Resonant converter for energy storage system bms and power flow control method thereof

Abstract

This invention relates to the field of battery management and power electronic conversion technology for energy storage systems, and particularly to a resonant converter for a BMS (Battery Management System) in an energy storage system and its power flow control method. The converter includes a battery module, a data acquisition and protection unit, a main controller, and a power conversion unit. The data acquisition and protection unit is connected to the main controller, and the battery module is connected to the data acquisition and protection unit. The power conversion unit is connected to both the battery module and the main controller. The power conversion unit includes a high-voltage side LLC circuit, a transformer, and a low-voltage side synchronous rectification circuit. The high-voltage side LLC circuit and the low-voltage side synchronous rectification circuit are connected to the transformer, the high-voltage side LLC circuit is connected to the main controller, and the low-voltage side synchronous rectification circuit is connected to both the battery module and the main controller. The main controller monitors the battery module status in real time and dynamically adjusts the operating mode of the power conversion unit. Compared with existing technologies, this invention protects the battery while maintaining the operation of some system functions as much as possible, thus improving the overall system efficiency.

Description

Technical Field This invention relates to the field of battery management and power electronic conversion technology for energy storage systems, and particularly to a resonant converter for a BMS in an energy storage system and its power flow control method. Background Technology In energy storage systems, the battery management system (BMS) is responsible for monitoring and protecting the battery pack, ensuring its safe and efficient operation. Resonant converters (such as LLC converters) are widely used in the charge and discharge control of energy storage systems due to their advantages such as high efficiency and low electromagnetic interference.

[0001] In existing bidirectional charge-discharge systems based on LLC resonant converters, power regulation is achieved by controlling the switching frequency using a microcontroller (such as a DSP or MCU). For example, existing technologies often employ an LLC converter combined with synchronous rectification technology, adjusting the switching frequency to regulate the output voltage and current, thus achieving bidirectional power flow. Simultaneously, the BMS collects battery voltage and temperature parameters through an AFE (analog front-end) chip and performs overvoltage, undervoltage, and overtemperature protection based on these parameters, typically limiting power by disconnecting contactors or adjusting the converter's operating mode.

[0002] The existing system architecture typically includes a microcontroller (such as a DSP or MCU), a dedicated BMS analog front-end (AFE) chip, an LLC resonant network (high voltage side) composed of a full-bridge or half-bridge circuit, a synchronous rectifier circuit (low voltage side), and a high-frequency transformer.

[0003] Working principle: In charging mode (energy flows from the grid to the battery), the controller drives the high-voltage side switch to transfer energy to the low-voltage side through the transformer, and controls the synchronous rectifier switch to achieve efficient rectification. In discharging mode, the roles are reversed: the low-voltage side synchronous rectifier circuit operates as an active inverter bridge, and the high-voltage side acts as a rectifier unit, realizing the reverse flow of energy.

[0004] Protection Mechanism: The AFE chip collects battery information in real time. When parameters (such as voltage and temperature) exceed preset thresholds, the BMS will send an alarm or fault signal to the main controller. Traditional protection measures are usually "one-size-fits-all," that is, directly shutting down all the switching transistors of the entire converter, or completely disconnecting the battery from the external circuit through mechanical contactors / relays, thereby simultaneously prohibiting charging and discharging.

[0005] However, existing solutions mostly employ bidirectional converter structures for power flow control, allowing free switching between charging and discharging, but lack a mechanism to forcibly limit power flow under specific fault conditions (such as voltage or temperature exceeding limits). For example, when the battery voltage is too high or too low, existing technologies typically protect the battery by completely disabling the converter or switching to bypass mode, but this may lead to system shutdown or reduced efficiency. The handling of specific fault scenarios suffers from insufficient flexibility and reduced system availability.

[0006] In summary, the main drawbacks of existing technologies include: The protection mechanism is too crude, resulting in poor system availability: When the battery only has local parameter abnormalities (such as only the voltage is too high but not reaching the dangerous value), the existing technology's practice of directly and completely cutting off the charging and discharging circuit will cause the entire energy storage system to shut down. It is impossible to maintain some functions (such as allowing discharge to reduce voltage) while ensuring safety, thus reducing the availability and reliability of the system.

[0007] The inability to achieve directional power control for proactive restoration to a safe state: When the battery voltage deviates from the normal range, existing technologies lack an active, directional power control mechanism to help the battery return to a safe state. For example, when the battery voltage is too high, the system needs to "discharge without charging" to consume the excess energy; while when the voltage is too low, it needs to "charge without discharging" to replenish the energy. Existing technologies cannot precisely achieve this unidirectional power clamping.

[0008] Inadequate trade-off between efficiency and safety under extreme conditions: Under no-load, light-load, or extreme voltage conditions, the traditional strategy of continuous operation or complete shutdown of bidirectional converters either leads to high switching losses and low efficiency, or results in a complete loss of control, making it impossible to utilize the inherent characteristics of the circuit (such as the body diode of the switching transistor) to achieve safe isolation. Summary of the Invention To overcome the above problems, this invention proposes a resonant converter for a BMS (Battery Management System) and its power flow control method, which can effectively solve the above problems.

[0009] The present invention provides a technical solution to solve the above-mentioned technical problems: a resonant converter for a battery management system (BMS), comprising a battery module, a data acquisition and protection unit, a main controller, and a power conversion unit. The data acquisition and protection unit is connected to the main controller, the battery module is connected to the data acquisition and protection unit, and the power conversion unit is connected to both the battery module and the main controller. The power conversion unit includes a high-voltage side LLC circuit, a transformer, and a low-voltage side synchronous rectification circuit. The high-voltage side LLC circuit and the low-voltage side synchronous rectification circuit are connected to the transformer, the high-voltage side LLC circuit is connected to the main controller, and the low-voltage side synchronous rectification circuit is connected to both the battery module and the main controller. The main controller monitors the battery module status in real time and dynamically adjusts the operating mode of the power conversion unit. Preferably, the battery module is composed of 16S1P lithium iron phosphate cells, and the data acquisition and protection unit is an AFE chip, which is directly connected to each cell of the battery module for high-precision real-time acquisition of voltage and module temperature.

[0010] Preferably, the main controller is an MCU or DSP microcontroller. The controller communicates with the AFE chip via I2C, receives the collected data, and executes the BMS protection algorithm.

[0011] Preferably, the high-voltage side LLC circuit consists of a full-bridge or half-bridge switch, a resonant inductor, a resonant capacitor, and a transformer magnetizing inductor forming an LLC resonant network. The switching drive signal for this part is generated by an MCU or DSP microcontroller. The transformer is a high-frequency transformer with a high-voltage to low-voltage turns ratio of 7:1, used for electrical isolation and voltage transformation. The low-voltage side synchronous rectification circuit consists of a synchronous rectifier switch and its drive circuit, used for rectification in discharge mode and inversion in charging mode.

[0012] Preferably, the MCU or DSP microcontroller independently generates and outputs two PWM control signals based on the BMS algorithm and system status: one signal is used to control the switching transistor of the high-voltage side LLC circuit; the other signal is used to control the switching transistor of the low-voltage side synchronous rectifier circuit.

[0013] A method for controlling the power flow direction of a resonant converter used in a BMS (Battery Management System) for an energy storage system includes the following steps: Step S1: Real-time parameter acquisition and monitoring. The main controller continuously acquires the total voltage, individual cell voltage and temperature data of the battery module through the data acquisition and protection unit. Step S2: Security threshold determination. The main controller compares the collected data with the internally preset security threshold. Step S3: Working mode decision and control output. Based on the judgment result of step S2, the main controller dynamically selects and switches to one of the following four working modes: normal bidirectional mode, charging prohibition mode, discharging prohibition mode, and no-load or low-load intermittent working mode.

[0014] Preferably, in step S3, when all battery parameters are within the normal range, the system switches to normal bidirectional mode: the main controller simultaneously enables high-voltage side LLC control and low-voltage side synchronous rectification control, and achieves open-loop 7:1 amplified voltage charging and discharging by fixing the switching frequency of LLC, at which time energy can flow freely in both directions.

[0015] Preferably, in step S3, when any single-cell voltage exceeds the upper limit of the charging threshold or the temperature exceeds the safe charging threshold, the charging is switched to the prohibited charging mode: the main controller stops sending PWM drive signals to the high-voltage side LLC switching transistor, keeping them all in the off state; the main controller continues to send PWM drive signals to the low-voltage side synchronous rectifier switching transistor, keeping it working normally.

[0016] Preferably, in step S3, when any single-cell voltage is detected to be below the discharge lower limit threshold or the temperature is abnormal, the system switches to the discharge prohibition mode: the main controller stops sending PWM drive signals to the low-voltage side synchronous rectifier switch, keeping them all in the off state; the main controller continues to send PWM drive signals to the high-voltage side LLC switch, keeping it working normally.

[0017] Preferably, in step S3, when the system is in an unloaded or lightly loaded state, it switches to an intermittent working mode: the main controller controls the power conversion unit to enter intermittent operation, that is, periodically switches between short-term operation and complete hibernation.

[0018] Compared with existing technologies, the resonant converter and its power flow control method for energy storage system BMS of the present invention can force the resonant converter to operate only in charging mode or only in discharging mode when the battery parameters exceed the limits. This protects the battery while maintaining the operation of some system functions as much as possible and actively pulls the battery back to the safe operating area. Through specific control logic, the operating state of the switching transistor is optimized under no-load, light-load and extreme voltage conditions. The body diode of the synchronous rectifier switching transistor is used to achieve the natural unidirectional conduction characteristic, thereby achieving the hardware-level protection effect of "can be charged but not discharged" or "can be discharged but not charged", while improving the overall system efficiency. Attached Figure Description Figure 1 This is a structural block diagram of the resonant converter used in the BMS of the energy storage system according to the present invention; Figure 2 This is a flowchart of the power flow control method for the resonant converter in the BMS of the energy storage system according to the present invention. Detailed Implementation To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the invention.

[0019] It should be noted that in the embodiments of the present invention, all directional indications (such as up, down, left, right, front, back, etc.) are limited to relative positions on the specified view, rather than absolute positions.

[0020] Furthermore, in this invention, descriptions involving "first," "second," etc., are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0021] Please see Figure 1 and Figure 2 The resonant converter for a battery storage system (BMS) of the present invention includes a battery module, a data acquisition and protection unit, a main controller, and a power conversion unit. The data acquisition and protection unit is connected to the main controller, the battery module is connected to the data acquisition and protection unit, and the power conversion unit is connected to both the battery module and the main controller.

[0022] The power conversion unit includes a high-voltage side LLC circuit, a transformer, and a low-voltage side synchronous rectification circuit. The high-voltage side LLC circuit and the low-voltage side synchronous rectification circuit are respectively connected to the transformer. The high-voltage side LLC circuit is connected to the main controller, and the low-voltage side synchronous rectification circuit is connected to both the battery module and the main controller. The main controller monitors the battery module status in real time and dynamically adjusts the operating mode of the power conversion unit to ensure battery safety.

[0023] The battery module consists of lithium iron phosphate cells connected in series (1P16S) with a nominal voltage of 51.2V.

[0024] The data acquisition and protection unit is an AFE chip, which is directly connected to each cell of the battery module to collect the voltage and module temperature of all cells in real time with high precision.

[0025] The main controller employs an STMicroelectronics MCU or DSP microcontroller. This controller communicates with the AFE chip via I2C, receives acquired data, and executes advanced BMS protection algorithms (such as overvoltage, undervoltage, and overtemperature detection). Based on the BMS algorithm and system status, the MCU or DSP microcontroller independently generates and outputs two PWM control signals: one to control the switching transistors of the high-voltage side LLC circuit; and the other to control the switching transistors of the low-voltage side synchronous rectifier circuit.

[0026] The high-voltage side LLC circuit consists of a full-bridge or half-bridge switching transistor (such as MOSFET), a resonant inductor, a resonant capacitor, and a transformer magnetizing inductor, forming an LLC resonant network. The switching drive signals for this part are generated by an MCU or DSP microcontroller.

[0027] The transformer is a high-frequency transformer with a high-voltage to low-voltage turns ratio of 7:1, used for electrical isolation and voltage transformation.

[0028] The low-voltage side synchronous rectification circuit consists of a synchronous rectifier switch (MOSFET) and its driving circuit, used to achieve rectification in discharge mode and inversion in charging mode.

[0029] The power flow control method for resonant converters in a BMS (Battery Management System) of this invention involves the main controller executing control logic. Upon starting the power flow control method logic, the BMS system boots up, and the main controller initializes. Protection parameters are initialized to default values, real-time parameter acquisition and monitoring are reset to zero, total voltage is reset to zero, individual cell voltages are reset to zero, current is reset to zero, and temperature is reset to zero.

[0030] The power flow control method for a resonant converter in a BMS (Battery Management System) of the present invention includes the following steps: Step S1: Real-time parameter acquisition and monitoring.

[0031] In step S1, the main controller continuously acquires the total voltage, individual cell voltage and temperature data of the battery module through the data acquisition and protection unit, which are used for the protection logic of each protection parameter value.

[0032] Step S2: Safety threshold determination.

[0033] In step S2, the main controller compares the collected data with internally preset safety thresholds (such as the upper limit of single-unit voltage 3.65V, the lower limit of 2.7V, and the upper limit of temperature 55℃).

[0034] Step S3: Working mode decision and control output.

[0035] In step S3, based on the judgment result of step S2, the main controller dynamically selects and switches to one of the following four working modes, which is achieved by controlling the "wave generation mode" (i.e., whether the PWM signal is output and its timing): Mode 1: Normal bidirectional mode.

[0036] Conditions: All battery parameters are within the normal range. That is, there is no charge-prohibition protection, no discharge-prohibition protection, and no no-load or light-load operating conditions.

[0037] Control Actions: The main controller simultaneously enables high-voltage side LLC control and low-voltage side synchronous rectification control. Open-loop 7:1 voltage amplification is achieved through a fixed LLC switching frequency, allowing energy to flow freely in both directions.

[0038] Mode 2: Charging prohibited mode (can be placed but not charged).

[0039] Condition: If any single cell voltage exceeds the upper charging limit threshold or the temperature exceeds the safe charging threshold, charging restriction protection is activated.

[0040] Control action: The main controller stops sending PWM drive signals to the high-voltage side LLC switching transistors, keeping them all in the off state.

[0041] The main controller continues to send PWM drive signals to the low-voltage side synchronous rectifier switch to ensure its normal operation.

[0042] Implementation and Principle: When discharging is required, the low-voltage side LLC circuit operates, and energy is transferred from the battery side to the high-voltage side via the transformer. Since all the high-voltage side LLC transistors are turned off, their body diodes naturally form a current path from the battery positive terminal to the low-voltage side of the transformer in the circuit structure, and the discharge function is normal. When attempting to charge, energy should flow from the high-voltage side to the battery via the transformer, but at this time the high-voltage side LLC transistors are not working and cannot actively conduct. The orientation of their body diodes precisely prevents current from flowing from the transformer to the battery positive terminal, thus achieving hardware-level unidirectional conduction of "dischargeable but not rechargeable" using the body diodes.

[0043] Mode 3: Discharge Prohibited Mode (Charging is allowed, but discharging is not).

[0044] Condition: Any cell voltage is detected to be below the discharge lower limit threshold or an abnormal temperature is detected. In other words, discharge protection is in effect.

[0045] Control action: The main controller stops sending PWM drive signals to the low-voltage side synchronous rectifier switch, keeping them all in the off state.

[0046] The main controller continues to send PWM drive signals to the high-voltage side LLC switch to ensure its normal operation.

[0047] Implementation and Principle: When charging is required, the high-voltage side LLC circuit operates actively, allowing energy to flow from the high-voltage side to the low-voltage side circuit (through the body diode path) to charge the battery. Since the low-voltage side synchronous rectifier circuit is not working, the body diode of its switching transistor prevents energy transfer from the battery side to the high-voltage side in the circuit structure, thus achieving "rechargeable but not dischargeable".

[0048] Mode 4: No-load and low-load intermittent working mode.

[0049] Condition: The system is in an unloaded or lightly loaded state. That is, there is an unloaded or lightly loaded operating condition.

[0050] Control action: The main controller controls the power conversion unit to enter intermittent (Burst Mode) operation, that is, periodically switching between "short-term operation" and "complete hibernation" to reduce switching losses under light load and improve efficiency.

[0051] The resonant converter and its power flow control method for a battery management system (BMS) of this invention can, based on the battery parameters (voltage, temperature) of the BMS, selectively stop sending drive signals to the high-voltage side LLC switch or the low-voltage side synchronous rectifier switch, rather than completely shutting off all switches, thereby forcing the converter to operate only in one direction (charging or discharging). This is a control strategy combining software and hardware. Hardware-level unidirectional conduction is achieved using a body diode: the body diode of the synchronous rectifier switch is used as a natural physical barrier to achieve unidirectional conduction and incorporated into the control logic as an active safety design element. Specifically, low-voltage side drive is disabled to achieve "discharge only"; high-voltage side drive is disabled to achieve "charge only". A single main control chip (such as an MCU or DSP) simultaneously completes the BMS protection algorithm and the charging / discharging control of the LLC resonant converter, achieving deep integration of BMS and PCS functions, simplifying the system structure, and making the aforementioned refined power flow control possible. Multi-mode hybrid control strategy: It organically combines normal bidirectional mode, charging prohibition mode, discharging prohibition mode and intermittent working mode to form a complete control scheme that adaptively switches according to system status (battery parameters, load conditions).

[0052] Compared with existing technologies, the resonant converter and its power flow control method for energy storage system BMS of the present invention can force the resonant converter to operate only in charging mode or only in discharging mode when the battery parameters exceed the limits. This protects the battery while maintaining the operation of some system functions as much as possible and actively pulls the battery back to the safe operating area. Through specific control logic, the operating state of the switching transistor is optimized under no-load, light-load and extreme voltage conditions. The body diode of the synchronous rectifier switching transistor is used to achieve the natural unidirectional conduction characteristic, thereby achieving the hardware-level protection effect of "can be charged but not discharged" or "can be discharged but not charged", while improving the overall system efficiency.

[0053] The above description is only a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any modifications, equivalent substitutions and improvements made within the concept of the present invention should be included within the patent protection scope of the present invention.

Claims

1. A resonant converter for a battery management system (BMS) of an energy storage system, characterized by, It includes a battery module, a data acquisition and protection unit, a main controller, and a power conversion unit. The data acquisition and protection unit is connected to the main controller, the battery module is connected to the data acquisition and protection unit, and the power conversion unit is connected to both the battery module and the main controller. The power conversion unit includes a high-voltage side LLC circuit, a transformer, and a low-voltage side synchronous rectification circuit. The high-voltage side LLC circuit and the low-voltage side synchronous rectification circuit are respectively connected to the transformer. The high-voltage side LLC circuit is connected to the main controller. The low-voltage side synchronous rectification circuit is connected to the battery module and the main controller. The main controller monitors the status of the battery module in real time and dynamically adjusts the working mode of the power conversion unit.

2. The resonant converter for an energy storage system BMS of claim 1, wherein, The battery module is composed of 16S1P lithium iron phosphate cells. The data acquisition and protection unit is an AFE chip, which is directly connected to each cell of the battery module to collect voltage and module temperature in real time with high precision.

3. The resonant converter for an energy storage system BMS of claim 2, wherein, The main controller is an MCU or DSP microcontroller. The controller communicates with the AFE chip via I2C, receives the collected data, and executes the BMS protection algorithm.

4. The resonant converter for an energy storage system BMS of claim 3, wherein, The high-voltage side LLC circuit consists of a full-bridge or half-bridge switch, a resonant inductor, a resonant capacitor, and a transformer magnetizing inductor forming an LLC resonant network. The switching drive signal for this part is generated by an MCU or DSP microcontroller. The transformer is a high-frequency transformer with a high-voltage to low-voltage turns ratio of 7:1, used for electrical isolation and voltage transformation. The low-voltage side synchronous rectification circuit consists of a synchronous rectifier switch and its drive circuit, used for rectification in discharge mode and inversion in charging mode.

5. The resonant converter for an energy storage system BMS of claim 4, wherein, The MCU or DSP microcontroller independently generates and outputs two PWM control signals based on the BMS algorithm and system status: one signal controls the switching transistor of the high-voltage side LLC circuit; the other signal controls the switching transistor of the low-voltage side synchronous rectifier circuit.

6. A method for resonant converter power flow direction control for energy storage system BMS, characterized in that, Includes the following steps: Step S1: Real-time parameter acquisition and monitoring. The main controller continuously acquires the total voltage, individual cell voltage and temperature data of the battery module through the data acquisition and protection unit. Step S2: Security threshold determination. The main controller compares the collected data with the internally preset security threshold. Step S3: Working mode decision and control output. Based on the judgment result of step S2, the main controller dynamically selects and switches to one of the following four working modes: normal bidirectional mode, charging prohibition mode, discharging prohibition mode, and no-load or low-load intermittent working mode.

7. The resonant converter power flow direction control method for an energy storage system BMS of claim 6, wherein, In step S3, when all battery parameters are within the normal range, the system switches to normal bidirectional mode: the main controller simultaneously enables high-voltage side LLC control and low-voltage side synchronous rectification control, and achieves open-loop 7:1 amplified voltage charging and discharging by fixing the switching frequency of LLC, at which time energy can flow freely in both directions.

8. The resonant converter power flow direction control method for an energy storage system BMS of claim 6, wherein, In step S3, when any single cell voltage exceeds the upper limit of the charging threshold or the temperature exceeds the safe charging threshold, the charging is switched to the prohibited charging mode: the main controller stops sending PWM drive signals to the high-voltage side LLC switching transistor, keeping them all in the off state; the main controller continues to send PWM drive signals to the low-voltage side synchronous rectifier switching transistor, keeping it working normally.

9. The method for controlling the power flow direction of a resonant converter for a BMS in an energy storage system as described in claim 6, characterized in that, In step S3, when any single cell voltage is detected to be lower than the discharge lower limit threshold or the temperature is abnormal, the system switches to the discharge prohibition mode: the main controller stops sending PWM drive signals to the low-voltage side synchronous rectifier switch, keeping them all in the off state; the main controller continues to send PWM drive signals to the high-voltage side LLC switch, keeping it working normally.

10. The method for controlling the power flow direction of a resonant converter for a BMS in an energy storage system as described in claim 6, characterized in that, In step S3, when the system is in an unloaded or lightly loaded state, it switches to an intermittent working mode: the main controller controls the power conversion unit to enter intermittent operation, that is, periodically switching between short-term operation and complete hibernation.

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