Elevator car load and position dynamic gain compensation

Claim 1

An elevator comprising: a polyphase electric motor, said motor having N phases and corresponding windings, N being two or more; a D.C. power source; an inverter for providing current or voltage from said source 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 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 being characterized in that said control 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 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, 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 varying the magnitude of each second signal as a function of the AMPLITUDE signal; means for applying each second signal to a different one of the inverter inputs according to said successive sequence; means for providing a dictated motor speed signal in response to the TACH signal, said dictated motor speed signal representing a desired motor speed; means for providing a cab load signal that represents the load in the car; and means for providing a first error signal in response to said dictated motor speed signal and said TACH signal, said error signal representing the difference between the actual motor speed and the desired motor speed, and for providing a second error signal by amplifying said first error signal in relation to said cab load signal so that the magnitude of said first error signal is increased when the motor is about to be started if the cab load is greater than a certain load; said means for providing said AMPLITUDE signal and means for providing said SLIP signal being responsive to said second error signal.