Comparative evaluation of passive damping topologies for parallel grid-connected converters with LCL filters

In this paper a comprehensive analysis of three passive damping methods is done under parallel operation of multiple current controlled voltage source converters. One could argue that a well damped LCL filter with no peaking in the output impedance and stable designed controllers will turn into stable status under the parallel operation with other converters that share similar configuration. However, it is shown that this is not always the case, especially because of the coupling between converters and the grid impedance. For the considered ratings, under grid impedance variation, it is found that with grid-side current feedback the stability may be improved in parallel operation while for converter-side feedback, the stability of the current controller is always decreased compared with the single converter case. The proposed stability analysis and experimental tests demonstrates the theoretical analysis.