Patent ID: 6158553
Filing Date: 2000-12-12
Classification: H02P

Abstract:
An elevator motor drive system, comprising:a multiple-wound, three-phase, variable speed motor having a plurality, N, of winding sets;a car and a counterweight roped to a sheave driven by said motor;a plurality, N, of pulse width modulation inverters, each for providing current to a corresponding one of said winding sets;an actual speed detector responsive to the angular motion of said motor to provide an actual speed signal;a speed controller receiving an angular speed command signal and providing a torque current command signal as a limited function of the difference between said angular speed command signal and said actual speed signal;means providing an excitation current command signal;a first arithmetic function for providing a torque current command limit equal to the square root of the difference between the square of the summation of maximum current which can be tolerated by all of said inverters collectively and the square of said excitation current command;characterized by the improvement comprising:a failure control for providing switch control output signals in response to a failure in any of said inverters and for disconnecting from said motor any inverter sensed to have failed;a second arithmetic function for providing a torque current command limit equal to the square root of the difference between the square of the summation of maximum current which may collectively be tolerated by those of said inverters which have not failed collectively and the square of said excitation current command; anda switch responsive to said failure control to cause said current control to limit said torque current command signal in response to said first arithmetic function when no inverter has failed and to cause said current control to limit said torque current command signal in response to said second arithmetic function in response to said switch control output signals.