Spread Spectrum Scheme for three-level inverters based on Space Vector Sigma Delta Modulator

A scheme for spreading the harmonic spectrum of Three-level Voltage Source Inverters is proposed in this paper. Space Vector based Sigma Delta Modulation is employed in the proposed scheme. The principle of Vector Quantization is applied for quantizing the reference Space Vector in the Sigma Delta Modulator. For the spatial quantization, the inverter voltage vector space is divided into different Voronoi regions. A method is proposed to code these Voronoi regions using instantaneous reference phase amplitudes without using lookup table. The proposed scheme naturally selects the outer vectors in the over-modulation condition and resulting in a smooth transition from linear to over-modulation region. The spectrum of inverter output is spread so that concentrations of power at switching frequency harmonics are avoided. The proposed scheme is implemented for 2-HP three phase induction motor in open-end winding configuration driven by dual 11.5 kVA two-level inverter driven from both ends. Experimental results of proposed scheme and comparison with Space Vector PWM are presented, including operation in over modulation region.