Position-sensorless method for electric braking commutation of brushless DC machines

To increase the cruising distance and braking reliability of various light electric vehicles (LEVs) actuated by brushless DC machines, this study proposes three cost-effective braking commutation strategies based on a general full-bridge DC/AC inverter without using position sensors. The braking commutation strategies investigated in this study are named according to the number of power switches in action over each commutation state; designated as single-switch, two-switch, and threeswitch, respectively. Theoretical analysis of the operation principle and important performance indices such as maximum voltage conversion ratio, braking torque, energy recovery ratio etc, are conducted and compared among each commutation strategy. Moreover, a cost-effective, sensorless method for each different braking commutation strategy is used. The commutation signals are extracted directly from the average terminal voltages. Since additional power switches, passive components and costly position sensors are not essential, the proposed method is particularly suitable for various LEVs such as electric bicycles, electric scooters, electric wheelchairs and so on. Finally, several experiments are performed to justify the effectiveness of the proposed method.