PC-AT based realtime closed loop speed control of single phase induction motor

摘要

Implementation of closed loop speed control schemes for ac motors using semi-conductor switching devices require means of computation and control in real time. The associated considerations are constant V/f strategy, elimination of dominant harmonics, monitoring of speed and operator interaction for speed setting, etc. in this paper it is sought to realize all these by incorporating a PC-AT into the feedback loop for the speed control of single phase induction motor driven from Power MOSFET PWM inverter. The PC is made to operate in real time and functions simultaneously as a computer; controller and user interface. The PC is interfaced with the Power MOSFET inverter so as to produce a variable frequency PWM signal which eliminates the third and fifth harmonic components in the stator voltage. The parameters of the PWM waveform are calculated using the speed error by solving a set of non-linear simultaneous equations. By use of an optical speed sensor; the PC is programmed to monitor and record the speed at every sampling instant Similarly, an operator can set the required speed through the keyboard at any time during the run. In this, the software developed has the attributes of real time operation and multi-tasking' capability. These are achieved by programming timer circuits on the motherboard for hardware interrupt. The paper covers the hardware and software details of the closed loop speed control scheme implemented on a 180 W, 1425 rpm, single phase induction motor. The on-line closed loop operation is investigated for various reference speeds, and the transient speed correction phenomena is recorded. The results indicate stability of the closed loop operation over a moderate range of speeds.