Digital control strategy for efficiency optimization of a BLDC motor driver with VOPFC

This paper proposes a dual-mode control strategy for BLDC motor drivers with power factor correction used in high-efficiency compressor applications. The motor driver consists of a front-stage variable output voltage PFC (VOPFC) converter and a rear-stage 3-phase PWM inverter. The VOPFC converter is a cascaded buck-boost converter with two power switches to regulate the input line current with low total harmonic distortion (THD) and at the same time to maintain an adjustable dc-link voltage which can be either higher or lower than the peak of the rectified line voltage. The output inverter stage can be operated in pulse amplitude modulation (PAM) mode or PWM mode with reduced switching frequency for efficiency optimization of the compressor motor driver to maintain a constant V/Hz ratio with specified current ripples. The proposed control scheme has been verified with a DSP-controlled VOPFC PWM/PAM motor driver and an efficiency improvement of 3% has been achieved.