Virtual-Space-Vector PWM for a Three-Level Neutral-Point-Clamped Inverter With Unbalanced DC-Links

• Published in: IEEE transactions on power electronics Vol. 33; no. 3; pp. 2630 - 2642
• Main Authors: Wu, Xiang, Tan, Guojun, Ye, Zongbin, Yao, Guangyao, Liu, Zhan, Liu, Guanghui
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.03.2018; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Capacitors; Inverters; Links; Pulse duration modulation; Pulse-width modulation (PWM); Reactive power; Space vector pulse width modulation; three-level neutral-point-clamped inverter (3L-NPC); virtual-space-vector PWM (VSVPWM); Voltage control
• ISSN: 0885-8993; 1941-0107
• DOI: 10.1109/TPEL.2017.2692272

In this paper, the properties and operation of the virtual-space-vector pulse-width modulation (PWM) for a three-level neutral-point-clamped inverter with unbalanced dc-links are studied. By quantitatively analyzing the characteristics of the revised space-vector diagram (SVD) with unbalanced dc-links, the defined virtual SVD (VSVD) for the unbalanced case is theoretically proven identical to the VSVD of the conventional virtual-space-vector PWM (VSVPWM) strategy with balanced dc-links. The well-developed and fast-processing methods to calculate the durations of the nearest three virtual vectors for the conventional VSVPWM can be directly utilized. In addition, a control strategy to realize the asymmetric control of the dc-link voltages with VSVPWM is also studied, and this method can adjust the unbalancing degree with a high accuracy for any modulation indexes and load power factors. Simulated and experimental results are given to validate the effectiveness.