Active filters for harmonics elimination in solar photovoltaic grid-connected and stand-alone systems

Power converter´s output signal harmonic control is currently becoming immensely important in medium and high power applications due to the development of new grid codes. Advancement in transistor technology has lead to significant changes from large thyristor-equipped grid-connected inverters to smaller and fast switching IGBT (Insulated Gate Bipolar Transistors) equipped converters. These IGBT´s increases the power switching frequency in order to extract more energy and fulfill the grid connecting standards. Grid codes usually define a maximum allowed level for each specific harmonic and determine the maximum tolerated THD (Total Harmonic Distortion) of the output signals. Unfortunately, these IGBT-based power drivers generate harmonics that are subsequently transmitted into the power bus. The harmonics are normally eliminated by passive LC or RLC filters. However this passive filtering system has its own limitations. In this paper, we analyze the harmonics created by the IGBT-equipped converter using Fast Fourier Transform (FFT) analysis. The converters are connected to the PV (Photovoltaic) arrays and the utility grid for grid-connected applications and PV arrays & battery modules for stand-alone applications. Using a second-order Butterworth Filter we showed that the THD has been reduced from 32.59% to 1.59%.