, taking the smaller value as the current given value of the final output, making a difference between the value and the actual output current of the module, and performing PI regulation, dq inverse transformation and PWM modulation to generate a modulation wave of the module, control the main circuit and realize module control.
Furthermore, in order to improve the working efficiency of the AC/DC power converter, when two or more AC/DC modules run in parallel, one of the AC/DC modules is a host and the other AC/DC modules are slaves, for the direct-current bus side, the host is used as a voltage source to support the bus voltage, a double-loop control mode of a voltage outer loop and a current inner loop is adopted, and the slaves are used as current sources to realize the current-sharing output among the modules; for the alternating current output side, all modules of the AC/DC power converter operate as current sources, parallel current sharing operation is achieved through high-speed communication, in order to guarantee that current loop setting of each unit charging module is the same, the main module achieves the function of a voltage loop, voltage loop output is sent to each AC/DC module through a high-speed SPI bus to serve as a set value Iref _ mod of the current loop, and other slave machines operate in a current control mode.
Further, in order to realize the safe transition from the grid-connected to the off-grid working mode, in the bidirectional transition working mode, the steps of converting the grid-connected to the off-grid comprise: the EMS control panel provides a mode switching and off-grid state information instruction, and controls and switches the fast switch, and the AC/DC power converter is switched from a grid-connected working mode to an off-grid working mode when switching from grid-connected to off-grid.
Further, in order to realize the safe transition from the off-grid to the grid-connected working mode, in the working mode of the bidirectional transition process, the steps of switching from the off-grid to the grid-connected comprise:
the method comprises the steps that an EMS control panel provides power grid voltage related information to an AC/DC power converter through phase-locked control, the power grid voltage related information specifically comprises grid-connected state information, power grid voltage, frequency information and synchronous signals, the AC/DC power converter achieves synchronization through adjusting amplitude, frequency and phase of output voltage and amplitude, frequency and phase of the power grid voltage, primary compensation is carried out through amplitude/phase angle, and whether synchronization is overtime or not is judged after compensation;
if overtime, the synchronization fails, and the reason is returned; if the voltage/frequency of the AC side of the AC/DC power converter is not overtime, judging whether the voltage/frequency of the AC side of the AC/DC power converter is too high or too low compared with the voltage/frequency in the AC power grid, if the voltage/frequency is judged to be too high or too low, failing in the same period, and returning to the reason; if the voltage/frequency is not too high or too low, respectively judging whether the differential pressure, the frequency difference and the angle difference are out of limit, and if so, adjusting the output of the energy storage converter; if the differential pressure, the frequency difference and the angle difference are not out of limit, judging whether the angle difference is changed, if so, calculating a closing advance angle, judging whether the current time is the optimal closing time according to the angle, if so, judging that the current time is the optimal closing time or judging that the angle difference is not changed, switching the AC/DC power converter from a voltage-frequency mode to a power-reactive power mode, and simultaneously, successfully obtaining the result;
the EMS control board sends a mode switching instruction, and simultaneously switches the fast switch, so that the AC/DC converter is converted into a grid-connected working mode from an inversion working mode.
Further, for the charging function and the voltage stabilizing function of the non-isolated DC/DC power converter, the non-isolated DC/DC power converter works in a master-slave parallel mode by connecting two or more modules in parallel, a host of the power converter serves as a voltage source to support bus voltage, the power converter works in a double-loop control mode of a voltage outer loop and a current inner loop to realize bidirectional flow of energy, a slave serves as a current source, current-sharing output among a plurality of modules is realized between the host and each slave through high-speed parallel communication, the non-isolated DC/DC power converter changes a working operation mode by self logic and receiving instructions, and the working operation mode comprises a constant power mode and a constant voltage mode.
Further, in order to realize the load charge and discharge function of the isolated DC/DC power converter, the BUCK-BOOST circuit of the preceding stage structure in the isolated DC/DC power converter adopts a double-loop control mode of a voltage outer loop and a current inner loop, and includes: given an output voltage reference value U * o And the actual output voltage U o Performing PI regulation to obtain a current output value I * o2 This value is related to the given current limit I * o1 Comparing, and taking the smaller value as the given current value I * o The value and the output current I o And performing PI regulation, and sending a signal to a PWM generator to generate a modulation signal of a power device in the BUCK-BOOST circuit.
Furthermore, the post-stage structure in the isolated DC/DC power converter adopts a double-loop control mode of a voltage outer loop and a current inner loop, and the output voltage is kept stable by adjusting the output frequency.
Further, in order to improve the effect of the resonant circuit, in the post-stage structure, the resonant circuit in the bidirectional AC/DC power resonant converter is an LLC resonant converter circuit.
Drawings
FIG. 1 is a schematic diagram of an energy conversion device of a microgrid according to an embodiment of the present invention;
FIG. 2 is a control block diagram of an off-grid mode of operation in an embodiment of the present invention;
fig. 3 is a control block diagram in the grid-connected operation mode in the embodiment of the present invention;
FIG. 4 is a logic control block diagram for grid-connected operation to off-grid operation in an embodiment of the present invention;
FIG. 5 is a logic control block diagram of the operation of converting off-grid operation to on-grid operation in the embodiment of the present invention;
FIG. 6 is a schematic diagram of a circuit model of a non-isolated DC/DC power converter in an embodiment of the invention;
FIG. 7 is a schematic diagram of a circuit model of an isolated DC/DC power converter in an embodiment of the invention;
FIG. 8 is a block diagram of the control of the BUCK-BOOST circuit in the embodiment of the present invention.
Detailed Description
The following description will further describe embodiments of the present invention with reference to the accompanying drawings.
In this embodiment, an energy conversion apparatus for a microgrid is provided, as shown in fig. 1, the hardware configuration of the apparatus includes: the device comprises an AC/DC power converter, a non-isolated DC/DC power converter and an isolated DC/DC power converter, wherein the AC side of the AC/DC power converter is used for connecting an AC power grid, the DC side of the AC/DC power converter is connected with the non-isolated DC/DC power converter and the isolated DC/DC power converter through a DC bus, the low-voltage side of the non-isolated DC/DC power converter is used for connecting an energy storage battery, and the low-voltage side of the isolated DC/DC power converter is used for supplying power and connecting a charging load (such as an electric automobile). In the following, specific descriptions are made for three power converters, respectively:
isolated AC/DC power converter
The isolated AC/DC power converter adopts a T-shaped three-level inverter circuit structure, is used for connecting the energy of an alternating current side and a direct current side, can be connected with an external network through a common coupling point and can exchange power with the external network, needs to be in two working modes of off-grid and on-grid in a system, and can complete the conversion of the working modes of a bidirectional transition process between grid-connection and off-grid.
When the AC/DC power converter is in an off-grid working mode, the working steps are as follows:
s1, in an off-grid working mode, an AC/DC power converter is in an independent inversion working mode, a control block diagram in the working mode is shown in figure 2, the AC/DC power converter presents voltage source characteristics to an alternating current load, and a module has a given alternating current effective value (V) * rms ) Is controlled by the output voltage (V) rms ) Feedback to generate amplitude (V) of AC voltage RMS ) With a given voltage value (V) ref ) Making a difference;
s2, amplitude (V) RMS -V ref ) And obtaining an instantaneous value of the moment through sine change (sin ω t), then calculating direct current component feedback corresponding to the voltage instantaneous value of the moment obtained through sine change, eliminating the direct current component, obtaining a given value of a control current loop I through PI operation of a voltage loop, and generating output through impedance conversion (Z) and drive (M).
In the embodiment of the present invention, as shown in fig. 3, the control loop in the grid-connected operating mode adopts a control strategy of a voltage control outer loop and a current control inner loop when the AC/DC power converter is in the grid-connected operating mode, specifically, the working steps are as follows:
t1, an AC/DC module (an AC/DC power converter is operated by two or more AC/DC modules in parallel) takes stable direct current bus voltage as a target, and voltage ring given values UDC + _ ref and UDC- _ ref are set as rated operation voltage of the direct current bus; the given value of the voltage loop is differenced with the corresponding output positive/negative voltage, and the difference is summed after PI regulation;
t2, when the generated power in the direct current bus is larger than the power consumption power, the voltage of the bus is increased, and the voltage loop outputs and adjusts the given current Iref _ total which is reduced to be transmitted to the bus;
t3, when the generated power in the direct current bus is smaller than the power consumption power, adjusting and increasing the transmission current Iref _ total to the direct current bus, namely the maximum limiting current of the module, so as to limit the maximum output power of the module and ensure the safety limit of the operation process, thereby realizing the voltage stabilization control of the direct current bus and achieving the purpose of limiting the maximum current;
and T4, comparing the output given current value Iref _ mod with the set current limit value Iref _ rating, taking the smaller value as the current given value of the final output, making a difference between the value and the actual output current of the module, and performing PI regulation, dq inverse transformation and PWM modulation to generate a modulation wave of the module, control the main circuit and realize the control of the module.
In the embodiment of the invention, when a plurality of modules (namely a plurality of AC/DC modules) run in parallel, one is a host computer, and the other modules are slave computers; for the alternating current output side, the modules of the AC/DC power converter operate as current sources, parallel current sharing operation is realized through high-speed communication, in order to ensure that the current loop settings of each unit charging module are the same, the main module realizes the function of a voltage loop, outputs the voltage loop to each unit module (i.e., AC/DC module) through a high-speed SPI bus, serves as the current loop settings of the unit module (i.e., iref _ mod), and other slave machines operate in a current control mode, such as the current control inner loop shown in fig. 3.
In the embodiment of the invention, in the working mode of the transition process from grid-connected to off-grid, the steps of the grid-connected to off-grid are shown in fig. 4, an off-grid detection module detects an off-grid trigger signal, an AC/DC power converter verifies the exchange power of grid-connected points, the power of the AC/DC becomes larger after balance, an EMS control panel (EMS full-name engine management system) provides a mode switching and off-grid state information instruction and controls and switches a quick switch at the same time, and the AC/DC power converter is switched from the grid-connected working mode to the off-grid working mode when the grid-connected to off-grid is switched.
In the embodiment of the present invention, in the working mode of the transition process from grid-connected to off-grid, the step of switching from off-grid to grid-connected is shown in fig. 5, and includes: the EMS control board provides power grid voltage related information to the AC/DC power converter through phase-locked control, the power grid voltage related information specifically comprises grid-connected and grid-disconnected state information, power grid voltage, frequency information and synchronous signals, the AC/DC power converter achieves synchronization through adjusting amplitude, frequency and phase of output voltage and amplitude, frequency and phase of the power grid voltage, as shown in figure 5, primary compensation is carried out through amplitude/phase angle, whether synchronization is overtime is judged after compensation (whether time is overtime is judged through a time relay module), if time is overtime, synchronization fails, and reasons are returned; if the voltage/frequency of the AC side of the AC/DC power converter is not overtime, judging whether the voltage/frequency of the AC side of the AC/DC power converter is too high or too low compared with the voltage/frequency in the AC power grid, if the voltage/frequency is judged to be too high or too low, failing in the same period, and returning to the reason; if the voltage/frequency is not too high or too low, respectively judging whether a differential pressure, a frequency difference and an angle difference are out of limit or not, if so, adjusting the output of an energy storage converter, wherein the energy storage converter is an AC/DC power converter, if the differential pressure, the frequency difference and the angle difference are not out of limit, judging whether the angle difference is changed (namely whether the angle difference is not equal to zero or not, and indicating change or not), if so, calculating a closing crossing front angle, judging whether the current time is the optimal closing time or not according to the angle, and if the current time is the optimal closing time or not, switching the AC/DC power converter from a VF mode (voltage-frequency mode) to a PQ mode (active power-reactive power mode), and synchronously, successfully. The four-quadrant converter can keep the voltage of the middle link of the system constant, so that the power factor is close to 1, the current waveform is close to sine, and when the AC/DC power converter is switched from the off-grid to the on-grid, the voltage is kept constant, so that the power factor is close to 1, and the circuit voltage is stable. At the moment, the EMS control board sends a mode switching instruction, and simultaneously switches the fast switch, so that the AC/DC converter is converted into a grid-connected working mode from an inversion working mode.
(II) non-isolated DC/DC power converter
The main circuit topology of the non-isolated DC/DC power converter adopts a three-level bidirectional conversion circuit, as shown in FIG. 6, when current control is performed from a DC1 +/-end (a first port) to a DC2 +/-end (a second port), the main circuit works in a BUCK working mode; the main circuit operates in BOOST operating mode when current is controlled from DC2 +/-to DC1 +/-terminal. The non-isolated DC/DC power converter works in a mode that a plurality of modules are connected in parallel and a master-slave parallel connection mode is adopted, the parallel connection needs a current sharing design to ensure that each module (a master machine and a slave machine) can bear power current averagely, the master machine of the DC/DC power converter is used as a voltage source to support bus voltage, the bidirectional flow of energy is realized in a double-ring control mode of a voltage outer ring and a current inner ring, the slave machine is used as a current source, the current sharing output among a plurality of modules is realized between the master machine and the slave machine through high-speed parallel connection communication, and the converter changes a working operation mode (a constant power mode or a constant voltage mode) through self logic and receiving instructions.
When the system works in a grid-connected mode, the non-isolation type DC/DC power converter is used for stabilizing disturbance of photovoltaic and direct-current loads, dissipating photovoltaic power generation, receiving control of an EMS (energy management system), performing peak clipping and valley filling by starting charging and discharging of an energy storage battery, and when the system works independently, the non-isolation type DC/DC power converter is used for stabilizing voltage of a direct-current bus.
(III) isolation type DC/DC power converter
As shown in fig. 7, the isolated DC/DC power converter includes a two-stage structure, i.e., a front-stage structure (a portion framed by a square frame in fig. 7) and a rear-stage structure (a portion not framed on the right side of fig. 7), the front-stage structure employs a BUCK-BOOST circuit with a voltage step-up and step-down function, and the rear-stage structure employs a high-efficiency LLC resonant converter circuit.
The BUCK-BOOST circuit of the preceding stage structure in the isolated DC/DC power converter adopts a double-loop control mode of a voltage outer loop and a current inner loop, as shown in fig. 8, an output voltage reference value U is given * o And the actual output voltage U o Performing PI regulation to obtain a current output value I * o2 This value is compared with a given current limit value I * o1 Comparing, and taking the smaller value as the given current value I * o The value of which is related to the output current I o And performing PI regulation, and sending a signal to a PWM generator to generate a modulation signal of a power device in the BUCK-BOOST circuit. The control mode achieves the effect that the output voltage is maintained in a certain range, the circuit of the rear-stage bidirectional AC/DC power resonant converter always works in a resonant state, and the overall efficiency of the system is improved.
In the embodiment of the invention, a backward-stage structure in the isolated DC/DC power converter adopts a bidirectional AC/DC power resonant converter (a resonant circuit in the bidirectional AC/DC power resonant converter is an LLC resonant converter circuit), and also adopts a double-loop control mode of a voltage outer loop and a current inner loop, so that the output voltage is kept stable by adjusting the output frequency in a narrow range, and the current-sharing output among a plurality of modules is realized between a host and a slave through high-speed parallel operation communication; the converter may change the operational mode of operation by receiving a command.
In this embodiment, the energy conversion device mainly includes an AC/DC power converter, a non-isolated DC/DC power converter, and an isolated DC/DC power converter, and as another embodiment, a unidirectional DC/DC power converter may be further added to the energy conversion device, where one end of the converter is connected to the DC bus and the other end is used to connect to an inverter of the photovoltaic power generation device, so as to implement photovoltaic power generation connected to the DC bus.
Compared with the prior art, the microgrid high-efficiency source conversion device has the following advantages:
(1) The high-efficiency source conversion device for the micro-grid can realize that the alternating current and direct current buses are linked by adopting a bidirectional AC/DC conversion device in the alternating current and direct current bus series-parallel system, so that the energy conversion of alternating current and direct current is realized; on the direct current side, unidirectional DC/DC conversion is adopted, so that solar photovoltaic power generation is connected into a direct current bus; the charge and discharge of the battery energy storage subsystem are realized by adopting bidirectional DC/DC conversion; the charge and discharge of the electric automobile are realized by adopting bidirectional isolation DC/DC conversion; meanwhile, the safety control technology, the flexible control technology, the control strategy and the economy are considered.
(2) The microgrid high-efficiency source conversion device can achieve the aims of high specific power, high power density and high efficiency by designing a high-efficiency, high-integration and power grid-friendly bidirectional AC/DC converter topology control system and designing a multifunctional fusion control system comprising reactive power decoupling control and harmonic suppression, analyzing the bidirectional gain characteristic of the circuit topology, realizing conditions of soft switching, controlling complexity, converter efficiency and reliability factors, and researching an optimal power circuit topology and an advanced control strategy aiming at isolating the bidirectional DC/DC circuit topology.
Finally, it should be noted that: the above embodiments are only for illustrating the technical solutions of the present invention and not for limiting the same, and although the present invention is described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that: modifications and equivalents may be made to the embodiments of the invention without departing from the spirit and scope of the invention, which is to be covered by the claims.
Claims (9)
1. An energy conversion device for a microgrid, comprising:
the AC/DC power converter adopts a T-shaped three-level inverter circuit structure, and the alternating current side of the AC/DC power converter is used for connecting an alternating current power grid and exchanging power with the alternating current power grid; the direct current side of the AC/DC power converter is connected with the non-isolated DC/DC power converter and the isolated DC/DC power converter through a direct current bus, the working modes of the AC/DC power converter in the microgrid comprise off-grid and on-grid, and the AC/DC power converter can complete the conversion of the working modes in the bidirectional transition process between on-grid and off-grid; when the AC/DC power converter is in an off-grid working mode, the working steps are as follows:
s1, under the off-grid working mode, the AC/DC power converter is in an independent inversion working modeIn the active mode, the AC/DC power converter presents a voltage source characteristic to the AC load, according to a given AC effective value V * rms Is controlled by an output voltage V rms Feedback to generate amplitude V of AC voltage RMS And a given voltage value V ref Making a difference;
s2, amplitude (V) RMS -V ref ) Obtaining an instantaneous value through sinusoidal variation, then calculating direct current component feedback corresponding to the instantaneous value, eliminating the direct current component, obtaining a given value of a control current loop through PI operation of a voltage loop, and generating output through impedance conversion and driving;
a main circuit topology of the non-isolated DC/DC power converter adopts a three-level bidirectional conversion circuit, a first port DC1 of the non-isolated DC/DC power converter is connected with the direct-current bus, and a second port DC2 of the non-isolated DC/DC power converter is used for connecting an energy storage battery; when current control is carried out from the first port DC1 to the second port DC2, the main circuit works in a BUCK working mode; when current control is carried out from the second port DC2 to the first port DC1, the main circuit works in a BOOST working mode, bidirectional flow of energy is realized in a double-loop control mode of a voltage outer loop and a current inner loop, and when the microgrid is connected to the power grid to work, the non-isolated DC/DC power converter is used for stabilizing disturbance of photovoltaic and direct-current loads, eliminating photovoltaic power generation, and carrying out peak clipping and valley filling by starting charging and discharging of an energy storage battery; when the micro-grid operates independently, the non-isolated DC/DC power converter is used for stabilizing the voltage of the direct-current bus;
a first port of the isolated DC/DC power converter is connected with the direct current bus, and a second port of the isolated DC/DC power converter is used for supplying power and connecting a charging load of the electric automobile; the isolated DC/DC power converter comprises a front-stage structure and a rear-stage structure, the output end of the front-stage structure is connected with the input end of the rear-stage structure, the front-stage structure adopts a BUCK-BOOST circuit with a voltage boosting and reducing function, the rear-stage structure adopts a bidirectional AC/DC power resonance converter, and when a micro-grid works, the isolated DC/DC power converter is used for receiving dispatching and achieving ordered operation of charging and discharging of electric automobile loads.
2. The microgrid energy conversion device of claim 1, wherein the AC/DC power converter is operated by two or more AC/DC modules in parallel, and when the AC/DC power converter is in a grid-connected operation mode, a control method of a voltage control outer loop and a current control inner loop is adopted, and the control method specifically comprises the following operation steps:
t1, each AC/DC module takes stable direct current bus voltage as a target, and given values UDC + _ ref and UDC- _ ref of a voltage ring are set as rated operation voltage of the direct current bus; the given value of the voltage loop is differenced with the corresponding output positive/negative voltage, and the difference is summed after PI regulation;
t2, when the generated power in the direct current bus is larger than the power consumption power, the voltage of the bus is increased, and the voltage loop outputs and adjusts the given current Iref _ total which is reduced to be transmitted to the bus;
t3, when the generated power in the direct current bus is smaller than the power consumption power, adjusting and increasing the given current Iref _ total transmitted to the direct current bus to be used as the maximum limiting current of the AC/DC module so as to limit the maximum output power of the module;
and T4, dividing the given current Iref _ total by the number of the AC/DC modules to obtain an output given current value Iref _ mod, comparing the output given current value Iref _ mod with a set current limit value Iref _ rating, taking a smaller value as a final output current given value, subtracting the value from the actual output current of the module, and generating a modulation wave of the module by PI regulation, dq inverse transformation and PWM modulation to control the main circuit and realize module control.
3. The energy conversion device of the microgrid according to claim 2, characterized in that when two or more AC/DC modules are operated in parallel, one of the AC/DC modules is a master and the others are slaves, for the DC bus side, the master is used as a voltage source to support the bus voltage, and the slaves are used as current sources to realize current sharing output among the modules by adopting a double-loop control mode of a voltage outer loop and a current inner loop; for the alternating current output side, all modules of the AC/DC power converter operate as current sources, parallel current sharing operation is achieved through high-speed communication, in order to guarantee that current loop setting of each unit charging module is the same, the main module achieves the function of a voltage loop, voltage loop output is sent to each AC/DC module through a high-speed SPI bus to serve as a set value Iref _ mod of the current loop, and other slave machines operate in a current control mode.
4. The microgrid energy conversion device of claim 1, wherein in the bidirectional transition process operating mode, the grid-connected to off-grid step comprises: the EMS control panel provides a mode switching and off-grid state information instruction, and controls and switches the fast switch, and the AC/DC power converter is switched from a grid-connected working mode to an off-grid working mode when switching from grid-connected to off-grid.
5. The device according to claim 1 or 4, wherein in the bidirectional transient operation mode, the step of switching from off-grid to on-grid comprises:
the method comprises the steps that an EMS control panel provides power grid voltage related information to an AC/DC power converter through phase-locked control, the power grid voltage related information specifically comprises grid-connected state information, power grid voltage, frequency information and synchronous signals, the AC/DC power converter achieves synchronization through adjusting amplitude, frequency and phase of output voltage and amplitude, frequency and phase of the power grid voltage, primary compensation is carried out through amplitude/phase angle, and whether synchronization is overtime or not is judged after compensation;
if overtime, the synchronization fails, and the reason is returned; if the voltage/frequency of the AC side of the AC/DC power converter is not overtime, judging whether the voltage/frequency of the AC side of the AC/DC power converter is too high or too low compared with the voltage/frequency in the AC power grid, if the voltage/frequency is judged to be too high or too low, failing in the same period, and returning to the reason; if the voltage/frequency is not too high or too low, respectively judging whether the differential pressure, the frequency difference and the angle difference are out of limit, and if so, adjusting the output of the energy storage converter; if the differential pressure, the frequency difference and the angle difference are not out of limit, judging whether the angle difference is changed, if so, calculating a closing advance angle, judging whether the current time is the optimal closing time according to the angle, if so, judging that the current time is the optimal closing time or judging that the angle difference is not changed, switching the AC/DC power converter from a voltage-frequency mode to an active power-reactive power mode, and simultaneously, successfully obtaining the result;
the EMS control panel sends a mode switching instruction, and simultaneously switches the fast switch, so that the AC/DC converter is converted into a grid-connected working mode from an inversion working mode.
6. The energy conversion device of the microgrid according to claim 1, characterized in that the non-isolated DC/DC power converter works in a master-slave parallel mode with two or more modules connected in parallel, a master of the power converter serves as a voltage source to support a bus voltage, bidirectional flow of energy is realized by working in a double-loop control mode of a voltage outer loop and a current inner loop, a slave serves as a current source, current-sharing output among a plurality of modules is realized between the master and each slave through high-speed parallel communication, the non-isolated DC/DC power converter changes the working operation mode by self logic and receiving instructions, and the working operation mode includes a constant power mode and a constant voltage mode.
7. The energy conversion device of claim 1, wherein the BUCK-BOOST circuit of the pre-stage structure in the isolated DC/DC power converter adopts a dual-loop control method of a voltage outer loop and a current inner loop, and comprises: given an output voltage reference value U * o And the actual output voltage U o Performing PI regulation to obtain a current output value I * o2 This value is related to the given current limit I * o1 Comparing, and taking the smaller value as the given current value I * o The value and the output current I o And performing PI regulation, and sending a signal to a PWM generator to generate a modulation signal of a power device in the BUCK-BOOST circuit.
8. The microgrid energy conversion device of claim 1, wherein a post-stage structure in the isolated DC/DC power converter adopts a double-loop control mode of a voltage outer loop and a current inner loop, and output voltage is kept stable by adjusting output frequency.
9. The microgrid energy conversion device of claim 1 or 7, wherein in the latter stage structure, the resonant circuit in the bidirectional AC/DC power resonant converter is an LLC resonant converter circuit.
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