PROJECT TITLE :

A Simplified Space Vector Modulation for Four-Level Nested Neutral-Point Clamped Inverters with Complete Control of Flying-Capacitor Voltages - 2017

ABSTRACT:

Four-level nested neutral-purpose clamped (NNPC) inverters experience severe voltage balancing issues beneath low output-frequency conditions when the traditional four-level space vector modulation (4L-SVM) technique is applied, which limits their wider application. In order to urge a whole control of the flying-capacitor voltages, and to alleviate the calculation burden of typical 4L-SVM, a simplified but effective 4L-SVM technique together with the voltage balance management (VBC) perform is proposed during this paper. For low modulation indexes, zero and tiny vectors are selectively utilized and distributed to force the common charging and discharging time of flying capacitors to be equal to each alternative throughout every switching amount, therefore that voltage ripples are greatly reduced to be within a suitable level underneath low output-frequency conditions. For high modulation indexes, the simplification of typical 4L-SVM for NNPC inverters into 2-level SVM is proposed to reduce the computation complexity. Principles of the proposed 4L-SVM and VBC are elaborated intimately. The steady-state, transient-state, and VBC performances are investigated and compared with the case where the traditional 4L-SVM is applied. Simulation results of a five MVA inverter system and experimental results of a scaled-down five kVA inverter system are presented to validate the proposed methodology.