A Hybrid Damping Method for LCL-Filter Based Grid-Tied Inverter

With more and more distributed renewable energy connecting to the power system, inverters are widely used as the power electronic interface. However, high-order filters will inevitably bring in problems of resonance. Additionally, long-distance transmission and quantities of inverters increase the grid impedance obviously. Wide variation of grid impedance will not only impact on the resonance of filters, but also challenge stability of inverters system. This paper investigates how resonance and stability of grid-tied inverter with LCL-filter will be affected by the grid impedance. And a hybrid damping method based on RC parallel damper and biquad digital filter is proposed, this method presents relatively low power losses, requires no extra sensors and control loops with its simple damping strategy design. Moreover, it apparently improves system stability and waveform quality of grid-side current when grid impedance varies in a comparatively large range. Both validity and feasibility of this algorithm are verified via simulations.