A two-stage photovoltaic grid-connected power generation optimization device, control system and method

Abstract

This invention relates to a two-stage photovoltaic grid-connected power generation optimization device, control system, and method, comprising: a second harmonic suppression unit for filtering out the second harmonic component in the voltage of the medium-voltage DC bus and the inductor current on the medium-voltage DC bus side; and a control unit for determining the optimal input current command value of the DC / DC converter connected to the photovoltaic system through the low-voltage DC bus based on the voltage command value of the medium-voltage DC bus, the current of the medium-voltage DC bus, the inductor current on the medium-voltage DC bus side, the voltage of the medium-voltage DC bus after filtering out the second harmonic component, and the inductor current on the medium-voltage DC bus side after filtering out the second harmonic component. This invention can suppress the second harmonic fluctuation of the medium-voltage DC bus voltage when a low-voltage fault occurs in a two-stage photovoltaic grid-connected power generation system, thereby improving the power quality of the medium-voltage DC bus.

Description

Technical Field

[0001] This invention relates to the field of new energy power generation control technology, specifically to a two-stage photovoltaic grid-connected power generation optimization device, control system, and method. Background Technology

[0002] A two-stage grid-connected photovoltaic power generation system collects the electrical energy from the photovoltaic systems within the station via a medium-voltage DC bus and then centrally feeds it into the AC grid through a grid-connected inverter. This significantly reduces the amount of cabling used within the station and also offers higher power generation efficiency. For example... Figure 1 As shown, compared with the structure of traditional distributed inverter photovoltaic systems, the two-stage photovoltaic grid-connected power generation system adds a DC / DC converter stage between the photovoltaic array and the grid-connected inverter. In order to meet the high step-up ratio requirement of photovoltaic energy access to the medium-voltage DC bus, the DC / DC converter usually adopts a cascaded structure with parallel inputs and series outputs.

[0003] However, when a voltage drop occurs in the AC grid, the medium-voltage DC bus voltage of a two-stage photovoltaic grid-connected power generation system will continue to rise. Exceeding a certain limit will cause the photovoltaic power station to disconnect from the grid, failing to meet the low-voltage ride-through capability requirements of photovoltaic power stations. Furthermore, when an unbalanced voltage drop occurs in the AC grid, the medium-voltage DC bus voltage will also experience second-harmonic fluctuations. This increases the number of charge-discharge cycles of the DC bus's equivalent capacitance, reducing its lifespan. It is also detrimental to the normal operation of loads with high power quality requirements (such as DC motors and precision electronic instruments) connected to the medium-voltage DC bus.

[0004] In the prior art, one approach is to use a load shedding circuit to consume the differential power on the medium-voltage DC bus during fault ride-through, thereby achieving low-voltage ride-through. However, the cost and heat dissipation issues of the load shedding circuit are prominent. Another approach is to eliminate the rise and fluctuation of the medium-voltage DC bus voltage through an inverter. However, for two-stage photovoltaic grid-connected power generation systems, this approach reduces the inverter's control freedom. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a two-stage photovoltaic grid-connected power generation optimization device, control system, and method. By controlling the DC / DC converter, the two-stage photovoltaic grid-connected power generation system enables low-voltage ride-through, thereby improving the power quality of the medium-voltage DC bus and increasing the control freedom of the inverter in the system.

[0006] The objective of this invention is achieved through the following technical solution:

[0007] This invention provides a two-stage photovoltaic grid-connected power generation optimization device, the improvement of which is that the device includes:

[0008] The second harmonic suppression unit is used to filter out the second harmonic component in the voltage of the medium-voltage DC bus and the inductor current on the medium-voltage DC bus side;

[0009] The control unit is used to determine the optimal input current command value of the DC / DC converter connected to the photovoltaic system through the low-voltage DC bus based on the voltage command value of the medium-voltage DC bus, the current of the medium-voltage DC bus and the inductor current on the side of the medium-voltage DC bus, the voltage of the medium-voltage DC bus after filtering out the second harmonic component and the inductor current on the side of the medium-voltage DC bus after filtering out the second harmonic component.

[0010] Preferably, the second harmonic suppression unit includes:

[0011] The first notch filter is used to filter out the second harmonic component in the voltage of the medium-voltage DC bus.

[0012] The second notch filter is used to filter out the second harmonic component in the current of the medium-voltage DC bus.

[0013] Preferably, the control unit includes:

[0014] The voltage control unit is used to determine the inductor current command value on the medium-voltage DC bus side based on the voltage command value of the medium-voltage DC bus and the voltage of the medium-voltage DC bus after filtering out the second harmonic component;

[0015] The current control unit is used to determine the optimal input current command value of the DC / DC converter connected to the photovoltaic system through the low-voltage DC bus based on the current of the medium-voltage DC bus, the inductor current on the medium-voltage DC bus side, the inductor current on the medium-voltage DC bus side after filtering out the second harmonic component, and the inductor current command value on the medium-voltage DC bus side.

[0016] Furthermore, the voltage control unit includes: a first subtractor and a first PI controller connected in sequence;

[0017] The input to the first subtractor is the voltage command value of the medium-voltage DC bus and the voltage of the medium-voltage DC bus after filtering out the second harmonic component;

[0018] The output of the first PI controller is the inductor current command value on the medium-voltage DC bus side.

[0019] Furthermore, the current control unit includes: a second subtractor, a third subtractor, a second PI controller connected to the second subtractor, a proportional resonator connected to the third subtractor, and an adder connected to the second PI controller and the proportional resonator;

[0020] The input to the second subtractor is the inductor current command value on the medium-voltage DC bus side and the inductor current on the medium-voltage DC bus side after filtering out the second harmonic component.

[0021] The input to the third subtractor is the inductor current on the medium-voltage DC bus side and the current of the medium-voltage DC bus.

[0022] The output of the adder is the optimal command value of the input current of the DC / DC converter connected to the photovoltaic system via the low-voltage DC bus.

[0023] Based on the same inventive concept, the present invention also provides a two-stage photovoltaic grid-connected power generation control system, wherein the improvement is that the system includes:

[0024] The optimization device as described above;

[0025] A control device is used to adjust the input current command value of the DC / DC converter in the maximum power point tracking control solar controller to the optimal input current command value of the DC / DC converter, and to control the DC / DC converter using the maximum power point tracking control solar controller.

[0026] Based on the same inventive concept, this invention also provides a two-stage photovoltaic grid-connected power generation control method, the improvement of which is that the method includes:

[0027] The optimal input current command value of the DC / DC converter connected to the photovoltaic system through the low-voltage DC bus is determined based on the voltage of the medium-voltage DC bus, the voltage command value of the medium-voltage DC bus, the current of the medium-voltage DC bus, and the inductor current on the medium-voltage DC bus side.

[0028] The input current command value of the DC / DC converter in the maximum power point tracking control solar controller is adjusted to the optimal input current command value of the DC / DC converter, and the DC / DC converter is controlled by the maximum power point tracking control solar controller.

[0029] Preferably, determining the optimal input current command value of the DC / DC converter connected to the photovoltaic system via the low-voltage DC bus based on the voltage of the medium-voltage DC bus, the voltage command value of the medium-voltage DC bus, the current of the medium-voltage DC bus, and the inductor current on the medium-voltage DC bus side includes:

[0030] The inductor current command value on the medium-voltage DC bus side is determined based on the voltage of the medium-voltage DC bus and the voltage command value of the medium-voltage DC bus.

[0031] The optimal input current command value of the DC / DC converter is determined based on the inductor current command value on the medium-voltage DC bus side, the inductor current on the medium-voltage DC bus side, and the current on the medium-voltage DC bus.

[0032] Further, determining the inductor current command value on the medium-voltage DC bus side based on the voltage of the medium-voltage DC bus and the voltage command value of the medium-voltage DC bus includes:

[0033] Input the voltage of the medium-voltage DC bus into the first notch filter;

[0034] Input the output of the first notch filter and the voltage command value of the medium-voltage DC bus into the first subtractor;

[0035] The output of the first subtractor is input into the first PI controller to obtain the inductor current command value on the medium-voltage DC bus side output by the first PI controller.

[0036] Further, determining the optimal input current command value of the DC / DC converter based on the inductor current command value on the medium-voltage DC bus side, the inductor current on the medium-voltage DC bus side, and the current of the medium-voltage DC bus includes:

[0037] Input the inductor current on the medium-voltage DC bus side into the second notch filter;

[0038] The output of the second notch filter and the inductor current command value on the medium-voltage DC bus side are input to the second PI controller.

[0039] The current of the medium-voltage DC bus and the inductor current on the medium-voltage DC bus side are input into the second subtractor;

[0040] The output of the second subtractor is input into the proportional resonator;

[0041] The output of the second PI controller and the output of the proportional resonator are input into the adder to obtain the optimal command value of the input current of the DC / DC converter output by the adder.

[0042] Compared with the closest existing technology, the present invention has the following advantages:

[0043] This invention provides a two-stage photovoltaic grid-connected power generation optimization device, including a second harmonic suppression unit for filtering out the second harmonic component in the voltage of the medium-voltage DC bus and the inductor current on the medium-voltage DC bus side; and a control unit for determining the optimal input current command value of the DC / DC converter connected to the photovoltaic system through the low-voltage DC bus based on the voltage command value of the medium-voltage DC bus, the current of the medium-voltage DC bus, the inductor current on the medium-voltage DC bus side, the voltage of the medium-voltage DC bus after filtering out the second harmonic component, and the inductor current on the medium-voltage DC bus side after filtering out the second harmonic component. This invention can suppress the second harmonic fluctuation of the medium-voltage DC bus voltage when a low-voltage fault occurs in the two-stage photovoltaic grid-connected power generation, thereby improving the power quality of the medium-voltage DC bus.

[0044] Among them, when obtaining the optimal command value of the input current of the DC / DC converter, the use of dual control units for voltage and current improves the fault response speed of the two-stage photovoltaic grid-connected power generation system and shortens the fault time.

[0045] The present invention provides a two-stage photovoltaic grid-connected power generation control system and method. This scheme can achieve low voltage ride-through in a two-stage photovoltaic grid-connected power generation system by controlling a DC / DC converter without adding additional hardware circuitry, thereby improving the control freedom of the inverter in the two-stage photovoltaic grid-connected power generation system. Attached Figure Description

[0046] Figure 1 This is a schematic diagram of the topology of a two-stage photovoltaic grid-connected power generation system;

[0047] Figure 2 This is a schematic diagram of the two-stage photovoltaic grid-connected power generation optimization device in Embodiment 1 of the present invention;

[0048] Figure 3 This is a connection diagram of the unit components in the two-stage photovoltaic grid-connected power generation optimization device in Embodiment 1 of the present invention;

[0049] Figure 4 This is a schematic diagram of the two-stage photovoltaic grid-connected power generation control system in Embodiment 2 of the present invention;

[0050] Figure 5 This is a flowchart of the two-stage photovoltaic grid-connected power generation control method in Embodiment 3 of the present invention. Detailed Implementation

[0051] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0052] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0053] Example 1

[0054] In such Figure 1 In the two-stage photovoltaic grid-connected power generation system shown, when the voltage of phase A on the AC side of the DC / AC converter drops, it causes the voltage of the medium-voltage DC bus to rise. To avoid the photovoltaic system disconnecting from the grid due to overvoltage protection, this invention provides a two-stage photovoltaic grid-connected power generation optimization device, such as... Figure 2 As shown, the device includes:

[0055] The second harmonic suppression unit is used to filter out the second harmonic component in the voltage of the medium-voltage DC bus and the inductor current on the medium-voltage DC bus side;

[0056] The control unit is used to determine the optimal input current command value of the DC / DC converter connected to the photovoltaic system through the low-voltage DC bus based on the voltage command value of the medium-voltage DC bus, the current of the medium-voltage DC bus and the inductor current on the side of the medium-voltage DC bus, the voltage of the medium-voltage DC bus after filtering out the second harmonic component and the inductor current on the side of the medium-voltage DC bus after filtering out the second harmonic component.

[0057] Figure 1 middle, I pv The current V input to the DC / DC converter from the photovoltaic system via the low-voltage DC bus. pv i is the voltage at the input terminal of the DC / DC converter. L i is the current in the inductor L on the medium-voltage DC bus side. C For the capacitor C bus The current.

[0058] In Embodiment 1 of the present invention, as Figure 3 As shown, the above-mentioned second harmonic suppression unit includes:

[0059] The first notch filter is used to filter out the second harmonic component in the voltage of the medium-voltage DC bus.

[0060] The second notch filter is used to filter out the second harmonic component in the current of the medium-voltage DC bus.

[0061] In Embodiment 1 of the present invention, in order to quickly suppress the rise of the medium-voltage DC bus voltage and the generation of the second harmonic component, and to obtain the optimal command value of the input current of the DC / DC converter, a dual-loop voltage and current control is adopted. Specifically, the control unit includes:

[0062] The voltage control unit is used to determine the inductor current command value on the medium-voltage DC bus side based on the voltage command value of the medium-voltage DC bus and the voltage of the medium-voltage DC bus after filtering out the second harmonic component;

[0063] The current control unit is used to determine the optimal input current command value of the DC / DC converter connected to the photovoltaic system through the low-voltage DC bus based on the current of the medium-voltage DC bus, the inductor current on the medium-voltage DC bus side, the inductor current on the medium-voltage DC bus side after filtering out the second harmonic component, and the inductor current command value on the medium-voltage DC bus side.

[0064] Specifically, such as Figure 3 As shown, the voltage control unit includes: a first subtractor and a first PI controller connected in sequence;

[0065] The input to the first subtractor is the voltage command value of the medium-voltage DC bus and the voltage of the medium-voltage DC bus after filtering out the second harmonic component;

[0066] The output of the first PI controller is the inductor current command value on the medium-voltage DC bus side.

[0067] like Figure 3 As shown, the aforementioned current control unit includes: a second subtractor, a third subtractor, a second PI controller connected to the second subtractor, a proportional resonator connected to the third subtractor, and an adder connected to the second PI controller and the proportional resonator.

[0068] The input to the second subtractor is the inductor current command value on the medium-voltage DC bus side and the inductor current on the medium-voltage DC bus side after filtering out the second harmonic component.

[0069] The input to the third subtractor is the inductor current on the medium-voltage DC bus side and the current of the medium-voltage DC bus.

[0070] The output of the adder is the optimal command value of the input current of the DC / DC converter connected to the photovoltaic system via the low-voltage DC bus.

[0071] When the grid voltage experiences an unbalanced drop, the addition of voltage and current dual-loop control will quickly stop the medium-voltage DC bus voltage from rising and maintain it at a normal value, thus resolving the second-harmonic frequency fluctuation problem.

[0072] Figure 3 Middle,U dc U is the voltage of the medium-voltage DC bus. dc,ref i represents the voltage command value for the medium-voltage DC bus. L i represents the inductor current on the medium-voltage DC bus side. g This represents the current of the medium-voltage DC bus.

[0073] Example 2

[0074] Based on the same inventive concept, this invention also provides a two-stage photovoltaic grid-connected power generation control system, such as... Figure 4 As shown, the system includes:

[0075] The optimized apparatus as described in Example 1;

[0076] A control device is used to adjust the input current command value of the DC / DC converter in the maximum power point tracking control solar controller to the optimal input current command value of the DC / DC converter, and to control the DC / DC converter using the maximum power point tracking control solar controller.

[0077] Example 3

[0078] Based on the same inventive concept, this invention also provides a two-stage photovoltaic grid-connected power generation control method, such as... Figure 5 As shown, the method includes:

[0079] Step 1. Determine the optimal input current command value of the DC / DC converter connected to the photovoltaic system through the low-voltage DC bus based on the voltage of the medium-voltage DC bus, the voltage command value of the medium-voltage DC bus, the current of the medium-voltage DC bus, and the inductor current on the medium-voltage DC bus side;

[0080] Step 2. Adjust the input current command value of the DC / DC converter in the maximum power point tracking control solar controller to the optimal input current command value of the DC / DC converter, and use the maximum power point tracking control solar controller to control the DC / DC converter.

[0081] In Embodiment 3 of the present invention, step 1 above includes:

[0082] The inductor current command value on the medium-voltage DC bus side is determined based on the voltage of the medium-voltage DC bus and the voltage command value of the medium-voltage DC bus.

[0083] The optimal input current command value of the DC / DC converter is determined based on the inductor current command value on the medium-voltage DC bus side, the inductor current on the medium-voltage DC bus side, and the current on the medium-voltage DC bus.

[0084] The determination of the inductor current command value on the medium-voltage DC bus side based on the voltage of the medium-voltage DC bus and the voltage command value of the medium-voltage DC bus includes:

[0085] Input the voltage of the medium-voltage DC bus into the first notch filter;

[0086] Input the output of the first notch filter and the voltage command value of the medium-voltage DC bus into the first subtractor;

[0087] The output of the first subtractor is input into the first PI controller to obtain the inductor current command value on the medium-voltage DC bus side output by the first PI controller.

[0088] Specifically, determining the optimal input current command value of the DC / DC converter based on the inductor current command value on the medium-voltage DC bus side, the inductor current on the medium-voltage DC bus side, and the current of the medium-voltage DC bus includes:

[0089] Input the inductor current on the medium-voltage DC bus side into the second notch filter;

[0090] The output of the second notch filter and the inductor current command value on the medium-voltage DC bus side are input to the second PI controller.

[0091] The current of the medium-voltage DC bus and the inductor current on the medium-voltage DC bus side are input into the second subtractor;

[0092] The output of the second subtractor is input into the proportional resonator;

[0093] The output of the second PI controller and the output of the proportional resonator are input into the adder to obtain the optimal command value of the input current of the DC / DC converter output by the adder.

[0094] In Embodiment 3 of the present invention, if the grid fault is resolved after performing step 2 above, i.e., the voltage of phase A returns to normal, the input current command value of the DC / DC converter in the maximum power point tracking control solar controller is adjusted to the input current command value of the DC / DC converter when the grid is normal, and the DC / DC converter of the maximum power point tracking control solar controller continues to be used; otherwise, the control method in this embodiment is executed continuously.

[0095] In summary, the present invention provides a two-stage photovoltaic grid-connected power generation optimization device, including a second harmonic suppression unit for filtering out the second harmonic component in the voltage of the medium-voltage DC bus and the inductor current on the medium-voltage DC bus side; and a control unit for determining the optimal input current command value of the DC / DC converter connected to the photovoltaic system through the low-voltage DC bus based on the voltage command value of the medium-voltage DC bus, the current of the medium-voltage DC bus, the inductor current on the medium-voltage DC bus side, the voltage of the medium-voltage DC bus after filtering out the second harmonic component, and the inductor current on the medium-voltage DC bus side after filtering out the second harmonic component. The present invention can suppress the second harmonic fluctuation of the medium-voltage DC bus voltage when a low-voltage fault occurs in the two-stage photovoltaic grid-connected power generation system, thereby improving the power quality of the medium-voltage DC bus.

[0096] Among them, when obtaining the optimal command value of the input current of the DC / DC converter, the use of dual control units for voltage and current improves the fault response speed of the two-stage photovoltaic grid-connected power generation system and shortens the fault time.

[0097] The present invention provides a two-stage photovoltaic grid-connected power generation control system and method. This scheme can achieve low voltage ride-through in a two-stage photovoltaic grid-connected power generation system by controlling a DC / DC converter without adding additional hardware circuitry, thereby improving the control freedom of the inverter in the two-stage photovoltaic grid-connected power generation system.

[0098] Those skilled in the art will understand that embodiments of this application can be provided as methods, systems, or computer program products. Therefore, this application can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, this application can take the form of a computer program product embodied on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0099] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this application. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart... Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0100] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0101] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0102] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A two-stage photovoltaic grid-connected power generation optimization device, characterized in that, The device includes: The second harmonic suppression unit is used to filter out the second harmonic component in the voltage of the medium-voltage DC bus and the inductor current on the medium-voltage DC bus side; The control unit is used to determine the optimal input current command value of the DC / DC converter connected to the photovoltaic system through the low-voltage DC bus based on the voltage command value of the medium-voltage DC bus, the current of the medium-voltage DC bus and the inductor current on the side of the medium-voltage DC bus, the voltage of the medium-voltage DC bus after filtering out the second harmonic component and the inductor current on the side of the medium-voltage DC bus after filtering out the second harmonic component. The control unit includes: The voltage control unit is used to determine the inductor current command value on the medium-voltage DC bus side based on the voltage command value of the medium-voltage DC bus and the voltage of the medium-voltage DC bus after filtering out the second harmonic component; The current control unit is used to determine the optimal input current command value of the DC / DC converter connected to the photovoltaic system through the low-voltage DC bus based on the current of the medium-voltage DC bus, the inductor current on the medium-voltage DC bus side, the inductor current on the medium-voltage DC bus side after filtering out the second harmonic component, and the inductor current command value on the medium-voltage DC bus side. The current control unit includes: a second subtractor, a third subtractor, a second PI controller connected to the second subtractor, a proportional resonator connected to the third subtractor, and an adder connected to the second PI controller and the proportional resonator. The input to the second subtractor is the inductor current command value on the medium-voltage DC bus side and the inductor current on the medium-voltage DC bus side after filtering out the second harmonic component. The input to the third subtractor is the inductor current on the medium-voltage DC bus side and the current of the medium-voltage DC bus. The output of the adder is the optimal command value of the input current of the DC / DC converter connected to the photovoltaic system via the low-voltage DC bus.

2. The apparatus as claimed in claim 1, characterized in that, The second harmonic suppression unit includes: The first notch filter is used to filter out the second harmonic component in the voltage of the medium-voltage DC bus. The second notch filter is used to filter out the second harmonic component in the current of the medium-voltage DC bus.

3. The apparatus as described in claim 2, characterized in that, The voltage control unit includes: a first subtractor and a first PI controller connected in sequence; The input to the first subtractor is the voltage command value of the medium-voltage DC bus and the voltage of the medium-voltage DC bus after filtering out the second harmonic component; The output of the first PI controller is the inductor current command value on the medium-voltage DC bus side.

4. A two-stage photovoltaic grid-connected power generation control system, characterized in that, The system includes: The optimization apparatus as described in any one of claims 1 to 3; A control device is used to adjust the input current command value of the DC / DC converter in the maximum power point tracking control solar controller to the optimal input current command value of the DC / DC converter, and to control the DC / DC converter using the maximum power point tracking control solar controller.

5. A two-stage photovoltaic grid-connected power generation control method, characterized in that, The method includes: The optimal input current command value of the DC / DC converter connected to the photovoltaic system through the low-voltage DC bus is determined based on the voltage of the medium-voltage DC bus, the voltage command value of the medium-voltage DC bus, the current of the medium-voltage DC bus, and the inductor current on the medium-voltage DC bus side. The input current command value of the DC / DC converter in the maximum power point tracking control solar controller is adjusted to the optimal input current command value of the DC / DC converter, and the DC / DC converter is controlled by the maximum power point tracking control solar controller. The step of determining the inductor current command value on the medium-voltage DC bus side based on the voltage of the medium-voltage DC bus and the voltage command value of the medium-voltage DC bus includes: Input the voltage of the medium-voltage DC bus into the first notch filter; Input the output of the first notch filter and the voltage command value of the medium-voltage DC bus into the first subtractor; The output of the first subtractor is input into the first PI controller to obtain the inductor current command value on the medium-voltage DC bus side output by the first PI controller. The step of determining the optimal input current command value of the DC / DC converter based on the inductor current command value on the medium-voltage DC bus side, the inductor current on the medium-voltage DC bus side, and the current of the medium-voltage DC bus includes: Input the inductor current on the medium-voltage DC bus side into the second notch filter; The output of the second notch filter and the inductor current command value on the medium-voltage DC bus side are input to the second PI controller. The inductor current value on the medium-voltage DC bus side and the inductor current on the medium-voltage DC bus side after filtering out the second harmonic component are input into the second subtractor; the output of the second subtractor is input into the proportional resonator. The output of the second PI controller and the output of the proportional resonator are input into the adder to obtain the optimal command value of the input current of the DC / DC converter output by the adder.

6. The method as described in claim 5, characterized in that, The process of determining the optimal input current command value of the DC / DC converter connected to the photovoltaic system via the low-voltage DC bus based on the voltage of the medium-voltage DC bus, the voltage command value of the medium-voltage DC bus, the current of the medium-voltage DC bus, and the inductor current on the medium-voltage DC bus side includes: The inductor current command value on the medium-voltage DC bus side is determined based on the voltage of the medium-voltage DC bus and the voltage command value of the medium-voltage DC bus. The optimal input current command value of the DC / DC converter is determined based on the inductor current command value on the medium-voltage DC bus side, the inductor current on the medium-voltage DC bus side, and the current on the medium-voltage DC bus.

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