Control strategies for solar panel companion inverters

This paper investigates a unique methodology that converts the conventional dc voltage output of a photovoltaic solar panel to switched quasi-square wave voltages with variable pulse width, which when aggregated realize a superior quality multilevel waveform that can be directly interfaced with the power grid. Termed Solar Panel Companion Inverters, this alternative approach offers advantages of micro-inverters in realizing panel-level maximum power point transfer and realization of system-level cost benefits of a central inverter approach. Various control strategies such as Unsorted Pulse Width Modulation, Sorted Stair Case Modulation and Sorted Pulse Width Modulation for these Solar Panel Companion Inverters are presented and analyzed in the paper. These control schemes are evaluated against a variety of solar irradiance operating scenarios with varying co-efficient of variation and varying mean irradiance levels. The resultant energy yields are documented for each control scheme. It is shown that the proposed structure of Solar Panel Companion Inverters is able to collectively perform as a conventional central inverter when irradiance conditions are uniform. However, under non-uniform irradiance conditions, proposed structure surpasses performance of central inverter in terms of power throughout and can be a commercially competitive solution when compared to microinverters for interfacing solar panels with the power grid.