A method and device for switching between on-grid and off-grid of energy storage inverter

Abstract

The present invention discloses a method and device for switching an energy storage inverter between grid and off-grid. The switching method controls the energy storage inverter with a first control strategy when the energy storage inverter operates in a grid-connected mode. The first control strategy is configured to control the output current of the energy storage inverter to be constant, so that the energy storage inverter is suitable for outputting a square wave output voltage waveform when a grid fault occurs. The instantaneous value of the output voltage and the DC bus voltage of the energy storage inverter are detected in real time, and a grid fault is determined to occur when the voltage difference between the two is less than a preset threshold for a period of time exceeding a preset time. When it is determined that a grid fault occurs, the energy storage inverter is switched from the grid-connected mode to the off-grid mode. The method and device for switching between grid and off-grid can greatly reduce the time required for switching between grid and off-grid of the energy storage inverter, thereby reducing the risk of damage to the energy storage inverter due to too slow switching between grid and off-grid.

Description

Technical Field

[0001] The present invention relates to the technical field of energy storage inverters, and in particular to a method and device for switching an energy storage inverter between a grid and an off-grid. Background Art

[0002] The energy storage inverter can work in grid-connected mode and off-grid mode. When it is in grid-connected mode, it is connected to the grid-connected end and the load end. When it is in off-grid mode, it is disconnected from the grid-connected end and supplies power to the load end. The energy storage inverter is required to switch between the above two modes quickly and accurately to avoid load damage, especially when switching from grid-connected mode to off-grid mode, it is required to switch the working mode as quickly as possible. In the prior art, the effective value of the output voltage of the energy storage inverter is usually detected to determine whether there is a fault in the grid-connected end. This detection method takes too long, resulting in a slow mode switching speed. Summary of the invention

[0003] The object of the present invention is to overcome the above-mentioned defects or problems existing in the background technology, and to provide a method and device for switching between on-grid and off-grid of an energy storage inverter. Compared with the fault detection method of detecting the effective value of the output voltage of the inverter circuit, the on-grid and off-grid switching method greatly reduces the time required for detecting the instantaneous value of the output voltage in the form of a square wave, so that the time required for switching between on-grid and off-grid of the energy storage inverter is also greatly reduced, thereby reducing the risk of damage to the energy storage inverter due to too slow switching between on-grid and off-grid.

[0004] To achieve the above object, the present invention adopts the following technical solution:

[0005] A method for switching between grid-connected and off-grid connected energy storage inverters, wherein the energy storage inverter has a DC bus, a grid-connected output terminal and an off-grid output terminal; the energy storage inverter is suitable for operating in an off-grid mode or a grid-connected mode; the switching method comprises: when the energy storage inverter operates in the grid-connected mode, controlling the energy storage inverter with a first control strategy; wherein the first control strategy is configured to control the output current of the energy storage inverter to be constant, so that the energy storage inverter is suitable for outputting a square wave output voltage waveform when a grid fault occurs; detecting the instantaneous value of the output voltage of the energy storage inverter and the DC bus voltage in real time, and determining that a grid fault occurs when the voltage difference between the two is less than a preset threshold for a period of time exceeding a preset time; and when it is determined that a grid fault occurs, switching the energy storage inverter from the grid-connected mode to the off-grid mode.

[0006] Furthermore, the preset threshold is between 15V and 25V.

[0007] Furthermore, the preset duration is between 3ms and 5ms.

[0008] Furthermore, after switching the energy storage inverter from the grid-connected mode to the off-grid mode, the method also controls the energy storage inverter using a second control strategy; wherein the second control strategy is configured to be suitable for controlling the output voltage of the energy storage inverter to be constant.

[0009] In addition, the present invention also provides a grid-connected and off-grid switching device for an energy storage inverter, wherein the energy storage inverter has a DC bus, a grid-connected output terminal and an off-grid output terminal; the energy storage inverter is suitable for operating in an off-grid mode or a grid-connected mode, and the device includes: a first control module, which is used to control the energy storage inverter with a first control strategy when the energy storage inverter operates in the grid-connected mode; wherein the first control strategy is configured to be suitable for controlling the output current of the energy storage inverter to be constant so that the energy storage inverter is suitable for outputting an output voltage waveform in the form of a square wave when a grid fault occurs; a detection module, which is used to detect the instantaneous value of the output voltage and the DC bus voltage of the energy storage inverter in real time; a switching module, which is used to determine that a grid fault occurs when the voltage difference between the instantaneous value of the output voltage of the energy storage inverter and the DC bus voltage is less than a preset threshold for a maintenance time exceeding a preset time length, and switch the energy storage inverter from the grid-connected mode to the off-grid mode when a grid fault occurs.

[0010] Furthermore, the preset threshold is between 15V and 25V.

[0011] Furthermore, the preset duration is between 3ms and 5ms.

[0012] Furthermore, it also includes a second control module, which is used to control the energy storage inverter according to a second control strategy after the switching module switches the energy storage inverter from the grid-connected mode to the off-grid mode; wherein the second control strategy is configured to be suitable for controlling the output voltage of the energy storage inverter to be constant.

[0013] In addition, the present invention also provides a controller, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein when the processor executes the computer program, the steps of the on-grid switching method as described in any one of the above items are implemented.

[0014] In addition, the present invention also provides a computer-readable storage medium, wherein the computer-readable storage medium stores a computer program, and when the computer program is executed by a processor, the steps of the on-grid switching and off-grid switching method as described in any one of the above items are implemented.

[0015] It can be seen from the above description of the present invention that, compared with the prior art, the present invention has the following beneficial effects:

[0016] 1. When the energy storage inverter operates in the grid-connected mode, the grid-connected operation of the energy storage inverter is controlled by the first control strategy of controlling its output current to be constant, so that when the energy storage inverter encounters a grid failure, the output current of the energy storage inverter will be uncontrolled because the load cannot be connected at this time. To this end, the energy storage inverter will increase the transmission frequency or duty cycle of its transmission pulse, which will not only make the waveform of its output voltage be pulled into a square wave, but also make the output voltage value of the square wave form close to the DC bus voltage value of the energy storage inverter.

[0017] On this basis, the grid-connected and off-grid switching method of the present invention detects the instantaneous value of the output voltage of the energy storage inverter and the output voltage of the DC bus in real time, and compares the two. When the voltage difference between the two is less than a preset threshold and the maintenance time exceeds the preset time, it can be determined that a grid fault has occurred. At this time, the energy storage inverter can be switched from the grid-connected mode to the off-grid mode. Compared with the fault detection method of detecting the effective value of the output voltage of the inverter circuit, the time required for detecting the instantaneous value of the output voltage in the form of a square wave is greatly reduced, so that the time required for the grid-connected and off-grid switching of the energy storage inverter is also greatly reduced, thereby reducing the risk of damage to the energy storage inverter due to too slow grid-connected and off-grid switching.

[0018] 2. Setting the above voltage difference to 15V-25V can avoid misjudgment due to setting the value too small, or avoid slow switching of the energy storage inverter to and from the grid due to setting the value too large. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0020] Figure 1 A schematic structural diagram of an embodiment of an energy storage inverter provided by the present invention. DETAILED DESCRIPTION

[0021] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are preferred embodiments of the present invention and should not be regarded as excluding other embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0022] In the claims, description and drawings of the present invention, if the terms "include", "have" and their variations are used, they are intended to mean "including but not limited to".

[0023] See also Figure 1 , Figure 1 A structural schematic diagram of an embodiment of an energy storage inverter provided by the present invention is shown, one end of which is connected to an energy storage device via a DC bus, and the other end has a grid-connected output end and an off-grid output end, and is suitable for operating in an off-grid mode or a grid-connected mode.

[0024] The energy storage inverter provided in this embodiment is suitable for controlling the switching between the grid-connected mode and the off-grid mode by the following on-grid and off-grid switching method, specifically:

[0025] When the energy storage inverter operates in the grid-connected mode, the energy storage inverter is controlled by a first control strategy; wherein the first control strategy is configured to be suitable for controlling the output current of the energy storage inverter to be constant, so that the energy storage inverter is suitable for outputting a square wave output voltage waveform when a grid fault occurs; the instantaneous value of the output voltage and the DC bus voltage of the energy storage inverter are detected in real time, and a grid fault is determined to have occurred when the voltage difference between the two is less than a preset threshold for a period of time exceeding a preset time; when it is determined that a grid fault has occurred, the energy storage inverter is switched from the grid-connected mode to the off-grid mode.

[0026] The preset threshold value may be between 15V and 25V. As a preferred embodiment, this embodiment uses 20V as the preset threshold value.

[0027] The preset duration may be between 3 ms and 5 ms. As a preferred embodiment, this embodiment uses 4 ms as the preset duration.

[0028] In addition, after the energy storage inverter is switched from the grid-connected mode to the off-grid mode by the above-mentioned grid-connected and off-grid switching method, the energy storage inverter is also controlled by the second control strategy, wherein the second control strategy is configured to be suitable for controlling the output voltage of the energy storage inverter to be constant.

[0029] The energy storage inverter provided in this embodiment further includes a grid-connected and off-grid switching device, which is used to implement the above-mentioned grid-connected and off-grid switching method, and includes a first control module, a second control module, a detection module and a switching module.

[0030] Among them, the first control module is used to control the energy storage inverter with the first control strategy when the energy storage inverter operates in the grid-connected mode; the detection module is used to detect the instantaneous value of the output voltage and the DC bus voltage of the energy storage inverter in real time; the switching module is used to determine that a grid fault has occurred when the voltage difference between the instantaneous value of the output voltage of the energy storage inverter and the DC bus voltage is less than a preset threshold for more than a preset time, and switch the energy storage inverter from the grid-connected mode to the off-grid mode when it is determined that a grid fault has occurred; the second control module is used to control the energy storage inverter with the second control strategy after the switching module switches the energy storage inverter from the grid-connected mode to the off-grid mode.

[0031] Specifically, the grid-connected and off-grid switching device includes a plurality of relays. When the switching module determines that the voltage difference between the instantaneous value of the output voltage of the energy storage inverter and the DC bus voltage is less than a preset threshold for a period of time exceeding a preset time, the relays are switched to switch the energy storage inverter from the grid-connected mode to the off-grid mode.

[0032] The grid-connected and off-grid switching method and grid-connected and off-grid switching device provided in this embodiment, when the energy storage inverter is operating normally in the grid-connected mode, the first control strategy is used to control the energy storage inverter so that its output current remains constant. Later, when the energy storage inverter encounters a grid failure, the output current will be uncontrollable because the energy storage inverter cannot connect to the load. At this time, the energy storage inverter will increase the wave frequency or duty cycle of its wave pulse, which will not only cause the waveform of its output voltage to be pulled into a square wave, but also make the output voltage value of the square wave form close to the DC bus voltage value of the energy storage inverter. On this basis, the instantaneous value of the output voltage of the energy storage inverter and the output voltage of the DC bus can be detected in real time, and the two can be compared. When the maintenance time of the voltage difference between the two being less than a preset threshold exceeds the preset time, it can be determined that the grid has failed, and at this time, the energy storage inverter can be switched from the grid-connected mode to the off-grid mode.

[0033] Compared with conventional fault detection methods for detecting the effective value of the output voltage of an inverter circuit, the on-grid and off-grid switching method and on-grid switching device greatly reduce the time required for detecting the instantaneous value of the output voltage in a square wave form, so that the time required for on-grid and off-grid switching of the energy storage inverter is also greatly reduced, thereby reducing the risk of damage to the energy storage inverter due to too slow on-grid and off-grid switching.

[0034] In addition, based on the above method, this embodiment also discloses a controller, which includes at least one processor and memory, and a computer program stored in the memory and can be run on the processor, and can also include a display screen, a communication interface and a bus. Among them, the processor, the display screen, the memory and the communication interface can communicate with each other through the bus. The display screen is set to display the user guide interface preset in the initial setting mode. The communication interface can transmit information. The processor can call the logic instructions in the memory to execute the method in the above embodiment.

[0035] In addition, the logic instructions in the above-mentioned memory can be implemented in the form of software functional units and can be stored in a computer-readable storage medium when sold or used as an independent product.

[0036] The memory, as a computer-readable storage medium, can be configured to store software programs, computer executable programs, such as program instructions or modules corresponding to the methods in the embodiments of the present disclosure. The processor executes functional applications and data processing by running the software programs, instructions or modules stored in the memory, that is, implementing the methods in the above embodiments.

[0037] The memory may include a program storage area and a data storage area, wherein the program storage area may store an operating system and at least one application required for a function; the data storage area may store data created according to the use of the terminal device, etc. In addition, the memory may include a high-speed random access memory and may also include a non-volatile memory. For example, a variety of media that can store program codes, such as a USB flash drive, a mobile hard disk, a read-only memory (ROM), a random access memory (RAM), a disk or an optical disk, may also be a transient storage medium.

[0038] The description of the above specification and embodiments is used to explain the protection scope of the present invention, but does not constitute a limitation on the protection scope of the present invention. Through the enlightenment of the present invention or the above embodiments, ordinary technicians in this field can obtain modifications, equivalent substitutions or other improvements to the embodiments of the present invention or part of the technical features thereof through logical analysis, reasoning or limited experiments, which should be included in the protection scope of the present invention.

Claims

1. A method for switching between an energy storage inverter and an off-grid inverter, wherein the energy storage inverter has a DC bus, a grid-connected output terminal and an off-grid output terminal; The energy storage inverter is suitable for operating in off-grid mode or grid-connected mode; its characteristics are: The switching method comprises: when the energy storage inverter is operating in the grid-connected mode, controlling the energy storage inverter with a first control strategy; wherein the first control strategy is configured to control the output current of the energy storage inverter to be constant, so that the energy storage inverter is suitable for outputting a square wave output voltage waveform when a grid fault occurs; Real-time detection of the instantaneous value of the output voltage and the DC bus voltage of the energy storage inverter, and determination of a grid fault when the output voltage waveform presents a square wave form and the voltage difference between the output voltage and the DC bus voltage is less than a preset threshold for a period of time exceeding a preset time; When it is determined that a grid fault occurs, the energy storage inverter is switched from a grid-connected mode to an off-grid mode.

2. A method for switching between on-grid and off-grid energy storage inverters according to claim 1, characterized in that: The preset threshold is between 15V and 25V.

3. A method for switching between on-grid and off-grid of an energy storage inverter as claimed in claim 2, characterized in that: The preset duration is between 3ms and 5ms.

4. A method for switching between an energy storage inverter and an off-grid energy storage inverter according to any one of claims 1 to 3, characterized in that: After switching the energy storage inverter from the grid-connected mode to the off-grid mode, the method further controls the energy storage inverter with a second control strategy; wherein the second control strategy is configured to be suitable for controlling the output voltage of the energy storage inverter to be constant.

5. A grid-connected and off-grid switching device for an energy storage inverter, wherein the energy storage inverter has a DC bus, a grid-connected output terminal and an off-grid output terminal; The energy storage inverter is suitable for operating in an off-grid mode or a grid-connected mode, and is characterized in that: The device comprises: A first control module, which is used to control the energy storage inverter with a first control strategy when the energy storage inverter operates in a grid-connected mode; wherein the first control strategy is configured to be suitable for controlling the output current of the energy storage inverter to be constant, so that the energy storage inverter is suitable for outputting an output voltage waveform in the form of a square wave when a grid fault occurs; A detection module, which is used to detect the instantaneous value of the output voltage and the DC bus voltage of the energy storage inverter in real time; A switching module is used to determine that a grid fault has occurred when the output voltage waveform of the energy storage inverter presents a square wave shape and the voltage difference between the output voltage and the DC bus voltage is less than a preset threshold for more than a preset time, and to switch the energy storage inverter from a grid-connected mode to an off-grid mode when a grid fault is determined to have occurred.

6. The on-grid and off-grid switching device of the energy storage inverter according to claim 5, characterized in that: The preset threshold is between 15V and 25V.

7. The on-grid and off-grid switching device of the energy storage inverter according to claim 6, characterized in that: The preset duration is between 3ms and 5ms.

8. The on-grid and off-grid switching device of the energy storage inverter according to claim 7, characterized in that: It also includes a second control module, which is used to control the energy storage inverter with a second control strategy after the switching module switches the energy storage inverter from the grid-connected mode to the off-grid mode; wherein the second control strategy is configured to be suitable for controlling the output voltage of the energy storage inverter to be constant.

9. A controller comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that: When the processor executes the computer program, the steps of the on-grid and off-grid switching method as described in any one of claims 1 to 4 are implemented.

10. A computer-readable storage medium storing a computer program, characterized in that: When the computer program is executed by a processor, the steps of the on-grid and off-grid switching method as described in any one of claims 1 to 4 are implemented.

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