A finite control set model predictive control scheme for single-phase grid-connected inverters

Abstract

Abstract The present article investigates a control scheme for single-phase grid-connected inverter based on the finite control set model predictive control (FCS-MPC) approach. The proposed grid integration scheme provides direct control of the active and reactive power (PQ) injected to the grid from distributed energy resources (DER) composed of a photovoltaic (PV) array as a renewable resource integrated with a battery bank as energy storage. The direct PQ control scheme includes also low voltage ride through (LVRT) capability of the inverter during voltage sag. The optimum inverter switching state is indicated via the employed FCS-MPC algorithm instantaneously such that the actual PQ, injected to the grid, will track the corresponding reference values. During normal operation, the active power, injected to the grid, is set to the maximum possible value, while the reactive power is nil. Under voltage sag, the PQ will be injected to the grid as a function of the percentage of voltage sag based on the existing grid codes and regulations. In single-phase systems, successful application of direct PQ control depends on accurately creating the fictitious orthogonal components of grid current and voltage required for instantaneous power computations. Therefore, the following three different orthogonal signal generation (OSG) methods are utilized in this study in order to create such virtual (quadrature) components: second-order generalized integrator (SOGI), all-pass filter (APF), and quarter cycle phase delay (QCPD). In addition, qualitative and quantitative analyses of the obtained results are involved in this study of the FCS-MPC PQ system in order to compare the three adopted OSG methods. The PSIM® software was utilized in this study for modeling and studying the overall FCS-MPC system and the DER grid integration system. According to the results, the investigated FCS-MPC approach is effective in providing quick response and flexible control of PQ injected to the grid through the use of the three OSG methods. Moreover, the investigated FCS-MPC scheme successfully involves the LVRT option in order to improve the dynamic grid voltage support during the permissible duration of voltage sag following the LVRT profiles and grid codes of many countries.