PERFORMANCE EVALUATION OF 3-PHASE 4-SWITCH INVERTER FED BRUSHLESS DC MOTOR DRIVE

Abstract

Brushless direct current (BLDC) motor is a self synchronous motor, similar to PMSM in structure. Its many advantages like easy speed control than other ac machines, high efficiency, high power density, low noise, and low maintenance cost while having characteristics similar to dc motor makes it suitable for many applications. A three phase BLDC motor is fed by six switch inverter operating in 1200 mode and only two phases are `on' at any instant. Other 60° of operation in a half cycle, one phase current is zero and other two phases are `on'. This concept led, to development of four switch inverter (FSTPI) fed BLDC motor drive. Different PWM techniques used for BLDC motor drives are triangular carrier method, hysteresis band control techniques. These are briefly explained. A most popular direct current control PWM technique using hysteresis band for current controlled voltage source inverter feeding BLDC motor is presented. In this work, first a six switch inverter fed is drive developed in matlab-simulink using simulink and power system block set toolboxes and its performance is evaluated with different speed controllers like pi, fuzzy. Next, a FSTPI fed BLDC motor drive is developed. The dynamic response of FSTPI-BLDCM drive under various operating conditions such as starting, speed reversal, and load perturbation is simulated using different speed controllers mentioned above. Results of four switch operation are compared with the six operation of BLDC motor drive. In four switch inverter fed drive, capacitors in one leg has its own affects on the performance of the drive and detailed analysis is done in all regions of operation. Drive performance is compared for different values of capacitances and initial rotor positions. Due to unbalanced voltage operation of FSTPI, at high speeds commutation torque ripple problem is seiere and introduces more noise in the drive and sometimes it may affect speed response. Commutation torque ripple in FSTPI drive is analyzed and compared with its six switch counterpart at all speeds of operation with rated load. A new way to reduce commutation torque ripple is presented. This developed technique is applied to forward motoring operation of the FSTPI-BLDCM drive. This technique ensures the FSTPI fed drive can be much more practically applied for the industrial applications. Validity of the proposed scheme is verified by the simulation results.