CN111585302B - Ship inverter grid-connected optimization method based on improved droop control - Google Patents

Ship inverter grid-connected optimization method based on improved droop control Download PDF

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CN111585302B
CN111585302B CN202010345064.0A CN202010345064A CN111585302B CN 111585302 B CN111585302 B CN 111585302B CN 202010345064 A CN202010345064 A CN 202010345064A CN 111585302 B CN111585302 B CN 111585302B
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inverter
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CN111585302A (en
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李峻宇
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Wuhan Tianfuhai Technology Development Co ltd
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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
    • 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
    • H02J13/00—Circuit arrangements for providing remote indication of network conditions, e.g. an instantaneous record of the open or closed condition of each circuitbreaker in the network; Circuit arrangements for providing remote control of switching means in a power distribution network, e.g. switching in and out of current consumers by using a pulse code signal carried by the network
    • H02J13/00006—Circuit arrangements for providing remote indication of network conditions, e.g. an instantaneous record of the open or closed condition of each circuitbreaker in the network; Circuit arrangements for providing remote control of switching means in a power distribution network, e.g. switching in and out of current consumers by using a pulse code signal carried by the network characterised by information or instructions transport means between the monitoring, controlling or managing units and monitored, controlled or operated power network element or electrical equipment
    • H02J13/00016—Circuit arrangements for providing remote indication of network conditions, e.g. an instantaneous record of the open or closed condition of each circuitbreaker in the network; Circuit arrangements for providing remote control of switching means in a power distribution network, e.g. switching in and out of current consumers by using a pulse code signal carried by the network characterised by information or instructions transport means between the monitoring, controlling or managing units and monitored, controlled or operated power network element or electrical equipment using a wired telecommunication network or a data transmission bus

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Abstract

The invention provides a naval inverter grid-connected optimization method based on improved droop control, which comprises the following steps: designing a voltage + current double closed-loop controller of an inverter for a ship; introducing a virtual impedance; the equivalent output impedance of the ship inverter is changed by changing the virtual impedance, so that the problem of power grid circulation caused by the traditional droop control is solved; the operation mode and the working state of the ship-based inverter are refined, the grid-connected working condition of the ship-based inverter is reduced, and the influence of different grid-connected devices on a grid-connected process when the ship-based inverter is connected to the grid is reduced; the invention has the beneficial effects that: the influence of different on-grid equipment on a grid-connected process when the ship inverter is connected to the grid is solved, and the stability of a ship power grid system is improved.

Description

Ship inverter grid-connected optimization method based on improved droop control
Technical Field
The invention relates to the field of grid connection of ship-based inverters, in particular to a grid connection optimization method of a ship-based inverter based on improved droop control.
Background
The grid-connected inverter system for the ship comprises a plurality of typical operation modes, such as parallel connection between two (or more) inverters, grid connection between the inverters and an auxiliary generator (which can be called as auxiliary generation for short) and switching between the inverters and shore power. When the low-voltage load changes greatly, the power supply equipment of the low-voltage power grid is frequently switched, so that risks such as grid connection failure and the like often occur during frequent inverter grid connection conversion. The grid-connected technology of the marine inverter aims at optimizing a parallel strategy of two inverters, an inverter and auxiliary power grid-connected strategy and an inverter and shore power switching strategy, simultaneously reduces the influence of electromagnetic interference of the inverters on other equipment, increases the stability and reliability of the system, and further plays a role in improving the life force of a ship power grid.
When one standby inverter is connected in parallel to the grid inverter, the standby inverter generally employs current control since voltage is supplied by the low voltage grid and no voltage control loop is required. In the prior art, bus current is compensated through droop control, harmonic content and reactive current in the bus current are detected firstly, then apparent power of the bus current is calculated, and reactive power of a ship inverter is apportioned by analyzing a droop relation between a compensation component and the apparent power. In the prior art, a method of amplitude limiting control is also utilized to optimize the compensation component, so that the reactive power distribution between two ship-based inverters is adjusted. When two inverters are connected in parallel on a ship, the ship inverter needs to consider the adjustment of self voltage while realizing reactive power distribution, so a more complex control mode is adopted. Besides frequency modulation and voltage regulation, the ship inverter and the auxiliary generator are connected in a grid mode, and harmonic waves also need to be compensated so as to reduce circulating currents in the bus. Because the ship-borne inverter adopts the virtual inertia control technology, when the ship-borne inverter is connected with the auxiliary generator in a grid mode, the same control strategy as that of the two inverters in parallel can be used. The original ship and shore power integration adopts a power-off switching strategy, when the ship is ready to land, a ship inverter for supplying power to a low-voltage power grid on the ship is cut off, and then the shore power supply and the low-voltage power grid are connected. In order to reduce the influence on the naval equipment as much as possible, a seamless grid-connection strategy is generally adopted at present, namely when the shore power is switched, a low-voltage power grid cannot be powered off, so that the normal power supply of the naval equipment cannot be influenced.
The main differences between the naval and terrestrial power networks are:
1) when high-energy weapons and high-power detection equipment on ships are started, high-power electric energy is needed, so that the ship power grid needs to meet the power consumption requirements of various weapons and equipment in a limited space.
2) Available space on ships is limited, but equipment is numerous, and the electromagnetic environment is severe, so the ship power grid needs to consider the influence of electromagnetic interference while meeting the reasonable distribution of power supply equipment.
3) No matter the ship is in a cruising state or a fighting state, when the ship power grid fails, the power supply must be quickly recovered, otherwise, the irretrievable result is caused, so the ship power grid has extremely high requirements on reliability and vitality.
Disclosure of Invention
In view of the above, the ship-based inverter of the invention adopts an improved droop control technology, so that the voltage and power of the ship-based inverter can be adjusted through droop control no matter whether the two inverters are connected in parallel, the inverter is connected with an auxiliary generator in a grid mode or the inverter is switched with shore power; according to the grid-connected mode and the state of the ship-based inverter, respective grid-connected flows are respectively designed for three working conditions of the ship-based inverter, the auxiliary generator and the shore power supply of the on-grid equipment, and the grid-connected flow under each working condition is explained.
The invention provides a naval inverter grid-connected optimization method based on improved droop control, which specifically comprises the following steps:
s101: designing a voltage closed-loop controller and a current closed-loop controller of the inverter for the warship, namely a voltage + current double closed-loop controller, and introducing virtual impedance to obtain equivalent output impedance of the inverter for the warship; the outer ring of the voltage + current double closed-loop controller is controlled by voltage and adopts a PI controller, the inner ring is controlled by current and also adopts a PI controller;
s102: the equivalent output impedance of the ship inverter is changed by changing the value of the introduced virtual impedance, so that the voltage + current double closed-loop controller controls and finishes the given of the reference voltage and the distribution of the power grid load power;
s103: the method comprises the steps of detailing and setting a naval inverter grid-connected process, wherein the process comprises six operation modes and four working states;
s104: adopting the method for adjusting the voltage + current double closed-loop controller in the step S102, setting different operation modes and working states in the step S103 for the ship-based inverter in the actual working condition of the ship-based inverter grid connection to optimize the actual working condition of the ship-based inverter grid connection, and completing the optimization of the ship-based inverter grid connection process; the practical working conditions of the ship inverter grid connection comprise that two inverters are connected in parallel, the inverters are connected with an auxiliary generator in a grid mode, and the inverters are switched with shore power;
further, step S101 specifically includes:
when the virtual impedance is not introduced, the equivalent output impedance of the inverter for the ship is shown as the formula (1):
Figure GDA0003092176040000031
in the formula (1), L is the inductance of the inverter for the ship; k is a radical ofUA control coefficient which is voltage feedback; k is a radical ofeIs the proportionality coefficient of the PI controller in the current control loop; k is a radical ofPWMInverter for shipGain factor in PWM control; k is a radical ofpIs the proportionality coefficient of the PI controller in the voltage control loop; k is a radical ofiIs the integral coefficient of the PI controller in the voltage control loop; s is the complex frequency;
introducing a virtual impedance to obtain formula (2):
Figure GDA0003092176040000032
in the formula (2), urefReference voltage u for the voltage control loop of a ship-based inverter* refThe voltage set value is optimized through a virtual impedance control strategy; zV(s) introducing a virtual impedance; i.e. ioThe output current of the inverter for the warship is obtained;
obtaining the equivalent output impedance Z of the inverter for the ship according to the formulas (1) and (2)* out(s) is of formula (3):
Figure GDA0003092176040000033
further, in step S102, the control parameter of the voltage + current dual closed-loop controller is adjusted by changing the value of the introduced virtual impedance, so that the voltage + current dual closed-loop controller controls to complete the setting of the reference voltage and the distribution of the grid load power, specifically:
when the impedance of a power supply line is very small and is less than or equal to m ohms, the virtual impedance is set as follows: zV(s)＝kULs, then Z* outLs, i.e. equivalent output impedance Z of the ship inverter* out(s) is Ls and represents the equivalent output impedance Z of the ship inverter* out(s) is determined by its own inductance L; the value range of m is (0, eta), and eta is a preset value;
when the impedance of the power supply line is larger than m ohms, setting the virtual impedance as ZV(s)＝sωcLV/(s+ωc) Wherein ω iscIs the cut-off frequency, L, of the low-pass filterVFor setting the virtual inductance by varying ωc、LVThe equivalent output impedance of the ship inverter is changed by the parameters, so that the voltage + current double closed-loop controller controls the given reference voltage and the distribution of the power grid load power.
Further, in the step S103, a naval inverter grid-connected process is set in a detailed manner, and includes six operation modes and four working states, specifically:
the six operation modes of the ship-based inverter comprise: the method comprises the following steps of (1) an inverter single machine mode, an inverter single machine on-line mode, an inverter pre-parallel mode, an inverter pre-grid mode and an inverter grid-connected mode;
the four working states of the inverter for the ship comprise: the inverter standby state, the inverter running state, the inverter stop state and the inverter remote control state.
Further, the inverter is in a single-machine mode, specifically, the inverter is started, but the inverter outlet breaker is opened;
the inverter single-machine on-grid mode is characterized in that the inverter is started, a breaker at the outlet of the inverter is switched on, and the whole low-voltage power grid is powered by only one inverter at the moment;
the inverter is in a pre-parallel mode, specifically, the inverter is started, but the breaker at the outlet of the inverter is opened, and the inverter is connected with another on-grid inverter in parallel;
the inverter is in a parallel mode, specifically, the inverter is started, and an inverter outlet breaker is switched on and is connected in parallel with another on-grid inverter;
the inverter is in a pre-grid-connected mode, specifically, the inverter is started, but a breaker at the outlet of the inverter is opened, and the inverter is to be connected with another on-grid auxiliary generator or shore power grid;
the inverter is in a grid-connected mode, specifically, the inverter is started, and an inverter outlet breaker is switched on and is connected with another on-grid auxiliary generator or shore power grid.
Further, the inverter is ready for starting, specifically, the temperature and humidity of the inverter and the internal state are normal;
the inverter running state is specifically that the inverter is started and running;
the inverter is in a shutdown state, specifically, the inverter stops running;
the inverter remote control state is specifically that the inverter is remotely controlled through a distribution board.
Further, for the parallel operating condition of the two inverters in step S104, the optimization of the grid-connected process specifically includes:
s201: the two inverters are respectively a first inverter and a second inverter; the outlet circuit breakers of the first inverter and the second inverter are controlled by corresponding distribution boards; the first inverter and the second inverter are also controlled by one inverter grid-connected controller; the inverter grid-connected controller is connected with the first inverter and the second inverter through a CAN communication network; the inverter grid-connected controller is used for acquiring the working state information of the first inverter and the second inverter;
s202: selecting inverters to be grid-connected as the first inverter and the second inverter through the distribution board;
s203: the inverter grid-connected controller acquires the state information of the first inverter and the second inverter through a CAN communication network;
s204: the inverter grid-connected controller judges whether the first inverter is in a ready state, a running state and a remote control state according to the state information of the first inverter; if yes, go to step S205; otherwise, the first inverter is not ready for error reporting, and the step S220 is skipped;
s205: setting the first inverter into an inverter single-machine on-grid mode through the inverter grid-connected controller;
s206: after receiving the control signal from the inverter grid-connected controller, the first inverter converts the operation mode of the first inverter into a single-machine grid-in mode and simultaneously returns a signal to the CAN communication network;
s207: if the inverter grid-connected controller receives that the operation mode of the first inverter in the CAN communication network is the inverter single-machine grid-connected mode, the operation step S208 is executed; otherwise, the inverter grid-connected controller reports that the first inverter has an error in the operation mode, and the step S220 is skipped;
s208: the inverter grid-connected controller sets reference voltages of the first inverter and the second inverter;
s209: after the first inverter and the second inverter receive the control signals, resetting the reference voltage of the first inverter and the second inverter, and simultaneously returning the reference voltage set by the first inverter and the second inverter through the CAN communication network; if the inverter grid-connected controller receives correct reference voltages from the first inverter and the second inverter in the CAN communication network, the step S210 is entered; otherwise, the inverter grid-connected controller reports that the reference voltage of the first inverter or the second inverter is set incorrectly, and the step S220 is skipped;
s210: the inverter grid-connected controller sets the operation mode of the first inverter to be an inverter pre-parallel mode and sets the operation mode of the second inverter to be an inverter parallel mode;
s211: after the first inverter and the second inverter receive the control signals from the inverter grid-connected controller, the operation modes of the first inverter and the second inverter are respectively converted into an inverter pre-parallel mode and an inverter parallel mode, and signals are simultaneously returned to the CAN communication network;
s212: if the inverter grid-connected controller receives that the operation mode of the first inverter is the inverter pre-parallel mode and the operation mode of the second inverter is the inverter parallel mode in the CAN communication network, the method goes to step S213; otherwise, the inverter grid-connected controller reports that the operation mode of the first inverter or the second inverter is wrong, and the step S220 is skipped;
s213: the inverter grid-connected controller sends a first inverter request permission outlet circuit breaker closing signal to an operator to inform the operator that the outlet circuit breaker of the first inverter can be closed currently;
s214: an operator permission request; the inverter grid-connected controller receives an operator permission signal and sends a closing signal to the first inverter;
s215: the distribution board switches on an outlet circuit breaker of the first inverter, and the first inverter returns a switching-on signal to the CAN communication network;
s216: the inverter grid-connected controller judges whether the first inverter is successfully switched on or not according to whether a return signal from the first inverter is received or not; if a return signal from the first inverter is received, indicating that the first inverter is successfully switched on, and entering step S217; otherwise, the inverter grid-connected controller reports the switching-on failure of the first inverter, and the step S220 is skipped;
s217: the inverter grid-connected controller cancels a closing signal sent to the first inverter and sets the operation mode of the first inverter to be a grid-connected mode of the inverter;
s218: after receiving the control signal from the inverter grid-connected controller, the first inverter converts the operation mode of the first inverter into a grid-connected mode of the inverter and simultaneously returns a signal to the CAN communication network;
s219: if the inverter grid-connected controller receives a return signal from the first inverter, the inverter grid-connected controller indicates that the first inverter and the second inverter are successfully connected, otherwise, the inverter grid-connected controller reports that the operation mode of the first inverter is set incorrectly;
s220: and ending the parallel connection process of the two inverters, and resetting the grid connection process.
Further, in step S104, for the grid-connected operating condition between the inverter and the auxiliary generator, the optimization of the grid-connected process specifically includes:
s301: selecting a working condition to grid the first inverter and the auxiliary generator through the distribution board;
s302: the inverter grid-connected controller sets the reference voltage of the first inverter through a CAN communication network;
s303: after receiving the control signal, the first inverter resets the self reference voltage and returns the self set reference voltage through the CAN communication network; if the inverter grid-connected controller receives the reference voltage from the first inverter in the CAN communication network correctly, the method goes to step S304; otherwise, the inverter grid-connected controller reports that the first inverter reference voltage is set incorrectly, and the step S314 is skipped;
s304: the inverter grid-connected controller sets the operation mode of the first inverter to be an inverter pre-grid-connected mode;
s305: after receiving a control signal from the inverter grid-connected controller, the first inverter converts the operation mode of the first inverter into an inverter pre-grid-connected mode and simultaneously returns a signal to the CAN communication network;
s306: if the inverter grid-connected controller receives a return signal from the first inverter, the process goes to step S307; otherwise, the inverter grid-connected controller reports an operation mode setting error of the first inverter, and the step S314 is skipped;
s307: the inverter grid-connected controller sends a first inverter request permission outlet circuit breaker closing signal to an operator to inform the operator that the outlet circuit breaker of the first inverter can be closed currently;
s308: an operator permission request; the inverter grid-connected controller receives an operator permission signal and sends a closing signal to the first inverter;
s309: the distribution board switches on an outlet circuit breaker of the first inverter, and the first inverter returns a switching-on signal to the CAN communication network;
s310: the inverter grid-connected controller judges whether the first inverter is successfully switched on or not according to whether a return signal from the first inverter is received or not; if a return signal from the first inverter is received, indicating that the first inverter is successfully switched on, and entering step S311; otherwise, the inverter grid-connected controller reports the switching-on failure of the first inverter, and the step S314 is skipped;
s311: the inverter grid-connected controller cancels a closing signal sent to the first inverter and sets the operation mode of the first inverter to be a grid-connected mode of the inverter;
s312: after receiving the control signal from the inverter grid-connected controller, the first inverter converts the operation mode of the first inverter into a grid-connected mode of the inverter and simultaneously returns a signal to the CAN communication network;
s313: if the inverter grid-connected controller receives a return signal from the first inverter, the inverter grid-connected controller indicates that the grid connection of the first inverter and the auxiliary generator is successful, otherwise, the inverter grid-connected controller reports that the operation mode of the first inverter is set incorrectly;
s314: and the grid connection process of the first inverter and the auxiliary generator is finished, and the grid connection process is reset.
In step S104, for the grid-connected operating condition between the inverter and the shore power, the optimization of the grid-connected process specifically includes:
s401: selecting a working condition to be grid-connected with the first inverter and shore power through the distribution panel;
s402: the inverter grid-connected controller sets the reference voltage of the first inverter through a CAN communication network;
s403: after receiving the control signal, the first inverter resets the self reference voltage and returns the self set reference voltage through the CAN communication network; if the inverter grid-connected controller receives the correct reference voltage from the first inverter in the CAN communication network, the method goes to step S404; otherwise, the inverter grid-connected controller reports that the first inverter reference voltage is set incorrectly, and the step S417 is skipped;
s404: the inverter grid-connected controller sets the operation mode of the first inverter to be an inverter pre-grid-connected mode;
s405: after receiving a control signal from the inverter grid-connected controller, the first inverter converts the operation mode of the first inverter into an inverter pre-grid-connected mode and simultaneously returns a signal to the CAN communication network;
s406: if the inverter grid-connected controller receives the feedback signal from the first inverter, step S407 is performed; otherwise, the inverter grid-connected controller reports an error in setting of the operation mode of the first inverter, and the step S417 is skipped;
s407: the inverter grid-connected controller sends a first inverter request permission outlet circuit breaker closing signal to an operator to inform the operator that the outlet circuit breaker of the first inverter can be closed currently;
s408: an operator permission request; the inverter grid-connected controller receives an operator permission signal and sends a closing signal to the first inverter;
s409: the distribution board switches on an outlet circuit breaker of the first inverter, and the first inverter returns a switching-on signal to the CAN communication network;
s410: the inverter grid-connected controller judges whether the first inverter is successfully switched on or not according to whether a return signal from the first inverter is received or not; if a return signal from the first inverter is received, indicating that the first inverter is successfully switched on, and entering step S411; otherwise, the inverter grid-connected controller reports the switching-on failure of the first inverter and jumps to the step S417;
s411: the inverter grid-connected controller cancels a closing signal sent to the first inverter and sets the operation mode of the first inverter to be a grid-connected mode of the inverter;
s412: after receiving the control signal from the inverter grid-connected controller, the first inverter converts the operation mode of the first inverter into a grid-connected mode of the inverter and simultaneously returns a signal to the CAN communication network;
s413: if the inverter grid-connected controller receives the feedback signal from the first inverter, it indicates that the operation mode of the first inverter is successfully converted, and the process goes to step S414; otherwise, the inverter grid-connected controller reports an error in setting of the operation mode of the first inverter, and the step S417 is skipped;
s414: the inverter grid-connected controller sends a brake-separating allowing signal to the shore power circuit breaker, and the operation mode of the first inverter is set to be an inverter single-machine grid-connected mode;
s415: the distribution board operates the breaker opening of the shore power; the first inverter receives a control signal from the inverter grid-connected controller, sets the operation mode of the first inverter to be an inverter single-machine grid-in mode, and simultaneously returns a signal to the CAN communication network;
s416: if the inverter grid-connected controller receives a return signal from the first inverter, the success of grid connection between the first inverter and shore power is indicated, and the grid connection process is finished; otherwise, the inverter grid-connected controller reports that the operation mode of the first inverter is set incorrectly;
s417: and the grid connection process of the first inverter and the shore power is finished, and the grid connection process is reset.
The technical scheme provided by the invention has the beneficial effects that: the influence of different on-grid equipment on a grid-connected process when the ship inverter is connected to the grid is solved, and the stability of a ship power grid system is improved.
Drawings
FIG. 1 is a flow chart of a naval inverter grid-connected optimization method based on improved droop control;
FIG. 2 is a control block diagram of the voltage + current dual closed-loop controller according to the present invention;
FIG. 3 is a graph of logarithmic frequency response characteristics of a naval inverter according to the present invention;
FIG. 4 is a schematic diagram of the operation mode and operation state of the ship-based inverter in the invention;
FIG. 5 is a flow chart of the grid connection of two ship-based inverters optimized in the invention;
FIG. 6 is a flow chart of the grid connection between the optimized naval inverter and the auxiliary generator in the present invention;
FIG. 7 is a flow chart of the grid connection between the optimized naval inverter and shore power in the invention;
FIG. 8 is a simulation result of an improved droop control strategy of the present invention;
FIG. 9 is a waveform diagram of an actual measurement of two ship-based inverters successfully connected in parallel according to an embodiment of the present invention;
FIG. 10 is a waveform diagram of measured results of successful synchronization of a naval inverter and an auxiliary generator in an embodiment of the present invention;
fig. 11 is a waveform diagram of actual measurement of successful grid connection between a ship-based inverter and shore power in the embodiment of the invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, embodiments of the present invention will be further described with reference to the accompanying drawings.
Referring to fig. 1, an embodiment of the present invention provides a flowchart of a grid-connected optimization method for a naval inverter based on improved droop control, which specifically includes:
s101: designing a voltage + current double closed-loop controller, namely a voltage + current double closed-loop controller, of the inverter for the ship, and introducing virtual impedance to obtain equivalent output impedance of the inverter for the ship; the outer ring of the voltage + current double closed-loop controller is controlled by voltage and adopts a PI controller, the inner ring is controlled by current and also adopts a PI controller;
s102: the equivalent output impedance of the ship inverter is changed by changing the value of the introduced virtual impedance, so that the voltage + current double closed-loop controller controls and finishes the given of the reference voltage and the distribution of the power grid load power;
s103: the method comprises the steps of detailing and setting a naval inverter grid-connected process, wherein the process comprises six operation modes and four working states;
s104: adopting the method for adjusting the voltage + current double closed-loop controller in the step S102, setting different operation modes and working states in the step S103 for the ship-based inverter in the actual working condition of the ship-based inverter grid connection to optimize the actual working condition of the ship-based inverter grid connection, and completing the optimization of the ship-based inverter grid connection process; the practical working conditions of the ship inverter grid connection comprise that two inverters are connected in parallel, the inverters are connected with an auxiliary generator in a grid mode, and the inverters are switched with shore power; the auxiliary generator is an auxiliary generator;
referring to fig. 2, fig. 2 is a control block diagram of the voltage + current dual closed-loop controller according to the present invention; in FIG. 2, kpIs the proportionality coefficient, k, of the PI controller in the voltage control loopiIs the integral coefficient, k, of the PI controller in the voltage control loopeIs the proportionality coefficient, k, of the PI controller in the current control loopPWMIs the gain coefficient, k, in PWM control of the inverter for shipsU、kIControl coefficients of voltage feedback and current feedback, iLIs the feedback current of the current control loop of the inverter for the ship, C is the capacitance value of the filter capacitor of the inverter for the ship, u, ioOutput voltage and output current, Z, of the inverter for ships, respectivelyloadFor equivalent impedance, Z, of the load side of the ship-based inverterV(s) is the virtual impedance, urefReference voltage u for the voltage control loop of a ship-based inverter* refThe voltage set value is optimized through a virtual impedance control strategy; the outer ring is set to be voltage controlled, the output voltage waveform of the ship-based inverter is optimized by using the PI controller, and the output precision of the inverter can be increased; the inner ring is set to be in current control, and the PI controller is used for increasing the overall dynamic performance of the ship-based inverter.
When the virtual impedance is not introduced, the equivalent output impedance of the inverter for the ship is shown as the formula (1):
Figure GDA0003092176040000111
introducing a virtual impedance to obtain formula (2):
Figure GDA0003092176040000112
obtaining the equivalent output impedance Z of the inverter for the warship according to the formulas (1) and (2)* out(s) is of formula (3):
Figure GDA0003092176040000121
if order ZV(s)＝kULs, i.e. having Z* outThis equation illustrates that the output impedance of the ship-based inverter can be approximately equal to Ls after the introduction of the virtual impedance, and the above analysis shows that if the power line impedance is small (due to the differences in transmission distances and the unequal capacity,generally between tens of m omega to several omega), if it can be ignored, the output impedance value of the ship inverter is only determined by the inductance L of the inverter, that is, when the impedance of the power supply line is very small and less than 10 ohms, the virtual impedance is set as: zV(s)＝kULs, then Z* outLs, i.e. equivalent output impedance Z of the ship inverter* out(s) is Ls and represents the equivalent output impedance Z of the ship inverter* out(s) is determined by its own inductance L.
When the impedance of the power supply line is greater than or equal to 10 ohms, the inductive virtual impedance value is set as ZV(s)＝sωcLV/(s+ωc) Wherein ω iscIs the cut-off frequency, L, of the low-pass filterVIs a virtual inductance set in the strategy.
The value of the virtual impedance can be changed by setting the size of the parameter, so that different virtual impedance values can be selected according to different models of the ship-based inverter. In practical application, the larger the inductive reactance is, the better the control effect of the virtual impedance is, but the value of the inductive reactance is in direct proportion to the size of the equipment, so that the influence of different parameter selections on the output impedance of the ship inverter is observed, and the selection of the value of the virtual impedance is facilitated.
Comparing the response conditions of the ship-borne inverters to the logarithmic frequency characteristics under the influence of different parameters, and the simulation model parameters of each group of ship-borne inverters are shown in table 1.
TABLE 1 naval inverter simulation model parameters
Figure GDA0003092176040000122
Referring to fig. 3, it can be found that when the frequency of the ship-based inverter is 50Hz, the output impedance is inductive, and normal use of the conventional droop control strategy is ensured.
Referring to fig. 4, in step S103, a naval inverter grid connection process is set in a detailed manner, and includes six operation modes and four working states, specifically:
the inverter is in a single-machine mode, specifically, the inverter is started, but the inverter outlet breaker is opened; the inverter single-machine on-grid mode specifically means that the inverter is started, a breaker at the outlet of the inverter is switched on, and only one inverter supplies power to the whole low-voltage power grid at the moment; the inverter is in a pre-parallel mode, specifically, the inverter is started, but the breaker at the outlet of the inverter is opened, and the inverter is connected with another on-grid inverter in parallel; the inverter is in a parallel mode, specifically, the inverter is started, and an inverter outlet breaker is switched on and is connected in parallel with another on-grid inverter; the inverter is in a pre-grid-connected mode, specifically, the inverter is started, but a breaker at the outlet of the inverter is opened, and the inverter is to be connected with another on-grid auxiliary generator or shore power grid; the inverter is in a grid-connected mode, specifically, the inverter is started, and the breaker at the outlet of the inverter is switched on and is connected with another on-grid auxiliary generator or shore power grid. The inverter is ready to be started, specifically, the temperature and humidity of the inverter and the internal state are normal; the inverter running state is specifically that the inverter is started and running; the inverter is in a shutdown state, specifically, the inverter stops running; the inverter remote control state is specifically that the inverter is remotely controlled through a distribution board.
Referring to fig. 5-7, fig. 5-7 are a flow chart of grid connection between two ship-based inverters, a flow chart of grid connection between a ship-based inverter and an auxiliary generator, and a flow chart of grid connection between a ship-based inverter and shore power, respectively, optimized in the present invention; in fig. 5-7, inverter # 1 is the first inverter and inverter # 2 is the second inverter in the process of the present invention;
1) the process begins. 2) The inverter grid-connected control module acquires the state information of the to-be-combined 1# inverter and the to-be-combined 2# inverter on the CAN communication network. 3) The inverter grid-connected control module judges whether the working state of the 1# inverter to be combined is running, remote-controlled and ready, if so, the next process is entered, and if not, the error is reported that the 1# inverter is not ready, and meanwhile, the parallel connection process is exited and the process is reset. 4) The inverter grid-connected control module sets the operation mode of the 1# inverter to be a single machine. 5) The inverter CAN change the state of the inverter into a single machine after receiving the operation mode setting signal, and simultaneously CAN return a signal to the CAN communication network, if the inverter grid-connected control module receives that the operation mode of the 1# inverter in the CAN communication network is the single machine, the next process is entered, if not, the error is reported as the 1# inverter mode error, the parallel process is exited, and the process is reset. 6) The inverter grid-connected control module sets reference voltages of the two inverters. 7) The inverter resets the reference voltage after receiving the signal, and simultaneously returns the reference voltage to the CAN communication network, if the reference voltage of the inverter is received by the inverter grid-connected control module in the CAN communication network correctly, the next process is entered, if not, an error is reported to set the reference voltage of the inverter, and meanwhile, the grid-connected controller exits the parallel process, and the process is reset. 8) The inverter grid-connected control module sets the operation mode of the 1# inverter to be pre-connected in parallel and sets the operation mode of the 2# inverter to be connected in parallel. 9) And 5) if the inverter mode is successfully set, entering the next process, if not, reporting an error to set the inverter mode, exiting the parallel process and resetting the process. 10) And the inverter grid-connected control module sends a closing permission signal to the distribution board to inform an operator that the 1# inverter can be closed currently. 11) And the distribution board is switched on after receiving the switching-on allowing signal. 12) And after receiving a distribution board closing signal, the inverter grid-connected control module sends a closing instruction to the 1# inverter. 13) And the inverter grid-connected control module judges whether the 1# inverter is successfully switched on, if so, the next process is entered, and if not, the error is reported as the failure of switching on the 1# inverter, and meanwhile, the parallel process is exited and the process is reset. 14) And the inverter grid-connected control module cancels the switching-on permission signal sent to the distribution board, and simultaneously sets the operation mode of the 1# inverter to be grid-connected. 15) And 5), if the inverter mode is successfully set, ending the process, if not, reporting an error to set the error for the 1# inverter mode, exiting the parallel process and resetting the process.
The inverter and the auxiliary transmission grid connection need information interaction between the inverter grid connection module and the auxiliary transmission controller, and certain requirements are made on communication quality between the controllers. The invention only considers the flow design of the inverter grid-connected module, and does not introduce the related flow of the auxiliary power generation controller. And setting the working condition as auxiliary power grid-connected operation, and preparing to operate the 1# inverter grid connection.
1) The process begins. 2) The inverter grid-connected control module sets the reference voltage of the 1# inverter. 3) The inverter resets the reference voltage after receiving the signal, and simultaneously returns the reference voltage to the CAN communication network, if the reference voltage of the inverter is received by the inverter grid-connected control module in the CAN communication network correctly, the next step is carried out, if not, an error is reported to set the reference voltage of the 1# inverter, and meanwhile, the grid-connected controller exits the grid-connected process, and the process is reset. 4) The inverter grid-connected control module sets the operation mode of the 1# inverter to be pre-grid-connected. 5) And step 3), if the inverter mode is successfully set, entering the next process, if not, reporting an error to set the error for the inverter mode, exiting the grid-connected process and resetting the process. 6) And the inverter grid-connected control module sends a closing permission signal to the distribution board to inform an operator that the 1# inverter can be closed currently. 7) And the distribution board is closed after receiving the closing permission signal. 8) And after receiving a distribution board closing signal, the inverter grid-connected control module sends a closing instruction to the 1# inverter. 9) And the inverter grid-connected control module judges whether the 1# inverter is successfully switched on, if so, the next process is entered, and if not, the error is reported as the failure of switching on the 1# inverter, and meanwhile, the grid-connected process is exited and the process is reset. 10) And the inverter grid-connected control module cancels the switching-on permission signal sent to the distribution board, and simultaneously sets the operation mode of the 1# inverter to be grid-connected. 11) And in the same step 3), if the inverter mode is successfully set, the process is ended, if not, an error is reported to be a 1# inverter mode setting error, and meanwhile, the grid-connected process is quitted, and the process is reset.
The switching between the inverter and the shore power is realized in consideration of actual conditions, and when a ship is in shore, a heavy load is not required, so the shore power and the inverter are not required to be simultaneously supplied to the load in a network, and information interaction between the inverter network controller and the shore power controller is also required. Compared with other grid-connected operations, the method has the advantages of higher switching flow difficulty, higher risk and stricter requirement on communication quality. And setting the working condition as shore power on-grid operation, and preparing to operate 1# inverter switching.
(1) The process begins. (2) The inverter grid-connected control module sets the reference voltage of the 1# inverter. (3) The inverter resets the reference voltage after receiving the signal, and simultaneously returns the reference voltage to the CAN communication network, if the reference voltage of the inverter is received by the inverter grid-connected control module in the CAN communication network correctly, the next process is entered, if not, an error is reported to set the reference voltage of the 1# inverter, and meanwhile, the grid-connected controller exits the switching process and resets the process. (4) The inverter grid-connected control module sets the operation mode of the 1# inverter to be pre-grid-connected. (5) And step 3), if the inverter mode is successfully set, entering the next process, if not, reporting an error to set the inverter mode, exiting the switching process and resetting the process. (6) And the inverter grid-connected control module sends a closing permission signal to the distribution board to inform an operator that the 1# inverter can be closed currently. (7) And the distribution board is closed after receiving the closing permission signal. (8) And after receiving a distribution board closing signal, the inverter grid-connected control module sends a closing instruction to the 1# inverter. (9) And the inverter grid-connected control module judges whether the 1# inverter is successfully switched on, if so, the next process is entered, and if not, the error is reported as the failure of switching on the 1# inverter, and meanwhile, the switching process is exited and the process is reset. (10) And the inverter grid-connected control module cancels the switching-on permission signal sent to the distribution board, and simultaneously sets the operation mode of the 1# inverter to be grid-connected. (11) And step 3), if the inverter mode is successfully set, entering the next process, if not, reporting an error to set the error for the 1# inverter mode, exiting the switching process and resetting the process. (12) The inverter grid-connected control module sends a shore power circuit breaker opening permission signal to the distribution board, and meanwhile the operation mode of the 1# inverter is set to be a single-machine on-grid mode. (13) And the distribution board operates the shore power opening after receiving the shore power breaker opening allowing signal. (14) And step 3), if the inverter mode is successfully set, the process is ended, if not, an error is reported to be a 1# inverter mode setting error, and meanwhile, the switching process is quitted, and the process is reset.
In the scheme, the principles of inversion and auxiliary power grid connection and inversion and shore power switching are basically consistent with those of two inversions in parallel connection, and thus, the details are not repeated here.
In the simulation model, the rated power of two ship-based inverters is 1MW, the rated voltage E is 390V, and the input direct current voltage U of the ship-based inverterdcIn the parameter design for the low-pass filter, filter inductance L is 56 μ H, filter capacitance C is 1200 μ F, and output inductance L is 710VoLine impedance Z of the ship-based inverter 1 (the first inverter) at 20 μ Hline1＝5×10-4+j6×10-5Ω, line impedance Zline2 of the ship-based inverter 2 (second inverter) is 2.5 × 10-4+j3×10-5Omega, active droop coefficient m is 4 x 10-7(rad/s)/W, reactive sag factor n is 2 x 10-6V/VA, virtual impedance integral coefficient Ki＝4×10-7。
When the improved droop control strategy of the present invention is adopted, please refer to fig. 8, where fig. 8 is a simulation result of the improved droop control strategy of the present invention, the inverter 1 in fig. 8 is the first inverter in the process of the present invention, and the inverter 2 is the second inverter in the process of the present invention.
Analysis is carried out on the three waveforms in fig. 8, and it is found that after real-time control optimization of CAN communication, the active power of the two ship-based inverters CAN still be accurately distributed, and the reactive power is rapidly adjusted after parallel connection is successful, so that accurate distribution is realized, and meanwhile, due to the introduction of virtual impedance, the circulating current in the low-voltage power grid is basically inhibited.
Three working conditions of the naval inverter grid connection have consistency on a grid connection strategy, an improved droop control strategy can be adopted, but the naval inverter, the auxiliary generator and the shore power supply have respective uniqueness, so that the invention develops inverter grid connection test work based on a test platform of a certain naval integrated power system, and a test device consists of two 1MW inverters, 500kW auxiliary generators, 100kW shore power supplies, a distribution panel, a junction box and a load box, which are respectively marked as a 1# inverter, a 2# inverter, an auxiliary generator and shore power.
When the two ship-borne inverters execute parallel operation, whether the parallel process is successful can be judged by observing the waveform of the alternating-current bus voltage and the output current waveforms of the two ship-borne inverters, and meanwhile, the effect of the ship-borne inverters on restraining power grid circulation by improving a droop control strategy can be judged according to the waveform. The initial working conditions of the experiment were set as follows: the inverter for the No. 1 ship normally runs on the network with 200kW load, the inverter for the No. 2 ship runs in a single-machine idle mode, the inverters for the No. 2 ship are operated to be connected in parallel, and the actual measurement waveform of the successfully connected inverters in parallel refers to FIG. 9, FIG. 9 is an actual measurement waveform diagram of the successfully connected inverters for the two ships in parallel according to the embodiment of the invention, wherein ia, ib and ic respectively represent the actual measurement waveform diagram of the output current after the successfully connected inverters in parallel;
fig. 9 (top) and fig. 9 (bottom) are waveforms of the parallel connection process of the two inverters from 2.4s to 3.4s, and it can be found that the current of the two inverters can be kept stable before the parallel connection, thereby indicating that the inverters are normally operated. At the moment of parallel connection, because the phases of the two inverters are not completely consistent, the current is changed rapidly, and the circulating current in the low-voltage power grid is obvious. Therefore, at the moment of parallel connection, the loop current generated in the low-voltage power grid has great influence on the output current of the two inverters. Fig. 9 (middle 1) and fig. 9 (middle 2) are waveforms of two inverters which are connected in parallel from 7.8s to 8s and then stably operate, and when observing the waveform situation of the output current of the inverters at this time, the phases of the current waveforms of the two inverters are basically the same, the amplitudes of the current waveforms are both smaller than the current waveform of a single inverter when the two inverters are connected to the grid, and the current amplitudes are basically the same, so that the current sharing between the two inverters is basically realized;
when the ship inverter and the auxiliary generator execute grid connection operation, the waveform of the alternating-current bus voltage and the output current waveform of the ship inverter and the auxiliary generator are observed to judge whether the grid connection process is successful, and meanwhile, the effect of the ship inverter for improving the droop control strategy to restrain the power grid circulation can be judged according to the waveform. The initial working conditions of the experiment were set as follows: the auxiliary power generation load 400kW normally operates in the grid, the 1# marine inverter single machine operates in no-load mode, the 1# marine inverter is operated to be connected to the grid, the actual measurement waveform of the successful grid connection refers to fig. 10, fig. 10 is an actual measurement waveform diagram of the successful grid connection of the marine inverter and the auxiliary power generation load in the embodiment of the invention, wherein ia, ib and ic respectively represent the actual measurement waveform diagrams of the output current after the successful grid connection.
Fig. 10 (top) and fig. 10 (middle 2) are waveforms of the inverter and auxiliary generator during the grid connection process from 4.5s to 5.2s, and analysis of the waveforms can find that the currents of the 1# inverter and the auxiliary generator can be kept stable before grid connection, so that the two inverters can operate normally, and at the moment of grid connection, because the phases of the 1# inverter and the auxiliary generator are not completely constant, the current changes sharply, and the circulating current in the low-voltage power grid is obvious. Therefore, at the moment of grid connection, the circulating current generated in the low-voltage power grid has great influence on the output current of the 1# inverter and the auxiliary generator. Fig. 10 (middle 1) and fig. 10 (lower) are waveforms of stable operation of two inverters after grid connection from 9s to 9.14s, and it can be known from analysis of output current waveforms of the auxiliary power and the 1# inverter at this time that current waveforms of the auxiliary power and the inverter are substantially the same in phase and substantially stable in amplitude, thereby explaining that power distribution is substantially achieved between the auxiliary power and the 1# inverter, and stable operation and grid connection are successful.
The inverter and shore power switching experiment is also an important item in the inverter grid-connected experiment, and because the ship is in shore, only the shore power supply supplies power to the low-voltage power grid illumination part, and the power is low, the ship needs to complete the replacement between the shore power supply and the inverter when in shore, so that the ship is changed from shore power supply to self power grid power supply, which is a necessary operation for the modern ship comprehensive power system. The working condition is set to be that the shore power supply is operated at 40kW with load, the 1# shipboard inverter is operated in a single-machine no-load mode, and then the 1# shipboard inverter is operated to switch. Please refer to fig. 11 for the successfully switched actual measurement waveforms, fig. 11 is an actual measurement waveform diagram of successful grid connection between the marine inverter and the shore power in the embodiment of the present invention, where ia, ib, and ic respectively represent actual measurement waveform diagrams of output current after successful grid connection;
fig. 11 (top) and fig. 11 (middle 2) are waveforms of the change from 4.76s to 4.92s during the operation of the load side and the inverter, the outlet current of the load side is stable before switching, and the shore power outlet breaker is rapidly opened after switching to realize seamless switching of the inverter, thereby illustrating the feasibility of the switching strategy. Fig. 11 (middle 1) and fig. 11 (lower) are waveforms of stable operation after the load end and the inverter are switched from 8s to 8.14s, and the output current waveforms of the load end and the inverter at this time are observed, and the current waveforms of the load end and the inverter are substantially consistent and the amplitude is substantially stable, so that the inverter is successfully switched after the load end is completely supplied with power by the inverter # 1 at this time.
The invention has the beneficial effects that: the influence of different on-grid equipment on a grid-connected process when the ship inverter is connected to the grid is solved, and the stability of a ship power grid system is improved.
The features of the above-described embodiments and embodiments of the invention may be combined with each other without conflict.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.

Claims (7)

1. A naval inverter grid-connected optimization method based on improved droop control is characterized by comprising the following steps: the method specifically comprises the following steps:
s101: designing a voltage closed-loop controller and a current closed-loop controller of the inverter for the warship, namely a voltage + current double closed-loop controller, and introducing virtual impedance to obtain equivalent output impedance of the inverter for the warship; the outer ring of the voltage + current double closed-loop controller is used for voltage control, a PI controller is adopted, the inner ring of the voltage + current double closed-loop controller is used for current control, and the PI controller is adopted;
s102: the equivalent output impedance of the ship inverter is changed by changing the value of the introduced virtual impedance, so that the voltage + current double closed-loop controller controls and finishes the given of the reference voltage and the distribution of the power grid load power;
s103: the method comprises the steps of detailing and setting a naval inverter grid-connected process, wherein the process comprises six operation modes and four working states;
s104: adopting the method for adjusting the voltage + current double closed-loop controller in the step S102, setting different operation modes and working states in the step S103 for the ship-based inverter in the actual working condition of the ship-based inverter grid connection to optimize the actual working condition of the ship-based inverter grid connection, and completing the optimization of the ship-based inverter grid connection process; the practical working conditions of the ship inverter grid connection comprise that two inverters are connected in parallel, the inverters are connected with an auxiliary generator in a grid mode, and the inverters are switched with shore power;
in the step S103, a naval inverter grid-connected process is set in a detailed manner, and includes six operation modes and four working states, specifically:
the six operation modes of the ship-based inverter comprise: the method comprises the following steps of (1) an inverter single machine mode, an inverter single machine on-line mode, an inverter pre-parallel mode, an inverter pre-grid mode and an inverter grid-connected mode;
the four working states of the inverter for the ship comprise: the inverter standby state, the inverter running state, the inverter stop state and the inverter remote control state;
the inverter is in a single-machine mode, specifically, the inverter is started, but the inverter outlet breaker is opened;
the inverter single-machine on-grid mode specifically means that the inverter is started, a breaker at the outlet of the inverter is switched on, and only one inverter supplies power to the whole low-voltage power grid at the moment;
the inverter is in a pre-parallel mode, specifically, the inverter is started, but the breaker at the outlet of the inverter is opened, and the inverter is connected with another on-grid inverter in parallel;
the inverter is in a parallel mode, specifically, the inverter is started, and an inverter outlet breaker is switched on and is connected in parallel with another on-grid inverter;
the inverter is in a pre-grid-connected mode, specifically, the inverter is started, but a breaker at the outlet of the inverter is opened, and the inverter is to be connected with another on-grid auxiliary generator or shore power grid;
the inverter is in a grid-connected mode, specifically, the inverter is started, and an inverter outlet breaker is switched on and is connected with another on-grid auxiliary generator or shore power grid.
2. The grid-connected optimization method for the inverter for the ship based on the improved droop control as claimed in claim 1, wherein the grid-connected optimization method comprises the following steps: step S101 specifically includes:
when the virtual impedance is not introduced, the equivalent output impedance of the inverter for the ship is shown as the formula (1):
Figure FDA0003092176030000021
in the formula (1), L is the inductance of the inverter for the ship; k is a radical ofUA control coefficient which is voltage feedback; k is a radical ofeIs the proportionality coefficient of the PI controller in the current control loop; k is a radical ofPWMIs a gain coefficient in PWM control of the inverter for warships; k is a radical ofpIs the proportionality coefficient of the PI controller in the voltage control loop; k is a radical ofiIs the integral coefficient of the PI controller in the voltage control loop; s is the complex frequency;
introducing a virtual impedance to obtain formula (2):
Figure FDA0003092176030000022
in the formula (2), urefFor a given reference voltage, u, of the voltage control loop of the ship-based inverter* refThe voltage set value is optimized through a virtual impedance control strategy; zV(s) introducing a virtual impedance; i.e. ioThe output current of the inverter for the warship is obtained;
obtaining the equivalent output impedance Z of the inverter for the ship according to the formulas (1) and (2)* out(s) is of formula (3):
Figure FDA0003092176030000023
3. the grid-connected optimization method for the inverter for the ship based on the improved droop control as claimed in claim 2, wherein the grid-connected optimization method comprises the following steps: in step S102, a control parameter of the voltage + current dual closed-loop controller is adjusted by changing a value of the introduced virtual impedance, so that the voltage + current dual closed-loop controller controls and completes the giving of the reference voltage and the distribution of the power grid load power, specifically:
when the impedance of a power supply line is very small and is less than or equal to m ohms, the virtual impedance is set as follows: zV(s)＝kULs, then Z* outLs, i.e. equivalent output impedance Z of the ship inverter* out(s) is Ls and represents the equivalent output impedance Z of the ship inverter* out(s) is determined by its own inductance L; the value range of m is (0, eta), and eta is a preset value;
when the impedance of the power supply line is larger than m ohms, setting the virtual impedance as ZV(s)＝sωcLV/(s+ωc) Wherein ω iscIs the cut-off frequency, L, of the low-pass filterVFor setting the virtual inductance by varying ωc、LVThe equivalent output impedance of the ship inverter is changed by the parameters, so that the voltage + current double closed-loop controller controls the given reference voltage and the distribution of the power grid load power.
4. The grid-connected optimization method for the inverter for the ship based on the improved droop control as claimed in claim 1, wherein the grid-connected optimization method comprises the following steps:
the inverter is ready to be started, specifically, the temperature and humidity of the inverter and the internal state are normal;
the inverter running state is specifically that the inverter is started and running;
the inverter is in a shutdown state, specifically, the inverter stops running;
the inverter remote control state is specifically that the inverter is remotely controlled through a distribution board.
5. The grid-connected optimization method for the inverter for the ship based on the improved droop control as claimed in claim 4, wherein the grid-connected optimization method comprises the following steps: in step S104, for the parallel connection condition of the two inverters, the optimization of the grid connection process specifically includes:
s201: the two inverters are respectively a first inverter and a second inverter; the outlet circuit breakers of the first inverter and the second inverter are controlled by corresponding distribution boards; the first inverter and the second inverter are also controlled by one inverter grid-connected controller; the inverter grid-connected controller is connected with the first inverter and the second inverter through a CAN communication network; the inverter grid-connected controller is used for acquiring the working state information of the first inverter and the second inverter;
s202: selecting inverters to be grid-connected as the first inverter and the second inverter through the distribution board;
s203: the inverter grid-connected controller acquires the state information of the first inverter and the second inverter through a CAN communication network;
s204: the inverter grid-connected controller judges whether the first inverter is in a ready state, a running state and a remote control state according to the state information of the first inverter; if yes, go to step S205; otherwise, the first inverter is not ready for error reporting, and the step S220 is skipped;
s205: setting the first inverter into an inverter single-machine on-grid mode through the inverter grid-connected controller;
s206: after receiving the control signal from the inverter grid-connected controller, the first inverter converts the operation mode of the first inverter into a single-machine grid-in mode and simultaneously returns a signal to the CAN communication network;
s207: if the inverter grid-connected controller receives that the operation mode of the first inverter in the CAN communication network is the inverter single-machine grid-connected mode, the operation step S208 is executed; otherwise, the inverter grid-connected controller reports that the first inverter has an error in the operation mode, and the step S220 is skipped;
s208: the inverter grid-connected controller sets reference voltages of the first inverter and the second inverter;
s209: after the first inverter and the second inverter receive the control signals, resetting the reference voltage of the first inverter and the second inverter, and simultaneously returning the reference voltage set by the first inverter and the second inverter through the CAN communication network; if the inverter grid-connected controller receives correct reference voltages from the first inverter and the second inverter in the CAN communication network, the step S210 is entered; otherwise, the inverter grid-connected controller reports that the reference voltage of the first inverter or the second inverter is set incorrectly, and the step S220 is skipped;
s210: the inverter grid-connected controller sets the operation mode of the first inverter to be an inverter pre-parallel mode and sets the operation mode of the second inverter to be an inverter parallel mode;
s211: after the first inverter and the second inverter receive the control signals from the inverter grid-connected controller, the operation modes of the first inverter and the second inverter are respectively converted into an inverter pre-parallel mode and an inverter parallel mode, and signals are simultaneously returned to the CAN communication network;
s212: if the inverter grid-connected controller receives that the operation mode of the first inverter is the inverter pre-parallel mode and the operation mode of the second inverter is the inverter parallel mode in the CAN communication network, the method goes to step S213; otherwise, the inverter grid-connected controller reports that the operation mode of the first inverter or the second inverter is wrong, and the step S220 is skipped;
s213: the inverter grid-connected controller sends a first inverter request permission outlet circuit breaker closing signal to an operator to inform the operator that the outlet circuit breaker of the first inverter can be closed currently;
s214: an operator permission request; the inverter grid-connected controller receives an operator permission signal and sends a closing signal to the first inverter;
s215: the distribution board switches on an outlet circuit breaker of the first inverter, and the first inverter returns a switching-on signal to the CAN communication network;
s216: the inverter grid-connected controller judges whether the first inverter is successfully switched on or not according to whether a return signal from the first inverter is received or not; if a return signal from the first inverter is received, indicating that the first inverter is successfully switched on, and entering step S217; otherwise, the inverter grid-connected controller reports the switching-on failure of the first inverter, and the step S220 is skipped;
s217: the inverter grid-connected controller cancels a closing signal sent to the first inverter and sets the operation mode of the first inverter to be a grid-connected mode of the inverter;
s218: after receiving the control signal from the inverter grid-connected controller, the first inverter converts the operation mode of the first inverter into a grid-connected mode of the inverter and simultaneously returns a signal to the CAN communication network;
s219: if the inverter grid-connected controller receives a return signal from the first inverter, the inverter grid-connected controller indicates that the first inverter and the second inverter are successfully connected, otherwise, the inverter grid-connected controller reports that the operation mode of the first inverter is set incorrectly;
s220: and ending the parallel connection process of the two inverters, and resetting the grid connection process.
6. The grid-connected optimization method for the inverter for the ship based on the improved droop control as claimed in claim 5, wherein the grid-connected optimization method comprises the following steps: in step S104, for the grid-connected condition between the inverter and the auxiliary generator, the optimization of the grid-connected process specifically includes:
s301: selecting a working condition to grid the first inverter and the auxiliary generator through the distribution board;
s302: the inverter grid-connected controller sets the reference voltage of the first inverter through a CAN communication network;
s303: after receiving the control signal, the first inverter resets the self reference voltage and returns the self set reference voltage through the CAN communication network; if the inverter grid-connected controller receives the reference voltage from the first inverter in the CAN communication network correctly, the method goes to step S304; otherwise, the inverter grid-connected controller reports that the first inverter reference voltage is set incorrectly, and the step S314 is skipped;
s304: the inverter grid-connected controller sets the operation mode of the first inverter to be an inverter pre-grid-connected mode;
s305: after receiving a control signal from the inverter grid-connected controller, the first inverter converts the operation mode of the first inverter into an inverter pre-grid-connected mode and simultaneously returns a signal to the CAN communication network;
s306: if the inverter grid-connected controller receives a return signal from the first inverter, the process goes to step S307; otherwise, the inverter grid-connected controller reports an operation mode setting error of the first inverter, and the step S314 is skipped;
s307: the inverter grid-connected controller sends a first inverter request permission outlet circuit breaker closing signal to an operator to inform the operator that the outlet circuit breaker of the first inverter can be closed currently;
s308: an operator permission request; the inverter grid-connected controller receives an operator permission signal and sends a closing signal to the first inverter;
s309: the distribution board switches on an outlet circuit breaker of the first inverter, and the first inverter returns a switching-on signal to the CAN communication network;
s310: the inverter grid-connected controller judges whether the first inverter is successfully switched on or not according to whether a return signal from the first inverter is received or not; if a return signal from the first inverter is received, indicating that the first inverter is successfully switched on, and entering step S311; otherwise, the inverter grid-connected controller reports the switching-on failure of the first inverter, and the step S314 is skipped;
s311: the inverter grid-connected controller cancels a closing signal sent to the first inverter and sets the operation mode of the first inverter to be a grid-connected mode of the inverter;
s312: after receiving the control signal from the inverter grid-connected controller, the first inverter converts the operation mode of the first inverter into a grid-connected mode of the inverter and simultaneously returns a signal to the CAN communication network;
s313: if the inverter grid-connected controller receives a return signal from the first inverter, the inverter grid-connected controller indicates that the grid connection of the first inverter and the auxiliary generator is successful, otherwise, the inverter grid-connected controller reports that the operation mode of the first inverter is set incorrectly;
s314: and the grid connection process of the first inverter and the auxiliary generator is finished, and the grid connection process is reset.
7. The grid-connected optimization method for the inverter for the ship based on the improved droop control as claimed in claim 6, wherein the grid-connected optimization method comprises the following steps: in step S104, for the grid-connected operating condition between the inverter and the shore power, the optimization of the grid-connected process specifically includes:
s401: selecting a working condition to be grid-connected with the first inverter and shore power through the distribution panel;
s402: the inverter grid-connected controller sets the reference voltage of the first inverter through a CAN communication network;
s403: after receiving the control signal, the first inverter resets the self reference voltage and returns the self set reference voltage through the CAN communication network; if the inverter grid-connected controller receives the correct reference voltage from the first inverter in the CAN communication network, the method goes to step S404; otherwise, the inverter grid-connected controller reports that the first inverter reference voltage is set incorrectly, and the step S417 is skipped;
s404: the inverter grid-connected controller sets the operation mode of the first inverter to be an inverter pre-grid-connected mode;
s405: after receiving a control signal from the inverter grid-connected controller, the first inverter converts the operation mode of the first inverter into an inverter pre-grid-connected mode and simultaneously returns a signal to the CAN communication network;
s406: if the inverter grid-connected controller receives the feedback signal from the first inverter, step S407 is performed; otherwise, the inverter grid-connected controller reports an error in setting of the operation mode of the first inverter, and the step S417 is skipped;
s407: the inverter grid-connected controller sends a first inverter request permission outlet circuit breaker closing signal to an operator to inform the operator that the outlet circuit breaker of the first inverter can be closed currently;
s408: an operator permission request; the inverter grid-connected controller receives an operator permission signal and sends a closing signal to the first inverter;
s409: the distribution board switches on an outlet circuit breaker of the first inverter, and the first inverter returns a switching-on signal to the CAN communication network;
s410: the inverter grid-connected controller judges whether the first inverter is successfully switched on or not according to whether a return signal from the first inverter is received or not; if a return signal from the first inverter is received, indicating that the first inverter is successfully switched on, and entering step S411; otherwise, the inverter grid-connected controller reports the switching-on failure of the first inverter and jumps to the step S417;
s411: the inverter grid-connected controller cancels a closing signal sent to the first inverter and sets the operation mode of the first inverter to be a grid-connected mode of the inverter;
s412: after receiving the control signal from the inverter grid-connected controller, the first inverter converts the operation mode of the first inverter into a grid-connected mode of the inverter and simultaneously returns a signal to the CAN communication network;
s413: if the inverter grid-connected controller receives the feedback signal from the first inverter, it indicates that the operation mode of the first inverter is successfully converted, and the process goes to step S414; otherwise, the inverter grid-connected controller reports an error in setting of the operation mode of the first inverter, and the step S417 is skipped;
s414: the inverter grid-connected controller sends a brake-separating allowing signal to the shore power circuit breaker, and the operation mode of the first inverter is set to be an inverter single-machine grid-connected mode;
s415: the distribution board operates the breaker opening of the shore power; the first inverter receives a control signal from the inverter grid-connected controller, sets the operation mode of the first inverter to be an inverter single-machine grid-in mode, and simultaneously returns a signal to the CAN communication network;
s416: if the inverter grid-connected controller receives a return signal from the first inverter, the success of grid connection between the first inverter and shore power is indicated, and the grid connection process is finished; otherwise, the inverter grid-connected controller reports that the operation mode of the first inverter is set incorrectly;
s417: and the grid connection process of the first inverter and the shore power is finished, and the grid connection process is reset.
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