Reliability and availability of megawatt drive concepts

In the process industries, reliability and availability of the production machines have a strong influence on the profitability of a plant. The concerning requirements to electric variable speed drive systems (VSDS) in such applications are extraordinarily high. In this paper, a comparison of the potential reliability and availability for different high-power medium-voltage drive concepts is made, including voltage source inverters, and cellular converters based on building blocks. Redundancy is introduced as a means of increasing reliability, and different approaches to redundancy in a VSDS are discussed. Besides component reliability and redundancy, the maintenance strategy has an impact on the reliability of a VSDS. The down times for repair including spare parts logistic have a major influence on the availability. As a result, recommendations for the choice of a drive concept and maintenance strategy are given.