At present, due to the increasingly serious problems of environmental pollution and energy crisis, the development of electric vehicles has begun to receive great attention from all countries and become the mainstream direction of future automobile development.
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Electric vehicles mainly have three key technologies: drive control system, battery power supply, and vehicle electronic control system. The vehicle electronic control system must meet the design concept of pure electric vehicles, making it energy-saving, simple and reliable. Under the current battery technology level, solving two key technologies will help electric vehicles to be marketed first in China, and its economic significance is self-evident. The electric vehicle power system has complex and diverse structure and various types of components. The advanced and efficient control architecture can make the data exchange between electric power systems of electric vehicles meet the requirements of simple and rapid, high reliability, strong anti-interference ability, good real-time performance, strong system error detection and isolation capability.
In this paper, an electronic control system for electric vehicles based on CAN bus is designed. The system is applied to pure electric vehicles driven by switched reluctance motors, which can greatly reduce the number of sensors in the vehicle and significantly improve the overall performance of the vehicle.
2. Performance characteristics and control methods of switched reluctance motors applied to electric vehicles:
Switched reluctance motor is a kind of motor with a long history. It was born more than 160 years ago. After more than one hundred years of development, especially the research and improvement of nearly 20 years, the performance of switched reluctance motor has been continuously improved. Its performance is superior to other forms of motors in a larger power range, and the performance characteristics of switched reluctance motors are particularly suitable for use in pure electric vehicles.
2.1, the performance characteristics of the switched reluctance motor:
(1) Simple structure and high efficiency;
The structure of the switched reluctance motor is simpler and more reliable than the induction motor. It is especially suitable for high speed, low speed torque and small current, and has high efficiency, especially the rotor has no winding. It is suitable for frequent positive and negative reversal and impact load conditions. .
(2) The control circuit is simple and reliable;
The driving power circuit uses fewer power switching components and the circuit is simpler. The power components are connected in series with the motor windings, making it difficult for a through-short.
(3) The speed adjustment range is large, and the torque and braking characteristics are good;
The use of a simpler control circuit enables a wide range of speed regulation, as well as low speed and high torque and brake energy feedback.
Therefore, the switched magnetic motor drive system is particularly suitable for use in electric vehicles.
2.2, the control method of switching reluctance motor applied to electric vehicles:
(1) The start of the car is stopped;
The switched reluctance motor controller can control the start, stop, acceleration, deceleration, forward rotation and reverse rotation of the motor. When applied to an electric vehicle, the start and stop of the vehicle can be achieved by activating the key system.
(2) Accelerated deceleration of the vehicle;
Acceleration deceleration through the pedal throttle, adjust the throttle output voltage to control the VI given to adjust the speed.
(3) Reversing the car forward;
Forward and reverse can be controlled by the gear rocker.
(4) the sudden braking of the car;
The sudden braking can activate the regenerative braking system via the brake pedal. Therefore, the switched reluctance motor can easily control the basic operation of the electric vehicle, which greatly simplifies the extremely critical motor control unit on the control system bus.
3. Technical characteristics of CAN bus:
CAN (Controller Area Network) controller local area network is a serial communication network developed by Bosch in Germany to solve the data exchange between many control and test instruments of Hyundai Motor. It can effectively support distributed control and real-time control. The fieldbus field. The CAN bus has the advantages of reliability, flexibility and real-time performance.
(1) The CAN bus adopts a multi-master structure, and any node on the network can send information to other nodes at any time, and the communication mode is flexible.
(2) Nodes on the network can respond as quickly as possible within 134μs depending on the priority of the bus access.
(3) Using non-destructive bus arbitration technology, bus arbitration arbitration time can be greatly saved, and the network will not be paralyzed in the case of congestion.
(4) CAN adopts NRZ coding, the direct communication distance is up to 10km (speed 5kbps), and the communication speed is up to 1Mbps (the communication distance is up to 40m at this time).
(5) Short frame structure, short transmission time and low probability of interference.
(6) The CAN node has an auto-shutdown output function in case of a serious error, so that the operation of other nodes on the bus is not affected.
(7) The communication medium can be twisted pair, coaxial cable or optical fiber, and the choice is flexible.
4, system design:
4.1, network node configuration and signal type:
4.1.1. The main CAN nodes in the electric vehicle and the CAN bus of each node mainly send and receive signals as follows:
(1) Battery management system node: battery state of charge (SOC), battery charge and discharge status, battery failure.
(2) Liquid crystal display node: battery state of charge (SOC), vehicle speed, motor speed, forward reverse state, door and window switch state, light switch state, motor temperature, interior temperature, regenerative braking state, battery charge and discharge status, battery Fault, air conditioning switch status, key signal.
(3) Motor control node: motor speed, forward reverse state, motor start stop, motor temperature, regenerative braking state.
(4) Joint assembly node: interior temperature, vehicle speed, door and window switch status, light switch status, air conditioning switch status.
(5) Human-machine dialogue node: control door and window switch, control light switch, liquid crystal display switch, air conditioner switch.
(6) Operation control node: start key signal, foot throttle, brake pedal, forward reverse gear rocker.
4.1.2, the type of data received and sent by the electric vehicle electronic control unit:
In this solution, the data type of receiving and transmitting by each electronic control unit of the electric vehicle is as shown in Table (1), where T represents transmission and R represents reception.
Table (1) Data types received and sent by electric vehicle electronic control unit
4.2, network architecture:
The electric vehicle electronic control system of the electric vehicle is composed of two buses, namely a high-speed CAN bus and a low-speed bus. The high speed CAN bus and low speed bus are two independent bus systems. In order to facilitate the management of all functions of the car, the two bus networks are connected through a gateway, and data between different buses is shared by the gateway. In this way, the two buses operate independently, and only the data that needs to be exchanged between the two buses is transmitted through the gateway. This approach separates different types of information, reducing the burden on each network bus.
The high-speed CAN bus is mainly connected to the drive system of the electric vehicle, which can realize rapid control of key systems such as motor, battery, steering and braking. The low-speed bus is mainly used to connect the body system, and accesses the high-speed CAN bus through the gateway as a subnet to form a unified multi-network.
The network architecture of this system is shown in Figure (1).
Figure (1) Network Architecture
4.3, battery management node introduction:
Battery management system has always been a key technology in the development of electric vehicles. Its most basic function is to monitor the working state of the battery. By measuring the parameters of battery voltage, current and temperature, predict the SOC of the battery and the corresponding remaining mileage. , manage the working condition of the battery. The battery management system block diagram is shown in Figure (2):
Figure (2) Battery Management System Block Diagram
4.4, LCD display node introduction:
This design adopts liquid crystal display, which can display more information than analog instrument, which is more conducive to centralized management of information and convenient for driver's operation. The information displayed mainly includes: battery status information, motor status information, vehicle operating status information, in-vehicle facility status information, and activation key information. Its main signal is shown in Figure (2):
Table (2) Main signal of liquid crystal display node
5. Conclusion:
There are more and more electronic devices on modern cars. The number of electrical nodes in a high-end car has reached thousands. If the traditional method is used for wiring, the number of connections will be very alarming and there will be great troubles. The switched reluctance motor drive system based on CAN bus can realize the sharing of information of each node in the car, greatly improve the layout of the car and improve the overall performance of the car.
At present, the vehicle electronic control system of hybrid vehicles has been developed in China, but the city is based on hybrid vehicles, and the control nodes and instrument displays are quite different from the pure electric vehicles developed in this paper. The control system is directly applied to pure electric vehicles and uses digital liquid crystal display to achieve higher requirements for energy saving, simplicity and reliability. From the current world's electric vehicle control system for electric vehicles, the motor control node uses AC induction motors in Europe and America, and DC motors in Japan. The instrument display nodes use analog instruments. The vehicle electronic control system designed in this paper is applied to the electric vehicle driven by the switched reluctance motor, and the digital liquid crystal display is used to make up for the research in this field.
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