A modular low-cost grid-connected and off-grid switching system and method

Abstract

This application relates to the technical field of energy storage control, and in particular, to a modular low-cost grid-connected and off-grid switching system and method, which includes: a grid-connected and off-grid switch module, with two ends respectively used to connect to the grid side and the user side; an off-grid action module, used to collect the voltage on the grid side to control the grid-connected and off-grid switch module to act to the open state; a grid-connected action module, used to control the grid-connected and off-grid switch module to act to the closed state according to the input signal; a grid-connected feedback module, used to collect real-time voltage information to generate a grid-connected feedback signal; an energy storage control unit, electrically connected to the grid-connected feedback module to obtain the grid-connected feedback signal, and generate a closing control signal based on the grid-connected feedback signal and send it to the grid-connected action module as the input signal; the energy storage control unit collects the closing feedback signal, and performs a matching analysis based on the grid-connected feedback signal and the closing feedback signal to switch the working mode. This application has the effect of realizing low-cost and highly applicable grid-connected and off-grid switching.

Description

Technical Field

[0001] The present application relates to the technical field of energy storage control, and in particular, to a modular low-cost grid-connected and off-grid switching system and method. Background Art

[0002] Grid-connected and off-grid switching refers to the process of switching a device from a grid-connected state to an off-grid state or from an off-grid state to a grid-connected state in a power system. This switching usually occurs when there is a grid fault or power outage, and the system automatically or manually switches to the off-grid mode to ensure uninterrupted power supply to the load; when the grid resumes normal operation, the system automatically switches back to the grid-connected mode.

[0003] In the current prior art, a seamless grid-connected and off-grid switching method is adopted. The STS module (static double-way switch) is used to monitor the power failure state of the grid, and at the moment of power failure, the STS module will send a signal to the PCS (energy storage converter management unit) in the energy storage. The energy storage will switch its grid-connected state to the off-grid state within dozens of milliseconds after receiving the signal, so as to realize the load power supply in the off-grid state.

[0004] However, due to the extremely high price of the PCS unit on the current market, for some low-cost power consumption environments or scenarios with little requirement for the accuracy of grid-connected and off-grid power consumption, the development, design, and use costs of this grid-connected and off-grid switching solution are relatively high. At the same time, the load adaptability is limited, and there are problems of high loss and high heat generation. Summary of the Invention

[0005] In order to achieve low-cost and highly applicable grid-connected and off-grid switching, the present application provides a modular low-cost grid-connected and off-grid switching system and method.

[0006] In a first aspect, the present application provides a modular low-cost grid-connected and off-grid switching system, adopting the following technical solution:

[0007] A modular low-cost grid-connected and off-grid switching system includes:

[0008] A grid-connected and off-grid switch module, with both ends respectively used to connect the grid side and the user side, where the user side includes an energy storage end and a load end;

[0009] An off-grid action module, coupled to the grid-connected and off-grid switch module and electrically connected to the grid side, for collecting the voltage on the grid side to control the grid-connected and off-grid switch module to act to the open state;

[0010] A grid-connected action module, coupled to the grid-connected and off-grid switch module, for controlling the grid-connected and off-grid switch module to act to the closed state according to an input signal;

[0011] The grid-connected feedback module is electrically connected between the grid side and the grid-connected / off-grid switch module, and is used to collect real-time voltage information to generate a grid-connected feedback signal;

[0012] The energy storage control unit is electrically connected to the grid-connected feedback module to obtain the grid-connected feedback signal, and generates a closing control signal based on the grid-connected feedback signal and sends it to the grid-connected action module as the input signal;

[0013] The energy storage control unit is also electrically connected to the grid-connected / off-grid switch module to collect a closing feedback signal, and performs a matching analysis based on the grid-connected feedback signal and the closing feedback signal to switch the working mode, and the working mode includes a grid-connected mode and an off-grid mode.

[0014] In some embodiments, the grid-connected / off-grid switch module includes a low-voltage circuit breaker QF, and the off-grid action module includes an under-voltage release X1. The under-voltage release X1 collects the voltage on the grid side and judges whether it is less than a first preset value;

[0015] If it is not less than the first preset value, the under-voltage release X1 is energized to control the low-voltage circuit breaker QF to remain closed;

[0016] If it is less than the first preset value, the under-voltage release X1 loses power to perform a tripping action to control the low-voltage circuit breaker QF to open.

[0017] In some embodiments, the grid-connected action module includes an electric operating switch X2, and the grid-connected feedback module includes a voltage relay D1;

[0018] The voltage relay D1 is used to detect the magnitude of the real-time voltage information between the low-voltage circuit breaker QF and the grid side, and generates a grid-connected feedback signal to the energy storage control unit when the real-time voltage information is greater than a second preset value, wherein the grid-connected feedback signal is a level signal;

[0019] The energy storage control unit obtains the grid-connected feedback signal and correspondingly generates a closing control instruction to send to the electric operating switch X2. After the electric operating switch X2 obtains the input signal containing the closing control instruction, it drives the low-voltage circuit breaker QF to close through the motor M.

[0020] In some embodiments, the energy storage control unit collects the action state of the grid-connected / off-grid switch module in real time to obtain the closing feedback signal, and performs a consistency comparison with the collected grid-connected feedback signal. Specifically,

[0021] If the grid-connected feedback signal corresponds to the grid-connected level signal and the closing feedback signal corresponds to closing, enter the grid-connected mode. At this time, control the energy storage terminal to shut down and send a grid-connected command to the PCS to perform the grid-connected charge and discharge control logic;

[0022] If the grid-connected feedback signal does not correspond to the grid-connected level signal and the closing feedback signal corresponds to opening, enter the off-grid mode. At this time, control the energy storage terminal to power on and send an off-grid command to the energy storage terminal to perform the off-grid charge and discharge control logic.

[0023] In some embodiments, when the voltage on the grid side is less than the first preset value, the energy storage control unit obtains the power supply priority of the load side;

[0024] If the power supply priority is high, generate a thermal response command based on the current voltage and send it to the energy storage terminal. After obtaining the thermal response command, the energy storage terminal enters the thermal start power supply mode to power on;

[0025] If the power supply priority is low, generate a cold response command based on the current voltage and send it to the energy storage terminal. After obtaining the cold response command, the energy storage terminal enters the cold start power supply mode to power on.

[0026] In some embodiments, the second preset value includes a pre-stage sub-value and a post-stage sub-value, where the pre-stage sub-value is less than the post-stage sub-value;

[0027] When the real-time voltage information is greater than the pre-stage sub-value and is stably maintained for the first duration, send the grid-connected feedback signal to the energy storage control unit;

[0028] When the real-time voltage information is greater than the post-stage sub-value and is stably maintained for the second duration, send a grid-connected command to the PCS and calculate the signal quality to generate a fluctuation coefficient;

[0029] Among them, after the energy storage control unit obtains the grid-connected feedback signal, it generates a reaction reserved time and sends it to the energy storage terminal. The energy storage terminal shuts down after the reaction reserved time arrives. The reaction reserved time is the second duration multiplied by the fluctuation coefficient.

[0030] In some embodiments, during the second duration, the energy storage control unit real-time collects the real-time voltage information, real-time frequency information, and real-time phase information and generates a synchronous change amount, and calculates a synchronous change rate through the ratio of the synchronous change amount to the reaction reserved time;

[0031] The energy storage control unit dynamically adjusts the output power of the energy storage terminal based on the synchronous change rate until it changes to 0 and shuts down.

[0032] In some of these embodiments, if the grid-connected feedback signal does not correspond to the grid-connected level signal and the closing feedback signal corresponds to closing, a first verification task of a preset duration is generated to send a first error correction trigger instruction to the under-voltage release X1, and it is determined whether the closing feedback signal is monitored to change during the first verification task. If there is no change, a fault alarm message is generated;

[0033] If the grid-connected feedback signal corresponds to the grid-connected level signal and the closing feedback signal corresponds to opening, a second verification task of a preset duration is generated to send a second error correction instruction to the electric operation switch X2, and it is determined whether the closing feedback signal is monitored to change during the second verification task. If there is no change, a fault alarm message is generated.

[0034] In some of these embodiments, it further includes a controllable load module, and the user side further includes a photovoltaic end;

[0035] In the off-grid energy storage mode:

[0036] The photovoltaic end is used to supply power to the load end through a photovoltaic panel;

[0037] The controllable load module is used to collect the energy storage power of the energy storage end, the photovoltaic power generation of the photovoltaic end, and the energy consumption power of the load end respectively;

[0038] The controllable load module compares the size of the energy storage power with a preset safe power. If the energy storage power is less than the preset safe power, it enters the load control mode;

[0039] In the load control mode, the controllable load module determines the size between the photovoltaic power generation and the energy consumption power;

[0040] If the energy consumption power is greater than the photovoltaic power generation, the connection between the energy storage end and the load end is cut off and the photovoltaic end is controlled to charge the energy storage end;

[0041] If the energy consumption power is not greater than the photovoltaic power generation, the photovoltaic end is controlled to supply power to the load end and an energy storage shutdown signal is generated to the energy storage control unit, and the energy storage control unit controls the energy storage end to shut down based on the energy storage shutdown signal.

[0042] In a second aspect, the present application provides a modular low-cost grid-connected and off-grid switching method, adopting the following technical solution:

[0043] A modular low-cost grid-connected and off-grid switching method, implemented based on the above system, includes the following steps:

[0044] When the grid side loses power, the off-grid action module collects the voltage on the grid side to control the on / off grid switch module connected between the grid side and the user side to act to the off state, and the load end in the user side loses power;

[0045] The energy storage control unit collects the closing feedback signal to obtain the disconnection of the on / off grid switch module, and obtains the grid connection feedback signal generated by the grid connection feedback module by collecting the real-time voltage information to control the energy storage end in the user side to switch to the off-grid mode to start up and supply power to the load end;

[0046] When the grid side has power, the grid connection feedback module detects the real-time voltage information between the grid side and the on / off grid switch module to generate a grid connection feedback signal and sends it to the energy storage control unit, and the energy storage control unit controls the shutdown of the energy storage end based on the grid connection feedback signal to switch to the grid connection mode;

[0047] The energy storage control unit generates a closing control signal based on the grid connection feedback signal and sends it to the grid connection action module as the input signal, and the grid connection action module controls the on / off grid switch action module to act to the closed state based on the input signal.

[0048] The following technical effects are achieved through the technical solution provided by the embodiments of the present application:

[0049] The components in the on / off grid process are modularly designed. Through the module combination composed of conventional relay protection devices, combined with software logic, the function of on / off grid switching is realized, and low-cost on / off grid switching is achieved. It is suitable for occasions with low requirements for power continuity, some high-power energy storage systems. The scheme has a simple structure, low cost, high reliability, can withstand large currents and powers, and at the same time, the action principles of each component are relatively simple, easy to understand and maintain. Description of the Drawings

[0050] Figure 1 It is a connection schematic diagram of the modular low-cost on / off grid switching system provided by this embodiment.

[0051] Figure 2 It is a step schematic diagram of the modular low-cost on / off grid switching method provided by the embodiments of the present application.

[0052] Description of the reference numerals: 1. On / off grid switch module; 2. Off-grid action module; 3. Grid connection action module; 4. Grid connection feedback module; 5. Energy storage control unit; 6. Controllable load module. Detailed Embodiments

[0053] To more clearly understand the purpose, technical solution, and advantages of the present application, the following describes and explains the present application in conjunction with the accompanying drawings and embodiments. However, those of ordinary skill in the art should understand that the present application can be implemented without these details. In some cases, to avoid unnecessary descriptions from obscuring various aspects of the present application, well-known methods, processes, systems, components, and / or circuits that have been described at a higher level will not be elaborated further. For those of ordinary skill in the art, it is obvious that various changes can be made to the disclosed embodiments of the present application, and without departing from the principles and scope of the present application, the general principles defined in the present application can be applied to other embodiments and application scenarios. Therefore, the present application is not limited to the illustrated embodiments, but rather conforms to the broadest scope consistent with the scope claimed in the present application.

[0054] It should be noted here that the descriptions of these embodiments are used to help understand the present invention, but do not constitute a limitation to the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0055] In the description of the present application, the meaning of "a number of" is one or more, the meaning of "a plurality of" is two or more, "greater than", "less than", "exceeding", etc. are understood as not including the number itself, and "above", "below", "within", etc. are understood as including the number itself. If there is a description of "first" and "second", it is only used to distinguish technical features and cannot be understood as indicating or implying relative importance or implicitly indicating the quantity of the indicated technical features or implicitly indicating the sequence relationship of the indicated technical features.

[0056] In the description of the present application, the description with reference to terms such as "one embodiment", "some embodiments", "illustrative embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic descriptions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in any one or more embodiments or examples in a combined manner.

[0057] As Figure 1 shown, the embodiments of the present application disclose a modular low-cost grid-connected and off-grid switching system, including:

[0058] A grid-connected and off-grid switch module, with two ends respectively used to connect the grid side and the user side, where the user side includes an energy storage end and a load end.

[0059] The grid-connected and off-grid switch module is mainly used to switch or connect the power circuit between the user side and the grid side. When performing grid-connected and off-grid switching, when the grid-connected and off-grid switch module is disconnected, it means that the power consumption circuit between the user side and the grid side is disconnected, and at this time it is in the off-grid state. When the grid-connected and off-grid switch module is connected, it means that the power consumption circuit between the user side and the grid side is connected, and at this time it is in the grid-connected state.

[0060] The grid side corresponds to the grid bus, and the grid side can also include a diesel generator terminal for supplementary power generation.

[0061] The user side corresponds to the energy storage terminal and the load terminal. The energy storage terminal corresponds to the energy storage device, and the load terminal corresponds to the user's electrical equipment.

[0062] The off-grid action module is coupled to the grid-connected and off-grid switch module and electrically connected to the grid side, and is used to collect the voltage on the grid side to control the grid-connected and off-grid switch module to act to the off state.

[0063] The off-grid action module first collects the voltage on the grid side. When the grid side voltage drops to a preset value, it triggers the off-grid action, and it controls the coupled grid-connected and off-grid switch module to perform the off-grid action to disconnect the power supply circuit between the grid and the load.

[0064] The grid-connected action module is coupled to the grid-connected and off-grid switch module and is used to control the grid-connected and off-grid switch module to act to the closed state according to the input signal.

[0065] The action target of the grid-connected action module is opposite to that of the off-grid action module. It takes the signal sent by the subsequent energy storage control unit as the input signal. When there is an input signal, it is considered that the current grid side has resumed power supply and is in a stable state. At this time, it is necessary to trigger the grid-connected action. Therefore, the grid-connected action module controls the coupled grid-connected and off-grid switch module to perform a closing action to connect the power supply circuit between the grid and the load.

[0066] The grid-connected feedback module is electrically connected between the grid side and the grid-connected and off-grid switch module, and is used to collect real-time voltage information to generate a grid-connected feedback signal.

[0067] The grid-connected feedback module collects the real-time voltage magnitude between the grid and the grid-connected and off-grid switch module in real time to judge whether the off-grid state of power failure from the grid changes to the grid-connected state of grid power supply, and generates a corresponding grid-connected feedback signal when the grid-connected condition is reached.

[0068] The energy storage control unit is electrically connected to the grid-connected feedback module to obtain the grid-connected feedback signal, and generates a closing control signal based on the grid-connected feedback signal and sends it to the grid-connected action module as the input signal.

[0069] The energy storage control unit includes several functional sub - modules. First, it determines the current power grid status by whether it can obtain the grid connection feedback signal uploaded by the grid connection feedback module. At the same time, when the grid connection feedback signal is obtained, it confirms that a grid connection action is required to generate a closing control signal and send it to the grid connection action module to control its grid connection closing action.

[0070] The energy storage control unit is also electrically connected to the grid - connected / off - grid switch module to collect the closing feedback signal, and performs a matching analysis based on the grid connection feedback signal and the closing feedback signal to switch the working mode. The working modes include the grid - connected mode and the off - grid mode.

[0071] The energy storage control unit is also used to collect the action feedback of the grid - connected / off - grid switch module as the closing feedback signal. At the same time, it determines the current grid - connected / off - grid status and determines the final grid - connected / off - grid control mode based on the consistency of the grid connection feedback signal and the closing feedback signal.

[0072] In some other embodiments, the grid - connected / off - grid switch module includes a low - voltage circuit breaker QF, and the off - grid action module includes an under - voltage release X1. The under - voltage release X1 collects the voltage on the grid side and judges whether it is less than the first preset value.

[0073] If it is not less than the first preset value, the under - voltage release X1 is not powered to control the low - voltage circuit breaker QF to remain in the closed state;

[0074] If it is less than the first preset value, the under - voltage release X1 is powered to perform a tripping action to control the low - voltage circuit breaker QF to open.

[0075] The low - voltage circuit breaker QF and the coupled under - voltage release X1 together constitute a simple circuit breaker structure, which can also achieve switch actions based on voltage detection, and at the same time, the cost is much lower than that of the STS module.

[0076] The under - voltage release X1 is composed of components such as an iron core, a coil, and an armature. It judges whether the voltage conforms to the preset magnitude in the electrical circuit. When the voltage is normal, the coil of the under - voltage release X1 is normally energized to generate sufficient electromagnetic force. At this time, the armature is attracted and the coupled low - voltage circuit breaker QF is in the closed closing state; when the voltage drops to, for example, 30% of the stable grid voltage, the voltage is low enough to cause insufficient electromagnetic force. At this time, the armature cannot maintain the attracted state and tripping occurs, and then the low - voltage circuit breaker QF is disconnected through transmission.

[0077] Through the combination of the under - voltage release X1 and the low - voltage circuit breaker QF, the effect exactly the same as the network disconnection action of the STS can be achieved at the lowest cost, greatly reducing the cost, and at the same time, problems such as high loss and high heat generation will not occur.

[0078] In some other embodiments, the grid connection operation module includes an electric operation switch X2, and the grid connection feedback module includes a voltage relay D1.

[0079] In an actual scenario, there is an interlock mechanism in the excitation coil of the under-voltage release X1. As long as the switch of the circuit breaker is opened, it cannot actively close when the power grid comes back on later. Generally, manual closing is required.

[0080] Therefore, when the power grid changes from power-off to power-on, it is necessary to switch from the off-grid state to the grid-connected state, that is, it is necessary to change the low-voltage circuit breaker QF from the open state to the re-closed state. At the same time, to solve the problem that the circuit breaker cannot actively close due to interlock, the present application also provides an electric operation switch X2 for controlling the switch action and a voltage relay D1 for feeding back the real-time grid connection situation.

[0081] The voltage relay D1 is used to detect the magnitude of the real-time voltage information between the low-voltage circuit breaker QF and the grid side, and generate a grid connection feedback signal to the energy storage control unit when the real-time voltage information is greater than the second preset value. The grid connection feedback signal is a level signal.

[0082] First, the coil of the voltage relay D1 corresponds to the grid side to collect the real-time voltage magnitude, and the switch action occurs after the voltage is greater than the preset magnitude, so that the state of whether the power grid is grid-connected can be converted into an on or off state. Then, according to the on or off action, a corresponding level signal of 1 or 0 can be output.

[0083] Specifically, for example, when the voltage relay D1 monitors that the voltage on the grid side reaches 200V and remains stable for a time length of 5 minutes, then the grid-connected state can be switched at this time. Therefore, the switch of the voltage relay D1 closes to generate a corresponding loop-connected "1" level signal, and the grid feedback signal at this time can inform the energy storage control unit of the current grid state.

[0084] The energy storage control unit obtains the grid connection feedback signal and correspondingly generates a closing control instruction to send to the electric operation switch X2. After obtaining the input signal containing the closing control instruction, the electric operation switch X2 drives the low-voltage circuit breaker QF to close through the motor M.

[0085] The electric operation switch has a functional module for receiving external control signals. This signal can be sent manually by a control button or a control panel, or may come from an automated control system, a protection device, etc. The control signal is usually transmitted to the electric operation switch in the form of an electric signal.

[0086] When a closing operation is required, a specific closing control signal is input; when a tripping is required, a tripping control signal is input.

[0087] The electric operation switch is internally equipped with a motor. When a control signal is received, the drive circuit of the motor will control the forward or reverse rotation of the motor according to the signal type (closing or opening).

[0088] In this application, after the energy storage control unit obtains the grid connection feedback signal, it needs to control the system to switch to the grid connection state. Therefore, an electronic instruction (closing control instruction) is sent to the electric operation switch X2 at this time. After the electric operation switch X2 obtains this instruction, it controls the internal motor M to rotate forward, and at the same time, through the transmission mechanism connected to the motor M, it pushes the low-voltage circuit breaker QF to close.

[0089] In this way, the grid connection control effect corresponding to the expensive STS can also be achieved through the combination of the simple-structured and low-cost electric operation switch X2 and the voltage relay D1. The voltage relay D1 judges whether grid connection is required, and when it is necessary to switch to the grid connection state, it issues a software control instruction of the system to control the electric operation switch X2 to perform a closing action on the interlocked low-voltage circuit breaker QF.

[0090] Therefore, this system uses a simple relay protection device to replace the STS to detect the triggering conditions for off-grid and grid connection, as well as the corresponding off-grid switching action and grid connection switching action.

[0091] In some other embodiments, the energy storage control unit continuously collects the action state of the off-grid switch module to obtain a closing feedback signal, and compares it with the collected grid connection feedback signal for consistency.

[0092] There is a closing state detection functional unit in the energy storage control unit, which can obtain the action feedback corresponding to the low-voltage circuit breaker QF after the opening and closing actions. Through this closing feedback signal, the energy storage control unit can clearly know the current state of the low-voltage circuit breaker QF.

[0093] At the same time, the energy storage control unit compares the collected closing feedback signal with the grid connection feedback signal to judge whether both signals match the grid connection state or the off-grid state at the same time, and selects the corresponding grid connection control logic or off-grid control logic according to the comparison result.

[0094] If the grid connection feedback signal corresponds to the grid connection level signal and the closing feedback signal corresponds to closing, it enters the grid connection mode. At this time, it controls the energy storage terminal to shut down and issues a grid connection instruction to the PCS to perform the grid connection charge and discharge control logic.

[0095] If the grid-connected feedback signal corresponds to the grid-connected level signal, and the closing feedback signal indicates that the low-voltage disconnector switch QF has been closed. Then it is currently determined that the grid-connected mode has been entered. In the grid-connected mode, the energy storage terminal does not need to charge and discharge the energy storage power to the load terminal, but the grid terminal supplies power to the load terminal. Therefore, at this time, the energy storage is controlled to shut down, and at the same time, a grid-connected command is sent to the PCS. The PCS is turned on and executes the corresponding grid-connected charge and discharge logic to control the power consumption between the grid terminal and the load terminal.

[0096] If the grid-connected feedback signal does not correspond to the grid-connected level signal and the closing feedback signal corresponds to opening the switch, then the off-grid mode is entered. At this time, the energy storage terminal is controlled to turn on and an off-grid command is sent to the energy storage terminal to perform the off-grid charge and discharge control logic.

[0097] If the grid-connected feedback signal does not indicate that the grid terminal is powered on, and at the same time the closing feedback signal indicates that the current low-voltage disconnector switch QF is in the open state, then it is determined that the off-grid mode has been entered. In the off-grid mode, since the grid terminal cannot charge the load, the energy storage terminal needs to be turned on and switched to the off-grid power supply state according to the off-grid command. In this scenario, the energy storage control unit sends an off-grid command to the energy storage terminal to perform the off-grid charge and discharge control logic.

[0098] In some other embodiments, when the voltage on the grid side is less than the first preset value, the energy storage control unit obtains the power supply priority of the load terminal.

[0099] When the grid experiences a power outage instantaneously, although the energy storage terminal will change from the shutdown state to the startup state to charge the load terminal, in the actual scenario, the power outage speed of the grid is often greater than the startup speed of the energy storage. Therefore, the time difference in the middle will cause the load terminal to be in a power-off state for a period of time. Then, different load terminals have different degrees of influence on the power loss. For example, in areas such as residences, the power loss for a period of time has little impact, while in some important places or important electrical equipment, such as communication equipment, factories, data centers, etc., if a power outage occurs, it will have a greater impact.

[0100] Then, based on the different priorities of the load terminals, different energy storage device startup methods can be selected when detecting an upcoming power outage scenario.

[0101] If the power supply priority is high, a thermal response command is generated based on the current voltage and sent to the energy storage terminal. After obtaining the thermal response command, the energy storage terminal enters the thermal startup power supply mode to turn on.

[0102] If the power supply priority of the load end is relatively high, it indicates that these load ends are relatively important. In this case, the energy storage end can be maintained in a hot start mode during normal grid-connected standby. Under hot start, the energy storage device is in a hot standby state, and its control module, communication module, etc. are all in low-power standby. When receiving the issued hot response instruction, the energy storage end can directly respond and enter the working state without parameter configuration, system self-check, and module power-on.

[0103] The overall startup response speed is fast under the hot start mode, but the power consumption in the standby state is relatively high.

[0104] If the power supply priority is low, a cold response instruction is generated based on the current voltage and issued to the energy storage end. After obtaining the cold response instruction, the energy storage end enters the cold start power supply mode to start up.

[0105] When the power supply priority of the load end is low, it indicates that these load ends are relatively unimportant. In this case, the energy storage end can be maintained in a cold start mode during normal grid connection. Under cold start, the energy storage device is in a full shutdown and sleep state, and each module in the system is powered off. When obtaining the issued cold response instruction, the energy storage end first performs steps such as power-on of each module unit, system self-check, and parameter configuration. After the steps are completed, it enters the working state of supplying power to the load end.

[0106] The overall startup response speed is slow under the cold start mode, but the power consumption in the standby state is relatively low.

[0107] In some other embodiments, the second preset value includes a pre-stage sub-value and a post-stage sub-value, where the pre-stage sub-value is less than the post-stage sub-value.

[0108] The second preset value is characterized as a voltage reference quantity for determining whether the grid end is in a voltage condition that meets the grid connection mode. When the reference quantity is met, it is considered that grid connection operation is required, that is, the energy storage end is shut down. However, generally, the closing action during grid connection and the shutdown action of the energy storage device cannot be completely simultaneous. The shutdown of the energy storage device requires a certain amount of time, while the time required for the circuit breaker switch to close is relatively short.

[0109] At this time, there is often a state where the switch has closed, but the energy storage end has not been completely shut down. At this time, the electric energy of the energy storage device and the electric energy of the grid are discharged to the load device together. On the one hand, this will cause a certain fluctuation at the load end during the closing instant, and on the other hand, it will also cause some electric energy of the energy storage to flow back to the grid and pose a risk.

[0110] Therefore, in order to optimize the synchronization between the closing action and the energy storage shutdown action, in the embodiments of the present application, the second preset value is divided into a pre-stage value and a post-stage value, where the voltage value in the pre-stage period is less than the voltage value in the post-stage period.

[0111] Among them, the early-stage value is used to first send the corresponding information of the grid side about to enter the grid-connected state to the energy storage control unit, and the late-stage value is used to wait for the energy storage control unit to send the corresponding instruction to enable the energy storage side to start the pre-shutdown preparation.

[0112] When the real-time voltage information is greater than the early-stage sub-value and stably maintains for the first duration, a grid-connected feedback signal is sent to the energy storage control unit.

[0113] When the real-time voltage information is greater than the early-stage sub-value and stably maintains for the first duration, at this time, it is considered that the grid has a tendency to resume power-on. At this time, it is necessary to send the grid-connected feedback signal to the energy storage control unit in advance so that the energy storage control unit can perform the grid-connected operation in advance.

[0114] When the real-time voltage information is greater than the late-stage sub-value and stably maintains for the second duration, a grid-connected instruction is sent to the PCS and the signal quality is calculated to generate a fluctuation coefficient.

[0115] When the real-time voltage information continuously rises until it is greater than the late-stage sub-value and stably maintains for the second duration, at this time, it is confirmed that the grid is about to resume power-on and grid connection. At this time, a grid-connected instruction is first sent to the PCS to enable the PCS to switch to the grid-connected state to prepare for the grid-side grid-connected control logic. At the same time, in order to determine the linear rate of voltage drop of the energy storage system from power supply to shutdown, the energy storage control unit also needs to calculate the signal instruction of the grid-side voltage based on the current voltage value, frequency, phase and other data to obtain the fluctuation coefficient.

[0116] The larger the fluctuation coefficient, the more unstable the current grid power-on recovery process is. If the grid is unstable, then in order to prevent subsequent re-entering the power-off state, at this time, it is necessary for the energy storage system to slowly reduce the output voltage to shut down; on the contrary, the smaller the fluctuation coefficient, the more stable the current grid power-on recovery process is, and the lower the possibility of subsequent re-power-off. Therefore, at this time, the energy storage system can relatively quickly and linearly reduce the output voltage to enter the shutdown state.

[0117] Among them, after the energy storage control unit obtains the grid-connected feedback signal, it generates a reaction reserved time and sends it to the energy storage side. The energy storage side shuts down after the reaction reserved time arrives. The reaction reserved time is the second duration multiplied by the fluctuation coefficient.

[0118] Then when the energy storage control unit sends the grid-connected feedback signal in the determination of the early-stage sub-value, a reaction reserved time is first generated to the energy storage side, and the energy storage side linearly reduces the output voltage until shutdown during the duration of the reaction reserved time.

[0119] At the beginning, the reaction reserve time is equal to the second duration. Then, as the sampling of the power fluctuations on the power grid corresponding to the fluctuation coefficient is carried out subsequently, the length of the reaction reserve time is adjusted in real time and dynamically. Therefore, the length of the dynamic reaction reserve time is equal to the second duration multiplied by the fluctuation coefficient.

[0120] Therefore, the process of carrying out the grid connection operation is as follows: First, the voltage on the power grid continues to rise. When the early sub-value is triggered first, a grid connection feedback signal is sent. The energy storage control unit generates a reaction reserve time equal to the second duration and sends it to the energy storage end. The energy storage end slowly reduces its output voltage based on the reaction reserve time. At the same time, when the real-time voltage on the power grid is greater than the late sub-value, the fluctuation coefficient of the real-time voltage is calculated, and the current reaction reserve time is adjusted based on the fluctuation coefficient. The energy storage end ensures that it shuts down when the reaction reserve time arrives.

[0121] In some other embodiments, during the second duration, the energy storage control unit collects real-time voltage information, real-time frequency information, and real-time phase information in real time and generates a synchronous change amount. The synchronous change rate is calculated through the ratio of the synchronous change amount to the reaction reserve time.

[0122] The energy storage control unit dynamically adjusts the output power of the energy storage end based on the synchronous change rate until it changes to 0 and shuts down.

[0123] The specific method for dynamically adjusting the voltage of the energy storage end in real time during the reaction reserve time is to generate a synchronous change amount through the real-time voltage information, frequency, phase, and other data collected by the energy storage control unit. The synchronous change amount specifically represents that the change amount when the power grid changes from a power-off state to a stable power-on state synchronously corresponds to the change amount of the energy storage end from the working power supply state to the non-working shutdown state. Therefore, in order to ensure synchronization between the power-on of the power grid end and the shutdown of the energy storage end, the synchronous change rate can be calculated through the ratio of the synchronous change amount to the reaction reserve time.

[0124] If the power grid needs to change by an amount X1 from power-off to power-on, then the corresponding synchronous change amount of the energy storage end is X2, and the synchronous change amount is X2 / t.

[0125] In some other embodiments, if the grid connection feedback signal does not correspond to the grid connection level signal and the closing feedback signal corresponds to closing, a first verification task with a preset duration is generated to send a first error correction trigger instruction to the under-voltage release X1, and it is determined whether the closing feedback signal is monitored to change during the first verification task. If it does not change, a fault alarm message is generated.

[0126] In some other scenarios, the states represented by the grid-connected feedback signal and the closing feedback signal may be different. For example, the grid-connected feedback signal indicates that the current state is a power-off state, but at this time, the low-voltage circuit breaker QF is in the closed state. Then, when the low-voltage circuit breaker QF closes, the load circuit and the grid circuit cannot be cut off and isolated. Therefore, when the energy storage device is turned on, part of the electric energy will flow into the grid side.

[0127] Therefore, in this case, the energy storage control unit generates a verification task. In the verification task, a first error correction trigger instruction is sent to the under-voltage release X1 to actively control the under-voltage release X1 to perform a tripping action so that the low-voltage circuit breaker QF performs an opening action. Then, if the closing feedback signal still does not change during the time corresponding to the verification task, it indicates that the low-voltage circuit breaker QF cannot be disconnected, and a fault alarm signal will be generated, indicating that the system has a fault.

[0128] In the embodiment of the present application, the duration corresponding to the first verification task is 10s.

[0129] If the grid-connected feedback signal corresponds to the grid-connected level signal and the closing feedback signal corresponds to the opening, a second verification task with a preset duration is generated to send a second error correction instruction to the electric operating switch X2, and it is determined whether the closing feedback signal is monitored to change during the second verification task. If it does not change, a fault alarm message is generated.

[0130] If the grid-connected feedback signal indicates that the grid side has resumed the grid-connected state, and the closing feedback signal corresponds to the open state of the low-voltage circuit breaker QF, then the grid circuit and the load circuit are still in the disconnected state, and the grid still cannot supply power to the load.

[0131] Therefore, in this case, the energy storage control unit will generate another verification task. In the verification task, a second error correction instruction is sent to the electric operating switch X2 to actively control the electric operating switch X2 to switch the low-voltage circuit breaker QF to the closing action through the system software instruction. Then, if the closing feedback signal still does not change during the event corresponding to the verification task, it indicates that the low-voltage circuit breaker QF cannot be closed, and a fault alarm signal will be generated, indicating that the system has a fault.

[0132] In the embodiment of the present application, the duration corresponding to the second verification task is 10s.

[0133] In some other embodiments, a controllable load module is further included, and the user side further includes a photovoltaic side.

[0134] In the off-grid energy storage mode:

[0135] The photovoltaic side is used to supply power to the load side through photovoltaic panels.

[0136] In some actual power consumption scenarios (such as residential communities), during off-grid energy storage, in addition to the energy storage system being able to supply power to the load, power can also be supplied through photovoltaics.

[0137] When the stored energy in the energy storage system is small, it is necessary to stop the energy storage system from supplying power to the load, because when the energy storage system has no power at all, it will cause irreversible harm to the energy storage battery, shorten the service life of the battery, and may even permanently damage the battery and make it unable to be charged again; the performance of some capacitor components may decline under the state of being without power for a long time, resulting in the system being unable to work properly after being powered on again.

[0138] Therefore, when the energy storage system has less power, the best response is to cut off the connection between the load end and the energy storage end. Then, when the system also includes a photovoltaic charging method, it is more important to make a power consumption decision between the power-deficient energy storage end and the photovoltaic end by controlling the load.

[0139] The controllable load module is used to collect the stored energy in the energy storage end, the photovoltaic power generation in the photovoltaic end, and the energy consumption in the load end.

[0140] The controllable load module compares the stored energy with the preset safe energy. If the stored energy is less than the preset safe energy, it enters the load control mode.

[0141] The controllable load module is used to collect the magnitudes of the stored energy, photovoltaic power generation, and energy consumption, and is also used to analyze whether the current stored energy is at a safe energy. If not, it corresponds to the load control mode, which means that certain adjustments need to be made to the power consumption situation between the load and the energy storage.

[0142] In the load control mode, the controllable load module judges the magnitude relationship between the photovoltaic power generation and the energy consumption.

[0143] If the energy consumption is greater than the photovoltaic power generation, the connection between the energy storage end and the load end is cut off and the photovoltaic end is controlled to charge the energy storage end.

[0144] If the energy consumption is not greater than the photovoltaic power generation, the photovoltaic end is controlled to supply power to the load end and a stored energy shutdown signal is generated to the energy storage control unit, and the energy storage control unit controls the energy storage end to shut down based on the stored energy shutdown signal.

[0145] Under load control, first compare the magnitude relationship between the photovoltaic power generation and the energy consumption, that is, judge whether the performance of the photovoltaic power generation matches the demand of the load power consumption;

[0146] If it is satisfied, it means that the photovoltaic power generation situation is good. At this time, the energy storage end is shut down, and at the same time, it is changed to supply power to the load through photovoltaics;

[0147] If not satisfied, it indicates that the photovoltaic power generation situation is not good and cannot meet the electricity demand of the load. In this case, on the one hand, even if the photovoltaic power supplies the load, the load cannot have a relatively stable electricity consumption experience. On the other hand, in order to avoid the problem that the energy storage end cannot be powered on again due to complete power shortage, the circuit between the energy storage end and the load end is directly cut off and the energy storage end is shut down. At the same time, in order not to waste the photovoltaic power generation, the photovoltaic power generation is used to charge the energy storage end instead. When the energy storage end resumes a safe power level after a period of photovoltaic charging, the circuit with the load is reconnected to supply power to the load again.

[0148] In some other embodiments,

[0149] The present application also discloses a modular low-cost grid-connected and off-grid switching method, which is implemented based on the above system and includes the following steps:

[0150] S100, when the grid side loses power, the off-grid action module collects the voltage of the grid side to control the grid-connected and off-grid switch module connected between the grid side and the user side to act to the off state, and the load end in the user side loses power.

[0151] S200, the energy storage control unit collects the closing feedback signal to obtain the disconnection of the grid-connected and off-grid switch module, and obtains the grid-connected feedback signal generated by the grid-connected feedback module by collecting the real-time voltage information to control the energy storage end in the user side to switch to the off-grid mode to start up and supply power to the load end.

[0152] S300, when the grid side has power, the grid-connected feedback module detects the real-time voltage information between the grid side and the grid-connected and off-grid switch module to generate a grid-connected feedback signal and sends it to the energy storage control unit. The energy storage control unit controls the energy storage end to shut down and switch to the grid-connected mode based on the grid-connected feedback signal.

[0153] S400, the energy storage control unit generates a closing control signal based on the grid-connected feedback signal and sends it to the grid-connected action module as an input signal. The grid-connected action module controls the grid-connected and off-grid switch action module to act to the closed state based on the input signal.

[0154] The implementation principle is:

[0155] The components in the grid-connected and off-grid process are modularly designed. Through the module combination composed of conventional relay protection devices, the function of grid-connected and off-grid switching is realized by cooperating with software logic to achieve low-cost grid-connected and off-grid switching. It is suitable for occasions with low requirements for power continuity, some large-power energy storage systems. The scheme has a simple structure, low cost, high reliability, can withstand large currents and powers, and at the same time, the action principles of each component are relatively simple, easy to understand and maintain.

[0156] It should be understood that although the steps in the flowchart of the accompanying drawings are shown sequentially according to the indication of the arrows, these steps are not necessarily executed sequentially in the order indicated by the arrows. Unless there is a clear indication in this document, there is no strict order restriction for the execution of these steps, and they can be executed in other orders.

[0157] The above are all preferred embodiments of the present application, and do not limit the protection scope of the present application accordingly. Therefore, all equivalent changes made according to the structure, shape, and principle of the present application shall be covered within the protection scope of the present application.

Claims

1. A modular low-cost grid-connected and off-grid switching system, characterized in that, Including: An off-grid switch module, with both ends respectively used to connect to the grid side and the user side. Among them, the user side includes an energy storage end and a load end; An off-grid operation module, coupled to the off-grid and grid-connected switch module and electrically connected to the grid side, for collecting the voltage on the grid side to control the off-grid and grid-connected switch module to act to the open state when it is less than a first preset value; A grid-connected operation module, coupled to the off-grid and grid-connected switch module, for controlling the off-grid and grid-connected switch module to act to the closed state according to an input signal; A grid-connected feedback module, electrically connected between the grid side and the off-grid and grid-connected switch module, for collecting real-time voltage information and generating a grid-connected feedback signal when it is greater than a second preset value. Specifically, The second preset value includes a pre-stage sub-value and a post-stage sub-value, where the pre-stage sub-value is less than the post-stage sub-value; When the real-time voltage information is greater than the pre-stage sub-value and stably maintains for a first duration, the grid-connected feedback signal is sent to the energy storage control unit; When the real-time voltage information is greater than the post-stage sub-value and stably maintains for a second duration, a grid-connected instruction is sent to the PCS and the signal quality is calculated to generate a fluctuation coefficient; Among them, after the energy storage control unit obtains the grid-connected feedback signal, it generates a reaction reserved time and sends it to the energy storage end. The energy storage end shuts down after the reaction reserved time arrives. The reaction reserved time is the second duration multiplied by the fluctuation coefficient; An energy storage control unit, electrically connected to the grid-connected feedback module to obtain the grid-connected feedback signal, and generating a closing control signal based on the grid-connected feedback signal and sending it to the grid-connected operation module as the input signal; The energy storage control unit is also electrically connected to the off-grid and grid-connected switch module to collect a closing feedback signal, and performs a matching analysis based on the grid-connected feedback signal and the closing feedback signal to switch the working mode. The working mode includes a grid-connected mode and an off-grid mode.

2. The modular low-cost off-grid switching system according to claim 1, characterized in that The off-grid and grid-connected switch module includes a low-voltage circuit breaker QF. The off-grid operation module includes an under-voltage release X1. The under-voltage release X1 collects the voltage on the grid side and judges whether it is less than a first preset value; If it is not less than the first preset value, the under-voltage release X1 is energized to control the low-voltage circuit breaker QF to maintain the closed state; If it is less than the first preset value, the under-voltage release X1 loses power to perform a tripping action to control the low-voltage circuit breaker QF to open.

3. The modular low-cost off-grid switching system according to claim 2, characterized in that, The grid-connected operation module includes an electric operation switch X2. The grid-connected feedback module includes a voltage relay D1; The voltage relay D1 is used to detect the magnitude of the real-time voltage information between the low-voltage circuit breaker QF and the grid side, and generate a grid-connected feedback signal to the energy storage control unit when the real-time voltage information is greater than the second preset value. Among them, the grid-connected feedback signal is a level signal; The energy storage control unit obtains the grid-connected feedback signal and correspondingly generates a closing control instruction to send to the electric operation switch X2. After the electric operation switch X2 obtains the input signal containing the closing control instruction, it drives the low-voltage circuit breaker QF to close through the motor M.

4. The modular low-cost off-grid switching system according to claim 3, characterized in that, The energy storage control unit collects the action status of the grid-connected and off-grid switch module in real time to obtain the closing feedback signal, and compares it with the collected grid-connected feedback signal. Specifically, if the grid-connected feedback signal corresponds to the grid-connected level signal and the closing feedback signal corresponds to closing, it enters the grid-connected mode. At this time, it controls the energy storage terminal to shut down and issues a grid-connected command to the PCS to perform the grid-connected charge and discharge control logic; if the grid-connected feedback signal does not correspond to the grid-connected level signal and the closing feedback signal corresponds to opening, it enters the off-grid mode. At this time, it controls the energy storage terminal to power on and issues an off-grid command to the energy storage terminal to perform the off-grid charge and discharge control logic.

5. The modular low-cost off-grid switching system according to claim 2, characterized in that, When the voltage on the grid side is less than the first preset value, the energy storage control unit obtains the power supply priority of the load side; if the power supply priority is high, it generates a thermal response command based on the current voltage and issues it to the energy storage terminal. After obtaining the thermal response command, the energy storage terminal enters the thermal start power supply mode to power on; if the power supply priority is low, it generates a cold response command based on the current voltage and issues it to the energy storage terminal. After obtaining the cold response command, the energy storage terminal enters the cold start power supply mode to power on.

6. The modular low-cost off-grid switching system according to claim 1, characterized in that In the second time period, the energy storage control unit collects the real-time voltage information, real-time frequency information, and real-time phase information in real time and generates a synchronous change amount, and calculates the synchronous change rate through the ratio of the synchronous change amount to the reaction reserved time; The energy storage control unit dynamically adjusts the output power of the energy storage terminal based on the synchronous change rate until it changes to 0 and shuts down.

7. The modular low-cost off-grid switching system according to claim 4, characterized in that, If the grid-connected feedback signal does not correspond to the grid-connected level signal and the closing feedback signal corresponds to closing, it generates a first verification task with a preset duration to issue a first error correction trigger command to the under-voltage release X1, and determines whether the closing feedback signal changes during the first verification task. If it does not change, it generates a fault alarm message; If the grid-connected feedback signal corresponds to the grid-connected level signal and the closing feedback signal corresponds to opening, it generates a second verification task with a preset duration to issue a second error correction command to the electric operating switch X2, and determines whether the closing feedback signal changes during the second verification task. If it does not change, it generates a fault alarm message.

8. The modular low-cost off-grid switching system according to claim 1, characterized in that, It further includes a controllable load module, and the user side further includes a photovoltaic terminal; In the off-grid mode: The photovoltaic terminal is used to supply power to the load terminal through photovoltaic panels; The controllable load module is used to collect the energy storage power of the energy storage terminal, the photovoltaic power generation of the photovoltaic terminal, and the energy consumption power of the load terminal respectively; The controllable load module compares the size of the energy storage power with the preset safe power. If the energy storage power is less than the preset safe power, it enters the load control mode; In the load control mode, the controllable load module judges the size between the photovoltaic power generation and the energy consumption power; If the energy consumption power is greater than the photovoltaic power generation, it cuts off the connection between the energy storage terminal and the load terminal and controls the photovoltaic terminal to charge the energy storage terminal; If the electricity consumption is not greater than the photovoltaic power generation, control the photovoltaic side to supply power to the load side and generate a storage shutdown signal to the energy storage control unit, and the energy storage control unit controls the energy storage side to shut down based on the energy storage shutdown signal.

9. A modular low-cost grid-connected and off-grid switching method, characterized in that, Implemented based on the system according to any one of claims 1-8, including the following steps: When the grid side loses power, the off-grid action module collects the voltage on the grid side to control the on / off grid switch module connected between the grid side and the user side to act to the off state, and the load side in the user side loses power. The energy storage control unit collects the closing feedback signal to obtain the disconnection of the on / off grid switch module, and obtains the grid connection feedback signal generated by the grid connection feedback module by collecting real-time voltage information to control the energy storage side in the user side to switch to the off-grid mode to start up and supply power to the load side. When the grid side is powered, the grid connection feedback module detects the real-time voltage information between the grid side and the on / off grid switch module to generate a grid connection feedback signal and sends it to the energy storage control unit, and the energy storage control unit controls the energy storage side to shut down to switch to the grid connection mode based on the grid connection feedback signal. The energy storage control unit generates a closing control signal based on the grid connection feedback signal and sends it to the grid connection action module as the input signal, and the grid connection action module controls the on / off grid switch action module to act to the closed state based on the input signal.

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