Cost and Performance Comparison of Cascaded Multi-level Converters for Residential Renewable Energy Conversion

This paper attempts to identify the best multi-level topology (cost and performance) for grid-connected converters supplied from residential renewable sources. This is done through a series of SABER time-domain simulations and the use of data about the devices currently found in the market. The cascaded multi-level topology and the triangular carrier based phase-shifted unipolar PWM switching scheme are used because of their straightforward approach to control. In addition to a PI current feedback loop, a voltage feedforward loop is introduced to further improve the output performance. For low switching frequencies (i.e. negligible switching losses), comparably efficient converters can be cheaper by implementing a multi-cell design. However, if the efficiency of such designs is to exceed that of the single-cell designs, the converter cost can become disadvantageous. If the switching frequency is high (i.e. considerable switching losses), the conversion efficiency of a single-cell converter is always higher than that of a multi-level converter.