Low-voltage battery bypass and step-down adaptive direct-current pile charging method and system

Abstract

The application discloses a low-voltage battery bypass and step-down adaptive direct-current pile charging method and system, and belongs to the technical field of direct-current charging control. A double charging path structure is arranged between a low-voltage battery and a national standard direct-current charging pile, the charging pile output capacity and the low-voltage response characteristic are identified through charging communication messages, input sampling and state quantity comprehensive identification, and the bypass direct charging or step-down charging mode is automatically determined and selected; a phased request voltage strategy is adopted to be compatible with the message response logic of different charging piles, and the adaptive adaptation of different output capacity direct-current piles is realized by cooperating with the hardware interlocking, pre-charging discharge and multi-source power taking design; when the charging pile can directly output low voltage, low-loss large-current direct charging is realized through the bypass path; when the minimum output voltage of the charging pile is higher than the battery voltage, safe low-voltage charging is realized through a controllable step-down circuit.

Description

Technical Field

[0001] This invention relates to the field of DC charging control and power electronic power conversion technology for electric vehicles and energy storage devices, specifically a low-voltage battery bypass and step-down adaptive DC charging method and system. Background Technology

[0002] With the increasing popularity of low-speed electric vehicles, two-wheeled electric vehicles, portable energy storage, and low-voltage special vehicles, the demand for fast charging of low-voltage power / energy storage batteries with a voltage platform of 50V to 150V is growing. The national standard GB / T DC charging piles widely deployed in the public sector were originally designed for high-voltage power battery vehicles, and the output capabilities of different charging piles vary significantly: some wide-range charging piles can support a full range of output from 50V to 1000V, and can directly output voltages compatible with low-voltage batteries; many conventional charging piles have a minimum output voltage of 200V, 250V, or even higher, and cannot directly output DC power lower than their minimum output voltage; and some charging piles, although nominally supporting low-voltage output, have different response logics to charging request messages during the charging handshake and parameter configuration stages, which can lead to handshake failure and no output at the charging pile if a direct request for low voltage is made.

[0003] Existing low-voltage battery DC charging solutions are mainly divided into three categories: The first category uses a dedicated on-board or external low-voltage charger to convert AC power into low-voltage DC power. This solution cannot utilize the high-power output capability of existing DC charging piles and requires additional chargers, heat dissipation, and installation space, resulting in low charging efficiency. The second category uses a fixed step-down charging module to step down the high-voltage DC power output from the charging pile to a low voltage before charging the battery. Although this solution can be adapted to charging piles with high minimum output voltages, all charging current needs to pass through the power conversion circuit regardless of whether the charging pile supports low-voltage output, resulting in significant conduction and switching losses. In low-voltage, high-current scenarios, it is inefficient, has high heat dissipation pressure, and is costly, failing to fully utilize the capabilities of charging piles that can directly output low voltage. The third category uses a simple bypass direct charging solution, directly connecting the charging pile to the battery when it can output low voltage. This solution has low conduction losses but cannot be adapted to conventional charging piles with minimum output voltages higher than the battery voltage. Furthermore, it lacks comprehensive judgment on the charging message stage and the charging pile response characteristics, which can easily lead to safety issues such as handshake failure and incorrect high-voltage connection to the battery, resulting in poor adaptability to real-world scenarios.

[0004] Existing solutions cannot simultaneously address the compatibility, charging efficiency, and safety issues of low-voltage batteries with DC charging piles of different output capabilities. There is an urgent need for a charging solution that can automatically identify the charging pile's capability, adaptively select the charging path, and has a complete safety interlock, so as to achieve compatibility and adaptation of low-voltage batteries with various national standard DC charging piles without modifying the charging pile's equipment, while also taking into account charging efficiency and safety. Summary of the Invention

[0005] The purpose of this invention is to provide a low-voltage battery bypass and step-down adaptive DC charging method and system to solve the problems mentioned in the background art.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a low-voltage battery bypass and step-down adaptive DC charging method, comprising the following steps: S1 Initial Safety State Configuration: After the charging gun is connected or the wake-up signal is triggered, the system completes communication, sampling, and drive channel initialization. By default, the bypass switching device and output protection switch are disconnected, and the drive output of the buck power conversion circuit is prohibited to ensure that the system has no main power path before the pile end capability identification is completed. S2 Charging Pile Capacity and Battery Demand Identification: Establish GB / T charging communication connection with the national standard DC charging pile, read the charging pile output capacity parameters, and obtain the charging demand parameters of the low-voltage battery through BMS communication. Real-time sampling of charging pile output voltage, battery terminal voltage, temperature, switch status and insulation status. S3 Adaptive Charging Mode Determination: Based on the output capacity parameters of the charging pile, the battery charging demand parameters, and the real-time sampled system status quantities, determine whether to select bypass charging mode or buck charging mode. S4 Phased Charging Request Voltage Control: Based on the charging pile response characteristics and the current charging stage, dynamically generate a charging request voltage message and send it to the charging pile to complete the charging pile output configuration; S5 corresponding mode charging control: After the hardware interlock condition is met, bypass charging control or buck charging control is executed according to the determined charging mode to complete the low-voltage battery charging. S6 Safety Switching and Shutdown: When the charging mode needs to be switched, charging is completed, or a stop charging command is received, the charging pile is first requested to reduce the current to zero or stop the output. After the current power path is disconnected and the bus voltage is discharged, the mode switch is executed or the charging process is terminated. S7 Fault Diagnosis and Protection: Real-time monitoring of system status throughout the charging process. When a fault threshold is triggered, a safety shutdown procedure is immediately executed to isolate the fault and report it.

[0007] Preferably, the output capability parameters of the charging pile in step S2 include the minimum output voltage, maximum output voltage, and maximum output current of the charging pile. The identification process also includes: during the charging handshake, parameter configuration, and charging operation phases, combining the charging pile status message, the sampling value of the charging pile output voltage, and the communication response time statistics to comprehensively determine whether the charging pile has low-voltage output following capability, rather than judging solely based on the charging pile nameplate or a single frame capability message.

[0008] Preferably, step S3, the adaptive charging mode determination, specifically involves: The bypass charging mode is determined when all of the following conditions are met: the minimum output voltage of the charging pile is not higher than the upper limit of the current allowable charging voltage of the battery, and the actual output voltage of the charging pile can enter the battery's allowable charging window following the low voltage request. At the same time, the charging pile current capability, voltage ripple, voltage difference between the charging pile and the battery, switching device status, system temperature, and insulation detection status all meet the preset thresholds. The charging mode is determined to be step-down when any of the following conditions are met: the minimum output voltage of the charging pile is higher than the upper limit of the allowable charging voltage of the low-voltage battery, or the charging pile responds to the low-voltage request for too long, the actual output voltage exceeds the allowable window of the battery, or the bypass circuit device has an abnormal self-test or the insulation condition does not meet the bypass requirements.

[0009] Preferably, step S4, the phased charging request voltage control, specifically involves: When it is determined that the charging pile can directly respond to the low-voltage charging request, the charging request voltage actually required by the battery is sent directly to the charging pile, and the output voltage of the pile end is confirmed to enter the battery allow window through status messages and input sampling. When it is determined that the charging pile cannot directly respond to the low-voltage request during the handshake phase, or the minimum output voltage of the charging pile is higher than the battery voltage window, a compatible request voltage within the voltage range that the charging pile can respond to is first sent to the charging pile, so that the charging pile completes the parameter configuration and enters a stable output state; if it is subsequently determined that the charging pile can follow the low-voltage request, the request voltage is switched to the actual required voltage of the battery and the bypass mode is entered for determination; otherwise, the high-voltage input is maintained and the low voltage is output by the step-down circuit.

[0010] Preferably, the bypass charging control in step S5 specifically includes: After entering the bypass preparation state, first confirm that the buck power conversion circuit driver hardware is disabled and there is no PWM output, confirm that the bypass switch device is not stuck, the output protection is in the allowed state, and the difference between the output voltage at the charging pile end and the voltage at the battery end is less than the preset closing threshold; then close the bypass switch device, so that the DC positive terminal of the charging pile is directly connected to the positive terminal of the low-voltage battery through the bypass path and the protection unit, and the DC negative terminal of the charging pile is connected to the negative terminal of the battery through a common negative low-resistance path, and the main charging current does not pass through the buck power conversion device; during the charging process, the charging voltage and current are controlled by the charging pile and battery BMS in a closed loop, and the system monitors the voltage, current, temperature and switch status in real time.

[0011] Preferably, the step-down charging control in step S5 specifically includes: After entering the buck conversion preparation state, firstly, confirm that the bypass switch is completely disconnected and complete the disconnection confirmation through auxiliary contacts or voltage difference detection; control the pre-charging circuit to complete the pre-charging of the input or output capacitors to suppress the closing inrush current; after closing the output protection switch, start the buck power conversion circuit, and perform constant current, constant voltage, and power limiting closed-loop control according to the charging requirements sent by the BMS to convert the high-voltage DC power at the pile end into the low-voltage DC power required by the low-voltage battery; the buck power conversion circuit includes any one of synchronous Buck, Buck-Boost, LLC resonant, DAB dual active bridge, phase-shifted full bridge, isolated or non-isolated DC / DC topology.

[0012] Preferably, the system also includes power supply and auxiliary power control steps: the system supplies power to the controller, communication unit, switching coil, drive circuit, sampling circuit and heat dissipation load through a multi-source power supply circuit. The power supply includes one or more of the following: vehicle 12V power supply, low-voltage battery, pile-end auxiliary power supply, and low-voltage power supply obtained by isolation conversion of pile-end DC input; the power supply circuit integrates current limiting, reverse connection protection, undervoltage lockout, isolation and power supply holding units, limits input current absorption during the charging pile insulation detection and handshake stage to avoid interfering with the pile-end insulation detection results; maintains continuous power supply to the controller and communication unit during fault or switching processes, and completes safe shutdown, discharge and fault reporting.

[0013] Preferably, step S6, safety switching and shutdown, specifically involves: prohibiting direct switching between bypass mode and buck mode under load; during switching, first requesting the charging pile to reduce the output current to zero or stop the output; in buck mode, first reducing the PWM duty cycle to zero and prohibiting drive output; in bypass mode, confirming that the loop current is lower than the switch disconnection threshold before disconnecting the corresponding switch; only after starting the bus discharge circuit to discharge the bus voltage to below the safety threshold is the preparation process for entering another mode allowed.

[0014] Preferably, step S7, fault diagnosis and protection, specifically involves: real-time monitoring of overvoltage, undervoltage, overcurrent, short circuit, reverse connection, overtemperature, insulation abnormality, high-voltage interlock abnormality, switch adhesion, inconsistent auxiliary contact status, abnormal circuit interlock, communication timeout, undervoltage power supply, inconsistent sampling values, and abnormal charging pile response; when any single-point fault is triggered, immediately request the charging pile to stop output, prohibit the step-down circuit drive, disconnect the bypass switch and output protection switch, turn off electronic protection devices, latch fault information and report to the BMS or vehicle controller to ensure that the high voltage at the charging pile end is not directly applied to the low-voltage battery end.

[0015] A low-voltage battery bypass and buck adaptive DC charging system includes: The DC charging interface conforms to the GB / T DC charging standard and is used to connect to a national standard DC charging pile. Input detection and communication unit for realizing GB / T charging communication with charging pile, sampling pile end input voltage and input current; Bypass charging path connected in series between charging pile DC positive pole and low-voltage battery positive pole, containing bypass switch device and short-circuit protection unit, for realizing low-resistance DC path; Buck charging path connected in parallel with bypass charging path, containing controllable buck power conversion circuit, for converting pile end high-voltage DC power into low-voltage DC power suitable for low-voltage battery; Common negative return path directly connecting charging pile DC negative pole and low-voltage battery negative pole by using low-resistance copper bar or bus bar; Output protection unit connected in series on the output side of the battery positive pole, for realizing output side overcurrent, short circuit protection and breaking; Pre-charging and discharge circuit for realizing capacitor pre-charging to suppress impact current and bus capacitor charge discharge after shutdown; Power taking auxiliary power supply for obtaining power from multiple power sources to supply power to various low-voltage loads of the system; Controller for executing charging logic control, mode determination, drive output and fault handling; Sampling and diagnosis unit for sampling voltage, current, temperature, switch state, insulation state and high-voltage interlocking signal to realize fault diagnosis; BMS communication interface for communicating with battery management system of low-voltage battery to obtain battery charging requirements and state information.

[0016] Compared with the prior art, the beneficial effects of the present application are: 1. Strong compatibility: without modifying the charging pile side equipment, it can automatically adapt to various national standard DC charging piles with minimum output voltage of 50V to 500V or above, covering 50V-150V full series of low-voltage batteries, solving the pain point that low-voltage batteries cannot use public DC pile fast charging.

[0017] 2. High charging efficiency: bypass direct charging is adopted on the charging pile supporting low-voltage output, the main current does not pass through inductors, switch tubes and other power devices, the conduction loss is reduced by more than 90%, and the overall efficiency of the system is increased by 8%-12% compared with the fixed buck scheme during large current charging, the heat dissipation pressure and device cost are significantly reduced.

[0018] 3. High safety: through initial safety state, path interlocking, no-load switching and multiple fault diagnosis, it is ensured that any single point fault will not cause high voltage to be directly applied to the low-voltage battery end, avoiding device damage and safety accidents; the power taking circuit design avoids interfering with the pile end insulation detection, and the charging process meets the national standard safety requirements.

[0019] 4. Good adaptability: the phased request voltage strategy is compatible with the message response logic of charging piles of different manufacturers, the handshaking success rate is high, the adaptation problem of wide-range piles and old conventional piles can be solved, and custom development is not needed for specific pile types. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 The system block diagram of the present application.

[0021] Figure 2 The charging mode selection logic flow chart of the present application.

[0022] Figure 3 The communication and switching timing diagram of the present application. DETAILED DESCRIPTION

[0023] In order to make the purpose, technical scheme and advantages of the present application clearer, the technical scheme in the embodiments of the present application will be described clearly and completely below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0024] Please refer to Figures 1 to 3 , the present application provides a technical scheme: as Figure 1 shown, the low-voltage battery bypass and step-down adaptive DC pile charging system disclosed in the present embodiment is adapted to low-voltage batteries with rated voltage of 50V-150V, including mainstream voltage platforms of 48V, 60V, 72V, 86.5V, 96V, 120V, 144V, etc. Lithium iron phosphate, ternary lithium, lead-carbon and other types of battery packs, the system is installed in the charging adapter or vehicle-mounted charger cabin as a whole, connected to the public DC charging pile through the national standard DC charging gun, and the output end is connected to the low-voltage battery pack and its BMS system.

[0025] The system specifically includes the following component units: 1. DC charging interface: using standard GB / T 20234.3 DC charging gun seat, containing DC+ and DC- power terminals and CC1, CC2, CAN communication terminals, rated current 250A, insulation withstand voltage 1000V, meeting the mechanical and electrical requirements of national standard DC charging.

[0026] 2. Input detection and communication unit: contains CAN communication transceiver, high-voltage differential sampling circuit, Hall current sensor, CAN communication transceiver connects the charging pile CAN bus to realize GB / T 27930 charging protocol communication; the high-voltage differential sampling circuit uses a resistance divider network with an accuracy of 0.5% to sample the input voltage between the pile end DC+ and DC-, with a sampling range of 0-1000V; the Hall current sensor samples the input total current, with a range of ±300A and an accuracy of 1%, for input power detection and overcurrent protection.

[0027] 3. Bypass charging path: connected in parallel at the input and output of the step-down power circuit, with a bypass DC contactor K_BP and an electronic fuse eFuse connected in series on the DC+ side; the bypass contactor uses a DC vacuum contactor with a rated current of 200A, with normally open / closed auxiliary contacts, and a contact voltage drop of less than 10mV@200A; the electronic fuse is implemented using back-to-back MOSFETs, with a response time of less than 10μs, capable of achieving short-circuit fast breaking and reverse current suppression, with a rated current of 200A and a breaking capacity of 1000A. The total resistance of the bypass path is less than 0.5mΩ when conducting, with extremely low conduction loss under high current.

[0028] 4. Step-down charging path: this embodiment uses a two-phase synchronous Buck topology as the step-down power conversion circuit, with an input voltage range of 150V-800V and an output voltage range of 40V-160V, a rated output current of 100A, and a switching frequency of 100kHz. The power inductor uses a Sendust magnetic core inductor with a single-phase inductance of 20μH, the switching tube uses an 80V / 200A low-resistance MOSFET, and the rectifier tube uses a synchronous rectification MOS, with a full-load conversion efficiency of greater than 96%. In other embodiments, the step-down circuit can be replaced by Buck-Boost, LLC resonant converter, DAB dual active bridge, phase-shift full-bridge, flyback, multi-phase interleaved Buck, etc. as long as it can achieve controllable voltage and current conversion.

[0029] 5. Common negative return path: uses a 30mm² tin-plated copper bar to directly connect the charging interface DC- terminal and the battery negative BAT- terminal, without any series switching devices in between, with a resistance of less than 0.2mΩ, achieving large-current low-resistance return and avoiding the loss and fault points caused by negative series devices.

[0030] 6. Output protection unit: series connected with an output contactor K_OUT and a current sensor on the battery positive BAT+ side, K_OUT uses a rated current of 200A DC contactor with auxiliary contact feedback for output side breaking and fault isolation; the current sensor samples the output total current to achieve battery side overcurrent protection.

[0031] 7. Pre-charge and discharge circuit: The pre-charge circuit is composed of a pre-charge relay and a 50Ω / 100W power resistor in series, and is connected in parallel across the main contactor. When powered on, it first charges the bus capacitor current-limiting, and charges the capacitor voltage to less than 10V difference with the input / output voltage before closing the main contactor, to suppress the closing impact current. The discharge circuit is composed of a discharge relay and a 100Ω / 200W power resistor in series, and is connected in parallel between the positive and negative poles of the high-voltage bus. When shutdown or fault occurs, the discharge relay is closed, and the bus voltage is discharged to below 36V safety voltage within 5s.

[0032] 8. Auxiliary power supply: A multi-source redundant power supply architecture is adopted, with four input sources including vehicle 12V battery, low-voltage battery pack, pile end A+ auxiliary power supply, and pile end high-voltage 12V power supply converted by isolated flyback. The ideal diode ORing circuit is used to realize seamless switching of the power supply, and the output of 12V / 5A and 5V / 2A is used to power the controller, communication, contactor coil, fan, and drive circuit. The input end of the power supply circuit is connected in series with a 100mA current-limiting resistor and an electronic switch. During the pile end insulation detection stage, the high-voltage side power supply path is turned off, and the power supply current is limited to less than 1mA, to avoid the capacitance or load of the power supply circuit changing the insulation resistance value of the pile end insulation detection, resulting in misjudgment of the insulation detection. The circuit is built-in with a 10000μF large-capacity holding capacitor, which can maintain the power supply of the controller and communication for more than 300ms during failure or power failure, to ensure the completion of contactor disconnection, fault reporting, and discharge control.

[0033] 9. Controller: A 32-bit vehicle-grade MCU is used as the main control, with a main frequency of 120MHz, built-in multi-channel ADC, PWM, CAN, and GPIO channels, running a charging state machine to realize protocol communication, mode determination, drive control, and fault handling logic. The controller is built-in with a hardware interlock logic. When the bypass contactor is closed, the hardware circuit automatically pulls down the enable pin of the PWM output of the step-down circuit, to prohibit the output of the step-down circuit from the hardware level, to avoid software exceptions causing common of the two paths.

[0034] 10. Sampling and diagnosis unit: including voltage sampling, current sampling, temperature sampling, contact detection, insulation detection, HVIL high-voltage interlock detection circuit, sampling channels including pile end input voltage, battery end voltage, bus voltage, output current, input current, power board temperature, contactor temperature, contactor auxiliary contact state, insulation resistance value, high-voltage interlock loop state, all sampling channels have redundancy verification, and sampling value deviation exceeding 5% triggers sampling abnormal fault.

[0035] 11. BMS communication interface: using CAN or RS485 interface to communicate with low-voltage battery BMS, periodically acquiring the allowed charging state, requested charging voltage, requested charging current, battery SOC, battery temperature, and fault code information sent by BMS, and simultaneously reporting the charging system state and fault information to BMS.

[0036] The complete charging control process of the system is executed in the following steps: S1 Initial safety state configuration: When the user inserts the charging gun, the CC1 / CC2 connection signal triggers the system to wake up, or the vehicle 12V power wakes up, the controller first completes the initialization: configure the CAN communication baud rate to 250kbps, initialize the ADC sampling channel and PWM output channel, read the fault storage record, read the auxiliary contactor contact state; After initialization, all switching devices are forced to be set to off state: bypass contactor K_BP is disconnected, output contactor K_OUT is disconnected, step-down circuit PWM output is disabled, electronic fuse is set to current-limiting off state, pre-charge and discharge relays are disconnected; At this time, the system has no main power path, and the pile end and the battery are completely disconnected, ensuring that there is no current path during the handshake and insulation detection stage, waiting for the charging pile to complete the insulation detection and handshake process.

[0037] S2 Pile end capability and battery demand identification: After the charging pile completes the insulation detection, the controller establishes GB / T27930 charging communication with the charging pile, first receives the CML charger capability message sent by the charging pile, and parses the minimum output voltage, maximum output voltage and maximum output current parameters in the message; At the same time, periodically receive BCL battery demand messages sent by BMS, parse the highest voltage allowed by the battery for charging, request charging current, allowed charging state, SOC, highest / lowest temperature, fault state information; During communication, the controller samples the pile end input voltage and input current in real time, and counts the response time of the charging pile to the request message. In the subsequent parameter configuration and charging stage, the actual output voltage and output state of the pile end are also read through the CCS charger state message, and whether the pile end truly follows the request voltage output is judged by combining the local sampling value, rather than only relying on the nominal value of the CML message to determine the pile end capability. For example, some charging piles with a nominal minimum output voltage of 200V can actually output 60V low voltage during charging. The system can identify this hidden capability through actual sampling and message feedback.

[0038] S3 Adaptive charging mode determination: As shown in Figure 2 , the controller determines the mode according to the pile end capability and system state: The following conditions must be met simultaneously to determine the bypass charging mode: (1) The nominal minimum output voltage of the CML message at the charging pile is ≤ the upper limit of the current allowable charging voltage of the battery (e.g., the battery requests 60V, and the minimum output voltage of the charging pile is ≤ 60V), or the actual sampling verifies that the charging pile can stably output the voltage within the allowable window of the battery; (2) The maximum output current of the charging pile is ≥ 50% of the charging current requested by the BMS, which meets the charging power requirements; (3) The actual output voltage ripple of the charging pile is less than 200mV, and the output is stable; (4) The voltage difference between the charging pile and the battery terminal is less than 5V before closing, to avoid the closing inrush current; (5) The feedback of the auxiliary contact of the bypass contactor K_BP is in the open state, and there is no sticking fault; (6) The temperature of each point in the system is within the working range of -20℃ to 85℃, the insulation resistance is greater than 100Ω / V, the HVIL circuit is normal, and there are no other faults. If all conditions are met, it is determined to be the bypass charging mode.

[0039] The charging mode is determined to be stepped-down when any of the following conditions occur: (1) The nominal minimum output voltage of the charging pile is higher than the upper limit of the battery's allowable charging voltage (e.g., the minimum output voltage of the charging pile is 200V and the maximum charging voltage of the battery is 88V); (2) After sending three consecutive low-voltage requests, the actual output voltage of the charging pile deviates from the requested value by more than 20%, and the response timeout exceeds 5s, which is determined to be unable to follow the low-voltage request; (3) The bypass path device has a self-test fault, such as contactor sticking or electronic fuse failure; (4) The insulation test value does not meet the bypass requirements.

[0040] S4 Phased Charging Request Voltage Control: The controller dynamically adjusts the BCL request voltage value sent to the charging pile based on the mode determination result and the charging stage. For low-voltage charging piles that are determined to be directly bypassable, the controller directly sends the actual charging voltage (e.g., 60V) and requested current requested by the BMS in the BCL message. After sending, it waits for 5 seconds and confirms through the CCS message and local sampling that the output voltage at the charging pile is stable within the 58V-62V window and the voltage deviation is less than ±2V, thus confirming that the charging pile has entered a stable low-voltage output state.

[0041] For charging piles determined to be high-voltage or unable to respond to low-voltage requests during the handshake phase, the controller first sends a compatible request voltage within the pile's responsive range. In this embodiment, it is set to 310V (a typical responsive voltage point for a conventional 200V minimum output pile), and the current request is set to the minimum allowable current of 1A. After the charging pile completes parameter configuration and the output voltage stabilizes within the 300V-320V window, subsequent control is executed based on the mode selection result: if it is in buck mode, the 310V high-voltage input is maintained, and the buck circuit is activated to output low voltage; if subsequent testing shows that the pile can follow the voltage reduction request, the request voltage is gradually reduced to the actual battery requirement value at a slope of 5V / 100ms. After confirming that the output is stable, the bypass mode determination process is initiated. This phased strategy can solve the problem that some charging piles must request high voltage before entering the output state, significantly improving the handshake success rate.

[0042] S5 corresponding charging control mode: Bypass charging control process: After entering the bypass preparation state, the interlock confirmation is first performed: the PWM enable of the buck circuit is confirmed to be low level through the hardware IO port, the buck driver chip is in the disabled state, and the driver status register is read by the software to confirm that there is no PWM output; the K_BP auxiliary contact is read to confirm that it is in the open state, the K_OUT auxiliary contact is read to confirm that it is in the closed state, and the electronic fuse is set to 200A current limiting protection mode; after confirming that the voltage difference between the charging pile and the battery is less than 5V, the K_BP contactor is controlled to close. After closing, the auxiliary contact is read again to confirm that it is closed in place. At this time, the DC+ of the charging pile is directly connected to the positive terminal of the battery through K_BP and the electronic fuse, and the DC- is directly connected to the negative terminal of the battery through the copper busbar. The main current does not pass through the inductor and switching transistor of the Buck circuit; during the charging process, the charging voltage and current are controlled by the charging pile in a closed loop according to the BMS message. The system only acts as a path and protection unit, and monitors the voltage, current and temperature in real time. When the current exceeds the threshold of the electronic fuse, it quickly limits the current and disconnects. In case of abnormality, it requests the charging pile to reduce the current or stop the machine through the message.

[0043] Buck charging control process: After entering the buck preparation state, first confirm that the K_BP auxiliary contact is in the open state. Detect that the voltage difference across K_BP is greater than 100V to confirm physical disconnection and avoid high voltage input due to sticking. Control the pre-charge relay to close, and pre-charge the Buck circuit input capacitor through the pre-charge resistor. After the voltage difference between the input capacitor and the terminal voltage is less than 10V, close the input main relay and open the pre-charge relay. Close the output contactor K_OUT. After confirming that there is no short circuit in the output, start the Buck circuit PWM output. Use voltage and current dual closed-loop control. The voltage loop samples the battery terminal voltage, and the current loop samples the output inductor current. Perform constant current-constant voltage charging control according to the voltage and current values ​​requested by the BMS, converting the high-voltage DC power above 200V input at the terminal to the low-voltage DC power required by the battery. The output current control accuracy is ±1A, and the voltage control accuracy is ±0.5V. During charging, adjust the PWM duty cycle in real time to limit the maximum output power to not exceed the rated power of the buck circuit. Automatically derating when the temperature is too high.

[0044] S6 Safety Switching and Shutdown: During charging, if switching between bypass and buck modes is required (e.g., changes in charging pile output capacity during charging), or when the BMS sends a full-charge stop command or the user presses the stop button, the no-load switching procedure must be strictly followed: First, a current request of 0 is sent to the charging pile via a CAN message, requesting the charging pile to stop output, and the pile output current is allowed to drop below 1A; if the current mode is buck, the PWM duty cycle is reduced to 0, and the drive enable is pulled low to disable the Buck circuit output; if the current mode is bypass, after confirming that the circuit current is less than 1A (the minimum breaking current of the contactor), the contactor of the current path is disconnected; the discharge relay is closed to discharge the bus capacitor voltage to below 36V, and after 1 second to confirm that the voltage discharge is complete, the preparation process for the other mode is allowed. Switching the contactor under load or simultaneously conducting two paths is prohibited. When charging is finished, after disconnecting all switches, a charging end message is sent to the charging pile to complete the charging process.

[0045] S7 Fault Diagnosis and Protection: Throughout the charging process, the controller performs fault diagnosis every 10ms, covering the following fault types: input overvoltage / undervoltage, output overvoltage / undervoltage, input overcurrent, output overcurrent, short circuit, battery reverse connection, power board overheating, contactor overheating, low insulation resistance, HVIL circuit disconnection, contactor sticking, inconsistent auxiliary contact status, dual-path interlocking abnormality, CAN communication timeout, auxiliary power supply undervoltage, excessive sampling value deviation, and abnormal output response at the charging station. When any fault is triggered, protection is executed according to the fault level: for general faults, the charging station is first requested to reduce the current; for severe faults, all drive outputs are immediately pulled low, K_BP and K_OUT contactors are disconnected, the electronic fuse is triggered to quickly trip, the discharge circuit is closed to discharge the bus voltage, the fault code is latched, and the fault is reported to the BMS and charging station via CAN, ensuring that no single-point fault will cause the high voltage at the charging station to be directly applied to the low-voltage battery terminal, thus ensuring charging safety.

[0046] Example Description Example 1: Low-voltage charging pile bypass charging: Taking a low-voltage lithium battery with a rated voltage of 72V as an example, the BMS requests a charging voltage of 84V and a current of 100A. The system connects to a wide-range DC charging pile with a minimum output voltage of 50V. The CML message provides feedback on the minimum output voltage of 50V, the maximum output voltage of 1000V, and the maximum current of 250A at the charging pile end. The controller directly sends an 84V charging request, samples and confirms that the output voltage at the charging pile end is stable within the range of 83.5V-84.5V, and the voltage difference meets the requirements, thus determining it to be in bypass mode. After confirming that the buck circuit is disabled, K_BP is closed to enter bypass charging. The main current is directly connected to the battery through the contactor. The total circuit loss is about 10W, and the charging efficiency can reach 99.5%. Compared with the fixed Buck buck scheme, the loss is reduced by about 150W, and the efficiency is improved by about 6%.

[0047] Example 2: High-voltage pile step-down charging: Connect a conventional DC pile with a minimum output voltage of 200V to a 72V battery pack. The CML message feedback indicates that the minimum output voltage at the pile end is 200V, which is determined to be step-down mode. The controller first sends a 310V compatibility request voltage. After the output voltage at the pile end stabilizes at 310V, K_BP is kept off. After pre-charging, the two-phase synchronous Buck circuit is started to step down the 310V input to 84V output with an output current of 100A to charge the battery. The conversion efficiency is about 96%, realizing compatible charging of high-voltage piles and solving the problem that low-voltage batteries cannot be used with conventional high-voltage DC piles.

[0048] Example 3: Wide-range charging pile mode switching: Connect a wide-range charging pile with a nominal minimum output of 200V but actually supports low-voltage output to the same battery pack. The controller first sends a 310V request to put the charging pile into the output state, and then gradually reduces the requested voltage to 84V. By sampling, it is confirmed that the charging pile can stably output 84V voltage, and it is determined that the bypass condition is met. Execute the safety switching procedure: first request the charging pile to reduce the current to 0, disable Buck output, disconnect the input switch, discharge the bus voltage, and then close K_BP to enter the bypass charging mode, switching from the buck mode to the high-efficiency bypass mode to further improve charging efficiency.

[0049] In this embodiment, all threshold voltage, current, and time parameters can be calibrated and adjusted according to the battery voltage platform, power device specifications, and charging pile characteristics, without departing from the core principle of this invention.

[0050] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for low-voltage battery bypass and step-down adaptive DC charging, characterized in that, Includes the following steps: S1 Initial Safety State Configuration: After the charging gun connection or wake-up signal is triggered, the system completes communication, sampling, and drive channel initialization. By default, the bypass switching device and output protection switch are disconnected, and the drive output of the buck power conversion circuit is prohibited, ensuring that the system has no main power path before the pile end capability identification is completed. S2 Charging Pile Capacity and Battery Demand Identification: Establish GB / T charging communication connection with the national standard DC charging pile, read the charging pile output capacity parameters, and at the same time obtain the charging demand parameters of the low-voltage battery through BMS communication, and sample the charging pile output voltage, battery terminal voltage, temperature, switch status and insulation status in real time. S3 Adaptive Charging Mode Determination: Based on the output capacity parameters of the charging pile, the battery charging demand parameters, and the real-time sampled system status quantities, determine whether to select bypass charging mode or buck charging mode. S4 phased charging request voltage control: Based on the charging pile response characteristics and the current charging stage, dynamically generate a charging request voltage message and send it to the charging pile to complete the charging pile output configuration; S5 corresponding mode charging control: After the hardware interlock conditions are met, bypass charging control or buck charging control is executed according to the determined charging mode to complete the low-voltage battery charging. S6 Safety Switching and Shutdown: When the charging mode needs to be switched, charging is completed, or a stop charging command is received, the charging pile is first requested to reduce the current to zero or stop the output. After the current power path is disconnected and the bus voltage is discharged, the mode switch is executed or the charging process is terminated. S7 Fault Diagnosis and Protection: Real-time monitoring of system status throughout the charging process. When a fault threshold is triggered, a safety shutdown procedure is immediately executed to isolate the fault and report it.

2. The low-voltage battery bypass and step-down adaptive DC charging method according to claim 1, characterized in that, The output capability parameters of the charging pile in step S2 include the minimum output voltage, maximum output voltage, and maximum output current of the charging pile. The identification process also includes: during the charging handshake, parameter configuration, and charging operation phases, combining the charging pile status message, the sampling value of the charging pile output voltage, and the communication response time statistics to comprehensively determine whether the charging pile has low-voltage output following capability, rather than judging solely based on the charging pile nameplate or a single frame capability message.

3. The low-voltage battery bypass and step-down adaptive DC charging method according to claim 2, characterized in that, The adaptive charging mode determination in step S3 specifically involves: The bypass charging mode is determined when all of the following conditions are met: the minimum output voltage of the charging pile is not higher than the upper limit of the current allowable charging voltage of the battery, and the actual output voltage of the charging pile can enter the battery's allowable charging window following the low voltage request. At the same time, the charging pile current capability, voltage ripple, voltage difference between the charging pile and the battery, switching device status, system temperature, and insulation detection status all meet the preset thresholds. The charging mode is determined to be step-down when any of the following conditions are met: the minimum output voltage of the charging pile is higher than the upper limit of the allowable charging voltage of the low-voltage battery, or the charging pile responds to the low-voltage request for too long, the actual output voltage exceeds the allowable window of the battery, or the bypass circuit device has an abnormal self-test or the insulation condition does not meet the bypass requirements.

4. The low-voltage battery bypass and step-down adaptive DC charging method according to claim 3, characterized in that, The specific steps of step S4, phased charging request voltage control, are as follows: When it is determined that the charging pile can directly respond to the low-voltage charging request, the charging request voltage actually required by the battery is sent directly to the charging pile, and the output voltage of the pile end is confirmed to enter the battery allow window through status messages and input sampling. When it is determined that the charging pile cannot directly respond to the low-voltage request during the handshake phase, or the minimum output voltage of the charging pile is higher than the battery voltage window, a compatible request voltage within the voltage range that the charging pile can respond to is first sent to the charging pile, so that the charging pile completes the parameter configuration and enters a stable output state; if it is subsequently determined that the charging pile can follow the low-voltage request, the request voltage is switched to the actual required voltage of the battery and the bypass mode is entered for determination; otherwise, the high-voltage input is maintained and the low voltage is output by the step-down circuit.

5. The low-voltage battery bypass and step-down adaptive DC charging method according to claim 4, characterized in that, The bypass charging control in step S5 specifically involves: After entering the bypass preparation state, first confirm that the buck power conversion circuit driver hardware is disabled and there is no PWM output, confirm that the bypass switch device is not stuck, the output protection is in the allowed state, and the difference between the output voltage at the charging pile end and the voltage at the battery end is less than the preset closing threshold; then close the bypass switch device, so that the DC positive terminal of the charging pile is directly connected to the positive terminal of the low-voltage battery through the bypass path and the protection unit, and the DC negative terminal of the charging pile is connected to the negative terminal of the battery through a common negative low-resistance path, and the main charging current does not pass through the buck power conversion device; during the charging process, the charging voltage and current are controlled by the charging pile and battery BMS in a closed loop, and the system monitors the voltage, current, temperature and switch status in real time.

6. The low-voltage battery bypass and step-down adaptive DC charging method according to claim 5, characterized in that, The step-down charging control in step S5 specifically involves: After entering the buck conversion preparation state, firstly, confirm that the bypass switch is completely disconnected and complete the disconnection confirmation through auxiliary contacts or voltage difference detection; control the pre-charging circuit to complete the pre-charging of the input or output capacitors to suppress the closing inrush current; after closing the output protection switch, start the buck power conversion circuit, and perform constant current, constant voltage, and power limiting closed-loop control according to the charging requirements sent by the BMS to convert the high-voltage DC power at the pile end into the low-voltage DC power required by the low-voltage battery; the buck power conversion circuit includes any one of synchronous Buck, Buck-Boost, LLC resonant, DAB dual active bridge, phase-shifted full bridge, isolated or non-isolated DC / DC topology.

7. The low-voltage battery bypass and step-down adaptive DC charging method according to claim 6, characterized in that, It also includes power acquisition and auxiliary power control steps: the system supplies power to the controller, communication unit, switching coil, drive circuit, sampling circuit and heat dissipation load through a multi-source power acquisition circuit. The power source includes one or more of the following: vehicle 12V power supply, low-voltage battery, pile-end auxiliary power supply, and low-voltage power supply obtained by isolation conversion of pile-end DC input; the power acquisition circuit integrates current limiting, reverse connection protection, undervoltage lockout, isolation and power supply holding units, limits input current absorption during the charging pile insulation detection and handshake stage to avoid interfering with the pile-end insulation detection results; maintains continuous power supply to the controller and communication unit during fault or switching process, and completes safe shutdown, discharge and fault reporting.

8. The low-voltage battery bypass and step-down adaptive DC charging method according to claim 7, characterized in that, The specific steps of step S6, safety switching and shutdown, are as follows: direct switching between bypass mode and buck mode is prohibited under load; when switching, the charging pile is first requested to reduce the output current to zero or stop the output. In buck mode, the PWM duty cycle is first reduced to zero and the drive output is prohibited. In bypass mode, the corresponding switch is disconnected after confirming that the loop current is lower than the switch disconnection threshold. Only after the bus voltage is discharged below the safety threshold by activating the bus discharge circuit can the preparation process for entering another mode be allowed.

9. A low-voltage battery bypass and step-down adaptive DC charging method according to claim 8, characterized in that, The specific steps of fault diagnosis and protection in step S7 are as follows: real-time monitoring of overvoltage, undervoltage, overcurrent, short circuit, reverse connection, overtemperature, insulation abnormality, high-voltage interlock abnormality, switch sticking, inconsistent auxiliary contact status, abnormal circuit interlock, communication timeout, undervoltage power supply, inconsistent sampling values, and abnormal response at the charging pile; when any single-point fault is triggered, immediately request the charging pile to stop output, prohibit the step-down circuit drive, disconnect the bypass switch and output protection switch, turn off the electronic protection devices, latch the fault information and report it to the BMS or vehicle controller to ensure that the high voltage at the charging pile is not directly applied to the low-voltage battery terminal.

10. A low-voltage battery bypass and buck adaptive DC charging system, used to implement the charging method according to any one of claims 1-9, characterized in that, include: The DC charging interface conforms to the GB / T DC charging standard and is used to connect to a national standard DC charging pile. The input detection and communication unit is used to realize GB / T charging communication with the charging pile and to sample the input voltage and input current at the charging pile end; The bypass charging path is connected in series between the DC positive terminal of the charging pile and the positive terminal of the low-voltage battery. It includes a bypass switching device and a short-circuit protection unit to achieve a low-resistance DC path. The step-down charging path, connected in parallel with the bypass charging path, includes a controllable step-down power conversion circuit to convert the high-voltage DC power at the charging pile end into low-voltage DC power adapted to the low-voltage battery. The common negative return path uses a low-resistance copper busbar or busbar to directly connect the DC negative terminal of the charging pile to the negative terminal of the low-voltage battery. The output protection unit is connected in series on the positive output side of the battery to realize overcurrent, short circuit protection and disconnection on the output side; The pre-charge and discharge circuit is used to suppress inrush current during capacitor pre-charging and to discharge the charge from the bus capacitors after shutdown. Auxiliary power supply is used to obtain power from multiple power sources to supply power to various low-voltage loads in the system. The controller is used to perform charging logic control, mode determination, drive output, and fault handling. The sampling and diagnostic unit is used to sample voltage, current, temperature, switch status, insulation status, and high-voltage interlock signals to achieve fault diagnosis. The BMS communication interface is used to communicate with the battery management system of the low-voltage battery to obtain battery charging requirements and status information.

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