Synchronous control method for improving multi-machine black-start frequency phase angle coupling effect

Abstract

The invention discloses a synchronous control method for improving a multi-machine black-start frequency phase angle coupling effect, and aims to improve the black-start recovery capability. The system adopts a parallel recovery strategy, so that a plurality of black-start micro-sources are started at the same time, and synchronization is quickly realized. However, the requirement of parallel recovery on the precision of pre-synchronization is extremely high, and due to the fact that in the pre-synchronization process before parallel connection and brake connection, the frequency and the phase angle have a coupling relation, and the rapid change of the phase angle difference in phase angle control easily causes frequency overshoot. In order to solve the problem, the system introduces a linear active disturbance rejection control (LADRC) method on the basis of traditional phase angle control, fast adjustment is made when frequency fluctuation is caused by phase angle difference change by means of high interference resistance and dynamic response speed, and phase angle change becomes more stable and controllable through timely and stable control of frequency, so that the system is more stable and controllable. Therefore, the interference on the frequency is reversely reduced, and the weakening of the frequency phase angle coupling effect is realized. The design not only ensures the rapidity of black start, but also improves the stability and recovery capability of the system.

Description

Technical Field

[0001] The invention relates to the field of microgrid power supply restoration, and in particular to a synchronous control method for improving frequency phase angle coupling effect of multi-machine black start. Background Art

[0002] As the global energy structure transforms towards low-carbon and renewable energy, the rapid development of new energy technologies has driven the popularization of microgrids in power systems. Microgrids have the advantages of flexible access to distributed energy, improved energy utilization and enhanced power supply reliability, so they have been widely used in various scenarios, such as independent power supply in remote areas, load regulation of urban power grids and emergency power supply guarantee. However, due to the volatility and intermittent characteristics of new energy generation, microgrids face great challenges in recovery and stability when encountering faults or external power supply interruptions. In this context, VSG technology came into being. VSG simulates the rotational inertia and electrical characteristics of traditional synchronous generators, so that inverters can be better integrated into grid operation, thereby enhancing the stability and inertial support of the system. In the operation and recovery of microgrids, VSG technology can provide dynamic response and smooth out voltage and frequency fluctuations. Although VSG technology has effectively improved the dynamic performance of microgrids, how to achieve fast and stable restart in the recovery phase after microgrid faults is still an urgent problem to be solved. Especially in the black start scenario, since the system has no support from the external grid in the initial state, the microgrid needs to rely on its own distributed power sources for startup and parallel operation without external support. At this time, multi-machine pre-synchronization is crucial because it directly determines whether the system can achieve impact-free parallel closing. However, the coupling characteristics of frequency and phase angle in multi-machine pre-synchronization will lead to additional challenges. If only the phase angle is controlled, the phase angle difference quickly approaches 0, which may cause drastic frequency fluctuations, resulting in frequency overshoot or even instability.

[0003] Compared with the prior art, the differences are as follows: Technical comparison with patent CN 113644653B "Power system black start path recovery method with coordinated cooperation of new energy and energy storage" Patent CN 113644653B optimizes the black start model based on the optimal recovery sequence and corresponding recovery path of each unit and load in the black start system. In contrast, our research focuses on an in-depth discussion of the pre-synchronization performance of black start micro-sources. In view of the importance of grid recovery in the black start process, we propose to directly use a parallel recovery strategy to start multiple black start micro-sources at the same time to give full play to their black start capabilities. At the same time, for the synchronization performance of black start micro-sources, we introduced an improved phase angle control pre-synchronization mechanism and linear anti-disturbance control LADRC. With its strong anti-interference ability and fast dynamic response characteristics, LADRC can quickly adjust the system when the phase angle difference causes frequency fluctuations, and by timely and smoothly controlling the frequency, ensure that the phase angle changes are also more stable and controllable, thereby effectively reducing the interference of frequency fluctuations on the system and achieving the weakening of the frequency and phase angle coupling effect. This design not only ensures the rapid recovery of the black start process, but also significantly improves the stability and safety of the system.

[0004] Patent CN 113644653B solves the problem of insufficient black start resources in some areas to a certain extent, but its path optimization process involves load forecasting technology, and the solution of the objective function is relatively complex. Our method focuses more on system stability and safety during the black start process. By introducing an improved phase angle control pre-synchronization mechanism and LADRC control, we ensure the smooth operation of the black start process under parallel recovery, and this method has excellent robustness and can more effectively cope with various disturbances.

[0005] Technical comparison with patent publication number CN 114094586A "Power network black start method considering power-gas network coupling characteristics" In CN 114094586A, the coupling characteristics of the power and natural gas networks were mainly considered, and then a hierarchical collaborative recovery model of the power-gas interconnected system was constructed. However, our research focuses on the pre-synchronization mechanism based on the improved phase angle control of the black start micro-source. This study fully considers the coupling relationship between frequency and phase angle during the pre-synchronization process, and effectively avoids the frequency overshoot problem caused by the frequency-phase angle coupling during the micro-source synchronization process by introducing LADRC control. This method significantly improves the rapid recovery capability of the black start system and ensures the stability of the system during the recovery process. Summary of the invention

[0006] In view of the above problems, the present invention proposes a synchronous control method for improving the frequency and phase angle coupling effect of multi-machine black start. The system adopts a parallel recovery strategy to realize the synchronous start of multiple VSG black start micro sources to improve the speed and recovery ability of black start. Its core innovation is to effectively deal with the frequency overshoot problem caused by the rapid change of phase angle difference during the pre-synchronization process by introducing the LADRC method. LADRC has strong anti-interference ability and fast dynamic response. It can quickly adjust when frequency fluctuations occur, improve the coupling effect of frequency phase angle, and thus improve the synchronization accuracy and stability of the system. This design balances the rapidity of black start and the stable operation of the system.

[0007] To achieve the above object, the technical solution adopted by the present invention is: A synchronous control method for improving the frequency phase angle coupling effect of multi-machine black start, characterized in that it includes the following steps: Step 1: The three black start micro-sources are started simultaneously, and each operates stably with load using a parallel recovery strategy; Step 2: After the black start micro source is started, the subsystem is established, and the first black start micro source is used as the main reference power supply to establish the reference voltage; Step 3: Using the reference voltage in step 2, synchronize the subsystems, and use LADRC to perform frequency adaptive adjustment, and finally achieve stable synchronization of the three machines; Step 4: After the voltages at the three machine terminals are synchronized, they are switched on and connected in parallel, and the remaining loads are put into operation to complete the island black start. To meet specific operating conditions, the island is eventually switched to grid-connected connection to complete the recovery of the entire system.

[0008] As a further improvement of the present invention, in step 1, three black-start micro-sources rely on photovoltaic energy storage to charge the DC bus, and the AC bus voltage is generated by virtual synchronous generator VSG control, which has the ability of one frequency regulation and one voltage regulation. The VSG control model includes an active loop and a reactive loop, which respectively undertake the frequency regulation and voltage regulation functions, wherein the active loop control equation is: ; The VSG speed regulator equation is: ; The above formula: J i is the virtual inertia; D i For damping; T ei and T mi are electromagnetic torque and mechanical torque respectively; P mi and P ei are mechanical power and electromagnetic power, and are the rated angular frequency and the actual angular frequency respectively, For VSG i Output voltage phase angle, set the given active power to P refi , K pi is the droop coefficient, i =1,2,3… n n Indicates that there are n Taiwan VSG; The reactive loop is; ; Set the given reactive power Q refi ; U 0i and U n They are rated voltage and actual voltage respectively; K ui and K qi are the droop coefficient and the integral coefficient respectively.

[0009] In order to further speed up the grid recovery, parallel recovery black start is adopted. Parallel recovery means starting all micro-sources at the same time to establish their own independent small systems, and then connecting each small system in parallel through pre-synchronization to form an independent microgrid. The three machines can run stably with their own loads at the same time.

[0010] As a further improvement of the present invention, in step 2, a subsystem is established according to step 1, with VSG 1 As the main reference power supply, VSG 1 The AC bus voltage is used as the reference voltage, and the remaining two VSGs are synchronized to this reference voltage.

[0011] As a further improvement of the present invention, in step 3, according to the subsystem established in step 1-2, an improved phase angle control strategy without a phase-locked loop is used to perform black start micro-source parallel networking, and the calculation process is as follows: First, the Clark transform is used to transform VSG i , i =2, 3 output voltage is transformed to obtain and Two components on the axis and , then VSG 1 The voltage is converted by Clark to obtain the output voltage component and Along and Axis, the calculation formula is as follows: ; For VSG i The output voltage phase angle, For VSG 1 The output voltage phase angle, is the phase angle difference between the two; Based on the improved phase angle control pre-synchronization, the linear active disturbance rejection LADRC control is introduced to adaptively adjust the frequency. The second-order LADRC consists of a linear extended state observer LESO and a linear state error feedback LSEF. The entire LADRC is added to the VSG active loop to adjust the output frequency. The frequency output dynamics can be modeled as a second-order linear system as follows: The original expectation is the rated angular frequency , the system output is the actual frequency output, b 0 is the system gain; Assume that the linear second-order single-input and single-output system object is: ; Where: u , They are the input and output of the system object respectively; r is the external disturbance of the system; a 1 , a 2 are the parameters of the system respectively; b is the system gain, b≈b 0 , b 0 is a nominal value, and a 1 , a 2 , b All unknown, if , , that is, the system output change rate, let is the total disturbance of the system, which includes the internal uncertainty of the system and the external disturbance, then the state equation can be obtained as: ; LESO is used to estimate the state of the system, namely the frequency and its rate of change and disturbance. The mathematical expression of LESO for a second-order system is: ; Z 1 , Z 2 , Z 3are the current frequency estimate, the current frequency change rate, and the total disturbance observation value, respectively. , , is the gain of the observer, which is used to adjust the observer's sensitivity to the state and the adjustment speed; According to the control strategy of LADRC, the control input u Make the frequency gradually approach the target frequency and effectively suppress frequency overshoot, which can be expressed as: ; In the formula, k p , k d are the undetermined parameters of the PD controller, k p , k d It can be expressed as: ; Where: is the controller bandwidth; is the damping ratio, the characteristic equation of LESO can be expressed as: ; In the formula, the complex frequency s = jw , select the ideal characteristic equation , then: ; In the formula, is the observer bandwidth, through , Parameter adjustment is performed to achieve the purpose of self-disturbance rejection.

[0012] As a further improvement of the present invention, in step 4, the three machines are closed and operated in parallel after the terminal voltages are synchronized, and finally the remaining load is switched on to complete the island black start.

[0013] In order to further increase system capacity and power supply restoration range, the entire system will be connected to the large power grid for stable operation, thereby reducing the risk of island operation.

[0014] Beneficial effects: Compared with the prior art, the present invention adopts the above technical solution and has the following advantages: The present invention improves the coupling effect of frequency and phase angle in the pre-synchronization process of multi-machine black start by introducing LADRC technology, thereby overcoming the frequency overshoot and system instability problems caused by the coupling of frequency and phase angle in the prior art. Traditional technology usually only controls the phase angle in pre-synchronization, which easily leads to frequency fluctuations or even over-limit when the phase angle difference changes rapidly. Especially under the parallel recovery strategy, such fluctuations will amplify system disturbances and affect the stability of the microgrid. The present invention adaptively adjusts the frequency through LADRC, timely suppresses the frequency fluctuations caused by phase angle changes, ensures the frequency is stable, and makes the phase angle changes more controllable, thereby reducing the mutual interference between frequency and phase angle. This design achieves higher synchronization accuracy and faster recovery speed in multi-machine systems, improves the safety and stability of black start, and meets the distributed power supply scenarios with high requirements for recovery speed and system reliability. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a block diagram of a synchronous control method for improving the frequency phase angle coupling effect of multi-machine black start; Figure 2 A flow chart of a synchronous control method for improving the frequency phase angle coupling effect of multi-machine black start; Figure 3 It is a block diagram of improved phase angle control pre-synchronization control; Figure 4 It is the block diagram of LADRC system; Figure 5 VSG before and after improvement 2 The waveform of the phase angle difference between the main reference power supply and the main reference power supply; Figure 6 VSG before and after improvement 3 The waveform of the phase angle difference between the main reference power supply and the main reference power supply; Figure 7 It is VSG 1 Frequency vs. waveform; Figure 8 It is VSG 2 Frequency vs. waveform; Fig. 9 It is VSG 3 Frequency vs. waveform; Fig.10 It is the power waveform of multi-machine black start under improved phase angle control; Fig.11 It is the power waveform of the synchronous control method for improving the frequency and phase angle coupling effect of multi-machine black start. DETAILED DESCRIPTION

[0016] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. The following embodiments are used to illustrate the present invention but are not used to limit the scope of the present invention.

[0017] like Figure 1 As shown, this is a block diagram of a synchronous control method for improving the frequency and phase angle coupling effect of multi-machine black start, including the following components: photovoltaic energy storage module, VSG control module, black start parallel pre-synchronization module, and grid-connected pre-synchronization module.

[0018] Photovoltaic energy storage module: This module includes a photovoltaic power generation unit and an energy storage device to provide power support and stable power output. In a multi-machine black start scenario, the photovoltaic energy storage module can provide the power required for the system to start up, helping the microgrid to start and operate without external power support. The energy storage unit can also perform power regulation during the grid recovery process to ensure that the entire system remains stable during load fluctuations.

[0019] VSG control module: The VSG control module is one of the core control units of the system. VSG technology achieves grid friendliness and stability of renewable energy power generation systems by simulating the inertia and damping characteristics of synchronous generators. During the black start process, the VSG control module provides a regulation capability similar to that of a traditional generator, enabling the photovoltaic and energy storage systems to operate independently and in parallel with the grid. It adjusts the voltage, frequency and phase angle in the pre-synchronization stage to create favorable conditions for grid connection.

[0020] Black start parallel pre-synchronization module: This module focuses on achieving the synchronous start of multiple VSG micro-sources in black start situations. Since multi-machine black start involves multiple power generation units being connected in parallel at the same time, the pre-synchronization module needs to ensure that the frequency and phase angle of each unit are as close as possible to avoid large fluctuations and system disturbances at the moment of parallel connection. LADRC is introduced to adjust the frequency response to improve the coupling effect of frequency and phase angle, and enhance the accuracy of synchronization and system stability.

[0021] Grid pre-synchronization module: This module is used to connect the independently operated microgrid to the main grid. The grid pre-synchronization module ensures that the system frequency, phase angle and voltage amplitude match the main grid to achieve seamless grid connection. Through the control of this module, the microgrid avoids shocks and disturbances during the grid connection process, ensures the stability and safety of the grid connection, and supports the smooth transition of the microgrid from island mode to grid connection mode. The phase angle and frequency regulation in the module cooperate with the black start parallel pre-synchronization module to jointly maintain the stable operation of the system.

[0022] The core idea of ​​the present invention is to design a synchronous control method to improve the frequency-phase coupling effect of multi-machine black start, so as to solve the frequency overshoot and system disturbance problems caused by the frequency-phase coupling when multiple VSGs are connected and switched in black start. Multiple VSGs are synchronized quickly through a parallel recovery strategy, and LADRC is introduced to adaptively adjust the frequency based on phase angle control to improve the coupling effect of frequency and phase angle, thereby improving the accuracy and stability of pre-synchronization, and enhancing the recovery capability of the system and the reliability of grid connection.

[0023] like Figure 2 As shown, this method includes the following specific steps: Step 1: The three black start micro sources are started simultaneously, and the parallel recovery strategy is adopted to ensure that each of them operates stably with load.

[0024] Step 2: Black start the micro source and then establish the subsystem, using VSG 1 As the main reference power supply, establish the reference voltage.

[0025] Step 3: Use the reference voltage in step 2 to synchronize the subsystems, use LADRC to perform frequency adaptive adjustment, improve the coupling effect of frequency phase angle, suppress frequency overshoot, and finally achieve smooth synchronization of the three machines.

[0026] Step 4: After the voltages at the three machine terminals are synchronized, they are switched on and connected in parallel, and the remaining loads are put into operation to complete the island black start. To meet specific operating conditions, the island is eventually switched to grid-connected connection to complete the recovery of the entire system.

[0027] Specifically, in step 1, the three black start micro sources rely on photovoltaic energy storage to charge the DC bus to ensure the capacity of the black start micro source. The AC bus voltage generation relies on VSG control, which has the ability to adjust the frequency and voltage once. The VSG control model mainly includes the active loop and the reactive loop, which respectively undertake the frequency and voltage regulation functions. The active loop control equation is: ; The VSG speed regulator equation is: ; The above formula: J i is the virtual inertia; D i for damping; T ei and T mi are electromagnetic torque and mechanical torque respectively; P mi and P ei are mechanical power and electromagnetic power, and are the rated angular frequency and the actual angular frequency respectively, For VSG i Output voltage phase angle, set the given active power to P refi , K pi is the droop coefficient, i =1,2,3… n n Indicates that there are n Taiwan VSG; The reactive loop is; ; Set the given reactive power Q refi ; U 0i and U n They are rated voltage and actual voltage respectively; K ui and K qi are the droop coefficient and the integral coefficient respectively.

[0028] In order to further speed up the grid recovery, parallel recovery black start is adopted. Parallel recovery means starting all micro-sources at the same time to establish their own independent small systems, and then connecting each small system in parallel through pre-synchronization to form an independent microgrid. The three machines can run stably with their own loads at the same time.

[0029] Specifically, in step 2, when the subsystem is established according to step 1, VSG 1 As the main reference power supply, the AC bus voltage of VSG1 is used as the reference voltage, and the remaining two VSGs are synchronized to this reference voltage.

[0030] Specifically, in step 3, according to the subsystems established in steps 1-2, it is ultimately necessary to realize synchronous parallel operation of the subsystems. Although the parallel recovery in step 1 can quickly restore the load power supply, in the parallel recovery process, due to the microgrid parallel system composed of power electronic devices, even a small difference may be magnified into a large fluctuation when connected in parallel, and impact current may occur when each micro source is connected in parallel. Therefore, although the parallel recovery speed is fast, it requires extremely high accuracy of pre-synchronization. In the multi-machine pre-synchronization process, both phase angle and frequency are nonlinear controls. If they are separated and adjusted separately using PI, it is difficult to handle. The phase angle is the result of frequency, so the frequency phase angle difference of the entire system can be converted into a single control phase angle difference.

[0031] In view of the problems of over-reliance on the phase-locked loop (PLL) and phase angle difference jump in traditional phase angle pre-synchronization, a strategy without a phase-locked loop is adopted in the present invention. The calculation process is as follows: First, the Clark transform is used to transform VSG i , i =2, 3 output voltage is transformed to obtain and Two components on the axis and , then VSG 1 The voltage is converted by Clark to obtain the output voltage component and Along and Axis, the calculation formula is as follows: ; For VSG i The output voltage phase angle, For VSG 1 The output voltage phase angle, is the phase angle difference between the two.

[0032] Although the above improved phase angle control pre-synchronization improves the performance to a certain extent, there will still be a certain impact in the black start synchronization of multiple machines. Since there is a coupling relationship between phase angle and frequency, when the phase angle difference quickly approaches 0, the frequency will also fluctuate rapidly, which is easy to cause frequency overshoot. Therefore, the present invention introduces LADRC control on the basis of improving phase angle control pre-synchronization to perform adaptive frequency adjustment.

[0033] On the basis of improving the phase angle control pre-synchronization, LADRC control is introduced to adaptively adjust the frequency. The second-order LADRC is composed of LESO and LSEF. The entire LADRC is added to the VSG active loop to adjust the output frequency. The frequency output dynamics can be modeled as a second-order linear system as follows: The original expectation is the rated angular frequency , the system output is the actual frequency output, b 0 is the system gain; Assume that the linear second-order single-input and single-output system object is: ; Where: u , They are the input and output of the system object respectively; r is the external disturbance of the system; a 1 , a 2 are the parameters of the system respectively; b is the system gain, b≈b 0 , b 0 is a nominal value, anda 1 , a 2 , b All unknown, if , , that is, the system output change rate, let is the total disturbance of the system, which includes the internal uncertainty of the system and the external disturbance, then the state equation can be obtained as: ; LESO is used to estimate the state of the system, namely the frequency and its rate of change and disturbance. The mathematical expression of LESO for a second-order system is: ; Z 1 , Z 2 , Z 3 are the current frequency estimate, the current frequency change rate, and the total disturbance observation value, respectively. , , is the gain of the observer, which is used to adjust the observer's sensitivity to the state and the adjustment speed.

[0034] The task of LSEF is to adjust the control input of the system through state feedback to achieve frequency regulation. According to the control strategy of LADRC, the control input u Make the frequency gradually approach the target frequency and effectively suppress frequency overshoot. It can be expressed as: ; In the formula, k p , k d are the undetermined parameters of the PD controller, k p , k d It can be expressed as: ; Where: is the controller bandwidth; is the damping ratio, the characteristic equation of LESO can be expressed as: ; In the formula, the complex frequency s = jw , select the ideal characteristic equation , then: ; In the formula, is the observer bandwidth, through , Parameter adjustment is performed to achieve the purpose of self-disturbance rejection.

[0035] In the VSG frequency regulation scenario, the role of LADRC is to control the method frequency through feedback regulation so that it follows the target value and avoids frequency overshoot in the face of disturbances or phase angle adjustments. Since LESO can observe the frequency changes and their derivatives of the system in real time, LADRC can respond quickly to frequency fluctuations and compensate for frequency disturbances caused by phase angle adjustments. The control law of LSEF not only considers the frequency deviation , and also through the frequency change rate Z 2 The feedback of the system can avoid the system from experiencing drastic frequency fluctuations due to too fast phase angle adjustment. This design ensures that the frequency can smoothly transition to the target value and has strong anti-interference performance. The final step 3 improves the coupling effect of the frequency and phase angle, and the subsystem is smoothly synchronized.

[0036] Specifically, in step 4, after the voltages at the three generator terminals are synchronized, they are switched on and operated in parallel, and finally the remaining loads are switched on to complete the island black start. In order to further increase the system capacity and power supply restoration range, the entire system is connected to the large power grid for stable operation, thereby reducing the risk of island operation.

[0037] In the Matlab / Simulink environment, a multi-machine black start parallel recovery simulation control model was built. Three VSGs with the same capacity were selected for simulation. i ( i =1, 2, 3) The simulation working conditions are shown in the following table.

[0038]

[0039] The present invention is achieved by Figure 3 LADRC is introduced on the basis of improving the phase angle control pre-synchronization. Relying on its strong anti-interference and dynamic response speed, the frequency is adaptively adjusted and quickly adjusted when the frequency fluctuates. When the frequency is controlled more accurately and quickly, the change of the phase angle will also tend to be smooth, improving the coupling effect of the frequency and phase angle. The block diagram of the LADRC system is shown in the figure. Figure 4 The traditional black start method is compared with the method proposed in the present invention, and finally the simulation results of the traditional black start and the present invention are obtained, as shown in FIG. Figure 5-Figure 11 . Figure 5-Figure 6 The comparison of the phase angle difference between the traditional black start and the method proposed in the present invention is shown in FIG. The phase angle difference in the present invention is relatively smoother and more controllable. Figure 7-Figure 9 The frequency waveform comparison in FIG. 1 also reflects the effectiveness of the frequency overshoot suppression in the present invention, and further Figure 10-11 The instantaneous power impact of parallel connection can also be suppressed to a certain extent, making the entire black start process more stable and reliable, and improving the recovery ability of the system.

[0040] The above description is only a preferred embodiment of the present invention and does not constitute any other form of limitation to the present invention. Any modification or equivalent change made based on the technical essence of the present invention still falls within the scope of protection required by the present invention.

Claims

1. A synchronous control method for improving the frequency phase angle coupling effect of multi-machine black start, characterized in that: The following steps are involved: Step 1: The three black start micro-sources are started simultaneously, and each operates stably with load using a parallel recovery strategy; Step 2: After the black start micro source is started, the subsystem is established, and the first black start micro source is used as the main reference power supply to establish the reference voltage; Step 3: Using the reference voltage in step 2, synchronize the subsystems, and use LADRC to perform frequency adaptive adjustment, and finally achieve stable synchronization of the three machines; Step 4: After the voltages at the three machine terminals are synchronized, they are switched on and connected in parallel, and the remaining loads are put into operation to complete the island black start. To meet specific operating conditions, the island is eventually switched to grid-connected connection to complete the recovery of the entire system.

2. The synchronous control method for improving the frequency phase angle coupling effect of multi-machine black start according to claim 1, characterized in that: In step 1, three black-start micro-sources rely on photovoltaic energy storage to charge the DC bus, and the AC bus voltage is generated by virtual synchronous generator VSG control, which has the ability of primary frequency regulation and primary voltage regulation. The VSG control model includes an active loop and a reactive loop, which respectively undertake frequency regulation and voltage regulation functions, wherein the active loop control equation is: ； The VSG speed regulator equation is: ； The above formula: J i is the virtual inertia; D i For damping; T ei and T mi are electromagnetic torque and mechanical torque respectively; P mi and P ei are mechanical power and electromagnetic power, and are the rated angular frequency and the actual angular frequency respectively, For VSG i Output voltage phase angle, set the given active power to P refi , K pi is the droop coefficient, i =1,2,3… nn Indicates that there are n Taiwan VSG; The reactive loop is; ； Set the given reactive power Q refi ; U 0i and U n They are rated voltage and actual voltage respectively; K ui and K qi are the droop coefficient and the integral coefficient respectively.

3. The synchronous control method for improving the frequency phase angle coupling effect of multi-machine black start according to claim 1, characterized in that: In step 2, a subsystem is established according to step 1, with VSG1 as the main reference power supply and the AC bus voltage of VSG1 as the reference voltage. The remaining two VSGs are subsequently synchronized with the reference voltage.

4. The synchronous control method for improving the frequency phase angle coupling effect of multi-machine black start according to claim 1, characterized in that: In step 3, according to the subsystem established in step 1-2, an improved phase angle control strategy without a phase-locked loop is used to perform black start micro-source parallel networking, and the calculation process is as follows: First, the Clark transform is used to transform VSG i , i =2, 3 output voltage is transformed to obtain and Two components on the axis and , and then the VSG1 voltage is converted by Clark to obtain the output voltage component and Along and Axis, the calculation formula is as follows: ； For VSG i The output voltage phase angle, is the output voltage phase angle of VSG1, is the phase angle difference between the two; Based on the improved phase angle control pre-synchronization, the linear active disturbance rejection LADRC control is introduced to adaptively adjust the frequency. The second-order LADRC consists of a linear extended state observer LESO and a linear state error feedback LSEF. The entire LADRC is added to the VSG active loop to adjust the output frequency. The frequency output dynamics can be modeled as a second-order linear system as follows: The original expectation is the rated angular frequency , the system output is the actual frequency output, b 0 is the system gain; Assume that the linear second-order single-input and single-output system object is: ； Where: u , They are the input and output of the system object respectively; r is the external disturbance of the system; a 1. a 2 are the parameters of the system respectively; b is the system gain, b≈b 0, b 0 is a nominal value, and a 1. a 2. b All unknown, if , , that is, the system output change rate, let is the total disturbance of the system, which includes the internal uncertainty of the system and the external disturbance, then the state equation can be obtained as: ； LESO is used to estimate the state of the system, namely the frequency and its rate of change and disturbance. The mathematical expression of LESO for a second-order system is: ； Z1, Z2, and Z3 are the current frequency estimate, the current frequency change rate, and the total disturbance observation value, respectively. , , is the gain of the observer, which is used to adjust the observer's sensitivity to the state and the adjustment speed; According to the control strategy of LADRC, the control input u Make the frequency gradually approach the target frequency and effectively suppress frequency overshoot, which can be expressed as: ； In the formula, k p , k d are the undetermined parameters of the PD controller, k p , k d It can be expressed as: ； Where: is the controller bandwidth; is the damping ratio, the characteristic equation of LESO can be expressed as: ； In the formula, the complex frequency s = jw , select the ideal characteristic equation , then: ； In the formula, is the observer bandwidth, through , Parameter adjustment is performed to achieve the purpose of self-disturbance rejection.

5. The synchronous control method for improving the frequency phase angle coupling effect of multi-machine black start according to claim 1, characterized in that: In step 4, after the terminal voltages of the three machines are synchronized, they are switched on and operated in parallel, and finally the remaining loads are switched on to complete the island black start.

Images