Optical storage system and method of controlling the same, controller

Abstract

The application provides a light storage system and a control method and a controller thereof, and relates to the technical field of power electronics. The light storage system comprises a photovoltaic module, an energy storage battery, a switch, a first power converter, a second power converter and a controller. The output end of the photovoltaic module is connected to the input end of the second power converter through the first power converter, the energy storage battery is connected to the input end of the second power converter through the switch, and the output end of the second power converter is connected to a power grid. The controller is used for controlling the absolute value of the difference between the output power of the photovoltaic module and the output power of the second power converter to be less than a power threshold value, and controlling the switch to be turned off in response to the current input or output by the energy storage battery being less than a current threshold value. The application can reduce voltage fluctuation caused by the switch connected to the energy storage battery being turned off.

Description

Technical Field

[0001] This application relates to the field of power electronics technology, and in particular to a photovoltaic energy storage system and its control method and controller. Background Technology

[0002] In a photovoltaic and energy storage system that includes photovoltaics and energy storage batteries, in certain operating conditions during the charging or discharging of the energy storage battery, it is necessary to disconnect the switch connected to the energy storage battery to disconnect the energy storage battery from the photovoltaic and energy storage system. For example, in the case of overcharging or over-discharging of the energy storage battery.

[0003] Directly disconnecting the switch connected to the energy storage battery during the operation of a photovoltaic-energy storage system can easily cause voltage fluctuations in the power converter connected to the energy storage battery in the system. Summary of the Invention

[0004] This application provides a photovoltaic energy storage system and its control method and controller, which are used to reduce voltage fluctuations caused when the switch connected to the energy storage battery is disconnected.

[0005] According to a first aspect of the embodiments of this application, a photovoltaic-storage system is provided, including a photovoltaic module, an energy storage battery, a switch, a first power converter, a second power converter, and a controller; The output terminal of the photovoltaic module is connected to the input terminal of the second power converter through the first power converter, the energy storage battery is connected to the input terminal of the second power converter through the switch, and the output terminal of the second power converter is connected to the power grid. The controller is configured to control the absolute value of the difference between the output power of the photovoltaic module and the output power of the second power converter to be less than a power threshold, and to control the switch to open in response to the input or output current of the energy storage battery being less than a current threshold.

[0006] According to a second aspect of the embodiments of this application, a control method for a photovoltaic-storage system is provided. The photovoltaic-storage system includes a photovoltaic module, an energy storage battery, a switch, a first power converter, and a second power converter. The output terminal of the photovoltaic module is connected to the input terminal of the second power converter through the first power converter. The energy storage battery is connected to the input terminal of the second power converter through the switch. The output terminal of the second power converter is connected to the power grid. The control method includes: The absolute value of the difference between the output power of the photovoltaic module and the output power of the second power converter is less than a power threshold. In response to the energy storage battery input or output current being less than a current threshold, the switch is controlled to open.

[0007] According to a third aspect of the embodiments of this application, a controller is provided for implementing the control method of the optical storage system as described in the second aspect.

[0008] In this application, the photovoltaic-storage system includes a photovoltaic module, an energy storage battery, a switch, a first power converter, a second power converter, and a controller. The output terminal of the photovoltaic module is connected to the input terminal of the second power converter through the first power converter. The energy storage battery is connected to the input terminal of the second power converter through the switch. The output terminal of the second power converter is connected to the power grid. The controller controls the absolute value of the difference between the output power of the photovoltaic module and the output power of the second power converter to be less than a power threshold, and controls the switch to open in response to the input or output current of the energy storage battery being less than a current threshold. By controlling the absolute value of the difference between the output power of the photovoltaic module and the output power of the second power converter to be less than a power threshold, the controller can reduce the energy input or output of the energy storage battery participating in this photovoltaic-storage system, and reduce the input or output current of the energy storage battery. In response to the input or output current of the energy storage battery being less than a current threshold, the controller controls the switch to open, thereby reducing the rate of change of the input or output current of the energy storage battery after the switch is opened, and reducing the voltage fluctuation on the input side of the second power converter, thus reducing the voltage fluctuation caused by the disconnection of the switch connected to the energy storage battery. Attached Figure Description

[0009] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of this application. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0010] Figure 1 This is a schematic diagram of the structure of a photovoltaic energy storage system provided in an embodiment of this application.

[0011] Figure 2 This is a schematic diagram of another optical energy storage system provided in an embodiment of this application.

[0012] Figure 3 This is a flowchart illustrating a control method for a photovoltaic energy storage system provided in an embodiment of this application. Detailed Implementation

[0013] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0014] Exemplary Optical Storage System Please see Figure 1 In one exemplary embodiment, an optical storage system is provided. For example... Figure 1 As shown, the photovoltaic-storage system includes photovoltaic modules, energy storage batteries, switches, a first power converter, a second power converter, and a controller; The output of the photovoltaic module is connected to the input of the second power converter through the first power converter, the energy storage battery is connected to the input of the second power converter through a switch, and the output of the second power converter is connected to the power grid. The controller is used to control the absolute value of the difference between the output power of the photovoltaic module and the output power of the second power converter to be less than a power threshold, and to control the switch to open in response to the input or output current of the energy storage battery being less than a current threshold.

[0015] In an exemplary embodiment, Figure 1 In this system, the first power converter is used to adjust the output power of the photovoltaic module, and the second power converter is used to realize power transmission and power conversion between the photovoltaic module, the energy storage battery and the power grid.

[0016] In an exemplary embodiment, Figure 1 In this circuit, the second power converter includes a DC-DC converter module and a DC-AC converter module. The input terminal of the DC-DC converter module serves as the input terminal of the second power converter, and the output terminal of the DC-DC converter module is connected to the input terminal of the DC-AC converter module. The output terminal of the DC-AC converter module serves as the output terminal of the second power converter, and the input terminal of the DC-AC converter module is connected to the bus capacitor C2. The output terminal of the photovoltaic module is connected to the input terminal of the second power converter through the first power converter. The energy storage battery is connected to the input terminal of the second power converter via switch K1, and the input terminal of the second power converter is connected to the battery-side capacitor C1.

[0017] In an exemplary embodiment, the first power converter may be a buck converter, such as a Buck circuit.

[0018] In the exemplary embodiment, the DC-DC converter module can be an isolated resonant converter module, and the DC-AC converter module can be an H-bridge inverter module.

[0019] In the exemplary embodiment, switch K1 can be a relay, or a semiconductor switch such as IGBT (Insulated-Gate Bipolar Transistor) or MOSFET (Metal-Oxide Semiconductor Field Effect Transistor), and this application does not limit it in this way.

[0020] In an exemplary embodiment, Figure 1 The controller is not shown in the image, but the photovoltaic-storage system actually includes a controller. The controller obtains information such as the output power of the photovoltaic module, the output power of the second power converter, and the input or output current of the energy storage battery through a sampling circuit, and generates control signals. The controller can control the first power converter, the second power converter, and switch K1.

[0021] In the exemplary embodiment, the power threshold is a preset power value close to zero, used to determine whether the absolute value of the difference between the output power of the photovoltaic module and the output power of the second power converter has dropped to close to or equal to zero.

[0022] In an exemplary embodiment, the current threshold is a preset near-zero current value used to determine whether the input or output current of the energy storage battery has dropped to near or equal to zero, so that the switch can be safely disconnected. For example, the current threshold may be 0.2A.

[0023] The controller ensures that the absolute value of the difference between the output power of the photovoltaic module and the output power of the second power converter is less than the power threshold. This reduces the amount of energy input or output from the energy storage battery participating in the photovoltaic-energy storage system, thereby reducing the input or output current of the energy storage battery. In response to the energy storage battery input or output current being less than the current threshold, the controller opens the switch. Consequently, after the switch is opened, the rate of change of the energy storage battery input or output current is small, and the voltage fluctuation on the input side of the second power converter is small. This reduces the voltage fluctuation caused by the disconnection of the switch connected to the energy storage battery, allowing the photovoltaic-energy storage system to quickly enter a steady state.

[0024] In addition, in response to the current input or output of the energy storage battery being less than the current threshold, the control switch is opened. As a result, the rate of change of the current input or output of the energy storage battery is small after the switch is opened. Since there is parasitic inductance in the circuit where the energy storage battery is located, the voltage stress on the switch after the switch is opened is equal to the parasitic inductance value multiplied by the rate of change of the current input or output of the energy storage battery. The rate of change of the current input or output of the energy storage battery is small, and therefore the voltage stress on the switch after the switch is opened is also small, which can avoid the switch from being subjected to overvoltage.

[0025] Meanwhile, since power regulation is performed online, the photovoltaic-storage system does not need to be shut down, and the photovoltaic modules can always maintain maximum power output, avoiding energy waste.

[0026] In some embodiments, there are various ways to ensure that the absolute value of the difference between the output power of the photovoltaic module and the output power of the second power converter is less than a power threshold, including but not limited to the following: Method 1 The controller responds to the photovoltaic module’s current output power being less than or equal to the rated power of the second power converter by controlling the photovoltaic module to output at its current output power and controlling the second power converter to output at a first target power, wherein the absolute value of the difference between the first target power and the photovoltaic module’s current output power is less than a power threshold.

[0027] For example, if the current overall sunlight is weak, the photovoltaic module's current output power is 700W, the second power converter's rated power is 1000W, and its current output power is 300W, and the photovoltaic module is charging the energy storage battery, the photovoltaic module's current output power is less than the second power converter's rated power, and the first target power is 700W. The controller sends a command to the second power converter to ramp up its output power from 300W to 700W. As the second power converter's output power increases, the absolute value of the difference between the photovoltaic module's output power and the second power converter's output power decreases, and the energy storage battery's input current gradually decreases. When the second power converter's output power stabilizes at 700W, all 700W of power generated by the photovoltaic module is transmitted to the grid through the second power converter (ignoring the power loss of the photovoltaic-energy storage system), and the energy storage battery's input current approaches 0A. The controller determines that the energy storage battery's input current is less than the current threshold, and the control switch is opened, completing the disconnection of the energy storage battery from the photovoltaic-energy storage system.

[0028] For example, the current output power of the photovoltaic module is 700W, the rated power of the second power converter is 1000W, and the current output power of the second power converter is 800W. The energy storage battery discharges to provide energy to the second power converter. The current output power of the photovoltaic module is less than the rated power of the second power converter, and the first target power is 700W. The controller sends a command to the second power converter to reduce its output power from 800W to 700W. As the output power of the second power converter decreases, the absolute value of the difference between the output power of the photovoltaic module and the output power of the second power converter decreases, and the current output by the energy storage battery gradually decreases. When the output power of the second power converter stabilizes at 700W, the power received by the second power converter is the 700W power output by the photovoltaic module (ignoring the power loss of the photovoltaic-energy storage system), and the current output by the energy storage battery is close to 0A. The controller determines that the current output by the energy storage battery is less than the current threshold, and the control switch is opened, completing the disconnection of the energy storage battery from the photovoltaic-energy storage system.

[0029] When the current output power of the photovoltaic module is less than or equal to the rated power of the second power converter, it means that the second power converter is capable of transmitting all the photovoltaic energy to the grid. In this case, the controller can control the photovoltaic module to output at its current output power and control the second power converter to output at a first target power. The absolute value of the difference between the first target power and the current output power of the photovoltaic module is less than a power threshold. In the scenario of charging the energy storage battery, the energy input to the battery decreases, and the input current gradually decreases below the current threshold. In the scenario of discharging the energy storage battery, the energy output to the battery decreases, and the output current gradually decreases below the current threshold. This method can, under normal lighting conditions, achieve the simplest and most direct reduction of the input or output current of the energy storage battery to below the current threshold without any power limiting operation on the photovoltaic module. Therefore, it can maximize the utilization of solar energy and achieve smooth battery disconnection.

[0030] Method 2 The controller responds to the photovoltaic module’s current output power being greater than the rated power of the second power converter by controlling the photovoltaic module to output at the second target power and controlling the second power converter to output at the rated power, wherein the absolute value of the difference between the second target power and the rated power is less than the power threshold.

[0031] For example, under strong overall sunlight, the photovoltaic (PV) module's current output power is 1400W, the second power converter's rated power is 1000W, and its current output power is 500W. The PV module is charging the energy storage battery, and its current output power exceeds the second power converter's rated power. The second target power is 1000W. The controller adjusts the duty cycle of the first power converter's drive signal to reduce the PV module's output power from 1400W to 1000W, effectively reducing it to the second power converter's rated power. Then, the controller sends a command to the second power converter to increase its output power from 500W to 1000W. When the second power converter's output power stabilizes at 1000W, all 1000W of power generated by the PV module is transmitted to the grid through the second power converter (ignoring power losses in the PV-energy storage system). The energy storage battery's input current approaches 0A. The controller determines that the energy storage battery's input current is less than the current threshold and opens the control switch, disconnecting the energy storage battery from the PV-energy storage system.

[0032] When the current output power of the photovoltaic module exceeds the rated power of the second power converter, the photovoltaic module charges the energy storage battery. If the output power of the second power converter is simply increased, it will enter a power saturation state and cannot be further increased. This results in a portion of the photovoltaic module's output power still flowing to the energy storage battery, preventing the battery's input current from falling below the current threshold. Therefore, the controller needs to first dredge the photovoltaic module, controlling it to output at a second target power while controlling the second power converter to output at its rated power. The absolute value of the difference between the second target power and the rated power is less than the power threshold. At this point, the photovoltaic module's output power matches the second power converter's output power, and the battery's input current drops to near zero. Under high sunlight and high power conditions, this avoids the battery's input current failing to fall below the current threshold due to power saturation.

[0033] In some embodiments, such as Figure 2 As shown, the photovoltaic module includes multiple photovoltaic modules, and the output of each photovoltaic module is connected to the input of a second power converter through a first power converter; The controller, specifically, is used to adjust the output power of the target photovoltaic module by adjusting the duty cycle of the drive signal of the first power converter connected to the target photovoltaic module in response to the current output power of the photovoltaic module being greater than the rated power of the second power converter, so that the photovoltaic module outputs at the second target power; wherein, the target photovoltaic module is the top N photovoltaic modules in the photovoltaic module whose output power is sorted from largest to smallest, and N is a positive integer.

[0034] In an exemplary embodiment, Figure 2 The photovoltaic module includes four photovoltaic modules, namely photovoltaic module 1, photovoltaic module 2, photovoltaic module 3 and photovoltaic module 4. Each photovoltaic module is connected to the input terminal of a second power converter through a corresponding first power converter. For example, the first power converter can be a Buck circuit. Figure 2 The number of photovoltaic modules in the photovoltaic module is for illustrative purposes only. In reality, the number of photovoltaic modules in the photovoltaic module can be other numbers, and this application does not limit this.

[0035] In an exemplary embodiment, the controller can collect the voltage and current of each photovoltaic module in real time, and then calculate the output power of each photovoltaic module.

[0036] For example, if the current overall sunlight is weak, and the output powers of photovoltaic modules 1, 2, 3, and 4 are 100W, 200W, 300W, and 100W respectively, the current output power of the photovoltaic modules is 100W + 200W + 300W + 100W = 700W. The rated power of the second power converter is 1000W, and its current output power is 300W. Since the photovoltaic modules are charging the energy storage battery, and the current output power of the photovoltaic modules is less than the rated power of the second power converter, the controller sends a command to the second power converter to ramp up its output power from 300W to 700W. As the output power of the second power converter increases, the absolute value of the difference between the output power of the photovoltaic modules and the output power of the second power converter decreases, and the current input to the energy storage battery gradually decreases. When the output power of the second power converter stabilizes at 700W, all 700W of power generated by the photovoltaic modules is transmitted to the grid through the second power converter (ignoring the power loss of the photovoltaic-energy storage system), and the current input to the energy storage battery approaches 0A. The controller determines that the input current of the energy storage battery is less than the current threshold, and controls the switch to open, thus disconnecting the energy storage battery from the photovoltaic energy storage system.

[0037] For example, if the current overall sunlight is weak, the output power of photovoltaic module 1, photovoltaic module 2, photovoltaic module 3, and photovoltaic module 4 are 100W, 200W, 300W, and 100W respectively. The current output power of the photovoltaic module is 100W + 200W + 300W + 100W = 700W. The rated power of the second power converter is 1000W, and the current output power of the second power converter is 800W. The energy storage battery discharges to provide energy for the second power converter. The current output power of the photovoltaic module is less than the rated power of the second power converter. The first target power is 700W. The controller sends a command to the second power converter to reduce the output power of the second power converter from 800W to 700W. As the output power of the second power converter decreases, the absolute value of the difference between the output power of the photovoltaic module and the output power of the second power converter decreases, and the current output by the energy storage battery gradually decreases. When the output power of the second power converter stabilizes at 700W, the power received by the second power converter is the 700W power emitted by the photovoltaic module (ignoring the power loss of the photovoltaic-energy storage system), and the current output by the energy storage battery is close to 0A. The controller determines that the current output by the energy storage battery is less than the current threshold, and controls the switch to open, thus disconnecting the energy storage battery from the photovoltaic-energy storage system.

[0038] For example, under strong overall sunlight, the output powers of photovoltaic modules 1, 2, 3, and 4 are 400W, 400W, 500W, and 100W respectively. The current output power of the photovoltaic module is 400W + 400W + 500W + 100W = 1400W. The rated power of the second power converter is 1000W, and its current output power is 500W. The photovoltaic module is charging the energy storage battery, and its current output power is greater than the rated power of the second power converter. Subsequently, the controller identifies that photovoltaic module 3 has the highest output power among all photovoltaic modules, at 500W. The controller adjusts the duty cycle of the drive signal of the first power converter 3, causing photovoltaic module 3 to deviate from its maximum power point, reducing its output power from 500W to 400W. At this point, the output power of the photovoltaic module is 400W + 400W + 400W + 100W = 1300W, which is still greater than 1000W. Since the output power of photovoltaic modules 1, 2, and 3 is all 400W, the controller adjusts the duty cycle of the drive signals of the first power converters 1, 2, and 3 to deviate from their maximum power points, reducing their output power from 400W to 300W. At this point, the current output power of the photovoltaic modules is 300W + 300W + 300W + 100W = 1000W, which means the current output power of the photovoltaic modules is reduced to the rated power of the second power converter. Then, the controller sends a command to the second power converter to increase its output power from 500W to 1000W. When the output power of the second power converter stabilizes at 1000W, all 1000W of power generated by the photovoltaic modules is transmitted to the grid through the second power converter (ignoring the power loss of the photovoltaic-storage system), and the input current of the energy storage battery is close to 0A. The controller determines that the input current of the energy storage battery is less than the current threshold, and controls the switch to open, thus disconnecting the energy storage battery from the photovoltaic energy storage system.

[0039] During derating, the controller identifies the top N photovoltaic (PV) modules in descending order of output power and designates them as target PV modules. The controller prioritizes adjusting the duty cycle of the drive signal for the first power converter corresponding to the target PV module, reducing its output power. If the output power of the PV module after derating is still greater than the rated power of the second power converter, the next higher-power PV module can be selected for derating, or multiple higher-power PV modules can be drated simultaneously until the output power of the PV module equals the rated power of the second power converter. Prioritizing the derating of higher-power PV modules allows for targeted reduction of the processing power of the power converters with the heaviest workload and highest heat generation, thereby balancing the thermal stress of each power converter, improving the overall thermal management of the photovoltaic-storage system, and preventing derating or damage caused by localized overheating.

[0040] In some embodiments, the controller is further configured to increase the output power of the second power converter in response to the current input to the energy storage battery being greater than or equal to a current threshold, until the current input to the energy storage battery is less than the current threshold; or, in response to the current output to the energy storage battery being greater than or equal to a current threshold, decrease the output power of the second power converter until the current output to the energy storage battery is less than the current threshold.

[0041] When the input current to the energy storage battery is greater than or equal to the current threshold, the battery charges, indicating that the current output power of the second power converter is insufficient and there is surplus output power from the photovoltaic module flowing into the energy storage battery. Therefore, the output power of the second power converter is increased. Conversely, when the output current of the energy storage battery is greater than or equal to the current threshold, the battery discharges, indicating that the current output power of the second power converter is too high and the energy storage battery is providing power. Therefore, the output power of the second power converter is decreased. Through this correction method, the input current of the energy storage battery can be gradually and precisely adjusted to near zero during charging scenarios. If the input current is found to be less than the current threshold, the control switch is opened, disconnecting the energy storage battery from the photovoltaic-energy storage system. Similarly, if the output current is found to be less than the current threshold during discharging scenarios, the control switch is opened, disconnecting the energy storage battery from the photovoltaic-energy storage system. Even under conditions where the photovoltaic power feedforward information is inaccurate or losses are difficult to model accurately, low-current disconnection of the energy storage battery can still be reliably achieved.

[0042] Without considering the power loss of the photovoltaic-storage system, or with a relatively small power loss, simply controlling the absolute value of the difference between the output power of the photovoltaic module and the output power of the second power converter to be less than the power threshold can reduce the input current of the energy storage battery to less than the current threshold in the energy storage battery charging scenario, and reduce the output current of the energy storage battery to less than the current threshold in the energy storage battery discharging scenario. In situations where power loss in a photovoltaic-storage system is significant, to accelerate the reduction of the input or output current of the energy storage battery to below a current threshold, the following methods can be employed: In a charging scenario, first control the absolute value of the difference between the output power of the photovoltaic module and the output power of the second power converter to be less than the power threshold. This reduces the input current of the energy storage battery to a smaller value, which is still greater than or equal to the current threshold. Then, in response to the input current of the energy storage battery being greater than or equal to the current threshold, increase the output power of the second power converter until the input current of the energy storage battery is less than the current threshold, and then fine-tune the output power of the second power converter. Alternatively, in a discharging scenario, first control the absolute value of the difference between the output power of the photovoltaic module and the output power of the second power converter to be less than the power threshold. This reduces the output current of the energy storage battery to a smaller value, which is still greater than or equal to the current threshold. Then, in response to the output current of the energy storage battery being greater than or equal to the current threshold, decrease the output power of the second power converter until the output current of the energy storage battery is less than the current threshold, and then fine-tune the output power of the second power converter.

[0043] In some embodiments, the controller is further configured to determine the input or output current of the energy storage battery based on the output power of the photovoltaic module, the power loss of the first power converter, the output power of the second power converter, the power loss of the second power converter, and the voltage of the energy storage battery.

[0044] In an exemplary embodiment, in the scenario of charging the energy storage battery, the input current of the energy storage battery = (output power of the photovoltaic module - power loss of the first power converter - output power of the second power converter - power loss of the second power converter) / voltage of the energy storage battery; in the scenario of discharging the energy storage battery, the output current of the energy storage battery = (output power of the second power converter + power loss of the second power converter + power loss of the first power converter - output power of the photovoltaic module) / voltage of the energy storage battery.

[0045] Even without sampling the input or output current of the energy storage battery, the input or output current of the energy storage battery can be estimated based on the output power of the photovoltaic module, the power loss of the first power converter, the output power and power loss of the second power converter, and the voltage of the energy storage battery. Without increasing the hardware cost of a current sensor for the energy storage battery's input or output, by utilizing the output power of the photovoltaic module and the second power converter, which are already required to be measured in the photovoltaic-energy storage system, along with the voltage of the energy storage battery, an estimated value of the energy storage battery's input or output current can be indirectly obtained. This estimate can then be used to determine whether a current threshold has been reached, thereby expanding the applicability of low-current cutoff strategies and reducing the overall cost of the photovoltaic-energy storage system. Even without sampling the input or output current of the energy storage battery, a seamless switch from "with battery" to "without battery" can still be achieved to a certain extent.

[0046] In some embodiments, the controller is further configured to acquire the target operating parameters of the second power converter when the switch is open, and determine the target operating parameters as the initial operating parameters of the second power converter after the switch is open.

[0047] In an exemplary embodiment, the target operating parameters of the second power converter may include control quantities such as the reference current, the inner loop integral value of the current, and the phase of the modulation wave of the DC-DC converter module and the DC-AC converter module.

[0048] For example, in related technologies, when the energy storage battery is in a photovoltaic-energy storage system, the voltage of the battery-side capacitor C1 is stable, the DC-DC converter module is responsible for stabilizing the voltage of the bus capacitor C2, and the DC-AC converter module outputs power according to the power command. After the battery is disconnected, the DC-DC converter module needs to stabilize the voltage of the battery-side capacitor C1, and the DC-AC converter module needs to stabilize the voltage of the bus capacitor C2. Therefore, when the battery is disconnected, the switching of the control loop can easily cause the voltage of the battery-side capacitor C1 to oscillate.

[0049] In this embodiment, the target operating parameters of the second power converter are obtained when the switch is disconnected, and these target operating parameters are determined as the initial operating parameters of the second power converter after the switch is disconnected. After the battery is disconnected, the controller directly inherits the state before disconnection as the initial value, avoiding abrupt changes in the control quantity. This allows the photovoltaic-storage system to seamlessly transition from a steady state with a battery to a steady state without a battery, eliminating the regulation oscillations caused by abrupt changes in the control loop, achieving a smooth transition of the control loop, avoiding oscillations, and improving the dynamic performance and stability of the photovoltaic-storage system. Moreover, when the battery is disconnected, the smaller oscillations help reduce the capacitance value of the battery-side capacitor C1, which can improve the size and cost of the photovoltaic-storage system.

[0050] Exemplary methods In one exemplary embodiment, a control method for a photovoltaic-storage system is provided. The photovoltaic-storage system includes a photovoltaic module, an energy storage battery, a switch, a first power converter, and a second power converter; the output terminal of the photovoltaic module is connected to the input terminal of the second power converter through the first power converter, the energy storage battery is connected to the input terminal of the second power converter through the switch, and the output terminal of the second power converter is connected to the power grid. like Figure 3 As shown, the control method for the photovoltaic energy storage system includes: Step S101: Control the absolute value of the difference between the output power of the photovoltaic module and the output power of the second power converter to be less than the power threshold.

[0051] In step S102, in response to the current input or output of the energy storage battery being less than the current threshold, the control switch is turned off.

[0052] By controlling the absolute value of the difference between the output power of the photovoltaic module and the output power of the second power converter to be less than the power threshold, the amount of energy input or output from the energy storage battery participating in the photovoltaic-energy storage system can be reduced, thus reducing the input or output current of the energy storage battery. In response to the energy storage battery input or output current being less than the current threshold, the control switch is opened. Consequently, after the switch is opened, the rate of change of the energy storage battery input or output current is small, and the voltage fluctuation on the input side of the second power converter is small. This reduces the voltage fluctuation caused by the disconnection of the switch connected to the energy storage battery, allowing the photovoltaic-energy storage system to quickly enter a steady state.

[0053] In addition, in response to the current input or output of the energy storage battery being less than the current threshold, the control switch is opened. As a result, the rate of change of the current input or output of the energy storage battery is small after the switch is opened. Since there is parasitic inductance in the circuit where the energy storage battery is located, the voltage stress on the switch after the switch is opened is equal to the parasitic inductance value multiplied by the rate of change of the current input or output of the energy storage battery. The rate of change of the current input or output of the energy storage battery is small, and therefore the voltage stress on the switch after the switch is opened is also small, which can avoid the switch from being subjected to overvoltage.

[0054] Meanwhile, since power regulation is performed online, the photovoltaic-storage system does not need to be shut down, and the photovoltaic modules can always maintain maximum power output, avoiding energy waste.

[0055] In some embodiments, step S101 can be implemented in various ways, including but not limited to the following: Method 1 In response to the photovoltaic module's current output power being less than or equal to the rated power of the second power converter, the photovoltaic module is controlled to output at its current output power, and the second power converter is controlled to output at a first target power, wherein the absolute value of the difference between the first target power and the photovoltaic module's current output power is less than a power threshold.

[0056] When the current output power of the photovoltaic module is less than or equal to the rated power of the second power converter, it means that the second power converter is capable of transmitting all the photovoltaic energy to the grid. In this case, the photovoltaic module can be controlled to output at its current output power, and the second power converter can be controlled to output at a first target power. The absolute value of the difference between the first target power and the current output power of the photovoltaic module is less than a power threshold. In the scenario of charging the energy storage battery, the energy input to the battery decreases, and the input current gradually decreases below the current threshold. In the scenario of discharging the energy storage battery, the energy output to the battery decreases, and the output current gradually decreases below the current threshold. This method can, under normal lighting conditions, achieve the simplest and most direct reduction of the input or output current of the energy storage battery to below the current threshold without any power limiting operation on the photovoltaic module. Therefore, it can maximize the utilization of solar energy and achieve smooth battery disconnection.

[0057] Method 2 In response to the photovoltaic module's current output power being greater than the second power converter's rated power, the photovoltaic module is controlled to output at a second target power, and the second power converter is controlled to output at its rated power, wherein the absolute value of the difference between the second target power and the rated power is less than a power threshold.

[0058] When the current output power of the photovoltaic module exceeds the rated power of the second power converter, the photovoltaic module charges the energy storage battery. If the output power of the second power converter is simply increased, it will enter a power saturation state and cannot be further increased. This results in a portion of the photovoltaic module's output power still flowing to the energy storage battery, preventing the battery's input current from falling below the current threshold. Therefore, it is necessary to first drate the photovoltaic module, controlling it to output at a second target power while controlling the second power converter to output at its rated power. The absolute value of the difference between the second target power and the rated power is less than the power threshold. At this point, the output power of the photovoltaic module matches the output power of the second power converter, and the battery's input current drops to near zero. Under high sunlight and high power conditions, this avoids the battery's input current failing to fall below the current threshold due to power saturation.

[0059] In some embodiments, the photovoltaic module includes multiple photovoltaic modules, and the output of each photovoltaic module is connected to the input of a second power converter through a first power converter. Controlling the photovoltaic module to output a second target power includes: The output power of the target photovoltaic module is adjusted by adjusting the duty cycle of the first power converter connected to the target photovoltaic module, so that the photovoltaic module outputs at the second target power; wherein, the target photovoltaic module is the top N photovoltaic modules in the photovoltaic module whose output power is sorted from largest to smallest, and N is a positive integer.

[0060] When implementing derating, the top N photovoltaic (PV) modules, ranked by output power from highest to lowest, are identified as target PV modules. The duty cycle of the drive signal for the first power converter corresponding to the target PV module is adjusted first to reduce its output power. If the output power of the PV module after derating is still greater than the rated power of the second power converter, the next higher-power PV module can be selected for derating, or multiple higher-power PV modules can be drated simultaneously until the output power of the PV module equals the rated power of the second power converter. Prioritizing the derating of higher-power PV modules allows for targeted reduction of the processing power of the power converters with the heaviest workload and highest heat generation, thereby balancing the thermal stress of each power converter, improving the overall thermal management of the photovoltaic-storage system, and preventing derating or damage caused by localized overheating.

[0061] In some embodiments, the control method for the optical storage system further includes: In response to the energy storage battery input current being greater than or equal to a current threshold, the output power of the second power converter is increased until the energy storage battery input current is less than the current threshold; or, in response to the energy storage battery output current being greater than or equal to a current threshold, the output power of the second power converter is decreased until the energy storage battery output current is less than the current threshold.

[0062] When the input current to the energy storage battery is greater than or equal to the current threshold, the battery charges, indicating that the current output power of the second power converter is insufficient and there is surplus output power from the photovoltaic module flowing into the energy storage battery. Therefore, the output power of the second power converter is increased. Conversely, when the output current of the energy storage battery is greater than or equal to the current threshold, the battery discharges, indicating that the current output power of the second power converter is too high and the energy storage battery is providing power. Therefore, the output power of the second power converter is decreased. Through this correction method, the input current of the energy storage battery can be gradually and precisely adjusted to near zero during charging scenarios. If the input current is found to be less than the current threshold, the control switch is opened, disconnecting the energy storage battery from the photovoltaic-energy storage system. Similarly, if the output current is found to be less than the current threshold during discharging scenarios, the control switch is opened, disconnecting the energy storage battery from the photovoltaic-energy storage system. Even under conditions where the photovoltaic power feedforward information is inaccurate or losses are difficult to model accurately, low-current disconnection of the energy storage battery can still be reliably achieved.

[0063] Without considering the power loss of the photovoltaic-storage system, or with a relatively small power loss, simply controlling the absolute value of the difference between the output power of the photovoltaic module and the output power of the second power converter to be less than the power threshold can reduce the input current of the energy storage battery to less than the current threshold in the energy storage battery charging scenario, and reduce the output current of the energy storage battery to less than the current threshold in the energy storage battery discharging scenario. In situations where power loss in a photovoltaic-storage system is significant, to accelerate the reduction of the input or output current of the energy storage battery to below a current threshold, the following methods can be employed: In a charging scenario, first control the absolute value of the difference between the output power of the photovoltaic module and the output power of the second power converter to be less than the power threshold. This reduces the input current of the energy storage battery to a smaller value, which is still greater than or equal to the current threshold. Then, in response to the input current of the energy storage battery being greater than or equal to the current threshold, increase the output power of the second power converter until the input current of the energy storage battery is less than the current threshold, and then fine-tune the output power of the second power converter. Alternatively, in a discharging scenario, first control the absolute value of the difference between the output power of the photovoltaic module and the output power of the second power converter to be less than the power threshold. This reduces the output current of the energy storage battery to a smaller value, which is still greater than or equal to the current threshold. Then, in response to the output current of the energy storage battery being greater than or equal to the current threshold, decrease the output power of the second power converter until the output current of the energy storage battery is less than the current threshold, and then fine-tune the output power of the second power converter.

[0064] For technical details not described in detail in this embodiment, please refer to the specific content of the optical storage system provided in the above embodiments of this application, which will not be repeated here.

[0065] Exemplary controller Accordingly, embodiments of this application also provide a controller for executing the control method of the optical storage system provided in any of the above embodiments of this application.

[0066] For technical details not described in detail in this embodiment, please refer to the specific processing content of the control method of the photovoltaic energy storage system provided in the above embodiments of this application, which will not be repeated here.

[0067] 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. The same or similar parts between the various embodiments can be referred to each other.

[0068] The modules and circuits in the various embodiments of this application can be merged, divided, and deleted according to actual needs.

[0069] Finally, it should be noted that in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0070] 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 photovoltaic energy storage system, characterized in that, It includes photovoltaic modules, energy storage batteries, switches, a first power converter, a second power converter, and a controller; The output terminal of the photovoltaic module is connected to the input terminal of the second power converter through the first power converter, the energy storage battery is connected to the input terminal of the second power converter through the switch, and the output terminal of the second power converter is connected to the power grid. The controller is configured to control the absolute value of the difference between the output power of the photovoltaic module and the output power of the second power converter to be less than a power threshold, and to control the switch to open in response to the input or output current of the energy storage battery being less than a current threshold.

2. The photovoltaic energy storage system according to claim 1, characterized in that, The controller is specifically configured to, in response to the current output power of the photovoltaic module being less than or equal to the rated power of the second power converter, control the photovoltaic module to output at the current output power and control the second power converter to output at a first target power, wherein the absolute value of the difference between the first target power and the current output power is less than the power threshold.

3. The photovoltaic energy storage system according to claim 1, characterized in that, The controller is specifically configured to, in response to the current output power of the photovoltaic module being greater than the rated power of the second power converter, control the photovoltaic module to output at a second target power and control the second power converter to output at the rated power, wherein the absolute value of the difference between the second target power and the rated power is less than the power threshold.

4. The photovoltaic energy storage system according to claim 3, characterized in that, The photovoltaic module includes multiple photovoltaic modules, and the output terminal of each photovoltaic module is connected to the input terminal of the second power converter through a first power converter. The controller is specifically configured to adjust the output power of the target photovoltaic module by adjusting the duty cycle of the drive signal of the first power converter connected to the target photovoltaic module in response to the current output power of the photovoltaic module being greater than the rated power of the second power converter, so that the photovoltaic module outputs at the second target power; wherein the target photovoltaic module is the top N photovoltaic modules in the photovoltaic module whose output power is sorted from largest to smallest, and N is a positive integer.

5. The photovoltaic energy storage system according to any one of claims 1 to 4, characterized in that, The controller is further configured to acquire the target operating parameters of the second power converter when the switch is open, and determine the target operating parameters as the initial operating parameters of the second power converter after the switch is open.

6. The photovoltaic energy storage system according to claim 1, characterized in that, The controller is further configured to, in response to the current input to the energy storage battery being greater than or equal to the current threshold, increase the output power of the second power converter until the current input to the energy storage battery is less than the current threshold, or, in response to the current output to the energy storage battery being greater than or equal to the current threshold, decrease the output power of the second power converter until the current output to the energy storage battery is less than the current threshold.

7. A control method for a photovoltaic energy storage system, characterized in that, The photovoltaic-storage system includes a photovoltaic module, an energy storage battery, a switch, a first power converter, and a second power converter; the output terminal of the photovoltaic module is connected to the input terminal of the second power converter through the first power converter, the energy storage battery is connected to the input terminal of the second power converter through the switch, and the output terminal of the second power converter is connected to the power grid; The control method includes: The absolute value of the difference between the output power of the photovoltaic module and the output power of the second power converter is less than a power threshold. In response to the energy storage battery input or output current being less than a current threshold, the switch is controlled to open.

8. The control method for the photovoltaic energy storage system according to claim 7, characterized in that, The absolute value of the difference between the output power of the photovoltaic module and the output power of the second power converter is less than a power threshold, including: In response to the photovoltaic module's current output power being less than or equal to the rated power of the second power converter, the photovoltaic module is controlled to output at the current output power, and the second power converter is controlled to output at a first target power, wherein the absolute value of the difference between the first target power and the current output power is less than the power threshold.

9. The control method for the photovoltaic energy storage system according to claim 7, characterized in that, The absolute value of the difference between the output power of the photovoltaic module and the output power of the second power converter is less than a power threshold, including: In response to the photovoltaic module's current output power being greater than the rated power of the second power converter, the photovoltaic module is controlled to output at a second target power, and the second power converter is controlled to output at the rated power, wherein the absolute value of the difference between the second target power and the rated power is less than the power threshold.

10. The control method for the photovoltaic energy storage system according to claim 9, characterized in that, The photovoltaic module includes multiple photovoltaic modules, and the output terminal of each photovoltaic module is connected to the input terminal of the second power converter through a first power converter. The control of the photovoltaic module to output at a second target power includes: The output power of the target photovoltaic module is adjusted by adjusting the duty cycle of the first power converter connected to the target photovoltaic module, so that the photovoltaic module outputs at the second target power; wherein, the target photovoltaic module is the top N photovoltaic modules in the photovoltaic module whose output power is sorted from largest to smallest, and N is a positive integer.

11. The control method for the photovoltaic energy storage system according to claim 7, characterized in that, The method further includes: In response to the current input to the energy storage battery being greater than or equal to the current threshold, the output power of the second power converter is increased until the current input to the energy storage battery is less than the current threshold; or, in response to the current output to the energy storage battery being greater than or equal to the current threshold, the output power of the second power converter is decreased until the current output to the energy storage battery is less than the current threshold.

12. A controller, characterized in that, A control method for implementing the photovoltaic energy storage system as described in any one of claims 7 to 11.

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