Synchronous Reference Frame current control of Aalborg-type PV inverters

Transformerless photovoltaic (PV) inverters with voltage step-up capability are currently the preferred interface for integrating PV generation to a single phase of the electric grid. Among the different topologies employed for such inverters, dual-mode time-sharing topologies offer high conversion efficiencies, but present control challenges that can result in significant grid current distortion. Existing control approaches operate in the stationary reference frame and use different controllers for the Buck and Boost modes of operation. This paper presents a new current control approach for Aalborg-type Buck in Buck, Boost in Boost PV inverters, which operates in the Synchronous Reference Frame and uses a common controller for Buck and Boost operation. The proposed method achieves high output current quality even at unfavourable conditions of low PV voltage and/or power levels. Simulation results in MATLAB-Simulink are presented to illustrate that it can reduce the Total Harmonic Distortion (THD) of the grid current by two to three times as compared to the existing alternative.