Analysis and Comparison of Two Types of Square-Wave Inverter Drives

The application of adjustable frequency static inverters to induction motor speed control has resulted in a diversity of inverter designs. In this paper, the state-variable formulation is applied to the analysis of two widely used drive systems incorporating square-wave inverters with 180° and 120° firing logic. Measured characteristics of an actual drive system are included, and the results are compared to an analytical solution. Steady-state speed-torque curves for each inverter supplying three markedly different types in induction motors are given. Performance of the two inverter drives are compared by a thorough investigation of typical operating points.