Self-balancing five-level current source inverters

Abstract

Five-level current source inverters (CSIs) inherit the advantages including voltageboosting capability, absence of dv/dt issues, and reliable short-circuit protection, etc. In addition, they have better harmonic performance compared to traditional three-level CSIs. Many five-level CSI topologies have been proposed for various applications such as wind energy conversion systems and high-power AC drives. However, traditional topologies, using parallel structures of modules or inductors, suffer from a common issue: current imbalance. The main cause of current imbalance is the unequal on-state voltages of switching devices, along with manufacturing tolerances and variations in the gating signal delays. This imbalance can degrade AC output quality, and potentially lead to overcurrent conditions that may damage components. The existing recommended solutions involve closed-loop control, using additional current sensors to sample DC inductor currents and adjust switching states accordingly. However, even the optimal approaches in the literature have drawbacks, such as increased switching frequency, high computational demands, and higher costs. To address the issue of current imbalance, three novel topologies: X-, Γ-, and H-type five-level CSIs have been proposed in this work. Unlike traditional five-level topologies, the proposed CSIs achieve self-balance of the inductor currents without using additional balancing control schemes. This reduces the complexity and cost of the system. New SVM-based modulation schemes, designed for the proposed inverters, ensure good harmonic performance and overvoltage clamping. Detailed analysis and calculations are provided for their configurations, operating principles, self-balancing mechanisms, modulation schemes, DC utilization, switch stresses, passive component sizes, and overall efficiency. The performance of the proposed inverters is validated through both simulations and lab-scaled experiments.