Space vector modulation for three-level NPC inverter using two-level space vector diagram

Abstract

A novel concept that uses two-level (2L) space vector diagram (SVD) to achieve three-level (3L) space vector modulation (SVM) is introduced in this paper. Main emphasis is given on neutral-point (NP) clamped (NPC) inverter, though, the idea does not depend on the topology. Two interesting schemes for NPC namely nearest three vector (N3V) modulation and nearest three virtual vector (N3VV) modulation are considered for detailed analysis. The main technical drawback of NP voltage oscillations with N3V is a effectively addressed by N3VV for full modulation and power factor range. However, the extensive calculations involved in the process of obtaining the duty ratios have made this method difficult to implement. In this paper, first, simple mathematical relations are established for N3V and N3VV modulation methods using 2L SVM. Later, appropriate modulation algorithms are developed for implementation. The simplicity of the proposed modulation approach has a significant impact on execution process. No simplifications have made in the Space vector diagram (SVD) unlike some newly proposed simplified schemes. The performance of the proposed modulation algorithm is simulated in MATLAB, Simulink for various operating conditions.