Patent ID: 8519664

Claim:
A method for controlling a machine or an electrical load supplied by a drive controller over a long AC power cable, in which method said drive controller is operated to provide AC current to said load or machine at a substantially constant ratio of voltage and frequency by obtaining an estimate or measurement of a current and voltage output in said drive controller, characterized by calculating an estimated voltage at the terminals of said machine or electrical load using a simplified load flow model of the drive controller, a step-up transformer, the long AC power cable, a step-down transformer and the machine, the estimated voltage being determined using dq-coordinates as a motor or electrical load absolute voltage vector Um _abs=(sqrt(( Umx^ 2)+( Umy^ 2)))*sqrt(3) where motor or electrical load dq voltage is defined by Umd=Ut 2 d−I 5 d*Rt 2 +I 5 q*w*Lt 2 Umq=Ut 2 q−I 5 q*Rt 2 −I 5 d*w*Lt 2, where Ut 2 d=Ut 1 d−I 3 d*Rcl+I 3 q*w*Lcl Ut 2 q=Ut 1 q−I 3 q*Rcl−I 3 d*w*Lcl are the step down transformer dq-voltages, I 5 x=I 3 x−I 4 x I 5 y=I 3 y−I 4 y are the motor or electrical load dq-currents, Rt2 is the step-down transformer resistance, Lt2 is the step-down transformer inductance, w is actual output electrical frequency per unit, Rcl is the cable inductance of the long AC power cable, Lcl is the cable inductance of the long AC power cable, Ut 1 d=Ucd−Icd*Rt 1 +Icq*w*Lt 1 Ut 1 q=Ucq−Icq*Rt 1 −Icd*w*Lt 1 are the step-up transformer output dq-voltage, I 2 d=−Ut 1 q*w*Ccc I 2 q=Ut 1 d*w*Ccc are the cable capacitance leakage dq-currents flowing through Ccc, the cable reactance of the long AC power cable, at the converter side, I 3 d=Icd−I 2 d I 3 q=Icq−I 2 q are the dq-Currents flowing through the cable inductance Lcl, I 4 d=−Ut 2 q*w*Ccc I 4 q=Ut 2 d*w*Ccc are the cable capacitance leakage dq-currents flowing through the cable reactance Ccc at the electrical load side, and Ucd is d-axis component of the converter voltage per unit, Icd is d-axis component of the converter current per unit, and Icq is q-axis component of the converter current per unit; and adding a difference between the estimate and the output to control the drive controller to provide said constant ratio of voltage and frequency at the terminals of said load or machine based on the estimated voltage at the terminals.