An alternative approach on three-dimensional space-vector modulation of three-phase inverters

This paper presents a new standpoint on the analysis of the space-vector modulation (SVM) in three-phase inverters. By means of a three-dimensional (3D) approach, a mathematically and physically sound explanation of the modulation process is obtained. As it is well known, a three-phase two-level voltage source inverter has eight switching states, which give rise to eight generating vectors (two of them are the zero-vectors). Taking into account that the reference voltage vector will be synthesized by these generating vectors, it seems interesting to translate the reference vector from the natural a-b-c reference base to a new one, which is directly based on the generating vectors (generating base). In this new base, one of the three unitary vectors always follows the direction of the zero-vectors (zero-sequence axis). Moreover, in a three-leg full-bridge (TLFB) inverter, the voltage synthesized over the zero-sequence axis does not appear in the load side. Therefore, it is logical to cancel the contribution of the zero-vectors on the inverter output in order to obtain the maximum use of the dc-link voltage. This cancellation is really easy when the reference vector is expressed on the new generating base, since it is only necessary to eliminate the zero-vectors direction component. As a result of this analysis, a very efficient three-dimensional space-vector modulation (3D-SVM) algorithm is introduced. In this algorithm, the modulator input variables are given in the natural a-b-c reference frame. The proposed modulation method rests on the well-known carried-based modulation technique, and avoids trigonometric calculations, definition of optimal sequences, and control of the switching intervals. The proposed 3D-SVM technique is verified by simulation and experiment.