90. DSP Based Implementation of Vector Controlled Induction Motor Drive – Using Different Speed Controllers

DC motors being simple in control offer better dynamic response inherently. Numerous economical reasons such as high initial cost, high maintenance cost for commutators, brushes and brush holders call for a substitute which is capable of eliminating the persisting problems and in addition is capable of providing the advantages of separately excited dc motors. Freedom from regular maintenance and brushless robust structure of three-phase squirrel cage induction motors are among the prime reasons that bring the motor forward as a good substitute. The Vector Control (VC) is a control technique by virtue of which two decoupled control signals are produced which are responsible for the control of flux and torque respectively. Therefore, VC mode of operation of a three-phase squirrel cage induction motor makes it an ideal substitutefor a separately excited dc motor drive. In this investigation, indirect VC or indirect FOC of the squirrel cage induction motor is implemented with proportional integral (PI), sliding mode (SM) and fuzzy pre-compensated proportional integral (FPPI) speed controllers, respectively. Three-phase induction motor is fed from a current controlled (CC) three-phase voltage source inverter (VSI). Current and speed signals are fed back to its closed loop control structure. The control algorithm is processed in real time using TMS320F240 DSP. High accuracy and fast speed of DSPs such as TMS320F240 (used for implementation here) enables high resolution control. DSP TMS320F240 has built in eatures like timers, 16 channels of ten bits analog to digital converter (ADC), four channels of digital to analog converter (DAC), digital input and output (I/O) units and twelve pulse width modulated (PWM) outputs along with central processing unit (CPU). Therefore, with the use of DSP TMS320F240, the required hardware for realizing a real time controller is reduced leading to improvement in reliability. In the present implementation, the external hardware electronics consists of a three-phase IGBT based VSI bridge, current sensing circuits, speed sensing circuit and the gate driver circuits.