Power conversion apparatus and control method therefor

Abstract

Provided in the present application are a power conversion apparatus and a control method therefor. The power conversion apparatus comprises a first DC / DC conversion circuit, a second DC / DC conversion circuit, a DC / AC conversion circuit and a controller, wherein the first DC / DC conversion circuit is connected in parallel to an output of the second DC / DC conversion circuit; when the power conversion apparatus switches from a non-power-limited state to a power-limited state, the controller adjusts an input voltage of the first DC / DC conversion circuit to a first voltage, and adjusts an input voltage of the second DC / DC conversion circuit to a second voltage, so as to reduce both an input power of the first DC / DC conversion circuit and an input power of the second DC / DC conversion circuit; and the first voltage is greater than the input voltage of the first DC / DC conversion circuit when the power conversion apparatus is in the non-power-limited state, and the second voltage is greater than the input voltage of the second DC / DC conversion circuit when the power conversion apparatus is in the non-power-limited state. Therefore, the power generation of a power conversion apparatus can be improved.

Description

Power conversion device and control method thereof

[0001] This application claims priority to the Chinese patent application filed with the State Intellectual Property Office of China on January 27, 2024, with application number 202410120548.3, and priority to the Chinese patent application entitled “Power conversion device and control method thereof”, all contents of which are incorporated by reference into this application. Technical Field

[0002] The present application relates to the field of power supply technology, and in particular to a power conversion device and a control method thereof. Background Art

[0003] In scenarios such as those with irregular roof areas, the number of PV modules in different PV strings connected to the PV inverter may be different. As a result, when the PV inverter switches from a non-power-limited state to a power-limited state, the different output voltages of different PV strings may cause additional power limiting, thereby losing the power generation of the PV inverter. Summary of the Invention

[0004] The present application provides a power conversion device and a control method thereof, which can avoid the situation where the power conversion device is additionally limited in power, thereby increasing the power generation of the power conversion device.

[0005] In a first aspect, the present application provides a power conversion device comprising a first DC / DC conversion circuit, a second DC / DC conversion circuit, a DC / AC conversion circuit, and a controller. The input of the first DC / DC conversion circuit and the input of the second DC / DC conversion circuit are both connected to photovoltaic modules. The output of the first DC / DC conversion circuit is connected in parallel with the output of the second DC / DC conversion circuit and then connected to the input of the DC / AC conversion circuit. The output of the DC / AC conversion circuit is connected to an AC power grid. The controller is configured to adjust the input voltage of the first DC / DC conversion circuit to a first voltage and the input voltage of the second DC / DC conversion circuit to a second voltage when the power conversion device switches from a non-limited power state to a limited power state, thereby reducing the input power of the first DC / DC conversion circuit and the input power of the second DC / DC conversion circuit. The first voltage is greater than the input voltage of the first DC / DC conversion circuit when the power conversion device is in the non-limited power state, and the second voltage is greater than the input voltage of the second DC / DC conversion circuit when the power conversion device is in the non-limited power state.

[0006] In this embodiment, when the power conversion device switches from a non-power-limited state to a power-limited state, the input voltages of the first DC / DC conversion circuit and the second DC / DC conversion circuit are adjusted to higher voltage values, so that when the output power of the power conversion device is reduced due to power limiting, its input power is correspondingly reduced. As a result, when the power conversion device is in the power-limited state, the rise in the input voltage of the DC / AC conversion circuit is relatively low, thereby avoiding the power conversion device from being additionally power-limited, thereby increasing the power generation of the power conversion device.

[0007] In conjunction with the first aspect, in a first possible implementation, when the power conversion device is in a non-power-limited state, the input voltage of the first DC / DC conversion circuit is different from the input voltage of the second DC / DC conversion circuit. The controller is configured to, when the power conversion device switches from the non-power-limited state to the power-limited state, adjust the input voltage of the first DC / DC conversion circuit to a first voltage and adjust the input voltage of the second DC / DC conversion circuit to a second voltage, and ensure that the difference between the second voltage and the first voltage is less than the difference between the input voltages of the second DC / DC conversion circuit and the first DC / DC conversion circuit when the power converter is in the non-power-limited state.

[0008] In this embodiment, in a scenario where the open-circuit voltages of multiple photovoltaic modules connected to the power conversion device are different, the power conversion device controls the input voltage equalization of the first DC / DC conversion circuit and the second DC / DC conversion circuit so that when the output power of the power conversion device is reduced due to power limiting, its input power is correspondingly reduced, thereby maximizing the reduction in the degree of increase in the input voltage of the DC / AC conversion circuit when the input power of the power conversion device is completed. This avoids the power conversion device from being subject to additional power limiting, thereby increasing the power generation of the power conversion device.

[0009] In combination with the first aspect, in a second possible implementation, when the power conversion device is in a non-power-limited state, the input voltage of the first DC / DC conversion circuit is the same as the input voltage of the second DC / DC conversion circuit. The controller is configured to, when the power conversion device switches from the non-power-limited state to the power-limited state, adjust the input voltage of the first DC / DC conversion circuit to a first voltage, and adjust the input voltage of the second DC / DC conversion circuit to a second voltage, and ensure that the difference between the second voltage and the first voltage is consistent with the difference between the input voltages of the second DC / DC conversion circuit and the first DC / DC conversion circuit when the power converter is in the non-power-limited state.

[0010] In this embodiment, in a scenario where the open-circuit voltages of multiple photovoltaic modules connected to the power conversion device are close and the output currents are different, the power conversion device controls the input voltage equalization of the first DC / DC conversion circuit and the second DC / DC conversion circuit so that when the output power of the power conversion device is reduced due to power limiting, its input power is correspondingly reduced, thereby maximizing the reduction in the degree of increase in the input voltage of the DC / AC conversion circuit when the input power of the power conversion device is completed. This avoids the power conversion device from being subject to additional power limiting, thereby increasing the power generation of the power conversion device.

[0011] In combination with any one of the first aspect to the second possible implementation of the first aspect, in a third possible implementation, the controller is used to adjust the target input voltage of the first DC / DC conversion circuit to a first voltage, and adjust the target input voltage of the second DC / DC conversion circuit to a second voltage, so as to adjust the input voltage of the first DC / DC conversion circuit to the first voltage, and adjust the input voltage of the second DC / DC conversion circuit to the second voltage.

[0012] In a second aspect, the present application provides a control method for a power conversion device, the method comprising: when the power conversion device switches from a non-power-limited state to a power-limited state, adjusting the input voltage of a first DC / DC conversion circuit to a first voltage, and adjusting the input voltage of a second DC / DC conversion circuit to a second voltage, so that the input power of the first DC / DC conversion circuit and the input power of the second DC / DC conversion circuit are both reduced. The first voltage is greater than the input voltage of the first DC / DC conversion circuit when the power conversion device is in the non-power-limited state, and the second voltage is greater than the input voltage of the second DC / DC conversion circuit when the power conversion device is in the non-power-limited state. The method is applicable to a power conversion device comprising a first DC / DC conversion circuit, a second DC / DC conversion circuit, and a DC / AC conversion circuit, wherein the input of the first DC / DC conversion circuit and the input of the second DC / DC conversion circuit are both used to connect to a photovoltaic module, the output of the first DC / DC conversion circuit is connected in parallel with the output of the second DC / DC conversion circuit and then connected to the input of the DC / AC conversion circuit, and the output of the DC / AC conversion circuit is used to connect to an AC power grid.

[0013] In conjunction with the second aspect, in a first possible implementation, when the power conversion device is in a non-power-limited state, the input voltage of the first DC / DC conversion circuit is different from the input voltage of the second DC / DC conversion circuit. When the power conversion device switches from the non-power-limited state to the power-limited state, the power conversion device adjusts the input voltage of the first DC / DC conversion circuit to a first voltage and adjusts the input voltage of the second DC / DC conversion circuit to a second voltage, and the difference between the second voltage and the first voltage is less than the difference between the input voltages of the second DC / DC conversion circuit and the first DC / DC conversion circuit when the power converter is in the non-power-limited state.

[0014] In conjunction with the second aspect, in a second possible implementation, when the power conversion device is in a non-power-limited state, the input voltage of the first DC / DC conversion circuit is the same as the input voltage of the second DC / DC conversion circuit. When the power conversion device switches from the non-power-limited state to the power-limited state, the power conversion device adjusts the input voltage of the first DC / DC conversion circuit to the first voltage and adjusts the input voltage of the second DC / DC conversion circuit to the second voltage, and makes the difference between the second voltage and the first voltage consistent with the difference between the input voltages of the second DC / DC conversion circuit and the first DC / DC conversion circuit when the power converter is in the non-power-limited state.

[0015] In combination with any one of the second aspect to the second possible implementation of the second aspect, in a third possible implementation, the power conversion device adjusts the target input voltage of the first DC / DC conversion circuit to the first voltage, and adjusts the target input voltage of the second DC / DC conversion circuit to the second voltage, so as to adjust the input voltage of the first DC / DC conversion circuit to the first voltage, and adjust the input voltage of the second DC / DC conversion circuit to the second voltage.

[0016] It should be understood that the implementation and beneficial effects of the above-mentioned aspects of the present application can be referenced to each other. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] FIG1 is a schematic diagram of an application scenario of a power conversion device provided by the present application;

[0018] FIG2 is a schematic diagram of a curve showing input voltage and input power of various Boost circuits provided by the prior art;

[0019] FIG3 is a schematic structural diagram of a power conversion device provided by the present application;

[0020] FIG4 is a schematic diagram of a curve showing input voltage and input power of two DC / DC conversion circuits provided by the present application;

[0021] FIG5 is a schematic diagram of a curve showing input voltage and input power of two DC / DC conversion circuits provided by the present application;

[0022] FIG6 is a schematic diagram of a process for generating target input currents of various DC / DC conversion circuits provided in the present application;

[0023] FIG7 is a flow chart of a control method for a power conversion device provided in the present application. DETAILED DESCRIPTION

[0024] The power conversion device provided in this application can be applied to various application fields such as photovoltaic power generation, energy storage power generation, new energy smart microgrid, and power transmission and distribution. The power conversion device provided in this application can be an inverter, a power storage converter (Power Conversion System, PCS), an uninterruptible power supply (Uninterrupted Power Supply, UPS), etc., and is suitable for different application scenarios, such as photovoltaic power supply scenarios, photovoltaic storage hybrid power supply scenarios, and UPS power supply scenarios. The photovoltaic power supply scenario is used as an example for explanation below.

[0025] Referring to FIG1 , FIG1 is a schematic diagram of an application scenario of the power conversion device provided by the present application. In the photovoltaic power supply scenario, the power conversion device provided by the present application is the inverter 1 shown in FIG1 , which includes two DC / DC conversion circuits, an inverter circuit 12 and a controller 13. Among them, the DC / DC conversion circuit includes one of Boost, Buck, and Buck-Boost. Here, the DC / DC conversion circuit is described as Boost. For example, the two Boost circuits include a Boost circuit 111 and a Boost circuit 112. After the input end of the Boost circuit 111 is connected to a set of DC input ends of the inverter 1, it is connected to the photovoltaic module 311 through the DC / DC converter 211; the input end of the Boost circuit 112 is connected to another set of DC input ends of the inverter 1, the output end of the DC / DC converter 221 and the output end of the DC / DC converter 222 are connected in parallel to the above-mentioned other set of DC input ends, the input end of the DC / DC converter 221 is connected to the photovoltaic module 321, and the input end of the DC / DC converter 222 is connected to the photovoltaic module 322. The output of the boost circuit 111 and the output of the boost circuit 112 are connected in parallel and then connected to the input of the inverter circuit 12. The output of the inverter circuit 12 is connected to the AC output of the inverter 1. The AC output of the inverter 1 is connected to the AC grid or household appliances.

[0026] After the photovoltaic power supply system consisting of inverter 1 and three DC / DC converters begins operation, each of the three DC / DC converters adjusts the output voltage of the connected photovoltaic modules to perform maximum power point tracking (MPPT) on the output power of the photovoltaic modules, maximizing the output power of the photovoltaic modules connected to each DC / DC converter. Simultaneously, each DC / DC converter performs DC conversion on the output voltage of the connected photovoltaic modules and outputs the converted DC voltage to each set of DC input terminals of inverter 1. The controller 13 in inverter 1 controls the two boost circuits and the inverter circuit 12 to sequentially boost and invert the DC voltage at its input terminals. It also adjusts the DC voltage at its input terminals to perform MPPT on the output power of inverter 1, maximizing the output power of inverter 1 and placing inverter 1 in an unlimited power state, thereby providing power to various types of electrical devices, such as AC grids or loads.

[0027] However, when the inverter 1 switches from a non-power-limited state to a power-limited state, the input voltage of the inverter circuit 12 may be raised to a greater extent due to the different numbers of photovoltaic modules connected to different groups of input terminals of the inverter 1, thereby causing the inverter 1 to be additionally power-limited, thereby losing the power generation of the inverter 1.

[0028] For example, as shown in FIG2 , the open-circuit voltage Voc1 of the first photovoltaic string connected to the boost circuit 111 is close to the open-circuit voltage Voc2 of the second photovoltaic string connected to the boost circuit 112, and the output current of the second photovoltaic string is twice the output current of the first photovoltaic string. The first photovoltaic string is composed of a photovoltaic module 311 and a DC / DC converter 211, and the second photovoltaic string is composed of a photovoltaic module 321, a photovoltaic module 322, a DC / DC converter 221, and a DC / DC converter 222. When the inverter 1 is in a non-power-limited state, the boost circuit 111 and the boost circuit 112 both operate at the MPPT points, namely, points P1-1 and P1-2. When the inverter 1 switches from a non-power-limited state to a power-limited state, the inverter 1 adjusts the input current sharing of the boost circuit 111 and the boost circuit 112 so that the input power of both the boost circuit 111 and the boost circuit 112 is reduced. Since the target current value for achieving equal flow of the input currents of the Boost circuit 111 and the Boost circuit 112 is between the output current of the first photovoltaic string and the output current of the second photovoltaic string, when the inverter 1 switches from the non-power-limited state to the power-limited state, the final steady-state operating point of the Boost circuit 111 may still be at point P1-1, and the final steady-state operating point of the Boost circuit 112 is P2-2. That is, only the input power of the Boost circuit 112 will decrease, which will cause the input voltage of the Boost circuit 112 to rise higher, thereby resulting in a higher input voltage of the inverter circuit 12, and further causing the inverter 1 to be additionally power-limited.

[0029] Based on the above problem, when the inverter 1 switches from the non-power-limited state to the power-limited state, the controller 13 adjusts the input voltage of the boost circuit 111 to a first voltage and adjusts the input voltage of the boost circuit 112 to a second voltage, so that the input power of the boost circuit 111 and the input power of the boost circuit 112 are both reduced. The first voltage is greater than the input voltage of the boost circuit 111 when the inverter 1 is in the power-limited state, and the second voltage is greater than the input voltage of the boost circuit 112 when the inverter 1 is in the power-limited state. Therefore, when the inverter 1 switches from the non-power-limited state to the power-limited state, the inverter 1 adjusts the input voltages of the two Boost circuits to higher voltage values, so that when the output power of the inverter 1 is reduced due to power limiting, its input power is correspondingly reduced. This can avoid the situation where the input power of only one Boost circuit is reduced, causing the input voltage of the Boost circuit to rise more, thereby causing the input voltage of the inverter circuit 12 to rise more. As a result, when the inverter 1 is in the power-limited state, the increase in the input voltage of the inverter circuit 12 is lower, thereby avoiding the inverter 1 from being additionally power-limited, thereby increasing the power generation of the inverter 1.

[0030] The above is only an example of the application scenarios of the power conversion device provided by this application, and is not an exhaustive list. This application does not limit the application scenarios.

[0031] The working principle of the power conversion device provided in this application is illustrated below with reference to FIG3 to FIG6 .

[0032] Referring to Figure 3, Figure 3 is a schematic diagram of the structure of the power conversion device provided in this application. As shown in Figure 3, the n groups of DC input terminals of the power conversion device 1 include the first group of DC input terminals (i.e., DC input terminals i111 and i112), the second group of DC input terminals (i.e., DC input terminals i121 and i122), ..., and the nth group of DC input terminals (i.e., DC input terminals i1n1 and i1n2). The AC output terminal of the power conversion device 1 includes o11 and o12. The power conversion device 1 includes n DC / DC conversion circuits, a DC / AC conversion circuit 12 and a controller 13. Among them, the n DC / DC conversion circuits include a DC / DC conversion circuit 111, a DC / DC conversion circuit 112, ..., and a DC / DC conversion circuit 11n, where n is an integer greater than 1. The input terminals of the n DC / DC converter circuits are connected to photovoltaic modules. Specifically, the input terminal of DC / DC converter circuit 111 is connected to photovoltaic module 311 via DC input terminals i111 and i112, respectively. The input terminal of DC / DC converter circuit 112 is connected to photovoltaic module 312 via DC input terminals i121 and i122, respectively. The input terminal of DC / DC converter circuit 11n is connected to photovoltaic module 31n via DC input terminals i1n1 and i1n2, respectively. The output terminals of the n DC / DC converter circuits are connected in parallel and then connected to the input terminal of DC / AC converter circuit 12. The output terminal of DC / AC converter circuit 12 is connected to the AC power grid. Specifically, the output terminal of DC / AC converter circuit 12 is connected to the AC power grid via the AC output terminal of power converter device 1.

[0033] After the power conversion device 1 is in operation, the controller 13 adjusts the output voltage of the photovoltaic module connected to each of the n DC / DC conversion circuits to perform MPPT on the output power of the photovoltaic module, so that the output power of the photovoltaic module connected to each DC / DC converter is maximized, thereby maximizing the output power of the power conversion device 1, that is, putting the power conversion device 1 in a non-power-limited state. Subsequently, when the power conversion device 1 triggers a power-limiting condition (such as when the device temperature of the power conversion device 1 exceeds a temperature threshold or receives a power-limiting scheduling instruction sent by a client), the controller 13 controls the output power of the power conversion device 1 to begin decreasing, so that the power conversion device 1 switches from the non-power-limited state to the power-limited state. When the power conversion device 1 switches from the non-power-limited state to the power-limited state, the controller 13 adjusts the input voltage of the DC / DC conversion circuit 111 to a first voltage, adjusts the input voltage of the DC / DC conversion circuit 112 to a second voltage, ..., and adjusts the input voltage of the DC / DC conversion circuit 11n to an nth voltage, so that the input power of the above n DC / DC conversion circuits is reduced. In the non-power-limited state, the power converter 1 performs MPPT to maximize its output power. In the power-limited state, the power converter 1 actively limits its output power. For example, if the photovoltaic power is greater than the maximum output power of the power converter 1, the power converter 1 receives power scheduling to limit the output power, or the device temperature of the power converter 1 is too high to limit the output power, the first voltage is greater than the input voltage of the DC / DC converter circuit 111 when the power converter 1 is in the non-power-limited state, the second voltage is greater than the input voltage of the DC / DC converter circuit 112 when the power converter 1 is in the non-power-limited state, and so on. The nth voltage is greater than the input voltage of the DC / DC converter circuit 11n when the power converter 1 is in the non-power-limited state.

[0034] In one embodiment, when the power conversion device 1 is in a non-power-limited state, the input voltages of the n DC / DC conversion circuits are different.

[0035] When the power conversion device 1 switches from the non-power-limited state to the power-limited state, the controller 13 adjusts the input voltage of the DC / DC conversion circuit 111 to the first voltage, adjusts the target input voltage of the DC / DC conversion circuit 112 to the second voltage, ..., adjusts the target input voltage of the DC / DC conversion circuit 11n to the nth voltage, and adjusts the input voltage of the DC / DC conversion circuit 111 to the first voltage, adjusts the input voltage of the DC / DC conversion circuit 112 to the second voltage, ..., adjusts the input voltage of the DC / DC conversion circuit 11n to the nth voltage, and The difference between any two voltages from the first voltage to the nth voltage is made smaller than the difference between the input voltages of the two DC / DC conversion circuits corresponding to the above-mentioned any two voltages when the power conversion device 1 is in the non-power limited state. For example, the difference between the first voltage and the second voltage is smaller than the difference between the input voltages of the DC / DC conversion circuit 111 and the DC / DC conversion circuit 112 when the power conversion device 1 is in the non-power limited state, and the difference between the second voltage and the nth voltage is smaller than the difference between the input voltages of the DC / DC conversion circuit 112 and the DC / DC conversion circuit 11n when the power conversion device 1 is in the non-power limited state.

[0036] Specifically, while ensuring that the input voltage of each DC / DC converter circuit is less than the open-circuit voltage of the photovoltaic module to which it is connected, controller 13 adjusts the input voltage of each DC / DC converter circuit upward and equalizes the input voltages of n DC / DC converter circuits, thereby reducing the input power of power converter 1 when it switches from a non-limited power state to a limited power state. It should be noted that when the input power required to be reduced by power converter 1 is relatively small, that is, when the first through nth voltages are all less than the minimum open-circuit voltage of the photovoltaic modules connected to the n DC / DC converter circuits, the absolute value of the difference between any two voltages from the first through nth voltages is less than a voltage threshold. Exemplarily, the voltage threshold is the maximum of 10V and 1% of the rated input voltage of the DC / DC converter circuit. When the input power required to be reduced by power converter 1 is relatively large, such as when n=2, when power converter 1 is in the non-limited power state, the input voltage of DC / DC converter circuit 111 is less than the input voltage of DC / DC converter circuit 112. Controller 13 controls the input voltage of DC / DC converter circuit 111 and the input voltage of DC / DC converter circuit 112 to increase to a first voltage, where the first voltage approaches the open-circuit voltage of photovoltaic module 311. Exemplarily, the first voltage is greater than or equal to 5% of the open-circuit voltage of photovoltaic module 311 and less than the open-circuit voltage of photovoltaic module 311. At this point, if the input power of DC / DC converter circuit 111 and the input power of DC / DC converter circuit 112 still need to be reduced, controller 13 controls the input voltage of DC / DC converter circuit 111 to remain at the first voltage and controls the input voltage of DC / DC converter circuit 112 to continue increasing to a second voltage. When the input voltage of DC / DC converter circuit 112 increases to the second voltage, the total reduction in input power of DC / DC converter circuit 111 and DC / DC converter circuit 112 is equal to the output power upper limit of power converter device 1 in the power-limited state.

[0037] In addition, this application does not limit the order of adjustment, adjustment rate or change trend of the input voltages of the n DC / DC conversion circuits (such as the input voltages of the two DC / DC conversion circuits are increased to the same voltage, or the input voltage of the DC / DC conversion circuit 111 in the two DC / DC conversion circuits slowly increases to a first voltage, and the input voltage of the DC / DC conversion circuit 112 first increases rapidly and then decreases to a second voltage). In this application, when the power conversion device 1 switches from a non-power-limited state to a power-limited state, it includes two situations: during the process of switching the power conversion device 1 from a non-power-limited state to a power-limited state, and after the power conversion device 1 switches to a power-limited state.

[0038] For ease of understanding, the control method of the power conversion device 1 in this embodiment is introduced below in combination with a curve diagram of the input voltage and input power of the DC / DC conversion circuit shown in Figure 4. Taking n=2, the open-circuit voltage voc1 of the photovoltaic component 311 is less than the open-circuit voltage voc2 of the photovoltaic component 312, and the output current of the photovoltaic component 311 is close to the output current of the photovoltaic component 312 as an example.

[0039] As shown in Figure 4, when the power conversion device 1 is in the non-power limited state, the DC / DC conversion circuit 111 and the DC / DC conversion circuit 112 both operate at the MPPT point, that is, the DC / DC conversion circuit 111 and the DC / DC conversion circuit 112 operate at points P1-1 and P1-2 respectively. At this time, the input voltage Vin1=v11 of the DC / DC conversion circuit 111 is less than the input voltage Vin2=v21 of the DC / DC conversion circuit 112. Afterwards, when the power conversion device 1 switches from the non-power-limited state to the power-limited state, the controller 13 controls the input voltage Vin1 of the DC / DC conversion circuit 111 to increase to the first voltage v12, and controls the input voltage of the DC / DC conversion circuit 112 to increase to the second voltage v22. That is, the DC / DC conversion circuit 111 is adjusted to operate at point P3-1 and the DC / DC conversion circuit 112 is adjusted to operate at point P3-2, so that the input power of the DC / DC conversion circuit 111 and the DC / DC conversion circuit 112 are both reduced. Therefore, when the output power of the power conversion device 1 is reduced due to power limiting, its input power is correspondingly reduced. Among them, the first voltage v12 is equal to the second voltage v22.

[0040] It can be understood that in a scenario where the multiple photovoltaic modules connected to the power conversion device 1 are long and short modules, that is, the open-circuit voltages of the photovoltaic modules are different, the power conversion device 1 controls the input voltage equalization of n DC / DC conversion circuits so that when the output power of the power conversion device 1 is reduced due to power limiting, its input power is correspondingly reduced, thereby maximizing the reduction in the degree of increase in the input voltage of the DC / AC conversion circuit 12 when the input power of the power conversion device 1 is completed. This avoids the power conversion device 1 from being subject to additional power limiting, thereby increasing the power generation of the power conversion device 1.

[0041] In another embodiment, when the power conversion device 1 is in a non-power-limited state, the input voltages of the n DC / DC conversion circuits are the same.

[0042] When the power conversion device 1 switches from the non-power-limited state to the power-limited state, the controller 13 adjusts the target input voltage of the DC / DC conversion circuit 111 to the first voltage, adjusts the target input voltage of the DC / DC conversion circuit 112 to the second voltage, ..., adjusts the target input voltage of the DC / DC conversion circuit 11n to the nth voltage, thereby adjusting the input voltage of the DC / DC conversion circuit 111 to the first voltage, adjusting the input voltage of the DC / DC conversion circuit 112 to the second voltage, ..., adjusting the input voltage of the DC / DC conversion circuit 11n to the nth voltage, and making the nth voltage The difference between any two voltages from the first voltage to the nth voltage is consistent with the difference between the input voltages of the two DC / DC conversion circuits corresponding to the aforementioned arbitrary two voltages when the power conversion device 1 is in a non-power-limited state. For example, the difference between the first voltage and the second voltage is consistent with the difference between the input voltages of the DC / DC conversion circuit 111 and the DC / DC conversion circuit 112 when the power conversion device 1 is in a non-power-limited state, and the difference between the second voltage and the nth voltage is consistent with the difference between the input voltages of the DC / DC conversion circuit 112 and the DC / DC conversion circuit 11n when the power conversion device 1 is in a non-power-limited state. The difference between any two voltages from the first voltage to the nth voltage is consistent with the difference between the input voltages of the two DC / DC conversion circuits corresponding to the aforementioned arbitrary two voltages when the power conversion device 1 is in a non-power-limited state, which means that the absolute value of the difference between the difference between any two voltages from the first voltage to the nth voltage and the difference between the input voltages of the two DC / DC conversion circuits corresponding to the aforementioned arbitrary two voltages when the power conversion device 1 is in a non-power-limited state is less than the voltage threshold. Exemplarily, the voltage threshold is a maximum value between 10 V and 1% of a rated input voltage of the DC / DC converter circuit.

[0043] Specifically, the controller 13 ensures that the input voltage of each DC / DC conversion circuit is less than the open-circuit voltage of the photovoltaic module to which it is connected. By adjusting the input voltage of each DC / DC conversion circuit upward and equalizing the input voltages of n DC / DC conversion circuits, the input power of the power conversion device 1 is correspondingly reduced when it switches from a non-power-limited state to a power-limited state.

[0044] For ease of understanding, the following is a curve diagram of the input voltage and input power of the DC / DC conversion circuit shown in Figure 5. Taking n=2, the open-circuit voltage voc1 of the photovoltaic component 311 is close to the open-circuit voltage voc2 of the photovoltaic component 312, and the output current of the photovoltaic component 311 is less than the output current of the photovoltaic component 312 as an example, the derating control method in this embodiment is introduced.

[0045] As shown in Figure 5, when the power conversion device 1 is in the non-power limited state, the DC / DC conversion circuit 111 and the DC / DC conversion circuit 112 both operate at the MPPT point, that is, the DC / DC conversion circuit 111 and the DC / DC conversion circuit 112 operate at points P1-1 and P1-2 respectively. At this time, the input voltage Vin1=v11 of the DC / DC conversion circuit 111 is the same as the input voltage Vin2=v21 of the DC / DC conversion circuit 112. Afterwards, when the power conversion device 1 switches from the non-power-limited state to the power-limited state, the controller 13 controls the input voltage Vin1 of the DC / DC conversion circuit 111 to increase to the first voltage v12, and controls the input voltage of the DC / DC conversion circuit 112 to increase to the second voltage v22. That is, the DC / DC conversion circuit 111 is adjusted to operate at point P3-1 and the DC / DC conversion circuit 112 is adjusted to operate at point P3-2, so that the input power of the DC / DC conversion circuit 111 and the DC / DC conversion circuit 112 are both reduced. Therefore, when the output power of the power conversion device 1 is reduced due to power limiting, its input power is correspondingly reduced. Among them, the first voltage v12 is equal to the second voltage v22.

[0046] It can be understood that in a scenario where the open-circuit voltages of multiple photovoltaic modules connected to the power conversion device 1 are close and the output currents are different, the power conversion device 1 controls the input voltage equalization of n DC / DC conversion circuits so that when the output power of the power conversion device 1 is reduced due to power limiting, its input power is correspondingly reduced, thereby maximizing the reduction in the degree of increase in the input voltage of the DC / AC conversion circuit 12 when the input power of the power conversion device 1 is completed. This avoids the power conversion device 1 from being subject to additional power limiting, thereby increasing the power generation of the power conversion device 1.

[0047] In addition, in the above embodiment, the controller 13 adjusts the target input voltage of each DC / DC conversion circuit by adjusting the input current of each DC / DC conversion circuit to the target input current shown in Figure 6. As shown in Figure 6, n is 2, and the controller 13 generates the first target input current iref11 of the DC / DC conversion circuit 111 and the first target input current iref21 of the DC / DC conversion circuit 112 through the bus voltage loop of the DC / DC conversion circuit 111 and the bus voltage loop of the DC / DC conversion circuit 112, respectively. When the input current of the DC / DC conversion circuit 111 is iref11 and the input current of the DC / DC conversion circuit 112 is iref21, the input power of the power conversion device 1 is correspondingly reduced when its output power is reduced due to power limiting. In addition, the controller 13 also inputs the input voltage Vin1 of the DC / DC converter circuit 111 and the average input voltage Vin_avg of the two DC / DC converter circuits when the power conversion device 1 is in the non-power-limited state into the subtractor FS1 to obtain the difference ΔVin1 between Vin1 and Vin_avg. Based on ΔVin1, the controller 13 uses the PI controller to obtain the second target input current iref12 of the DC / DC converter circuit 111. Subsequently, iref12 is input to the limiter, and the controller 13 uses the limiter to ensure that the third target input current iref13 of the DC / DC converter circuit 111 is greater than or equal to the preset current. Subsequently, the controller 13 uses the adder Adder1 to obtain the target input current iref1=iref11+iref13 of the DC / DC converter circuit 111. The controller 13 also inputs the input voltage Vin2 of the DC / DC converter circuit 112 and the average input voltage Vin_avg of the two DC / DC converter circuits when the power converter device 1 is in the non-power-limited state into the subtractor FS2 to obtain the difference ΔVin2 between Vin2 and Vin_avg. Based on ΔVin2, the controller 13 uses the PI controller to obtain the second target input current iref22 of the DC / DC converter circuit 112. iref22 is then input to the limiter, and the controller 13 uses the limiter to ensure that the third target input current iref23 of the DC / DC converter circuit 112 is greater than or equal to a preset current. The controller 13 then uses the adder Adder2 to obtain the target input current iref2 = iref21 + iref23 of the DC / DC converter circuit 112.

[0048] In the present application, when the power conversion device 1 switches from a non-power-limited state to a power-limited state, the input voltage of the n DC / DC conversion circuits is adjusted to a higher voltage value, so that when the output power of the power conversion device 1 decreases due to power limiting, its input power is correspondingly reduced. This can reduce the rise in the input voltage of the DC / AC conversion circuit 12 when the power conversion device 1 is in the power-limited state, thereby avoiding additional power limiting of the power conversion device 1 and increasing the power generation of the power conversion device 1. In addition, the input power control method provided in the present application is not only applicable to scenarios where the open-circuit voltages of multiple photovoltaic modules connected to the power conversion device 1 are similar and the output currents are different, but also applicable to scenarios where the open-circuit voltages of multiple photovoltaic modules connected to the power conversion device 1 are different, and has strong applicability.

[0049] See Figure 7, which is a flow chart of a control method for a power conversion device provided by the present application. The control method for a power conversion device provided by an embodiment of the present application is applicable to the power conversion device 1 shown in Figure 3. The control method for a power conversion device may include the following steps:

[0050] S101, controlling the power conversion device to be in a non-power-limited state.

[0051] Specifically, the power conversion device adjusts the output voltage of the photovoltaic module to which it is connected to perform MPPT on the output power of the photovoltaic module, so that the output power of the photovoltaic module to which it is connected is maximized, thereby maximizing the output power of the power conversion device, that is, the power conversion device is in a non-power-limited state.

[0052] S102, when the power conversion device switches from a non-power-limited state to a power-limited state, adjusting the input voltage of the first DC / DC conversion circuit to a first voltage, and adjusting the input voltage of the second DC / DC conversion circuit to a second voltage, so that the input power of the first DC / DC conversion circuit and the input power of the second DC / DC conversion circuit are both reduced.

[0053] The first voltage is greater than the input voltage of the first DC / DC converter circuit when the power converter is in a non-power-limited state, and the second voltage is greater than the input voltage of the second DC / DC converter circuit when the power converter is in a non-power-limited state.

[0054] In one embodiment, when the power conversion device is in a non-power-limited state, an input voltage of the first DC / DC conversion circuit is different from an input voltage of the second DC / DC conversion circuit.

[0055] The power conversion device adjusts the input voltage of the first DC / DC conversion circuit to a first voltage and adjusts the input voltage of the second DC / DC conversion circuit to a second voltage when the power conversion device switches from a non-power-limited state to a power-limited state, and makes the difference between the second voltage and the first voltage smaller than the difference between the input voltages of the second DC / DC conversion circuit and the first DC / DC conversion circuit when the power converter is in the non-power-limited state, so that the input power of the first DC / DC conversion circuit and the input power of the second DC / DC conversion circuit are both reduced.

[0056] In another embodiment, when the power conversion device is in a non-power-limited state, the input voltage of the first DC / DC conversion circuit is the same as the input voltage of the second DC / DC conversion circuit.

[0057] When the power conversion device switches from a non-power-limited state to a power-limited state, the power conversion device adjusts the input voltage of the first DC / DC conversion circuit to a first voltage and adjusts the input voltage of the second DC / DC conversion circuit to a second voltage, and makes the difference between the second voltage and the first voltage consistent with the difference between the input voltages of the second DC / DC conversion circuit and the first DC / DC conversion circuit when the power converter is in the non-power-limited state, so that the input power of the first DC / DC conversion circuit and the input power of the second DC / DC conversion circuit are both reduced.

[0058] In a specific implementation, more operations performed by the power conversion device in the control method of the power conversion device provided in this application can be referred to the implementation method performed by the power conversion device 1 shown in Figure 3, and will not be repeated here.

[0059] In an embodiment of the present application, when the power conversion device switches from a non-power-limited state to a power-limited state, the input voltage of each DC / DC conversion circuit inside the power conversion device is adjusted to a higher voltage value, so that when the output power of the power conversion device is reduced due to power limiting, its input power is correspondingly reduced. As a result, the input voltage of the DC / AC conversion circuit rises at a lower level when the input power of the power conversion device completes the corresponding reduction, thereby avoiding additional power limiting of the power conversion device and increasing the power generation of the power conversion device.

[0060] The above are only specific embodiments of the present application, but the scope of protection of this application is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in this application should be included in the scope of protection of this application. Therefore, the scope of protection of this application should be based on the scope of protection of the claims.

Claims

1. A power conversion device, characterized in that: The power conversion device includes a first DC / DC conversion circuit, a second DC / DC conversion circuit, a DC / AC conversion circuit and a controller, wherein: The input of the first DC / DC conversion circuit and the input of the second DC / DC conversion circuit are both used to connect to the photovoltaic module, the output of the first DC / DC conversion circuit and the output of the second DC / DC conversion circuit are connected in parallel and then connected to the input of the DC / AC conversion circuit, and the output of the DC / AC conversion circuit is used to connect to the AC power grid; The controller is configured to adjust the input voltage of the first DC / DC conversion circuit to a first voltage and the input voltage of the second DC / DC conversion circuit to a second voltage when the power conversion device switches from a non-power-limited state to a power-limited state, so as to reduce both the input power of the first DC / DC conversion circuit and the input power of the second DC / DC conversion circuit, wherein the first voltage is greater than the input voltage of the first DC / DC conversion circuit when the power conversion device is in the non-power-limited state, and the second voltage is greater than the input voltage of the second DC / DC conversion circuit when the power conversion device is in the non-power-limited state.

2. The power conversion device according to claim 1, characterized in that: When the power conversion device is in the non-power-limited state, the input voltage of the first DC / DC conversion circuit is different from the input voltage of the second DC / DC conversion circuit; The controller is configured to, when the power conversion device switches from a non-power-limited state to a power-limited state, adjust the input voltage of the first DC / DC conversion circuit to a first voltage, and adjust the input voltage of the second DC / DC conversion circuit to a second voltage, and ensure that a difference between the second voltage and the first voltage is less than a difference between the input voltages of the second DC / DC conversion circuit and the first DC / DC conversion circuit when the power converter is in the non-power-limited state.

3. The power conversion device according to claim 1, wherein: When the power conversion device is in the non-power-limited state, the input voltage of the first DC / DC conversion circuit is the same as the input voltage of the second DC / DC conversion circuit; The controller is configured to, when the power conversion device switches from a non-power-limited state to a power-limited state, adjust the input voltage of the first DC / DC conversion circuit to a first voltage, and adjust the input voltage of the second DC / DC conversion circuit to a second voltage, and ensure that a difference between the second voltage and the first voltage is consistent with a difference between the input voltages of the second DC / DC conversion circuit and the first DC / DC conversion circuit when the power converter is in the non-power-limited state.

4. The power conversion device according to any one of claims 1 to 3, characterized in that: The controller is used to adjust the target input voltage of the first DC / DC conversion circuit to the first voltage and adjust the target input voltage of the second DC / DC conversion circuit to the second voltage, so as to adjust the input voltage of the first DC / DC conversion circuit to the first voltage and adjust the input voltage of the second DC / DC conversion circuit to the second voltage.

5. A control method for a power conversion device, characterized in that: The method comprises: When the power conversion device switches from a non-power-limited state to a power-limited state, the input voltage of the first DC / DC conversion circuit is adjusted to a first voltage, and the input voltage of the second DC / DC conversion circuit is adjusted to a second voltage, so that the input power of the first DC / DC conversion circuit and the input power of the second DC / DC conversion circuit are both reduced, wherein the first voltage is greater than the input voltage of the first DC / DC conversion circuit when the power conversion device is in the non-power-limited state, and the second voltage is greater than the input voltage of the second DC / DC conversion circuit when the power conversion device is in the non-power-limited state. The method is applicable to the power conversion device, which includes the first DC / DC conversion circuit, the second DC / DC conversion circuit, and a DC / AC conversion circuit, wherein the input of the first DC / DC conversion circuit and the input of the second DC / DC conversion circuit are both used to connect to photovoltaic modules, the output of the first DC / DC conversion circuit and the output of the second DC / DC conversion circuit are connected in parallel and then connected to the input of the DC / AC conversion circuit, and the output of the DC / AC conversion circuit is used to connect to an AC power grid.

6. The method according to claim 5, characterized in that When the power conversion device is in the non-power-limited state, the input voltage of the first DC / DC conversion circuit is different from the input voltage of the second DC / DC conversion circuit; The step of adjusting the input voltage of the first DC / DC conversion circuit to a first voltage and adjusting the input voltage of the second DC / DC conversion circuit to a second voltage includes: Adjusting the input voltage of the first DC / DC conversion circuit to a first voltage, and adjusting the input voltage of the second DC / DC conversion circuit to a second voltage, and making the difference between the second voltage and the first voltage smaller than the difference between the input voltages of the second DC / DC conversion circuit and the first DC / DC conversion circuit when the power converter is in the non-power-limited state.

7. The method according to claim 5, characterized in that When the power conversion device is in the non-power-limited state, the input voltage of the first DC / DC conversion circuit is the same as the input voltage of the second DC / DC conversion circuit; The step of adjusting the input voltage of the first DC / DC conversion circuit to a first voltage and adjusting the input voltage of the second DC / DC conversion circuit to a second voltage includes: Adjusting the input voltage of the first DC / DC conversion circuit to a first voltage, and adjusting the input voltage of the second DC / DC conversion circuit to a second voltage, and making the difference between the second voltage and the first voltage consistent with the difference between the input voltages of the second DC / DC conversion circuit and the first DC / DC conversion circuit when the power converter is in the non-power limited state.

8. The method according to any one of claims 5 to 7, characterized in that: The step of adjusting the input voltage of the first DC / DC conversion circuit to a first voltage and adjusting the input voltage of the second DC / DC conversion circuit to a second voltage includes: The target input voltage of the first DC / DC conversion circuit is adjusted to the first voltage, and the target input voltage of the second DC / DC conversion circuit is adjusted to the second voltage.

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