Photovoltaic inverter and control method thereof
By disconnecting the energy storage device when it is fully charged and reducing the DC bus voltage, the loss and derating problems of photovoltaic inverters are solved, thereby improving the reliability and economic efficiency of the system.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- HUAWEI TECH CO LTD
- Filing Date
- 2026-02-28
- Publication Date
- 2026-07-03
Smart Images
Figure CN122338899A_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of power electronics technology, and in particular to a photovoltaic inverter and its control method. Background Technology
[0002] The photovoltaic inverter in a photovoltaic energy storage system includes a direct current to direct current (DC-DC) conversion circuit, a DC bus, and a direct current to alternating current (DC-AC) conversion circuit. The input terminal of the DC-DC conversion circuit is used to connect to the photovoltaic modules. The output terminal of the DC-DC conversion circuit and the DC terminal of the DC-AC conversion circuit are both connected to the DC bus. The AC terminal of the DC-AC conversion circuit is used to connect to the power grid and the load. The DC bus is also used to connect energy storage devices.
[0003] The DC-DC converter circuit is used for maximum power point tracking (MPPT) of the photovoltaic module, and also for voltage conversion of the DC power provided by the photovoltaic module, and charging the energy storage device through the DC bus.
[0004] However, when the output voltage of the photovoltaic (PV) modules is relatively low and the energy storage device is fully charged, the continuous output power of the PV modules causes a significant rise in the DC bus voltage. This results in a large voltage difference between the output and input terminals of the DC-DC converter circuit, increasing the turn-on and turn-off losses of the switching transistors in the DC-DC converter circuit. Simultaneously, due to the high DC bus voltage, the PV inverter is prone to triggering voltage derating, leading to input-side power limiting and reducing the power output of the PV energy storage system. Input-side power limiting refers to restricting the power input from the PV modules to the PV inverter. Therefore, how to reduce the losses of the PV inverter and avoid derating operation after the energy storage device is fully charged has become an urgent problem to be solved. Summary of the Invention
[0005] This application provides a photovoltaic inverter and its control method, which solves the problem of how to reduce the loss of the photovoltaic inverter and avoid the photovoltaic inverter from operating at reduced capacity after the energy storage device is fully charged.
[0006] To achieve the above objectives, the embodiments of this application adopt the following technical solutions: A first aspect of this application provides a photovoltaic inverter, which includes a controller and a power converter. The input terminal of the power converter is used to connect to photovoltaic modules, and the output terminal of the power converter is used to connect to an AC power grid and / or a load. The power converter includes a DC-AC conversion circuit, the DC terminal of which is the DC bus of the power converter, and the DC bus is used to connect to an energy storage device. The controller is configured to disconnect the energy storage device from the DC bus when the power converter is in grid-connected operation and the state of charge (SOC) of the energy storage device is greater than or equal to a first SOC threshold. The controller is also configured to control the power converter to reduce the voltage of the DC bus to a first preset voltage value after disconnecting the energy storage device from the DC bus.
[0007] Based on this scheme, when the photovoltaic inverter is operating in grid-connected mode and charging the energy storage device, if the SOC of the energy storage device is greater than or equal to a first SOC threshold and the energy storage device is fully charged, the controller disconnects the energy storage device from the DC bus, stops charging the energy storage device, and then controls the DC bus voltage to drop to a first preset voltage value after the energy storage device is disconnected from the DC bus. This avoids the problem of a large voltage difference between the output and input terminals of the DC-DC conversion circuit in the power converter due to the high DC bus voltage after the energy storage device is fully charged. It can reduce the turn-on and turn-off losses of the switching transistors in the DC-DC conversion circuit, and also avoid the photovoltaic inverter triggering voltage derating, thus preventing the photovoltaic inverter from limiting power generation on the input side and reducing the power generation of the photovoltaic energy storage system. Furthermore, if the controller reduces the DC bus voltage to the first preset voltage value before disconnecting the energy storage device from the DC bus, the voltage difference between the DC bus and the energy storage device may be large after the voltage reduction, potentially damaging the components in the photovoltaic inverter or the energy storage device. Therefore, after the energy storage device and the DC bus are disconnected, the controller controls the voltage of the DC bus to be reduced to the first preset voltage value, thereby avoiding damage to the components in the photovoltaic inverter or energy storage device and improving the reliability of the photovoltaic inverter and energy storage device.
[0008] In conjunction with the first aspect, in one embodiment, the controller is specifically used to disconnect the energy storage device from the DC bus when the power converter is in grid-connected operation, the SOC of the energy storage device is greater than or equal to a first SOC threshold, the output power of the power converter is less than or equal to the power at the maximum power point of the photovoltaic module, or when the grid electricity price is at its lowest point, or when the grid electricity price is positive for a first preset time period.
[0009] Based on this scheme, the output power of the aforementioned power converter is the sum of the output power of the photovoltaic module and the output power of the energy storage device. If the output power of the power converter is less than or equal to the power at the maximum power point of the photovoltaic module, it indicates that the output power of the photovoltaic module is sufficient to meet the power demand of the AC grid and / or the load, and there is no need for the energy storage device to discharge power. After the energy storage device is fully charged, if the photovoltaic energy storage system is operating during off-peak hours when the grid electricity price is low, the output power of the photovoltaic module cannot meet the load's electricity demand. In this case, electricity can be purchased from the grid at a lower price to supply the load, without requiring the energy storage device to discharge power. The energy storage device then discharges power during peak hours when the grid electricity price is high, thereby generating economic benefits. After the energy storage device is fully charged, if the controller uses artificial intelligence (AI) photovoltaic technology to predict a negative electricity price in the future, the controller will maintain the connection between the energy storage device and the DC bus during periods of positive grid electricity prices and control the energy storage device to discharge. During periods of negative grid electricity prices, the controller will then purchase electricity from the grid to recharge the energy storage device, thus generating economic benefits. However, if the controller uses AI photovoltaic technology to predict that the grid electricity price will be positive for a first preset time period, discharging the energy storage device first and then purchasing electricity from the grid to recharge it during this first preset time period will result in a loss of economic benefits. Therefore, during the first preset time period, there is no need for the energy storage device to discharge power. Thus, in scenarios where there is no need for the energy storage device to discharge power, the controller can disconnect the energy storage device from the DC bus, improving the power supply reliability of the photovoltaic inverter and the energy storage device, and avoiding economic losses for the photovoltaic energy storage system.
[0010] In conjunction with the first aspect, in one embodiment, the energy storage device includes a DC-DC converter circuit and a battery. One end of the DC-DC converter circuit is connected to the battery, and the other end is used to connect to a DC bus. Specifically, the controller is used to turn off all the switching transistors in the DC-DC converter circuit, thereby disconnecting the energy storage device from the DC bus.
[0011] Based on this scheme, controlling the disconnection between the energy storage device and the DC bus in this way can reduce the control loss of the energy storage device and the conduction and turn-off losses of the switching transistors in the DC-DC conversion circuit.
[0012] In conjunction with the first aspect, in one embodiment, the controller is further configured to, when the power converter is in grid-connected operation, control the power converter to increase the voltage of the DC bus from a first preset voltage value to a second preset voltage value, and after the voltage of the DC bus increases to the second preset voltage value, control the energy storage device to connect to the DC bus, wherein the second preset voltage value is greater than the first preset voltage value.
[0013] Based on this solution, if the controller connects the energy storage device to the DC bus before the DC bus voltage is raised to the second preset voltage value, the voltage difference between the DC bus voltage and the energy storage device voltage may be large, which could damage the components in the photovoltaic inverter or the energy storage device. Therefore, the controller connects the energy storage device to the DC bus only after the DC bus voltage has been raised to the second preset voltage value, thereby avoiding damage to the components in the photovoltaic inverter or the energy storage device and improving the reliability of the photovoltaic inverter and the energy storage device.
[0014] In conjunction with the first aspect, in one embodiment, the controller is specifically configured to, when the power converter is in grid-connected operation, and the output power of the photovoltaic modules is less than the load power, or during peak grid electricity price periods, or after a second preset time period when the grid electricity price is negative, control the power converter to increase the DC bus voltage from a first preset voltage value to a second preset voltage value. After the DC bus voltage increases to the second preset voltage value, the controller controls the energy storage device to connect to the DC bus. The energy storage device is also configured to supply power to the DC bus after being connected to it.
[0015] Based on this solution, if the energy storage device needs to output power together with the photovoltaic module to provide the power required by the AC grid and / or load, or if it is during the peak period of the grid electricity price and the energy storage device needs to discharge to bring economic benefits, or if the controller uses AI photovoltaic technology to predict that a negative electricity price will occur after a second preset time period, the energy storage device needs to be discharged first and then charged during the negative electricity price period to bring economic benefits, the controller controls the connection between the energy storage device and the DC bus. After the energy storage device is connected to the DC bus, it supplies power to the DC bus, thereby meeting the power supply needs of the AC grid and / or load and improving the economic benefits of the photovoltaic energy storage system.
[0016] In conjunction with the first aspect, in one embodiment, the controller is specifically configured to, when the power converter is in grid-connected operation and the SOC of the energy storage device is less than or equal to a second SOC threshold, control the power converter to increase the voltage of the DC bus from a first preset voltage value to a second preset voltage value. After the DC bus voltage increases to the second preset voltage value, the controller controls the energy storage device to connect to the DC bus. After controlling the connection between the energy storage device and the DC bus, the controller controls the power converter to charge the energy storage device.
[0017] Based on this solution, due to the self-discharge effect of energy storage devices, the State of Charge (SOC) of the energy storage device will decrease if it remains in a state of neither charging nor discharging for an extended period, or if it discharges. If the SOC of the energy storage device remains below or equal to the second SOC threshold for a prolonged period, it will be in a low SOC state, leading to irreversible damage and shortening its lifespan. Therefore, when the energy storage device needs charging, the controller connects the energy storage device to the DC bus. After connecting the energy storage device to the DC bus, the controller controls the power converter to charge the energy storage device, thereby ensuring the lifespan of the energy storage device and preventing irreversible damage.
[0018] A second aspect of this application provides a control method for a photovoltaic inverter. The photovoltaic inverter includes a power converter, an input terminal for connecting photovoltaic modules, and an output terminal for connecting an AC power grid and / or a load. The power converter includes a DC-AC conversion circuit, the DC terminal of which is the DC bus of the power converter, and the DC bus is used to connect an energy storage device. The method includes: when the power converter is in grid-connected operation and the state of charge (SOC) of the energy storage device is greater than or equal to a first SOC threshold, controlling the energy storage device to disconnect from the DC bus. After controlling the disconnection of the energy storage device from the DC bus, controlling the power converter to reduce the voltage of the DC bus to a first preset voltage value.
[0019] In conjunction with the second aspect, in one embodiment, controlling the disconnection of the energy storage device from the DC bus when the power converter is in grid-connected operation and the SOC of the energy storage device is greater than or equal to the first SOC threshold includes: controlling the disconnection of the energy storage device from the DC bus when the power converter is in grid-connected operation, the SOC of the energy storage device is greater than or equal to the first SOC threshold, and the output power of the power converter is less than or equal to the power at the maximum power point of the photovoltaic module, or when the grid electricity price is at its lowest point, or when the grid electricity price is positive for a first preset time period.
[0020] In conjunction with the second aspect, in one embodiment, the energy storage device includes a DC-DC converter circuit and a battery. One end of the DC-DC converter circuit is connected to the battery, and the other end of the DC-DC converter circuit is used to connect to a DC bus. The aforementioned control of disconnecting the energy storage device from the DC bus includes: controlling all switches in the DC-DC converter circuit to turn off, thereby controlling the disconnection of the energy storage device from the DC bus.
[0021] In conjunction with the second aspect, in one embodiment, the method further includes: when the power converter is in grid-connected operation, controlling the power converter to increase the voltage of the DC bus from a first preset voltage value to a second preset voltage value; after the voltage of the DC bus increases to the second preset voltage value, controlling the energy storage device to connect to the DC bus, wherein the second preset voltage value is greater than the first preset voltage value.
[0022] In conjunction with the second aspect, in one embodiment, the aforementioned method of controlling the power converter to increase the DC bus voltage from a first preset voltage value to a second preset voltage value when the power converter is in grid-connected operation, and controlling the energy storage device to connect to the DC bus after the DC bus voltage has increased to the second preset voltage value, includes: when the output power of the photovoltaic module is less than the load power, or during peak grid electricity price periods, or after a second preset time period when the grid electricity price is negative, controlling the power converter to increase the DC bus voltage from the first preset voltage value to the second preset voltage value, and controlling the energy storage device to connect to the DC bus after the DC bus voltage has increased to the second preset voltage value. The energy storage device is also used to supply power to the DC bus after being connected to the DC bus.
[0023] In conjunction with the second aspect, in one embodiment, the aforementioned method of controlling the power converter to increase the DC bus voltage from a first preset voltage value to a second preset voltage value when the power converter is in grid-connected operation, and controlling the energy storage device to connect to the DC bus after the DC bus voltage has increased to the second preset voltage value, includes: when the power converter is in grid-connected operation, if the SOC of the energy storage device is less than or equal to a second SOC threshold, controlling the power converter to increase the DC bus voltage from the first preset voltage value to the second preset voltage value; and controlling the energy storage device to connect to the DC bus after the DC bus voltage has increased to the second preset voltage value. After controlling the energy storage device to connect to the DC bus, controlling the power converter to charge the energy storage device.
[0024] A third aspect of this application provides a photovoltaic energy storage system, which includes a photovoltaic inverter and an energy storage device. The photovoltaic inverter includes a photovoltaic input terminal, a battery terminal, and an AC terminal. The photovoltaic input terminal is used to connect to photovoltaic modules, the battery terminal is connected to the energy storage device, and the AC terminal is used to connect to the power grid and a load. The photovoltaic inverter is used to perform power conversion on the electrical energy provided by the photovoltaic modules and / or the power grid to charge the energy storage device, or to perform power conversion on the electrical energy provided by the energy storage device to provide electrical energy to the power grid and / or the load. The photovoltaic inverter is the photovoltaic inverter described in the first aspect or any embodiment of the first aspect.
[0025] The descriptions of the second and third aspects in this application can be referenced to the detailed description of the first aspect; and the beneficial effects of the second and third aspects can be referenced to the analysis of the beneficial effects of the first aspect, which will not be repeated here. Attached Figure Description
[0026] Figure 1 A circuit topology diagram of a photovoltaic energy storage system provided in this application embodiment; Figure 2 An interaction flowchart of a photovoltaic inverter and an energy storage device is provided as an embodiment of this application; Figure 3 A flowchart illustrating a control method for a photovoltaic inverter provided in this application embodiment; Figure 4 A flowchart illustrating another control method for a photovoltaic inverter provided in this application embodiment. Detailed Implementation
[0027] The following sections will discuss the fabrication and use of various embodiments in detail. However, it should be understood that many applicable inventive concepts provided in this application can be implemented in a variety of specific environments. The specific embodiments discussed are merely illustrative of specific ways of implementing and using this description and technology, and do not limit the scope of this application.
[0028] Unless otherwise defined, all technical terms used herein have the same meaning as commonly known to one of ordinary skill in the art.
[0029] Each circuit or other component may be described or referred to as "for" performing one or more tasks. In this context, "for" is used to imply a structure by indicating that the circuit / component includes a structure (e.g., a circuit system) that performs one or more tasks during operation. Therefore, even when the specified circuit / component is currently inoperable (e.g., not turned on), it can still be referred to as "for performing that task." Circuits / components used with the term "for" include hardware, such as circuits that perform operations.
[0030] The technical solutions in the embodiments of this application will be described below with reference to the accompanying drawings. In this application, "and / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone, where A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects have an "or" relationship. Furthermore, in the embodiments of this application, the words "first," "second," etc., do not limit the quantity or order.
[0031] In this application, the terms "exemplary" or "for example" are used to indicate that something is an example, illustration, or illustration. Any embodiment or design described as "exemplary" or "for example" in this application should not be construed as being more preferred or advantageous than other embodiments or designs. Specifically, the use of the terms "exemplary" or "for example" is intended to present the relevant concepts in a specific manner.
[0032] Before introducing the embodiments of this application, the background technology involved in this application will be introduced first.
[0033] like Figure 1 The diagram shown is a circuit topology schematic of a photovoltaic energy storage system 100 provided in an embodiment of this application. The photovoltaic energy storage system 100 includes a photovoltaic inverter 110 and an energy storage device 120.
[0034] Reference Figure 1 The photovoltaic inverter 110 includes a power converter 111. The input terminal of the power converter 111 is used to connect to the photovoltaic module 200, and the output terminal of the power converter 111 is used to connect to the AC grid 300 and / or the load 400. The power converter 111 includes a DC-AC conversion circuit 1111. The DC terminal of the DC-AC conversion circuit 1111 is the DC bus BUS of the power converter 111. The DC bus BUS is used to connect to the energy storage device 120.
[0035] In one implementation, reference Figure 1 The power converter 111 also includes a first DC-DC converter circuit 1112. The input terminal of the first DC-DC converter circuit 1112 is used to connect to the photovoltaic module 200, and the output terminal of the first DC-DC converter circuit 1112 is connected to the DC bus BUS. The input terminal of the first DC-DC converter circuit 1112 is the photovoltaic input terminal of the photovoltaic inverter 110. The DC bus BUS is connected to the energy storage device 120 through the battery terminal of the photovoltaic inverter 110, and the AC terminal of the DC-AC converter circuit 1111 is the AC terminal of the photovoltaic inverter 110.
[0036] The first DC-DC converter circuit 1112 is used for maximum power point tracking of the photovoltaic module 200, and also for voltage conversion of the DC power provided by the photovoltaic module 200 to provide DC power to the DC bus BUS, and to charge the energy storage device 120 through the DC bus BUS. The DC-AC converter circuit 1111 is used for power conversion of the DC power provided by the DC bus BUS to provide power to the AC grid 300 and / or the load 400, and also for rectification of the AC power provided by the AC grid 300 to provide DC power to the DC bus BUS, and to charge the energy storage device 120 through the DC bus BUS.
[0037] However, during the process of the first DC-DC converter circuit 1112 converting the DC power supplied by the photovoltaic module 200 and charging the energy storage device 120 via the DC bus, if the output voltage of the photovoltaic module 200 is low, and the energy storage device 120 is fully charged, the photovoltaic module 200 will continuously output power, causing a significant rise in the voltage of the DC bus. This results in a large voltage difference between the output and input terminals of the first DC-DC converter circuit 1112, increasing the turn-on and turn-off losses of the switching transistors in the first DC-DC converter circuit 1112. Simultaneously, due to the high voltage of the DC bus, the photovoltaic inverter 110 is prone to triggering voltage derating, leading to input-side power limitation on the photovoltaic inverter 110 and reducing the power generation of the photovoltaic energy storage system 100. Therefore, how to reduce the losses of the photovoltaic inverter 110 and avoid derating operation after the energy storage device 120 is fully charged becomes an urgent problem to be solved.
[0038] Based on this, this application provides a photovoltaic inverter. In the process of converting the DC power provided by the photovoltaic module to charge the energy storage device, after the energy storage device is fully charged, the connection between the energy storage device and the DC bus is disconnected and the voltage of the DC bus is reduced, thereby reducing the loss of the photovoltaic inverter and avoiding derating operation of the photovoltaic inverter.
[0039] In one embodiment, the circuit topology of the photovoltaic inverter provided in this application can be as described above. Figure 1 The circuit topology of the photovoltaic inverter 110 shown is described below. The following embodiments of this application use the circuit topology of the photovoltaic inverter 110 as an example to introduce the photovoltaic inverter provided in the embodiments of this application. All the relevant descriptions of the photovoltaic inverter 110 above can be referenced in the photovoltaic inverter provided in the embodiments of this application, and will not be repeated here.
[0040] Continue to refer to Figure 1 The photovoltaic inverter 110 also includes a controller 112. The controller 112 is used to control the power converter 111 to charge the energy storage device 120 when the power converter 111 is in grid-connected operation. When the state of charge (SOC) of the energy storage device 120 is greater than or equal to a first SOC threshold, satisfying the blocking condition of the energy storage device 120, the controller 112 controls the energy storage device 120 to disconnect from the DC bus BUS. The controller 112 is also used to control the power converter 111 to reduce the voltage of the DC bus BUS to a first preset voltage value after disconnecting the energy storage device 120 from the DC bus BUS.
[0041] The power converter 111 charging the energy storage device 120 includes: a first DC-DC converter circuit 1112 performing voltage conversion on the DC power provided by the photovoltaic module 200 to charge the energy storage device 120, or a DC-AC converter circuit 1111 rectifying the AC power provided by the AC grid 300 to charge the energy storage device 120.
[0042] If the State of Charge (SOC) of the energy storage device 120 is greater than or equal to the first SOC threshold, it indicates that the energy storage device 120 is fully charged. In this embodiment, the specific value of the first SOC threshold is not limited; for example, the first SOC threshold can be 95%. The SOC of the energy storage device 120 is the ratio of its current remaining capacity to its rated capacity.
[0043] The first preset voltage value is greater than or equal to the peak voltage of the AC power grid 300. In this embodiment of the application, the specific value of the first preset voltage value is not limited.
[0044] In one embodiment, the controller 112 is specifically used to control the first DC-DC converter circuit 1112 or the DC-AC converter circuit 1111 to reduce the voltage of the DC bus BUS to a first preset voltage value. This application embodiment does not limit this.
[0045] In one embodiment, the controller 112 is specifically used to disconnect the energy storage device 120 from the DC bus when the power converter 111 is in grid-connected operation, the SOC of the energy storage device 120 is greater than or equal to a first SOC threshold, the output power of the power converter 111 is less than or equal to the power at the maximum power point of the photovoltaic module 200, or the grid electricity price is in a low period, or the grid electricity price is positive for a first preset period of time, etc., and the blocking conditions of the energy storage device 120 are met.
[0046] The aforementioned off-peak period for municipal electricity prices refers to the period during which the AC power grid has the lowest load, the most abundant power supply, and the lowest electricity price under the time-of-use pricing mechanism.
[0047] The aforementioned first preset time period is related to the characteristics of new energy output periods and the fluctuation patterns of power load in various countries or regions. This application embodiment does not limit the specific value of the first preset time period.
[0048] The output power of the aforementioned power converter 111 is the sum of the output power of the photovoltaic module 200 and the output power of the energy storage device 120. The output power of the power converter 111 is less than or equal to the power at the maximum power point of the photovoltaic module 200, indicating that the output power of the photovoltaic module 200 is sufficient to meet the power demands of the AC grid 300 and / or the load 400, eliminating the need for the energy storage device 120 to discharge power. After the energy storage device 120 is fully charged, if the photovoltaic energy storage system 100 is operating during off-peak hours of the grid electricity price, and the output power of the photovoltaic module 200 cannot meet the electricity demand of the load 400, then electricity can be purchased from the grid at a lower price to supply power to the load 400, without requiring the energy storage device 120 to discharge power. The energy storage device 120 then discharges power during peak hours of the grid electricity price, thereby generating economic benefits. After the energy storage device 120 is fully charged, if the controller 112 uses AI photovoltaic technology to predict that the grid electricity price will be negative in the future, the controller 112 will first control the energy storage device 120 to maintain connection with the DC bus BUS during periods when the grid electricity price is positive, and control the energy storage device 120 to discharge. During periods when the grid electricity price is negative, the controller will then purchase electricity from the grid to recharge the energy storage device 120, thereby generating economic benefits. However, if the controller 112 uses AI photovoltaic technology to predict that the grid electricity price will be positive throughout the first preset time period, the energy storage device 120 will first discharge during the first preset time period, and then the controller will purchase electricity from the grid to recharge the energy storage device 120, resulting in a loss of economic benefits. Therefore, the energy storage device 120 does not need to discharge or output power during the first preset time period. Therefore, in scenarios where the energy storage device 120 does not require discharge output power, the controller 112 controls the energy storage device 120 to disconnect from the DC bus, which can improve the power supply reliability of the photovoltaic inverter 110 and the energy storage device 120, and avoid economic loss of the photovoltaic energy storage system 100.
[0049] The aforementioned peak period for municipal electricity prices refers to the period during which the AC power grid has the highest load, the highest power supply cost, and the highest electricity price under the time-of-use pricing mechanism.
[0050] In one implementation, continue to refer to Figure 1 The energy storage device 120 includes a second DC-DC converter circuit 121 and a battery 122. One end of the second DC-DC converter circuit 121 is connected to the battery 122, and the other end is used to connect to the DC bus BUS. The controller 112 is used to control the disconnection of the energy storage device 120 from the DC bus BUS, specifically controlling the switching transistors in the second DC-DC converter circuit 121 to turn off, thereby controlling the disconnection of the energy storage device 120 from the DC bus BUS.
[0051] In specific implementation, such as Figure 2The diagram shown is an interaction flowchart between a photovoltaic inverter 110 and an energy storage device 120 according to an embodiment of this application. (Refer to...) Figure 2 The controller 112 in the photovoltaic inverter 110 is used to send a lockout control command to the energy storage device 120 when the lockout conditions of the energy storage device 120 are met. The controller in the energy storage device 120 ( Figure 1 (Not shown) is used to execute a blocking action according to the blocking control command, stopping the transmission of waves to the switching transistors in the second DC-DC converter circuit 121, and controlling all the switching transistors in the second DC-DC converter circuit 121 to turn off, so as to disconnect the energy storage device 120 from the DC bus BUS, thereby reducing the control loss of the energy storage device 120 and the conduction and turn-off losses of the switching transistors in the second DC-DC converter circuit 121. The controller in the energy storage device 120 is also used to report to the controller 112 after the transmission of waves stops that the blocking of the energy storage device 120 has been completed and the energy storage device 120 and the DC bus BUS have been disconnected. The controller 112 then controls the first DC-DC converter circuit 1112 or the DC-AC converter circuit 1111 to reduce the voltage of the DC bus BUS to a first preset voltage value.
[0052] In one embodiment, the solution provided in this application can also be applied to a device that includes a DC-DC conversion circuit 1111 and needs to charge an energy storage device 120, such as a power conversion system (PCS). This application does not limit this application.
[0053] The photovoltaic inverter 110 provided in this embodiment, when operating in grid-connected mode and charging the energy storage device 120, if the SOC of the energy storage device 120 is greater than or equal to a first SOC threshold and the energy storage device 120 is fully charged, the controller 112 controls the energy storage device 120 to disconnect from the DC bus BUS, stopping charging the energy storage device 120. After the energy storage device 120 is disconnected from the DC bus BUS, the controller controls the voltage of the DC bus BUS to decrease to a first preset voltage value. This avoids the problem of a large voltage difference between the output and input terminals of the first DC-DC conversion circuit 1112 in the power converter 111 due to the high voltage of the DC bus BUS after the energy storage device 120 is fully charged. It can reduce the conduction and turn-off losses of the switching transistors in the first DC-DC conversion circuit 1112, and at the same time, it can avoid the photovoltaic inverter 110 triggering voltage derating, avoiding the input-side power limitation of the photovoltaic inverter 110 and reducing the power generation of the photovoltaic energy storage system 100. Furthermore, if the controller 112 reduces the voltage of the DC bus to a first preset voltage value before disconnecting the energy storage device 120 from the DC bus, the voltage difference between the DC bus and the energy storage device 120 may be too large, potentially damaging the components in the photovoltaic inverter 110 or the energy storage device 120. Therefore, the controller 112 reduces the voltage of the DC bus to the first preset voltage value only after disconnecting the energy storage device 120 from the DC bus, thus avoiding damage to the components in the photovoltaic inverter 110 or the energy storage device 120 and improving the reliability of both.
[0054] In one implementation, continue to refer to Figure 1 The controller 112 is also used to control the power converter 111 to increase the voltage of the DC bus BUS from a first preset voltage value to a second preset voltage value when the power converter 111 is in grid-connected operation. After the voltage of the DC bus BUS is increased to the second preset voltage value, the controller controls the energy storage device 120 to connect to the DC bus BUS. The second preset voltage value is greater than the first preset voltage value.
[0055] In one embodiment, the controller 112 is specifically used to control the first DC-DC conversion circuit 1112 or the DC-AC conversion circuit 1111 to increase the voltage of the DC bus BUS from a first preset voltage value to a second preset voltage value. This application embodiment does not limit this.
[0056] The second preset voltage value is less than or equal to the withstand voltage value of the switching transistor in the first DC-DC converter circuit 1112 or DC-AC converter circuit 1111. This application embodiment does not limit the specific value of the second preset voltage value.
[0057] In one embodiment, the controller 112 is specifically used to supply power to the load 400 when the power converter 111 switches from grid-connected operation to off-grid operation; or, when the power converter 111 is in grid-connected operation, if the output power of the photovoltaic module 200 is less than the power of the load 400, or if it is during a peak period of the mains electricity price, or if the mains electricity price is negative after a second preset period, and the unlocking conditions of the energy storage device 120 are met, the controller 112 controls the power converter 111 to increase the voltage of the DC bus BUS from a first preset voltage value to a second preset voltage value. After the voltage of the DC bus BUS increases to the second preset voltage value, the controller controls the energy storage device 120 to connect to the DC bus BUS. The energy storage device 120 is also used to supply power to the DC bus BUS after connecting to it.
[0058] If the energy storage device 120 needs to output power together with the photovoltaic module 200 to provide the power required by the AC grid 300 and / or load 400, or if it is during the peak period of the grid electricity price and the energy storage device 120 needs to discharge to bring economic benefits, or if the controller 112 uses AI photovoltaic technology to predict that a negative electricity price will occur after a second preset time period, and the energy storage device 120 needs to be discharged first and then charged during the negative electricity price to bring economic benefits, the controller 112 controls the connection between the energy storage device 120 and the DC bus BUS. After the energy storage device BUS is connected to the DC bus BUS, it supplies power to the DC bus BUS, thereby meeting the power supply needs of the AC grid 300 and / or load 400 and improving the economic benefits of the photovoltaic energy storage system 100.
[0059] In one embodiment, the controller 112 is specifically used to control the power converter 111 to increase the voltage of the DC bus BUS from a first preset voltage value to a second preset voltage value when the SOC of the energy storage device 120 is less than or equal to a second SOC threshold, thus satisfying the unlocking condition of the energy storage device 120, when the power converter 111 is in grid-connected operation, and after the voltage of the DC bus BUS has increased to the second preset voltage value, control the energy storage device 120 to connect to the DC bus BUS, and after controlling the energy storage device 120 to connect to the DC bus BUS, control the power converter 111 to charge the energy storage device 120.
[0060] Due to the self-discharge effect of the energy storage device 120, if the energy storage device 120 remains in a state of neither charging nor discharging for an extended period, or if the energy storage device 120 discharges, its State of Charge (SOC) will decrease. If the SOC of the energy storage device 120 remains below or equal to the second SOC threshold for an extended period, resulting in a low SOC state, irreversible damage will occur, shortening its lifespan. Therefore, when the energy storage device 120 requires charging, the controller 112 controls the connection between the energy storage device 120 and the DC bus. After connecting the energy storage device 120 to the DC bus, the controller 112 controls the power converter 111 to charge the energy storage device 120, thereby ensuring the lifespan of the energy storage device 120 and preventing irreversible damage.
[0061] In one implementation, continue to refer to Figure 2 In specific implementation, controller 112, when the unlocking conditions of the energy storage device 120 are met, controls power converter 111 to increase the voltage of DC bus BUS from a first preset voltage value to a second preset voltage value. After the DC bus BUS voltage increases to the second preset voltage value, controller 112 sends an unlocking control command to energy storage device 120. The controller in energy storage device 120 performs unlocking condition judgment according to the unlocking control command, detects the DC bus BUS voltage, and if the DC bus BUS voltage is greater than or equal to the minimum charging voltage of energy storage device 120, and the duration is greater than or equal to a preset time threshold, then performs the unlocking action, resumes sending waves to the switching transistor in the second DC-DC converter circuit 121, controls the second DC-DC converter circuit 121 to perform voltage conversion on the DC power supplied by battery 122 to supply DC power to DC bus BUS, and reports to controller 112 that the unlocking of energy storage device 120 has been completed. Afterwards, energy storage device 120 discharges normally.
[0062] In the photovoltaic inverter 110 provided in this application embodiment, if the controller 112 controls the energy storage device 120 to connect to the DC bus BUS before the controller 112 controls the DC bus BUS voltage to rise to the second preset voltage value, the voltage difference between the DC bus BUS voltage and the energy storage device 120 voltage may be large, which will damage the components in the photovoltaic inverter 110 or the energy storage device 120. Therefore, the controller 112 controls the energy storage device 120 to connect to the DC bus BUS only after the DC bus BUS voltage has risen to the second preset voltage value, thereby avoiding damage to the components in the photovoltaic inverter 110 or the energy storage device 120 and improving the reliability of the photovoltaic inverter 110 and the energy storage device 120.
[0063] like Figure 3The diagram shows a control method for a photovoltaic inverter 110 provided in an embodiment of this application. The method is applied to the photovoltaic inverter 110 and includes steps S301-S302.
[0064] S301, when the power converter 111 is in grid-connected operation, the controller 112 controls the power converter 111 to charge the energy storage device 120. When the SOC of the energy storage device 120 is greater than or equal to the first SOC threshold, the controller controls the energy storage device 120 to disconnect from the DC bus BUS.
[0065] If the SOC of the energy storage device 120 is greater than or equal to the first SOC threshold, the controller 112 can determine that the energy storage device 120 is fully charged.
[0066] In one embodiment, the controller 112 is specifically used to disconnect the energy storage device 120 from the DC bus when the power converter 111 is in grid-connected operation, the SOC of the energy storage device 120 is greater than or equal to a first SOC threshold, the output power of the power converter 111 is less than or equal to the power at the maximum power point of the photovoltaic module 200, or the grid electricity price is in a low period, or the grid electricity price is positive for a first preset period of time, etc., and the blocking conditions of the energy storage device 120 are met.
[0067] In one implementation, reference Figure 1 The energy storage device 120 includes a second DC-DC converter circuit 121 and a battery 122. One end of the second DC-DC converter circuit 121 is connected to the battery 122, and the other end of the second DC-DC converter circuit 121 is used to connect to the DC bus BUS. The controller 112 controls the energy storage device 120 to disconnect from the DC bus BUS, including: the controller 112 controls all the switching transistors in the second DC-DC converter circuit 121 to turn off, so as to control the energy storage device 120 to disconnect from the DC bus BUS.
[0068] In one implementation, reference Figure 3 If the conditions in step S301 are not met, the controller 112 can continuously detect whether the conditions are met.
[0069] S302, after the controller 112 disconnects the energy storage device 120 from the DC bus BUS, it controls the power converter 111 to reduce the voltage of the DC bus BUS to a first preset voltage value.
[0070] The control method for the photovoltaic inverter 110 provided in this application embodiment, when the photovoltaic inverter 110 is operating in grid-connected mode and charging the energy storage device 120, if the SOC of the energy storage device 120 is greater than or equal to a first SOC threshold and the energy storage device 120 is fully charged, the controller 112 controls the energy storage device 120 to disconnect from the DC bus BUS, stops charging the energy storage device 120, and after the energy storage device 120 is disconnected from the DC bus BUS, controls the voltage of the DC bus BUS to decrease to a first preset voltage value. This avoids the problem of a large voltage difference between the output and input terminals of the first DC-DC conversion circuit 1112 in the power converter 111 due to the high voltage of the DC bus BUS after the energy storage device 120 is fully charged. It also reduces the turn-on and turn-off losses of the switching transistors in the first DC-DC conversion circuit 1112, and prevents the photovoltaic inverter 110 from triggering voltage derating, thus avoiding input-side power limiting of the photovoltaic inverter 110 and reducing the power generation of the photovoltaic energy storage system 100. Furthermore, if the controller 112 reduces the voltage of the DC bus to a first preset voltage value before disconnecting the energy storage device 120 from the DC bus, the voltage difference between the DC bus and the energy storage device 120 may be too large, potentially damaging the components in the photovoltaic inverter 110 or the energy storage device 120. Therefore, the controller 112 reduces the voltage of the DC bus to the first preset voltage value only after disconnecting the energy storage device 120 from the DC bus, thus avoiding damage to the components in the photovoltaic inverter 110 or the energy storage device 120 and improving the reliability of both.
[0071] In one implementation, such as Figure 4 The diagram shows a control method for another photovoltaic inverter 110 provided in an embodiment of this application. The method further includes step S303, which is performed after step S302.
[0072] S303, when the power converter 111 is in grid-connected operation, the controller 112 controls the power converter 111 to increase the voltage of the DC bus BUS from a first preset voltage value to a second preset voltage value. After the voltage of the DC bus BUS increases to the second preset voltage value, the controller controls the energy storage device 120 to connect to the DC bus BUS. The second preset voltage value is greater than the first preset voltage value.
[0073] In one embodiment, the controller 112 is specifically used to supply power to the load 400 when the power converter 111 switches from grid-connected operation to off-grid operation; or, when the power converter 111 is in grid-connected operation, if the output power of the photovoltaic module 200 is less than the power of the load 400, or if it is during a peak period of the mains electricity price, or if the mains electricity price is negative after a second preset period, and the unlocking conditions of the energy storage device 120 are met, the controller 112 controls the power converter 111 to increase the voltage of the DC bus BUS from a first preset voltage value to a second preset voltage value. After the voltage of the DC bus BUS increases to the second preset voltage value, the controller controls the energy storage device 120 to connect to the DC bus BUS. The energy storage device 120 is also used to supply power to the DC bus BUS after connecting to it.
[0074] In one embodiment, the controller 112 is specifically used to control the power converter 111 to increase the voltage of the DC bus BUS from a first preset voltage value to a second preset voltage value when the SOC of the energy storage device 120 is less than or equal to a second SOC threshold, thus satisfying the unlocking condition of the energy storage device 120, when the power converter 111 is in grid-connected operation, and after the voltage of the DC bus BUS has increased to the second preset voltage value, control the energy storage device 120 to connect to the DC bus BUS, and after controlling the energy storage device 120 to connect to the DC bus BUS, control the power converter 111 to charge the energy storage device 120.
[0075] In one implementation, reference Figure 4 If the conditions in step S303 are not met, the controller 112 can continuously detect whether the conditions are met.
[0076] The control method for the photovoltaic inverter 110 provided in this application embodiment addresses the issue that if the controller 112 controls the connection between the energy storage device 120 and the DC bus BUS before the controller 112 controls the DC bus BUS voltage to rise to the second preset voltage value, the voltage difference between the DC bus BUS voltage and the energy storage device 120 may be large, potentially damaging the components in the photovoltaic inverter 110 or the energy storage device 120. Therefore, the controller 112 controls the connection between the energy storage device 120 and the DC bus BUS only after the DC bus BUS voltage has risen to the second preset voltage value, thereby avoiding damage to the components in the photovoltaic inverter 110 or the energy storage device 120 and improving the reliability of the photovoltaic inverter 110 and the energy storage device 120.
[0077] Based on this, refer to Figure 1This application also provides a photovoltaic energy storage system 100, which includes a photovoltaic inverter 110 and an energy storage device 120. The photovoltaic inverter 110 includes a photovoltaic input terminal, a battery terminal, and an AC terminal. The photovoltaic input terminal is used to connect to a photovoltaic module 200, the battery terminal is connected to the energy storage device 120, and the AC terminal is used to connect to an AC power grid 300 and a load 400. The photovoltaic inverter 110 is used to perform power conversion on the electrical energy provided by the photovoltaic module 200 and / or the AC power grid 300 to charge the energy storage device 120, or to perform power conversion on the electrical energy provided by the energy storage device 120 to provide electrical energy to the AC power grid 300 and / or the load 400. The photovoltaic inverter 110 is the photovoltaic inverter 110 described in the above embodiments of this application.
[0078] In one embodiment, the energy storage device 120 is the energy storage device 120 as described in the above embodiments of this application.
[0079] The above detailed description of the photovoltaic inverter 110 and the analysis of its beneficial effects can be applied to the control method of the photovoltaic inverter 110 and the photovoltaic energy storage system 100, and will not be repeated here in the embodiments of this application.
[0080] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.
Claims
1. A photovoltaic inverter, characterized in that, The photovoltaic inverter includes a controller and a power converter; The input terminal of the power converter is used to connect to photovoltaic modules, and the output terminal of the power converter is used to connect to the AC grid and / or load. The power converter includes a DC-AC conversion circuit, and the DC terminal of the DC-AC conversion circuit is the DC bus of the power converter. The DC bus is used to connect to energy storage devices. The controller is configured to disconnect the energy storage device from the DC bus when the power converter is in grid-connected operation and the SOC of the energy storage device is greater than or equal to a first SOC threshold. The controller is further configured to, after controlling the energy storage device and the DC bus to disconnect, control the power converter to reduce the voltage of the DC bus to a first preset voltage value.
2. The photovoltaic inverter according to claim 1, characterized in that, The controller is specifically configured to disconnect the energy storage device from the DC bus when the power converter is in grid-connected operation, the SOC of the energy storage device is greater than or equal to a first SOC threshold, the output power of the power converter is less than or equal to the power at the maximum power point of the photovoltaic module, or when the grid electricity price is at its lowest point, or when the grid electricity price is positive for a first preset time period.
3. The photovoltaic inverter according to claim 1 or 2, characterized in that, The energy storage device includes a DC-DC converter circuit and a battery. One end of the DC-DC converter circuit is connected to the battery, and the other end of the DC-DC converter circuit is used to connect to the DC bus. The controller is specifically used to turn off all the switching transistors in the DC-DC converter circuit, so as to disconnect the energy storage device from the DC bus.
4. The photovoltaic inverter according to any one of claims 1-3, characterized in that, The controller is also configured to, when the power converter is in grid-connected operation, control the power converter to increase the voltage of the DC bus from the first preset voltage value to the second preset voltage value, and after the voltage of the DC bus increases to the second preset voltage value, control the energy storage device to connect to the DC bus; The second preset voltage value is greater than the first preset voltage value.
5. The photovoltaic inverter according to claim 4, characterized in that, The controller is specifically configured to, when the power converter is in grid-connected operation, and the output power of the photovoltaic module is less than the load power, or during the peak period of the mains electricity price, or after the second preset period when the mains electricity price is negative, control the power converter to increase the voltage of the DC bus from the first preset voltage value to the second preset voltage value, and after the voltage of the DC bus increases to the second preset voltage value, control the energy storage device to connect to the DC bus; The energy storage device is also used to supply power to the DC bus after being connected to the DC bus.
6. The photovoltaic inverter according to claim 4 or 5, characterized in that, The controller is specifically configured to, when the power converter is in grid-connected operation and the SOC of the energy storage device is less than or equal to a second SOC threshold, control the power converter to increase the voltage of the DC bus from the first preset voltage value to the second preset voltage value, and after the voltage of the DC bus increases to the second preset voltage value, control the energy storage device to connect to the DC bus. After the controller connects the energy storage device to the DC bus, it controls the power converter to charge the energy storage device.
7. A control method for a photovoltaic inverter, characterized in that, The photovoltaic inverter includes a power converter; The input terminal of the power converter is used to connect to photovoltaic modules, and the output terminal of the power converter is used to connect to the AC grid and / or load. The power converter includes a DC-AC conversion circuit, the DC terminal of which is the DC bus of the power converter, and the DC bus is used to connect to an energy storage device. The method includes: When the power converter is in grid-connected operation and the SOC of the energy storage device is greater than or equal to the first SOC threshold, the energy storage device is controlled to disconnect from the DC bus. After the energy storage device and the DC bus are disconnected, the power converter is controlled to reduce the voltage of the DC bus to a first preset voltage value.
8. The control method according to claim 7, characterized in that, The step of controlling the disconnection of the energy storage device from the DC bus when the power converter is in grid-connected operation and the SOC of the energy storage device is greater than or equal to a first SOC threshold includes: When the power converter is in grid-connected operation, and the SOC of the energy storage device is greater than or equal to the first SOC threshold, and the output power of the power converter is less than or equal to the power at the maximum power point of the photovoltaic module, or when the grid electricity price is at its lowest point, or when the grid electricity price is positive for a first preset time period, the energy storage device and the DC bus are disconnected.
9. The control method according to claim 7 or 8, characterized in that, The energy storage device includes a DC-DC converter circuit and a battery. One end of the DC-DC converter circuit is connected to the battery, and the other end of the DC-DC converter circuit is used to connect to the DC bus. Controlling the disconnection of the energy storage device from the DC bus includes: The switching transistors in the DC-DC converter circuit are all turned off to disconnect the energy storage device from the DC bus.
10. The control method according to any one of claims 7-9, characterized in that, The method further includes: When the power converter is in grid-connected operation, the power converter is controlled to increase the voltage of the DC bus from the first preset voltage value to the second preset voltage value. After the voltage of the DC bus is increased to the second preset voltage value, the energy storage device is controlled to connect to the DC bus. The second preset voltage value is greater than the first preset voltage value.
11. The control method according to claim 10, characterized in that, The step of controlling the power converter to increase the voltage of the DC bus from a first preset voltage value to a second preset voltage value when the power converter is in grid-connected operation includes: When the power converter is in grid-connected operation, if the output power of the photovoltaic module is less than the load power, or if it is during the peak period of the mains electricity price, or if the mains electricity price is negative after the second preset period, the power converter is controlled to increase the voltage of the DC bus from the first preset voltage value to the second preset voltage value. After the voltage of the DC bus is increased to the second preset voltage value, the energy storage device is controlled to connect to the DC bus. The energy storage device is also used to supply power to the DC bus after being connected to the DC bus.
12. The control method according to claim 10 or 11, characterized in that, The step of controlling the power converter to increase the voltage of the DC bus from a first preset voltage value to a second preset voltage value when the power converter is in grid-connected operation includes: When the power converter is in grid-connected operation, if the SOC of the energy storage device is less than or equal to the second SOC threshold, the power converter is controlled to increase the voltage of the DC bus from the first preset voltage value to the second preset voltage value. After the voltage of the DC bus is increased to the second preset voltage value, the energy storage device is controlled to connect to the DC bus. After controlling the connection between the energy storage device and the DC bus, the power converter is controlled to charge the energy storage device.
13. A photovoltaic energy storage system, characterized in that, The photovoltaic energy storage system includes a photovoltaic inverter and an energy storage device. The photovoltaic inverter includes a photovoltaic input terminal, a battery terminal, and an AC terminal. The photovoltaic input terminal is used to connect to the photovoltaic module, the battery terminal is connected to the energy storage device, and the AC terminal is used to connect to the power grid and the load. The photovoltaic inverter is used to perform power conversion on the power supplied by the photovoltaic module and / or the power grid to charge the energy storage device, or to perform power conversion on the power supplied by the energy storage device to provide power to the power grid and / or the load. The photovoltaic inverter is the photovoltaic inverter as described in any one of claims 1-6.