Current unbalance degree and power oscillation suppression method based on virtual synchronous generator

Abstract

This invention discloses a method for suppressing current imbalance and power oscillations based on a virtual synchronous generator (VSG). First, a traditional VSG loop model is established and its parameters are tuned. Then, the positive and negative sequence components of the grid-connected voltage, filter capacitor terminal voltage, and grid-connected current are extracted using a time-delay cancellation method and transformed to a synchronous rotating coordinate system. An equivalent VSG grid-connected loop model is added to the traditional VSG model. The traditional active power and extended reactive power calculation methods are transformed to the synchronous rotating coordinate system, and a reference value for the grid-connected current that suppresses the second harmonic component of the power is derived. A PI controller is used to make the actual grid-connected current track the reference value, and the output modulated wave drives the inverter. This invention can simultaneously suppress the second harmonic oscillations of active and reactive power, improve grid-connected current imbalance and distortion problems, while retaining the active power frequency regulation, reactive power voltage regulation, and inertial support characteristics of the VSG, thus improving the stability and power quality of the new energy grid-connected system.

Description

Technical Field

[0001] This invention belongs to the field of new energy grid-connected power generation technology, specifically involving an improved VSG control strategy based on extended reactive power theory and the equivalent circuit of virtual synchronous generator (VSG) grid connection, to suppress grid current imbalance and power oscillation under grid voltage imbalance conditions. Background Technology

[0002] With the increasing severity of the energy crisis and environmental problems, distributed generation technologies, represented by photovoltaics and wind power, have received widespread attention worldwide as an effective way to utilize new energy sources. However, the large-scale connection of distributed power sources to the grid via power electronic grid-connected inverters results in the grid exhibiting characteristics of low inertia and weak damping, posing new challenges to the safe and stable operation of the power system. Traditional grid-connected inverters mostly adopt current source control mode, lacking the ability to support grid frequency and voltage, making it difficult to meet the frequency and voltage regulation requirements of power systems with high penetration rates.

[0003] To address this, virtual synchronous generator technology has emerged. By simulating the rotor motion equations and mechanical characteristics of a synchronous generator, it endows grid-connected inverters with equivalent rotational inertia and damping, enabling them to possess "plug-and-play, grid-friendly" characteristics, thereby effectively supporting grid stability. Among grid-connected inverters, the T-type three-level inverter has the advantages of low switching stress and low switching losses, making it the target of the control strategy.

[0004] Most existing VSG control strategies are based on the ideal assumption of three-phase symmetry of the grid voltage. However, in practical engineering applications, distribution networks often face complex operating environments. Affected by factors such as unbalanced three-phase loads, asymmetrical line parameters, non-full-phase operation, or short-circuit faults (such as single-phase ground faults), the grid voltage frequently exhibits three-phase imbalance. Under unbalanced voltage conditions, if the traditional VSG control strategy is used, the system will face severe challenges: on the one hand, the presence of negative-sequence voltage will lead to severe imbalance and distortion of the grid-connected current, which may trigger overcurrent protection actions or even damage power electronic devices; on the other hand, the interaction between the negative-sequence components of voltage and current will generate second-harmonic oscillations in the active and reactive power output of the VSG. This power oscillation not only degrades power quality but also transmits to the frequency and voltage control loops through the power loop, causing fluctuations in the output frequency and amplitude of the VSG, and in severe cases, even disrupting the synchronous stability of the system.

[0005] For grid-connected control under unbalanced power grids, traditional inverter control strategies are relatively mature, typically employing dual current loops or power compensation to suppress current imbalance or eliminate power oscillations. However, the VSG control mechanism differs fundamentally from traditional vector control or droop control; its core lies in simulating the dynamic characteristics of rotating machinery, and its control bandwidth is primarily concentrated in the low-frequency band. Directly applying traditional unbalanced control strategies often fails to consider the VSG's inertial response characteristics, or requires the introduction of complex coordinate transformations and multi-resonant controllers, increasing the complexity of the control system. Furthermore, existing improvement schemes mostly modify the current loop level, easily weakening the VSG's characteristics as a voltage source, degenerating it into a controlled current source, thereby reducing its active support capability for the power grid. Therefore, how to effectively suppress power oscillations and improve grid-connected current quality under unbalanced grid voltage conditions, based on the VSG's equivalent circuit model, by improving power calculation or control loops, while preserving the VSG's inertial and damping support characteristics, has become an urgent problem to be solved. Summary of the Invention

[0006] Purpose of the Invention: To address the problem that existing Virtual Synchronous Generator (VSG) technology cannot simultaneously suppress power oscillations and improve grid-connected current quality under grid voltage imbalance conditions, this invention aims to provide an improved VSG control strategy. Specifically, this invention mainly solves the following technical problems:

[0007] 1. Solve the problem of double-frequency oscillation in the output active and reactive power due to the influence of negative sequence voltage when the grid voltage is unbalanced in traditional VSG control;

[0008] 2. To address the problem that control strategies often lead to grid-connected current imbalance and distortion when suppressing power oscillations;

[0009] 3. Ensure the active power frequency regulation and reactive power voltage regulation characteristics of VSG under normal grid operation, providing inertia and support.

[0010] Technical solution: The present invention provides a method for suppressing current imbalance and power oscillation based on a virtual synchronous generator, comprising the following steps:

[0011] Step 1: Establish a traditional virtual synchronous generator (VSG) circuit model, simulate the rotor motion equation, stator electromagnetic equation, and primary frequency regulation and primary voltage regulation characteristics of the synchronous generator, and tune the model parameters;

[0012] Step 2: When the grid voltage is unbalanced, based on the symmetrical component method, the delayed cancellation method is used to separate the positive and negative sequence components of the grid connection point voltage, the filter capacitor terminal voltage and the grid connection current. Then, through Clark transformation and Park transformation, the separated positive and negative sequence components are transformed into a synchronous rotating coordinate system for representation.

[0013] Step 3: Establish the equivalent circuit model of VSG grid connection, and convert the inverter output phase voltage into the back electromotive force of synchronous generator rotor, the filter into the stator winding resistance and inductance, and the voltage at the filter capacitor terminal into the generator terminal voltage. Integrate the equivalent circuit model into the traditional virtual synchronous generator VSG circuit model established in Step 1 to improve the calculation logic of VSG power output.

[0014] Step 4: Based on the positive and negative sequence components of electrical quantities in the synchronous rotating coordinate system obtained in Step 2, and combined with the equivalent circuit model in Step 3, the traditional active power calculation method and the extended reactive power calculation method are converted to the synchronous rotating coordinate system. The grid-connected current reference value that makes the amplitude of the second harmonic component of active power and reactive power zero is derived, thus achieving the core objective of power oscillation suppression.

[0015] Step 5: Establish a current loop. Calculate the difference between the grid-connected current reference value obtained in Step 4 and the positive and negative sequence components obtained in Step 2. Use a PI controller to adjust the difference and output a modulated wave to drive the T-type three-level inverter to work, so that the actual grid-connected current tracks the reference value and suppresses current imbalance and distortion.

[0016] Step 6: Through simulation experiments, the active power, reactive power, and grid-connected current waveforms of this method are compared with those of the traditional VSG control strategy under normal grid operation and voltage imbalance conditions to verify the effectiveness of this method.

[0017] Furthermore, in step 1, the rotor motion equation is as follows:

[0018]

[0019] In the formula, The virtual angular frequency of the VSG. The rated angular frequency, For the angle of attack, For virtual rotational inertia, For virtual mechanical torque, For virtual electromagnetic torque, The damping coefficient;

[0020] The primary frequency modulation is represented as:

[0021]

[0022] In the formula, For the set active power, This is the active frequency regulation coefficient;

[0023] The primary voltage regulation characteristic is expressed as follows:

[0024]

[0025] In the formula, This is the reactive power command value. This is the reactive power setpoint. This is the reactive power voltage regulation coefficient. This is the effective value of the rated phase voltage. This represents the effective value of the phase voltage of the filter capacitor.

[0026] Furthermore, step 2 specifically involves dividing the voltage into positive-sequence, negative-sequence, and zero-sequence components according to the symmetrical component method when the grid voltage is unbalanced. The positive-sequence separation method used is the delayed cancellation method, based on the PCC voltage at the grid connection point. For example, among which The three-phase phase voltages at point PCC, voltage vector Represented as:

[0027]

[0028] In the formula, and They represent The positive and negative order components. and These represent the effective values ​​of the positive-order and negative-order components, respectively. for angular frequency, and These are the phases of the positive-sequence and negative-sequence components, respectively. for The voltage signal after a quarter cycle delay, with superscript P indicating positive sequence and superscript N indicating negative sequence;

[0029] Based on the Clark and Park transformations, the positive and negative sequence components are transformed onto the dq axis of the synchronous rotating coordinate system. Similarly, the grid-side current can be transformed. Phase voltage of filter capacitor Perform the same positive and negative separation.

[0030] Furthermore, in step 3, the integration of the equivalent loop model into the traditional virtual synchronous generator (VSG) loop model established in step 1 is specifically as follows:

[0031]

[0032] In the formula, Represents the current vector in the equivalent circuit The conjugate vector, for The effective value, The impedance of the equivalent circuit. The impedance angle of the equivalent circuit. R is the effective value of the virtual internal potential generated by the VSG reactive power regulation stage, R is the equivalent resistance of the filter circuit, and L is the equivalent inductance of the filter circuit. , These represent the active power and reactive power output by the VSG, respectively.

[0033] Furthermore, step 4 specifically involves the following traditional methods for calculating active and reactive power:

[0034]

[0035] In the formula, and Represents the instantaneous active power and instantaneous reactive power output of VSG, Re represents taking the real part of the complex number, and Im represents taking the imaginary part of the complex number;

[0036] Expanding reactive power The calculation method is as follows:

[0037]

[0038] In the formula, for The voltage vector after a quarter-cycle delay. and Expression on the dq axis:

[0039]

[0040] In the formula, , For active power and extended reactive power DC components, , , , The amplitudes of the second harmonic components of active power and extended reactive power.

[0041] Furthermore, the inverter mentioned in step 5 is a T-type three-level inverter, the modulation method is SVPWM, the filter is an LCL type filter, and the PI controller is used to eliminate the difference between the actual value and the reference value of the grid-connected current to ensure current tracking accuracy.

[0042] Furthermore, the simulation experiment described in step 6 was built in the MATLAB / Simulink environment. By simulating the unbalanced condition of a 20% voltage drop in phase A of the power grid, the power oscillation and current imbalance suppression effects of the traditional VSG and the present method were compared. At the same time, the frequency and voltage regulation characteristics of the present method under normal power grid operation were verified.

[0043] The present invention also discloses a computer device, including a memory, a processor, and a computer program stored in the memory, wherein the processor executes the computer program to implement the steps of the method of the present invention.

[0044] The present invention also discloses a computer-readable storage medium having a computer program / instructions stored thereon, which, when executed by a processor, implements the steps of the method of the present invention.

[0045] The present invention also discloses a computer program product, including a computer program / instructions that, when executed by a processor, implement the steps of the method of the present invention.

[0046] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages:

[0047] 1. Simultaneous suppression of the second harmonic components of active and reactive power: By extending the reactive power calculation method and deriving the reference current in the synchronous rotating coordinate system, the second harmonic oscillation of active and reactive power is effectively suppressed, avoiding the impact of power oscillation on the grid frequency and voltage, and improving power quality.

[0048] 2. Suppressing grid-connected current imbalance: Through precise current reference value design and closed-loop control of the PI controller, the actual grid-connected current can accurately track the reference value, effectively improving the imbalance and distortion of grid-connected current when the grid voltage is unbalanced, and reducing the risk of overcurrent protection action and damage to power electronic devices.

[0049] 3. Retaining the core supporting characteristics of VSG: When improving the control strategy, this invention, based on the equivalent circuit model and rotor motion characteristics of VSG, does not weaken the essence of VSG as a voltage source. It ensures that VSG can still maintain good active power frequency regulation and reactive power voltage regulation characteristics when the power grid is operating normally, providing reliable inertial and damping support for the power grid and improving the stability of the new energy grid-connected system.

[0050] 4. Low control complexity and strong practicality: The positive and negative sequence components are separated by the delayed phase cancellation method, eliminating the need for a complex multi-resonant controller. Combined with a PI controller, current closed-loop control is achieved. The control structure is simple, the parameters are easy to tune, and it is easy to implement in engineering. It is suitable for various distributed new energy VSG grid connection scenarios. Attached Figure Description

[0051] Figure 1 The diagram shows the topology of a T-type three-level inverter system with an LCL filter and the equivalent circuit of a virtual synchronous generator, where C1 and C2 are DC bus capacitors, and S... ix For each phase's switching transistor, D ix The diodes are anti-parallel to the switching transistor (i=1,2,3,4, x=A,B,C). The three-phase voltage of the power grid. This refers to the DC-side voltage of the inverter.

[0052] Figure 2 VSG control block diagram, Figure 2 (a) is the VSG active power control loop. Figure 2 (b) is the VSG reactive power control loop;

[0053] Figure 3 This is the control block diagram for the time-delay cancellation method;

[0054] Table 1 shows the parameters and their values ​​involved in the control strategy;

[0055] Figure 4 The improved VSG control block diagram after incorporating the VSG grid-connected equivalent circuit model;

[0056] Figure 5 This is the block diagram for the current loop control.

[0057] Figure 6 This represents the active power of a traditional VSG under normal grid operation and imbalance conditions.

[0058] Figure 7 This refers to the reactive power of a traditional VSG under normal grid operation and imbalance conditions.

[0059] Figure 8 The waveform of the three-phase grid-connected current of a traditional VSG under normal grid operation and unbalanced grid conditions;

[0060] Figure 9 for Figure 8 A magnified view of the medium current under unbalanced conditions;

[0061] Figure 10 To improve the active power of VSG under normal grid operation and imbalance conditions;

[0062] Figure 11 To improve the reactive power of VSG under normal grid operation and imbalance conditions;

[0063] Figure 12 To improve the grid-connected current waveform of VSG under normal grid operation and unbalanced grid conditions;

[0064] Figure 13 To improve the active power variation diagram of VSG when the grid frequency drops by 0.05Hz;

[0065] Figure 14 To improve the frequency change graph generated by VSG when the grid frequency drops by 0.05Hz;

[0066] Figure 15To improve the reactive power variation diagram of VSG when the three-phase voltage of the power grid drops by 2%;

[0067] Figure 16 To improve the graph of the positive sequence component of the filter capacitor terminal voltage on the d-axis when the three-phase voltage of the power grid drops by 2%;

[0068] Figure 17 This is for the overall control process. Detailed Implementation

[0069] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0070] Step 1: Combining Figure 1 To explain, Virtual Synchronous Generator (VSG) technology simulates the rotor motion equations and stator electromagnetic equations of a synchronous generator. The stator electromagnetic equations in the inverter system can be represented by the following equations:

[0071]

[0072] In the formula, , , , The voltage across the three phase terminals of the filter capacitor ABC is... This refers to the three-phase inductor current on the inverter side. This refers to the output phase voltage of a T-type three-level inverter. , These are the resistors and inductors on the inverter side.

[0073] The rotor motion equations in the inverter system are expressed as follows:

[0074]

[0075] In the formula, The virtual angular frequency of the VSG. The rated angular frequency, For the angle of attack, For virtual rotational inertia, For virtual mechanical torque, For virtual electromagnetic torque, For the damping coefficient, in equation (2) The grid angular frequency can also be used. replace.

[0076] and It can be expressed by the following formula:

[0077]

[0078] In the formula, For virtual mechanical power, This refers to virtual electromagnetic power.

[0079] In addition to simulating the rotor motion equations and stator electromagnetic equations of a synchronous generator, a VSG also needs to possess primary frequency regulation and primary voltage regulation characteristics. The primary frequency regulation characteristic can be expressed as:

[0080]

[0081] In the formula, For the set active power, This is the active frequency regulation coefficient.

[0082] The primary voltage regulation characteristic can be expressed as:

[0083]

[0084] In the formula, This is the reactive power command value. This is the reactive power setpoint. This is the reactive power voltage regulation coefficient. This is the effective value of the rated phase voltage. This represents the effective value of the phase voltage of the filter capacitor.

[0085] The equation for VSG to generate the reference voltage amplitude is as follows:

[0086]

[0087] In the formula, This represents the effective value of the VSG virtual internal potential. This is the rated value of the virtual internal potential amplitude. This is the integral adjustment coefficient. This is virtual reactive power.

[0088] Combining equations (2) to (6), we can obtain Figure 2 The VSG control block diagram is shown below, and Table 1 provides the relevant parameter values ​​for VSG.

[0089] Step Two: When the grid voltage is unbalanced, according to the symmetrical component method, the voltage can always be divided into positive-sequence, negative-sequence, and zero-sequence components. In a three-phase three-wire system, there is no zero-sequence component. The positive and negative sequence separation method used is the delayed phase cancellation method. The voltage at the grid connection point (PCC) is used as the reference. For example, among which The three-phase phase voltages at point PCC, voltage vector It can be represented as:

[0090]

[0091] In the formula, and They represent The positive and negative order components. and These represent the effective values ​​of the positive-order and negative-order components, respectively. for angular frequency, and These are the phases of the positive-sequence and negative-sequence components, respectively. for The voltage signal after a quarter-cycle delay, with superscript P indicating positive sequence and superscript N indicating negative sequence.

[0092] From equation (7), we can obtain Figure 3 The control block diagram for the time-delay cancellation method is shown. After obtaining the positive and negative sequence components, they are transformed to a synchronous rotating coordinate system (dq axis) according to the Clark and Park transforms. Similarly, the grid-side current can be... Phase voltage of filter capacitor Perform the same positive and negative separation.

[0093] Step 3: The VSG converts the inverter output phase voltage into the back electromotive force generated by the synchronous generator rotor on the stator, the filter into the resistance and inductance of the stator winding, and the voltage at the filter capacitor terminal into the generator terminal voltage. The equivalent structure is as follows: Figure 1 As shown, assuming the voltage phase at point PCC is 0° relative to the inverter output voltage, the filter is equivalent to an inductor. and a resistor In series, where , For the inverter side inductance and resistance, , Using the grid-side inductance and resistance, we obtain the equivalent circuit model of the VSG grid connection. Based on this model, the apparent power output of the VSG is... It can be represented as:

[0094]

[0095] In the formula, Represents the current vector in the equivalent circuit The conjugate vector, for The effective value, The impedance of the equivalent circuit. The impedance angle of the equivalent circuit.

[0096] Due to the parasitic resistance of the filter circuit Generally much smaller than the filter inductance. And the angle of attack When the inverter is synchronized with the grid, the value is almost zero, therefore it can be assumed that:

[0097]

[0098] According to equation (9), equation (8) can be simplified to:

[0099]

[0100] According to equation (10), a power calculation module can be added after the VSG control block diagram, such as... Figure 4 As shown.

[0101] Step 4: The traditional methods for calculating active and reactive power are as follows:

[0102]

[0103] In the formula, and Represents the instantaneous active power and instantaneous reactive power output of VSG, Re represents taking the real part of the complex number, and Im represents taking the imaginary part of the complex number.

[0104] To simplify calculations, voltage is used. and current The initial phases of the positive and negative sequence components are set to 0, and they can be represented in the two-phase stationary coordinate system and on the dq axis as follows:

[0105]

[0106] In the formula, , , , These represent the positive and negative sequence components of voltage and current, respectively. Components on the axis, , , , These represent the positive and negative sequence components of voltage and current on the dq axis, respectively.

[0107] Expanding reactive power The calculation method is as follows:

[0108]

[0109] In the formula, for The voltage vector after a quarter-cycle delay. The expression for the dq axis is:

[0110]

[0111] According to equations (11) to (14), we can obtain and Expression on the dq axis:

[0112]

[0113] In the formula, , For active power and extended reactive power DC components, , , , Let be the amplitudes of the second harmonic components of active power and extended reactive power. They are expressed by the following formula:

[0114]

[0115] To ensure that the instantaneous active and reactive power output of the VSG is free from second harmonic ripple, it is necessary to... , , , The value is 0, and it can be seen from equation (16) that the extended reactive power calculation is used. , That is, as long as the amplitude of the second harmonic component of the active power is 0, the reactive power will also not produce pulsation.

[0116] Therefore, in order to ensure that the active and reactive power are pulsating and that the DC flow meets the set reference value, equation (16) can be transformed into the following expression:

[0117]

[0118] In the formula, , for , Reference values.

[0119] Solving equation (17) yields the following solution:

[0120]

[0121] In the formula, , , , The solution vector of equation (17) is used as the current reference value for the subsequent current loop. , They are respectively The magnitudes of the positive-sequence and negative-sequence components can be expressed by the following formula:

[0122]

[0123] Step 5: Combine the current reference value from equation (18) with the grid-side current obtained by the time-delay cancellation method in step 2. The positive and negative sequence components on the dq axis are subtracted and then input into the current loop. The current loop uses PI control, and the output of the current loop serves as the input signal for SVPWM. The process is as follows: Figure 5 As shown.

[0124] Step Six: Build a Simulink simulation in MATLAB. At 0.4s, cause the voltage of phase A of the grid to drop by 20%. The waveforms of active power, reactive power, and grid-connected current of a traditional VSG under grid imbalance are as follows: Figure 6 , Figure 7 , Figure 8 , Figure 9 As shown, it is evident that the power exhibits significant second-harmonic oscillations, and the current imbalance is high; while the improved VSG control strategy shows... Figure 10 , Figure 11 , Figure 12 As shown, both active and reactive power achieved no second-harmonic oscillation, which is in line with the theory, and the current waveform imbalance was reduced. Figure 13 and Figure 14 It was verified that the improved VSG control strategy still maintains active power frequency regulation characteristics under normal grid operation; Figure 15 and Figure 16 The improved VSG control strategy was verified to maintain reactive power voltage regulation characteristics under normal grid operation; the overall system control block diagram is as follows: Figure 17 As shown.

[0125] The above are merely preferred embodiments of the present invention, but do not limit the patent scope of the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing specific embodiments, or make equivalent substitutions for some of the technical features. Any equivalent structures made using the content of the present invention specification and drawings, directly or indirectly applied to other related technical fields, are similarly within the patent protection scope of the present invention.

Claims

1. A method for suppressing current imbalance and power oscillation based on a virtual synchronous generator, characterized in that, Includes the following steps: Step 1: Establish a traditional virtual synchronous generator (VSG) circuit model, simulate the rotor motion equation, stator electromagnetic equation, and primary frequency regulation and primary voltage regulation characteristics of the synchronous generator, and tune the model parameters; Step 2: When the grid voltage is unbalanced, based on the symmetrical component method, the delayed cancellation method is used to separate the positive and negative sequence components of the grid connection point voltage, the filter capacitor terminal voltage and the grid connection current. Then, through Clark transformation and Park transformation, the separated positive and negative sequence components are transformed into a synchronous rotating coordinate system for representation. Step 3: Establish the equivalent circuit model of VSG grid connection, and convert the inverter output phase voltage into the back electromotive force of synchronous generator rotor, the filter into the stator winding resistance and inductance, and the voltage at the filter capacitor terminal into the generator terminal voltage. Integrate the equivalent circuit model into the traditional virtual synchronous generator VSG circuit model established in Step 1 to improve the calculation logic of VSG power output. Step 4: Based on the positive and negative sequence components of electrical quantities in the synchronous rotating coordinate system obtained in Step 2, and combined with the equivalent circuit model in Step 3, the traditional active power calculation method and the extended reactive power calculation method are converted to the synchronous rotating coordinate system. The grid-connected current reference value that makes the amplitude of the second harmonic component of active power and reactive power zero is derived, thus achieving the core objective of power oscillation suppression. Step 5: Establish a current loop. Calculate the difference between the grid-connected current reference value obtained in Step 4 and the positive and negative sequence components obtained in Step 2. Use a PI controller to adjust the difference and output a modulated wave to drive the T-type three-level inverter to work, so that the actual grid-connected current tracks the reference value and suppresses current imbalance and distortion. Step 6: Through simulation experiments, the active power, reactive power, and grid-connected current waveforms of this method are compared with those of the traditional VSG control strategy under normal grid operation and voltage imbalance conditions to verify the effectiveness of this method.

2. The method for suppressing current imbalance and power oscillation based on a virtual synchronous generator according to claim 1, characterized in that, In step 1, the rotor motion equation is as follows: ； In the formula, The virtual angular frequency of the VSG. The rated angular frequency, For the angle of attack, For virtual rotational inertia, For virtual mechanical torque, For virtual electromagnetic torque, The damping coefficient; The primary frequency modulation is represented as: ； In the formula, For the set active power, This is the active frequency regulation coefficient; The primary voltage regulation characteristic is expressed as follows: ； In the formula, This is the reactive power command value. This is the reactive power setpoint. This is the reactive power voltage regulation coefficient. This is the effective value of the rated phase voltage. This represents the effective value of the phase voltage of the filter capacitor.

3. The method for suppressing current imbalance and power oscillation based on a virtual synchronous generator according to claim 1, characterized in that, Step 2 specifically involves dividing the voltage into positive-sequence, negative-sequence, and zero-sequence components according to the symmetrical component method when the grid voltage is unbalanced. The positive-sequence separation method used is the time-delayed cancellation method, based on the PCC voltage at the grid connection point. For example, among which The three-phase phase voltages at point PCC, voltage vector Represented as: ； In the formula, and They represent The positive-order components and negative-order components, and These represent the effective values ​​of the positive-order and negative-order components, respectively. for angular frequency, and These are the phases of the positive-sequence and negative-sequence components, respectively. for The voltage signal after a quarter cycle delay, with superscript P indicating positive sequence and superscript N indicating negative sequence; Based on the Clark and Park transformations, the positive and negative sequence components are transformed onto the dq axis of the synchronous rotating coordinate system. Similarly, the grid-side current can be transformed. Phase voltage of filter capacitor Perform the same positive and negative separation.

4. The method for suppressing current imbalance and power oscillation based on a virtual synchronous generator according to claim 2, characterized in that, In step 3, the integration of the equivalent loop model into the traditional virtual synchronous generator (VSG) loop model established in step 1 is specifically as follows: ； In the formula, Represents the current vector in the equivalent circuit The conjugate vector, for The effective value, The impedance of the equivalent circuit. The impedance angle of the equivalent circuit. R is the effective value of the virtual internal potential generated by the VSG reactive power regulation stage, R is the equivalent resistance of the filter circuit, and L is the equivalent inductance of the filter circuit. , These represent the active power and reactive power output by the VSG, respectively.

5. The method for suppressing current imbalance and power oscillation based on a virtual synchronous generator according to claim 4, characterized in that, Step 4 specifically involves the following traditional methods for calculating active and reactive power: ； In the formula, and Represents the instantaneous active power and instantaneous reactive power output of VSG, Re represents taking the real part of the complex number, and Im represents taking the imaginary part of the complex number; Expanding reactive power The calculation method is as follows: ； In the formula, for The voltage vector after a quarter-cycle delay. and Expression on the dq axis: ； In the formula, , For active power and extended reactive power DC components, , , , The amplitudes of the second harmonic components of active power and extended reactive power.

6. The method for suppressing current imbalance and power oscillation based on a virtual synchronous generator according to claim 1, characterized in that, The inverter mentioned in step 5 is a T-type three-level inverter, with SVPWM modulation and an LCL filter. The PI controller is used to eliminate the difference between the actual grid current and the reference value to ensure current tracking accuracy.

7. The method for suppressing current imbalance and power oscillation based on a virtual synchronous generator according to claim 1, characterized in that, The simulation experiment described in step 6 was built in the MATLAB / Simulink environment. By simulating the unbalanced condition of a 20% voltage drop in phase A of the power grid, the power oscillation and current imbalance suppression effects of the traditional VSG and the present method were compared. At the same time, the frequency and voltage regulation characteristics of the present method under normal power grid operation were verified.

8. A computer device comprising a memory, a processor, and a computer program stored in the memory, characterized in that, The processor executes the computer program to implement the steps of the method of claim 1.

9. A computer-readable storage medium having a computer program / instructions stored thereon, characterized in that, When the computer program / instructions are executed by the processor, they implement the steps of the method of claim 1.

10. A computer program product, comprising a computer program / instructions, characterized in that, When the computer program / instructions are executed by the processor, they implement the steps of the method of claim 1.

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