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This paper presents system modeling and nonlinear control design of static compensators (STATCOMs) for fast voltage regulation in the presence of load uncertainty and voltage flicker. A simplified power distribution system is modeled using ideas similar to field oriented control of three phase ac machines. Zero dynamics of the system show that the system is nonminimum phase for certain operating conditions, thus, imposing restrictions on the achievable dynamic response. The control design involves estimation of the load conductance via a gradient-based estimator, and state feedback control to reach an equilibrium point established by the estimated load conductance and knowledge of system parameters. A Lyapunov function is used to establish asymptotic stability in the large for the closed-loop system. To account for practical implementation issues, a new controller relying on feedback of a readily measurable state is also proposed. Simulations results are presented to show efficacy of both controllers with regard to bus voltage regulation and suppression of voltage flicker.
Date of Publication: Nov. 2004