A method and device for switching between grid-connected and off-grid operation of an energy storage inverter, and a medium

Abstract

The present application relates to photovoltaic grid-connected power generation technology field, disclose a kind of energy storage inverter's on-grid and off-grid switching method, device, equipment and medium, the method includes: when meeting predictive off-grid trigger condition, pre-opening SCR drive;When determining current zero, RST relay is disconnected, until RST relay is completely disconnected, close SCR drive, from grid-connected to off-grid;Receive off-grid and grid-connected instruction, close NPE relay, carry out fast phase synchronization;When phase synchronization is completed, issue off-grid and grid-connected RST relay closing instruction, close RST relay, wait for first preset duration after closing SCR drive and SCR relay, wait for second preset duration after disconnecting SCR drive, from off-grid to grid-connected, the present application is pre-opened by SCR drive, and impact current is borne by SCR, RST relay is disconnected when current zero, fundamentally eliminate the physical condition that arc generates, prolongs relay service life.

Description

Technical Field

[0001] This invention relates to the field of photovoltaic grid-connected power generation technology, specifically to a method, apparatus, equipment, and medium for switching between grid-connected and off-grid operation of an energy storage inverter. Background Technology

[0002] Currently, integrated photovoltaic and energy storage systems use traditional relay solutions. During grid-connected / off-grid switching and bypass operations, these relays need to operate with high current. However, the selected relays are all three-stage relays, which can only connect and disconnect with low current and have a constant current carrying capacity. In areas with unstable power grids, traditional relay solutions cause frequent relay operation, posing a challenge to relay lifespan. Summary of the Invention

[0003] This invention provides a method, apparatus, equipment, and medium for switching energy storage inverters between grid and off-grid, in order to solve the problem of frequent relay operation during the grid-to-off-grid switching process in traditional relay solutions, which affects the lifespan of the relays.

[0004] In a first aspect, the present invention provides a method for switching an energy storage inverter between the grid and off-grid, the method comprising: When the predictive off-grid trigger condition is met, pre-open the SCR driver; When the current is determined to be zero, disconnect the RST relay until the RST relay is completely disconnected, shut down the SCR drive, and switch from grid-connected to off-grid. Upon receiving the off-grid to grid-connected command, close the NPE relay to perform rapid phase synchronization; When phase synchronization is completed, an off-grid to grid-connected RST relay closing command is issued, the RST relay is closed, and after waiting for the first preset time, the SCR drive and SCR relay are closed. After waiting for the second preset time, the SCR drive is disconnected, and the off-grid to grid-connected switch is initiated.

[0005] This invention pre-opens the SCR drive during grid-connected to off-grid switching, allowing the SCR to bear the inrush current and ensuring that the RST relay disconnects when the current crosses zero. This fundamentally eliminates the physical conditions for arc generation. During off-grid to grid-connected switching, the SCR drive and SCR relay remain disconnected when the RST relay is closed, ensuring that there is no risk in closing the RST relay at this time. When the SCR relay is closed subsequently, the SCR bears the transient surge current, thus solving the risk of RST relay during grid-connected to off-grid switching, effectively extending the service life of the RST relay, and ensuring operational stability.

[0006] In one alternative implementation, the predictive churn trigger is determined as follows: Periodically sample the inverter output power and calculate the power change rate; If the power change rate is negative for a continuous preset number of cycles and the absolute value exceeds the change rate threshold, it is determined to be a predictive off-grid trigger.

[0007] This invention periodically samples the inverter's output power, calculates the power change rate, and uses the power change rate to predict grid disconnection, thereby initiating the grid-connected / off-grid switching process in advance and shortening the grid-connected / off-grid switching response time.

[0008] In one alternative implementation, the current zero-crossing is determined as follows: Calculate the current load rate in real time and dynamically adjust the zero-crossing threshold according to the current load rate; Real-time acquisition of grid current; If the product of the zero-crossing threshold, the rated current of the RST relay, and the temperature compensation coefficient of the RST relay is greater than the absolute value of the real-time collected grid current, then the current is determined to be zero-crossing.

[0009] This invention identifies the current zero-crossing point by determining the current zero-crossing point, thereby ensuring that the RST relay can achieve arc-free safe shutdown under zero-current conditions and effectively extending the service life of the RST relay.

[0010] In an alternative implementation, before receiving the off-grid to grid connection command, the method further includes: Detect whether the power grid has switched from off-grid to on-grid; If the off-grid to grid connection is confirmed, then issue a power generation grid amplitude and phase synchronization command; Issue NPE relay disconnection command and off-grid to on-grid disconnection command.

[0011] This invention detects the grid status and, upon confirming the transition from off-grid to on-grid, issues a phase synchronization command to control the NPE relay to disconnect, thereby avoiding grid-connection inrush currents caused by unstable grid status or phase asynchrony.

[0012] In one alternative implementation, fast phase synchronization is performed, including: When the phase difference between the inverter output and the grid is greater than the first threshold, the inverter output frequency bias is increased by the first frequency bias value, and the phase difference is detected by the first detection cycle. When the phase difference between the inverter output and the grid is greater than or equal to the second threshold and less than or equal to the first threshold, the inverter output frequency bias is increased by the second frequency bias value, and the phase difference is detected by the second detection cycle. When the phase difference between the inverter output and the grid is less than the second threshold, the inverter output frequency bias is increased by the third frequency bias value. When the phase difference between the inverter output and the grid is less than the third threshold and the frequency difference is less than the preset frequency threshold, it is determined that phase synchronization is completed. The first threshold is greater than the second threshold, the second threshold is greater than the third threshold, and the first detection period is greater than the second detection period.

[0013] This invention reduces the off-grid to grid switching time by setting a frequency offset value and detection period based on the phase difference between the inverter output and the grid. When the phase difference is large, it uses a large offset and a long period to catch up quickly; when the phase difference is small, it uses a small offset and a short period to catch up.

[0014] In an alternative implementation, after disconnecting the SCR driver, the method further includes: Detect the voltage across the RST relay and read the RST relay feedback status; If the RST relay is in a normal closed state, then set the RST relay self-test flag to valid.

[0015] This invention ensures that the RST relay is in a closed state by detecting the voltage across the RST relay and reading the feedback state of the RST relay.

[0016] In an alternative implementation, after the RST relay self-test flag is set to valid, the method further includes: If the SCR relay feedback state is detected as closed, then it is determined again whether the current of the RST relay is greater than the preset current threshold. If the current of the RST relay is greater than the preset current threshold, then switch to grid connection.

[0017] This invention verifies the SCR relay feedback status and RST relay current to ensure that the grid connection switching conditions are met, thus avoiding the risk of grid connection failure when the SCR relay feedback status is incorrect or the RST relay current is abnormal.

[0018] In a second aspect, the present invention provides a grid-connected / off-grid switching device for an energy storage inverter, the device comprising: The pre-open module is used to pre-open the SCR driver when the predictive off-grid triggering conditions are met; The first switching module is used to disconnect the RST relay when the current is determined to be zero, and to shut down the SCR drive and switch from grid-connected to off-grid when the RST relay is completely disconnected. The phase synchronization module is used to receive off-grid to grid-connected commands, close the NPE relay, and perform rapid phase synchronization. The second switching module is used to issue an off-grid to grid-connected RST relay closing command when phase synchronization is completed, close the RST relay, wait for a first preset time, close the SCR drive and SCR relay, wait for a second preset time, and then disconnect the SCR drive to switch from off-grid to grid-connected.

[0019] Thirdly, the present invention provides an electronic device, comprising: a memory and a processor, wherein the memory and the processor are communicatively connected to each other, the memory stores computer instructions, and the processor executes the computer instructions to perform the grid-connected / off-grid switching method of the energy storage inverter described in the first aspect or any corresponding embodiment thereof.

[0020] Fourthly, the present invention provides a computer-readable storage medium storing computer instructions for causing a computer to execute the grid-connected / off-grid switching method of the energy storage inverter described in the first aspect or any corresponding embodiment thereof. Attached Figure Description

[0021] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0022] Figure 1 This is a schematic flowchart of the grid-connected / off-grid switching method for an energy storage inverter according to an embodiment of the present invention; Figure 2 This is a schematic diagram of the operation process of the grid-connected to off-grid relay according to an embodiment of the present invention; Figure 3 This is a schematic diagram of the first part of the operation of the off-grid to on-grid relay according to an embodiment of the present invention; Figure 4 This is a schematic diagram of the second part of the operation of the off-grid to on-grid relay according to an embodiment of the present invention; Figure 5 This is a structural block diagram of the grid-connected / off-grid switching device for an energy storage inverter according to an embodiment of the present invention; Figure 6 This is a schematic diagram of the hardware structure of an electronic device according to an embodiment of the present invention. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] It is understood that before using the technical solutions disclosed in the various embodiments of the present invention, users should be informed of the types, scope of use, and usage scenarios of the personal information involved in the present invention in an appropriate manner in accordance with relevant laws and regulations, and their permission should be obtained.

[0025] In related technologies, outdoor energy storage systems employ electromagnetic relays as switching elements during grid-connected / off-grid switching. The physical characteristics of relay contacts—current flowing down when closed and voltage dropping when open—pose significant challenges during grid-connected / off-grid switching. During disconnection under high current and large voltage differential conditions, high-temperature arcs are generated between the contacts. These arcs can reach thousands of degrees Celsius, melting and evaporating the metal on the contact surface, leading to pitting and protrusion on the contacts and increased contact resistance. Each disconnection also causes irreversible wear on the contact material, typically reducing contact lifespan to only 10 years. 4 ~10 5 Secondly, when the contact surface wears out rapidly or the temperature rises abnormally, the molten metal may permanently bond together after cooling, forming an adhesion fault. Once adhesion occurs, the relay will lose its ability to disconnect or close, leading to failure of parallel / offline switching, and in severe cases, it may cause islanding or equipment damage.

[0026] This invention provides a method for grid-connected / off-grid switching of an energy storage inverter. In the traditional grid-side relay scheme, a set of SCR (Silicon Controlled Rectifier) ​​relays is added. When the inverter performs grid-connected / off-grid switching, predictive SCR pre-triggering is performed. Combined with adaptive zero-crossing grid-connected switching, the SCR bears the transient surge current, and the relay only needs to carry steady-state current, thereby reducing the risk of relay sticking and enhancing its lifespan.

[0027] According to an embodiment of the present invention, a method for switching between grid and off-grid of an energy storage inverter is provided. It should be noted that the steps shown in the flowchart in the accompanying drawings can be executed in a computer system such as a set of computer-executable instructions. Furthermore, although a logical order is shown in the flowchart, in some cases, the steps shown or described may be executed in a different order than that shown here.

[0028] This embodiment provides a method for switching between grid connection and off-grid operation of an energy storage inverter. Figure 1 This is a flowchart of a grid-connected / off-grid switching method for an energy storage inverter according to an embodiment of the present invention, such as... Figure 1 As shown, the process includes the following steps: Step S101: When the predictive off-grid triggering condition is met, pre-open the SCR driver.

[0029] In this embodiment of the invention, when the predictive off-grid triggering condition is met, the SCR drive is pre-activated, causing the SCR to enter a conduction preparation state before the RST relay operates, and the SCR bears the current. It should be noted that the RST relay is the same as the grid-side RST relay.

[0030] Step S102: When the current is determined to be zero, disconnect the RST relay until the RST relay is completely disconnected, shut down the SCR drive, and switch from grid-connected to off-grid.

[0031] In this embodiment of the invention, when the current is determined to be zero, the RST relay is disconnected. At this time, since the SCR has been turned on in advance, the time difference for detecting SCR take-off is shortened from 10-20ms to less than 1ms, and the RST relay achieves zero-current disconnection. After detecting that the RST relay has been completely disconnected, the SCR drive is turned off, and the RST relay disconnection command is cleared, realizing the switch from grid-connected to off-grid.

[0032] During grid connection and off-grid switching, based on predictive grid connection and off-grid detection, the RST relay achieves adaptive zero-current disconnection, replacing the traditional single relay or similar dual relay scheme. This optimizes the switching delay time from 15ms to 1~3ms, while eliminating the risk of electric arc when the relay is disconnected, and significantly reducing the grid connection and off-grid switching time.

[0033] Step S103: Receive the off-grid to grid-connected command, close the NPE relay, and perform rapid phase synchronization.

[0034] In this embodiment of the invention, after receiving the off-grid to on-grid command, the NPE relay is closed. After 200ms, the closure status of the NPE relay is checked. If the NPE relay reports a closed state within 3 seconds, rapid phase synchronization is performed; otherwise, an NPE relay fault is reported. It should be noted that the NPE relay is the grid-side N-line to ground relay.

[0035] Step S104: When phase synchronization is completed, a command to close the off-grid to grid-connected RST relay is issued, the RST relay is closed, the SCR drive and SCR relay are closed after waiting for a first preset time, the SCR drive is disconnected after waiting for a second preset time, and the off-grid to grid-connected switch is initiated.

[0036] In this embodiment of the invention, when phase synchronization is completed, an off-grid to grid-connected RST relay closing command is issued, the RST relay is closed, and after waiting for a first preset time, the SCR drive and SCR relay are closed, and after waiting for a second preset time, the SCR drive is disconnected, and the off-grid to grid-connected state is switched.

[0037] It should be noted that although there are differences in relay hardware, the differences in hardware testing time are small, usually around 20 milliseconds. To prevent inconsistencies in action time caused by differences in relay hardware, and to allow for margin, the first and second preset durations are usually set to 30 milliseconds.

[0038] During the off-grid to grid-connected transition, fast phase synchronization detection is adopted. When the RST relay is closed, the SCR drive and SCR relay remain open. At this time, closing the RST relay is risk-free. After waiting for the first preset time, when the SCR relay is closed, the transient surge current is borne by the SCR. The use of fast phase synchronization effectively reduces the off-grid to grid-connected transition time compared to traditional synchronization schemes.

[0039] The grid-connected / off-grid switching method for energy storage inverters provided in this embodiment pre-opens the SCR drive when switching from grid connection to off-grid, allowing the SCR to bear the inrush current and ensuring that the RST relay disconnects when the current crosses zero. This fundamentally eliminates the physical conditions for arc generation. When switching from off-grid to grid connection, the SCR drive and SCR relay remain disconnected when the RST relay is closed, ensuring that there is no risk in closing the RST relay at this time. Subsequently, when the SCR relay is closed, the SCR bears the transient surge current, thus solving the risk of the RST relay during grid-connected / off-grid switching, effectively extending the service life of the RST relay, and ensuring operational stability.

[0040] This embodiment provides a method for switching an energy storage inverter between the grid and off-grid, the process of which includes the following steps: Step S201: When the predictive off-grid triggering condition is met, pre-open the SCR driver.

[0041] Specifically, the predictive churn trigger is determined by following these steps: Step Sa: Periodically sample the inverter output power and calculate the power change rate; In step Sb, if the power change rate is negative for a consecutive preset number of cycles and the absolute value exceeds the change rate threshold, it is determined to be a predictive off-grid trigger. In this embodiment of the invention, the inverter output power P(n) is continuously sampled at a fixed period, and the power change rate ΔP is determined based on the difference in output power between two adjacent periods.

[0042] If the power change rate is negative for a continuous preset number of periods, and its absolute value exceeds the change rate threshold, it is predicted that the power grid may be about to experience a power outage. This is then determined as a predictive off-grid trigger, meaning the power grid status changes from grid-connected to off-grid. For example... Figure 2 As shown, if the grid status changes from grid-connected to off-grid, an RST relay disconnect command is output, and the RST relay disconnect command is set to 1; otherwise, no action is taken.

[0043] For example, the preset quantity is 3, that is, the power change rate is negative for 3 consecutive cycles and the absolute value exceeds the change rate threshold, which is determined to be a predictive off-grid trigger.

[0044] It should be noted that the process is the same whether it is a predictive churn trigger or a normal churn detection.

[0045] By periodically sampling the inverter's output power and calculating the power change rate, the grid disconnection process can be predicted based on the power change rate, thereby initiating the grid disconnection process in advance and shortening the grid disconnection response time.

[0046] Step S202: When the current is determined to be zero, disconnect the RST relay until the RST relay is completely disconnected, shut down the SCR drive, and switch from grid-connected to off-grid.

[0047] Specifically, the current zero-crossing is determined as follows: Step S202a: Calculate the current load rate in real time and dynamically adjust the zero-crossing threshold according to the current load rate; Step S202b: Real-time acquisition of grid current; In step S202c, if the product of the zero-crossing threshold, the rated current of the RST relay, and the temperature compensation coefficient of the RST relay is greater than the absolute value of the real-time collected grid current, then the current is determined to be zero-crossing.

[0048] In this embodiment of the invention, the current load rate ΔLoad is calculated in real time, and the zero-crossing threshold Ith is dynamically adjusted according to the current load rate. Its expression is as follows: Ith = max(0.5%, 10% -ΔLoad×9.5%).

[0049] Upon receiving the RST relay disconnect command, the disconnection process is executed, and the grid current Igrid is collected in real time, while a temperature compensation coefficient K_temp is introduced. Because the on-resistance of the RST relay varies under different ambient temperatures, the contact voltage drop differs. In high-temperature scenarios (above 40℃), the threshold is appropriately relaxed by 5%~10%, increasing the temperature compensation coefficient K_temp. In low-temperature scenarios (below 5℃), the threshold is appropriately tightened, decreasing the temperature compensation coefficient K_temp. It should be noted that this temperature compensation coefficient K_temp is specific to the RST relay.

[0050] The product of the zero-crossing threshold, the rated current of the RST relay, and the temperature compensation coefficient of the RST relay is compared with the absolute value of the real-time acquired grid current. If the product of these three factors is greater than the absolute value of the real-time acquired grid current, the current is determined to have crossed zero. The expression for this is as follows: |Igrid| <Ith×I_rated×K_temp Where I_rated is the rated current, which is also for the RST relay.

[0051] By identifying the current zero-crossing point, the RST relay can achieve arc-free safe shutdown under zero-current conditions, effectively extending the service life of the RST relay.

[0052] like Figure 2 As shown, when switching from grid-connected to off-grid, the process first determines whether the grid status has changed from grid-connected to off-grid. If not, no action is taken and the process ends. If it has changed, the RST relay disconnect command is set to 1. The RST relay disconnect command is checked to be 1. If not, no action is taken and the process ends. If it is 1, the SCR driver is activated, the SCR relay is disconnected, and high-frequency current sampling is started, continuously monitoring the grid-side current until it drops below 5% of the rated current. Then, the RST relay zero-current disconnect operation is performed. The RST relay is checked to be disconnected. If disconnected, the SCR driver is disconnected, the RST relay disconnect command is cleared, the process switches to off-grid, and the process ends.

[0053] In some alternative implementations, the method further includes: Step S203: Detect whether the power grid has switched from off-grid to on-grid; Step S204: If the off-grid to grid connection is confirmed, then issue a power generation grid amplitude and phase synchronization command. Step S205: Issue NPE relay disconnection command and off-grid to on-grid disconnection command.

[0054] In this embodiment of the invention, when switching from off-grid to grid-connected operation, the grid status is first detected to determine whether the grid status at the previous moment has changed from off-grid to grid-connected. If the off-grid to grid-connected transition is confirmed, a power generation and grid amplitude and phase synchronization command is issued, and the grid amplitude and phase synchronization command is set to 1.

[0055] After the grid amplitude and phase synchronization command is set to 1, an NPE relay disconnect command is issued, an off-grid to on-grid disconnect command is issued, and the off-grid to on-grid disconnect command is set to 1.

[0056] By detecting the grid status, a phase synchronization command is issued after the off-grid to on-grid transition, controlling the NPE relay to disconnect, thus avoiding grid connection inrush current caused by grid instability or phase asynchrony.

[0057] Step S206: Receive the off-grid to grid-connected command, close the RST relay, and perform rapid phase synchronization.

[0058] Specifically, the fast phase synchronization in step S206 above includes: Step S2061: When the phase difference between the inverter output and the grid is greater than the first threshold, the inverter output frequency bias is increased by the first frequency bias value, and the phase difference is detected by the first detection cycle. Step S2062: When the phase difference between the inverter output and the grid is greater than or equal to the second threshold and less than or equal to the first threshold, the inverter output frequency bias is increased by the second frequency bias value, and the phase difference is detected by the second detection cycle. Step S2063: When the phase difference between the inverter output and the grid is less than the second threshold, the inverter output frequency bias is increased by the third frequency bias value. Step S2064: When the phase difference between the inverter output and the grid is less than the third threshold and the frequency difference is less than the preset frequency threshold, it is determined that phase synchronization is completed. The first threshold is greater than the second threshold, the second threshold is greater than the third threshold, and the first detection period is greater than the second detection period.

[0059] In this embodiment of the invention, the RST relay detection stage adopts fast phase synchronization to calculate the phase difference Δφ and frequency difference Δf between the inverter output and the power grid in real time.

[0060] Approximation using the following four stages of variable speed: Phase 1: When the phase difference Δφ between the inverter output and the grid is greater than the first threshold of 30°, the inverter output frequency bias is increased by 1Hz with the first frequency bias value. The inverter output frequency bias is +1Hz, and it catches up with about 7.2° per cycle. The phase difference is detected once every 10ms with the first detection cycle. Phase Two: If the first threshold of 30° ≤ the phase difference Δφ between the inverter output and the grid ≤ the second threshold of 10°, the inverter output frequency bias is increased by a second frequency bias value of 0.3Hz, switching to +0.3Hz. The inverter output frequency bias catches up approximately 2.16° per cycle, and the phase difference is detected once every 5ms in the second detection cycle. Phase 3: When the phase difference Δφ between the inverter output and the grid is less than the second threshold of 10°, the inverter output frequency bias is increased by the third frequency bias value of 0.05Hz, and the inverter output frequency bias is switched to +0.05Hz, catching up by about 0.36° per cycle. Phase 4: When the phase difference Δφ between the inverter output and the grid is less than the third threshold of 5°, and the frequency difference Δf is less than the preset frequency threshold of 0.1Hz, phase synchronization is considered complete. If phase synchronization is not completed within 3 seconds, a fault is reported.

[0061] By setting the frequency offset value and detection period according to the phase difference between the inverter output and the grid, when the phase difference is large, a large offset and a long period are used to catch up quickly; when the phase difference is small, a small offset and a short period are used to catch up, thereby reducing the off-grid to grid-connected time.

[0062] Step S207: When phase synchronization is completed, a command to close the off-grid to grid-connected RST relay is issued, the RST relay is closed, the SCR drive and SCR relay are closed after a first preset time, the SCR drive is disconnected after a second preset time, and the off-grid to grid-connected switch is initiated.

[0063] Please see details Figure 1 Step S104 of the illustrated embodiment will not be described again here.

[0064] In some alternative implementations, after disconnecting the SCR driver, the method further includes: Step S208: Detect the voltage across the RST relay and read the RST relay feedback status; Step S209: If the RST relay is in a normal closed state, then set the RST relay self-test flag to valid.

[0065] In this embodiment of the invention, after disconnecting the SCR driver, the voltage across the RST relay is detected after waiting 170ms, and the feedback status of the RST relay is read.

[0066] If the RST relay is in a normal closed state, set the RST relay self-test flag to valid and set the RST relay self-test flag to 1; otherwise, report an RST relay fault.

[0067] The RST relay is kept in a closed state by detecting the voltage across its terminals and reading its feedback status.

[0068] In some optional implementations, after the RST relay self-test flag is set to valid, the method further includes: Step S210: If the SCR relay feedback state is detected as closed, then determine again whether the current of the RST relay is greater than the preset current threshold. Step S211: If the current of the RST relay is greater than the preset current threshold, then switch to grid connection.

[0069] In this embodiment of the invention, after the RST relay completes its self-test, if the SCR relay feedback state is closed, it will again determine whether the current of the RST relay is greater than the preset current threshold. If the current of the RST relay is greater than the preset current threshold, it will switch to grid connection; otherwise, it will report a fault.

[0070] By verifying the SCR relay feedback status and RST relay current, we can ensure that the grid connection switching conditions are met and avoid the risk of grid connection when the SCR relay feedback status is incorrect or the RST relay current is abnormal.

[0071] like Figure 3 and Figure 4As shown, during the off-grid to grid-connected switch, the process first checks whether the grid status has changed from off-grid to grid-connected. If not, no action is taken and the process ends. If it has changed, the amplitude and phase synchronization command is set to 1. The amplitude and phase synchronization command is checked to ensure it is 1. If it is not 1, no action is taken and the process ends. If it is 1, the NPE relay disconnect command and the off-grid to grid-connected switch command are set to 1. The NPE relay disconnect command is checked to ensure it is 1. If it is 1, the NPE relay is disconnected. If it is not 1, no action is taken and the process ends. After closing the NPE relay, a 200ms wait is required. Within 3 seconds, the NPE relay feedback status is checked to ensure it is closed. If closed, within 3 seconds, the voltage across the RST relay is checked to ensure it is normal. This process continues until both the off-grid to grid-connected switch and the off-grid to grid-connected switch detection commands are set to 1. Close the RST relay and wait 30ms. Close the SCR driver and SCR relay and wait 30ms. Disconnect the SCR driver and wait 170ms. Check whether the voltage across the RST relay and the feedback signal are closed. If closed, check whether the SCR relay feedback signal is closed. If closed, determine whether the grid-side current is greater than a certain threshold. If it is greater, the detection ends and grid-connected operation is switched.

[0072] The grid-connected / off-grid switching method for energy storage inverters provided in this embodiment adds a set of SCR relays. Compared to the traditional single-relay solution, which carries the risk of relay sticking during the large voltage difference and high current at the moment of grid-connected / off-grid switching, potentially leading to machine failure, this method controls the closing / opening sequence of the SCR and RST relays during grid-connected / off-grid switching. The SCR relay is prioritized to bear this inrush current, and the zero-crossing closing / opening capability of the SCR relay eliminates the risk of RST relay failure during grid-connected / off-grid switching, extending the RST relay's lifespan and greatly ensuring the stability of machine operation.

[0073] The advantages of this grid-connected / off-grid switching method for energy storage inverters are: (1) Significantly reduced switching latency: The switching latency has been reduced from a fixed 15ms delay in the traditional solution to 1~3ms. For sensitive loads (such as data centers and hospital power supply), this means that the switching process has changed from "perceptible interruption" to "perceptible switching". (2) RST relay zero-current disconnection: By real-time current zero-crossing detection, the RST relay is ensured to perform disconnection when the current is close to zero, which fundamentally eliminates the physical conditions for the generation of electric arc; (3) SCR bears the inrush current: The inrush current during switching is completely borne by SCR. As a semiconductor device, SCR can withstand hundreds of thousands of inrush currents without mechanical wear. (4) Improved system reliability: It fundamentally eliminates the most common failure mode of energy storage systems, namely RST relay sticking, and improves the reliability of the system throughout its entire life cycle; (5) Reduced maintenance costs: The lifespan of the RST relay has been increased from 50,000 to 100,000 cycles to more than 500,000 cycles, and it is expected that the RST relay will not need to be replaced during the 10-year operation period.

[0074] This embodiment also provides a grid-connected / off-grid switching device for an energy storage inverter. This device is used to implement the above embodiments and preferred embodiments, and details already described will not be repeated. As used below, the term "module" can refer to a combination of software and / or hardware that implements a predetermined function. Although the device described in the following embodiments is preferably implemented in software, hardware implementation, or a combination of software and hardware, is also possible and contemplated.

[0075] This embodiment provides a grid-connected / off-grid switching device for an energy storage inverter, such as... Figure 5 As shown, it includes: The pre-open module 501 is used to pre-open the SCR driver when the predictive off-grid triggering conditions are met. The first switching module 502 is used to disconnect the RST relay when the current is determined to be zero, and to turn off the SCR drive and switch from grid-connected to off-grid when the RST relay is completely disconnected. The phase synchronization module 503 is used to receive off-grid to grid-connected commands, close the NPE relay, and perform rapid phase synchronization. The second switching module 504 is used to issue an off-grid to grid-connected RST relay closing command when phase synchronization is completed, close the RST relay, wait for a first preset time, close the SCR drive and SCR relay, wait for a second preset time, and then disconnect the SCR drive to switch from off-grid to grid-connected.

[0076] In some alternative implementations, predictive churn triggering is determined as follows: Periodically sample the inverter output power and calculate the power change rate; If the power change rate is negative for a continuous preset number of cycles and the absolute value exceeds the change rate threshold, it is determined to be a predictive off-grid trigger.

[0077] In some alternative implementations, the current zero-crossing is determined as follows: Calculate the current load rate in real time and dynamically adjust the zero-crossing threshold according to the current load rate; Real-time acquisition of grid current; If the product of the zero-crossing threshold, the rated current of the RST relay, and the temperature compensation coefficient of the RST relay is greater than the absolute value of the real-time collected grid current, then the current is determined to be zero-crossing.

[0078] In some alternative embodiments, the device further includes: The detection module is used to detect whether the power grid has switched from off-grid to on-grid. The first issuing module is used to issue a power generation grid amplitude and phase synchronization command if the off-grid to grid conversion is confirmed. The second sending module is used to send NPE relay disconnection commands and off-grid to on-grid switching commands.

[0079] In some alternative implementations, the phase synchronization module 503 includes: The first bias module is used to increase the inverter output frequency bias with a first frequency bias value and detect the phase difference with a first detection period when the phase difference between the inverter output and the grid is greater than a first threshold. The second bias module is used to increase the inverter output frequency bias with a second frequency bias value and detect the phase difference with a second detection cycle when the phase difference between the inverter output and the grid is greater than or equal to a second threshold and less than or equal to a first threshold. The third bias module is used to increase the inverter output frequency bias by a third frequency bias value when the phase difference between the inverter output and the grid is less than the second threshold. The synchronization determination module is used to determine that phase synchronization is complete when the phase difference between the inverter output and the grid is less than a third threshold and the frequency difference is less than a preset frequency threshold. The first threshold is greater than the second threshold, the second threshold is greater than the third threshold, and the first detection period is greater than the second detection period.

[0080] In some alternative embodiments, the device further includes: The status reading module is used to detect the voltage across the RST relay and read the feedback status of the RST relay. The setting module is used to set the RST relay self-test flag to valid if the RST relay is in a normal closed state.

[0081] In some alternative embodiments, the device further includes: The judgment module is used to determine whether the current of the RST relay is greater than the preset current threshold if the feedback state of the SCR relay is detected as closed. The switching module is used to switch to grid connection if the current of the RST relay is greater than a preset current threshold.

[0082] The grid-connected / off-grid switching device for energy storage inverters provided in this embodiment of the invention can execute the grid-connected / off-grid switching method for energy storage inverters provided in any embodiment of the invention, and has the corresponding functional modules and beneficial effects for executing the method. Further functional descriptions of the above modules and units are the same as in the corresponding embodiments described above, and will not be repeated here.

[0083] Figure 6 This is a schematic diagram of the structure of an electronic device provided in an embodiment of the present invention.

[0084] The following is a detailed reference. Figure 6 This diagram illustrates a suitable structural design for implementing an electronic device according to embodiments of the present invention. The electronic device may include a processor (e.g., a central processing unit, graphics processor, etc.) 601, which can perform various appropriate actions and processes based on a program stored in read-only memory (ROM) 602 or a program loaded from memory 608 into random access memory (RAM) 603. RAM 603 also stores various programs and data required for the operation of the electronic device. The processor 601, ROM 602, and RAM 603 are interconnected via a bus 604. An input / output (I / O) interface 605 is also connected to the bus 604.

[0085] Typically, the following devices can be connected to I / O interface 605: input devices 606 including, for example, touchscreens, touchpads, keyboards, mice, cameras, microphones, accelerometers, gyroscopes, etc.; output devices 607 including, for example, liquid crystal displays (LCDs), speakers, vibrators, etc.; memory devices 608 including, for example, magnetic tapes, hard disks, etc.; and communication devices 609. Communication device 609 allows electronic devices to communicate wirelessly or wiredly with other devices to exchange data. Although Figure 6 Electronic devices with various devices are shown, but it should be understood that it is not required to implement or have all of the devices shown, and more or fewer devices may be implemented or have instead.

[0086] In particular, according to embodiments of the present invention, the processes described above with reference to the flowcharts can be implemented as computer software programs. For example, embodiments of the present invention include a computer program product comprising a computer program carried on a non-transitory computer-readable medium, the computer program containing program code for performing the methods shown in the flowcharts. In such embodiments, the computer program can be downloaded and installed from a network via a communication device 609, or installed from a memory 608, or installed from a ROM 602. When the computer program is executed by the processor 601, it performs the functions defined in the grid-connected / off-grid switching method of the energy storage inverter according to embodiments of the present invention.

[0087] Figure 6 The electronic device shown is merely an example and should not be construed as limiting the functionality and scope of use of the embodiments of the present invention.

[0088] This invention also provides a computer-readable storage medium. The methods described above according to embodiments of the invention can be implemented in hardware or firmware, or implemented as computer code that can be recorded on a storage medium, or implemented as computer code downloaded via a network and originally stored on a remote storage medium or a non-transitory machine-readable storage medium and then stored on a local storage medium. Thus, the methods described herein can be processed by software stored on a storage medium using a general-purpose computer, a dedicated processor, or programmable or dedicated hardware. The storage medium can be a magnetic disk, optical disk, read-only memory, random access memory, flash memory, hard disk, or solid-state drive, etc.; further, the storage medium can also include combinations of the above types of memory. It is understood that computers, processors, microprocessor controllers, or programmable hardware include storage components capable of storing or receiving software or computer code. When the software or computer code is accessed and executed by the computer, processor, or hardware, the grid-connected / off-grid switching method for the energy storage inverter shown in the above embodiments is implemented.

[0089] A portion of this invention can be applied as a computer program product, such as computer program instructions, which, when executed by a computer, can invoke or provide the methods and / or technical solutions according to the invention through the operation of the computer. Those skilled in the art will understand that the forms in which computer program instructions exist in a computer-readable medium include, but are not limited to, source files, executable files, installation package files, etc. Correspondingly, the ways in which computer program instructions are executed by a computer include, but are not limited to: the computer directly executing the instructions, or the computer compiling the instructions and then executing the corresponding compiled program, or the computer reading and executing the instructions, or the computer reading and installing the instructions and then executing the corresponding installed program. Here, the computer-readable medium can be any available computer-readable storage medium or communication medium accessible to a computer.

[0090] Although embodiments of the invention have been described in conjunction with the accompanying drawings, those skilled in the art can make various modifications and variations without departing from the spirit and scope of the invention, and all such modifications and variations fall within the scope defined by the appended invention.

Claims

1. A method for switching between grid connection and off-grid operation of an energy storage inverter, characterized in that, The method includes: When the predictive off-grid trigger condition is met, pre-open the SCR driver; When the current is determined to be zero, disconnect the RST relay until the RST relay is completely disconnected, shut down the SCR drive, and switch from grid-connected to off-grid. Upon receiving the off-grid to grid-connected command, close the NPE relay to perform rapid phase synchronization; When phase synchronization is completed, an off-grid to grid-connected RST relay closing command is issued, the RST relay is closed, and after waiting for the first preset time, the SCR drive and SCR relay are closed. After waiting for the second preset time, the SCR drive is disconnected, and the off-grid to grid-connected switch is initiated.

2. The method according to claim 1, characterized in that, Predictive churn triggering is determined as follows: Periodically sample the inverter output power and calculate the power change rate; If the power change rate is negative for a continuous preset number of cycles and the absolute value exceeds the change rate threshold, it is determined to be a predictive off-grid trigger.

3. The method according to claim 1, characterized in that, Determine if the current crosses zero as follows: Calculate the current load rate in real time and dynamically adjust the zero-crossing threshold according to the current load rate; Real-time acquisition of grid current; If the product of the zero-crossing threshold, the rated current of the RST relay, and the temperature compensation coefficient of the RST relay is greater than the absolute value of the real-time collected grid current, then the current is determined to be zero-crossing.

4. The method according to claim 1, characterized in that, Before receiving the off-grid to on-grid switch command, the method further includes: Detect whether the power grid has switched from off-grid to on-grid; If the off-grid to grid connection is confirmed, then issue a power generation grid amplitude and phase synchronization command; Issue NPE relay disconnection command and off-grid to on-grid disconnection command.

5. The method according to claim 1, characterized in that, The process of performing fast phase synchronization includes: When the phase difference between the inverter output and the grid is greater than the first threshold, the inverter output frequency bias is increased by the first frequency bias value, and the phase difference is detected by the first detection cycle. When the phase difference between the inverter output and the grid is greater than or equal to the second threshold and less than or equal to the first threshold, the inverter output frequency bias is increased by the second frequency bias value, and the phase difference is detected by the second detection cycle. When the phase difference between the inverter output and the grid is less than the second threshold, the inverter output frequency bias is increased by the third frequency bias value. When the phase difference between the inverter output and the grid is less than the third threshold and the frequency difference is less than the preset frequency threshold, it is determined that phase synchronization is completed. The first threshold is greater than the second threshold, the second threshold is greater than the third threshold, and the first detection period is greater than the second detection period.

6. The method according to claim 1, characterized in that, After disconnecting the SCR driver, the method further includes: Detect the voltage across the RST relay and read the RST relay feedback status; If the RST relay is in a normal closed state, then set the RST relay self-test flag to valid.

7. The method according to claim 6, characterized in that, After setting the RST relay self-test flag to active, the method further includes: If the SCR relay feedback state is detected as closed, then it is determined again whether the current of the RST relay is greater than the preset current threshold. If the current of the RST relay is greater than the preset current threshold, then switch to grid connection.

8. A grid-connected / off-grid switching device for an energy storage inverter, characterized in that, The device includes: The pre-open module is used to pre-open the SCR driver when the predictive off-grid triggering conditions are met; The first switching module is used to disconnect the RST relay when the current is determined to be zero, and to shut down the SCR drive and switch from grid-connected to off-grid when the RST relay is completely disconnected. The phase synchronization module is used to receive off-grid to grid-connected commands, close the NPE relay, and perform rapid phase synchronization. The second switching module is used to issue an off-grid to grid-connected RST relay closing command when phase synchronization is completed, close the RST relay, wait for a first preset time, close the SCR drive and SCR relay, wait for a second preset time, and then disconnect the SCR drive to switch from off-grid to grid-connected.

9. An electronic device, characterized in that, include: The device includes a memory and a processor, which are interconnected. The memory stores computer instructions, and the processor executes the computer instructions to perform the grid-connected / off-grid switching method of the energy storage inverter as described in any one of claims 1 to 7.

10. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores computer instructions for causing the computer to execute the grid-connected / off-grid switching method of the energy storage inverter as described in any one of claims 1 to 7.

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