Mathematical analysis and experimental validation of transient over-voltage higher than 2 per unit along industrial ASDM long cables

A mathematical technique to compute incident and reflected waves in long cable PWM drives has been developed. The mathematical formulas describing these waves are developed in the frequency domain. The inverse Laplace transform is then applied to obtain the time domain sets of equations for their computation at any point along the cable. This technique has permitted to investigate over-voltage transients and the dv/dt not only at the motor terminals, but all along the inverter-to-motor cable. As a result, the oscillation frequency, the critical cable length and the possible peak voltage could be determined. Over- voltage investigations has been done for i) inverter wide and spaced output voltage pulses ii) successive small and close pulses. Contrary to most previous papers, this work shows analytically that i) in the first case over-voltage can go up to 2 p.u ii) in the second case over-voltage can go higher than the known 2 p.u level and can reach up to 4 p.u in the worst conditions. This paper includes simulations and experiments that were carried out on an industrial 5 kVA ASD prototype using a 4-wire braided-shielded long cable. The simulation results are compared with the obtained experimental waveforms so as to validate the proposed technique.