A wireless permanent-magnet brushless DC motor using contactless feedback and autonomous commutation

Abstract

This article proposes and implements a wireless permanent-magnet brushless DC (PM-BLDC) motor, which realizes precise closed-loop speed control and autonomous commutation by offering rotor position feedback in a contactless approach. To reduce the system complexity, a three-phase four-switch (TPFS) inverter is newly used to control the wireless motor. Incorporated with two orthogonal bipolar coils, the high-order compensation network provides four decoupled current paths to control the four self-drive switches in the TPFS inverter. By changing the frequency of the wireless power transfer, the motor phases can be properly energized to ensure a smooth operation in both directions without any microcontrollers at the secondary side. To equalize the motor current transmitted under different frequencies across a wide speed range, sigma-delta modulated pulse frequency modulation is adopted together with pulsewidth modulation, which also achieves higher efficiency and fewer effects from unexpected harmonics. The feasibility of the proposed design is validated by prototyping and testing a 4000-rpm 134-W PM-BLDC motor platform. Experimentations verify that the proposed wireless PM-BLDC motor achieves reliable commutation and precise speed tracking against load variations using contactless feedback.