Centralized photovoltaic direct-current power generation collecting and sending-out multistage coupling voltage control method and centralized photovoltaic direct-current power generation collecting and sending-out multistage coupling voltage control system

Abstract

The invention relates to the technical field of flexible direct-current power transmission, and discloses a centralized photovoltaic direct-current power generation collecting and sending-out multi-stage coupling voltage control method and a centralized photovoltaic direct-current power generation collecting and sending-out multi-stage coupling voltage control system. Switching among a maximum power tracking control mode, a dynamic voltage control mode and a constant power control mode according to the voltage state of the low-voltage bus; switching between a fixed gain control mode and a fixed frequency and fixed width control mode is carried out according to the gain change between the low-voltage bus and the medium-voltage bus based on the direct-current converter; the system comprises a photovoltaic power generation area; the photovoltaic confluence area is used for connecting a plurality of groups of photovoltaic power generation groups in series through a confluence line and connecting the photovoltaic power generation groups to a confluence converter; the direct-current boosting area is used for performing voltage boosting by utilizing a direct-current converter after the plurality of groups of confluence converters are connected to a low-voltage bus; a direct current collection area; a centralized inversion area; and a grid-connected area. According to the invention, the voltage control problem of the multi-stage coupling cascade system is solved, and the efficiency of the photovoltaic power generation system is improved.

Description

Technical Field

[0001] This invention relates to the field of flexible DC power transmission technology, and more specifically, to a method and system for controlling the multi-stage coupling voltage of centralized photovoltaic DC power generation and transmission. Background Technology

[0002] Large-scale photovoltaic (PV) power generation systems have become an important direction for the development of new energy. Compared with traditional AC collection systems, DC collection and transmission systems have shown significant advantages in large-scale PV grid-connected applications. DC systems have fewer stability dimensions; theoretically, only maintaining the DC voltage is needed to achieve stable system operation. There are no synchronization or frequency stability issues, fewer control targets, and faster response speeds. This makes them more conducive to solving the intermittency problem of new energy sources, improving the collection and transmission capacity of new energy sources, and enhancing system stability.

[0003] Currently, multi-stage DC boost schemes based on DC converters have been applied in some projects in my country. However, existing applications are mainly concentrated in low voltage levels and small capacity systems, utilizing the strong tolerance of power electronic equipment and the system voltage control capability to achieve stable operation. A mature technical solution suitable for medium and high voltage large capacity systems has not yet been formed.

[0004] To meet the collection and transmission requirements of medium- and high-voltage photovoltaic power generation systems with large capacity, a centralized collection and inverter transmission scheme using combiner converters, DC converters, and AC / DC converters has become an inevitable choice for technological development. This scheme achieves energy transmission and voltage level upgrades from photovoltaic strings to the grid through multi-stage conversion, effectively supporting higher voltage levels and larger system capacities. However, with the expansion of system scale and the increase in voltage levels, the number of devices increases significantly, the system topology becomes more complex, and a high degree of coordinated control is required between the converters at each stage. This places higher demands on the real-time performance of the control system, the effectiveness of the control algorithm, and the reliability of the system. Existing control technologies are difficult to directly apply to such complex multi-stage systems.

[0005] In centralized photovoltaic DC power generation and transmission systems, power needs to be transmitted through multiple stages of converters. The front-end DC converters need to maintain a stable low-voltage DC bus voltage to support the normal operation of the combiner converters, while the rear-end AC / DC converters need to maintain a stable medium-voltage bus voltage to ensure grid connection quality. When the system experiences faults or abnormal operating conditions that cause power fluctuations, if the rear-end converters respond slowly, the DC bus voltage will fluctuate drastically due to energy accumulation or shortage. At the same time, if the medium-voltage bus voltage controlled by the front-end becomes unstable, it will further aggravate the overall voltage fluctuation of the system, and may even trigger cascading faults that lead to the collapse and disconnection of the entire system from the grid. In addition, existing technologies mostly use independent control strategies for each stage of the converter, lacking an effective multi-stage coupling and coordination mechanism, making it difficult to achieve rapid response and stable control when disturbances occur. The system's anti-disturbance capability is insufficient, which seriously restricts the promotion and application of centralized photovoltaic DC power generation and transmission systems in medium- and high-voltage, large-capacity scenarios.

[0006] No effective solutions have yet been proposed to address the problems in the relevant technologies. Summary of the Invention

[0007] To address the problems in related technologies, this invention proposes a multi-stage coupled voltage control method and system for centralized photovoltaic DC power generation and transmission, in order to overcome the aforementioned technical problems existing in the prior art.

[0008] Therefore, the specific technical solution adopted by the present invention is as follows:

[0009] According to a first aspect of the present invention, a method for centralized photovoltaic DC power generation and transmission of multi-stage coupled voltage is provided, the method comprising:

[0010] Based on the bus converter, the system switches between maximum power point tracking (MPPT) control mode, dynamic voltage control mode, and constant power control mode according to the low-voltage bus voltage state. Based on the DC-DC converter, the system switches between constant gain control mode and constant frequency and constant bandwidth control mode according to the gain variation between the low-voltage bus and the medium-voltage bus. Specifically, the MPPT control mode is used to achieve the maximum power output of the photovoltaic power generation unit under normal operating conditions; the dynamic voltage control mode is used to stabilize the low-voltage bus voltage through the PU droop curve when the low-voltage bus voltage rises, ensuring that the photovoltaic power generation unit does not disconnect from the grid; the constant power control mode is used to control the low-voltage bus voltage after receiving external power commands; the constant gain control mode is used to cope with voltage disturbances and accelerate the recovery of the low-voltage bus and medium-voltage bus voltages to improve system stability; and the constant frequency and constant bandwidth control mode is used to maintain the resonant cavity operating gain and maintain the DC-DC converter operating efficiency during voltage surges to reduce excessive heat generation.

[0011] Furthermore, the dynamic voltage control mode adopts a dual closed-loop control method, which specifically includes: controlling the inductor current based on the PU droop curve of the maximum power point before mode switching, so as to achieve stable maintenance of the DC voltage of the low-voltage bus.

[0012] Furthermore, controlling the inductor current based on the PU droop curve of the maximum power point before mode switching includes: when switching to dynamic voltage control mode, the bus converter operates at the maximum power point under the current environmental constraints; the slope of the PU droop curve is set according to the current output power of each bus converter; wherein the slope of the PU droop curve is proportional to the output power to avoid the photovoltaic panel stopping power output due to excessively low input voltage of the bus converter.

[0013] Furthermore, the constant power control mode adopts a dual closed-loop control consisting of an outer gain loop and an inner inductor current loop. Specifically, it includes: receiving an external input command value as an outer loop power reference value, making the actual gain track the reference gain and then generating a current reference value through a PI controller, and making the actual inductor current track the current reference value and then generating a modulation wave through a PI controller again to achieve the stability of the low-voltage bus voltage.

[0014] Furthermore, the constant gain control mode adopts a dual closed-loop control consisting of a gain outer loop and an inductor current inner loop; specifically, it includes: setting the gain outer loop reference value to 1, so that the actual gain tracks the reference gain and then passes through the PI controller to generate a current reference value, and so that the actual inductor current tracks the current reference value and then passes through the PI controller again to generate a modulation wave.

[0015] Furthermore, the fixed frequency and fixed width control mode adopts an open-loop control method, which specifically includes: maintaining the working gain of the resonant cavity by setting a fixed duty cycle and a trigger signal of a fixed frequency; wherein, the fixed duty cycle is set according to the soft switching condition; and the fixed frequency is set as the resonant frequency.

[0016] Furthermore, based on the bus converter, the switching between maximum power point tracking (MPPT) control mode, dynamic voltage control mode, and constant power control mode according to the low-voltage bus voltage status includes: Under normal operating conditions, the bus converter operates in MPPT control mode; when the low-voltage bus voltage exceeds the overvoltage control switching threshold but falls below the overvoltage lockout threshold for a preset duration, the bus converter control mode switches from MPPT control mode to dynamic voltage control mode, and the low-voltage bus voltage is controlled between the overvoltage control switching threshold and the overvoltage control return threshold using the PU droop curve; when the low-voltage bus voltage falls below the overvoltage control return threshold for a preset duration, it switches back to MPPT control mode; when the bus converter receives a power command from the upper-level control system, it switches to constant power control mode; when the low-voltage bus voltage reaches or exceeds the overvoltage lockout threshold for a preset duration, the bus converter locks out until a reset command is received for charging and unlocking.

[0017] Furthermore, based on the DC-DC converter, the switching between constant-gain control mode and constant-frequency, constant-width control mode according to the gain change between the low-voltage bus and the medium-voltage bus includes: under normal operating conditions, the DC-DC converter operates in constant-gain control mode; when a sudden change in the low-voltage bus voltage or the medium-voltage bus voltage causes the DC-DC converter gain to be less than or equal to the low-gain switching threshold, or the DC-DC converter gain to be greater than or equal to the high-gain switching threshold, and this continues for a preset duration, the switch is made to constant-frequency, constant-width control mode; when the DC-DC converter gain is between the low-gain return threshold and the high-gain return threshold, and this continues for a preset duration, the switch is made back to constant-gain control mode; when the low-voltage bus voltage or the medium-voltage bus voltage is greater than or equal to the corresponding overvoltage blocking threshold, and this continues for a preset duration, the DC-DC converter is blocked until a reset command is received for charging and unlocking.

[0018] According to a second aspect of the present invention, a centralized photovoltaic DC power generation collection and transmission system is also provided, the system comprising:

[0019] The photovoltaic (PV) power generation area includes several sets of PV power generation units and string lines, used for generating PV power through PV panels and connecting them in strings via string lines; the PV combiner area includes several sets of combiner converters and combiner lines, used to collect several sets of PV power generation strings via combiner lines and connect them to combiner converters; the DC boost area includes several sets of low-voltage buses and DC converters, used to connect several sets of combiner converters to the low-voltage buses and use DC converters to boost the voltage; the DC collection area includes several sets of DC combiner lines and DC isolation devices, used to connect several sets of DC converters to the medium-voltage bus via DC isolation devices, and to isolate single-phase grounding faults in each DC converter branch via DC isolation devices; the centralized inverter area includes a medium-voltage bus and AC / DC converters, used to convert the DC power from the medium-voltage bus to AC power; and the grid-connected area includes a connecting transformer and a grid-connected bus, used to transform the AC power output from the centralized inverter area and connect it to the AC grid bus via the connecting transformer.

[0020] Furthermore, the photovoltaic power generation unit includes several photovoltaic panels and a matching combiner converter; the photovoltaic panels work together through the combiner converter to achieve power transmission and voltage boosting, and the boosted DC power is connected in parallel to the low-voltage bus; the low-voltage bus is connected to the DC converter and then connected in parallel to the medium-voltage bus; the medium-voltage bus is connected to the AC-DC converter and then connected to the connecting transformer, and finally connected to the AC power grid.

[0021] According to a third aspect of the present invention, an electronic device is provided.

[0022] Furthermore, the electronic device includes: a processor; a system bus; a main memory communicatively connected to the processor via the system bus; and an auxiliary memory communicatively connected to the processor via the system bus. The main memory or auxiliary memory stores a computer program executable by the processor, which, when executed by the processor, implements the steps of the above-described method.

[0023] According to a fourth aspect of the present invention, a computer-readable storage medium is provided.

[0024] Furthermore, the computer-readable storage medium stores computer instructions that, when executed by a processor, cause the processor to perform the steps of the above-described method. The computer-readable storage medium includes main memory or auxiliary memory.

[0025] The beneficial effects of this invention are as follows:

[0026] (1) The centralized photovoltaic DC power generation collection and transmission system proposed in this invention adopts a multi-stage power conversion architecture of bus converter, DC converter and AC-DC converter. It realizes the collection and transmission of photovoltaic power generation based on DC grid. Compared with the traditional AC collection scheme, it eliminates the problems of synchronization and frequency stability, reduces the loss of multiple AC-DC conversions, reduces the overall loss of photovoltaic power generation system, and improves the power generation efficiency and economy of photovoltaic power generation system. At the same time, by reasonably configuring the topology of bus converter and DC converter, it realizes efficient voltage boosting and power collection from low voltage to medium voltage, providing a reliable technical solution for medium and high voltage large capacity photovoltaic DC collection system.

[0027] (2) The centralized photovoltaic DC power generation collection and output multi-level coupling voltage control method proposed in this invention achieves rapid decoupling and coordinated control between each level of converter through intelligent switching between the maximum power point tracking control mode, dynamic voltage control mode and constant power control mode of the bus converter, as well as coordinated switching between the constant gain control mode and constant frequency and constant width control mode of the DC converter. This effectively solves the problem of severe fluctuation of DC bus voltage caused by the lag in the response of the preceding and following stages in the multi-level coupled cascaded system. When the low-voltage bus voltage rises abnormally, the bus converter uses the PU droop curve in the dynamic voltage control mode to quickly stabilize the low-voltage bus voltage and ensure that the photovoltaic power generation unit does not disconnect from the grid. When the gain of the DC converter changes abnormally, the constant frequency and constant width control mode maintains the working gain of the resonant cavity and maintains the working efficiency, avoiding the problem of decreased operating efficiency and increased heat loss of the DC converter under abnormal and fault conditions, and improving the overall voltage stability of the system and the output stability of the photovoltaic power generation unit.

[0028] (3) By setting reasonable voltage thresholds and time delays, this invention achieves precise switching and protection interlocking of control modes for each level of converter, ensuring rapid system response while avoiding frequent malfunctions. The bus converter sets overvoltage control switching thresholds, overvoltage control return thresholds, and overvoltage interlocking thresholds according to the low-voltage bus voltage status. The DC converter sets low-gain switching thresholds, high-gain switching thresholds, and corresponding return thresholds according to gain changes. Combined with a preset time delay judgment, this ensures the accuracy and reliability of control mode switching. When the voltage reaches the interlocking threshold, the converter is interlocked in time and waits for the reset command, effectively protecting the power electronic equipment body and its accessories, avoiding equipment damage caused by overvoltage impact, and improving the safety and reliability of the medium- and high-voltage large-capacity photovoltaic DC collection and transmission system. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 This is a schematic diagram of a centralized photovoltaic DC power generation collection and transmission system according to an embodiment of the present invention.

[0031] Figure 2 This is a schematic diagram of the connection structure of a photovoltaic power generation unit, a combiner converter, and a DC converter in a centralized photovoltaic DC power generation collection and transmission system according to an embodiment of the present invention.

[0032] Figure 3 This is a droop curve diagram of the dynamic voltage control of the combiner converter in a multi-level coupled voltage control method for centralized photovoltaic DC power generation and transmission according to an embodiment of the present invention.

[0033] Figure 4 This is a flowchart of the DC converter fixed-frequency and fixed-width mode control in a centralized photovoltaic DC power generation collection and transmission multi-level coupling voltage control method according to an embodiment of the present invention;

[0034] Figure 5 This is a flowchart of the constant gain mode control of the DC converter in a multi-stage coupled voltage control method for centralized photovoltaic DC power generation and transmission according to an embodiment of the present invention.

[0035] Figure 6 This is a flowchart of the control mode switching of the bus converter in a centralized photovoltaic DC power generation collection and transmission multi-level coupling voltage control method according to an embodiment of the present invention;

[0036] Figure 7 This is a flowchart of the DC converter control mode switching in a centralized photovoltaic DC power generation collection and transmission multi-level coupling voltage control method according to an embodiment of the present invention; Figure 8 This is a schematic diagram of the structure of a computer device according to an embodiment of the present invention. Detailed Implementation

[0037] To further illustrate the various embodiments, the present invention provides accompanying drawings, which are part of the disclosure of the present invention. These drawings are mainly used to illustrate the embodiments and can be used in conjunction with the relevant descriptions in the specification to explain the operating principles of the embodiments. With reference to these drawings, those skilled in the art should be able to understand other possible implementation methods and the advantages of the present invention. The components in the drawings are not drawn to scale, and similar component symbols are generally used to represent similar components.

[0038] According to an embodiment of the present invention, a method and system for controlling the multi-stage coupling voltage of centralized photovoltaic DC power generation collection and transmission is provided.

[0039] The present invention will now be further described in conjunction with the accompanying drawings and specific embodiments, such as... Figure 1 As shown, according to an embodiment of the present invention, a centralized photovoltaic DC power generation collection and transmission system is provided. The system includes: a photovoltaic power generation area, comprising several sets of photovoltaic power generation units and string lines, for generating photovoltaic power through photovoltaic panels and connecting them in strings via the string lines; a photovoltaic combiner area, comprising several sets of combiner converters and combiner lines, for collecting several sets of photovoltaic power generation strings via the combiner lines and connecting them to the combiner converters; and a DC boost area, comprising several sets of low-voltage buses and DC converters, for connecting several sets of combiner converters to the low-voltage buses. The voltage is boosted by a DC-DC converter after the line; the DC collection area includes several sets of DC bus lines and DC isolation devices, which are used to connect several sets of DC converters to the medium-voltage bus through the DC isolation devices, and to isolate single-phase ground faults in each DC converter branch through the DC isolation devices; the centralized inverter area includes the medium-voltage bus and AC-DC converters, which are used to convert the DC power from the medium-voltage bus to AC power; the grid-connected area includes a connecting transformer and a grid-connected bus, which are used to transform the AC power output from the centralized inverter area and connect it to the AC grid bus through the connecting transformer.

[0040] In one embodiment, the photovoltaic power generation unit includes several photovoltaic panels and a matching combiner converter; the several photovoltaic panels work together through the combiner converter to achieve power transmission and voltage boosting, and the boosted DC power is connected in parallel to the low-voltage bus; the low-voltage bus is connected to the DC converter and then connected in parallel to the medium-voltage bus; the medium-voltage bus is connected to the AC-DC converter and then connected to the connecting transformer, and finally connected to the AC power grid.

[0041] In one embodiment, the bus converter adopts a non-isolated topology, including: a two-level single-inductor single-switch Boost topology, a two-inductor dual-switch three-level Boost topology, a three-level Boost topology with a bridging capacitor, and a Buck-Boost topology.

[0042] In one embodiment, the DC-DC converter employs an isolated topology, including LLC converter topology and CLLC converter topology.

[0043] In one embodiment, the AC / DC converter employs a modular multilevel converter valve, and adopts a constant DC voltage and constant reactive power control mode when the system is operating.

[0044] Specifically, such as Figure 1As shown, the present invention proposes a centralized photovoltaic DC power generation collection and transmission system, including: a photovoltaic power generation area, a photovoltaic combiner area, a DC booster area, a DC collection area, a centralized inverter area, and a grid-connected area.

[0045] The photovoltaic power generation area mainly includes multiple photovoltaic power generation units and string lines, which are responsible for photovoltaic panel power generation and string connection.

[0046] The photovoltaic combiner area mainly includes multiple combiner converters and combiner lines. Multiple photovoltaic power generation strings pass through the combiner lines and then connect to the combiner converters for collection of photovoltaic strings.

[0047] The DC boost section mainly includes multiple low-voltage buses and DC converters. Multiple bus converters are connected to the low-voltage buses and then boosted by the DC converters. Isolated DC converters are used.

[0048] The DC collection area mainly includes multiple sets of DC bus lines and DC isolation devices. Multiple DC converters are connected to the DC medium voltage bus through DC isolation devices. The DC isolation devices are responsible for isolating single-phase grounding faults in each DC converter branch.

[0049] The centralized inverter area mainly includes the medium-voltage bus and AC / DC converter; the grid-connected area mainly includes the connecting transformer and the grid-connected bus. The connecting transformer is responsible for connecting the AC grid bus and the medium-voltage DC power generation system.

[0050] It should be noted that the system power is transmitted unidirectionally, from the photovoltaic power generation area to the grid-connected area. Voltage anomalies or over-voltage situations may occur in the system as follows: When the system is abnormal or there is a fault on the grid-connected side, the medium-voltage DC bus voltage will over-voltage, and due to the control characteristics of the DC transformer, the low-voltage bus voltage will rise; A fault between the poles of the medium-voltage bus will cause the medium-voltage bus voltage to drop, leading to rapid blocking of the AC / DC converter, and a rapid rise in the low-voltage bus voltage; An abnormality or fault on the low-voltage bus will cause the voltage of this group of low-voltage buses to decrease; Increased local load absorption and power output less than load demand will cause the medium-voltage bus voltage to decrease, and due to the control characteristics of the DC transformer, the low-voltage bus voltage will also decrease.

[0051] Specifically, taking a single-string DC-DC converter as an example, such as Figure 2 As shown in the diagram, according to the present invention, a photovoltaic power generation unit-combiner converter-DC converter connection structure is formed by multiple photovoltaic panels connected to a combiner converter. The two work together to achieve power transmission (the output power and output voltage relationship curve of the photovoltaic panel is provided by the photovoltaic panel manufacturer, and different power transmissions are achieved by adjusting the input port of the combiner converter) and after boosting the voltage, they are connected in parallel to the low-voltage bus. The low-voltage bus is connected to the DC converter and then connected in parallel to the medium-voltage bus. The medium-voltage bus is connected to the AC-DC converter and then connected to the connecting transformer, and finally connected to the power grid.

[0052] Specifically, the bus converter adopts a non-isolated topology, including a two-level single-inductor single-switch Boost topology, a two-inductor dual-switch three-level Boost topology, a three-level Boost topology with a bridging capacitor, a Buck-Boost topology, etc. This embodiment will use the two-level single-inductor single-switch Boost topology as an example for explanation.

[0053] Specifically, the DC-DC converter adopts an isolated topology, including LLC converter topology, CLLC converter topology, etc. This embodiment will use LLC converter topology as an example for explanation.

[0054] Specifically, the AC / DC converter adopts a modular multilevel converter valve (MMC converter valve), and the system operates in a constant DC voltage and constant reactive power control mode.

[0055] According to another embodiment of the present invention, a multi-stage coupled voltage control method for centralized photovoltaic DC power generation and output is also provided. The method includes: switching between a maximum power point tracking (MPPT) control mode, a dynamic voltage control mode, and a constant power control mode based on the low-voltage bus voltage state, using a current converter; and switching between a constant gain control mode and a constant frequency and constant width control mode based on the gain change between the low-voltage bus and the medium-voltage bus, using a DC converter. Specifically, the MPPT control mode is used to achieve the maximum power output of the photovoltaic power generation unit under normal operating conditions; the dynamic voltage control mode is used to stabilize the low-voltage bus voltage through a PU droop curve when the low-voltage bus voltage rises, ensuring that the photovoltaic power generation unit does not disconnect from the grid; the constant power control mode is used to control the low-voltage bus voltage after receiving external power commands; the constant gain control mode is used to cope with voltage disturbances and accelerate the recovery of the low-voltage bus and medium-voltage bus voltages to improve system stability; and the constant frequency and constant width control mode is used to maintain the resonant cavity operating gain and maintain the DC converter operating efficiency during voltage surges to reduce excessive heat generation.

[0056] In one embodiment, the dynamic voltage control mode adopts a dual closed-loop control method, specifically including: controlling the inductor current based on the PU droop curve of the maximum power point before mode switching, so as to achieve stable maintenance of the DC voltage of the low-voltage bus.

[0057] In one embodiment, controlling the inductor current using the PU droop curve based on the maximum power point before mode switching includes: when switching to dynamic voltage control mode, the bus converter operates at the maximum power point under the current environmental constraints; the slope of the PU droop curve is set according to the current output power of each bus converter; wherein the slope of the PU droop curve is proportional to the output power to avoid the photovoltaic panel stopping power output due to excessively low input voltage of the bus converter.

[0058] In one embodiment, the constant power control mode adopts a dual closed-loop control consisting of an outer gain loop and an inner inductor current loop. Specifically, it includes: receiving an external input command value as an outer loop power reference value, making the actual gain track the reference gain and then generating a current reference value through a PI controller, and making the actual inductor current track the current reference value and then generating a modulation wave through a PI controller again to achieve the stability of the low-voltage bus voltage.

[0059] In one embodiment, the external input command value comes from the photovoltaic power station AGC / AVC power command, the photovoltaic power station pole controller power command, the photovoltaic power station DC station controller power command, and the photovoltaic power station DC operation background command.

[0060] In one embodiment, the constant gain control mode employs a dual closed-loop control consisting of a gain outer loop and an inductor current inner loop; specifically, it includes: setting the gain outer loop reference value to 1, enabling the actual gain to track the reference gain and then generating a current reference value through a PI controller, and enabling the actual inductor current to track the current reference value and then generating a modulation wave through a PI controller again.

[0061] In one embodiment, the fixed frequency and fixed width control mode adopts an open-loop control method, specifically including: maintaining the working gain of the resonant cavity by setting a fixed duty cycle and a trigger signal of a fixed frequency; wherein, the fixed duty cycle is set according to the soft switching condition; and the fixed frequency is set as the resonant frequency.

[0062] In one embodiment, switching between maximum power point tracking (MPPT) control mode, dynamic voltage control mode, and constant power control mode based on the low-voltage bus voltage state, according to the bus converter, includes: Under normal operating conditions, the bus converter operates in MPPT control mode; when the low-voltage bus voltage exceeds the overvoltage control switching threshold but falls below the overvoltage lockout threshold for a preset duration, the bus converter control mode switches from MPPT control mode to dynamic voltage control mode, and the low-voltage bus voltage is controlled between the overvoltage control switching threshold and the overvoltage control return threshold using the PU droop curve; when the low-voltage bus voltage falls below the overvoltage control return threshold for a preset duration, the bus converter switches back to MPPT control mode; when the bus converter receives a power command from the upper-level control system, it switches to constant power control mode; when the low-voltage bus voltage reaches or exceeds the overvoltage lockout threshold for a preset duration, the bus converter locks out until a reset command is received, after which it is charged and unlocked.

[0063] In one embodiment, the overvoltage blocking threshold is set to a first preset multiple of the rated voltage of the low-voltage bus, the overvoltage control switching threshold is set to a second preset multiple of the rated voltage of the low-voltage bus, and the overvoltage control return threshold is set to a third preset multiple of the overvoltage control switching threshold; the first preset multiple is greater than the second preset multiple, the second preset multiple is greater than 1, and the third preset multiple is less than 1.

[0064] In one embodiment, based on the DC-DC converter, switching between a constant-gain control mode and a constant-frequency, constant-width control mode according to the gain change between the low-voltage bus and the medium-voltage bus includes: under normal operating conditions, the DC-DC converter operates in the constant-gain control mode; when a sudden change in the low-voltage bus voltage or the medium-voltage bus voltage causes the DC-DC converter gain to be less than or equal to a low-gain switching threshold, or the DC-DC converter gain to be greater than or equal to a high-gain switching threshold, and this continues for a preset duration, the converter switches to the constant-frequency, constant-width control mode; when the DC-DC converter gain is between a low-gain return threshold and a high-gain return threshold, and this continues for a preset duration, the converter switches back to the constant-gain control mode; when the low-voltage bus voltage or the medium-voltage bus voltage is greater than or equal to the corresponding overvoltage blocking threshold, and this continues for a preset duration, the DC-DC converter is blocked until a reset command is received for charging and unlocking.

[0065] In one embodiment, the low-gain switching threshold is less than 1, and the high-gain switching threshold is greater than 1; the low-gain return threshold is set to a first preset ratio of the low-gain switching threshold, and the high-gain return threshold is set to a second preset ratio of the high-gain switching threshold; the first preset ratio is greater than 1, and the second preset ratio is less than 1; the low-voltage bus overvoltage blocking threshold and the medium-voltage bus overvoltage blocking threshold are respectively set to preset multiples of the rated voltage of the corresponding bus, and the preset multiples are greater than 1.

[0066] Specifically, based on a centralized photovoltaic DC power generation collection and transmission system, this invention proposes a multi-stage coupling voltage control method for centralized photovoltaic DC power generation collection and transmission, such as... Figures 3-7 As shown, this method is based on local electrical quantity characteristics and is divided into bus converter control strategy and mode switching method and DC converter control strategy and mode switching method.

[0067] Specifically, in terms of the bus converter control strategy and mode switching method, the bus converter is configured with three control modes: maximum power point tracking control mode (mode 1), dynamic voltage control mode (mode 2), and constant power control mode (mode 3).

[0068] Specifically, regarding the control strategy and mode switching method of the DC-DC converter, two control modes are configured: constant-gain control and constant-frequency-constant-width control. Constant-gain control can quickly respond to disturbances, accelerate bus voltage recovery, and improve stability. Constant-frequency-constant-width control maintains the operating gain of the resonant cavity, which can maintain the operating efficiency of the DC-DC converter and reduce excessive heat generation when facing voltage surges, thus benefiting equipment design.

[0069] Specifically, the dynamic voltage control mode adopts a dual closed-loop control method. The control target is the low-voltage bus DC voltage, the control method is the PU droop curve (based on the maximum power point before mode switching), and the controlled object is the inductor current. During switching, the bus converter operates at its maximum power point (maximum power under current environmental constraints). The slope of the droop curve is set according to the current output power of each bus converter. In principle, the slope is proportional to the output power (if the input voltage of the bus converter is too low, the photovoltaic panel will stop outputting power; the threshold is provided by the photovoltaic panel manufacturer).

[0070] like Figure 3 The figure shows the droop curve of the dynamic voltage control of the bus converter. It indicates that the slope of the droop curve is set according to the current output power of each bus converter. In principle, the slope is proportional to the output power. If the input voltage of the bus converter is too low, the photovoltaic panel will stop outputting power. The threshold is provided by the photovoltaic panel manufacturer.

[0071] Specifically, the constant power control mode is a dual closed-loop control, consisting of an outer gain loop and an inner inductor current loop, with the outer loop power reference value P. * To receive external input command values, the actual gain tracks the reference gain, and then the current reference value is generated by the PI controller. The actual inductor current tracks the current reference value, and then the modulated wave is generated by the PI controller.

[0072] Specifically, the upper-level power allocation instructions (sources include power instructions from the photovoltaic power plant's AGC / AVC, power instructions from the photovoltaic power plant's pole controller, power instructions from the photovoltaic power plant's DC station controller, and instructions from the photovoltaic power plant's DC operation backend) are based on the actual design of the photovoltaic power plant's control and protection system. The sources include, but are not limited to, power instructions from the photovoltaic power plant's AGC / AVC, power instructions from the photovoltaic power plant's pole controller, power instructions from the photovoltaic power plant's DC station controller, and instructions from the photovoltaic power plant's DC operation backend. This embodiment uses the power instructions from the photovoltaic power plant's DC station controller as an example for explanation.

[0073] Specifically, the DC-DC converter is configured with two control modes: constant gain control mode (mode 1) and constant frequency and constant width control mode (mode 2).

[0074] Specifically, the specific process of the constant-gain control mode of the DC-DC converter is as follows: Figure 5 As shown, the expression for generating the current reference value by the PI controller after the actual gain tracks the reference gain is:

[0075] ;

[0076] In the formula, M is the transmission gain of the DC-DC converter, used as a current reference value; V out V is the output voltage. in For input voltage; Lr For resonant inductance (including transformer leakage inductance); L m f is the magnetizing inductance of the transformer; n Here, Q is the normalized frequency; Q is the quality factor.

[0077] The expression for normalized frequency is:

[0078] ;

[0079] In the formula, f s For the operating frequency, f r The resonant frequency;

[0080] The expression for the quality factor is:

[0081] ;

[0082] ;

[0083] In the formula, C r R is the resonant capacitor; R is an intermediate parameter; R load is the equivalent load; n is the turns ratio of the isolation transformer.

[0084] Specifically, the control strategy of the constant gain control mode is a dual closed-loop control, consisting of an outer gain loop and an inner inductor current loop. The reference value of the outer gain loop is 1, the actual gain tracks the reference gain, and then the current reference value is generated by the PI controller. The actual inductor current tracks the current reference value, and then the modulated wave is generated by the PI controller.

[0085] Specifically, the specific process of the DC-DC converter's fixed-frequency, fixed-width control mode is as follows: Figure 4 As shown, an open-loop control method is adopted, with a fixed duty cycle and a fixed frequency trigger signal. Considering soft-switching conditions, the duty cycle can be set to 0.49-0.5, and the frequency is set to the resonant frequency (considering the main resonant frequency). The expression for this resonant frequency is:

[0086] ;

[0087] In the formula, f r L is the resonant frequency; r For resonant inductance; C r It is a resonant capacitor.

[0088] It should be noted that the control mode switching method for the bus converter control voltage is as follows: Figure 6 As shown, under normal operating conditions, the bus converter operates in mode 1. When a rise in the low-voltage bus voltage occurs, the bus converter detects the low-voltage bus voltage U. DCL , when U DCL_OV >U DCL >U DCL_OLTime (U) DCL_OV The overvoltage lockout value for the low-voltage busbar is 1.1 pu-1.2 pu, which can be considered based on the configuration of the busbar assembly project. DCL_OL The setting for the low-voltage bus overvoltage control mode switching is determined based on the configuration selected for the bus converter project (1.05 pu-1.15 pu can be considered). After a delay time t1 (generally considered to be 20ms-40ms), the bus converter control mode switches from mode 1 to mode 2, and the low-voltage bus voltage is maintained at U using the pu droop curve control. DCL_OL and U DCL_RE (The return value for switching the low-voltage bus overvoltage control mode is generally considered to be 0.9-0.92 times U.) DCL_OL The intermediate value ensures that the photovoltaic power generation unit does not disconnect from the grid.

[0089] Specifically, the use of PU droop curve control for low-voltage bus voltage includes: multiple sets of bus converters connected to the low-voltage bus; when the bus voltage fluctuates, the multiple sets of bus converters adjust their power output according to their current maximum power output (reduce power output when bus voltage rises, increase power output when bus voltage falls); DC converters with lower power output capacity adjust less, while converters with higher power output capacity adjust more.

[0090] Specifically, the subsequent collector converter waits to receive the DC station control power adjustment command. If U... DCL DCL_RE And maintain the delay time t2 (generally considered 20ms-40ms), then switch back to mode 1. After receiving the adjustment command, the pooling converter simultaneously sends the output power command of each pooling converter to the DC station control, and the pooling converter switches to mode 3, using constant power control to accurately control the low-voltage bus voltage.

[0091] Specifically, U is satisfied at any time DCL >U DCL_OV With a maintenance delay time t3 (the low-voltage busbar has a relatively large current, and is generally considered to be 10ms-20ms depending on the actual device and equipment requirements), the bus converter is locked, and charging and unlocking are performed after receiving the reset command.

[0092] It should also be noted that the control mode switching method for the DC-DC converter control voltage is as follows: Figure 7 As shown, under normal operating conditions, the DC-DC converter operates in mode 1.

[0093] Specifically, when a sudden change in low-voltage bus voltage or medium-voltage bus voltage occurs, the DC-DC converter gain M increases or decreases, provided that M ≤ M L or M≥M H (M) L ​For low-gain mode switching, a setpoint of 0.85-0.95 is generally considered; M H The high-gain mode switching setpoint is generally considered to be 1.05-1.15), and the maintenance delay time t1 is generally considered to be 10ms-30ms. The DC-DC converter control mode switches to mode 2.

[0094] Specifically, when the gain satisfies M≤M HRE or M≥M LRE (M) HRE and M LRE The return value for mode switching is generally considered to be 1.03-1.05 times the switching setpoint and 0.95-0.97 times the switching setpoint, and the maintenance delay time t2 is generally considered to be 15ms-35ms. The DC converter control mode switches to mode 1.

[0095] Specifically, U is satisfied at any time DCTL >U DCTL_OV or U DCTM >U DCTM_OV (U) DCTL U DCTM These are the sampled values ​​of the low and medium voltage bus voltages of the DC-DC converter; U DCTL_OV U DCTM_OV The overvoltage setting values ​​for the low and medium voltage bus are respectively taken into account (considering the tolerance of the DC converter body and its accessories, generally 1.05pu-1.1pu), and a delay time t3 is maintained (considering the tolerance of the DC converter body and its accessories, generally 10ms-20ms). The DC converter is locked, and charging and unlocking are performed after receiving the reset command.

[0096] To facilitate understanding of the above-mentioned technical solution of the present invention, the following is a detailed description using a centralized photovoltaic medium-voltage DC collection and transmission system with a single-string DC converter as an example:

[0097] The system mainly comprises six functional areas: a photovoltaic (PV) power generation area, a PV combiner area, a DC boost area, a DC collection area, a centralized inverter area, and a grid-connected area. The PV power generation area includes multiple PV power generation units and string lines. The PV power generation units are connected in series and parallel through the string lines to output DC power. The PV combiner area includes multiple PV combiner converters with maximum power point tracking (MPPT) and combiner lines, used to collect the outputs of multiple PV power generation units and perform primary voltage boosting. The DC boost area includes multiple low-voltage buses and DC converters with an isolated topology. The outputs of the multiple combiner converters are connected in parallel to the low-voltage buses. Subsequently, the voltage level is upgraded from low voltage to medium voltage through DC converters; the DC collection area includes multiple DC bus lines and DC isolation devices, which are used to collect the outputs of multiple DC converters to the medium voltage bus and effectively isolate single-phase grounding faults in each branch through DC isolation devices; the centralized inverter area includes the medium voltage bus and AC / DC converters, which convert the DC power on the medium voltage bus to AC power; the grid connection area includes connecting transformers and grid connection buses, which convert the AC power output from the AC / DC converters to AC power before connecting it to the AC grid bus, thus realizing reliable grid connection between the photovoltaic power generation system and the grid.

[0098] During rated steady-state operation of the system, the AC / DC converter adopts a constant DC voltage and constant reactive power control mode, maintaining the medium-voltage DC bus voltage at its rated value through closed-loop control. The DC converter operates in a constant gain control mode, maintaining the transmission gain at its rated value of 1 through a dual closed-loop control consisting of an outer gain loop and an inner inductor current loop, maximizing the efficient power transmission between the low-voltage bus and the medium-voltage bus. At this time, the low-voltage bus voltage is naturally clamped to a stable value by being jointly determined by the medium-voltage bus voltage and the DC converter gain. The photovoltaic combiner converter operates in a maximum power point tracking control mode, adjusting the operating point of the combiner converter in real time through maximum power point tracking algorithms such as the perturbation observation method or the incremental conductance method, so that the photovoltaic power generation unit outputs electrical energy at maximum power under the current environmental conditions (illuminance and temperature), ensuring that the overall power generation efficiency of the system reaches the optimal level.

[0099] When the system experiences a sudden decrease in absorbable power or a fault on the AC grid side, the limited output power of the AC-DC converter leads to power accumulation on the medium-voltage bus, causing a rapid rise in the medium-voltage bus voltage. Since the DC converter maintains the voltage ratio between the low-voltage bus and the medium-voltage bus in constant gain mode, the rise in the medium-voltage bus voltage will be transmitted to the low-voltage bus, causing the low-voltage bus voltage to rise synchronously. Based on real-time monitoring of local electrical quantity changes, when the DC converter detects a sudden change in the low-voltage bus voltage or the medium-voltage bus voltage that causes the transmission gain to deviate from the rated value and exceed the switching threshold, it immediately switches from constant gain control mode to constant frequency and constant width control mode. By setting a trigger signal with a fixed duty cycle and resonant frequency, the working gain of the resonant cavity is maintained, avoiding efficiency degradation and excessive heat generation caused by voltage sudden changes.

[0100] Meanwhile, when the bus converter detects that the low-voltage bus voltage exceeds the overvoltage control switching threshold but is below the overvoltage blocking threshold for a preset duration, it immediately switches from the maximum power point tracking (MPPT) control mode to the dynamic voltage control mode. It employs PU droop curve control based on the maximum power point before mode switching, using a dual-loop control method to precisely control the inductor current, dynamically stabilizing the low-voltage bus voltage and limiting it within a safe range. This prevents the photovoltaic power generation unit from stopping power output due to excessively low input voltage or disconnecting from the grid due to excessively high voltage. After the bus converter receives an external power command from the upper-level control system, it switches from the dynamic voltage control mode to the constant power control mode. Through a dual-loop control consisting of a gain outer loop and an inductor current inner loop, the actual output power accurately tracks the command value, achieving stable control of the low-voltage bus voltage.

[0101] When the fluctuation amplitude of the low-voltage bus voltage or the medium-voltage bus voltage exceeds the respective set overvoltage blocking threshold and continues for a preset duration, the bus converter and the DC converter are blocked and stop working according to their respective protection settings, enter the protection state and wait for the fault to be cleared. Until a reset command is received, the charging and unlocking operations are performed according to the preset program to gradually restore the normal operation state. Through the coordinated cooperation of the above-mentioned multi-level coupled voltage control method, the present invention realizes the stable and reliable operation of the centralized photovoltaic DC power generation collection and transmission system under various operating conditions.

[0102] In one embodiment, an electronic device is provided. For example... Figure 8 As shown, the electronic device includes a processor, a system bus, main memory, and auxiliary memory. The processor communicates with both the main memory and the auxiliary memory via the system bus.

[0103] The processor provides computational and control capabilities. Main memory, or internal memory, provides the environment for the computer program to run. Secondary memory is a non-volatile storage medium that stores the operating system and the computer program. When the computer program is executed by the processor, it implements the steps described in the above method embodiments.

[0104] Those skilled in the art will understand that Figure 8 The structure shown is only a block diagram of a part of the structure related to the present invention and does not constitute a limitation. The specific electronic device may include more or fewer components, or have different component arrangements.

[0105] In addition, the present invention also provides a computer-readable storage medium having computer instructions stored thereon, which, when executed by a processor, implement the steps in the above method embodiments.

[0106] The computer-readable storage medium includes main memory or secondary memory. The main memory may be random access memory (RAM), and the secondary memory may be a non-volatile storage medium such as read-only memory (ROM), flash memory, hard disk, or optical storage.

[0107] Those skilled in the art will understand that all or part of the processes in the above embodiments can be implemented by a computer program instructing related hardware.

[0108] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A centralized photovoltaic direct current power generation collection and sending out multi-stage coupling voltage control method, characterized in that, The application relates to a photovoltaic power generation system, and particularly relates to a photovoltaic power generation system with a maximum power point tracking control mode, a dynamic voltage control mode and a constant power control mode. The application relates to a photovoltaic power generation system, and particularly relates to a photovoltaic power generation system with a maximum power point tracking control mode, a dynamic voltage control mode and a constant power control mode. The maximum power point tracking control mode is used for realizing maximum power output of the photovoltaic power generation unit in a normal working state. The dynamic voltage control mode is used for controlling the low-voltage bus voltage to be stable through a P-U droop curve when the low-voltage bus voltage rises, and guaranteeing that the photovoltaic power generation unit does not disconnect from the grid. The constant power control mode is used for controlling the low-voltage bus voltage after receiving an external power instruction. The constant gain control mode is used for coping with voltage disturbance and accelerating voltage recovery of the low-voltage bus and the medium-voltage bus, so as to improve system stability. The constant frequency and width control mode is used for maintaining the working gain of the resonant cavity and keeping the working efficiency of the direct-current converter when voltage suddenly changes, so as to reduce excessive heating. The dynamic voltage control mode adopts a double closed-loop control mode, and specifically comprises the following steps.

2. The centralized photovoltaic DC power generation collection and sending multi-stage coupling voltage control method according to claim 1, characterized in that, The inductor current is controlled through a P-U droop curve based on the maximum power point before mode switching, so as to realize stable maintenance of the low-voltage bus direct-current voltage. The inductor current is controlled through a P-U droop curve based on the maximum power point before mode switching, so as to realize stable maintenance of the low-voltage bus direct-current voltage.

3. The centralized photovoltaic DC power generation collection and sending out multi-stage coupling voltage control method according to claim 2, characterized in that, When the dynamic voltage control mode is switched to, the current-converging converter works at the maximum power point under the current environmental constraint. The slope of the P-U droop curve is set according to the size of the current output power of each current-converging converter. The slope of the P-U droop curve is directly proportional to the size of the output power, so as to avoid the photovoltaic panel from stopping power output due to too low input voltage of the current-converging converter. The constant power control mode adopts double closed-loop control composed of a gain outer ring and an inductor current inner ring, and specifically comprises the following steps.

4. The centralized photovoltaic DC power generation collection and sending out multi-stage coupling voltage control method according to claim 1, characterized in that, The actual gain is tracked to the reference gain, and then the current reference value is generated through a PI controller; and the actual inductor current is tracked to the current reference value, and then the modulation wave is generated through a PI controller again, so as to realize stable control of the low-voltage bus voltage. The constant gain control mode adopts double closed-loop control composed of a gain outer ring and an inductor current inner ring; and specifically comprises the following steps.

5. The centralized photovoltaic DC power generation collection and sending out multi-stage coupling voltage control method according to claim 1, characterized in that, The actual gain is tracked to the reference gain, and then the current reference value is generated through a PI controller; and the actual inductor current is tracked to the current reference value, and then the modulation wave is generated through a PI controller again, so as to realize stable control of the low-voltage bus voltage. The expression for generating the current reference value through a PI controller after the actual gain is tracked to the reference gain is as follows. The constant frequency and width control mode adopts open-loop control, and specifically comprises the following steps. ； where M is the dc-to-dc converter transfer gain used as a current reference; V out is the output voltage; V in is the input voltage; L r is the resonant inductance; L m is the transformer magnetizing inductance; f n is the normalized frequency; and Q is the quality factor.

6. The centralized photovoltaic DC power generation collection and sending out multi-stage coupling voltage control method according to claim 5, characterized in that, The working gain of the resonant cavity is maintained by setting a fixed duty ratio and a fixed frequency trigger signal; the fixed duty ratio is set according to a soft switching condition; and the fixed frequency is set as a resonant frequency; and the expression of the resonant frequency is as follows. The constant frequency and width control mode adopts open-loop control, and specifically comprises the following steps. ； where f r is the resonant frequency; L r is the resonant inductance; C r is the resonant capacitance.

7. The centralized photovoltaic DC power generation collection and sending out multi-stage coupling voltage control method according to claim 1, characterized in that, ​ In a normal working state, the bus converter works in a maximum power tracking control mode; When it is detected that the low-voltage bus voltage exceeds an overvoltage control switching threshold and is lower than an overvoltage locking threshold and lasts for a preset time length, the bus converter control mode is switched from the maximum power tracking control mode to a dynamic voltage control mode, and the low-voltage bus voltage is controlled between the overvoltage control switching threshold and an overvoltage control return threshold through a P-U droop curve; When the low-voltage bus voltage is lower than the overvoltage control return threshold and lasts for a preset time length, the maximum power tracking control mode is switched back; When the bus converter receives a power instruction issued by a superior control system, the bus converter is switched to a constant power control mode; When the low-voltage bus voltage reaches or exceeds the overvoltage locking threshold and lasts for a preset time length, the bus converter is locked until a reset instruction is received to charge and unlock.

8. The centralized photovoltaic DC power generation collection and sending out multi-stage coupling voltage control method according to claim 1, characterized in that, The DC converter switches between a constant gain control mode and a constant frequency and width control mode according to gain changes between the low-voltage bus and the medium-voltage bus, and the switching comprises: In a normal working state, the DC converter works in a constant gain control mode; When the low-voltage bus voltage or the medium-voltage bus voltage suddenly changes to cause the DC converter gain to be less than or equal to a low-gain switching threshold, or the DC converter gain to be greater than or equal to a high-gain switching threshold, and lasts for a preset time length, the DC converter is switched to a constant frequency and width control mode; When the DC converter gain is between a low-gain return threshold and a high-gain return threshold and lasts for a preset time length, the DC converter is switched back to the constant gain control mode; When the low-voltage bus voltage or the medium-voltage bus voltage is greater than or equal to a corresponding overvoltage locking threshold and lasts for a preset time length, the DC converter is locked until a reset instruction is received to charge and unlock.

9. A centralized photovoltaic direct current power generation collection and transmission system for implementing the centralized photovoltaic direct current power generation collection and transmission multi-stage coupling voltage control method of any one of claims 1-8, characterized in that, The system comprises: A photovoltaic power generation area comprising a plurality of groups of photovoltaic power generation units and group string lines, for generating photovoltaic power through photovoltaic panels and connecting the groups in series through the group string lines; A photovoltaic bus area comprising a plurality of groups of bus converters and bus lines, for collecting the groups of photovoltaic power generation groups through the bus lines and connecting the groups to the bus converters; A DC voltage boosting area comprising a plurality of groups of low-voltage buses and DC converters, for connecting the groups of bus converters to the low-voltage buses and boosting the voltage through the DC converters; A DC collection area comprising a plurality of groups of DC bus lines and DC isolation devices, for connecting the groups of DC converters to the medium-voltage buses through the DC isolation devices and isolating single-phase ground faults of the branches of the DC converters through the DC isolation devices; A centralized inverter area comprising a medium-voltage bus and an AC / DC converter, for converting the DC power of the medium-voltage bus into AC power; A grid connection area comprising a tie transformer and a grid bus, for connecting the AC power output by the centralized inverter area to the AC grid bus through the tie transformer.

10. The centralized photovoltaic DC power generation, collection and transmission system according to claim 9, characterized in that, The photovoltaic power generation units comprise a plurality of photovoltaic panels and matching bus converters; The plurality of photovoltaic panels work cooperatively to achieve power transmission and voltage boosting by connecting to the bus converters and connecting the boosted DC power in parallel to the low-voltage buses; The low-voltage buses are connected to the DC converters and connected in parallel to the medium-voltage buses; The medium-voltage buses are connected to the AC / DC converters and connected to the tie transformers, and finally connected to the AC grid.

11. The centralized photovoltaic DC power generation, collection and transmission system according to claim 10, characterized in that, The current collector converter adopts a non-isolated topology structure, including a two-level single-inductor single-switch Boost topology, a double-inductor double-switch three-level Boost topology, a cross-capacitance three-level Boost topology and a Buck-Boost topology.

12. The centralized photovoltaic DC power generation, collection and transmission system according to claim 11, characterized in that, The direct current converter adopts an isolated topology structure, including an LLC converter topology and a CLLC converter topology.

13. The centralized photovoltaic DC power generation, collection and transmission system according to claim 10, characterized in that, The AC / DC converter adopts a modular multilevel converter valve, and adopts a constant direct voltage and constant reactive power control mode when the system works.

14. An electronic device, comprising: The electronic device comprises: a processor; a system bus; a main memory in communication with the processor through the system bus; an auxiliary memory in communication with the processor through the system bus; wherein the main memory or the auxiliary memory stores a computer program executable by the processor, and the computer program is executed by the processor to implement the method in any one of claims 1-8.

15. A computer-readable storage medium, characterized in that, The computer readable storage medium stores computer instructions, and the computer instructions are executed by the processor to make the processor implement the method in any one of claims 1-8, and the computer readable storage medium comprises the main memory or the auxiliary memory.

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