Passivity Based Control of STATCOMs

Abstract

One interesting application of STATCOM, besides reactive power compensation, is for compensation of harmonic currents produced by nonlinear loads in electrical grids. Such nonlinear loads consume high harmonic currents, which are supplied by the power source and transported by transmission lines. Harmonic currents produce additional losses, reduce the quality of the supplied energy, and may undergo penalties. Therefore, avoiding or eliminating harmonic currents implies a reduction in costs of the whole system operation. In order to compensate harmonic currents, the use of Shunt Active Power Filter (SAPF) has been proposed. These power filters must inject compensation currents with the appropriate waveform into the power system, so that those currents supplied by the grid remain sinusoidal and balanced, regardless of the grid voltages waveform. This implies a correct calculation and control of the compensation currents. Control algorithms with good steady-state performance and high dynamic response are required to control the SAPF that injects compensation currents into the system. Passivity-based control is a control design technique for nonlinear systems, currently being used satisfactorily in many electrical systems. Particularly, Interconnection and Damping Assignment (IDA) is a passivity-based design technique which consists in modifying the system?s energy function to obtain a desired closed-loop structure, allowing system stabilization. This book presents the basis for designing a control strategy for Shunt Active Power Filters used for the compensation of harmonic currents consumed by nonlinear loads. The design of the SAPF controller is carried out using the interconnection and damping assignment technique. The control objective is to inject the adequate compensation current into the power system, so that the grid current is sinusoidal and balanced, regardless of whether the grid voltage is distorted or unbalanced. This application uses a design methodology based on interconnection and damping assignment that allows trajectory tracking control because the references of the compensating currents are variable, and they depend on the performance of the load and the grid. References of the compensation currents are calculated by using Instantaneous Active-Reactive Power Theory. The book revises the model of SAPFs, presents the theory of IDA technique with the modifications needed to use this theory for control design in SAPF, and includes a control design example and a simulation study.