Detailed Design of a 6 KWp Grid Connected PV Plant with Storage Batteries: Part-I- Central Inverter Benchmark Study & Simulation

Abstract

The distributed and intermittent characters of electrical energy production from renewable resources constitute the main challenges in the way of optimising the power transfer for grid connected systems in terms of efficiency, quality and reliability. Concerning the photovoltaic solar energy conversion, such performances being mainly related to the DC-AC stage, the grid connected inverter control strategy design became a major research subject to bring answers for the ever challenging grid technical regulations (grid codes). As a prerequisite option for active power bi-directional operation, the storage batteries pack is assumed here as an energy buffer directly connected between the DC-DC and DC-AC stages. As a consequence, the strong decoupling effect induced by imposing a constant DC link voltage, allows conducting the analysis and design of both parts separately. In this context and as part- I of the overall undertaken design project, a grid connected inverter using a hysteresis current control (HCC) strategy is pre-designed and optimised to serve as an open loop, bidirectional DC-AC power converter benchmark. Foreseeing the main practical realization constraints, an original sizing process of the associated line inductor is applied to limit the maximum switching frequency. Then, making use of the rich electrical engineering library of the SimPowerSystems toolbox under Matlab/Simulink environment, the designed grid connected installation is analysed through detailed simulations. Furthermore, particular control circuits are elaborated to generate properly the corresponding AC current reference and allow bi-directional active and reactive power flow decoupled control. Finally, reproducing tightly the detailed and realistic architecture of the planned realization, the resulting DC-AC stage structure is submitted to numerous validating tests as a power converter which may be further included in simple but robust active and reactive power control closed loops.