An LCL-filtered Single-phase Multilevel Inverter for Grid Integration of PV Systems

Integration of the PV into the electrical grid needs power electronic interface. This power electronic interface should have some key features and should come up with grid codes. One of the important criteria is the quality and harmonic contents of the current being injected to the grid. High-order harmonics of the grid current should be very limited (lower than 0.3% of the fundamental current). Beside the topology of the power electronic interface, the output filter also affects the quality of the grid current. In this paper, a 5-level inverter is presented for grid integration of PV systems along with its output LCL filter design. Analytical calculation of losses for the 5-level inverter and the output LCL filter is presented. It is also compared to the H-bridge inverter in terms of output voltage and current harmonics, and the overall losses. Second-order generalized integral phase locked loop is used to synchronize the system with the grid voltage and the proportional resonant (PR) with harmonic compensation control method is used to control the output current. The proposed system has been simulated in the PSCAD/EMTDC environment to verify its operation and control.