Inverter apparatus and a restarting method at an instantaneous power failure

An inverter apparatus comprising:

• a converter for converting AC power to DC power;
• a smoothing capacitor for smoothing said DC power, said smoothing capacitor being connected to an output of said converter;
• an inverter connected to said converter and having switching elements and diodes for supplying AC power having a frequency obtained in converting said DC power to an induction motor connected at an output thereof;
• current detection means for detecting an output current of said inverter;
• power failure detection means for detecting a power failure of an input AC voltage of said converter;
• simultaneous ON/OFF control means for making switching elements on one of an upper arm and lower arm of said inverter operate ON/OFF simultaneously based on the output of said power failure detection means during free running of said induction motor;
• current direction detection means for detecting a direction of an output current of said inverter based on the output of said current detection means;
• frequency detection means for detecting a frequency of a residual voltage of said induction motor during the operation of said simultaneous ON/OFF control means based on said current direction detection means;
• restart timing signal generation means for outputting a restart instruction based on the output of said power failure detection means and the output of said current direction detection means;
• phase detection means for detecting a phase of a residual voltage based on the restart instruction and the output of said current direction detection means;
• and
• means for restarting said induction motor with an AC power having a frequency and phase based on the output of said frequency detection means and the output of said phase detection means.

A restarting method for an inverter apparatus at an instantaneous power failure comprising:

• a first step of executing ON/OFF control of switching elements of one of an upper arm and lower arm of an inverter of the inverter apparatus simultaneously from a time after elapse of a predetermined period of time from the occurrence of a power failure;
• a second step of detecting a frequency of a residual voltage of an induction motor connected to an output of the inverter apparatus during the first step;
• a third step of detecting a reversal of direction of an output current after the recovery of the power failure;
• a fourth step of suspending the first step at a time of detection of the reversal of the direction of the output current in the third step;
• and
• a fifth step, at the suspension of the first step, of restarting the induction motor by applying a voltage having a frequency, phase and voltage value corresponding to the frequency detected in the second step and the direction of the output current detected in the third step to the induction motor.