ABSTRACT
This study developedmethods to improve the efficiency and torque production of the single phase induction machine using a sinusoidal pulse width modulation (SPWM) control scheme. This research targets the capacitor-run single phase induction motor(CRSPIM) which is a large consumer of domestic and industrial power supply with the goal of improving its operation at light load conditions.This motor suffers fromlow efficiency when operating under non-rated conditions,leading to wastage of significant amount of electric power since rated voltage is applied fully across its terminals and the flux in the machine operates approximately at rated value regardless of the applied load on the machine. Moreover, during starting time and at steady state, the motor exhibits significant torque pulsations which gives rise to noise and vibration in the machine. In efforts to address these problems, a performance improvement scheme using a pulse width modulated single phase inverter and a PID controller was first developed and implemented in MATLAB/Simulink environment to eliminate steady state torque pulsations in the motor. Although system simulation shows reduction in torque pulsations in the motor under the scheme compared to the performance of the same motor under nominal power supply, this scheme could not eliminate torque pulsations in steady state. Consequently, a pragmatic design modification to the parameters of the auxiliary winding of the existing CRSPIM was proposed. In addition to the design modification, a vector-controlled drive with an efficiency-optimizing function for the modified single phase induction machine was also proposed. This second approachuses a two-phase, two-leg inverter structure. Theproposed scheme was also implemented in the MATLAB/Simulink environment. Simulation results have demonstrated that the proposed strategy eliminates torque pulsations at steady state in comparison to the existing line-operated CRSPIM. It is also shown that the proposed drive control strategy increased machine efficiency over that of the existing CRSPIM significantly at light loads. Specifically, the proposed scheme yielded machine efficiency of 80.8% on all loads whereas the existing CRSPIM gives an efficiency of 79.3%, 47% and 28% for a rated load of 5.1Nm and light loads of 2Nm and 1Nm respectively. Consequently, the proposed drive scheme gives improvements of 1.5%, 33.8% and 52.8% respectively for the 5.1Nm, 2Nm and 1Nm loads over that of the conventionally-driven CRSPIM. The corresponding improvement in power consumption is a decrease of 1.6%, 45.1% and 67.6% for loads of 5.1Nm, 2Nm and 1Nm respectively.These results unveil the capability of the proposed scheme toachieve significant energy saving at light loads. The scheme is potentially able to cancel undesirable noise, reduce energy cost of running the motor, and offer possibility of cumulative savings in electric power resources of electric utilities.