Energy storage systems and their grid-connected to off-grid control methods and devices, storage media

Abstract

This invention discloses an energy storage system and its grid-connected to off-grid switching control method and device, as well as a storage medium. The method includes: when any energy storage converter detects a grid anomaly, setting the connection port between the energy storage converter and the synchronization signal line to a low level, thereby blocking the PWM pulse in each energy storage converter and controlling multiple energy storage converters to disconnect from the grid, thus entering an off-grid mode preparation state; in the off-grid mode preparation state, adjusting the phase angle of the sine wave generator in the energy storage converter to a preset value, thereby switching the connection port of the energy storage converter to an input / high impedance mode, and causing the synchronization signal line to jump to a high-level signal; taking the moment when the synchronization signal line jumps to a high-level signal as a zero point, so that each energy storage converter synchronously outputs PWM pulses when detecting the zero point, and causes multiple energy storage converters to output sinusoidal voltages of the same phase. This enables synchronous blocking and zero-phase synchronous startup of all energy storage converters during grid faults.

Description

Technical Field

[0001] This invention relates to the field of energy storage control technology, and in particular to an energy storage system and its grid-connected to off-grid control method and device, as well as a storage medium. Background Technology

[0002] With the development of renewable energy and energy storage technologies, energy storage systems composed of multiple power conversion systems (PCS) connected in parallel are widely used. Under normal circumstances, such systems operate in grid-connected mode, supplying or absorbing electrical energy to the grid; when a grid fault occurs, they need to quickly and smoothly switch to off-grid mode to provide continuous power for critical loads.

[0003] In related technologies, the grid-connected / off-grid switching of multi-machine parallel systems typically employs a master-slave control architecture, relying on communication buses such as CAN and RS485 for coordination. After detecting a grid fault, the master sends a switching command to all slaves via the communication network. However, this approach has significant drawbacks: First, the communication process suffers from millisecond-level delays, failing to meet the microsecond-level rapid response requirements of power systems and easily leading to voltage dips or current surges during switching. Second, due to the inconsistent timing of command reception by each slave, the starting phase of their internal sine wave generators differs, resulting in phase differences between the output voltages of multiple PCS units. This creates harmful circulating currents on the parallel bus, which can reduce system efficiency or even trigger protection shutdowns or damage equipment. Third, this approach is highly dependent on the reliability of the communication network; if the network fails, the entire system loses its coordination capability, resulting in switching failure.

[0004] Therefore, there is an urgent need for a grid-to-off-grid control scheme that does not rely on complex communication, can achieve microsecond-level synchronous response, and fundamentally eliminates phase differences between multiple machines. Summary of the Invention

[0005] This invention aims to at least partially solve one of the technical problems in related technologies. Therefore, the first objective of this invention is to propose a grid-to-off-grid control method for energy storage systems. Utilizing a shared synchronization signal line and its electrical characteristics, this method enables microsecond-level synchronous blocking and zero-phase synchronous startup of all energy storage converters during grid faults, effectively avoiding circulating currents and ensuring a safe, reliable, and seamless switching process.

[0006] A second objective of the present invention is to provide a computer-readable storage medium.

[0007] The third objective of this invention is to provide a grid-connected to off-grid control device for an energy storage system.

[0008] The fourth objective of this invention is to provide an energy storage system.

[0009] To achieve the above objectives, a first aspect of the present invention proposes a grid-connected to off-grid control method for an energy storage system, wherein the energy storage system includes multiple energy storage converters, each of which is connected to a synchronization signal line via a connection port. The method includes: when any energy storage converter detects a grid anomaly, setting the connection port of the energy storage converter to the synchronization signal line to a low level, thereby blocking the PWM pulse for each energy storage converter, and controlling the multiple energy storage converters to disconnect from the grid to enter an off-grid mode preparation state; In the off-grid mode preparation state, the phase angle of the sine wave generator in the energy storage converter is adjusted to a preset value so that the connection port of the energy storage converter is switched to the input / high impedance mode. When the connection port of each energy storage converter is in the input / high impedance mode, the synchronization signal line jumps to a high level signal. The moment when the synchronization signal line jumps to the high level signal is taken as the zero point so that each energy storage converter synchronously outputs the PWM pulse when it detects the zero point, and the multiple energy storage converters output the same phase sine wave voltage.

[0010] According to the grid-connected to off-grid control method of the energy storage system of the present invention, by utilizing a shared synchronization signal line and its electrical characteristics, all energy storage converters can be synchronously blocked and start-up with zero phase during grid faults, thereby effectively avoiding circulating current and ensuring a safe, reliable and seamless switching process.

[0011] In addition, the grid-connected to off-grid control method for the energy storage system according to the above embodiments of the present invention may further include the following additional technical features:

[0012] According to one embodiment of the present invention, all the connection ports are GPIO interfaces, and all the GPIO interfaces are configured in open-drain output mode.

[0013] According to one embodiment of the present invention, the energy storage system further includes a grid-connected contactor disposed between the power grid and the AC bus to be connected to the plurality of energy storage converters via the AC bus.

[0014] According to one embodiment of the present invention, controlling the multiple energy storage converters to disconnect from the power grid includes: sending a shutdown signal to the grid-connected contactor so that the grid-connected contactor performs a shutdown operation based on the shutdown signal; and obtaining operation feedback from the grid-connected contactor to confirm that the grid-connected contactor is in a shutdown state.

[0015] According to one embodiment of the present invention, the energy storage system further includes a pull-up resistor and a high-level power supply, wherein the high-level power supply is connected to the synchronization signal line through the pull-up resistor.

[0016] According to an embodiment of the present invention, the method further includes: when outputting the PWM pulse to each energy storage converter, controlling the energy storage converter to perform a voltage soft-start operation and a droop control current sharing operation, so that the output voltage of the multiple energy storage converters is increased to a preset voltage amplitude according to a preset slope and the output current of the multiple energy storage converters is in a balanced state.

[0017] According to one embodiment of the present invention, the power grid anomaly includes the voltage change rate of the power grid being greater than a preset change rate or the frequency being outside a preset frequency range.

[0018] To achieve the above objectives, a second aspect of the present invention provides a computer-readable storage medium storing a grid-connected to off-grid control program for an energy storage system. When the grid-connected to off-grid control program is executed by a processor, it implements the aforementioned grid-connected to off-grid control method for the energy storage system according to the embodiments of the present invention.

[0019] According to the computer-readable storage medium of the present invention, the grid-connected to off-grid control program of the energy storage system is executed by a processor. By utilizing a shared synchronization signal line and its electrical characteristics, all energy storage converters can be synchronously blocked and start-up with zero phase during grid faults, thereby effectively avoiding circulating currents and ensuring a safe, reliable and seamless switching process.

[0020] To achieve the above objectives, a third aspect of the present invention provides a grid-connected to off-grid control device for an energy storage system. The energy storage system includes multiple energy storage converters, each connected to a synchronization signal line via a connection port. The device includes: a control module, configured to set the connection port of the energy storage converter to the synchronization signal line to a low level when any energy storage converter detects a grid anomaly, thereby blocking the PWM pulse in each energy storage converter and disconnecting the multiple energy storage converters from the grid to enter an off-grid mode preparatory state; and an adjustment module. The system is used to adjust the phase angle of the sine wave generator in the energy storage converter to a preset value in the off-grid mode preparation state, so that the connection port of the energy storage converter is switched to the input / high impedance mode. When the connection port of each energy storage converter is in the input / high impedance mode, the synchronization signal line jumps to a high level signal. The synchronization output module is used to take the moment when the synchronization signal line jumps to the high level signal as the zero point, so that each energy storage converter synchronously outputs the PWM pulse when it detects the zero point, and makes the multiple energy storage converters output the same phase sine wave voltage.

[0021] According to an embodiment of the present invention, the grid-connected to off-grid control device of the energy storage system can realize the synchronous blocking and zero-phase synchronous start-up of all energy storage converters in the event of a grid fault by utilizing a shared synchronization signal line and its electrical characteristics, thereby effectively avoiding circulating current and ensuring a safe, reliable and seamless switching process.

[0022] To achieve the above objectives, a fourth aspect of the present invention provides an energy storage system, including a grid-connected to off-grid control device for the energy storage system described in the foregoing embodiments of the present invention.

[0023] According to the energy storage system of the present invention, by adopting the grid-connected to off-grid control device of the energy storage system of the above-described embodiments of the present invention, by utilizing a shared synchronization signal line and its electrical characteristics, all energy storage converters can achieve synchronous blocking and zero-phase synchronous start-up during grid faults, thereby effectively avoiding circulating currents and ensuring a safe, reliable, and seamless switching process.

[0024] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0025] Figure 1 This is a hardware topology diagram of the energy storage system according to an embodiment of the present invention; Figure 2 This is a circuit schematic diagram of the energy storage converter and the synchronization signal line according to an embodiment of the present invention; Figure 3 This is a schematic flowchart of the grid-connected to off-grid control method for an energy storage system according to an embodiment of the present invention; Figure 4 This is a timing diagram of the grid-connected to off-grid control method for an energy storage system according to an embodiment of the present invention; Figure 5 This is a block diagram of the grid-connected to off-grid control device of the energy storage system according to an embodiment of the present invention; Figure 6 This is a block diagram of an energy storage system according to an embodiment of the present invention.

[0026] Figure label: Energy storage system 1000, power grid 10, grid-connected contactor 11, AC bus 12, energy storage converter 13, synchronization signal line 14, pull-up resistor 15, grid-connected to off-grid control device 100 for energy storage system, control module 20, adjustment module 30, synchronization output module 40. Detailed Implementation

[0027] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0028] The energy storage system and its grid-connected to off-grid control method and apparatus, as well as the storage medium, according to embodiments of the present invention are described below with reference to the accompanying drawings.

[0029] Before introducing the grid-connected to off-grid control method and device of the energy storage system of the present invention, the energy storage system of the present invention will be described accordingly, such as... Figure 1 As shown, the energy storage system 1000 of the present invention includes a power grid 10, a grid-connected contactor 11 (KM), an AC bus 12 (AC BUS), and N energy storage converters 13 (PCS) connected in parallel (N is an integer greater than or equal to 2). Each energy storage converter 13 is connected to the AC bus 12 through its internal MOSFET switches Q1 to Qn to realize bidirectional conversion of electrical energy.

[0030] The power grid 10, serving as an external public power supply source, is connected to the AC bus 12 via a grid-connected contactor 11. This grid-connected contactor 11 is a high-voltage switching device used for physical isolation between the energy storage system and the power grid. During normal grid-connected operation, the grid-connected contactor 11 is in a closed state, allowing electrical energy to flow freely between the power grid and the energy storage system. When switching to off-grid mode is required, the control system sends a shutdown command to the grid-connected contactor 11 to open it, thereby ensuring electrical isolation between the energy storage system and the power grid, preventing backfeeding, and ensuring the safety of personnel and equipment.

[0031] The AC outputs of all energy storage converters 13 (PCS 1, PCS 2, ..., PCS N) are connected in parallel to the same AC bus 12, collectively providing power to the load. Each energy storage converter 13 integrates a power conversion circuit (represented by MOSFETs), a controller (such as a DSP or MCU), and an internal detection point for monitoring the grid status. This internal detection point collects grid voltage, frequency, and other parameters in real time to determine whether any abnormalities have occurred in the grid.

[0032] To achieve hardware-level synchronization control among multiple energy storage converters 13, this invention introduces a shared synchronization signal line 14 (Sync_Bus). One end of this synchronization signal line 14 is connected to the general purpose input / output interface GPIO of each energy storage converter 13, and the other end is connected to the high-level power supply VCC (e.g., ...) via a pull-up resistor 15 (R_up). Figure 2(As shown). In this embodiment, the GPIO interface of each energy storage converter 13 is configured in open-drain output mode, allowing any PCS to actively pull the synchronization signal line 14 low. Only when all energy storage converters 13 cease actively pulling it low can the synchronization signal line 14 be pulled back to a high level by the pull-up resistor 15. This wired-AND logic structure is the core hardware foundation for achieving multi-machine synchronization.

[0033] Specifically, such as Figure 2 As shown, the interface circuit between each energy storage converter 13 and the synchronization signal line 14 includes the following key components: GPIO (OD): This is the general-purpose input / output pin of the controller, configured in open-drain output mode. When the GPIO output is low, its internal drive circuit is turned on, pulling the synchronization signal line 14 low; when the GPIO output is high or floating, it is not driven and is in a high-impedance state. MOSFET switches Q1 to Qn serve as the main control switches. Their gates are driven by the "blocking control signal". An N-channel MOSFET can be used. When the blocking control signal is valid (usually high), the MOSFET switch is turned on, forcibly pulling the synchronization signal line 14 low to achieve fast blocking; when the blocking signal is invalid, the MOSFET switch is turned off, allowing the GPIO to control the state of the synchronization signal line 14. Current-limiting resistor Rf is used to limit the current flowing from the GPIO or MOSFET switch to the synchronization signal line 14, protecting the interface chip and MOSFET from damage caused by short circuits or surges. A filter capacitor Cf is connected between the synchronization signal line 14 and ground to filter out noise and glitches in the signal, improve signal integrity, and prevent false triggering due to interference (such as incorrect detection of rising or falling edges). A pull-up resistor 15 (Rup) is connected between the synchronization signal line 14 and the high-level power supply VCC. Its function is to pull the bus level to a high level (logic "1") when no energy storage converter 13 actively pulls the synchronization signal line 14 low, ensuring signal stability in the default state.

[0034] In summary, the energy storage system of this invention provides robust hardware support for subsequent fast, reliable, and non-circulating current-free grid-to-off-grid control by connecting multiple energy storage converters in parallel to the same AC bus and utilizing a hard-wired synchronization network composed of shared synchronization signal lines and open-drain GPIO interfaces. This interface circuit design is simple, low-cost, and possesses good anti-interference capabilities and electrical safety, making it particularly suitable for industrial-grade energy storage applications.

[0035] Figure 3 This is a schematic flowchart of the grid-connected to off-grid control method for an energy storage system according to an embodiment of the present invention.

[0036] Specifically, in some embodiments of the present invention, the energy storage system includes multiple energy storage converters, all of which are connected to a synchronization signal line via connection ports, such as... Figure 3 As shown, the grid-connected to off-grid control method for energy storage systems includes: S101 When any energy storage converter detects a grid anomaly, it sets the connection port between the energy storage converter and the synchronization signal line to a low level, so that each energy storage converter blocks the PWM pulse and controls multiple energy storage converters to disconnect from the grid, so as to enter the off-grid mode preparation state.

[0037] Specifically, in this embodiment, each energy storage converter is equipped with a grid status monitoring module to collect parameters such as grid voltage amplitude, frequency, and rate of change in real time. "Grid anomaly" can be defined as: a grid voltage drop exceeding a preset threshold (e.g., below 85% of the rated value), a voltage change rate (dV / dt) exceeding a safety limit, or a grid frequency deviating from the normal range (e.g., 50Hz ± 0.5Hz). Once any energy storage converter detects a grid anomaly, its controller immediately drives its connection port (e.g., a GPIO pin configured as an open-drain output) to output a low level, thereby pulling the shared synchronization signal line low. Because the synchronization signal line uses a wired-AND electrical structure (maintained at a high level through a pull-up resistor), this low-level signal will instantaneously propagate to all parallel energy storage converters. Upon detecting the falling edge on the synchronization signal line, the remaining energy storage converters immediately perform a double isolation operation: First, at the software level: the controller issues a command to immediately block the PWM drive pulses of all power switching devices (such as IGBTs or MOSFETs), cut off the energy output to the AC bus, and prevent current surges or reverse power supply during the switching process; Secondly, at the hardware level: a shutdown command is sent to the grid-connected contactor, and the contactor status feedback detection mechanism is activated. Physical isolation is considered complete only after receiving an auxiliary contact signal indicating that the contactor has reliably disconnected. After completing the above operations, the system officially enters the "off-grid mode preparation state." At this time, although each energy storage converter has been decoupled from the grid, it has not yet started to supply power independently and is in a standby preparation stage.

[0038] S102, in the off-grid mode preparation state, the phase angle of the sine wave generator in the energy storage converter is adjusted to a preset value so that the connection port of the energy storage converter is switched to the input / high impedance mode. When the connection port of each energy storage converter is in the input / high impedance mode, the synchronization signal line jumps to a high level signal.

[0039] Specifically, in this embodiment, after entering the off-grid mode preparation state, each energy storage converter independently executes internal control algorithm reconstruction and state reset: the control strategy is switched from the PQ (constant power) mode commonly used in grid connection to the VF (constant voltage and constant frequency) mode required for off-grid operation; the integral terms of the voltage loop and current loop PI controllers are cleared to eliminate the interference of historical errors on the new steady state; most importantly, the initial phase angle of the internal digital sine wave generator is forcibly reset to a unified preset value (preferably 0 degrees) to lay the phase foundation for subsequent synchronous startup.

[0040] Once all the above preparations are completed and the self-test is fault-free, the energy storage converter switches its connection port from the "open-drain output low level" mode to the "input" or "high impedance" mode, meaning it no longer actively drives the synchronization signal line. Since all energy storage converters use the same logic, the synchronization signal line only transitions from low to high under the influence of an external pull-up resistor, forming a clear rising edge signal, after the last device has completed its preparations and released its synchronization signal line.

[0041] S103 takes the moment when the synchronization signal line jumps to a high-level signal as the zero point, so that each energy storage converter synchronously outputs a PWM pulse when it detects the zero point, and makes multiple energy storage converters output sinusoidal voltages in the same phase.

[0042] Specifically, in this embodiment, all energy storage converters are pre-configured to be sensitive to the rising edge of the synchronization signal line. When the rising edge is detected, each controller simultaneously marks the reference time of its internal timer or phase accumulator as zero (t = 0). From this moment on, all energy storage converters synchronously release the PWM lockout, begin synchronously outputting PWM pulses, and start generating in-phase sinusoidal voltages based on their respective internal sine wave generators, which have been reset to 0 degrees. Since the phase start point and time start point of all devices are completely consistent, their output sinusoidal voltages are highly aligned in frequency, amplitude, and phase, fundamentally avoiding circulating current problems caused by phase differences. Subsequently, the system can further perform voltage soft start (gradually increasing the output voltage to the rated value according to a preset slope) and droop control to achieve balanced distribution of active / reactive power among multiple units, ultimately smoothly transitioning to a stable off-grid operation state.

[0043] Furthermore, in some embodiments of the present invention, the connection ports are all GPIO interfaces, and the GPIO interfaces are all configured in open-drain output mode. Specifically, the operating mode of the GPIO interface is set to "open-drain output" through software configuration. In this mode, the GPIO can only actively drive the signal line to a low level (logic "0"), and cannot actively output a high level; when a high level is required, the GPIO enters a high-impedance state, and the high level is provided by an external pull-up circuit. This configuration allows multiple devices to safely share the same signal line; any device can pull it low without electrical conflict caused by multiple devices simultaneously outputting high / low levels. This naturally supports "wired-AND" logic functions and is the foundation for achieving hardware-level synchronous control.

[0044] Furthermore, in some embodiments of the present invention, the energy storage system also includes a grid-connected contactor, which is disposed between the power grid and the AC bus to connect to multiple energy storage converters via the AC bus. This provides reliable physical electrical isolation during switching between grid-connected and off-grid modes. During normal grid-connected operation, the contactor's main contacts are closed, allowing bidirectional flow of electrical energy; when the system needs to switch to off-grid mode, the control system must first disconnect this contactor to ensure complete decoupling of the energy storage system from the public power grid. This effectively prevents accidental backfeeding to a faulty grid in off-grid mode, ensuring the personal safety of on-site maintenance personnel.

[0045] Furthermore, in some embodiments of the present invention, controlling multiple energy storage converters to disconnect from the grid includes: sending a shutdown signal to a grid-connected contactor so that the grid-connected contactor performs a shutdown operation based on the shutdown signal; and obtaining operational feedback from the grid-connected contactor to confirm that the grid-connected contactor is in a shutdown state.

[0046] Specifically, in this embodiment, the grid-connected contactor is equipped with auxiliary contacts to provide status feedback signals for the position of its main contacts. When performing a disconnection operation, the control system first sends a shutdown command (typically a low-level or high-level pulse signal) to the contactor's coil drive circuit, driving its mechanical mechanism. Simultaneously, the control system continuously monitors the feedback signal from the auxiliary contacts. Only when the feedback signal clearly indicates that the main contacts have reliably separated (i.e., the contactor is in the "open" state) is the physical connection to the power grid considered successfully disconnected, allowing the system to proceed with the subsequent off-grid startup process. This dual confirmation mechanism of "command + feedback" effectively avoids the risk of "false disconnection" caused by contactor sticking, jamming, or drive failure, greatly improving the safety and reliability of system switching.

[0047] Furthermore, in some embodiments of the present invention, the energy storage system further includes a pull-up resistor and a high-level power supply, wherein the high-level power supply is connected to the synchronization signal line through the pull-up resistor.

[0048] Specifically, in this embodiment, one end of the pull-up resistor is connected to a stable high-level power supply, and the other end is connected to the synchronization signal line. The pull-up circuit and the open-drain GPIO interface of each energy storage converter together form a robust wired-AND bus, which is the hardware basis for the default high-level state of the synchronization signal line and the generation of the rising edge.

[0049] Furthermore, in some embodiments of the present invention, the method further includes: when outputting PWM pulses to each energy storage converter, controlling the energy storage converter to perform voltage soft-start operation and droop control current sharing operation, so that the output voltage of multiple energy storage converters is increased to a preset voltage amplitude according to a preset slope and the output current of multiple energy storage converters is in a balanced state.

[0050] Specifically, in this embodiment, after synchronous startup, each energy storage converter does not immediately output its rated voltage, but instead initiates a voltage soft-start procedure. This procedure controls the outer voltage reference value in VF mode, causing it to start from zero or a lower value and linearly increase at a preset, gentle slope until the target amplitude is reached. This effectively suppresses inrush current during startup, protecting the load and the power devices of the energy storage converter itself.

[0051] Meanwhile, in order to achieve reasonable power distribution among multiple units, the system adopts a droop control strategy. All energy storage converters use the same droop coefficient, and then automatically share the load current proportionally according to their own capacity, thereby achieving dynamic balance of output current, avoiding overload of a certain device, and ensuring long-term stable operation of the system.

[0052] Furthermore, in some embodiments of the present invention, a power grid anomaly includes a voltage change rate greater than a preset change rate or a frequency not within a preset frequency range.

[0053] Specifically, in this embodiment, the criteria for determining "grid anomalies" are not limited to voltage amplitude drops, but also include more sensitive dynamic indicators. The rate of change of voltage (dV / dt) refers to the speed at which the grid voltage changes per unit time. When disturbances such as short circuits or heavy load switching occur in the grid, even if the voltage does not ultimately drop to the undervoltage threshold, its instantaneous rate of change may be extremely high. This invention, by calculating dV / dt in real time and comparing it with a preset safety threshold (such as 50V / ms), can detect potential serious faults in advance and trigger faster protection actions.

[0054] Furthermore, grid frequency is a key parameter for measuring grid stability. In this embodiment, if the grid frequency is detected to deviate continuously from the standard power frequency (e.g., 50Hz or 60Hz) beyond the allowable range (e.g., ±0.5Hz), it is determined to be a grid anomaly. This comprehensive multi-dimensional criterion (amplitude, rate of change, frequency) significantly improves the sensitivity and accuracy of fault detection, ensuring that the system can initiate a seamless switching process at the most appropriate time.

[0055] In one specific embodiment of the present invention, such as Figure 4 As shown, when the grid voltage drops abnormally at time T0, any energy storage converter (such as PCS 1) immediately pulls down the synchronization signal line (Sync_Bus) after detecting the fault. The remaining converters (such as PCS 2) synchronously block the PWM output and disconnect the grid-connected contactor after detecting the falling edge of the synchronization signal line at time T1, entering the off-grid preparation state. Subsequently, each converter independently completes the preparation work such as switching the control mode, clearing the PI integrator, and resetting the sine wave phase angle to 0°, and releases its own GPIO to a high impedance state in sequence, waiting for the rising edge interruption. When the last converter completes the preparation, the synchronization signal line generates a rising edge at time T3 under the action of the pull-up resistor. All converters use this rising edge as the time zero point, synchronously release the PWM block and output a sine wave voltage from the reset phase angle, thereby realizing seamless off-grid start-up of multiple machines with zero phase difference and no circulating current.

[0056] In summary, the grid-connected to off-grid control method for energy storage systems according to embodiments of the present invention, by utilizing a shared synchronization signal line and its electrical characteristics, can achieve synchronous blocking and zero-phase synchronous startup of all energy storage converters during grid faults, thereby effectively avoiding circulating currents and ensuring a safe, reliable, and seamless switching process.

[0057] Based on the grid-connected to off-grid control method for energy storage systems proposed in the foregoing embodiments of the present invention, the present invention also proposes a computer-readable storage medium storing a grid-connected to off-grid control program for an energy storage system. When the grid-connected to off-grid control program for an energy storage system is executed by a processor, it implements the grid-connected to off-grid control method for an energy storage system as described in the above embodiments of the present invention.

[0058] According to the computer-readable storage medium of the present invention, the grid-connected to off-grid control program of the energy storage system is executed by a processor. By utilizing a shared synchronization signal line and its electrical characteristics, all energy storage converters can be synchronously blocked and start-up with zero phase during grid faults, thereby effectively avoiding circulating currents and ensuring a safe, reliable and seamless switching process.

[0059] Figure 5 This is a block diagram of the grid-connected to off-grid control device of an energy storage system according to an embodiment of the present invention.

[0060] like Figure 5 As shown, the energy storage system includes multiple energy storage converters, all of which are connected to the synchronization signal line through connection ports. The grid-connected to off-grid control device 100 of the energy storage system includes a control module 20, an adjustment module 30, and a synchronization output module 40.

[0061] The control module 20 is used to set the connection port of the energy storage converter and the synchronization signal line to a low level when any energy storage converter detects a grid anomaly, so that each energy storage converter blocks the PWM pulse and controls multiple energy storage converters to disconnect from the grid to enter the off-grid mode preparation state; the adjustment module 30 is used to adjust the phase angle of the sine wave generator in the energy storage converter to a preset value in the off-grid mode preparation state, so that the connection port of the energy storage converter switches to the input / high impedance mode. When the connection port of each energy storage converter is in the input / high impedance mode, the synchronization signal line jumps to a high level signal; the synchronization output module 40 is used to take the moment when the synchronization signal line jumps to a high level signal as the zero point, so that each energy storage converter synchronously outputs PWM pulses when it detects the zero point, and makes multiple energy storage converters output sine wave voltages in the same phase.

[0062] In some embodiments of the present invention, the connection ports are all GPIO interfaces, and the GPIO interfaces are all configured in open-drain output mode.

[0063] In some embodiments of the present invention, the energy storage system further includes a grid-connected contactor disposed between the power grid and the AC bus to connect to multiple energy storage converters via the AC bus.

[0064] In some embodiments of the present invention, the control module 20 is specifically used to send a shutdown signal to the grid-connected contactor so that the grid-connected contactor performs a shutdown operation based on the shutdown signal; and to obtain operation feedback from the grid-connected contactor to confirm that the grid-connected contactor is in a shutdown state.

[0065] In some embodiments of the present invention, the energy storage system further includes a pull-up resistor and a high-level power supply, wherein the high-level power supply is connected to a synchronization signal line through the pull-up resistor.

[0066] In some embodiments of the present invention, the control module 20 is further configured to control the energy storage converter to perform voltage soft-start operation and droop control current sharing operation when outputting PWM pulses to each energy storage converter, so that the output voltage of multiple energy storage converters is increased to a preset voltage amplitude according to a preset slope and the output current of multiple energy storage converters is in a balanced state.

[0067] In some embodiments of the present invention, a power grid anomaly includes a voltage change rate greater than a preset change rate or a frequency not within a preset frequency range.

[0068] It should be noted that other specific implementations of the grid-connected to off-grid control device for the energy storage system proposed in the embodiments of the present invention can be found in the specific implementations of the grid-connected to off-grid control method for the energy storage system described in the foregoing embodiments of the present invention. To reduce redundancy, they will not be repeated here.

[0069] In summary, the grid-connected to off-grid control device of the energy storage system according to the embodiments of the present invention can realize the synchronous blocking and zero-phase synchronous start-up of all energy storage converters during grid faults by utilizing a shared synchronization signal line and its electrical characteristics, thereby effectively avoiding circulating currents and ensuring a safe, reliable, and seamless switching process.

[0070] Figure 6 This is a block diagram of an energy storage system according to an embodiment of the present invention.

[0071] like Figure 6 As shown, the energy storage system 1000 includes the grid-connected to off-grid control device 100 of the energy storage system described in the above embodiment of the present invention.

[0072] According to the energy storage system of the present invention, by adopting the grid-connected to off-grid control device of the energy storage system of the above-described embodiments of the present invention, by utilizing a shared synchronization signal line and its electrical characteristics, all energy storage converters can achieve synchronous blocking and zero-phase synchronous start-up during grid faults, thereby effectively avoiding circulating currents and ensuring a safe, reliable, and seamless switching process.

[0073] It should be noted that the logic and / or steps represented in the flowchart or otherwise described herein, for example, can be considered as a sequenced list of executable instructions for implementing logical functions, and can be specifically implemented in any computer-readable medium for use by, or in conjunction with, an instruction execution system, apparatus, or device (such as a computer-based system, a processor-included system, or other system that can fetch and execute instructions from, an instruction execution system, apparatus, or device). For the purposes of this specification, "computer-readable medium" can be any means that can contain, store, communicate, propagate, or transmit programs for use by, or in conjunction with, an instruction execution system, apparatus, or device. More specific examples (a non-exhaustive list) of computer-readable media include: an electrical connection having one or more wires (electronic device), a portable computer disk drive (magnetic device), random access memory (RAM), read-only memory (ROM), erasable and editable read-only memory (EPROM or flash memory), fiber optic devices, and portable optical disc read-only memory (CDROM). Alternatively, the computer-readable medium may be paper or other suitable media on which the program can be printed, since the program can be obtained electronically, for example, by optically scanning the paper or other medium, followed by editing, interpreting, or otherwise processing as necessary, and then stored in a computer memory.

[0074] It should be understood that various parts of the present invention can be implemented in hardware, software, firmware, or a combination thereof. In the above embodiments, multiple steps or methods can be implemented in software or firmware stored in memory and executed by a suitable instruction execution system. For example, if implemented in hardware, as in another embodiment, it can be implemented using any one or a combination of the following techniques known in the art: discrete logic circuits having logic gates for implementing logical functions on data signals, application-specific integrated circuits (ASICs) having suitable combinational logic gates, programmable gate arrays (PGAs), field-programmable gate arrays (FPGAs), etc.

[0075] In the description of this specification, references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0076] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0077] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0078] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0079] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0080] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A grid-connected to off-grid control method for an energy storage system, characterized in that, The energy storage system includes multiple energy storage converters, all of which are connected to a synchronization signal line via connection ports. The method includes: When any energy storage converter detects a grid anomaly, it sets the connection port between the energy storage converter and the synchronization signal line to a low level, so that each energy storage converter blocks the PWM pulse and controls the multiple energy storage converters to disconnect from the grid in order to enter the off-grid mode preparation state. In the off-grid mode preparation state, the phase angle of the sine wave generator in the energy storage converter is adjusted to a preset value so that the connection port of the energy storage converter is switched to the input / high impedance mode. When the connection port of each energy storage converter is in the input / high impedance mode, the synchronization signal line jumps to a high level signal. The moment when the synchronization signal line jumps to the high-level signal is taken as the zero point, so that each energy storage converter synchronously outputs the PWM pulse when it detects the zero point, and the multiple energy storage converters output the same-phase sine wave voltage.

2. The grid-connected to off-grid control method for an energy storage system according to claim 1, characterized in that, All connection ports are GPIO interfaces, and all GPIO interfaces are configured in open-drain output mode.

3. The grid-connected to off-grid control method for an energy storage system according to claim 1, characterized in that, The energy storage system also includes a grid-connected contactor, which is located between the power grid and the AC bus to connect to the multiple energy storage converters via the AC bus.

4. The grid-connected to off-grid control method for the energy storage system according to claim 3, characterized in that, Disconnecting the multiple energy storage converters from the power grid includes: Send a shutdown signal to the grid-connected contactor so that the grid-connected contactor performs a shutdown operation based on the shutdown signal; Obtain operational feedback from the grid-connected contactor to confirm that the grid-connected contactor is in the off state.

5. The grid-connected to off-grid control method for an energy storage system according to claim 1, characterized in that, The energy storage system also includes a pull-up resistor and a high-level power supply, wherein the high-level power supply is connected to the synchronization signal line through the pull-up resistor.

6. The grid-connected to off-grid control method for an energy storage system according to claim 1, characterized in that, The method further includes: When outputting the PWM pulse to each energy storage converter, the energy storage converter is also controlled to perform voltage soft-start operation and droop control current sharing operation, so that the output voltage of the multiple energy storage converters is increased to the preset voltage amplitude according to the preset slope and the output current of the multiple energy storage converters is in a balanced state.

7. The grid-connected to off-grid control method for an energy storage system according to claim 1, characterized in that, The power grid anomaly includes the voltage change rate of the power grid being greater than a preset change rate or the frequency being outside the preset frequency range.

8. A computer-readable storage medium, characterized in that, It stores a grid-connected to off-grid control program for an energy storage system. When the processor executes the grid-connected to off-grid control program for the energy storage system, it implements the grid-connected to off-grid control method for the energy storage system according to any one of claims 1-7.

9. A grid-connected to off-grid control device for an energy storage system, characterized in that, The energy storage system includes multiple energy storage converters, all of which are connected to a synchronization signal line via connection ports. The device includes: The control module is used to set the connection port between the energy storage converter and the synchronization signal line to a low level when any energy storage converter detects a grid anomaly, so that each energy storage converter blocks the PWM pulse and controls the multiple energy storage converters to disconnect from the grid to enter the off-grid mode preparation state. The adjustment module is used to adjust the phase angle of the sine wave generator in the energy storage converter to a preset value in the off-grid mode preparation state, so that the connection port of the energy storage converter is switched to the input / high impedance mode. When the connection port of each energy storage converter is in the input / high impedance mode, the synchronization signal line jumps to a high level signal. The synchronous output module is used to take the moment when the synchronous signal line jumps to the high-level signal as the zero point, so that each energy storage converter synchronously outputs the PWM pulse when it detects the zero point, and makes the multiple energy storage converters output the same-phase sine wave voltage.

10. An energy storage system, characterized in that, Includes the grid-connected to off-grid control device for the energy storage system as described in claim 9.

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