Positive and negative sequence adaptive virtual impedance control method and system based on reactive circulating current

Abstract

The application provides a positive and negative sequence adaptive virtual impedance control method and system based on reactive circulating current, and relates to the technical field of power electronics. Three-phase voltage and current signals of each parallel inverter are separated into positive and negative sequence signals; coordinate transformation is performed on the signals to obtain positive and negative sequence voltage signals and current signals; active and reactive power is calculated based on the positive and negative sequence voltage and current signals to obtain a virtual electromotive force; positive and negative sequence reactive circulating currents of the parallel inverters are calculated according to positive and negative sequence q-axis current components; the positive sequence reactive circulating current is used as a feedback quantity to adaptively adjust the positive sequence virtual impedance, and the negative sequence reactive circulating current is used as a feedback quantity to adaptively adjust the negative sequence virtual impedance; a voltage drop of the positive sequence virtual impedance and the virtual electromotive force are used as a reference value of a positive sequence voltage loop, and a voltage drop of the negative sequence virtual impedance is fed forward to a negative sequence voltage loop as a reference value of a negative sequence voltage loop; voltage commands output by the positive sequence voltage loop and the negative sequence voltage loop are superposed to form a modulation signal, so that the stability of the system and the voltage quality are improved.

Description

Technical Field

[0001] This invention relates to the field of power electronics technology, and in particular to a positive and negative sequence adaptive virtual impedance control method and system based on reactive circulating current. Background Technology

[0002] Parallel inverters controlled by virtual synchronous generators (VSGs) can simulate the inertia and damping characteristics of synchronous generators. They are one of the core technologies of distributed generation systems. By suppressing circulating current and improving power distribution through virtual impedance technology, they have become the mainstream engineering solution.

[0003] In practical engineering, parallel inverters often face complex operating conditions such as load imbalance and inconsistent line impedance, which can easily lead to positive and negative sequence circulating currents, resulting in decreased reactive power distribution accuracy, voltage distortion, and system oscillations, threatening the stable operation of microgrids. Traditional fixed-parameter virtual impedance cannot adapt to dynamic operating conditions, and although existing research on adaptive virtual impedance attempts to adjust it dynamically, it still has significant limitations.

[0004] Existing adaptive virtual impedance technologies mostly use reactive power deviation as the feedback variable, resulting in slow dynamic response and failure to decouple positive and negative sequence impedances. They are also designed only for a single inverter and do not consider the circulating current coupling problem unique to parallel systems. Some parallel schemes use the same set of impedance parameters for positive and negative sequence circulating currents, making it difficult to simultaneously achieve the dual objectives of reactive power distribution and positive and negative sequence circulating current suppression under unbalanced load conditions, thus failing to meet the stable operation requirements in complex scenarios. Summary of the Invention

[0005] To address the aforementioned issues, this invention proposes a positive and negative sequence adaptive virtual impedance control method and system based on reactive power circulation. By directly adjusting the adaptive virtual impedance through positive and negative sequence reactive power circulation, the parallel VSG inverter achieves precise reactive power distribution and positive and negative sequence circulation suppression under load imbalance and line impedance inconsistency conditions, thereby improving system stability and voltage quality.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a positive and negative sequence adaptive virtual impedance control method based on reactive circulating current, comprising: Collect the three-phase voltage and current signals of each parallel inverter, and obtain the positive-sequence signal and the negative-sequence signal by positive-negative sequence separation; The positive-sequence signal and the negative-sequence signal are respectively subjected to coordinate transformation to obtain positive-sequence and negative-sequence voltage signals and current signals; Active power and reactive power are calculated based on positive sequence voltage and current signals, and then input into the VSG control module to obtain the virtual electromotive force of the system. Calculate the positive and negative sequence reactive circulating current of the parallel inverter based on the positive and negative sequence q-axis current components; The positive-sequence reactive current is used as feedback quantity to adaptively adjust the positive-sequence virtual impedance; the negative-sequence reactive current is used as feedback quantity to adaptively adjust the negative-sequence virtual impedance. The voltage drop of the positive-sequence virtual impedance and the virtual electromotive force are used together as the reference value of the positive-sequence voltage loop, and the voltage drop of the negative-sequence virtual impedance is fed forward to the negative-sequence voltage loop as the reference value of the negative-sequence voltage loop. The voltage commands output from the positive-sequence voltage loop and the negative-sequence voltage loop are superimposed to generate a modulation signal.

[0007] Secondly, the present invention provides a positive and negative sequence adaptive virtual impedance control system based on reactive circulating current, comprising: The signal acquisition module is configured to acquire the three-phase voltage and current signals of each parallel inverter, and obtain positive-sequence and negative-sequence signals by positive-negative sequence separation. The coordinate transformation module is configured to perform coordinate transformation on the positive-sequence signal and the negative-sequence signal respectively to obtain positive-sequence and negative-sequence voltage signals and current signals; The power calculation module is configured to calculate active power and reactive power based on positive sequence voltage signal and positive sequence current signal, and input the VSG control module to obtain the virtual electromotive force of the system. The circulating current calculation module is configured to calculate the positive and negative sequence reactive circulating current of the parallel inverter based on the positive and negative sequence q-axis current components. The impedance adjustment module is configured to adaptively adjust the positive-sequence virtual impedance using the positive-sequence reactive circulating current as feedback, and to adaptively adjust the negative-sequence virtual impedance using the negative-sequence reactive circulating current as feedback. The voltage reference module is configured to use the voltage drop of the positive-sequence virtual impedance and the virtual electromotive force together as the positive-sequence voltage loop reference value, and feed forward the voltage drop of the negative-sequence virtual impedance to the negative-sequence voltage loop as the negative-sequence voltage loop reference value. The modulation module is configured to superimpose the voltage commands output by the positive-sequence voltage loop and the negative-sequence voltage loop to generate a modulation signal.

[0008] Thirdly, the present invention provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of the positive and negative sequence adaptive virtual impedance control method based on reactive circulating current described in the first aspect.

[0009] Fourthly, the present invention provides a computer device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the program to implement the steps of the positive and negative sequence adaptive virtual impedance control method based on reactive circulating current described in the first aspect.

[0010] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention optimizes the feedback variable from the traditional "reactive power deviation" to "positive and negative sequence reactive circulating current between inverters," directly addressing the essence of current sharing. Compared to feedback based on power deviation, it offers faster dynamic response, clearer physical meaning, and more accurate capture of the circulating current coupling problem unique to parallel systems. By designing separate positive-sequence and negative-sequence adaptive virtual impedances, complete decoupling control of the two types of impedances is achieved. This allows for independent suppression of negative-sequence circulating current caused by load imbalance and positive-sequence circulating current caused by line impedance inconsistency, avoiding the limitations of traditional methods that cannot simultaneously address reactive power sharing and circulating current suppression when using a single set of impedance parameters. The positive-sequence virtual impedance voltage drop, superimposed with the VSG electromotive force, participates in the positive-sequence voltage loop, ensuring the accuracy of active-reactive power decoupling and reactive power sharing. The negative-sequence virtual impedance voltage drop is fed forward to the negative-sequence voltage loop, specifically suppressing the negative-sequence component, effectively reducing voltage distortion and system oscillation risks, and improving the stable operation capability of the microgrid under complex conditions.

[0011] Advantages of additional aspects of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0012] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute a limitation thereof.

[0013] Figure 1 A main flowchart of a positive and negative sequence adaptive virtual impedance control method based on reactive circulating current provided in an embodiment of the present invention; Figure 2 A control block diagram of a positive and negative sequence adaptive virtual impedance control method based on reactive circulating current provided in an embodiment of the present invention; Figure 3 This is a control structure diagram of the positive-sequence adaptive virtual impedance provided in an embodiment of the present invention; Figure 4 The control structure diagram of the negative sequence adaptive virtual impedance provided in the embodiment of the present invention is shown. Detailed Implementation

[0014] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0015] As described in the background section, with the development of microgrid technology, VSG (Virtual Synchronous Generator) controlled parallel inverters have been widely used in distributed generation systems because they can simulate the inertia and damping characteristics of synchronous generators. In practical engineering scenarios, parallel inverter systems often face problems such as load imbalance (e.g., single-phase load switching, nonlinear load connection) and inconsistent inverter line impedance. These problems can lead to positive and negative sequence circulating currents in the system, resulting in reduced reactive power sharing accuracy, output voltage distortion, system oscillation, and other issues, seriously affecting the stable operation of the parallel system.

[0016] Virtual impedance technology is currently the main method for suppressing circulating current and improving power sharing performance in parallel inverters in engineering. Traditional virtual impedance often uses fixed parameter design, meaning that the resistance and reactance of the virtual impedance are fixed values ​​set offline, and cannot be dynamically adjusted with changes in system operating conditions. While there is some research on adaptive virtual impedance, research on unbalanced load conditions is still lacking. Under ideal conditions of load balance and consistent parameters, traditional adaptive virtual impedance technology can play a certain role in suppressing circulating current. However, under actual conditions of simultaneous load imbalance and inconsistent line impedance, it has significant limitations. Traditional adaptive virtual impedance technology uses the same set of impedance parameters for both positive-sequence and negative-sequence circulating currents, and when facing unbalanced load conditions, it cannot simultaneously achieve the dual goals of reactive power sharing and suppression of positive and negative-sequence circulating currents.

[0017] In the existing technology, some studies have proposed adaptive virtual impedance control methods, but most of them are aimed at a single VSG inverter and do not consider the circulating current coupling problem unique to parallel systems. In addition, some adaptive virtual impedance methods for parallel systems mostly use reactive power deviation as feedback, which has a slow dynamic response and does not achieve complete decoupling of positive and negative sequence impedances, and cannot effectively solve the problem of negative sequence circulating current suppression under load imbalance.

[0018] To address the issues of uneven reactive power distribution and positive and negative sequence reactive circulating currents caused by inconsistent line impedances in VSG parallel inverters under unbalanced load conditions, this invention proposes a positive and negative sequence adaptive virtual impedance control method, system, medium, and device based on reactive circulating currents. To address the inconsistent line impedance under unbalanced load conditions, a dual second-order generalized integrator (DSOGI) is employed to separate the positive and negative sequences of the system's unbalanced signal. A control model based on reactive power circulation feedback and decoupled adaptive virtual impedance is constructed, with independent control loops for positive and negative sequences. The positive sequence control loop includes VSG control, positive sequence adaptive virtual impedance control, and positive sequence voltage and current dual closed-loop control. This ensures that reactive power is evenly distributed and reactive power circulation is effectively suppressed without affecting the inertia and damping characteristics of the VSG. The negative sequence control loop includes negative sequence adaptive virtual impedance control and negative sequence voltage and current dual closed-loop control. This eliminates the negative sequence component in the output three-phase voltage, thus ensuring its balance. Under unbalanced three-phase output current conditions, it ensures that the negative sequence component is evenly distributed, effectively suppressing negative sequence reactive power circulation.

[0019] Example 1 like Figure 1 As shown, this embodiment discloses a positive and negative sequence adaptive virtual impedance control method based on reactive circulating current, including the following steps: S1: Collect the three-phase voltage and current signals of each parallel inverter, and obtain the positive sequence signal and negative sequence signal by positive and negative sequence separation; S2: Perform coordinate transformation on the positive-sequence signal and the negative-sequence signal respectively to obtain positive-sequence and negative-sequence voltage signals and current signals; S3: Calculate active power and reactive power based on positive sequence voltage signal and positive sequence current signal, and input them into VSG control module to obtain the virtual electromotive force of the system; S4: Calculate the positive and negative sequence reactive circulating current of the parallel inverter based on the positive and negative sequence q-axis current components; S5: The positive-sequence reactive current circulation is used as feedback quantity to adaptively adjust the positive-sequence virtual impedance; the negative-sequence reactive current circulation is used as feedback quantity to adaptively adjust the negative-sequence virtual impedance. S6: The voltage drop of the positive sequence virtual impedance and the virtual electromotive force are used together as the reference value of the positive sequence voltage loop, and the voltage drop of the negative sequence virtual impedance is fed forward to the negative sequence voltage loop as the reference value of the negative sequence voltage loop. S7: Superimpose the voltage commands output by the positive sequence voltage loop and the negative sequence voltage loop to generate a modulation signal.

[0020] Next, combined Figure 2 This embodiment provides a detailed description of a positive and negative sequence adaptive virtual impedance control method based on reactive circulating current.

[0021] S1: Collect the filtered three-phase voltage signal from each parallel inverter. Three-phase current signal and the three-phase current signal before filtering The three-phase signals are separated into positive-sequence and negative-sequence signals by passing them through a dual second-order generalized integrator; the positive-sequence signal includes the positive-sequence three-phase voltage signal. Positive sequence three-phase current signal and positive sequence inductor current signal Negative sequence signals include negative sequence three-phase voltage signals. Negative sequence three-phase current signal and negative sequence inductor current signal .

[0022] Three-phase current signal For example, the calculation formula is as follows:

[0023] in, , , This is the positive sequence current component. , , The negative sequence current component is represented by q, which indicates that the input signal is hysteresis-90°.

[0024] This embodiment utilizes dual second-order generalized integrators to separate positive-sequence and negative-sequence components. Compared to the traditional method of extracting only the positive-sequence component, it also retains the negative-sequence component, enabling the negative-sequence circulating current to be effectively sensed and controlled. This is a prerequisite for the stable operation of parallel inverters under unbalanced conditions and provides an electrical quantity basis for subsequent circulating current suppression and power control in parallel systems.

[0025] S2: The positive sequence signal obtained in step S1 , , and negative sequence signal , , The positive-sequence voltage and current signals, as well as the negative-sequence voltage and current signals, are obtained by performing Clark and Park transformations respectively. Positive sequence voltage signals include d-axis positive sequence voltage signals. q-axis positive sequence voltage signal Positive sequence current signals include d-axis positive sequence current signals. q-axis positive sequence current signal d-axis positive sequence inductor current signal q-axis positive sequence inductor current signal Negative sequence voltage signals include d-axis negative sequence voltage signals. q-axis negative sequence voltage signal Negative sequence current signals include d-axis negative sequence current signals. q-axis negative sequence current signal d-axis negative sequence inductor current signal q-axis negative sequence inductor current signal .

[0026] In this embodiment, by performing Clark and Park transformations on the positive and negative sequence components respectively, an independent dq-axis mathematical model for the positive and negative sequences is established, providing a decoupled control channel for subsequent positive sequence power control and negative sequence circulating current suppression. This ensures that positive sequence VSG control and negative sequence virtual impedance adjustment do not interfere with each other, realizing coordinated control of the parallel system under unbalanced power grid conditions.

[0027] S3: Based on the d-axis positive sequence voltage signal obtained in step S2 q-axis positive sequence voltage signal With d-axis positive sequence current signal q-axis positive sequence current signal The instantaneous active and reactive power of each inverter are calculated using the following formula:

[0028] The calculated active and reactive power are input into the VSG control module. The angular velocity and virtual electromotive force of the system are obtained by adjusting the active and reactive power loops of the VSG. The control equations are as follows:

[0029] in, For virtual rotational inertia, Rated active power, The rated angular velocity, Let be the system angular velocity. This is the virtual damping coefficient. The rated voltage of the system. This is the positive sequence component of the output three-phase voltage. Rated reactive power, and The droop coefficient is... The virtual electromotive force output by VSG.

[0030] S4: The positive and negative sequence q-axis current components of the two inverters obtained in step S2. , , , The formula for calculating the positive and negative sequence reactive circulating current signals of a parallel inverter is as follows:

[0031] in, The positive-sequence reactive power circulating current component. This is the negative-sequence reactive power circulating component.

[0032] Since the formulas for calculating active and reactive power in the dq coordinate system are: ; In the dq synchronous rotating coordinate system, the d-axis is usually oriented to the bus voltage. In this way, the bus voltage retains only the d-axis component in the dq coordinate system, while the q-axis component is 0, i.e.: , .

[0033] The above equation then becomes: ; Therefore, it is called Active current This is reactive current.

[0034] By calculating the positive-sequence and negative-sequence reactive circulating currents between parallel inverters, these are used as adaptive adjustment feedback quantities for the positive-sequence and negative-sequence virtual impedances, respectively. Compared to traditional methods that use the reactive power difference between the two inverters as the basis for adjustment, this embodiment directly starts from the fundamental principle of reactive current equalization and uses circulating current signals for feedback, resulting in clearer physical meaning and more direct adjustment.

[0035] S5: When the line impedance is relatively low, the line impedance satisfies... At this point, the line resistance can be ignored, and the output voltage power angle is small during steady-state operation, allowing for decoupled power control. Due to the active-frequency droop characteristic of VSG control, each VSG operates at the same frequency in steady state, naturally achieving active power distribution and suppressing active circulating current, unaffected by inconsistent line impedance.

[0036] Due to the inconsistent line impedance, the output voltage amplitudes of the two inverters are inconsistent, resulting in reactive circulating current and uneven reactive power distribution. When the line resistance is not negligible, a virtual impedance is usually introduced to make the equivalent output impedance in the line meet the requirements. and This allows for decoupled power control and addresses the issues of reactive circulating current and uneven reactive power distribution.

[0037] Furthermore, with positive-sequence reactive power circulating components Adaptive adjustment of positive sequence virtual impedance This improves the positive-sequence reactive power distribution accuracy of the two VSG parallel inverters and suppresses positive-sequence reactive power circulating current; it also reduces the negative-sequence reactive power circulating current component. As a feedback signal, the negative sequence virtual impedance is adaptively adjusted. This enables the negative sequence reactive current to be evenly distributed between the two VSG parallel inverters, thus suppressing the negative sequence circulating current.

[0038] Specifically, in step S4, such as Figure 3 As shown, this invention addresses the positive-sequence adaptive virtual impedance. A PI controller with positive-sequence reactive power circulation feedback is used for regulation, and the specific regulation rules are as follows: The first inverter's positive-sequence adaptive virtual impedance From positive sequence reactive power circulation Adjustment, the adjustment formula is as follows:

[0039] in, , These are the proportional and integral adjustment coefficients for the positive-sequence adaptive virtual impedance, respectively.

[0040] Since the same circulating current signal has the same magnitude but opposite direction for both inverters, the positive-sequence adaptive virtual impedance of the second inverter... The first inverter is the opposite, and the formula is as follows:

[0041] Through the above adjustment mechanism, the positive sequence reactive circulating current component is used as a feedback quantity to drive the positive sequence virtual impedance to change adaptively until the positive sequence q-axis currents of the two inverters are equal. At this time, the positive sequence reactive power is accurately divided and the positive sequence circulating current is synchronously suppressed.

[0042] This embodiment provides a specific PI control formula for the positive-sequence virtual impedance, clarifies the dynamic adjustment relationship between the positive-sequence reactive circulating current and the positive-sequence virtual impedance, and designs complementary adjustment directions for two parallel inverters. This ensures that the adjustment of the positive-sequence virtual impedance is both rapid and error-free, while also guaranteeing coordinated changes in the positive-sequence virtual impedance of the two inverters, avoiding adjustment conflicts, and improving the accuracy of positive-sequence reactive power distribution.

[0043] Furthermore, in step S4, as Figure 4 As shown, this invention provides an adaptive virtual impedance for negative order. A PI controller with negative-sequence reactive power circulation feedback is used for regulation, and the specific regulation rules are as follows: The first inverter's negative sequence adaptive virtual impedance By negative sequence reactive power circulation Adjustment, the adjustment formula is as follows:

[0044] in, , These are the proportional and integral adjustment coefficients for the negative-sequence adaptive virtual impedance, respectively.

[0045] Similarly, the negative sequence adaptive virtual impedance of the second inverter The formula is the opposite of the first inverter:

[0046] By driving the negative-sequence virtual impedance to adaptively change through the negative-sequence reactive circulating current component until the negative-sequence q-axis currents of the two inverters are equal, the negative-sequence circulating current is effectively suppressed.

[0047] Among them, the positive and negative sequence adaptive virtual impedance uses traditional PI regulation. Taking the positive sequence as an example, the regulation method is to first set... It starts at 0 and gradually increases from 0. Observation of reactive power circulation Reduce the pressure significantly until the circulation no longer decreases significantly and no longer oscillates, then adjust accordingly. The steady-state error of reactive power circulation is eliminated to 0.

[0048] Specifically, and The tuning is performed in the order of proportion first, then integration.

[0049] First let It retains only the proportional regulation function; under conditions of unbalanced load and inconsistent line impedance, it ensures stable system operation and records the initial positive sequence reactive circulating current.

[0050] Then from the smaller Gradually increase the voltage and observe the changes in positive-sequence reactive circulating current, positive-sequence virtual impedance output, and three-phase output voltage and current. When increasing the ratio significantly reduces the positive-sequence reactive circulating current, and the system output voltage and current do not exhibit continuous oscillations, it indicates that the proportional coefficient can effectively suppress the positive-sequence reactive circulating current; further increasing it... If the decrease in positive-sequence reactive circulating current is no longer significant, or if further increases lead to phenomena such as output voltage oscillation, current oscillation, and increased virtual impedance output fluctuations, then stop increasing the current. And before the above-mentioned oscillation phenomenon occurs As the final scaling factor.

[0051] Next, after determining Then, adjust. Specifically: maintain The value remains unchanged, and gradually increases from 0. Observe the steady-state value of the positive-sequence reactive power circulation. When After increasing the value, the steady-state error of the positive-sequence reactive power circulation gradually decreases, indicating that the integral element can eliminate the residual error caused by proportional control; further increasing the value... Until the positive-sequence reactive circulating current essentially converges to zero, and the system output voltage, current, and positive-sequence virtual impedance no longer oscillate continuously, then... As the final integral coefficient. If If further increases result in oscillations, increased overshoot, or longer convergence time, then decrease the value. Take the value before the oscillation occurs.

[0052] therefore, The determination is mainly based on the rate of decrease of the positive-sequence reactive power circulating current and whether the system oscillates. The determination is mainly based on whether the steady-state error of the negative-sequence reactive power circulation can be eliminated and whether the system oscillates.

[0053] The same applies to negative order. and The tuning method and , Same. That is, severance. Gradually increase This significantly reduces the negative-sequence reactive power circulation and prevents system oscillation; then maintain Unchanged, gradually increasing This eliminates the steady-state error of the negative-sequence reactive circulating current to zero, and the setting termination condition is to prevent continuous oscillation of the output voltage, current, and virtual impedance.

[0054] This embodiment designs an independent negative-sequence virtual impedance PI regulation rule for negative-sequence circulating current, achieving equal-sharing control of negative-sequence reactive current. The negative-sequence virtual impedance is completely decoupled from the positive-sequence virtual impedance, and its regulation does not affect the positive-sequence power control of the VSG: the negative-sequence virtual impedance is in the negative-sequence control loop and is independent of the VSG, while the positive-sequence virtual impedance calculates the difference between its voltage drop and the virtual electromotive force generated by the VSG before entering the voltage loop (discussed in detail below), and the two do not interfere with each other. This fills the gap in negative-sequence circulating current suppression in existing parallel VSG control, and is particularly suitable for severe operating conditions such as grid voltage imbalance or load asymmetry.

[0055] In this embodiment, the adjustment of the positive-sequence virtual impedance effectively improves the distribution accuracy of positive-sequence reactive power and suppresses positive-sequence circulating current; the adjustment of the negative-sequence virtual impedance achieves, for the first time, the equal distribution of negative-sequence reactive current in the parallel VSG system, fundamentally suppressing negative-sequence circulating current. This provides a key guarantee for the efficient and stable operation of the parallel system under unbalanced power grids.

[0056] S6: Calculate the positive sequence voltage drop based on the positive sequence adaptive virtual impedance obtained in step S5. The specific formula is as follows:

[0057] This voltage drop, together with the virtual electromotive force output by the VSG, is used as the reference value for the positive sequence voltage loop. The specific formula is as follows:

[0058] The negative-sequence voltage drop is calculated based on the obtained negative-sequence virtual impedance, using the following formula:

[0059] This voltage drop is fed forward to the negative sequence voltage loop as a voltage reference value. The specific formula is as follows:

[0060] S7: The voltage command output by the positive sequence voltage and current loop control is superimposed with the voltage command output by the negative sequence voltage and current loop control as the PWM signal to maintain the stable operation of the system.

[0061] Thus, by adjusting the positive and negative sequence virtual impedances respectively through positive and negative sequence reactive current feedback, the parallel inverter achieves accurate equalization of positive sequence reactive power and effective suppression of negative sequence circulating current under unbalanced load conditions, thus forming a complete closed loop of positive and negative sequence adaptive virtual impedance control based on reactive current.

[0062] This embodiment uses the superposition of the positive-sequence virtual impedance voltage drop and the VSG virtual electromotive force as the reference value for the positive-sequence voltage loop, and feeds the negative-sequence virtual impedance voltage drop forward to the negative-sequence voltage loop, thus achieving independent correction of the positive and negative-sequence voltage commands. Finally, a PWM modulation wave is generated by superimposing the outputs of the positive and negative-sequence voltage and current loops, ensuring stable output of the system under parallel operation and unbalanced conditions. This structure organically integrates positive-sequence VSG control and negative-sequence circulating current suppression within the same control framework, preserving the voltage source characteristics of the VSG while effectively suppressing parallel circulating current.

[0063] This specific embodiment addresses the shortcomings of existing adaptive virtual impedance technology, such as slow dynamic response, lack of decoupling between positive and negative sequence impedances, and difficulty in simultaneously achieving reactive power sharing and circulating current suppression. Taking parallel VSG inverters as the object, it optimizes the feedback variable from the traditional reactive power deviation to the positive and negative sequence reactive power circulating currents between the two inverters, directly starting from the essence of current sharing, resulting in faster dynamic response and clearer physical meaning. By designing positive-sequence and negative-sequence adaptive virtual impedances separately, complete decoupling control of the two types of impedances is achieved, which can independently suppress positive-sequence circulating currents caused by inconsistent line impedances and negative-sequence circulating currents caused by load imbalance. At the same time, the positive-sequence virtual impedance voltage drop is superimposed with the VSG electromotive force to participate in the positive-sequence voltage loop, and the negative-sequence virtual impedance voltage drop is fed forward to the negative-sequence voltage loop. This not only ensures the accuracy of reactive power sharing but also specifically suppresses the negative-sequence component, effectively reducing voltage distortion and system oscillation, and improving the stable operation capability of the microgrid under complex operating conditions.

[0064] Example 2 This embodiment provides a positive and negative sequence adaptive virtual impedance control system based on reactive circulating current, including: The signal acquisition module is configured to acquire the three-phase voltage and current signals of each parallel inverter, and obtain positive-sequence and negative-sequence signals by positive-negative sequence separation. The coordinate transformation module is configured to perform coordinate transformation on the positive-sequence signal and the negative-sequence signal respectively to obtain positive-sequence and negative-sequence voltage signals and current signals; The power calculation module is configured to calculate active power and reactive power based on positive sequence voltage signal and positive sequence current signal, and input the VSG control module to obtain the virtual electromotive force of the system. The circulating current calculation module is configured to calculate the positive and negative sequence reactive circulating current of the parallel inverter based on the positive and negative sequence q-axis current components. The impedance adjustment module is configured to adaptively adjust the positive-sequence virtual impedance using the positive-sequence reactive circulating current as feedback, and to adaptively adjust the negative-sequence virtual impedance using the negative-sequence reactive circulating current as feedback. The voltage reference module is configured to use the voltage drop of the positive-sequence virtual impedance and the virtual electromotive force together as the positive-sequence voltage loop reference value, and feed forward the voltage drop of the negative-sequence virtual impedance to the negative-sequence voltage loop as the negative-sequence voltage loop reference value. The modulation module is configured to superimpose the voltage commands output by the positive-sequence voltage loop and the negative-sequence voltage loop to generate a modulation signal.

[0065] Example 3 This embodiment provides a computer-readable storage medium storing a computer program that, when executed by a processor, implements the steps of the positive and negative sequence adaptive virtual impedance control method based on reactive circulating current as described in Embodiment 1 above.

[0066] Example 4 This embodiment provides a computer device, including a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the program, it implements the steps in the positive and negative sequence adaptive virtual impedance control method based on reactive circulating current as described in Embodiment 1 above.

[0067] The steps or modules involved in Embodiments 2 to 4 above correspond to those in Embodiment 1. For specific implementation details, please refer to the relevant description section of Embodiment 1. The term "computer-readable storage medium" should be understood as a single medium or multiple media including one or more instruction sets; it should also be understood as including any medium capable of storing, encoding, or carrying an instruction set for execution by a processor and enabling the processor to perform any of the methods in this invention.

[0068] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A positive and negative sequence adaptive virtual impedance control method based on reactive circulating current, characterized in that, include: Collect the three-phase voltage and current signals of each parallel inverter, and obtain the positive-sequence signal and the negative-sequence signal by positive-negative sequence separation; The positive-sequence signal and the negative-sequence signal are respectively subjected to coordinate transformation to obtain positive-sequence and negative-sequence voltage signals and current signals; Active power and reactive power are calculated based on positive sequence voltage and current signals, and then input into the VSG control module to obtain the virtual electromotive force of the system. Calculate the positive and negative sequence reactive circulating current of the parallel inverter based on the positive and negative sequence q-axis current components; Using the positive-sequence reactive circulating current as feedback, the positive-sequence virtual impedance is adaptively adjusted. Using negative-sequence reactive circulating current as feedback, the negative-sequence virtual impedance is adaptively adjusted. The voltage drop of the positive-sequence virtual impedance and the virtual electromotive force are used together as the reference value of the positive-sequence voltage loop, and the voltage drop of the negative-sequence virtual impedance is fed forward to the negative-sequence voltage loop as the reference value of the negative-sequence voltage loop. The voltage commands output from the positive-sequence voltage loop and the negative-sequence voltage loop are superimposed to generate a modulation signal.

2. The positive and negative sequence adaptive virtual impedance control method based on reactive circulating current as described in claim 1, characterized in that, The process of acquiring the three-phase voltage and current signals of each parallel inverter, and obtaining positive-sequence and negative-sequence signals through positive-negative sequence separation, specifically includes: Collect the filtered three-phase voltage signal and three-phase current signal of each parallel inverter, as well as the unfiltered three-phase current signal. Separate the positive and negative sequences of the signals by using a dual second-order generalized integrator to obtain positive and negative sequence signals. The positive sequence signal includes a positive sequence three-phase voltage signal, a positive sequence three-phase current signal, and a positive sequence inductor current signal; the negative sequence signal includes a negative sequence three-phase voltage signal, a negative sequence three-phase current signal, and a negative sequence inductor current signal.

3. The positive and negative sequence adaptive virtual impedance control method based on reactive circulating current as described in claim 1, characterized in that, The step of performing coordinate transformations on the positive-sequence and negative-sequence signals to obtain positive-sequence and negative-sequence voltage and current signals specifically includes: performing Clark transformation and Park transformation on the positive-sequence and negative-sequence signals to obtain positive-sequence voltage and current signals, as well as negative-sequence voltage and current signals on the dq axis.

4. The positive and negative sequence adaptive virtual impedance control method based on reactive circulating current as described in claim 1, characterized in that, The calculation of active and reactive power based on positive sequence voltage and current signals, and input into the VSG control module to obtain the virtual electromotive force of the system, specifically includes: calculating the instantaneous active and reactive power of each inverter based on the d-axis positive sequence voltage signal, q-axis positive sequence voltage signal, d-axis positive sequence current signal, and q-axis positive sequence current signal, inputting them into the VSG control module, and obtaining the system's angular velocity and virtual electromotive force through the VSG's active and reactive power loops.

5. The positive and negative sequence adaptive virtual impedance control method based on reactive circulating current as described in claim 1, characterized in that, The step of calculating the positive and negative sequence reactive circulating currents of the parallel inverters based on the positive and negative sequence q-axis current components specifically includes: extracting the positive sequence q-axis current component and the negative sequence q-axis current component of each inverter in the dq coordinate system, subtracting the positive sequence q-axis current components of the two inverters to obtain the positive sequence reactive circulating current, and subtracting the negative sequence q-axis current components of the two inverters to obtain the negative sequence reactive circulating current.

6. The positive and negative sequence adaptive virtual impedance control method based on reactive circulating current as described in claim 1, characterized in that, Using the positive-sequence reactive circulating current as feedback, the positive-sequence virtual impedance is adaptively adjusted. Using negative-sequence reactive circulating current as feedback, the negative-sequence virtual impedance is adaptively adjusted. Specifically, this includes: inputting positive-sequence reactive circulating current into the PI controller to dynamically adjust the resistance value of the positive-sequence virtual impedance, with the positive-sequence virtual impedance of the two parallel inverters being adjusted in opposite directions; and inputting negative-sequence reactive circulating current into the PI controller to dynamically adjust the resistance value of the negative-sequence virtual impedance, with the negative-sequence virtual impedance of the two parallel inverters being adjusted in opposite directions.

7. The positive and negative sequence adaptive virtual impedance control method based on reactive circulating current as described in claim 1, characterized in that, The step of using the voltage drop of the positive-sequence virtual impedance and the virtual electromotive force together as the reference value for the positive-sequence voltage loop, and feeding the voltage drop of the negative-sequence virtual impedance forward to the negative-sequence voltage loop as the reference value for the negative-sequence voltage loop, specifically includes: Multiply the positive-sequence virtual impedance by the positive-sequence current flowing through the inverter to obtain the positive-sequence voltage drop; The positive sequence voltage drop is superimposed on the virtual electromotive force and used as the voltage reference command for the positive sequence voltage loop. Multiplying the negative-sequence virtual impedance by the negative-sequence current flowing through the inverter yields the negative-sequence voltage drop; The negative sequence voltage drop is directly fed forward to the negative sequence voltage loop as a voltage reference command for the negative sequence voltage loop.

8. A positive and negative sequence adaptive virtual impedance control system based on reactive circulating current, characterized in that, include: The signal acquisition module is configured to acquire the three-phase voltage and current signals of each parallel inverter, and obtain positive-sequence and negative-sequence signals by positive-negative sequence separation. The coordinate transformation module is configured to perform coordinate transformation on the positive-sequence signal and the negative-sequence signal respectively to obtain positive-sequence and negative-sequence voltage signals and current signals; The power calculation module is configured to calculate active power and reactive power based on positive sequence voltage signal and positive sequence current signal, and input the VSG control module to obtain the virtual electromotive force of the system. The circulating current calculation module is configured to calculate the positive and negative sequence reactive circulating current of the parallel inverter based on the positive and negative sequence q-axis current components. The impedance adjustment module is configured to adaptively adjust the positive-sequence virtual impedance using the positive-sequence reactive circulating current as feedback. Using negative-sequence reactive circulating current as feedback, the negative-sequence virtual impedance is adaptively adjusted. The voltage reference module is configured to use the voltage drop of the positive-sequence virtual impedance and the virtual electromotive force together as the positive-sequence voltage loop reference value, and feed forward the voltage drop of the negative-sequence virtual impedance to the negative-sequence voltage loop as the negative-sequence voltage loop reference value. The modulation module is configured to superimpose the voltage commands output by the positive-sequence voltage loop and the negative-sequence voltage loop to generate a modulation signal.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the program is executed by the processor, it implements the steps in the positive and negative sequence adaptive virtual impedance control method based on reactive circulating current as described in any one of claims 1-7.

10. A computer device, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, When the processor executes the program, it implements the steps in the positive and negative sequence adaptive virtual impedance control method based on reactive circulating current as described in any one of claims 1-7.

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