Optimal control of brushless PM motor in parallel hybrid propulsion system

The paper outlines a case study on optimal control of a brushless direct-current (BLDC) motor as a part of an Integrated Starter-Generator and torque Booster (ISGtB) application in a hybrid propulsion system. The main scope of the introduced research work is the optimization of the BLDC motor torque characteristics. The discussed hybrid propulsion system consists of an internal combustion (IC) engine and a BLDC machine and is in its origin intended to drive the motorcycle. Stringent starting torque demands, electrical machine geometry limitations and a wide rotational speed range of the BLDC motor are reasons for control algorithm analysis in the low-speed operation range. Two approaches for the optimization of the torque characteristics are discussed, the flux-weakening method and a modification of transistor conduction angle. A novel control principle which includes both of the above approaches is proposed. A comparison between a commonly used control method and the proposed control method is presented. Simulation and experimental results fully confirm improvements in the starting procedure of the hybrid propulsion system attained by the proposed control algorithm of the BLDC motor.