A power conversion system and control method
By identifying the power capacity of the energy storage battery and dynamically adjusting the DC bus voltage, the loss and stress problems during high-voltage power grid crossings are solved, achieving the effect of reducing the loss and stress of switching devices in the photovoltaic-energy storage system.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- SUNGROW (SHANGHAI) CO LTD
- Filing Date
- 2026-03-25
- Publication Date
- 2026-06-16
AI Technical Summary
In photovoltaic-storage systems, during high-voltage power grid ride-through, the rise in bus voltage leads to increased losses and switching stress in power switching devices. Existing technologies struggle to reduce losses and stress while ensuring high-voltage power grid ride-through.
By identifying the power capacity of the energy storage battery, the DC bus voltage is dynamically adjusted. Utilizing the current-limiting capability of the energy storage system, the DC bus voltage is controlled to different voltage levels under different conditions, thus avoiding overcurrent and reducing losses in switching devices.
While ensuring high-voltage power grid ride-through, it reduces the losses and switching stress of power switching devices, thereby improving the reliability of the power converter.
Smart Images
Figure CN122225508A_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of power electronics technology, specifically to a power conversion system and control method. Background Technology
[0002] A photovoltaic-storage system, also known as a solar photovoltaic energy storage power generation system, includes a photovoltaic power generation system and an energy storage system. The photovoltaic-storage system can use photovoltaic modules to convert solar energy into electrical energy, and then use energy storage devices (usually energy storage batteries) to store the electrical energy and release it when needed.
[0003] The power converter in a photovoltaic-storage system can not only generate electricity by connecting to the grid, but also has the ability to operate independently with a load when the grid is abnormal. When a high-voltage ride occurs in the grid, in order to resist the energy impact of the excessively high grid voltage, it is necessary to increase the bus voltage of the power converter. However, the increase in bus voltage will lead to increased losses of power switching devices and increased switching stress. Summary of the Invention
[0004] In view of this, this application provides a power conversion system and control method that can reduce the losses of power switching devices and reduce switching stress while ensuring high-voltage power grid crossing and avoiding overcurrent.
[0005] In a first aspect, this application provides a power conversion system, the power converter including: a DC bus, a controller, and a power conversion circuit; the DC side of the power conversion circuit is connected to the DC bus, and the AC side of the power conversion circuit is connected to the power grid; the DC bus is coupled to an energy storage system, the energy storage system including an energy storage battery; the controller is configured to determine the power capability of the energy storage battery based on the state information of the energy storage battery, and when the power capability of the energy storage battery is less than or equal to the power capability of the power conversion circuit, control the voltage of the DC bus to a first voltage; when the power capability of the energy storage battery is greater than the power capability of the power conversion circuit, control the voltage of the DC bus to a second voltage, the first voltage being less than the second voltage.
[0006] In this implementation, the power converter can dynamically adjust the DC bus voltage based on the power capability of the power conversion circuit and the power capability of the energy storage battery. Specifically, when the power capability of the energy storage battery is less than or equal to the power capability of the power conversion circuit, the DC bus voltage is controlled to a lower first voltage. When the power conversion circuit operates at a lower first voltage on the DC bus, it can reduce the losses of the power switching devices and reduce switching stress. When a high-voltage ride-through occurs, after the grid energy is transferred to the DC bus, because the power capability of the energy storage battery is lower at this time, the energy storage system will limit the current of the DC bus to not exceed the current that the energy storage battery can withstand to protect the energy storage battery and ensure that the power conversion circuit does not experience overcurrent. Once the DC bus voltage rises to a level greater than the voltage at which the grid high-voltage ride-through occurred, the grid energy can no longer be transferred to the DC bus, ensuring that the power converter can successfully complete the high-voltage ride-through. When the power capacity of the energy storage battery is greater than the power capacity of the power conversion circuit, the voltage of the DC bus is controlled at a higher second voltage. When a high voltage ride occurs, because the operating voltage of the DC bus is higher than the instantaneous voltage during the high voltage ride, the grid energy will not be transferred to the DC bus, thus avoiding overcurrent in the power conversion circuit.
[0007] In summary, the solution proposed in this application identifies the power capacity of the energy storage battery and dynamically adjusts the operating voltage of the DC bus, rather than always maintaining the DC bus voltage at a high level. This ensures high-voltage power grid crossing while reducing losses in power switching devices and minimizing switching stress.
[0008] In one possible implementation, the power converter further includes: a DC / DC conversion circuit; a first DC side of the DC / DC conversion circuit connected to an energy storage battery; a second DC side of the DC / DC conversion circuit connected to a DC bus; and a controller configured to control the DC / DC conversion circuit to make the voltage of the DC bus a first voltage when the power capability of the energy storage battery is less than or equal to the power capability of the power conversion circuit; and to control the DC / DC conversion circuit to make the voltage of the DC bus a second voltage when the power capability of the energy storage battery is greater than the power capability of the power conversion circuit.
[0009] In this implementation, the power converter integrates a DC / DC conversion circuit. The controller can actively regulate the DC bus voltage by controlling the DC / DC conversion circuit when there is no high-voltage ride-through in the power grid.
[0010] In one possible implementation, the energy storage system further includes: a DC / DC converter circuit; a first DC side of the DC / DC converter circuit connected to an energy storage battery; a DC bus connected to a second DC side of the DC / DC converter circuit; and a controller configured to control the DC / DC converter circuit to make the voltage of the DC bus a first voltage when the power capability of the energy storage battery is less than or equal to the power capability of the power conversion circuit; and to control the DC / DC converter circuit to make the voltage of the DC bus a second voltage when the power capability of the energy storage battery is greater than the power capability of the power conversion circuit.
[0011] In this implementation, the energy storage system integrates a DC / DC converter circuit. The controller can actively regulate the DC bus voltage by controlling the DC / DC converter circuit when there is no high-voltage ride-through in the power grid.
[0012] In one possible implementation, the power converter circuit is a full-bridge circuit; each power switching device in the full-bridge circuit is connected in anti-parallel with a diode.
[0013] In one possible implementation, the state information includes one or more of the following: state of charge (SOC), state of health (SOH), temperature, charging current, or discharging current.
[0014] In one possible implementation, the second voltage is greater than or equal to 1.3 times the rated voltage of the power grid.
[0015] The voltage range for high-voltage ride-through is typically 1.10-1.30 times the rated voltage of the grid. After adjusting the DC bus to the second voltage, it is sufficient to ensure that grid energy will not be supplied to the DC bus during high-voltage ride-through, thus ensuring that the power conversion system can successfully pass through the high-voltage ride-through.
[0016] Secondly, this application also provides a control method for a power conversion system, the power conversion system including a power converter and an energy storage system. The method includes: determining the power capacity of the energy storage battery based on the state information of the energy storage battery in the energy storage system; the energy storage system is coupled to a DC bus; the DC bus is connected to the DC side of the power conversion circuit of the power converter; the AC side of the power conversion circuit is connected to the power grid; when the power capacity of the energy storage battery is less than or equal to the power capacity of the power conversion circuit, controlling the voltage of the DC bus to a first voltage; when the power capacity of the energy storage battery is greater than the power capacity of the power conversion circuit, controlling the voltage of the DC bus to a second voltage, wherein the first voltage is less than the second voltage.
[0017] The method of this application identifies the power capability of the energy storage battery and dynamically adjusts the operating voltage of the DC bus, rather than always maintaining the DC bus voltage at a high voltage. This can ensure high-voltage power grid crossing while reducing the losses of power switching devices and reducing switching stress.
[0018] In one possible implementation, controlling the voltage of the DC bus to be a first voltage includes: controlling a DC / DC converter circuit to make the voltage of the DC bus the first voltage, wherein a first DC side of the DC / DC converter circuit is connected to an energy storage battery, a second DC side of the DC / DC converter circuit is connected to the DC bus, and the DC / DC converter circuit is located in the energy storage system or in the power converter; and controlling the DC / DC converter circuit to make the voltage of the DC bus the second voltage when the power capacity of the energy storage battery is greater than the power capacity of the power converter circuit.
[0019] In one possible implementation, the state information includes one or more of the following: state of charge (SOC), state of health (SOH), temperature, charging current, or discharging current.
[0020] Thirdly, this application also provides a controller for executing the methods provided in the second aspect and any implementation thereof. Attached Figure Description
[0021] Figure 1 This is a diagram illustrating the application scenarios of power converters;
[0022] Figure 2 This is a schematic diagram of the current path during high voltage ride-through.
[0023] Figure 3 The waveform diagram shows the power converter when overcurrent occurs.
[0024] Figure 4 A schematic diagram of the power conversion system provided in the embodiments of this application. Figure 1 ;
[0025] Figure 5 A waveform diagram provided for an embodiment of this application;
[0026] Figure 6 A schematic diagram of the power conversion system provided in the embodiments of this application. Figure 2 ;
[0027] Figure 7 A schematic diagram of the control topology provided in an embodiment of this application;
[0028] Figure 8 A schematic diagram of the power conversion system provided in the embodiments of this application. Figure 3 ;
[0029] Figure 9 A flowchart of a control method for a power conversion system provided in an embodiment of this application;
[0030] Figure 10 This is a schematic diagram of a controller provided in an embodiment of this application. Detailed Implementation
[0031] To enable those skilled in the art to more clearly understand the technical solution of this application, the application scenario of the technical solution of this application will be described first. The following explanation will use a power converter as an example of an inverter.
[0032] See Figure 1 The figure illustrates an application scenario for a power converter.
[0033] The photovoltaic-storage system mainly includes: a power converter 10, a photovoltaic module 30, and an energy storage system 20.
[0034] The photovoltaic module 30 is used to convert solar energy into electrical energy, and the output of the photovoltaic module 30 is direct current.
[0035] Taking the power converter 10 as an inverter as an example, the power converter 10 can convert the DC power output by the photovoltaic module 30 into AC power and then supply it to the load 40.
[0036] The energy storage system 20 can store excess electricity generated by the photovoltaic module 30 and release it for use when needed. The energy storage system 20 may include one or more energy storage batteries.
[0037] The power converter 10 can not only generate electricity through grid connection, but also has the ability to operate independently with load in case of grid anomalies. The load interface of the power converter 10 is used to connect the load 40, and the grid connection interface of the power converter 10 is used to connect to the power grid 60 through the meter 50.
[0038] Under normal grid conditions, the power converter operates in parallel with the grid. At this time, the load 40 is powered by the power converter 10; or, the load 40 is powered by the power converter 10 and the energy storage system 20 together; or, the load 40 is powered by the power converter 10 and the grid 60 together.
[0039] See also Figure 2 and Figure 3 ,in, Figure 2 This is a schematic diagram of the current path during high voltage ride-through. Figure 3 This is a waveform diagram of the power converter when overcurrent occurs.
[0040] Figure 2The power converter 10 uses a full-bridge inverter circuit as an example for illustration, but this does not constitute a limitation on the technical solution of this application. The power converter 10 can also employ other inverter topologies, such as a T-type three-level circuit, a neutral point clamped (NPC) three-level circuit, an active neutral point clamped (ANPC) three-level circuit, a flying capacitor topology, or a highly efficient and reliable inverter concept (Heric), etc.
[0041] The full-bridge circuit includes power switching devices S1-S4, each connected in anti-parallel with a diode. The power switching devices S1-S4 can be insulated-gate bipolar transistors (IGBTs), integrated gate-commutated thyristors (IGCTs), metal-oxide-semiconductor field-effect transistors (MOSFETs), silicon carbide metal-oxide-semiconductor field-effect transistors (SiC MOSFETs), etc., and are not specifically limited in this embodiment. For example, when the power switching device is a MOSFET, each diode in the figure is a body diode; when the power switching device is an IGBT or IGCT, each diode in the figure is a separately configured anti-parallel diode, which can be a fast recovery diode (FRD). In the following description, an IGBT is used as an example of a power switching device, where each diode is a separately configured anti-parallel diode.
[0042] Figure 2 The DC bus capacitor C1 is connected between the positive DC bus Bus+ and the negative DC bus Bus-. The DC bus voltage is denoted by Udc. The DC bus voltage Udc is maintained by the bus capacitor C1. The AC side of the full-bridge inverter circuit is connected to the AC grid through an LCL filter. The LCL filter includes a first inductor L1, a second capacitor C2, and a second inductor L2. The first inductor L1 limits the variation in the output current of the power converter 10, suppressing high-frequency harmonics. The second capacitor C2 provides a discharge path for high-frequency harmonics and compensates for some reactive power. The second inductor L2 smooths the grid-connected current and isolates grid disturbances.
[0043] When the grid voltage is normal, the bus voltage Udc of the power converter is U1. After t1, a high-voltage ride-through occurs in the grid. The diode connected in anti-parallel with the power switching device in the power converter 10 performs uncontrolled rectification of the grid current. The current reaches the DC bus through diode D1, charging the bus capacitor C1, causing the bus voltage Udc of the power converter to rise from U1 to U2.
[0044] For the energy storage system 20, the energy storage battery serves as the carrier for energy absorption and release. When the power capacity of the battery side exceeds that of the power converter 10, the energy from high-voltage ride-through may be uncontrollably transferred from the DC bus of the power converter 10 to the energy storage battery, leading to an overcurrent fault in the power converter 10. Therefore, to withstand the energy surge caused by excessively high grid voltage, it is currently necessary to increase the bus voltage of the power converter 10 to suppress grid energy injection into the bus. However, increasing the bus voltage leads to increased losses and switching stress in the power switching devices.
[0045] To address the above technical issues, this application provides a power conversion system and control method that can dynamically adjust the DC bus voltage of the power converter based on the power capacity of the energy storage battery. This ensures high-voltage grid crossing and avoids overcurrent faults while reducing losses of power switching devices, decreasing switching stress, and improving the reliability of the power converter.
[0046] The terms "first" and "second" used in this application description are for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated.
[0047] In this application, unless otherwise expressly specified and limited, the term "connection" shall be interpreted broadly. For example, "connection" may be a fixed connection, a detachable connection, or an integral part; it may be a direct connection or an indirect connection through an intermediate medium.
[0048] See Figure 4 This figure is a schematic diagram of the power conversion system provided in an embodiment of this application. Figure 1 .
[0049] The power conversion system 90 includes a power converter 10 and an energy storage system 20. The power converter 10 includes a DC bus, a controller 11, and a power conversion circuit 12.
[0050] The DC bus includes the positive DC bus DC+ and the negative DC bus DC-.
[0051] The DC side of the power conversion circuit 12 is connected to the DC bus, and the AC side of the power conversion circuit 12 is used to connect to the power grid.
[0052] The DC bus is coupled to the energy storage system 20, which includes an energy storage battery 21.
[0053] In this embodiment of the application, the controller 11 of the power converter 10 can obtain the status information of the energy storage battery 21 in the energy storage system 20, and determine the power capacity of the energy storage battery based on the status information of the energy storage battery 21.
[0054] The power capacity of the energy storage battery, as well as the number of energy storage batteries in the energy storage system (the more energy storage batteries, the larger the capacity of the energy storage system), together determine the energy storage capacity boundary of the energy storage system.
[0055] The power capability of an energy storage battery refers to the maximum energy that the battery can safely charge or release per unit time without damaging the battery, triggering safety protection mechanisms, or significantly impairing its lifespan. In other words, the power capability of an energy storage battery can be measured in absolute power (P), which can be measured in watts (W), kilowatts (kW), megawatts (MW), etc. The higher the absolute power, the more energy the battery releases or absorbs per unit time. For example, the power capability range of energy storage batteries for residential applications is 5kW-20kW; while the power capability range for commercial and industrial energy storage applications is approximately 50kW-500kW.
[0056] In addition, power capability can also be measured using charge / discharge rate. The charge / discharge rate indicates the ratio of charge / discharge current to rated capacity, directly reflecting the power capability. For example, a charge / discharge rate of 1C means the energy storage battery requires 1 hour to fully charge or discharge, while a charge / discharge rate of 0.5C means it takes 2 hours. The charge / discharge rate range for energy storage batteries in commercial and industrial applications is 0.3C-1C; for residential energy storage applications, it is 0.2–0.5C.
[0057] Power capability is affected by state of charge (SOC), state of health (SOH), and battery temperature.
[0058] Power capability is typically limited when the State of Charge (SOC) is extremely low or high. For example, the power capability for discharging decreases when the SOC is less than 10%, and the power capability for charging decreases when the SOC is greater than 90%.
[0059] When the State of Harmony (SOH) is low, the battery ages severely, its internal resistance increases, and its peak power capability is significantly reduced. SOH is generally related to the cycle life of an energy storage battery. As the cycle life increases, battery aging becomes more severe, SOH decreases accordingly, and power capability continuously declines. For example, for energy storage batteries with the same specifications, under the same conditions, the power capability after 10 cycles is greater than that after 100 cycles.
[0060] Low temperatures increase the internal resistance of energy storage batteries, limiting their power output. For example, the optimal temperature range for energy storage batteries to achieve their power output is -15℃ to 45℃. Outside this range, their power output decreases.
[0061] In this embodiment of the application, the power capability of the power conversion circuit refers to the maximum power that the power conversion circuit can continuously, stably and safely achieve energy conversion within the range of rated voltage, rated frequency and allowable operating temperature. The unit can be watt (W), kilowatt (kW), megawatt (MW), etc.
[0062] In this embodiment of the application, in order to compare the power capabilities of the power conversion circuit and the energy storage battery, absolute power is used to measure the power capability of the energy storage battery, so as to achieve the unification of dimensions.
[0063] See Figure 5 The figure shown is a waveform diagram provided in an embodiment of this application.
[0064] Figure 5 The horizontal axis t represents time. The vertical axis Udc represents the DC bus voltage, i.e. Figure 2 The voltage between the positive DC bus Bus+ and the negative DC bus Bus-. The power capacity of energy storage battery 21 is represented by P. bat The power capability of a power conversion circuit is represented by P. inv express.
[0065] In this embodiment of the application, the controller 11 controls the power capability P of the energy storage battery 21. bat The power capability P of the power conversion circuit is less than or equal to that of the power conversion circuit. inv In this case, the voltage of the control DC bus Udc is set to the first voltage U1. For example, in Figure 5Before time t1, the voltage of the DC bus Udc is U1, and the rated voltage of the power grid is Ug. U1 is in the range of 1.0Ug-1.1Ug, meaning U1 is greater than the rated voltage of the power grid at 1.0 pu and less than the rated voltage of the power grid at 1.1 pu. Here, 1.0 pu is the rated voltage of the power grid. At this time, the voltage of the DC bus Udc is smaller than U2, but still greater than the rated voltage of the power grid at 1.0 pu. Therefore, when the power grid voltage is normal, it is possible to prevent power grid energy from being fed into the DC bus. Furthermore, because the DC bus Udc is relatively small at this time, it also reduces the losses of the power switching devices in the power converter and reduces switching stress.
[0066] The controller 11 controls the power capacity P of the energy storage battery 21. bat The power capability P of the power conversion circuit is greater than that of the power conversion circuit. inv In this case, the voltage of the DC bus is controlled to be the second voltage U2, and the first voltage U1 is less than the second voltage U2. For example, in Figure 5 After time t1, the voltage of the DC bus Udc is U2, which is greater than 1.3Ug, meaning U2 is greater than the grid's rated voltage of 1.3 pu. It should be understood that the voltage range during grid high-voltage ride-through is typically between 1.10 pu and 1.30 pu. Therefore, the DC bus voltage at this time is sufficient to ensure that grid energy will not be transferred to the DC bus during grid high-voltage ride-through, guaranteeing that the power conversion system can successfully pass through the grid high-voltage ride-through.
[0067] It should be understood that the value ranges of the first voltage U1 and the second voltage U2 in the above description are merely examples and do not constitute a limitation on the technical solution of this application. In practical applications, the first voltage U1 and the second voltage U2 can also be reasonably set based on the stability of the power grid and the voltage fluctuation range during high-voltage ride-through. In one possible implementation, see [link to relevant documentation]. Figure 6 This figure is a schematic diagram of the power conversion system provided in an embodiment of this application. Figure 2 .
[0068] The power conversion system also includes a DC / DC converter circuit 22. The first DC side of the DC / DC converter circuit 22 is connected to the energy storage battery 21, and the second DC side of the DC / DC converter circuit 22 is connected to the DC bus of the power converter 10. In this embodiment, the controller 11 can adjust the output voltage of the second DC side of the DC / DC converter circuit 22 by controlling its operating state, thereby actively adjusting the voltage of the DC bus of the power converter 10.
[0069] The controller 11 can adjust the voltage of the DC bus through active adjustment. This active adjustment process can be carried out in real time while the power converter and energy storage system are operating, rather than only during high-voltage ride-through.
[0070] Controller 11 in the power capability P of the energy storage battery bat The power capability P of the power conversion circuit is less than or equal to that of the power conversion circuit. inv In this case, the DC bus voltage is actively regulated to a lower first voltage U1. Because the DC bus voltage is lower at this time, the losses of the power switching devices during power converter operation are reduced, and the switching stress is decreased. When a high-voltage ride-through occurs, if the grid voltage is higher than the first voltage U1, grid energy will be transferred to the DC bus. Since the power capacity P of the energy storage battery is [not specified] at this time... bat The DC bus current is relatively low, but the energy storage system has current-limiting capabilities. To protect the energy storage battery, the energy storage system limits the DC bus current to a level that the battery can withstand, ensuring that the DC bus current remains within a safe range and that the power conversion circuit 12 does not experience overcurrent. This causes grid energy to transfer to the bus capacitor C1, resulting in an increase in the DC bus voltage Udc. Once the DC bus voltage Udc rises above the voltage during high-voltage ride-through, grid energy can no longer be transferred to the DC bus, ensuring that the power converter can successfully complete the high-voltage ride-through.
[0071] The controller 11 has a power capability P in the energy storage battery 21 bat The power capability P of the power conversion circuit is greater than that of the power conversion circuit. inv In this case, the voltage of the DC bus is adjusted to a higher second voltage U2. When a high voltage ride-through occurs, because the voltage U2 of the DC bus is higher than the instantaneous voltage during the high voltage ride-through, the grid energy will not be transferred to the DC bus. This avoids overcurrent in the power conversion circuit caused by the power converter using the energy injected by the grid to charge the energy storage battery, and ensures that the power converter can successfully complete the high voltage ride-through.
[0072] In this embodiment of the application, under the high voltage ride-through scenario of the power grid, the charging process of the energy storage battery by the DC bus is mainly considered. At this time, the power capability of the energy storage battery is not fixed. For example, when the SOC of the energy storage battery is high, the power capability of the energy storage battery is low. Then the controller can adjust the voltage of the DC bus to a lower first voltage U1. If the SOC of the energy storage battery is low, the power capability of the energy storage battery is high. Then the controller can adjust the voltage of the DC bus to a higher second voltage U1 to avoid energy flowing into the DC bus during the high voltage ride-through of the power grid.
[0073] In summary, the solution proposed in this application can dynamically adjust the operating voltage of the DC bus by identifying the power capability of the energy storage battery, instead of always maintaining the DC bus voltage at a high voltage. Therefore, it can reduce the loss of power switching devices and reduce switching stress while ensuring high-voltage power grid crossing.
[0074] The following section will explain the specific implementation method.
[0075] See also Figure 6 In this embodiment of the application, the power converter 10 includes: a DC bus (DC+ and DC-), a controller 11, and a power conversion circuit 12.
[0076] The power conversion circuit 12 is a full-bridge circuit, in which each power switching device is connected in anti-parallel with a diode. Specifically, the power switching devices S1-S4 can be insulated-gate bipolar transistors (IGBTs), integrated gate-commutated thyristors (IGCTs), metal-oxide-semiconductor field-effect transistors (MOSFETs), silicon carbide metal-oxide-semiconductor field-effect transistors (SiC MOSFETs), etc., and this application embodiment does not impose specific limitations. For example, when the power switching device is a MOSFET, each diode in the figure is a body diode; when the switching device is an IGBT or IGCT, each diode in the figure is a separately configured anti-parallel diode, which can be a fast recovery diode (FRD).
[0077] The controller 11 in this embodiment can be an application-specific integrated circuit (ASIC), a programmable logic device (PLD), a digital signal processor (DSP), or a combination thereof. The PLD can be a complex programmable logic device (CPLD), a field-programmable gate array (FPGA), a generic array logic (GAL), or any combination thereof; this embodiment does not impose specific limitations.
[0078] In this embodiment of the application, the energy storage system 20 includes: an energy storage battery 21 and a DC / DC converter circuit 22.
[0079] The DC / DC converter circuit 22 can achieve bidirectional power conversion, that is, it can convert the DC power provided by the energy storage battery 21 into DC power and output it to the DC bus, or it can convert the DC power provided by the DC bus into DC power and output it to the energy storage battery 21, thereby charging the energy storage battery 21.
[0080] The controller 11 in this embodiment can regulate the bus voltage by controlling the operating state of the DC / DC converter circuit 22.
[0081] See Figure 7 This figure is a schematic diagram of the control topology provided in an embodiment of this application.
[0082] In one possible implementation, the status information may also include the discharge current or charging current of the energy storage battery. The controller 11 can characterize the power capability of the energy storage battery based on the battery's discharge current or charging current (represented uniformly by IbatFbk), and use the current reference value IbatRef to represent the power capability of the power conversion circuit.
[0083] When IbatRef is greater than or equal to IbatFbk, controller 11 determines the power capability P of the energy storage battery. bat The power capability P of the power conversion circuit is less than or equal to that of the power conversion circuit. inv The controller 11 controls the DC / DC converter circuit 22 to maintain a lower first voltage U1 on the DC bus, which reduces the losses of the power switching devices and decreases switching stress. When a high-voltage ride-through occurs, if the grid voltage is higher than the first voltage U1, grid energy will be transferred to the DC bus. Since the power capacity P of the energy storage battery is limited at this time... bat The DC bus current is relatively low, but the energy storage system has current-limiting capabilities. To protect the energy storage battery, the energy storage system limits the current to the DC bus to a current that the energy storage battery can withstand. That is, the DC / DC converter circuit 22 limits the charging current to the battery, ensuring that the DC bus current is always within a safe range and the power conversion circuit 12 will not experience overcurrent. This causes grid energy to be transferred to the bus capacitor C1, resulting in an increase in the DC bus voltage Udc. Once the DC bus voltage Udc rises to a level greater than the voltage at which the grid experiences high-voltage ride-through, grid energy can no longer be transferred to the DC bus, ensuring that the power converter can successfully complete the high-voltage ride-through.
[0084] When IbatRef is less than IbatFbk, controller 11 indicates that the power capability P of the energy storage battery 21 is currently... bat The power capability P of the power conversion circuit is greater than that of the power conversion circuit. invThe controller 11 controls the DC / DC converter circuit 22 to make the DC bus voltage a higher second voltage U2. When a high voltage ride occurs, because the DC bus operating voltage is higher than the instantaneous voltage during the high voltage ride, the grid energy will not be transferred to the DC bus. This avoids the overcurrent in the power conversion circuit caused by the power converter using the energy injected by the grid to charge the energy storage battery, and ensures that the power converter can successfully complete the high voltage ride.
[0085] In summary, the solution proposed in this application identifies the power capacity of the energy storage battery and dynamically adjusts the operating voltage of the DC bus, rather than always maintaining the DC bus voltage at a high level. This ensures high-voltage power grid crossing while reducing losses in power switching devices and minimizing switching stress.
[0086] In another possible implementation, the DC / DC conversion circuit is located within the power converter, as detailed below with reference to the accompanying drawings.
[0087] See Figure 8 This figure is a schematic diagram of the power converter provided in an embodiment of this application. Figure 3 .
[0088] In this implementation, the power converter 10 includes: a DC bus (DC+ and DC-), a controller 11, a power conversion circuit 12, and a DC / DC conversion circuit 22. That is, the DC / DC conversion circuit 22 is integrated inside the power converter 10, rather than integrated into the energy storage system 20.
[0089] The energy storage system 20 includes an energy storage battery 21.
[0090] The power conversion circuit 12 is a full-bridge circuit, in which each power switching device is connected in anti-parallel with a diode.
[0091] The DC / DC converter circuit 22 can realize bidirectional power conversion, that is, the DC power provided by the energy storage battery 21 can be converted into DC power and output to the DC bus, or the DC power provided by the DC bus can be converted into DC power and output to the energy storage battery 21, thereby charging the energy storage battery 21.
[0092] Controller 11 in the power capability P of the energy storage battery bat The power capability P of the power conversion circuit is less than or equal to that of the power conversion circuit. inv In this case, controller 11 controls the DC / DC converter circuit 22 to make the DC bus voltage a lower first voltage U1, which can reduce the loss of power switching devices and reduce switching stress. When a high voltage ride-through occurs, after the grid energy is transferred to the DC bus, the power capacity P of the energy storage battery is reduced. batThe current is relatively low, so the energy storage system limits the current of the DC bus to no more than the current that the energy storage battery can withstand. That is, the DC / DC converter circuit 22 limits the charging current to the battery. This causes the grid energy to be transferred to the bus capacitor C1, resulting in an increase in the DC bus voltage Udc. Once the DC bus voltage Udc rises to a level greater than the voltage at which the grid experiences high-voltage ride-through, the grid energy can no longer be transferred to the DC bus, ensuring that the power converter can successfully complete the high-voltage ride-through.
[0093] The controller 11 has a power capability P in the energy storage battery 21 bat The power capability P of the power conversion circuit is greater than that of the power conversion circuit. inv In this case, the controller 11 controls the DC / DC converter circuit 22 to make the DC bus voltage a higher second voltage U2. When a high voltage ride occurs, since the DC bus operating voltage is higher than the instantaneous voltage during the high voltage ride, grid energy will not be transferred to the DC bus. This avoids overcurrent in the power converter circuit caused by the power converter using the energy injected by the grid to charge the energy storage battery, and ensures that the power converter can successfully complete the high voltage ride.
[0094] In summary, the solution proposed in this application identifies the power capacity of the energy storage battery and dynamically adjusts the operating voltage of the DC bus, rather than always maintaining the DC bus voltage at a high level. This ensures high-voltage power grid crossing while reducing losses in power switching devices and minimizing switching stress.
[0095] Based on the power conversion system provided in the above embodiments, this application also provides a control method for the power conversion system, which will be described in detail below with reference to the accompanying drawings.
[0096] See Figure 9 The figure is a flowchart of the control method of the power conversion system provided in the embodiment of this application.
[0097] This method is applied to the power converter provided in any of the above embodiments. For a description of the power converter, please refer to the above embodiments; it will not be repeated here. The method includes the following steps:
[0098] S11: Determine the power capacity of the energy storage battery based on the state information of the energy storage battery in the energy storage system.
[0099] The energy storage system is coupled to a DC bus, which is connected to the DC side of the power conversion circuit of the power converter, while the AC side of the power conversion circuit is connected to the power grid.
[0100] Status information includes one or more of the following: State of Charge (SOC), State of Health (SOH), temperature, charging current, or discharging current.
[0101] S12: Determine whether the power capability of the energy storage battery is less than or equal to the power capability of the power conversion circuit.
[0102] If yes, execute S13; otherwise, execute S14.
[0103] S13: Controls the voltage of the DC bus to the first voltage.
[0104] At this point, the DC bus voltage is a relatively low initial voltage, which reduces losses in the power switching devices and decreases switching stress. When a high-voltage ride-through occurs, after grid energy is transferred to the DC bus, the energy storage system limits the DC bus current to the level that the energy storage battery can withstand due to the lower power capacity at this time. This causes grid energy to transfer to the bus capacitor C1, resulting in an increase in the DC bus voltage Udc. Once the DC bus voltage Udc rises above the voltage at the time of the high-voltage ride-through, grid energy can no longer be continuously transferred to the DC bus, ensuring that the power converter can successfully complete the high-voltage ride-through.
[0105] S14: Control the voltage of the DC bus to the second voltage, where the first voltage is less than the second voltage.
[0106] When a high-voltage ride-through occurs, the DC bus operates at a higher voltage than the instantaneous voltage during the high-voltage ride-through. As a result, grid energy will not be transferred to the DC bus. This prevents the power converter from using the grid-poured energy to charge the energy storage battery, thus avoiding overcurrent in the power converter circuit and ensuring that the power converter can successfully complete the high-voltage ride-through.
[0107] In one possible implementation, the second voltage is greater than or equal to 1.3 times the rated voltage of the power grid.
[0108] In summary, the method and solution provided in this application identify the power capacity of the energy storage battery and dynamically adjust the operating voltage of the DC bus, thereby avoiding overcurrent in the power conversion circuit caused by the power converter using energy injected from the grid to charge the energy storage battery. It can reduce the loss of power switching devices and reduce switching stress while ensuring high-voltage grid crossing.
[0109] See Figure 10 This figure is a schematic diagram of a controller provided in an embodiment of this application.
[0110] The controller may include a memory 111 and a processor 112. The processor 112 may be connected to the power conversion circuit 12 and the DC / DC conversion circuit 22, and may drive various power switching devices. As shown in the figure, the memory 111 may be random access memory (RAM), flash memory, read-only memory (ROM), EPROM, non-volatile read-only memory (EEPROM), registers, hard disk, removable disk, etc.
[0111] The memory 111 can store computer instructions. When the computer instructions stored in the memory 111 are executed by the processor 112, the processor 112 can be used to execute the control method of the power converter. The memory 111 can also store data, such as information like the first voltage and the second voltage involved in the above embodiments.
[0112] In the above embodiments, implementation can be achieved, in whole or in part, through software, hardware, firmware, or any combination thereof. When implemented in software, it can be implemented, in whole or in part, as a computer program product. A computer program product includes one or more computer instructions. When the computer program instructions are loaded and executed on a computer, all or part of the flow or function according to the embodiments of this application is generated. The computer can be a general-purpose computer, a special-purpose computer, a computer network, or other programmable device. The computer instructions can be stored in a computer-readable storage medium or transmitted from one computer-readable storage medium to another. For example, computer instructions can be transmitted from one website, computer, server, or data center to another website, computer, server, or data center via wired (e.g., coaxial cable, fiber optic, digital subscriber line (DSL)) or wireless (e.g., infrared, wireless, microwave, etc.) means. The computer-readable storage medium can be any available medium that a computer can access or a data storage device such as a server or data center that integrates one or more available media. The available medium can be a magnetic medium (e.g., floppy disk, hard disk, magnetic tape) or a semiconductor medium (e.g., solid-state disk (SSD)).
[0113] This application also provides a readable storage medium for storing the methods provided in the above embodiments. Examples include random access memory (RAM), flash memory, read-only memory (ROM), EPROM, non-volatile read-only memory (EPROM), registers, hard disks, removable disks, or any other form of storage medium in the art.
[0114] It should be noted that the various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. Regarding the methods disclosed in the embodiments, since they correspond to the product embodiments disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to in the description of the product embodiments.
[0115] The above description of the disclosed embodiments enables those skilled in the art to make or use this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
Claims
1. A power conversion system, characterized in that, The power conversion system includes a power converter and an energy storage system; the power converter includes: a DC bus, a controller, and a power conversion circuit; The DC side of the power conversion circuit is connected to the DC bus, and the AC side of the power conversion circuit is connected to the power grid. The DC bus is coupled to the energy storage system, which includes an energy storage battery. The controller is configured to determine the power capability of the energy storage battery based on the state information of the energy storage battery, and to control the voltage of the DC bus to a first voltage when the power capability of the energy storage battery is less than or equal to the power capability of the power conversion circuit; and to control the voltage of the DC bus to a second voltage when the power capability of the energy storage battery is greater than the power capability of the power conversion circuit, wherein the first voltage is less than the second voltage.
2. The power conversion system according to claim 1, characterized in that, The power converter also includes: a DC / DC conversion circuit; The first DC side of the DC / DC converter circuit is connected to the energy storage battery; The second DC side of the DC / DC converter circuit is connected to the DC bus. The controller is configured to control the DC / DC converter to make the voltage of the DC bus a first voltage when the power capability of the energy storage battery is less than or equal to the power capability of the power conversion circuit; and to control the DC / DC converter to make the voltage of the DC bus a second voltage when the power capability of the energy storage battery is greater than the power capability of the power conversion circuit.
3. The power conversion system according to claim 1, characterized in that, The energy storage system also includes: a DC / DC converter circuit; The first DC side of the DC / DC converter circuit is connected to the energy storage battery; The DC bus is connected to the second DC side of the DC / DC converter circuit; The controller is configured to control the DC / DC converter to make the voltage of the DC bus a first voltage when the power capability of the energy storage battery is less than or equal to the power capability of the power conversion circuit; and to control the DC / DC converter to make the voltage of the DC bus a second voltage when the power capability of the energy storage battery is greater than the power capability of the power conversion circuit.
4. The power conversion system according to claim 1, characterized in that, The power converter circuit is a full-bridge circuit; Each power switching device in the full-bridge circuit is connected in anti-parallel with a diode.
5. The power conversion system according to any one of claims 1 to 4, characterized in that, The status information includes one or more of the following: State of charge (SOC), state of health (SOH), temperature, charging current or discharging current.
6. The power conversion system according to claim 1, characterized in that, The second voltage is greater than or equal to 1.3 times the rated voltage of the power grid.
7. A control method for a power conversion system, characterized in that, Power conversion systems include power converters and energy storage systems, and the methods include: The power capacity of the energy storage battery is determined based on the state information of the energy storage battery in the energy storage system. The energy storage system is coupled to a DC bus, which is connected to the DC side of the power conversion circuit of the power converter. The AC side of the power conversion circuit is connected to the power grid. When the power capability of the energy storage battery is less than or equal to the power capability of the power conversion circuit, the voltage of the DC bus is controlled to be a first voltage. When the power capacity of the energy storage battery is greater than the power capacity of the power conversion circuit, the voltage of the DC bus is controlled to be a second voltage, wherein the first voltage is less than the second voltage.
8. The control method according to claim 7, characterized in that, The control of the DC bus voltage to be a first voltage includes: A DC / DC converter circuit is controlled to make the voltage of the DC bus a first voltage. The first DC side of the DC / DC converter circuit is connected to the energy storage battery, and the second DC side of the DC / DC converter circuit is connected to the DC bus. The DC / DC converter circuit is located in the energy storage system or in the power converter. When the power capacity of the energy storage battery is greater than the power capacity of the power conversion circuit, the DC / DC conversion circuit is controlled to make the voltage of the DC bus a second voltage.
9. The control method according to claim 7, characterized in that, The status information includes one or more of the following: State of charge (SOC), state of health (SOH), temperature, charging current or discharging current.
10. A controller, characterized in that, The controller is used to perform the method according to any one of claims 7-9.