Ac-Ac three-phase drive system based on twelve-leg de-link converter

This paper presents a three-phase AC drive system to cope with three-phase applications in which high performance and reliability are required with reduced dc-link and switch voltages. The proposed topology employs a single isolation transformer processing only part of the total system power. Another interesting characteristic of the system is to adapt its configuration as a function of the machine speed: series mode, the machine is side converter operates in a series configuration at high speed and high voltage and parallel mode, the machine is side converter operates in a parallel configuration at low speed and low voltage. The parallel mode allows for a more balanced modulation index and becomes the drive capable to furnish high current at low speed, interesting for constant mechanical load power applications. The comprehensive model of the proposed systems and modulation strategies are presented. Simulated and experimental results are also presented.