High input power factor adjustable-speed drive system based on an electrolytic capacitor-less single-stage boost inverter

This paper presents an electrolytic capacitor-less adjustable-speed drive (ASD) system fed by single-phase power supply with almost unit input power factor. The tapped inductor quasi-Z-source inverter (TL-qZSI) is used to replace the dc-bus electrolytic capacitors, which can maintain the dc-bus voltage during voltage sag, and enhance system reliability. Without the electrolytic capacitors to balance the input and output power, higher input power factor will lead to more low-frequency harmonic distortion of dc-bus voltage due to the 2nd harmonic current drawn by the input. The proposed Low-frequency Harmonics Minimization (LFHM) method by using the shoot-through zero state and input Power Factor Improvement PWM (PFI-PWM) by using the modulation index are presented, which can greatly reduce the low-frequency dc-bus voltage ripple while improving the input power factor. The system structure and the proposed LFHM and PFI-PWM method are analyzed in detail. The effectiveness of the proposed system has been verified by simulation and experimental results.