Vector quantized spread spectrum Pulse Density Modulation for four level inverters

A Pulse Density Modulation scheme based on Space Vector with Vector Quantization for four level inverter is proposed in this paper. The scheme disperses the power spectrum of the inverter output voltage as a wide-spectrum noise. The vector space of inverter reference space vector region is divided into voronoi regions to find out switching vectors. A new method is presented 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 space-vector diagram of four-level inverter is simplified to two-level space-vector diagram by the principle of mapping. The switching vectors are determined for two-level inverter using the proposed scheme and these switching vectors are then translated to the actual switching vectors of the four-level inverter by reverse mapping. The proposed scheme naturally selects the outer vectors in the over-modulation condition and hence results in a smooth transition from linear to over-modulation region. The scheme is implemented for 2-HP three phase open ended winding induction motor.