Grid construction type photovoltaic black-start method, photovoltaic power generation device and photovoltaic power generation system

Abstract

The invention discloses a network construction type photovoltaic black start method, a photovoltaic power generation device and a photovoltaic power generation system, and relates to the technical field of network construction type photovoltaic black start, and the method comprises the steps: controlling a chopping protection device to work under the condition that the DC side voltage of a main photovoltaic source exceeds a preset threshold value after the main photovoltaic source and an auxiliary photovoltaic source are connected to a grid; wherein the main photovoltaic source and the auxiliary photovoltaic source are merged into the same alternating current bus, the chopping protection device is connected between a chopping circuit and an inverter circuit of the main photovoltaic source in parallel, the chopping protection device comprises an energy consumption resistor, and the energy consumption resistor is used for absorbing transient active impact of grid connection of the auxiliary photovoltaic source; and under the condition that the direct-current side voltage of the main photovoltaic source and the direct-current side voltage of the auxiliary photovoltaic source are in a stable state, controlling the extended photovoltaic source and the load to be connected to the grid, and completing the grid-forming type photovoltaic black start. According to the invention, the stability and reliability of the black-start process of the network-building type photovoltaic field station under the condition of no energy storage support can be improved.

Description

Technical Field

[0001] The present application relates to the technical field of grid-forming photovoltaic black start, and particularly relates to a grid-forming photovoltaic black start method, a photovoltaic power generation device, and a photovoltaic power generation system. Background Art

[0002] In the related art, the black start technology of grid-forming photovoltaic power stations generally relies on an energy storage system or an external stable synchronous power source (such as a diesel generator, a traditional synchronous unit, etc.) to provide dynamic power support. And in some extreme working conditions (such as energy storage mismatch or external power source loss), the power system needs to completely rely on the independent network building ability of grid-forming inverters to realize the reconstruction of voltage / frequency reference, and needs to have the multi-level cascaded self-starting ability.

[0003] However, in the above extreme working conditions without energy storage support, the photovoltaic power station, as the only black start source, due to its characteristic of unidirectional active power flow, any transient impact of reverse active power during the black start process will raise its DC voltage, and the rise of the DC voltage will cause the DC protection device to act to cut off the photovoltaic panel and the inverter, thus resulting in black start failure. Therefore, it is necessary to seek a grid-forming photovoltaic black start path applicable to the situation without energy storage support. Summary of the Invention

[0004] The main purpose of the present application is to provide a grid-forming photovoltaic black start method, a photovoltaic power generation device, and a photovoltaic power generation system, aiming to solve the technical problem that the grid-forming photovoltaic power station is prone to black start failure due to transient impact in the case of no energy storage support in the related art.

[0005] To achieve the above purpose, the present application proposes a grid-forming photovoltaic black start method, which can be used for the black start control device of a photovoltaic power generation system. The photovoltaic power generation system further includes a main photovoltaic source, a secondary photovoltaic source, and a chopper protection device, all of which are connected to the black start control device; the main photovoltaic source and the secondary photovoltaic source are incorporated into the same AC bus; the main photovoltaic source includes a photovoltaic panel, a chopper circuit, an inverter circuit, and a step-up transformer connected in sequence; the chopper protection device is connected in parallel between the chopper circuit and the inverter circuit; the chopper protection device includes a dissipating resistor, and the dissipating resistor is used to absorb the transient active power impact of the secondary photovoltaic source grid connection. The grid-forming photovoltaic black start method includes: When the DC side voltage of the main photovoltaic source exceeds a preset threshold after the main photovoltaic source and the secondary photovoltaic source are grid-connected, controlling the chopper protection device to work; When the DC side voltages of the main photovoltaic source and the secondary photovoltaic source are in a stable state, controlling the extended photovoltaic source and the load to be grid-connected to complete the grid-forming photovoltaic black start.

[0006] In one embodiment, before the step of controlling the operation of the chopper protection device when the DC-side voltage of the main photovoltaic source exceeds a preset threshold after the main photovoltaic source and the secondary photovoltaic source are connected to the grid, the method further includes: Controlling the startup of the main photovoltaic source and increasing the primary frequency modulation coefficient of the main photovoltaic source and / or reducing the inertia time constant of the main photovoltaic source.

[0007] In one embodiment, the step of increasing the primary frequency modulation coefficient of the main photovoltaic source includes: Increasing the primary frequency modulation coefficient of the main photovoltaic source within a preset frequency modulation coefficient range until the main photovoltaic source operates stably.

[0008] In one embodiment, the step of reducing the inertia time constant of the main photovoltaic source includes: Reducing the inertia time constant of the main photovoltaic source within a preset inertia time constant range until the main photovoltaic source operates stably.

[0009] In one embodiment, after the step of controlling the startup of the main photovoltaic source and increasing the primary frequency modulation coefficient of the main photovoltaic source and / or reducing the inertia time constant of the main photovoltaic source, the method further includes: Controlling the startup of the secondary photovoltaic source in zero-power mode and reducing the inertia time constant of the secondary photovoltaic source; Based on the amplitude, frequency, and phase of the main photovoltaic source, controlling the pre-synchronization connection of the secondary photovoltaic source to the grid.

[0010] In one embodiment, the step of reducing the inertia time constant of the secondary photovoltaic source includes: Reducing the inertia time constant of the secondary photovoltaic source within a preset inertia time constant range until the secondary photovoltaic source operates stably.

[0011] In one embodiment, when the DC-side voltages of the main photovoltaic source and the secondary photovoltaic source are in a stable state, the steps of controlling the connection of the extended photovoltaic source and the load to the grid to complete the grid-forming photovoltaic black start include: When the DC-side voltages of the main photovoltaic source and the secondary photovoltaic source are in a stable state, controlling the connection of the critical load to the grid; When the frequency of the power system is in a stable state, controlling the connection of the extended photovoltaic source and / or the non-critical load to the grid to complete the grid-forming photovoltaic black start.

[0012] In one embodiment, when the frequency of the power system is in a stable state, the steps of controlling the connection of the extended photovoltaic source and / or the non-critical load to the grid to complete the grid-forming photovoltaic black start include: When the frequency of the power system is in a stable state, controlling the pre-synchronization connection of all extended photovoltaic sources according to a preset startup sequence; After all extended photovoltaic sources are connected to the grid, the inertia time constant of the non-primary photovoltaic sources and the primary frequency modulation coefficient of the non-primary photovoltaic sources are controlled to be consistent with the primary frequency modulation coefficient of the primary photovoltaic sources and the inertia time constant of the primary photovoltaic sources, respectively; the non-primary photovoltaic sources include secondary photovoltaic sources and all extended photovoltaic sources; Control all non-critical loads to be gradually connected to the grid.

[0013] In addition, to achieve the above object, the present application also proposes a photovoltaic power generation device, which includes a primary photovoltaic source and a chopper protection device; the primary photovoltaic source includes a photovoltaic panel, a chopper circuit, an inverter circuit, and a step-up transformer connected in sequence; The chopper protection device is connected in parallel between the chopper circuit and the inverter circuit, and the chopper protection device includes a dissipative resistor, which is used to absorb transient active power surges.

[0014] In addition, to achieve the above object, the present application also proposes a photovoltaic power generation system, which includes: A black start control device, which includes a memory, a processor, and a computer program stored on the memory and executable on the processor, and the computer program is configured to implement the steps of the grid-forming photovoltaic black start method as described above; and The photovoltaic power generation device as described above, which is connected to the black start control device.

[0015] One or more technical solutions proposed by the present application have at least the following technical effects: The grid-forming photovoltaic black start method provided by the present application can monitor the DC side voltage of the primary photovoltaic source after the primary photovoltaic source and the secondary photovoltaic source are connected to the grid, and when the DC side voltage of the primary photovoltaic source exceeds a preset threshold, control the chopper protection device to operate; the chopper protection device is configured between the chopper circuit and the inverter circuit of the primary photovoltaic source, and the chopper protection device includes a dissipative resistor, which can absorb the transient active power surge brought by the connection of the secondary photovoltaic source through the dissipative resistor when the DC side voltage exceeds the preset threshold; and when the DC side voltage of the primary photovoltaic source and the DC side voltage of the secondary photovoltaic source are in a stable state, then control the extended photovoltaic sources and loads to be connected to the grid to complete the entire process of grid-forming photovoltaic black start. The configuration of the chopper protection device in the present application can avoid the reverse active power transient impact of the secondary photovoltaic source from raising the DC side voltage of the primary photovoltaic source, resulting in misoperation of the DC protection device and causing black start failure. Therefore, a grid-forming photovoltaic black start path applicable to the situation without energy storage support can be provided. Description of the Drawings

[0016] The drawings here are incorporated into the specification and constitute a part of the specification, showing embodiments consistent with the present application, and are used together with the specification to explain the principles of the present application.

[0017] To more clearly illustrate the technical solutions in the embodiments of the present application or the related art, the following will briefly introduce the accompanying drawings required for the description of the embodiments or the related art. Obviously, for those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0018] Figure 1 It is a schematic structural diagram of a photovoltaic power generation system related to the solution of the embodiment of the present application; Figure 2 It is a schematic structural diagram of a black start control device for the hardware operation environment related to the embodiment of the present application; Figure 3 It is a schematic structural diagram of a photovoltaic power generation device related to the embodiment of the present application; Figure 4 It is a schematic flowchart provided by the first embodiment of the grid-forming photovoltaic black start method of the present application; Figure 5 It is a schematic diagram of a brief black start process based on an example proposed in the first embodiment; Figure 6 It is a simulation diagram of the main photovoltaic source power waveform during the black start process without chopper protection; Figure 7 It is a simulation diagram of the AC voltage and DC voltage amplitude waveforms of the main photovoltaic source during the black start process without chopper protection; Figure 8 It is a simulation diagram of the secondary photovoltaic source power waveform during the black start process without chopper protection; Figure 9 It is a simulation diagram of the AC voltage and DC voltage amplitude waveforms of the secondary photovoltaic source during the black start process without chopper protection; Figure 10 It is a simulation diagram of the main photovoltaic source power waveform during the black start process using the method of the present application; Figure 11 It is a simulation diagram of the AC voltage and DC voltage amplitude waveforms of the main photovoltaic source during the black start process using the method of the present application; Figure 12 It is a simulation diagram of the secondary photovoltaic source power waveform during the black start process using the method of the present application; Figure 13 It is a simulation diagram of the AC voltage and DC voltage amplitude waveforms of the secondary photovoltaic source during the black start process using the method of the present application.

[0019] The realization, functional features, and advantages of the objectives of the present application will be further described in conjunction with the embodiments with reference to the accompanying drawings. Detailed Embodiments

[0020] It should be understood that the specific embodiments described herein are only used to explain the technical solutions of the present application and are not used to limit the present application.

[0021] To better understand the technical solution of this application, the following will be described in detail in conjunction with the accompanying drawings of the specification and specific embodiments.

[0022] The main solution of the embodiment of this application is: when the DC side voltage of the main photovoltaic source exceeds a preset threshold after the main photovoltaic source and the secondary photovoltaic source are connected to the grid, control the chopper protection device to operate; a chopper protection device is configured on the DC side of the main photovoltaic source, and the chopper protection device includes a dissipating resistor, and the dissipating resistor is used to absorb the transient active power impact of the secondary photovoltaic source connected to the grid; when the DC side voltage of the main photovoltaic source and the DC side voltage of the secondary photovoltaic source are in a stable state, control the extended photovoltaic source and the load to be connected to the grid to complete the grid-forming photovoltaic black start.

[0023] As the new power system accelerates its development towards the direction of high proportion of renewable energy penetration, the power grid operation faces multiple challenges: the superposition of uncertainties on both the source and load sides leads to a continuous narrowing of the voltage stability region, and the power fluctuations at multiple time scales significantly increase the dynamic regulation pressure of the system. In this context, the black start technology, as one of the core technologies for enhancing the resilience of the power grid, can reduce the power supply interruption time by quickly reconstructing the system voltage and frequency support, and become a key technical means to enhance the elasticity of the power system and ensure the reliable operation of independent microgrids. Among them, the grid-forming photovoltaic power station, as the core power generation unit of the new power system, the development of its black start ability can realize the transformation from passive response to active construction, providing important technical support for building a highly resilient new power system.

[0024] However, there are still significant limitations in the implementation path of the black start technology for grid-forming photovoltaic power stations. In related technologies, the black start technology of grid-forming photovoltaic power stations relies on energy storage systems or external stable synchronous sources (such as diesel generators, traditional synchronous units) to provide dynamic power support. Typical technical routes include using an energy storage bidirectional DC / AC converter to support the AC bus voltage, or configuring a buffer supercapacitor or battery on the DC bus of the photovoltaic. In some extreme working conditions (such as energy storage mismatch or lack of external power supply), the power system needs to completely rely on the independent network-forming ability of the grid-forming inverter to realize the reconstruction of the voltage / frequency reference, and needs to have the multi-level cascaded self-starting ability.

[0025] In the above extreme working conditions without energy storage support, the photovoltaic power station will be the only black start source. Due to its characteristic of unidirectional active power flow, any transient reverse active power impact during the black start process will raise its DC voltage, and the increase in the DC voltage will cause the DC protection device to operate to cut off the photovoltaic panel and the inverter, which will result in the failure of the black start. Therefore, it is necessary to seek a grid-forming photovoltaic black start path applicable to the situation without energy storage support.

[0026] The present application provides a solution. When the DC side voltage of the main photovoltaic source exceeds a preset threshold after the main photovoltaic source and the secondary photovoltaic source are grid-connected, the chopper protection device can be controlled to operate; the transient active power impact brought by the grid connection of the secondary photovoltaic source is absorbed by the energy-consuming resistor in the chopper protection device; and after the DC side voltage of the main photovoltaic source and the DC side voltage of the secondary photovoltaic source are stabilized, the remaining extended photovoltaic sources and loads are controlled to be grid-connected to complete the entire process of grid-forming photovoltaic black start. The configuration of the chopper protection device can avoid the reverse active power transient impact of the secondary photovoltaic source from raising the DC side voltage of the main photovoltaic source, resulting in misoperation of the DC protection device and black start failure. Therefore, a grid-forming photovoltaic black start path applicable to the situation without energy storage support is provided.

[0027] The following will be described and introduced in detail through multiple embodiments.

[0028] Refer to Figure 1 , Figure 1 which is a schematic structural diagram of the photovoltaic power generation system involved in the solution of the embodiment of the present application.

[0029] In the photovoltaic power generation system provided by the present application, the photovoltaic power generation system may include a black start control device and a photovoltaic power generation device connected to the black start control device.

[0030] Among them, the black start control device includes at least one processor; and a memory communicatively connected to the at least one processor; wherein, the memory stores instructions executable by the at least one processor, and the instructions are executed by the at least one processor to enable the at least one processor to execute the grid-forming photovoltaic black start method in the first embodiment as described later.

[0031] Next, refer to Figure 2 , which shows a schematic structural diagram of the black start control device suitable for implementing the embodiment of the present application. The black start control device in the embodiment of the present application may include, but is not limited to, mobile terminals such as laptop computers, digital broadcast receivers, PDAs (Personal Digital Assistants), PADs (Portable Application Descriptions: tablet computers), etc., and fixed terminals such as desktop computers, etc. Figure 2 The black start control device shown is only an example and should not impose any limitations on the functions and usage scope of the embodiments of the present application.

[0032] As Figure 2As shown, the black start control device may include a processing device 1001 (such as a central processing unit, a graphics processing unit, etc.), which may perform various appropriate actions and processes according to a program stored in a read-only memory (ROM: Read Only Memory) 1002 or a program loaded from a storage device 1003 into a random access memory (RAM: Random Access Memory) 1004. In the RAM 1004, various programs and data required for the operation of the black start control device are also stored. The processing device 1001, the ROM 1002, and the RAM 1004 are connected to each other through a bus 1005. An input / output (I / O) interface 1006 is also connected to the bus. Generally, the following systems may be connected to the I / O interface 1006: an input device 1007 including, for example, a touch screen, a touch pad, a keyboard, a mouse, an image sensor, a microphone, etc.; an output device 1008 including, for example, a liquid crystal display (LCD: Liquid Crystal Display), a speaker, a vibrator, etc.; a storage device 1003 including, for example, a magnetic tape, a hard disk, etc.; and a communication device 1009. The communication device 1009 may allow the black start control device to communicate with other devices wirelessly or wiredly to exchange data. Although the figure shows a black start control device having various systems, it should be understood that it is not required to implement or have all the shown systems. More or fewer systems may be alternatively implemented or had.

[0033] The photovoltaic power generation device may include a main photovoltaic source and a chopping protection device; the chopping protection device may be connected in parallel to the DC side of the main photovoltaic source, and the chopping protection device includes a power-consuming resistor, and the power-consuming resistor is used to absorb the transient active power impact brought by the grid connection of the secondary photovoltaic source, the extended photovoltaic source, etc. As Figure 1 shown, the photovoltaic power generation system may further include a secondary photovoltaic source, and both the main photovoltaic source and the secondary photovoltaic source are connected to the same AC bus, and may cooperate with each other to provide energy support for the system during the black start process; the main photovoltaic source is the core power source during the black start process. As the first photovoltaic source connected to the grid during the black start process, the main photovoltaic source needs to have the ability to build a network independently. After the system is completely powered off, it can quickly establish the stability of the voltage and frequency reference; generally, a photovoltaic power station with a larger power generation capacity and stable light conditions is selected as the main photovoltaic source during the black start process; while the secondary photovoltaic source is the second photovoltaic source connected to the system after the main photovoltaic source establishes the voltage and frequency reference. The secondary photovoltaic source works together with the main photovoltaic source to further stabilize the system and provide support for the subsequent connection of the extended photovoltaic source; the secondary photovoltaic source generally selects a photovoltaic power station composed of a medium-sized photovoltaic array, and its power generation capacity is smaller than that of the main photovoltaic source, but it is sufficient to provide additional power support during the black start process.

[0034] Figure 3 This is a schematic structural diagram of the photovoltaic power generation device according to an embodiment of the present application. AsFigure 3 As shown, the main photovoltaic power source may include a photovoltaic panel, a DC-DC chopper circuit on the DC side, a DC-AC inverter circuit on the AC side, and a step-up transformer connected in sequence. The main photovoltaic power source is connected to the AC bus through the step-up transformer. As Figure 3 shown, a chopper protection device (Chopper device) may be connected in parallel at the DC-DC chopper circuit on the DC side. The chopper protection device includes a dissipative resistor R and a switch K connected in series with the dissipative resistor R; in practical applications, after the auxiliary photovoltaic power source is incorporated into the AC bus, when it is monitored that the DC side voltage U of the main photovoltaic power source dc exceeds the preset threshold, the switch K will close. At this time, the Chopper device will be put into operation, and the dissipative resistor R will absorb the transient active power impact generated when the auxiliary photovoltaic power source is connected to the grid, avoiding the instantaneous rise of the DC side voltage of the main photovoltaic power source; after the DC side voltage region is stable, the switch K will be disconnected to make the Chopper device exit the working state. Thus, the transient active power impact can be consumed, the DC voltage of the main photovoltaic power source can be stabilized, and the misoperation of the DC protection device of the main photovoltaic power source caused by the instantaneous rise of the voltage can be effectively prevented, enabling the main photovoltaic power source to smoothly pass through the transient process of active power connection and laying a solid foundation for the stable access of the subsequent black-start photovoltaic power source, improving the reliability of the black-start process.

[0035] In addition, the above photovoltaic power generation system may further include an extended photovoltaic power source and a load connected to the black-start control device. The extended photovoltaic power source and the load are both incorporated into the same AC bus; among them, the extended photovoltaic power source is one or more photovoltaic power sources subsequently connected to the system after the main photovoltaic power source and the auxiliary photovoltaic power source are successfully connected to the grid, mainly used to further expand the power generation capacity of the system in order to gradually restore the full-load operation of the system; the extended photovoltaic power source can provide more electric energy when the power demand is large, thereby improving the stability and reliability of the power system; in practical applications, the extended photovoltaic power source may be a photovoltaic power station composed of a small photovoltaic array, and its power generation capacity is small, and the power generation capacity of the system can be steadily expanded by gradually connecting to the grid. The load may include critical loads and non-critical loads. During the black-start process, after the load access conditions are met, the critical loads can be preferentially connected to ensure that the critical loads can be powered in time to maintain the normal operation of critical infrastructure. The non-critical loads can be connected after all the photovoltaic power sources are connected to the grid, the power system tends to be stable and the energy supply is sufficient, so as to avoid affecting the stability of the system black-start.

[0036] It can be understood that in the photovoltaic power generation system provided in this embodiment, by installing a chopper protection device on the DC side of the main photovoltaic source, the transient active power impact brought by the grid connection of the auxiliary photovoltaic source can be consumed by the energy-consuming resistor in the chopper protection device, avoiding the instantaneous rise of the DC side voltage of the main photovoltaic source. Therefore, the misoperation of the DC protection device of the main photovoltaic source caused by the instantaneous voltage rise can be effectively prevented, enabling the main photovoltaic source to smoothly pass through the transient process of active power connection and improving the reliability of the black start process.

[0037] Based on the above photovoltaic power generation system, an embodiment of the present application provides a grid-forming photovoltaic black start method, referring to Figure 4 , Figure 4 which is a schematic flowchart of the first embodiment of the grid-forming photovoltaic black start method of the present application.

[0038] In this embodiment, the above grid-forming photovoltaic black start method includes steps S100 to S200: Step S100, when the DC side voltage of the main photovoltaic source exceeds a preset threshold after the main photovoltaic source and the auxiliary photovoltaic source are grid-connected, control the chopper protection device to operate.

[0039] Step S200, when the DC side voltages of the main photovoltaic source and the auxiliary photovoltaic source are in a stable state, control the extended photovoltaic source and the load to be grid-connected to complete the grid-forming photovoltaic black start.

[0040] Specifically, during the black start process, the main photovoltaic source, as the first grid-connected reference energy source, can establish the initial voltage and frequency reference of the AC bus through a grid-forming inverter (Grid-Forming mode). On this basis, the auxiliary photovoltaic source is controlled to be grid-connected, and the system output power is adjusted by the coordinated action of the main photovoltaic source and the auxiliary photovoltaic source, enabling the photovoltaic power generation system to efficiently and stably restore power supply during the black start process. However, the auxiliary photovoltaic source may bring a certain transient impact after grid connection, and the DC side voltage of the main photovoltaic source will instantaneously rise due to the transient impact after the auxiliary photovoltaic source is grid-connected, exceeding the protection threshold of the DC protection device, resulting in the photovoltaic panel and the inverter being cut out from the DC bus and the black start failing.

[0041] Therefore, the DC side voltage of the main photovoltaic source can be monitored in real time, and when the DC side voltage of the main photovoltaic source exceeds the preset threshold after the main photovoltaic source and the secondary photovoltaic source are grid-connected, the chopper protection device can be controlled to operate; as described in the system embodiment part above, a chopper protection device is arranged between the chopper circuit and the inverter circuit of the main photovoltaic source, and the energy-consuming resistor of the chopper protection device can absorb the transient active power impact brought by the grid connection of the secondary photovoltaic source, thereby reducing the voltage rise on the DC side of the main photovoltaic source and avoiding the failure of black start; the above preset threshold can be a preset value slightly less than the protection threshold to trigger the chopper protection device in advance and discharge the transient active power impact to prevent the DC protection device from operating first. The chopper protection device can enable the main photovoltaic source to smoothly pass through the transient process of active power connection during the grid connection of the secondary photovoltaic source and maintain the stability of the system; on this basis, when the DC side voltages of the main photovoltaic source and the secondary photovoltaic source are in a stable state, the extended photovoltaic source and the load can be controlled to be grid-connected to complete the grid-forming photovoltaic black start process.

[0042] During the black start process, in addition to the main photovoltaic source, the photovoltaic power generation system also includes a secondary photovoltaic source and other extended photovoltaic sources. If chopper protection devices are set on the DC side of each photovoltaic source, although the transient active power impact brought by the grid connection of each photovoltaic source can be effectively alleviated and the system stability can be maintained; however, introducing chopper protection devices for each photovoltaic source will inevitably increase the construction cost of the system. Therefore, in order to achieve cost-optimal black start control, chopper protection devices are not set for non-main photovoltaic sources such as secondary photovoltaic sources and extended photovoltaic sources, and only a chopper protection device is set on the DC side of the main photovoltaic source, and then the transient active power impact that may be brought by the grid connection of the remaining photovoltaic sources is reduced through parameter regulation to maintain the system stability.

[0043] In the power system, the relationship between the inertia time constant and the active power can be expressed as:

[0044] Among them, is the change in active power when the frequency changes, is the inertia time constant, is the rated frequency of 50Hz, is the frequency change rate, is the rated active power of the photovoltaic source; analyzing this relationship shows that reducing the inertia time constant can reduce the change in active power. Therefore, the transient active power impact can be regulated by adjusting the inertia time constant. Thus, in a feasible implementation manner, before step S100, it may include controlling the main photovoltaic source to start and increasing the primary frequency modulation coefficient of the main photovoltaic source and / or reducing the inertia time constant of the main photovoltaic source. It can be understood that although a chopper protection device is added to the main photovoltaic source, no additional chopper protection device is added to the other photovoltaic sources operating in parallel. Therefore, in order to keep the voltage fluctuation of the main photovoltaic source within the allowable range, the primary frequency modulation coefficient of the main photovoltaic source can be increased, and / or the inertia time constant of the main photovoltaic source can be reduced; the primary frequency modulation coefficient represents the power adjustment amount corresponding to a unit frequency deviation. Under the same frequency deviation, a larger primary frequency modulation coefficient can make the adjustment range of the active power output by the main photovoltaic source larger, thereby being able to bear more power disturbances; while reducing the inertia time constant of the main photovoltaic source can reduce the change in active power of the main photovoltaic source to maintain the stability of the main photovoltaic source.

[0045] In actual operation, the primary frequency modulation coefficient of the main photovoltaic source can be increased within the preset frequency modulation coefficient range until the main photovoltaic source operates stably; after starting the main photovoltaic source, based on the initial primary frequency modulation coefficient corresponding to the main photovoltaic source, the initial primary frequency modulation coefficient can be gradually increased in accordance with the first set step size, or adjusted randomly each time until the main photovoltaic source operates stably; the adjustment range of the primary frequency modulation coefficient should be controlled within the preset frequency modulation coefficient range, that is, the adjusted primary frequency modulation coefficient still remains within the corresponding preset frequency modulation coefficient range, and this range is an optimal primary frequency modulation coefficient range applicable to the photovoltaic source. Exceeding the range of the primary frequency modulation coefficient of the main photovoltaic source may lead to aggressive power response and overshoot phenomenon; it should be noted that the preset frequency modulation coefficient range can be set to 10 - 50, and this preset frequency modulation coefficient range of 10 - 50 is mainly determined according to the Technical Regulations for Photovoltaic Power Generation Stations Connected to the Power System GB / T1994 - 2024. In actual applications, the actual and more accurate coefficient range can be determined according to the inverter characteristics. The inertia time constant of the main photovoltaic source can also be reduced within the preset inertia time constant range until the main photovoltaic source operates stably (the DC voltage of the main photovoltaic source is constant, or the voltage fluctuation is within the allowable range); based on the initial inertia time constant corresponding to the main photovoltaic source, the initial inertia time constant can be gradually reduced in accordance with the second set step size, or adjusted randomly each time until the main photovoltaic source operates stably; the adjusted value of the inertia time constant should still be controlled within the preset inertia time constant range; the above preset inertia time constant range can be set to 4 - 14, and this preset inertia time constant range can refer to the Technical Regulations for Electrochemical Energy Storage Power Stations Connected to the Grid GB / T36547 - 2024. In actual applications, the actual and more accurate coefficient range can also be determined according to the inverter characteristics. By adjusting the primary frequency modulation coefficient and inertia time constant of the main photovoltaic source and connecting the DC side chopper protection device of the main photovoltaic source, more dynamic power support margin and transient stability guarantee are provided for the grid connection of the remaining photovoltaic sources (such as secondary photovoltaic sources and extended photovoltaic sources), ensuring the reliability of the black start process.

[0046] After regulating the main photovoltaic source, the auxiliary photovoltaic source can be further incorporated. The auxiliary photovoltaic source is controlled to start in a zero-power mode, and its inertia time constant is reduced. Based on the amplitude, frequency, and phase of the main photovoltaic source, the auxiliary photovoltaic source is controlled to pre-synchronously connect to the grid. After the main photovoltaic source starts and the area is stable, the grid connection operation of the auxiliary photovoltaic source can be carried out. The zero-power mode can reduce the impact during the start-up of the auxiliary photovoltaic source and, at the same time, reduce its inertia time constant to make the active power change smaller, thereby reducing the possible transient active power impact. Similar to the regulation of the inertia time constant of the main photovoltaic source, the inertia time constant of the auxiliary photovoltaic source can be reduced within a preset inertia time constant range until the auxiliary photovoltaic source operates stably. The adjusted inertia time constant of the auxiliary photovoltaic source remains within the corresponding preset inertia time constant range. It should be noted that the adjustment of the primary frequency modulation coefficient, inertia time constant, etc. can also be achieved by setting and optimizing the inverter control parameters of the corresponding photovoltaic power station of the photovoltaic source, and calculating and optimizing the adjustment according to actual factors such as the power level and station line in different regions. After the main photovoltaic source and the auxiliary photovoltaic source start and operate stably, their output amplitude, frequency, and phase can be monitored in real time, and the output frequency and phase of the auxiliary photovoltaic source can be adjusted accordingly to ensure its synchronization with the main photovoltaic source and avoid grid connection shocks caused by frequency and phase differences. When the frequency and phase of the auxiliary photovoltaic source are completely consistent with those of the main photovoltaic source, the auxiliary photovoltaic source can be smoothly incorporated and jointly provide black start power support with the main photovoltaic source.

[0047] After the main photovoltaic source and the auxiliary photovoltaic source are successfully connected to the grid and operate stably, the remaining extended photovoltaic sources and loads can be connected to complete the entire process of grid-forming photovoltaic black start without energy storage support. It should be noted that in this embodiment, the extended photovoltaic source also does not need to be equipped with a chopper protection device, and its grid connection impact is regulated only by adjusting the inertia time constant, which can refer to the regulation of the inertia time constant of the auxiliary photovoltaic source. By increasing the primary frequency modulation coefficient of the main photovoltaic source, reducing the inertia time constant of the main photovoltaic source, reducing the inertia time constant of the non-main photovoltaic source, and adding a chopper protection device to the main photovoltaic source to reversely absorb the transient active power impact, the comprehensive operation can enable the main photovoltaic source to bear more transient active power impact when other photovoltaic sources are connected. In this way, even if the other parallel-operating photovoltaic sources do not add additional chopper protection devices, it can ensure that the DC voltage fluctuation is maintained within the allowable range, which can save the system construction cost while ensuring the stability and reliability of the black start process.

[0048] In a feasible implementation, the grid connection of critical loads can be controlled when the DC-side voltages of the main photovoltaic source and the secondary photovoltaic source are in a stable state; when the frequency of the power system is in a stable state, the grid connection of the extended photovoltaic source and / or non-critical loads can be controlled to complete the network-forming photovoltaic black start. Critical loads refer to the loads that need to be prioritized for power restoration in the event of a power outage or power interruption in the power system to ensure the normal operation of important facilities or services; after the DC-side voltages of the main photovoltaic source and the secondary photovoltaic source are stable, critical loads (such as hospitals, communication equipment, important equipment, etc.) can be connected to the grid first to ensure the guarantee and power supply of these important loads. Then, when the frequency of the power system is in a stable state, the grid connection of the extended photovoltaic source and / or non-critical loads can be controlled to complete the network-forming photovoltaic black start; the frequency of the power system is a key indicator of the balance between power supply and demand. Frequency stability means that the power system has reached a stable state, and the power supply and demand have reached a certain balance. At this time, the load of the power grid can be further expanded to connect the extended photovoltaic source and some non-critical loads.

[0049] Specifically, when the frequency of the power system is in a stable state, all extended photovoltaic sources can be controlled to pre-synchronously connect to the grid according to a preset start sequence; after all extended photovoltaic sources are connected to the grid, the inertia time constant of the non-main photovoltaic source and the primary frequency modulation coefficient of the non-main photovoltaic source are controlled to be consistent with the primary frequency modulation coefficient of the main photovoltaic source and the inertia time constant of the main photovoltaic source respectively; among them, the non-main photovoltaic source includes the secondary photovoltaic source and all extended photovoltaic sources; all non-critical loads are controlled to gradually connect to the grid. After the frequency is stable, all extended photovoltaic sources can be connected in sequence according to a preset order (such as the order from large to small of the extended photovoltaic source level) to gradually increase the power generation capacity and avoid connecting too many photovoltaic sources at one time, resulting in system frequency fluctuations. After all extended photovoltaic sources are connected to the grid, the inertia time constant of the non-main photovoltaic source and the primary frequency modulation coefficient of the non-main photovoltaic source can be controlled to be consistent with the main photovoltaic source to ensure the overall coordination of the power system, and then all non-critical loads are gradually connected to the grid to enable the system to make a smooth transition and reduce grid fluctuations. Thus, all photovoltaic sources and loads can be connected to the grid, and finally the full-capacity black start can be completed.

[0050] It can be understood that the grid-forming photovoltaic black start method provided by the first embodiment of the present application can control the operation of the chopper protection device when the DC side voltage of the main photovoltaic source exceeds a preset threshold after the main photovoltaic source and the auxiliary photovoltaic source are connected to the grid; absorb the transient active power impact brought by the connection of the auxiliary photovoltaic source through the energy-consuming resistor in the chopper protection device; and after the DC side voltages of the main photovoltaic source and the auxiliary photovoltaic source are stable, control the connection of the remaining extended photovoltaic sources and loads to complete the entire process of grid-forming photovoltaic black start. The configuration of the chopper protection device can avoid the reverse active transient impact of the auxiliary photovoltaic source from raising the DC side voltage of the main photovoltaic source, resulting in the failure of black start caused by the misoperation of the DC protection device, thereby providing a grid-forming photovoltaic black start path applicable to the situation without energy storage support.

[0051] Exemplarily, to facilitate understanding of the implementation process of the grid-forming photovoltaic black start method in this embodiment, the following example is given. Specifically, Figure 5 As a schematic diagram of a brief black start process for an example proposed based on the first embodiment, as Figure 5 shown, the entire black start process mainly includes the following steps: 1) System initialization and load shedding: After the microgrid enters the black start state, first cut off all loads in the system to establish a load-free operating environment; 2) Establishment of the main photovoltaic source voltage and frequency: Under sufficient light conditions, build the initial voltage and frequency through the main photovoltaic source for black start to provide basic power support for the system; on this basis, the primary frequency modulation coefficient and inertia time constant of the main photovoltaic source can also be adjusted to maintain the stability of the main photovoltaic source. For specific regulation, refer to the first embodiment part of the foregoing method; 3) Pre-synchronization control of the auxiliary photovoltaic source: Control the auxiliary photovoltaic source for black start to start in zero power mode, and set the inertia time constant and primary frequency modulation coefficient in the black start mode. On this basis, pre-synchronize with the amplitude, frequency, and phase of the main photovoltaic source; 4) Multi-source parallel operation: When the auxiliary photovoltaic source meets the synchronization conditions such as amplitude, frequency, and phase, perform the grid connection closing operation to form a coordinated parallel operation mechanism with the main photovoltaic source; after grid connection, the chopper protection device of the main photovoltaic source can operate according to the DC side voltage of the main photovoltaic source. When its DC side voltage exceeds the preset threshold, absorb the transient active power impact brought by the connection of the auxiliary photovoltaic source through the energy-consuming resistor in the chopper protection device; 5) Key load connection and frequency stability: Priority is given to power supply or restoration of power supply for key loads, and the outputs of the main photovoltaic source and the auxiliary photovoltaic source are adjusted proportionally according to the primary frequency modulation coefficient to maintain the system frequency stability; 6) Grid connection of extended photovoltaic sources: The remaining black start photovoltaic sources (extended photovoltaic sources) can refer to the pre-synchronization and parallel control logic of the auxiliary photovoltaic source to complete grid connection operation in sequence; 7) Full - load recovery and system reconstruction: After all PV sources complete parallel operation, adjust the inertia time constant and primary frequency regulation coefficient of non - primary PV sources to be consistent with those of the primary PV source, and power distribution can be re - carried out; then gradually connect the remaining non - critical loads, and achieve frequency dynamic balance through multi - source collaborative power output regulation, and finally complete the full - capacity black - start of the micro - grid.

[0052] Meanwhile, in order to verify the black - start effect of this application, a simulation experiment was carried out. Figure 6 、 Figure 7 、 Figure 8 and Figure 9 are the simulation waveform diagrams of the two - stage black - start process of a grid - forming PV power station without energy storage support and without a chopper protection device; Figure 10 、 Figure 11 、 Figure 12 and Figure 13 are the simulation waveform diagrams of the three - stage black - start process of a grid - forming PV power station without energy storage support using the grid - forming PV black - start method of this application (in Figure 6 、 Figure 7 、 Figure 8 、 Figure 9 、 Figure 10 、 Figure 11 、 Figure 12 and Figure 13 ), in the power waveform diagram, the blue waveform is the waveform of the active power Pe, and the green waveform is the waveform of the reactive power Qe ; in the voltage amplitude waveform diagram, the blue waveform is the waveform of the DC voltage Vdc_INV_pu, and the green waveform is the waveform of the AC voltage uqm ).

[0053] The simulation of the two - stage black - start process of a grid - forming PV power station without energy storage support and without a chopper protection device mainly takes the example of directly paralleling the secondary PV source with the primary PV source after pre - synchronization. The primary PV source starts at 1.2 s, completes frequency and voltage establishment at 2.2 s, and the secondary PV source completes pre - synchronization and closes and merges into the primary PV source at 4 s, and the waveforms shown in the figure can be obtained; among them, Figure 6 is the power waveform of the primary PV source, Figure 7 is the waveform of the AC voltage and DC voltage amplitude of the primary PV source, Figure 8 is the power waveform of the secondary PV source, Figure 9 is the waveform of the AC voltage and DC voltage amplitude of the secondary PV source. From the Figure 8 simulation test waveforms, it can be seen that although after the pre - synchronization process, the power impact at the moment of closing the secondary PV source is about 0.07 pu, which is within a reasonable range. However, since the PV source can only output active power unidirectionally, as the only voltage and frequency support source in the system, the 0.07 pu active power output of the secondary PV source can only be absorbed by the primary PV source. Therefore, the DC voltage of the primary PV source is lifted to the protection threshold. Figure 7It is shown that the DC voltage of the main photovoltaic source can reach 2.7 pu, which exceeds the protection threshold of the DC protection device. In actual situations, the DC protection device may cut off the photovoltaic panels and inverters, resulting in the failure of black start.

[0054] Therefore, on this basis, an improved design of the grid-forming photovoltaic black start method of this application is carried out. First, it is necessary to avoid the DC overvoltage protection action caused by the transient impact during the sequential start of the photovoltaic system. Secondly, the multi-region coordinated control parameters (such as the inertia time constant and the primary frequency modulation coefficient) are regulated to ensure the smooth completion of the hierarchical black start. The simulation of the three-stage black start process of the grid-forming photovoltaic power station without energy storage support by setting the chopper protection device mainly takes the parallel connection of the main photovoltaic source, the secondary photovoltaic source, and an extended photovoltaic source (the third-stage photovoltaic source) as an example. The main photovoltaic source starts at 1.2 s, completes frequency and voltage establishment at 2.2 s, the photovoltaic source is pre-synchronized and then switched in parallel with the main photovoltaic source at 4 s, and the third-stage photovoltaic source is pre-synchronized and then switched in parallel with the established microgrid system at 6 s, and the waveform shown in the figure can be obtained. Among them, Figure 10 is the power waveform of the main photovoltaic source using the black start method of this application, Figure 11 is the AC voltage and DC voltage amplitude waveforms of the main photovoltaic source using the black start method of this application, Figure 12 is the power waveform of the secondary photovoltaic source using the black start method of this application, Figure 13 is the AC voltage and DC voltage amplitude waveforms of the secondary photovoltaic source using the black start method of this application. From Figure 10 、 Figure 11 、 Figure 12 and Figure 13 it is not difficult to see that after reducing the inertia time constant, the main photovoltaic source can undertake more transient active power. At the same time, because it is equipped with a chopper protection device, it can absorb additional transient active power shocks and can well stabilize the DC side voltage. Therefore, the secondary photovoltaic source only undertakes a small amount of transient active power. Therefore, when the third-stage photovoltaic source is connected, the DC side voltage only has a small fluctuation and is within the allowable range. The three-stage photovoltaic power station without energy storage support realizes sequential parallel operation.

[0055] It should be noted that the above examples are only for understanding this application and do not constitute a limitation on the grid-forming photovoltaic black start method of this application. Based on this technical concept, more forms of simple transformations are within the protection scope of this application.

[0056] The above are only some embodiments of this application, and do not limit the protection scope accordingly. Any equivalent structural transformation made under the technical concept of this application by using the content of the specification and drawings of this application, or directly / indirectly applied in other related technical fields, is included in the protection scope.

Claims

1. A grid-forming type photovoltaic black start method, characterized in that Black start control device for a photovoltaic power generation system, the photovoltaic power generation system further comprising a main photovoltaic source, a secondary photovoltaic source and a chopper protection device all connected to the black start control device; the main photovoltaic source and the secondary photovoltaic source are incorporated into the same AC bus; the main photovoltaic source includes a photovoltaic panel, a chopper circuit, an inverter circuit and a step-up transformer connected in sequence; the chopper protection device is connected in parallel between the chopper circuit and the inverter circuit; the chopper protection device includes a dissipative resistor for absorbing the transient active power impact during the grid connection of the secondary photovoltaic source. The grid-forming photovoltaic black start method includes: Controlling the chopper protection device to operate when the DC side voltage of the main photovoltaic source exceeds a preset threshold after the main photovoltaic source and the secondary photovoltaic source are grid-connected. When the DC side voltages of the main photovoltaic source and the secondary photovoltaic source are in a stable state, controlling the extended photovoltaic source and the load to be grid-connected to complete the grid-forming photovoltaic black start.

2. The grid-forming type photovoltaic black start method according to claim 1, wherein Before the step of controlling the chopper protection device to operate when the DC side voltage of the main photovoltaic source exceeds a preset threshold after the main photovoltaic source and the secondary photovoltaic source are grid-connected, the method further includes: Controlling the main photovoltaic source to start and increasing the primary frequency modulation coefficient of the main photovoltaic source and / or reducing the inertia time constant of the main photovoltaic source.

3. The grid-forming type photovoltaic black start method according to claim 2, characterized in that, The step of increasing the primary frequency modulation coefficient of the main photovoltaic source includes: Increasing the primary frequency modulation coefficient of the main photovoltaic source within a preset frequency modulation coefficient range until the main photovoltaic source operates stably.

4. The grid-forming type photovoltaic black start method according to claim 2, wherein The step of reducing the inertia time constant of the main photovoltaic source includes: Reducing the inertia time constant of the main photovoltaic source within a preset inertia time constant range until the main photovoltaic source operates stably.

5. The network-forming type photovoltaic black start method according to claim 2, wherein After the step of controlling the main photovoltaic source to start and increasing the primary frequency modulation coefficient of the main photovoltaic source and / or reducing the inertia time constant of the main photovoltaic source, the method further includes: Controlling the secondary photovoltaic source to start in a zero-power mode and reducing the inertia time constant of the secondary photovoltaic source; Based on the amplitude, frequency and phase of the main photovoltaic source, controlling the secondary photovoltaic source to pre-synchronously connect to the grid.

6. The grid-forming type photovoltaic black start method according to claim 5, characterized in that, The step of reducing the inertia time constant of the secondary photovoltaic source includes: Reducing the inertia time constant of the secondary photovoltaic source within a preset inertia time constant range until the secondary photovoltaic source operates stably.

7. The grid-forming type photovoltaic black start method according to claim 1, characterized in that, The step of controlling the extended photovoltaic source and the load to be grid-connected to complete the grid-forming photovoltaic black start when the DC side voltages of the main photovoltaic source and the secondary photovoltaic source are in a stable state includes: When the DC side voltages of the main photovoltaic source and the secondary photovoltaic source are in a stable state, controlling the key load to be grid-connected; When the frequency of the power system is in a stable state, controlling the extended photovoltaic source and / or the non-critical load to be grid-connected to complete the grid-forming photovoltaic black start.

8. The grid-forming type photovoltaic black start method according to claim 7, wherein, The step of controlling the extended photovoltaic source and / or the non-critical load to be grid-connected to complete the grid-forming photovoltaic black start when the frequency of the power system is in a stable state includes: When the frequency of the power system is in a stable state, controlling all extended photovoltaic sources to pre-synchronously connect to the grid according to a preset start sequence. After all the extended photovoltaic sources are connected to the grid, control the inertia time constant of the non-primary photovoltaic source and the primary frequency regulation coefficient of the non-primary photovoltaic source to be consistent with the primary frequency regulation coefficient of the primary photovoltaic source and the inertia time constant of the primary photovoltaic source respectively; the non-primary photovoltaic sources include the secondary photovoltaic source and all the extended photovoltaic sources; Control all the non-critical loads to be gradually connected to the grid.

9. A photovoltaic power generation device, characterized in that, The photovoltaic power generation device includes a primary photovoltaic source and a chopper protection device; the primary photovoltaic source includes a photovoltaic panel, a chopper circuit, an inverter circuit, and a step-up transformer connected in sequence; The chopper protection device is connected in parallel between the chopper circuit and the inverter circuit, and the chopper protection device includes a dissipative resistor for absorbing transient active power surges.

10. A photovoltaic power generation system, characterized in that, The photovoltaic power generation system includes: A black start control device, which includes a memory, a processor, and a computer program stored on the memory and executable on the processor, and the computer program is configured to implement the steps of the grid-forming photovoltaic black start method according to any one of claims 1 to 8; and The photovoltaic power generation device according to claim 9, connected to the black start control device.

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