CN104218590A - Unbalance voltage compensation and control method based on virtual synchronous machine - Google Patents

Abstract

The invention discloses an unbalance voltage compensation and control method based on a virtual synchronous machine. According to the method, the power calculating method on the basis of notch filter is adopted, the problems that a first order low pass filter is low in responding speed and stability and cannot eliminate secondary harmonic caused by unbalance load can be eliminated, the calculated total active power and reactive power serves as the feedback input of droop control, and part of produced unbalance voltage is suppressed by the proportional integral and the resonance control method; meanwhile, an unbalance voltage compensation controller is adopted to eliminate the unbalance quantity. The unbalance voltage can be compensated, the fine equalizing current balance of parallelly-connected multiple machines can be maintained, the method can be widely applied to micro grid inverter control on the unbalance loaded condition so as to maintain the output voltage balance during off-grid operation, and parallelly-connected operation of multiple machines is allowed.

Description

Virtual synchronous machine-based unbalanced voltage compensation control method

Technical Field

The invention relates to an unbalanced voltage compensation control method, in particular to an unbalanced voltage compensation control method based on a virtual synchronous machine.

Background

In recent years, virtual synchronous generator technology has received much attention from scholars as a new power generation mode of the microgrid inverter. The microgrid inverter adopting the virtual synchronous generator technology is called a virtual synchronous generator. Virtual Synchronous Generators (VSGs) need to operate in two modes, grid-connected and island-connected parallel operation.

A large number of unbalanced loads exist in the microgrid, and the unbalanced loads can seriously affect the output voltage power supply quality of the VSG, so that the output voltage is unbalanced, and the overvoltage of electric equipment is caused. In order to achieve good output voltage supply quality, the unbalance degree of the output voltage is required to be controlled within a certain range, and meanwhile, good power sharing performance of the parallel connection of multiple units is kept.

For this reason, various efforts have been made, such as an article entitled "a grid-interfacing power quality compensator for a three-phase three-wire microgrid," Li YW, vilthgamawa D M, Loh pc, "IEEE Transactions on power electronics, 2006, 21(4), 1021" (grid-connected power quality compensator for a three-phase three-wire microgrid, "IEEE stk — electric power electronics, volume 21, pages 4 1021-1031, 2006); the paper provides a solution for controlling the voltage unbalance, which is to add an electric energy quality compensation device (APF) (active Power Filter) or UPQC (unified Power quality controller) at the Power supply end, and the control scheme adds an additional device and has higher cost.

An article entitled "Autonomous voltage unbalancing in an island deddroop-controlled micro computer", Savaghebi M, Jalian A, Vasquez J C, et al, IEEE Transactions on Industrial Electronics ", 2013, 60(4), 1390-; this article proposes a resonant voltage controller to compensate for the unbalanced voltage, but the compensation effect is poor because the influence of unbalanced voltage drop on the virtual impedance is not considered.

An article entitled "Voltage unbalances and harmonics compensation for island electronic inverter", Liu Q, Tao Y, Liu X, et al, Power electronics IET ", 2014, 7(5), 1055-; the paper proposes that a multi-resonance controller is adopted to suppress voltage imbalance, but the control bandwidth is narrow, and the compensation effect is poor when the frequency of the microgrid system changes.

An article entitled "A method of three-phase balance in micro-grid by photovoltaic generation system", Hojo M, Iwase Y, Funabashi T, et al, Power electronics and Motion Control Conference2008.EPE-PEMC ", 2008, 13th. IEEE, 2008, 2487-; the paper proposes to compensate for the unbalanced voltage by injecting negative sequence current, however, under severe conditions, the injection of negative sequence current may cause the microgrid inverter to overcurrent, resulting in shutdown.

In summary, the prior art fails to solve the problem of parallel connection and current sharing of inverters during isolated island operation while ensuring good balance of output voltage when unbalanced load is applied in a microgrid inverter parallel operation system.

Disclosure of Invention

The technical problem to be solved by the invention is to overcome the limitations of the various technical schemes, and to solve the problem of unbalanced output voltage with unbalanced load when the virtual synchronous generators are operated in an off-grid parallel mode, the invention provides the unbalanced voltage compensation control method based on the virtual synchronous generators, which can compensate the unbalanced voltage and maintain good current-sharing degree of multi-machine parallel connection.

In order to solve the technical problem of the invention, the adopted technical scheme is as follows: the unbalanced voltage compensation control method based on the virtual synchronous machine comprises the following steps of collecting the voltage of a capacitor output by a microgrid inverter, and particularly comprises the following main steps:

step 1, firstly, acquiring output capacitor voltage U of the microgrid inverter_ca,U_cb,U_ccBridge arm side induction current I_la,I_lb,I_lcAnd an output current I_oxThrough single synchronous rotation coordinate transformationObtaining a component U of the output capacitor voltage dq_cd,U_cqComponent I of bridge arm side inductor current dq_ld,I_lqAnd a component I of the output current dq_od,I_oqReuse of output capacitor voltage U_ca,U_cb,U_ccAnd bridge arm side inductor current I_la,I_lb,I_lcObtaining the negative sequence component U of the capacitor voltage through double synchronous rotation coordinate transformation_CN-d,U_CN-qAnd the negative sequence component I of the inductor current_LN-d,I_LN-q；

Step 2, according to the component U of the output capacitor voltage dq obtained in the step 1_cd,U_cqAnd a component I of the output current dq_od,I_oqObtaining the average active power through an active power calculation equation and a reactive power calculation equationAnd average reactive power

Step 3, obtaining the average active power according to the step 2And active power instruction P given by microgrid inverter_refGiven angular frequency command omega of micro-grid inverter_refObtaining angular frequency omega of the virtual synchronous generator through a power angle control equation, and integrating the angular frequency omega to obtain a vector angle theta of the virtual synchronous generator;

step 4, according to the average reactive power obtained in the step 2Given reactive power instruction Q of microgrid inverter_refVoltage command U_refObtaining the terminal voltage U of the virtual synchronous machine through a reactive power control equation^*；

Step 5, firstly obtaining the compound according to step 4Terminal voltage U to^*And U obtained in step 1_cd,U_cqObtaining a capacitance current command signal by a voltage control equationThen according to the capacitor current command signalAnd component I of bridge arm side inductor current dq in step 1_ld,I_lqAnd a component I of the output current dq_od,I_oqObtaining the control signal U by a current control equation_d1,U_q1；

Step 6, according to the negative sequence component U of the capacitor voltage obtained in the step 1_CN-d,U_CN-qAnd the negative sequence component I of the inductor current_LN-d,I_LN-qObtaining a control signal U through a negative sequence voltage compensation control equation_d2,U_q2；

Step 7, the control signal U obtained in the step 5 and the step 6 is processed_d1,U_q1And U_d2,U_q2Respectively added to obtain control signals U_d,U_q；

Step 8, firstly according to the control signal U in the step 7_d,U_qAnd step 3, obtaining a three-phase bridge arm voltage control signal U through single synchronous rotation coordinate inverse transformation of the vector angle theta obtained in the step_a,U_b,U_cThen according to U_a,U_b,U_cAnd generating PWM control signals of the switching tubes of the inverter bridge of the microgrid inverter.

The unbalance voltage compensation control method based on the virtual synchronous machine is further improved as follows:

preferably, the active power calculation equation in step 2 is

<math> <mrow> <mover> <mi>P</mi> <mo>&OverBar;</mo> </mover> <mo>=</mo> <mrow> <mo>(</mo> <munder> <mi>&Pi;</mi> <mi>h</mi> </munder> <mfrac> <mrow> <msup> <mi>s</mi> <mn>2</mn> </msup> <mo>+</mo> <msup> <msub> <mi>&omega;</mi> <mi>h</mi> </msub> <mn>2</mn> </msup> </mrow> <mrow> <msup> <mi>s</mi> <mn>2</mn> </msup> <mo>+</mo> <mn>2</mn> <mi>Q</mi> <msub> <mi>&omega;</mi> <mi>h</mi> </msub> <mi>s</mi> <mo>+</mo> <msup> <msub> <mi>&omega;</mi> <mi>h</mi> </msub> <mn>2</mn> </msup> </mrow> </mfrac> <mo>)</mo> </mrow> <mo>&CenterDot;</mo> <mfrac> <mn>1.5</mn> <mrow> <mi>&tau;s</mi> <mo>+</mo> <mn>1</mn> </mrow> </mfrac> <mo>&CenterDot;</mo> <mrow> <mo>(</mo> <msub> <mi>U</mi> <mi>cq</mi> </msub> <msub> <mi>I</mi> <mi>oq</mi> </msub> <mo>+</mo> <msub> <mi>U</mi> <mi>cd</mi> </msub> <msub> <mi>I</mi> <mi>od</mi> </msub> <mo>)</mo> </mrow> <mo>,</mo> </mrow> </math>

Wherein Q is the quality factor of the resonance controller, omega_hThe harmonic angular frequency to be filtered by the trap, s is the laplacian operator, and τ is the time constant of the first-order low-pass filter.

Preferably, the reactive power calculation equation in step 2 is

<math> <mrow> <mover> <mi>Q</mi> <mo>&OverBar;</mo> </mover> <mo>=</mo> <mrow> <mo>(</mo> <munder> <mi>&Pi;</mi> <mi>h</mi> </munder> <mfrac> <mrow> <msup> <mi>s</mi> <mn>2</mn> </msup> <mo>+</mo> <msup> <msub> <mi>&omega;</mi> <mi>h</mi> </msub> <mn>2</mn> </msup> </mrow> <mrow> <msup> <mi>s</mi> <mn>2</mn> </msup> <mo>+</mo> <mn>2</mn> <mi>Q</mi> <msub> <mi>&omega;</mi> <mi>h</mi> </msub> <mi>s</mi> <mo>+</mo> <msup> <msub> <mi>&omega;</mi> <mi>h</mi> </msub> <mn>2</mn> </msup> </mrow> </mfrac> <mo>)</mo> </mrow> <mo>&CenterDot;</mo> <mfrac> <mn>1.5</mn> <mrow> <mi>&tau;s</mi> <mo>+</mo> <mn>1</mn> </mrow> </mfrac> <mo>&CenterDot;</mo> <mrow> <mo>(</mo> <msub> <mi>U</mi> <mi>cd</mi> </msub> <msub> <mi>I</mi> <mi>oq</mi> </msub> <mo>-</mo> <msub> <mi>U</mi> <mi>cq</mi> </msub> <msub> <mi>I</mi> <mi>od</mi> </msub> <mo>)</mo> </mrow> <mo>,</mo> </mrow> </math>

Wherein Q is the quality factor of the resonance controller, omega_hThe harmonic angular frequency to be filtered by the trap, s is the laplacian operator, and τ is the time constant of the first-order low-pass filter.

Preferably, the power angle control equation in step 3 is

<math> <mrow> <mi>&omega;</mi> <mo>=</mo> <msub> <mi>&omega;</mi> <mi>ref</mi> </msub> <mo>+</mo> <mfrac> <mi>m</mi> <mrow> <mi>J</mi> <msub> <mi>&omega;</mi> <mn>0</mn> </msub> <mi>s</mi> <mo>+</mo> <mn>1</mn> </mrow> </mfrac> <mrow> <mo>(</mo> <msub> <mi>P</mi> <mi>ref</mi> </msub> <mo>-</mo> <mover> <mi>P</mi> <mo>&OverBar;</mo> </mover> <mo>)</mo> </mrow> <mo>,</mo> </mrow> </math>

Wherein, ω is_refGiving an active power instruction P for the microgrid inverter_refThe nominal angular frequency of the time, m is a power angle control droop coefficient, J is a virtual moment of inertia time constant, omega of the simulation synchronous generator set₀The angular frequency is fixed for the grid.

Preferably, the reactive power control equation in step 4 is

<math> <mrow> <msup> <mi>U</mi> <mo>*</mo> </msup> <mo>=</mo> <msub> <mi>U</mi> <mi>ref</mi> </msub> <mo>+</mo> <mi>n</mi> <mrow> <mo>(</mo> <msub> <mi>Q</mi> <mi>ref</mi> </msub> <mo>-</mo> <mover> <mi>Q</mi> <mo>&OverBar;</mo> </mover> <mo>)</mo> </mrow> <mo>,</mo> </mrow> </math>

Wherein, U_refGiving a reactive power instruction Q for a microgrid inverter_refAnd the voltage of the rated output capacitor and n are power angle control droop coefficients.

Preferably, the voltage control equation in step 5 is

<math> <mrow> <msubsup> <mi>I</mi> <mi>cd</mi> <mo>*</mo> </msubsup> <mo>=</mo> <msub> <mi>K</mi> <mi>p</mi> </msub> <mo>+</mo> <msub> <mi>K</mi> <mi>i</mi> </msub> <mo>/</mo> <mi>s</mi> <mo>+</mo> <mfrac> <mrow> <msub> <mi>K</mi> <mi>r</mi> </msub> <mi>s</mi> </mrow> <mrow> <msup> <mi>s</mi> <mn>2</mn> </msup> <mo>+</mo> <mn>2</mn> <mi>Q</mi> <msub> <mi>&omega;</mi> <mn>0</mn> </msub> <mi>s</mi> <mo>+</mo> <msup> <mrow> <mo>(</mo> <mn>2</mn> <msub> <mi>&omega;</mi> <mn>0</mn> </msub> <mo>)</mo> </mrow> <mn>2</mn> </msup> </mrow> </mfrac> <mrow> <mo>(</mo> <msup> <mi>U</mi> <mo>*</mo> </msup> <mo>-</mo> <msub> <mi>U</mi> <mi>cd</mi> </msub> <mo>)</mo> </mrow> </mrow> </math> ，

<math> <mrow> <msubsup> <mi>I</mi> <mi>cq</mi> <mo>*</mo> </msubsup> <mo>=</mo> <msub> <mi>K</mi> <mi>p</mi> </msub> <mo>+</mo> <msub> <mi>K</mi> <mi>i</mi> </msub> <mo>/</mo> <mi>s</mi> <mo>+</mo> <mfrac> <mrow> <msub> <mi>K</mi> <mi>r</mi> </msub> <mi>s</mi> </mrow> <mrow> <msup> <mi>s</mi> <mn>2</mn> </msup> <mo>+</mo> <mn>2</mn> <mi>Q</mi> <msub> <mi>&omega;</mi> <mn>0</mn> </msub> <mi>s</mi> <mo>+</mo> <msup> <mrow> <mo>(</mo> <mn>2</mn> <msub> <mi>&omega;</mi> <mn>0</mn> </msub> <mo>)</mo> </mrow> <mn>2</mn> </msup> </mrow> </mfrac> <mrow> <mo>(</mo> <mn>0</mn> <mo>-</mo> <msub> <mi>U</mi> <mi>cq</mi> </msub> <mo>)</mo> </mrow> </mrow> </math>

Wherein, K_pIs a proportional control coefficient, K_iFor integral control coefficient, K_rIs the resonant controller scaling factor.

Preferably, the current control equation in step 5 is

$U_{d1}=K(I_{\mathrm{cd}}^{*}-I_{\mathrm{ld}}+I_{\mathrm{od}})$

$U_{q1}=K(I_{\mathrm{cq}}^{*}-I_{\mathrm{lq}}+I_{\mathrm{oq}}),$

Wherein K is a proportional control coefficient.

Preferably, the negative sequence voltage compensation control equation in step 6 is

<math> <mrow> <msub> <mi>U</mi> <mrow> <mi>d</mi> <mn>2</mn> </mrow> </msub> <mo>=</mo> <mfrac> <mrow> <msub> <mi>K</mi> <mn>1</mn> </msub> <mrow> <mo>(</mo> <mn>0</mn> <mo>-</mo> <msub> <mi>U</mi> <mrow> <mi>C</mi> <mo>_</mo> <mi>N</mi> <mo>-</mo> <mi>d</mi> </mrow> </msub> <mo>)</mo> </mrow> <mo>-</mo> <msub> <mi>K</mi> <mn>2</mn> </msub> <msub> <mi>&omega;</mi> <mn>0</mn> </msub> <msub> <mi>LI</mi> <mrow> <mi>L</mi> <mo>_</mo> <mi>N</mi> <mo>-</mo> <mi>q</mi> </mrow> </msub> </mrow> <mrow> <mi>&tau;s</mi> <mo>+</mo> <mn>1</mn> </mrow> </mfrac> </mrow> </math> ，

<math> <mrow> <msub> <mi>U</mi> <mrow> <mi>q</mi> <mn>2</mn> </mrow> </msub> <mo>=</mo> <mfrac> <mrow> <msub> <mi>K</mi> <mn>1</mn> </msub> <mrow> <mo>(</mo> <mn>0</mn> <mo>-</mo> <msub> <mi>U</mi> <mrow> <mi>C</mi> <mo>_</mo> <mi>N</mi> <mo>-</mo> <mi>q</mi> </mrow> </msub> <mo>)</mo> </mrow> <mo>-</mo> <msub> <mi>K</mi> <mn>2</mn> </msub> <msub> <mi>&omega;</mi> <mn>0</mn> </msub> <msub> <mi>LI</mi> <mrow> <mi>L</mi> <mo>_</mo> <mi>N</mi> <mo>-</mo> <mi>d</mi> </mrow> </msub> </mrow> <mrow> <mi>&tau;s</mi> <mo>+</mo> <mn>1</mn> </mrow> </mfrac> </mrow> </math>

Wherein, K₁For compensating the coefficient, K, for the voltage₂The current compensation coefficient is, L is a bridge side inductance value of the microgrid inverter, and tau is a filtering time constant.

Compared with the prior art, the beneficial effects are that:

after the invention is adopted, the virtual synchronous generator has the following advantages on the basis of not only compensating unbalanced voltage but also keeping good current-sharing degree of multi-machine parallel connection when in operation:

1. no additional device is needed, and the manufacturing and operating cost is reduced.

2. The problem of unbalanced voltage drop on impedance is solved.

3. The problem of narrow control bandwidth is solved by only adding one compensation control algorithm.

4. Negative sequence current does not need to be injected, and the generation of overcurrent is avoided.

Drawings

Fig. 1 is a basic control block diagram of the present invention.

Fig. 2 is an overall control block diagram of the present invention.

Fig. 3 is a topological structure diagram of a virtual synchronous generator employed in the present invention.

Fig. 4 is a block diagram of a method for calculating the average active power and the average reactive power in the present invention.

Detailed Description

Preferred embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

The relevant electrical parameters when the invention is implemented are set as follows:

the direct current bus voltage Udc of the virtual synchronous generator is 550V, the effective value of the output alternating current voltage is 380V/50Hz, the rated capacity is 100KW, the alternating current voltage filter inductance is 0.5mH, and the filter capacitance is 200 muF. The transformer is a Dyn11 type transformer with 100KVA of 270/400V.

Referring to fig. 1, 2,3 and 4, the implementation of the present invention is as follows:

step 1, firstly, acquiring output capacitor voltage U of the microgrid inverter_ca,U_cb,U_ccBridge arm side induction current I_la,I_lb,I_lcAnd an output current I_oxObtaining the component U of the output capacitor voltage dq through the transformation of the single synchronous rotation coordinate_cd,U_cqComponent I of bridge arm side inductor current dq_ld,I_lqAnd a component I of the output current dq_od,I_oq. Reuse of output capacitor voltage U_ca,U_cb,U_ccAnd bridge arm side inductor current I_la,I_lb,I_lcObtaining the negative sequence component U of the capacitor voltage through double synchronous rotation coordinate transformation_CN-d,U_CN-qAnd the negative sequence component I of the inductor current_LN-d,I_LN-q。

Step 2, according to the component U of the output capacitor voltage dq obtained in the step 1_cd,U_cqAnd a component I of the output current dq_od,I_oqObtaining the average active power through an active power calculation equation and a reactive power calculation equationAnd average reactive powerWherein,

the active power calculation equation is

<math> <mrow> <mover> <mi>P</mi> <mo>&OverBar;</mo> </mover> <mo>=</mo> <mrow> <mo>(</mo> <munder> <mi>&Pi;</mi> <mi>h</mi> </munder> <mfrac> <mrow> <msup> <mi>s</mi> <mn>2</mn> </msup> <mo>+</mo> <msup> <msub> <mi>&omega;</mi> <mi>h</mi> </msub> <mn>2</mn> </msup> </mrow> <mrow> <msup> <mi>s</mi> <mn>2</mn> </msup> <mo>+</mo> <mn>2</mn> <mi>Q</mi> <msub> <mi>&omega;</mi> <mi>h</mi> </msub> <mi>s</mi> <mo>+</mo> <msup> <msub> <mi>&omega;</mi> <mi>h</mi> </msub> <mn>2</mn> </msup> </mrow> </mfrac> <mo>)</mo> </mrow> <mo>&CenterDot;</mo> <mfrac> <mn>1.5</mn> <mrow> <mi>&tau;s</mi> <mo>+</mo> <mn>1</mn> </mrow> </mfrac> <mo>&CenterDot;</mo> <mrow> <mo>(</mo> <msub> <mi>U</mi> <mi>cq</mi> </msub> <msub> <mi>I</mi> <mi>oq</mi> </msub> <mo>+</mo> <msub> <mi>U</mi> <mi>cd</mi> </msub> <msub> <mi>I</mi> <mi>od</mi> </msub> <mo>)</mo> </mrow> <mo>,</mo> </mrow> </math>

Wherein Q is the quality factor of the resonant controller, omega_hThe harmonic angular frequency to be filtered by the wave trap, s is a Laplace operator, and tau is a time constant of a first-order low-pass filter;

reactive power calculation equation of

<math> <mrow> <mover> <mi>Q</mi> <mo>&OverBar;</mo> </mover> <mo>=</mo> <mrow> <mo>(</mo> <munder> <mi>&Pi;</mi> <mi>h</mi> </munder> <mfrac> <mrow> <msup> <mi>s</mi> <mn>2</mn> </msup> <mo>+</mo> <msup> <msub> <mi>&omega;</mi> <mi>h</mi> </msub> <mn>2</mn> </msup> </mrow> <mrow> <msup> <mi>s</mi> <mn>2</mn> </msup> <mo>+</mo> <mn>2</mn> <mi>Q</mi> <msub> <mi>&omega;</mi> <mi>h</mi> </msub> <mi>s</mi> <mo>+</mo> <msup> <msub> <mi>&omega;</mi> <mi>h</mi> </msub> <mn>2</mn> </msup> </mrow> </mfrac> <mo>)</mo> </mrow> <mo>&CenterDot;</mo> <mfrac> <mn>1.5</mn> <mrow> <mi>&tau;s</mi> <mo>+</mo> <mn>1</mn> </mrow> </mfrac> <mo>&CenterDot;</mo> <mrow> <mo>(</mo> <msub> <mi>U</mi> <mi>cd</mi> </msub> <msub> <mi>I</mi> <mi>oq</mi> </msub> <mo>-</mo> <msub> <mi>U</mi> <mi>cq</mi> </msub> <msub> <mi>I</mi> <mi>od</mi> </msub> <mo>)</mo> </mrow> <mo>,</mo> </mrow> </math>

Wherein Q is the quality factor of the resonant controller, omega_hThe harmonic angular frequency to be filtered by the trap, s is the laplacian operator, and τ is the time constant of the first-order low-pass filter.

In this embodiment, the number of harmonics to be mainly filtered is considered to be 2 and 3, so h is 2,3, where ω is_h628.3186rad/s and 942.4779rad/s first-order low-pass filter mainly considers filtering out higher harmonics and does not influence dynamic response, and tau is generally less than or equal to 2e^-3s, the value τ in this case is 1.5e^-4s; the quality factor Q mainly considers the filtering effect of the trap, and in this case, Q is 0.5.

A block diagram of the calculation of the average active power and the average reactive power is shown in fig. 4.

Step 3, obtaining the average active power according to the step 2And active power instruction P given by microgrid inverter_refGiven angular frequency command omega of micro-grid inverter_refObtaining angular frequency omega of the virtual synchronous generator through a power angle control equation, and integrating the angular frequency omega to obtain a vector angle theta of the virtual synchronous generator; wherein,

the equation for power angle control is

<math> <mrow> <mi>&omega;</mi> <mo>=</mo> <msub> <mi>&omega;</mi> <mi>ref</mi> </msub> <mo>+</mo> <mfrac> <mi>m</mi> <mrow> <mi>J</mi> <msub> <mi>&omega;</mi> <mn>0</mn> </msub> <mi>s</mi> <mo>+</mo> <mn>1</mn> </mrow> </mfrac> <mrow> <mo>(</mo> <msub> <mi>P</mi> <mi>ref</mi> </msub> <mo>-</mo> <mover> <mi>P</mi> <mo>&OverBar;</mo> </mover> <mo>)</mo> </mrow> <mo>,</mo> </mrow> </math>

In which ω is_refGiving an active power instruction P for the microgrid inverter_refThe nominal angular frequency of the time, m is a power angle control droop coefficient, J is a virtual moment of inertia time constant, omega of the simulation synchronous generator set₀The angular frequency is fixed for the grid.

The power angle control equation shows the active power droop curve relation and the virtual inertia of the microgrid inverter. The virtual inertia indicates the change rate of the system frequency, and a larger virtual inertia is needed to ensure the stable change of the system frequency; however, the virtual inertia is equivalent to adding a first-order inertia element in the system, and too large virtual inertia may cause instability of the system. Thus, the parameter selection requires a compromise process. To ensure system stability, in this embodiment, the inertia time constant is in the range of τ_virtual＝Jω₀m≤2e^-3s; the active power droop curve relation in the power angle control equation comprises three coefficients, the power angle control droop coefficient m represents the slope of the droop curve, and the value principle is that when the active power changes by 100%, the frequency changes within 0.5 Hz; given active power command P_refAnd corresponding nominal angular frequency omega_refThe position relation of the droop curve is represented, and the active power output by the microgrid inverter is mainly considered to be P_refThe output frequency is larger or smaller;

in the embodiment, the angular frequency of the power grid adopts the angular frequency corresponding to the rated frequency of 50Hz, namely omega₀314.1593rad/s, the power angle control droop coefficient takes the value ofTaking tau according to the principle of inertia time constant value_virtual＝Jω₀m＝1.5e^-3s, can obtain J as 0.2 Kg.m²In order to ensure that the energy does not flow to the direct current side during the control operation, the value of the active power instruction is given as P_refWhen the rated angular frequency is 1KW, the corresponding rated angular frequency is omega_ref＝314.1593rad/s。

Step 4, according to the average reactive power obtained in the step 2Given reactive power instruction Q of microgrid inverter_refVoltage command U_refObtaining the terminal voltage U of the virtual synchronous machine through a reactive power control equation^*(ii) a Wherein,

the reactive power control equation is

<math> <mrow> <msup> <mi>U</mi> <mo>*</mo> </msup> <mo>=</mo> <msub> <mi>U</mi> <mi>ref</mi> </msub> <mo>+</mo> <mi>n</mi> <mrow> <mo>(</mo> <msub> <mi>Q</mi> <mi>ref</mi> </msub> <mo>-</mo> <mover> <mi>Q</mi> <mo>&OverBar;</mo> </mover> <mo>)</mo> </mrow> <mo>,</mo> </mrow> </math>

Wherein U_refGiving a reactive power instruction Q for a microgrid inverter_refAnd the voltage of the rated output capacitor and n are power angle control droop coefficients.

When the reactive power change with the reactive control droop coefficient n value principle of 100%, the voltage amplitude value is changed within 2%; given reactive power command Q_refAnd corresponding rated output capacitor voltage U_refThe position relation of the droop curve is represented, and the output reactive power of the microgrid inverter is mainly considered to be Q_refWhen the voltage is high, the output voltage is large.

In this embodiment, the droop coefficient of reactive power control takes the value ofGiven reactive power command Q_refConsidering the system output reactive power as Q_refWhen it is 0, the corresponding rated output capacitor voltage U_ref＝380V。

Step 5, firstly obtaining the terminal voltage U obtained in the step 4 and the terminal voltage U obtained in the step 1_cd,U_cqObtaining a capacitance current command signal by a voltage control equationWherein,

the voltage control equation is

<math> <mrow> <msubsup> <mi>I</mi> <mi>cd</mi> <mo>*</mo> </msubsup> <mo>=</mo> <msub> <mi>K</mi> <mi>p</mi> </msub> <mo>+</mo> <msub> <mi>K</mi> <mi>i</mi> </msub> <mo>/</mo> <mi>s</mi> <mo>+</mo> <mfrac> <mrow> <msub> <mi>K</mi> <mi>r</mi> </msub> <mi>s</mi> </mrow> <mrow> <msup> <mi>s</mi> <mn>2</mn> </msup> <mo>+</mo> <mn>2</mn> <mi>Q</mi> <msub> <mi>&omega;</mi> <mn>0</mn> </msub> <mi>s</mi> <mo>+</mo> <msup> <mrow> <mo>(</mo> <mn>2</mn> <msub> <mi>&omega;</mi> <mn>0</mn> </msub> <mo>)</mo> </mrow> <mn>2</mn> </msup> </mrow> </mfrac> <mrow> <mo>(</mo> <msup> <mi>U</mi> <mo>*</mo> </msup> <mo>-</mo> <msub> <mi>U</mi> <mi>cd</mi> </msub> <mo>)</mo> </mrow> </mrow> </math> ，

<math> <mrow> <msubsup> <mi>I</mi> <mi>cq</mi> <mo>*</mo> </msubsup> <mo>=</mo> <msub> <mi>K</mi> <mi>p</mi> </msub> <mo>+</mo> <msub> <mi>K</mi> <mi>i</mi> </msub> <mo>/</mo> <mi>s</mi> <mo>+</mo> <mfrac> <mrow> <msub> <mi>K</mi> <mi>r</mi> </msub> <mi>s</mi> </mrow> <mrow> <msup> <mi>s</mi> <mn>2</mn> </msup> <mo>+</mo> <mn>2</mn> <mi>Q</mi> <msub> <mi>&omega;</mi> <mn>0</mn> </msub> <mi>s</mi> <mo>+</mo> <msup> <mrow> <mo>(</mo> <mn>2</mn> <msub> <mi>&omega;</mi> <mn>0</mn> </msub> <mo>)</mo> </mrow> <mn>2</mn> </msup> </mrow> </mfrac> <mrow> <mo>(</mo> <mn>0</mn> <mo>-</mo> <msub> <mi>U</mi> <mi>cq</mi> </msub> <mo>)</mo> </mrow> </mrow> </math>

Wherein K is_pIs a proportional control coefficient, K_iFor integral control coefficient, K_rIs the resonant controller scaling factor.

Then according to the capacitor current command signalAnd component I of bridge arm side inductor current dq in step 1_ld,I_lqAnd a component I of the output current dq_od,I_oqObtaining the control signal U by a current control equation_d1,U_q1(ii) a Wherein,

the current control equation is

$U_{d1}=K(I_{\mathrm{cd}}^{*}-I_{\mathrm{ld}}+I_{\mathrm{od}})$

$U_{q1}=K(I_{\mathrm{cq}}^{*}-I_{\mathrm{lq}}+I_{\mathrm{oq}}),$

Wherein K is a proportional control coefficient.

Parameters in the voltage and current control equation mainly consider the stability and the dynamic and steady-state performance of the control system; in this example, take K_p＝0.03,K_i＝0.8,K_r＝120,Q＝16,K＝0.05。

The control process of steps 1-5 can be seen in FIG. 1.

Step 6, according to the negative sequence component U of the capacitor voltage obtained in the step 1_CN-d,U_CN-qAnd the negative sequence component I of the inductor current_LN-d,I_LN-qObtaining a control signal U through a negative sequence voltage compensation control equation_d2,U_q2(ii) a Wherein,

the negative sequence voltage compensation control equation is

<math> <mrow> <msub> <mi>U</mi> <mrow> <mi>d</mi> <mn>2</mn> </mrow> </msub> <mo>=</mo> <mfrac> <mrow> <msub> <mi>K</mi> <mn>1</mn> </msub> <mrow> <mo>(</mo> <mn>0</mn> <mo>-</mo> <msub> <mi>U</mi> <mrow> <mi>C</mi> <mo>_</mo> <mi>N</mi> <mo>-</mo> <mi>d</mi> </mrow> </msub> <mo>)</mo> </mrow> <mo>-</mo> <msub> <mi>K</mi> <mn>2</mn> </msub> <msub> <mi>&omega;</mi> <mn>0</mn> </msub> <msub> <mi>LI</mi> <mrow> <mi>L</mi> <mo>_</mo> <mi>N</mi> <mo>-</mo> <mi>q</mi> </mrow> </msub> </mrow> <mrow> <mi>&tau;s</mi> <mo>+</mo> <mn>1</mn> </mrow> </mfrac> </mrow> </math> ，

<math> <mrow> <msub> <mi>U</mi> <mrow> <mi>q</mi> <mn>2</mn> </mrow> </msub> <mo>=</mo> <mfrac> <mrow> <msub> <mi>K</mi> <mn>1</mn> </msub> <mrow> <mo>(</mo> <mn>0</mn> <mo>-</mo> <msub> <mi>U</mi> <mrow> <mi>C</mi> <mo>_</mo> <mi>N</mi> <mo>-</mo> <mi>q</mi> </mrow> </msub> <mo>)</mo> </mrow> <mo>-</mo> <msub> <mi>K</mi> <mn>2</mn> </msub> <msub> <mi>&omega;</mi> <mn>0</mn> </msub> <msub> <mi>LI</mi> <mrow> <mi>L</mi> <mo>_</mo> <mi>N</mi> <mo>-</mo> <mi>d</mi> </mrow> </msub> </mrow> <mrow> <mi>&tau;s</mi> <mo>+</mo> <mn>1</mn> </mrow> </mfrac> </mrow> </math>

Wherein K is₁For compensating the coefficient, K, for the voltage₂The current compensation coefficient is, L is a bridge side inductance value of the microgrid inverter, and tau is a filtering time constant.

The compensation coefficient mainly considers the effectiveness of dynamic output impedance compensation, and generally takes a value of K being more than or equal to 0.5₁＝K₂Less than or equal to 1. For filtering out negative sequence component U of capacitor voltage_CN-d,U_CN-qAnd the negative sequence component I of the inductor current_LN-d,I_LN-qConsidering the time constant tau of the first-order low-pass filter is less than or equal to 2e^-3And s. In this example, take K₁＝1、K₂＝1、τ＝0.00115。

Step 7, the control signal U obtained in the step 5 and the step 6 is processed_d1,U_q1And U_d2,U_q2Respectively added to obtain control signals U_d,U_q；

Step 8, firstly according to the control signal U in the step 7_d,U_qAnd step 3, obtaining a three-phase bridge arm voltage control signal U through single synchronous rotation coordinate inverse transformation of the vector angle theta obtained in the step_a,U_b,U_cThen according to U_a,U_b,U_cAnd generating PWM control signals of the switching tubes of the inverter bridge of the microgrid inverter.

It is apparent that those skilled in the art can make various changes and modifications to the virtual synchronous machine-based unbalance voltage compensation control method of the present invention without departing from the spirit and scope of the present invention. Thus, if such modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is intended to include such modifications and variations.

Claims (8)

1. The unbalanced voltage compensation control method based on the virtual synchronous machine comprises the acquisition of the output capacitor voltage of the microgrid inverter, and is characterized by mainly comprising the following steps of:

step 1, firstly, acquiring output capacitor voltage U of the microgrid inverter_ca,U_cb,U_ccBridge arm side induction current I_la,I_lb,I_lcAnd an output current I_oxObtaining the component U of the output capacitor voltage dq through the transformation of the single synchronous rotation coordinate_cd,U_cqComponent I of bridge arm side inductor current dq_ld,I_lqAnd a component I of the output current dq_od,I_oqReuse of output capacitor voltage U_ca,U_cb,U_ccAnd bridge arm side inductor current I_la,I_lb,I_lcObtaining the negative sequence component U of the capacitor voltage through double synchronous rotation coordinate transformation_{C_N-d},U_{C_N-q}And the negative sequence component I of the inductor current_{L_N-d},I_{L_N-q}；

Step 2, according to the component U of the output capacitor voltage dq obtained in the step 1_cd,U_cqAnd a component I of the output current dq_od,I_oqObtaining the average active power through an active power calculation equation and a reactive power calculation equationAnd average reactive power

Step 3, obtaining the average active power according to the step 2And active power instruction P given by microgrid inverter_refGiven angular frequency command omega of micro-grid inverter_refObtaining angular frequency omega of the virtual synchronous generator through a power angle control equation, and integrating the angular frequency omega to obtain a vector angle theta of the virtual synchronous generator;

step 4, according to the average reactive power obtained in the step 2Given reactive power instruction Q of microgrid inverter_refVoltage command U_refObtaining the terminal voltage U of the virtual synchronous machine through a reactive power control equation^*；

Step 5, firstly, according to the terminal voltage U obtained in the step 4^*And U obtained in step 1_cd,U_cqObtaining a capacitance current command signal by a voltage control equationThen according to the capacitor current command signalAnd component I of bridge arm side inductor current dq in step 1_ld,I_lqAnd a component I of the output current dq_od,I_oqObtaining the control signal U by a current control equation_d1,U_q1；

Step 6, according to the negative sequence component U of the capacitor voltage obtained in the step 1_CN-d,U_CN-qAnd the negative sequence component I of the inductor current_LN-d,I_LN-qObtaining a control signal U through a negative sequence voltage compensation control equation_d2,U_q2；

Step 7, the control signal U obtained in the step 5 and the step 6 is processed_d1,U_q1And U_d2,U_q2Respectively added to obtain control signals U_d,U_q；

Step 8, firstly according to the control signal U in the step 7_d,U_qAnd step 3, obtaining a three-phase bridge arm voltage control signal U through single synchronous rotation coordinate inverse transformation of the vector angle theta obtained in the step_a,U_b,U_cThen according to U_a,U_b,U_cAnd generating PWM control signals of the switching tubes of the inverter bridge of the microgrid inverter.

2. The virtual synchronous machine-based unbalance voltage compensation control method according to claim 1, wherein the active power calculation equation in the step 2 is

<math> <mrow> <mover> <mi>P</mi> <mo>&OverBar;</mo> </mover> <mo>=</mo> <mrow> <mo>(</mo> <munder> <mi>&Pi;</mi> <mi>h</mi> </munder> <mfrac> <mrow> <msup> <mi>s</mi> <mn>2</mn> </msup> <mo>+</mo> <msup> <msub> <mi>&omega;</mi> <mi>h</mi> </msub> <mn>2</mn> </msup> </mrow> <mrow> <msup> <mi>s</mi> <mn>2</mn> </msup> <mo>+</mo> <mn>2</mn> <mi>Q</mi> <msub> <mi>&omega;</mi> <mi>h</mi> </msub> <mi>s</mi> <mo>+</mo> <msup> <msub> <mi>&omega;</mi> <mi>h</mi> </msub> <mn>2</mn> </msup> </mrow> </mfrac> <mo>)</mo> </mrow> <mo>&CenterDot;</mo> <mfrac> <mn>1.5</mn> <mrow> <mi>&tau;s</mi> <mo>+</mo> <mn>1</mn> </mrow> </mfrac> <mo>&CenterDot;</mo> <mrow> <mo>(</mo> <msub> <mi>U</mi> <mi>cq</mi> </msub> <msub> <mi>I</mi> <mi>oq</mi> </msub> <mo>+</mo> <msub> <mi>U</mi> <mi>cd</mi> </msub> <msub> <mi>I</mi> <mi>od</mi> </msub> <mo>)</mo> </mrow> <mo>,</mo> </mrow> </math>

Wherein Q is the quality factor of the resonance controller, omega_hThe harmonic angular frequency to be filtered by the trap, s is the laplacian operator, and τ is the time constant of the first-order low-pass filter.

3. The virtual synchronous machine-based unbalance voltage compensation control method according to claim 1, wherein the reactive power calculation equation in the step 2 is as follows

<math> <mrow> <mover> <mi>Q</mi> <mo>&OverBar;</mo> </mover> <mo>=</mo> <mrow> <mo>(</mo> <munder> <mi>&Pi;</mi> <mi>h</mi> </munder> <mfrac> <mrow> <msup> <mi>s</mi> <mn>2</mn> </msup> <mo>+</mo> <msup> <msub> <mi>&omega;</mi> <mi>h</mi> </msub> <mn>2</mn> </msup> </mrow> <mrow> <msup> <mi>s</mi> <mn>2</mn> </msup> <mo>+</mo> <mn>2</mn> <mi>Q</mi> <msub> <mi>&omega;</mi> <mi>h</mi> </msub> <mi>s</mi> <mo>+</mo> <msup> <msub> <mi>&omega;</mi> <mi>h</mi> </msub> <mn>2</mn> </msup> </mrow> </mfrac> <mo>)</mo> </mrow> <mo>&CenterDot;</mo> <mfrac> <mn>1.5</mn> <mrow> <mi>&tau;s</mi> <mo>+</mo> <mn>1</mn> </mrow> </mfrac> <mo>&CenterDot;</mo> <mrow> <mo>(</mo> <msub> <mi>U</mi> <mi>cd</mi> </msub> <msub> <mi>I</mi> <mi>oq</mi> </msub> <mo>-</mo> <msub> <mi>U</mi> <mi>cq</mi> </msub> <msub> <mi>I</mi> <mi>od</mi> </msub> <mo>)</mo> </mrow> <mo>,</mo> </mrow> </math>

Wherein Q is the quality factor of the resonance controller, omega_hThe harmonic angular frequency to be filtered by the trap, s is the laplacian operator, and τ is the time constant of the first-order low-pass filter.

4. The virtual synchronous machine-based unbalanced voltage compensation control method of claim 1, wherein the power angle control equation in step 3 is

<math> <mrow> <mi>&omega;</mi> <mo>=</mo> <msub> <mi>&omega;</mi> <mi>ref</mi> </msub> <mo>+</mo> <mfrac> <mi>m</mi> <mrow> <mi>J</mi> <msub> <mi>&omega;</mi> <mn>0</mn> </msub> <mi>ms</mi> <mo>+</mo> <mn>1</mn> </mrow> </mfrac> <mrow> <mo>(</mo> <msub> <mi>P</mi> <mi>ref</mi> </msub> <mo>-</mo> <mover> <mi>P</mi> <mo>&OverBar;</mo> </mover> <mo>)</mo> </mrow> <mo>,</mo> </mrow> </math>

Wherein, ω is_refGiving an active power instruction P for the microgrid inverter_refThe nominal angular frequency of the time, m is a power angle control droop coefficient, J is a virtual moment of inertia time constant, omega of the simulation synchronous generator set₀The angular frequency is fixed for the grid.

5. The virtual synchronous machine-based unbalanced voltage compensation control method of claim 1, wherein the reactive power control equation in the step 4 is

<math> <mrow> <msup> <mi>U</mi> <mo>*</mo> </msup> <mo>=</mo> <msub> <mi>U</mi> <mi>ref</mi> </msub> <mo>+</mo> <mi>n</mi> <mrow> <mo>(</mo> <msub> <mi>Q</mi> <mi>ref</mi> </msub> <mo>-</mo> <mover> <mi>Q</mi> <mo>&OverBar;</mo> </mover> <mo>)</mo> </mrow> <mo>,</mo> </mrow> </math>

Wherein, U_refGiving a reactive power instruction Q for a microgrid inverter_refAnd the voltage of the rated output capacitor and n are power angle control droop coefficients.

6. The virtual synchronous machine-based unbalance voltage compensation control method according to claim 1, wherein the voltage control equation in the step 5 is

<math> <mrow> <msubsup> <mi>I</mi> <mi>cd</mi> <mo>*</mo> </msubsup> <mo>=</mo> <msub> <mi>K</mi> <mi>p</mi> </msub> <mo>+</mo> <msub> <mi>K</mi> <mi>i</mi> </msub> <mo>/</mo> <mi>s</mi> <mo>+</mo> <mfrac> <mrow> <msub> <mi>K</mi> <mi>r</mi> </msub> <mi>s</mi> </mrow> <mrow> <msup> <mi>s</mi> <mn>2</mn> </msup> <mo>+</mo> <mn>2</mn> <mi>Q</mi> <msub> <mi>&omega;</mi> <mn>0</mn> </msub> <mi>s</mi> <mo>+</mo> <msup> <mrow> <mo>(</mo> <mn>2</mn> <msub> <mi>&omega;</mi> <mn>0</mn> </msub> <mo>)</mo> </mrow> <mn>2</mn> </msup> </mrow> </mfrac> <mrow> <mo>(</mo> <msup> <mi>U</mi> <mo>*</mo> </msup> <mo>-</mo> <msub> <mi>U</mi> <mi>cd</mi> </msub> <mo>)</mo> </mrow> </mrow> </math> ，

<math> <mrow> <msubsup> <mi>I</mi> <mi>cq</mi> <mo>*</mo> </msubsup> <mo>=</mo> <msub> <mi>K</mi> <mi>p</mi> </msub> <mo>+</mo> <msub> <mi>K</mi> <mi>i</mi> </msub> <mo>/</mo> <mi>s</mi> <mo>+</mo> <mfrac> <mrow> <msub> <mi>K</mi> <mi>r</mi> </msub> <mi>s</mi> </mrow> <mrow> <msup> <mi>s</mi> <mn>2</mn> </msup> <mo>+</mo> <mn>2</mn> <mi>Q</mi> <msub> <mi>&omega;</mi> <mn>0</mn> </msub> <mi>s</mi> <mo>+</mo> <msup> <mrow> <mo>(</mo> <mn>2</mn> <msub> <mi>&omega;</mi> <mn>0</mn> </msub> <mo>)</mo> </mrow> <mn>2</mn> </msup> </mrow> </mfrac> <mrow> <mo>(</mo> <mn>0</mn> <mo>-</mo> <msub> <mi>U</mi> <mi>cq</mi> </msub> <mo>)</mo> </mrow> </mrow> </math>

Wherein, K_pIs a proportional control coefficient, K_iFor integral control coefficient, K_rIs the resonant controller scaling factor.

7. The virtual synchronous machine-based unbalance voltage compensation control method according to claim 1, wherein the current control equation in the step 5 is

$U_{d1}=K(I_{\mathrm{cd}}^{*}-I_{\mathrm{ld}}+I_{\mathrm{od}})$

$U_{q1}=K(I_{\mathrm{cq}}^{*}-I_{\mathrm{lq}}+I_{\mathrm{oq}}),$

Wherein K is a proportional control coefficient.

8. The virtual synchronous machine-based unbalance voltage compensation control method according to claim 1, wherein the negative sequence voltage compensation control equation in step 6 is

<math> <mrow> <msub> <mi>U</mi> <mrow> <mi>d</mi> <mn>2</mn> </mrow> </msub> <mo>=</mo> <mfrac> <mrow> <msub> <mi>K</mi> <mn>1</mn> </msub> <mrow> <mo>(</mo> <mn>0</mn> <mo>-</mo> <msub> <mi>U</mi> <mrow> <mi>C</mi> <mo>_</mo> <mi>N</mi> <mo>-</mo> <mi>d</mi> </mrow> </msub> <mo>)</mo> </mrow> <mo>-</mo> <msub> <mi>K</mi> <mn>2</mn> </msub> <msub> <mi>&omega;</mi> <mn>0</mn> </msub> <msub> <mi>LI</mi> <mrow> <mi>L</mi> <mo>_</mo> <mi>N</mi> <mo>-</mo> <mi>q</mi> </mrow> </msub> </mrow> <mrow> <mi>&tau;s</mi> <mo>+</mo> <mn>1</mn> </mrow> </mfrac> </mrow> </math> ，

<math> <mrow> <msub> <mi>U</mi> <mrow> <mi>q</mi> <mn>2</mn> </mrow> </msub> <mo>=</mo> <mfrac> <mrow> <msub> <mi>K</mi> <mn>1</mn> </msub> <mrow> <mo>(</mo> <mn>0</mn> <mo>-</mo> <msub> <mi>U</mi> <mrow> <mi>C</mi> <mo>_</mo> <mi>N</mi> <mo>-</mo> <mi>q</mi> </mrow> </msub> <mo>)</mo> </mrow> <mo>-</mo> <msub> <mi>K</mi> <mn>2</mn> </msub> <msub> <mi>&omega;</mi> <mn>0</mn> </msub> <msub> <mi>LI</mi> <mrow> <mi>L</mi> <mo>_</mo> <mi>N</mi> <mo>-</mo> <mi>d</mi> </mrow> </msub> </mrow> <mrow> <mi>&tau;s</mi> <mo>+</mo> <mn>1</mn> </mrow> </mfrac> </mrow> </math>

Wherein, K₁For compensating the coefficient, K, for the voltage₂The current compensation coefficient is, L is a bridge side inductance value of the microgrid inverter, and tau is a filtering time constant.