CN114243784A - Virtual synchronous machine balance current output control method under unbalanced voltage condition - Google Patents

Virtual synchronous machine balance current output control method under unbalanced voltage condition Download PDF

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CN114243784A
CN114243784A CN202111617855.5A CN202111617855A CN114243784A CN 114243784 A CN114243784 A CN 114243784A CN 202111617855 A CN202111617855 A CN 202111617855A CN 114243784 A CN114243784 A CN 114243784A
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positive
negative sequence
voltage
sequence
synchronous machine
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CN114243784B (en
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石章海
阮锦浩
王仕松
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Southwest Jiaotong University
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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
    • 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
    • H02J3/16—Circuit arrangements for ac mains or ac distribution networks for adjusting voltage in ac networks by changing a characteristic of the network load by adjustment of reactive power
    • 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
    • H02J3/38—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
    • 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
    • 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
    • Y02E40/50—Arrangements for eliminating or reducing asymmetry in polyphase networks

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  • Power Engineering (AREA)
  • Control Of Ac Motors In General (AREA)
  • Control Of Eletrric Generators (AREA)

Abstract

The invention provides a virtual synchronous machine balanced current output control method under the condition of unbalanced voltage, which comprises the following steps: step one, sampling voltage and current at the output end of a virtual synchronous machine, and extracting positive and negative sequence components through a filter; step two, calculating the extracted positive and negative sequence voltage and current to obtain instantaneous positive and negative sequence active and reactive power; step three, decoupling control is carried out on positive and negative sequence power; and step four, superposing the output voltage commands of the positive and negative sequence conventional virtual synchronous machine, and outputting an inverter gate signal through SPWM modulation. According to the invention, the control structure of the virtual synchronous machine is improved, so that the virtual synchronous machine can normally work under an unbalanced power grid.

Description

Virtual synchronous machine balance current output control method under unbalanced voltage condition
Technical Field
The invention belongs to the technical field of power control, and particularly relates to a balance current output control method of a virtual synchronous machine under an unbalanced voltage condition.
Background
The invention discloses a CN105098804B method and a device for controlling three-phase unbalanced current of a virtual synchronous generator, wherein the method comprises the following steps of establishing a VSG rotor motion equation and a VSG virtual excitation equation; decomposing unbalanced grid voltage into positive sequence voltage, negative sequence voltage, zero sequence voltage and corresponding phase sequence current so as to decompose active power and reactive power output by the VSG to analyze the encountered unbalanced problem; calculating a reference instruction of the dq axis current according to the output three-phase voltage signal; the reference instruction of the current is converted into a PWM voltage modulation signal through a self-designed current inner ring, and the virtual synchronous machine is controlled to run through the PWM voltage modulation signal, so that the output three-phase current of the virtual synchronous machine is balanced. This method has the following disadvantages:
1. according to the method, a current control inner ring is introduced on the basis of a conventional virtual synchronous machine to inhibit unbalanced current, so that the control complexity and instability are increased;
2. the conversion of the voltage and the current command in the current loop needs to acquire the impedance parameter of the power transmission line in advance, and the line impedance is difficult to obtain in practice. In addition, the line impedance can change along with time and external factors of weather, and if the line impedance is measured in advance and then is brought in by using a fixed value, the control precision is reduced due to errors;
3. the technology needs to convert the original signal into a dq coordinate system through coordinate transformation, the operation is complex, and the requirement on the operation capability of the controller is high.
CN112271740A discloses a virtual synchronous machine current balancing method and device applied to an unbalanced power grid, and belongs to the technical field of converter control. When the virtual synchronous machine works in an unbalanced power grid, on the basis of a traditional voltage control type virtual synchronous machine control algorithm, negative sequence current information is extracted, the negative sequence current information is reasonably fed forward to a modulation wave to form a new modulation wave by combining a virtual impedance method, and the new modulation wave is subjected to PWM modulation to obtain PWM pulses to control the virtual synchronous machine. Therefore, the purposes of reducing the negative sequence current component on the AC side of the virtual synchronous machine and balancing the three-phase current are achieved, the working state of the three-phase bridge arm is balanced as much as possible, and the reliability of the equipment working under the unbalanced power grid is improved. This method has the following disadvantages:
1. the negative sequence current is suppressed by virtual impedance control. The introduction of the virtual impedance requires coordinate transformation or differential calculation, and the calculation amount is large.
2. The larger the virtual impedance is, the better the effect of suppressing the negative-sequence current is, but the larger the virtual impedance is, the larger the equivalent line impedance is, the instability is caused, which is contradictory. Therefore, the virtual impedance method can suppress the unbalanced current to some extent only on the premise that the virtual synchronous machine is stabilized (the virtual impedance is smaller than a certain value), and cannot achieve more complete suppression. The inhibitory ability has certain limitations.
CN111193291A provides a composite virtual synchronous machine control method suitable for an unbalanced condition, and belongs to the technical field of virtual synchronous machine control. The method comprises the following steps: calculating positive sequence fundamental wave active power and positive sequence fundamental wave reactive power output by an inverter; obtaining a phase instruction of the output voltage of the inverter by using the virtual speed regulation control loop; thirdly, obtaining an amplitude instruction of the output voltage of the inverter by using the virtual excitation control loop, and obtaining a reference voltage by combining a phase instruction; step four, adding virtual impedance control in the voltage ring, and decoupling active power and reactive power by adopting positive sequence virtual impedance control; step five, correcting the reference current value in the step four, and setting a coefficient N to coordinate and control power fluctuation and current quality; setting a coefficient k for selecting a reference current to obtain an actual reference current value of the current loop; and seventhly, sampling the inductor current, and performing quasi-PR control on the current reference value and the inductor current by using a current ring to obtain a modulation signal. This method has the following disadvantages:
1. this technique introduces current loops, increasing complexity. And the current is controlled by a proportional resonant controller. The proportional resonant controller has great phase change at the resonant point, so that the proportional resonant controller is difficult to avoid error in practical use and has low control precision.
2. This approach also requires the introduction of a virtual impedance to achieve unbalanced current suppression.
Disclosure of Invention
The method aims at the problem that the traditional virtual synchronous machine cannot normally work under the unbalanced power grid. The invention provides a method for controlling the output of balanced current of a virtual synchronous machine under the condition of unbalanced voltage, which can normally work (namely output three-phase balanced current) under an unbalanced power grid by improving the control structure of the virtual synchronous machine.
The specific technical scheme is as follows:
the method for controlling the balance current output of the virtual synchronous machine under the condition of unbalanced voltage comprises the following steps:
step one, sampling a three-phase voltage v ═ v [ v ] at the output end of the virtual synchronous machine through a voltage sensor and a current sensora vb vc]TWith three-phase current i ═ ia ib ic]TAnd the obtained analog signal is converted into a digital signal through an ADC (analog-to-digital converter) and transmitted to a Microprocessor (MCU).
Step two, extracting positive and negative sequence components from the obtained voltage and current digital quantity through a filter algorithm:
Figure BDA0003437072690000021
Figure BDA0003437072690000022
wherein the superscript + -represents positive and negative sequence, respectively;
any filter capable of separating positive and negative sequences of voltage and current may be used.
Step three, calculating the extracted positive and negative sequence voltage and current to obtain instantaneous positive and negative sequence active and reactive power, wherein the specific formula is as follows:
Figure BDA0003437072690000023
Figure BDA0003437072690000024
Figure BDA0003437072690000025
Figure BDA0003437072690000031
wherein p and q are instantaneous active power and instantaneous reactive power, respectively, and the superscript + -represents positive sequence and negative sequence, respectively;
and step four, the improved virtual synchronous machine control method provided by the invention mainly comprises two sets of control loops of positive sequence and negative sequence, and after the positive sequence and the negative sequence of the previous step are separated, the two sets of control loops can realize the decoupling control of the positive sequence and the negative sequence. And step four to step five are used for carrying out decoupling control on the positive sequence active power. Will positive sequence power p+Feeding to a conventional positive sequence virtual synchronous machine, and setting the power reference value of the positive sequence to a required rated value Pref。
Figure BDA0003437072690000032
P can be expressed by using the rotor oscillation equation of the positive sequence virtual synchronous machine (as shown above)refAnd p+To generate a positive sequence output voltage frequency omega+. Wherein T isjIs the rotor inertia time constant and D is the damping coefficient.
Step five, integrating the frequency to obtain the phase theta of the positive sequence output voltage instruction+The equation is as follows:
Figure BDA0003437072690000033
where ω n is the rated grid power.
And step six, and step six to step seven, performing decoupling control on the negative sequence active power. Will negative sequence active power p-And sending the power reference value to a traditional negative sequence virtual synchronous machine, and setting the power reference value of the negative sequence to be 0.
Figure BDA0003437072690000034
The reference values 0 and p can be compared using the rotor oscillation equation of a negative sequence virtual synchronous machine (as shown above)-To generate a positive sequence output voltage frequency omega-。
Step seven, integrating the frequency to obtain the phase theta of the negative sequence output voltage instruction-The equation is as follows:
Figure BDA0003437072690000035
and step eight, performing decoupling control on the sequential reactive power. Q can be controlled by the reactive power control link of the virtual synchronous machinerefAnd q is+Comparing the error of the positive sequence output voltage command to generate the amplitude V of the positive sequence output voltage command+. The equation is as follows:
Figure BDA0003437072690000036
wherein D isQIs the voltage-reactive droop coefficient,
Figure BDA0003437072690000037
is the feedback quantity of the positive sequence voltage amplitude of the power grid,
Figure BDA0003437072690000038
is a positive sequence voltage reference. Grid voltage feedback
Figure BDA0003437072690000039
In order to realize the voltage-reactive droop characteristic, the method is an unnecessary link and can also be deleted.
And step nine, performing decoupling control on the negative sequence reactive power. The reactive power control link of the virtual synchronous machine can be used for comparing 0 with q-To generate the amplitude V of the negative sequence output voltage command-. The equation is as follows:
Figure BDA00034370726900000310
wherein the content of the first and second substances,
Figure BDA0003437072690000041
is the feedback quantity of the negative sequence voltage amplitude of the power grid,
Figure BDA0003437072690000042
is a negative sequence voltage reference. Grid voltage feedback
Figure BDA0003437072690000043
And can be deleted as an unnecessary link.
Step ten, obtaining the amplitude V of the positive sequence voltage instruction+And phase theta+Converted into three-phase voltage command urefa +、urefb +、 urefc +：
Figure BDA0003437072690000044
Figure BDA0003437072690000045
Figure BDA0003437072690000046
Eleven, obtaining the amplitude V of the voltage command of the negative sequence-And phase theta-Converted into three-phase voltage command urefa -、urefb-、urefc -:
Figure BDA0003437072690000047
Figure BDA0003437072690000048
Figure BDA0003437072690000049
Step twelve, outputting a voltage command uref +And uref -The final control voltage command u is obtained by superpositionrefAnd the gate signals of the inverter are output through SPWM modulation, so that the grid-connected work of the inverter is realized.
The invention has the following benefits:
1. in the current method, the negative sequence current is controlled by a control method (current loop control) of a traditional inverter. The negative sequence current is essentially not controlled by the virtual synchronous machine, so the negative sequence current has no inertia and no damping. After power decoupling, the two sets of virtual synchronizers carry out decoupling control on unbalanced voltage, so that the positive and negative sequence output currents have the characteristics of inertia, damping and the like of the virtual synchronizers. Better ability to fight grid faults (better support of the grid);
2. the invention can realize unbalanced current suppression without virtual impedance, thereby increasing stability
3. The invention only needs the power outer ring to generate the voltage reference instruction, does not need PI, PR and other controllers to control the inner ring current, and has simple structure and wide application range. The PI controller needs to re-set parameters aiming at different power grades, and each set of PI controller needs to independently set parameters when popularized in a large range, so that the convenience is poor.
Drawings
FIG. 1 is a main circuit and control block diagram of the present invention;
FIG. 2 is a control block diagram of a conventional virtual synchronous machine utilized by the present invention.
Detailed Description
The embodiments of the present invention will be described with reference to the accompanying drawings.
Example (b):
fig. 1 is a main circuit and a control block diagram of the invention, and illustrates a control method based on a three-phase grid-connected inverter. Fig. 2 is a control block diagram of a conventional virtual synchronous machine utilized by the present invention, which is a supplementary explanation of the control structure of fig. 1.
The overall process comprises the following steps:
step one, sampling a three-phase voltage v ═ v [ v ] at the output end of the virtual synchronous machine through a voltage sensor and a current sensora vb vc]TWith three-phase current i ═ ia ib ic]TAnd the obtained analog signal is converted into a digital signal through an ADC (analog-to-digital converter) and transmitted to a Microprocessor (MCU).
In the embodiment of fig. 1, represented by the module "sensor/ADC", which represents three sets of voltage sensors, three sets of current sensors, the sensors need to be isolated, and signal acquisition can be performed using sensors including but not limited to hall sensors. The acquired signals are subjected to analog-to-digital conversion through an ADC (analog-to-digital converter) carried by a TMS320F28379D controller to obtain digital signals required by the MCU. If the ADC precision needs to be improved, an external high-precision ADC can also be used.
Step two, extracting positive and negative sequence components from the obtained voltage and current digital quantity through a filter algorithm:
Figure BDA0003437072690000051
Figure BDA0003437072690000052
wherein the superscript + -represents positive and negative sequence, respectively;
any filter capable of separating positive and negative sequences of voltage and current can be used, and the invention is not limited by the type of filter.
In the embodiment of fig. 1, this step is represented by two "filter" modules, that is, digital signals obtained by sampling the ADC are processed by a filter algorithm to separate three-phase positive and negative sequence voltage and current. The filter algorithm may be implemented by a microprocessor such as TMS320F 28379.
Step three, calculating the extracted positive and negative sequence voltage and current to obtain instantaneous positive and negative sequence active and reactive power, wherein the specific formula is as follows:
Figure BDA0003437072690000053
Figure BDA0003437072690000054
Figure BDA0003437072690000055
Figure BDA0003437072690000056
wherein p and q are instantaneous active power and instantaneous reactive power, respectively, and the superscript + -represents positive sequence and negative sequence, respectively;
in the embodiment of FIG. 1, this step is represented by the "Positive sequence Power calculation" and "negative sequence Power calculation" modules
And step four, the improved virtual synchronous machine control method provided by the invention mainly comprises two sets of control loops of a positive sequence and a negative sequence, and after the positive sequence and the negative sequence of the previous step are separated, the decoupling control of the positive sequence and the negative sequence power can be realized by the two sets of control loops, namely the traditional VSG plus module and the traditional VSG minus module in the figure 1, wherein the two modules have the same structure, and the specific structure is shown in the figure 2. And step four to step five are used for carrying out decoupling control on the positive sequence active power. Will positive sequence power p+Feeding to a conventional positive sequence virtual synchronous machine, and setting the power reference value of the positive sequence to a required rated value Pref。
Figure BDA0003437072690000061
P can be expressed by using the rotor oscillation equation of the positive sequence virtual synchronous machine (as shown above)refAnd p+To generate a positive sequence output voltage frequency omega+. Wherein T isjIs the rotor inertia time constant and D is the damping coefficient.
This step corresponds to the first-order inertial element portion of the P-f control element of fig. 2. T isjThe selection of D depends on the actual power level and damping effect, in this case the value of the selected region is Tj＝10、D＝160。PrefIs chosen as the nominal value 1.
Step five, integrating the frequency to obtain the phase theta of the positive sequence output voltage instruction+The equation is as follows:
Figure BDA0003437072690000062
where ω n is the nominal grid frequency.
This step corresponds to the output integration segment of the P-f segment in fig. 2.
And step six, and step six to step seven, performing decoupling control on the negative sequence active power. Will negative sequence active power p-And sending the power reference value to a traditional negative sequence virtual synchronous machine, and setting the power reference value of the negative sequence to be 0.
Figure BDA0003437072690000063
The reference values 0 and p can be compared using the rotor oscillation equation of a negative sequence virtual synchronous machine (as shown above)-To generate a positive sequence output voltage frequency omega-。
This step corresponds to the first-order inertial element portion of the P-f control element of fig. 2. To zero the negative sequence current output, the negative sequence power reference is therefore made to be 0.TjThe selection of D can be the same as that of the positive sequence link, and can also be adjusted according to the required effect of the negative sequence, and the value of the selected area is T in the examplej＝10、D＝120。PrefIs chosen to be the nominal value 0.
Step seven, integrating the frequency to obtain negative sequence output powerPhase theta of pressure command-The equation is as follows:
Figure BDA0003437072690000064
this step corresponds to the output integration segment of the P-f segment in fig. 2.
And step eight, performing decoupling control on the sequential reactive power. Q can be controlled by the reactive power control link of the virtual synchronous machinerefAnd q is+Comparing the error of the positive sequence output voltage command to generate the amplitude V of the positive sequence output voltage command+. The equation is as follows:
Figure BDA0003437072690000065
wherein D isQIs the voltage-reactive droop coefficient,
Figure BDA0003437072690000066
is the feedback quantity of the positive sequence voltage amplitude of the power grid,
Figure BDA0003437072690000067
is a positive sequence voltage reference. Grid voltage feedback
Figure BDA0003437072690000068
In order to realize the voltage-reactive droop characteristic, the method is an unnecessary link and can also be deleted.
This step corresponds to the Q-V link of FIG. 2. Wherein DQThe choice of (c) depends on the specific degree of sagging, which in this example is 0.8.
And step nine, performing decoupling control on the negative sequence reactive power. The reactive power control link of the virtual synchronous machine can be used for comparing 0 with q-To generate the amplitude V of the negative sequence output voltage command-. The equation is as follows:
Figure BDA0003437072690000071
wherein the content of the first and second substances,
Figure BDA0003437072690000072
is the feedback quantity of the negative sequence voltage amplitude of the power grid,
Figure BDA0003437072690000073
is a negative sequence voltage reference. Grid voltage feedback
Figure BDA0003437072690000074
And can be deleted as an unnecessary link.
This step corresponds to the Q-V link of FIG. 2. No negative sequence voltage feedback is used in this embodiment.
Step ten, obtaining the amplitude V of the positive sequence voltage instruction+And phase theta+Converted into three-phase voltage command urefa +、urefb +、urefc +：
Figure BDA0003437072690000075
Figure BDA0003437072690000076
Figure BDA0003437072690000077
Eleven, obtaining the amplitude V of the voltage command of the negative sequence-And phase theta-Converted into three-phase voltage command urefa -、urefb-、urefc -:
Figure BDA0003437072690000078
Figure BDA0003437072690000079
Figure BDA00034370726900000710
The positive-sequence and negative-sequence modulated wave conversion equations differ in that the phase needs to be added with a negative sign since the frequency of the negative sequence is opposite to that of the positive sequence.
Step twelve, outputting a voltage command uref +And uref -The final control voltage command u is obtained by superpositionrefAnd the gate signals of the inverter are output through SPWM modulation, so that the grid-connected work of the inverter is realized.

Claims (1)

1. The method for controlling the balance current output of the virtual synchronous machine under the condition of unbalanced voltage is characterized by comprising the following steps of:
step one, sampling a three-phase voltage v ═ v [ v ] at the output end of the virtual synchronous machine through a voltage sensor and a current sensora vbvc]TWith three-phase current i ═ ia ib ic]TThe obtained analog signal is converted into a digital signal through ADC analog-to-digital conversion and is transmitted to a microprocessor;
step two, extracting positive and negative sequence components from the obtained voltage and current digital quantity through a filter algorithm:
Figure FDA0003437072680000011
Figure FDA0003437072680000012
wherein the superscript + -represents positive and negative sequence, respectively;
step three, calculating the extracted positive and negative sequence voltage and current to obtain instantaneous positive and negative sequence active and reactive power, wherein the specific formula is as follows:
Figure FDA0003437072680000013
Figure FDA0003437072680000014
Figure FDA0003437072680000015
Figure FDA0003437072680000016
wherein p and q are instantaneous active power and instantaneous reactive power, respectively, and the superscript + -represents positive sequence and negative sequence, respectively;
step four, two sets of control loops including a positive sequence and a negative sequence are included, and after positive and negative sequence separation in the previous step, decoupling control of positive and negative sequence power is realized by the two sets of control loops;
will positive sequence power p+Feeding to a conventional positive sequence virtual synchronous machine, and setting the power reference value of the positive sequence to a required rated value Pref；
Rotor oscillation equation of positive sequence virtual synchronous machine:
Tjω′+＝Pref-p+-D(ω+-1)
using rotor oscillation equation of positive sequence virtual synchronous machine to convert PrefAnd p+To generate a positive sequence output voltage frequency omega+(ii) a Wherein T isjIs the rotor inertia time constant, D is the damping coefficient;
step five, integrating the frequency to obtain the phase theta of the positive sequence output voltage instruction+The equation is as follows:
θ′+＝ωnω+
where ω n is the rated grid power;
step six, converting the negative sequence active power p-Sending the data to a traditional negative sequence virtual synchronous machine, and setting the power reference value of a negative sequence to be 0;
rotor oscillation equation of the negative sequence virtual synchronous machine:
Tjω′-＝-p--D(ω--1)
using rotor oscillation equation of negative sequence virtual synchronous machine to convert reference value 0 and p-To generate a negative sequence output voltage frequency omega-；
Step seven, integrating the frequency to obtain the phase theta of the negative sequence output voltage instruction-The equation is as follows:
θ′-＝ωnω-
step eight, decoupling control is carried out on the positive sequence reactive power; q is controlled by the reactive power control link of the virtual synchronous machinerefAnd q is+Comparing the error of the positive sequence output voltage command to generate the amplitude V of the positive sequence output voltage command+(ii) a The equation is as follows:
Figure FDA0003437072680000021
wherein D isQIs the voltage-reactive droop coefficient,
Figure FDA00034370726800000213
is the feedback quantity of the positive sequence voltage amplitude of the power grid,
Figure FDA0003437072680000023
is a positive sequence voltage reference value;
step nine, decoupling control is carried out on negative sequence reactive power; the reactive power control link of the virtual synchronous machine is utilized to control 0 and q-To generate the amplitude V of the negative sequence output voltage command-(ii) a The equation is as follows:
Figure FDA0003437072680000024
wherein the content of the first and second substances,
Figure FDA0003437072680000025
is the feedback quantity of the negative sequence voltage amplitude of the power grid,
Figure FDA0003437072680000026
is a negative sequence voltage reference value;
step ten, obtaining the amplitude V of the positive sequence voltage instruction+And phase theta+Converted into three-phase voltage command urefa +、urefb +、urefc +：
Figure FDA0003437072680000027
Figure FDA0003437072680000028
Figure FDA0003437072680000029
Eleven, obtaining the amplitude V of the voltage command of the negative sequence-And phase theta-Converted into three-phase voltage command urefa -、urefb -、urefc -：
Figure FDA00034370726800000210
Figure FDA00034370726800000211
Figure FDA00034370726800000212
Step twelve, outputting a voltage command uref +And uref -The final control voltage command u is obtained by superpositionrefAnd the gate signals of the inverter are output through SPWM modulation, so that the grid-connected work of the inverter is realized.
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CN105811470A (en) * 2016-04-27 2016-07-27 南京南瑞太阳能科技有限公司 Virtual synchronous machine control system and control method under unbalanced power grid condition
CN105958552A (en) * 2016-06-24 2016-09-21 西安交通大学 Control method for virtual synchronous generator capable of being adapted to imbalanced power grid and load conditions
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