Extreme low temperature environment starting control method and system and new energy vehicle

Abstract

The application provides an extreme low-temperature environment starting control method, system and new energy vehicle, and relates to the technical field of low-temperature starting control of new energy vehicles. The method comprises the following steps: acquiring vehicle state parameters and power battery pack state parameters; when it is determined that the extreme low-temperature starting condition is met, generating a hierarchical heating initial power according to the initial temperature of the battery cell and starting the electric heater to heat; dynamically adjusting the heating power through PID closed-loop operation during the heating process; simultaneously, generating a polarization degree comprehensive index by comprehensively evaluating the polarization degree of the battery according to the ohmic resistance, polarization resistance, battery cell voltage and discharge current, and performing discharge current dynamic limit value operation according to the polarization degree comprehensive index to generate a maximum discharge current limit value; performing heating power upper limit constraint according to the maximum discharge current limit value, and outputting the real-time heating power by the upper limit value constraint. The application realizes accurate matching and closed-loop adjustment of the battery heating power in the extreme cold environment, thereby guaranteeing the starting efficiency and protecting the battery life.

Description

Technical Field

[0001] This invention relates to the field of low-temperature start-up control technology for new energy vehicles, and particularly to a start-up control method, system, and new energy vehicle for extreme low-temperature environments. Background Technology

[0002] When new energy vehicles are used in cold northern regions during winter, and the vehicle remains stationary for extended periods in extreme low-temperature environments ranging from -30°C to -40°C, the temperature of the battery pack cells can drop below -30°C. At this temperature, the activity of lithium ions inside the battery decreases significantly, the viscosity of the electrolyte increases, and the migration rate of lithium ions drops sharply. To protect battery life, the battery management system (BMS) typically shuts down the battery's charging and discharging capabilities, effectively prohibiting the battery from outputting power.

[0003] To address the aforementioned issues, existing technologies involve the Vehicle Control Unit (VCU) controlling the discharge of the power battery to drive the power heater (PTC) to heat the battery pack when it detects that the battery temperature is too low. The vehicle is then allowed to operate again once the battery temperature rises back to the permissible discharge threshold. However, this fixed-power heating strategy fails to consider the differences in battery heating requirements at different initial temperatures, resulting in low energy utilization efficiency. Furthermore, during the heating process, the VCU relies entirely on the Battery Management System (BMS) for passive feedback on the battery status, lacking active monitoring and dynamic response capabilities for battery polarization. This makes the battery more susceptible to irreversible lifespan degradation due to high-current discharge at low temperatures exacerbating battery polarization. Summary of the Invention

[0004] To address the technical problems mentioned above, this invention provides a method, system, and new energy vehicle for starting control in extreme low-temperature environments.

[0005] To achieve the above objectives, a first aspect of the present invention provides a start-up control method for extreme low-temperature environments, comprising: Obtain vehicle status parameters and power battery pack status parameters; the status parameters include at least the initial cell temperature, real-time cell temperature, state of charge, ohmic internal resistance, polarization internal resistance, cell voltage, and real-time discharge current; When the extreme low-temperature start-up conditions are met based on the vehicle status parameters and the initial temperature of the battery cell, the graded heating initial power is generated based on the initial temperature of the battery cell, and the electric heater is controlled to start heating with the initial power. During the heating process, the real-time temperature of the battery cell is acquired and the actual temperature rise rate is calculated. The heating power adjustment amount is obtained by performing PID closed-loop calculation based on the deviation between the preset target temperature rise rate and the actual temperature rise rate. The real-time heating power is generated based on the initial power and the adjustment amount, and the heating power of the electric heater is dynamically adjusted. During the heating process, the degree of battery polarization is comprehensively evaluated based on the ohmic internal resistance, the polarization internal resistance, the cell voltage, and the discharge current, and a comprehensive polarization index is generated. Based on the comprehensive polarization index, the state of charge and the real-time temperature of the cell, the dynamic limit of the discharge current is calculated to generate the maximum allowable discharge current limit of the current battery. The heating power is constrained by the maximum discharge current limit, and the output of the real-time heating power is constrained by the upper limit value.

[0006] Furthermore, the generation of graded heating initial power based on the initial temperature of the battery cell specifically includes: The initial power is calculated based on the initial temperature of the battery cell, the preset lower limit of extreme low temperature, the preset target exit temperature, the rated maximum power of the electric heater, the power adjustment depth coefficient, and the temperature level nonlinearity index. The initial power Determine using the following formula: ; in, The rated maximum power of the electric heater. The preset lower limit of extreme low temperature, The preset target exit temperature, This is the power regulation depth coefficient. The temperature level nonlinearity index is used to adjust the variation of heating power in different temperature ranges. The temperature level nonlinearity index is used to characterize the nonlinear characteristics of heating demand in low-temperature areas. The initial power decreases smoothly as the initial temperature of the battery cell increases.

[0007] Furthermore, the step of performing PID closed-loop calculation to obtain the heating power adjustment amount specifically includes: The heating power adjustment amount is calculated based on the deviation between the target temperature rise rate and the actual temperature rise rate, the proportional coefficient, the integral coefficient, and the derivative coefficient. The proportional coefficient is used to generate a proportional adjustment amount based on the current deviation, the integral coefficient is used to generate an integral adjustment amount based on the historical accumulation of the deviation, and the derivative coefficient is used to generate a derivative adjustment amount based on the changing trend of the deviation.

[0008] Furthermore, the status parameters also include: the average voltage of all cells, the rated voltage of the cells, and the maximum allowable discharge current of the battery at the current state of charge and temperature; The process of comprehensively evaluating battery polarization and generating a comprehensive polarization index includes: The polarization degree comprehensive index is calculated by weighted summation based on the ratio of the ohmic internal resistance to the room temperature reference ohmic internal resistance, the ratio of the polarization internal resistance to the room temperature reference polarization internal resistance, the absolute value of the ratio of the difference between the lowest cell voltage and the average voltage of all cells to the rated voltage of the cell, the ratio of the real-time discharge current to the maximum allowable discharge current of the battery, and the preset weighting coefficients corresponding to each ratio. The comprehensive index of polarization Determine using the following formula: ; in, For real-time ohmic internal resistance, The internal resistance is the reference ohm at room temperature. For real-time polarization internal resistance, The reference polarization internal resistance at room temperature, This is the lowest cell voltage. The average voltage of all cells. This is the rated voltage of the battery cell. For real-time discharge current, The maximum allowable discharge current of the battery under the current state of charge and temperature; the sum of the weighting coefficients is 1, and the comprehensive polarization index comprehensively considers four dimensions: ohmic polarization, electrochemical polarization, cell inconsistency, and discharge current margin.

[0009] Furthermore, the step of performing dynamic discharge current limit calculation to generate the maximum allowable discharge current limit for the current battery specifically includes: Based on the comprehensive polarization index, the maximum rated discharge current of the battery at room temperature, the minimum discharge current limit for battery protection, the preset midpoint of the polarization threshold, and the curve steepness coefficient, the maximum discharge current limit is calculated using the Sigmoid function so that the maximum discharge current limit decreases smoothly as the comprehensive polarization index increases. The maximum discharge current limit Determine using the following formula: ; in, This refers to the battery's rated maximum discharge current at room temperature. This is the minimum discharge current limit for battery protection. As a comprehensive index of polarization degree, The midpoint of the polarization threshold, The curve steepness coefficient is the midpoint of the polarization threshold, which is the comprehensive polarization index value corresponding to the inflection point of the Sigmoid curve. The curve steepness coefficient is used to adjust the steepness of the current limiting curve as the comprehensive polarization index changes.

[0010] Furthermore, the heating power upper limit constraint based on the maximum discharge current limit specifically includes: calculating the heating power upper limit based on the battery pack terminal voltage, the maximum discharge current limit, and the heating efficiency of the electric heater; and limiting the real-time heating power to a range not exceeding the heating power upper limit.

[0011] Furthermore, it also includes: When the comprehensive polarization index exceeds a preset first threshold, the maximum discharge current limit is reduced. When the polarization degree comprehensive index exceeds the preset second threshold, the maximum discharge current limit is further reduced to close to the minimum discharge current limit of the battery protection, wherein the second threshold is greater than the first threshold. When the comprehensive polarization index exceeds a preset third threshold, heating is paused and a fault is reported, wherein the third threshold is greater than the second threshold.

[0012] Furthermore, the method also includes: When the preset exit conditions are met, the extreme low temperature start-up mode will be exited. The preset exit conditions include at least one of the following: the minimum cell temperature is greater than the target exit temperature for a preset duration, the electric heater malfunctions, the charging state is entered, the heating countdown is reset to zero, or the high voltage is cut off.

[0013] Furthermore, the method also includes: When the extreme low temperature start-up conditions are met, the range extender is started by battery pulse discharge to generate electricity so that the range extender can provide the heating power required by the electric heater. After the range extender starts successfully, after a preset delay, the thermal management power is limited to the initial power. The real-time power consumption of the high-voltage accessory is obtained, wherein the high-voltage accessory includes at least the electric heater and the DC-DC converter; The power generation of the range extender is controlled to follow the real-time power consumption of the high-voltage accessory. A safety window is set for the battery pack's charging and discharging current. When the actual charging and discharging current of the battery pack exceeds the safety window, the range extender's emergency power adjustment is triggered.

[0014] A second aspect of the present invention provides a start-up control system for extreme low-temperature environments, comprising: The parameter acquisition module is used to acquire vehicle status parameters and power battery pack status parameters; the status parameters include at least the initial temperature of the cell, the real-time temperature of the cell, the state of charge, the ohmic internal resistance, the polarization internal resistance, the cell voltage, and the real-time discharge current. The start-up control module is used to generate a graded heating initial power based on the initial temperature of the battery cell when the extreme low-temperature start-up conditions are met according to the vehicle status parameters and the initial temperature of the battery cell, and control the electric heater to start heating with the initial power. The PID temperature control module is used to acquire the real-time temperature of the battery cell and calculate the actual temperature rise rate during the heating process. It performs PID closed-loop calculation based on the deviation between the preset target temperature rise rate and the actual temperature rise rate to obtain the heating power adjustment amount. It generates real-time heating power based on the initial power and the adjustment amount, and controls the electric heater to dynamically adjust the heating power. The polarization evaluation module is used to comprehensively evaluate the degree of polarization during the heating process based on the ohmic internal resistance, the polarization internal resistance, the cell voltage and the discharge current, and generate a comprehensive polarization index. The current limiting module is used to perform dynamic discharge current limit calculation based on the comprehensive polarization index, the state of charge and the real-time temperature of the cell, and generate the maximum allowable discharge current limit of the current battery. A power constraint module is used to constrain the upper limit of heating power based on the maximum discharge current limit, and to constrain the output of real-time heating power with the upper limit value.

[0015] A third aspect of the present invention provides a new energy vehicle, including a vehicle controller, a battery management system, an electric heater, and a power battery pack. The vehicle controller is communicatively connected to the battery management system and the electric heater, respectively. The vehicle controller is configured to execute the extreme low temperature environment start-up control method provided in the first aspect of the present invention.

[0016] Compared with existing technologies, the present invention provides a start-up control method, system, and new energy vehicle for extreme low-temperature environments. It generates graded initial heating power based on the initial temperature of the battery cell, precisely matching the heating power with the actual coldness of the battery, avoiding energy waste caused by fixed high-power heating and improving heating efficiency. Furthermore, by performing PID closed-loop calculations based on the target temperature rise rate and dynamically adjusting the heating power during the heating process, the cell temperature rise process becomes more stable and controllable, effectively avoiding overshoot or underheating. Simultaneously, by real-time evaluation of battery polarization and smooth adjustment of the discharge current limit accordingly, this limit is converted into a heating power upper limit to constrain the actual output. This provides a dynamic safety boundary for the battery while ensuring heating speed, minimizing irreversible damage caused by high-current discharge at low temperatures, and achieving synergistic optimization of start-up efficiency and battery life protection. Attached Figure Description

[0017] The accompanying drawings, which form part of this disclosure, are used to provide a further understanding of this disclosure. The illustrative embodiments of this disclosure and their descriptions are used to explain this disclosure and do not constitute an undue limitation of this disclosure.

[0018] Figure 1 This is a flowchart of the extreme low temperature environment start-up control method provided in Embodiment 1 of the present invention.

[0019] Figure 2 This is an architecture diagram of the extreme low temperature environment start-up control system provided in Embodiment 2 of the present invention. Detailed Implementation

[0020] Embodiments of the present invention will now be described in more detail with reference to the accompanying drawings. While some embodiments of the invention are shown in the drawings, it should be understood that the invention can be implemented in various forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the invention. It should be understood that the drawings and embodiments of the present invention are for illustrative purposes only and are not intended to limit the scope of protection of the invention. In the description of the embodiments of the present invention, the term "comprising" and similar terms should be understood as open-ended inclusion, i.e., "including but not limited to". The term "based on" should be understood as "at least partially based on". The term "one embodiment" or "this embodiment" should be understood as "at least one embodiment". The terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this embodiment, unless otherwise stated, "a plurality of" means two or more.

[0021] Before describing specific embodiments of the present invention, the key terms involved in the present invention will first be explained: 1. VCU (Vehicle Control Unit), also known as vehicle control unit, is the "brain" and "central nervous system" of new energy vehicles. It is the highest-level decision controller in the entire vehicle's electronic and electrical architecture. It is responsible for conducting comprehensive analysis and decision-making based on the driver's operating intentions (accelerator pedal, brake pedal, gear position, etc.) and the vehicle's current status (vehicle speed, battery charge, fault information, etc.). It also issues coordinated control commands to various subsystems such as motor controller, battery management system, and range extender controller to realize core functions such as vehicle power drive, energy recovery, and safety protection.

[0022] 2. BMS (Battery Management System) is mainly responsible for real-time monitoring of parameters such as voltage, current, temperature, state of charge (SOC), and internal resistance of the battery pack, and undertakes the functions of battery charging and discharging management and safety protection.

[0023] 3. PTC (Positive Temperature Coefficient) is a type of electric heater used to provide heating for power battery packs in low-temperature environments.

[0024] Example 1 like Figure 1 This embodiment provides a start-up control method for extreme low-temperature environments. This method is executed by the vehicle control unit (VCU). The VCU communicates with the battery management system (BMS) via a CAN bus to obtain battery pack status parameters and connects to the drive module of the electric heater (PTC) via a hardwired connection or PWM signal to output heating power control commands. The method includes: S101. Obtain vehicle status parameters and power battery pack status parameters; the status parameters include at least the initial temperature of the cell, the real-time temperature of the cell, the state of charge, the ohmic internal resistance, the polarization internal resistance, the cell voltage, and the real-time discharge current.

[0025] In extreme low-temperature environments, the VCU needs to acquire sufficient status information to accurately determine the current operating condition of the vehicle and battery. Specifically, after high-voltage power-on, the VCU sends a data request frame to the BMS via the CAN bus. In response, the BMS sends the real-time collected and packaged battery pack status parameters to the VCU via the CAN bus. Upon receiving the data frame, the VCU's CAN receive buffer verifies the data (CRC check, Cyclic Redundancy Check) to confirm its validity, then parses and stores it in the VCU's internal RAM (Random Access Memory) for subsequent strategy calculations. Cell temperature is the core criterion for determining whether to enter extreme low-temperature mode. It is acquired by the BMS through temperature sensors (typically NTC thermistors, Negative Temperature Coefficient) located at multiple sampling points within the battery pack. The VCU obtains the lowest cell temperature value reported by the BMS. State of charge (SOC) is used to confirm whether the battery has sufficient energy to support the heating process: when the SOC is too low, even heating will not provide enough driving range, and the VCU will not allow it to enter heating mode. Ohmic internal resistance, polarization internal resistance, cell voltage, and real-time discharge current are necessary input data for subsequent polarization assessment. The internal resistance parameter is estimated in real-time by the BMS using an online identification algorithm (usually based on an equivalent circuit model, such as the Thevenin model or DP model, obtained online through Kalman filtering or least squares method). The cell voltage is collected by the BMS through a voltage sampling circuit (AFE chip, Analog Front End) and reported. This step provides the data foundation for all subsequent control decisions, solving the problem of the VCU lacking information on the battery's current temperature, remaining capacity, and discharge capacity.

[0026] S102. When the extreme low temperature start-up conditions are met according to the vehicle status parameters and the initial temperature of the battery cell, the graded heating initial power is generated according to the initial temperature of the battery cell, and the electric heater is controlled to start heating with the initial power.

[0027] The VCU first makes a comprehensive judgment based on the vehicle status parameters obtained in step S101 (including but not limited to gear position signal, charging gun connection status signal, high voltage power-on status signal, etc., which are obtained from nodes such as the gear position controller, charging controller, and high voltage power distribution unit via hardwire or CAN bus) and the initial temperature of the battery cells. The specific extreme low-temperature start-up conditions include (as shown in Table 1): Table 1. Policy Enabling Conditions

[0028] The trigger conditions for entering the cryogenic strategy are: conditions 1, 3, 4, and 5 must all be met simultaneously (i.e., 1&&3&&4&&5); the trigger conditions for entering the cryogenic heating strategy are: conditions 1, 2, 3, 4, and 5 must all be met simultaneously (i.e., 1&&2&&3&&4&&5). The judgment logic for the above conditions is implemented by the state machine module inside the VCU. The VCU reads the flag bits corresponding to each condition at a fixed period (e.g., 10ms, which can be calibrated). When all flag bits are set, the state machine switches from the idle state to the cryogenic mode state.

[0029] If conditions 1, 3, 4, and 5 are met, but condition 2 is not met, the vehicle enters the extreme low temperature mode but not the extreme low temperature heating mode. In this case, if the gear is in Park (P), shifting out of Park is prohibited. The VCU outputs an extreme low temperature mode flag signal and sends it to the instrument cluster controller via the CAN bus to alert the driver. If condition 1 is not met, the vehicle does not enter the extreme low temperature mode, and the VCU maintains its normal energy management strategy. When the extreme low temperature heating strategy conditions are met, the VCU enters the extreme low temperature heating mode. If the gear is in Park (P), shifting out of Park is prohibited (this restriction is achieved by the VCU sending a command to the Transmission Control Unit (TCU) to prohibit shifting out of Park). The VCU also queries the battery performance table based on the initial cell temperature to obtain the initial heating duration, which is then sent to the instrument cluster controller via the CAN bus for a countdown display, allowing the driver to know the remaining heating time.

[0030] Upon entering the extreme low-temperature heating mode, the VCU executes a staged heating strategy. The physical basis of staged heating lies in the quantitative relationship between the battery pack's equivalent heat capacity and the power required to raise the temperature, i.e., the net heating power provided by the PTC. Subtracting heat loss from the battery pack to the environment This is equal to the equivalent heat capacity of the battery pack. With total mass The product multiplied by the cell temperature rise rate ,Right now:

[0031] in, The heating power provided by the PTC to the battery pack, in W; The power loss due to heat dissipation from the battery pack to the surrounding environment is expressed in watts (W). This loss is related to the temperature difference between the battery pack and the environment, the heat dissipation area of ​​the battery pack casing, and the heat dissipation coefficient. It is the equivalent specific heat capacity of the battery pack, measured in J / (kg·K). It is determined by the combination of the cell, module structure and heat transfer medium, and is usually taken as 800~1200 J / (kg·K). This refers to the total mass of the battery pack, in kg. The cell temperature rise rate is expressed in K / s. This formula reveals the quantitative relationship between heating power and temperature rise rate, and is the theoretical basis for determining staged heating power and PID closed-loop control.

[0032] Based on the above thermodynamic relationship, the VCU determines the initial temperature of the battery cell. The initial heating power is determined by a temperature level weighting function. This invention maps the extreme low-temperature range (-30℃ to -40℃) into a continuous power curve. Unlike existing technologies that use discrete temperature ranges corresponding to fixed power levels (e.g., -40℃ to -37℃ corresponds to one power level, and -37℃ to -34℃ corresponds to another power level), this invention uses a continuous function mapping, allowing the power to change smoothly with temperature and avoiding power jumps at the boundaries of the temperature range. The specific formula for determining the initial heating power is as follows:

[0033] in, The rated maximum heating power of the PTC is expressed in W. This value is an inherent parameter of the PTC heater and is provided by the PTC manufacturer. The VCU obtains this value through an internally stored calibration parameter table. The lower limit of the extreme low temperature is set at -40℃. This value is determined based on the physical characteristics of lithium iron phosphate or ternary lithium batteries, where the electrolyte almost completely solidifies and lithium ion migration basically stops below -40℃. The target exit temperature is set to -30℃. This value is the minimum temperature threshold for normal charging and discharging of the battery provided by the battery manufacturer. When the cell temperature is higher than this value, the BMS releases the discharge restriction, and the vehicle can run normally. This is the power regulation depth coefficient, with a value ranging from 0.5 to 0.9. The larger the value, the more significant the power increase in the low-temperature zone, which is used to adjust the variation of heating power in different temperature ranges; This is a non-linear index for temperature levels, with a value ranging from 1.0 to 3.0. When =1, there is a linear relationship. When the value is greater than 1, the power weight in the low-temperature region is larger, used to characterize the nonlinear characteristics of heating demand in the low-temperature region—the lower the temperature, the more drastic the increase in battery internal resistance, and the required heating power growth rate should be higher than the linear growth rate of temperature; the initial power decreases smoothly as the initial temperature of the cell increases. For example, when... =0.7、 When the value is 1.5, -40℃ corresponds to 100% rated power, -35℃ corresponds to approximately 65% ​​rated power, and -30℃ corresponds to approximately 30% rated power. The above parameters... , All can be flexibly configured through calibration to adapt to the thermal characteristics of different battery packs (different electrochemical systems, different module structures, and different thermal management designs correspond to different optimal configurations). and value).

[0034] This method for determining the initial power of graded heating maps discrete temperature levels to a continuous power curve, enabling a smooth transition of heating power with temperature. This avoids the impact of segmented power jumps on the system (power jumps can cause sudden current changes, leading to DC bus voltage fluctuations, and in severe cases, triggering the BMS overcurrent protection or causing high-voltage relays to stick). It solves the technical problems of insufficient heating in low-temperature zones (fixed low power heating at -40℃ results in excessively long temperature rise times or even failure to heat up) and energy waste in high-temperature zones (high power heating is still used at -31℃, and excess heat generated by the PTC is dissipated into the environment through the battery pack casing, resulting in low energy utilization efficiency) caused by the "one-size-fits-all" fixed power heating in existing technologies. It achieves precise matching between heating power and the actual coldness of the battery, improving energy utilization efficiency.

[0035] The initial heating power calculation result is directly used as the reference value for the PTC heating power command in pure electric vehicles; in range-extended vehicles, this initial power also serves as an important reference for the range extender's power generation requirements. The VCU adds the initial power value to the power requirements of other high-voltage accessories (DC-CDC, air conditioning, etc.), and the sum is used as the target power generation of the range extender. This is then sent to the range extender controller (including EMS—Engine Management System and GCU—Generator Control Unit) via the CAN bus.

[0036] For range-extended electric vehicles, under extreme low-temperature start-up conditions, the VCU first starts the range extender to generate electricity through battery pulse discharge. The range extender then provides the heating power required by the electric heater, rather than the battery pack directly discharging a large current to power the PTC. The range extender start-up process is as follows: The VCU sends a start command to the EMS via the CAN bus. The EMS controls the starter motor to drive the engine crankshaft to rotate, and simultaneously sends control signals to the fuel injectors and ignition coils to start the engine. After the engine starts, it drives the generator under the control of the GCU to rotate and generate electricity. During this process, the energy required for the range extender to start is provided by the power battery pack through pulse discharge. Pulse discharge refers to the BMS outputting a pulse discharge every 100ms for 50ms, with a current of... The discharge pulse (the pulse width and amplitude of which can be calibrated) intermittently supplies power to the starter motor. Compared to continuous high-current discharge, pulse discharge can provide sufficient starting energy without triggering low-temperature overcurrent protection. The VCU monitors the status signals fed back by the EMS and GCU in real time (including engine speed signal, generator output voltage signal, fault level signal, etc.). If the range extender fails to start successfully (for example, the engine speed fails to reach idle speed within a preset time, or the EMS feeds back a start failure fault code), it exits the extreme low-temperature mode and reports a range extender start fault. After the range extender starts successfully, after a preset delay (e.g., 10 seconds, calibrable, this delay is to wait for the engine to stabilize and the generator output voltage to establish and reach the rated value), the VCU limits the thermal management power to the initial power of the aforementioned graded heating. (Replacing the original fixed power of 4kW, in existing technology, range-extended vehicles typically have a fixed PTC power of 4kW during heating in extremely cold weather, without considering the differences in heating requirements at different temperatures). After the range extender starts up and before the delay period ends, the VCU limits the thermal management power to 0, that is, it disables the PTC, to ensure that the power generated during the start-up and initial power generation of the range extender is used entirely for its own stable operation.

[0037] If the range extender stops due to a fault after starting (e.g., engine misfire, generator overheating, EMS fault level > 3 or GCU fault level > 3), the VCU will detect the corresponding fault flag, execute the exit from extreme low temperature mode procedure, and report the corresponding fault code to the diagnostic system.

[0038] S103. During the heating process, the real-time temperature of the battery cell is obtained and the actual temperature rise rate is calculated. The heating power adjustment amount is obtained by performing PID closed-loop calculation based on the deviation between the preset target temperature rise rate and the actual temperature rise rate. The real-time heating power is generated based on the initial power and the adjustment amount, and the heating power of the electric heater is dynamically adjusted.

[0039] After PTC is enabled, the system determines the initial power according to the staged heating strategy. Initiate battery pack heating. During heating, the VCU continuously acquires the real-time cell temperature through the BMS and calculates the actual temperature rise rate based on the aforementioned formula relating the battery pack's equivalent heat capacity to the power-temperature-rise relationship. Specifically, the VCU operates on a sampling cycle. (Typically 1 second, calibrable) Read the lowest cell temperature once. Through difference calculation The actual temperature rise rate within this cycle is obtained. Simultaneously, the VCU has a preset target temperature rise rate (e.g., 2℃ / min, or 0.033K / s). This target value is set after comprehensively balancing heating efficiency and battery safety: if the target value is too high, it can easily lead to the PTC operating at full power for an extended period, causing overload in the heating circuit. Furthermore, excessively rapid temperature rise will increase the internal temperature gradient of the cell, generating thermal stress and accelerating cell aging; if the target value is too low, the heating time will be too long, affecting the user experience.

[0040] The VCU uses the target temperature rise rate as the control objective and takes the difference between the target temperature rise rate and the actual temperature rise rate as the deviation value. ,Right now The unit is K / s. The deviation value is calculated by performing proportional, integral, and differential operations respectively, and then summed to obtain the heating power adjustment amount. The PID closed-loop control output formula is:

[0041] in, This is a proportional gain, measured in W / (K / s), typically ranging from 50 to 200. It is used to generate a proportional adjustment based on the current deviation; the larger the deviation, the larger the adjustment range. Its main function is to achieve rapid response. Excessive temperature can easily cause system oscillations, that is, after temperature overshoot, repeated adjustments occur, resulting in constant amplitude oscillations or divergent oscillations. This is the integral coefficient, measured in W / (K·s), with a typical value range of 5~30. It is used to generate the integral adjustment quantity based on the historical accumulation of the deviation. If the system has a long-term steady-state deviation (e.g., a persistently low rate of temperature rise, usually caused by deteriorating environmental heat dissipation conditions, PTC aging leading to a decrease in actual output power, etc.), the integral term will continue to accumulate to eliminate this deviation. Its main function is to eliminate steady-state error; however... Excessive power can easily lead to integral saturation, meaning the output power reaches... The integral term continues to accumulate, and it takes a long time for the deviation to exit the saturation region after it reverses, which in turn causes system overshoot and response lag. This is the differential coefficient, measured in W·s / K, with a typical value range of 10~50. It is used to generate a differential adjustment amount based on the trend of deviation changes. If the temperature rise rate deviates rapidly from the target (with a large deviation slope), the differential term will adjust in the opposite direction in advance to suppress overshoot, mainly improving system stability; however, Excessive values ​​can amplify measurement noise; that is, high-frequency noise in the temperature sampling signal is amplified through differentiation, leading to frequent fluctuations in the PTC power command. The above three coefficients... , , All can be flexibly configured through calibration to adapt to the thermal characteristics of different battery packs (including equivalent specific heat capacity, total mass, heat dissipation conditions, etc.). Those skilled in the art can determine the optimal PID parameters for a specific vehicle model through step response experiments combined with the Ziegler-Nichols engineering tuning method.

[0042] Actual output PTC heating power It is the sum of the initial power and the heating power adjustment, that is:

[0043] Actual output power is limited by Interval: where This is the minimum heating power of the PTC. If the PTC's operating power is lower than this value, it may not be able to work stably or its heating efficiency may be too low. This is the rated maximum heating power of the PTC. Exceeding this value may cause the PTC to overheat and be damaged, or trigger high-pressure overcurrent protection. When the actual temperature rise rate is lower than the target temperature rise rate (…), The PID controller outputs a positive adjustment, increasing the heating power and improving the temperature rise rate; when the actual temperature rise rate is higher than the target temperature rise rate ( The system outputs a negative adjustment value to reduce heating power and prevent temperature overshoot. The actual temperature rise rate calculation and PID control are performed once per control cycle of the VCU (typically 10ms~100ms) to ensure real-time control. This step achieves smooth regulation of the temperature rise process through closed-loop feedback, ensuring a stable increase in cell temperature and preventing temperature overshoot or insufficient heating.

[0044] For range-extended electric vehicles, the VCU also implements the aforementioned PID closed-loop temperature control. Based on the deviation e(t) between the actual and target temperature rise rates of the battery cells, it dynamically adjusts the PTC heating power demand according to the PID closed-loop control output formula, and the range extender's power generation is adjusted accordingly. Specifically, the VCU sends the calculated PTC power demand (including the sum of the initial power for staged heating and the PID adjustment) to the GCU via the CAN bus. The GCU then controls the generator to adjust the excitation current and speed, changing the power output to match the real-time power demand of the PTC. (PID controller parameters...) , , Independent calibration is possible for range-extended vehicles: Since the PTC power in range-extended vehicles comes from the range extender's generator, rather than the direct discharge from the battery in pure electric vehicles, the power response characteristics of the range extender (typically with a response time on the order of 200ms) differ from the power response characteristics of the direct discharge from the battery in pure electric vehicles (with a response time on the order of milliseconds). Therefore, the PID parameters for range-extended vehicles need to be readjusted to accommodate the slower response characteristics of the generator system; for example, the PID parameters can be appropriately reduced. This is to avoid frequent fluctuations in the range extender's power, which could lead to unstable engine operating conditions.

[0045] S104. During the heating process, the degree of battery polarization is comprehensively evaluated based on the ohmic internal resistance, the polarization internal resistance, the cell voltage, and the discharge current, and a comprehensive polarization index is generated.

[0046] During the heating process, the battery needs to continuously discharge to power the PTC. In pure electric vehicles, the battery discharges directly, while in range-extended vehicles, the battery also needs to output some power during the range extender startup and power-following transition phases. Due to the low-temperature environment, the migration rate of lithium ions inside the battery decreases. If the discharge current is too large, lithium ions will accumulate in large quantities on the negative electrode surface, resulting in a "polarization" phenomenon. Specifically, polarization refers to the phenomenon where the electrode potential deviates from the equilibrium potential when current passes through the battery. Its physical nature includes ohmic polarization (caused by the resistance of the conductive path inside the battery, resulting in an ohmic voltage drop when current passes through), electrochemical polarization (caused by the limitation of the electrode reaction rate, where the rate of lithium ion insertion / extraction from the electrode material cannot keep up with the current demand), and concentration polarization (caused by the lithium ion concentration gradient in the electrolyte). Electrochemical polarization and concentration polarization are reversible polarizations, recovering spontaneously after current removal. However, severe electrochemical polarization can cause lithium ions to precipitate as metallic lithium on the negative electrode surface, forming lithium dendrites. This process is irreversible and will cause permanent capacity decay. In severe cases, lithium dendrites may penetrate the separator, causing an internal short circuit and ultimately inducing thermal runaway. To address this, the VCU simultaneously activates the battery polarization state monitoring function during the heating process to monitor the degree of battery polarization in real time.

[0047] Specifically, the VCU obtains the ohmic internal resistance of the battery pack in real time through the BMS. Polarization internal resistance Minimum cell voltage Average voltage of all cells and real-time discharge current Parameters such as internal resistance in ohms. The unit is mΩ, reflecting the total resistance of the internal conductive path of the battery. It encompasses the sum of electrode material resistance, electrolyte resistance, separator resistance, current collector resistance, and contact resistance. It is obtained online by the BMS using the HPPC (Hybrid Pulse Power Characterization) method: the BMS applies a short-duration pulse current (typically a 1C discharge pulse lasting 10s, followed by a 40s rest period) at a specific SOC and temperature point, collects the voltage change before and after the pulse, and applies Ohm's law... The instantaneous ohmic resistance and polarization resistance were calculated. The unit is mΩ, determined by the BMS through a battery equivalent circuit model (usually a first-order or second-order RC model, where the time constant of the RC network is...). , The polarization resistance and polarization capacitance of the two RC networks are obtained through online identification (for double-layer capacitance). Taking a second-order RC model as an example, the BMS estimates the polarization resistance and polarization capacitance of the two RC networks in real time using a Kalman filter algorithm (Extended Kalman Filter EKF or Unscented Kalman Filter UKF), and uses the sum of the two polarization resistances as the polarization internal resistance. Output; Minimum cell voltage and the average voltage of all cells Both units are in volts (V). The deviation between them reflects the consistency between battery cells: the larger the deviation, the more severe the voltage drop of individual "weak cells" at low temperatures, and the more likely that cell will be the first to enter the over-discharge risk zone; real-time discharge current. The unit is ampere (A), acquired by the BMS via a Hall current sensor or shunt, reflecting the current discharge load. The VCU also acquires the following parameters: ambient temperature reference ohmic internal resistance. (Reference value at 25℃, unit is mΩ, obtained by the battery manufacturer through HPPC testing and calibration before leaving the factory), reference polarization internal resistance at room temperature. (Unit is mΩ, also specified by the battery manufacturer), rated cell voltage (Unit: V), and the maximum allowable discharge current of the battery obtained by querying a two-dimensional table from the BMS based on the current state of charge and temperature. (Unit: A) This two-dimensional table has SOC on the horizontal axis and temperature on the vertical axis. The data in the table are the maximum allowable discharge current corresponding to each SOC and temperature point, measured through numerous experiments. The BMS packages the above parameters into data frames and sends them to the VCU via the CAN bus in a periodic manner (usually a 100ms period).

[0048] The VCU inputs the above parameters into the comprehensive polarization evaluation model to calculate the comprehensive polarization index of the current battery. This indicator comprehensively considers four dimensions: ohmic polarization, electrochemical polarization, cell inconsistency, and discharge current margin, and is determined by the following formula:

[0049] In the formula, It is a comprehensive index of battery polarization, dimensionless, and its value range is usually 0~10. The larger the value, the more severe the polarization. For real-time ohmic internal resistance, The internal resistance is the reference ohm at room temperature; For real-time polarization internal resistance, The reference polarization internal resistance at room temperature; This is the lowest cell voltage in the battery pack. This represents the average voltage of all cells in the battery pack. This is the rated voltage of the battery cell; This refers to the real-time discharge current of the battery pack. The maximum allowable discharge current for the battery at the current SOC and temperature; , , , Let be the weight coefficients of each factor, satisfying Typical values ​​are 0.30, 0.35, 0.20, and 0.15.

[0050] The weighting coefficients are determined based on the following: polarization resistance ratio. It is the most direct indicator of electrochemical polarization, reflecting the degree of resistance to the lithium-ion insertion / extraction process in the electrode material. Among all polarization types, it has the greatest impact on battery life, therefore it is assigned the highest weight of 0.35; Ohmic internal resistance ratio. Reflecting changes in resistance along the conductive path, it is significantly affected by temperature but the changes are relatively stable, and is assigned a weight of 0.30; the absolute value of the voltage deviation term... This reflects the degree of cell consistency degradation, and its impact gradually increases in the later stages of battery aging, so it is assigned a weight of 0.20; the discharge current margin term... Reflecting the urgency of the current discharge load, this is a dynamic tracking indicator, assigned a weight of 0.15. The above weighting coefficient can be calibrated and adjusted according to different battery types (lithium iron phosphate vs. ternary lithium). For example, lithium iron phosphate batteries have a flatter voltage plateau, and voltage deviation contributes relatively less to polarization, so the weighting can be appropriately reduced. And improve and .

[0051] This step enables the quantification and multi-dimensional real-time assessment of polarization, providing a quantitative basis for subsequent dynamic current limiting and solving the problem that existing technologies cannot know the polarization of the battery under the current operating conditions in real time: In existing technologies, the VCU can only obtain a single protection trigger signal reported by the BMS (such as a binary signal of "discharge prohibited" or "discharge permitted"), and cannot know whether the battery is in an intermediate state between "healthy" and "discharge prohibited". Therefore, it is impossible to implement proactive derating protection during the heating process, and can only wait for the BMS to trigger the protection and then respond passively. At this time, the battery may have already suffered a certain degree of damage.

[0052] Additional notes for range-extended electric vehicles: For range-extended electric vehicles, the VCU also simultaneously activates the battery polarization state monitoring function. Based on the aforementioned comprehensive polarization assessment formula, it calculates a comprehensive polarization index in real time, which is used for subsequent dynamic discharge current limit calculations and adjustment of the range extender's power-following strategy response parameters. When the polarization level is high, the VCU not only limits the battery's discharge current but also increases the power generation capacity through the range extender's emergency power adjustment command, further reducing the battery's discharge burden.

[0053] S105. Based on the comprehensive polarization index, the state of charge, and the real-time temperature of the cell, perform dynamic discharge current limit calculation to generate the maximum allowable discharge current limit for the current battery.

[0054] After obtaining the comprehensive polarization index, the VCU will not directly shut off the discharge in a "one-size-fits-all" manner when the index exceeds the limit (i.e., it will use a step-down derating method, such as instantaneously reducing the current limit when the polarization index exceeds the threshold). A sudden jump to 0 would cause the PTC heating power to instantly drop to zero, resulting in a rapid drop in cell temperature. Furthermore, this current jump would cause severe fluctuations in the DC bus voltage, potentially triggering undervoltage protection in other loads within the high-voltage system (such as the drive motor controller and DC-DC converter), leading to a cascading system failure. Instead, a sigmoid smoothing current-limiting curve is used to map the polarization level to a continuously changing current limit, dynamically adjusting the maximum allowable discharge current limit of the battery pack. Determine using the following formula:

[0055] in, This represents the maximum allowable discharge current limit of the battery at the current moment, in amperes (A). This refers to the battery's rated maximum discharge current at room temperature, expressed in amperes (A). It is determined by the battery manufacturer based on the cell's rated capacity and maximum discharge rate (e.g., if the cell's rated capacity is 100Ah and the maximum continuous discharge rate is 2C, then...). ; The minimum discharge current limit for battery protection is expressed in amperes (A), typically 5-10A, to ensure the minimum power supply requirements of necessary loads such as the PTC (if the current limit drops to 0, the PTC will be completely de-energized, heating will stop, and the battery temperature may drop further due to the low ambient temperature, making it more difficult to start up later). This is a dimensionless comprehensive index of the polarization degree at the current moment. The polarization threshold is the midpoint of the polarization threshold, i.e., the inflection point of the Sigmoid curve, corresponding to a comprehensive polarization index value. A typical value ranges from 2.0 to 4.0. This value is determined based on experimental data of the battery's tolerance to polarization—through cycle life tests on the same cell at different polarization levels (e.g., at different polarization conditions). (During continuous discharge at the maximum permissible current, the capacity decay curve was recorded.) The point at which the capacity decay rate began to accelerate significantly (e.g., decay exceeding 5% per 100 cycles) was recorded. Value as k is the sigmoid curve steepness coefficient, dimensionless, ranging from 1.0 to 5.0. A larger k results in a steeper current-limiting curve—when k approaches 1.0, the current-limiting change is gradual, with a wide range of polarization, suitable for battery systems sensitive to sudden current changes; when k approaches 5.0, the current-limiting change is rapid, within a wide range of polarization. The system quickly transitions from full capacity to minimum limit, adapting to protection scenarios requiring rapid response. The k-value, determined through offline simulation and real-vehicle calibration, is used to adjust the steepness of the current limiting curve as the comprehensive index of polarization changes.

[0056] This Sigmoid smooth current limiting model replaces the traditional piecewise derating with a continuously smooth current limiting curve. Its working principle is as follows: when the polarization is low... Sigmoid term Approaching 0, limit value near .in, (As a bias term, ensuring the limit is always positive), it allows for high-current heating to achieve rapid temperature rise; as the polarization gradually increases to exceed the midpoint of the threshold... At that time, the Sigmoid term rapidly transitions from 0 to 1, and the limit value begins to change from... Towards Smooth descent; when polarization is severely excessive The Sigmoid term approaches 1, and the limit value drops rapidly. Nearby. This smooth current limiting method avoids the impact of traditional segmented derating on the system and battery caused by current surges (current surges generate...). Voltage spikes will be induced in the battery's internal resistance and the circuit inductance. This could lead to false triggering of the BMS overvoltage protection or damage to power devices.

[0057] Furthermore, this embodiment also sets up a three-level protection mechanism based on polarization degree: when Exceeding the preset first threshold (For example, at 2.5), the VCU initiates current-limiting intervention, reducing the maximum discharge current limit. This first threshold is set based on the inflection point where battery polarization begins to significantly affect discharge efficiency—experiments show that when… When the polarization is below 2.5, the effect of polarization on discharge efficiency is less than 5%; when Beyond 2.5, the discharge efficiency decreases more rapidly with increasing polarization.

[0058] when Exceeding the preset second threshold (For example, at 4.0), the current limiting curve enters the steep drop region, further reducing the maximum discharge current limit to near the lower limit of the minimum discharge current for battery protection. At this time, the Sigmoid function The term increases, causing the exponential term in the denominator to... Approaching 0, Approaching The heating power is significantly reduced and the temperature rise rate is significantly slowed down to prioritize battery safety.

[0059] when Exceeding the preset third threshold (For example, at 6.0), it indicates that battery polarization has approached a dangerous level, and the risk of lithium ion deposition on the negative electrode surface has reached an unacceptable level. The VCU immediately suspends heating and reports a fault (sending a fault code DTC to the diagnostic system via the CAN bus, and simultaneously illuminating the malfunction indicator light on the instrument panel), requesting driver intervention or automatically exiting the heating mode. The above three threshold levels... The specific values ​​are determined based on the cell polarization tolerance curve provided by the battery manufacturer. The threshold values ​​differ for different electrochemical systems (lithium iron phosphate vs. ternary lithium) and can be precisely adjusted through bench calibration experiments.

[0060] This three-level protection mechanism solves the drawbacks of single threshold protection, which either intervenes too early (affecting heating efficiency—if the threshold is set too low, the derating will be significantly reduced before polarization poses a real threat to the battery, resulting in an unnecessary extension of heating time) or intervenes too late (damaging battery life—if the threshold is set too high, action will be taken only when polarization is already severe, and the battery may have already suffered irreversible lithium plating damage). It achieves a progressive safety guarantee of "early warning → moderate intervention → mandatory protection".

[0061] (Supplementary Notes for Range-Extended Vehicles) For range-extended electric vehicles, the VCU also dynamically adjusts the maximum allowable charge and discharge current limit of the battery pack according to the dynamic limit formula for discharge current. This protects the battery from damage during low-temperature heating. Simultaneously, the VCU sets a safety window for the battery pack's charge and discharge current. (e.g., ±5A, calibrable) When the actual charging and discharging current of the battery pack exceeds this safety window, the range extender's emergency power adjustment is triggered—the VCU sends an emergency power adjustment command to the GCU via the CAN bus (this command contains the target power generation increment). Its value is equal to the current deviation exceeding the safety window multiplied by the battery pack terminal voltage. Divide by power generation efficiency ,Right now This allows the range extender to respond quickly to adjust its power output, ensuring that the battery pack's charging and discharging current returns to within a safe window. The response time requirement for this safe window is: from detecting current exceeding the window to the range extender adjusting its power to the desired level, the total response time should not exceed 200ms (approximately 20ms for detection and calculation, 20ms for CAN bus communication, and 160ms for GCU and EMS execution), ensuring real-time power balancing and battery safety.

[0062] S106. The heating power upper limit is constrained according to the maximum discharge current limit, and the output of the real-time heating power is constrained by the upper limit value.

[0063] The VCU converts the current limit generated in step S105 into a heating power limit. Specifically, this is based on the battery pack's terminal voltage. (Unit: V, collected and reported in real time by BMS, this value changes dynamically with SOC and discharge current—due to internal resistance voltage drop during high current discharge.) (Terminal voltage will decrease) Maximum discharge current limit and the heating efficiency of the electric heater (Typically 0.90~0.98, this efficiency is the electrothermal conversion efficiency of the PTC heater, that is, the ratio of input electrical energy to heat energy. Some heat is lost to the environment through the PTC casing, so the actual heat power used to heat the battery pack is less than the input electrical power.) Calculate the upper limit of the heating power at the current moment. Determine using the following formula:

[0064] VCU will heat power in real time Constrained within the upper limit of this heating power, i.e. Specifically, within each control cycle, the VCU's PID temperature control module first calculates the PID power demand based on the temperature rise rate deviation. Then, upper limit constraints are applied: Final output This serves as the actual power command for the PTC driver module. This constraint ensures that at any given time, the discharge current corresponding to the actual power consumed by the PTC is... None of them will exceed the maximum value allowed by the BMS in the current battery state. When the current limit is lowered due to increased polarization, the upper limit of heating power also decreases. If the real-time power demand calculated by the PID temperature control module exceeds this upper limit, the actual output is limited to the upper limit, and the temperature rise rate will temporarily decrease. When the discharge current limit decreases, causing the heating power to be unable to maintain the target temperature rise rate, the VCU prioritizes battery safety and accepts a lower temperature rise rate. If the actual value is lower than the preset target value, the VCU will re-estimate the remaining heating time based on the formula relating the battery pack's equivalent heat capacity to the temperature rise power. Specifically, the VCU will adjust the heating time according to the current actual temperature rise rate. Residual temperature rise Recalculate remaining time The updated remaining heating time is then sent to the instrument controller via the CAN bus to update the displayed value, so that the driver can obtain the accurate remaining waiting time.

[0065] This step, as the final "safety valve" of the entire control logic, ultimately implements the results of "polarization monitoring" and "dynamic current limiting" at the power execution level, thus establishing a hard safety boundary between heating power regulation and battery protection.

[0066] In addition, during the heating process, the VCU exits the extreme low temperature start-up mode when the preset exit conditions are met. Specifically, for pure electric vehicles, the preset exit conditions include at least one of the following: the lowest cell temperature is higher than the target exit temperature (-30℃) and remains so for a preset duration (e.g., 10s – using a duration-based confirmation mechanism rather than exiting immediately upon overheating avoids frequent mode switching caused by temperature sampling noise or instantaneous temperature fluctuations, improving system stability); electric heater malfunction (e.g., PTC drive module feedback of overcurrent or overtemperature fault, and the fault lasting for 1s confirms that the fault is not caused by instantaneous interference); entering AC / DC charging state, or detecting the insertion of the charging gun or discharging gun during the pre-charging heating stage (the charging pile itself usually has a heating function during charging, or the BMS will execute a dedicated charging heating strategy; to avoid conflicts between the two heating logics, the VCU actively exits); battery pack heating countdown reaches zero (this condition is set to avoid infinite heating: if the cell temperature is still below -30℃ after the heating countdown reaches zero, it indicates that the battery may be abnormal, such as insufficient actual usable energy due to SOC estimation deviation, or decreased PTC heating capacity; in this case, heating exits and prompts the driver to check); high voltage power-off (the entire vehicle is shut down, and all high voltage loads are disconnected). After exiting the extreme low-temperature start-up mode, the vehicle distributes power according to the VCU's normal energy management strategy, with the energy source being the battery's discharge capacity. The VCU removes the restriction that prevents the driver from exiting the P gear while the vehicle is parked, allowing the driver to engage gear and drive. It also outputs a non-extreme low-temperature mode signal to the instrument controller, updating the instrument display. If the heating process stops but the minimum cell temperature is still below -30°C (e.g., due to a PTC malfunction causing the heating to stop), the VCU sends a non-extreme low-temperature heating mode signal (indicating that the vehicle is no longer in a heating state but the cell temperature has not yet reached the target, reminding the driver that the temperature is not up to standard and not to drive forcibly).

[0067] For range-extended electric vehicles, the preset exit conditions, in addition to the above, include engine shutdown (EMS reports engine speed as 0 and not in the starting process) and range extender malfunction (EMS fault level > 3 or GCU fault level > 3, where the fault level is a severity classification defined internally by the controller: 0 for no fault, 1-2 for minor faults that can be downgraded, 3 for moderate faults requiring power limitation, and 4-5 for severe faults requiring immediate shutdown). After exiting, the vehicle distributes power according to the VCU's normal energy management strategy (energy source is the sum of battery discharge capacity and range extender power generation); the VCU removes the restriction prohibiting exiting P gear while in P gear parking mode; and outputs a non-extreme low temperature mode signal. If the heating process stops but the minimum cell temperature is still below -30°C, the VCU sends a non-extreme low temperature heating mode signal.

[0068] For range-extended vehicles, the VCU also controls the range extender to perform on-demand power generation in extreme low-temperature heating mode. The power generation demand is the power consumed by the high-voltage accessories (real-time power of DC-DC converter + real-time power of PTC converter). The power generation is required to follow the power changes of the high-voltage accessories in real time, and the power fluctuation response must be completed within 200ms to achieve power balance. Specifically, the VCU collects the output power of DC-DC converter (obtained from DC-DC controller via CAN bus) and the real-time power of PTC converter (calculated from the current and voltage values ​​fed back by PTC drive module) in real time, and uses the sum of the two as the target power generation. Send to GCU; GCU controls generator output Power. At the power balance level, the battery pack only bears the difference in power charging and discharging when the high-voltage accessory power fluctuates and the range extender cannot keep up in time. Specifically, when the PTC power or DC-DC power changes instantaneously (e.g., a sudden change in power command due to PTC PID regulation), the range extender, limited by mechanical inertia (the engine's flywheel has a large moment of inertia, and speed adjustment takes time), cannot instantly follow the power change. In this case, the battery pack will briefly output or absorb the difference in power, acting as a power buffer. Once the range extender completes power adjustment, the battery pack returns to a near-zero current float charging state. This strategy significantly reduces the discharge load on the battery pack during extreme cold starts in range-extended vehicles, reducing the total PTC power (potentially as high as 5-10 kW) that the battery pack must bear in pure electric mode to only bearing the power fluctuation difference (usually within a few hundred watts), effectively protecting battery life.

[0069] Example 2 like Figure 2 This embodiment provides a start-up control system for extreme low temperature environments, including: The parameter acquisition module is used to acquire vehicle status parameters and power battery pack status parameters; the status parameters include at least the initial temperature of the cell, the real-time temperature of the cell, the state of charge, the ohmic internal resistance, the polarization internal resistance, the cell voltage, and the real-time discharge current. The start-up control module is used to generate a graded heating initial power based on the initial temperature of the battery cell when the extreme low-temperature start-up conditions are met according to the vehicle status parameters and the initial temperature of the battery cell, and control the electric heater to start heating with the initial power. The PID temperature control module is used to acquire the real-time temperature of the battery cell and calculate the actual temperature rise rate during the heating process. It performs PID closed-loop calculation based on the deviation between the preset target temperature rise rate and the actual temperature rise rate to obtain the heating power adjustment amount. It generates real-time heating power based on the initial power and the adjustment amount, and controls the electric heater to dynamically adjust the heating power. The polarization evaluation module is used to comprehensively evaluate the degree of polarization during the heating process based on the ohmic internal resistance, the polarization internal resistance, the cell voltage and the discharge current, and generate a comprehensive polarization index. The current limiting module is used to perform dynamic discharge current limit calculation based on the comprehensive polarization index, the state of charge and the real-time temperature of the cell, and generate the maximum allowable discharge current limit of the current battery. A power constraint module is used to constrain the upper limit of heating power based on the maximum discharge current limit, and to constrain the output of real-time heating power with the upper limit value.

[0070] Example 3 Embodiment 3 of the present invention provides a new energy vehicle, including a vehicle controller (VCU), a battery management system (BMS), a power heater (PTC), and a power battery pack. The vehicle controller is communicatively connected to the battery management system and the power heater, respectively. The vehicle controller is configured to execute the extreme low temperature environment start-up control method as described in Embodiment 1.

[0071] This new energy vehicle, through the coordinated operation of the VCU, BMS, and PTC, achieves a complete control chain under extreme low-temperature conditions, including graded heating start-up, PID closed-loop temperature control, real-time monitoring of battery polarization state, smooth discharge current limiting, and coordinated constraint of heating power. It possesses the ability to start safely in extreme low-temperature environments ranging from -30℃ to -40℃. This vehicle can be a pure electric vehicle or a range-extended electric vehicle.

[0072] The above description is merely a preferred embodiment of this practice and is not intended to limit the scope of this practice. Various modifications and variations can be made to this practice by those skilled in the art. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of this practice should be included within the protection scope of this practice.

Claims

1. A start-up control method for extreme low-temperature environments, characterized in that, include: Obtain vehicle status parameters and power battery pack status parameters; the status parameters include at least the initial cell temperature, real-time cell temperature, state of charge, ohmic internal resistance, polarization internal resistance, cell voltage, and real-time discharge current; When the extreme low-temperature start-up conditions are met based on the vehicle status parameters and the initial temperature of the battery cell, the graded heating initial power is generated based on the initial temperature of the battery cell, and the electric heater is controlled to start heating with the initial power. During the heating process, the real-time temperature of the battery cell is acquired and the actual temperature rise rate is calculated. The heating power adjustment amount is obtained by performing PID closed-loop calculation based on the deviation between the preset target temperature rise rate and the actual temperature rise rate. The real-time heating power is generated based on the initial power and the adjustment amount, and the heating power of the electric heater is dynamically adjusted. During the heating process, the degree of battery polarization is comprehensively evaluated based on the ohmic internal resistance, the polarization internal resistance, the cell voltage, and the discharge current, and a comprehensive polarization index is generated. Based on the comprehensive polarization index, the state of charge and the real-time temperature of the cell, the dynamic limit of the discharge current is calculated to generate the maximum allowable discharge current limit of the current battery. The heating power is constrained by the maximum discharge current limit, and the output of the real-time heating power is constrained by the upper limit value.

2. The method according to claim 1, characterized in that, The initial power for graded heating is generated based on the initial temperature of the battery cell, specifically including: The initial power is calculated based on the initial temperature of the battery cell, the preset lower limit of extreme low temperature, the preset target exit temperature, the rated maximum power of the electric heater, the power adjustment depth coefficient, and the temperature level nonlinearity index. The initial power Determine using the following formula: ； in, The rated maximum power of the electric heater. The preset lower limit of extreme low temperature, The preset target exit temperature, This is the power regulation depth coefficient. The temperature level nonlinearity index is used to adjust the variation of heating power in different temperature ranges. The temperature level nonlinearity index is used to characterize the nonlinear characteristics of heating demand in low-temperature areas. The initial power decreases smoothly as the initial temperature of the battery cell increases.

3. The method according to claim 1, characterized in that, The process of obtaining the heating power adjustment amount through PID closed-loop calculation specifically includes: The heating power adjustment amount is calculated based on the deviation between the target temperature rise rate and the actual temperature rise rate, the proportional coefficient, the integral coefficient, and the derivative coefficient. The proportional coefficient is used to generate a proportional adjustment amount based on the current deviation, the integral coefficient is used to generate an integral adjustment amount based on the historical accumulation of the deviation, and the derivative coefficient is used to generate a derivative adjustment amount based on the changing trend of the deviation.

4. The method according to claim 1, characterized in that, The status parameters also include: the average voltage of all cells, the rated voltage of the cells, and the maximum allowable discharge current of the battery at the current state of charge and temperature; The process of comprehensively evaluating battery polarization and generating a comprehensive polarization index includes: The polarization degree comprehensive index is calculated by weighted summation based on the ratio of the ohmic internal resistance to the room temperature reference ohmic internal resistance, the ratio of the polarization internal resistance to the room temperature reference polarization internal resistance, the absolute value of the ratio of the difference between the lowest cell voltage and the average voltage of all cells to the rated voltage of the cell, the ratio of the real-time discharge current to the maximum allowable discharge current of the battery, and the preset weighting coefficients corresponding to each ratio. The comprehensive index of polarization Determine using the following formula: ； in, For real-time ohmic internal resistance, The internal resistance is the reference ohm at room temperature. For real-time polarization internal resistance, The reference polarization internal resistance at room temperature, This is the lowest cell voltage. The average voltage of all cells. This is the rated voltage of the battery cell. For real-time discharge current, The maximum allowable discharge current of the battery under the current state of charge and temperature; the sum of the weighting coefficients is 1, and the comprehensive polarization index comprehensively considers four dimensions: ohmic polarization, electrochemical polarization, cell inconsistency, and discharge current margin.

5. The method according to claim 1, characterized in that, The step of performing dynamic discharge current limit calculation to generate the maximum allowable discharge current limit for the current battery specifically includes: Based on the comprehensive polarization index, the maximum rated discharge current of the battery at room temperature, the minimum discharge current limit for battery protection, the preset midpoint of the polarization threshold, and the curve steepness coefficient, the maximum discharge current limit is calculated using the Sigmoid function so that the maximum discharge current limit decreases smoothly as the comprehensive polarization index increases. The maximum discharge current limit Determine using the following formula: ； in, This refers to the battery's rated maximum discharge current at room temperature. This is the minimum discharge current limit for battery protection. As a comprehensive index of polarization degree, The midpoint of the polarization threshold, The curve steepness coefficient is the midpoint of the polarization threshold, which is the comprehensive polarization index value corresponding to the inflection point of the Sigmoid curve. The curve steepness coefficient is used to adjust the steepness of the current limiting curve as the comprehensive polarization index changes.

6. The method according to claim 1, characterized in that, The heating power upper limit constraint based on the maximum discharge current limit specifically includes: calculating the upper limit of heating power based on the terminal voltage of the battery pack, the maximum discharge current limit, and the heating efficiency of the electric heater; and limiting the real-time heating power to a range not exceeding the upper limit of heating power.

7. The method according to claim 1, characterized in that, Also includes: When the comprehensive polarization index exceeds a preset first threshold, the maximum discharge current limit is reduced. When the polarization degree comprehensive index exceeds the preset second threshold, the maximum discharge current limit is further reduced to close to the minimum discharge current limit of the battery protection, wherein the second threshold is greater than the first threshold. When the comprehensive polarization index exceeds a preset third threshold, heating is paused and a fault is reported, wherein the third threshold is greater than the second threshold.

8. The method according to claim 1, characterized in that, The method further includes: When the preset exit conditions are met, the extreme low temperature start-up mode will be exited. The preset exit conditions include at least one of the following: the minimum cell temperature is greater than the target exit temperature for a preset duration, the electric heater malfunctions, the charging state is entered, the heating countdown is reset to zero, or the high voltage is cut off.

9. The method according to claim 1, characterized in that, The method further includes: When the extreme low temperature start-up conditions are met, the range extender is started by battery pulse discharge to generate electricity so that the range extender can provide the heating power required by the electric heater. After the range extender starts successfully, after a preset delay, the thermal management power is limited to the initial power. The real-time power consumption of the high-voltage accessory is obtained, wherein the high-voltage accessory includes at least the electric heater and the DC-DC converter; The power generation of the range extender is controlled to follow the real-time power consumption of the high-voltage accessory. A safety window is set for the battery pack's charging and discharging current. When the actual charging and discharging current of the battery pack exceeds the safety window, the range extender's emergency power adjustment is triggered.

10. A start-up control system for extreme low-temperature environments, characterized in that, include: The parameter acquisition module is used to acquire vehicle status parameters and power battery pack status parameters; the status parameters include at least the initial temperature of the cell, the real-time temperature of the cell, the state of charge, the ohmic internal resistance, the polarization internal resistance, the cell voltage, and the real-time discharge current. The start-up control module is used to generate a graded heating initial power based on the initial temperature of the battery cell when the extreme low-temperature start-up conditions are met according to the vehicle status parameters and the initial temperature of the battery cell, and control the electric heater to start heating with the initial power. The PID temperature control module is used to acquire the real-time temperature of the battery cell and calculate the actual temperature rise rate during the heating process. It performs PID closed-loop calculation based on the deviation between the preset target temperature rise rate and the actual temperature rise rate to obtain the heating power adjustment amount. It generates real-time heating power based on the initial power and the adjustment amount, and controls the electric heater to dynamically adjust the heating power. The polarization evaluation module is used to comprehensively evaluate the degree of polarization during the heating process based on the ohmic internal resistance, the polarization internal resistance, the cell voltage and the discharge current, and generate a comprehensive polarization index. The current limiting module is used to perform dynamic discharge current limit calculation based on the comprehensive polarization index, the state of charge and the real-time temperature of the cell, and generate the maximum allowable discharge current limit of the current battery. The power constraint module is used to constrain the upper limit of heating power according to the maximum discharge current limit, and to constrain the output of real-time heating power with the upper limit value.

11. A new energy vehicle, comprising a vehicle controller, a battery management system, an electric heater, and a power battery pack, wherein the vehicle controller is communicatively connected to the battery management system and the electric heater, characterized in that, The vehicle controller is configured to perform the extreme low temperature environment start-up control method as described in any one of claims 1 to 9.

Images