Elevator polyphase motor control

Claim 1

An elevator system comprising: a polyphase electric motor, said motor having N phases and corresponding windings, N being two or more; a D.C. power supply; an inverter, powered by the supply, for providing current or voltage to each stator winding in the motor, said inverter having an input for each winding and a corresponding output; a position encoder for providing a signal (TACH) that identifies the motor shaft position; an elevator car that is propelled by the motor; an elevator control system for controlling the operation of the inverter to produce alternating N phase current or voltage for said stator windings to control motor speed (r.p.m.), slip and direction; the elevator system being characterized in that said control system comprises: means for providing a signal (AMPLITUDE) in response to the TACH signal to control motor speed (r.p.m.); means for providing a signal (SLIP) in response to the TACH signal to control the difference between the motor r.p.m. and the frequency (F SYNCH) of the alternating current or voltage that is supplied to the motor by the inverter; means, responsive to the SLIP signal and TACH signal, for providing a signal that repeats at F SYNCH, said signal identifying an angular position on a sine curve, and for providing, from said signal that repeats at F SYNCH, N second signals, each representing the Y-coordinate on said sine curve at different angular positions thereon, said positions being equally spaced apart by 360°/N, and said N second signals being provided in a successive sequence during each motor rotation, the sequence in one motor direction being the reverse of the sequence in the opposite direction; means for providing an inverter drive signal from each second signal as it is produced, and varying the magnitude of the inverter drive signal as a function of the AMPLITUDE signal; means for applying each inverter drive signal to the correct one of the inverter inputs according to said successive sequence in response to one of N control signals; means for generating N signals in a repeated succession during each motor rotation, each identifying an inverter input, to provide the N control signals; means for providing a third signal in response to said TACH signal and said SLIP signal, said third signal representing a motor shaft position within one of four possible quadrants on a sine curve with a frequency of F SYNCH and being repeated a plurality of times during each shaft rotation, and for providing a fourth signal in response to said third signal, said fourth signal representing a position of 0°-180° on said sine curve, said plurality being a function of the magnitude of said SLIP signal and proportional to motor slip represented by said SLIP signal; and means for providing corresponding pairs of fifth and sixth signals in response to said fourth signal, each of said fifth signals representing an angular position on the sine wave between 0°-180°, said positions being 180°/N degrees apart for each fourth signal, each of said sixth signals representing the correct sign, either plus or minus, for its corresponding fifth signal; and means for providing a corresponding seventh signal in response to each fifth signal, said seventh signal being the sine X, where X identifies an angular position between 0°-180° that is identified by the fifth signal.