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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. [ABSTRACT FROM AUTHOR]

Two techniques are presented to balance the filter capacitor voltages of a multipulse rectifier with the active injection operating on a variable-frequency supply. The active injector consists of a low-rated bidirectional switch that modifies the behavior of a 12-pulse rectifier at either low or high frequency, resulting in 24-pulse or multilevel pulse width modulation operation, respectively. The operation of the rectifier and the injector, the practical issues that unbalance the capacitor voltages, and the methods to correct this imbalance are explained together with experimental results obtained with a 4-kW prototype. [ABSTRACT FROM AUTHOR]