Sistemas de acionamentos CA multifases com estratégias de controle tolerante a faltas e redução da tensão de modo comum.

Abstract

This work includes two areas of research, with a common subject of improving AC drive system reliability. In the first, AC drive system control strategies with fault tolerant properties are investigated. These properties, are obtained from the adoption of a system with phase number higher than three. The use of multi-phase machines possesses several advantages over machine of three-phase machine as a result of the high number of phases: reduction of the torque pulsation, reduction of the current per phase, reduction in the harmonic content of the DC link current, higher power/torque for a machine of same frame and higher reliability of the drive system in relation to the conventional three-phase drives. The control strategies allow for continuous and disturbance free-operation of the drive with complete loss of one leg of the inverter or motor phase. The fault tolerant are obtained using two approaches: strategies with or without reconfiguration of inverter. The solutions without reconfiguration are based on the redefinition of new voltages or currents references in such a way to maintain the operation balanced of the components dq in the torque control of the machine without additional connections of hardware. The reconfiguration is obtained by insulation the faulty leg, by means of auxiliary semiconductor switches and fuses, and connecting to faulty phase to another converter leg, resulting in a structure with reduced number of components. Post-fault control action of short circuit mode operation is presented. Design considerations are presented which relate the shortcircuit fault response to system parameters. The second subject, is on common mode voltage mitigation. The application of machines with even number of phases is explored with the objective to reduce or even to eliminate the common-mode voltage responsible to cause premature motor bearing failures among variable speed induction motor drive systems. Three configurations of drive systems are presented using four-leg inverter. This inverter is used to feed a four-phase machine or a six-phase machine with appropriate connections. Different strategies of PWM modulation allow to reduce or even to eliminate the common mode voltage. The fault tolerant strategies and reduction of common-mode voltage have been evaluated by simulation studies and experimental tests.