Soft-restarting of free-run induction motors driven by small DC-link capacitor inverters

This paper presents a small film capacitor inverter-based induction motor control approach to enhance with reliability and power density of three-phase variable speed drive applications. A robust hybrid motor controller is developed to prevent performance degradation caused by the electrolytic capacitor-less inverter fed by front-end diode rectifiers. The structure of the controller combines a model-based voltage controller (MVC) and a hexagon voltage manipulating controller (HVMC). The MVC determines the command output voltage with the intersection of the torque and rotor flux linkage command. In HVMC mode, the command voltage vector is determined simply by the torque command and the hexagon-shaped inverter voltage boundary. Successful application of the control approach is corroborated by a graphical and analytical means that naturally lead to a single voltage selection rule. This paper also examines the operation sensitivity under motor parameter drifts to determine how to decouple its effect using a voltage disturbance state-filter design.