Control of AC Induction Motor Drive System Based on Voltage-Compensated Flux Estimator for Electric Vehicle

Abstract

In this dissertation, the following problems are considered. The first one is to present technical theories for voltage source inverter-fed AC induction motor. The second one is to present control methods applied to control torque, flux and speed of AC induction motor. The last one is to present hardware and software design for simulation and experiment. Technical theories for voltage source inverter-fed AC induction motor are given. The voltage source inverter inverts DC voltage to AC voltage with the help of DC capacitor stabilizing the input. Because of its simplicity and controllability, this type of inverter is very common in the industrial fields. To present control algorithms for torque, flux and speed of AC induction motor, the mathematical modeling of induction motor is proposed. This mathematical description of the modeling is based on space vector notation. The inverter is controlled in pulse width modulation fashion. Review of the modulation technique is also presented in this dissertation. The electric vehicle requires fast response and high efficiency for the drive. Because AC motors are highly non-linear devices with their flux and torque coupled, they cannot provide fast dynamic response with normal control (Scalar based control). Field oriented control (FOC) method, one type of vector based control method, has made a fundamental change with regard to dynamic performance of AC motor. FOC makes it possible to control induction motor in a manner similar to control scheme used for the separately excited DC motor. These methods were investigated and discussed by several researchers and have now become an industry standard. In these methods, the motor equations are transformed into a coordinate system that rotates in synchronism with the rotor flux vector. The FOC method guarantees flux and torque decoupling. In this dissertation, first, a Volts/Hz (scalar) control as a scalar based control method is presented. The Volts/Hz control is only applied to low performance drive systems, in which precise speed control is not required. Secondly, to overcome the limit of scalar control, our study focuses on FOC method as a vector based control. In FOC method, there are two methods: Direct Field Oriented Control (DFOC) method and Indirect Field Oriented Control (IFOC) method. Advantages and disadvantages of each method are analyzed and compared. Furthermore, sensorless control for AC induction motor is also considered in this dissertation. For developing the control algorithm, estimators of flux, slip ratio and speed of induction motor drive are presented. These estimators are the main contributions in this dissertation. The electrical vehicle use motors with diverse electric powers from 25 to 100 . It is difficult to study these motors because they need big power and high cost. Therefore, this dissertation obtains basic technology for developing the voltage source inverter of electrical vehicles by designing the controller with high capacity and high efficiency using high speed DSP through testing motor system of the 1.5 induction motor. Because the difference between motors with electric power from 25 to 100 and motor with electric power of 1.5 is power circuit, the control system in this dissertation can be applied to AC induction motor used for real electrical vehicles by changing the specification of power circuit. Hardware and software for developing the voltage source inverter are introduced. Hardware is designed to control 1.5 AC induction motor. The TMS320F28335 DSP is selected as the digital controller for the system. Peripheral and interface circuits are necessary built for signal measurement, the three-phase inverter control and the system protection. Finally, simulation results are done to demonstrate the effectiveness of the proposed controllers for electric vehicle of the proposed inverter. Keywords: Induction Motor, Vector Control, Field Oriented Control (FOC), Space vector Modulation (SVM), Electric Vehicles.