Back-to-back configuration of multilevel converters providing redundant operation mode

In recent years multilevel converters become more important. On the one hand, they are essential in terms of output power for medium and high-voltage applications in industry and renewable energy. And on the other hand, they are important in terms of filtering requirements for low power applications, too. For high power wind energy plants at low voltage paralleled converters are used to split up power and obtain redundancy. At medium and high voltage a single converter is used for total output causing a lack of redundancy in case of a failure of a power semiconductor. This paper investigates the back-to-back configuration of multilevel converters for wind energy application based on the principle of partial converters. These converters provide a redundant operation mode after a failure of a power semiconductor. The defective partial converter is disconnected and the remaining parts can continue to operate at reduced output power. Therefore, a lower number of voltage levels is available as well as only half of the DC-link voltage remains. But the downtime until maintenance of the entire system is reduced.