A BLDCM drive with trapezoidal back EMF using four-switch three phase inverter

The BLDCM (brushless DC motor) has a trapezoidal back EMF since it has a surface magnet rotor with nonlinear distribution and full-pitch windings. Theoretically, it should be fed with rectangular phase current in order to minimize torque ripple. But because voltage source inverters drive a BLDCM, a perfect rectangular phase current is not available. In recent years, BLDCM drives have used a 120° electrical conduction method with special a control algorithm which boosts phase current by comparing the magnitude between the back EMF and input voltage or hysteresis controller or noncommutation current control. In this paper, using Fourier series coefficients, calculating the coefficients of harmonic current within available orders and each harmonic component is controlled on a stationary αβ frame. The output of a current controller generates PWM patterns for a FSTPI (four-switch three-phase inverter) fed BLDCM drive. The Fourier series coefficients using FSTPI are useful to control both torque and speed, each phase current is a more rectangular shape than other methods. Only using four switches, a low cost and small size drive can be made and the proposed method will be more advantages in industrial applications. Simulation and experimental results prove the validity of the proposed method