Design of a multispeed winding for a brushless DC motor and its sensorless control

V-belt-linked continuously variable transmissions (CVTs) find extensive use in both internal-combustion-engined and electric scooters. The CVTs are used to increase the starting torque and also extend the range of the operating speed of the vehicles. Unfortunately, the efficiency of a CVT is relatively low due to friction effects and the alternative techniques based on flux weakening control are both complex and costly to implement. To circumvent these problems a multispeed winding is designed that is able to increase the starting torque at low speeds and extend the constant-power speed ratio for small and midsized brushless DC motors. Moreover, in order to increase the reliability of the drive system, a cost-effective sensorless control algorithm is developed. The commutation signals can be directly extracted from the average terminal voltages of the motor using simple RC circuits and comparators. This means that the sensorless commutation can be implemented by simply using low-cost CPLDs or microcontrollers. The proposed approach is particularly suitable for application to cost-sensitive electric vehicles such as wheel chairs, bikes and scooters and also hybrid electric scooters. A theoretical analysis of the pattern is performed and various experiments are conducted to evaluate the effectiveness of the proposed method.