Active damping techniques for LCL-filtered inverters-based microgrids

LCL-type filters are widely used in grid-connected voltage source inverters, since it provides switching ripples reduction with lower cost and weight than the L-type counterpart. However, the inclusion of LCL-filters in voltage source inverters complicates the current control design regarding system stability issues; because an inherent resonance peak appears due to zero impedance at that resonance frequency. Moreover, in grid-interactive low-voltage microgrids, the interactions among the LCL-filtered-based parallel inverters may result in a more complex multi-resonance issue which may compromise the power quality and stability of the microgrid. Therefore, due to the effect of resonances on the system stability and power quality, this paper presents a state-of-the-art review of resonance characteristics and related issues in single- and multi-inverter-systems. Furthermore, this paper introduces the different active damping approaches for grid-connected inverters with LCL filters, which are based on high-order filters and additional feedbacks methods. These techniques are analyzed and discussed in detail.