Active suppression of photovoltaic system related harmonics in a DC microgrid

A photovoltaic (PV) generator is one of the primary power sources in a DC micro-grid (MG). The power generated by PV systems may inject high-order transient harmonics and low frequency ripple into the DC MG, especially if a conventional widely used Perturbation and Observation (P&O) maximum power point tracker is employed. In this paper a novel active filtering approach is proposed to improve the power quality of a parallel-connected double-stage PV system with dedicated decentralized P&O controllers, by eliminating or reducing the progression of the P&O related harmonics into the grid. The proposed active filtering approach is based on implementing a system-level controller that can control the operation of multiple decentralized P&O controllers and as a consequence can improve the efficiency of the overall system. The proposed solution is tested on a system consisting of multiple parallel-connected self-controlled PV modules which are connected to a DC MG through a common DC/DC boost converter. The simulation results demonstrate that the quality of the power injected to the DC MG can be significantly improved. Further, the DC-link current ripple of the double-stage converter is also notably reduced so that a smaller DC-link capacitor can be used. Improved control dynamics for the first and second converter stages can also be achieved.