Modelling and identification for reduction of overvoltage transients

The main problems that appear when using a long cable connection between a variable frequency drive (VFD) and the AC motor are overvoltages and bearing currents. The latter concerns especially EMC, while the overvoltage transients can be fatal to the motor. The ´converter-cable-motor´ system behaviour concerning overvoltages is investigated and then an online identification of the cable parameters is proposed. This result could be used to reduce overvoltages. An algorithm is introduced that decreases the amplitude of the adverse overvoltage effect. The algorithm is based on the modification of the applied PWM pattern.