Investigation of capacitor voltage balancing issues in a five-level inverter with multicarrier modulation schemes

Abstract

Five-level inverters are widely used in medium-voltage (MV) wind energy and electric drive systems. However, the use of a large number of components (including passive and active components) and complex control methods are the major issues in the existing inverters. Also, some of the inverters are difficult to control using multicarrier modulation schemes due to the lack of redundancy switching states. In this research work, a new five-level inverter is introduced for MV applications. The new inverter requires only flying capacitors and switching devices and has a low total component count. Also, it requires only a flying capacitor voltage balancing method to achieve a safe and reliable operation. Hence, the new inverter is cost-effective and has less control complexity compared with the existing inverter topologies. The flying capacitor's voltage in the new inverter is analysed with the help of charge-balance theory and established as a theoretical basis for the capacitor voltage balancing method. Through this analysis, a simple voltage balancing method is developed. The developed balancing method is further analyzed with the conventional multicarrier modulation schemes using MATLAB simulations at different operating scenarios. Also, a modified multicarrier modulation scheme is introduced to handle the new inverter operation at higher load power factors. Finally, the performance comparison of the conventional and modified multicarrier modulation schemes is presented.