CN114567014B - Flexible change-over switch with voltage supporting function and control method thereof - Google Patents

Flexible change-over switch with voltage supporting function and control method thereof Download PDF

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CN114567014B
CN114567014B CN202210465014.5A CN202210465014A CN114567014B CN 114567014 B CN114567014 B CN 114567014B CN 202210465014 A CN202210465014 A CN 202210465014A CN 114567014 B CN114567014 B CN 114567014B
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phase
voltage
transformer
grid
primary side
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CN114567014A (en
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孙建军
庄凯勋
彭珉轩
方仍存
雷何
杨东俊
查晓明
瞿李锋
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Wuhan University WHU
Economic and Technological Research Institute of State Grid Hubei Electric Power Co Ltd
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Wuhan University WHU
Economic and Technological Research Institute of State Grid Hubei Electric Power 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
    • H02J3/40—Synchronising a generator for connection to a network or to another generator
    • H02J3/44—Synchronising a generator for connection to a network or to another generator with means for ensuring correct phase sequence
    • 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
    • H02J3/001—Methods to deal with contingencies, e.g. abnormalities, faults or failures
    • 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
    • H02J3/12—Circuit arrangements for ac mains or ac distribution networks for adjusting voltage in ac networks by changing a characteristic of the network load
    • 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
    • H02J3/18—Arrangements for adjusting, eliminating or compensating reactive power in networks
    • H02J3/1821—Arrangements for adjusting, eliminating or compensating reactive power in networks using shunt compensators
    • H02J3/1835—Arrangements for adjusting, eliminating or compensating reactive power in networks using shunt compensators with stepless control
    • H02J3/1842—Arrangements for adjusting, eliminating or compensating reactive power in networks using shunt compensators with stepless control wherein at least one reactive element is actively controlled by a bridge converter, e.g. active filters
    • 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
    • H02J3/26—Arrangements for eliminating or reducing asymmetry in polyphase networks
    • 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
    • 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
    • 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
    • Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
    • Y02E40/30—Reactive power compensation

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Control Of Eletrric Generators (AREA)
  • Inverter Devices (AREA)

Abstract

The invention provides a flexible change-over switch with a voltage supporting function and a control method thereof, belonging to the technical field of power electronic converters, wherein the control method comprises the following steps: when a normal power supply feeder line has a fault, the flexible switch rapidly cuts off the fault, the three-phase IGBT inverter controlled by the virtual synchronous generator control unit is adopted to independently provide power for a load, meanwhile, the pre-synchronous control unit is adopted to judge whether the condition of grid connection of the three-phase IGBT inverter and the feeder line to be connected to the grid is met, when the condition is met, the three-phase IGBT inverter and the feeder line to be connected to the grid are connected to the grid, and the feeder line after grid connection supplies power for the load. The whole flexible switch is simple to control, and is stable and quick in the flexible switching process of the feeder line; the virtual synchronous generator control unit is adopted for control, the phase-locked loop is prevented from being adopted for obtaining the voltage phase information of the power grid side, and the stability and the reliability of the control system are greatly improved.

Description

Flexible change-over switch with voltage supporting function and control method thereof
Technical Field
The invention belongs to the technical field of power electronic converters, and particularly relates to a flexible change-over switch with a voltage supporting function and a control method thereof.
Background
New energy power generation is usually connected to a power grid in a distributed power supply mode, and the power grid has the characteristics of volatility and intermittence, and a new energy automobile is taken as a novel power load, so that the change trend difference of new energy power generation output and the power load is obvious, the power prediction difficulty is high, the power distribution network tide distribution shows volatility, the traditional power distribution network control means is not applicable any more, and more researches are focused on an intelligent power distribution technology with flexible regulation and control capability. In addition, large-scale new energy is connected into the power distribution network, the equivalent rotational inertia of the power grid is greatly reduced, and the disturbance resistance of the system is greatly weakened. In order to ensure reliable power supply and safe operation, the capacities of power system such as peak regulation, frequency regulation and voltage regulation need to be greatly improved. Therefore, the inverter is controlled by adopting the virtual synchronous generator control, so that the inverter has the characteristics of a synchronous generator, and the operation stability of the system is effectively improved.
In the prior art, in the process of pre-synchronization grid connection, a phase-locked loop is often used to obtain voltage phase information of a power grid side, however, the phase-locked loop brings instability to a certain degree to system control, and even causes system oscillation. In addition, aiming at flexible switching between feeder lines, the conventional control method mainly solves the problem of bus synchronization in switching, but still has the problems of large impact current and large voltage and current fluctuation.
Disclosure of Invention
The invention aims to provide a flexible change-over switch with a voltage support function and a control method thereof, aiming at solving the problems that the current power system has poor anti-jamming capability, and when a feeder line fails and the running stability of the system is improved by utilizing the characteristic that an inverter has a synchronous generator, a phase-locked loop is often used to obtain voltage phase information of a power grid side in the pre-synchronization grid connection process, but the phase-locked loop brings instability to a certain degree on the system control.
To achieve the above object, the present invention provides a flexible transfer switch having a voltage supporting function, comprising: the system comprises a three-phase IGBT inverter, a filter, an energy storage capacitor, a transformer, a virtual synchronous generator control unit, a pre-synchronous control unit and an IGCT switch;
the direct current port side of the three-phase IGBT inverter is connected with an energy storage capacitor, and the alternating current side of the three-phase IGBT inverter is connected with a transformer through a filter; secondary side pass through of transformernAn IGCT switch andnthe strip feeder lines are connected; one IGCT switch is correspondingly connected with a normal power supply feeder or a feeder to be connected to the grid; the output end of the pre-synchronization control unit is connected with the control port of the IGCT switch corresponding to the feeder line to be connected to the grid and the virtual synchronous generator control unit; the virtual synchronous generator control unit is connected with a control port of the three-phase IGBT inverter;
the virtual synchronous generator control unit is used for generating PWM signals to control the three-phase IGBT inverter by combining the primary side three-phase voltage of the transformer, the alternating current three-phase current of the three-phase IGBT inverter, the angular frequency reference value of the primary side voltage of the transformer, the active power reference value and the reactive power reference value and by utilizing frequency-active power droop control, a rotating speed controller, reactive power-voltage droop control, alternating voltage control, alternating current control and coordinate inverse transformation;
the three-phase IGBT inverter is used for inverting the energy stored by the energy storage capacitor to supply power to a load under the control of the PWM signal after a normal power supply feeder line fails; the frequency correction unit is used for correcting the frequency and the phase of the primary side voltage of the transformer under the control of the virtual synchronous generator control unit and the pre-synchronous control unit so as to realize grid connection with a feeder line to be connected;
the pre-synchronization control unit is used for providing a conducting signal for an IGCT switch corresponding to a feeder line to be connected to the grid when the difference between the secondary side voltage of the transformer and the d-axis component and the difference between the q-axis component of the voltage of the feeder line to be connected to the grid under the two-phase rotating coordinate system are smaller than an error threshold value; otherwise, outputting virtual mechanical power to the virtual synchronous generator control unit, correcting the primary side voltage phase of the transformer, and simultaneously providing a turn-off signal to the IGCT switch corresponding to the feeder line to be connected to the grid until the grid connection condition is met.
Further preferably, the virtual synchronous generator control unit includes:
the virtual synchronous generator control unit includes:
the actual power calculator is used for calculating an actual value of active power and an actual value of reactive power input into an alternating current port of the three-phase IGBT inverter by adopting primary side voltage of the transformer and current of the three-phase IGBT inverter under a two-phase synchronous rotating coordinate system; the parameter setting device is used for setting a primary side voltage angular frequency reference value, an active power reference value and a reactive power reference value of the transformer;
the first subtracter is used for subtracting the angular frequency reference value of the primary side voltage of the transformer from the frequency of the primary side voltage of the transformer to obtain a frequency difference value; subtracting the actual value from the reactive power reference value output by the alternating current side of the three-phase IGBT inverter to obtain a reactive power difference value;
the transformer primary side voltage phase reference value controller is used for controlling the frequency difference value through frequency-active power droop, and acquiring a transformer primary side voltage phase reference value by combining an active power reference value, virtual mechanical power and a rotating speed controller; the transformer primary side voltage amplitude reference value controller is used for controlling the reactive power difference value through reactive power-voltage droop and obtaining a transformer primary side voltage amplitude reference value by combining a transformer primary side voltage rated value;
the first coordinate converter is used for performing coordinate conversion on the three-phase voltage on the primary side of the transformer and the three-phase current input by the alternating current port of the three-phase IGBT inverter by adopting the reference value of the voltage phase of the primary side of the transformer as the reference value of the coordinate conversion phase, and acquiring the voltage on the primary side of the transformer and the current on the alternating current side of the three-phase IGBT inverter under a two-phase synchronous rotating coordinate system;
the alternating voltage controller is used for inputting a primary side voltage reference value of the transformer under the two-phase rotating coordinate system into an alternating voltage control loop in combination with a primary side voltage of the transformer to obtain a current reference value on an alternating side of the three-phase IGBT inverter under the two-phase rotating coordinate system; the alternating current controller is used for inputting an alternating current control loop to a three-phase IGBT inverter alternating current side current reference value under the two-phase rotation coordinate, combining the three-phase IGBT inverter alternating current side current and a transformer primary side voltage, and obtaining a PWM modulation voltage under the two-phase rotation coordinate;
the coordinate inverse converter is used for performing inverse coordinate conversion on the PWM modulation voltage under the two-phase rotating coordinate system to obtain the PWM modulation voltage under the three-phase static coordinate system; and the PWM controller is used for obtaining a PWM signal by combining PWM voltage under a three-phase static coordinate system through pulse width modulation, and controlling the three-phase IGBT inverter.
Further preferably, the pre-synchronization control unit includes:
a second coordinate converter for converting the secondary side three-phase voltage of the transformer by using the primary side voltage phase reference value of the transformer as the coordinate conversion phase reference valueu ga、u gb、u gcAnd three-phase voltage of feeder line to be connected to gridu sa、u sb、u scCoordinate transformation is carried out to respectively obtain voltages under two-phase rotating coordinate systemU gd、U gqAndU sd、U sq；
a second subtractor for subtractingU gdMinus one (C) ofU sdTo obtain the d-axis voltage difference value deltaU dWill beU gqMinus one (C) ofU sqTo obtain the q-axis voltage difference value deltaU q；
A logic determiner for determining ΔU dAnd ΔU qWhether the voltage of the secondary side of the transformer and the voltage of the feeder line to be connected to the grid meet the grid-connected condition is judged if the voltages are smaller than the error threshold value, and a conducting signal is sent to an IGCT switch corresponding to the feeder line to be connected to the grid; otherwise, sending a disconnection signal to an IGCT switch corresponding to the feeder line to be connected to the grid until the grid connection condition is met;
a transformer secondary side voltage phase corrector for converting the deltaU dMinus deltaU qThe difference being determined by the coefficientK wAnd correcting the primary side voltage phase of the transformer and correcting the secondary side voltage phase of the transformer synchronously by combining the virtual synchronous generator control unit until the grid-connected condition is met.
Further preferably, the filter comprises: the system comprises a grid-connected resistor, a grid-connected inductor and a filter capacitor;
and the filter is connected between the alternating current port of the three-phase IGBT inverter and the primary side of the transformer.
Further preferably, the rotation speed controller simulates a synchronous generator rotor motion equation, and the expression is as follows:
Figure 892346DEST_PATH_IMAGE001
；
wherein,P t andP e respectively the mechanical power and the electromagnetic power of the synchronous generator,Din order to obtain a damping coefficient for the synchronous generator,Jis the inertia coefficient of the synchronous generator; delta ofωIs the frequency difference;tis time;ωis the primary side voltage frequency of the transformer.
It should be noted that in the present invention, the angular frequency of the voltage on the primary side of the transformer is equal to the angular frequency of the voltage on the secondary side of the transformer, and from the perspective of the principle, the virtual synchronous generator control unit controls the angular frequency of the voltage on the primary side of the transformer; the presynchronization control unit adopts the condition that the voltage frequency of the secondary side of the transformer is compared with the voltage frequency of a feeder line to be connected to the grid, when the voltage frequency of the secondary side of the transformer does not accord with the grid-connected condition, the voltage phase of the primary side of the transformer is corrected, and the correction of the voltage phase of the secondary side of the transformer is synchronously realized.
Based on the flexible change-over switch with the voltage supporting function provided by the invention, the invention provides a corresponding control method, which comprises the following steps:
(1) when a normal power supply feeder line fails, an IGCT switch corresponding to the feeder line removes the fault;
(2) the method comprises the steps that a three-phase IGBT inverter controlled by a virtual synchronous generator control unit is adopted to supply power to a load, meanwhile, a pre-synchronous control unit is started, the secondary side voltage of a transformer and the voltage of a feeder line to be connected to the grid are logically judged, when the grid-connected condition is not met, the pre-synchronous control unit outputs virtual mechanical power to the virtual synchronous generator control unit, and the phase of the primary side voltage of the transformer is corrected until the grid-connected condition is met; (3) judging whether the difference between the voltage of the secondary side of the transformer and the output voltage of a feeder line to be connected in the second feeder line under the two-phase rotating coordinate system is smaller than an error threshold value, if so, closing an IGCT switch corresponding to the feeder line to be connected in the grid; otherwise, disconnecting the IGCT switch corresponding to the feeder line to be connected to the grid, correcting the voltage frequency of the secondary side of the transformer, and turning to the step (1) until the IGCT switch corresponding to the feeder line to be connected to the grid is closed.
Further preferably, the control method of the three-phase IGBT inverter includes the steps of:
(1.1) carrying out coordinate transformation on three-phase voltage at the primary side of the transformer and three-phase current input by an alternating current port of a three-phase IGBT inverter to obtain the voltage at the primary side of the transformer and the current of the three-phase IGBT inverter under a two-phase synchronous rotating coordinate system, and calculating an actual value of active power and an actual value of reactive power input by the alternating current port of the three-phase IGBT inverter;
(1.2) setting a primary side voltage angular frequency reference value, an active power reference value and a reactive power reference value of the transformer;
(1.3) subtracting the angular frequency reference value of the primary side voltage of the transformer from the angular frequency of the primary side voltage of the transformer to obtain a frequency difference value;
meanwhile, subtracting the actual value from the reference value of the reactive power output by the alternating current side of the three-phase IGBT inverter to obtain a reactive power difference value;
(1.4) controlling the frequency difference value through frequency-active power droop, and combining an active power reference value, a virtual mechanical power output by a presynchronization control unit and a rotating speed controller to obtain a primary side voltage phase reference value of the transformer;
meanwhile, the reactive power difference value is controlled through reactive power-voltage droop, and a primary side voltage amplitude reference value of the transformer is obtained by combining a primary side voltage rated value of the transformer;
(1.5) combining the primary side voltage phase reference value and the voltage amplitude reference value of the transformer, and obtaining the primary side voltage reference value of the transformer under a two-phase rotating coordinate by taking the primary side voltage phase reference value of the transformer as a reference through coordinate transformation;
(1.6) inputting a primary side voltage reference value of a transformer under the two-phase rotating coordinate into an alternating current voltage control loop in combination with a primary side voltage of the transformer to obtain a current reference value on an alternating current side of the three-phase IGBT inverter under the two-phase rotating coordinate;
(1.7) inputting an alternating current control loop to a three-phase IGBT inverter alternating current side current reference value under a two-phase rotating coordinate by combining a three-phase IGBT inverter alternating current side current and a transformer primary side voltage to obtain a PWM modulation voltage under the two-phase rotating coordinate;
and (1.8) carrying out coordinate inverse transformation on the PWM modulation voltage under the two-phase rotating coordinate system to obtain the PWM modulation voltage under the three-phase static coordinate system, and carrying out pulse width modulation to obtain a PWM signal to control the three-phase IGBT inverter.
Further preferably, the grid connection method of the three-phase IGBT inverter and the feeder line to be connected to the grid includes the following steps:
secondary side three-phase voltage of transformeru ga、u gb、u gcAnd the second feeder line three-phase voltageu sa、u sb、u scCoordinate transformation is carried out to respectively obtain voltage phase reference valuesθVoltage under two-phase rotating coordinate system as referenceU gd、U gqAndU sd、U sq；
will be provided withU gdMinus one (C) ofU sdTo obtain the d-axis voltage difference value deltaU dWill beU gqMinusU sqTo obtain the q-axis voltage difference value deltaU q；
Determination of DeltaU dAnd ΔU qMeanwhile, the voltage of the secondary side of the transformer and the voltage of the feeder line to be connected to the grid meet the grid-connected condition if the voltage of the secondary side of the transformer and the voltage of the feeder line to be connected to the grid meet the grid-connected condition, and a conducting signal is sent to an IGCT switch corresponding to the feeder line to be connected to the grid; otherwise, sending a disconnection signal to an IGCT switch corresponding to the feeder line to be connected to the grid until the grid connection condition is met;
will be deltaU dMinus deltaU qThe difference being determined by the coefficientK wAnd correcting the primary side voltage phase of the transformer and correcting the secondary side voltage phase of the transformer synchronously by combining the virtual synchronous generator control unit until the grid-connected condition is met.
Further preferably, the speed controller simulates a synchronous generator rotor equation of motion, and the expression is as follows:
Figure 92383DEST_PATH_IMAGE002
；
wherein,P t andP e respectively the mechanical power and the electromagnetic power of the synchronous generator,Din order to obtain a damping coefficient for the synchronous generator,Jis the inertia coefficient of the synchronous generator; deltaωIs the frequency difference;tis time;ωis the secondary side voltage frequency of the transformer.
Generally, compared with the prior art, the above technical solution conceived by the present invention has the following beneficial effects:
the invention provides a flexible change-over switch with a voltage support function and a control method thereof, when a normal power supply feeder line fails, an IGCT switch corresponding to the feeder line removes the failure; the method comprises the steps that a three-phase IGBT inverter controlled by a virtual synchronous generator control unit is adopted to supply power to a load, meanwhile, a pre-synchronous control unit is started, the secondary side voltage of a transformer and the voltage of a feeder line to be connected to the grid are logically judged, when the grid-connected condition is not met, the pre-synchronous control unit outputs virtual mechanical power to the virtual synchronous generator control unit, and the phase of the primary side voltage of the transformer is corrected until the grid-connected condition is met; and after the grid-connected condition is met, the pre-synchronization control unit sends a conducting signal to the IGCT switch corresponding to the feeder line to be connected to the grid, and flexible switching between the feeder lines is completed. Therefore, the invention has good economy, can quickly and safely realize the switching among different feeders, and can realize quick fault isolation and recovery after a fault occurs. In the invention, the parallel converters are adopted to assist in current conversion, so that the switching speed is high; reactive and three-phase unbalance compensation is realized, and peak load elimination and valley filling of a power distribution network can be realized by matching with a high-capacity energy storage battery; and a phase-locked loop is avoided, and the reliability and stability of the control system are improved.
Drawings
Fig. 1 is a circuit topology structure diagram of a flexible switch provided in an embodiment of the present invention;
FIG. 2 is a control block diagram of a control unit of a virtual synchronous generator provided by an embodiment of the present invention;
FIG. 3 is a block diagram of a fast synchronization grid-connected control provided by an embodiment of the present invention;
fig. 4 is waveforms of effective values of currents at the ac side and the load side of the IGBT inverter circuit according to the embodiment of the present invention;
FIG. 5 is a waveform of an effective value of a primary-side voltage of a transformer according to an embodiment of the present invention;
fig. 6 is a voltage waveform of a dc side capacitor of an IGBT inverter circuit according to an embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
Example 1
Fig. 1 is a schematic structural diagram of a flexible switch with a voltage supporting function according to the present invention, which includes: a three-phase IGBT (Insulated Gate Bipolar Transistor)Inverter, filter and energy storage capacitor CdcThe device comprises a transformer, a virtual synchronous generator control unit, a pre-synchronous control unit and two IGCTs (integrated Gate Commutated Thyristors) switch circuits;
the three-phase IGBT inverter comprises a direct current port and an alternating current port; the DC port of the three-phase IGBT inverter is connected with an energy storage capacitor with a capacitance value ofC dc(ii) a The AC port of the three-phase IGBT inverter outputs 220V three-phase AC, and is connected with two groups of feeders via the primary side of the transformer, and the grid-connected resistor isR 1The grid-connected inductance isL 1Filter capacitance ofC 1；
The two groups of feed lines comprise a first feed line and a second feed line;
the two IGCT switch circuits comprise a first IGCT and a second IGCT;
the first feeder line is connected with the load and the secondary side of the transformer through the first IGCT;
the second feeder line is connected with the secondary side of the transformer through a second IGCT;
the virtual synchronous generator control unit is connected with a control port of the three-phase IGBT inverter;
the first feeder line is equivalent to a power grid and is used for supplying power to a load in a normal working state; the second feeder line is used for supplying power to the load after the first feeder line is in fault and is connected with the three-phase IGBT inverter in a grid mode; the transformer is used for boosting the output voltage of the three-phase IGBT inverter to an alternating current bus voltage magnitude;L 1、C 1andR 1forming a filter for filtering harmonic waves in the output voltage of the three-phase IGBT inverter; the three-phase IGBT inverter is used for supplying power to a load through inversion of energy stored by the energy storage capacitor under the control of the virtual synchronous generator control unit after the first feeder line fails; and the grid connection with the second feeder line is realized under the control of the pre-synchronization control unit.
When the flexible change-over switch with the voltage support function provided by the invention operates, the flexible change-over switch is quickly and synchronously connected with the second feeder line through the control of the virtual synchronous generator control unit and the pre-synchronous control method. The following describes embodiments of the present invention with reference to fig. 1 to 6:
in fig. 1, a three-phase IGBT inverter, a filter, an energy storage capacitor, a transformer and two IGCT switch circuits form a main circuit topology;
in the main circuit topological structure, the primary side three-phase voltage of the transformer is as follows:u ca、u cb、u ccand the secondary side three-phase voltage is as follows:u ga、u gb、u gc(ii) a The input three-phase voltage of the second feeder line is:u sa、u sb、u sc(ii) a The output three-phase current of the second feeder line is as follows:i ga、i gb、i gc(ii) a Three-phase current input to an alternating current port of the three-phase IGBT inverter is as follows:i a、i b、i cthe output three-phase voltage of the direct current port is as follows:U dc；
fig. 2 is a control block diagram of the virtual synchronous generator control unit controlling the three-phase IGBT inverter according to the present invention, including the following steps:
carrying out PARK conversion on the three-phase voltage at the primary side of the transformer and the three-phase current input by the alternating current port of the three-phase IGBT inverter to respectively obtain the voltage at the primary side of the transformer under a two-phase synchronous rotating coordinate systemU d、U qAnd three-phase IGBT inverter currentI d、I qCalculating the actual value of active power input into the AC port of the three-phase IGBT inverterP e And actual value of reactive powerQ e ；
Setting angular frequency reference value of output voltage at alternating current side of three-phase IGBT inverterω 0Reference value of active powerP 0And a reactive power reference valueQ 0；
The angular frequency reference value of the output voltage of the AC side of the inverterω 0And secondary side voltage frequency of transformerωSubtracting to obtain a frequency difference value deltaω(ii) a Reference value for outputting reactive power from alternating current side of three-phase IGBT inverterQ 0And realityValue ofQ e Subtracting to obtain the reactive power difference value deltaQ；
Difference of frequency ΔωCombined with active power reference valueP 0By frequency-active power droop control, according to the equation of motion of the rotor of the synchronous generator
Figure 351326DEST_PATH_IMAGE003
To obtain the reference value of the primary side voltage phase of the transformerθ(ii) a Difference value delta of reactive powerQObtaining a reference value of a primary side voltage amplitude of a transformer through reactive power-voltage droop controlU m(ii) a The two are combined and then transformed by coordinates to obtain a primary side voltage phase reference value of the transformerθReference value of primary side voltage of transformer under two-phase rotating coordinate as referenceU d *、U q *(ii) a Wherein,U m0is a rated value of the amplitude of the primary side voltage of the transformer;
wherein, in the equation of motion of the rotor of the synchronous generatorP t AndP e respectively the mechanical power and the electromagnetic power of the synchronous generator,Din order to obtain a damping coefficient for the synchronous generator,Jis the inertia coefficient of the synchronous generator;
reference value of primary side voltage of transformer under two-phase rotating coordinateU d *、U q *Combined with the primary side voltage of the transformerU d、U qInputting the AC voltage control loop to obtain the current reference value under the two-phase rotation coordinateI d *、I q *(ii) a Reference value of current under two-phase rotating coordinateI d *、I q *Combined with three-phase IGBT inverter currentI d、I qAnd primary side voltage of transformerU d、U qInputting an AC current control loop to obtain a reference value of the modulation voltage under the two-phase rotation coordinateU md *、U mq *Outputting three-phase voltage reference values through inverse transformationu a⃰、u b⃰、u c⃰; and inputting the three-phase voltage reference value into a PWM generator to form a PWM signal, and controlling the three-phase IGBT inverter.
Fig. 3 is a method for implementing a fast synchronous grid-connection optimization with a second feeder line by providing a flexible switch controlled by an IGCT switching and virtual synchronous generator control unit, which is operated off-line after a failure of the first feeder line, and specifically includes the following steps:
using voltage phase referenceθPre-synchronously controlling the voltages at two sides of the second IGCT by using the two-phase rotating coordinate as reference, wherein the voltage vector at the secondary side of the transformer is a vector relatively static in the coordinate system under the two-phase rotating coordinate system; and the voltage vector of the second feeder line is a vector rotating relative to the coordinate axis, the two vectors rotate relatively, and when the relative rotation angular velocity of the two vectors is very small and the phases of the two vectors are close, the grid connection can be carried out. Therefore, the voltages on the two sides of the second IGCT are subjected to pre-synchronous control, the vector rotation angle speed of the voltage on the secondary side of the transformer is changed, the vector phase relation of the voltages on the two sides is accelerated to meet grid-connected conditions, and the second IGCT is quickly connected with a second feeder line in a grid-connected mode. More specifically:
secondary side three-phase voltage of transformeru ga、u gb、u gcAnd the second feeder line three-phase voltageu sa、u sb、u sc(namely three-phase voltage at two sides of the second IGCT) to respectively obtain voltage phase reference valuesθVoltage under two-phase rotating coordinate system as referenceU gd、U gqAndU sd、U sq(ii) a Will be provided withU gdMinusU sdTo obtain the d-axis voltage difference value deltaU dWill beU gqMinus one (C) ofU sqTo obtain the q-axis voltage difference value deltaU q；
If ΔU dAnd ΔU qMeanwhile, when the voltage of the secondary side of the transformer and the voltage of the second feeder line meet the grid-connected condition, the logic judger sends a conducting signal to the second IGCT switch; if ΔU dOr ΔU qIs not simultaneously less than errorA difference threshold epsilon is not satisfied with the grid-connected condition, the logic judger sends a disconnection signal to the second IGCT, and meanwhile, delta is used for realizing the fast synchronous grid-connected with the second feeder lineU dMinus deltaU qThe difference being determined by the coefficientK wTo obtain virtual mechanical powerP wrefFor the secondary side voltage frequency of the transformerωAnd correcting, and controlling by a virtual synchronous generator control unit to accelerate the voltages at two sides of the second IGCT to meet grid-connected conditions, so as to realize quick synchronous grid connection with the second feeder line.
Example 2
The invention provides a control method of a flexible selector switch with a voltage supporting function, which comprises the following steps:
(1) when a normal power supply feeder line fails, an IGCT switch corresponding to the feeder line removes the fault;
(2) the method comprises the steps that a three-phase IGBT inverter controlled by a virtual synchronous generator control unit is adopted to supply power to a load, meanwhile, a pre-synchronous control unit is started, the secondary side voltage of a transformer and the voltage of a feeder line to be connected to the grid are logically judged, when the grid-connected condition is not met, the pre-synchronous control unit outputs virtual mechanical power to the virtual synchronous generator control unit, and the phase of the primary side voltage of the transformer is corrected until the grid-connected condition is met;
(3) judging whether the difference between the voltage of the secondary side of the transformer and the output voltage of a feeder line to be connected in the second feeder line under the two-phase rotating coordinate system is smaller than an error threshold value, if so, closing an IGCT switch corresponding to the feeder line to be connected in the grid; otherwise, the IGCT switch corresponding to the feeder line to be connected to the grid is disconnected, the voltage frequency of the secondary side of the transformer is corrected, and the step (1) is carried out until the IGCT switch corresponding to the feeder line to be connected to the grid is closed.
Further preferably, the control method of the three-phase IGBT inverter includes the steps of:
(1.1) carrying out coordinate transformation on three-phase voltage at the primary side of the transformer and three-phase current input by an alternating current port of a three-phase IGBT inverter to obtain the voltage at the primary side of the transformer and the current of the three-phase IGBT inverter under a two-phase synchronous rotating coordinate system, and calculating an actual value of active power and an actual value of reactive power input by the alternating current port of the three-phase IGBT inverter;
(1.2) setting a primary side voltage angular frequency reference value, an active power reference value and a reactive power reference value of the transformer;
(1.3) subtracting the angular frequency reference value of the primary side voltage of the transformer from the angular frequency of the primary side voltage of the transformer to obtain a frequency difference value;
meanwhile, subtracting the actual value from the reference value of the reactive power output by the alternating current side of the three-phase IGBT inverter to obtain a reactive power difference value;
(1.4) controlling the frequency difference value through frequency-active power droop, and combining an active power reference value, a virtual mechanical power output by a presynchronization control unit and a rotating speed controller to obtain a primary side voltage phase reference value of the transformer;
meanwhile, the reactive power difference value is controlled through reactive power-voltage droop, and a primary side voltage amplitude reference value of the transformer is obtained by combining a primary side voltage rated value of the transformer;
(1.5) combining a primary side voltage phase reference value and a voltage amplitude reference value of the transformer, and obtaining a primary side voltage reference value of the transformer under a two-phase rotation coordinate by taking the primary side voltage phase reference value of the transformer as a reference through coordinate transformation;
(1.6) inputting a primary side voltage reference value of a transformer under the two-phase rotating coordinate into an alternating current voltage control loop in combination with a primary side voltage of the transformer to obtain a current reference value on an alternating current side of the three-phase IGBT inverter under the two-phase rotating coordinate;
(1.7) inputting an alternating current control loop to a three-phase IGBT inverter alternating current side current reference value under the two-phase rotation coordinate by combining the three-phase IGBT inverter alternating current side current and a transformer primary side voltage to obtain a PWM modulation voltage under the two-phase rotation coordinate;
and (1.8) carrying out coordinate inverse transformation on the PWM modulation voltage under the two-phase rotating coordinate system to obtain the PWM modulation voltage under the three-phase static coordinate system, and carrying out pulse width modulation to obtain a PWM signal to control the three-phase IGBT inverter.
Further preferably, the grid connection method of the three-phase IGBT inverter and the feeder line to be connected to the grid includes the following steps:
secondary side three-phase voltage of transformeru ga、u gb、u gcAnd the second feeder line three-phase voltageu sa、u sb、u scCoordinate transformation is carried out to respectively obtain voltage phase reference valuesθVoltage under two-phase rotating coordinate system as referenceU gd、U gqAndU sd、U sq；
will be provided withU gdMinus one (C) ofU sdTo obtain d-axis voltage difference value deltaU dWill beU gqMinusU sqTo obtain the q-axis voltage difference value deltaU q；
Judgment of DeltaU dAnd deltaU qMeanwhile, the voltage of the secondary side of the transformer and the voltage of the feeder line to be connected to the grid meet the grid-connected condition if the voltage of the secondary side of the transformer and the voltage of the feeder line to be connected to the grid meet the grid-connected condition, and a conducting signal is sent to an IGCT switch corresponding to the feeder line to be connected to the grid; otherwise, sending a disconnection signal to an IGCT switch corresponding to the feeder line to be connected to the grid until the grid connection condition is met;
will be aU dMinus deltaU qThe difference of which is determined by the coefficientK wAnd correcting the primary side voltage phase of the transformer and correcting the secondary side voltage phase of the transformer synchronously by combining the virtual synchronous generator control unit until the grid-connected condition is met.
Further preferably, the synchronous generator rotor motion equation is:
Figure 636814DEST_PATH_IMAGE003
；
wherein,P t andP e respectively the mechanical power and the electromagnetic power of the synchronous generator,Din order to obtain a damping coefficient for the synchronous generator,Jis the inertia coefficient of the synchronous generator; deltaωIs the frequency difference;tis time;ωis the secondary side voltage frequency of the transformer.
Example 3
Verifying the scheme provided by the invention by using an MATLAB/Simulink simulation experiment platform, wherein the simulation result is shown in FIGS. 4-6; the simulation process is as follows, two groups of feeder lines are 1000V alternating current, the direct current side port of the IGBT inverter is connected with a 700V super capacitor, and the alternating current side port outputs 380V alternating current and is connected with two IGCT switch circuits through a transformer; the first feeder line is cut off when the first IGCT is in 1s, the IGBT inverter starts to operate in an isolated island mode, and after 0.1s, the IGBT inverter starts to perform pre-synchronization grid connection control; fig. 4 shows an IGBT inverter ac side current waveform, fig. 5 shows a transformer primary side voltage waveform, and fig. 6 shows an IGBT inverter dc side capacitance voltage waveform.
Before the island operation in fig. 4, the load power is provided by the first feeder, and the current on the ac side of the inverter is small; the first IGCT cuts off a first feeder line at 1s, the load power is provided by the inverter, the current on the alternating current side of the inverter is increased remarkably, and the current on the load side is reduced rapidly in a short time and recovers a steady state rapidly; the inverter completes grid connection with the second feeder line within 1.5s, and the load power is provided by the second feeder line, so that the current on the alternating current side of the inverter is slightly reduced; at this time, the current is rapidly increased due to the unbalanced power, and then gradually decays after a period of time, and the steady state is recovered. In fig. 5, at 1s, the effective value of the primary side voltage of the transformer suddenly drops in a short time and rapidly recovers to a steady state; and about 1.5s, the voltage waveform is less influenced by grid connection. The virtual synchronous generator control unit equivalently increases the power grid inertia and embodies the superiority in the grid connection process. In fig. 6, after 1s the inverter is in islanding operation, the dc side voltage of the inverter supplies power to the load via the inverter, so the dc side capacitor voltage gradually decreases; and after the time reaches 1.5s, the inverter is connected with the second feeder in a grid mode, the load power is provided by the second feeder, and the direct-current side capacitor voltage is recovered and stabilized after the transient process.
In summary, compared with the prior art, the invention has the following advantages:
the invention provides a flexible change-over switch with a voltage supporting function and a control method thereof, wherein when a normal power supply feeder line fails, an IGCT switch corresponding to the feeder line removes the fault; the method comprises the steps that a three-phase IGBT inverter controlled by a virtual synchronous generator control unit is adopted to supply power to a load, meanwhile, a pre-synchronous control unit is started, logic judgment is conducted on the voltage of a secondary side of a transformer and the voltage of a feeder line to be connected to the grid, when grid-connected conditions are not met, the pre-synchronous control unit outputs virtual mechanical power to the virtual synchronous generator control unit, and the phase of the voltage of a primary side of the transformer is corrected until the grid-connected conditions are met; and after the grid-connected condition is met, the pre-synchronization control unit sends a conducting signal to the IGCT switch corresponding to the feeder line to be connected to the grid, and flexible switching between the feeder lines is completed.
The invention has good economy, can quickly and safely realize the switching between different feeders, and can realize quick fault isolation and recovery after a fault occurs. In the invention, the parallel converters are adopted to assist in current conversion, so that the switching speed is high; reactive and three-phase unbalance compensation is realized, and peak load elimination and valley filling of a power distribution network can be realized by matching with a high-capacity energy storage battery; and a phase-locked loop is avoided, and the reliability and stability of the control system are improved.
It will be understood by those skilled in the art that the foregoing is only an exemplary embodiment of the present invention, and is not intended to limit the invention to the particular forms disclosed, since various modifications, substitutions and improvements within the spirit and scope of the invention are possible and within the scope of the appended claims. It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.

Claims (9)

1. A flexible diverter switch with voltage support, comprising: the system comprises a three-phase IGBT inverter, a filter, an energy storage capacitor, a transformer, an IGCT switch, a virtual synchronous generator control unit and a pre-synchronous control unit;
the direct current side port of the three-phase IGBT inverter is connected with the energy storage capacitor, and the alternating current side of the three-phase IGBT inverter is connected with the primary side of the transformer through the filter; the secondary side of the transformer is respectively connected with a normal power supply feeder and a feeder to be connected to the grid through different IGCT switches; the output end of the pre-synchronization control unit is connected with the control port of the IGCT switch corresponding to the feeder line to be connected to the grid and the virtual synchronous generator control unit; the virtual synchronous generator control unit is connected with the control port of the three-phase IGBT inverter;
the virtual synchronous generator control unit is used for generating PWM signals to control the three-phase IGBT inverter by combining the primary side three-phase voltage of the transformer, the alternating current three-phase current of the three-phase IGBT inverter, the angular frequency reference value of the primary side voltage of the transformer, the active power reference value and the reactive power reference value and by utilizing frequency-active power droop control, a rotating speed controller, reactive power-voltage droop control, alternating voltage control, alternating current control and coordinate inverse transformation;
the three-phase IGBT inverter is used for inverting the energy stored by the energy storage capacitor to supply power to a load under the control of the PWM signal after a normal power supply feeder line fails; the frequency correction unit is used for correcting the frequency and the phase of the primary side voltage of the transformer under the control of the virtual synchronous generator control unit and the pre-synchronous control unit so as to realize grid connection with a feeder line to be connected;
the pre-synchronization control unit is used for providing a conducting signal for an IGCT switch corresponding to a feeder line to be connected to the grid when the difference between the secondary side voltage of the transformer and the d-axis component and the difference between the q-axis component of the voltage of the feeder line to be connected to the grid under the two-phase rotating coordinate system are smaller than an error threshold value; otherwise will be ΔU dMinus deltaU qThe difference of which is determined by the coefficientK wObtaining virtual mechanical power, correcting the primary side voltage phase of the transformer by combining a virtual synchronous generator control unit, and simultaneously providing a turn-off signal for an IGCT switch corresponding to a feeder line to be connected to the grid until a grid-connected condition is met;
wherein, DeltaU dAnd ΔU qThe difference between the secondary side voltage of the transformer and the d-axis component and the difference between the q-axis component of the voltage of the feeder line to be connected to the grid under the two-phase rotating coordinate system are respectively obtained.
2. The flexible diverter switch according to claim 1, wherein said virtual synchronous generator control unit comprises:
the actual power calculator is used for calculating an actual value of active power and an actual value of reactive power input into an alternating current port of the three-phase IGBT inverter by adopting primary side voltage of the transformer and current of the three-phase IGBT inverter under a two-phase synchronous rotating coordinate system; the parameter setting device is used for setting a primary side voltage angular frequency reference value, an active power reference value and a reactive power reference value of the transformer;
the first subtracter is used for subtracting the angular frequency reference value of the primary side voltage of the transformer from the frequency of the primary side voltage of the transformer to obtain a frequency difference value; subtracting the reference value of reactive power output by the alternating current side of the three-phase IGBT inverter from the actual value to obtain a reactive power difference value;
the transformer primary side voltage phase reference value controller is used for controlling the frequency difference value through frequency-active power droop, and combining the active power reference value, the virtual mechanical power and the rotating speed controller to obtain a transformer primary side voltage phase reference value; the transformer primary side voltage amplitude reference value controller is used for controlling the reactive power difference value through reactive power-voltage droop and obtaining a transformer primary side voltage amplitude reference value by combining a transformer primary side voltage rated value;
the first coordinate converter is used for performing coordinate conversion on a transformer primary side three-phase voltage and a three-phase current input by a three-phase IGBT inverter alternating current port by adopting a transformer primary side voltage phase reference value as a coordinate conversion phase reference value to obtain the transformer primary side voltage and the three-phase IGBT inverter alternating current side current under a two-phase synchronous rotation coordinate system;
the alternating voltage controller is used for inputting a primary side voltage reference value of the transformer under the two-phase rotating coordinate system into an alternating voltage control loop in combination with a primary side voltage of the transformer to obtain a current reference value on an alternating side of the three-phase IGBT inverter under the two-phase rotating coordinate system; the alternating current controller is used for inputting an alternating current control loop to a three-phase IGBT inverter alternating current side current reference value under the two-phase rotation coordinate, combining the three-phase IGBT inverter alternating current side current and a transformer primary side voltage, and obtaining a PWM modulation voltage under the two-phase rotation coordinate;
the coordinate inverse transformer is used for performing coordinate inverse transformation on the PWM modulation voltage under the two-phase rotating coordinate system to obtain the PWM modulation voltage under the three-phase static coordinate system; and the PWM controller is used for obtaining a PWM signal by combining PWM modulation voltage under a three-phase static coordinate system through pulse width modulation and controlling the three-phase IGBT inverter.
3. The flexible diverter switch according to claim 1 or 2, characterized in that said pre-synchronization control unit comprises:
a second coordinate converter for converting the secondary side three-phase voltage of the transformer by using the primary side voltage phase reference value of the transformer as the coordinate conversion phase reference valueu ga、u gb、u gcAnd three-phase voltage of feeder line to be connected to gridu sa、u sb、u scCoordinate transformation is carried out to respectively obtain voltages under two-phase rotating coordinate systemU gd、U gqAndU sd、U sq；
a second subtractor for subtractingU gdMinusU sdTo obtain d-axis voltage difference value deltaU dWill beU gqMinusU sqTo obtain the q-axis voltage difference value deltaU q；
A logic determiner for determining ΔU dAnd ΔU qWhether the voltage of the secondary side of the transformer and the voltage of the feeder line to be connected to the grid meet the grid-connected condition is judged if the voltages are smaller than the error threshold value, and a conducting signal is sent to an IGCT switch corresponding to the feeder line to be connected to the grid; otherwise, sending a disconnection signal to an IGCT switch corresponding to the feeder line to be connected to the grid until the grid connection condition is met;
a transformer secondary side voltage phase corrector for converting the deltaU dMinus deltaU qThe difference being determined by the coefficientK wObtaining virtual mechanical power, correcting the primary side voltage phase of the transformer and correcting the secondary side voltage phase of the transformer synchronously by combining a virtual synchronous generator control unitAnd positive until the grid-connected condition is met.
4. The flexible diverter switch according to claim 1, wherein said filter comprises: the system comprises a grid-connected resistor, a grid-connected inductor and a filter capacitor;
and the filter is connected between the alternating current port of the three-phase IGBT inverter and the primary side of the transformer.
5. The flexible diverter switch according to claim 2, wherein the speed controller simulates the equation of motion of a synchronous generator rotor as expressed in the equation:
Figure 664944DEST_PATH_IMAGE002
；
wherein,P t andP e respectively the mechanical power and the electromagnetic power of the control unit of the virtual synchronous generator,Din order to obtain a damping coefficient for the synchronous generator,Jis the inertia coefficient of the synchronous generator; deltaωIs the frequency difference;tis time;ωis the primary side voltage frequency of the transformer.
6. A control method of the flexible diverter switch with voltage support function according to claim 1, characterized by comprising the following steps:
(1) when a normal power supply feeder line has a fault, an IGCT switch corresponding to the feeder line cuts off the fault;
(2) the method comprises the steps that a three-phase IGBT inverter controlled by a virtual synchronous generator control unit is adopted to supply power to a load, meanwhile, a pre-synchronous control unit is started, the secondary side voltage of a transformer and the voltage of a feeder line to be connected to the grid are logically judged, when the grid-connected condition is not met, the pre-synchronous control unit outputs virtual mechanical power to the virtual synchronous generator control unit, and the phase of the primary side voltage of the transformer is corrected until the grid-connected condition is met;
(3) and after the grid-connected condition is met, the pre-synchronization control unit sends a conducting signal to the IGCT switch corresponding to the feeder line to be connected to the grid, and flexible switching between the feeder lines is completed.
7. The control method according to claim 6, characterized in that the control method of a three-phase IGBT inverter comprises the steps of:
(1.1) carrying out coordinate transformation on three-phase voltage at the primary side of the transformer and three-phase current input by an alternating current port of a three-phase IGBT inverter to obtain the voltage at the primary side of the transformer and the current of the three-phase IGBT inverter under a two-phase synchronous rotating coordinate system, and calculating an actual value of active power and an actual value of reactive power input by the alternating current port of the three-phase IGBT inverter;
(1.2) setting a primary side voltage angular frequency reference value, an active power reference value and a reactive power reference value of the transformer;
(1.3) subtracting the angular frequency reference value of the primary side voltage of the transformer from the angular frequency of the primary side voltage of the transformer to obtain a frequency difference value;
meanwhile, subtracting the actual value from the reference value of the reactive power output by the alternating current side of the three-phase IGBT inverter to obtain a reactive power difference value;
(1.4) controlling the frequency difference value through frequency-active power droop, and combining an active power reference value, a virtual mechanical power output by a presynchronization control unit and a rotating speed controller to obtain a primary side voltage phase reference value of the transformer;
meanwhile, the reactive power difference value is controlled through reactive power-voltage droop, and a primary side voltage amplitude reference value of the transformer is obtained by combining a primary side voltage rated value of the transformer;
(1.5) combining the primary side voltage phase reference value and the voltage amplitude reference value of the transformer, and obtaining the primary side voltage reference value of the transformer under a two-phase rotating coordinate by taking the primary side voltage phase reference value of the transformer as a reference through coordinate transformation;
(1.6) inputting a primary side voltage reference value of a transformer under the two-phase rotating coordinate into an alternating current voltage control loop in combination with a primary side voltage of the transformer to obtain a current reference value on an alternating current side of the three-phase IGBT inverter under the two-phase rotating coordinate;
(1.7) inputting an alternating current control loop to a three-phase IGBT inverter alternating current side current reference value under a two-phase rotating coordinate by combining a three-phase IGBT inverter alternating current side current and a transformer primary side voltage to obtain a PWM modulation voltage under the two-phase rotating coordinate;
and (1.8) carrying out coordinate inverse transformation on the PWM modulation voltage under the two-phase rotating coordinate system to obtain the PWM modulation voltage under the three-phase static coordinate system, and carrying out pulse width modulation to obtain a PWM signal to control the three-phase IGBT inverter.
8. The control method according to claim 6 or 7, wherein the grid connection method of the three-phase IGBT inverter and the feeder line to be connected to the grid comprises the following steps:
secondary side three-phase voltage of transformeru ga、u gb、u gcAnd the second feeder line three-phase voltageu sa、u sb、u scPerforming coordinate transformation to obtain the primary side voltage phase reference value of the transformerθVoltage under two-phase rotating coordinate system as referenceU gd、U gqAndU sd、U sq；
will be provided withU gdMinusU sdTo obtain the d-axis voltage difference value deltaU dWill beU gqMinusU sqTo obtain the q-axis voltage difference value deltaU q；
Judgment of DeltaU dAnd deltaU qMeanwhile, the voltage of the secondary side of the transformer and the voltage of the feeder line to be connected to the grid meet the grid-connected condition if the voltage of the secondary side of the transformer and the voltage of the feeder line to be connected to the grid meet the grid-connected condition, and a conducting signal is sent to an IGCT switch corresponding to the feeder line to be connected to the grid; otherwise, sending a disconnection signal to an IGCT switch corresponding to the feeder line to be connected to the grid until the grid connection condition is met;
will be aU dMinus deltaU qThe difference of which is determined by the coefficientK wAnd correcting the primary side voltage phase of the transformer and correcting the secondary side voltage phase of the transformer synchronously by combining the virtual synchronous generator control unit until the grid-connected condition is met.
9. The control method of claim 7, wherein the speed controller simulates the equation of motion of a synchronous generator rotor expressed as:
Figure 50926DEST_PATH_IMAGE002
；
wherein,P t andP e respectively the mechanical power and the electromagnetic power of the synchronous generator,Din order to obtain a damping coefficient for the synchronous generator,Jis the inertia coefficient of the synchronous generator; delta ofωIs the frequency difference;tis time;ωis the secondary side voltage frequency of the transformer.
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