This article mainly discusses the design and implementation technology of communication system in electric vehicle power management based on CAN bus. The power management scheme of electric vehicles involves many parameters such as the working conditions of the engine, motor, and battery, the driving speed of the vehicle, the driving resistance, and the driver's operation. The CAN bus technology is used to connect the measurement and control devices of the above parameters to realize the electric A key step in the power management of a car.
With the rise of oil prices and the improvement of environmental protection requirements, electric power has become an important direction for the future development of automobiles. For a battery-powered all-electric power system or an engine and battery hybrid power system, the design of the power management system is an important factor that affects the performance of the vehicle. The design needs to consider the overall vehicle design and the external use environment in order to save power. , You also need to design a certain control strategy to ensure the best use of power. Therefore, it is necessary to conduct an in-depth discussion on the power management system of all-electric vehicles.
1. The importance of electric vehicle energy management
The main function of electric vehicle power management is to give full play to the combustion efficiency of the fuel, so that the engine works near the optimal operating point, and through the energy storage and output of the electric motor and battery, timely adjust the vehicle operating conditions and the external road conditions Matching relationship. After more than ten years of development, the power system design of electric vehicles is currently the most practical and has a commercial operation mode, only hybrid vehicles. The hybrid powertrain assembly has evolved from the original discrete structure of the engine and motor to the integrated structure of the engine motor and gearbox, that is, the integrated hybrid powertrain system. Therefore, only the power management situation of the hybrid power system is considered here. From a functional perspective, the power management of a hybrid power system needs to achieve the following two goals:
(1) Ensure the best working conditions of the engine and avoid the inefficient work of the engine. Generally, the engine can be adjusted to run stably near the optimal operating point, and the output of the battery and the motor can be adjusted to adapt to changes in various external road conditions. For example, when the vehicle is in low speed, coasting, and idling conditions, the battery pack drives the motor. When the vehicle is starting, accelerating, and climbing, the engine-motor pack and battery pack provide electrical energy to the motor. In this way, since the engine avoids idling and low-speed operation, the efficiency of the engine is improved, which not only reduces exhaust emissions, but also saves power.
(2) Make full use of the inertial energy of the vehicle. When the vehicle decelerates, brakes, or travels downhill, the motor is driven by the inertial force of the wheels. At this time, the motor becomes a generator, and the battery can be charged in reverse, which saves fuel.
Statistics show that under 80% of road conditions, an ordinary car only uses 40% of its power potential, and it will fall to 25% in urban areas. However, electric vehicles that use power optimization management, such as Toyota â€™s Prius, Its power has exceeded the level of the same class car, and fuel saving is 75%.
2. Communication requirements of power management system and CAN bus technology
The power management of electric vehicles needs to monitor the working conditions of the engine, motor, and battery, vehicle speed, driving resistance data, and driver's operating conditions at any time, and can automatically control energy-saving devices or circuits after intelligent processing based on the above data Therefore, it is necessary to first solve the connection method of the component operation status sensor related to energy consumption and energy conversion.
At present, the data communication between the internal measurement and execution components of the car mainly uses the CAN bus technology. This bus technology was first introduced by the German BOSCH company. It is mainly used to solve the data exchange problem between many control and test instruments in modern cars. The electric vehicle power management system developed by the CAN bus is not only high in communication rate, accurate and reliable, but also easy to be compatible with the vehicle control network. Or provide a basic platform for the diagnosis of off-vehicle faults, etc., so in this topic, the CAN bus is used as the basic communication technology for power management.
3. Topology structure of energy management and control system based on CAN bus
The topology of the energy management and control network based on the CAN bus is formed by connecting part of the energy consumption of the electric vehicle chassis and the energy-saving system. Several lower-level key monitoring nodes and an upper-level main control node composed of on-board computer system.
Figure 1 Topology structure of energy management and control network based on CAN bus
The braking energy conversion device works with the driver's control monitoring system and the battery motor controller. When the driver steps on the brake pedal, first the brake motor is close to the rotating device to be braked, such as the transmission shaft, which consumes the vehicle's inertial energy and converts it into electrical energy. At the same time, the control monitoring system detects the brake pedal movement and charges the battery The circuit is adjusted to realize the storage of the electrical energy transmitted by the brake motor.
The powertrain system is mainly used to realize the optimized operation of the engine operating conditions. In the case of normal exercise, the energy of the engine is divided into two channels, one is transmitted to the vehicle transmission and propulsion system to drive the vehicle to exercise normally, and the other channel drives the motor to work to supply power to the battery. At this time, the auxiliary power system composed of the motor and the battery is equivalent to an energy adjustment device. Through the battery motor controller and the running resistance test device, the output energy of the two circuits of the engine is adjusted and distributed according to the changes of the external road conditions.
Through the CAN bus, the upper main control node formed by the on-board computer system connects the entire energy management and control network. Through a special software system, data acquisition, data analysis, and control strategy output are performed to achieve the relationship between external driving resistance and engine energy adjustment. Optimize matching, realize the energy conversion and utilization inside the vehicle, and realize the energy-saving, energy storage and supplementary energy adjustment functions of the motor and battery system.
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