Stability Synthesis of Control System in Current Fed Inverter Driven Induction Motor

This paper presents a new method of synthesizing a stabilizing control system in current fed inverter driven induction motor (CFIDIM). The method is focused on rotor dynamics and a concept of ``damping torque coefficient (DTC)´´ is introduced concerning the electrical torque. At first the control system is synthesized on the assumption that an induction motor is driven by an ideally controllable current source. Then perturbed linearized technique indicates that the system can be stabilized if the stator current or frequency is controlled so as to make the DTC positive by feeding back a signal composed of rotor speed. Next, based on this fact, an approach of synthesizing the converter output voltage is presented under a fixed stator frequency. This result clarifies that the stable operation can be achieved by controlling the voltage in proportion to the acceleration of rotor speed or the deviation of electrical torque. These analytical results are verified by laboratory field tests.