Direct Space Vector Modulation with Novel DC-Link Voltage Balancing Algorithm for Easy Software Implementation of Three-Phase Three-Level Converter

Abstract

The present paper proposes a direct space vector modulation and novel balance algorithm for easy software application of three-level converters which operate in three-phase. In the case of the conventional space vector modulation, to get the on-state times of the switches, the dwell times of the three nearest stationary vectors, which are obtained after sector and region selection algorithms, should be rearranged. These processes, therefore, contain diverse conditional statements and complicated calculations such as inverse trigonometric functions and square roots. However, the burden of the software application of the proposed algorithm is greatly reduced by not using the sector selection algorithm, the region selection algorithm, and the on-state time allocation process as the proposed modulation can directly control the switch on-state time. In a three-level topology, it is required to balance top and bottom capacitor voltages because the DC-link voltage is composed of two capacitor voltages; the unbalanced voltage of each DC-link capacitor causes the overvoltage of the switching devices. Thus, the DC-link voltage balancing algorithm is proposed, and it is also very simple and effective without additional circuits because it controls the switch on-state time directly as well. The 5-kW prototype proved the validity of the proposed algorithm with its feasibility.