Making Inverters for Domestic Photovoltaic Applications More Robust: The Relevance of a Mixed 5-level Topology

Under the growing impetus of renewable energy policies, the number of grid-connected domestic
photovoltaic power plants will increase considerably in the coming years. Inverters are important links
because they must not penalize the energy efficiency of the systems and the quality of the signals
injected into the AC grid must be indisputable. Transformerless multilevel inverters are well used in
grid connected home photovoltaic applications because of their ability to generate very good
waveforms, reducing switching frequency, and their low voltage on power devices. However, this type
of inverter needs to be modified to both limit common-mode currents and improve system robustness.
Neutral point clamped topologies can certainly provide an answer to these problems, but their
electronic structure can sometimes be difficult to implement and development costs can be important.
This chapter presents a new 5-level mixed-mode inverter that meets these challenges. The operating
principle of the inverter is proposed. Many experimental measurements, carried out at low output
power, are described to validate this new concept. In particular, the output voltage and current as well
as the total harmonic distortion of the output voltage underline the relevance of such a structure.