A new approach to analyze the overvoltages due to the cable lengths and EMI on adjustable speed drive motors

This paper presents a new model allowing the evaluation of the over voltages caused by the length of the cables feeding motors driven by PWM-controlled VSI. This model is elaborated using the mobile-wave theory. A full mathematical analysis of the voltage at the motor terminals is developed taking into account inverter output voltage rise and fall times and cable length effect. The established model is validated by simulation, using Matlab/Simulink software. Experimentation is also carried out on a 5 kVA industrial prototype. This paper gives also a practical approach of the model in order to coordinate the adjustable speed drive ASD systems with their feeding cables. Moreover, it presents a prospect extending this application to the treatment of EMI problems. This is possible since we can model electromagnetic couplings as induced voltage and current generators. So, the propagation of the electromagnetic noise can be studied using the same principle of the mobile-wave theory in the circuits made up of multiconductor cables. Simulation and experimental results are shown to validate some of the theoretical concepts proposed.