A synchronous control method for improving the phase angle coupling effect of the multi-machine black start frequency

Abstract

A synchronous control method for improving the frequency-phase coupling effect of multi-machine black start is designed to improve the black start recovery capability. The system adopts a parallel recovery strategy to start multiple black start micro-sources at the same time and quickly achieve synchronization. However, parallel recovery has extremely high requirements for the accuracy of pre-synchronization. Since there is a coupling relationship between frequency and phase angle in the pre-synchronization process before the parallel gate, the rapid change of phase angle difference in phase angle control can easily lead to frequency overshoot. In order to solve this problem, this system introduces the linear active disturbance rejection control LADRC method based on traditional phase angle control. With strong anti-interference and dynamic response speed, it can quickly make adjustments when frequency fluctuations are caused by changes in phase angle difference. Through timely and stable control of frequency, the phase angle change also becomes more stable and controllable, thereby reducing the interference to frequency in reverse and achieving the weakening of frequency-phase coupling effect. This 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 present invention relates to the field of microgrid power supply restoration, and specifically to a synchronous control method for improving the frequency and phase angle coupling effect of multi-machine black start. Background Art

[0002] With the global energy structure transformation towards low-carbon and renewable directions, the rapid development of new energy technologies has promoted the popularization of microgrids in the power system. Microgrids have the advantages of flexible access to distributed energy sources, improved energy utilization efficiency, and enhanced power supply reliability, and thus have been widely applied in various scenarios, such as independent power supply in remote and isolated areas, load regulation of urban power grids, and emergency power supply guarantee. However, due to the volatility and intermittency characteristics of new energy generation, microgrids face significant challenges in restoration and stability when encountering faults or external power supply interruptions. Against this background, the VSG technology has emerged. By simulating the moment of inertia and electrical characteristics of traditional synchronous generators, VSG enables inverters to better integrate into grid operation, thereby enhancing the system's stability and inertia support. In the operation and restoration of microgrids, the VSG technology can provide dynamic responses to suppress voltage and frequency fluctuations. Although the VSG technology effectively improves the dynamic performance of microgrids, how to achieve a fast and stable restart during the restoration stage after microgrid faults remains an urgent problem to be solved. Especially in the black start scenario, since the system has no external grid support in the initial state, the microgrid needs to rely on its own distributed power sources for start-up and parallel operation without external support. At this time, multi-machine pre-synchronization is crucial because it directly determines whether the system can achieve a shock-free parallel switch-on. 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, when the phase angle difference rapidly approaches 0, it may trigger severe frequency fluctuations, resulting in frequency overshoot or even unstable states.

[0003] The differences compared with the prior art are as follows:

[0004] Technical comparison with the patent CN 113644653B "Power system black start path restoration method for new energy and energy storage coordination"

[0005] Patent CN 113644653B optimizes the black - start model by using the optimal restoration sequence and corresponding restoration paths of each unit and load in the black - start system. In contrast, our research focuses on deeply exploring the pre - synchronization performance of black - start micro - sources. Given the importance of network restoration in the black - start process, we propose to directly use the parallel restoration strategy to start multiple black - start micro - sources simultaneously, giving full play to their black - start capabilities. At the same time, for the synchronization performance of black - start micro - sources, we introduce an improved phase - angle control pre - synchronization mechanism and linear active disturbance rejection control (LADRC). With its strong anti - interference ability and fast dynamic response characteristics, LADRC can quickly adjust the system when phase - angle differences cause frequency fluctuations, and ensure that the phase - angle change is also more stable and controllable by timely and smoothly controlling the frequency, thus effectively reducing the interference of frequency fluctuations on the system and weakening the frequency - phase coupling effect. This design not only ensures the rapid restoration of the black - start process but also significantly improves the stability and security of the system.

[0006] Patent CN 113644653B solves the problem of insufficient black - start resources that may exist in some regions to a certain extent. However, its path - optimization process involves load - forecasting technology, and the solution of the objective function is relatively complex. Our method focuses more on the system stability and security 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 restoration, and this method has excellent robustness and can more effectively cope with various disturbances.

[0007] Technical comparison with the patent publication number CN 114094586A, "Power network black - start method considering the coupling characteristics of power - natural gas networks"

[0008] In CN 114094586A, the coupling characteristics of power and natural - gas networks are mainly considered, and then a hierarchical collaborative restoration model of the power - gas interconnected system is constructed. However, our research focuses on the pre - synchronization mechanism based on the improved phase - angle control of black - start micro - sources. This research fully considers the coupling relationship between frequency and phase angle during the pre - synchronization process, and effectively avoids the frequency overshoot problem caused by frequency - phase coupling during the micro - source synchronization process by introducing LADRC control. This method significantly improves the rapid restoration ability of the black - start system and ensures the stability of the system during the restoration process. Summary of the Invention

[0009] To address the above problems, the present invention proposes a synchronous control method for improving the frequency-phase angle coupling effect in multi-machine black start. The system adopts a parallel restoration strategy to achieve the synchronous start-up of multiple VSG black start micro-sources, thereby enhancing the speed and restoration ability of black start. Its core innovation lies in the introduction of the LADRC method to effectively address the frequency overshoot problem caused by the rapid change of phase angle difference during the pre-synchronization process. LADRC has strong anti-interference ability and fast dynamic response, and can quickly adjust when frequency fluctuations occur, improving the frequency-phase angle coupling effect, and thus enhancing the synchronous accuracy and stability of the system. This design balances the rapidity of black start and the stable operation of the system.

[0010] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0011] A synchronous control method for improving the frequency-phase angle coupling effect in multi-machine black start, characterized by comprising the following steps:

[0012] Step 1: Three black start micro-sources start simultaneously, and each operates stably with a load using a parallel restoration strategy;

[0013] Step 2: After the black start micro-source starts, a subsystem is established. Using the first black start micro-source as the main reference power source, a reference voltage is established;

[0014] Step 3: Using the reference voltage in Step 2, synchronize each subsystem, and perform frequency adaptive adjustment using LADRC to ultimately achieve the smooth synchronization of the three machines;

[0015] Step 4: After the terminal voltages of the three machines reach synchronization, close the switch for parallel operation, connect the remaining load, complete the island black start, and finally switch from the island to grid connection to complete the restoration of the entire system to meet specific working conditions.

[0016] As a further improvement of the present invention, in Step 1, the three black start micro-sources rely on photovoltaic energy storage to charge the DC bus, and the AC bus voltage is generated by the control of the virtual synchronous generator (VSG), which has the ability of primary frequency regulation and primary voltage regulation. The VSG control model includes an active power loop and a reactive power loop, which respectively undertake the functions of frequency regulation and voltage regulation. The active power loop control equation is:

[0017] ;

[0018] The VSG governor equation is:

[0019] ;

[0020] In the above formula: J i is the virtual inertia; D i is the damping; Tei and T mi are the electromagnetic torque and the mechanical torque respectively; P mi and P ei are the mechanical power and the electromagnetic power, and are the rated angular frequency and the actual angular frequency respectively, is the output voltage phase angle of the VSG i Set the given active power to be P refi , K pi is the droop coefficient, i = 1, 2, 3… n n indicates that there are n VSGs in the independent microgrid;

[0021] The reactive power loop is;

[0022] ;

[0023] Set the given reactive power Q refi ; U 0i and U n are the rated voltage and the actual voltage respectively; K ui and K qi are the droop coefficient and the integral coefficient respectively.

[0024] To further accelerate the grid framework restoration, parallel restoration black start is adopted. Parallel restoration means that all micro-sources are started simultaneously to establish their respective independent small systems, and then the small systems are paralleled through pre-synchronization to form an independent microgrid. Three machines simultaneously operate stably with their respective loads.

[0025] As a further improvement of the present invention, in step 2, according to the subsystem established in step 1, using the VSG 1 as the main reference power supply, and using the AC bus voltage of the VSG 1 as the reference voltage, and the subsequent remaining two VSGs are synchronized to this reference voltage.

[0026] As a further improvement of the present invention, in step 3, according to the subsystem established in steps 1 - 2, an improved phase angle control strategy without a phase-locked loop is adopted for black start micro-source parallel networking, and the calculation process is as follows:

[0027] First, perform Clark transformation on the VSG i ,i = 2, 3 output voltages are transformed to obtain two components on the and axes and , and then the VSG 1 voltage is converted by Clark transformation to obtain the output voltage components and along and axes, and the calculation formula is as follows:

[0028] ;

[0029] is the output voltage phase angle of the VSG i , is the output voltage phase angle of the VSG 1 , is the phase angle difference between the two;

[0030] Based on the improved phase angle control pre-synchronization, a linear active disturbance rejection control (LADRC) 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 active power loop of the VSG to adjust the output frequency. Assuming that the frequency output dynamics can be modeled as a second-order linear system, as follows:

[0031] The original expectation is the rated angular frequency , the system output is the actual frequency output, b 0 is the system gain;

[0032] Assuming that the linear second-order single-input, single-output system object is:

[0033] ;

[0034] In the formula: u , 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 the nominal value, and a 1 , a 2 , b are all unknown. If we let , , that is, the system output change rate. Let be the total system disturbance, which includes internal system uncertainties and external disturbances. Then the state equation can be obtained as follows:

[0035] ;

[0036] The LESO is used to estimate the state of the system, namely the frequency, its change rate, and the disturbance. The mathematical expression of the LESO for a second-order system is:

[0037] ;

[0038] Z 1 , Z 2 , Z 3 are the current frequency estimate, the current frequency change rate, and the total disturbance observation value respectively. , , are the gains of the observer, which are used to adjust the sensitivity and adjustment speed of the observer to the state;

[0039] According to the control strategy of LADRC, the control input u makes the frequency gradually approach the target frequency and effectively suppresses the frequency overshoot, which is expressed as:

[0040] ;

[0041] In the formula, k p , k d are the undetermined parameters of the PD controller. k p , k d can be expressed as:

[0042] ;

[0043] In the formula: is the controller bandwidth; is the damping ratio. The characteristic equation of the LESO can be expressed as:

[0044] ;

[0045] In the formula, the complex frequency s = jw Select the ideal characteristic equation , then there is:

[0046] ;

[0047] In the formula, is the observer bandwidth. By , Carry out parameter tuning to achieve the purpose of active disturbance rejection.

[0048] As a further improvement of the present invention, in step 4, after the terminal voltages of the three machines reach synchronization, they are closed and operated in parallel, and finally the remaining load is switched to complete the island black start.

[0049] To further increase the system capacity and the power supply restoration range, the entire system is connected to the large power grid for stable operation, thereby reducing the risk of island operation.

[0050] Beneficial effects: Compared with the prior art, the present invention adopts the above technical solutions and has the following advantages:

[0051] By introducing the LADRC technology, the present invention improves the coupling effect of the frequency phase angle during the pre-synchronization process of multi-machine black start, and overcomes the problems of frequency overshoot and system instability caused by the coupling of frequency and phase angle in the prior art. The traditional technology usually only controls the phase angle during pre-synchronization, which is likely to cause frequency fluctuations or even over-limit when the phase angle difference changes rapidly. Especially under the parallel restoration strategy, this kind of fluctuation will amplify the system disturbance and affect the stability of the microgrid. The present invention adaptively adjusts the frequency through LADRC, timely suppresses the frequency fluctuations caused by the phase angle change, ensures the frequency stability while making the phase angle change more controllable, thereby reducing the mutual interference between the frequency and the phase angle. This design realizes higher synchronization accuracy and faster restoration speed in the multi-machine system, improves the safety and stability of black start, and meets the distributed power supply scenarios with higher requirements for restoration speed and system reliability. Description of the Drawings

[0052] Figure 1 It is a block diagram of a synchronization control method for improving the frequency phase angle coupling effect of multi-machine black start;

[0053] Figure 2 A flow chart of a synchronization control method for improving the frequency phase angle coupling effect of multi-machine black start;

[0054] Figure 3 It is an improved phase angle control pre-synchronization control block diagram;

[0055] Figure 4 It is a block diagram of the LADRC system;

[0056] Figure 5 It is the VSG before and after improvement 2 The waveform of the phase angle difference change between the main reference power supply;

[0057] Figure 6 It is the VSG before and after improvement 3 The waveform of the phase angle difference change between the main reference power supply;

[0058] Figure 7 It is the VSG 1 Frequency comparison waveform;

[0059] Figure 8 It is the VSG 2 Frequency comparison waveform;

[0060] Figure 9 It is the VSG 3 Frequency comparison waveform;

[0061] Figure 10 It is the power waveform under multi - machine black start with improved phase - angle control;

[0062] Figure 11 It is the power waveform of the synchronous control method for improving the frequency - phase - angle coupling effect in multi - machine black start. Specific implementation manner

[0063] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described 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.

[0064] As Figure 1 shown, this is a block diagram of a synchronous control method for improving the frequency - phase - angle coupling effect in multi - machine black start, including the following components: photovoltaic energy storage module, VSG control module, black - start parallel pre - synchronization module, grid - connection pre - synchronization module.

[0065] Photovoltaic energy storage module: This module includes a photovoltaic power generation unit and an energy storage device, and is used to provide power support and stable power output. In the multi - machine black - start scenario, the photovoltaic energy storage module can provide the power required for the initial start - up of the system, and help the micro - grid to start and operate without external power support. The energy storage unit can also perform power regulation during the grid recovery process to ensure the stability of the entire system under load fluctuations.

[0066] VSG control module: The VSG control module is one of the core control units of the system. The VSG technology realizes the grid - friendliness and stability of the renewable energy power generation system by simulating the inertia and damping characteristics of a synchronous generator. During the black - start process, the VSG control module provides an adjustment ability similar to that of a traditional generator, enabling the photovoltaic and energy storage systems to have the ability to operate independently and in parallel with the grid. It regulates voltage, frequency, and phase angle during the pre - synchronization stage to create favorable conditions for grid connection.

[0067] Black - start parallel pre - synchronization module: This module focuses on achieving the synchronous start - up of multiple VSG micro - sources in the black - start scenario. Since multi - machine black - start involves the simultaneous parallel connection of multiple power generation units, the pre - synchronization module needs to ensure that the frequencies and phase angles of each unit are as close as possible to avoid large fluctuations and system disturbances during the parallel connection. The LADRC is introduced to adjust the frequency response to improve the coupling effect of frequency and phase angle, and enhance the synchronization accuracy and system stability.

[0068] Grid - connection pre - synchronization module: This module is used to connect an independently operating micro - grid to the main grid. The grid - connection pre - synchronization module ensures that the system frequency, phase angle, and voltage amplitude match those of the main grid to achieve seamless grid - connection. Through the control of this module, the micro - grid avoids shocks and disturbances during the grid - connection process, ensuring the smoothness and safety of grid - connection, and supporting the smooth transition of the micro - grid from the island mode to the 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.

[0069] The core idea of the present invention is to design a synchronous control method to improve the coupling effect of frequency and phase angle in multi - machine black - start, so as to solve the problems of frequency overshoot and system disturbances caused by the coupling of frequency and phase angle when multiple VSGs are black - started and connected to the grid. The parallel recovery strategy is used to achieve the rapid synchronization of multiple VSGs, and the LADRC is introduced to adaptively adjust the frequency based on the phase - angle control, improve the coupling effect of frequency and phase angle, thereby improving the accuracy and stability of pre - synchronization, enhancing the system recovery ability and grid - connection reliability.

[0070] As Figure 2 shown, the method includes the following specific steps:

[0071] Step 1: Three black - start micro - sources start simultaneously, and each uses the parallel recovery strategy to operate stably with load.

[0072] Step 2: After the black - start micro - sources start, a subsystem is established, and the VSG 1 is used as the main reference power source to establish a reference voltage.

[0073] Step 3: Using the reference voltage in Step 2, synchronize each subsystem, and use the LADRC for adaptive frequency regulation to improve the coupling effect of frequency and phase angle, suppress frequency overshoot, and finally achieve the smooth synchronization of the three machines.

[0074] Step 4: After the terminal voltages of the three machines reach synchronization, conduct closing and parallel operation, input the remaining load, complete the island black - start, and finally switch from the island to the grid - connection to complete the recovery of the entire system to meet specific working conditions.

[0075] Specifically, in step 1, three black-start micro-sources rely on photovoltaic energy storage to charge the DC bus to ensure the capacity of the black-start micro-sources. The AC bus voltage is generated by VSG control, which has the ability of primary frequency regulation and primary voltage regulation. The VSG control model mainly includes an active loop and a reactive loop, which are responsible for frequency regulation and voltage regulation functions respectively. The active loop control equation is:

[0076] ;

[0077] The VSG governor equation is:

[0078] ;

[0079] In the above formula: J i is the virtual inertia; D i is the damping; T ei and T mi are the electromagnetic torque and mechanical torque respectively; P mi and P ei are the mechanical power and electromagnetic power, and are the rated angular frequency and actual angular frequency respectively, is the output voltage phase angle of VSG i Set the given active power as P refi , K pi is the droop coefficient, i = 1, 2, 3… n n represents that there are n VSGs in the independent microgrid;

[0080] The reactive power loop is;

[0081] ;

[0082] Set the given reactive power Q refi ; U 0i and U n are the rated voltage and actual voltage respectively; K ui and K qi are the droop coefficient and integral coefficient respectively.

[0083] To further accelerate the restoration of the grid framework, parallel restoration black start is adopted. Parallel restoration means starting all micro-sources simultaneously to establish their respective independent small systems, and then paralleling the individual small systems through pre-synchronization to form an independent microgrid. Three machines operate stably while carrying their respective loads.

[0084] Specifically, in step 2, when establishing the subsystem according to step 1, using VSG 1 as the main reference power supply and the AC bus voltage of VSG1 as the reference voltage, the subsequent remaining two VSGs are synchronized to this reference voltage.

[0085] Specifically, in step 3, according to the subsystem established in steps 1 - 2, it is ultimately necessary to achieve the synchronous parallel operation of the subsystems. Although parallel restoration in step 1 can quickly restore power supply to the load, during the parallel restoration process, in the microgrid parallel system composed of power electronic devices, even a very small difference may be amplified into a large fluctuation when paralleling, and there may be inrush currents when the individual micro-sources are paralleled. Therefore, although parallel restoration has a fast restoration speed, it has extremely high requirements for the accuracy of pre-synchronization. During the multi-machine pre-synchronization process, both the phase angle and frequency are non-linear controls. If PI regulation is used separately, it is difficult to handle. The phase angle is the result of the frequency generation. Therefore, the frequency phase angle difference of the entire system can be transformed into a separate control of the phase angle difference.

[0086] Aiming at the problems of traditional phase angle pre-synchronization such as over-reliance on the phase-locked loop PLL and phase angle difference jumps, a phase-locked loop-free strategy is adopted in the present invention. The calculation process is as follows:

[0087] First, perform a Clark transformation on the output voltages of VSG i i =2, 3 to obtain two components on the and axes and , and then the voltage of VSG 1 is converted by Clark to obtain the output voltage components and along the and axes. The calculation formulas are as follows:

[0088] ;

[0089] is the output voltage phase angle of VSG i , is the output voltage phase angle of VSG 1 , is the phase angle difference between the two.

[0090] ​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 multi-machine black start synchronization. Due to the coupling relationship between the phase angle and the frequency, when the phase angle difference rapidly approaches 0, the frequency will also rapidly fluctuate, easily causing frequency overshoot. Therefore, the present invention introduces LADRC control on the basis of the improved phase angle control pre-synchronization to adaptively adjust the frequency.

[0091] On the basis of the improved 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 active power loop of the VSG to adjust the output frequency. Suppose the frequency output dynamics can be modeled as a second-order linear system as follows:

[0092] The original expectation is the rated angular frequency , and the system output is the actual frequency output. b 0 is the system gain;

[0093] Suppose the linear second-order single-input and single-output system object is:

[0094] ;

[0095] In the formula: u , 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 the nominal value, and a 1 , a 2 , b are all unknown. If , , that is, the system output change rate. Suppose is the total disturbance of the system, which includes the internal uncertainty and external disturbance of the system, then the state equation can be obtained as:

[0096] ;

[0097] LESO is used to estimate the state of the system, that is, the frequency, its change rate and the disturbance. The mathematical expression of LESO for the second-order system is:

[0098] ;

[0099] Z1 , 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 sensitivity and adjustment speed of the observer to the state.

[0100] The task of LSEF is to regulate the control input of the system through state feedback, so as to achieve frequency regulation. According to the control strategy of LADRC, the control input u makes the frequency gradually approach the target frequency and effectively suppresses the frequency overshoot. It can be expressed as:

[0101] ;

[0102] In the formula, k p , k d are the undetermined parameters of the PD controller, k p , k d can be expressed as:

[0103] ;

[0104] In the formula: is the controller bandwidth; is the damping ratio, and the characteristic equation of LESO can be expressed as:

[0105] ;

[0106] In the formula, the complex frequency s = jw Select the ideal characteristic equation , then there is:

[0107] ;

[0108] In the formula, is the observer bandwidth, and the auto-disturbance rejection purpose is achieved by tuning the parameters of , .

[0109] In the scenario of VSG frequency regulation, the role of LADRC is to control the method frequency through feedback regulation, make it follow the target value, and avoid frequency overshoot when facing disturbances or phase angle adjustments. Since LESO can observe the frequency change and its derivative of the system in real time, LADRC can quickly respond to the frequency fluctuation and compensate for the frequency disturbance caused by phase angle adjustment. The control law of LSEF not only considers the frequency deviation , and also by feedback on the rate of change of frequency Z 2 , to avoid the system's frequency from fluctuating violently due to too rapid phase angle adjustment. This design ensures that the frequency can smoothly transition to the target value and has strong anti-interference ability. The final step 3 improves the coupling effect of the frequency and phase angle, and the subsystem achieves stable synchronization.

[0110] Specifically, in step 4, after the terminal voltages of the three machines reach synchronization, they are closed and operated in parallel, and finally the remaining load is switched on and off to complete the island black start. To further increase the system capacity and the power supply restoration range, the entire system is connected to the large power grid for stable operation, thereby reducing the risk of island operation.

[0111] In the Matlab / Simulink environment, a multi-machine black start parallel recovery simulation control model is built. Three VSGs with the same capacity are selected for simulation, and the VSG i ( i = 1, 2, 3) The simulation conditions are shown in the following table.

[0112]

[0113] The present invention, based on improving the phase angle control pre-synchronization, introduces LADRC. Relying on its strong anti-interference ability and dynamic response speed, it adaptively adjusts the frequency, makes rapid adjustments when the frequency fluctuates. When the frequency is controlled more precisely and quickly, the change of the phase angle will also tend to be gentle, improving the coupling effect of the frequency and phase angle. The LADRC system block diagram is as Figure 3 shown. Comparing the traditional black start with the method proposed by the present invention, the simulation results of the traditional black start and the present invention are finally obtained, as Figure 4 shown. Figures 5 - 11 . Figures 5 - 6 This is the comparison of the phase angle difference change under the traditional black start and the method proposed by the present invention. The phase angle difference in the present invention is relatively more gentle and controllable. Figures 7 - 9 The comparison of the frequency waveforms in Figures 10 - 11 also reflects the effectiveness of suppressing the frequency overshoot in the present invention, and thus has a certain inhibitory effect on the power impact during the parallel connection moment in

[0114] , making the entire black start process more stable and reliable, and improving the system's recovery ability. The above is only a preferred embodiment of the present invention, and it is not any other form of limitation to the present invention. Any modification or equivalent change made according to the technical essence of the present invention still belongs to the scope protected 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; 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 , Perform parameter adjustment to achieve the purpose of self-disturbance rejection; 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 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.

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