A coordinated control method of virtual synchronous machine grid-connected converter under voltage sag

Abstract

The application discloses a kind of coordinated control methods of virtual synchronous machine grid-connected converter under voltage sag, belong to new energy grid-connected control field, including the following steps: S1 data acquisition: including voltage, net side current, inductance current;S2 virtual synchronous machine basic control: VSG model is built, including active ring, reactive ring and voltage-current double closed loop control structure;S3 symmetric voltage sag control: before voltage-current double closed loop decoupling control, voltage ring correction is carried out to series virtual impedance, equivalent increase grid-connected impedance, stabilize voltage;S4 asymmetric voltage sag control: voltage / current is separated to positive and negative sequence, correct virtual impedance, generate PWM drive signal.This method does not need mode switching, pure algorithm implementation, can simultaneously adapt symmetric and asymmetric fault, significantly inhibit impact current, stabilize power, improve transient stability, meet the requirement of national standard low voltage ride through, be applicable to photovoltaic, wind power and other grid-connected inverters, engineering practicability is strong.

Description

Technical Field

[0001] This invention belongs to the field of power electronic grid-connected control technology, and particularly relates to a low-voltage ride-through control method for a virtual synchronous machine during voltage dips in a three-phase LC grid-connected converter. Specifically, it is a collaborative control method for a virtual synchronous machine grid-connected converter under voltage dips. Background Technology

[0002] With the large-scale integration of new energy sources such as wind power and photovoltaics into the power grid via power electronic inverters, system inertia has decreased, highlighting voltage stability issues. When voltage dips occur in the grid, grid-connected equipment must possess low-voltage ride-through (LVRT) capabilities to prevent grid disconnection and system collapse. Existing technologies mainly suffer from the following drawbacks: 1. Traditional PQ control is prone to overcurrent and power oscillations during voltage dips, and is susceptible to loss of control and grid disconnection during deep dips, exhibiting weak reactive power support capabilities. 2. Conventional virtual synchronous machine (VSG) control exhibits large inrush currents, power angle oscillations, and poor transient stability during voltage dips, failing to effectively suppress overcurrent and unbalanced currents. 3. Existing LVRT methods often employ mode switching, amplitude limiting, or simple power regulation, resulting in complex control and insufficient capacity to handle both symmetrical and asymmetrical voltage dips, making it difficult to simultaneously meet the requirements of current limiting, voltage support, and stable operation.

[0003] The following relevant published patent documents were retrieved: A collaborative control method for grid-type converters based on bidirectional virtual impedance (CN122203457 A) is proposed. The system collects terminal voltage and output current in real time. When a voltage drop occurs and the current exceeds the safety threshold, a positive virtual impedance is introduced to limit the fault current. When the voltage drops but the current is within the safety range, a negative virtual impedance is introduced to compensate for the voltage drop caused by reactive voltage droop, thereby achieving collaborative control of current limiting protection and voltage support capability.

[0004] A method for rapid support of a grid-connected MMC during a voltage dip (CN118983812 A) is disclosed. This method controls the output reference voltage through virtual impedance control at the instant of a grid voltage drop, and adjusts the input setpoints of the active and reactive power of the grid-connected MMC during the dip to achieve steady-state current limiting. This method effectively avoids overcurrent problems, achieving rapid support and stable operation of the grid. Compared with the above technical solutions, the technical solutions adopted by the prior art and the effects that can be achieved are quite different from those of this application. Summary of the Invention

[0005] This invention aims to address the shortcomings of existing technologies. To overcome the defects of existing virtual synchronous machines in terms of overcurrent, power oscillation, insufficient reactive power support, and weak low-voltage ride-through capability during symmetrical / asymmetrical voltage dips in the grid, this invention provides a collaborative control method for virtual synchronous machine grid-connected converters under voltage dips. This method ensures that the grid-connected converter remains reliably connected to the grid during voltage dips, suppresses overcurrent, stabilizes power, improves transient voltage support, and meets the national standard requirements for low-voltage ride-through.

[0006] This technical solution is implemented in the following way: A collaborative control method for a virtual synchronous machine grid-connected converter under voltage dips, characterized by comprising the following steps: S1 Data Acquisition: Includes PCC voltage, grid-side current, and inductor current; S2 Virtual Synchronous Machine Basic Control: Based on the collected data, a VSG model is constructed, including active loop, reactive loop, and voltage-current dual closed-loop control structure; S3 Symmetrical voltage drop control: A virtual impedance is connected in series before the voltage-current dual closed-loop decoupling control to correct the voltage loop, which effectively increases the grid-connected impedance, suppresses inrush current, and stabilizes the PCC voltage. S4 Asymmetric Voltage Drop Control: Separates voltage / current into positive and negative sequences, corrects virtual impedance, and superimposes the positive and negative sequence control outputs through Park inverse transformation to generate a PWM drive signal.

[0007] Furthermore, in step S2, the VSG model is as follows: , in, J Let be the moment of inertia of the rotor. ω v The virtual power angle frequency of the VSG. ω 0 is the rated angular frequency, t is time, and K is the frequency. ω This is the primary frequency modulation coefficient. P ref For reference active power; P e To simulate the mechanical power of a synchronous generator, T e = P e / w 0, where T e Simulate the electromagnetic torque of a synchronous generator; D p Damping coefficient of a simulated synchronous generator.

[0008] Furthermore, in step 2, The active power loop simulates the rotor motion equation of a synchronous generator, including virtual inertia, damping, and primary frequency regulation, and outputs a virtual power angle θv. The reactive power loop employs voltage droop control, with an output voltage reference amplitude E. ref ; The voltage-current dual closed-loop control structure uses the virtual power angle θ generated by the VSG. v With voltage amplitude E ref As a reference, decoupled control is implemented in the dq coordinate system, thereby generating a corresponding PWM modulation signal to drive the inverter output.

[0009] In step S3, the voltage loop correction specifically includes: , , in, E dref This is the reference amplitude of the d-axis voltage output by the VSG. E qref This is the reference amplitude of the q-axis voltage output by the VSG. v dref This is the original voltage reference value for the d-axis. v qref This is the original q-axis voltage reference value. i d with i q Let be the currents along the d-axis and q-axis, respectively. R V The introduced virtual resistance, L V For the introduced virtual inductance, ω is the angular frequency.

[0010] Furthermore, in step S4, positive and negative sequence separation of voltage / current is performed. Specifically, a second-order notch filter is used to separate the positive and negative sequence of voltage / current. The positive sequence channel embeds a virtual impedance to stabilize the positive sequence voltage and current; the negative sequence channel is closed-loop to suppress the negative sequence current and achieve unbalanced control.

[0011] Furthermore, the positive sequence voltage loop control formula for the positive sequence channel is: , in, These are the integral terms of the voltage errors along the d and q axes, respectively. These are the positive sequence reference voltages for the d and q axes, respectively. These are the positive-sequence output voltage feedback values ​​on the d and q axes, obtained after separating the positive and negative sequences of the three-phase voltages. These are the reference values ​​for the generated d-axis and q-axis positive sequence currents. These are the positive sequence currents on the d and q axes obtained after separating the positive and negative sequences of the three-phase currents, respectively. Here is the value of the filter capacitor. The term is a feedforward decoupling term used to compensate for capacitor current. This is the voltage loop proportionality coefficient; The voltage loop integral coefficient; , in, These are the integral terms of the positive sequence current errors along the d and q axes, respectively. These are the positive-sequence components of the inductor currents on the d and q axes, obtained by separating the three-phase currents into positive and negative sequences, respectively. These are the positive-sequence voltage reference values ​​for the final generated PWM modulation waveforms on the d and q axes, respectively. This is the value of the filter inductance. This is the proportionality coefficient of the current loop. is the integral coefficient of the current loop.

[0012] Furthermore, the negative sequence current loop control formula for the negative sequence channel is: , in, These are the integral terms of the negative sequence current errors along the d and q axes, respectively. These are the reference values ​​for the generated d-axis and q-axis negative sequence currents. These are the negative-sequence components of the inductor currents on the d and q axes, obtained by separating the three-phase currents into positive and negative sequences, respectively. These are the negative sequence voltage reference values ​​for the final generated PWM modulation waveforms on the d and q axes, respectively. This is the value of the filter inductance. This is the proportionality coefficient of the current loop. is the integral coefficient of the current loop.

[0013] A collaborative control device for a virtual synchronous machine grid-connected converter under voltage dips, characterized in that it is used to execute any of the methods described above, comprising: The data acquisition module is used to acquire PCC voltage, grid-side current, and inductor current. The virtual synchronous machine basic control module is used to build the VSG model, including the active loop, reactive loop, and voltage-current dual closed-loop control structure. The symmetrical voltage drop control module is used to correct the voltage loop by connecting a virtual impedance in series before the voltage-current dual closed-loop decoupling control, which effectively increases the grid-connected impedance, suppresses inrush current, and stabilizes the PCC voltage. The asymmetric voltage drop control module is used to separate the positive and negative sequences of voltage / current, correct the virtual impedance, and the positive and negative sequence control outputs are superimposed after Park inverse transformation to generate PWM drive signals.

[0014] An electronic device includes: a memory interconnected with the processors, the memory storing computer instructions, and the processors executing the computer instructions to perform the method described above.

[0015] A computer-readable storage medium storing instructions that, when executed by one or more processors, cause an electronic device to perform any of the methods described above.

[0016] Compared with the prior art, the present invention has the following beneficial effects: 1. Significant overcurrent suppression: Under symmetrical dropout, the current drops from 1.54 pu to 0.09 pu; under asymmetrical dropout, the current drops from 1.6 pu to 1.09 pu, meeting the current limiting requirements.

[0017] 2. Strong pass-through capability: It can maintain network connection for 150ms at 0 voltage and 625ms at 0.2 pu, in accordance with GB / T19964-2024 standard.

[0018] 3. Power stability: Suppresses active / reactive oscillations, provides stable voltage support, and has a fast recovery speed.

[0019] 4. Good versatility: It is compatible with both symmetrical and asymmetrical drops, without the need for complex mode switching, and has strong robustness.

[0020] 5. Simple to implement: Pure algorithm implementation, no increase in hardware cost, easy to deploy in engineering. Attached Figure Description

[0021] Figure 1 This is the overall system topology diagram (DC power supply → three-phase converter → LC filter → power grid). Figure 2 : These are the VSG active / reactive power control block diagrams; (a) VSG active power control block diagram; (b) VSG reactive power control block diagram; Figure 3 This is a diagram of a dual closed-loop control structure for voltage and current. Figure 4 This is an inner-loop control structure diagram based on virtual impedance; Figure 5 It is the separation of positive and negative order during asymmetric drop; Figure 6 This is a virtual impedance control block diagram; Figure 7 The waveforms of the voltage and current at point PCC when the VSG active / reactive power control drops to 0.8 pu are shown; (a) voltage at point PCC; (b) current at point PCC. Figure 8 It dropped to 0.8 pu active power P and reactive power Q Curve; (a) Active powerP； (b) Reactive power Q； Figure 9 The waveforms of the voltage and current at the PCC point are as follows: (a) Voltage at the PCC point; (b) Current at the PCC point. Figure 10 The VSG active / reactive power control dropped to 0.2 pu active power. P and reactive power Q Curve; (a) Active power P； (b) Reactive power Q； Figure 11 The waveforms of the voltage and current at point PCC are as follows: (a) Voltage at point PCC; (b) Current at point PCC. Figure 12 It refers to the active power when phases B and C drop to 0.6 pu under VSG active / reactive power control. P and reactive power Q Curve; (a) Active power P； (b) Reactive power Q； Figure 13 The simulated waveforms of the voltage and current at the PCC point are as follows: (a) PCC point voltage; (b) PCC point current. Figure 14 The power curve is shown when the grid voltage dips to 0.8 pu and a virtual impedance is introduced; (a) Active power P ； (b) Reactive power Q； Figure 15 The waveforms of the PCC point voltage and current when the grid voltage drops to 0.5pu and 0.2pu and virtual impedance is introduced are: (a) Voltage waveform when the voltage drops to 0.5pu; (b) Voltage waveform when the voltage drops to 0.2pu; (c) Current waveform when the voltage drops to 0.5pu; (d) Current waveform when the voltage drops to 0.2pu. Figure 16 These are the voltage and current waveforms at point CC when the grid voltage drops to 0 and a virtual impedance is introduced; (a) voltage at point PCC; (b) current at point PCC. Figure 17 It is the power waveform when the grid voltage drops to 0 and a virtual impedance is introduced; (a) Active power P ； (b) Reactive power Q； Figure 18 This is the current waveform at point PCC when phases B and C drop to 0.6pu after the introduction of virtual impedance; Figure 19 The active and reactive power of phases b and c when the voltage drops to 0.6 pu after the introduction of virtual impedance; (a) active power; (b) reactive power; Figure 20 These are the active and reactive currents of phases b and c when the voltage drops to 0.6 pu after the introduction of virtual impedance; (a) active current; (b) reactive current.

[0022] Attached image label: 1. Detailed Implementation

[0023] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0024] A collaborative control method for a virtual synchronous machine grid-connected converter under voltage dips, see appendix. Figure 1 As shown, this invention targets a three-phase LC grid-connected converter and adopts a collaborative control architecture of VSG main control + virtual impedance + positive and negative sequence separation, the core of which is as follows: 1. Basic control of the virtual synchronous machine, see appendix. Figure 2 The following is a block diagram of VSG active / reactive power control: Active power loop: Simulates the rotor motion equations of a synchronous generator, including virtual inertia, damping, and primary frequency regulation, outputting a virtual power angle θ. v .

[0025] Reactive power loop: Employs voltage droop control, with output voltage reference amplitude E ref .

[0026] Voltage-current dual closed-loop: See appendix Figure 3 The voltage and current dual closed-loop control structure diagram shown is used to achieve decoupled control in the dq coordinate system with the VSG output as a reference.

[0027] The VSG model is as follows:

[0028] in, J Let be the moment of inertia of the rotor. ω v The virtual power angle frequency of the VSG. ω 0 is the rated angular frequency, t is time, and K is the frequency. ω This is the primary frequency modulation coefficient. P ref For reference active power; P e To simulate the mechanical power of a synchronous generator, T e = P e / w 0, where Te Simulate the electromagnetic torque of a synchronous generator; D p Damping coefficient of a simulated synchronous generator.

[0029] 2. Symmetrical voltage drop control See appendix Figure 4 The diagram shown is an inner-loop control structure based on virtual impedance. The symmetrical voltage drop control is implemented by connecting a virtual impedance (Rv+jωLv) in series before the voltage and current dual closed loop, which effectively increases the grid-connected impedance, suppresses inrush current, and stabilizes the PCC voltage.

[0030] Voltage loop correction formula: , , in E dref , E qref The dq axis reference value output by VSG v dref and v qref The difference between the output voltage and the virtual impedance. R V， L V， The introduced virtual impedance, i d and i q Let be the current in the dq coordinate system.

[0031] Specifically E dref This is the reference amplitude of the d-axis voltage output by the VSG. E qref This is the reference amplitude of the q-axis voltage output by the VSG. v dref This is the original voltage reference value for the d-axis. v qref This is the original q-axis voltage reference value. i d with i q Let be the currents along the d-axis and q-axis, respectively. R V The introduced virtual resistance, L V For the introduced virtual inductance, It is the angular frequency (angular velocity in the dq rotating coordinate system).

[0032] 3. Asymmetrical voltage sag control, see appendix. Figure 5 The positive and negative sequence separation during asymmetric drops is shown, and a second-order notch filter is used to separate the positive and negative sequence of voltage / current.

[0033] Positive sequence path: Embedded virtual impedance to stabilize positive sequence voltage and current.

[0034] Negative sequence channel: Closed-loop suppression of negative sequence current to achieve unbalanced control.

[0035] The positive and negative sequence control outputs are superimposed after Park inverse transformation to generate a PWM drive signal.

[0036] Among them, the positive sequence voltage loop control in the asymmetric control method is shown in the appendix. Figure 6 The virtual impedance control block diagram is shown below: , in, These are the integral terms of the voltage errors along the d and q axes, respectively. These are the positive sequence reference voltages for the d and q axes, respectively. These are the positive sequence output voltage feedback values ​​for the d and q axes, respectively. These are the reference values ​​for the generated d-axis and q-axis positive sequence currents. i d with i q Let be the positive sequence currents along the d and q axes, respectively. Here is the value of the filter capacitor. The term is a feedforward decoupling term used to compensate for capacitor current. This is the voltage loop proportionality coefficient; The voltage loop integral coefficient; , in, These are the integral terms of the positive sequence current errors along the d and q axes, respectively. These are the positive-sequence components of the inductor current along the d and q axes, respectively. These are the positive-sequence voltage reference values ​​for the final generated PWM modulation waveforms on the d and q axes, respectively. This is the value of the filter inductance. This is the proportionality coefficient of the current loop. is the integral coefficient of the current loop.

[0037] Negative sequence current loop control: , in, These are the integral terms of the negative sequence current errors along the d and q axes, respectively. These are the reference values ​​for the generated d-axis and q-axis negative sequence currents. These are the negative-sequence components of the inductor current along the d and q axes, respectively. These are the negative sequence voltage reference values ​​for the final generated PWM modulation waveforms on the d and q axes, respectively. This is the value of the filter inductance. This is the proportionality coefficient of the current loop. is the integral coefficient of the current loop.

[0038] Overall control process: Collect PCC voltage, grid-side current, and inductor current → calculate active power P / reactive power Q → generate VSG with angle and voltage reference → determine symmetry / asymmetry → separate positive and negative sequence → correct virtual impedance → dual closed-loop control → drive converter. Example 1

[0039] Symmetrical voltage drop control System parameters: Three-phase LC grid-connected converter, DC voltage 800V, grid rated voltage 311V / 50Hz; filter inductor Lf=1mH, filter capacitor Cf=25μF, grid-side inductance Lg=2mH; control parameters: virtual inertia J=0.2, virtual resistance Rv=0.1Ω, virtual inductance Lv=12mH.

[0040] The operating condition is set so that the grid voltage drops symmetrically to 0.8 pu for 1-2 seconds, and then returns to normal after 2 seconds.

[0041] Control process and waveform description The system detects a symmetrical voltage drop, keeps the VSG main control framework unchanged, and applies a virtual impedance Rv+jωLv before the voltage and current double closed loop, correcting the dq axis voltage reference value according to the voltage loop correction formula.

[0042] correspond Figure 7 , Figure 8 , Figure 9 , Figure 10 Without the addition of virtual impedance, the voltage drop at point PCC and the significant current surge (approximately 1.54 pu) cause significant oscillations in active and reactive power.

[0043] correspond Figure 13 , Figure 14 After adding virtual impedance, the voltage at point PCC is effectively raised and supported, the inrush current is significantly suppressed to 0.09 pu, the active and reactive power are stable without obvious oscillation, and the system operates stably.

[0044] Deep drop verification (corresponding) Figure 15 When the voltage drops to 0.5 pu and 0.2 pu, the virtual impedance can still stabilize the voltage and limit the current; when it drops to 0 voltage (corresponding to...). Figure 16 , Figure 17 The system can maintain network connectivity for 150ms, meeting the GB / T19964-2024 standard.

[0045] After the voltage recovers in 2 seconds, the system quickly exits virtual impedance control and smoothly returns to rated steady-state operation. Example 2

[0046] Asymmetric voltage drop control The system parameters are the same as those in Example 1, except that a positive-negative sequence separation and negative sequence current closed-loop suppression circuit are added.

[0047] The operating condition is set to cause the voltage to drop to 0.6 pu in phases b and c of the power grid due to asymmetry for 1-2 seconds, and then return to normal after 2 seconds.

[0048] Control process and waveform description The system detects an asymmetric drop and activates a second-order notch filter to separate the voltage and current into positive and negative sequences, extracting the positive / negative sequence components (corresponding to...). Figure 5 ).

[0049] The positive sequence channel embeds a virtual impedance to stabilize the positive sequence voltage and current; the negative sequence channel closes the loop to suppress the negative sequence current and reduce the three-phase imbalance.

[0050] correspond Figure 11 , Figure 12 Without the addition of coordinated control, the three-phase current at the PCC point is severely unbalanced and exceeds the limit (approximately 1.6 pu), resulting in drastic fluctuations in active and reactive power.

[0051] correspond Figure 18 , Figure 19 , Figure 20 After adding virtual impedance and positive and negative sequence coordinated control, the three-phase current imbalance is significantly reduced, and the peak value is limited to 1.09 pu; the active power is stable, the reactive power support meets the national standard requirements, and the positive sequence voltage is stable.

[0052] The positive and negative sequence control outputs are superimposed after Park inverse transformation to generate PWM drive signals. The system does not disconnect from the grid or switch modes throughout the entire process, and quickly reaches steady state after the voltage recovers.

[0053] Unless otherwise specifically stated, the relative steps, numerical expressions, and values ​​of the components and steps described in these embodiments do not limit the scope of the invention.

[0054] The flowcharts and block diagrams in the accompanying drawings illustrate possible architectures, functions, and operations according to the invention. In this regard, each block in a flowchart or block diagram may represent a module, segment, or portion of code containing one or more executable instructions for implementing the specified logical function. It should also be noted that in some alternative implementations, the functions marked in the blocks may occur in a different order than those shown in the drawings. For example, two consecutive blocks may actually be executed substantially in parallel, and they may sometimes be executed in reverse order, depending on the functions involved. It should also be noted that each block in the block diagrams and / or flowcharts, and combinations of blocks in the block diagrams and / or flowcharts, can be implemented using a dedicated hardware-based system that performs the specified function or action, or using a combination of dedicated hardware and computer instructions.

[0055] This application also provides an electronic device, which may include at least one processor and at least one memory. The processor may include one or more processing cores. The processor connects to various parts of the server using various interfaces and lines, and performs various functions of the server and processes data by running or executing instructions, programs, code sets, or instruction sets stored in the memory, and by calling data stored in the memory.

[0056] This application also provides a computer-readable storage medium storing instructions. When executed by one or more processors, these instructions cause an electronic device to perform one or more of the methods described in the above embodiments.

[0057] Furthermore, the functional units in this application can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit.

[0058] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A collaborative control method for a virtual synchronous machine grid-connected converter under voltage dips, characterized in that, Includes the following steps: S1 Data Acquisition: Includes PCC voltage, grid-side current, and inductor current; S2 Virtual Synchronous Machine Basic Control: Based on the collected data, a VSG model is constructed, including active loop, reactive loop, and voltage-current dual closed-loop control structure; S3 Symmetrical voltage drop control: A virtual impedance is connected in series before the voltage-current dual closed-loop decoupling control to correct the voltage loop, which effectively increases the grid-connected impedance, suppresses inrush current, and stabilizes the PCC voltage. S4 Asymmetric Voltage Drop Control: Separates voltage / current into positive and negative sequences, corrects virtual impedance, and superimposes the positive and negative sequence control outputs through Park inverse transformation to generate a PWM drive signal.

2. The collaborative control method for a virtual synchronous machine grid-connected converter under voltage dips according to claim 1, characterized in that, In step S2, the VSG model is as follows: ， in, J Let be the moment of inertia of the rotor. ω v The virtual power angle frequency of the VSG. ω 0 is the rated angular frequency, t is time, and K is the frequency. ω This is the primary frequency modulation coefficient. P ref For reference active power; P e To simulate the mechanical power of a synchronous generator, T e = P e / w 0, where T e Simulate the electromagnetic torque of a synchronous generator; D p Damping coefficient of a simulated synchronous generator.

3. The collaborative control method for a virtual synchronous machine grid-connected converter under voltage dips according to claim 1, characterized in that, In step 2, The active power loop simulates the rotor motion equation of a synchronous generator, including virtual inertia, damping, and primary frequency regulation, and outputs a virtual power angle θv. The reactive power loop employs voltage droop control, with an output voltage reference amplitude E. ref ; The voltage-current dual closed-loop control structure uses the virtual power angle θ generated by the VSG. v With voltage amplitude E ref As a reference, decoupled control is implemented in the dq coordinate system, thereby generating a corresponding PWM modulation signal to drive the inverter output.

4. The collaborative control method for a virtual synchronous machine grid-connected converter under voltage dips according to claim 1, characterized in that, In step S3, the voltage loop correction specifically includes: ， ， in, E dref This is the reference amplitude of the d-axis voltage output by the VSG. E qref This is the reference amplitude of the q-axis voltage output by the VSG. v dref This is the original voltage reference value for the d-axis. v qref This is the original q-axis voltage reference value. R V The introduced virtual resistance, L V For the introduced virtual inductance, i d with i q Let be the currents along the d-axis and q-axis, respectively. This is the angular frequency.

5. The collaborative control method for a virtual synchronous machine grid-connected converter under voltage dips according to claim 1, characterized in that, In step S4, positive and negative sequence separation of voltage / current is performed. Specifically, a second-order notch filter is used to separate the positive and negative sequence of voltage / current. The positive sequence channel embeds a virtual impedance to stabilize the positive sequence voltage and current; the negative sequence channel closes the loop to suppress the negative sequence current and achieve unbalanced control.

6. The collaborative control method for a virtual synchronous machine grid-connected converter under voltage dips according to claim 5, characterized in that, The positive sequence voltage loop control formula for the positive sequence channel is: ， in, These are the integral terms of the voltage errors along the d and q axes, respectively. These are the positive sequence reference voltages for the d and q axes, respectively. These are the positive-sequence output voltage feedback values ​​on the d and q axes, obtained after separating the positive and negative sequences of the three-phase voltages. These are the reference values ​​for the generated d-axis and q-axis positive sequence currents. These are the positive sequence currents on the d and q axes obtained after separating the positive and negative sequences of the three-phase currents, respectively. Here is the value of the filter capacitor. The term is a feedforward decoupling term used to compensate for capacitor current. This is the voltage loop proportionality coefficient; The voltage loop integral coefficient; ， in, These are the integral terms of the positive sequence current errors along the d and q axes, respectively. These are the positive-sequence components of the inductor currents on the d and q axes, obtained by separating the three-phase currents into positive and negative sequences, respectively. These are the positive-sequence voltage reference values ​​for the final generated PWM modulation waveforms on the d and q axes, respectively. This is the value of the filter inductance. This is the proportionality coefficient of the current loop. is the integral coefficient of the current loop.

7. The collaborative control method for a virtual synchronous machine grid-connected converter under voltage dips according to claim 5, characterized in that, The negative sequence current loop control formula for the negative sequence channel is: ， in, These are the integral terms of the negative sequence current errors along the d and q axes, respectively. These are the reference values ​​for the generated d-axis and q-axis negative sequence currents. These are the negative-sequence components of the inductor currents on the d and q axes, obtained by separating the three-phase currents into positive and negative sequences, respectively. These are the negative sequence voltage reference values ​​for the final generated PWM modulation waveforms on the d and q axes, respectively. This is the value of the filter inductance. This is the proportionality coefficient of the current loop. is the integral coefficient of the current loop.

8. A collaborative control device for a virtual synchronous grid-connected converter under voltage dips, characterized in that, For performing the method as described in any one of claims 1 to 7, comprising: The data acquisition module is used to acquire PCC voltage, grid-side current, and inductor current. The virtual synchronous machine basic control module is used to build the VSG model, including the active loop, reactive loop, and voltage-current dual closed-loop control structure. The symmetrical voltage drop control module is used to correct the voltage loop by connecting a virtual impedance in series before the voltage-current dual closed-loop decoupling control, which effectively increases the grid-connected impedance, suppresses inrush current, and stabilizes the PCC voltage. The asymmetric voltage drop control module is used to separate the positive and negative sequences of voltage / current, correct the virtual impedance, and the positive and negative sequence control outputs are superimposed after Park inverse transformation to generate PWM drive signals.

9. An electronic device, comprising: The processors are interconnected by a memory, which stores computer instructions, and the processors execute the computer instructions to perform the method as described in any one of claims 1 to 7.

10. A computer-readable storage medium storing instructions, characterized in that, When executed by one or more processors, the electronic device performs the method as described in any one of claims 1 to 7.

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