Electrical two-speed propulsion by motor winding switching and its control strategies for electric vehicles

Theoretical analyses and computer simulation studies lead the authors to propose: 1) a new electrical two-speed propulsion system for electric vehicles (EV's) by switching induction motor windings and 2) an improved fuzzy logic control-continuous defuzzification method for the control of this system. The two-speed propulsion is achieved by connecting the motor stator windings in series for starting an EV and then switching the windings to parallel connection for normal speed operation. The method produces a high starting torque, yet maintains the inverter within its rated power range. As compared with Star-Delta starting of induction motors, the proposed series-parallel method offers higher starting torque and acceleration. The control strategies for this system are investigated. A comparison of fuzzy logic control with a conventional proportional-integral (PI) shows that a fuzzy logic controller (FLC) can be applied to EV propulsion systems. Simulation studies also demonstrate that an improved FLC method using a continuous defuzzification technique provides smoother torque and leads to lower harmonic components in motor currents, thus further enhancing this EV propulsion system.