Modular Capacitive-Link-Based Three-Phase AC-AC Power Converter

Abstract

Modular converters with stacked cells are widely used in high power applications, where the voltages and/or currents are beyond the voltage/current ratings of the commercially available switches. A common solution is to employ multilevel converters. However, most of the existing multilevel topologies are based on dc-link converters and require a large number of unreliable and bulky electrolytic capacitors with high capacitances. This paper proposes a three-phase ac-ac power cell topology formed by three identical and stackable modules. The modules are derived from a new class of reliable capacitive-link universal power converters and operate in discontinuous capacitor voltage mode. Moreover, each module in the proposed power cell topology provides galvanic isolation using high-frequency transformers and requires only two small film capacitors for transferring the power. This eliminates the need for electrolytic capacitors, which have high failure rates. Using capacitive-link-based modules to form the power cells enables scalable and modular design of the proposed converter for higher levels of voltage and current. The proposed ac-ac power cell topology is evaluated in this paper, and the simulation and preliminary experimental results verify its promising features.