An inverter parallel control system and control method based on improved droop control

Abstract

An inverter parallel control system and control method based on improved droop control belongs to the research field of smooth switching of off-grid / grid-connected mode in low-voltage microgrid. The present invention includes a grid-connected pre-synchronization control unit, the voltage amplitude and phase of the microgrid output, the grid voltage amplitude and phase are controlled by PI to obtain the system voltage amplitude and frequency; an adaptive control unit, the system voltage amplitude and frequency and the voltage are adaptively corrected according to the droop coefficient of PI control; a virtual impedance unit, sampling current and virtual resistance to obtain a virtual voltage value, and the virtual voltage value and the reference voltage are used to obtain a new voltage reference value; the present invention realizes decoupling control and impact-free smooth grid connection, solves the problem of large voltage and frequency fluctuations when the grid-connected mode switches to the off-grid mode, and ensures that the microgrid system can operate stably.

Description

Technical Field

[0001] The present invention belongs to the field of smooth switching of off-grid / grid-connected modes in low-voltage microgrids, and in particular relates to an inverter parallel control system and a control method based on improved droop control. Background Art

[0002] With the rapid development of power grid technology, the application of renewable energy power generation technology in power grid is becoming more and more popular. When the microgrid is off-grid, it is necessary to meet the user's requirements for power quality. When the microgrid is connected to the grid on a large scale, the safe and stable operation of the grid system must be achieved. Therefore, microgrid control technology has been valued by many scholars and has become the focus of research at home and abroad. Microgrid has two working modes: off-grid operation and grid-connected operation. In the grid-connected operation mode, the microgrid is connected to the large grid through a public connection point (PCC). The voltage and frequency in the microgrid system are provided by the large grid. When the large grid fails, the PCC is disconnected and the microgrid system enters the off-grid operation mode; when the large grid resumes normal power supply, the microgrid system is connected to the grid again through the PCC. Because the system will have a huge impact during the mode switching process. Therefore, achieving smooth switching in the off-grid mode conversion has become the key to the safe and stable operation of the system.

[0003] When the microgrid system enters the off-grid operation state, due to the influence of distributed power capacity and line length, the system will generate circulating current, resulting in the system being unable to achieve uniform distribution of load reactive power, and may also directly cause damage to the inverter. Therefore, suppressing the circulating current in the system is conducive to the safe and stable operation of the microgrid. By adding virtual impedance to change the equivalent output impedance of the inverter, the problem of power coupling can be solved, thereby achieving the goal of uniform distribution of reactive power. However, adding virtual impedance may cause voltage drop, and the problem of reactive power distribution still exists. When the microgrid system enters the grid-connected operation state, the PQ control strategy is generally adopted to ensure the stability of the microgrid, but it is easy to generate huge impact during the mode switching process. In order to reduce the impact of microgrid switching, the commonly used method is to control it in a way similar to the motor droop characteristic curve. Droop control has the characteristics of plug-and-play and can be switched between two operating modes. However, direct grid connection still has the problem of slow synchronization speed of voltage phase angle and voltage amplitude between microgrid and large grid. Summary of the invention

[0004] In order to solve the above problems, the present invention provides an inverter parallel control system and control method based on improved droop control, which can realize impact-free grid connection of microgrid and smooth switching of off-grid / grid connection mode, and ensure the stable operation of microgrid system.

[0005] The first aspect of the present invention discloses an inverter parallel control system based on improved droop control, comprising:

[0006] The grid-connected pre-synchronization control unit, the voltage amplitude and phase of the microgrid output, the voltage amplitude and phase of the grid are controlled by PI to obtain the system voltage amplitude and frequency;

[0007] An adaptive control unit, wherein the system voltage amplitude and frequency are adaptively corrected with the voltage droop coefficient according to PI control;

[0008] The droop control unit converts the system voltage amplitude and frequency into active power and reactive power, and obtains the voltage phase reference value and the voltage amplitude reference value by combining the corrected droop coefficient, and obtains the reference voltage by voltage synthesis;

[0009] A virtual impedance unit, sampling current and virtual resistance to obtain a virtual voltage value, and the virtual voltage value and the reference voltage to obtain a new voltage reference value;

[0010] The dual closed-loop control unit obtains an inverter modulation signal according to the new voltage reference value.

[0011] Furthermore, the grid-connected pre-synchronization control unit includes:

[0012] System frequency generation module, the phase difference between the microgrid voltage and the system grid voltage is obtained through the PI controller to obtain the system frequency;

[0013] The system voltage amplitude generation module uses the difference between the microgrid voltage amplitude and the system grid voltage amplitude to obtain the system voltage amplitude through a PI controller.

[0014] Furthermore, the control equation of the grid-connected pre-synchronization control unit is:

[0015]

[0016] k pθ , k iθ k is the proportional integral coefficient of the voltage phase; pu , k iu is the proportional integral coefficient of the voltage amplitude; θ grid 、u grid is the phase and amplitude of the grid voltage; θ micro-grid 、u micro-grid is the phase and amplitude of the microgrid voltage.

[0017] Furthermore, the adaptive control unit comprises:

[0018] A reactive-voltage adaptive droop coefficient generating module, wherein the difference between the system voltage amplitude and the system voltage rated amplitude is used to obtain a reactive-voltage adaptive droop coefficient via a PI controller;

[0019] Active power-frequency adaptive droop coefficient generating module, the difference between the system frequency and the system frequency rated value is used to obtain the active power-frequency adaptive droop coefficient through a PI controller.

[0020] Furthermore, the control equation of the adaptive control unit is:

[0021]

[0022] k′ q is the reactive-voltage adaptive droop coefficient, k′ p is the active-frequency adaptive droop coefficient, U and f are the system piezoelectric amplitude and the corresponding frequency respectively, U n and f n They are the rated amplitudes of system voltage and frequency respectively.

[0023] Furthermore, the virtual voltage value output by the virtual impedance module is negatively fed back to the reference voltage to obtain a new reference voltage value.

[0024] Furthermore, the droop control unit comprises:

[0025] Power calculation module, which calculates the active power and reactive power of the system;

[0026] A voltage phase reference value generation module, which obtains a voltage phase reference value by combining the difference between the system active power and the system active power rating with the active-frequency adaptive droop coefficient;

[0027] A voltage amplitude reference value generation module, in which the difference between the system reactive power and the system reactive power rating is combined with the reactive-voltage adaptive droop coefficient to obtain a voltage amplitude reference value;

[0028] The voltage synthesis module synthesizes the reference voltage using the reference value of the voltage phase and the reference value of the voltage amplitude.

[0029] A second aspect of the present invention provides an inverter parallel control method based on improved droop control, which is used to control the inverter parallel control system based on improved droop control described in the first aspect of the present invention, and comprises the following steps:

[0030] The voltage amplitude and phase of the microgrid output and the grid voltage amplitude and phase are controlled by PI to obtain the system voltage and frequency;

[0031] The system voltage and frequency are adaptively corrected with the voltage droop coefficient according to PI control;

[0032] The system voltage and frequency are converted into active power and reactive power, and the voltage phase reference value and voltage amplitude reference value are obtained by combining the corrected droop coefficient, and the reference voltage is obtained by voltage synthesis;

[0033] The sampling current and the virtual resistance obtain a virtual voltage value, and the virtual voltage value and the reference voltage obtain a new voltage reference value;

[0034] An inverter modulation signal is obtained according to the new voltage reference value.

[0035] Furthermore, the steps of obtaining the system voltage and frequency by PI control of the voltage amplitude and phase output by the microgrid and the voltage amplitude and phase of the grid include:

[0036] The phase difference between the microgrid voltage and the system grid voltage is used to obtain the system frequency through a PI controller;

[0037] The difference between the voltage amplitude of the microgrid and the voltage amplitude of the system grid is obtained by the PI controller to obtain the system voltage amplitude.

[0038] Furthermore, the step of adaptively correcting the droop coefficient includes:

[0039] The difference between the system voltage amplitude and the system voltage rated amplitude is used to obtain a reactive-voltage adaptive droop coefficient via a PI controller;

[0040] The difference between the system frequency and the rated value of the system frequency is used to obtain an active power-frequency adaptive droop coefficient via a PI controller.

[0041] As described above, compared with the prior art, the present invention has the following beneficial effects:

[0042] 1. This application uses a droop pre-synchronization controller to ensure that the amplitude and phase of the microgrid output voltage can follow the amplitude and phase of the system grid voltage. The amplitude and phase of the voltage of both are within a certain allowable range, which can reduce the current impact during the grid connection process and achieve smooth and impact-free grid connection;

[0043] 2. In order to solve the problem of power coupling in the low-voltage system, virtual impedance is added to the control system to keep the inverter parallel system working in a perceptual environment. By reasonably adjusting the size of the virtual impedance, the inverter equivalent output impedance is much larger than the line impedance, reducing the impact of the line impedance on the output power, and realizing low-voltage system structure control;

[0044] 3. This application uses an adaptive droop coefficient to stabilize the fluctuations of system voltage and frequency to ensure that the microgrid system can operate stably. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 It is an overall structural block diagram of a specific embodiment of the present invention;

[0046] Figure 2 It is a current and voltage dual-loop control diagram of a specific embodiment of the present invention;

[0047] Figure 3 A virtual impedance control diagram of a specific embodiment of the present invention;

[0048] Figure 4 A diagram of a grid-connected droop pre-synchronization controller according to a specific embodiment of the present invention;

[0049] Figure 5 It is a structural diagram of an improved droop controller according to a specific embodiment of the present invention;

[0050] Figure 6 This is a diagram showing the experimental results of unplanned traditional mode switching in a specific embodiment of the present invention. Figure 6 a is the inverter output current waveform, Figure 6 b is the voltage waveform output by the inverter;

[0051] Figure 7 This is a diagram showing the experimental results of the improved droop control strategy mode switching in a specific embodiment of the present invention. Figure 7 a is the inverter output current waveform, Figure 7 b is the voltage waveform output by the inverter;

[0052] Figure 8 It is the droop QU control characteristic curve diagram;

[0053] Fig. 9 It is a structural principle diagram of an adaptive control unit according to a specific embodiment of the present invention. DETAILED DESCRIPTION

[0054] The following describes the embodiments of the present invention by specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the following embodiments and features in the embodiments can be combined with each other without conflict.

[0055] It should be noted that the illustrations provided in the following embodiments are only used to illustrate the basic concept of the present invention in a schematic manner, and thus the illustrations only show components related to the present invention rather than being drawn according to the number, shape and size of components in actual implementation. In actual implementation, the type, quantity and proportion of each component may be changed arbitrarily, and the component layout may also be more complicated.

[0056] An inverter parallel control system based on improved droop control in this embodiment, such as Figure 1 As shown, including:

[0057] The grid-connected pre-synchronization control unit, the voltage amplitude and phase of the microgrid output, the voltage amplitude and phase of the grid are controlled by PI to obtain the system voltage amplitude and frequency;

[0058] like Figure 4 As shown, the grid-connected pre-synchronization control unit of this embodiment includes:

[0059] System frequency generation module, the phase difference between the microgrid voltage and the system grid voltage is obtained through the PI controller to obtain the system frequency f;

[0060] The system voltage amplitude generation module uses the difference between the microgrid voltage amplitude and the system grid voltage amplitude to obtain the system voltage amplitude U through a PI controller.

[0061] According to the specific structure of the grid-connected pre-synchronization control unit, the control equation of the grid-connected pre-synchronization control unit is obtained as follows:

[0062]

[0063] f is the system frequency, U is the system voltage amplitude, k pθ , k iθ k is the proportional integral coefficient of the voltage phase; pu , k iu is the proportional integral coefficient of the voltage amplitude; θ grid 、u grid is the phase and amplitude of the grid voltage; θ micro-grid 、u micro-grid is the phase and amplitude of the microgrid voltage; U n is the system voltage rating, f n is the system frequency rating, P n Reactive power rating, Q n Active power rating, k P is the coefficient of the active power-frequency proportional controller, k q is the coefficient of the reactive-voltage proportional controller.

[0064] Adaptive control unit, the voltage and frequency of the inverter output, the voltage and frequency of the grid are adaptively corrected through the PI controller to achieve the droop coefficient;

[0065] The adaptive control unit comprises:

[0066] The reactive power-voltage adaptive droop coefficient generation module, the system voltage amplitude U and the system voltage rated amplitude U n The difference is obtained by PI controller to obtain reactive power-voltage adaptive droop coefficient k′ q ;

[0067] Active power-frequency adaptive droop coefficient generation module, the system frequency f and the system frequency rated value fn The difference is obtained by PI controller to obtain the active-frequency adaptive droop coefficient k′ p .

[0068] According to the specific structure of the adaptive control unit, the corresponding control equation is:

[0069]

[0070] k′ p is the active power-frequency adaptive droop coefficient, k′ q is the reactive-voltage adaptive droop coefficient, U and f are the system piezoelectric amplitude and the corresponding frequency respectively, U n and f n are the rated values ​​of system voltage and frequency respectively.

[0071] The droop control unit converts the system voltage and frequency into active power and reactive power, and combines the corrected droop coefficient to obtain the voltage phase reference value θ * And the voltage amplitude reference value U * , the reference voltage is obtained by voltage synthesis

[0072] like Figure 5 As shown, the droop control unit includes:

[0073] The power calculation module calculates the active power P and reactive power Q of the system according to the voltage and current output by the inverter;

[0074] Voltage phase reference value generation module, system active power P and system active power rated value P n The difference of active power-frequency adaptive droop coefficient k′ p Get the voltage phase reference value θ * ;

[0075] Voltage amplitude reference value generation module, system reactive power Q and system reactive power rated value Q n The difference between the voltage amplitude change ΔU, the system voltage U and the voltage at the common connection point U PCC Make a difference, combined with the voltage compensation value U cmp and reactive-voltage adaptive droop coefficient k′ q Get the reference value U of the voltage amplitude * .

[0076] When the voltage drop of the inverter parallel system is different, it will cause different output reactive power, and then generate reactive circulating current. Therefore, by calculating the longitudinal component U of the line voltage drop cmp As a compensation voltage, it is used to offset the voltage drop of the line and solve the generation of reactive circulating current from the root cause. The compensation voltage is:

[0077]

[0078] Where: P, Q are the inverter output powers; R, X are the line impedances; U is the inverter output voltage;

[0079] In order to solve the problem that reactive power cannot be distributed according to the inverter capacity ratio under the conditions of different inverter capacities and different line impedances, the present application achieves the goal of inverter output voltage difference ΔU≈0 by adding a voltage feedback link and a voltage compensation link in the droop controller.

[0080] A virtual impedance unit, sampling current and virtual resistance to obtain a virtual voltage value, the virtual voltage value and the reference voltage to obtain a new voltage reference value; combining Figure 3 As shown, the virtual voltage value output by the virtual impedance module is negatively fed back to the reference voltage to obtain a new reference voltage value.

[0081] The dual closed-loop control unit obtains an inverter modulation signal according to the new voltage reference value. The structure of the dual closed-loop control unit of this embodiment is as follows: Figure 2 shown.

[0082] A method for controlling inverter parallel connection based on improved droop control according to a specific embodiment of the present invention is used to control the inverter parallel connection control system based on improved droop control, and comprises the following steps:

[0083] S1, the step of pre-synchronization control, the voltage amplitude and phase of the microgrid output, the voltage amplitude and phase of the grid are controlled by PI to obtain the system voltage and frequency, so as to achieve smooth and impact-free grid connection; specifically, the steps include:

[0084] S11, the phase difference between the microgrid voltage and the system grid voltage is obtained through the PI controller to obtain the system frequency;

[0085] S12, the difference between the amplitude of the microgrid voltage and the amplitude of the system grid voltage is obtained by the PI controller to obtain the system voltage amplitude.

[0086] In this embodiment, the amplitude and phase of the microgrid output voltage and the amplitude and phase of the system grid voltage are collected to ensure that the former can follow the amplitude and phase of the latter grid voltage, and to ensure that the amplitude and phase difference between the two are within a certain allowable range, which can reduce the current shock during the grid connection process and achieve smooth and impact-free grid connection.

[0087] S2, the step of adaptive control of droop coefficient, wherein the system voltage and frequency and the voltage are adaptively corrected according to the PI control to realize the droop coefficient, specifically comprising the following steps:

[0088] S21, the difference between the system voltage amplitude and the system voltage rated amplitude is used to obtain a reactive-voltage adaptive droop coefficient through a PI controller;

[0089] S22, the difference between the system frequency and the rated value of the system frequency is used to obtain an active-frequency adaptive droop coefficient through a PI controller.

[0090] The droop coefficient adaptive adjustment process is as follows: Figure 8 As shown in the figure, taking the QU droop characteristic as an example, when the microgrid is connected to the grid, it operates stably at point A, and the corresponding voltage is U1. When the microgrid is disconnected from the grid and switched to the island mode, the microgrid may have a reactive power shortage inside, causing the inverter operating point to shift from point A to point B, and the corresponding voltage is U2. The droop coefficient is reduced by adaptive control of the droop coefficient, and the droop coefficient is k′ q1 becomes k′ q2 , the inverter works at point C, and the corresponding voltage is U3, which reduces the voltage drop and reduces the fluctuation of the microgrid during the switching process from grid-connected to islanded.

[0091] S3, droop control step, the system voltage and frequency are converted into active power and reactive power, and the voltage phase reference value and voltage amplitude reference value are obtained by combining the corrected droop coefficient, and the reference voltage is obtained by voltage synthesis;

[0092] The specific steps include:

[0093] S31. Calculate the active power and reactive power of the system;

[0094] S32, system active power P and system active power rating P n The difference of active power-frequency adaptive droop coefficient k′ p Get the reference value of voltage phase θ * ;

[0095] S33, system reactive power Q and system reactive power rating Q n The difference of the reactive power-voltage adaptive droop coefficient k′ q Get the reference value U of the voltage amplitude * ;

[0096] S34, reference value of voltage phase θ * And the reference value of voltage amplitude U * Synthesized reference voltage.

[0097] S4, sampling the current and the virtual resistance to obtain a virtual voltage value, and the virtual voltage value and the reference voltage to obtain a new voltage reference value. The present application can achieve decoupling control of the low-voltage system by adding a virtual resistance;

[0098] like Figure 3As shown, the virtual impedance of this embodiment is composed of the sampling current i0 of the system and the virtual resistance Z V The voltage value is synthesized by negative feedback and droop control to obtain the reference voltage. Add and generate a new voltage reference value u ref In order to enable the low-voltage microgrid inverter parallel system to directly use droop control and realize system decoupling control, this paper selects a purely inductive virtual impedance Z V (s) = sL. However, since the system adds virtual impedance, some voltage drop will be generated. The larger the impedance value of the virtual impedance, the greater the voltage drop. Therefore, under the premise of ensuring that the system equivalent impedance is inductive, the virtual impedance should be as small as possible.

[0099] S5, a dual closed-loop control step, obtaining an inverter modulation signal according to the new voltage reference value.

[0100] The newly generated voltage reference value u ref Output to Figure 2 In the current and voltage dual-loop control link shown, the modulated signal is finally sent to the inverter for control.

[0101] This embodiment uses an adaptive droop coefficient to stabilize the fluctuations of system voltage and frequency, ensuring that the microgrid system can operate stably.

[0102] In order to verify the feasibility and correctness of this embodiment, two inverter parallel test benches were built. The microgrid system is in off-grid operation mode from 0 to 0.35s; it starts to switch to grid-connected operation mode at 0.35s; it is disconnected from the grid at 0.75s and re-enters off-grid operation mode. Figure 6 This is the result of the unplanned traditional mode switching experiment. Figure 7 Figure 2. Experimental results of mode switching for improving droop control strategy.

[0103] like Figure 6 As shown in the figure, from 0 to 0.35s, the microgrid is off-grid, and the current and voltage waveforms are stable; at 0.35s, the microgrid switches to the grid-connected operation mode, and the output current of the inverter increases from 90A to 180A, and the impact current is too large. The inverter output voltage amplitude drops from 310V to 200V. Due to the phase asynchrony, the current and voltage waveforms are severely distorted; at 0.75s, the microgrid is disconnected from the grid and re-enters the off-grid operation mode, and the inverter output current drops from 180A to 60A. The inverter output voltage amplitude remains unchanged. However, due to the phase synchronization, the problem of inverter output current and voltage waveform distortion always exists.

[0104] like Figure 7As shown in the figure, at -0.35s, the microgrid is off-grid, and the current and voltage waveforms are stable; at 0.35s, the microgrid switches to the grid-connected operation mode, the output current of the inverter increases from 60A to 90A, and the impact current is relatively small. The inverter output voltage amplitude remains unchanged at 310V. Due to the use of the grid-connected pre-synchronization controller, the microgrid and the grid are in phase and the experimental waveform is good; the connection is disconnected at 0.75s, the inverter output current drops from 90A to 60A, and the inverter output voltage remains unchanged. Comparing the waveforms of the two mode switching methods, the effectiveness of the proposed control strategy is verified.

[0105] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical concept disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. An inverter parallel control system based on improved droop control, characterized in that: include: The grid-connected pre-synchronization control unit includes a system frequency generation module and a system voltage amplitude generation module. In the system frequency generation module, the difference between the phase of the microgrid voltage and the phase of the system grid voltage is obtained by a PI controller to obtain the system frequency; in the system voltage amplitude generation module, the difference between the amplitude of the microgrid voltage and the amplitude of the system grid voltage is obtained by a PI controller to obtain the system voltage amplitude; the control equation of the grid-connected pre-synchronization control unit is: ； k pθ , k iθ k is the proportional integral coefficient of the voltage phase; pu , k iu is the proportional integral coefficient of the voltage amplitude; θ grid , u grid is the phase and amplitude of the grid voltage; θ micro-grid , θ micro-grid is the phase and amplitude of the microgrid voltage; k p is the coefficient of the active power-frequency proportional controller; k q is the coefficient of the reactive-voltage proportional controller, P is the system active power; P n is the active power rating; Q is the system reactive power; Q n is the reactive power rating; An adaptive control unit, wherein the system voltage amplitude and frequency are adaptively corrected with the voltage droop coefficient according to PI control; The adaptive control unit comprises: A reactive-voltage adaptive droop coefficient generating module, wherein the difference between the system voltage amplitude and the system voltage rated amplitude is used to obtain a reactive-voltage adaptive droop coefficient via a PI controller; Active power-frequency adaptive droop coefficient generating module, wherein the difference between the system frequency and the system frequency rated value is used to obtain the active power-frequency adaptive droop coefficient through a PI controller; The control equation of the adaptive control unit is: ； is the reactive-voltage adaptive droop coefficient, is the active power-frequency adaptive droop coefficient, U and f are the system piezoelectric amplitude and the corresponding frequency, U n and f n are the rated amplitudes of system voltage and frequency respectively; The droop control unit converts the system voltage amplitude and frequency into active power and reactive power, and obtains the voltage phase reference value and the voltage amplitude reference value by combining the corrected droop coefficient, and obtains the reference voltage by voltage synthesis; A virtual impedance unit, sampling current and virtual resistance to obtain a virtual voltage value, and the virtual voltage value and the reference voltage to obtain a new voltage reference value; The dual closed-loop control unit obtains an inverter modulation signal according to the new voltage reference value.

2. The inverter parallel control system based on improved droop control according to claim 1, characterized in that: The virtual voltage value output by the virtual impedance unit is negatively fed back to the reference voltage to obtain a new reference voltage value.

3. The inverter parallel control system based on improved droop control according to claim 1, characterized in that: The droop control unit comprises: Power calculation module, which calculates the active power and reactive power of the system; A voltage phase reference value generation module, which obtains a voltage phase reference value by combining the difference between the system active power and the system active power rating with the active-frequency adaptive droop coefficient; A voltage amplitude reference value generation module, in which the difference between the system reactive power and the system reactive power rating is combined with the reactive-voltage adaptive droop coefficient to obtain a voltage amplitude reference value; The voltage synthesis module synthesizes the reference voltage using the reference value of the voltage phase and the reference value of the voltage amplitude.

4. An inverter parallel control method based on improved droop control, characterized in that: The method for controlling an inverter parallel control system based on improved droop control according to any one of claims 1 to 3 comprises the following steps: S1, the voltage amplitude and phase of the microgrid output, the voltage amplitude and phase of the grid are controlled by PI to obtain the system voltage and frequency, including the following steps: S11, the phase difference between the microgrid voltage and the system grid voltage is obtained through the PI controller to obtain the system frequency; S12, the difference between the amplitude of the microgrid voltage and the amplitude of the system grid voltage is obtained by a PI controller to obtain the system voltage amplitude; The system frequency f and the system voltage amplitude U are: ； k pθ , k iθ k is the proportional integral coefficient of the voltage phase; pu , k iu is the proportional integral coefficient of the voltage amplitude; θ grid , u grid is the phase and amplitude of the grid voltage; θ micro-grid , θ micro-grid is the phase and amplitude of the microgrid voltage; k p is the coefficient of the active power-frequency proportional controller; k q is the coefficient of the reactive-voltage proportional controller, P is the system active power; P n is the active power rating; Q is the system reactive power; Q n is the reactive power rating; S2, the system voltage and frequency are adaptively corrected with the voltage droop coefficient according to PI control, including the following steps: S21, the difference between the system voltage amplitude and the system voltage rated amplitude is used to obtain a reactive-voltage adaptive droop coefficient through a PI controller; S22, the difference between the system frequency and the rated value of the system frequency is used to obtain an active-frequency adaptive droop coefficient through a PI controller; The reactive-voltage adaptive droop coefficient and active power-frequency adaptive droop coefficient They are: ； is the reactive-voltage adaptive droop coefficient, is the active power-frequency adaptive droop coefficient, U and f are the system piezoelectric amplitude and the corresponding frequency, U n and f n are the rated amplitudes of system voltage and frequency respectively; S3, the system voltage and frequency are converted into active power and reactive power, and the voltage phase reference value and voltage amplitude reference value are obtained by combining the corrected droop coefficient, and the reference voltage is obtained by voltage synthesis; S4, sampling the current and the virtual resistance to obtain a virtual voltage value, and the virtual voltage value and the reference voltage to obtain a new voltage reference value; S5. Obtain an inverter modulation signal according to the new voltage reference value.

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