INDUCTION MOTOR DRIVE APPARATUS

PROBLEM TO BE SOLVED: To provide an induction motor drive apparatus, which switches inverter units promptly and can minimize the reduction of a rotational speed of an induction motor during switching. SOLUTION: In the induction motor drive apparatus comprising inverter units 1, 2 and inverter control circuits 5, 6; a plurality of inverter controllers that operate one induction motor 3 at variable speeds; and circuit breakers 12, 22, which are respectively arranged between the inverter units 1, 2 and the induction motor 3 and are connected in parallel with each other, induction motor rotational frequency-phase detection circuits 15', 25' for the inverter control circuits 5, 6 are provided in the side of the induction motor 3 rather than the circuit breakers 12, 22 to detect a frequency and a phase of a terminal voltage of the induction motor 3, regardless of ON/OFF of the circuit breakers, and input to failure-time input frequency-phase setting circuits 17, 27; and thus, an operation of the failure-time input frequency-phase setting circuits is always performed so as to shorten the time period for calculating an inverter unit starting frequency-phase. COPYRIGHT: (C)2009,JPO&INPIT