A Direct Method for Generating Optimum Sequence of Switching Vectors for Multilevel Inverters

The paper presents a generalized method for generating Space Vector PWM (SVPWM) signals in an optimum sequence directly from the instantaneous amplitudes of the reference vector without using any look up tables. The proposed method is based on the observation that for every inverter voltage vector in each of the three 120 degrees regions in the space vector representation of a multilevel inverter, one of the three switches (defining the switching state) is at '0' level. The overall voltage space vector representation of a multilevel inverter is thus divided into three segments on the basis of the switching state at '0' level. This observation is used to generate the switching states directly from the coordinates of the inverter switching vectors. The relation between the inverter switching vectors and their corresponding switching states emerge as a consequence of representing the vectors in the sixty-degree coordinate framework thus avoiding fractional coordinates of the switching vectors. In the present work, simple generalized equations involving only arithmetic operation are also developed for generating the duty cycles for the gating signals in optimum sequence, from the switching states and their durations. The proposed method can be used for the direct generation of SVPWM for any n-level inverter. Experimental results are presented for an open-end winding based 5-level inverter.