A modified higher order power filter for grid-connected renewable energy systems

In order to reduce the influence of the grid harmonic currents and voltages, harmonic compensation is regularly implemented for a grid-tied inverter. In this paper a new topology of higher order power filter for single-phase grid-tied voltage-source inverters (VSI), named L(LCL)2, is introduced. The subscript is added to the name to avoid confusion with LLCL filter. In the proposed design the inverter side inductance is divided into three parts, and the grid side inductor is removed. Also an additional resonant branch at the double of switching frequency is added to the traditional LLCL filter to attenuate high frequency harmonics. The total inductance of this filter is less than LLCL filter with the amount of the grid side inductor. A comparative study and discussions on the subject of the traditional LLCL filter and the proposed L(LCL)2 filter have been conducted and assessed through both experimental hardware implementation and Matlab/Simulink-based simulation on a 700 W, 120V / 60 Hz single-phase grid-tied inverter. Also, a straightforward engineering design benchmark is suggested to discover parameters of the proposed L(LCL)2 filter. It is concluded that, compared with the LLCL filter, the L(LCL)2 filter not only has less voltage drop and total inductor size, but also has better performance on reducing high order current harmonics.