The Resonance Analysis Of Distributed Grid-connected Inverter System And Its Active Damping Method

Distributed generation combined with intelligent grid is a mainstream in the near future. Distributed generation have the ability to provide electrical energy to the local customer in an efficient way which drastically reduce the construction cost in transmission line and promptly enhance grid security through intelligent dispatch. Grid-connected inverter by using LCL-filter has ability to enhance power density. Under the condition of a certain harmonic attenuating effectiveness, LCL-filter has less inductance volume than L-type has. Therefore, LCL-type filter is widely used in distributed generation. However, LCL-type filter has an intrinsic resonance peak at specific frequency domain. And THD of output current from inverter will increase largely if control scheme and parameter is not chosen properly.In this thesis, the control schemes of grid-connected LCL-type inverter to advance output current of inverter are discussed. Firstly, the Norton’s equivalent models are built for two control constructs of inverter: outer grid-side current feedback loop and inner inverter-side current loop, outer grid-side current feedback loop and inner capacitor current loop. Secondly, the features of frequency domain of these two control construct are analyzed. And capacitor current loop can effectively damp resonance peak in frequency domain without change lower and higher frequency characteristics of LCL-filter. Finally, comparative simulation are conducted to verify the dynamic response, decoupling degree of output current among inverters, and disturbance-rejection ability in the case of grid voltage distortion. And simulation result shows that the active damping of capacitor current loop has ability to effectively decoupling the interference between output currents of inverters, to reduce the influence of grid voltage on output current of inverter and to enhance the dynamic response and disturbance-rejection ability.