Inverter, maximum power point tracking method, and photovoltaic power generation system

Abstract

An inverter (21), a maximum power point tracking method, and a photovoltaic power generation system (2). In the inverter, an input of a DC / DC conversion circuit (210a, 210b,..., 210n) is connected to an output of a converter array (20a, 20b,..., 20n), an input of a DC / AC conversion circuit (211) is connected to an output of the DC / DC conversion circuit, and an output of the DC / AC conversion circuit is connected to a power grid (4); and a controller (212) controls the DC / DC conversion circuit to periodically perform the following operations: controlling the DC / DC conversion circuit to be in a maximum power tracking mode so as to perform maximum power point tracking on the converter array; after a preset duration, controlling the DC / DC conversion circuit to exit the maximum power tracking mode, and controlling the input power of the DC / DC conversion circuit to decrease by a preset power value; and when the input power of the DC / DC conversion circuit decreases by the preset power value, controlling the DC / DC conversion circuit to enter the maximum power tracking mode again, and identifying an actual maximum power point of the converter array.

Description

Inverters, maximum power point tracking methods, and photovoltaic power generation systems

[0001] This application claims priority to Chinese Patent Application No. 202410974008.1, filed on July 19, 2024, with the China National Intellectual Property Administration, entitled "Inverter, Maximum Power Point Tracking Method and Photovoltaic Power Generation System", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of photovoltaic power generation technology, and in particular to an inverter, a maximum power point tracking method, and a photovoltaic power generation system. Background Technology

[0003] In a photovoltaic (PV) power generation system, the converter array comprises multiple converters. The input of each converter is connected to one or more PV modules, and the outputs of the multiple converters are connected in series to the DC terminal of an inverter. When the PV power generation system is supplying power, the inverter is used to perform maximum power point tracking (MPPT) on the converter array in real time, thereby ensuring that the PV power generation system supplies power to the grid at maximum power output.

[0004] During the maximum power point tracking (MPPT) process of the inverter and converter array, the output power P-output voltage V curve of the converter array can be shown in Figure 1. This PV curve includes a constant power curve segment from point (V1, P1) to point (V4, P4). However, due to limitations in sampling accuracy and nonlinearity, the constant power curve segment may exhibit a convex hull. If the inverter's input voltage operating point (i.e., the point corresponding to the input voltage value in the PV curve) is located within the convex hull, the inverter may mistakenly identify point (V3, P3) within the convex hull as the maximum power point. This results in the inverter's input voltage operating point being stuck within the convex hull, thus preventing it from tracking the actual maximum power point, such as point (V4, P4). Summary of the Invention

[0005] This application provides an inverter, a maximum power point tracking method, and a photovoltaic power generation system, which can intelligently identify the actual maximum power point of the converter array, avoiding misidentification of other points (such as points within the convex hull) in the PV curve of the converter array as the maximum power point, thereby improving the accuracy of maximum power point identification.

[0006] In a first aspect, embodiments of this application provide an inverter for connecting an array of multiple DC / DC converters connected in series between the inverter and the power grid for energy conversion. The inverter includes a direct current (DC) / DC conversion circuit, an alternating current (AC) conversion circuit, and a controller. The number of DC / DC conversion circuits can be one or more. The input of the DC / DC conversion circuit is connected to the output of the converter array, the input of the DC / AC conversion circuit is connected to its output, and the output of the DC / AC conversion circuit is connected to the power grid. The controller is used to control the DC / DC conversion circuit to perform the following operations periodically: The controller controls the DC / DC conversion circuit to be in maximum power point tracking (MPPT) mode to perform MPPT on the converter array. Further, the controller is also used to control the DC / DC conversion circuit to exit MPPT mode after a preset time period and control the input power of the DC / DC conversion circuit to decrease by a preset power value. It should be understood that as the input power of the DC / DC converter circuit decreases to a preset power value, the operating point of the input voltage of the DC / DC converter circuit will continuously shift in the direction of increasing output voltage on the output power P-output voltage V curve of the converter array, until it is located on the right slope of the PV curve. The operating point of the input voltage of the DC / DC converter circuit is also the operating point of the inverter's input voltage. Furthermore, the controller is also used to control the DC / DC converter circuit to re-enter the maximum power point tracking mode after the input power of the DC / DC converter circuit decreases to the preset power value, thereby intelligently identifying the actual maximum power point of the converter array.

[0007] By implementing the embodiments of this application, the power of the DC / DC conversion circuit can be periodically limited to ensure that the inverter's input voltage operating point is located on the right slope of the PV curve. This guarantees that the DC / DC conversion circuit performs maximum power point tracking (MPPT) on the converter array starting from the right slope of the PV curve, intelligently identifying the actual maximum power point of the converter array. This avoids misidentifying other points in the PV curve (such as points within the convex hull) as the maximum power point, improving the accuracy of MPPT identification. Once the actual maximum power point of the converter array is identified, it ensures that the converter array operates on the high-voltage side of the constant power curve segment of the PV curve, thereby reducing the voltage difference between the output and input voltages of the converter array and improving the efficiency of the converter array. Furthermore, it also reduces the voltage difference between the inverter's input voltage and the inverter's DC bus voltage, effectively increasing the inverter's power generation and demonstrating strong applicability.

[0008] Optionally, the controller is further configured to control the DC / DC converter to exit the maximum power point tracking (MPPT) mode when the input power of the DC / DC converter is less than or equal to the mode exit threshold, and to control the input power of the DC / DC converter to decrease by a preset power value. The mode exit threshold is less than the estimated maximum power of the converter array, which can be determined by the open-circuit voltage of the converter array. Optionally, the controller is further configured to control the DC / DC converter to exit the MPPT mode after a preset time period, and when the input power of the DC / DC converter is less than or equal to the mode exit threshold, and to control the input power of the DC / DC converter to decrease by a preset power value. Implementing the embodiments of this application ensures that the input voltage operating point of the DC / DC converter when it begins MPPT is located on the right slope of the PV curve, thereby preventing the input voltage operating point of the DC / DC converter from being stuck within the convex hull and unable to exit, significantly reducing the inverter's power generation loss.

[0009] In one possible implementation, when the input power of the DC / DC converter circuit is less than or equal to a power threshold, the preset power value is a fixed value. By implementing the embodiments of this application, the preset power value can be flexibly adjusted according to the input power of the DC / DC converter circuit, thereby ensuring that the operating point of the input voltage after power limiting of the DC / DC converter circuit exits the convex hull and is located on the right slope of the PV curve.

[0010] In one possible implementation, when the input power of the DC / DC converter circuit is greater than a power threshold, the preset power value is k times the input power of the DC / DC converter circuit, where k is less than 1. By implementing the embodiments of this application, the preset power value can be flexibly adjusted according to the input power of the DC / DC converter circuit, thereby ensuring that the operating point of the input voltage after power limiting of the DC / DC converter circuit exits the convex hull and is located on the right slope of the PV curve.

[0011] In one possible implementation, k is 0.01.

[0012] In one possible implementation, when the input power of the DC / DC converter circuit is reduced by a preset power value, the input voltage of the DC / DC converter circuit gradually increases. Therefore, the input voltage of the DC / DC converter circuit is greater than the input voltage when the DC / DC converter circuit is in maximum power point tracking (MPPT) mode. Implementing this embodiment allows the input voltage operating point of the DC / DC converter circuit to continuously move in the direction of increasing output voltage on the PV curve until it exits the convex hull of the PV curve. This avoids the misidentification of the maximum power point caused by the input voltage operating point being stuck within the convex hull, thereby improving the accuracy of maximum power point identification.

[0013] In one possible implementation, the inverter further includes a capacitor connected in parallel to the input of either the DC / DC converter circuit or the DC / AC converter circuit. This capacitor stores energy output from the converter array when the input power of the DC / DC converter circuit decreases by a preset power value, thereby increasing the input voltage of the DC / DC converter circuit. The energy output by the converter array is the remaining energy from all outputs of the converter array, excluding the energy output to the DC / DC converter circuit; the value of this remaining energy is the aforementioned preset power value. It is understood that, based on the characteristics of a capacitor, when the energy stored in the capacitor increases, the voltage across the capacitor increases, thereby increasing the input voltage of the DC / DC converter circuit. Therefore, as the input power of the DC / DC converter circuit decreases by the preset power value, the operating point of the DC / DC converter circuit's input voltage will continuously shift in the direction of increasing output voltage on the PV curve of the converter array until it reaches the right slope of the PV curve.

[0014] Secondly, embodiments of this application provide a maximum power point tracking (MPPT) method for an inverter. This method can be executed by an inverter connected between a converter array consisting of multiple DC / DC converters connected in series and the power grid. The inverter includes a DC / DC conversion circuit, a DC / AC conversion circuit, and a controller. The controller can control the DC / DC conversion circuit to periodically execute the following steps: The controller controls the DC / DC conversion circuit to be in maximum power point tracking mode to track the converter array. Further, after a preset time, the controller controls the DC / DC conversion circuit to exit the maximum power point tracking mode and controls the input power of the DC / DC conversion circuit to decrease by a preset power value. Even further, when the input power of the DC / DC conversion circuit decreases by the preset power value, the controller controls the DC / DC conversion circuit to re-enter the maximum power point tracking mode, thereby intelligently identifying the actual maximum power point of the converter array. Implementing embodiments of this application can avoid misidentifying other points (such as points within the convex hull) in the PV curve of the converter array as the maximum power point, improving the accuracy of maximum power point identification. Once the actual maximum power point of the converter array is identified, it can be ensured that the converter array operates on the high-voltage side of the constant power curve segment, thereby improving the efficiency of the converter array and effectively increasing the power generation of the inverter, making it highly applicable.

[0015] Optionally, when the input power of the DC / DC converter circuit is less than or equal to the mode exit threshold, the controller controls the DC / DC converter circuit to exit the maximum power point tracking (MPPT) mode and reduces the input power of the DC / DC converter circuit by a preset power value. The mode exit threshold is less than the estimated maximum power of the converter array, which can be determined by the open-circuit voltage of the converter array. Optionally, after a preset time, when the input power of the DC / DC converter circuit is less than or equal to the mode exit threshold, the controller controls the DC / DC converter circuit to exit the MPPT mode and reduces the input power of the DC / DC converter circuit by a preset power value. Implementing this embodiment ensures that the input voltage operating point of the DC / DC converter circuit when it begins MPPT is located on the right slope of the PV curve, thereby preventing the input voltage operating point of the DC / DC converter circuit from being stuck within the convex hull and unable to exit, significantly reducing the inverter's power generation loss.

[0016] In one possible implementation, when the input power of the DC / DC converter circuit is less than or equal to a power threshold, the preset power value is a fixed value. By implementing the embodiments of this application, the preset power value can be flexibly adjusted according to the input power of the DC / DC converter circuit, thereby ensuring that the operating point of the input voltage after power limiting of the DC / DC converter circuit exits the convex hull and is located on the right slope of the PV curve.

[0017] In one possible implementation, when the input power of the DC / DC converter circuit is greater than a power threshold, the preset power value is k times the input power of the DC / DC converter circuit, where k is less than 1. By implementing the embodiments of this application, the preset power value can be flexibly adjusted according to the input power of the DC / DC converter circuit, thereby ensuring that the operating point of the input voltage after power limiting of the DC / DC converter circuit exits the convex hull and is located on the right slope of the PV curve.

[0018] In one possible implementation, k is 0.01.

[0019] In one possible implementation, when the controller reduces the input power of the DC / DC converter circuit by a preset power value, it controls the input voltage of the DC / DC converter circuit to be greater than the input voltage when the DC / DC converter circuit is in maximum power point tracking (MPPT) mode. Implementing this embodiment allows the input voltage operating point of the DC / DC converter circuit to continuously move in the direction of increasing output voltage on the PV curve until it exits the convex hull of the PV curve. This avoids the misidentification of the maximum power point caused by the input voltage operating point being stuck within the convex hull, thereby improving the accuracy of maximum power point identification.

[0020] Thirdly, embodiments of this application provide a photovoltaic power generation system, which includes multiple converter arrays and an inverter as provided in any of the first aspects and possible embodiments described above. Each of the multiple converter arrays consists of multiple DC / DC converters connected in series. The inverter includes a multi-channel DC / DC conversion circuit, a DC / AC conversion circuit, and a controller. Each of the multi-channel DC / DC conversion circuits is connected to each of the multiple converter arrays in a one-to-one correspondence. The input of each of the multi-channel DC / DC conversion circuits is connected to the output of the corresponding converter array. The output of the multi-channel DC / DC conversion circuit is connected to the input of the DC / AC conversion circuit, and the output of the DC / AC conversion circuit is used to connect to the power grid. The controller is used to control the multi-channel DC / DC conversion circuits to perform the following operations periodically: The controller controls the multi-channel DC / DC conversion circuits to be in maximum power point tracking mode to perform maximum power point tracking on the converter arrays corresponding to the multi-channel DC / DC conversion circuits. Furthermore, the controller is also configured to, after a preset time period, control the multiple DC / DC converter circuits to exit the maximum power point tracking (MPPT) mode and control the input power of the multiple DC / DC converter circuits to decrease by a preset power value. Even further, the controller is also configured to, after the input power of the multiple DC / DC converter circuits decreases by the preset power value, control the multiple DC / DC converter circuits to re-enter the MPPT mode, thereby intelligently identifying the actual maximum power point of the multiple converter arrays. Implementing the embodiments of this application ensures that multiple converter arrays operate at their actual maximum power point, thereby ensuring that the photovoltaic power generation system supplies power to the grid at maximum power output, thus increasing the power generation of the photovoltaic power generation system.

[0021] In one possible implementation, when the input power of each DC / DC converter in a multi-channel DC / DC converter circuit is less than or equal to a power threshold, a preset power value is set to a fixed value. By implementing the embodiments of this application, the preset power value can be flexibly adjusted according to the input power of each DC / DC converter circuit, thereby ensuring that the operating point of the input voltage after power limiting of each DC / DC converter circuit exits the convex hull and is located on the right slope of the PV curve.

[0022] In one possible implementation, when the input power of each DC / DC converter in a multi-channel DC / DC converter circuit exceeds a power threshold, a preset power value is set to k times the input power of each DC / DC converter circuit, where k is less than 1. By implementing the embodiments of this application, the preset power value can be flexibly adjusted according to the input power of each DC / DC converter circuit, thereby ensuring that the operating point of the input voltage after power limiting of each DC / DC converter circuit exits the convex hull and is located on the right slope of the PV curve.

[0023] In one possible implementation, the inverter further includes a capacitor connected in parallel to the input of each DC / DC converter circuit or the input of a DC / AC converter circuit in the multi-channel DC / DC converter circuit. This capacitor stores energy output from the converter array corresponding to the multi-channel DC / DC converter circuit when the input power of the multi-channel DC / DC converter circuit decreases by a preset power value, thereby increasing the input voltage of the multi-channel DC / DC converter circuit. The energy output from the converter array corresponding to the multi-channel DC / DC converter circuit is the remaining energy from all the energy output by the converter array, excluding the energy output to the multi-channel DC / DC converter circuit; the value of this remaining energy is the aforementioned preset power value. It is understood that, based on the characteristics of a capacitor, when the energy stored in the capacitor increases, the voltage across the capacitor increases, thereby increasing the input voltage of the multi-channel DC / DC converter circuit. Therefore, during the process of the input power of the multi-channel DC / DC converter circuit decreasing by the preset power value, the operating point of the input voltage of the multi-channel DC / DC converter circuit will continuously shift in the direction of increasing output voltage on the PV curve of the converter array until it reaches the right slope of the PV curve.

[0024] It should be understood that the implementations and beneficial effects of the above-mentioned aspects of this application can be referenced from each other. Attached Figure Description

[0025] Figure 1 is a schematic diagram of the PV curve of a converter array provided by the prior art;

[0026] Figure 2 is a schematic diagram of the structure of the photovoltaic power generation system provided in an embodiment of this application;

[0027] Figure 3 is a schematic diagram of the circuit architecture of the photovoltaic power generation system provided in an embodiment of this application;

[0028] Figure 4 is a schematic diagram of the PV curve of the converter array provided in the embodiment of this application;

[0029] Figure 5 is a schematic diagram of the circuit architecture of the DC / DC converter provided in the embodiment of this application;

[0030] Figure 6 is a flowchart illustrating the maximum power point tracking method for an inverter provided in an embodiment of this application. Detailed Implementation

[0031] The inverter provided in this application is applicable to various fields, including new energy smart microgrids, power transmission and distribution, new energy, photovoltaic power generation, photovoltaic-energy storage power generation, and high-power converters. The specific application can be determined based on the actual application scenario, and no restrictions are imposed here. The inverter provided in this application can be adapted to different application scenarios, such as photovoltaic power supply scenarios, photovoltaic-energy storage power supply scenarios, or other application scenarios. The following explanation will use a photovoltaic power supply application scenario as an example; further details will not be provided here.

[0032] Referring to Figure 2, which is a schematic diagram of the photovoltaic power generation system provided in this application, the photovoltaic power generation system includes a converter array 11 and an inverter 12. The converter array 11 consists of DC / DC converters 111a to 111n connected in series. Each DC / DC converter 111a to 111n is used to connect at least one photovoltaic module. These DC / DC converters 111a to 111n can also be referred to as optimizers. For example, the input of DC / DC converter 111a is used to connect to photovoltaic module 10a, the input of DC / DC converter 111b is used to connect to photovoltaic module 10b, and so on, with the input of DC / DC converter 111n being used to connect to photovoltaic module 10n. The inverter 12 includes a capacitor C0, a DC / DC conversion circuit, a DC / AC conversion circuit, and a controller. The input of the DC / DC converter circuit is connected to the output of the converter array 11, and capacitor C0 is connected in parallel between the input of the DC / DC converter circuit and the output of the converter array 11. The output of the DC / DC converter circuit is connected to the input of the DC / AC converter circuit, and the output of the DC / AC converter circuit is used to connect to the power grid 13.

[0033] When the photovoltaic power generation system supplies power to the grid 13, each of the DC / DC converters 111a to 111n converts the DC voltage output by the photovoltaic module corresponding to each DC / DC converter into a first DC voltage. At this time, the converter array 11 outputs a certain output voltage to the inverter 12, wherein this output voltage is the sum of the first DC voltages output by the DC / DC converters 111a to 111n. Further, the aforementioned DC / DC conversion circuit converts the output voltage of the converter array 11 into a second DC voltage and outputs the second DC voltage to the DC / AC conversion circuit. The DC / AC conversion circuit inverts the second DC voltage into an AC voltage and supplies power to the grid 13.

[0034] During the process of the photovoltaic power generation system supplying power to the grid 13, the inverter 12 is also used to perform maximum power point tracking of the converter array 11 in real time.

[0035] In specific implementation, the controller described above is used to control the DC / DC conversion circuit to perform the following operations periodically. The controller is used to control the DC / DC conversion circuit to be in maximum power point tracking mode to perform maximum power point tracking on the converter array 11. The maximum power point tracking mode is an operating mode in which the output voltage of the converter array 11 is controlled in real time so that the converter array 11 supplies power to the inverter 12 at maximum power output.

[0036] Furthermore, the controller is also used to control the DC / DC converter circuit to exit the maximum power point tracking mode after a preset time, and to control the input power of the DC / DC converter circuit to decrease by a preset power value. It should be understood that when the input power of the DC / DC converter circuit decreases by the preset power value, capacitor C0 is used to store the energy output by the converter array 11, thereby increasing the input voltage of the DC / DC converter circuit. The energy output by the converter array 11 is the remaining energy from all the energy output by the converter array 11, excluding the energy output to the DC / DC converter circuit; the value of this remaining energy is the preset power value. According to the characteristics of capacitor C0, when the energy stored in capacitor C0 increases, the voltage across capacitor C0 will increase, meaning the input voltage of the DC / DC converter circuit will also increase. Therefore, during the process of the input power of the DC / DC converter circuit decreasing by the preset power value, the operating point of the input voltage of the DC / DC converter circuit will continuously move in the direction of increasing output voltage on the PV curve of the converter array 11, until it is located on the right slope of the PV curve. This operating point of the input voltage of the DC / DC converter circuit is also the operating point of the input voltage of the inverter 12.

[0037] It is easy to understand that the location of capacitor C0 is not limited to the location shown in Figure 1. The location shown in Figure 1 is only an example. Capacitor C0 can also be located in other locations in the circuit of inverter 12, or even be a parasitic capacitance formed by the circuit. This application embodiment does not impose any restrictions.

[0038] Furthermore, the controller is also used to control the DC / DC conversion circuit to re-enter the maximum power point tracking mode when the input power of the DC / DC conversion circuit decreases to a preset power value, thereby identifying the actual maximum power point of the converter array 11.

[0039] By implementing the embodiments of this application, the power of the DC / DC conversion circuit can be periodically limited to ensure that the input voltage operating point of the inverter 12 is located on the right slope of the PV curve. This guarantees that the DC / DC conversion circuit performs maximum power point tracking (MPPT) on the converter array 11 starting from the right slope of the PV curve, intelligently identifying the actual maximum power point of the converter array 11. This avoids misidentifying other points (such as points within the convex hull) in the PV curve of the converter array 11 as the maximum power point, thus improving the accuracy of MPPT identification. Furthermore, it ensures that the converter array 11 operates at its actual maximum power point, thereby ensuring that the photovoltaic power generation system supplies power to the grid 13 at maximum power output, increasing the power generation of the photovoltaic power generation system.

[0040] Referring to Figure 3, which is a schematic diagram of the circuit architecture of a photovoltaic power generation system provided in an embodiment of this application, the photovoltaic power generation system 2 includes converter arrays 20a to 20n and an inverter 21. Each converter array 20a to 20n consists of multiple DC / DC converters connected in series, and each DC / DC converter is used to connect at least one photovoltaic module (i.e., one or more photovoltaic modules). For example, converter array 20a consists of DC / DC converters 201a to 20na connected in series. DC / DC converter 201a is used to connect photovoltaic module 31a, DC / DC converter 202a is used to connect photovoltaic module 32a, ..., and DC / DC converter 20na is used to connect photovoltaic module 3na. Photovoltaic modules 31a, 32a, ..., and 3na constitute photovoltaic array 3a. Converter array 20b is used to connect photovoltaic array 3b, ..., and converter array 20n is used to connect photovoltaic array 3n. The specific structure of each converter array in converter arrays 20b to 20n and its connection relationship with the corresponding photovoltaic array can be found in the specific structure of converter array 20a and its connection relationship with photovoltaic array 3a mentioned above, and will not be repeated here.

[0041] Inverter 21 is used to connect the converter arrays 20a to 20n and the power grid 4 for energy conversion. Specifically, inverter 21 is used to convert the DC power output from converter arrays 20a to 20n into AC power and supply it to the power grid 4. Inverter 21 includes DC / DC conversion circuits 210a to 210n, a DC / AC conversion circuit 211, and a controller 212. The DC / DC conversion circuits 210a to 210n are connected one-to-one with the converter arrays 20a to 20n. The input of each DC / DC conversion circuit in the DC / DC conversion circuits 210a to 210n is used to connect to the output of the corresponding converter array. For example, the input of DC / DC converter circuit 210a is used to connect to the output of converter array 20a, the input of DC / DC converter circuit 210b is used to connect to the output of converter array 20b, ..., the input of DC / DC converter circuit 210n is used to connect to the output of converter array 20n. The outputs of DC / DC converter circuits 210a to DC / DC converter circuit 210n are connected to the input of DC / AC converter circuit 211, and the output of DC / AC converter circuit 211 is used to connect to the power grid 4.

[0042] The controller 212 is used to control the DC / DC converter circuits 210a to 210n to periodically perform the following operations: The controller 212 controls the DC / DC converter circuits 210a to 210n to be in maximum power point tracking (MPPT) mode, so as to perform MPPT on the converter arrays corresponding to the DC / DC converter circuits 210a to 210n. Further, the controller is also used to control the DC / DC converter circuits 210a to 210n to exit the MPPT mode after a preset time, and to control the input power of the DC / DC converter circuits 210a to 210n to decrease by a preset power value. Furthermore, the controller is also used to control the DC / DC converter circuits 210a to 210n to re-enter the maximum power point tracking mode when the input power of the DC / DC converter circuits 210a to 210n decreases to a preset power value, thereby intelligently identifying the actual maximum power point of the converter arrays 20a to 20n.

[0043] By implementing the embodiments of this application, it can be ensured that converter arrays 20a to 20n all operate at their actual maximum power points, thereby ensuring that the photovoltaic power generation system 2 supplies power to the grid 4 at maximum power output and improving the power generation of the photovoltaic power generation system 2.

[0044] For ease of description, the following example will be used to illustrate the specific implementation of maximum power point tracking of the inverter 21 on the converter array, taking the DC / DC converter circuit 210a and the converter array 20a as examples.

[0045] The controller 212 described above is used to control the DC / DC converter circuit 210a to perform the following operations periodically. The duration of this period can be preset or determined by electronic components within the DC / DC converter circuit.

[0046] The controller 212 is used to control the DC / DC converter circuit 210a to be in maximum power point tracking mode, so as to perform maximum power point tracking on the converter array 20a. Further, the controller 212 is also used to control the DC / DC converter circuit 210a to exit the maximum power point tracking mode after a preset time, and to control the input power of the DC / DC converter circuit 210a to decrease by a preset power value. The preset time can be set in advance or determined by the electronic components within the DC / DC converter circuit, and is not limited here. Furthermore, the preset time is less than the aforementioned periodic duration. It should be understood that when the input power of the DC / DC converter circuit 210a decreases by the preset power value, the capacitor in the inverter 21 is used to store the energy output by the converter array 20a, so as to increase the input voltage of the DC / DC converter circuit 210a. The energy output by the converter array 20a is the remaining energy from all the energy output by the converter array 20a, excluding the energy output to the DC / DC converter circuit 210a; the value of this remaining energy is the preset power value. For example, the capacitor in inverter 21 can be the input capacitor C1 connected in parallel to the input of DC / DC converter circuit 210a, or the bus capacitor C2 connected in parallel to the input of DC / AC converter circuit 211, or a parasitic capacitor formed by the circuit in inverter 21, which can be equivalent to the input capacitor C1 or the bus capacitor C2. According to the characteristics of a capacitor, when the energy stored in the capacitor increases, the voltage across the capacitor increases, thereby gradually increasing the input voltage of DC / DC converter circuit 210a. Therefore, as the input power of DC / DC converter circuit 210a decreases by a preset power value, the operating point of the input voltage of DC / DC converter circuit 210a will continuously move in the direction of increasing output voltage in the PV curve of converter array 20a, until it is located on the right slope of the PV curve. The operating point of the input voltage of DC / DC converter circuit 210a is also the operating point of the input voltage of inverter 21. Furthermore, the controller 212 is also used to control the DC / DC conversion circuit 210a to re-enter the maximum power point tracking mode when the input power of the DC / DC conversion circuit 210a decreases to a preset power value, thereby intelligently identifying the actual maximum power point of the converter array 20a.

[0047] By implementing the embodiments of this application, the power of the DC / DC converter circuit 210a can be periodically limited to ensure that the operating point of the inverter 21's input voltage is located on the right slope of the PV curve. This ensures that the DC / DC converter circuit 210a performs maximum power point tracking (MPPT) on the converter array 20a starting from the right slope of the PV curve, intelligently identifying the actual maximum power point of the converter array 20a. This avoids misidentifying other points in the PV curve (such as points within the convex hull) as the maximum power point, improving the accuracy of MPPT identification. Once the actual maximum power point of the converter array 20a is identified, it ensures that the converter array 20a operates on the high-voltage side of the constant power curve segment of the PV curve, thereby reducing the voltage difference between the output voltage and input voltage of the converter array 20a and improving its efficiency. Furthermore, it also reduces the voltage difference between the input voltage of the inverter 21 and the DC bus voltage (i.e., the voltage across the bus capacitor C2), effectively increasing the power generation of the inverter 21 and demonstrating strong applicability.

[0048] It is understandable that when the PV curve includes a convex hull, the power generation loss caused by periodically limiting the power of the DC / DC converter circuit 210a is smaller than the power generation loss caused by the input voltage operating point being stuck inside the convex hull. Therefore, by periodically limiting the power of the DC / DC converter circuit 210a, it can be ensured that the input voltage operating point of the DC / DC converter circuit 210a when it starts maximum power point tracking is located on the right slope of the PV curve, thereby avoiding the input voltage operating point of the DC / DC converter circuit 210a being stuck inside the convex hull and significantly reducing the power generation loss of the inverter 21.

[0049] It can be understood that within the constant power curve segment of the PV curve, the fluctuation of the output power of converter array 20a is less than the fluctuation threshold. That is, within the constant power curve segment, the output power of converter array 20a is greater than or equal to the difference between the constant output power and the fluctuation threshold, and less than or equal to the sum of the constant output power and the fluctuation threshold. Here, the constant output power and the fluctuation threshold can be pre-set values, or values ​​determined by the internal components of converter array 20a and inverter 21. This fluctuation threshold is typically one-thousandth of the constant output power. For example, when the PV curve of converter array 20a is as shown in Figure 4, the constant power curve segment can be the curve segment between points (V5, P5) and (V6, P61) in PV curve 1, and the right slope of PV curve 1 can be the curve segment to the right of point (V6, P61) in PV curve 1. Alternatively, the constant power curve segment can be the curve segment between points (V7, P7) and (V9, P9) in PV curve 2, and the right slope of PV curve 2 can be the curve segment to the right of point (V9, P9) in PV curve 2.

[0050] It is understood that when inverter 21 is applied in a photovoltaic-storage power generation system, inverter 21 is also used to invert the DC power output from the energy storage device (not shown in the figure) into AC power and supply power to the grid 4. Optionally, inverter 21 is also used to convert the AC power output from the grid 4 into DC power and charge the energy storage device. In this case, the input of DC / DC converter circuit 210a and the input of DC / AC converter circuit 211 are both replaced with outputs, and the outputs of DC / DC converter circuit 210a and DC / AC converter circuit 211 are both replaced with inputs.

[0051] When the input power of the DC / DC converter circuit 210a is less than or equal to the power threshold, the preset power value is a fixed value. This power threshold and the fixed value can be determined by the sampling accuracy of the inverter 21. For example, the power threshold can be 3 kW, and the fixed value can be 10 W. When the input power of the DC / DC converter circuit 210a is greater than the power threshold, the preset power value is k times the input power of the DC / DC converter circuit 210a, where k is less than 1. For example, k is 0.01. By implementing this embodiment, the preset power value can be flexibly adjusted according to the input power of the DC / DC converter circuit 210a, thereby ensuring that the operating point of the input voltage after power limiting of the DC / DC converter circuit 210a exits the convex hull and is located on the right slope of the PV curve.

[0052] After confirming the preset power value based on the input power of the DC / DC converter circuit 210a, the controller 212 is further configured to control the DC / DC converter circuit 210a to exit the maximum power point tracking (MPPT) mode after a preset time period, and to control the input power of the DC / DC converter circuit 210a to decrease by the preset power value. Optionally, the controller 212 is further configured to control the DC / DC converter circuit 210a to exit the MPPT mode and control the input power of the DC / DC converter circuit 210a to decrease by the preset power value when the input power of the DC / DC converter circuit 210a is less than or equal to the mode exit threshold. The input power of the DC / DC converter circuit 210a can be detected by a power detection circuit inside the controller 212, or detected by a power detection device external to the controller 212 and then sent to the controller 212. The mode exit threshold is a threshold used to indicate that the DC / DC converter circuit 210a exits the MPPT mode. This mode exit threshold is less than the estimated maximum power of the converter array 20a, which can be determined by the open-circuit voltage of the converter array 20a. Optionally, the controller 212 is further configured to, after a preset time period and when the input power of the DC / DC converter 210a is less than or equal to the mode exit threshold, control the DC / DC converter 210a to exit the maximum power point tracking mode and control the input power of the DC / DC converter 210a to decrease by a preset power value. Implementing this embodiment ensures that the input voltage operating point of the DC / DC converter 210a when it begins maximum power point tracking is located on the right slope of the PV curve, thereby preventing the input voltage operating point of the DC / DC converter 210a from being stuck within the convex hull and unable to exit, significantly reducing the power generation loss of the inverter 21.

[0053] When the input power of the DC / DC converter circuit 210a is reduced to a preset power value, the input voltage of the DC / DC converter circuit 210a gradually increases. Therefore, the input voltage of the DC / DC converter circuit 210a is greater than the input voltage when the DC / DC converter circuit 210a is in maximum power point tracking (MPPT) mode. By implementing the embodiments of this application, the operating point of the input voltage of the DC / DC converter circuit 210a can continuously move in the direction of increasing output voltage in the PV curve until it exits the convex hull of the PV curve. This avoids the situation where the maximum power point is misidentified because the input voltage operating point is stuck in the convex hull and cannot exit, thereby improving the accuracy of maximum power point identification.

[0054] For example, at time t1, the PV curve of converter array 20a can be shown as PV curve 1 in Figure 4. At this time, the input voltage operating point of DC / DC converter circuit 210a is (V6, P61), and (V6, P61) is the maximum power point of converter array 20a at time t1. At time t2, due to changes in the external environment (such as light, temperature, etc.), the PV curve of converter array 20a will also change accordingly, specifically as shown as PV curve 2 in Figure 4. The input voltage operating point of DC / DC converter circuit 210a will change from (V6, P61) to (V6, P62), and (V6, P62) is located within the convex hull a in PV curve 2. At this time, the controller 212 is used to control DC / DC converter circuit 210a to exit the maximum power point tracking mode, and uses closed-loop control or open-loop control to control the input power of DC / DC converter circuit 210a to reduce the preset power value. During the process of reducing the preset power value, the input power of the DC / DC converter circuit 210a will gradually decrease from the power value P62 to the power value P8, and the operating point of the input voltage of the DC / DC converter circuit 210a will change from (V6, P61) to (V8, P8). At this time, the operating point of the input voltage of the DC / DC converter circuit 210a has exited the convex hull a and is located on the right slope of the PV curve 2. After the operating point of the input voltage of the DC / DC converter circuit 210a is located on the right slope, the controller 212 is used to control the DC / DC converter circuit 210a to re-enter the maximum power point tracking mode. Specifically, one of the methods of perturbation observation, constant voltage observation, and incremental conductance is used to perform maximum power point tracking on the converter array 20a, so that the right inflection point of the constant power curve segment (i.e., the high voltage side inflection point), such as (V9, P9), is identified as the actual maximum power point of the converter array 20a at time t2. By implementing the embodiments of this application, the power of the DC / DC converter circuit 210a can be limited so that the input voltage operating point of the DC / DC converter circuit 210a exits the convex hull a, thereby significantly reducing the power generation loss of the inverter 21.

[0055] Taking the disturbance observation method as an example, the controller 212 is used to adjust the input voltage or input current of the DC / DC converter circuit 210a and determine the power change trend of the input power of the DC / DC converter circuit 210a before and after the input voltage or input current adjustment. It should be understood that the input power of the DC / DC converter circuit 210a before the input voltage or input current adjustment can be simply referred to as the first input power, and the input power of the DC / DC converter circuit 210a after the input voltage or input current adjustment can be simply referred to as the second input power. When the second input power is greater than the first input power, the power change trend is an increasing trend; when the second input power is less than or equal to the first input power, the power change trend is a decreasing trend.

[0056] Furthermore, the controller 212 is also used to continuously adjust the input voltage or input current of the DC / DC converter circuit 210a according to the power change trend until the maximum power point of the converter array 20a is identified. Specifically, taking the continuous adjustment of the input voltage of the DC / DC converter circuit 210a as an example, the controller 212 is used to continue increasing the input voltage of the DC / DC converter circuit 210a when the power change trend is increasing and the adjusted input voltage is greater than the original input voltage; and to decrease the input voltage of the DC / DC converter circuit 210a when the power change trend is decreasing and the adjusted input voltage is greater than the original input voltage. The controller 212 is also used to continue decreasing the input voltage of the DC / DC converter circuit 210a when the power change trend is increasing and the adjusted input voltage is less than the original input voltage; and to increase the input voltage of the DC / DC converter circuit 210a when the power change trend is decreasing and the adjusted input voltage is less than the original input voltage. For example, when maximum power point tracking starts from point (V8, P8), the controller 212 reduces the input voltage of the DC / DC converter circuit 210a to move the operating point of the input voltage of the DC / DC converter circuit 210a from point (V8, P8) to point (V9, P9). When |P8-P9| is less than or equal to a preset threshold, point (V9, P9) is identified as the maximum power point of the converter array 20a. When |P8-P9| is greater than the preset threshold, the input voltage of the DC / DC converter circuit 210a is further reduced until the actual maximum power point of the converter array 20a is identified. This preset threshold can also be called a constant power threshold. For example, the preset threshold can be five ten-thousandths of the first input power.

[0057] It should be understood that the specific implementation of the controller 212 for maximum power point tracking of other converter arrays in converter arrays 20a to 20n can be found in the relevant description of the controller 212 performing maximum power point tracking of converter array 20a through DC / DC conversion circuit 210a, and will not be repeated here.

[0058] Referring to Figure 5, which is a circuit diagram of a DC / DC converter provided in an embodiment of this application, the DC / DC converter 201a shown in Figure 3 includes capacitors C3 and C4, switches Q1 and Q2, inductor L1, and diode D1. The two ends of capacitor C4 are used to connect to the photovoltaic module 31a. Switches Q1 and Q2 are connected in series and then in parallel with capacitor C4. The series connection point of switches Q1 and Q2 is connected to one end of diode D1 and one end of capacitor C4 through inductor L1. One end of switch Q2 is connected to the other end of diode D1 and the other end of capacitor C4. The controller inside the DC / DC converter 201a controls the complementary conduction of switches Q1 and Q2, thereby converting the DC voltage output from the photovoltaic module 31a into a target DC voltage and outputting it to the DC / DC conversion circuit 210a for power supply. In this embodiment, the circuit topology of the DC / DC converter 201a shown in Figure 5 is only an example, and the circuit topology of the DC / DC converter 201a is not limited here. It should be understood that the circuit topology and working principle of the other converters in the DC / DC converters 201a to 20na can be found in the above description of the circuit topology and working principle of DC / DC converter 201a, and will not be repeated here.

[0059] Referring to Figure 6, which is a flowchart illustrating the maximum power point tracking (MPPT) method for an inverter provided in this embodiment, the method can be executed by the inverter, such as by a controller within the inverter. The inverter is used to connect between a converter array consisting of multiple DC / DC converters connected in series and the power grid. The inverter includes a DC / DC conversion circuit, a DC / AC conversion circuit, and a controller. The controller can control the DC / DC conversion circuit to periodically execute the following steps, specifically steps S101 to S103 as shown in Figure 6.

[0060] In step S101, the controller controls the DC / DC conversion circuit to be in maximum power point tracking mode in order to perform maximum power point tracking on the converter array.

[0061] In step S102, after a preset time, the controller controls the DC / DC conversion circuit to exit the maximum power point tracking mode and controls the input power of the DC / DC conversion circuit to decrease to a preset power value.

[0062] When the input power of the DC / DC converter circuit is less than or equal to the power threshold, the preset power value is a fixed value. When the input power of the DC / DC converter circuit is greater than the power threshold, the preset power value is k times the input power of the DC / DC converter circuit, where k is less than 1. For example, k is 0.01. By implementing the embodiments of this application, the preset power value can be flexibly adjusted according to the input power of the DC / DC converter circuit, thereby ensuring that the operating point of the input voltage after power limiting of the DC / DC converter circuit exits the convex hull and is located on the right slope of the PV curve.

[0063] After confirming the preset power value based on the input power of the DC / DC converter circuit, the controller can, after a preset time, control the DC / DC converter circuit to exit the maximum power tracking mode and reduce its input power by the preset power value. Optionally, the controller can also control the DC / DC converter circuit to exit the maximum power tracking mode and reduce its input power by the preset power value when the input power of the DC / DC converter circuit is less than or equal to a mode exit threshold. This mode exit threshold is a threshold used to indicate when the DC / DC converter circuit exits the maximum power tracking mode. This mode exit threshold is less than the estimated maximum power of the converter array, which can be determined by the open-circuit voltage of the converter array. Optionally, the controller can also control the DC / DC converter circuit to exit the maximum power tracking mode and reduce its input power by the preset power value after a preset time, provided that the input power of the DC / DC converter circuit is less than or equal to the mode exit threshold. By implementing the embodiments of this application, it can be ensured that the input voltage operating point of the DC / DC converter circuit when it starts maximum power point tracking is located on the right slope of the PV curve, thereby avoiding the input voltage operating point of the DC / DC converter circuit being stuck in the convex hull and unable to exit, and significantly reducing the power generation loss of the inverter.

[0064] When the controller reduces the input power of the DC / DC converter circuit by a preset power value, it controls the input voltage of the DC / DC converter circuit to be greater than the input voltage when the DC / DC converter circuit is in maximum power point tracking (MPPT) mode. Implementing this embodiment allows the input voltage operating point of the DC / DC converter circuit to continuously move in the direction of increasing output voltage on the PV curve until it exits the convex hull of the PV curve. This avoids the misidentification of the maximum power point caused by the input voltage operating point being stuck within the convex hull, thereby improving the accuracy of maximum power point identification.

[0065] Step S103: When the input power of the DC / DC converter circuit decreases to a preset power value, the controller controls the DC / DC converter circuit to re-enter the maximum power point tracking mode.

[0066] In specific implementation, the controller can use one of the following methods: disturbance observation method, constant voltage observation method, and incremental conductance method to control the DC / DC conversion circuit to perform maximum power point tracking on the converter array, thereby intelligently identifying the actual maximum power point of the converter array.

[0067] In specific implementation, the further operations performed by the controller in the maximum power point tracking method of the inverter provided in this application and their corresponding beneficial effects can be found in the implementation method and corresponding beneficial effects of the controller in the inverter and its working principle shown in Figures 3 to 5 above, which will not be repeated here.

[0068] The maximum power point tracking method provided in this application avoids misidentifying other points (such as points within the convex hull) in the PV curve of the converter array as the maximum power point, thus improving the accuracy of maximum power point identification. Furthermore, once the actual maximum power point of the converter array is identified, the efficiency of the converter array can be improved, and the power generation of the inverter can be effectively increased, demonstrating strong applicability.

[0069] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. An inverter for connecting between a converter array composed of a plurality of DC / DC converters connected in series and a power grid, and performing energy conversion, characterized by, The inverter comprises a direct current (DC) / DC conversion circuit, a DC / alternating current (AC) conversion circuit, and a controller; an input of the DC / DC conversion circuit is connected to an output of the conversion array; an input of the DC / AC conversion circuit is connected to an output of the DC / DC conversion circuit, and an output of the DC / AC conversion circuit is connected to the power grid; The controller is configured to periodically: control the DC / DC conversion circuit to be in a maximum power point tracking (MPPT) mode to track a maximum power point of the conversion array; after a preset time period, control the DC / DC conversion circuit to exit the MPPT mode and reduce an input power of the DC / DC conversion circuit by a preset power value; after the input power of the DC / DC conversion circuit is reduced by the preset power value, control the DC / DC conversion circuit to re-enter the MPPT mode.

2. The inverter of claim 1, wherein, When the input power of the DC / DC conversion circuit is less than or equal to a power threshold, the preset power value is a fixed value.

3. The inverter of claim 1, wherein, When the input power of the DC / DC conversion circuit is greater than the power threshold, the preset power value is k times of the input power of the DC / DC conversion circuit, and k is less than 1.

4. The inverter of claim 3, wherein, The k is 0.

01.

5. The inverter according to any one of claims 1 to 4, characterized by, When the input power of the DC / DC conversion circuit is reduced by the preset power value, an input voltage of the DC / DC conversion circuit is greater than an input voltage of the DC / DC conversion circuit in the MPPT mode.

6. The inverter according to any one of claims 1 to 5, characterized by The inverter further comprises a capacitor connected in parallel to an input of the DC / DC conversion circuit or an input of the DC / AC conversion circuit, so as to store energy output by the conversion array when the input power of the DC / DC conversion circuit is reduced by the preset power value, and increase the input voltage of the DC / DC conversion circuit.

7. A maximum power point tracking method, characterized by, The method is performed by an inverter connected between a conversion array composed of a plurality of DC / DC converters in series and a power grid, and the inverter comprises a DC / DC conversion circuit, a DC / AC conversion circuit, and a controller, and the method comprises: periodically: controlling the DC / DC conversion circuit to be in an MPPT mode to track a maximum power point of the conversion array; after a preset time period, controlling the DC / DC conversion circuit to exit the MPPT mode and reduce an input power of the DC / DC conversion circuit by a preset power value; after the input power of the DC / DC conversion circuit is reduced by the preset power value, controlling the DC / DC conversion circuit to re-enter the MPPT mode.

8. The maximum power point tracking method of claim 7, wherein, The method further comprises: When the input power of the DC / DC conversion circuit is less than or equal to a power threshold, the preset power value is a fixed value.

9. The maximum power point tracking method of claim 7, wherein, The method further comprises: When the input power of the DC / DC conversion circuit is greater than a power threshold, the preset power value is k times of the input power of the DC / DC conversion circuit, and the k is less than 1.

10. The maximum power point tracking method as claimed in claim 9, characterized in that, The k is 0.

01.

11. The maximum power point tracking method according to any one of claims 7-10, characterized in that, The method further comprises: When the input power of the DC / DC conversion circuit is reduced by the preset power value, the input voltage of the DC / DC conversion circuit is controlled to be greater than the input voltage when the DC / DC conversion circuit is in the maximum power tracking mode.

12. A photovoltaic power system, characterized by, The photovoltaic power generation system comprises a plurality of converter arrays and an inverter; wherein, Each of the plurality of converter arrays is composed of a plurality of DC / DC converters in series; The inverter comprises a plurality of DC / DC conversion circuits, a DC / AC conversion circuit, and a controller, each of the plurality of DC / DC conversion circuits is connected in one-to-one correspondence with each of the plurality of converter arrays; the input of each of the plurality of DC / DC conversion circuits is connected to the output of the corresponding converter array of each of the plurality of DC / DC conversion circuits, the output of the plurality of DC / DC conversion circuits is connected to the input of the DC / AC conversion circuit, and the output of the DC / AC conversion circuit is used to connect to a power grid; The controller is configured to periodically: control the plurality of DC / DC conversion circuits to be in the maximum power tracking mode to track the maximum power point of the corresponding converter array of the plurality of DC / DC conversion circuits; after a preset time period, control the plurality of DC / DC conversion circuits to exit the maximum power tracking mode, and control the input power of the plurality of DC / DC conversion circuits to be reduced by a preset power value; When the input power of each of the plurality of DC / DC conversion circuits is less than or equal to a power threshold, the preset power value is a fixed value.

13. The photovoltaic power system of claim 12, wherein, When the input power of each of the plurality of DC / DC conversion circuits is greater than a power threshold, the preset power value is k times of the input power of each of the plurality of DC / DC conversion circuits, and the k is less than 1.

14. The photovoltaic power system of claim 12, wherein, The inverter further comprises a capacitor, wherein the capacitor is connected in parallel at the input of each of the plurality of DC / DC conversion circuits or the input of the DC / AC conversion circuit, for storing the energy output by the corresponding converter array of the plurality of DC / DC conversion circuits when the input power of the plurality of DC / DC conversion circuits is reduced by the preset power value, so as to increase the input voltage of the plurality of DC / DC conversion circuits.

15. The photovoltaic power system according to any of claims 12-14, characterized in that, ​

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