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

Abstract

The application discloses a grid-connected pre-synchronization method and electronic equipment of a virtual synchronous generator parallel system. The grid-connected pre-synchronization method of the virtual synchronous generator parallel system comprises the following steps: after 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; the frequency, phase pre-synchronization comprises the following steps: a frequency, phase pre-synchronization control quantity is calculated, a damping power is calculated according to the frequency, phase pre-synchronization control quantity, an output angular frequency difference of the virtual synchronous generator is calculated according to mechanical power, electromagnetic power and the damping power, and a virtual synchronous generator power angle is determined according to the output angular frequency difference of the virtual synchronous generator and a rated angular frequency. The application can realize non-communication pre-synchronization, and can also be realized through a communication method, is flexible and simple to control, and has low requirements on communication reliability.

Description

TECHNICAL FIELD

[0001] The embodiment of the present application relates to the field of new energy power generation technology, and particularly relates to a grid-connected pre-synchronization method of a virtual synchronous generator parallel system and electronic equipment. BACKGROUND

[0002] With the proposal of the target of constructing 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, and too much proportion of new energy power generation will weaken the strength of the power grid and lack voltage, frequency, inertia support and the like. In recent years, grid-connected converters mainly controlled by virtual synchronous generators (VSG) can improve the voltage, frequency and inertia support capacity of the power system, and are widely researched and applied. The capacity and overcurrent capacity of new energy power generation equipment based on power electronic devices are far lower than those of traditional synchronous generators, and 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 the off-grid state to the 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 reduce the impact current at the grid-connected moment. Meanwhile, the VSG-controlled converter can be regarded as a voltage source, and 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, threatening the safety of the converter. Therefore, how to synchronously implement grid-connected pre-synchronization control when multiple VSGs are parallel-connected is one of the technical difficulties.

[0003] 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 issues it to each VSG through communication. Patent 202310238937.1 transfers active and reactive power information between VSGs in the form of 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 transfer control information to each VSG, and have high requirements for communication reliability. Patent 201710692259.0 only issues a working mode signal to each VSG through a dispatching center, and pre-synchronization is completed in each VSG. Specifically, the pre-synchronization frequency adjustment amount is obtained by closed-loop control using the reactive power deviation between the grid voltage and the PCC voltage. The document (Yan Xiangwu, Wang Desheng, Jia Juxin. Virtual synchronous generator communication-free 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 communication-free multi-VSG grid connection pre-synchronization scheme, but the control is relatively complex. SUMMARY

[0004] The present application provides a kind of virtual synchronous generator parallel system's grid connection pre-synchronization method and electronic equipment, solve the problem of relatively complex control of multi-VSG grid connection pre-synchronization scheme, can realize communication-free pre-synchronization, also can be realized by communication method, control is flexible and simple, and the requirement of communication reliability is not high.

[0005] According to an aspect of the present application, a grid connection pre-synchronization method for a virtual synchronous generator parallel system is provided, the virtual synchronous generator parallel system comprising: n virtual synchronous generators, an AC bus and a first circuit breaker, the AC outputs of the n virtual synchronous generators being connected in parallel with the AC bus, the first circuit breaker being connected between the AC bus and a grid, and n being an integer greater than or equal to 2.

[0006] The grid connection pre-synchronization method for the virtual synchronous generator parallel system comprises:

[0007] After receiving the pre-synchronization instruction, the n virtual synchronous generators start to perform grid connection pre-synchronization, and the grid connection pre-synchronization includes frequency, phase and amplitude pre-synchronization.

[0008] The frequency and phase presynchronization comprises: calculating a frequency and phase presynchronization control quantity, calculating damping power according to the frequency and phase presynchronization control quantity, calculating an output angular frequency difference of the virtual synchronous generator according to mechanical power, 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;

[0009] 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;

[0010] According to a preset condition, it is determined whether the n virtual synchronous generators complete presynchronization, and a determination result is obtained;

[0011] If the determination result is that the n virtual synchronous generators do not complete presynchronization, the grid-connected presynchronization is continued to be executed;

[0012] If the determination result is that the n virtual synchronous generators complete presynchronization, the first circuit breaker is closed and the grid-connected presynchronization is closed.

[0013] Optionally, the preset condition comprises:

[0014] An absolute value of a grid voltage phase angle and a virtual synchronous generator power angle difference value is less than a preset presynchronization phase synchronization threshold value;

[0015] An absolute value of a grid voltage amplitude and a point of common coupling voltage amplitude difference value is less than a preset presynchronization amplitude synchronization threshold value.

[0016] An absolute value of a grid voltage amplitude and a point of common coupling voltage amplitude difference value is less than a preset presynchronization amplitude synchronization threshold value.

[0017] Optionally, the calculating a frequency and phase presynchronization control quantity, calculating damping power according to the frequency and phase presynchronization control quantity, calculating an output angular frequency difference of the virtual synchronous generator according to mechanical power, 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 comprises:

[0018] The grid voltage phase angle is obtained by phase-locked loop control on the grid voltage obtained by the virtual synchronous generator;

[0019] The point of common coupling voltage d-axis and q-axis components in a rotating coordinate system are obtained by Park transformation on the point of common coupling voltage according to the grid voltage phase angle, and the frequency and phase presynchronization control quantity is obtained by PI control on the point of common coupling voltage q-axis component;

[0020] According to the frequency, phase pre-synchronization control quantity, rated angular frequency, frequency-active droop coefficient, virtual synchronous generator control angular frequency difference and active instruction value, mechanical power is calculated, and according to the virtual synchronous generator control angular frequency difference, the rated angular frequency and virtual synchronous generator damping coefficient, damping power is calculated;

[0021] According to the mechanical power, electromagnetic power, the damping power, virtual inertia, the rated angular frequency, the output angular frequency difference of the virtual synchronous generator is calculated, and after the output angular frequency difference of the virtual synchronous generator is superimposed on the rated angular frequency, integral operation is carried out to obtain the virtual synchronous generator power angle.

[0022] Optionally, the grid voltage phase angle obtained by the phase-locked loop control on the grid voltage obtained by the virtual synchronous generator comprises:

[0023] Park transformation is performed on the grid voltage to obtain d-axis and q-axis components of the grid voltage in the rotating coordinate system, PI control is performed on the q-axis component of the grid voltage, and the rated angular frequency is added to obtain the grid frequency, and the grid frequency is integrated to obtain the grid voltage phase angle.

[0024] Optionally, the calculation formula of the q-axis component of the grid voltage is as follows:

[0025]

[0026] Wherein, v gq is the q-axis component of the grid voltage, V ga , V gb , V gc are three-phase voltages, and θ g is the grid voltage phase angle.

[0027] The calculation formula of the q-axis component of the point of common coupling voltage is as follows:

[0028]

[0029] Wherein, v PCCq is the q-axis component of the point of common coupling voltage, V PCCa , V PCCb , V PCCc are three-phase point of common coupling voltages, and θ g is the grid voltage phase angle.

[0030] Optionally, the calculation formula of the mechanical power is as follows:

[0031] P m = P ref + Δω·ω0k ω - Δω PS ·ω0kω

[0032] wherein P m is the mechanical power, P ref is the active command value, Δω is the output angular frequency difference of the virtual synchronous generator, ω0 is the rated angular frequency, k ω is the frequency-active droop coefficient, Δω PS is the frequency, phase pre-synchronization control quantity;

[0033] The calculation formula of the damping power is as follows:

[0034] P D = Δω·ω0D

[0035] wherein P D is the damping power, Δω is the output angular frequency difference of the virtual synchronous generator, ω0 is the rated angular frequency, and D is the damping coefficient of the virtual synchronous generator;

[0036] The calculation formula of the output angular frequency difference of the virtual synchronous generator is as follows:

[0037]

[0038] wherein Δω is the output angular frequency difference of the virtual synchronous generator, P m is the mechanical power, P e is the electromagnetic power, P D is the damping power, J is the virtual inertia, ω0 is the rated angular frequency, and s is the Laplace operator.

[0039] Optionally, the calculation of the no-load electromotive force adjustment quantity, the determination of the no-load electromotive force reference value according to the no-load electromotive force adjustment quantity and the rated no-load electromotive force value comprises:

[0040] The no-load electromotive force adjustment quantity is calculated according to the reactive power command 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 ring PI controller and the integral coefficient of the reactive ring PI controller.

[0041] The no-load electromotive force reference value is obtained by superimposing the no-load electromotive force adjustment quantity on the rated no-load electromotive force value.

[0042] Optionally, the calculation formula of the no-load electromotive force adjustment quantity is as follows:

[0043]

[0044] wherein ΔE is the no-load electromotive force adjustment quantity, Q ref is the reactive power command value, Q e is the actual reactive power value, k vV is the voltage-reactive droop coefficient, |V g V is the grid voltage amplitude, |V PCC V is the point of common coupling voltage amplitude, k vp K is the proportional coefficient of the reactive loop PI controller vi K is the integral coefficient of the reactive loop PI controller, s is the Laplace operator.

[0045] According to another aspect of the present application, there is also provided an electronic device comprising:

[0046] one or more processors;

[0047] a memory for storing one or more programs;

[0048] When the one or more programs are executed by the one or more processors, the one or more processors implement the method for grid-connected pre-synchronization of a virtual synchronous generator and grid-connected system as described in any embodiment of the present application.

[0049] The embodiments of the present application also provide a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the method for grid-connected pre-synchronization of a virtual synchronous generator and grid-connected system as described in any embodiment of the present application.

[0050] The technical solution of the embodiments of the present application provides a method for grid-connected pre-synchronization of a plurality of virtual synchronous generators (VSGs) in parallel connection, wherein the VSGs are operated as virtual synchronous generators by photovoltaic inverters or energy storage converters. When the off-grid operation is switched to the grid-connected operation, the method for grid-connected pre-synchronization of a plurality of VSGs in parallel connection can realize the pre-synchronization without communication, or can be realized through communication, and the control is flexible and simple, and the communication reliability requirement is not high. In summary, the present application solves the problems in the prior art that the control information needs to be transmitted to each VSG through communication, the communication reliability requirement is high, and the control of the pre-synchronization of a plurality of VSGs without communication is relatively complex.

[0051] It should be understood that the content described in this part is not intended to identify key or important features of the embodiments of the present application, nor is it used to limit the scope of the present application. Other features of the present application will become apparent through the following description. BRIEF DESCRIPTION OF DRAWINGS

[0052] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed in the embodiment description will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0053] Figure 1is a circuit diagram of a virtual synchronous generator parallel system provided by an embodiment of the present application;

[0054] Figure 2 is a flow chart of a grid-connected pre-synchronization method of a virtual synchronous generator parallel system provided by an embodiment of the present application;

[0055] Figure 3 is a frequency, phase pre-synchronization control block diagram in each VSG provided by an embodiment of the present application;

[0056] Figure 4 is an active power loop control block diagram in each VSG provided by an embodiment of the present application;

[0057] Figure 5 is an amplitude pre-synchronization control block diagram in each VSG provided by an embodiment of the present application;

[0058] Figure 6 is a grid-connected pre-synchronization control block diagram of a multi-VSG parallel system provided by an embodiment of the present application;

[0059] Figure 7 is a waveform diagram of the PCC voltage and the grid voltage before and after the pre-synchronization signal is set high provided by an embodiment of the present application;

[0060] Figure 8 is a PCC voltage frequency waveform diagram of the entire grid-connected pre-synchronization process provided by an embodiment of the present application;

[0061] Figure 9 is a waveform diagram of the PCC voltage and the grid voltage after the pre-synchronization provided by an embodiment of the present application;

[0062] Figure 10 is a structural diagram of an electronic device provided by an embodiment of the present application. DETAILED DESCRIPTION

[0063] In order to enable persons skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part 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 persons skilled in the art without creative labor should belong to the protection scope of the present application.

[0064] It should be noted that the terms "first", "second" and the like in the description and in the claims of the present application and the above-described accompanying drawings are used to distinguish similar objects, and do not necessarily indicate 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 application described herein can be implemented in other than the order 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 list of steps or units does not necessarily limit to those steps or units clearly listed, but can include other steps or units not clearly listed or inherent to such processes, methods, products or devices.

[0065] The embodiment of the present application provides a grid-connected pre-synchronization method of a virtual synchronous generator and grid-connected system, Figure 1 is a circuit diagram of a virtual synchronous generator and grid-connected system according to the embodiment of the present application, referring to Figure 1 The virtual synchronous generator and grid-connected system comprises n virtual synchronous generators (VSG1, VSG2,..., VSGn), an alternating-current bus and a first circuit breaker Kg, alternating-current output ends of the n virtual synchronous generators are connected in parallel with the alternating-current bus, the first circuit breaker Kg is connected between the alternating-current bus and a power grid, and n is an integer greater than or equal to 2.

[0066] Specifically, a typical multi-VSG grid-connected system is as shown in Figure 1 The n VSG alternating-current output ends are connected in parallel with the alternating-current bus, which is referred to as a point of common coupling (PCC), the PCC is connected with the power grid through the 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 grid-connected system works in an off-grid mode, and the second circuit breaker K L on the load side can be closed or disconnected. Before the first circuit breaker Kg is closed to grid-connect the multi-VSG grid-connected system, grid-connected pre-synchronization control needs to be performed, the control is completed in each VSG, after all the VSGs complete the grid-connected pre-synchronization, the first circuit breaker Kg is closed, and the grid-connected system is grid-connected and runs. In the pre-synchronization process, each VSG directly samples the power grid voltage Vg through a sensor, and can realize a non-communication pre-synchronization scheme; or the VGS1 samples the power grid voltage Vg, then communicates with other VGSs, and sends the power grid voltage information to each VSG through a communication line, to become a communication-based pre-synchronization scheme. In practice, the communication-based pre-synchronization scheme can be selected according to communication reliability. Compared with the prior art, the control of the embodiment is flexible and simple.

[0067] Figure 2 is a flow chart of a grid-connected pre-synchronization method of a virtual synchronous generator and grid-connected system according to the embodiment of the present application, referring toFigure 2 The grid-connected pre-synchronization method of the virtual synchronous generator and system includes:

[0068] S110, after receiving the pre-synchronization instruction, the n virtual synchronous generators start to perform the grid-connected pre-synchronization, and the grid-connected pre-synchronization includes frequency, phase pre-synchronization and amplitude pre-synchronization.

[0069] The frequency, phase pre-synchronization includes: calculating a frequency, phase pre-synchronization control quantity, calculating damping power according to the frequency, phase pre-synchronization control quantity, calculating an output angular frequency difference of the virtual synchronous generator according to the mechanical power, the electromagnetic power and the damping power, and determining a virtual synchronous generator power angle according to the output angular frequency difference of the virtual synchronous generator and the rated angular frequency.

[0070] The amplitude pre-synchronization includes: 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 the rated no-load electromotive force value.

[0071] Specifically, after receiving the pre-synchronization instruction, all the n VSGs start to perform the pre-synchronization, including the frequency, phase pre-synchronization and the amplitude pre-synchronization.

[0072] Figure 3 is a frequency, phase pre-synchronization control block diagram in each VSG according to an embodiment of the present application, referring to Figure 3 Optionally, the calculating of the frequency, phase pre-synchronization control quantity, the calculating of the damping power according to the frequency, phase pre-synchronization control quantity, the calculating 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 determining of the virtual synchronous generator power angle according to the output angular frequency difference of the virtual synchronous generator and the rated angular frequency include: performing phase-locked loop control on the grid voltage obtained by the virtual synchronous generator to obtain a grid voltage phase angle.

[0073] Continuing to refer to Figure 3 Optionally, the performing of the phase-locked loop control on the grid voltage obtained by the virtual synchronous generator to obtain the grid voltage phase angle includes: performing Park transformation on the grid voltage to obtain d-axis and q-axis components of the grid voltage in a rotating coordinate system, performing PI control on the q-axis component of the grid voltage and adding the rated angular frequency to obtain the grid frequency, and integrating the grid frequency to obtain the grid voltage phase angle.

[0074] Optionally, the calculation formula of the q-axis component of the grid voltage is as follows:

[0075]

[0076] Wherein, v gq is the q-axis component of the grid voltage, V ga , V gb , V gc are three-phase voltages, and θ gis the grid voltage phase angle.

[0077] Specifically, the q-axis component of the grid voltage v gq Δω is obtained through PI control g , added to the rated angular frequency ω0 to obtain the grid frequency ω g ,ω g Integrate to get the grid voltage phase angle θ g .

[0078] Continue to refer Figure 3 According to the grid voltage phase angle, the common coupling point voltage is subjected to Park transformation to obtain the d-axis and q-axis components of the common coupling point voltage in the rotating coordinate system. The q-axis component of the common coupling point voltage is subjected to PI control to obtain the frequency and phase pre-synchronization control quantities.

[0079] Optionally, the calculation formula of the q-axis component of the common coupling point voltage is as follows:

[0080]

[0081] Among them, v PCCq is the q-axis component of the common coupling point voltage, V PCCa 、V PCCb 、V PCCc are the three-phase common coupling point voltages, θ g is the grid voltage phase angle.

[0082] Specifically, the q-axis common coupling point voltage v PCCq The frequency and phase pre-synchronization control quantities Δω are obtained through PI control PS .

[0083] Figure 4 This is a block diagram of the active power loop control of each VSG provided according to an embodiment of the present invention, refer to Figure 4 The mechanical power is calculated based on the frequency, phase pre-synchronization control quantity, rated angular frequency, frequency-active power droop coefficient, angular frequency difference of virtual synchronous generator control and active power instruction value, and the damping power is calculated based on the angular frequency difference of virtual synchronous generator control, rated angular frequency and virtual synchronous generator damping coefficient.

[0084] Specifically, such as Figure 4 As shown, the frequency and phase pre-synchronization control amount Δω PS Frequency and phase pre-synchronization has been achieved at the active power instruction acting on the VSG active power loop.

[0085] Continue to refer Figure 4The output angular frequency difference of the virtual synchronous generator is calculated according to mechanical power, electromagnetic power, damping power, virtual inertia, and rated angular frequency, and the output angular frequency difference of the virtual synchronous generator is integrated after being superimposed with the rated angular frequency to obtain the power angle of the virtual synchronous generator.

[0086] Optionally, the calculation formula of the mechanical power is as follows:

[0087] P m = P ref + Δω·ω0k ω - Δω PS · ω0k ω

[0088] wherein P m is the mechanical power, P ref is the active instruction value, Δω is the output angular frequency difference of the virtual synchronous generator, ω0 is the rated angular frequency, k ω is the frequency-active droop coefficient, and Δω PS is the frequency and phase pre-synchronization control quantity.

[0089] Specifically, the active instruction value P ref is subtracted by the value of the output angular frequency difference Δω of the virtual synchronous generator multiplied by the rated angular frequency and the frequency-active droop coefficient k ω , and then subtracted by the value of the frequency and phase pre-synchronization control quantity Δω PS multiplied by the rated angular frequency ω0 and the frequency-active droop coefficient k ω , and finally the mechanical power P m is obtained.

[0090] The calculation formula of the damping power is as follows:

[0091] P D = Δω·ω0D

[0092] wherein P D is the damping power, Δω is the output angular frequency difference of the virtual synchronous generator, ω0 is the rated angular frequency, and D is the damping coefficient of the virtual synchronous generator.

[0093] The calculation formula of the output angular frequency difference of the virtual synchronous generator is as follows:

[0094]

[0095] wherein Δω is the output angular frequency difference of the virtual synchronous generator, P m is the mechanical power, P e is the electromagnetic power, P D is the damping power, J is the virtual inertia, ω0 is the rated angular frequency, and s is the Laplace operator.

[0096] Specifically, the output angular frequency difference Δω of the virtual synchronous generator is integrated after being superimposed with the rated angular frequency ω0 to obtain the power angle δ of the virtual synchronous generator. The above is the frequency and phase pre-synchronization process.

[0097] VSG power angle refers to the phase difference between the output power and the grid voltage of a virtual synchronous generator (VSG) 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 (J) and damping coefficient (D), the power angle stability of the system can be affected. Increasing virtual inertia can improve the stability of the system to a certain extent, but at the same time, it may 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.

[0098] Figure 5 is a VSG amplitude pre-synchronization control block diagram according to an embodiment of the application, referring to Figure 5 Optionally, the no-load electromotive force adjustment amount is 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:

[0099] 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 ring PI controller, and the integral coefficient of the reactive ring PI controller, the no-load electromotive force adjustment amount is calculated;

[0100] The no-load electromotive force adjustment amount is superimposed with the rated no-load electromotive force value to obtain the no-load electromotive force reference value.

[0101] Optionally, the calculation formula of the no-load electromotive force adjustment amount is as follows:

[0102]

[0103] where ΔE is the no-load electromotive force adjustment amount, Q ref is the reactive power instruction value, Q e is the actual reactive power value, k v is the voltage-reactive power droop coefficient, |V g | is the grid voltage amplitude, |V PCC | is the point of common coupling voltage amplitude, k vp is the proportional coefficient of the reactive ring PI controller, k viis the integral coefficient of the reactive loop PI controller, and s is the Laplace operator.

[0104] Specifically, the no-load electromotive force adjustment value ΔE is added to 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.

[0105] It should be noted that the pre-synchronization algorithm is implemented based on the VSG control. ref The virtual synchronous generator power angle δ obtained by frequency and phase pre-synchronization is a variable required for VSG control. The subsequent specific VSG control block diagram has been omitted as it is content that people with professional background knowledge can understand.

[0106] S120: Determine whether n virtual synchronous generators have completed pre-synchronization according to preset conditions, and obtain a determination result.

[0107] Optionally, the preset conditions include:

[0108] The absolute value of the difference between the grid frequency and the output angular frequency of the virtual synchronous generator is less than the set pre-synchronization frequency synchronization threshold;

[0109] The absolute value of the difference between the grid voltage phase angle and the virtual synchronous generator power angle is less than the set pre-synchronization phase synchronization threshold;

[0110] The absolute value of the difference between the grid voltage amplitude and the common coupling point voltage amplitude is less than the set pre-synchronization amplitude synchronization threshold.

[0111] Specifically, it is determined whether all n VSGs have completed pre-synchronization. The determination method is that when the following preset conditions are satisfied, pre-synchronization is completed. The calculation formula of the preset conditions is as follows:

[0112]

[0113] Among them, ω g is the grid frequency, ω is the output angular frequency of the virtual synchronous generator, ω th is the pre-synchronization frequency synchronization threshold, θ g is the grid voltage phase angle, δ is the virtual synchronous generator power angle, θ th is the pre-synchronization phase synchronization threshold, |V g | is the grid voltage amplitude, |V PCC | is the voltage amplitude at the common coupling point, V th is the pre-synchronization amplitude synchronization threshold.

[0114] S130: If the judgment result is that the n virtual synchronous generators have not completed pre-synchronization, the process returns to continue executing grid-connected pre-synchronization.

[0115] S140, if the result of the judgment is that the n virtual synchronous generators complete the pre-synchronization, then close the first circuit breaker and close the grid pre-synchronization.

[0116] Specifically, Figure 6 is a multi-VSG parallel system grid pre-synchronization control block diagram provided by the embodiment of the application, referring to Figure 6 , after the n VSGs complete the pre-synchronization, the first circuit breaker Kg on the side of the power grid is closed. The n VSGs close the grid pre-synchronization function, that is, the frequency and 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 |.

[0117] The technical scheme of the embodiment of the application provides a photovoltaic inverter or energy storage converter as a virtual synchronous generator and parallel connection of multiple machines, and a no-communication pre-synchronization method of multiple virtual synchronous generators is provided when the off-grid to grid function is implemented. The grid pre-synchronization method of the multi-virtual synchronous generator parallel 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 of the prior art, such as high requirement for communication reliability, no-communication multi-VSG grid pre-synchronization scheme control, and relatively complex control.

[0118] Figure 7 is a pre-synchronization signal setting high waveform diagram of the PCC voltage and the grid voltage before and after the pre-synchronization signal is set high, provided by the embodiment of the application, referring to Figure 7 Taking the grid pre-synchronization of a 3*200kW energy storage converter parallel 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 pre-synchronization function of the multi-VSG parallel system is executed under the off-grid condition, the waveform of the PCC voltage and the grid voltage is as shown in Figure 7 , the horizontal coordinate unit is s, the vertical coordinate unit is V, the 0 channel in the figure is the PCC voltage, the 1 channel is the grid voltage, the 2 channel is the pre-synchronization signal, the setting high indicates that the pre-synchronization function is executed, and the zero clearing indicates that the pre-synchronization function is closed. When off-grid operation, due to the droop link, the initial frequency of the PCC voltage is not 50Hz, therefore, the phase deviation of the PCC voltage and the grid voltage is large or small. At 21.46s, the pre-synchronization function is started.

[0119] Figure 8 is a PCC voltage frequency waveform diagram of the entire grid pre-synchronization process, provided by the embodiment of the application, referring to Figure 8 , the PCC voltage frequency waveform of the entire multi-VSG parallel system pre-synchronization process is as shown in Figure 8As shown, the horizontal axis is in seconds, and the vertical axis is in Hz. Due to the droop factor, the PCC voltage frequency is approximately 49.6 Hz when the system is operating off-grid. The pre-synchronization function is activated at 21.46 seconds, and the PCC voltage frequency gradually approaches 50 Hz, eventually stabilizing at around 50 Hz, with a fluctuation of less than 0.1 Hz. The grid-connected circuit breaker Kg is closed at 32.75 seconds, and after grid connection, the PCC voltage frequency equals the grid frequency at 50 Hz. The pre-synchronization function is deactivated at 34.05 seconds, and the PCC voltage frequency briefly drops before quickly recovering to 50 Hz.

[0120] Figure 9 Schematic diagram of the waveforms of the PCC voltage and the grid voltage after pre-synchronization according to an embodiment of the present invention, with reference to Figure 9 After pre-synchronization, the waveforms of PCC voltage and grid voltage are as follows: Figure 9 As shown, the horizontal axis is in seconds, and the vertical axis is in volts. At around 29 seconds, the PCC voltage and the grid voltage are essentially identical in frequency, phase, and amplitude. The frequency, phase, and amplitude differences are all below the threshold, allowing the grid circuit breaker to be closed and connected to the grid. This demonstrates the effectiveness of the presynchronization method for the multi-VSG parallel system.

[0121] Figure 10 A schematic diagram of the structure of an electronic device 1 that can be used to implement an embodiment of the present invention is shown. The electronic device is intended to represent various forms of digital computers, such as laptop computers, desktop computers, workstations, personal digital assistants, servers, blade servers, mainframe computers, and other suitable computers. The electronic device can also represent various forms of mobile devices, such as personal digital processing, cellular phones, smart phones, wearable devices (such as helmets, glasses, watches, etc.) and other similar computing devices. The components shown herein, their connections and relationships, and their functions are merely examples and are not intended to limit the implementation of the present invention described and / or claimed herein.

[0122] like Figure 10 As shown, 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 at least one processor 11. The memory stores a computer program that can be executed by the at least one processor, and processor 11 can perform various appropriate actions and processes according to the computer program stored in read-only memory (ROM) 12 or the computer program loaded from storage unit 18 into random access memory (RAM) 13. Various programs and data required for the operation of electronic device 1 can also be stored in RAM 13. Processor 11, ROM 12, and RAM 13 are connected to each other via bus 14. Input / output (I / O) interface 15 is also connected to bus 14.

[0123] A plurality of 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, speakers, 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 telecommunication networks.

[0124] The processor 11 can be various general 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 special-purpose 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, such as the grid-connection pre-synchronization method of the virtual synchronous generator grid-connected system.

[0125] In some embodiments, the grid-connection pre-synchronization method of the virtual synchronous generator grid-connected system can be implemented as a computer program tangibly embodied in a computer readable storage medium, such as 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-connection pre-synchronization method of the virtual synchronous generator grid-connected system described above can be performed. Alternatively, in other embodiments, the processor 11 can be configured to perform the grid-connection pre-synchronization method of the virtual synchronous generator grid-connected system by any other appropriate means, such as by means of firmware.

[0126] 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), a system on a chip (SOC), a programmable logic device (PLD), a 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.

[0127] Computer programs for implementing the methods of the present application can be written in any combination of one or more programming languages. These computer programs can be implemented on general purpose computers, special purpose computers, or other programmable data processing apparatus to produce the functions / acts specified in the flow diagrams and / or block diagrams. Computer programs can be applied to input data to perform the functions of the present application and to generate output information. The output information can be applied to one or more output devices such as a display screen, printer, storage, etc. These functions / acts performed by the computer programs are referred to as being computer-executed. Computer programs, also referred to as programs, software, software applications, applications, components, or code, can be written in any form of programming language, including compiled or interpreted languages, and can be deployed in any form, including as a stand-alone program or as a module, component, subroutine, or other unit suitable for use in a computing environment. A computer program can be deployed to be executed by a host machine, a server, a client, or other computing device.

[0128] In the context of the present application, a computer-readable storage medium can be a tangible medium that can contain or store computer programs for use by or in connection with an instruction execution system, apparatus, or device. Computer-readable storage media can include, but are not limited to, electronic, magnetic, optical, electromagnetic, infrared, or semiconductor systems, apparatus, or devices, or any suitable combination of the foregoing. Alternatively, a computer-readable storage medium can be a machine-readable signal medium. More specific examples of a machine-readable storage medium will include one or more lines of a program of instructions in a transitory signal form, a portable computer diskette, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or Flash memory), an optical fiber, a portable compact disc read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing.

[0129] 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 CRT (cathode ray tube) or LCD (liquid crystal display) 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.

[0130] The systems and techniques described herein 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 herein, 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.

[0131] 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. A 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 VPS service.

[0132] It should be understood that the various forms of flow shown above can be re-ordered, added to, or deleted from without departing from the scope of the present disclosure. For example, the steps recited in the present disclosure can be executed in parallel, executed in series, or executed in different orders, as long as the desired results of the technical solutions of the present disclosure can be achieved, and the present disclosure is not limited herein.

[0133] The above detailed description does not constitute a limitation on the protection scope of the present application. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent replacements, and improvements made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A method of grid connection pre-synchronization of a virtual synchronous generator parallel system, characterized in that, The virtual synchronous generator parallel system comprises 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, and 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 a pre-synchronization instruction, the n virtual synchronous generators start to perform grid-connected pre-synchronization, and the grid-connected pre-synchronization comprises frequency and phase pre-synchronization and amplitude pre-synchronization; The frequency and phase pre-synchronization comprises: Phase-locked loop control is performed on a power grid voltage obtained by the virtual synchronous generator to obtain a power grid voltage phase angle; Park transformation is performed on a point of common coupling voltage according to the power grid voltage phase angle to obtain d-axis and q-axis components of the point of common coupling voltage in a rotating coordinate system, and PI control is performed on the q-axis component of the point of common coupling voltage to obtain a frequency and phase pre-synchronization control quantity; According to the frequency and phase pre-synchronization control quantity, a rated angular frequency, a frequency-active droop coefficient, an angular frequency difference controlled by a virtual synchronous generator and an active instruction value, mechanical power is calculated, and according to the angular frequency difference controlled by the virtual synchronous generator, the rated angular frequency and a virtual synchronous generator damping coefficient, damping power is calculated; According to the mechanical power, electromagnetic power, the damping power, 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 virtual synchronous generator power angle; The calculation formula of the mechanical power is as follows: P m = P ref + Δω·ω0k ω - Δω PS · ω0k ω where P m is the mechanical power, P ref is the active power reference value, Δω is the output angular frequency difference of the virtual synchronous generator, ω0 is the rated angular frequency, k ω is the frequency-active droop coefficient, Δω PS is the frequency, phase pre-synchronization control quantity; 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; According to a preset condition, whether the n virtual synchronous generators complete pre-synchronization is determined, and a determination result is obtained; If the determination result is that the n virtual synchronous generators do not complete pre-synchronization, the grid-connected pre-synchronization is continued to be performed; If the determination result is that the n virtual synchronous generators complete pre-synchronization, the first circuit breaker is closed and the grid-connected pre-synchronization is closed; The calculation formula of the no-load electromotive force adjustment quantity is as follows: wherein, ΔE is the no-load electromotive force adjustment amount, Q ref is the reactive power command value, Q e is the actual reactive power value, k v is the voltage-reactive droop coefficient, |V g is the grid voltage amplitude, |V PCC is the point of common coupling voltage amplitude, k vp is the proportional coefficient of the reactive loop PI controller, k vi is the integral coefficient of the reactive loop PI controller, s is the Laplace operator.

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 virtual synchronous generator power angle 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 phase-locked loop control on the power grid voltage obtained by the virtual synchronous generator to obtain the power grid voltage phase angle comprises: Park transformation is performed on the power grid voltage to obtain d-axis and q-axis components of the power grid voltage in a rotating coordinate system, PI control is performed on the q-axis component of the power grid voltage, and the rated angular frequency is added to obtain a power grid frequency, and the power grid frequency is integrated to obtain the power grid voltage phase angle.

4. The method of claim 3, wherein, The calculation formula of the q-axis component of the power grid voltage is as follows: wherein v gq is the grid voltage q-axis component, V ga , V gb , V gc are the three-phase voltages, θ g is the grid voltage phase angle; The calculation formula of the common coupling point voltage q-axis component is as follows: where v PCCq is the q-axis component of the common coupling point voltage V PCCa , V PCCb , V PCCc are the three-phase common coupling point voltages, θ g is the grid voltage phase angle.

5. The method of claim 1, wherein, The calculation formula of the damping power is as follows: P D = Δω · ω0D where P D is the damping power, Δω is the output angular frequency difference of the virtual synchronous generator, ω0 is the rated angular frequency, and D is the damping coefficient of the virtual synchronous generator. The calculation formula of the output angular frequency difference of the virtual synchronous generator is as follows: where Δω is the output angular frequency difference of the virtual synchronous generator, P m is the mechanical power, P e is the electromagnetic power, P D is the damping power, J is the virtual inertia, ω0is the rated angular frequency, s is the Laplace operator.

6. The method of claim 1, wherein, The calculation of the no-load electromotive force adjustment amount, and the determination of the no-load electromotive force reference value according to the no-load electromotive force adjustment amount and the rated no-load electromotive force value include: The no-load electromotive force reference value is obtained by superimposing the no-load electromotive force adjustment amount and the rated no-load electromotive force value.

7. An electronic device, comprising: It comprises: One or more processors; Memory for storing 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 grid-connected pre-synchronization method of the virtual synchronous generator and the system as claimed in any one of claims 1-6.

8. A computer-readable storage medium having stored thereon a computer program, characterized in that, The computer program is executed by the processor to implement the grid-connected pre-synchronization method of the virtual synchronous generator and the system as claimed in any one of claims 1-6.

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