Cross tie for induction motor drive

Claim 1

An alternating current motor drive comprising: (a) an alternating current induction motor; (b) an alternating current to direct current converter for providing an output voltage and current of variable magnitude to a link circuit; (c) control means for controlling said output current including, (i) means responsive to an input signal representing desired motor speed to establish a control signal representing a desired output voltage of said alternating current to direct current converter, and, (ii) means for limiting the magnitude of said control signal at a limited value; (d) a direct current to alternating current converter for converting the direct current on said link circuit to an alternating load current for application to said motor; (e) control means for controlling frequency of said load current including means responsive to the input signal representing desired motor speed for establishing an initial flux set point signal; and, (f) a cross tie circuit for selectively effecting a modification of said initial flux set point signal to provide a final flux set point signal for use in the control of said converter, said cross tie circuit comprising: (i) means to establish a reference signal representative of a percentage of the limited value of said control signal, (ii) means to combine said reference signal with said control signal to provide a difference signal when said control signal exceeds said reference signal, (iii) means to modify said difference signal to provide a cross tie signal and, (iv) means to combine said cross tie signal with said initial flux set point signal to provide said final flux set point signal.