Patent ID: 7122992

Claim:
An inverter system for driving an induction motor, comprising: a rectifying circuit for rectifying an AC voltage from a three-phase AC power supply and outputting the same; a smoothing circuit being connected to the rectifying circuit and for smoothing an output voltage from the rectifying circuit to provide the same; a controller for detecting a DC link voltage of the smoothing circuit, determining a power failure mode, a normal mode or a power restoration mode according to the detected DC link voltage and time, determining the normal mode to output a voltage pulse signal according to a target frequency if the detected DC link voltage is higher than or the same as a predetermined normal reference voltage, outputting a voltage pulse signal having a voltage smaller than the voltage according to the target frequency by a regeneration bias voltage obtained by calculation if the detected DC link voltage is the same as or smaller than a predetermined electrostatic reference voltage, and outputting a voltage pulse signal according to the frequency finally outputted and stored at the time of power failure if the detected DC link voltage is higher than the predetermined electrostatic reference voltage and smaller than or the same as the normal reference voltage and when in the power restoration mode in which a predetermined power restoration time has passed; and an inverter for driving the induction motor by converting the DC voltage outputted from the smoothing circuit into an AC voltage of variable frequency and variable voltage according to the voltage pulse signal outputted from the controller.