The elimination of leakage currents in the neutral point clamped photovoltaic grid-connected inverter by the improved space vector pulse width modulation method

Abstract

In this paper, the reason of high-frequency leakage current in neutral point clamped photovoltaic grid-connected inverters that adopts traditional modulations is analysed. In order to solve the problem, this article puts forward two improved methods based on the three-level space vector pulse width modulation (SVPWM), which can reduce the leakage current by applying three medium vectors or using only two medium vectors and one specific zero vector to compose the reference vector. In addition, the system control method adopts the coordination control of the current inner loop and the DC voltage outer loop, which can reduce voltage fluctuation at the DC side. Thereby, the suppression of leakage current can be realised without requiring any modification on the multilevel inverter. Compared with the traditional three-level sinusoidal pulse width modulation (SPWM) and SVPWM, the two new methods are advantageous in having a stable common-mode voltage, low leakage current, and low harmonic component of grid current. The theoretical analysis and results show the effectiveness of the proposed methods.