Space Vector based pulse Density Modulation scheme for two level voltage source inverter

Abstract

A Space Vector based Pulse Density Modulation scheme for spreading the spectra of Voltage Source Inverters is proposed in this paper. The proposed scheme employs first order Sigma-Delta Modulator. The principle of Vector Quantization is applied for quantizing the reference voltage Space Vector in the Sigma Delta Modulator. For the spatial quantization, the inverter voltage vector space is divided into seven Voronoi regions. In this paper, a method is proposed to code these Voronoi regions using instantaneous reference phase amplitudes without using lookup table. To avoid fractional arithmetic sixty degree coordinate system is used. The proposed scheme automatically selects the apex vectors in the over-modulation condition and hence results in a smooth transition from linear to over-modulation region. In Pulse Density Modulation, the switching frequency varies randomly, resulting in the spreading of harmonic spectra. The proposed scheme uses only instantaneous reference phase amplitudes to obtain switching vectors without using lookup table and timer. The proposed scheme is implemented and tested with 11.5 kVA two-level inverter driving 2-HP three phase induction motor. Experimental results of proposed scheme are compared with Space Vector PWM and Random Space Vector PWM.