Control of single-phase permanent magnet brushless DC drives for high-speed applications

Single-phase permanent magnet brushless DC (BLDC) motors are widely used for low cost applications. The authors have developed a single-phase BLDC drive for retrofitting into a state-of-the-art vacuum cleaner. However, it was found that due to high operation speed (20,000 RPM) and high winding inductance, the current and EMF waveforms were out of phase if the conventional control technique was used. Consequently, a negative torque component is generated and the overall torque is significantly reduced. In order to maximise the motor power density and to minimise the motor peak phase current so as to reduce the power device ratings for high-speed applications, two alternative commutation strategies are studied-one using the phase commutation advancing technique and another using conducting pulse-width control. The paper describes the techniques and reports the corresponding simulated and measured performance.