Hybrid System Simulation of Current Controlled BLDC Drive

Permanent magnet brushless DC (BLDC) machine with trapezoidal back emf is a common choice for low power electric drive applications such as electric bicycle and wheelchair. These applications require smooth operation with a good dynamic performance which necessitates high bandwidth controller. In this paper, the cascaded control loop with outer speed and inner current control loop is used for the BLDC drive. For the current loop, peak and average current programmed control are utilized and compared in simulation using MATLAB/Simulink and PLECS software. The simulation model for the drive is implemented as a hybrid system. In this hybrid system, the speed and average current controller are implemented as discrete system blocks, and the models for the pulse width modulator, the three-phase converter, and the machine are implemented using continuous system blocks. This way of simulation is a more realistic simulation compared to the conventional way of simulation with continuous system blocks only. In addition, the peak current programmed control is also implemented and compared with average current programmed control. The instability involved with the peak current control where the duty cycle is more than 0.5 is observed and solved with the slope compensation. The slope selection of the compensation signal from the speed reference signal is also presented. The results are compared with that of the average current controlled drive system. A reduced torque ripple is observed for the peak current controlled drive system.