Distributed energy control in electric energy systems

The power interactions of any component in electric energy systems with the rest of the system happen naturally, as governed by the energy conservation principles. However, instabilities may get induced when the dynamics of power produced by local energy conversion and local control do not align with the incoming power dynamics from the rest of the system. To model and control such instabilities, this paper introduces a notion of a common variable shared by components called interaction variable. The same variable captures aggregate system-wide effects and sets reference points for multi-layered distributed output feedback control. It has a physical interpretation of instantaneous power and generalized reactive power. The higher layer design utilizes the interactive energy state-space model to derive intermediate reactive power control, which becomes a control command to the lower layer physical model. This command is implemented using either Feedback Linearizing Control (FBLC) or Sliding Mode Control (SMC), for which sufficient stability conditions are stated. This paper proves that the proposed design is fundamental to aligning dynamic interactions between components for stability and feasibility. Without loss of generality, we utilize a simple RLC circuit with a controllable voltage source for illustrations, which is a simplified representation of any controllable component in microgrids.