Design of AC side filter for Grid Tied Solar Inverter

Solar inverter is a power electronics based converter which acts as interfacing media between solar PV panels and utility grid. IEEE 1547 has imposed limit on the magnitude of current harmonics around the inverter switching frequency. This limit necessitates the use of AC side filter at the output of the grid connected solar inverter, for connection with grid. This filter reduces the harmonic content in grid current so as to inject pure sinusoidal waveform into the grid. The filter should be so designed that it provides sufficient attenuation for the switching frequency harmonics but at the same time should allow a low impedance path for the fundamental component. Moreover the system size / volume must not increase significantly with the addition of filter. The AC side filter design needs the trade-off when considering the efficiency / switching loss and fundamental voltage drop. In this paper control theory modelling of LCL type filter is developed. Comparison of LCL filter with other filter topologies is carried out with respect to the control theory parameters like Bode plot. Detailed calculation of LCL filter for single phase grid connected solar inverter is also elaborated.