Novel switching strategy for high-efficiency of single-phase three-level inverters

Abstract

This paper proposes a novel switching strategy for high efficiency of a single-phase three-level inverter. Normally, the conventional unipolar and bipolar switching methods are used in the single-phase three-level inverter. In comparison with two conventional switching methods, the proposed switching method, which keeps switching state of some switches for switching period, is advantageous in efficiency. In this paper, an operation principle of the proposed switching strategy is introduced. It is easy to implement because the operation principle is based on the unipolar switching method. Furthermore, in comparison with the unipolar switching method, the efficiency and the current total harmonic distortion of the proposed switching method are shown by simulations results. bipolar switching methods are the conventional method for the single-phase two-level inverter. These switching methods can be applied in the single-phase three-level inverter. In (10), an optimal switching method is introduced for both the high efficiency and current ripple reduction in the two-level inverter. It is based on analysis of time-domain current ripple. In (11), a flexible switching speed control to reduce the gate driver current is proposed to decrease switching loss. In this paper, the operation principle and characteristic of the unipolar and bipolar switching methods are introduced. Then, this paper proposes a novel switching method for the switching loss reduction in the single-phase three-level NPC inverter. The unipolar switching method, which has performance better than the bipolar switching method (12), is applied to the single-phase three-level inverter. Then, It is compared with the proposed switching strategy. In the proposed switching strategy, reference signals used in the unipolar switching method are changed. As a result, in one leg, one switch is fixed to ON- or OFF-state while another switch is operating. Therefore, it is possible to obtain the advantage of that switching loss is reduced. Simulations are implemented to demonstrate feasibility of the proposed switching method for high efficiency of the single-phase three-level inverter. Additionally, based on simulations, the efficiency and current total harmonic distortion (THD) are shown by comparing the proposed switching method with the unipolar switching method.