A Multilevel Nine-Concentric Octadecagonal Space Vector Structure for Induction Motor Drives Using a Single DC Source

Low frequency switching of voltage source inverters generates low order harmonic voltages in the output causing torque and speed ripple. In this paper, a multilevel space vector diagram formed by nine-concentric octadecagons (polygons with 18 sides) using a single DC source is presented which eliminates lower order harmonics till seventeenth order from the phase voltage output over the entire modulation range including overmodulation. The topology consists of a flying capacitor (FC) inverter followed by a capacitor fed cascaded H-bridge (CHB) inverter. Single DC source permits easy four quadrant operation. The PWM scheme implemented results in quasi-square waveform operation of the FC inverter resulting in low switching losses. The CHB inverter switching removes the harmonics generated by FC inverter, but operates at a lower voltage. Hence the switching loss is low in the CHB inverter also. The power circuit topology, the formation of the space vector structure and the steady state and transient simulation results are presented in this paper