Design and Analysis of a Higher Order Power Filter for Grid-Connected Renewable Energy Systems

Harmonic compensation is regularly implemented for a grid-tied inverter to reduce the influence of the grid current and voltage harmonics. In this study, the L(LCL)(2) filter, which is a high-order power filter for single-phase grid-tied voltage-source inverters, is designed and analyzed. In order to attenuate the high-frequency harmonics, additional resonant branch at the double of the switching frequency is added to the LLCL filter. The total inductance of this filter is almost less than the LLCL filter with the amount of the grid-side inductor. A comparative study on filter parameter design, size estimation, efficiency, stability, and dc-link dynamics in bidirectional power flow applications between the LLCL filter and the proposed L(LCL)(2) filter has been conducted. The assessment of these studies is presented through both experimental hardware implementation and MATLAB/Simulink-based simulation on a 700 W, 120 V/60 Hz single-phase grid-tied inverter. It is concluded that, compared with the LLCL filter, the L(LCL)(2) filter not only has less voltage drop and total component size, but also has better performance on reducing high-order current harmonics. Additionally, the L(LCL)(2) filter has a smaller size, less losses, stable closed-loop control system, and compared with traditional LLCL filter, it does not add any control difficulty to the system.