Mathematical Problems in Engineering

Volume 2015 (2015), Article ID 875843, 9 pages

http://dx.doi.org/10.1155/2015/875843

## Vector Control Algorithm for Electric Vehicle AC Induction Motor Based on Improved Variable Gain PID Controller

^{1}School of Automation Engineering, University of Electronic Science and Technology of China, Chengdu 610023, China^{2}School of Microelectronics and Solid-State Electronics, University of Electronic Science and Technology of China, Chengdu 610023, China

Received 3 December 2014; Revised 28 December 2014; Accepted 28 December 2014

Academic Editor: Hui Zhang

Copyright © 2015 Gang Qin et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

#### Abstract

The acceleration performance of EV, which affects a lot of performances of EV such as start-up, overtaking, driving safety, and ride comfort, has become increasingly popular in recent researches. An improved variable gain PID control algorithm to improve the acceleration performance is proposed in this paper. The results of simulation with Matlab/Simulink demonstrate the effectiveness of the proposed algorithm through the control performance of motor velocity, motor torque, and three-phase current of motor. Moreover, it is investigated that the proposed controller is valid by comparison with the other PID controllers. Furthermore, the AC induction motor experiment set is constructed to verify the effect of proposed controller.

#### 1. Introduction

With the increased emphasis on saving energy and reducing emission, electric vehicles (EVs) have emerged as very strong candidates to achieve these goals [1–5]. Moreover, the acceleration performance of EV, which affects a lot of performances of EV such as start ability, passing ability, driving safety, and ride comfort, is the key point of EV researches.

Vector control algorithm, which can accurately control the torque and has a wide control range of motor velocity and also has a current loop which can be used for current limiting protection, is widely used in EV driving control. However, the velocity loop controller of vector control algorithm, which uses traditional PID control algorithm generally, limits the dynamic performance of driving system and the acceleration performance of EV. During the last few years, the velocity loop controller of EV AC induction motor (ACIM) controller system is researched and improved unceasingly and many methods are presented. One method is using the fuzzy controller to replace velocity loop traditional PID controller and current loop traditional PID controller of vector control algorithm [6–8], which can make the control system track the different given velocity rapidly and without overshoot in different load and has strong ability against load disturbance, but its steady-state accuracy is not high because of no existing integration element. Another method is using the neutral network PID controller to replace velocity loop traditional PID controller of vector control algorithm [9–11], which has the advantages of adjusting velocity rapidly, zero overshoot, smooth and small-fluctuation control signals, and good system tracking, but it reduces the EV control performance due to learning slowly in learning process and long response time. Literature [12] also presented a method using the fuzzy-PI controller which executes fuzzy control algorithm when velocity deviation is greater than given threshold and executes traditional PID control algorithm when velocity deviation is less instead of velocity loop traditional PID controller [13]. The method can make velocity response rapidly with small overshoot [14], but it is difficult to achieve completely smooth switching and may cause velocity hop when control algorithm switches, thereby affecting the driving safety and ride comfort when EV accelerates.

In this paper, we design a vector control algorithm for vehicle asynchronous motor based on improved variable gain PID controller which can make motor velocity rise rapidly and no overshoot. Moreover, it can satisfy the demands of EV driving system dynamic performance and acceleration performance no matter whether the EV runs in low velocity, normal velocity, high velocity, or variable velocity.

The sections are organized as follows. In Section 2, asynchronous motor model is studied. In Section 3, improved variable gain PID control algorithm is designed to improve the acceleration performance. In Section 4, vector control algorithm for EV asynchronous motor based on improved variable gain PID controller is proposed. Furthermore the stability condition is given. In Section 5, the effectiveness of controller is demonstrated by simulation with Matlab/Simulink (Figure 4). Section 6 presents some concluding remarks.

#### 2. AC Induction Motor Model

ACIM is widely applied to EV driving system, which has many good characteristics such as robustness, durability, simple structure, reliable operation, low cost, low torque ripple, low noise, no position sensor, and high velocity limit. The design of ACIM for EV which is different from normal ACIM and must satisfy the power performance of EV must have the following characteristics: (1) constant power output and big velocity adjustable range for satisfying the demands for flat road, overtaking, and so on when run in high/low velocity, smaller mass and volume in the condition of certain power level, and robust structure and resistance to vibrations [15].

This paper which takes ACIM for example researches motor mathematical model of EV driving system. The mathematical model of ACIM is a nonlinear, high order, close coupling multivariable system. Ignore these factors such as core loss, space harmonics, the change of frequency, the change of temperature, and the saturation of magnetic circuit on the impact of winding resistances when establishing motor model [16].

A physical model of ACIM is shown in Figure 1. The three-phase winding resistances which are 120° phase different in the space are symmetrical, and the mutual inductance and self-inductance of every winding resistance are constant. The mathematical models of ACIM, which consist of voltage matrix equation, magnetic linkage matrix equation, and torque equation, can be obtained according to the physical model of ACIM.