| A multitude of industrial processes use Adjustable Speed Drive (ASD) systems, which consist of a Pulse Width Modulation (PWM) source inverter with Insulated Gate Bipolar Transistor (IGBT) power devices. These drives offer many advantages including precise control of the motor speed, high efficiency, and retention of the motor torque at very low speed. However, in many applications, these systems require long motor leads; this is why motors often undergo overvoltages stress due to the reflected wave. These overvoltages increase with the length of the feeding cables (up to a critical cable distance) and the dv/dt generated by the inverter IGBT switches. In addition to torque oscillation and localized heating problems, they can cause the destruction of the motor insulation, in particular in the early turns. They can also cause partial discharges in the drive-to-motor cable thereby reducing its lifespan. Besides, the reflected waves affect the common mode (CM) voltage and the bearing current problems. As it will be shown in this thesis, they are also associated with oscillating currents in differential mode (DM) with a frequency range that can go up to several MHz (depending on the cable length), that have not been previously examined in detail. As a result, the conducted EMI problem, which is a common problem in ASD systems, gets worse.;First, It offers a new method of direct and fast calculation of the overvoltages due to the traveling waves. This method does not require any representation of the system components since it uses a mathematical formula which is well adapted to computer solutions. Besides, it expresses overvoltages not only at the cable terminals but also at any point along the cable.;Then, the thesis offers new mathematical expressions and new modeling schemes for incident and reflected waves of both current and voltage. Moreover, it identifies expresses and models the parasitic DM currents that have not been previously examined. These mathematical developments have led to some simulation tools for diagnosing ovevoltages and their associated DM currents along the cable, at the motor terminals and at the inverter output. These methods take into account the cable characteristics (e.g. type, length), the motor impedance, the inverter impedance, its voltage rise and fall times and finally its carrier frequency. As a result, the oscillation frequency, the critical cable length, the peak voltage and the parasitic current amplitude could all be determined. Overvoltages higher than 2 p.0 are also be investigated. To validate the proposed techniques, simulations and experiments have been carried out on an industrial 5 kVA ASD prototype using a 4-wire braided-shielded long cable.;Apart from the developed tools, which are useful in design and implementation of ASDs, the thesis offers a major contribution to solve the problem. In fact, a new mitigation device has been designed, realized and tested on the previous 5kVA prototype. The proposed device could be implemented during exploitation, and allows eliminating over-voltages at the motor terminals, whatever the cable length. This constitutes an important industrial innovation; that is why an application for patenting has been already submitted. (Abstract shortened by UMI.).;This thesis gives both theoretical and practical contributions to the reflected wave phenomenon with the principal aim of solving the high frequency overvoltage problems in industrial ASD-Motor Drives. |
