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A Single DC-Source Seven-Level Inverter for Utility Equipment of Metro Railway, Power-Land Substations

This paper presents an unusual topology of a medium-power seven-level inverter that utilizes a single dc source and a three-phase transformer to generate high-performance seven-level voltage waveforms without complex cascade H-bridges with isolated dc supplies or neutral-point-clamped circuits with capacitor balancing techniques. In contrast to typical topologies of multilevel inverters, the control strategy of the presented circuit facilitates its implementation on a simple 16-bit microcontroller, such that the proposed inverter is operated under a space vector mode. The principle of operation of the seven-level inverter is analyzed, using idealized waveforms for easy and straight implementation together with a description of its practical development, showing experimental results obtained with a 1-kW prototype.