Sensorless Control of Four-Switch, Brushless DC Motor Drive without Phase Shifter

Abstract

This paper presents analysis, design and implementation of a cost effective sensorless control technique for a low-cost four switch, three-phase inverter brushless DC motor drive. The proposed sensorless technique is based on the detection of zero crossing points of three voltage functions that are derived from the filtered terminal voltages v_ao, and v_bo. Six commutation instants are provided which coincide to zero crossing points of voltage functions. Hence, there is no need to any 30^o or 90^o phase delay that is prevalent in conventional sensorless methods. Two low-pass filters are used for elimination of high frequency noises and calculation of average terminal voltages. Also, direct phase current control method is used to control the phase currents in the four-switch inverter. An analytical study on position estimation error is discussed and a correction method for certain applications is suggested. The performance of the developed sensorless technique is demonstrated by simulation and then it is implemented using TMS320LF2407A digital signal processor (DSP). Experimental results are provided to confirm our simulations.