CN111431211A - Micro-grid inverter parallel control method based on active curve droop - Google Patents

Micro-grid inverter parallel control method based on active curve droop Download PDF

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CN111431211A
CN111431211A CN202010377884.8A CN202010377884A CN111431211A CN 111431211 A CN111431211 A CN 111431211A CN 202010377884 A CN202010377884 A CN 202010377884A CN 111431211 A CN111431211 A CN 111431211A
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inverter
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closed
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axis
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CN111431211B (en
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徐海珍
余畅舟
刘淳
陈琛
余俊杰
王庆龙
孙强
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Hefei 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
    • H02J3/381—Dispersed generators
    • 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
    • H02J3/01—Arrangements for reducing harmonics or ripples
    • 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
    • Y02E40/40—Arrangements for reducing harmonics

Abstract

The invention discloses a microgrid inverter parallel control method based on active curve droop. The invention ensures that the inverter parallel system has the advantages of droop control and better system stability under the conditions of nonlinear and unbalanced load of the islanded microgrid belt.

Description

Micro-grid inverter parallel control method based on active curve droop
Technical Field
The invention belongs to the field of control of parallel operation of distributed power inverters in island micro-grids by adopting droop control, and particularly relates to a micro-grid inverter parallel control method based on active curve droop.
Background
In order to solve the problems of intermittency, volatility and uncontrollable property of distributed energy sources such as photovoltaic energy, wind energy and the like, distributed power sources in various forms are effectively integrated and are friendly to be connected into a power grid, and the micro-grid technology becomes a research hotspot at home and abroad. The microgrid can operate not only in a grid-connected mode but also in an island mode. In a micro-grid system formed by multiple distributed power sources, droop control based on active-frequency and reactive-voltage is adopted by a micro-grid inverter to provide voltage and frequency support, and the reliability and the redundancy of the system are improved.
The micro-grid contains not only linear loads but also motors, rectifier bridges, various active loads and unbalanced loads. When the nonlinear load and the unbalanced load operate, harmonic waves exist in the output voltage and the current of the inverter, so that each harmonic wave exists in the output power of the inverter, and the droop control characteristic based on the fundamental wave power is seriously influenced. Therefore, the output active power and reactive power of the inverter need to be filtered and then subjected to droop operation. However, the introduction of power filters can impair the dynamics of the inverter parallel system and even lead to system oscillations and instability. Therefore, under the operating environment with nonlinear load and unbalanced load, it is necessary to realize reliable and stable parallel operation of the island microgrid inverter based on droop control.
Filtering is performed by reducing the cut-off frequency of the filter for active and reactive power or by using a specific subharmonic trap. The wave trap of each main harmonic wave contained in the output power of the inverter needs to be designed and controlled in parallel respectively by adopting a filtering method of the wave trap, and the calculation is complex; although the filtering method for reducing the cut-off frequency of the first-order filter is simple in design and calculation, a smaller cut-off frequency of the filter is required to be set for filtering low-frequency harmonics, and the oscillation and even instability of an inverter parallel system can be caused by the small cut-off frequency.
At present, for the problem of parallel operation of inverters based on droop control when an islanded microgrid belt is subjected to nonlinear load and unbalanced load, a plurality of academic papers are used for analyzing and proposing solutions, for example:
1. the subject matter "An Adaptive visual Impedance Control Scheme on Small-AC-Signal Injection for Un-balanced and Harmonic Power Sharing in island-down microgrids" Baojin L iu, et al, IEEE Transactions on Power Electronics ", 2019,34(12): 12333-.
2. An article 6086-. However, this method has the following disadvantages:
1) a single trap filter can only filter fixed subharmonics, and each subtrap filter needs to be connected in parallel if multiple subharmonics need to be filtered, so that the calculation is complex;
2) when the frequency of the output voltage of the inverter changes, the filtering effect of the wave trap is weakened.
Disclosure of Invention
The invention aims to solve the problem of reliable and stable parallel operation of inverters based on droop control in the case of nonlinear load and unbalanced load of an island microgrid belt, and provides a microgrid inverter parallel control method based on active curve droop, which can simply and effectively filter the output power of the inverters and improve the stability of a parallel system.
In order to achieve the purpose, the invention provides a micro-grid inverter parallel control method based on active curve droop, which comprises the following steps of:
step 1, setting the number of the micro-grid inverters as k, wherein the k micro-grid inverters have the same capacity and are connected in parallel, marking any one micro-grid inverter as an inverter # i, wherein the # i represents the number of the micro-grid inverters, i ∈ [2, k ], and k is more than or equal to 2;
step 2, sampling output phase voltage E of microgrid inverter # ioai,EobiAnd bridge arm inductive current ILai,ILbiAnd respectively obtaining the output voltage dq axis component E of the inverter # i through single synchronous rotation coordinate transformationodi,EoqiAnd inverter # I bridge arm inductive current dq axis component ILdi,ILqiWherein the d axis is an active axis and the q axis is a reactive axis;
step 3, according to the output voltage dq axis component E of the inverter # i obtained in the step 2odi,EoqiAnd component I of inverter # I bridge arm inductance current dq axisLdi,ILqiFiltering the power through a first-order low-pass filter to obtain the average active power output by the inverter # i
Figure BDA0002480708640000031
And inverter # i outputs the average reactive power
Figure BDA0002480708640000032
Inverter # i average active power
Figure BDA0002480708640000033
And inverter # i average reactive power
Figure BDA0002480708640000034
The calculation formulas of (A) and (B) are respectively as follows:
Figure BDA0002480708640000035
Figure BDA0002480708640000036
wherein T isfIs the time constant of the first-order low-pass filter, s is the Laplace operator;
step 4, outputting the average active power according to the inverter # i obtained in the step 3
Figure BDA0002480708640000037
Obtaining inverter # i frequency instruction omega through active outer loop controlrefiFrequency command ω of inverter # irefiObtaining a phase angle instruction theta of the inverter # i through integral operationrefi；
The active outer ring control algorithm is a curve droop control algorithm, and the calculation formula is as follows:
Figure BDA0002480708640000038
the calculation formula of the integral operation is as follows:
Figure BDA0002480708640000039
in both formulae, ω*Rated frequency, omega, of the output voltage of inverter # iΔFor a steady state deviation of the specified inverter # i output voltage frequency, e is the base of the natural logarithm, TPiIs the active power time constant, T, of inverter # iPi＝Pratei/mi，PrateiRated capacity of inverter # i, miIs the coefficient of the active power time constant;
step 5, outputting average reactive power according to the inverter # i obtained in the step 3
Figure BDA00024807086400000310
Obtaining a closed loop instruction E of the inverter # i d shaft voltage through a reactive outer loop control algorithmdrefi；
The reactive outer loop control algorithm is a voltage-reactive power linear droop control algorithm, and the calculation formula is as follows:
Figure BDA0002480708640000041
wherein E is*Rated output phase voltage amplitude, n, for inverter # iiIs the reactive power droop coefficient for inverter # i;
step 6, setting a voltage closed-loop instruction E of a q axisqrefiWhen the inverter # i d shaft voltage obtained in step 5 is set to 0, the closed loop command E is givendrefiD-axis component E of inverter # i output voltage obtained in step 2odiObtaining an inverter # I d axle arm inductance current closed-loop instruction I through d-axle voltage closed-loop controlLdrefi(ii) a Closed-loop instruction E for shaft voltage of inverter # i qqrefiWith the q-axis component E of the inverter # i output voltage obtained in step 2oqiObtaining an inverter # I q axle arm inductance current closed-loop instruction I through q-axis voltage closed-loop controlLqrefi；
The d-axis voltage closed-loop control equation and the q-axis voltage closed-loop control equation are respectively as follows:
ILdrefi＝(Edrefi-Eodi)GV(s)
ILqrefi＝(Eqrefi-Eoqi)GV(s)
wherein G isV(s) is a voltage closed-loop proportional-integral regulator, whose expression is:
GV(s)＝kpvi+kivi/s
kpvifor voltage closed-loop proportional regulator coefficient, kiviIs a voltage closed loop integral regulator coefficient;
step 7, carrying out closed-loop instruction I on the inverter # I d shaft bridge arm inductance current obtained in the step 6LdrefiAnd obtained in step 2Inverter # I d axle arm inductor current component ILdiObtaining an output signal E of an inverter # i d shaft through d-shaft bridge arm inductance current closed-loop controldi(ii) a Carrying out closed-loop instruction I on the induction current of the shaft-bridge arm of the inverter # I q obtained in the step 6LqrefiAnd the inverter # I q shaft bridge arm inductive current component I obtained in the step 2LqiObtaining a q-axis output signal E through q-axis bridge arm inductance current closed-loop controlqi；
The d-axis bridge arm inductance current closed-loop control equation and the q-axis bridge arm inductance current closed-loop control equation are respectively as follows:
Edi＝(ILdrefi-ILdi)GI(s)
Eqi＝(ILqrefi-ILqi)GI(s)
wherein G isI(s) is a bridge arm inductive current closed-loop proportional regulator, and the expression is as follows:
GI(s)＝kpi
kpithe closed-loop proportional regulator coefficient of bridge arm inductive current;
step 8, carrying out closed-loop command E on the shaft voltage of the inverter # i d obtained in the step 5drefiAnd inverter # i q shaft voltage closed-loop command EqrefiThe inverter # i d shaft output signals E obtained in step 7 were added as voltage command feedforwarddiAnd inverter # i q shaft output signal EqiObtaining a modulated wave E under a dq coordinate systemmdi,Emqi；
Emdi＝Edi+Edrefi
Emqi＝Eqi+Eqrefi
Step 9, modulating wave E under dq coordinate system obtained in step 8mdi,EmqiFirstly, a modulated wave E under αβ rotating coordinate system is obtained by conversionmαi,EmβiThen obtaining the three-phase modulation wave E under the three-phase coordinate system through the inverse transformation of the single synchronous rotating coordinatemai,Embi,Emci，Emai,Embi,EmciThe modulated signal is used as a driving signal of an IGBT circuit;
Emαi＝Emdicosθrefi-Emqisinθrefi
Emβi＝Emdisinθrefi+Emqicosθrefi
Emai＝Emαi
Figure BDA0002480708640000051
Figure BDA0002480708640000052
preferably, the inverter # i outputs the voltage dq axis component E in step 2odi,EoqiThe transformation formula of the single synchronous rotation coordinate is as follows:
Eoαi＝-Eobi
Figure BDA0002480708640000053
Figure BDA0002480708640000054
wherein, thetarefi-1The phase angle command for inverter # i for the previous calculation cycle.
Preferably, the inverter # I bridge arm inductor current dq axis component I in step 2Ldi,ILqiThe transformation formula of the single synchronous rotation coordinate is as follows:
ILαi＝-ILbi
Figure BDA0002480708640000061
Figure BDA0002480708640000062
wherein, thetarefi-1The inverter # i phase angle command for the previous calculation cycle.
Compared with the existing micro-grid inverter parallel control method based on linear droop in the operating environment of nonlinear load and unbalanced load, the micro-grid inverter parallel control method based on active curve droop has the beneficial effects that:
1. according to the control method, the stability of the system is improved without increasing a droop coefficient, and the steady-state frequency deviation is reduced;
2. the control method adopts the first-order low-pass filter to filter the output power of the inverter, the design and the realization are simple, and the filtering effect is insensitive to the output frequency change of the inverter;
3. the inverter parallel system in the control method can provide voltage and frequency support for the island microgrid, and has good system stability when the island microgrid operates with nonlinear load and unbalanced load.
Drawings
Fig. 1 is a diagram of a parallel connection structure of microgrid inverters according to an embodiment of the present invention.
Fig. 2 is a block diagram of a microgrid inverter control structure according to an embodiment of the present invention.
Fig. 3 is a block diagram of a specific control structure for droop of an active curve according to an embodiment of the present invention.
Fig. 4 shows an output active waveform of a microgrid inverter parallel system based on linear droop according to an embodiment of the present invention.
Fig. 5 is an output active waveform of the linear droop-based microgrid inverter parallel system after the first-order filtering cutoff frequency of the inverter output active is increased according to the embodiment of the invention.
Fig. 6 shows an output active waveform of the microgrid inverter parallel system based on active curve droop according to the embodiment of the invention.
Fig. 7 is a frequency waveform of output voltage of a microgrid inverter parallel system based on active linear droop and active curve droop respectively according to an embodiment of the present invention.
Detailed Description
The present embodiment will be described in detail below with reference to the accompanying drawings.
FIG. 1 shows a parallel system of 2 identical-capacity microgrid inverters numbered #i 1, 2, two inverters are connected in parallel to a common connection point (PCC point), UpccThe filter inductance of the bridge arm of the inverter is L for the voltage of the common connection pointiThe inductive current flowing through the bridge arm is ILai,ILbiFilter capacitance of CiThe inverter output phase voltage at the filter capacitor end is Eoai,EobiThe line impedance between the output end of the inverter and the PCC point is ZLiThe specific parameters are that the direct current voltage is 600V, the rated output line voltage is 380V/50Hz, and the bridge arm filter inductance value is Li0.5mH, filter capacitance value CiIs 200uF, line impedance ZLi0.001+ j1.25 Ω, and a rated capacity of 100 KVar.
Fig. 2 is a block diagram of an inverter control structure according to an embodiment of the present invention, and it can be seen from the diagram that the steps of the control method of the present invention are as follows:
step 1, setting the number of the micro-grid inverters as k, wherein the k micro-grid inverters have the same capacity and are connected in parallel, marking any one micro-grid inverter as an inverter # i, wherein the # i represents the number of the micro-grid inverters, i ∈ [2, k ], and k is more than or equal to 2.
In the present embodiment, k is 2, and inverter numbers # i are #1 and #2, respectively.
Step 2, sampling output phase voltage E of microgrid inverter # ioai,EobiAnd bridge arm inductive current ILai,ILbiAnd respectively obtaining the output voltage dq axis component E of the inverter # i through single synchronous rotation coordinate transformationodi,EoqiAnd inverter # I bridge arm inductive current dq axis component ILdi,ILqiWherein the d axis is an active axis and the q axis is a reactive axis.
Output voltage dq axis component Eodi,EoqiThe transformation formula of the single synchronous rotation coordinate is as follows:
Eoαi＝-Eobi
Figure BDA0002480708640000071
Figure BDA0002480708640000072
bridge arm inductive current dq axis component ILdi,ILqiThe transformation formula of the single synchronous rotation coordinate is as follows:
ILαi＝-ILbi
Figure BDA0002480708640000081
Figure BDA0002480708640000082
wherein, thetarefi-1The phase angle command for inverter # i for the previous calculation cycle.
Step 3, according to the output voltage dq axis component E of the inverter # i obtained in the step 2odi,EoqiAnd component I of inverter # I bridge arm inductance current dq axisLdi,ILqiFiltering the power through a first-order low-pass filter to obtain the average active power output by the inverter # i
Figure BDA0002480708640000083
And inverter # i outputs the average reactive power
Figure BDA0002480708640000084
Inverter # i average active power
Figure BDA0002480708640000085
And inverter # i average reactive power
Figure BDA0002480708640000086
The calculation formulas of (A) and (B) are respectively as follows:
Figure BDA0002480708640000087
Figure BDA0002480708640000088
wherein T isfIs aThe time constant of the order low pass filter, s, is the laplacian operator.
The first-order low-pass filter is used for filtering out instantaneous power harmonics generated by nonlinear loads and unbalanced loads and for pulling a power loop and a voltage loop apart to control bandwidth. In this embodiment, the first order low pass filter cutoff frequency is set to 1Hz, and therefore T is takenf＝1s。
Step 4, outputting the average active power according to the inverter # i obtained in the step 3
Figure BDA0002480708640000089
Obtaining inverter # i frequency instruction omega through active outer loop controlrefiFrequency command ω of inverter # irefiObtaining a phase angle instruction theta of the inverter # i through integral operationrefi。
The active outer ring control algorithm is a curve droop control algorithm, and the calculation formula is as follows:
Figure BDA00024807086400000810
the calculation formula of the integral operation is as follows:
Figure BDA00024807086400000811
in both formulae, ω*Rated frequency, omega, of the output voltage of inverter # iΔFor a steady state deviation of the specified inverter # i output voltage frequency, e is the base of the natural logarithm, TPiIs the active power time constant, T, of inverter # iPi＝Pratei/mi，PrateiRated capacity of inverter # i, miIs the coefficient of the time constant of the active power.
Fig. 3 is a block diagram of a specific control structure for droop of an active curve of the inverter # i. OmegaΔFor a specified steady state deviation of the inverter output voltage frequency, the maximum fluctuation of the output voltage frequency is 1% when the inverter output active power is rated capacity. T isPiIs the active power time constant of inverter # i, which representsThe time constant of the active droop curve is larger, and the initial slope of the droop curve is smaller at the intersection point of the tangent line of the active droop curve at the moment t being 0 and the output active coordinate axis. In the present embodiment, the inverter rated capacity Pratei＝100Kvar，ω*Selecting T as 314.159rad/sPi＝PrateiAnd 6, calculating to obtain omegaΔ＝1％ω*/Pratei＝3.14e-5rad/W，mi＝6。
Step 5, outputting average reactive power according to the inverter # i obtained in the step 3
Figure BDA0002480708640000091
Obtaining a closed loop instruction E of the inverter # i d shaft voltage through a reactive outer loop control algorithmdrefi。
The reactive outer loop control algorithm is a voltage-reactive power linear droop control algorithm, and the calculation formula is as follows:
Figure BDA0002480708640000092
wherein E is*Rated output phase voltage amplitude, n, for inverter # iiIs the reactive power droop coefficient of inverter # i.
kiThe droop slope of the voltage-reactive power is generally taken as the maximum fluctuation 5% of the voltage amplitude when the output reactive power of the inverter is rated capacity. In this embodiment, E*＝220V，ni＝5％E*/Pratei＝11e-5V/Var。
Step 6, setting a voltage closed-loop instruction E of a q axisqrefiWhen the voltage is equal to 0, closing loop command E of the inverter # id shaft voltage obtained in the step 5drefiD-axis component E of inverter # i output voltage obtained in step 2odiObtaining an inverter # I d axle arm inductance current closed-loop instruction I through d-axle voltage closed-loop controlLdrefi(ii) a Closed-loop instruction E for shaft voltage of inverter # i qqrefiWith the q-axis component E of the inverter # i output voltage obtained in step 2oqiObtaining an inverter # I q axle arm inductance current closed-loop instruction I through q-axis voltage closed-loop controlLqrefi。
The d-axis voltage closed-loop control equation and the q-axis voltage closed-loop control equation are respectively as follows:
ILdrefi＝(Edrefi-Eodi)GV(s)
ILqrefi＝(Eqrefi-Eoqi)GV(s)
wherein G isV(s) is a voltage closed-loop proportional-integral regulator, whose expression is:
GV(s)＝kpvi+kivi/s
kpvifor inverter # i voltage closed loop proportional regulator coefficient, kiviThe regulator coefficients are closed loop integral of the inverter # i voltage.
The voltage closed-loop control is used for enabling the output voltage to quickly follow the instruction voltage, a proportional-integral controller is adopted under a synchronous rotating coordinate system, and the dynamic characteristic of the output voltage and the output impedance characteristic of the inverter under load disturbance are integrated. In the present embodiment, kpvi＝0.01，kivi＝800。
Step 7, carrying out closed-loop instruction I on the inverter # I d shaft bridge arm inductance current obtained in the step 6LdrefiAnd the inverter # I d shaft bridge arm inductive current component I obtained in the step 2LdiObtaining an output signal E of an inverter # i d shaft through d-shaft bridge arm inductance current closed-loop controldi(ii) a Carrying out closed-loop instruction I on the induction current of the shaft-bridge arm of the inverter # I q obtained in the step 6LqrefiAnd the inverter # I q shaft bridge arm inductive current component I obtained in the step 2LqiObtaining a q-axis output signal E through q-axis bridge arm inductance current closed-loop controlqi。
The d-axis bridge arm inductance current closed-loop control equation and the q-axis bridge arm inductance current closed-loop control equation are respectively as follows:
Edi＝(ILdrefi-ILdi)GI(s)
Eqi＝(ILqrefi-ILqi)GI(s)
wherein G isI(s) is a bridge arm inductive current closed-loop proportional regulator, and the expression is as follows:
GI(s)＝kpi
kpiand the closed-loop proportional regulator coefficient of bridge arm inductive current of the inverter # i.
The closed loop of the inductive current acts to improve the dynamic characteristics of the output voltage of the inverter, and in order to ensure the rapidity thereof, the closed loop of the current adopts a proportional regulator, in the embodiment, kpi＝0.02。
Step 8, carrying out closed-loop command E on the shaft voltage of the inverter # i d obtained in the step 5drefiAnd inverter # i q shaft voltage closed-loop command EqrefiThe inverter # i d shaft output signals E obtained in step 7 were added as voltage command feedforwarddiAnd inverter # i q shaft output signal EqiObtaining a modulated wave E under a dq coordinate systemmdi,Emqi。
Emdi＝Edi+Edrefi
Emqi＝Eqi+Eqrefi
Step 9, modulating wave E under dq coordinate system obtained in step 8mdi,EmqiFirstly, a modulated wave E under αβ rotating coordinate system is obtained by conversionmαi,EmβiThen obtaining the three-phase modulation wave E under the three-phase coordinate system through the inverse transformation of the single synchronous rotating coordinatemai,Embi,Emci，Emai,Embi,EmciAnd the modulated signal is used as a driving signal of the IGBT circuit.
Emαi＝Emdicosθrefi-Emqisinθrefi
Emβi＝Emdisinθrefi+Emqicosθrefi
Emai＝Emαi
Figure BDA0002480708640000111
Figure BDA0002480708640000112
The following is a simulation waveform of the two 100kW three-phase inverter parallel systems with the same capacity shown in FIG. 1 by adopting an active curve droop algorithm.
The outer ring of the inverter power adopts a droop control algorithm, inverters #1 and #2 run in parallel at 0.6s, and a load is imposed on a PCC point by adding 145KW at 0.8 s.
Fig. 4 shows that the microgrid inverters #1 and #2 based on linear droop output active power waveforms, the cut-off frequency of a first-order low-pass filter of active power and reactive power is 10Hz, after 145kW active load is suddenly added to a PCC point, the inverter parallel system quickly reaches a steady state, and the active power is equally divided by the two inverters in the steady state.
Fig. 5 shows that the microgrid inverters #1 and #2 output active power waveforms based on linear droop, the cut-off frequency of a first-order low-pass filter of the active power is reduced to 1Hz, after 145kW active load is suddenly added to a PCC point, the active power output by the inverters oscillates and gradually diverges, and the system is unstable.
Fig. 6 shows that active power waveforms are output by the microgrid inverters #1 and #2 based on active curve droop, the cutoff frequency of a first-order low-pass filter of the active power is still 1Hz, after 145kW active load is suddenly added to a PCC point, the parallel inverter system can stably operate, the active power is equally divided by the two inverters in a steady state, and the stability of the parallel inverter system is improved based on a control algorithm of the active curve droop.
Fig. 7 is a microgrid inverter output voltage frequency waveform based on active linear droop and active curve droop respectively. Under the condition of the same output active power, the steady-state frequency of the inverter adopting active curve droop is slightly lower than that of the inverter adopting active linear droop, but the steady-state frequency is smaller than the maximum fluctuation amount of the output voltage frequency of the microgrid inverter by one order of magnitude and basically can be ignored. When the output active power of the inverter is the rated capacity of the inverter, the steady-state frequency of the inverter based on the two types of droop control is the same.

Claims (3)

1. A micro-grid inverter parallel control method based on active curve droop is characterized by comprising the following steps:
step 1, setting the number of the micro-grid inverters as k, wherein the k micro-grid inverters have the same capacity and are connected in parallel, marking any one micro-grid inverter as an inverter # i, wherein the # i represents the number of the micro-grid inverters, i ∈ [2, k ], and k is more than or equal to 2;
step 2, sampling output phase voltage E of microgrid inverter # ioai,EobiAnd bridge arm inductive current ILai,ILbiAnd respectively obtaining the output voltage dq axis component E of the inverter # i through single synchronous rotation coordinate transformationodi,EoqiAnd inverter # I bridge arm inductive current dq axis component ILdi,ILqiWherein the d axis is an active axis and the q axis is a reactive axis;
step 3, according to the output voltage dq axis component E of the inverter # i obtained in the step 2odi,EoqiAnd component I of inverter # I bridge arm inductance current dq axisLdi,ILqiFiltering the power through a first-order low-pass filter to obtain the average active power output by the inverter # i
Figure FDA0002480708630000015
And inverter # i outputs the average reactive power
Figure FDA0002480708630000017
Inverter # i average active power
Figure FDA0002480708630000016
And inverter # i average reactive power
Figure FDA0002480708630000018
The calculation formulas of (A) and (B) are respectively as follows:
Figure FDA0002480708630000011
Figure FDA0002480708630000012
wherein T isfIs the time constant of a first-order low-pass filter, s is LaplaceAn operator;
step 4, outputting the average active power according to the inverter # i obtained in the step 3
Figure FDA0002480708630000019
Obtaining inverter # i frequency instruction omega through active outer loop controlrefiFrequency command ω of inverter # irefiObtaining a phase angle instruction theta of the inverter # i through integral operationrefi；
The active outer ring control algorithm is a curve droop control algorithm, and the calculation formula is as follows:
Figure FDA0002480708630000013
the calculation formula of the integral operation is as follows:
Figure FDA0002480708630000014
in both formulae, ω*Rated frequency, omega, of the output voltage of inverter # iΔFor a steady state deviation of the specified inverter # i output voltage frequency, e is the base of the natural logarithm, TPiIs the active power time constant, T, of inverter # iPi＝Pratei/mi，PrateiRated capacity of inverter # i, miIs the coefficient of the active power time constant;
step 5, outputting average reactive power according to the inverter # i obtained in the step 3
Figure FDA0002480708630000022
Obtaining a closed loop instruction E of the inverter # id shaft voltage through a reactive outer loop control algorithmdrefi；
The reactive outer loop control algorithm is a voltage-reactive power linear droop control algorithm, and the calculation formula is as follows:
Figure FDA0002480708630000021
wherein E is*Rated output phase voltage amplitude, n, for inverter # iiIs the reactive power droop coefficient for inverter # i;
step 6, setting a voltage closed-loop instruction E of a q axisqrefiWhen the voltage is equal to 0, closing loop command E of the inverter # id shaft voltage obtained in the step 5drefiD-axis component E of inverter # i output voltage obtained in step 2odiObtaining an induction current closed-loop instruction I of a # id axle arm of the inverter through d-axle voltage closed-loop controlLdrefi(ii) a Closed-loop instruction E for inverter # iq axis voltageqrefiWith the q-axis component E of the inverter # i output voltage obtained in step 2oqiObtaining an induction current closed-loop instruction I of an inverter # iq shaft bridge arm through q shaft voltage closed-loop controlLqrefi；
The d-axis voltage closed-loop control equation and the q-axis voltage closed-loop control equation are respectively as follows:
ILdrefi＝(Edrefi-Eodi)GV(s)
ILqrefi＝(Eqrefi-Eoqi)GV(s)
wherein G isV(s) is a voltage closed-loop proportional-integral regulator, whose expression is:
GV(s)＝kpvi+kivi/s
kpvifor voltage closed-loop proportional regulator coefficient, kiviIs a voltage closed loop integral regulator coefficient;
step 7, carrying out closed-loop instruction I on the inverter # I d shaft bridge arm inductance current obtained in the step 6LdrefiAnd the inverter # I d shaft bridge arm inductive current component I obtained in the step 2LdiObtaining an output signal E of an inverter # i d shaft through d-shaft bridge arm inductance current closed-loop controldi(ii) a Carrying out closed-loop instruction I on the induction current of the shaft-bridge arm of the inverter # I q obtained in the step 6LqrefiAnd the inverter # I q shaft bridge arm inductive current component I obtained in the step 2LqiObtaining a q-axis output signal E through q-axis bridge arm inductance current closed-loop controlqi；
The d-axis bridge arm inductance current closed-loop control equation and the q-axis bridge arm inductance current closed-loop control equation are respectively as follows:
Edi＝(ILdrefi-ILdi)GI(s)
Eqi＝(ILqrefi-ILqi)GI(s)
wherein G isI(s) is a bridge arm inductive current closed-loop proportional regulator, and the expression is as follows:
GI(s)＝kpi
kpithe closed-loop proportional regulator coefficient of bridge arm inductive current;
step 8, carrying out closed-loop command E on the shaft voltage of the inverter # i d obtained in the step 5drefiAnd inverter # i q shaft voltage closed-loop command EqrefiThe inverter # i d shaft output signals E obtained in step 7 were added as voltage command feedforwarddiAnd inverter # iq shaft output signal EqiObtaining a modulated wave E under a dq coordinate systemmdi,Emqi；
Emdi＝Edi+Edrefi
Emqi＝Eqi+Eqrefi
Step 9, modulating wave E under dq coordinate system obtained in step 8mdi,EmqiFirstly, a modulated wave E under αβ rotating coordinate system is obtained by conversionmαi,EmβiThen, the three-phase modulation wave E under the three-phase coordinate system is obtained through the inverse transformation of the single synchronous rotating coordinatemai,Embi,Emci，Emai,Embi,EmciThe modulated signal is used as a driving signal of an IGBT circuit;
Emαi＝Emdicosθrefi-Emqisinθrefi
Emβi＝Emdisinθrefi+Emqicosθrefi
Emai＝Emαi
Figure FDA0002480708630000031
Figure FDA0002480708630000032
2. the active curve droop-based microgrid inverter parallel control method according to claim 1, characterized in that the inverter # i in step 2 outputs a voltage dq axis component Eodi,EoqiThe transformation formula of the single synchronous rotation coordinate is as follows:
Eoαi＝-Eobi
Figure FDA0002480708630000041
Figure FDA0002480708630000042
wherein, thetarefi-1The phase angle command for inverter # i for the previous calculation cycle.
3. The active curve droop-based micro grid inverter parallel control method according to claim 1, wherein the inverter # I bridge arm inductor current dq axis component I in step 2Ldi,ILqiThe transformation formula of the single synchronous rotation coordinate is as follows:
ILαi＝-ILbi
Figure FDA0002480708630000043
Figure FDA0002480708630000044
wherein, thetarefi-1The phase angle command for inverter # i for the previous calculation cycle.
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