Steady-State and Stability Analysis of Induction Motor Driven by Current Source Inverter

Steady-state characteristics and instability of an induction motor driven by current source inverter are studied in comparison with the system driven by voltage source inverter. It is shown that as the speed is increased the electromagnetic torque takes three extremities a maximum torque is close to the standstill and a minimum and a second maximum torques are near to the synchronous speed. Thus the magnitude of the starting torque is slightly less than the breakdown torque and larger than that for the voltage source type. Operation close to the synchronous speed is impractical, because of the higher copper loss and lower efficiency due to the increase of current and the decrease of the power factor with increasing speed. As this fact prevails also in the negative slip region, a dynamic brake action rather than a regenerative braking action will be obtained. Over a wide range of slip, higher torques than those for the voltage source type are obtained. Instability appears usually as a sustained oscillation on armature voltage and current. Applying the Routh-Hurwitz criterion, several instability boundaries for various parameters are described. Some experimental results are presented which show essential agreement with the theory.