Research on cascaded multilevel converters for dual motor drive systems based on a nine-switch converter

In order to address the issues of complexity, high cost, large volume, and low reliability associated with traditional H-bridge cascaded converters when operating under high voltage, high capacity, and dual electric motor loads, the authors propose the utilisation of a nine-switch converter as an alternative to the conventional H-bridge converter for implementing cascaded multilevel converters in dual electric motor drive systems. After conducting an analysis and research on the topology and operational control strategy of cascaded multilevel converters based on the nine-switch converter, a design is presented using six individual nine-switch converter units to develop a cascaded multilevel converter capable of driving two 3 MW asynchronous electric motors at a 6 kV voltage level. Simulation verification is performed, and a scaled-down prototype is built for experimental validation. The results demonstrate that, in comparison to traditional H-bridge cascaded converters, the proposed cascaded multilevel converter can effectively drive dual electric motors at the same or different frequencies while reducing the number of switches to 1/4, the total transformer windings to 1/2, and Direct Current-side capacitors to 1/6. This improvement enhances system reliability, portability, and load adaptability, thus offering increased versatility in dual electric motor drive applications.