A New Modulation Method for a 13-Level Asymmetric Inverter Toward Minimum THD

An asymmetric inverter features different dc-link voltages for each power cell and depending on the dc voltage ratios, there are binary, trinary, etc., asymmetric topologies. In particular, the trinary one can provide a waveform with 3n levels, where n is the number of cells connected in cascade. Hence, for n = 3, an output voltage with 27 levels can be obtained, ensuring a low total harmonic distortion (THD) and reduced dv/dt. However, when the load consumes active power, some power cells of the inverter can operate in regeneration mode, complicating the topology and control. To overcome this problem, a new modulation method for asymmetric inverters is presented. It features an ac output voltage of 13 levels for n = 3, and ensures unidirectional power flow in every power cell. This new modulation method also provides a voltage waveform with low dv/dt and reduced THD (5.7%). To confirm the approach, power flow and sensitivity analysis to changes in the dc voltage ratios are performed. Finally, simulation and experimental results are provided.