Analysis and design of a current-sensorless synchronous rectification power factor correction SEPIC converter applying to brushless DC motors

This paper proposed a current-sensorless synchronous rectification (SR) PFC SEPIC converter applying to brushless DC motors. A novel control method was proposed to the SEPIC converter to save a current sensor. Through the relationship between the input voltage and the output voltage, the duty ratio of the synchronous rectifier switch can be obtained without any current sensing element and the cost can be reduced. In order to avoid the conduction time overlap of the main switch and the synchronous rectifier switch, the charging time causing by the parasitic capacitor of the switch has to be estimated. The digital control method used in the current-sensorless PFC technology would not suffer the problem of possible variation in analog control. Two modulation control methods “PWM” (Pulse Width Modulation) and “PAM” (Pulse Amplitude Modulation) were used in the succeeding motor control. The interface of control was DSP TMS32028335 of Texas Instruments.