An Arcless Theory of Mechanical-Electronic Hybrid Commutation

The mechanical commutator of a brushed dc motor has a risk of arcing, and the electronic commutator of a brushless dc (BLdc) motor has a high cost and complicated control. In this article, a novel topology for mechanical-electronic hybrid commutation is proposed, and a hybrid commutation theory considering contact resistance is established. In the hybrid commutator, the mechanical component consisting of a commutator and three brushes is used to generate three-phase 120 degrees square waves. The electronic component is a freewheeling circuit consisting of a capacitor, inductors, and diodes that can suppress the arcing caused by the mechanical component. In contrast with the mechanical commutation of a brushed dc motor, the hybrid commutator fundamentally solves the problems of the interrupting arc and closing arc. Compared with the electronic commutation of a BLdc motor, the hybrid commutator does not require power electronic switches and position sensors and has a low cost and simple control. The validity of the proposed hybrid commutation theory is verified by experiments and the practicality is discussed.