LVRT capability of single-phase grid-connected HERIC inverter in PV systems by a look-up table based predictive control

Nowadays capacity of the photovoltaic systems in the grid is remarkable and provides a major part of energy in the grid. Therefore, an abruption of these systems from the grid can create a damage to the grid. Unlike in the past that PV systems disconnected from the grid when a voltage drop occurred, nowadays these systems should have Low Voltage Ride-Through (LVRT) capability. The PV system should stay connected to the grid at fault time and help to recover the grid voltage by injecting the reactive power like in a power plant or a custom power device. There are two important factors for single phase grid connected PV inverters. The first one is the structure of the inverter and the second one is the control part. In this regard, the HERIC inverter can be a good selection among the transformerless inverters for a PV system due to its high efficiency. For the control part, this paper presents a look-up table based Model Predictive Control (MPC) that is simple, fast and has soft behavior in tracking of the reference during LVRT. The proposed control method has been implemented in a 1 kW single-phase transformerless HERIC (Highly Efficient and Reliable Inverter Concept) inverter using an LCL filter.