Comprehensive predictive control of neutral-point voltage balancing for back-to-back three-level NPC converters

FAN Bi-shuang(范必双)^{1, 2}, TAN Guan-zheng(谭冠政)¹, FAN Shao-sheng(樊绍胜)², YE Ji-xiang(叶吉祥)^{1, 2}

(1. School of Information Science and Engineering, Central South University, Changsha 410083, China
2. School of Electrical and Information Engineering, Changsha University of Science and Technology,
Changsha 410076, China)

Abstract:A comprehensive predictive strategy was proposed for the neutral-point balancing control of back-to-back three-level converters. The phase currents at both sides and the DC-link capacitor voltages were measured for the prediction of the neutral-point current. A quality function was found to balance the neutral-point, and a metabolic on-times distribution factor was used as a predicator to minimize the quality function at each switching state. Simulation results show that the proposed method produces smaller ripples in tested signals compared with the established one, namely, 9.15% less in a total harmonic distortion (THD) of line-to-line voltage, 1.08% less in the THD of phase current, and 0.9 V less in the ripple of the neutral-point voltage. The obtained experimental results show that the main harmonics of the line-to-line voltage and the phase current in the proposed method are improved by 10 dB and 6 dB, respectively, and the ripple of neutral-point voltage is halved compared to the established one.

Key words:back-to-back converter; three-level converter; neutral-point balancing; comprehensive control; predictive control