Grid-connection pre-synchronization method for virtual synchronous generator parallel system, and electronic device

Abstract

A grid-connection pre-synchronization method for a virtual synchronous generator parallel system, and an electronic device. The grid-connection pre-synchronization method for the virtual synchronous generator parallel system comprises: after receiving a pre-synchronization instruction, n virtual synchronous generators start to perform grid-connection pre-synchronization, wherein the grid-connection pre-synchronization comprises frequency and phase pre-synchronization, and amplitude pre-synchronization (S110). The frequency and phase pre-synchronization comprises: calculating control amounts for the frequency and phase pre-synchronization; according to the control amounts for the frequency and phase pre-synchronization, calculating a damping power; according to a mechanical power, an electromagnetic power and the damping power, calculating an output angular frequency difference of the virtual synchronous generators; and according to the output angular frequency difference of the virtual synchronous generator sand a rated angular frequency, determining a power angle of the virtual synchronous generators.

Description

Grid-connected pre-synchronization method and electronic device of virtual synchronous generator parallel system

[0001] The present application claims priority to the Chinese patent application No. 202411294460.X, filed on September 14, 2024, with the Chinese Patent Office, the content of which is incorporated herein by reference in its entirety. TECHNICAL FIELD

[0002] Embodiments of the present application relate to the field of new energy power generation technology, for example, to a grid-connected pre-synchronization method and electronic device of a virtual synchronous generator parallel system. BACKGROUND

[0003] With the proposal of the goal of building a new power system, the proportion of new energy power generation will be further improved. However, new energy power generation equipment usually works in a grid-connected mode to pursue maximum power tracking. Excessive proportion of new energy power generation will weaken the strength of the power grid, lack of voltage, frequency, inertia support, etc. In recent years, grid-connected converters based on virtual synchronous generator (VSG) control can improve the voltage, frequency, and inertia support capability of the power system, and are widely studied and applied. The capacity and overcurrent capability of new energy power generation equipment based on power electronic devices are much lower than that of traditional synchronous generators, therefore, it is imperative to parallel multiple VSG-controlled converters to improve the capacity of the system. The VSG-controlled converter can work in an off-grid state, and when switching from off-grid to grid-connected state, the frequency, phase, and amplitude of the VSG output voltage need to be pre-synchronized to reduce the difference between the VSG output voltage and the grid voltage, and to reduce the impact current at the moment of grid connection. At the same time, the VSG-controlled converter can be regarded as a voltage source, when multiple voltage sources are parallel-connected and work in an off-grid mode, small differences in frequency, phase, and amplitude between the voltage sources will cause considerable circulating current, which threatens the safety of the converter. Therefore, how to achieve pre-synchronization control when multiple VSGs are parallel-connected is one of the technical difficulties.

[0004] To solve the above problems, patent 202010064431.X uses a synchronization device to judge the amplitude and frequency difference between the grid voltage and the point of common coupling (PCC) voltage, adjusts the voltage and frequency according to the set step, and sends it to multiple VSGs through communication. Patent 202310238937.1 transmits active and reactive power information between VSGs through a communication bus, and compensates for the no-load electromotive force and frequency according to the maximum reactive and active power information. The above methods all rely on communication to transmit control information to multiple VSGs, and have high requirements for communication reliability. Patent 201710692259.0 only sends a working mode signal to multiple VSGs through a dispatching center, and pre-synchronization is completed in multiple VSGs. The pre-synchronization frequency adjustment amount is obtained by closed-loop control of the reactive power between the grid voltage and the PCC voltage. The literature (Xiangwu Yan, De-sheng Wang, Jia Jiaxin. Virtual synchronous generator without communication pre-synchronization grid connection scheme based on distributed microgrid [J]. Transactions of Electrical Engineering Technology, 2019, 34(19): 4143-53) uses the frequency difference, amplitude difference and virtual active power constructed between the PCC voltage and the grid voltage to realize the pre-synchronization of frequency, amplitude and phase, respectively. The above two schemes belong to the non-communication multi-VSG grid-connected pre-synchronization scheme, but the control is relatively complex. SUMMARY

[0005] The present application provides a grid-connected pre-synchronization method and electronic equipment for a virtual synchronous generator parallel system, which solves the problem of relatively complex control of multi-VSG grid-connected pre-synchronization scheme, can realize non-communication pre-synchronization, and can also be realized through communication method, with flexible and simple control and low requirements for communication reliability.

[0006] The present application provides a grid-connected pre-synchronization method for a virtual synchronous generator parallel system, which includes: n virtual synchronous generators, an AC bus and a first circuit breaker, the AC output ends of the n virtual synchronous generators are connected in parallel with the AC bus, the first circuit breaker is connected between the AC bus and the grid, and n is an integer greater than or equal to 2.

[0007] The grid-connected pre-synchronization method for the virtual synchronous generator parallel system includes:

[0008] After receiving the pre-synchronization instruction, the n virtual synchronous generators start to perform grid-connected pre-synchronization, which includes frequency, phase and amplitude pre-synchronization.

[0009] The frequency and phase presynchronization comprises: calculating a frequency and phase presynchronization control quantity, calculating a damping power according to the frequency and phase presynchronization control quantity, calculating an output angular frequency difference of the virtual synchronous generator according to a mechanical power, an electromagnetic power and the damping power, and determining a power angle of the virtual synchronous generator according to the output angular frequency difference of the virtual synchronous generator and a rated angular frequency;

[0010] The amplitude presynchronization comprises: calculating a no-load electromotive force adjustment quantity, and determining a no-load electromotive force reference value according to the no-load electromotive force adjustment quantity and a rated no-load electromotive force value;

[0011] According to a preset condition, it is determined whether the n virtual synchronous generators complete presynchronization, and a determination result is obtained.

[0012] In response to the determination result being that the n virtual synchronous generators do not complete presynchronization, the grid-connected presynchronization is returned to continue to be executed.

[0013] In response to the determination result being that the n virtual synchronous generators complete presynchronization, the first circuit breaker is closed and the grid-connected presynchronization is closed.

[0014] Embodiments of the present application further provide an electronic device, which comprises:

[0015] One or more processors;

[0016] A memory configured to store one or more programs;

[0017] When the one or more programs are executed by the one or more processors, the one or more processors implement the grid-connected presynchronization method of the virtual synchronous generator and system as described in any embodiment of the present application.

[0018] Embodiments of the present application further provide a computer readable storage medium, which stores a computer program, and the computer program is executed by a processor to implement the grid-connected presynchronization method of the virtual synchronous generator and system as described in any embodiment of the present application. BRIEF DESCRIPTION OF DRAWINGS

[0019] FIG. 1 is a circuit diagram of a virtual synchronous generator and system according to an embodiment of the present application;

[0020] FIG. 2 is a flowchart of a grid-connected presynchronization method of a virtual synchronous generator and system according to an embodiment of the present application;

[0021] FIG. 3 is a frequency and phase presynchronization control block diagram of multiple VSGs according to an embodiment of the present application;

[0022] FIG. 4 is an active power loop control block diagram of multiple VSGs according to an embodiment of the present application;

[0023] Figure 5 is a block diagram of amplitude pre-synchronization control in multiple VSGs according to an embodiment of the present application;

[0024] Figure 6 is a block diagram of grid-connection pre-synchronization control in a multiple-VSG parallel system according to an embodiment of the present application;

[0025] Figure 7 is a waveform diagram of PCC voltage and grid voltage before and after the pre-synchronization signal is set high according to an embodiment of the present application;

[0026] Figure 8 is a waveform diagram of PCC voltage frequency during the entire grid-connection pre-synchronization process according to an embodiment of the present application;

[0027] Figure 9 is a waveform diagram of PCC voltage and grid voltage after pre-synchronization according to an embodiment of the present application;

[0028] Figure 10 is a structural diagram of an electronic device according to an embodiment of the present application. DETAILED DESCRIPTION

[0029] The technical solutions in the embodiments of the present application will be described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work should fall within the scope of protection of the present application.

[0030] It should be noted that the terms "first", "second", etc. in the specification and claims of the present application and the above-mentioned drawings are used to distinguish similar objects, and do not necessarily describe a specific order or sequence. It should be understood that the data thus used can be interchanged under appropriate circumstances, so that the embodiments of the present application described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "include" and "have" and any variations thereof are intended to cover non-exclusive inclusion, for example, a process, method, system, product or device that includes a series of steps or units does not necessarily have to be limited to those steps or units clearly listed, but can include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0031] The embodiment of the present application provides a grid-connected pre-synchronization method of a virtual synchronous generator parallel system, Figure 1 is a circuit diagram of a virtual synchronous generator parallel system according to the embodiment of the present application, referring to Figure 1, the virtual synchronous generator parallel system comprises: n virtual synchronous generators (VSG1, VSG2,..., VSGn), an AC bus and a first circuit breaker Kg, the AC output ends of the n virtual synchronous generators are connected in parallel with the AC bus, the first circuit breaker Kg is connected between the AC bus and a power grid, and n is an integer greater than or equal to 2.

[0032] A typical multi-VSG parallel system is shown in Figure 1, the AC output ends of the n VSGs are connected in parallel with an AC bus, referred to as a point of common coupling (PCC), the PCC is connected with the power grid through a first circuit breaker Kg, and the PCC is connected with a load through a second circuit breaker K L When the first circuit breaker Kg is disconnected, the multi-VSG parallel system works in an off-grid mode, and the second circuit breaker K L on the load side can be closed or disconnected. Before closing the first circuit breaker Kg to grid-connect the multi-VSG parallel system, grid-connected pre-synchronization control needs to be performed, the control is completed inside the multiple VSGs, after all the VSGs complete the grid-connected pre-synchronization, the first circuit breaker Kg is closed, and the parallel system is grid-connected and runs. During the pre-synchronization process, the multiple VSGs directly sample the grid voltage Vg through sensors, and can realize a communication-free pre-synchronization scheme; or the VGS1 samples the grid voltage Vg, then communicates with other VGSs, and sends the grid voltage information to the remaining other VSGs through a communication line, to become a communication-based pre-synchronization scheme. In practice, the communication reliability can be selected. Compared with the related art, the control is flexible and simple.

[0033] Figure 2 is a flowchart of a grid-connected pre-synchronization method of a virtual synchronous generator parallel system according to the embodiment of the present application, referring to Figure 2, the grid-connected pre-synchronization method of the virtual synchronous generator parallel system comprises:

[0034] S110, after the n virtual synchronous generators receive a pre-synchronization instruction, the grid-connected pre-synchronization is started to be executed, and the grid-connected pre-synchronization comprises frequency, phase pre-synchronization and amplitude pre-synchronization.

[0035] The frequency, phase pre-synchronization comprises: calculating a frequency, phase pre-synchronization control quantity, calculating a damping power according to the frequency, phase pre-synchronization control quantity, calculating an output angular frequency difference of the virtual synchronous generator according to a mechanical power, an electromagnetic power and the damping power, and determining a power angle of the virtual synchronous generator according to the output angular frequency difference of the virtual synchronous generator and a rated angular frequency.

[0036] The amplitude pre-synchronization comprises: calculating a no-load electromotive force adjustment amount, and determining a no-load electromotive force reference value according to the no-load electromotive force adjustment amount and a rated no-load electromotive force value.

[0037] The n VSGs start to perform pre-synchronization after receiving the pre-synchronization instruction, including frequency, phase pre-synchronization and amplitude pre-synchronization.

[0038] FIG. 3 is a frequency, phase pre-synchronization control block diagram of the plurality of VSGs according to an embodiment of the present application. Referring to FIG. 3, the frequency, phase pre-synchronization control amount is calculated, the damping power is calculated according to the frequency, phase pre-synchronization control amount, the output angular frequency difference of the virtual synchronous generator is calculated according to the mechanical power, the electromagnetic power and the damping power, and the power angle of the virtual synchronous generator is determined according to the output angular frequency difference of the virtual synchronous generator and the rated angular frequency, which comprises: performing phase-locked loop control on the grid voltage obtained by the virtual synchronous generator to obtain the grid voltage phase angle.

[0039] Continuing to refer to FIG. 3, the phase-locked loop control on the grid voltage obtained by the virtual synchronous generator to obtain the grid voltage phase angle comprises: performing Park transformation on the grid voltage to obtain the d-axis and q-axis components of the grid voltage in the rotating coordinate system, performing proportional-integral (PI) control on the q-axis component of the grid voltage and adding the rated angular frequency to obtain the grid frequency, and performing integration on the grid frequency to obtain the grid voltage phase angle.

[0040] Optionally, the calculation formula of the q-axis component of the grid voltage is as follows:

[0041] ;

[0042] wherein, is the q-axis component of the grid voltage, , , are three-phase voltages, is the grid voltage phase angle.

[0043] The q-axis component of the grid voltage is subjected to PI control to obtain Δω g , is added to the rated angular frequency ω0 to obtain the grid frequency , is integrated to obtain the grid voltage phase angle .

[0044] Continuing to refer to FIG. 3, the PCC voltage is subjected to Park transformation according to the grid voltage phase angle to obtain the d-axis and q-axis components of the PCC voltage in the rotating coordinate system, and the PI control is performed on the q-axis component of the PCC voltage to obtain the frequency, phase pre-synchronization control amount.

[0045] Optionally, the calculation formula of the q-axis component of the point of common coupling voltage is as follows:

[0046] ;

[0047] wherein, is the q-axis component of the point of common coupling voltage, , , are three-phase point of common coupling voltages, is a grid voltage phase angle.

[0048] q-axis component of the point of common coupling voltage PI control to obtain frequency, phase pre-synchronization control quantity .

[0049] FIG. 4 is a block diagram of active power loop control of multiple VSGs according to an embodiment of the present application. Referring to FIG. 4, mechanical power is calculated according to the frequency, phase pre-synchronization control quantity, rated angular frequency, frequency-active droop coefficient, angular frequency difference of virtual synchronous generator control, and active instruction value. Damping power is calculated according to the angular frequency difference of virtual synchronous generator control, rated angular frequency, and virtual synchronous generator damping coefficient.

[0050] As shown in FIG. 4, the frequency, phase pre-synchronization control quantity acts on the active instruction in the VSG active loop, and frequency, phase pre-synchronization is achieved.

[0051] Continuing to refer to FIG. 4, the output angular frequency difference of the virtual synchronous generator is calculated according to the mechanical power, electromagnetic power, damping power, virtual inertia, and rated angular frequency. The output angular frequency difference of the virtual synchronous generator is integrated after being superimposed on the rated angular frequency to obtain the power angle of the virtual synchronous generator.

[0052] Optionally, the calculation formula of the mechanical power is as follows:

[0053] ;

[0054] wherein, is the mechanical power, is the active instruction value, is the output angular frequency difference of the virtual synchronous generator, is the rated angular frequency, is the frequency-active droop coefficient, is the frequency, phase pre-synchronization control quantity.

[0055] active instruction value is subtracted by the output angular frequency difference of the virtual synchronous generator is multiplied by the rated angular frequency and the frequency-active droop coefficient minus the frequency, phase pre-synchronization control amount multiplied by the rated angular frequency and the frequency-active droop coefficient value, finally obtaining the mechanical power .

[0056] The calculation formula of the damping power is as follows:

[0057] ;

[0058] wherein, is the damping power, is the output angular frequency difference of the virtual synchronous generator, is the rated angular frequency, is the damping coefficient of the virtual synchronous generator.

[0059] The calculation formula of the output angular frequency difference of the virtual synchronous generator is as follows:

[0060] ;

[0061] wherein, is the output angular frequency difference of the virtual synchronous generator, is the mechanical power, is the electromagnetic power, is the damping power, is the virtual inertia, is the rated angular frequency, is the Laplace operator.

[0062] The output angular frequency difference of the virtual synchronous generator superimposes the rated angular frequency and then does integral operation to obtain the power angle of the virtual synchronous generator . The above is the frequency, phase pre-synchronization process.

[0063] VSG power angle refers to the phase difference between the output power of a virtual synchronous generator (VSG) and the grid voltage during operation, i.e. the power angle. This concept is of great significance in power system analysis, especially in studying the dynamic behavior and stability of VSG. VSG power angle is similar to the concept of power angle of actual synchronous generators, but VSG does not have actual rotating mechanical components, but simulates the rotational inertia and damping characteristics of the rotor through control algorithms. The study of VSG power angle stability involves multiple aspects, including control strategies, system parameter design, and the influence of external disturbances, etc. For example, by changing the virtual inertia ( ) and damping coefficient ( ) can affect the power angle stability of the system. Increasing virtual inertia can improve the stability of the system to some extent, but at the same time it can also weaken the damping ratio of the system, thereby affecting the frequency stability of the system. Therefore, a balance point needs to be found between virtual inertia and damping to ensure stable operation of the system.

[0064] Figure 5 is a block diagram of amplitude pre-synchronization control in multiple VSGs according to an embodiment of the present application. Referring to Figure 5, the no-load electromotive force adjustment amount is optionally calculated, and the no-load electromotive force reference value is determined according to the no-load electromotive force adjustment amount and the rated no-load electromotive force value, comprising:

[0065] The no-load electromotive force adjustment amount is calculated according to the reactive power instruction value, the actual reactive power value, the voltage-reactive droop coefficient, the grid voltage amplitude, the point of common coupling voltage amplitude, the proportional coefficient of the reactive loop PI controller, and the integral coefficient of the reactive loop PI controller;

[0066] The no-load electromotive force reference value is obtained by superimposing the rated no-load electromotive force value on the no-load electromotive force adjustment amount.

[0067] Optionally, the calculation formula of the no-load electromotive force adjustment amount is as follows:

[0068] ;

[0069] wherein, is the no-load electromotive force adjustment amount, is the reactive power instruction value, is the actual reactive power value, is the voltage-reactive droop coefficient, is the grid voltage amplitude, is the point of common coupling voltage amplitude, is the proportional coefficient of the reactive loop PI controller, is the integral coefficient of the reactive loop PI controller, is the Laplace operator.

[0070] The no-load electromotive force adjustment amount is superimposed on the rated no-load electromotive force value E0 to obtain the no-load electromotive force reference value E ref . The above is the amplitude pre-synchronization process.

[0071] The pre-synchronization algorithm is realized by relying on VSG control. The no-load electromotive force reference value E ref obtained by amplitude pre-synchronization and the power angle of the virtual synchronous generator obtained by frequency and phase pre-synchronization are variables required by VSG control, and the subsequent VSG control block diagram has been omitted, which is content that people with professional background knowledge understand.

[0072] S120, judging whether the n virtual synchronous generators complete pre-synchronization according to preset conditions, and obtaining a judgment result.

[0073] Optionally, the preset conditions include:

[0074] an absolute value of a difference between the grid frequency and an output angular frequency of the virtual synchronous generator is less than a preset pre-synchronization frequency synchronization threshold value;

[0075] an absolute value of a difference between a grid voltage phase angle and a virtual synchronous generator power angle is less than a preset pre-synchronization phase synchronization threshold value;

[0076] an absolute value of a difference between a grid voltage amplitude and a point of common coupling voltage amplitude is less than a preset pre-synchronization amplitude synchronization threshold value.

[0077] judging whether the n VSGs complete pre-synchronization, and the judgment method is that when the following preset conditions are met, the pre-synchronization is completed. The calculation formula of the preset conditions is as follows:

[0078] ;

[0079] wherein, is the grid frequency, is the output angular frequency of the virtual synchronous generator, is the pre-synchronization frequency synchronization threshold value, is the grid voltage phase angle, is the virtual synchronous generator power angle, is the pre-synchronization phase synchronization threshold value, is the grid voltage amplitude, is the point of common coupling voltage amplitude, is the pre-synchronization amplitude synchronization threshold value.

[0080] S130, if the judgment result is that the n virtual synchronous generators do not complete pre-synchronization, returning to continue executing the grid connection pre-synchronization.

[0081] S140, if the judgment result is that the n virtual synchronous generators complete pre-synchronization, closing the first circuit breaker and closing the grid connection pre-synchronization.

[0082] FIG. 6 is a grid connection pre-synchronization control block diagram of a multi-VSG parallel system according to an embodiment of the present application. Referring to FIG. 6, after the n VSGs complete pre-synchronization, the first circuit breaker Kg on the grid side is closed. The n VSGs close the grid connection pre-synchronization function, i.e., the frequency, phase pre-synchronization control quantity is zero, and the voltage reference value of the amplitude pre-synchronization is replaced from the grid voltage amplitude |Vg| to the rated voltage amplitude |V N |.

[0083] The technical scheme of the embodiment of the application provides a photovoltaic inverter or energy storage converter which works as a virtual synchronous generator and is in parallel connection, and a no-communication pre-synchronization method of multiple virtual synchronous generators is provided when realizing off-grid to grid function. The grid-connected pre-synchronization method of the multiple virtual synchronous generator parallel connection system can realize no-communication pre-synchronization, and can also be realized through a communication method, and the control is flexible and simple, and the communication reliability requirement is not high. In summary, the application solves the problems that related technologies rely on communication to transmit control information to multiple VSGs, the communication reliability requirement is high, and the no-communication multiple VSG grid-connected pre-synchronization scheme control is relatively complex.

[0084] FIG. 7 is a waveform diagram of PCC voltage and grid voltage before and after the pre-synchronization signal is set high, provided by the embodiment of the application. Referring to FIG. 7, taking the grid-connected pre-synchronization of a 3-unit 200kW energy storage converter parallel connection system as an example, the rated power of a single converter is 200kW, the rated voltage is 800V, the rated frequency is 50Hz, and the grid frequency is 50Hz. Before and after the grid-connected pre-synchronization function of the multiple VSG parallel connection system is executed under off-grid conditions, the waveform of PCC voltage and grid voltage is shown in FIG. 7, the horizontal coordinate unit is s, and the vertical coordinate unit is V. In the figure, channel 0 is PCC voltage, channel 1 is grid voltage, and channel 2 is pre-synchronization signal. Setting high indicates that the pre-synchronization function is executed, and clearing indicates that the pre-synchronization function is closed. When off-grid operation, due to the action of the droop link, the initial frequency of PCC voltage is not 50Hz, and therefore, the phase deviation of PCC voltage and grid voltage is large or small. At 21.46s, the pre-synchronization function is started.

[0085] FIG. 8 is a waveform diagram of PCC voltage frequency provided by the embodiment of the application, and the entire grid-connected pre-synchronization process is shown. Referring to FIG. 8, the PCC voltage frequency waveform of the entire multiple VSG parallel connection system pre-synchronization process is shown in FIG. 8, the horizontal coordinate unit is s, and the vertical coordinate unit is Hz. Due to the action of the droop link, when the system works off-grid, the PCC voltage frequency is about 49.6Hz. At 21.46s, the pre-synchronization function is started, the PCC voltage frequency gradually changes to 50Hz, and finally stabilizes at about 50Hz with a fluctuation amplitude of less than 0.1Hz. At 32.75s, the grid-connected breaker Kg is closed, and after grid connection, the PCC voltage frequency is equal to the grid frequency, which is 50Hz. At 34.05s, the pre-synchronization function is closed, the PCC voltage frequency temporarily decreases and then quickly recovers to 50Hz.

[0086] FIG. 9 is a waveform diagram of the PCC voltage and the grid voltage after pre-synchronization according to an embodiment of the present application. Referring to FIG. 9, the waveform of the PCC voltage and the grid voltage after pre-synchronization is shown in FIG. 9, where the horizontal axis unit is s and the vertical axis unit is V. At about 29s, the PCC voltage and the grid voltage are substantially consistent in frequency, phase, and amplitude, and the frequency difference, the phase difference, and the amplitude difference are all less than the threshold value, so the grid breaker can be closed and connected to the grid. The above verifies the effectiveness of the pre-synchronization method of the multi-VSG parallel system.

[0087] FIG. 10 shows a structural schematic diagram of an electronic device 1 that can be used to implement embodiments of the present application. The electronic device is intended to represent a variety of forms of digital computers, such as laptops, desktops, workstations, personal digital assistants, servers, blade servers, mainframes, and other appropriate computers. The electronic device can also represent a variety of forms of mobile devices, such as personal digital processors, cellular telephones, smart phones, wearable devices (e.g., headsets, glasses, watches, etc.), and other similar computing devices. The components shown herein, their connections and relationships, and their functions, are meant to be examples only, and are not intended to limit the implementations of the present application described and / or claimed in this document.

[0088] As shown in FIG. 10, the electronic device 1 includes at least one processor 11, and a memory, such as a Read-Only Memory (ROM) 12, a Random Access Memory (RAM) 13, etc., which is communicatively connected to the at least one processor 11, wherein the memory stores a computer program that can be executed by the at least one processor. The processor 11 can perform various appropriate actions and processes according to the computer program stored in the Read-Only Memory (ROM) 12 or loaded from the storage unit 18 into the Random Access Memory (RAM) 13. In the RAM 13, various programs and data required for the operation of the electronic device 1 can also be stored. The processor 11, the ROM 12, and the RAM 13 are connected to each other through a bus 14. An Input / Output (I / O) interface 15 is also connected to the bus 14.

[0089] Various components in the electronic device 1 are connected to the I / O interface 15, including an input unit 16, such as a keyboard, a mouse, etc.; an output unit 17, such as various types of displays, a loudspeaker, etc.; a storage unit 18, such as a magnetic disk, an optical disk, etc.; and a communication unit 19, such as a network card, a modem, a wireless communication transceiver, etc. The communication unit 19 allows the electronic device 1 to exchange information / data with other devices through a computer network, such as the Internet, and / or various telecommunications networks.

[0090] The processor 11 can be various general-purpose and / or special-purpose processing components with processing and computing capabilities. Some examples of the processor 11 include, but are not limited to, a Central Processing Unit (CPU), a Graphics Processing Unit (GPU), various specialized Artificial Intelligence (AI) computing chips, various processors running machine learning model algorithms, a Digital Signal Processor (DSP), and any appropriate processor, controller, microcontroller, etc. The processor 11 performs various methods and processes described above, e.g., the grid pre-synchronization method of the virtual synchronous generator parallel system.

[0091] In some embodiments, the grid pre-synchronization method of the virtual synchronous generator parallel system can be implemented as a computer program tangibly embodied in a computer readable storage medium, e.g., the storage unit 18. In some embodiments, part or all of the computer program can be loaded and / or installed onto the electronic device 1 via the ROM 12 and / or the communication unit 19. When the computer program is loaded onto the RAM 13 and executed by the processor 11, one or more steps of the grid pre-synchronization method of the virtual synchronous generator parallel system described above can be performed. Alternatively, in other embodiments, the processor 11 can be configured to perform the grid pre-synchronization method of the virtual synchronous generator parallel system by other any appropriate means, e.g., by means of firmware.

[0092] Various implementations of the systems and techniques described above can be realized in digital electronic circuitry, integrated circuitry, a Field-Programmable Gate Array (FPGA), an Application-Specific Integrated Circuit (ASIC), an Application Specific Standard Parts (ASSP), a System on Chip (SOC), a Complex Programmable Logic Device (CPLD), computer hardware, firmware, software, and / or combinations thereof. These various implementations can include implementation in one or more computer programs that are executable and / or interpretable on a programmable system including at least one programmable processor, which can be special or general purpose, coupled to receive data and instructions from, and to transmit data and instructions to, a storage system, at least one input device, and at least one output device.

[0093] Computer programs implementing methods of the present application can be written in any combination of one or more programming languages. These computer programs can be provided to a processor of a general purpose computer, special purpose computer, or other programmable data processing apparatus to produce a machine, such that the computer program, when executed by the processor of the machine, implements the functions / acts specified in the flow diagrams and / or block diagrams. The computer program can be executed entirely on a machine, partially on a machine, partially on a machine as part of a standalone software package, partially on a machine and partially on a remote machine or entirely on a remote machine or server.

[0094] In the context of this application, a computer readable storage medium can be a tangible medium that can contain or store a computer program for use by or in connection with an instruction execution system, apparatus, or device. A computer readable storage medium can include, but is not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any suitable combination of the foregoing. Alternatively, a computer readable storage medium can be a machine readable signal medium. Examples of a machine readable signal medium will include one or any combination of a line based electrical connection, a portable computer disk, a hard disk, a random access memory (RAM), a read only memory (ROM), an erasable programmable read only memory (EPROM) or a flash memory, a fiber optic, a compact disk read only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing.

[0095] To provide for interaction with a user, the systems and techniques described here can be implemented on an electronic device having a display device (e.g., a Cathode Ray Tube (CRT) or a Liquid Crystal Display (LCD) monitor) for displaying information to the user and a keyboard and a pointing device (e.g., a mouse or a trackball) by which the user can provide input to the electronic device. Other kinds of devices can be used to provide for interaction with a user as well; for example, feedback provided to the user can be any form of sensory feedback (e.g., visual feedback, auditory feedback, or tactile feedback); and input from the user can be received in any form, including acoustic, speech, or tactile input.

[0096] The systems and techniques described here can be implemented in a computing system that includes a back end component (e.g., as a data server), or that includes a middleware component (e.g., an application server), or that includes a front end component (e.g., a user computer having a graphical user interface or a Web browser through which a user can interact with an implementation of the systems and techniques described here), or any combination of such back end, middleware, or front end components. The components of the system can be interconnected by any form or medium of digital data communication (e.g., a communication network). Examples of communication networks include a local area network (LAN), a wide area network (WAN), a blockchain network, and the Internet.

[0097] The computing system can include clients and servers. A client and server are generally remote from each other and typically interact through a communication network. The relationship of client and server arises by virtue of computer programs running on the respective computers and having a client-server relationship to each other. The server can be a cloud server, also known as a cloud computing server or cloud host, which is a host product in the cloud computing service system, to solve the defects of large management difficulty and weak business scalability in traditional physical host and virtual private server (VPS) services.

[0098] It should be understood that the steps shown in the above forms of flow can be reordered, added or deleted. For example, the steps described in this application can be executed in parallel, sequentially or in different order, as long as the desired results of the technical solutions of this application can be achieved, which are not limited herein.

Claims

1. A method of grid pre-synchronization for a virtual synchronous generator parallel system, the virtual synchronous generator parallel system comprising: n virtual synchronous generators, an AC bus and a first circuit breaker, AC outputs of the n virtual synchronous generators are connected in parallel with the AC bus, the first circuit breaker is connected between the AC bus and a power grid, and n is an integer greater than or equal to 2; The grid-connected pre-synchronization method of the virtual synchronous generator parallel system comprises: After the n virtual synchronous generators receive the pre-synchronization instruction, the grid-connected pre-synchronization is started to be executed, and the grid-connected pre-synchronization comprises frequency and phase pre-synchronization and amplitude pre-synchronization; The frequency and phase pre-synchronization comprises: calculating a frequency and phase pre-synchronization control quantity, calculating a damping power according to the frequency and phase pre-synchronization control quantity, calculating an output angular frequency difference of the virtual synchronous generator according to a mechanical power, an electromagnetic power and the damping power, and determining a power angle of the virtual synchronous generator according to the output angular frequency difference of the virtual synchronous generator and a rated angular frequency; The amplitude pre-synchronization comprises: calculating a no-load electromotive force adjustment quantity, and determining a no-load electromotive force reference value according to the no-load electromotive force adjustment quantity and a rated no-load electromotive force value; A judgment result is obtained according to a preset condition whether the n virtual synchronous generators complete the pre-synchronization; In response to the judgment result that the n virtual synchronous generators do not complete the pre-synchronization, the grid-connected pre-synchronization is continued to be executed; In response to the judgment result that the n virtual synchronous generators complete the pre-synchronization, the first circuit breaker is closed and the grid-connected pre-synchronization is closed.

2. The method of claim 1, wherein, The preset condition comprises: An absolute value of a difference between a power grid frequency and an output angular frequency difference of the virtual synchronous generator is less than a set pre-synchronization frequency synchronization threshold value; An absolute value of a difference between a power grid voltage phase angle and a power angle difference of the virtual synchronous generator is less than a set pre-synchronization phase synchronization threshold value; An absolute value of a difference between a power grid voltage amplitude and a point of common coupling voltage amplitude is less than a set pre-synchronization amplitude synchronization threshold value.

3. The method of claim 1, wherein, The calculation of the frequency and phase pre-synchronization control quantity, the calculation of the damping power according to the frequency and phase pre-synchronization control quantity, the calculation of the output angular frequency difference of the virtual synchronous generator according to the mechanical power, the electromagnetic power and the damping power, and the determination of the power angle of the virtual synchronous generator according to the output angular frequency difference of the virtual synchronous generator and the rated angular frequency comprise: The grid voltage obtained by the virtual synchronous generator is subjected to phase-locked loop control to obtain the power grid voltage phase angle; Park transformation is performed on the point of common coupling voltage according to the power grid voltage phase angle to obtain the point of common coupling voltage d-axis and q-axis components in a rotating coordinate system, and proportional integral (PI) control is performed on the point of common coupling voltage q-axis component to obtain the frequency and phase pre-synchronization control quantity; The mechanical power is calculated according to the frequency and phase pre-synchronization control quantity, the rated angular frequency, a frequency-active droop coefficient, an angular frequency difference controlled by the virtual synchronous generator and an active instruction value, and the damping power is calculated according to the angular frequency difference controlled by the virtual synchronous generator, the rated angular frequency and a damping coefficient of the virtual synchronous generator; According to the mechanical power, the electromagnetic power, the damping power, the virtual inertia, and the rated angular frequency, an output angular frequency difference of the virtual synchronous generator is calculated, and the output angular frequency difference of the virtual synchronous generator is integrated after being superimposed on the rated angular frequency to obtain a power angle of the virtual synchronous generator.

4. The method of claim 3, wherein, The grid voltage obtained by the virtual synchronous generator is subjected to phase-locked loop control to obtain a grid voltage phase angle, and the grid voltage phase angle comprises: Park transformation is performed on the grid voltage to obtain d-axis and q-axis components of the grid voltage in a rotating coordinate system, PI control is performed on the q-axis component of the grid voltage, and the grid frequency is obtained by adding the rated angular frequency, and the grid voltage phase angle is obtained by integrating the grid frequency.

5. The method of claim 4, wherein, The calculation formula of the q-axis component of the grid voltage is as follows: ； wherein for the grid voltage q-axis component, 、 、 respectively three-phase voltages, The grid voltage phase angle is obtained by integrating the grid frequency. The calculation formula of the q-axis component of the point of common coupling voltage is as follows: ； wherein, for the common coupling point voltage q-axis component, 、 、 the three-phase common coupling point voltages, respectively, The grid voltage phase angle is obtained by integrating the grid frequency.

6. The method of claim 3, wherein, The calculation formula of the mechanical power is as follows: ； wherein for mechanical power, for the active command value, for the output angular frequency difference of the virtual synchronous generator, for the rated angular frequency, for the frequency-active droop coefficient, The frequency and phase pre-synchronization control quantity are obtained by integrating the grid frequency. The calculation formula of the damping power is as follows: ； wherein, to dampen power, for the output angular frequency difference of the virtual synchronous generator, for the rated angular frequency, The damping coefficient of the virtual synchronous generator is obtained by integrating the grid frequency. The calculation formula of the output angular frequency difference of the virtual synchronous generator is as follows: ； wherein for the output angular frequency difference of the virtual synchronous generator, for mechanical power, for electromagnetic power, to dampen the power, for virtual inertia, for the rated angular frequency, The Laplace operator is obtained by integrating the grid frequency.

7. The method of claim 1, wherein, The no-load electromotive force reference value is determined according to the no-load electromotive force regulation quantity and a rated no-load electromotive force value, and the no-load electromotive force regulation quantity is calculated according to the reactive power instruction value, the actual reactive power value, the voltage-reactive power droop coefficient, the grid voltage amplitude, the point of common coupling voltage amplitude, the proportional coefficient of the reactive power ring PI controller, and the integral coefficient of the reactive power ring PI controller. The no-load electromotive force reference value is obtained by superimposing the rated no-load electromotive force value on the no-load electromotive force regulation quantity. The calculation formula of the no-load electromotive force regulation quantity is as follows:

8. The method of claim 7, wherein, The Laplace operator is obtained by integrating the grid frequency. ； wherein, for the no-load electromotive force, for the reactive power command value, for the actual real power value, for voltage-reactive droop coefficients, for the grid voltage amplitude, for the public coupling point voltage amplitude, Kp is a proportional coefficient of the reactive loop PI controller, Kp is a proportional coefficient of the PI controller, 9.An electronic device, comprising: one or more processors; a memory configured to store one or more programs; when the one or more programs are executed by the one or more processors, the one or more processors implement the virtual synchronous generator and the grid connection pre-synchronization method of the system according to any one of claims 1-8. The computer program is executed by the processor to implement the virtual synchronous generator and the grid connection pre-synchronization method of the system according to any one of claims 1-8.

10. A computer readable storage medium having stored thereon a computer program, wherein, ​

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