Forced redundant states of 5-level single-phase diode-clamped multilevel inverters

Diode-clamped multilevel inverters belong to one of the three main multilevel inverter topologies. To date, the single-phase versions of these inverters have been characterized as not having redundant states. Significantly, such states are useful for reducing device switching frequency during inverter operation, and hence for decreasing switching power losses and conducted electromagnetic interference effects, and also improving other aspects of inverter performance such as enabling capacitor voltage balancing. This paper describes a study of single-phase diode-clamped multilevel inverters with their output connected in series with a voltage source. Doing so for a five-level inverter resulted in additional switch states producing the expected output levels, as compared to not having a voltage source so connected. Hence these are referred to as forced redundant states; they are determined by the source's magnitude and its polarity. Both simulation and experimental results are described to help analyze and verify this advantageous behavior.