Power conversion system and power updating control method

Abstract

The invention discloses a power conversion system and a power update control method, and the system comprises N power conversion units and a control unit. The working mode of one or more target power conversion units in N power conversion units can be controlled to be switched between a power reservation (PR) mode and a maximum power point tracking (MPPT) mode, and reference power is updated according to the maximum power obtained in the MPPT mode. The working power of the target power conversion unit in the PR mode is the updated reference power, and the updated reference power is smaller than or equal to the maximum power. And the control unit also controls the working modes of the power conversion units except the target power conversion unit in the N power conversion units to be kept unchanged, so that the power conversion units except the target power conversion unit are not subjected to mode switching. Therefore, the fluctuation of the total output power and the output voltage of the power conversion unit is reduced.

Description

Technical Field

[0001] The present application relates to the field of power electronics technology, and in particular to a power conversion system and a power update control method. Background Art

[0002] The power supply system is a new type of power generation system that uses the photovoltaic effect of photovoltaic modules to convert solar radiation energy into electrical energy. The power converter is the core component of the power supply system, which is mainly responsible for converting the direct current generated by the photovoltaic module into alternating current and outputting the alternating current to the power grid. The inverter usually includes a power conversion unit. By controlling the power conversion unit to work in the maximum power point tracking (MPPT) mode, the maximum power of the photovoltaic module can be tracked, so that the power supply system can work at the maximum power point in real time.

[0003] In practical applications, the voltage amplitude, frequency, and phase on the power grid will have dynamic fluctuations, and the power conversion unit works in the MPPT mode, which makes the power supply system unable to freely adjust the power to support the power during the dynamic fluctuation of the power grid (it can only reduce the power in one direction, but cannot increase the power). Based on this, by reserving power (power reserve, PR) for the output power of the photovoltaic module, that is, controlling the power conversion unit to work in the PR mode, so that the output power of the photovoltaic module is lower than the maximum power, the power supply system can increase and reduce the output power based on the reserved power during the period when the voltage amplitude, frequency, and phase of the power grid are in dynamic fluctuations, so as to meet the needs of the power grid. In addition, when the power conversion unit works in the PR mode, it is also necessary to rely on the MPPT mode to detect the maximum power of the photovoltaic module, which causes the power conversion unit to switch between the PR mode and the MPPT mode, resulting in fluctuations in the total output power and output voltage of the power conversion unit, endangering the stability and control accuracy of the power supply system, and even increasing the mechanical stress and thermal stress of the equipment. Summary of the invention

[0004] The embodiments of the present application provide a power conversion system and a power update control method, which are used to track the maximum power and timely and accurately update the working power of the power conversion unit in the PR mode, and reduce the fluctuation of the output power and output voltage of the power conversion unit.

[0005] In the first aspect, an embodiment of the present application provides a power conversion system, which includes: N power conversion units and a control unit, N is an integer and N≥2; the first end of each power conversion unit is used to connect to a DC power supply or an AC power supply, and the second end of each power conversion unit is used to connect to a load or an energy storage unit or a power generation unit or a power grid, and the power conversion unit is used to convert the DC power input by the DC power supply or the AC power input by the AC power supply and output it. In addition, the control unit can control the working mode of one or more target power conversion units in the N power conversion units to switch between the power reservation PR mode and the maximum power point tracking MPPT mode during the control cycle, and after the working mode of the target power conversion unit is switched to the MPPT mode, the maximum power can be obtained in the MPPT mode. Therefore, the reference power can be updated according to the maximum power obtained in the MPPT mode to obtain the updated reference power, so that the working power of the target power conversion unit after switching from the MPPT mode to the PR mode can be changed to the updated reference power, and the updated reference power is less than or equal to the maximum power. Furthermore, in the control cycle, the control unit can also control the working modes of the power conversion units other than the target power conversion unit among the N power conversion units to remain unchanged, so that the power conversion units other than the target power conversion unit do not perform mode switching. With this arrangement, some of the N power conversion units can perform mode switching between the PR mode and the MPPT mode, while the remaining power conversion units do not perform mode switching. Compared with all the power conversion units among the N power conversion units performing mode switching between the PR mode and the MPPT mode, the fluctuation of the total output power and output voltage of the power conversion units can be reduced, and the stability and control accuracy of the power supply system can be improved.

[0006] Furthermore, through the above-mentioned embodiments, the mechanical stress, thermal stress, etc. of the power conversion system equipment can be reduced, thereby improving the overall stability of the power conversion system.

[0007] In the present application, the target power conversion unit can be randomly selected. Specifically, in one or more control cycles within a plurality of consecutive control cycles, one or more power conversion units are randomly selected from N power conversion units as the target power conversion unit. Thus, the target power conversion unit can be selected by random selection.

[0008] In the present application, at least some of the power conversion units have different probabilities of being selected as the target power conversion units. Exemplarily, the probabilities of all the power conversion units being selected as the target power conversion units can be made different, or the probabilities of some of the power conversion units being selected as the target power conversion units can be made different, and the probabilities of the remaining power conversion units being selected as the target power conversion units are the same.

[0009] In some examples, when randomly selecting a target power conversion unit, the probability of each power conversion unit being selected as the target power conversion unit is made equal. Thus, a power conversion unit can be randomly selected as the target power conversion unit with equal probability. Further, in each control cycle, a power conversion unit is randomly selected as the target power conversion unit with equal probability.

[0010] In some other examples, when randomly selecting a target power conversion unit, the probability of at least some of the power conversion units being selected as the target power conversion unit is made different. With this arrangement, it is possible to randomly select power conversion units as target power conversion units with different probabilities. Exemplarily, the probabilities of all power conversion units being selected as target power conversion units can be made different, or the probabilities of some power conversion units being selected as target power conversion units can be made different, and the probabilities of the remaining power conversion units being selected as target power conversion units are the same.

[0011] In a specific implementation, the control unit can also obtain the selection probability of each power conversion unit, and randomly select a target power conversion unit from the N power conversion units according to the selection probability of each power conversion unit. For example, the selection probability of each power conversion unit can be stored in a storage unit of the power supply system, and the control unit can obtain the selection probability of each power conversion unit from the storage unit, so that the corresponding power conversion unit can be randomly selected as the target power conversion unit according to the obtained selection probability of each power conversion unit.

[0012] The selection probability corresponding to each power conversion unit can be configured as a fixed value in an offline or online manner. For example, if the operator needs to configure the selection probability in an online manner, the operator can input a probability adjustment instruction corresponding to the selection probability of some or all power conversion units through the user interface (UI). When the control unit receives the probability adjustment instruction, it can adjust the selection probability of some or all power conversion units according to the probability adjustment instruction.

[0013] In the present application, the target power conversion unit may also be selected in a fixed order. Specifically, in one or more control cycles within a plurality of consecutive control cycles, the target power conversion unit is one or more power conversion units selected from N power conversion units in a fixed order. Thus, the target power conversion unit can be selected in a specific selection order.

[0014] In a specific implementation, the N power conversion units include the 1st unit group to the Mth unit group arranged in sequence, and any unit group includes one or more power conversion units, M is an integer and M≥2. And, a plurality of consecutive cycles include one or a combination of the first cycle and the second cycle. Among them, in the first cycle, a unit group selected in sequence from the 1st unit group to the Mth unit group is used as the target power conversion unit. And, in the second cycle, a unit group selected in sequence from the Mth unit group to the 1st unit group is used as the target power conversion unit.

[0015] In some examples, each control cycle selects a unit group as a target power conversion unit according to a unidirectional fixed timing (e.g., positive sequence) cycle, based on which, each M control cycles constitute a cycle, thereby allowing multiple consecutive cycles to appear, and the multiple cycles have a first cycle. Exemplarily, part of the cycle can be set as the first cycle, or all the cycle can be set as the first cycle.

[0016] In some other examples, each control cycle selects a unit group as the target power conversion unit according to a unidirectional fixed timing (e.g., reverse order), based on which every M control cycles can constitute a cycle, thereby allowing multiple consecutive cycles to appear, and the multiple cycles have a second cycle. Exemplarily, part of the cycle can be set as the second cycle, or all the cycle can be set as the second cycle.

[0017] In some other examples, the first cycle and the second cycle are combined with each other, based on which, when the plurality of cycles include the first cycle and the second cycle, the first cycle and the second cycle are alternately displayed. Alternatively, at least two adjacent first cycles and at least two adjacent second cycles may be alternately displayed.

[0018] In this application, multiple updating methods can be used to obtain the updated reference power P res '. Next, we get the updated reference power P res ' is updated with an example.

[0019] Update method 1: The updated reference power is equal to the target maximum power minus the reserved power.

[0020] Update method 2: The updated reference power is equal to the target maximum power minus the reserved power.

[0021] Update method three: The updated reference power is equal to the target maximum power multiplied by the reference percentage.

[0022] Update method 4: The updated reference power is equal to the target maximum power multiplied by the reference percentage.

[0023] The target maximum power is a maximum power or an average maximum power among the maximum powers of one or more target power conversion units.

[0024] It is understandable that the reference power updated in the kth control cycle may be the same as the reference power in the k-1th control cycle. Alternatively, the reference power updated in the kth control cycle may be greater than the reference power in the k-1th control cycle. Alternatively, the reference power updated in the kth control cycle may be less than the reference power in the k-1th control cycle. Wherein, k is an integer greater than 0.

[0025] In some examples, a constant power threshold is set as the reserved power according to experimental data or experience, so that the reserved power is a constant value.

[0026] In some examples, the reserved power is updated by the target maximum power, for example, the reserved power is equal to the target maximum power multiplied by a percentage, and the updated reference power is the target maximum power minus the reserved power calculated by the above update. It is understandable that the updated reserved power in the kth control cycle may be the same as the reserved power in the k-1th control cycle. Alternatively, the updated reserved power in the kth control cycle may also be greater than the reserved power in the k-1th control cycle. Alternatively, the updated reserved power in the kth control cycle may also be less than the reserved power in the k-1th control cycle.

[0027] In the present application, the operating modes of the power conversion units other than the target power conversion unit among the N power conversion units remain unchanged, which means that the operating modes of the part of the power conversion units do not switch modes, but constantly operate in one operating mode. The following is an example of the implementation of the operating mode of the part of the power conversion units.

[0028] Implementation method one: The working mode of the power conversion units other than the target power conversion unit among the N power conversion units is the PR mode, and the working power of the power conversion units other than the target power conversion unit is the updated reference power. With this configuration, all power conversion units can work in the PR mode to realize photovoltaic grid construction. In addition, some power conversion units are used as target power conversion units to switch between the PR mode and the MPPT mode, and the working modules of the remaining power conversion units are always in the PR mode, which can reduce the fluctuation of the output power and output voltage of the power conversion unit and improve the stability and control accuracy of the power supply system. In addition, in order to update the reference power of the power conversion units other than the target power conversion unit in the PR mode, after the target power conversion unit updates the reference power, the working power of the power conversion units other than the target power conversion unit is also switched to the updated reference power.

[0029] Implementation method 2: The working mode of the power conversion units other than the target power conversion unit among the N power conversion units is set to the MPPT mode, and the working power of the power conversion units other than the target power conversion unit is the maximum power obtained by the MPPT mode. According to this setting, some power conversion units are used as target power conversion units and work in the PR mode and perform mode switching between the PR mode and the MPPT mode, and the working mode of the remaining power conversion units is always the MPPT mode, so as to realize photovoltaic grid construction. In addition, the target power conversion unit is switched between the PR mode and the MPPT mode, and the remaining power conversion units are always in the MPPT mode, which can reduce the fluctuation of the output power and output voltage of the power conversion unit and improve the stability and control accuracy of the power supply system.

[0030] Implementation method three: For the power conversion units other than the target power conversion unit among the N power conversion units, the working mode of some power conversion units is PR mode, and the working power of some power conversion units is updated with the updated reference power, and the working mode of the remaining power conversion units is MPPT mode, and the working power of the remaining power conversion units is the maximum power obtained by the MPPT mode. Thus, some power conversion units are switched between PR mode and MPPT mode as target power conversion units, and the working mode of the remaining power conversion units remains unchanged, so as to realize photovoltaic grid construction. Moreover, since the working mode of some power conversion units other than the target power conversion unit is constant to PR mode, in order to update the reference power of some power conversion units in PR mode, the working power of some power conversion units can be switched to the updated reference power after the target power conversion unit updates the reference power. And, since the working mode of the remaining power conversion units other than the target power conversion unit is constant to MPPT mode. Based on this, the fluctuation of the output power and output voltage of the power conversion unit can be reduced, and the stability and control accuracy of the power supply system can be improved.

[0031] Implementation method four: The working power of the power conversion unit other than the target power conversion unit among the N power conversion units is less than the maximum power, and the working power of the power conversion unit other than the target power conversion unit is different from the updated reference power. Among them, the working power of the power conversion unit other than the target power conversion unit may be greater than or less than the updated reference power. In a specific implementation, the updated reference power may be used to determine the working power of the power conversion unit other than the target power conversion unit, thereby eliminating the need to switch the working power of the power conversion unit other than the target power conversion unit, thereby reducing the fluctuation of the output power and output voltage of the power conversion unit, and improving the stability and control accuracy of the power supply system.

[0032] It is understandable that after the target power conversion unit updates the reference power, the operating power of the power conversion unit other than the target power conversion unit can be controlled to switch to the updated reference power. Of course, it is not necessary to update the reference power of the power conversion unit other than the target power conversion unit in the PR mode, but the reference power of the power conversion unit other than the target power conversion unit in the PR mode is controlled to continue to work with the reference power in the previous control cycle.

[0033] In some examples, the power conversion unit includes a direct current-direct current (DC-DC) conversion circuit, and the power conversion system also includes a direct current-alternating current (DC-AC) conversion circuit. Wherein, the first end of the direct current-direct current conversion circuit is used to connect to a direct current power supply, the second end of the direct current-direct current conversion circuit is connected to the first end of the direct current-alternating current conversion circuit, and the second end of the direct current-alternating current conversion circuit is used to connect to a load or a power grid. Exemplarily, the DC-DC conversion circuit is used to convert the direct current input by the direct current power supply into alternating current and output it to the load or the power grid.

[0034] In some other examples, the power conversion unit includes a direct current-alternating current (DC-AC) conversion circuit. The first end of the direct current-alternating current conversion circuit is used to connect to a direct current power source, and the second end of the direct current-alternating current conversion circuit is used to connect to a load or a power grid or an alternating current system. Exemplarily, the DC-AC conversion circuit is used to convert direct current input from a direct current power source into alternating current and then output it to a load or a power grid or an alternating current system.

[0035] In some other examples, the power conversion unit includes a direct current-to-direct current (DC-DC) conversion circuit. The first end of the direct current-to-direct current conversion circuit is used to connect a direct current power supply, and the second end of the direct current-to-direct current conversion circuit is used to connect a load or an energy storage unit or a power generation unit. Exemplarily, the DC-DC conversion circuit is used to convert the direct current input by the direct current power supply into power and output it to the load or the energy storage unit or the power generation unit. Alternatively, the DC-DC conversion circuit can also be used to convert the direct current input by the energy storage unit or the power generation unit into power and output it to the direct current power supply.

[0036] In some other examples, the power conversion unit includes an alternating current-direct current (AC-DC) conversion circuit. The first end of the AC-DC conversion circuit is used to connect to an AC power source, and the second end of the AC-DC conversion circuit is used to connect to a load or an energy storage unit or a power generation unit. Exemplarily, the AC-DC conversion circuit is used to convert the AC power input from the AC power source into DC power and then output it to the load or the energy storage unit or the power generation unit. Alternatively, the AC-DC conversion circuit can also be used to convert the DC power input from the energy storage unit or the power generation unit into AC power and then output it to the AC power source.

[0037] In some other examples, the power conversion system includes an AC-DC (AC-DC) conversion circuit, and the power conversion system also includes a DC-AC (DC-AC) conversion circuit. Wherein, the first end of the AC-DC conversion circuit is used to connect to an AC power supply, the second end of the AC-DC conversion circuit is connected to the first end of the DC-AC conversion circuit, and the second end of the DC-AC conversion circuit is used to connect to a load or a power grid. Exemplarily, the AC-DC conversion circuit is used to convert the AC power input from the AC power supply into DC power and then output it to the DC-AC conversion circuit, and the DC-AC conversion circuit is used to convert the input DC power into AC power and then output it to a load or an energy storage unit or a power generation unit. Alternatively, the DC-AC conversion circuit can also convert the AC power input from the energy storage unit or the power generation unit into DC power and then output it to the AC-DC conversion circuit, and the AC-DC conversion circuit can convert the input DC power into AC power and then output it to the AC power supply.

[0038] In a specific implementation, the control unit can be a field programmable gate array (FPGA), a central processing unit (CPU), a general-purpose processor, a digital signal processing (DSP), an application specific integrated circuit (ASIC), or other programmable logic devices, transistor logic devices, hardware components, or any combination thereof. It can implement or execute various exemplary logic blocks, modules, and circuits described in conjunction with the disclosure of this application. The above-mentioned control unit can also be a combination that implements computing functions, such as a combination of one or more microprocessors, a combination of a DSP and a microprocessor, etc.

[0039] In the second aspect, the embodiment of the present application also provides a power update control method, which is applied to a power conversion system, wherein the power conversion system includes N power conversion units, N is an integer and N≥2; the first end of each power conversion unit is used to connect to a DC power supply or an AC power supply, and the second end of each power conversion unit is used to connect to a load or an energy storage unit or a power grid, and the power conversion unit is used to convert the DC power input by the DC power supply or the AC power input by the AC power supply and output it. In addition, the power update control method includes: controlling the working mode of one or more target power conversion units among the N power conversion units to switch between the power reservation PR mode and the maximum power point tracking MPPT mode, updating the reference power according to the maximum power obtained in the MPPT mode, so that the working power of the target power conversion unit after switching from the MPPT mode to the PR mode is the updated reference power; wherein the updated reference power is less than or equal to the maximum power. And, controlling the working mode of the power conversion units other than the target power conversion unit among the N power conversion units to remain unchanged.

[0040] Furthermore, the method for selecting the target power conversion unit may refer to the method in the first aspect or any embodiment of the first aspect, and will not be elaborated here.

[0041] In a third aspect, an embodiment of the present application further provides a power supply system, which includes a power conversion system, wherein the first end of the power conversion unit in the power conversion system is connected to a DC power supply or an AC power supply, and the second end of the power conversion system is used to connect a load or an energy storage unit or a power generation unit or a power grid. In addition, the power conversion system is used to convert the direct current input by the DC power supply or the alternating current input by the AC power supply and then output it. Among them, the power conversion system is the power conversion system in the first aspect or any embodiment of the first aspect.

[0042] The above power supply system can be configured as a photovoltaic system, then the power supply system further includes a photovoltaic component, and the first end of the power conversion unit in the power conversion system is connected to the photovoltaic component, and the photovoltaic component serves as a DC power supply.

[0043] In addition, the technical effects of the corresponding schemes in the second and third aspects can refer to the technical effects that can be obtained by the corresponding schemes in the first aspect, and the repeated parts will not be described in detail. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 A schematic diagram of an application scenario of a power supply system provided in an embodiment of the present application;

[0045] Figure 2a A schematic diagram of a structure of a power conversion system provided in an embodiment of the present application;

[0046] Figure 2bA schematic diagram of a specific structure of a power conversion system provided in an embodiment of the present application;

[0047] Figure 3 A schematic diagram of the working mode of the power conversion unit in the embodiment of the present application in the control cycle;

[0048] Figure 4 A schematic diagram of selecting a target power conversion unit in an embodiment of the present application;

[0049] Figure 5 It is another schematic diagram of the working mode of the power conversion unit in the embodiment of the present application in the control cycle;

[0050] Figure 6 This is another schematic diagram of selecting a target power conversion unit in an embodiment of the present application;

[0051] Figure 7 It is another schematic diagram of the working mode of the power conversion unit in the embodiment of the present application in the control cycle;

[0052] Figure 8 This is another schematic diagram of selecting a target power conversion unit in an embodiment of the present application;

[0053] Fig. 9 It is another schematic diagram of the working mode of the power conversion unit in the embodiment of the present application in the control cycle;

[0054] Fig.10 This is another schematic diagram of selecting a target power conversion unit in an embodiment of the present application;

[0055] Fig.11 It is another schematic diagram of the working mode of the power conversion unit in the embodiment of the present application in the control cycle;

[0056] Fig.12 This is another schematic diagram of selecting a target power conversion unit in an embodiment of the present application;

[0057] Fig.13 A schematic diagram of a cycle in an embodiment of the present application;

[0058] Fig.14 This is another schematic diagram of the cycle in the embodiment of the present application;

[0059] Fig.15a A schematic diagram of another structure of a power conversion system provided in an embodiment of the present application;

[0060] Fig.15b A schematic diagram of another structure of a power conversion system provided in an embodiment of the present application.

[0061] Reference numerals:

[0062] 100-photovoltaic module; 200-power conversion system; 300-grid-connected transformer; 400-grid; 210_1~210_N-power conversion unit; 211-DC-DC conversion circuit; 220-DC-AC conversion unit; 212 / 221-DC-AC conversion circuit; 230-control unit; Bus+-positive DC bus; Bus--negative DC bus. DETAILED DESCRIPTION

[0063] In order to make the purpose, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the accompanying drawings. The specific operating methods in the method embodiments can also be applied to device embodiments or system embodiments. It should be noted that in the description of the present application, "multiple" can be understood as "at least two". In addition, it should be understood that in the description of the present application, words such as "first" and "second" are only used to distinguish the purpose of description, and cannot be understood as indicating or implying relative importance, nor can they be understood as indicating or implying order.

[0064] It should be noted that the same reference numerals in the drawings of this application represent the same or similar structures, and thus their repeated description will be omitted. The words expressing positions and directions described in this application are all explained using the drawings as examples, but they can be changed as needed, and the changes are included in the protection scope of this application. The drawings of this application are only used to illustrate the relative position relationship and do not represent the true proportion.

[0065] In order to facilitate the understanding of the technical solution provided by the embodiment of the present application, the application scenario of the solution of the present application is first described below. The power conversion system provided by the embodiment of the present application can be applied to the power supply system. The power supply system can be a photovoltaic system based on solar power generation or a wind power generation system based on wind power generation, or it can also be other energy conversion products and power generation products. Among them, the power conversion system is suitable for outputting electric energy to the power grid through a grid-connected transformer, and is also suitable for powering base station equipment (such as base station equipment in remote areas without mains power or poor mains power), or for powering batteries, or for powering power generation units (such as motors), or for powering various types of electrical equipment such as household appliances (such as refrigerators, air conditioners, etc.) in the power grid. Alternatively, the power conversion system is also suitable for transmitting the electric energy generated by the power generation unit to a DC power supply or an AC power supply, and reversely providing electric energy to the DC power supply or the AC power supply. Of course, in actual applications, the specific implementation of the power conversion system can be determined according to the actual application scenario, and is not limited here.

[0066] The following is a detailed description of the application of the power conversion system provided by the embodiment of the present application in the photovoltaic system scenario. For the working process of the power conversion system provided by the embodiment of the present application in other scenarios, the working process applied to the power supply system can be referred to, and the repetitions are not discussed.

[0067] Figure 1 This is a schematic diagram of an application scenario of a power supply system provided in an embodiment of the present application. Figure 1 , the power supply system includes: a photovoltaic module 100 and a power conversion system 200, the input end of the power conversion system 200 is connected to the photovoltaic module 100, the output end of the power conversion system 200 is connected to the input end of the grid-connected transformer 300, and the output end of the grid-connected transformer 300 is connected to the power grid 400 (for example, an AC power grid). In specific applications, the power conversion system 200 converts the direct current input by the photovoltaic module 100 into alternating current and outputs it to the grid-connected transformer 300, and the grid-connected transformer 300 performs step-up or step-down conversion and outputs it to the power grid 400. Of course, in actual applications, it is also possible not to set up the grid-connected transformer 300, but to directly connect the output end of the power conversion system 200 to the power grid 400. In addition, the output end of the power conversion system can also be connected to a load to supply power to the load. Alternatively, the output end of the power conversion system can also be connected to an AC system.

[0068] Figure 2a A schematic diagram of a power conversion system provided in an embodiment of the present application. Figure 2aThe power conversion system 200 includes: N power conversion units 210_1 to 210_N (N is an integer and N≥2), a DC-AC conversion unit 220 and a control unit 230, so that the power conversion system is set as a bipolar photovoltaic inverter. The input end of each power conversion unit 210_1 to 210_N is respectively connected to the photovoltaic module 100 as a DC power supply, the output end of each power conversion unit 210_1 to 210_N is connected to the input end of the DC-AC conversion unit 220 through a DC bus (including a positive DC bus Bus+ and a negative DC bus Bus-), and the output end of the DC-AC conversion unit 220 is connected to the power grid 400 through a grid-connected transformer 300. In specific applications, each power conversion unit 210_1 to 210_N converts the DC power input by the photovoltaic module 100 and outputs it to the DC bus (including the positive DC bus Bus+ and the negative DC bus Bus-), and the DC-AC conversion unit 220 converts the DC power on the DC bus (including the positive DC bus Bus+ and the negative DC bus Bus-) into AC power and outputs it to the grid-connected transformer 300, and the grid-connected transformer 300 performs step-up or step-down conversion and outputs it to the power grid 400. Alternatively, the output end of the DC-AC conversion unit is connected to the load to supply power to the load. It is understandable that N can be set to 2, 3, 4, 5 or more, and the specific value of N can be determined according to the needs of the actual application scenario, which is not limited here. In addition, the control unit can also be set to 1, 2, 3 or more, and the specific value of the control unit can also be determined according to the needs of the actual application scenario, which is not limited here.

[0069] The power conversion unit in the embodiment of the present application can operate in the MPPT mode to output the maximum power P of the photovoltaic module. mpp Tracking, at this time the working power of the power conversion unit is also the maximum power P mpp In order to enable the power supply system in this application to have the output capability of increasing power and decreasing power and realize photovoltaic grid construction, it is necessary to make the power conversion unit work in PR mode. When the power conversion unit works in PR mode, the working power of the power conversion unit is the reference power P res , the reference power P res Less than or equal to the maximum power P mpp At the same time, the output power of the photovoltaic module is approximately equal to the reference power P res (Equipment losses are ignored). However, as the environment in which the photovoltaic module is located changes, its power output characteristics change, and the maximum power P mpp Therefore, the reference power P needs to be adjusted accordingly. resTherefore, the power conversion unit can be controlled to work in MPPT mode, detect the current maximum power of the photovoltaic module, and then adjust the reference power P based on the detected current maximum power. res Update to get the updated reference power P res ', so that the working power of the power conversion unit when working in PR mode is the updated reference power P res '. Based on this, in order to realize photovoltaic grid construction, the power conversion unit needs to work in PR mode, and also relies on MPPT mode to detect the maximum power of the photovoltaic module to update the reference power. This causes the power conversion unit to switch between PR mode and MPPT mode, which leads to fluctuations in the total output power and output voltage of the power conversion unit, endangering the stability and control accuracy of the power supply system, and even increasing the mechanical stress and thermal stress of the equipment.

[0070] To this end, in the present application, in each control cycle, the control unit 230 controls the working mode of one or more target power conversion units among the N power conversion units to switch between the PR mode and the MPPT mode. After the working mode of the target power conversion unit is switched to the MPPT mode, the maximum power P output by the photovoltaic module can be obtained in the MPPT mode. mpp . Thus, the maximum power P obtained in the MPPT mode of the kth control cycle can be mpp For the original reference power P in the k-1th control cycle res Update to obtain the updated reference power P in the kth control cycle res ', and thus in the kth control cycle, the operating power of the target power conversion unit after switching from the MPPT mode to the PR mode can be changed to the updated reference power P res '. In addition, in each control cycle, the control unit 230 also controls the working modes of the power conversion units other than the target power conversion unit among the N power conversion units to remain unchanged, that is, the power conversion units other than the target power conversion unit do not perform mode switching. With this arrangement, some of the N power conversion units can perform mode switching between PR mode and MPPT mode, while the remaining power conversion units do not perform mode switching. Compared with all the power conversion units among the N power conversion units performing mode switching between PR mode and MPPT mode, the fluctuation of the output power and output voltage of the power conversion units can be reduced, and the stability and control accuracy of the power supply system can be improved.

[0071] It is understandable that P res ' <P mpp , in order to realize photovoltaic grid construction. Of course, in practical applications, P res '=Pmpp , which is not limited here.

[0072] Furthermore, through the above-mentioned embodiments, the mechanical and thermal stresses of the power conversion system equipment can be reduced, thereby improving the overall stability of the power conversion system.

[0073] In this application, multiple updating methods can be used to obtain the updated reference power P res '. Next, we get the updated reference power P res ' is updated with an example.

[0074] Update method 1: In a control cycle, if the control unit 230 selects a power conversion unit (for example, 210_1) from the N power conversion units as the target power conversion unit, after the working mode of the power conversion unit 210_1 is switched to the MPPT mode, the maximum power P output by the photovoltaic assembly 100 can be obtained in the MPPT mode. mpp _1, so that the maximum power P mpp _1 as the target maximum power P a1 , that is, P a1 =P mpp _1. Based on this, the updated reference power P res 'Equal to the target maximum power P a1 Subtract the reserved power ΔP, that is, P res '=P a1 -ΔP. A constant power threshold can be set as the reserved power ΔP based on experimental data or experience. Alternatively, the maximum power P mpp _1 obtains a power threshold value that can be updated accordingly as the reserved power ΔP. For example, before the working mode of the power conversion unit 210_1 is switched to the MPPT mode, its working mode is still the PR mode. At this time, the power conversion unit 210_1 corresponds to a reserved power ΔP'. After the control unit 230 controls the working mode of the power conversion unit 210_1 to switch to the MPPT mode, it can control the maximum power P obtained by the power conversion unit 210_1 in the MPPT mode. mpp _1, so that according to the maximum power P mpp _1 updates the reserved power ΔP' to obtain the updated reserved power ΔP", so that P res '=P a1 -ΔP". For example, the maximum power P mpp _1 multiplied by the percentage C C As the reserved power ΔP", that is, ΔP" = P mpp _1*C C , where 0%≤C C ≤100%, 70%≤C C≤100%, e.g. 80%≤C C ≤100%, e.g. 85%≤C C ≤95%. In specific applications, C C The settings are 70%, 75%, 80%, 85%, 90%, 95%, etc., and are not limited here.

[0075] Update method 2: In a control cycle, if the control unit 230 selects multiple power conversion units from N power conversion units as target power conversion units, for example, taking two power conversion units 210_1 and 210_2 as target power conversion units, after the working mode of the power conversion unit 210_1 is switched to the MPPT mode, the maximum power P output by the photovoltaic module can be obtained in the MPPT mode. mpp _1, after the working mode of the power conversion unit 210_2 is switched to the MPPT mode, the maximum power P output by the photovoltaic module can be obtained in the MPPT mode. mpp _2, so that the maximum power P mpp _1 and P mpp The average value (e.g., arithmetic mean, weighted mean) of _2 is taken as the target maximum power P b1 , that is, P b1 Equal to P mpp _1 and P mpp Based on this, the updated reference power P res 'Equal to the target maximum power P b1 Subtract the reserved power ΔP, that is, P res '=P b1 -ΔP. A constant power threshold can be set as the reserved power ΔP based on experimental data or experience. Alternatively, the maximum power P mpp _1 or P mpp _2 obtains a power threshold that can be updated accordingly as the reserved power ΔP. For example, with the maximum power P mpp _1 as an example, according to the maximum power P mpp _1 Update the reserved power ΔP' to obtain an updated reserved power ΔP" (for example, the maximum power P mpp _1 or P mpp _2 multiplied by the percentage as the reserved power ΔP”), so that P res '=P b1 -ΔP". For example, the maximum power P mpp _1 or P mpp _2 times the percentage C C As the reserved power ΔP", that is, ΔP" = P mpp _1*C COr, ΔP” = P mpp _2*C C Alternatively, the target maximum power P b1 A power threshold that can be updated accordingly is obtained as the reserved power ΔP, and then the target maximum power P b1 Update the reserved power ΔP' to obtain the updated reserved power ΔP", so that P res '=P b1 -ΔP". For example, the target maximum power P b1 Multiply by the percentage to get the reserved power ΔP”, that is, ΔP” = P b1 *C C .

[0076] Update method three: In a control cycle, if the control unit 230 selects a power conversion unit (for example, 210_1) from the N power conversion units as the target power conversion unit, after the working mode of the power conversion unit 210_1 is switched to the MPPT mode, the maximum power P output by the photovoltaic module can be obtained in the MPPT mode. mpp _1, so that the maximum power P mpp _1 as the target maximum power P a2 , that is, P a2 =P mpp Based on this, the updated reference power P res 'Equal to the target maximum power P a2 Multiply by the reference percentage C A , that is, P res '=P a2* C A Among them, 70% ≤ C A <100%, e.g. 80%≤C A <100%, e.g. 85%≤C A ≤95%. In specific applications, C A The settings are 70%, 75%, 80%, 85%, 90%, 95%, etc., and are not limited here.

[0077] Update method 4: In a control cycle, if the control unit 230 selects multiple power conversion units from N power conversion units as target power conversion units, for example, taking two power conversion units 210_1 and 210_2 as target power conversion units, after the working mode of the power conversion unit 210_1 is switched to the MPPT mode, the maximum power P output by the photovoltaic module can be obtained in the MPPT mode. mpp _1, after the working mode of the power conversion unit 210_2 is switched to the MPPT mode, the maximum power P output by the photovoltaic module can be obtained in the MPPT mode.mpp _2, so that the maximum power P mpp _1 and P mpp The average value (e.g., arithmetic mean, weighted mean) of _2 is taken as the target maximum power P b2 , that is, P b2 Equal to P mpp _1 and P mpp Based on this, the updated reference power P res 'Equal to the target maximum power P b2 Multiply by the reference percentage C B , that is, P res '=P a2* C B Among them, 70% ≤ C B <100%, e.g. 80%≤C B <100%, e.g. 85%≤C B ≤95%. In specific applications, C B The settings are 70%, 75%, 80%, 85%, 90%, 95%, etc., and are not limited here.

[0078] It is understandable that, in each of the multiple consecutive control cycles, any one of the above-mentioned updating modes 1 to 4 can be used to obtain the updated reference power. Alternatively, two, three, or four of the above-mentioned updating modes 1 to 4 can be combined to obtain the updated reference power in the multiple consecutive control cycles.

[0079] It is understandable that the reference power updated in the kth control cycle may be the same as the reference power in the k-1th control cycle. Alternatively, the reference power updated in the kth control cycle may be greater than the reference power in the k-1th control cycle. Alternatively, the reference power updated in the kth control cycle may be less than the reference power in the k-1th control cycle. Where k is an integer greater than 0. That is, the maximum power P corresponding to the target power conversion unit when operating in the MPPT mode mpp There will be a power greater than the original reference power P res In the case of res 'Less than or equal to the maximum power P mpp , then the updated reference power P res 'With the original reference power P res There is the following relationship: P res '>P res , or P res ' <P res , or, P res '=Pres .

[0080] And, the reserved power after update in the k-th control cycle may be the same as the reserved power in the k-1-th control cycle. Alternatively, the reserved power after update in the k-th control cycle may be greater than the reserved power in the k-1-th control cycle. Alternatively, the reserved power after update in the k-th control cycle may be less than the reserved power in the k-1-th control cycle.

[0081] Figure 2b A specific structural diagram of a power conversion system provided in an embodiment of the present application. Figure 2b Each power conversion unit 210_1~210_N can be set as a direct current-direct current (DC-DC) conversion circuit 211, the direct current-alternating current conversion unit 220 can be set as a direct current-alternating current (DC-AC) conversion circuit 221, and the control unit 230 can be a field programmable gate array (FPGA), a general-purpose central processing unit (CPU), a general-purpose processor, a digital signal processing (DSP), an application-specific integrated circuit (ASIC), or other programmable logic devices, transistor logic devices, hardware components or any combination thereof. It can implement or execute various exemplary logic blocks, modules and circuits described in conjunction with the disclosure of this application. The above-mentioned control unit can also be a combination that implements computing functions, such as a combination of one or more microprocessors, a combination of DSP and microprocessors, etc.

[0082] And, refer to Figure 2b , the first end of the DC-DC conversion circuit 211 is connected to the photovoltaic module 100 as a DC power source, the second end of the DC-DC conversion circuit 211 is connected to the first end of the DC-AC conversion circuit 221 through the DC bus, and the second end of the DC-AC conversion circuit 221 is used to connect to the power grid. Exemplarily, the DC-DC conversion circuit 211 converts the DC power input by the photovoltaic module 100 and outputs it to the DC-AC conversion circuit 221, and the DC-AC conversion circuit 221 converts the input DC power into AC power and outputs it to the power grid 400. In addition, the second end of the DC-AC conversion circuit 221 can also be connected to a load to supply power to the load.

[0083] In this application, the working mode of the power conversion unit other than the target power conversion unit remaining unchanged means that: the working mode of this part of the power conversion unit does not switch modes, but operates constantly in one working mode. The following is an example of the implementation manner of the working mode of the power conversion unit other than the target power conversion unit.

[0084] Embodiment 1: Set the working mode of the power conversion unit other than the target power conversion unit among the N power conversion units to the PR mode, and the working power of this part of the power conversion unit is updated along with the updated reference power P res ’. With this setting, all the power conversion units 210_1 to 210_N can operate in the PR mode to achieve photovoltaic grid formation. Moreover, making some of the power conversion units 210_1 to 210_k serve as target power conversion units to switch between the PR mode and the MPPT mode, and the remaining power conversion units 210_k + 1 to 210_N not switching modes can reduce the fluctuations of the output power and output voltage of the power conversion unit, and improve the stability and control accuracy of the power supply system. Also, in order to enable the reference power of the power conversion unit other than the target power conversion unit in the PR mode to be updated accordingly, after the target power conversion unit updates the reference power, the working power of this part of the power conversion unit is also switched to the updated reference power P res ’. It can be understood that k is an integer, and 1 ≤ k < N, and k needs to be determined according to the actual application scenario.

[0085] It can be understood that after the target power conversion unit updates the reference power, it is possible to control the working power of the power conversion unit other than the target power conversion unit to also switch to the updated reference power. Of course, it is not necessary to update the reference power of the power conversion unit other than the target power conversion unit in the PR mode accordingly, but to control the reference power of this part of the power conversion unit in the PR mode to continue to work with the reference power in its previous control cycle.

[0086] Embodiment 2: The working mode of the power conversion units other than the target power conversion unit among the N power conversion units is set to the MPPT mode, and the working power of the part of the power conversion units is the maximum power obtained by the MPPT mode. According to this setting, some power conversion units 210_1 to 210_k are used as target power conversion units and work in the PR mode and perform mode switching between the PR mode and the MPPT mode, and the remaining power conversion units 210_k+1 to 210_N do not perform mode switching, thereby realizing photovoltaic grid construction. In addition, the target power conversion units 210_1 to 210_k perform mode switching between the PR mode and the MPPT mode, and the power conversion units 210_k+1 to 210_N are constantly in the MPPT mode, which can reduce the fluctuation of the output power and output voltage of the power conversion units and improve the stability and control accuracy of the power supply system.

[0087] Implementation method 3: For the power conversion units other than the target power conversion unit among the N power conversion units, the working mode of some power conversion units is set to PR mode, and the working power of some power conversion units is the updated reference power P res ', the working mode of the remaining power conversion units is the MPPT mode, and the working power of the remaining power conversion units is the maximum power obtained by the MPPT mode. With this setting, some power conversion units 210_1~210_k are used as target power conversion units to switch between the PR mode and the MPPT mode, and the remaining power conversion units 210_k+1~210_N do not switch modes, thereby realizing photovoltaic grid construction. In addition, the working mode of some power conversion units 210_k+1~210_k+m is always the PR mode. In order to update the reference power of the partial power conversion units 210_k+1~210_k+m in the PR mode, after the target power conversion unit updates the reference power, the working power of the partial power conversion units 210_k+1~210_k+m can also be switched to the updated reference power P res '. And the working mode of the remaining power conversion units 210_k+m+1~210_k+N is constant as the MPPT mode. Based on this, the fluctuation of the output power and output voltage of the power conversion unit can be reduced, and the stability and control accuracy of the power supply system can be improved. Wherein, m is an integer greater than 1, and m needs to be determined according to the actual application scenario.

[0088] Implementation method four: The working power of the power conversion unit other than the target power conversion unit among the N power conversion units is less than the maximum power, and the working power of this part of the power conversion units is different from the updated reference power. Among them, the working power of this part of the power conversion unit can be greater than or less than the updated reference power. In the specific implementation, the working power of this part of the power conversion unit can be determined according to the updated reference power, so that the working power of this part of the power conversion unit does not need to be switched in mode, which can reduce the fluctuation of the output power and output voltage of the power conversion unit, and improve the stability and control accuracy of the power supply system.

[0089] It is understandable that, in each of a plurality of consecutive control cycles, one of the above-mentioned embodiments 1 to 4 may be used to control the operation of power conversion units other than the target power conversion unit. Alternatively, two, three, or four of the above-mentioned embodiments 1 to 4 may be combined to control the operation of power conversion units other than the target power conversion unit in a plurality of consecutive control cycles.

[0090] In the present application, the target power conversion unit can be randomly selected. Specifically, in one or more control cycles within a plurality of consecutive control cycles, one or more power conversion units are randomly selected from N power conversion units as the target power conversion unit. Thus, the target power conversion unit can be selected by random selection.

[0091] In the present application, the probability of at least some power conversion units being selected as target power conversion units can be made different. Exemplarily, the probability of all power conversion units being selected as target power conversion units can be made different, or the probability of some power conversion units being selected as target power conversion units can be made different, and the probability of the remaining power conversion units being selected as target power conversion units is the same.

[0092] The working process of randomly selecting a target power conversion unit in the embodiment of the present application is described in detail below in conjunction with specific embodiments.

[0093] Embodiment 1:

[0094] When randomly selecting the target power conversion unit, the probability x0 of each power conversion unit being selected as the target power conversion unit is made the same. With this arrangement, the power conversion unit can be randomly selected with equal probability as the target power conversion unit. Further, in each control cycle, the power conversion unit is randomly selected with equal probability as the target power conversion unit.

[0095] The following takes the continuous control period T_c~T_c+d+5 as an example, and selects a power conversion unit as the target power conversion unit in each control period. Figure 3 and Figure 4 Detailed description is given. Figure 3 is a schematic diagram of the working mode of the power conversion unit in the embodiment of the present application in the control cycle, Figure 4 A schematic diagram of selecting a target power conversion unit in an embodiment of the present application.

[0096] Reference Figure 3 and Figure 4 , in the cth control cycle T_c, the control unit 230 randomly selects the power conversion unit 210_1 from the power conversion units 210_1 to 210_N as the target power conversion unit according to the same probability χ0, and the power conversion units 210_2 to 210_N are used as power conversion units other than the target power conversion unit. Based on this, in the Tm stage, the control unit 230 controls the working mode of the power conversion unit 210_1 to switch to the MPPT mode, and obtains the maximum power P that the photovoltaic module 100 can output in the MPPT mode. mpp _1, thereby obtaining the updated reference power P according to the above-mentioned updating method 1 or updating method 3 res In the Tr stage, the control unit 230 controls the working mode of the power conversion unit 210_1 to switch from the MPPT mode to the PR mode, and makes the working power of the power conversion unit 210_1 after switching to the PR mode be the updated reference power P res '. Moreover, taking the case where the power conversion units 210_2 to 210_N both operate in the PR mode in the Tm phase and the Tr phase, when the power conversion unit 210_1 switches the mode, the power conversion units 210_2 to 210_N remain in the PR mode and obtain the updated reference power P res After that, the control unit 230 controls the working power of the power conversion units 210_2 to 210_N to switch to the updated reference power P res'. Similarly, in the c+1th control cycle T_c+1, the control unit 230 selects the power conversion unit 210_3 as the target power conversion unit, in the c+2th control cycle T_c+2, the control unit 230 selects the power conversion unit 210_2 as the target power conversion unit, in the c+3th control cycle T_c+3, the control unit 230 selects the power conversion unit 210_N as the target power conversion unit, in the c+dth control cycle T_c+d, the control unit 230 selects the power conversion unit 210_4 as the target power conversion unit, and in the c+d+1th control cycle T_c+d+1, the control unit 230 selects the power conversion unit 210_5 as the target power conversion unit. The conversion unit 210_2 is used as the target power conversion unit. In the c+d+2th control cycle T_c+d+2, the control unit 230 selects the power conversion unit 210_2 as the target power conversion unit. In the c+d+3th control cycle T_c+d+3, the control unit 230 selects the power conversion unit 210_1 as the target power conversion unit. In the c+d+4th control cycle T_c+d+4, the control unit 230 selects the power conversion unit 210_4 as the target power conversion unit. In the c+d+5th control cycle T_c+d+5, the control unit 230 selects the power conversion unit 210_3 as the target power conversion unit. In addition, the remaining working processes in the c+1th control cycle to the c+d+5th control cycle T_c+1~T_c+d+5 can refer to the working process in the cth control cycle T_c, which will not be repeated here.

[0097] It can be understood that χ0∈[0,1], wherein the sum of the probabilities χ0 corresponding to the power conversion units 210_1~210_N can be 1, or the sum of the probabilities χ0 corresponding to the power conversion units 210_1~210_N can also be greater than or less than 1. In a specific implementation, the selection probability χ0A of each power conversion unit 210_1~210_N can be stored in the storage unit of the power supply system, and the control unit 230 can obtain the selection probability χ0A of each power conversion unit 210_1~210_N from the storage unit, and randomly select the corresponding power conversion unit as the target power conversion unit according to the selection probability χ0A of each power conversion unit 210_1~210_N. Among them, the selection probability χ0A corresponding to each power conversion unit 210_1~210_N can be configured as a fixed value in an offline or online manner. For example, if the operator needs to configure the selection probability χ0A in an online manner, the operator can input the probability adjustment instruction of the selection probability of the corresponding part or all power conversion units through the user interface (UI). When the control unit 230 receives the probability adjustment instruction, it can adjust the selection probability of part or all power conversion units according to the probability adjustment instruction. For example, if the target power conversion unit is selected from all power conversion units 210_1~210_N by using equal probability random, the selection probability χ0A corresponding to each power conversion unit 210_1~210_N can be configured to the same value χ0A_1 according to the probability adjustment instruction. For example, if the target power conversion unit is selected from some power conversion units 210_2~210_N by using equal probability random, the selection probability χ0A corresponding to each power conversion unit 210_2~210_N can be configured to the same value χ0A_2 according to the probability adjustment instruction. For example, if the target power conversion unit is randomly selected from some of the power conversion units 210_3 to 210_N with equal probability, the selection probability χ0A corresponding to each power conversion unit 210_3 to 210_N can be configured to the same value χ0A_3 according to the probability adjustment instruction.

[0098] It is understandable that each control cycle includes the MPPT mode stage Tm and the PR mode stage Tr, that is, the MPPT mode stage Tm and the PR mode stage Tr constitute a control cycle. In addition, the cycle durations of the control cycles may be the same or different. Also, the cycle duration of the control cycle may be a fixed constant or may not be a fixed constant, that is, the cycle duration is not fixed. In practical applications, the cycle duration may be adjusted and changed in real time according to the duration of the MPPT mode stage Tm and the duration of the PR mode stage Tr. The control cycles in the following embodiments may be set similarly, and will not be described one by one below.

[0099] Embodiment 2:

[0100] When randomly selecting a target power conversion unit, the probability of at least some of the power conversion units being selected as the target power conversion unit is made different. With this arrangement, it is possible to randomly select power conversion units as target power conversion units with different probabilities. Exemplarily, the probabilities of all power conversion units being selected as target power conversion units can be made different, for example, the probability of power conversion unit 210_1 being selected as the target power conversion unit is χ_1, the probability of power conversion unit 210_2 being selected as the target power conversion unit is χ_2, ... the probability of power conversion unit 210_N being selected as the target power conversion unit is χ_N, and χ_1 to χ_N are different from each other. Alternatively, the probabilities of some power conversion units being selected as target power conversion units can be made different, and the probabilities of the remaining power conversion units being selected as target power conversion units can be made the same. For example, the probability that the power conversion unit 210_1 is selected as the target power conversion unit is χ_1, the probability that the power conversion unit 210_2 is selected as the target power conversion unit is χ_2, the probability that the power conversion unit 210_3 is selected as the target power conversion unit is χ_3, ... the probability that the power conversion unit 210_N is selected as the target power conversion unit is χ_N, and χ_1=χ_2, and χ_3~χ_N are different. Exemplarily, in each control cycle, a power conversion unit is randomly selected as the target power conversion unit with different probabilities.

[0101] The following takes the continuous control period T_c~T_c+d+5 as an example, and selects a power conversion unit as the target power conversion unit in each control period. Figure 5 and Figure 6 Detailed description is given. Figure 5 is another schematic diagram of the working mode of the power conversion unit in the embodiment of the present application in the control cycle, Figure 6 This is another schematic diagram of selecting a target power conversion unit in an embodiment of the present application.

[0102] Reference Figure 5 and Figure 6In the cth control cycle T_c, the control unit 230 randomly selects the power conversion unit 210_1 from the power conversion units 210_1 to 210_N as the target power conversion unit according to the set probability, and the power conversion units 210_2 to 210_N are used as power conversion units other than the target power conversion unit. The operation of the power conversion unit 210_1 and the power conversion units 210_2 to 210_N can refer to the operation process in the above-mentioned embodiment 1, and will not be described in detail here. Similarly, in the c+1th control cycle T_c+1, the control unit 230 selects the power conversion unit 210_1 as the target power conversion unit, in the c+2th control cycle T_c+2, the control unit 230 selects the power conversion unit 210_2 as the target power conversion unit, in the c+3th control cycle T_c+3, the control unit 230 selects the power conversion unit 210_3 as the target power conversion unit, in the c+dth control cycle T_c+d, the control unit 230 selects the power conversion unit 210_4 as the target power conversion unit, and in the c+d+1th control cycle T_c+d+1, the control unit 230 selects the power conversion unit 210_5 as the target power conversion unit. The conversion unit 210_2 is used as the target power conversion unit. In the c+d+2th control cycle T_c+d+2, the control unit 230 selects the power conversion unit 210_2 as the target power conversion unit. In the c+d+3th control cycle T_c+d+3, the control unit 230 selects the power conversion unit 210_N as the target power conversion unit. In the c+d+4th control cycle T_c+d+4, the control unit 230 selects the power conversion unit 210_4 as the target power conversion unit. In the c+d+5th control cycle T_c+d+5, the control unit 230 selects the power conversion unit 210_3 as the target power conversion unit. In addition, the remaining working processes in the c+1th control cycle to the c+d+5th control cycle T_c+1~T_c+d+5 can refer to the working process in the cth control cycle T_c, which will not be repeated here.

[0103] It is understandable that any one of χ_1~χ_N is in [0, 1], wherein the sum of χ_1~χ_N may be 1, or the sum of the probabilities χ_1~χ_N may also be greater than or less than 1. Moreover, in a specific application, the storage unit of the power supply system also stores the selection probabilities χB_1~χB_N of each power conversion unit. The control unit 230 can obtain the selection probabilities χB_1~χB_N of each power conversion unit 210_1~210_N from the storage unit, so that the corresponding power conversion unit can be randomly selected from the power conversion units 210_1~210_N as the target power conversion unit according to the selection probabilities χB_1~χB_N of each power conversion unit. Among them, any one of the selection probabilities χB_1~χB_N corresponding to each power conversion unit 210_1~210_N can also be configured as an arbitrary fixed value in an offline or online manner. For example, if the operator needs to configure one or more of the selection probabilities χB_1 to χB_N online, the operator can input a probability adjustment instruction through the user interface (UI). When the control unit 230 receives the probability adjustment instruction, it can adjust the selection probabilities corresponding to some or all power conversion units according to the probability adjustment instruction. For example, if the selection probability χB_1 needs to be adjusted, the operator inputs the probability adjustment instruction to the control unit 230 through the user interface to change the selection probability of the power conversion unit 210_1 from χB_1 to χB_1'. Or, for example, if the selection probabilities χB_1 to χB_3 need to be adjusted, the operator inputs the probability adjustment instruction to the control unit 230 through the user interface to change χB_1 to χB_1', χB_2 to χB_2', and χB_3 to χB_3'.

[0104] In the present application, the target power conversion unit can also be selected in a fixed order. Specifically, in one or more control cycles within a plurality of consecutive control cycles, the target power conversion unit is one or more power conversion units selected from N power conversion units in a fixed order. With this arrangement, the target power conversion unit can be selected in a specific selection order. The working process of selecting the target power conversion unit in a fixed order in the embodiment of the present application is described in detail below in conjunction with specific embodiments.

[0105] Embodiment 1:

[0106] Each control cycle selects a unit group as the target power conversion unit according to a unidirectional fixed timing (for example, a positive sequence) cycle. Based on this, each M control cycle constitutes a cycle, so that multiple continuous cycles can appear, and the multiple cycles have a first cycle. Specifically, the power conversion units 210_1~210_N are divided into the first unit group Z_1 to the Mth unit group Z_M arranged in sequence, and any unit group Z_1~Z_M includes one or more power conversion units, M is an integer and M≥2. Among them, the power conversion units in different unit groups are different. Exemplarily, each unit group Z_1~Z_M can include a power conversion unit, then M=N, for example, unit group Z_1 includes power conversion unit 210_1, unit group Z_2 includes power conversion unit 210_2,...unit group Z_N includes power conversion unit 210_N. Alternatively, each unit group Z_1 to Z_M includes a plurality of power conversion units. For example, when each unit group Z_1 to Z_M includes two power conversion units, then M=N / 2, unit group Z_1 includes power conversion units 210_1 to 210_2, unit group Z_2 includes power conversion units 210_3 to 210_4, ... unit group Z_M includes power conversion units 210_N-1 to 210_N. Alternatively, some unit groups may include one power conversion unit, and the rest may include a plurality of power conversion units. It is understandable that the power conversion units in different units may also be partially identical, which is not limited here.

[0107] Moreover, for the M control cycles in the first cycle, the target power conversion unit in each control cycle is a unit group selected in the order of the first unit group Z_1 to the Mth unit group Z_M. Figure 7 and Figure 8 Detailed description is given. Figure 7 is another schematic diagram of the working mode of the power conversion unit in the embodiment of the present application in the control cycle, Figure 8 This is another schematic diagram of selecting a target power conversion unit in an embodiment of the present application.

[0108] Reference Figure 7 and Figure 8, there are N control cycles in the first cycle X1_1: the 1st control cycle to the Nth control cycle T1_1~T1_N. Specifically, in the 1st control cycle T1_1, the control unit 230 selects the power conversion unit 210_1 as the target power conversion unit, and the power conversion units 210_2~210_N are used as power conversion units other than the target power conversion unit. In the 2nd control cycle T1_2, the control unit 230 selects the power conversion unit 210_2 as the target power conversion unit, and the power conversion units 210_1, 210_3~210_N are used as power conversion units other than the target power conversion unit. ... In the Nth control cycle T1_N, the control unit 230 selects the power conversion unit 210_N as the target power conversion unit, and the power conversion units 210_1~210_N-1 are used as power conversion units other than the target power conversion unit. Furthermore, the remaining working processes in the first control period to the Nth control period T1_1 to T1_N may refer to the working processes in the above-mentioned first embodiment, and will not be described in detail herein.

[0109] After the first cycle X1_1 is completed, the first cycle X2_1 is entered, and the selection process starts again from the power conversion unit 210_1. Specifically, the first cycle X2_1 has N control cycles: the first control cycle to the Nth control cycle T2_1~T2_N. In the first control cycle T2_1, the control unit 230 selects the power conversion unit 210_1 as the target power conversion unit, and the power conversion units 210_2~210_N are used as power conversion units other than the target power conversion unit. In the second control cycle T2_2, the control unit 230 selects the power conversion unit 210_2 as the target power conversion unit, and the power conversion units 210_1, 210_3~210_N are used as power conversion units other than the target power conversion unit. ... In the Nth control cycle T2_N, the control unit 230 selects the power conversion unit 210_N as the target power conversion unit, and the power conversion units 210_1~210_N-1 are used as power conversion units other than the target power conversion unit. Furthermore, the remaining working processes in the first control period to the Nth control period T2_1 to T2_N may refer to the working processes in the first embodiment, and will not be described in detail herein.

[0110] The rest is similar. After the first cycle X2_1 is completed, the power conversion unit 210_1 restarts the selection process, which will not be described in detail here.

[0111] It is understandable that part of the cycle period may be set as the first cycle period, or all of the cycle period may be set as the first cycle period.

[0112] Embodiment 2:

[0113] Each control cycle selects a unit group as the target power conversion unit in a unidirectional fixed timing (for example, in reverse order). Based on this, each M control cycles can constitute a cycle, so that multiple continuous cycles can appear, and the multiple cycles have a second cycle. Specifically, the power conversion units 210_1~210_N are divided into the first unit group Z_1 to the Mth unit group Z_M arranged in sequence. For the M control cycles in the second cycle, the target power conversion unit in each control cycle is a unit group selected in the order of the Mth unit group Z_M to the first unit group Z_1. In addition, the implementation of the unit groups Z_1~Z_M can refer to the above-mentioned embodiment 1, which will not be repeated here.

[0114] In the following, any unit group Z_1~Z_M includes a power conversion unit and the second cycle X1_2~X2_2 as an example. Fig. 9 and Fig.10 Detailed description is given. Fig. 9 is another schematic diagram of the working mode of the power conversion unit in the embodiment of the present application in the control cycle, Fig.10 This is another schematic diagram of selecting a target power conversion unit in an embodiment of the present application.

[0115] Reference Fig. 9 and Fig.10 , the second cycle X1_2 has N control cycles: the 1st control cycle to the Nth control cycle T1_1~T1_N. Specifically, in the 1st control cycle T1_1, the control unit 230 selects the power conversion unit 210_N as the target power conversion unit, ... in the N-1th control cycle T1_N-1, the control unit 230 selects the power conversion unit 210_2 as the target power conversion unit, and in the Nth control cycle T1_N, the control unit 230 selects the power conversion unit 210_1 as the target power conversion unit. In addition, the remaining working processes in the 1st control cycle to the Nth control cycle T1_1~T1_N can refer to the working process in the above-mentioned embodiment 1, and will not be repeated here.

[0116] After the second cycle X1_2 is completed, the second cycle X2_2 is entered, and the selection process starts again from the power conversion unit 210_N. Specifically, the second cycle X2_2 has N control cycles: the 1st control cycle to the Nth control cycle T2_1~T2_N. In the 1st control cycle T2_1, the control unit 230 selects the power conversion unit 210_N as the target power conversion unit, ... In the N-1th control cycle T2_N-1, the control unit 230 selects the power conversion unit 210_2 as the target power conversion unit, and in the Nth control cycle T2_N, the control unit 230 selects the power conversion unit 210_1 as the target power conversion unit. In addition, the remaining working processes in the 1st control cycle to the Nth control cycle T2_1~T2_N can refer to the working process in the above-mentioned embodiment 1, and will not be repeated here.

[0117] The rest is similar. After the second cycle X2_2 is completed, the power conversion unit 210_N restarts the selection process, which will not be described in detail here.

[0118] It is understandable that part of the cycle period may be set as the second cycle period, or the entire cycle period may be set as the second cycle period.

[0119] Embodiment three:

[0120] The first cycle and the second cycle are combined with each other, and the first cycle and the second cycle appear alternately. In this way, a bidirectional fixed timing cycle can be realized. Specifically, the implementation of the unit groups Z_1 to Z_M can refer to the above-mentioned embodiment 1, and will not be repeated here. Moreover, taking any unit group Z_1 to Z_M including a power conversion unit, and the first cycle X1_1 to X2_1 and the second cycle X1_2 to X2_2 as an example, combined Figures 11 to 13 Detailed description is given. Fig.11 is another schematic diagram of the working mode of the power conversion unit in the embodiment of the present application in the control cycle, Fig.12 This is another schematic diagram of selecting a target power conversion unit in an embodiment of the present application. Fig.13 This is a schematic diagram of the cycle in the embodiment of the present application. Figures 11 to 13 First, the working process in the first cycle X1_1 is performed. Then, the working process in the second cycle X1_2 is performed. Then, the working process in the first cycle X2_1 is performed. Then, the working process in the second cycle X2_2 is performed. The rest is similar, and can be deduced in sequence, which will not be described in detail here. In addition, the working processes in the first cycle X1_1~X2_1 and the second cycle X1_2~X2_2 can refer to the above embodiment, which will not be described in detail here.

[0121] Embodiment 4:

[0122] The first cycle and the second cycle are combined with each other, and at least two adjacent first cycle periods and at least two adjacent second cycle periods are alternately appeared. Thus, a bidirectional fixed timing cycle can also be realized. Specifically, the implementation of the unit group Z_1~Z_M can refer to the above-mentioned embodiment 1, which is not repeated here. In the specific implementation, the number of adjacent first cycle periods can be made the same as the number of adjacent second cycle periods, for example, two adjacent first cycle periods and two adjacent second cycle periods alternately appear. Or, three adjacent first cycle periods and three adjacent second cycle periods alternately appear. Or, four adjacent first cycle periods and four adjacent second cycle periods alternately appear. It is also possible to make the number of adjacent first cycle periods different from the number of adjacent second cycle periods, for example, two adjacent first cycle periods and three adjacent second cycle periods alternately appear. Or, two adjacent first cycle periods and four adjacent second cycle periods alternately appear. Or, three adjacent first cycle periods and four adjacent second cycle periods alternately appear.

[0123] The following takes the alternation of two adjacent first cycles and two adjacent second cycles as an example. Fig.14 Detailed description is given. Fig.14 This is another schematic diagram of the cycle period in the embodiment of the present application. Fig.14 , first, the working process in the first cycle X1_1 is performed. Afterwards, the working process in the first cycle X2_1 is performed. Afterwards, the working process in the second cycle X1_2 is performed. Afterwards, the working process in the second cycle X2_2 is performed. Afterwards, the working process in the first cycle X3_1 is performed. Afterwards, the working process in the first cycle X4_1 is performed. Afterwards, the working process in the second cycle X3_2 is performed. Afterwards, the working process in the second cycle X4_2 is performed. The rest is similar, and can be deduced in sequence, which will not be described in detail here. In addition, the working processes in the first cycle X1_1~X4_1 and the second cycle X1_2~X4_2 can refer to the above embodiments, which will not be described in detail here.

[0124] It is understandable that the embodiment of randomly selecting the target power conversion unit and the embodiment of selecting the target power conversion unit in a fixed order can be performed independently of each other. Alternatively, the embodiment of randomly selecting the target power conversion unit and the embodiment of selecting the target power conversion unit in a fixed order can also be arbitrarily combined. For example, after performing one or more first cycles and / or one or more second cycles, the target power conversion unit can be randomly selected.

[0125] Fig.15aThis is another structural diagram of a power conversion system provided in an embodiment of the present application. Fig.15a The power conversion system 200 includes: N power conversion units 210_1 to 210_N (N is an integer and N≥2) and a control unit 230, so that the power conversion system is set as a photovoltaic inverter with a monopolar architecture. Among them, the input end of each power conversion unit 210_1 to 210_N is respectively connected to the photovoltaic module 100 as a DC power supply, and the output end of each power conversion unit 210_1 to 210_N is connected to the power grid 400 through the grid-connected transformer 300. In specific applications, each power conversion unit 210_1 to 210_N converts the DC power input by the photovoltaic module 100 into AC power and outputs it to the grid-connected transformer 300, and the grid-connected transformer 300 performs step-up or step-down conversion and outputs it to the power grid 400. Of course, in actual applications, it is also possible not to set up the grid-connected transformer 300, but to directly connect the output end of the power conversion system 200 to the power grid 400. In addition, the output end of the power conversion unit can also be connected to the load to supply power to the load. Alternatively, the output end of the power conversion unit can also be directly connected to the AC system.

[0126] Fig.15b This is another structural diagram of a power conversion system provided in an embodiment of the present application. Fig.15b , the power conversion unit may be a DC-AC conversion circuit 212, and the first end of the DC-AC conversion circuit 212 is used to connect the photovoltaic module 100 as a DC power source, and the second end of the DC-AC conversion circuit 212 is used to connect the load or the power grid or the AC system. Exemplarily, the DC-AC conversion circuit 212 is used to convert the DC power input by the photovoltaic module into AC power and then output it to the load or the power grid or the AC system. The rest of the content in this embodiment may be basically the same as the content in the above embodiment, and will not be repeated here.

[0127] In some other examples, the power conversion unit can also be configured as a direct current-to-direct current (DC-DC) conversion circuit. Among them, the first end of the direct current-to-direct current conversion circuit is used to connect a direct current power supply, and the second end of the direct current-to-direct current conversion circuit is used to connect a load or an energy storage unit or a power generation unit. Exemplarily, the DC-DC conversion circuit is used to convert the direct current input by the direct current power supply into power and output it to the load or the energy storage unit or the power generation unit. Alternatively, the DC-DC conversion circuit can also be used to convert the direct current input by the energy storage unit or the power generation unit into power and output it to the direct current power supply. For example, the direct current power supply is a photovoltaic module.

[0128] In some other examples, the power conversion unit can also be set as an alternating current-direct current (AC-DC) conversion circuit. Among them, the first end of the AC-DC conversion circuit is used to connect to an AC power supply, and the second end of the AC-DC conversion circuit is used to connect to a load or an energy storage unit or a power generation unit. Exemplarily, the AC-DC conversion circuit is used to convert the AC power input from the AC power supply into DC power and then output it to the load or the energy storage unit or the power generation unit. Alternatively, the AC-DC conversion circuit can also be used to convert the DC power input from the energy storage unit or the power generation unit into AC power and then output it to the AC power supply.

[0129] In some other examples, the power conversion system can also be set as an AC-DC (AC-DC) conversion circuit, and the power conversion system also includes a DC-AC (DC-AC) conversion circuit. Wherein, the first end of the AC-DC conversion circuit is used to connect to the AC power supply, the second end of the AC-DC conversion circuit is connected to the first end of the DC-AC conversion circuit, and the second end of the DC-AC conversion circuit is used to connect to the load or the power grid. Exemplarily, the AC-DC conversion circuit is used to convert the AC power input by the AC power supply into DC power and then output it to the DC-AC conversion circuit, and the DC-AC conversion circuit is used to convert the input DC power into AC power and then output it to the load or energy storage unit or power generation unit. Alternatively, the DC-AC conversion circuit can also convert the AC power input by the energy storage unit or the power generation unit into DC power and then output it to the AC-DC conversion circuit, and the AC-DC conversion circuit can convert the input DC power into AC power and then output it to the AC power supply.

[0130] In addition, when the power conversion unit in the power conversion system provided in the embodiment of the present application is connected to the energy storage unit, the power conversion unit can also be configured as an energy storage inverter to be applied to the energy storage system.

[0131] The embodiment of the present application also provides a power update control method, which is applied to a power conversion system. The power update control method is applied to a power conversion system, and the power conversion system includes N power conversion units, N is an integer and N≥2; the first end of each power conversion unit is used to connect to a DC power supply or an AC power supply, and the second end of each power conversion unit is used to connect to a load or an energy storage unit or a power grid, and the power conversion unit is used to convert the DC power input by the DC power supply or the AC power input by the AC power supply and output it. In addition, the power update control method includes: controlling the working mode of one or more target power conversion units in the N power conversion units to switch between the power reservation PR mode and the maximum power point tracking MPPT mode, and updating the reference power according to the maximum power obtained in the MPPT mode, so that the working power of the target power conversion unit after switching from the MPPT mode to the PR mode is the updated reference power; wherein the updated reference power is less than or equal to the maximum power. And, controlling the working mode of the power conversion units other than the target power conversion unit in the N power conversion units to remain unchanged.

[0132] The embodiment of the present application also provides a power supply system, a power supply system, which includes a power conversion system, wherein the first end of the power conversion unit in the power conversion system is connected to a DC power supply or an AC power supply, and the second end of the power conversion system is used to connect a load or an energy storage unit or a power generation unit or a power grid. In addition, the power conversion system is used to convert the direct current input by the DC power supply or the alternating current input by the AC power supply for output. The power conversion system is the power conversion system in any of the above-mentioned embodiments. Since the power conversion system provided in the embodiment of the present application can realize the update of the working power of the power conversion unit in the PR mode, and reduce the fluctuation of the output power and output voltage of the power conversion unit, the stability and control accuracy of the power supply system can be improved.

[0133] The above power supply system can be configured as a photovoltaic system, then the power supply system further includes a photovoltaic component, and the first end of the power conversion unit in the power conversion system is connected to the photovoltaic component, and the photovoltaic component serves as a DC power supply.

[0134] The above contents are only specific implementation methods of the present application, but the protection scope of the present application is not limited thereto. Any technician familiar with the technical field can easily think of changes or substitutions within the technical scope disclosed in the present application, which should be covered by the protection scope of the present application.

Claims

1. A power conversion system, characterized in that: include: N power conversion units and control units, wherein N is an integer and N≥2; the first end of each of the power conversion units is used to connect to a DC power supply or an AC power supply, the second end of each of the power conversion units is used to connect to a load or an energy storage unit or a power grid, and the power conversion unit is used to convert the DC power input by the DC power supply or the AC power input by the AC power supply and output it; The control unit is used for: In a control cycle, the working mode of one or more target power conversion units among the N power conversion units is controlled to switch between a power reservation PR mode and a maximum power point tracking MPPT mode, and a reference power is updated according to the maximum power obtained in the MPPT mode, so that the working power of the target power conversion unit after switching from the MPPT mode to the PR mode is the updated reference power; wherein the updated reference power is less than or equal to the maximum power; The operating modes of the power conversion units other than the target power conversion unit among the N power conversion units are controlled to remain unchanged.

2. The power conversion system according to claim 1, characterized in that: The target power conversion unit is one or more power conversion units randomly selected from the N power conversion units.

3. The power conversion system according to claim 1, characterized in that: The probabilities of at least some of the power conversion units being selected as the target power conversion units are different.

4. The power conversion system according to any one of claims 2 to 3, characterized in that: The control unit is also used for: Obtaining a selection probability of each of the power conversion units; The target power conversion unit is randomly selected from the N power conversion units according to the selection probability of each of the power conversion units.

5. The power conversion system according to claim 4, characterized in that: The control unit is also used for: receiving a probability adjustment instruction; According to the probability adjustment instruction, the selection probability of at least part of the power conversion units is adjusted.

6. The power conversion system according to any one of claims 1 to 5, characterized in that: The target power conversion unit is one or more power conversion units selected from the N power conversion units in a fixed order.

7. The power conversion system according to claim 6, characterized in that: The N power conversion units include a first unit group to an Mth unit group arranged in sequence, any of the unit groups includes one or more power conversion units, and M is an integer and M≥2; The plurality of consecutive cycles include one or a combination of a first cycle and a second cycle; In the first cycle, a unit group is selected in sequence from the first unit group to the Mth unit group as a target power conversion unit; In the second cycle, a unit group is selected in sequence from the Mth unit group to the first unit group as a target power conversion unit.

8. The power conversion system according to claim 7, characterized in that: When the plurality of cycles include the first cycle and the second cycle, the first cycle and the second cycle appear alternately.

9. The power conversion system according to any one of claims 1 to 8, characterized in that: The updated reference power is equal to the target maximum power minus the reserved power, or the updated reference power is equal to the target maximum power multiplied by the reference percentage; The target maximum power is a maximum power or a maximum power average value among the maximum powers of one or more target power units.

10. The power conversion system according to claim 9, characterized in that: The reserved power is a constant value; Alternatively, the reserved power is equal to the target maximum power multiplied by a percentage.

11. The power conversion system according to any one of claims 1 to 10, characterized in that: The operating mode of the power conversion units other than the target power conversion unit among the N power conversion units is the PR mode, and the operating power of the power conversion units other than the target power conversion unit is updated with the updated reference power; or, The operating mode of the power conversion units other than the target power conversion unit among the N power conversion units is the MPPT mode, and the operating power of the power conversion units other than the target power conversion unit is the maximum power obtained by the MPPT mode; or, Among the N power conversion units other than the target power conversion unit, the operating mode of some power conversion units is the PR mode, and the operating power of some power conversion units is the updated reserved power, and the operating mode of the remaining power conversion units is the MPPT mode, and the operating power of the remaining power conversion units is the maximum power obtained by the MPPT mode.

12. A power update control method, characterized in that: The method is applied to a power conversion system, which includes N power conversion units, where N is an integer and N≥2; a first end of each of the power conversion units is used to connect to a DC power supply or an AC power supply, a second end of each of the power conversion units is used to connect to a load or an energy storage unit or a power grid, and the power conversion unit is used to convert the DC power input by the DC power supply or the AC power input by the AC power supply and output the converted power; The method comprises: Controlling the working mode of one or more target power conversion units among the N power conversion units to switch between a power reservation PR mode and a maximum power point tracking MPPT mode, updating a reference power according to the maximum power obtained in the MPPT mode, so that the working power of the target power conversion unit after switching from the MPPT mode to the PR mode is the updated reference power; wherein the updated reference power is less than or equal to the maximum power; The operating modes of the power conversion units other than the target power conversion unit among the N power conversion units are controlled to remain unchanged.

13. The power update control method according to claim 12, characterized in that: The target power conversion unit is one or more power conversion units randomly selected from the N power conversion units.

14. The power update control method according to claim 12, characterized in that: The probabilities of at least some of the power conversion units being selected as the target power conversion units are different.

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