Assessment and Optimization of the Transient Response of Proportional-Resonant Current Controllers for Distributed Power Generation Systems

The increasing number of distributed power generation systems (DPGSs) is changing the traditional organization of the electrical network. An important part of these DPGSs is based on renewable energy sources. In order to guarantee an efficient integration of renewable-based generation units, grid codes must be fulfilled. Their most demanding requirements, such as low-voltage ride-through and grid support, need a really fast transient response of the power electronics devices. In this manner, the current controller speed is a key point. This paper proposes a methodology to assess and optimize the transient response of proportional-resonant current controllers. The proposed methodology is based on the study of the error signal transfer function roots by means of pole-zero plots. Optimal gains are set to achieve fast and nonoscillating transient responses, i.e., to optimize the settling time. It is proved that optimal gain selection results from a tradeoff between transients caused by reference changes and transients caused by changes at the point of common coupling. Experimental results obtained by means of a three-phase voltage source converter prototype validate the approach. Short transient times are achieved even when tests emulate very demanding realistic conditions: a +90 degrees phase-angle jump in the current reference and a "type C" voltage sag at the point of common coupling.