| 摘要 |
The load side converter or inverter in a load commutated inverter motor drive, including a source side AC to DC converter coupled to a DC to AC converter via a DC link circuit, is adapted to have at least three and preferably four modes of operation for bringing an AC motor load, and more particularly a synchronous motor, up to speed. In the preferred embodiment, the first mode constitutes an idle mode wherein the converter thyristors are maintained in a non-conducting state until commanded for normal operation. The second mode constitutes an initial start-up mode which assumes no knowledge of initial rotor position of the motor and simply utilizes a fixed low frequency firing signal to sequentially gate the thyristors using forced commutation to commutate the off-going thyristor. Thirdly, a second type of forced commutation mode is next entered into where the inverter frequency is synchronized to the rotor of the motor by sensing pseudo-flux waveforms until 5% to 10% of rated motor speed is achieved whereupon a fourth mode is entered into which comprises a self-commutation mode utilizing a phase lock loop operation using pseudo-flux wave zero crossings as synchronizing signals. In the three mode embodiment, the third mode is eliminated and the second mode modified to vary the load side converter frequency on a time basis until reaching some preset value (e.g., five (5) to fifteen (15) percent of motor rated frequency) at which time transition is made to the self-commutation mode.
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