Grid-connected and off-grid switching method, control system and split-phase energy storage inverter

Abstract

The invention provides a grid-connected and off-grid switching method, a control system and a split-phase energy storage inverter, the method is applied to the control system of the split-phase energy storage inverter, the split-phase energy storage inverter comprises a T-type three-level circuit, and an inductor and a grid side capacitor are connected in series between the output end of the T-type three-level circuit and a zero potential reference point; according to the method, in response to a mains supply off-grid action of the split-phase energy storage inverter, the T-type three-level circuit is turned off, and the voltage at the two ends of the grid-side capacitor rises to a high voltage threshold value; in response to determining that the voltage at the two ends of the grid-side capacitor rises to a high voltage threshold value, switching on a switching tube between the output end of the T-type three-level circuit and a zero potential reference point, and discharging the grid-side capacitor; and in response to determining that the voltages at the two ends of the grid-side capacitor are reduced to a low voltage threshold, controlling the split-phase energy storage inverter to be switched to an off-grid working condition, thereby reducing the duration of voltage rise of the grid-side capacitor and accelerating the speed of power grid detection.

Description

Technical Field

[0001] The present application relates to the technical field of on-grid and off-grid switching, and in particular to an on-grid and off-grid switching method, a control system and a split-phase energy storage inverter. Background Art

[0002] The American Standard Split Phase Energy Storage Inverter is a photovoltaic household bidirectional energy storage inverter that integrates a photovoltaic grid-connected inverter and battery energy storage. It is compatible with grid-connected, off-grid, and off-grid switching working conditions. Off-grid switching conditions are a relatively important research object for energy storage inverters. According to industry standards, the time from grid-connected to off-grid is no more than 10ms. The switching time is composed of the grid abnormality fast detection time + the relay disconnection flight time. Since the relay flight time is about 5ms, the grid abnormality fast detection time must be controlled and reduced. Summary of the invention

[0003] In view of this, the purpose of the present application is to provide a grid-connected and off-grid switching method, a control system and a split-phase energy storage inverter, which can effectively reduce the rapid detection time of grid abnormalities and ensure that the time for switching from grid-connected to off-grid meets the requirements.

[0004] The embodiment of the present application provides a grid-connected and off-grid switching method, which is applied to a control system of a split-phase energy storage inverter, wherein the split-phase energy storage inverter includes a T-type three-level circuit, and an inductor and a grid-side capacitor are connected in series between an output end and a zero potential reference point of the T-type three-level circuit; the method includes the following steps:

[0005] In response to the mains disconnection action of the split-phase energy storage inverter, the T-type three-level circuit is turned off to increase the voltage across the grid-side capacitor to a high voltage threshold;

[0006] In response to determining that the voltage across the grid-side capacitor rises to a high voltage threshold, turning on a switch tube between the output end of the T-type three-level circuit and a zero potential reference point to discharge the grid-side capacitor;

[0007] In response to determining that the voltage across the grid-side capacitor drops to a low voltage threshold, determining that the split-phase energy storage inverter completes disconnection from the mains, and controlling the split-phase energy storage inverter to switch to an off-grid operating state.

[0008] In some embodiments, in the on-grid and off-grid switching method, in response to determining that the voltage across the grid-side capacitor rises to a high voltage threshold, turning on a switch tube between the output end of the T-type three-level circuit and a zero potential reference point includes:

[0009] In response to the waiting time after the T-type three-level circuit is turned off reaching the preset capacitor boost time, determining that the voltage across the grid-side capacitor rises to a high voltage threshold, turning on a switch tube between the output end of the T-type three-level circuit and a zero potential reference point;

[0010] The preset capacitor boost time is determined based on the capacitance of the grid-side capacitor, the bus voltage, and the peak current of the inductor when the T-type three-level circuit is turned off.

[0011] In some embodiments, in the on-grid and off-grid switching method, the preset capacitor boosting time is determined based on the following steps:

[0012] Calculating the product of the capacitance of the grid-side capacitor, the bus voltage and a preset parameter;

[0013] The ratio of the product to the peak current is calculated, and the ratio is used as the preset capacitor boost time.

[0014] In some embodiments, the on-grid and off-grid switching method further includes:

[0015] In response to the split-phase energy storage inverter switching from an off-grid operating condition to a grid-connected operating condition, shutting down the T-type three-level circuit;

[0016] In response to the voltage across the grid-side capacitor decreasing to a low voltage threshold, the split-phase energy storage inverter is controlled to switch to an off-grid operating state.

[0017] In some embodiments, in the on-grid and off-grid switching method, in response to determining that the voltage across the grid-side capacitor is reduced to a low voltage threshold, determining that the split-phase energy storage inverter has completed the mains off-grid operation includes:

[0018] Collecting the voltage across the grid-side capacitor at a preset sampling frequency;

[0019] Determining whether the voltage across the grid-side capacitor is less than a low voltage threshold;

[0020] If so, it is determined that the split-phase energy storage inverter has completed the mains disconnection.

[0021] In some embodiments, a control system is further provided for controlling a split-phase energy storage inverter, wherein the split-phase energy storage inverter comprises a T-type three-level circuit, wherein an inductor and a grid-side capacitor are connected in series between an output end of the T-type three-level circuit and a zero potential reference point;

[0022] The control system is used to shut down the T-type three-level circuit in response to the mains disconnection action of the split-phase energy storage inverter, so that the voltage across the grid-side capacitor increases to a high voltage threshold;

[0023] In response to determining that the voltage across the grid-side capacitor rises to a high voltage threshold, turning on a switch tube between the output end of the T-type three-level circuit and a zero potential reference point to discharge the grid-side capacitor;

[0024] In response to determining that the voltage across the grid-side capacitor drops to a low voltage threshold, determining that the split-phase energy storage inverter completes disconnection from the mains, and controlling the split-phase energy storage inverter to switch to an off-grid operating state.

[0025] In some embodiments, in the control system, the control system, in response to determining that the voltage across the grid-side capacitor rises to a high voltage threshold, turns on the switch tube between the output end of the T-type three-level circuit and the zero potential reference point, is specifically used to:

[0026] In response to the waiting time after the T-type three-level circuit is turned off reaching the preset capacitor boost time, determining that the voltage across the grid-side capacitor rises to a high voltage threshold, turning on a switch tube between the output end of the T-type three-level circuit and a zero potential reference point;

[0027] The preset capacitor boost time is determined based on the capacitance of the grid-side capacitor, the bus voltage, and the peak current of the inductor when the T-type three-level circuit is turned off.

[0028] In some embodiments, in the control system, the preset capacitor boost time is determined:

[0029] Calculating the product of the capacitance of the grid-side capacitor, the bus voltage and a preset parameter;

[0030] The ratio of the product to the peak current is calculated, and the ratio is used as the preset capacitor boost time.

[0031] In some embodiments, in the control system, the split-phase energy storage inverter is further used to shut down the T-type three-level circuit in response to the action of the split-phase energy storage inverter switching from an off-grid operating condition to a grid-connected operating condition;

[0032] In response to the voltage across the grid-side capacitor decreasing to a low voltage threshold, the split-phase energy storage inverter is controlled to switch to an off-grid operating state.

[0033] In some embodiments, a split-phase energy storage inverter is also provided, and the split-phase energy storage inverter performs on-grid and off-grid switching based on the control of a control system of the split-phase energy storage inverter, and the control system executes the on-grid and off-grid switching method.

[0034] The embodiment of the present application provides a grid-connected and off-grid switching method, a control system and a split-phase energy storage inverter. The method is applied to a control system of a split-phase energy storage inverter. The split-phase energy storage inverter includes a T-type three-level circuit. An inductor and a grid-side capacitor are connected in series between the output end and a zero potential reference point of the T-type three-level circuit. In response to the mains disconnection action of the split-phase energy storage inverter, the method shuts down the T-type three-level circuit to increase the voltage across the grid-side capacitor to a high voltage threshold. In response to determining that the voltage across the grid-side capacitor has increased to a high voltage threshold, the method turns on the T-type three-level circuit. A switch tube is connected between the output end of the three-level circuit and the zero potential reference point to discharge the grid-side capacitor; in response to determining that the voltage at both ends of the grid-side capacitor is reduced to a low voltage threshold, it is determined that the split-phase energy storage inverter has completed the mains disconnection, and the split-phase energy storage inverter is controlled to switch to an off-grid condition. In the grid-connected mode, when the grid voltage is reduced, the method adjusts the split-phase wave generation logic according to the current bus voltage, inductor current and capacitance on the grid side, thereby reducing the duration of the grid-side capacitor voltage increase, thereby speeding up the speed of grid detection, so that the time for switching from grid-connected to off-grid meets industry standards. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.

[0036] Figure 1 A flow chart of the on-grid and off-grid switching method described in an embodiment of the present application is shown;

[0037] Figure 2 A circuit state diagram of inductive energy storage in a positive half-wave cycle of a split-phase energy storage inverter in a grid-connected mode according to an embodiment of the present application is shown;

[0038] Figure 3 A circuit state diagram showing the inductor energy release during the positive half-wave cycle of the split-phase energy storage inverter in the grid-connected mode according to the embodiment of the present application is shown;

[0039] Figure 4 A circuit state diagram of inductive energy storage during a negative half-wave cycle of a split-phase energy storage inverter in a grid-connected mode according to an embodiment of the present application is shown;

[0040] Figure 5 A circuit state diagram showing the inductor energy release during the negative half-wave cycle of the split-phase energy storage inverter in the grid-connected mode according to the embodiment of the present application is shown;

[0041] Figure 6The circuit state diagram of the split-phase energy storage inverter after the drive is directly turned off during grid connection and disconnection described in the embodiment of the present application is shown;

[0042] Figure 7 The circuit state diagram of the wave generation logic when the mains power is disconnected from the grid according to the embodiment of the present application is shown;

[0043] Figure 8 A schematic diagram of the grid-side capacitor voltage of the wave generation logic when the mains power is disconnected from the grid according to an embodiment of the present application is shown. DETAILED DESCRIPTION

[0044] To make the purpose, technical scheme and advantages of the embodiments of the present application clearer, the technical scheme in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. It should be understood that the drawings in the present application only serve the purpose of explanation and description and are not used to limit the scope of protection of the present application. In addition, it should be understood that the schematic drawings are not drawn in real proportion. The flowchart used in this application shows the operations implemented according to some embodiments of the present application. It should be understood that the operations of the flowchart can be implemented out of sequence, and the steps without logical context can be reversed in order or implemented simultaneously. In addition, those skilled in the art can add one or more other operations to the flowchart under the guidance of the content of the present application, or remove one or more operations from the flowchart.

[0045] In addition, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. The components of the embodiments of the present application described and shown in the drawings here can be arranged and designed in various configurations. Therefore, the following detailed description of the embodiments of the present application provided in the drawings is not intended to limit the scope of the application claimed for protection, but merely represents the selected embodiments of the present application. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without making creative work belong to the scope of protection of the present application.

[0046] It should be noted that the term "comprising" will be used in the embodiments of the present application to indicate the existence of the features declared thereafter, but does not exclude the addition of other features.

[0047] The American Standard Split Phase Energy Storage Inverter is a photovoltaic household bidirectional energy storage inverter that integrates a photovoltaic grid-connected inverter and battery energy storage. It is compatible with grid-connected, off-grid, and off-grid switching working conditions. Off-grid switching conditions are a relatively important research object for energy storage inverters. According to industry standards, the time from grid-connected to off-grid is no more than 10ms. The switching time is composed of the grid abnormality fast detection time + the relay disconnection flight time. Since the relay flight time is about 5ms, the grid abnormality fast detection time must be controlled and reduced.

[0048] Based on this, an embodiment of the present application provides a grid-connected and off-grid switching method, a control system and a split-phase energy storage inverter. The method is applied to the control system of the split-phase energy storage inverter. The split-phase energy storage inverter includes a T-type three-level circuit. An inductor and a grid-side capacitor are connected in series between the output end and the zero potential reference point of the T-type three-level circuit. The method responds to the mains disconnection action of the split-phase energy storage inverter by shutting down the T-type three-level circuit to increase the voltage across the grid-side capacitor to a high voltage threshold. In response to determining that the voltage across the grid-side capacitor has increased to a high voltage threshold, the method turns on the A switch tube is connected between the output end of the T-type three-level circuit and the zero potential reference point to discharge the grid-side capacitor; in response to determining that the voltage at both ends of the grid-side capacitor is reduced to a low voltage threshold, it is determined that the split-phase energy storage inverter has completed the mains disconnection, and the split-phase energy storage inverter is controlled to switch to an off-grid condition. In the grid-connected mode, when the grid voltage is reduced, the method adjusts the split-phase wave generation logic according to the current bus voltage, inductor current and grid-side capacitance, thereby reducing the duration of the grid-side capacitor voltage increase, thereby speeding up the speed of grid detection, so that the time for switching from grid-connected to off-grid meets industry standards.

[0049] Please refer to Figure 1 , Figure 1 A flow chart of the on-grid and off-grid switching method described in an embodiment of the present application is shown, and the on-grid and off-grid switching method is applied to a control system of a split-phase energy storage inverter, wherein the split-phase energy storage inverter comprises a T-type three-level circuit, and an inductor and a grid-side capacitor are connected in series between the output end and the zero potential reference point of the T-type three-level circuit; Figure 1 As shown, the method includes the following steps S101-S103:

[0050] S101, in response to the mains disconnection action of the split-phase energy storage inverter, shutting down the T-type three-level circuit to increase the voltage across the grid-side capacitor to a high voltage threshold;

[0051] S102: in response to determining that the voltage across the grid-side capacitor rises to a high voltage threshold, turning on a switch tube between the output end of the T-type three-level circuit and a zero potential reference point to discharge the grid-side capacitor;

[0052] S103, in response to determining that the voltage across the grid-side capacitor drops to a low voltage threshold, determining that the split-phase energy storage inverter completes disconnection from the mains, and controlling the split-phase energy storage inverter to switch to an off-grid operating state.

[0053] Under grid-connected operation, the loop is composed of PI loop + grid voltage feedforward. Under steady-state conditions, the grid voltage feedforward accounts for a larger proportion of the loop output, and the PI loop accounts for a smaller proportion. When the mains is disconnected from the grid, the grid voltage will decrease due to the decrease in grid voltage feedforward. As the PI loop increases, the grid voltage will increase. In this process, it will cause false detection of grid anomalies, thereby extending the detection time.

[0054] Please refer to Figure 2-Figure 5 , Figure 2-Figure 5 : shows a circuit schematic diagram of the split-phase energy storage inverter described in the embodiment of the present application; Figure 2-Figure 5 As shown, in the grid-connected mode, taking one of the split-phase as an example, the drivers T1A and T1B in the split-phase energy storage inverter complement each other, and T1C and T1D complement each other; Figure 2 As mentioned above, when the grid voltage is in a positive half-wave cycle, the switch tube T1A is closed and the inductor stores energy; Figure 3 As shown, the switch tube T1A is turned off, the switch tube T1D is turned on, and the inductor releases energy; Figure 4 As shown, when the grid voltage is in the negative half-wave cycle, the switch tube T1C is closed and the inductor stores energy; Figure 5 As shown, the switch tube T1C is opened, the switch tube T1B is closed, and the inductor releases energy.

[0055] Therefore, when the grid voltage decreases, the energy storage inverter (T-type three-level circuit) is driven off to prevent the PI loop calculation from increasing and driving to cause the voltage to increase, which can reduce the detection time.

[0056] However, when the grid voltage drops and the drive is turned off directly, the inductor has energy storage characteristics, which charges the capacitor on the grid side and causes the voltage to rise. This will still lead to false detection of grid anomalies, thereby extending the detection time.

[0057] The voltage across the grid-side capacitor increases to a high voltage threshold, that is, the voltage across the grid-side capacitor increases to a stable level; when the capacitor is just beginning to be charged, since the capacitor has less internal charge and the electric field strength is weak, the current is large and the voltage rises rapidly; as the internal charge of the capacitor gradually accumulates, the electric field strength gradually increases, the current begins to decrease, and the rate of voltage rise also slows down; when the internal charge of the capacitor accumulates to a certain extent, the electric field strength reaches a stable value, at which time the current is almost zero and the voltage remains stable.

[0058] Therefore, the high voltage threshold is the rated voltage of the capacitor or the stable voltage after charging.

[0059] Please refer to Figure 6 The schematic circuit diagram of the split-phase energy storage inverter after the driver is directly turned off according to the embodiment of the present application is shown; Figure 2 and Figure 7 As shown, Figure 2 When the grid voltage is in the positive half-wave cycle, the switch tube T1A is closed, and the inductor stores energy. Figure 6 After the grid is disconnected from the grid, the existing technology shuts down all drivers to store energy in the inductor. Since the direction of the inductor current does not change, it will continue to charge the grid-side capacitor, causing the voltage to rise. Eventually, the grid-side capacitor voltage will be the same as the half-bus voltage. During the grid rapid detection, it will be mistakenly believed that the grid is not disconnected, resulting in false detection of grid abnormalities, which in turn prolongs the detection time.

[0060] Based on this, the embodiment of the present application further adjusts the wave generation logic of the split phase by discharging the charged grid-side capacitor to reduce the duration of the grid-side capacitor voltage increase, thereby speeding up the speed of power grid detection.

[0061] Please refer to 7. Figure 7 The circuit schematic diagram of the wave generation logic when the mains power is disconnected from the grid according to the embodiment of the present application is shown; Figure 2 , Figure 6 and Figure 7 As shown, Figure 2 When the grid voltage is in the positive half-wave cycle, the switch tube T1A is closed, and the inductor stores energy. Figure 6 When the city power is disconnected from the grid, the T-type three-level circuit is turned off, and this time is set as t1. After the preset capacitor boost time (set this time as t2), the grid-side capacitor voltage increases and stabilizes. Figure 7 As shown, the switch tube T1B and the switch tube T1D are turned on, and the capacitor voltage is discharged to 0.

[0062] Please refer to Figure 8 , Figure 8 The schematic diagram of the grid-side capacitor voltage of the wave generation logic when the mains is disconnected from the grid according to the embodiment of the present application is shown; Figure 8 As shown, under the control of the wave generation logic described in the embodiment of the present application, the grid-side capacitor voltage increases and stabilizes and then rapidly decreases to 0, thereby reducing the duration of the grid-side capacitor voltage increase and speeding up the grid detection speed.

[0063] In the embodiment of the present application, in the on-grid and off-grid switching method, in response to determining that the voltage across the grid-side capacitor rises to a high voltage threshold, turning on a switch tube between the output end of the T-type three-level circuit and the zero potential reference point includes:

[0064] In response to the waiting time after the T-type three-level circuit is turned off reaching the preset capacitor boost time, determining that the voltage across the grid-side capacitor rises to a high voltage threshold, turning on a switch tube between the output end of the T-type three-level circuit and a zero potential reference point;

[0065] The preset capacitor boost time is determined based on the capacitance of the grid-side capacitor, the bus voltage, and the peak current of the inductor when the T-type three-level circuit is turned off.

[0066] Specifically, in some embodiments, the preset capacitor boost time is determined based on the following steps:

[0067] Calculating the product of the capacitance of the grid-side capacitor, the bus voltage and a preset parameter;

[0068] The ratio of the product to the peak current is calculated, and the ratio is used as the preset capacitor boost time.

[0069] Specifically, the preset capacitor boost time t is:

[0070] t=C*0.5*V bus / I L ;

[0071] Wherein, t is the preset capacitor boost time (i.e., the waiting time from t1 to t2), C represents the capacitance of the grid-side capacitor, Vbus is the bus voltage, and IL is the inductor peak current at time t1.

[0072] The wave generation control is performed based on the preset capacitor boost time, and there is no need to detect in real time whether the grid-side capacitor rises to a high voltage threshold, and there is no need to modify the inverter circuit, which facilitates the implementation of the on-grid and off-grid switching method described in this application.

[0073] In some embodiments, in response to determining that the voltage across the grid-side capacitor drops to a low voltage threshold, determining that the split-phase energy storage inverter completes disconnection from the mains includes:

[0074] Collecting the voltage across the grid-side capacitor at a preset sampling frequency;

[0075] Determining whether the voltage across the grid-side capacitor is less than a low voltage threshold;

[0076] If so, it is determined that the split-phase energy storage inverter has completed the mains disconnection.

[0077] In some embodiments, a low voltage threshold is set inside the split-phase energy storage inverter system. When the inverter is turned off, each time the voltage across the grid-side capacitor is collected, the split-phase energy storage inverter system will compare it with the low voltage threshold. If the voltage is less than the threshold, the split-phase energy storage inverter system can determine that the split-phase energy storage inverter has completed the process of disconnecting from the mains, triggering subsequent operations and switching to the off-grid state.

[0078] It is particularly important to note that if the T-type three-level circuit is turned off when the mains is disconnected, the switch tube between the output end of the T-type three-level circuit and the zero potential reference point is directly turned on, the grid-side capacitor will produce self-oscillation, and it will take a certain amount of time to recover to 0, which cannot reduce the detection time.

[0079] In some embodiments, the on-grid and off-grid switching method further includes:

[0080] In response to the split-phase energy storage inverter switching from an off-grid operating condition to a grid-connected operating condition, shutting down the T-type three-level circuit;

[0081] In response to the voltage across the grid-side capacitor decreasing to a low voltage threshold, the split-phase energy storage inverter is controlled to switch to an off-grid operating state.

[0082] That is to say, when the split-phase energy storage inverter switches from off-grid operation to grid-connected operation, a simple wave generation logic is used, which does not affect the performance of the split-phase energy storage inverter, reduces the complexity of switching control, and improves the efficiency and reliability of the split-phase energy storage inverter system.

[0083] Based on the same inventive concept, a control system for a split-phase energy storage inverter corresponding to the grid-connected and off-grid switching method is also provided in the embodiment of the present application. Since the principle of solving the problem by the control system in the embodiment of the present application is similar to the above-mentioned grid-connected and off-grid switching method in the embodiment of the present application, the implementation of the split-phase energy storage inverter can refer to the implementation of the method, and the repeated parts will not be repeated.

[0084] In some embodiments, a control system is further provided for controlling a split-phase energy storage inverter, wherein the split-phase energy storage inverter comprises a T-type three-level circuit, wherein an inductor and a grid-side capacitor are connected in series between an output end of the T-type three-level circuit and a zero potential reference point;

[0085] The control system is used to shut down the T-type three-level circuit in response to the mains disconnection action of the split-phase energy storage inverter, so that the voltage across the grid-side capacitor increases to a high voltage threshold;

[0086] In response to determining that the voltage across the grid-side capacitor rises to a high voltage threshold, turning on a switch tube between the output end of the T-type three-level circuit and a zero potential reference point to discharge the grid-side capacitor;

[0087] In response to determining that the voltage across the grid-side capacitor drops to a low voltage threshold, determining that the split-phase energy storage inverter completes disconnection from the mains, and controlling the split-phase energy storage inverter to switch to an off-grid operating state.

[0088] In some embodiments, in the control system,

[0089] The control system, in response to determining that the voltage across the grid-side capacitor rises to a high voltage threshold, turns on a switch tube between the output end of the T-type three-level circuit and the zero potential reference point, is specifically used to:

[0090] In response to the waiting time after the T-type three-level circuit is turned off reaching the preset capacitor boost time, determining that the voltage across the grid-side capacitor rises to a high voltage threshold, turning on a switch tube between the output end of the T-type three-level circuit and a zero potential reference point;

[0091] The preset capacitor boost time is determined based on the capacitance of the grid-side capacitor, the bus voltage, and the peak current of the inductor when the T-type three-level circuit is turned off.

[0092] In some embodiments, in the control system, the preset capacitor boost time is determined based on the following steps:

[0093] Calculating the product of the capacitance of the grid-side capacitor, the bus voltage and a preset parameter;

[0094] The ratio of the product to the peak current is calculated, and the ratio is used as the preset capacitor boost time.

[0095] In some embodiments, in the control system, the split-phase energy storage inverter is further used to shut down the T-type three-level circuit in response to the action of the split-phase energy storage inverter switching from an off-grid operating condition to a grid-connected operating condition;

[0096] In response to the voltage across the grid-side capacitor decreasing to a low voltage threshold, the split-phase energy storage inverter is controlled to switch to an off-grid operating state.

[0097] Based on the same inventive concept, a split-phase energy storage inverter corresponding to the grid-connected and off-grid switching method is also provided in the embodiment of the present application. Since the principle of solving the problem by the split-phase energy storage inverter in the embodiment of the present application is similar to the above-mentioned grid-connected and off-grid switching method in the embodiment of the present application, the implementation of the split-phase energy storage inverter can refer to the implementation of the method, and the repeated parts will not be repeated.

[0098] In some embodiments, a split-phase energy storage inverter is also provided, and the split-phase energy storage inverter performs on-grid and off-grid switching based on the control of a control system of the split-phase energy storage inverter, and the control system executes the on-grid and off-grid switching method.

[0099] Those skilled in the art can clearly understand that, for the convenience and simplicity of description, the specific working process of the system and device described above can refer to the corresponding process in the method embodiment, and will not be repeated in this application. In the several embodiments provided in this application, it should be understood that the disclosed system, device and method can be implemented in other ways. The device embodiments described above are merely schematic. For example, the division of the modules is only a logical function division. There may be other division methods in actual implementation. For example, multiple modules or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be through some communication interfaces, indirect coupling or communication connection of devices or modules, which can be electrical, mechanical or other forms.

[0100] The modules described as separate components may or may not be physically separated, and the components shown as modules may or may not be physical units, that is, they may be located in one place or distributed on multiple network units. Some or all of the units may be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0101] In addition, each functional unit in each embodiment of the present application may be integrated into one processing unit, or each unit may exist physically separately, or two or more units may be integrated into one unit.

[0102] If the functions are implemented in the form of software functional units and sold or used as independent products, they can be stored in a non-volatile computer-readable storage medium that is executable by a processor. Based on this understanding, the technical solution of the present application, or the part that contributes to the prior art or the part of the technical solution, can be embodied in the form of a software product, which is stored in a storage medium and includes several instructions for a computer device (which can be a personal computer, a platform server, or a network device, etc.) to perform all or part of the steps of the method described in each embodiment of the present application. The aforementioned storage medium includes: various media that can store program codes, such as USB flash drives, mobile hard drives, ROM, RAM, magnetic disks, or optical disks.

[0103] The above are only specific implementations of the present application, but the protection scope of the present application is not limited thereto. Any technician familiar with the technical field can easily think of changes or substitutions within the technical scope disclosed in the present application, which should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. A method for switching between on-grid and off-grid, characterized in that: A control system applied to a split-phase energy storage inverter, wherein the split-phase energy storage inverter comprises a T-type three-level circuit, wherein an inductor and a grid-side capacitor are connected in series between an output end of the T-type three-level circuit and a zero potential reference point; the method comprises the following steps: In response to the mains disconnection action of the split-phase energy storage inverter, the T-type three-level circuit is turned off to increase the voltage across the grid-side capacitor to a high voltage threshold; In response to determining that the voltage across the grid-side capacitor rises to a high voltage threshold, turning on a switch tube between the output end of the T-type three-level circuit and a zero potential reference point to discharge the grid-side capacitor; In response to determining that the voltage across the grid-side capacitor drops to a low voltage threshold, determining that the split-phase energy storage inverter completes disconnection from the mains, and controlling the split-phase energy storage inverter to switch to an off-grid operating state.

2. The on-grid and off-grid switching method according to claim 1, characterized in that: In response to determining that the voltage across the grid-side capacitor rises to a high voltage threshold, turning on a switch tube between the output end of the T-type three-level circuit and a zero potential reference point, comprising: In response to the waiting time after the T-type three-level circuit is turned off reaching the preset capacitor boost time, determining that the voltage across the grid-side capacitor rises to a high voltage threshold, turning on a switch tube between the output end of the T-type three-level circuit and a zero potential reference point; The preset capacitor boost time is determined based on the capacitance of the grid-side capacitor, the bus voltage, and the peak current of the inductor when the T-type three-level circuit is turned off.

3. The on-grid and off-grid switching method according to claim 2, characterized in that: The preset capacitor boost time is determined based on the following steps: Calculating the product of the capacitance of the grid-side capacitor, the bus voltage and a preset parameter; The ratio of the product to the peak current is calculated, and the ratio is used as the preset capacitor boost time.

4. The on-grid and off-grid switching method according to claim 1, characterized in that: The method further comprises: In response to the split-phase energy storage inverter switching from an off-grid operating condition to a grid-connected operating condition, shutting down the T-type three-level circuit; In response to the voltage across the grid-side capacitor decreasing to a low voltage threshold, the split-phase energy storage inverter is controlled to switch to an off-grid operating state.

5. The on-grid and off-grid switching method according to claim 1, characterized in that: In response to determining that the voltage across the grid-side capacitor is reduced to a low voltage threshold, determining that the split-phase energy storage inverter completes the mains disconnection, comprising: Collecting the voltage across the grid-side capacitor at a preset sampling frequency; Determining whether the voltage across the grid-side capacitor is less than a low voltage threshold; If so, it is determined that the split-phase energy storage inverter has completed the mains disconnection.

6. A control system, characterized in that: Used to control a split-phase energy storage inverter, wherein the split-phase energy storage inverter comprises a T-type three-level circuit, wherein an inductor and a grid-side capacitor are connected in series between an output end of the T-type three-level circuit and a zero potential reference point; The control system is used to shut down the T-type three-level circuit in response to the mains disconnection action of the split-phase energy storage inverter, so that the voltage across the grid-side capacitor increases to a high voltage threshold; In response to determining that the voltage across the grid-side capacitor rises to a high voltage threshold, turning on a switch tube between the output end of the T-type three-level circuit and a zero potential reference point to discharge the grid-side capacitor; In response to determining that the voltage across the grid-side capacitor drops to a low voltage threshold, determining that the split-phase energy storage inverter completes disconnection from the mains, and controlling the split-phase energy storage inverter to switch to an off-grid operating state.

7. The control system according to claim 6, characterized in that: The control system, in response to determining that the voltage across the grid-side capacitor rises to a high voltage threshold, turns on a switch tube between the output end of the T-type three-level circuit and the zero potential reference point, is specifically used to: In response to the waiting time after the T-type three-level circuit is turned off reaching the preset capacitor boost time, determining that the voltage across the grid-side capacitor rises to a high voltage threshold, turning on a switch tube between the output end of the T-type three-level circuit and a zero potential reference point; The preset capacitor boost time is determined based on the capacitance of the grid-side capacitor, the bus voltage, and the peak current of the inductor when the T-type three-level circuit is turned off.

8. The control system according to claim 7, characterized in that: The preset capacitor boost time is determined based on the following steps: Calculating the product of the capacitance of the grid-side capacitor, the bus voltage and a preset parameter; The ratio of the product to the peak current is calculated, and the ratio is used as the preset capacitor boost time.

9. The control system according to claim 6, characterized in that: The split-phase energy storage inverter is further used to shut down the T-type three-level circuit in response to the action of the split-phase energy storage inverter switching from an off-grid operating condition to a grid-connected operating condition; In response to the voltage across the grid-side capacitor decreasing to a low voltage threshold, the split-phase energy storage inverter is controlled to switch to an off-grid operating state.

10. A split-phase energy storage inverter, characterized in that: The split-phase energy storage inverter performs on-grid and off-grid switching based on the control of a control system of the split-phase energy storage inverter, and the control system executes the on-grid and off-grid switching method described in any one of claims 1-5.

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