Energy storage system and pre-charge control method

Abstract

This disclosure provides an energy storage system and a pre-charging control method applied to the energy storage system, relating to the field of new energy technology. The system includes: an energy storage module connected to a DC bus, comprising one or more batteries; a bus capacitor connected to the DC bus; a pre-charging module connected in series on the DC bus, including multiple pre-charging branches connected in parallel, each pre-charging branch including a switching element and / or a current-limiting resistor, with one pre-charging branch including only a switching element; and a control module connected to the energy storage module, the bus capacitor, and the pre-charging module, used to monitor the voltage difference between the energy storage module and the bus capacitor during the pre-charging phase, control the switching elements in the multiple pre-charging branches based on the voltage difference to reduce the equivalent resistance of the pre-charging module as the voltage difference decreases, and control the closing of the switching elements in the pre-charging branch including only a switching element when the voltage difference is less than a preset threshold. Embodiments of this disclosure can improve the safety of the energy storage system.

Description

Technical Field

[0001] This disclosure relates to the field of new energy technology, and more specifically, to an energy storage system and a pre-charging control method applied to the energy storage system. Background Technology

[0002] An energy storage system is a power system that stores and releases electrical energy. During system startup, the initial voltage of the DC bus capacitor is low, and direct power-on would generate a huge inrush current, damaging components. Therefore, a pre-charging circuit is needed to first charge the bus capacitor with current limiting.

[0003] In related technologies, a relay on the DC bus is disconnected during pre-charging, and a fixed-value resistor connected in parallel with the relay is used to limit the current. After pre-charging is complete, the relay is closed to short-circuit the resistor. However, this method, when applied to high-current pre-charging applications, often leads to large voltage differential activation of the relay and contact erosion accidents. Therefore, it is necessary to improve the safety of the pre-charging process of the energy storage system.

[0004] It should be noted that the information disclosed in the background section above is only used to enhance the understanding of the background of this disclosure, and therefore may include information that does not constitute prior art known to those skilled in the art. Summary of the Invention

[0005] The purpose of this disclosure is to provide an energy storage system and a pre-charge control method applied to the energy storage system, so as to improve the safety of the energy storage system during the start-up pre-charge process.

[0006] According to a first aspect of this disclosure, an energy storage system is provided, comprising: an energy storage module connected to a DC bus, the energy storage module including one or more batteries; a bus capacitor connected to the DC bus; a pre-charge module connected in series on the DC bus, including multiple pre-charge branches connected in parallel, each pre-charge branch including a switching element and / or a current-limiting resistor, at least one of the pre-charge branches including only the switching element; and a control module connected to the energy storage module, the bus capacitor, and the pre-charge module, configured to monitor the voltage difference between the energy storage module and the bus capacitor during the pre-charge phase, control the switching elements in the multiple pre-charge branches according to the voltage difference to reduce the equivalent resistance of the pre-charge module as the voltage difference decreases, and control the switching elements in the pre-charge branches including only the switching elements to close when the voltage difference is less than a preset threshold.

[0007] In the exemplary embodiments of this disclosure, the resistance values ​​of the current-limiting resistors in different pre-charge branches are not exactly the same.

[0008] In an exemplary embodiment of this disclosure, the control module is configured to simultaneously control the switching element of one of the pre-charging branches to close and the switching elements of other pre-charging branches to open during the process of the voltage difference decreasing.

[0009] In an exemplary embodiment of this disclosure, the current-limiting resistors of at least two of the pre-charge branches have the same resistance value.

[0010] In an exemplary embodiment of this disclosure, the control module is configured to increase the number of closed switching elements of the pre-charging branch during the process of the voltage difference decreasing.

[0011] In an exemplary embodiment of this disclosure, the pre-charge module is disposed on the positive DC bus, or the pre-charge module is disposed on the negative DC bus.

[0012] In an exemplary embodiment of this disclosure, the control module includes: a first voltage detection circuit connected to the energy storage module for detecting the voltage of the energy storage module; a second voltage detection circuit connected to the bus capacitor for detecting the voltage of the bus capacitor; a differential circuit with a first input terminal connected to the first voltage detection circuit, a second input terminal connected to the second voltage detection circuit, and an output terminal for outputting the voltage difference between the energy storage module and the bus capacitor; and a controller electrically connected to the output terminal of the differential circuit.

[0013] In an exemplary embodiment of this disclosure, the control module further includes: a comparator, with a first input terminal connected to the differential circuit, a second input terminal connected to a preset voltage, and an output terminal outputting a control signal; the control module is configured to control the switching element in the pre-charging branch to close when the voltage difference is less than the preset voltage.

[0014] In an exemplary embodiment of this disclosure, the pre-charge branch further includes a diode.

[0015] In the exemplary embodiments of this disclosure, the type of the switching element includes at least one of MOSFET, IGBT, and relay, and the types of switching elements in different precharge branches are not exactly the same.

[0016] According to a second aspect of this disclosure, a pre-charge control method is provided, applied to an energy storage system as described in any of the preceding claims, comprising: acquiring a voltage difference between an energy storage module and a bus capacitor; controlling the switching elements in the plurality of pre-charge branches according to the voltage difference to reduce the equivalent resistance of the pre-charge module as the voltage difference decreases; and controlling the switching elements in the pre-charge branches comprising only the switching elements to close when the voltage difference is less than a preset threshold.

[0017] In the exemplary embodiments of this disclosure, by setting a pre-charging module with adjustable equivalent resistance and dynamically adjusting the equivalent resistance of the pre-charging module according to the voltage difference across the pre-charging module, pre-charging can be performed using a large resistance current limit when the voltage difference is large, which can effectively suppress the initial inrush current of pre-charging the bus capacitor; when the voltage difference decreases, the equivalent resistance is reduced for pre-charging, reducing the residual voltage across the pre-charging module, reducing the voltage difference when the relay is energized, effectively preventing relay contact erosion, extending the relay's service life, and improving the safety of the energy storage system during use.

[0018] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and are not intended to limit this disclosure. Attached Figure Description

[0019] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this disclosure and, together with the description, serve to explain the principles of this disclosure. It is obvious that the drawings described below are merely some embodiments of this disclosure, and those skilled in the art can obtain other drawings based on these drawings without any inventive effort.

[0020] Figure 1 This is a schematic diagram of the energy storage system in an exemplary embodiment of this disclosure.

[0021] Figures 2A-2D This is a schematic diagram illustrating a scenario application of the energy storage module 1 in an exemplary embodiment of this disclosure.

[0022] Figures 3A-3C This is a schematic diagram of the pre-charge branch in an exemplary embodiment of this disclosure.

[0023] Figure 4 This is a schematic diagram of the connection method of the pre-charging module in an embodiment of this disclosure.

[0024] Figure 5 This is a schematic diagram of the control module in an exemplary embodiment of this disclosure.

[0025] Figure 6 This is a schematic diagram of the control module in an exemplary embodiment of this disclosure.

[0026] Figure 7 This is a flowchart of a pre-charge control method provided in an exemplary embodiment of this disclosure.

[0027] Figure 8 This is a schematic diagram of the pre-charging module in an exemplary embodiment of this disclosure. Detailed Implementation

[0028] Example embodiments will now be described more fully with reference to the accompanying drawings. However, example embodiments can be implemented in many forms and should not be construed as limited to the examples set forth herein; rather, these embodiments are provided to make this disclosure more comprehensive and complete, and to fully convey the concept of the example embodiments to those skilled in the art. The described features, structures, or characteristics can be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are provided to give a full understanding of embodiments of this disclosure. However, those skilled in the art will recognize that the technical solutions of this disclosure can be practiced with one or more of the specific details omitted, or other methods, components, apparatus, steps, etc., can be employed. In other instances, well-known technical solutions are not shown or described in detail to avoid obscuring various aspects of this disclosure.

[0029] Furthermore, the accompanying drawings are merely illustrative of this disclosure, and the same reference numerals in the drawings denote the same or similar parts, thus repeated descriptions of them will be omitted. Some block diagrams shown in the drawings are functional entities and do not necessarily correspond to physically or logically independent entities. These functional entities may be implemented in software, in one or more hardware modules or integrated circuits, or in different network and / or processor devices and / or microcontroller devices.

[0030] The exemplary embodiments of this disclosure will now be described in detail with reference to the accompanying drawings.

[0031] Figure 1 This is a schematic diagram of the energy storage system in an exemplary embodiment of this disclosure.

[0032] refer to Figure 1 The energy storage system 100 may include: Energy storage module 1 is connected to the DC bus and includes one or more batteries; Bus capacitor C is connected to the DC bus; The pre-charge module 2 is connected in series to the positive or negative terminal of the DC bus and includes multiple pre-charge branches 21 connected in parallel. Each pre-charge branch 21 includes a switching element K and / or a current-limiting resistor R. One of the pre-charge branches 21 includes only the switching element K. The control module 3 is connected to the energy storage module 1, the bus capacitor C, and the pre-charge module 2. It is used to monitor the voltage difference between the energy storage module 1 and the bus capacitor C during the pre-charge stage. Based on the voltage difference, it controls the switching element K in multiple pre-charge branches 21 to reduce the equivalent resistance of the pre-charge module 2 as the voltage difference decreases. When the equivalent resistance is less than a preset value or the voltage difference between the energy storage module 1 and the bus capacitor C is less than a preset threshold, it controls the switching element K in the pre-charge branch that only includes the switching element to close.

[0033] The bus capacitor C, acting as a stabilizer and energy buffer for the DC bus voltage, primarily absorbs voltage ripple and suppresses voltage spikes during system operation, while providing high current to downstream inverter circuits, thus ensuring the dynamic response and stability of the power circuit. In practical applications, the bus capacitor C can be constructed from multiple electrolytic capacitors, film capacitors, or ceramic capacitors connected in series or parallel, depending on the system's withstand voltage, capacitance, and ripple current requirements. The selection of its capacitance and withstand voltage rating must comprehensively consider factors such as the system power level, voltage fluctuation range, and the time constant of the pre-charging process to ensure that the system's requirements for bus voltage quality are met during both the pre-charging and normal operation phases.

[0034] Energy storage module 1 can be used to provide power to the DC bus. The type of energy storage module 1 includes, but is not limited to, energy storage batteries. In energy storage module 1, multiple battery cells can be connected in series and parallel to form a battery cluster or battery stack to achieve specific voltage levels and capacity specifications. Furthermore, energy storage module 1 may also include battery monitoring and control circuitry for real-time monitoring and safety protection of battery status (such as voltage, current, temperature, SOC, SOH).

[0035] Figures 2A-2D This is a schematic diagram illustrating a scenario application of the energy storage module 1 in an exemplary embodiment of this disclosure.

[0036] refer to Figures 2A-2D Energy storage module 1 can be applied to various scenarios, including but not limited to independent energy storage systems (energy storage, such as...) in terms of energy coupling methods. Figure 2A and Figure 2B ) and photovoltaic-storage systems (photovoltaic and energy storage, such as Figure 2C and Figure 2D ), according to the device operation topology, including scenarios where a single device operates independently (single machine, such as Figure 2A and Figure 2C ) and scenarios where multiple devices operate in parallel and collaboratively (multiple machines, such as Figure 2B and Figure 2D The access method and control strategy of energy storage module 1 can be adapted to different scenarios according to system requirements.

[0037] refer to Figure 2A In standalone operation mode with independent energy storage, energy storage module 1 is connected to the rectifier / inverter module via a DC bus. The rectifier / inverter module is connected to the public power grid and the local load via an AC distribution circuit. A single energy storage module 1 independently constitutes the energy storage power supply link. The pre-charge module 2 can be installed on the DC bus between energy storage module 1 and the rectifier / inverter module.

[0038] refer to Figure 2BIn the independent energy storage multi-unit operation mode, multiple energy storage modules 1 are connected to the corresponding rectifier / inverter modules via independent DC branches. Multiple rectifier / inverter modules are connected in parallel on the AC side and connected to the public power grid and large loads via a high-voltage AC distribution circuit. In this application scenario, a corresponding pre-charging module 2 can be installed on each DC branch.

[0039] refer to Figure 2C In the photovoltaic-storage coupled single-unit operation mode, the photovoltaic modules are connected to the common DC bus via a dedicated photovoltaic DC branch, and energy storage module 1 is simultaneously connected to the same common DC bus via an energy storage DC branch. The common DC bus is connected to the rectifier / inverter module via DC cables, and the rectifier / inverter module is connected to the public power grid and the local load respectively via AC distribution circuits. In this application scenario, each DC branch is equipped with a DC / DC converter module to adapt to the common DC bus. At this time, a pre-charging module 2 can be installed on the energy storage DC branch where energy storage module 1 is located.

[0040] refer to Figure 2D In the multi-unit operation mode of photovoltaic-storage coupling, multiple rectifier / inverter modules corresponding to a single photovoltaic-storage coupling unit are connected in parallel on the AC side and connected to the public power grid or large loads through a high-voltage AC power distribution circuit. In this application scenario, a pre-charging module 2 can be set on the energy storage DC branch where the energy storage module 1 corresponding to each photovoltaic-storage coupling unit is located.

[0041] In this embodiment, the pre-charging module 2 achieves adjustable equivalent resistance through multiple parallel pre-charging branches 21. The control module 3 is used to dynamically adjust the equivalent resistance of the pre-charging module 2 according to the voltage difference across the pre-charging module 2, thereby enabling the energy storage system 100 to perform pre-charging with large resistance current limiting when the voltage difference is large, effectively suppressing the initial inrush current of pre-charging the bus capacitor; when the voltage difference decreases, the equivalent resistance is reduced for pre-charging, reducing the residual voltage across the pre-charging module, reducing the voltage difference when the relay is energized, which can reduce relay contact erosion, extend relay service life, and improve the safety of the energy storage system during use.

[0042] The following section details the pre-charge module 2 and its control method.

[0043] Figures 3A-3C This is a schematic diagram of the pre-charge branch in an exemplary embodiment of this disclosure.

[0044] In this embodiment of the disclosure, the pre-charging module 2 can realize a pre-charging branch topology with various functional characteristics by combining different numbers and types of components.

[0045] refer to Figure 3AIn this embodiment of the disclosure, the form of the pre-charge branch 21 includes, but is not limited to, only a current-limiting resistor R ( Figure 3A (a) Only includes switching element K ( Figure 3A (b) The switching element K is connected in series with the current-limiting resistor R. Figure 3A (c)).

[0046] The circuit includes several branches, each containing only the current-limiting resistor R. This structure is simple and reliable, suitable for the pre-charging stage where a fixed current-limiting resistor value is required. Another branch contains only the switching element K, in which case the switching element K must be a relay or contactor with on-resistance characteristics. When closed, it can be considered a path with minimal resistance, suitable for completely bypassing the current-limiting element at the end of the pre-charging stage. A branch consisting of the switching element K and the current-limiting resistor R connected in series is a typical controllable current-limiting structure; this pre-charging branch can be flexibly switched by controlling the on / off state of the switching element K. The resistance values ​​of the current-limiting resistors in each branch can be the same or different, and each branch can consist of a single resistor or multiple resistors connected in series and / or in parallel.

[0047] refer to Figure 3B To further enhance system reliability or achieve specific functions, a diode D can be introduced into the pre-charging branch. For example, a branch consisting of diode D connected in series with a current-limiting resistor R can achieve unidirectional control of the pre-charging current direction, preventing reverse current or voltage from affecting the pre-charging circuit. It should be noted that when diode D is connected in series with the current-limiting resistor R, it is necessary to ensure that the positive terminal of diode D is connected to the direction of current inflow and the negative terminal is connected to the direction of current outflow. For example, when pre-charging module 2 is connected to the positive terminal of the DC bus, the positive terminal of diode D is connected to energy storage module 1; when pre-charging module 2 is connected to the negative terminal of the DC bus, the negative terminal of diode D is connected to energy storage module 1.

[0048] refer to Figure 3C The components can be further flexibly combined to form a series branch containing any two or three components (current-limiting resistor R, switching element K, and diode D). In an exemplary embodiment, when the pre-charge branch 21 includes two or three components, it can be any two or three of the current-limiting resistor R, switching element K, and diode D connected in series. The types of switching elements include MOSFETs, IGBTs, and relays. The types of switching elements in different pre-charge branches 21 can be different or identical.

[0049] The type of switching element K can be selected according to the actual operating conditions. For example, in scenarios requiring high-frequency switching or precise control of the conduction sequence, MOSFETs or IGBTs can be selected; in situations where frequent operation is not required but a large continuous current needs to be carried, relays or contactors can be selected; the type of switching element in different pre-charge branches can be configured differently according to its function in that branch. For example, one branch uses IGBTs to achieve fine adjustment, while another branch uses relays as the final bypass switch.

[0050] like Figure 3C In the above, (a) the scheme uses a combination of IGBT and diode; (b) the scheme uses a combination of MOSFET and diode; (c) the scheme uses a combination of relay and IGBT; (d) the scheme uses a combination of IGBT and MOSFET; (e) the scheme uses a combination of MOSFET and relay; (f) the scheme uses a combination of MOSFET and MOSFET; (g) the scheme uses a combination of relay and relay; (h) the scheme uses a combination of IGBT and IGBT, etc.

[0051] It should be noted that, for example Figure 3A (b) and Figure 3C As shown in the diagram, a branch containing a diode D but no resistor is used. When the pre-charge branch contains only a switching element K (or only K and D in series), the switching element K must be a relay or contactor. This is because such a branch has extremely low resistance when conducting, and if used directly in the initial stage of pre-charge, it may cause excessive inrush current. Therefore, it is suitable to be activated when the bus voltage is close to the energy storage module voltage, so as to ultimately bypass all current-limiting resistors and complete the pre-charge process.

[0052] pass Figures 3A-3C In the embodiment shown, the pre-charging module 2 can achieve flexible and accurate control of the pre-charging process by setting different combinations of pre-charging branches 21 in different quantities and forms, in accordance with actual working conditions.

[0053] Figure 4 This is a schematic diagram of the connection method of the pre-charging module in an embodiment of this disclosure.

[0054] refer to Figure 4 In the exemplary embodiments disclosed herein, the pre-charge module 2 can be disposed on the negative DC bus, such as... Figure 1 It can also be set on the positive DC bus, such as Figure 4 .

[0055] In practical applications, a suitable layout scheme can be selected based on the overall electrical design, safety requirements, and grounding method of the system. The logic and function of the pre-charge module 2 on the positive and negative busbars are essentially equivalent; both limit the inrush current by inserting a controllable impedance network in series in the busbar circuit. It is worth noting that placing the pre-charge module 2 on the positive or negative busbar may have different effects on insulation monitoring, fault detection logic, and the reference potential of the power device drive signals in the system. Therefore, in specific designs, it should be considered holistically in conjunction with the circuit layout and protection strategies of the rest of the system. Furthermore, regardless of whether the pre-charge module 2 is placed on the positive or negative busbar, the control module 3 must accurately measure the voltage difference between the energy storage module 1 and the busbar capacitor C, and execute the control strategy based on this measurement to ensure the reliability and efficiency of the pre-charge process.

[0056] Figure 5 This is a schematic diagram of the control module in an exemplary embodiment of this disclosure.

[0057] refer to Figure 5 In an exemplary embodiment of this disclosure, the control module 3 includes: The first voltage detection circuit 31 is connected to the energy storage module 1 and is used to detect the voltage Vbat of the energy storage module 1. The second voltage detection circuit 32 is connected to the bus capacitor C and is used to detect the voltage Vbus of the bus capacitor C. The differential circuit 33 has a first input terminal connected to the first voltage detection circuit 31, a second input terminal connected to the second voltage detection circuit 32, and an output terminal used to output the voltage difference Vbat-Vbus between the energy storage module 1 and the bus capacitor C. The controller 34 is electrically connected to the output terminal of the differential circuit 33.

[0058] The first voltage detection circuit 31 and the second voltage detection circuit 32 are used to accurately and in real-time sample the voltage signal of the energy storage module 1 on the high-voltage side and the voltage signal of the bus capacitor C, respectively. The specific implementations of the first voltage detection circuit 31 and the second voltage detection circuit 32 can be the same or different. In an exemplary embodiment, the first voltage detection circuit 31 and the second voltage detection circuit 32 may include a precision resistor divider network, a filter unit, and electrical isolation components (such as an isolation operational amplifier or a linear optocoupler) to ensure that the high-voltage DC signal is converted into a low-voltage, common-ground signal that matches the input range of the analog-to-digital converter (ADC) of the controller 34. Furthermore, the circuit design must consider interference immunity and measurement accuracy to provide stable and reliable voltage data.

[0059] The differential circuit 33 is used to acquire the voltage difference between the energy storage module 1 and the bus capacitor C in real time, serving as the feedback signal source in the control algorithm. Its implementation methods include, but are not limited to: directly performing analog subtraction on the two voltage signals after voltage division conditioning using a differential operational amplifier with a high common-mode rejection ratio; or, provided there is sufficient sampling accuracy, having the controller 34 sample the A / D conversion values ​​of the two voltages separately and then perform digital subtraction. The design of this circuit or software module must ensure that the linearity, response speed, and accuracy of the voltage difference signal meet the requirements of closed-loop control across the entire system voltage range.

[0060] The controller 34 can be composed of a microprocessor, a programmable logic device, or a combination thereof. Based on the received real-time voltage difference signal, it performs calculations using a built-in control algorithm (such as lookup table method, proportional control, or multi-stage judgment logic) and outputs corresponding switching control signals to each switching element in the pre-charging module 2. The output of the controller 34 is connected to the switching element K in the pre-charging branch 21. By controlling the on / off state of the switching element K, the controller dynamically adjusts the conduction state of multiple pre-charging branches 21 to change the equivalent resistance of the pre-charging module 2, thereby achieving stable and rapid tracking and elimination of the voltage difference, and thus completing the automated control of the entire pre-charging process.

[0061] In some embodiments, the controller 34 can be directly connected to the output of the differential circuit 33, and directly control the pre-charging branch 21 based on the voltage difference between the energy storage module 1 and the bus capacitor C. In other embodiments, the control module 3 may further include a comparator 35 connected between the differential circuit 33 and the controller 34.

[0062] Figure 6 This is a schematic diagram of the control module in an exemplary embodiment of this disclosure.

[0063] refer to Figure 6 In an exemplary embodiment, the control module 3 further includes: Comparator 35 has its first input terminal connected to the differential circuit 33, its second input terminal connected to the preset voltage Vth, and its output terminal outputting the control signal S. The control module 3 is configured to close the switching element in the pre-charging branch 21 when the voltage difference between the energy storage module 1 and the bus capacitor C is less than the preset voltage Vth.

[0064] exist Figure 6 In the illustrated embodiment, comparator 35 performs a high-speed, hysteretic comparison of the real-time voltage difference between the energy storage module 1 and the bus capacitor C with a preset voltage threshold Vth. Its output is a high- or low-level control signal S, which directly controls the switching element K in the pre-charging branch 21. This hardware comparator circuit provides a fast and deterministic response path for critical state switching, helping to improve the reliability of the system during dynamic processes.

[0065] The operating logic of control module 3 can be set as follows: monitor the output status of comparator 35 in real time, and when it is determined that the voltage difference has dropped below the preset threshold Vth, close the switching element K of a certain pre-charging branch in the pre-charging module to reduce the overall equivalent resistance of the pre-charging module. Thus, the hardware comparator ensures the speed and determinism of critical timing determination.

[0066] Figure 7 This is a flowchart of a pre-charge control method provided in an exemplary embodiment of this disclosure. Figure 7 The pre-charge control method 700 shown can be executed by the control module 3.

[0067] refer to Figure 7 The pre-charge control method may include: Step S1: Obtain the voltage difference between the energy storage module and the bus capacitor; Step S2: Control the switching elements in the plurality of pre-charging branches according to the voltage difference to reduce the equivalent resistance of the pre-charging module as the voltage difference decreases. When the voltage difference is less than a preset threshold, control the switching elements in the pre-charging branches that only include the switching elements to close.

[0068] Below, in conjunction with Figure 5 , Figure 6 The circuit shown and Figure 7 The method shown describes the pre-charge control process.

[0069] In some embodiments, the preset voltage Vth can be set to a large value, and the control module 3 can be configured to initiate dynamic adjustment of the switching element K in the pre-charging branch 21 only after the voltage difference is less than the preset voltage Vth, thereby ensuring that the current surge in the early stage of pre-charging is completely limited and improving the system startup safety.

[0070] In other embodiments, the preset voltage Vth can be set to a lower threshold close to zero. The control module 3 can be configured such that when the voltage difference is less than this value, the controller 34 directly controls the relay (as a main circuit switch or a bypass switch in the pre-charge module) to close, thereby short-circuiting the entire pre-charge module 2 from the DC bus, causing it to stop working, and the system then ends the pre-charge phase and enters the normal operation mode.

[0071] When multiple pre-charge branches 21 with switching elements K are configured, each switching element K can be equipped with a corresponding comparator 35. Different preset thresholds can be set for each comparator 35 (e.g., Vth1, Vth2, Vth3, where Vth1>Vth2>Vth3). This allows for the construction of a purely hardware-controlled cascaded pre-charge logic: as the voltage difference Vbat-Vbus gradually decreases, each comparator flips sequentially, automatically and sequentially closing or turning on the corresponding switching element K, thereby progressively reducing the equivalent resistance of the pre-charge module and achieving a fully hardware-based automatic pre-charge process. In an exemplary embodiment, a preset threshold can be set to correspond to one or more switching elements K to flexibly adjust the number of switching elements K closed each time.

[0072] In some embodiments of this disclosure, to improve the control accuracy and flexibility of the pre-charging process, the resistance values ​​of the current-limiting resistors in different pre-charging branches are not entirely the same. For example, a resistor array containing different resistance values ​​(such as high, medium, and low resistance values) can be constructed, enabling the control module 3 to achieve a step-like or approximately continuous fine adjustment of the equivalent resistance of the pre-charging module 2 by selecting and switching pre-charging branches 21 with different resistance values ​​in the pre-charging module 2, thereby more smoothly controlling the charging current and voltage change rate.

[0073] In other embodiments, for the purpose of simplifying design, reducing costs, or improving interchangeability, at least two pre-charging branches can be configured to use current-limiting resistors with identical resistance values. In this configuration, the control module 3 can achieve digital adjustment of the equivalent resistance of the pre-charging module 2 (such as binary weighting or unit resistance multiplication) by controlling the parallel connection and disconnection of multiple branches with the same resistance value, thus enabling effective management of the charging process while ensuring basic functionality.

[0074] In some embodiments, the control module 3 can be configured to simultaneously close the switching element of one pre-charging branch and open the switching elements of other pre-charging branches during the voltage difference reduction process. That is, the control module 3 is configured to use a single-branch switching mode during the voltage difference reduction process, controlling only the switching element in one pre-charging branch to close (connecting that branch to the loop) at the same time, while keeping the switching elements of all other pre-charging branches in the open state. The single-branch switching mode is suitable for scenarios where the current-limiting resistor values ​​of different pre-charging branches are not completely identical. By switching between individual branches with different resistance values ​​to change the total equivalent resistance, the control logic is clear and concise, making it suitable for scenarios with relatively relaxed dynamic response requirements.

[0075] In other embodiments, the control module 3 may be configured (which the pre-charge control method 700 may include) to increase the number of closed switching elements in the pre-charge branch as the voltage difference decreases. That is, the control module 3 may be configured to use a branch parallel accumulation mode. Specifically, as the voltage difference decreases and charging progresses, the control module 3 gradually increases the number of pre-charge branches 21 connected to the circuit, thereby reducing the total equivalent resistance of the pre-charge module 2.

[0076] For example, in the initial stage of pre-charging, only the branch containing the maximum resistance is closed to limit the maximum inrush current; as the voltage difference decreases, branches containing smaller resistances are gradually closed, and the parallel operation of multiple branches gradually reduces the total equivalent resistance, thereby achieving a smooth transition of charging current or accelerating the charging process. This mode can achieve faster and smoother resistance changes, optimizing the dynamic performance of the pre-charging stage.

[0077] Furthermore, control module 3 can also be configured to perform adaptive multi-mode switching control. Specifically, the controller can dynamically select and switch to the most suitable pre-charge control strategy based on real-time monitored system parameters (such as initial voltage difference, ambient temperature, and the state of charge (SOC) of the energy storage module). For example, during a cold start with a large voltage difference, the aforementioned single-branch switching mode is used to ensure the highest safety and reliability; during a hot restart or with a smaller voltage difference, it may automatically switch to a branch parallel accumulation mode to pursue a faster pre-charge speed. This adaptive capability, combined with operating conditions, allows the pre-charge process to further optimize start-up time and overall efficiency while ensuring safety.

[0078] Figure 8 This is a schematic diagram of the pre-charging module in an exemplary embodiment of this disclosure.

[0079] refer to Figure 8 In an exemplary embodiment, the pre-charging module 2 may include three pre-charging branches 211, 212, and 213.

[0080] The first pre-charge branch 211 is composed of a switching element K1. When the switching element K1 in this branch is closed, it provides a direct path with near-zero resistance. The switching element K1 is preferably a relay or contactor capable of carrying the system's rated current. At the end of the pre-charge phase, when the bus voltage approaches the energy storage module voltage, this branch is closed by the control module, thereby completely bypassing all current-limiting components and allowing the system to transition to a fully conductive, low-loss operating state.

[0081] The second pre-charge branch 212 consists of a diode D connected in series with a current-limiting resistor R1. This branch provides a unidirectional fixed current-limiting path. Diode D ensures that current can only flow from the energy storage module side to the bus capacitor side, effectively preventing reverse current under specific fault or reverse voltage conditions. This branch is typically used as a basic or backup current-limiting path.

[0082] The third pre-charge branch 213 consists of a switching element K2 connected in series with a current-limiting resistor R2. This branch is a typical controllable current-limiting channel, where the switching element K2 is preferably a fully controllable device with excellent high-frequency performance (such as a MOSFET or IGBT). The control module can drive K2 with a precise PWM signal to achieve dynamic and continuous adjustment of the equivalent resistance of this branch (by changing the duty cycle), thereby providing a smooth and controllable current rise in the early stage of pre-charge.

[0083] In addition, the circuit also includes an energy storage inductor L connected in series with the DC bus, a switching transistor Q2, and a switching transistor Q1 connected between the positive and negative DC buses.

[0084] In the initial stage of pre-charging, the control module 3 can first refrain from controlling the switching elements and utilize the diode D and current-limiting resistor R1 in the second pre-charging branch 212, along with the filtering effect of the inductor L and the current-limiting effect of the resistor R1, to achieve stable and controlled charging of the bus capacitor C.

[0085] As the charging process progresses, the voltage difference across pre-charge module 2 decreases, enabling the third pre-charge branch 213. This closes switch element K2 to connect resistor R2 to the circuit. Utilizing the filtering effect of inductor L and the current-limiting effect of resistors R1 and R2, stable and controlled charging of the bus capacitor C is achieved. As the bus capacitor voltage rises, the voltage difference decreases, and the control module can adjust the PWM duty cycle of switch element Q1 to control the current. When the voltage difference drops to a safe threshold, the control module controls switch element K1 to close, switching the main power path to this low-impedance path, completing the pre-charge process. This multi-branch combination design integrates dynamic PWM regulation, switchable resistance current limiting, and final zero-impedance bypass functions, balancing the smoothness, controllability, safety, and final operating efficiency of the pre-charge process.

[0086] In conjunction with the foregoing embodiments, the pre-charging process control of this disclosure can be implemented through hardware, software, or a hybrid mode thereof, as described in the following detailed implementation: In a hardware-based implementation, the switching element K2 can be implemented through a switching transistor. The difference Vbat - Vbus between the voltage Vbat of the energy storage module 1 and the voltage Vbus of the bus capacitor C can be directly and continuously compared with a preset voltage threshold Vth through an analog comparator circuit. When the comparator detects that Vbat - Vbus < Vth, a control signal is directly generated to control the switching transistor that implements the switching element K2 to conduct. At this time, the current-limiting resistor R2 and the current-limiting resistor R1 form a parallel relationship, reducing the overall equivalent resistance of the pre-charge module, thereby accelerating the charging rate of the bus capacitor C and ensuring that when the subsequent main relay K1 is actuated, the voltage difference across its contacts has been significantly reduced, effectively reducing arcs and impacts, and improving the service life of the relay and the system reliability.

[0087] In a software- or digital-control-based implementation, the switching element K2 can be implemented through a switching transistor. The control module 3 respectively and continuously acquires the voltage Vbat of the energy storage module 1 and the voltage Vbus of the DC bus C through the first voltage detection circuit 31 and the second voltage detection circuit 32. The controller 34 obtains the real-time voltage difference Vbat - Vbus through internal calculation and compares and judges it with the voltage threshold V preset in the software. When the judgment condition Vbat - Vbus < V is satisfied, the controller 43 outputs a PWM wave with a specific duty cycle through its I / O port to drive the switching transistor that implements the switching element K2 to conduct. By adjusting the duty cycle of the PWM signal, the effective conduction degree of the switching transistor that implements the switching element K2 can be more finely controlled, realizing continuous or segmented adjustment of the pre-charge current, making the pre-charge process smoother and more controllable.

[0088] The above hardware control and software control modes can be selected or combined according to the different requirements of the system for response speed, control accuracy, and cost. For example, a hardware comparison circuit can be used in critical stages requiring extremely high reliability and fast response; software control can be used in situations where complex logic and flexible adjustment are needed. The two can also work together, with the hardware circuit ensuring the fast operation of critical safety thresholds and the software achieving more optimized process control.

[0089] Through this pre-charge strategy, in an 1100V energy storage system, a pre-charge circuit can be implemented with 2 resistors, and in a 1500V energy storage system, a pre-charge circuit can be implemented with 3 resistors, greatly reducing the number of power resistors and saving the board area.

[0090] In an exemplary embodiment, the control module 3 can be further configured to perform online fault diagnosis during the pre-charging process. For example, by monitoring the current of each pre-charging branch or the voltage across the switching element, it can determine whether there are faults such as an open circuit in the current-limiting resistor, sticking of the switching element, or drive failure. When an abnormality is detected in a branch, the controller can automatically switch to the backup branch combination or adjust the control strategy (such as using the remaining effective branches to complete the pre-charging or triggering a safety shutdown), thereby improving the availability and reliability of the system.

[0091] Furthermore, the control module 3 can communicate with the battery management system (BMS) inside the energy storage module 1. By controlling the equivalent resistance of the pre-charge module 2, the parameters of the pre-charge process (such as the maximum allowable surge current and the pre-charge target voltage slope) are dynamically adjusted according to the real-time battery status (such as temperature, SOC, and SOH) provided by the BMS. For example, under low-temperature battery conditions, the BMS can request the control module to extend the pre-charge time or reduce the charging current to protect battery health. In this case, the control module 3 can fulfill the BMS's request by increasing the equivalent resistance of the pre-charge module 2 (such as reducing the number of pre-charge branches 21 that are switched on or switching to the pre-charge branch 21 with the largest current-limiting resistor value).

[0092] In summary, in the exemplary embodiments of this disclosure, by setting an adjustable equivalent resistance pre-charge module and dynamically adjusting the equivalent resistance of the pre-charge module according to the voltage difference across the pre-charge module, pre-charging can be performed using a large resistance current limit when the voltage difference is large, which can effectively suppress the initial inrush current of pre-charging the bus capacitor; when the voltage difference decreases, the equivalent resistance is reduced for pre-charging, reducing the residual voltage across the pre-charge module, reducing the voltage difference when the relay is energized, effectively preventing relay contact erosion, extending the relay's service life, and improving the safety of the energy storage system during use.

[0093] It should be noted that although several modules or units for the device used to perform actions have been mentioned in the detailed description above, this division is not mandatory. In fact, according to embodiments of this disclosure, the features and functions of two or more modules or units described above can be embodied in one module or unit. Conversely, the features and functions of one module or unit described above can be further divided and embodied by multiple modules or units.

[0094] Other embodiments of this disclosure will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This application is intended to cover any variations, uses, or adaptations of this disclosure that follow the general principles of this disclosure and include common knowledge or customary techniques in the art not disclosed herein. The specification and examples are to be considered exemplary only, and the true scope and concept of this disclosure are indicated by the claims.

Claims

1. An energy storage system, characterized by, include: An energy storage module is connected to a DC bus, and the energy storage module includes one or more batteries; Bus capacitor, connected to the DC bus; A pre-charge module is connected in series on the DC bus and includes multiple pre-charge branches connected in parallel. Each pre-charge branch includes a switching element and / or a current-limiting resistor, and at least one of the pre-charge branches includes only the switching element. A control module, connected to the energy storage module, the bus capacitor, and the pre-charge module, is used to monitor the voltage difference between the energy storage module and the bus capacitor during the pre-charge phase, control the switching elements in the plurality of pre-charge branches according to the voltage difference, so as to reduce the equivalent resistance of the pre-charge module as the voltage difference decreases, and control the switching elements in the pre-charge branches that only include the switching elements to close when the voltage difference is less than a preset threshold.

2. The energy storage system as described in claim 1, characterized in that, The resistance values ​​of the current-limiting resistors in different pre-charge branches are not exactly the same.

3. The energy storage system as described in claim 2, characterized in that, The control module is configured to simultaneously close the switching element of one of the pre-charging branches and open the switching elements of other pre-charging branches during the process of the voltage difference decreasing.

4. The energy storage system as described in claim 1, characterized in that, The current-limiting resistors of at least two of the pre-charge branches have the same resistance value.

5. The energy storage system as described in claim 2 or 4, characterized in that, The control module is configured to increase the number of closed switching elements in the pre-charging branch as the voltage difference decreases.

6. The energy storage system as described in claim 1, characterized in that, The pre-charge module is located on the positive DC bus, or the pre-charge module is located on the negative DC bus.

7. The energy storage system as described in claim 1, characterized in that, The control module includes: A first voltage detection circuit is connected to the energy storage module and is used to detect the voltage of the energy storage module. The second voltage detection circuit is connected to the bus capacitor and is used to detect the voltage of the bus capacitor. The differential circuit has a first input terminal connected to the first voltage detection circuit, a second input terminal connected to the second voltage detection circuit, and an output terminal used to output the voltage difference between the energy storage module and the bus capacitor. The controller is electrically connected to the output terminal of the differential circuit.

8. The energy storage system as described in claim 7, characterized in that, The control module also includes: The comparator has a first input terminal connected to the differential circuit, a second input terminal connected to a preset voltage, and an output terminal that outputs a control signal. The control module is configured to control the switching element in the pre-charging branch to close when the voltage difference is less than the preset voltage.

9. The energy storage system as described in claim 1, characterized in that, The pre-charge branch also includes a diode.

10. The energy storage system as described in claim 1 or 9, characterized in that, The switching element type includes at least one of MOSFET, IGBT, and relay, and the switching element types of different pre-charge branches are not exactly the same.

11. A pre-charge control method, characterized in that, Applied to the energy storage system as described in any one of claims 1-10, comprising: Obtain the voltage difference between the energy storage module and the bus capacitor; The switching elements in the plurality of pre-charging branches are controlled according to the voltage difference to reduce the equivalent resistance of the pre-charging module as the voltage difference decreases. When the voltage difference is less than a preset threshold, the switching elements in the pre-charging branches that only include the switching elements are controlled to close.

Images