Grid-connected switch detection method and device of energy storage system and storage medium

Abstract

This application relates to the field of switch fault detection technology, and particularly to a method, device, and storage medium for detecting grid-connected switches in an energy storage system. The method includes controlling the controller to send a grid-connected closing signal to the grid-connected switch; when the battery connected to the inverter meets a first preset battery condition, determining whether a grid-connected switch has experienced a grid-connected closing fault based on the inverter's inverter grid-connected voltage condition, the inverter grid-connected current condition, and the duty cycle change condition of the energy storage system's grid-connected loop output; and when the battery connected to the inverter meets a second preset battery condition, determining whether a grid-connected switch has experienced a grid-connected closing fault based on the inverter grid-connected current condition and the duty cycle change condition of the energy storage system's grid-connected loop output. This application can detect whether the grid-connected switch has successfully engaged in a timely and accurate manner at the moment of switching between grid-connected and off-grid modes.

Description

Technical Field

[0001] This application relates to the field of switch fault detection technology, and in particular to a method, device and storage medium for detecting grid-connected switches in an energy storage system. Background Technology

[0002] In energy storage systems, the grid-connection switch is a key actuator connecting the inverter output to the public power grid. Its activation and deactivation directly determine whether the inverter establishes an effective electrical connection with the grid, thus affecting the safety and stability of the grid connection process. During grid connection, the energy storage system's controller performs voltage regulation control on the inverter output in off-grid operation mode, and sends a grid-connection switch activation drive signal after the grid connection conditions are met, switching the inverter from off-grid control to grid-connected control.

[0003] When the energy storage system meets the grid connection conditions, such as voltage, frequency, and phase synchronization, the controller sends a drive signal to command the grid connection switch to engage. Ideally, the grid connection switch should act immediately, connecting the inverter output to the grid. However, if the grid connection switch fails to engage due to coil damage, mechanical jamming, contact oxidation, or other reasons, the inverter output remains in an "off-grid" no-load state. However, the energy storage system's control loop has already switched from "off-grid voltage regulation control" to "grid-connected power control." Because the grid connection switch is not engaged, the inverter and grid are not effectively connected, and the inverter's output voltage loses grid clamping, rapidly deviating from its normal value. To track current commands, the control loop continuously adjusts the output voltage, easily leading to inverter output erratic behavior, triggering protection alarms such as "inverter overvoltage" and "frequency anomaly," and ultimately shutting down the system.

[0004] Therefore, there is an urgent need for a method that can detect whether the grid-connected switch has been successfully engaged in a timely and accurate manner at the moment of switching between off-grid and grid-connected modes. Summary of the Invention

[0005] This application provides a method, device, and storage medium for detecting the grid-connected switch of an energy storage system, which can detect in a timely and accurate manner whether the grid-connected switch has successfully engaged at the moment of switching between off-grid and grid-connected modes. This application provides the following technical solution: In a first aspect, this application provides a method for detecting a grid-connected switch in an energy storage system, the energy storage system including an inverter, a grid-connected switch for connecting the inverter and the power grid, and a controller connecting the inverter and the grid-connected switch, characterized in that the method includes: The controller is controlled to send a grid connection closing signal to the grid connection switch; When the battery connected to the inverter meets the first battery preset condition, the grid-connected switch is determined to have a grid-connected closing fault based on the inverter grid-connected voltage condition, the inverter grid-connected current condition, and the duty cycle change condition of the grid-connected loop output of the energy storage system. When the battery connected to the inverter meets the second battery preset conditions, the grid-connected switch is determined to have experienced a grid-connected closing fault based on the inverter's grid-connected current conditions and the duty cycle change conditions of the grid-connected loop output of the energy storage system.

[0006] In one specific implementation scheme, the preset condition for the first battery is that the sum of the voltages of all the cells of the battery is greater than a first threshold. The second battery preset condition is: the sum of the voltages of all the battery cells is less than or equal to a first threshold. The first threshold is determined based on the effective value of the grid voltage and the turns ratio of the transformer in the resonant circuit, which is used to connect the battery and the inverter.

[0007] In one specific implementation scheme, the inverter grid connection voltage condition is: the inverter grid connection voltage value of the inverter is greater than the rated value of the grid voltage by a preset multiple; The preset multiple is determined based on the power grid and the load powered by the inverter.

[0008] In one specific implementation scheme, the preset multiple is determined based on the power grid and the load powered by the inverter, including: The first ratio is determined based on the quotient of the maximum grid-connected voltage of the inverter and the maximum grid voltage. A second ratio is determined based on the quotient of the upper limit of the operating voltage of the load connected to the inverter and the rated voltage of the load connected to the inverter. The preset multiple is determined to be the smaller value between the first ratio and the second ratio.

[0009] In one specific implementation, the inverter grid-connected current condition is: the inverter grid-connected current value of the inverter is less than or equal to the current threshold. The current threshold is determined based on the inverter's current values ​​in standby and grid-connected charging states.

[0010] In a specific feasible implementation, the current threshold is determined based on the inverter's current values ​​in standby and grid-connected charging states, including: The current threshold is determined to be the average of the first current value and the second current value; Wherein, the first current value is the standby current of the inverter in standby mode, and the second current value is the grid-connected current of the inverter when the energy storage system is operating at the set minimum charging power.

[0011] In one specific implementation scheme, the duty cycle change condition is: during the PI control process, the change in the duty cycle of each PI adjustment of the grid-connected loop exceeds a preset duty cycle threshold. Wherein, the preset duty cycle threshold is the change in duty cycle of the grid-connected loop during each PI adjustment when the energy storage system operates at the set maximum charging power.

[0012] In one specific implementation scheme, the grid-connected switch detection method further includes: When the battery connected to the inverter meets the first battery preset condition or the second battery preset condition, the grid connection failure determination is performed after a first preset time; the first preset time is consistent with the closing response time of the grid connection switch.

[0013] In one specific implementation scheme, the grid-connected switch detection method further includes: The grid connection failure determination is performed within a second preset time: it is determined whether the inverter grid connection voltage condition, the inverter grid connection current condition, and the duty cycle change condition of the grid connection loop output of the energy storage system are met within the second preset time. The grid connection failure determination is performed within a third preset time period: it is determined whether the inverter grid connection current condition of the inverter and the duty cycle change condition of the grid connection loop output of the energy storage system are met within the third preset time period. Wherein, the second preset time is less than the third preset time, and the sum of the first preset time and the second preset time, as well as the sum of the first preset time and the third preset time, are all less than the fault response judgment time of the energy storage system.

[0014] Secondly, this application provides an electronic device, including a processor and a memory, wherein the memory stores a program, which is loaded and executed by the processor to implement the grid-connected switch detection method as described above.

[0015] Thirdly, this application provides a computer-readable storage medium storing a program that, when executed by a processor, is used to implement the grid-connected switch detection method as described above.

[0016] This application, based on an energy storage system including an inverter, a grid-connected switch, and a controller, first sends a grid-connected closing signal to the grid-connected switch through the controller. Then, it employs different fault determination paths depending on the state of the battery connected to the inverter: when the battery meets the first preset battery condition, it determines whether a grid-connected switch has experienced a grid-connected closing fault by combining the inverter's inverter grid-connected voltage condition, the inverter's inverter grid-connected current condition, and the duty cycle change condition of the grid-connected loop output of the energy storage system; when the battery meets the second preset battery condition, it determines whether a grid-connected switch has experienced a grid-connected closing fault by combining the inverter's inverter grid-connected current condition and the duty cycle change condition of the grid-connected loop output of the energy storage system. Therefore, this application does not use a single parameter to judge the grid connection switch status during grid connection switching. Instead, it combines the voltage response, current response, and grid connection loop control output changes of the inverter output side, and distinguishes the judgment method according to different battery states. This allows abnormal states caused by unsuccessful grid connection switch closure to be identified more specifically, thereby improving the accuracy and adaptability of grid connection switch closure status detection. It also helps to promptly detect abnormal control states caused by unsuccessful grid connection switch closure during off-grid to grid-connected switching, thereby improving the operational stability and safety of the energy storage system during grid connection switching.

[0017] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, the preferred embodiments of this application are described in detail below with reference to the accompanying drawings. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the energy storage system in an embodiment of this application.

[0019] Figure 2 This is a control block diagram of the inverter grid-connected control loop in the embodiments of this application.

[0020] Figure 3 This is a flowchart illustrating the grid connection switch detection method for an energy storage system in an embodiment of this application.

[0021] Figure 4 This is a schematic diagram of the overall process of the grid connection switch detection method for the energy storage system in the embodiments of this application.

[0022] Figure 5 This is a block diagram of the electronic device for detecting the grid connection switch of the energy storage system in an embodiment of this application. Detailed Implementation

[0023] The specific embodiments of this application will be described in further detail below with reference to the accompanying drawings and examples. The following examples are used to illustrate this application, but are not intended to limit the scope of this application.

[0024] This application provides a method for detecting the grid connection switch of an energy storage system, referring to... Figure 1 The diagram below illustrates the structure of an energy storage system in this embodiment. The energy storage system includes an inverter, a grid-connected switch for connecting the inverter and the power grid, and a controller connecting the inverter and the grid-connected switch. The grid-connected switch is located between the inverter and the power grid and is used to control the connection and disconnection between the inverter and the power grid. The controller is connected to both the inverter and the grid-connected switch and is used to control the switching of the inverter's operating state. When the grid connection conditions are met, the controller closes the grid-connected switch to establish an electrical connection between the inverter and the power grid.

[0025] In this embodiment, the energy storage system further includes a battery for supplying power to the inverter and a resonant circuit disposed between the battery and the inverter. Specifically, the resonant circuit is an LLC circuit. The battery provides electrical energy, the LLC circuit converts the electrical energy output from the battery and transmits it to the inverter, and the inverter converts the input electrical energy into AC output.

[0026] Optionally, in this embodiment, the grid-connected switch is a relay. Therefore, the following description of the grid-connected switch closing process and its fault detection process will be based on a relay as the specific execution structure. Other types of grid-connected switches may also be selected in specific implementations, and this application does not limit the specific type of grid-connected switch.

[0027] Combination Figure 1 and Figure 2 The bus voltage V_BUS is the voltage on the bus side between the LLC circuit and the inverter. The actual bus voltage value BUS_real corresponds to the bus voltage V_BUS. The inverter grid-connected current value I_inv is the output current of the inverter port used to connect to the grid. The inverter grid-connected voltage value V_inv is the voltage of the inverter port used to connect to the grid.

[0028] Reference Figure 2 This is a control block diagram of the inverter grid-connected control loop provided in this application embodiment. The grid-connected control loop is divided into a bus voltage outer loop and a current inner loop. The bus voltage outer loop is used to generate the outer loop adjustment result based on the deviation between the bus voltage reference value BUS_ref and the actual bus voltage value BUS_real. The current inner loop is used to generate the duty cycle control quantity D of the grid-connected loop output based on the deviation between the inverter current target value I_ref and the inverter grid-connected current value I_inv.

[0029] Specifically, in the voltage outer loop, the bus voltage reference value BUS_ref is compared with the actual bus voltage value BUS_real to obtain the bus voltage deviation signal. This deviation signal is then regulated by a PI controller and output to the limiting module Limit. The limiting module Limit limits the output of the PI-regulated signal to obtain the input for the current inner loop. In the current inner loop, the inverter current target value I_ref is compared with the actual sampled inverter grid-connected current value I_inv to obtain the current deviation signal. This deviation signal is then regulated by a PI controller and outputs a duty cycle control quantity D. D characterizes the output control result of the grid-connected control loop, thereby achieving closed-loop control of the inverter grid-connected process.

[0030] In this embodiment, the bus voltage V_BUS corresponds to the bus-side voltage on the inverter input side, the inverter grid-connected current value I_inv and the inverter grid-connected voltage value V_inv correspond to the current and voltage on the AC side of the inverter, and the grid-connected switch is used to connect the inverter and the power grid. This embodiment utilizes the inverter's AC-side current, AC-side voltage, and loop control results to determine whether the grid-connected switch closes normally when receiving the grid-connected closing signal sent by the controller, i.e., whether the grid-connected switch has a grid-connected closing fault.

[0031] Reference Figure 3 This is a flowchart illustrating a grid connection switch detection method for an energy storage system according to an embodiment of this application. The method includes at least the following steps: Step S1: The controller sends a grid connection closing signal to the grid connection switch.

[0032] In step S1, when the energy storage system is in off-grid operation, the controller determines whether the grid connection conditions are met. If the grid connection conditions are met, the controller synchronizes the inverter output with the grid voltage. The grid connection conditions include at least synchronization of the inverter output with the grid voltage in terms of voltage amplitude, frequency, and phase. Subsequently, the controller sends a grid connection closing signal to the grid connection switch to control the grid connection switch to close.

[0033] Step S2: When the battery connected to the inverter meets the first battery preset conditions, determine whether the grid connection switch has a grid connection failure based on the inverter grid connection voltage condition, the inverter grid connection current condition, and the duty cycle change condition of the grid connection loop output of the energy storage system.

[0034] Step S3: When the battery connected to the inverter meets the preset conditions of the second battery, determine whether the grid connection switch has a grid connection failure based on the inverter grid connection current conditions and the duty cycle change conditions of the grid connection loop output of the energy storage system.

[0035] In the grid-connected switch detection method, after the controller sends a grid-connected closing signal to the grid-connected switch, it does not use a single parameter to uniformly determine whether the grid-connected switch is properly closed. Instead, it uses corresponding fault judgment paths based on the different preset states of the batteries connected to the inverter: when the battery meets the first preset battery condition, the judgment is made in combination with the inverter grid-connected voltage condition, the inverter grid-connected current condition, and the duty cycle change condition of the grid-connected loop output; when the battery meets the second preset battery condition, the judgment is made in combination with the inverter grid-connected current condition and the duty cycle change condition of the grid-connected loop output. Through this method, the success of the grid-connected switch closure can be more specifically identified based on the response differences during grid-connected switching under different battery states. This improves the accuracy and adaptability of the grid-connected switch closure detection and facilitates timely detection of whether the grid-connected switch has successfully engaged during the switchover between off-grid and on-grid modes.

[0036] In the grid-connected switch detection method, after the controller sends a grid-connected closing signal to the grid-connected switch, and if the battery connected to the inverter meets either the first preset battery condition or the second preset battery condition, the controller determines whether a grid-connected switch has experienced a grid-connected closing fault after a first preset time t1. The first preset time t1 is consistent with the closing response time of the grid-connected switch and is used to reserve response time for the grid-connected switch closing action. For example, when the closing response time of the grid-connected switch is less than 10ms, the first preset time can be set to 10ms.

[0037] In the grid-connected switch detection method, after a first preset time t1, the controller uses a sliding detection window to detect the operating parameters of the grid-connected control loop. The duration of the sliding detection window is used to limit the time range of real-time parameter detection, and its specific duration can be set according to the controller's computing power and the response requirements of the control system.

[0038] In one specific embodiment, when the battery connected to the inverter meets the first battery preset condition, the duration of the sliding detection window can be set to a second preset time t21. During the second preset time t21, a grid connection failure determination is performed: it is determined whether the inverter grid connection voltage condition, the inverter grid connection current condition, and the duty cycle change condition of the grid connection loop output of the energy storage system are met within the second preset time t21.

[0039] In one specific embodiment, when the battery connected to the inverter meets the second battery preset condition, the duration of the sliding detection window can be set to a second preset time t21. Based on the inverter grid-connected current condition and the duty cycle change condition of the grid-connected loop output of the energy storage system, it is determined whether the grid-connected switch has experienced a grid-connected closing fault.

[0040] In the above embodiment, the second preset time t21 is less than the third preset time t22. This is because the second preset time t21 is the detection duration set for step S2, and the third preset time t22 is the detection duration set for step S3. Compared to the fault detection process in step S3, the fault detection process in step S2 includes an additional "inverter grid-connected voltage condition." If a grid-connected switch closure fault occurs, causing an overvoltage phenomenon, this is a high-risk phenomenon caused by a grid-connected switch closure fault. Therefore, if the inverter grid-connected voltage is involved in the fault detection process, the detection duration should be slightly shorter. Thus, the continuous detection time in step S2 is less than the continuous detection time in step S3, i.e., t21 < t22.

[0041] In the above embodiments, the sum of the first preset time t1 and the second preset time t21, and the sum of the first preset time t1 and the third preset time t22 are both less than the fault response judgment time t of the energy storage system.

[0042] In one specific embodiment, the second preset time is used to continuously determine the inverter grid-connected voltage condition, inverter grid-connected current condition, and duty cycle change condition of the grid-connected loop output of the energy storage system when the first battery preset condition is met. To prevent malfunctions caused by transient interference and to avoid misjudgments caused by critical fluctuations in the inverter grid-connected voltage or current value, the sampled inverter grid-connected voltage and / or inverter grid-connected current values ​​can be filtered, and the number of filtering operations is determined according to the sampling accuracy. Generally, the number of filtering operations is less when the sampling accuracy is higher, and more when the sampling accuracy is lower. Let the number of filtering operations be n, and the time required for the controller to execute the filtering algorithm once be Tn; at the same time, to ensure the continuity of the fault determination result, let the number of continuous fault judgments be m, and the time required for the controller to execute a fault judgment once be Tm. Then, the second preset time includes the time required to complete the filtering process and the time required to complete the preset number of fault judgments. The second preset time can be expressed as: t21 = nTn + mTm. Where nTn represents the time required to complete the filtering process, and mTm represents the time required to complete the preset number of fault judgments. In this embodiment, the second preset time t21 can be 5ms. Since the inverter grid-connected voltage value may enter the abnormal judgment range when the first battery preset condition is met, and the abnormal inverter grid-connected voltage corresponds to overvoltage risk, the overvoltage fault has a more direct impact on the inverter and its connected load. Therefore, the second preset time is set to a relatively short duration to complete fault identification and output fault processing and alarms more quickly.

[0043] In one specific embodiment, the third preset time is used to continuously determine the inverter grid-connected current condition of the inverter and the duty cycle change condition of the grid-connected loop output of the energy storage system when the second battery preset condition is met. The setting of the third preset time is constrained by both the controller's computing power and the energy storage system's fault response determination time. Specifically, the maximum detection time window that can be tolerated without affecting the controller's normal control response is predetermined as T1; at the same time, let the energy storage system's fault response determination time be T. Since the first preset time t1 has elapsed after the grid-connection closing signal is issued, the remaining available time for fault determination is T-t1. Therefore, the third preset time is the smaller value between the maximum detection time window T1 and the remaining available time T-t1, and the third preset time can be expressed as: t22=min(T1, T-t1). In this embodiment, the third preset time t22 can be 10ms. Since the inverter grid-connected voltage condition is no longer used when the second battery preset condition is met, but the grid-connected current condition and duty cycle change condition are used to determine the grid-connected fault, a relatively long third preset time can be used to improve the stability and accuracy of the fault determination.

[0044] Within the sliding detection window, the controller monitors the parameters of the grid-connected control loop in real time. These parameters include at least the inverter grid-connected voltage value V_inv, the inverter grid-connected current value I_inv, and the duty cycle change ΔD of the grid-connected loop output. The duty cycle change ΔD represents the change in duty cycle of the grid-connected loop during each PI adjustment in the PI control process. These parameters are collected by the voltage and current sampling circuit in the energy storage system and processed and calculated by the controller to serve as the basis for determining grid-connected switch closure faults.

[0045] In one specific embodiment, for step S2, the first battery preset condition is that the sum of the voltages of all battery cells is greater than a first threshold. The first threshold is used to characterize whether, in the current energy storage system, the battery side, after being transformed by the resonant circuit, has the voltage support capability to raise the inverter grid-connected voltage value to the corresponding judgment range. Specifically, the first threshold is determined based on the effective value of the grid voltage and the turns ratio of the transformer. This can be understood as follows: the voltage reference corresponding to the grid side is converted to the battery side according to the transformer's transformation relationship to obtain the corresponding threshold voltage on the battery side. When the sum of the voltages of all battery cells is greater than this threshold voltage, it indicates that the battery side, after being transformed by the LLC circuit, can provide voltage support to the inverter side to further increase the inverter grid-connected voltage. At this time, the battery is determined to meet the first battery preset condition.

[0046] Specifically, the controller acquires the number of cells connected in series, n, and the voltage of a single cell, V. bat Given the transformer turns ratio N, then the first threshold T1 = V eff / N, V eff =Vgrid , where V grid V is the grid voltage value. eff Here, N represents the effective value of the grid voltage, and N is the transformer turns ratio of the resonant circuit (LLC circuit). The controller then compares the sum of the voltages of all battery cells with a first threshold to determine if the first battery preset condition is met. When the product of the number of cells connected in series and the voltage of a single cell is greater than the first threshold, i.e. The conditions for the first battery are determined to be met.

[0047] In one specific embodiment, for step S3, the preset conditions for the second battery are: , where V grid V is the grid voltage value. eff is the effective value of the grid voltage, and N is the turns ratio of the transformer in the resonant circuit (LLC circuit).

[0048] It is worth noting that the first battery preset condition and the second battery preset condition are set because when the grid connection switch fails to close successfully, the voltage support capability that the battery side can provide after transformation by the resonant circuit is different, and the abnormal phenomena that the inverter side may exhibit are also different. Therefore, it is necessary to distinguish the operating conditions based on the voltage support capability of the battery side.

[0049] Specifically, in combination Figure 1 The battery is connected to the inverter via a resonant circuit. The battery-side voltage is transformed by the transformer in the resonant circuit to form the bus voltage, which further affects the output voltage of the inverter. During the inverter's transition from off-grid to grid-connected mode, the grid-connected voltage reference on the inverter side is related to the grid voltage value. For the grid voltage value V_grid, the corresponding peak voltage V_grid × [missing value] can be calculated first. Then, the voltage is calculated based on the transformer's turns ratio N, and applied to the battery side. This yields the corresponding threshold voltage on the battery side, i.e., the first threshold voltage T1 = (V_grid × ... ) / N. The first threshold is used to characterize whether, in the current energy storage system, the battery side, after being converted by the resonant circuit, has the ability to support the inverter side to reach the corresponding grid-connected voltage level.

[0050] For example, when the voltage of a single battery cell is relatively high, such as 3.7V per cell, 2 cells, a transformer turns ratio of 60:1, and a gain of 1, the maximum bus voltage that the battery side can provide can reach 3.7V × 2 × 60 × 1 = 444V, and the corresponding inverter-side voltage is approximately 444V / ... ≈314V. This result indicates that, under these conditions, the battery side, after being converted by the resonant circuit, can provide strong voltage support to the inverter side.

[0051] When the voltage of a single battery cell is low, for example, 2.6V per cell, with 2 cells, a transformer turns ratio of 60:1, and a gain of 1, the maximum bus voltage that the battery side can provide is 2.6V × 2 × 60 × 1 = 312V, and the corresponding inverter-side voltage is approximately 312V / ... ≈220.6V. This result indicates that, under these conditions, the voltage support that the battery side can provide after being converted by the resonant circuit is relatively limited.

[0052] Based on the above analysis, when the sum of the voltages of all battery cells is greater than the first threshold T1, i.e., n×V_bat>(V_grid× The value of ) / N indicates that the battery side has a strong voltage support capability after being transformed by the resonant circuit. Therefore, this operating condition is set as the first battery preset condition. When the sum of the voltages of all battery cells is less than or equal to the first threshold T1, that is, n×V_bat≤(V_grid× The value of ) / N indicates that the voltage support capability that the battery side can provide after being transformed by the resonant circuit is limited. Therefore, this operating condition is set as the preset condition for the second battery.

[0053] In the above embodiments, regarding steps S2 and S3, the "inverter grid-connected voltage condition of the inverter" is set as condition a, the "inverter grid-connected current condition of the inverter" is set as condition b, and the "duty cycle change condition of the grid-connected loop output of the energy storage system" is set as condition c. The specific implementation process of conditions a, b, and c will be described in detail below.

[0054] It is worth noting that when the first battery preset condition is met, conditions a, b, and c need to be jointly determined; when the second battery preset condition is met, only conditions b and c need to be determined. This is because the abnormal phenomena exhibited by the inverter side when the grid-connected switch fails to close under the two operating conditions are different.

[0055] Specifically, in combination Figure 1 and Figure 2 When the first battery's preset conditions are met, it indicates that the battery side has a strong voltage support capability after being transformed by the resonant circuit. In this case, if the grid-connected switch fails to close successfully, the inverter grid-connected current value cannot be effectively established, and the grid-connected control loop output will continuously change. Simultaneously, since the battery side can still continue to provide high voltage support to the inverter side, the inverter grid-connected voltage value will further increase and enter the abnormal judgment range. Therefore, under this operating condition, the failure of the grid-connected switch to close successfully will not only manifest as abnormal inverter grid-connected current value and abnormal grid-connected loop output, but will also further manifest as an abnormal increase in the inverter grid-connected voltage value, requiring a combined judgment based on conditions a, b, and c.

[0056] For example, when the voltage of a single battery cell is 3.7V, the number of battery cells is 2, the transformer turns ratio is 60:1, and the gain is 1, then the maximum bus voltage that the current battery cell can provide is BUS_real = 3.7V × 2 × 60 × 1 = 444V, and the corresponding inverter grid-connected voltage is V_inv = 444V / ≈314V. 314V is significantly higher than the normal grid-connected voltage of 220V, indicating that the inverter grid-connected voltage has entered an abnormally high range. This suggests that under this operating condition, if the grid-connected switch fails to close successfully, the inverter grid-connected voltage may increase significantly. Therefore, condition a needs to be considered as one of the fault diagnosis criteria.

[0057] When the preset conditions of the second battery are met, it indicates that the voltage support capability that the battery side can provide after transformation by the resonant circuit is limited. In this case, when the grid-connected switch fails to close successfully, the inverter grid-connected current still cannot be effectively established, and the output of the grid-connected control loop will continue to change. However, the inverter grid-connected voltage value is usually difficult to continue to be pushed up to the abnormally high judgment range. Therefore, condition a no longer has an effective distinguishing function under this operating condition.

[0058] For example, when the voltage of a single battery cell is 2.6V, the number of battery cells is 2, the transformer turns ratio is 60:1, and the gain is 1, then BUS_real = 2.6V × 2 × 60 × 1 = 312V, and the corresponding inverter voltage is V_inv = 312V / ≈220.6V. 220.6V is still within the reasonable fluctuation range of the grid voltage of 220V, and the inverter will not generate an overvoltage alarm. This indicates that under this operating condition, even if the grid connection switch fails to close successfully, the inverter grid connection voltage value will usually not enter the abnormally high judgment range. Therefore, it is only necessary to combine conditions b and c for judgment.

[0059] In one specific embodiment, regarding condition a, the inverter grid-connected voltage condition is used to characterize whether an abnormal voltage rise occurs on the inverter output side. Specifically, the inverter grid-connected voltage condition is: the inverter grid-connected voltage value is greater than the rated value of the grid voltage by a preset multiple, i.e.: V_inv>A×V_grid; where A represents the preset multiple and A is greater than 1. The preset multiple A is determined based on the grid and the load powered by the inverter.

[0060] Specifically, based on the power grid and the load powered by the inverter, a preset multiplier is determined, including: The first ratio A1 is determined based on the quotient of the maximum grid-connected voltage of the inverter and the maximum grid voltage; that is, A1 = Vinv_max / Vgrid_max, where Vinv_max is the maximum grid-connected voltage of the inverter and Vgrid_max is the maximum grid voltage.

[0061] The second ratio A2 is obtained by dividing the upper limit of the operating voltage of the load connected to the inverter by the rated voltage of the load connected to the inverter; that is, A2 = Vload_max / Vload_rated, where Vload_max is the upper limit of the operating voltage of the load connected to the inverter, and Vload_rated is the rated voltage of the load connected to the inverter.

[0062] The preset multiple A is determined to be the smaller value between the first ratio A1 and the second ratio A2, that is: A = min(A1, A2).

[0063] In the above embodiments, the rated voltage of the load represents the voltage value at which the load can operate normally for a long period of time, and the upper limit of the operating voltage of the load represents the highest operating voltage value that the load can withstand. The rated voltage is less than or equal to the upper limit of the operating voltage. By calculating the ratio of the upper limit of the operating voltage of the load connected to the inverter to the rated voltage of the load, the allowable voltage fluctuation range of the load based on the normal operating voltage can be characterized. Combined with the upper limit requirement of the inverter's grid connection voltage, a preset multiple A is determined, which enables the inverter's grid connection voltage conditions to simultaneously meet the grid connection requirements and the load withstand voltage requirements.

[0064] In one specific embodiment, regarding condition b, the inverter grid-connected current condition is used to characterize that the inverter output current cannot be effectively established when the grid-connected switch is not successfully closed. Specifically, the inverter grid-connected current value of the inverter is less than or equal to the current threshold, i.e.: I_inv≤I_min; where I_min represents the current threshold, which is determined based on the current value of the inverter in standby state and grid-connected charging state.

[0065] Specifically, the current threshold is determined as the average of the first current value I1 and the second current value I2, i.e.: I_min = (I1 + I2) / 2; where the first current value I1 is the standby current of the inverter in standby mode, and the second current value I2 is the grid-connected current of the inverter when the energy storage system is operating at the set minimum charging power.

[0066] It should be noted that the standby state here is not a shutdown state, but rather a standby operating state where the energy storage system remains operational but is not performing grid-connected charging. In this state, the system itself still has a corresponding standby current. Simultaneously, the set minimum charging power is the minimum power value within the charging power range that the energy storage system can withstand during normal operation. Therefore, the grid-connected current value corresponding to the minimum charging power is also a known reference current value for the system. Furthermore, the first current value I1 and the second current value I2 both correspond to reference current values ​​under normal operating conditions when the grid-connected switch is normally closed. By using the average of the standby current and the grid-connected current at the minimum charging power as the current threshold, the determined threshold can be kept within a reasonable range of the low current output interval, thus balancing detection sensitivity and judgment accuracy.

[0067] In one specific embodiment, regarding condition c, the duty cycle change condition is used to characterize an abnormality in the grid-connected loop output. Specifically, during the PI control process, the change in duty cycle D ΔD of each PI adjustment in the grid-connected loop exceeds a preset duty cycle threshold ΔD_th. That is: ΔD > ΔD_th; the preset duty cycle threshold ΔD_th is the change in duty cycle of each PI adjustment in the grid-connected loop when the energy storage system is operating at the set maximum charging power.

[0068] It should be noted that the set maximum charging power corresponds to the maximum charging power that the energy storage system can withstand under normal grid-connected operation when the grid-connected switch is normally closed. Under this condition, the change in the duty cycle of the grid-connected loop can reflect the control output change boundary corresponding to a larger load condition under normal closed state. Therefore, using the change in the duty cycle under this condition as the preset duty cycle threshold can be used to distinguish between the duty cycle change during normal grid-connected regulation and the abnormal duty cycle change when the grid-connected switch fails to close.

[0069] Combination Figure 2 The grid-connected control loop shown provides a specific example illustrating the determination process for condition c above.

[0070] In one specific embodiment, assuming the nominal voltage of the battery cell is 3.7V, the number of battery cells is 2, the transformer turns ratio is 60:1, and the gain is 1, taking an inverter output of 220V as an example, at the instant the inverter switches from off-grid to grid-connected mode, the lowest value of the actual bus voltage BUS_real is 220V × ≈311V. At this time, the inverter grid-connected voltage V_inv is 220V, the grid voltage V_grid is 220V, and the amplitude, phase and frequency of the inverter grid-connected voltage V_inv and the grid voltage V_grid are synchronized. The controller issues a grid-connected switch closing command and sets the target charging power to 220W.

[0071] Under this operating condition, the target inverter current value I_ref is calculated based on the target charging power, i.e., I_ref = P / U = 220W / 220V = 1A. Assuming the line voltage drop is set to 10V, the bus voltage reference value BUS_ref = BUS_real + 10V = 311V + 10V = 321V. At this time, BUS_real is 311V, and the inverter grid-connected current value I_inv is 0.

[0072] When the grid-connected switch can be closed normally, the grid and the inverter form an effective connection. The grid can clamp the inverter voltage, the grid-connected control loop operates according to the normal grid-connected operating conditions, the inverter grid-connected current value is gradually established, and the grid-connected charging process proceeds normally.

[0073] When the grid-connected switch malfunctions and fails to close, the controller is unaware of this failure and continues to switch from the off-grid loop to the grid-connected loop. At this time, there is a 10V error between BUS_ref and BUS_real. After PI regulation, the outer loop output of the bus voltage is limited to I_ref, i.e., 1A. Because the grid-connected switch has not closed successfully, the inverter has not formed an effective connection with the grid; therefore, the inverter grid-connected current value I_inv remains 0, and the error between the target inverter current value I_ref and the inverter grid-connected current value I_inv remains constant at 1A. This error, after PI regulation in the inner current loop, is used to output the duty cycle control quantity D of the grid-connected loop.

[0074] Taking the first control cycle after switching into the grid-connected loop as an example, during this control cycle, the change in the inverter grid-connected current value ΔI_inv = 0, and the change in the output of the grid-connected loop ΔD = D1 - 0, where D1 represents the duty cycle control value obtained after PI regulation in this control cycle. As the grid-connected control loop continues to operate, since the grid-connected switch is not successfully closed, the grid cannot effectively clamp the inverter voltage. After the duty cycle control value D output by the grid-connected loop increases, the inverter grid-connected voltage value V_inv increases, and the actual bus voltage value BUS_real increases accordingly, while the inverter grid-connected current value I_inv remains at 0.

[0075] Subsequently, errors persist between BUS_ref and BUS_real, and errors also persist between the inverter current target value I_ref and the inverter grid-connected current value I_inv. The integral error in the inner current loop PI regulation continuously accumulates, causing the duty cycle control quantity D of the grid-connected loop output to continuously increase, thus leading to a continuous increase in the duty cycle change ΔD between adjacent control cycles. In other words, even when the grid-connected switch fails to close successfully, although the inverter grid-connected current value cannot be effectively established, the grid-connected control loop will continue to adjust, exhibiting an abnormal output characteristic of continuously increasing duty cycle.

[0076] Therefore, it can be seen that when the grid-connected switch fails to close successfully, the duty cycle change ΔD of the grid-connected control loop output will continue to increase; when ΔD exceeds the preset duty cycle threshold ΔD_th, the duty cycle change condition ΔD>ΔD_th is satisfied. Thus, condition c can be used to characterize the abnormal output of the grid-connected loop and reflect the fault characteristics formed by the continuous adjustment of the control loop when the grid-connected switch fails to close successfully.

[0077] In summary, combining Figure 4This application proposes a grid-connected switch detection method for an energy storage system. The energy storage system includes an inverter, a grid-connected switch for connecting the inverter and the power grid, and a controller connecting the inverter and the grid-connected switch. The controller first sends a grid-connected closing signal to the grid-connected switch. Instead of using a single parameter to determine whether the grid-connected switch is successfully closed, different fault determination paths are adopted based on the different preset states of the batteries connected to the inverter: when the batteries meet the first preset battery condition, the controller simultaneously combines the inverter's inverter grid-connected voltage condition, the inverter grid-connected current condition, and the duty cycle change condition of the energy storage system's grid-connected loop output to determine whether a grid-connected switch has experienced a grid-connected closing fault; when the batteries meet the second preset battery condition, the controller combines the inverter grid-connected current condition and the duty cycle change condition of the energy storage system's grid-connected loop output to determine whether a grid-connected switch has experienced a grid-connected closing fault. Therefore, this application incorporates the voltage response, current response, and grid loop control output changes of the inverter output side during grid connection switching into the closed state identification process, and further distinguishes the judgment method based on the battery state difference, so that the abnormal state corresponding to the grid connection switch failing to engage can be identified more specifically, thereby enabling timely and accurate detection of whether the grid connection switch has successfully engaged at the moment of switching between grid connection and off-grid modes.

[0078] Figure 5 This is a block diagram of an electronic device for detecting the grid connection switch of an energy storage system according to one embodiment of this application. The electronic device includes at least a processor 501 and a memory 502.

[0079] The processor 501 may include one or more processing cores, such as a multi-core microcontroller or a digital signal processor, for executing control logic in the energy storage system. In the context of this application, the processor 501 is specifically used to execute grid-connected switch detection-related program instructions, including: determining whether grid connection conditions are met when the energy storage system is in off-grid operation, and controlling the grid-connected switch to close; when the battery connected to the inverter meets the first battery preset conditions, determining whether a grid-connected switch has experienced a grid-connected closing fault based on the inverter's inverter grid-connected voltage condition, the inverter's inverter grid-connected current condition, and the duty cycle change condition of the energy storage system's grid-connected loop output; when the battery connected to the inverter meets the second battery preset conditions, determining whether a grid-connected switch has experienced a grid-connected closing fault based on the inverter's inverter grid-connected current condition and the duty cycle change condition of the energy storage system's grid-connected loop output; and after completing the fault determination, executing corresponding fault handling, alarm reporting, or exiting the detection process.

[0080] The processor 501 can also be used to implement timing control corresponding to the first preset time, the second preset time, and the third preset time. The memory 502 may include one or more non-transitory computer-readable storage media for storing program instructions, operating parameters, and system status information. Specifically, the memory 502 may store program instructions corresponding to the grid-connected switch detection method, as well as parameter information related to fault determination, including a first threshold, a preset multiple, a current threshold, a preset duty cycle threshold, a first preset time, a second preset time, and a third preset time; the memory 502 can also be used to record the detection status, determination result, and fault information of the grid-connected switch. When the processor 501 executes the program instructions stored in the memory 502, it implements the steps in the aforementioned method embodiments.

[0081] In some embodiments, the electronic device may further include a peripheral device interface and at least one peripheral device, and the processor 501, memory 502, and peripheral device interface may be connected via a bus or signal line. In accordance with the application scenario of this application, the peripheral device may include a voltage and current sampling interface for collecting inverter grid-connected voltage values, inverter grid-connected current values, and parameter information corresponding to the grid voltage values; a control signal output interface for outputting grid-connected switch drive signals and inverter control signals; and a communication interface for reporting grid-connected switch status and fault information to external devices. Of course, the electronic device may also include other functional modules, which are not limited in this embodiment.

[0082] Optionally, this application also provides a computer-readable storage medium storing a program that is loaded and executed by a processor to implement the grid-connected switch detection method of the above-described method embodiments.

[0083] Optionally, this application also provides a computer product including a computer-readable storage medium storing a program, which is loaded and executed by a processor to implement the grid-connected switch detection method of the above method embodiments.

[0084] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0085] The above embodiments merely illustrate several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A method for detecting a grid-connected switch in an energy storage system, the energy storage system comprising an inverter, a grid-connected switch for connecting the inverter and a power grid, and a controller connecting the inverter and the grid-connected switch, characterized in that, The method includes: The controller is controlled to send a grid connection closing signal to the grid connection switch; When the battery connected to the inverter meets the first battery preset condition, the grid-connected switch is determined to have a grid-connected closing fault based on the inverter grid-connected voltage condition, the inverter grid-connected current condition, and the duty cycle change condition of the grid-connected loop output of the energy storage system. When the battery connected to the inverter meets the second battery preset conditions, the grid-connected switch is determined to have experienced a grid-connected closing fault based on the inverter's grid-connected current conditions and the duty cycle change conditions of the grid-connected loop output of the energy storage system.

2. The grid-connected switch detection method according to claim 1, characterized in that, The first battery is pre-defined as follows: the sum of the voltages of all the battery cells is greater than a first threshold. The second battery preset condition is: the sum of the voltages of all the battery cells is less than or equal to a first threshold. The first threshold is determined based on the effective value of the grid voltage and the turns ratio of the transformer in the resonant circuit, which is used to connect the battery and the inverter.

3. The grid-connected switch detection method according to claim 1, characterized in that, The inverter grid connection voltage condition is: the inverter grid connection voltage value of the inverter is greater than the rated value of the grid voltage by a preset multiple; The preset multiple is determined based on the power grid and the load powered by the inverter.

4. The grid-connected switch detection method according to claim 3, characterized in that, Determining the preset multiple based on the power grid and the load powered by the inverter includes: The first ratio is determined based on the quotient of the maximum grid-connected voltage of the inverter and the maximum grid voltage. A second ratio is determined based on the quotient of the upper limit of the operating voltage of the load connected to the inverter and the rated voltage of the load connected to the inverter. The preset multiple is determined to be the smaller value between the first ratio and the second ratio.

5. The grid-connected switch detection method according to claim 1, characterized in that, The inverter grid-connected current condition is: the inverter grid-connected current value of the inverter is less than or equal to the current threshold. The current threshold is determined based on the inverter's current values ​​in standby and grid-connected charging states.

6. The grid-connected switch detection method according to claim 5, characterized in that, The current threshold is determined based on the inverter's current values ​​in standby and grid-connected charging states, including: The current threshold is determined to be the average of the first current value and the second current value; Wherein, the first current value is the standby current of the inverter in standby mode, and the second current value is the grid-connected current of the inverter when the energy storage system is operating at the set minimum charging power.

7. The grid-connected switch detection method according to claim 1, characterized in that, The duty cycle change condition is: during the PI control process, the change in the duty cycle of each PI adjustment of the grid-connected loop exceeds the preset duty cycle threshold. Wherein, the preset duty cycle threshold is the change in duty cycle of the grid-connected loop during each PI adjustment when the energy storage system operates at the set maximum charging power.

8. The grid-connected switch detection method according to any one of claims 1 to 7, characterized in that, The grid-connected switch detection method further includes: When the battery connected to the inverter meets the first battery preset condition or the second battery preset condition, the grid connection failure determination is performed after a first preset time; the first preset time is consistent with the closing response time of the grid connection switch.

9. The grid-connected switch detection method according to claim 8, characterized in that, The grid-connected switch detection method further includes: The grid connection failure determination is performed within a second preset time: it is determined whether the inverter grid connection voltage condition, the inverter grid connection current condition, and the duty cycle change condition of the grid connection loop output of the energy storage system are met within the second preset time. The grid connection failure determination is performed within a third preset time period: it is determined whether the inverter grid connection current condition of the inverter and the duty cycle change condition of the grid connection loop output of the energy storage system are met within the third preset time period. Wherein, the second preset time is less than the third preset time, and the sum of the first preset time and the second preset time, as well as the sum of the first preset time and the third preset time, are all less than the fault response judgment time of the energy storage system.

10. An electronic device, characterized in that, It includes a processor and a memory, wherein the memory stores a program that is loaded and executed by the processor to implement the grid-connected switch detection method as described in any one of claims 1-9.

11. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores a program that, when executed by a processor, is used to implement the grid-connected switch detection method as described in any one of claims 1-9.

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