# Adaptive Cruise Control in Electric Vehicles with Field-Oriented Control
## 2 Adaptive Cruise Control
In an EV, there is no throttle valve, throttle control, or throttle position sensor; the engine is replaced with an electric machine, and the acceleration of the motor is handled by the motor control block through the inverter. Therefore, for an EV, the ACC block output signal is applied to the motor control block--in this paper, an indirect field-oriented control block. In the same manner as in the ICE vehicle, the field-oriented control block is based on the acceleration ratio set by the ACC block, and the motor speed feedback signal generates the corresponding PWM driving signals for the inverter to control the electric machine  
Figure 1: Working modes of adaptive cruise control. working mode (motor or generator) and required speed. Figure 3 illustrates a block diagram of an EV with an ACC system. In comparison with the ICE vehicle, the EV has fewer mechanical and moving parts, and the motor control block through the inverter handles the acceleration without throttle, throttle control, or a throttle position sensor so there are fewer maintenance costs and, also, fewer mechanical losses; therefore, the efficiency of the vehicle increases. The overall efficiency of EVs is higher also because electric machines have a higher efficiency compared with the ICEs used in classic vehicles. Vehicle torque should be high at low speeds and decrease as the speed increases. One should note that, because ICE does not have, by nature, the corresponding torque-speed characteristics, ICE vehicles have a gear box. Meanwhile, the torque-speed characteristics of the electric machine are exactly what is needed for vehicles. The torque-speed characteristics of the electric machine and ICE are presented in Figure 4.  
Figure 3: EV propulsion system with adaptive cruise control. Figure 2: ICE propulsion system with adaptive cruise control. Regardless of the vehicle type, there are many adaptive cruise control methods developed and that are currently under development. The focus of this paper is not the implementation of adaptive cruise control but to present how the output of the ACC block is applied to an indirect field-oriented control block. To prove the concept of an ACC in an electric vehicle, a simple ACC block was used in this paper. The ACC block used in this paper requires a set velocity value as the velocity set by the driver, a time gap value, a feedback value of the longitudinal velocity of the ego vehicle, the longitudinal velocity of the leading vehicle, and the relative distance between the two vehicles. A default safe distance is set to 10 m. The variables enumerated previously are applied to a Model Predictive Control (MPC). The output of the ACC block is the output of the MPC and represents the longitudinal acceleration/deceleration, which is applied to the input of the field-oriented control block. The ACC output can be a positive or a negative value. When the output is a positive value, it represents an acceleration, which is transformed in angular velocity and added to the speed reference of the field-oriented control. In the opposite case, when the output value of the ACC is a negative value, it means that the vehicle should decelerate, and adding a negative value to the speed reference of the field-oriented block will result in a smaller value of the reference speed, so the vehicle speed will decrease; this is as the engine brake in the case of the ICE vehicle. A real vehicle also has a mechanical brake for a full stop, but in this paper, the mechanical parts of the vehicle are not considered; only the deceleration base on the engine brake is presented. The MPC has the following inputs: measured outputs of the system, an output reference value, and a disturbance signal that affects the system. In the ACC case, the measured variables are the longitudinal velocity of the ego vehicle and the relative distance between the vehicles. For the reference value, the set velocity and the default safe distance are required. The disturbance is the velocity of the leading vehicle.