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

Abstract

The invention discloses a grid-connected pre-synchronization method of a virtual synchronous generator parallel system and electronic equipment. The grid-connected pre-synchronization method of the virtual synchronous generator parallel system comprises the following steps: n virtual synchronous generators start to execute grid-connected pre-synchronization after receiving a pre-synchronization instruction, wherein the grid-connected pre-synchronization comprises frequency and phase pre-synchronization and amplitude pre-synchronization; the frequency and phase pre-synchronization comprises the steps of calculating frequency and phase pre-synchronization control quantity, calculating damping power according to the frequency and phase pre-synchronization control quantity, and calculating an output angular frequency difference of the virtual synchronous generator according to mechanical power, electromagnetic power and damping power; and determining 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. According to the invention, communication-free pre-synchronization can be realized, communication can also be realized through a communication method, the control is flexible and simple, and the requirement on communication reliability is not high.

Description

Technical Field

[0001] The embodiments of the present invention relate to the technical field of renewable energy power generation, and in particular to a grid-connected pre-synchronization method and electronic equipment for a virtual synchronous generator parallel system. Background Art

[0002] With the goal of building a new power system, the proportion of renewable energy power generation will further increase. However, renewable energy power generation equipment usually works in a grid-following mode to pursue maximum power tracking. Too much renewable energy power generation will weaken the strength of the power grid and lack 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 capabilities of power systems and have been widely studied and applied. However, the capacity and overcurrent capacity of renewable energy power generation equipment based on power electronic devices are much lower than those of traditional synchronous generators. Therefore, it is imperative to parallel multiple machines based on VSG control converters to increase the capacity of the system. Converters based on VSG control can work in an off-grid state. 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 with the grid voltage and reduce the instantaneous impact current of grid connection. At the same time, the converter based on VSG control can be regarded as a voltage source. When multiple voltage sources are connected in parallel and work in off-grid mode, the small frequency, phase, and amplitude differences between the voltage sources will cause considerable circulating current, threatening the safety of the converter. Therefore, how to synchronously realize grid-connected pre-synchronization control when multiple VSGs are connected in parallel is one of the technical difficulties.

[0003] To solve the above problems, Patent 202010064431.X uses a synchronous device to determine the amplitude and frequency difference between the grid voltage and the voltage at the point of common coupling (PCC), adjusts the voltage and frequency according to the set step size, and sends it to each VSG through communication. Patent 202310238937.1 transmits active and reactive information between VSGs in the form of a communication bus, and compensates for the no-load electromotive force and frequency based on the maximum reactive and active information. The above methods all rely on communication to transmit control information to each VSG, and have high requirements for communication reliability. Patent 201710692259.0 only sends a working mode signal to each VSG through the dispatching center, and pre-synchronization is completed in each VSG. Specifically, the reactive power of the deviation between the grid voltage and the PCC voltage is used for closed-loop control to obtain the pre-synchronization frequency adjustment amount. Reference (Yan Xiangwu, Wang Desheng, Jia Jiaoxin. Virtual synchronous generator non-communication pre-synchronization grid-connected scheme based on distributed microgrid [J]. Transactions of China Electrotechnical Society, 2019, 34(19): 4143-53) uses the frequency difference, amplitude difference and constructed virtual active power between the PCC voltage and the grid voltage to achieve frequency, amplitude and phase pre-synchronization respectively. The above two schemes are both multi-VSG grid-connected pre-synchronization schemes without communication, but the control is relatively complex. Summary of the invention

[0004] The present invention provides a grid-connected pre-synchronization method and electronic equipment for a virtual synchronous generator parallel system, which solves the problem that the control of a multi-VSG grid-connected pre-synchronization scheme is relatively complex. Pre-synchronization can be achieved without communication or through a communication method. The control is flexible and simple, and the communication reliability requirement is not high.

[0005] According to one aspect of the present invention, a grid-connected 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 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 power grid, and n is an integer greater than or equal to 2;

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

[0007] The n virtual synchronous generators start to perform grid-connected pre-synchronization after receiving the pre-synchronization instruction, and the grid-connected pre-synchronization includes frequency, phase pre-synchronization and amplitude pre-synchronization;

[0008] The frequency and phase pre-synchronization includes: calculating the frequency and phase pre-synchronization control amount, calculating the damping power according to the frequency and phase pre-synchronization control amount, calculating the output angular frequency difference of the virtual synchronous generator according to the mechanical power, the electromagnetic power and the damping power, and determining 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;

[0009] The amplitude pre-synchronization includes: 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;

[0010] Determine whether the n virtual synchronous generators have completed pre-synchronization according to preset conditions, and obtain a determination result;

[0011] If the judgment result is that the n virtual synchronous generators have not completed pre-synchronization, returning to continue to execute the grid-connected pre-synchronization;

[0012] If the judgment result is that the n virtual synchronous generators have completed pre-synchronization, the first circuit breaker is closed and the grid-connected pre-synchronization is turned off.

[0013] Optionally, the preset conditions include:

[0014] 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;

[0015] 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;

[0016] 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.

[0017] Optionally, the calculating frequency and phase presynchronization control amount, calculating the damping power according to the frequency and phase presynchronization control amount, calculating the output angular frequency difference of the virtual synchronous generator according to the mechanical power, the electromagnetic power and the damping power, and determining the power angle of the virtual synchronous generator according to the output angular frequency difference and the rated angular frequency of the virtual synchronous generator includes:

[0018] Performing phase-locked loop control on the grid voltage obtained by the virtual synchronous generator to obtain the grid voltage phase angle;

[0019] Performing Park transformation on the common coupling point voltage according to the grid voltage phase angle to obtain d-axis and q-axis components of the common coupling point voltage in a rotating coordinate system, and performing PI control on the q-axis component of the common coupling point voltage to obtain frequency and phase pre-synchronization control quantities;

[0020] Calculate the mechanical power according to the frequency, phase pre-synchronization control amount, rated angular frequency, frequency-active power droop coefficient, angular frequency difference controlled by the virtual synchronous generator and active power instruction value, and calculate the damping power according to the angular frequency difference controlled by the virtual synchronous generator, the rated angular frequency and the damping coefficient of the virtual synchronous generator;

[0021] The output angular frequency difference of the virtual synchronous generator is calculated according to the mechanical power, the electromagnetic power, the damping power, the virtual inertia and the rated angular frequency. The output angular frequency difference of the virtual synchronous generator is superimposed on the rated angular frequency and then integrated to obtain the power angle of the virtual synchronous generator.

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

[0023] The grid voltage is subjected to Park transformation to obtain d-axis and q-axis components of the grid voltage in a rotating coordinate system, the q-axis component of the grid voltage is subjected to PI control and added to the rated angular frequency 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] Among them, v gq is the q-axis component of the grid voltage, V ga 、V gb 、V gc They are three-phase voltage, θ g is the grid voltage phase angle;

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

[0028]

[0029] 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 voltage, 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] Among them, P m is the mechanical power, P ref is the active power 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 power droop coefficient, Δω PS It is the frequency and phase pre-synchronization control quantity;

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

[0034] P D =Δω·ω0D

[0035] Among them, 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] 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, ω0 is the rated angular frequency, and s is the Laplace operator.

[0039] Optionally, the calculating the no-load electromotive force adjustment amount and determining the no-load electromotive force reference value according to the no-load electromotive force adjustment amount and the rated no-load electromotive force value comprises:

[0040] The no-load electromotive force regulation amount is calculated according to the reactive power command value, the actual reactive power value, the voltage-reactive power droop coefficient, the grid voltage amplitude, the common coupling point voltage amplitude, the proportional coefficient of the reactive loop PI controller and the integral coefficient of the reactive loop PI controller;

[0041] The no-load electromotive force adjustment amount is superimposed on the rated no-load electromotive force value to obtain the no-load electromotive force reference value.

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

[0043]

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

[0045] According to another aspect of the present invention, there is also provided an electronic device, the 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 grid-connected pre-synchronization method for a virtual synchronous generator parallel system as described in any embodiment of the present invention.

[0049] An embodiment of the present invention further provides a computer-readable storage medium having a computer program stored thereon. When the computer program is executed by a processor, the grid-connected pre-synchronization method of the virtual synchronous generator parallel system as described in any embodiment of the present invention is implemented.

[0050] The technical solution of the embodiment of the present invention provides a photovoltaic inverter or energy storage converter that works as a virtual synchronous generator and multiple machines are connected in parallel. When realizing the off-grid to grid-connected function, a method for pre-synchronization of multiple virtual synchronous generators without communication is used. The grid-connected pre-synchronization method of a system of multiple virtual synchronous generators in parallel can achieve pre-synchronization without communication, and can also be achieved through a communication method. The control is flexible and simple, and the requirements for communication reliability are not high. In summary, the present invention solves the problem that the prior art relies on communication to transmit control information to each VSG, has high requirements for communication reliability, and the control of the multi-VSG grid-connected pre-synchronization scheme without communication is relatively complex.

[0051] It should be understood that the contents described in this section are not intended to identify the key or important features of the embodiments of the present invention, nor are they intended to limit the scope of the present invention. Other features of the present invention will become easily understood through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

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

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

[0055] Figure 3 is a block diagram of frequency and phase pre-synchronization control in each VSG provided according to an embodiment of the present invention;

[0056] Figure 4 is a control block diagram of active power loops of each VSG provided according to an embodiment of the present invention;

[0057] Figure 5 is a block diagram of amplitude pre-synchronization control in each VSG provided according to an embodiment of the present invention;

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

[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 according to an embodiment of the present invention;

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

[0061] Fig. 9 is a waveform diagram of a PCC voltage and a grid voltage after pre-synchronization provided in an embodiment of the present invention;

[0062] Fig.10 It is a schematic diagram of the structure of an electronic device provided according to an embodiment of the present invention. DETAILED DESCRIPTION

[0063] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0064] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0065] The embodiment of the present invention provides a grid-connected pre-synchronization method for a virtual synchronous generator parallel system. Figure 1 is a circuit diagram of a virtual synchronous generator parallel system provided according to an embodiment of the present invention, with reference to Figure 1 The virtual synchronous generator parallel system includes: 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 the power grid, and n is an integer greater than or equal to 2.

[0066] Specifically, a typical multi-VSG parallel system is as follows Figure 1 As shown, n VSG AC output terminals are connected in parallel to the AC bus, which is called the point of common coupling (PCC). The PCC is connected to the grid through the first circuit breaker Kg, and the PCC is connected to the load through the second circuit breaker Kg. L When the first circuit breaker Kg is disconnected, the multi-VSG parallel system works in off-grid mode, and the second circuit breaker Kg next to the load L It can be closed or opened. Before closing the first circuit breaker Kg to connect the multi-VSG parallel system to the grid, grid pre-synchronization control is required. This control is completed inside each VSG. After all VSGs have completed the grid pre-synchronization, close the first circuit breaker Kg and the parallel system is connected to the grid and operated. During the pre-synchronization process, each VSG directly samples the grid voltage Vg through a sensor, which can realize a communication-free pre-synchronization scheme; it can also sample the grid voltage Vg through VGS1, and then communicate with other VGSs, and send the power grid voltage information to each VSG through the communication line, which becomes a communication-based pre-synchronization scheme. The actual selection can be made based on the reliability of the communication. Compared with the prior art, the control of this embodiment is flexible and simple.

[0067] Figure 2 is a flowchart of a grid-connected pre-synchronization method for a virtual synchronous generator parallel system provided according to an embodiment of the present invention, with reference to Figure 2 , the grid-connected pre-synchronization method of the virtual synchronous generator parallel system includes:

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

[0069] The frequency and phase pre-synchronization includes: calculating the frequency and phase pre-synchronization control amount, calculating the damping power according to the frequency and phase pre-synchronization control amount, calculating the output angular frequency difference of the virtual synchronous generator according to the mechanical power, the electromagnetic power and the damping power, and determining 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;

[0070] Amplitude pre-synchronization includes: calculating the no-load electromotive force adjustment amount, and determining the no-load electromotive force reference value according to the no-load electromotive force adjustment amount and the rated no-load electromotive force value.

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

[0072] Figure 3 is a frequency and phase pre-synchronization control block diagram of each VSG provided according to an embodiment of the present invention, and reference is made to Figure 3 Optionally, the frequency and phase pre-synchronization control quantities are calculated, the damping power is calculated according to the frequency and phase pre-synchronization control quantities, 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 and the rated angular frequency of the virtual synchronous generator, including: performing phase-locked loop control on the grid voltage obtained by the virtual synchronous generator to obtain the grid voltage phase angle.

[0073] Continue to refer Figure 3 Optionally, performing 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 it to 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] Among them, v gq is the q-axis component of the grid voltage, V ga 、V gb 、V gc They are three-phase voltage, θ gis the grid voltage phase angle.

[0077] Specifically, the q-axis component of the grid voltage v gq After PI control, Δω is obtained 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 Park transformed to obtain the d-axis and q-axis components of the common coupling point voltage in the rotating coordinate system, and the q-axis component of the common coupling point voltage is PI controlled 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 voltage, 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 quantity Δω is obtained through PI control PS .

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

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

[0085] Continue to refer Figure 4The 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 superimposed on the rated angular frequency and then integrated to obtain the power angle of the virtual synchronous generator.

[0086] Optionally, the mechanical power is calculated as follows:

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

[0088] Among them, P m is the mechanical power, P ref is the active power 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 power droop coefficient, Δω PS It is the frequency and phase pre-synchronization control quantity.

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

[0090] The damping power is calculated as follows:

[0091] P D =Δω·ω0D

[0092] Among them, 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] 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, 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 superimposed on the rated angular frequency ω0 and then integrated to obtain the virtual synchronous generator power angle δ. The above is the frequency and phase pre-synchronization process.

[0097] The VSG power angle refers to the phase difference between the output power and the grid voltage of the virtual synchronous generator (VSG) during operation, that is, the power angle. This concept is of great significance in power system analysis, especially when studying the dynamic behavior and stability of VSG. The VSG power angle is similar to the power angle concept of the actual synchronous generator, but the VSG does not have actual rotating mechanical parts. Instead, the rotor's rotational inertia and damping characteristics are simulated by the control algorithm. The study of VSG power angle stability involves many aspects, including control strategy, system parameter design, and the influence of external disturbances. For example, the power angle stability of the system can be affected by changing the virtual inertia (J) and the damping coefficient (D). Increasing the virtual inertia can improve the stability of the system to a certain extent, but it may also weaken the damping ratio of the system, thereby affecting the frequency stability of the system. Therefore, it is necessary to find a balance between virtual inertia and damping to ensure the stable operation of the system.

[0098] Figure 5 is a block diagram of amplitude pre-synchronization control in each VSG provided according to an embodiment of the present invention, with reference to Figure 5 Optionally, calculating the no-load electromotive force adjustment amount, and determining the no-load electromotive force reference value according to the no-load electromotive force adjustment amount and the rated no-load electromotive force value includes:

[0099] The no-load electromotive force regulation amount is calculated according to the reactive power command value, the actual reactive power value, the voltage-reactive power droop coefficient, the grid voltage amplitude, the common coupling point voltage amplitude, the proportional coefficient of the reactive loop PI controller and the integral coefficient of the reactive loop PI controller;

[0100] The no-load electromotive force adjustment amount is superimposed on 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] Among them, ΔE is the no-load electromotive force adjustment, Q ref is the reactive power command 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 voltage amplitude at the common coupling point, k vp is the proportional coefficient of the reactive loop 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 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.

[0105] It should be noted that the pre-synchronization algorithm is implemented on the VSG control. The no-load electromotive force reference value E obtained by amplitude pre-synchronization ref The virtual synchronous generator power angle δ obtained by frequency and phase pre-synchronization are all variables required for VSG control. The subsequent specific VSG control block diagram has been omitted, which 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 calculation formula of the preset condition is satisfied, the pre-synchronization is completed. The calculation formula of the preset condition 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 to execute the grid-connected pre-synchronization.

[0115] S140: If the judgment result is that the n virtual synchronous generators have completed pre-synchronization, close the first circuit breaker and turn off the grid-connected pre-synchronization.

[0116] Specifically, Figure 6 is a grid-connected pre-synchronization control block diagram of a multi-VSG parallel system provided according to an embodiment of the present invention, with reference to Figure 6 After all n VSGs have completed pre-synchronization, close the first circuit breaker Kg next to the grid. n VSGs turn off the grid pre-synchronization function, that is, set the frequency and phase pre-synchronization control quantities to zero, and replace the voltage reference value of amplitude pre-synchronization from the grid voltage amplitude |Vg| to the rated voltage amplitude |V N |.

[0117] The technical solution of the embodiment of the present invention provides a photovoltaic inverter or energy storage converter that works as a virtual synchronous generator and multiple machines are connected in parallel. When realizing the off-grid to grid-connected function, a method for pre-synchronization of multiple virtual synchronous generators without communication is used. The grid-connected pre-synchronization method of a system of multiple virtual synchronous generators in parallel can achieve pre-synchronization without communication, and can also be achieved through a communication method. The control is flexible and simple, and the requirements for communication reliability are not high. In summary, the present invention solves the problem that the prior art relies on communication to transmit control information to each VSG, has high requirements for communication reliability, and the control of the multi-VSG grid-connected pre-synchronization scheme without communication is relatively complex.

[0118] Figure 7 Schematic diagram of waveforms of the PCC voltage and the grid voltage before and after the pre-synchronization signal is set high according to an embodiment of the present invention, with reference to Figure 7 , taking the grid-connected pre-synchronization of three 200kW energy storage converters in parallel 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. Under off-grid conditions, before and after the execution of the grid-connected pre-synchronization function of the multi-VSG parallel system, the waveforms of the PCC voltage and the grid voltage are as follows: Figure 7 As shown, the horizontal axis unit is s, the vertical axis unit is V, in the figure, channel 0 is the PCC voltage, channel 1 is the grid voltage, channel 2 is the pre-synchronization signal, setting high means executing the pre-synchronization function, and clearing means turning off the pre-synchronization function. During off-grid operation, due to the effect of the droop link, the initial frequency of the PCC voltage is not 50Hz, so the phase deviation between the PCC voltage and the grid voltage is sometimes large and sometimes small. At 21.46s, the pre-synchronization function is turned on.

[0119] Figure 8 This is a schematic diagram of the PCC voltage-frequency waveform of the entire grid-connected pre-synchronization process provided according to an embodiment of the present invention, with reference to Figure 8 The PCC voltage-frequency waveform of the entire multi-VSG parallel system pre-synchronization process is as follows: Figure 8As shown, the horizontal axis unit is s, and the vertical axis unit is Hz. Due to the effect of the droop link, the PCC voltage frequency is about 49.6Hz when the system is off-grid. The pre-synchronization function is turned on at 21.46s, and the PCC voltage frequency gradually changes to 50Hz, and finally stabilizes at around 50Hz, with a fluctuation amplitude of less than 0.1Hz. The grid-connected circuit breaker Kg is closed at 32.75s. After grid connection, the PCC voltage frequency is equal to the grid frequency of 50Hz. The pre-synchronization function is turned off at 34.05s, and the PCC voltage frequency drops briefly and then quickly recovers to 50Hz.

[0120] Fig. 9 Schematic diagram of waveforms of PCC voltage and grid voltage after pre-synchronization provided in an embodiment of the present invention, with reference to Fig. 9 After pre-synchronization, the waveforms of the PCC voltage and the grid voltage are as follows: Fig. 9 As shown, the horizontal axis unit is s, and the vertical axis unit is V. At about 29 seconds, the PCC voltage is basically consistent with the grid voltage frequency, phase, and amplitude, and the frequency difference, phase difference, and amplitude difference are all less than the threshold, so the grid circuit 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.

[0121] Fig.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 required herein.

[0122] like Fig.10 As shown, the electronic device 1 includes at least one processor 11, and a memory connected to the at least one processor 11, such as a read-only memory (ROM) 12, a random access memory (RAM) 13, etc., wherein the memory stores a computer program that can be executed by at least one processor, and the processor 11 can perform various appropriate actions and processes according to the computer program stored in the read-only memory (ROM) 12 or the computer program loaded from the storage unit 18 to 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.

[0123] A number 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 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 may be a variety of general and / or special 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 artificial intelligence (AI) computing chips, various processors running machine learning model algorithms, digital signal processors (DSPs), and any appropriate processors, controllers, microcontrollers, etc. The processor 11 executes the various methods and processes described above, for example, a grid-connected pre-synchronization method for a virtual synchronous generator parallel system.

[0125] In some embodiments, the grid-connected presynchronization method of the virtual synchronous generator parallel system can be implemented as a computer program, which is tangibly contained in a computer-readable storage medium, such as a storage unit 18. In some embodiments, part or all of the computer program can be loaded and / or installed on the electronic device 1 via the ROM 12 and / or the communication unit 19. When the computer program is loaded into the RAM 13 and executed by the processor 11, one or more steps of the grid-connected presynchronization method of the virtual synchronous generator parallel system described above can be performed. Alternatively, in other embodiments, the processor 11 can be configured to execute the grid-connected presynchronization method of the virtual synchronous generator parallel system in any other appropriate manner (for example, by means of firmware).

[0126] Various implementations of the systems and techniques described above herein can be implemented in digital electronic circuit systems, integrated circuit systems, field programmable gate arrays (FPGAs), application specific integrated circuits (ASICs), application specific standard products (ASSPs), systems on chips (SOCs), load programmable logic devices (CPLDs), computer hardware, firmware, software, and / or combinations thereof. These various implementations can include: being implemented in one or more computer programs that can be executed and / or interpreted on a programmable system including at least one programmable processor, which can be a special purpose or general purpose programmable processor that can receive data and instructions from a storage system, at least one input device, and at least one output device, and transmit data and instructions to the storage system, the at least one input device, and the at least one output device.

[0127] Computer programs for implementing the methods of the present invention may be written in any combination of one or more programming languages. These computer programs may be provided to a processor of a general-purpose computer, a special-purpose computer, or other programmable data processing device, so that when the computer program is executed by the processor, the functions / operations specified in the flow chart and / or block diagram are implemented. The computer program may be executed entirely on the machine, partially on the machine, partially on the machine and partially on a remote machine as a stand-alone software package, or entirely on a remote machine or server.

[0128] In the context of the present invention, a computer-readable storage medium may be a tangible medium that may contain or store a computer program for use by or in combination with an instruction execution system, device or equipment. A computer-readable storage medium may include, but is not limited to, electronic, magnetic, optical, electromagnetic, infrared, or semiconductor systems, devices or equipment, or any suitable combination of the foregoing. Alternatively, a computer-readable storage medium may be a machine-readable signal medium. A more specific example of a machine-readable storage medium may include an electrical connection based on one or more lines, 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 flash memory), an optical fiber, a portable compact disk read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing.

[0129] To provide interaction with a user, the systems and techniques described herein may 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 trackball) through which the user can provide input to the electronic device. Other types of devices may also be used to provide interaction with the user; for example, the feedback provided to the user may be any form of sensory feedback (e.g., visual feedback, auditory feedback, or tactile feedback); and input from the user may be received in any form (including acoustic input, voice input, or tactile input).

[0130] The systems and techniques described herein may be implemented in a computing system that includes backend components (e.g., as a data server), or a computing system that includes middleware components (e.g., an application server), or a computing system that includes frontend components (e.g., a user computer with a graphical user interface or a web browser through which a user can interact with implementations of the systems and techniques described herein), or a computing system that includes any combination of such backend components, middleware components, or frontend components. The components of the system may 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] A computing system may include a client and a server. The client and the server are generally remote from each other and usually interact through a communication network. The client and server relationship is generated by computer programs running on the corresponding computers and having a client-server relationship with each other. The server may 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 difficult management and weak business scalability in traditional physical hosts and VPS services.

[0132] It should be understood that the various forms of processes shown above can be used to reorder, add or delete steps. For example, the steps described in the present invention can be executed in parallel, sequentially or in different orders, as long as the desired results of the technical solution of the present invention can be achieved, and this document does not limit this.

[0133] The above specific implementations do not constitute a limitation on the protection scope of the present invention. It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and substitutions can be made according to design requirements and other factors. Any modification, equivalent substitution and improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A grid-connected pre-synchronization method for 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, 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 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: The n virtual synchronous generators start to perform grid-connected pre-synchronization after receiving the pre-synchronization instruction, and the grid-connected pre-synchronization includes frequency, phase pre-synchronization and amplitude pre-synchronization; The frequency and phase pre-synchronization includes: calculating the frequency and phase pre-synchronization control amount, calculating the damping power according to the frequency and phase pre-synchronization control amount, calculating the output angular frequency difference of the virtual synchronous generator according to the mechanical power, the electromagnetic power and the damping power, and determining 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; The amplitude pre-synchronization includes: 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; Determine whether the n virtual synchronous generators have completed pre-synchronization according to preset conditions, and obtain a determination result; If the judgment result is that the n virtual synchronous generators have not completed pre-synchronization, returning to continue to execute the grid-connected pre-synchronization; If the judgment result is that the n virtual synchronous generators have completed pre-synchronization, the first circuit breaker is closed and the grid-connected pre-synchronization is turned off.

2. The method according to claim 1, characterized in that The preset conditions include: 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; 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; 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.

3. The method according to claim 1, characterized in that The calculating frequency and phase presynchronization control amount, calculating the damping power according to the frequency and phase presynchronization control amount, calculating the output angular frequency difference of the virtual synchronous generator according to the mechanical power, the electromagnetic power and the damping power, and determining 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 include: Performing phase-locked loop control on the grid voltage obtained by the virtual synchronous generator to obtain the grid voltage phase angle; Performing Park transformation on the common coupling point voltage according to the grid voltage phase angle to obtain d-axis and q-axis components of the common coupling point voltage in a rotating coordinate system, and performing PI control on the q-axis component of the common coupling point voltage to obtain frequency and phase pre-synchronization control quantities; Calculate the mechanical power according to the frequency, phase pre-synchronization control amount, rated angular frequency, frequency-active power droop coefficient, angular frequency difference controlled by the virtual synchronous generator and active power instruction value, and calculate the damping power according to the angular frequency difference controlled by the virtual synchronous generator, the rated angular frequency and the damping coefficient of the virtual synchronous generator; The output angular frequency difference of the virtual synchronous generator is calculated according to the mechanical power, the electromagnetic power, the damping power, the virtual inertia and the rated angular frequency. The output angular frequency difference of the virtual synchronous generator is superimposed on the rated angular frequency and then integrated to obtain the power angle of the virtual synchronous generator.

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

5. The method according to claim 4, characterized in that The calculation formula of the q-axis component of the grid voltage is as follows: Among them, v gq is the q-axis component of the grid voltage, V ga 、V gb 、V gc are the three-phase voltages, θ g is the grid voltage phase angle; The calculation formula of the q-axis component of the common coupling point voltage is as follows: 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 voltage, θ g is the grid voltage phase angle.

6. The method according to claim 3, characterized in that The calculation formula of the mechanical power is as follows: P m =P ref +Dω·ω0k ω -See PS ·ω0k ω Among them, P m is the mechanical power, P ref is the active power 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 power droop coefficient, Δω PS It is the frequency and phase pre-synchronization control quantity; The calculation formula of the damping power is as follows: P D =Dω·ω0D Among them, 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, ω0 is the rated angular frequency, and s is the Laplace operator.

7. The method according to claim 1, characterized in that The calculating of the no-load electromotive force adjustment amount and determining the no-load electromotive force reference value according to the no-load electromotive force adjustment amount and the rated no-load electromotive force value comprises: The no-load electromotive force regulation amount is calculated according to the reactive power command value, the actual reactive power value, the voltage-reactive power droop coefficient, the grid voltage amplitude, the common coupling point voltage amplitude, the proportional coefficient of the reactive loop PI controller and the integral coefficient of the reactive loop PI controller; The no-load electromotive force adjustment amount is superimposed on the rated no-load electromotive force value to obtain the no-load electromotive force reference value.

8. The method according to claim 7, characterized in that The calculation formula of the no-load electromotive force adjustment amount is as follows: Among them, ΔE is the no-load electromotive force adjustment, Q ref is the reactive power command 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 voltage amplitude at the common coupling point, k vp is the proportional coefficient of the reactive loop PI controller, k vi is the integral coefficient of the reactive loop PI controller, and s is the Laplace operator.

9. An electronic device, characterized in that: include: one or more processors; A 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 parallel system as described in any one of claims 1-8.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the grid-connected pre-synchronization method of the virtual synchronous generator parallel system as described in any one of claims 1-8 is implemented.

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