Function Of a Controller In Electric Vehicles

In recent years, global concern has occurred due to air pollution emissions, greenhouse gas emissions, and energy consumption by vehicles. Electric vehicles are assumed to be one of the most promising alternatives to engine-only vehicles. The major components of an electric vehicle system are the motor, controller, power supply, charger, and drive train, which is shown in the below diagram.

Here, we will be focusing basically on the Controller of an electric vehicle. The controller is the heart of an electric vehicle, and it is the key to the realization of a high-performance electric vehicle with an optimal balance of maximum speed, acceleration performance, and traveling range per charge. It is the electronics package that operates between the batteries and the motor to control the electric vehicle's speed and acceleration, much like a carburetor in a gasoline-powered vehicle. The motor control system signal, the acceleration pedal signal, the brake pedal signal, and the signals of other parts are first collected by the Vehicle Control Unit, which analyzes the driver’s intention and makes the corresponding judgment. To coordinate the movement of various power components and protect the normal driving of electric vehicles, the required motor output torque, and other parameters are calculated.

The driver block receives the control signal output from the control system and, after processing, sends a drive signal to control the on/off state of the power devices of the power converter. It also shapes the drive signal to have efficient switching and provides protection to the control system during malfunctioning. The driver circuit takes care of the fault conditions such as over-current or over-voltage faults occurring in the system. It also provides the necessary isolation between the control circuit and the power circuit. The vehicle is driven by a motor, and the energy is supplied by the battery through a controlled power circuit. The motor is driven by the motor controller, and it transfers the e-power into mechanical power to drive the vehicle.

Vehicle controllers are often produced by large automobile industries with advanced technologies and are mainly used for complex four-wheel drive and wheel motor drive pure electric vehicles. For example, the vehicle controller of Toyota mainly receives the driver’s operation signal and the motion sensor signal. Then, it calculates these signals by the control strategy and drives the left rear wheel and the right rear wheel, respectively, through the left and right sets of motor controllers and inverters. In the case of the vehicle controller of Nissan LEAF receives electronic signals from the speed sensor and accelerator pedal position sensor of the combination instrument and controls the motor, generator, power cell, solar cell, and regenerative braking system through the sub-controller.

The vehicle control system consists of a vehicle controller, motor and motor controller, power battery, power battery management system (BMS), fault diagnosis management unit, gearbox, main reducer, auxiliary system, and other components. The auxiliary system includes the steering motor and its controller, air conditioning motor and its controller, braking system, DC-DC converters, etc. The driver achieves the overall control of the vehicle through the vehicle control system.

How does the control system function in an electric vehicle?

The controller receives the operation information from the driver, such as the accelerator pedal, the brake pedal, and the shift lever signals. Then the driver’s intention and the corresponding operation are determined based on the information. When the vehicle is running, the vehicle output torque and the vehicle status are sent to the motor control unit. When the vehicle starts and stops, the high and low voltage power, which is supplied by the external related equipment, is controlled to turn on and off in sequence. The start and running state of the motor controller and power management system is controlled to meet the vehicle control needs. To coordinate the working status of each module, the vehicle controller with other control units is connected by the CAN (controller area network).

The CAN network topology is widely used in vehicle controls. Generally, the system consists of two communication channels. Channel 1 (a high-speed CAN bus) and Channel 2 (a low-speed CAN bus). Power system components with high real-time requirements, such as motor controller, BMS, fault diagnosis system, and on-board charger, adopt high-speed CAN bus connections, and the communication rate is up to 500 kbps. A Low-speed CAN bus is employed for the acquisition and feedback of control signals with low real-time requirements in the vehicle, such as air conditioning, combination instrument, cooling system, and vacuum booster pump brake system, and the communication rate can reach up to 100 kbps.

The basic signals required for the vehicle controller are as follows:

1. Accelerator pedal signal: Based on the different degrees of the accelerator pedal, the vehicle controller is used to calculate the whole speed or torque requirements.
2. Brake pedal signal: Based on the brake pedal signal, the power on and power off of the motor is controlled by the vehicle.
3. Gear signal: Based on the gear signal, the neutral, forward, and reverse motions of the motor are controlled by the vehicle to achieve vehicle forward and reverse driving.
4. Wheel rotational speed signal: The vehicle controller needs to collect the wheel speed signal to determine the driving state of the vehicle and to perform closed-loop control of the wheel speed.
5. Speed signal: The speed signal is collected to help determine the vehicle driving state and for display.

Let us discuss the merits of the control system in Electric vehicles:

(1)The torque generation is very quick and accurate hence electric motors can be controlled much more quickly and precisely.

(2) Output torque is easily comprehensible.

(3) According to the energy resource combination mechanism, we can easily retrieve the braking energy or potential energy when declining. Thus the continual mileage increases (by 10%-15%).

(4)The controller can be easily designed and implemented with excellent performance in motion control.