A method for low-temperature protection of batteries in series hybrid electric vehicles

Abstract

This invention discloses a low-temperature protection method for a series hybrid electric vehicle battery, comprising the following steps: Step S10, high voltage is applied to the vehicle; Step S20, it is determined whether the temperature of the battery cell (minimum cell temperature) is less than or equal to -25°C. If yes, proceed to Step S30; otherwise, repeat Step S20; Step S30, it is determined whether the engine coolant temperature is less than or equal to -25°C. If yes, proceed to Step S40; otherwise, repeat Step S30; Step S40, it is enabled to activate the battery low-temperature protection strategy, raising the temperature of the battery cell and the engine coolant. When the battery cell temperature and engine coolant temperature are below a threshold, this invention requests a small-power APU to generate electricity to heat the battery heating film, thereby quickly warming up the engine and rapidly bringing the battery temperature to a comfortable range, thus preventing overcharging and allowing the entire system to quickly reach its optimal state in terms of power and economy.

Description

Technical Field

[0001] This invention belongs to the field of plug-in hybrid electric vehicle technology. Specifically, this invention relates to a method for low-temperature protection of batteries in series hybrid electric vehicles. Background Technology

[0002] Series hybrid electric vehicles are sometimes also defined as range-extended electric vehicles. Their power source consists of at least two different energy devices, such as a traditional internal combustion engine that converts the chemical energy of fuel into mechanical energy and a battery system that can store electrical energy. Generally speaking, the series hybrid electric vehicle we are talking about refers to an electric motor driven by an internal combustion engine that drives a generator to produce electricity, while the battery system provides some energy.

[0003] For series hybrid electric vehicles, the vehicle can run on pure electric power or in series mode. In series mode, the engine starts to generate electricity, which, together with the battery, powers the vehicle to meet power requirements such as driving. In winter, when the temperature is low, the battery's discharge capacity drops significantly. Generally, the engine needs to be started to generate electricity to ensure the vehicle's power and drivability. However, in winter, the engine's lubrication system is also at a low temperature, and the friction torque increases, resulting in a large deviation between the engine's actual torque and the target torque. This leads to a large deviation in the power generation control. The battery cell temperature is also relatively low. The battery will not be allowed to charge below a certain temperature. After the range extender is working, if the power generation control accuracy is poor, it will affect the vehicle's energy management and may also cause the battery to overcharge.

[0004] Therefore, for series hybrid electric vehicles, the low temperatures in winter place more stringent requirements on the energy management of the vehicle controller and the accuracy and responsiveness of the power generation of the range extender system, due to the chemical characteristics of the battery itself. Summary of the Invention

[0005] This invention provides a method for low-temperature protection of batteries in series hybrid electric vehicles, which solves the problems mentioned in the background art.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: a low-temperature protection method for a series hybrid electric vehicle battery, comprising the following steps:

[0007] Step S10: High voltage is ready for the entire vehicle;

[0008] Step S20: Determine whether the temperature of the battery cell (min temperature of the cell) is less than or equal to -25°C. If yes, proceed to step S30; otherwise, repeat step S20 to determine the temperature.

[0009] Step S30: Determine whether the engine coolant temperature is less than or equal to -25°C. If yes, proceed to step S40; otherwise, repeat step S30 to determine the temperature.

[0010] Step S40: Enable the battery low temperature protection strategy to prevent the temperature of the battery cells and the engine coolant from rising.

[0011] Step S50: Determine whether the temperature of the battery cell (min temperature of the cell) is greater than -15℃. If yes, proceed to step S60; otherwise, return to step S20.

[0012] Step S60: Determine whether the engine coolant temperature is greater than 30°C. If yes, proceed to step S70; otherwise, return to step S20.

[0013] Step S70: Turn off the battery low temperature protection strategy.

[0014] Preferably, step S40 includes the following steps:

[0015] Step S41: Determine whether the battery heating film relay is in a closed state. If yes, proceed to step S42; otherwise, repeat step S41 to determine the status.

[0016] In step S42, the vehicle controller requests 2.7kW of power from the range extender system, and then proceeds to step S50.

[0017] Step S43, which runs synchronously with step S41, calculates the drive power discharge coefficient f based on the temperature difference and the current battery SOC;

[0018] Step S44: Determine whether the driving power discharge coefficient f is greater than zero. If yes, proceed to step S45; otherwise, proceed to step S46.

[0019] In step S45, the vehicle controller proceeds to step S47 based on the final calculated allowable discharge power of the vehicle and the drive torque requested by the driver's accelerator pedal opening.

[0020] Step S46: Preheat the vehicle in place;

[0021] In step S47, the motor controller controls the motor drive according to the drive torque requested by the vehicle controller, and then proceeds to step S50.

[0022] Preferably, after step S70, the following step is further included:

[0023] Step S80: The vehicle controller switches to the normal energy management strategy;

[0024] Step S90: Determine whether the vehicle controller has detected the falling edge of the battery low temperature protection strategy enable shutdown. If yes, proceed to step S91; otherwise, proceed to step S92.

[0025] In step S91, after the vehicle controller uses the battery low temperature protection enable to turn off, it sends a power demand to the range extender system through the power generation request filter gradient.

[0026] In step S92, the vehicle controller uses the normal range extender system's power generation request filter gradient to send a power demand to the range extender system.

[0027] The beneficial effects of adopting the above technical solutions are:

[0028] I. This invention protects and controls the battery in low-temperature winter conditions from three aspects: the trigger boundary conditions for battery low-temperature protection, how to control the APU power generation request during low-temperature protection, and the limitation of drive power triggered from a functional safety perspective. When the battery cell temperature and engine coolant temperature are below the threshold, the APU is requested to generate a small amount of power to heat the battery heating film, so that the engine can quickly reach the warm-up state and the battery temperature can quickly reach a more comfortable range, thus avoiding battery overcharging and allowing the entire system to quickly reach the optimal state of power and economy. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the process provided by the present invention;

[0030] Figure 2 This is a flowchart illustrating the battery low-temperature protection strategy.

[0031] Figure 3 This is a flowchart illustrating the process after disabling the battery low-temperature protection strategy. Detailed Implementation

[0032] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings, in order to help those skilled in the art to have a more complete, accurate and in-depth understanding of the concept and technical solutions of the present invention, and to facilitate its implementation.

[0033] Specifically, such as Figures 1 to 3 As shown, a low-temperature protection method for a series hybrid electric vehicle battery includes the following steps:

[0034] Step S10: High voltage is ready for the entire vehicle;

[0035] Step S20: Determine whether the temperature of the battery cell (min temperature of the cell) is less than or equal to -25°C. If yes, proceed to step S30; otherwise, repeat step S20 to determine the temperature.

[0036] Step S30: Determine whether the engine coolant temperature is less than or equal to -25°C. If yes, proceed to step S40; otherwise, repeat step S30 to determine the temperature.

[0037] Step S40: Enable the battery low temperature protection strategy to prevent the temperature of the battery cells and the engine coolant from rising.

[0038] Step S50: Determine whether the temperature of the battery cell (min temperature of the cell) is greater than -15℃. If yes, proceed to step S60; otherwise, return to step S20.

[0039] Step S60: Determine whether the engine coolant temperature is greater than 30°C. If yes, proceed to step S70; otherwise, return to step S20.

[0040] Step S70: Turn off the battery low temperature protection strategy.

[0041] It should be noted that the power battery system described in this invention is a thermal management system that uses natural cooling / heating film heating. When the temperature is low in winter, the battery management system will control the battery heating film relay to close, and the battery heating film will work to heat the battery cells. The specific control strategy is as follows:

[0042] Battery low temperature protection strategy enabled

[0043] In winter, when the temperature of the battery cell (min temperature) is ≤-25℃ (hysteresis range, upper limit -15℃, calibrable)℃ and the engine coolant temperature is ≤-25℃ (hysteresis range, upper limit 30℃, calibrable)℃, the battery low temperature protection strategy is enabled. When the temperature of the battery cell (min temperature) is >-15℃ and the engine coolant temperature is >30℃, the battery low temperature protection strategy is disabled.

[0044] In addition, the battery management system is abbreviated as "BMS", the vehicle controller is abbreviated as "VCU", and the range extender system is abbreviated as "APU".

[0045] Step S40 includes the following steps:

[0046] Step S41: Determine whether the battery heating film relay is in a closed state. If yes, proceed to step S42; otherwise, repeat step S41 to determine the status.

[0047] In step S42, the vehicle controller requests 2.7kW of power from the range extender system, and then proceeds to step S50.

[0048] It should be noted that if the battery low-temperature protection strategy is enabled, and if the VCU requests the APU to generate high power, the APU's starting power control accuracy will decrease in low winter temperatures, which may lead to excess power being fed into the battery and causing overcharging. Therefore, the power request issued by the VCU to the APU at this time only includes the power required by the battery heating film (2.7kW, calibrable). In this way, the APU can generate low power to warm up the engine, and at the same time, the power consumed by the battery heating film can be requested to avoid further battery discharge and ensure optimal overall performance.

[0049] Additionally, the VCU needs to determine whether the power generated by the APU is consumed by the heating film based on whether the battery heating film is actually working. Therefore, the VCU needs to simultaneously check the status of the battery heating relay. If the heating relay is in the open state, it will not request low-power power generation to heat the heating film, preventing power from being charged into the battery when the heating relay closes during the initial high-voltage BMS delay (5s) or when the heating relay fails. If the battery low-temperature protection strategy is not enabled, the VCU will normally send a power request to the APU.

[0050] Step S43, which runs synchronously with step S41, calculates the drive power discharge coefficient f based on the temperature difference and the current battery SOC;

[0051] Step S44: Determine whether the driving power discharge coefficient f is greater than zero. If yes, proceed to step S45; otherwise, proceed to step S46.

[0052] In step S45, the vehicle controller proceeds to step S47 based on the final calculated allowable discharge power of the vehicle and the drive torque requested by the driver's accelerator pedal opening.

[0053] Step S46: Preheat the vehicle in place;

[0054] In step S47, the motor controller controls the motor drive according to the drive torque requested by the vehicle controller, and then proceeds to step S50.

[0055] It should be noted that, considering the risk of vehicle breakdown if the battery is allowed to discharge at high power when the battery's SOC and temperature are low, when the battery's low-temperature protection strategy is enabled, a discharge coefficient f is added to limit the battery's discharge capacity (or disallow driving, depending on the calibration). f is obtained by looking up the cell temperature difference and the current SOC in a table. The temperature difference, Temperatureerror = TBD (e.g., -10℃) - Temperature (cell minimum). The battery's peak power limit (for Sport mode) and continuous power limit (for Eco mode) need to be multiplied by this coefficient. If the battery's low-temperature protection strategy is not enabled, it is not necessary to multiply by this coefficient.

[0056] The following steps are included after step S70:

[0057] Step S80: The vehicle controller switches to the normal energy management strategy;

[0058] Step S90: Determine whether the vehicle controller has detected the falling edge of the battery low temperature protection strategy enable shutdown. If yes, proceed to step S91; otherwise, proceed to step S92.

[0059] In step S91, after the vehicle controller uses the battery low temperature protection enable to turn off, it sends a power demand to the range extender system through the power generation request filter gradient.

[0060] In step S92, the vehicle controller uses the normal range extender system's power generation request filter gradient to send a power demand to the range extender system.

[0061] It should be noted that, considering the risk of the vehicle lurching forward and posing a safety hazard when switching to normal energy management strategy after the battery temperature rises and the driver keeps pressing the accelerator pedal hard, the VCU will switch to normal requesting APU power generation, releasing the power demand for driving. Therefore, when the VCU switches the APU power demand calculation strategy, the power generation demand of the APU is filtered separately. The VCU performs gradient switching by judging the falling edge after the battery low temperature protection strategy is enabled, with the gradient set to 5 kW / s. This ensures that the APU power generation does not increase rapidly, and the vehicle power increases slowly, avoiding the danger caused by the rapid increase in vehicle power without the driver's awareness. Otherwise, there is no need to switch. Example 1

[0062] The battery protection and control system in winter low temperatures is implemented from three aspects: the trigger boundary conditions for battery low temperature protection, how to control the APU power generation request during low temperature protection, and the limitation of drive power triggered from a functional safety perspective. When the battery cell temperature and engine coolant temperature are below the threshold, the APU is requested to generate a small amount of power to heat the battery heating film, so that the engine can quickly reach the warm-up state and the battery temperature can quickly reach a more comfortable range, thus avoiding battery overcharging and allowing the entire system to quickly reach the optimal state of power and economy.

[0063] The present invention has been described above by way of example with reference to the accompanying drawings. Obviously, the specific implementation of the present invention is not limited to the above-described manner. Any non-substantial improvements made using the inventive concept and technical solution of the present invention, or the direct application of the inventive concept and technical solution of the present invention to other situations without modification, are all within the protection scope of the present invention.

Claims

1. A method for low-temperature protection of a series hybrid electric vehicle battery, characterized in that, Includes the following steps: Step S10: High voltage is ready for the entire vehicle; Step S20: Determine whether the temperature of the battery cell is less than or equal to -25°C. If yes, proceed to step S30; otherwise, repeat step S20 to determine the temperature. Step S30: Determine whether the engine coolant temperature is less than or equal to -25°C. If yes, proceed to step S40; otherwise, repeat step S30 to determine the temperature. Step S40: Enable the battery low temperature protection strategy to prevent the temperature of the battery cells and the engine coolant from rising. Step S41: Determine whether the battery heating film relay is in a closed state. If yes, proceed to step S42; otherwise, repeat step S41 to determine the status. In step S42, the vehicle controller requests 2.7kW of power from the range extender system, and then proceeds to step S50. Step S43, which runs synchronously with step S41, calculates the drive power discharge coefficient f based on the cell temperature difference and the current battery SOC; Step S44: Determine whether the driving power discharge coefficient f is greater than zero. If yes, proceed to step S45; otherwise, proceed to step S46. In step S45, the vehicle controller proceeds to step S47 based on the final calculated allowable discharge power of the vehicle and the drive torque requested by the driver's accelerator pedal opening. Step S46: Preheat the vehicle in place; In step S47, the motor controller controls the motor drive according to the drive torque requested by the vehicle controller, and then proceeds to step S50. Step S50: Determine whether the temperature of the battery cell is greater than -15℃. If yes, proceed to step S60; otherwise, return to step S20. Step S60: Determine whether the engine coolant temperature is greater than 30°C. If yes, proceed to step S70; otherwise, return to step S20. Step S70: Turn off the battery low temperature protection strategy.

2. The method for low-temperature protection of a series hybrid electric vehicle battery according to claim 1, characterized in that, The following steps are included after step S70: Step S80: The vehicle controller switches to the normal energy management strategy; Step S90: Determine whether the vehicle controller has detected the falling edge of the battery low temperature protection strategy enable shutdown. If yes, proceed to step S91; otherwise, proceed to step S92. In step S91, after the vehicle controller uses the battery low temperature protection enable to turn off, it sends a power demand to the range extender system through the power generation request filter gradient. In step S92, the vehicle controller uses the normal range extender system's power generation request filter gradient to send a power demand to the range extender system.

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