MPPT (Maximum Power Point Tracking) method and related device

Abstract

The invention relates to an MPPT tracking method and a related device. The method is applied to a photovoltaic power generation system, the photovoltaic power generation system comprises n photovoltaic branches and an inverter circuit, and n is an integer greater than 1; the method comprises the steps that S1, a control loop comprising a bus voltage loop, n PV voltage outer loops, n PV current inner loops and an inverter voltage outer loop is constructed, and each PV voltage outer loop and each PV current inner loop correspond to each photovoltaic branch; s2, open-circuit voltages of the photovoltaic branches are obtained respectively, whether the open-circuit voltages of the photovoltaic branches are smaller than the sum of the preset bus target voltage and a first preset value or not is determined, if yes, the control loop is controlled to be in a first working mode, and if not, the control loop is controlled to be in a second working mode; and the inverter circuit is controlled through the first working mode or the second working mode. According to the invention, the MPPT mode can be adjusted according to the scene, the primary power conversion loss can be eliminated in some application scenes, and the system efficiency is improved.

Description

Technical Field

[0001] This invention relates to the field of energy optimization control technology for photovoltaic power generation systems, and more specifically, to an MPPT tracking method and related apparatus. Background Technology

[0002] Current mainstream MPPT (Maximum Power Point Tracking) solutions are all implemented based on Boost circuit architecture. For example... Figure 6 The diagram shows the circuit schematic of a photovoltaic system. Switches V1 and V2 control the Boost circuits of photovoltaic branches PV1 and PV2, respectively. The outputs of multiple photovoltaic branches are converted into the final output by an inverter circuit composed of switches V2 to V5. According to the maximum power transfer theorem in circuit theory, the photovoltaic cell output power reaches its maximum value when the equivalent input impedance Rin of the DC-DC converter circuit matches the internal resistance Rpv of the photovoltaic cell (i.e., Rin = Rpv). If the load impedance is constant, the larger the duty cycle of the switches, the smaller the equivalent input impedance of the Boost converter circuit. Therefore, by changing the duty cycle of the Boost switches to make the input impedance of the Boost circuit equal to the output impedance of the photovoltaic cell, the output power of the photovoltaic cell can be maximized.

[0003] Current common methods rely on the coordinated operation of the front-end boost circuit and the back-end inverter circuit to achieve impedance transformation and MPPT control. This results in power flowing through two stages of power conversion (DC-DC + DC-AC), generating additional switching and conduction losses and reducing overall efficiency. Furthermore, to meet grid connection regulations, the inverter needs to achieve a ramp-up of output power at a specified rate. However, the traditional disturbance observation method, due to the randomness of power disturbances, cannot accurately control the increment of photovoltaic output power, leading to sudden power changes on the inverter side and posing a risk of grid impact or protection malfunction. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide an MPPT tracking method and related apparatus in view of the above-mentioned technical defects of the prior art.

[0005] The technical solution adopted by this invention to solve its technical problem is: constructing an MPPT tracking method and applying it to a photovoltaic power generation system, wherein the photovoltaic power generation system includes: n photovoltaic branches and an inverter circuit, where n is an integer greater than 1; the method includes:

[0006] S1. Construct a control loop that includes a bus voltage loop, n PV voltage outer loops, n PV current inner loops, and an inverter voltage outer loop, wherein each PV voltage outer loop and PV current inner loop corresponds to each photovoltaic branch.

[0007] S2. Obtain the open-circuit voltage of the photovoltaic branch respectively, and when the open-circuit voltage of the photovoltaic branch is less than the sum of the preset bus target voltage and the first preset value, control the control loop to the first working mode; otherwise, control the control loop to the second working mode.

[0008] The control loop performs the following steps in the first operating mode:

[0009] S31. Using the preset bus target voltage as the reference value of the bus voltage loop, obtain the first reference current corresponding to the photovoltaic branch according to the current bus voltage on the PV side.

[0010] S32. Obtain the MPPT tracking voltage of the photovoltaic branch, and use the maximum value of the MPPT tracking voltage as the reference value of the corresponding PV voltage outer loop of the photovoltaic branch. Obtain the second reference current corresponding to the photovoltaic branch based on the current output voltage of the photovoltaic branch.

[0011] S33. Obtain the smaller of the first reference current and the second reference current corresponding to the photovoltaic branch as the reference value of the inner loop of the PV current corresponding to the photovoltaic branch, and obtain the control parameters of the Boost circuit in the photovoltaic branch according to the current output current corresponding to the photovoltaic branch.

[0012] S34. The maximum value of the MPPT tracking voltage corresponding to all photovoltaic branches and the maximum value of the preset bus minimum voltage are the reference values ​​of the inverter voltage outer loop, so as to control the inverter circuit through the inverter voltage outer loop;

[0013] The control loop performs the following steps in the second operating mode:

[0014] S35. Identify the photovoltaic branch whose open-circuit voltage is greater than or equal to the sum of the preset bus target voltage and the first preset value, and shut down the Boost circuit of the photovoltaic branch.

[0015] S36. Obtain the MPPT tracking voltage of the photovoltaic branch, and use the maximum value of the MPPT tracking voltage of the photovoltaic branch as the reference value of the inverter voltage outer loop, so as to control the inverter circuit through the inverter voltage outer loop.

[0016] Preferably, in one embodiment of the MPPT tracking method of the present invention, in step S34 or step S36, the control of the inverter circuit through the inverter voltage outer loop includes: obtaining the target current of the inverter circuit based on the current bus voltage according to the inverter voltage outer loop.

[0017] Preferably, in one embodiment of the MPPT tracking method of the present invention, the method further includes: obtaining the smaller value between the target current of the inverter circuit and a preset current threshold value as the final target current of the inverter circuit.

[0018] Preferably, in one embodiment of the MPPT tracking method of the present invention, the method further includes: setting the preset current threshold value according to the output power ramp-up rate of the inverter circuit.

[0019] Preferably, in one embodiment of the MPPT tracking method of the present invention, the control loop further performs the following steps in the second operating mode:

[0020] S37. Monitor the current bus voltage, and when the current bus voltage is less than the preset minimum bus voltage, turn on the Boost circuit of the photovoltaic branch and control the control loop to switch to the first working mode.

[0021] Preferably, in one embodiment of the MPPT tracking method of the present invention, the method further includes the following steps:

[0022] S4. When the MPPT tracking voltage meets the maximum power range corresponding to the photovoltaic branch, continuously monitor the current output voltage of all photovoltaic branches within a preset time.

[0023] S5. Determine whether there are two photovoltaic branches whose current output voltage difference is less than or equal to the second set value, and whether the current output voltage of the two photovoltaic branches is greater than the preset bus target voltage. If so, turn off the Boost circuit of the two photovoltaic branches at the same time; otherwise, proceed to step S6.

[0024] S6. Determine whether there are two photovoltaic branches whose current output voltage difference is less than or equal to the second set value, and the current output voltage of one of the photovoltaic branches is greater than the preset bus target voltage. If so, turn off the Boost circuit of the photovoltaic branch; otherwise, proceed to step S7.

[0025] S7. Maintain the Boost circuit of the photovoltaic branch on.

[0026] Preferably, in one embodiment of the MPPT tracking method of the present invention, the method further includes obtaining the second preset value based on the steady-state shutdown tolerance of the photovoltaic branch.

[0027] Preferably, in one embodiment of the MPPT tracking method of the present invention, in step S34 or S36, obtaining the MPPT tracking voltage of the photovoltaic branch includes: obtaining the MPPT tracking voltage of the photovoltaic branch by perturbation observation method.

[0028] The present invention also constructs an MPPT tracking device for use in a photovoltaic power generation system, the photovoltaic power generation system comprising: n photovoltaic branches and an inverter circuit, wherein n is an integer greater than 1, and the device includes a module for implementing the MPPT tracking method as described above.

[0029] The present invention also constructs a photovoltaic power generation system, comprising: a controller, n photovoltaic branches and an inverter circuit, wherein n is an integer greater than 1, and the controller is used to implement the MPPT tracking method as described above.

[0030] The MPPT tracking method and related apparatus of the present invention have the following beneficial effects: by adjusting the MPPT mode according to the scenario, the first-stage power conversion loss can be eliminated in some application scenarios, thereby improving system efficiency. Attached Figure Description

[0031] The present invention will be further described below with reference to the accompanying drawings and embodiments. In the accompanying drawings:

[0032] Figure 1 This is a flowchart of an embodiment of the MPPT tracing method of the present invention;

[0033] Figure 2 This is a schematic diagram of a structural embodiment of the controlled circulation of the present invention;

[0034] Figure 3 This is a flowchart of another embodiment of the MPPT tracing method of the present invention;

[0035] Figure 4 This is a flowchart of another embodiment of the MPPT tracing method of the present invention;

[0036] Figure 5 This is a flowchart of another embodiment of the MPPT tracing method of the present invention;

[0037] Figure 6 This is a partial circuit structure diagram of a photovoltaic power generation system. Detailed Implementation

[0038] To provide a clearer understanding of the technical features, objectives, and effects of the present invention, specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0039] like Figure 1 As shown, an embodiment of the MPPT tracking method of the present invention is illustrated. This method is applied to a photovoltaic power generation system. (Refer to...) Figure 6The photovoltaic power generation system includes n photovoltaic branches and an inverter circuit, where n is an integer greater than 1. The outputs of the n photovoltaic branches are connected to the input of the inverter circuit via a bus. That is, the input of the inverter circuit receives the power supply voltage from the outputs of the photovoltaic branches, and the output of the inverter circuit provides the final output voltage. Each photovoltaic branch can have its voltage input process controlled by a corresponding boost circuit.

[0040] exist Figure 1 and Figure 2 In an embodiment of the MPPT tracking method of the present invention shown, the method includes the following steps: S1, constructing a control loop including a bus voltage loop 110, n PV voltage outer loops 120, n PV current inner loops 130, and an inverter voltage outer loop 140, wherein each PV voltage outer loop 120 and PV current inner loop 130 corresponds to each photovoltaic branch; S2, obtaining the open-circuit voltage of each photovoltaic branch, and confirming whether the open-circuit voltage of each photovoltaic branch is less than the sum of a preset bus target voltage and a first preset value. If so, controlling the control loop to a first working mode; otherwise, controlling the control loop to a second working mode.

[0041] Based on step S1, such as Figure 2 As shown, a control loop is constructed for the entire method execution process to realize the specific control process. In this control loop, each loop is equipped with a corresponding PI controller to perform the loop calculation process. Among them, the multi-channel PV voltage outer loop 120 and the PV current inner loop 130 correspond one-to-one with the multi-channel photovoltaic branches.

[0042] Based on step S2, before the photovoltaic system begins to provide power output, the status of each photovoltaic branch is confirmed. The open-circuit voltage of each photovoltaic branch is obtained, and the control mode of the photovoltaic system is determined based on the open-circuit voltage of the photovoltaic branch. That is, the operating mode of the control loop is set. When the open-circuit voltage of all photovoltaic branches is less than the sum of the preset bus target voltage and the first preset value, the control loop is in the first operating mode; otherwise, the control loop is set to the second operating mode. In a specific embodiment, the first preset value can be set to 100V. In one embodiment, the preset bus target voltage is the minimum bus voltage calculated based on the current grid voltage and modulation method.

[0043] Among them, such as Figure 3As shown, the control loop executes the following steps in the first operating mode: S31, using the preset bus target voltage as the reference value of the bus voltage loop, obtain the first reference current corresponding to the photovoltaic branch based on the current bus voltage on the PV side; S32, obtain the MPPT tracking voltage of the photovoltaic branch, and use the maximum value of the MPPT tracking voltage as the reference value of the corresponding PV voltage outer loop 120 of the photovoltaic branch, obtain the second reference current corresponding to the photovoltaic branch based on the current output voltage of the photovoltaic branch; S33, obtain the smaller value between the first reference current and the second reference current corresponding to the photovoltaic branch as the reference value of the corresponding PV current inner loop 130 of the photovoltaic branch, obtain the control parameters of the Boost circuit in the photovoltaic branch based on the current output current corresponding to the photovoltaic branch; S34, obtain the maximum value of the MPPT tracking voltage of all photovoltaic branches and the maximum value of the preset minimum bus voltage as the reference value of the inverter voltage outer loop 140, so as to control the inverter circuit through the inverter voltage outer loop 140.

[0044] Based on steps S31 to S34, in the first operating mode, the bus voltage loop 110 uses a preset target bus voltage as a reference value and calculates the first reference current value for the photovoltaic branch based on the current bus voltage on the PV side through a PI controller. Simultaneously, MPPT calculation is performed for each photovoltaic branch to obtain the MPPT tracking voltage, and the maximum MPPT tracking voltage is used as the reference value for the PV voltage outer loop 120 of that photovoltaic branch. The PV voltage outer loop 120 corresponding to the photovoltaic branch calculates the second reference current corresponding to that photovoltaic branch based on this reference value and the current output voltage of that photovoltaic branch through a PI controller. It can be understood that multiple photovoltaic branches can obtain multiple second reference currents. When the PV current inner loop 130 corresponding to each photovoltaic branch is operating, the second reference current corresponding to that photovoltaic branch is compared with the first reference current, and the smaller of the two is used as the reference value for the PV current inner loop 130 corresponding to that photovoltaic branch. The PV current inner loop 130 calculates the control parameters of the Boost circuit in that photovoltaic branch based on this reference value and the current output current of that photovoltaic branch through a PI controller. The control parameters of the Boost circuit can be understood as the switching cycle of the switching transistor in the Boost circuit. That is, the generated control parameters can be the PWM pulse signal used to control the operation of the Boost circuit. The process of adjusting the control parameters can be understood as the process of adjusting the duty cycle of the PWM pulse signal.

[0045] Furthermore, during the control process of the photovoltaic system, the maximum value of the MPPT tracking voltage of all photovoltaic branches is compared with the preset minimum bus voltage. The maximum value is used as the reference value for the inverter voltage outer loop 140. Based on this reference value and the current bus voltage on the PV side, the inverter voltage outer loop 140 obtains the target current of the inverter circuit through the PI controller. The inverter circuit performs specific control procedures based on this target current. In one specific embodiment, the control parameters of the inverter circuit can be obtained through the corresponding inverter current inner loop based on the target current, and the operation of the inverter circuit can be controlled according to these control parameters.

[0046] Based on the above process, by setting the control loop in the first operating mode, it is ensured that the bus voltage of the PV-side Boost circuit can be clamped when the PV energy is sufficient, and that the maximum power point (MPPT) can be tracked when the PV energy is sufficient. At the same time, the inverter side can also ensure that the power rise slope is met at the start-up time through the loop, so that the photovoltaic system can adapt to various grid connection regulations.

[0047] Furthermore, the control loop executes the following steps in the second operating mode: S35, acquire the photovoltaic branch whose open-circuit voltage is greater than or equal to the sum of the preset bus target voltage and the first preset value, and shut down the Boost circuit of the photovoltaic branch; S36, acquire the MPPT tracking voltage of the photovoltaic branch, and use the maximum value of the MPPT tracking voltage of the photovoltaic branch as the reference value of the inverter voltage outer loop 140, so as to control the inverter circuit through the inverter voltage outer loop 140.

[0048] Based on steps S35 and S36, and the above process, when acquiring the open-circuit voltage of all photovoltaic branches, if the open-circuit voltage of one photovoltaic branch is greater than or equal to the sum of the preset bus target voltage and the first preset value, the control loop is switched to operate in the second working mode. In the second working mode, the control loop can acquire the MPPT tracking voltage of the photovoltaic branch based on the MPPT algorithm, simultaneously shutting down the Boost circuit of that photovoltaic branch, and directly using the MPPT tracking voltage of that photovoltaic branch as the reference value for the inverter voltage outer loop 140. This allows the inverter voltage outer loop 140 to control the inverter circuit through the PI controller based on this reference value. At this time, it is equivalent to the PV current inner loop 130 corresponding to that photovoltaic branch not operating, the Boost circuit of the photovoltaic branch not functioning, and tracking directly through the inverter circuit.

[0049] Based on the above process, by setting the control loop in the second operating mode, impedance transformation no longer requires the front-end Boost circuit as long as the PV voltage is sufficient; MPPT can be achieved solely through disturbances on the inverter side. In this operating mode, the entire system is controlled only by the inverter loop, which is simpler and more stable than simultaneously controlling the Boost circuit of the photovoltaic branch and the inverter circuit.

[0050] Through the above process, hybrid MPPT control can be achieved based on the switching of the control loop's operating mode. That is, when the photovoltaic output voltage meets the preset conditions, the Boost circuit of the photovoltaic branch is turned off and switched to the inverter direct-control MPPT mode, eliminating first-stage power conversion losses and improving system efficiency.

[0051] In one embodiment, in step S34 or S35, controlling the inverter circuit via the inverter voltage outer loop 140 includes: obtaining the target current of the inverter circuit based on the current bus voltage using the inverter voltage outer loop 140. Specifically, in the control process of the inverter circuit, the inverter voltage outer loop 140 is used to obtain the target current of the inverter circuit based on a reference value and the current bus voltage on the PV side. The inverter circuit performs the control process based on this target current. The inverter circuit may include several switching transistors. During the operation of the inverter circuit, control voltages for each switching transistor can be generated based on the target current to control the on or off time of the switching transistors, thereby controlling the output of the inverter circuit.

[0052] In one embodiment, the PPT tracking method of the present invention further includes: obtaining the smaller of the target current of the inverter circuit and a preset current threshold value as the final target current of the inverter circuit. Specifically, the final target current of the inverter circuit can also be set based on the target current of the inverter circuit obtained from the inverter voltage outer loop 140 and the set preset current threshold value, that is, the control process of the inverter circuit is limited by the preset current threshold value so that the output current of the inverter circuit does not exceed the preset current threshold value. It can be understood that the smaller of the target current and the preset current threshold value is obtained as the final target current of the inverter circuit, so that the inverter circuit implements the control process according to the final target current.

[0053] The preset current threshold value can be set according to the specific application scenario. In one specific embodiment, the preset current threshold value can be set according to the output power ramp rate of the inverter circuit. This is because the inverter output power must follow a ramp rate to meet grid connection regulations and avoid grid impact. Synchronously constraining the rise rate of the inverter output power during MPPT tracking ensures grid compatibility for power ramping and effectively suppresses bus voltage fluctuations caused by power step jumps.

[0054] like Figure 4As shown, in one embodiment, the control loop further executes the following steps in the second operating mode: S37, monitoring the current bus voltage, and when the current bus voltage is less than the preset minimum bus voltage, activating the Boost circuit of the photovoltaic branch, and controlling the control loop to switch to the first operating mode. Specifically, when the control loop is in the second operating mode, it continuously monitors the current bus voltage on the PV side. When the current bus voltage on the PV side drops to the preset minimum bus voltage, the Boost circuit of all photovoltaic branches can be activated, allowing all photovoltaic branches to provide power input to the inverter circuit based on the Boost circuit. Simultaneously, the control loop performs the control process of the Boost circuit in the photovoltaic branch and the control process of the inverter circuit through the first operating mode. The specific process of the first operating mode can be referred to above, and will not be repeated here.

[0055] In one embodiment, such as Figure 5 As shown, the MPPT tracking method of the present invention further includes the following steps: S4, when the MPPT tracking voltage meets the maximum power range corresponding to the photovoltaic branch, continuously monitor the current output voltage of all photovoltaic branches within a preset time; S5, determine whether there are two photovoltaic branches whose current output voltage difference is less than or equal to a second preset value, and both of the current output voltages of the two photovoltaic branches are greater than the preset bus target voltage. If so, simultaneously turn off the Boost circuit of the two photovoltaic branches; otherwise, proceed to step S6; S6, determine whether there are two photovoltaic branches whose current output voltage difference is less than or equal to a second preset value, and one of the photovoltaic branches whose current output voltage is greater than the preset bus target voltage. If so, turn off the Boost circuit of the photovoltaic branch; otherwise, proceed to step S7; S7, maintain the Boost circuit of the photovoltaic branch on.

[0056] Specifically, based on the above process, during the control process of the Boost circuit and the inverter circuit in the photovoltaic branch, when the photovoltaic branch catches up to the vicinity of the maximum power point through the MPPT algorithm, that is, when the MPPT tracking voltage meets the maximum power range corresponding to the photovoltaic branch, the current output voltage of all photovoltaic branches is continuously monitored for a preset time. In one specific embodiment, the preset time can be set to 1 minute. When the current output voltage of both photovoltaic branches is greater than the preset bus target voltage, and the difference between the current output voltages of the two photovoltaic branches is less than or equal to a second preset value, the Boost circuits of the two photovoltaic branches are simultaneously turned off. When the current output voltage of one of the two photovoltaic branches is greater than the preset bus target voltage, and the difference between the current output voltages of the two photovoltaic branches is less than or equal to the second preset value, the Boost circuit of the photovoltaic branch with the current output voltage greater than the preset bus target voltage is turned off. In all other cases, such as when the current output voltage difference between any two photovoltaic branches is less than or equal to the second set value, or when the current output voltage of any photovoltaic branch is greater than the preset bus target voltage, the Boost circuits of all photovoltaic branches remain on. This process ensures that when the output voltage of a photovoltaic branch is sufficient, the impedance transformation of that branch does not require the Boost circuit. Therefore, the Boost circuit of that photovoltaic branch can be directly turned off, and MPPT can be achieved through the disturbance of the inverter circuit.

[0057] In one specific embodiment, a second preset value can be obtained based on the steady-state shutdown tolerance of the photovoltaic branch. The steady-state shutdown tolerance is the allowable voltage difference range for the shutdown decision of the two photovoltaic branches. In one specific embodiment, when "Vpv1 - Vpv2| ≤ 30V" is satisfied, a power balance state is determined, triggering the shutdown of the two photovoltaic branches. Vpv1 and Vpv2 are the current output voltages of the two photovoltaic branches, respectively. Therefore, in one specific embodiment, the second preset value can be set to be less than or equal to 30V.

[0058] In one embodiment, obtaining the MPPT tracking voltage of the photovoltaic branch in step S34 or S35 includes: obtaining the MPPT tracking voltage of the photovoltaic branch using the perturbation-observation method. That is, the MPPT tracking voltage of the photovoltaic branch can be obtained by MPPT calculation using the perturbation-observation method. In the MPPT calculation, it can be performed at preset intervals for a long period; for example, in different embodiments, MPPT calculations can be performed at intervals of 0.1s, 0.2s, 0.5s, and 1s, respectively.

[0059] Furthermore, the MPPT tracking device of the present invention is applied to a photovoltaic power generation system, which includes n photovoltaic branches and an inverter circuit, where n is an integer greater than 1. The device includes modules for implementing the above-described MPPT tracking method. That is, the MPPT tracking device of the present invention has the function of implementing the corresponding steps performed in the above-described method. Each function can be implemented by hardware or by hardware executing corresponding software. The corresponding hardware or software includes one or more modules corresponding to the above functions. That is, the steps in the above-described method are executed by one or more modules respectively. The specific cooperative operation between the modules can be referred to the specific process of the above-described method, and will not be repeated here.

[0060] In one embodiment, a photovoltaic power generation system of the present invention includes: a controller, n photovoltaic branches, and an inverter circuit, wherein n is an integer greater than 1, and the controller is used to implement the MPPT tracking method described above. According to an embodiment of the present invention, the process described in the flowchart above can be implemented by the controller according to a computer program.

[0061] It is understood that the above embodiments only illustrate preferred embodiments of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can freely combine the above technical features without departing from the concept of the present invention, and can also make several modifications and improvements, all of which fall within the protection scope of the present invention. Therefore, all equivalent transformations and modifications made with respect to the scope of the claims of the present invention should fall within the scope of the claims of the present invention.

Claims

1. An MPPT tracking method, characterized in that, The method is applied to a photovoltaic power generation system, which includes n photovoltaic branches and an inverter circuit, where n is an integer greater than 1; the method includes: S1. Construct a control loop that includes a bus voltage loop, n PV voltage outer loops, n PV current inner loops, and an inverter voltage outer loop, wherein each PV voltage outer loop and PV current inner loop corresponds to each photovoltaic branch. S2. Obtain the open-circuit voltage of the photovoltaic branch respectively, and confirm whether the open-circuit voltage of the photovoltaic branch is less than the sum of the preset bus target voltage and the first preset value. If so, control the control loop to the first working mode; otherwise, control the control loop to the second working mode. The control loop performs the following steps in the first operating mode: S31. Using the preset bus target voltage as the reference value of the bus voltage loop, obtain the first reference current corresponding to the photovoltaic branch according to the current bus voltage on the PV side. S32. Obtain the MPPT tracking voltage of the photovoltaic branch, and use the maximum value of the MPPT tracking voltage as the reference value of the corresponding PV voltage outer loop of the photovoltaic branch. Obtain the second reference current corresponding to the photovoltaic branch based on the current output voltage of the photovoltaic branch. S33. Obtain the smaller of the first reference current and the second reference current corresponding to the photovoltaic branch as the reference value of the inner loop of the PV current corresponding to the photovoltaic branch, and obtain the control parameters of the Boost circuit in the photovoltaic branch according to the current output current corresponding to the photovoltaic branch. S34. The maximum value of the MPPT tracking voltage corresponding to all photovoltaic branches and the maximum value of the preset bus minimum voltage are the reference values ​​of the inverter voltage outer loop, so as to control the inverter circuit through the inverter voltage outer loop; The control loop performs the following steps in the second operating mode: S35. Identify the photovoltaic branch whose open-circuit voltage is greater than or equal to the sum of the preset bus target voltage and the first preset value, and shut down the Boost circuit of the photovoltaic branch. S36. Obtain the MPPT tracking voltage of the photovoltaic branch, and use the maximum value of the MPPT tracking voltage of the photovoltaic branch as the reference value of the inverter voltage outer loop, so as to control the inverter circuit through the inverter voltage outer loop.

2. The MPPT tracking method according to claim 1, characterized in that, In step S34 or step S36, controlling the inverter circuit through the inverter voltage outer loop includes: obtaining the target current of the inverter circuit based on the current bus voltage according to the inverter voltage outer loop.

3. The MPPT tracking method according to claim 2, characterized in that, The method further includes: obtaining the smaller value between the target current of the inverter circuit and a preset current threshold value as the final target current of the inverter circuit.

4. The MPPT tracking method according to claim 3, characterized in that, The method further includes setting the preset current threshold value according to the output power ramp-up rate of the inverter circuit.

5. The MPPT tracking method according to claim 1, characterized in that, The control loop further performs the following steps in the second operating mode: S37. Monitor the current bus voltage, and when the current bus voltage is less than the preset minimum bus voltage, turn on the Boost circuit of the photovoltaic branch and control the control loop to switch to the first working mode.

6. The MPPT tracking method according to claim 1, characterized in that, The method further includes the following steps: S4. When the MPPT tracking voltage meets the maximum power range corresponding to the photovoltaic branch, continuously monitor the current output voltage of all photovoltaic branches within a preset time. S5. Determine whether there are two photovoltaic branches whose current output voltage difference is less than or equal to the second set value, and whether the current output voltage of the two photovoltaic branches is greater than the preset bus target voltage. If so, turn off the Boost circuit of the two photovoltaic branches at the same time; otherwise, proceed to step S6. S6. Determine whether there are two photovoltaic branches whose current output voltage difference is less than or equal to the second set value, and if the current output voltage of one of the photovoltaic branches is greater than the preset bus target voltage, then turn off the Boost circuit of the photovoltaic branch; otherwise, proceed to step S7. S7. Maintain the Boost circuit of the photovoltaic branch on.

7. The MPPT tracking method according to claim 6, characterized in that, The method further includes obtaining the second preset value based on the steady-state shutdown tolerance of the photovoltaic branch.

8. The MPPT tracking method according to claim 1, characterized in that, In step S34 or S36, obtaining the MPPT tracking voltage of the photovoltaic branch includes: obtaining the MPPT tracking voltage of the photovoltaic branch by means of the perturbation observation method.

9. An MPPT tracking device, characterized in that, The device is applied to a photovoltaic power generation system, the photovoltaic power generation system comprising: n photovoltaic branches and an inverter circuit, wherein n is an integer greater than 1, and the device includes a module for implementing the MPPT tracking method as described in any one of claims 1 to 8.

10. A photovoltaic power generation system, characterized in that, include: The controller comprises an n-channel photovoltaic branch and an inverter circuit, wherein n is an integer greater than 1, and the controller is used to implement the MPPT tracking method as described in any one of claims 1 to 8.

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