Voltage and power regulators guaranteeing stability of dc-links between DERs and the electricity grid

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Abstract
An alternative control design for dc-links used to connect distributed energy resources (DERs) with the main power grid, is proposed and studied for its stability. As DERs are considered to be weak, unpredictable power sources, ac voltage regulation is applied at the side of DER connection while at the grid side, dc voltage and reactive power control is implemented. The challenging issue of achieving these tasks effectively through the design of a rather simple control scheme is examined in this paper. While the traditionally proposed techniques involve parameter-dependent controllers in order to make possible simple linear designs, in this paper, the proposed controllers are clearly simpler ones, parameter-free of proportional-integral (PI) type, but require a more complicated and advanced nonlinear analysis. To that end, incorporating the controllers into the nonlinear dc-link model, the closed-loop system is analyzed by applying advanced Lyapunov techniques combined with input to state stability notions. As shown in the paper, stability and convergence to the equilibrium is guaranteed while the extended simulations presented, fully verify the theoretical analysis.

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