Direction sensing system for an AC power supply and AC motor drive with such direction sensing system

Claim 3

Apparatus for deriving an indication of the phase rotation of a three-phase AC power supply, comprising: means for sensing the phase voltages of said three-phase AC power supply and for deriving a waveform representative signal for each phase; means responsive to said waveform representative signals for detecting the occurrence of zero-crossovers for said phase voltages; three timer means each associated with one phase and respectively responsive to said waveform representative signals for counting with each waveform the amount of electrical degrees accumulated thereon, counting being initiated upon the occurrence of one zero-crossover and being reset upon the occurrence of the same zero-crossover in each of said timer means, thereby to derive a corresponding phase count; means for deriving upon a command signal a read count simultaneously from each phase count of said timer means; means for comparing said read counts in magnitude by pairs to derive a sign of inequality characterizing signal for each pair of read counts; means for establishing a first reference set of inequality signs characterizing for the three pairs of phases one direction of phase rotation and a second reference set of inequality signs characterizing for the respective pairs of phases another direction of phase rotation; and look-up table means for relating read count inequality characterizing signals to one of said first and second reference sets to derive a signal representing an actual phase rotation direction for said AC power supply.

Claim 4

Apparatus for deriving an indication of the phase rotation of a three-phase AC power supply, comprising: means for sensing the phase voltages of said three-phase AC power supply and for deriving a waveform representative signal for each phase; means responsive to said waveform representative signals for detecting the occurrence of zero-crossovers for said phase voltages; three timer means each associated with one phase and respectively responsive to said waveform representative signals for counting with each waveform the amount of electrical degrees accumulated thereon, counting being initiated upon the occurrence of one zero-crossover and being reset upon the occurrence of the same zero-crossover in each of said timer means, thereby to derive a corresponding phase count; means for deriving upon a command signal a read count simultaneously from each phase count of said timer means; means for comparing said read counts in magnitude by pairs to derive a sign of inequality characterizing signal for each pair of read counts; means for establishing a first reference set of inequality signs characterizing for the three pairs of phases one direction of phase rotation and a second reference set of inequality signs characterizing for the respective pairs of phases another direction of phase rotation; and look-up table means for relating read count inequality characterizing signals to one of said first and second reference sets to derive a signal representing an actual phase rotation direction for said AC power supply.

Claim 5

The apparatus of claim 2, with said AC power supply being the output of an inverter and the input of an induction motor in an AC motor drive system.

Claim 6

The AC motor drive system of claim 3 with said motor drive being a synchronous motor drive including an open-loop for controlling said inverter, said open-loop being responsive to a speed reference signal; with said feedback speed signal including an absolute value and a sign given by said direction of rotation of said AC power supply as representing one of the Forward and Reverse direction of rotation of said motor, with said sign of said feedback speed signal being derived from said look-up table means derived signal.