Sistemas de acionamento de máquinas de seis e nove fases.

Abstract

This work discusses some multilevel converter structures for six- and nine-phase machine drives. The machine may operate as motor or generator. In the case in which the machine operates as generator, it is possible to make use of semi-controlled converters, in which part of the controlled switches, of higher cost, may be replaced by non-controlled switches (diodes), of lower cost. This decreases the system cost and simplifies the gating circuitry without compromising the multilevel waveform with low harmonic distortion. In this sense, two unidirectional topologies for connection with six-phase machines and three for connection with nine-phase machines are studied. Besides, two six-phase hybrid topologies are discussed. They are called hybrid because different types of converter feed each machine three-phase group. It is shown that by using them it is possible to obtain low machine torque ripple, similar to the ones observed in multilevel topologies such as dual and NPC, but employing a lower number of devices. A study of an ac-dc-ac converter for nine-phase drives is also carried out. In this converter, the rectifier is composed of three star-connected H-bridges. It is shown that its advantages are lower harmonic distortion and lower dc-link voltages when compared to conventional two-level rectifier. For all topologies, PWM strategies are developed and explained. At last, comparison among the topologies in terms of harmonic distortion and semiconductor losses are performed.