Asea Brown Boveri Ab

Abb Power Td & Company

Hisham A Othman

Kevin J Timko

Rajkumar Vedam

Voltage flicker is a power quality problem in power distribution circuits which is caused by the operation of fluctuating loads such as AC and DC electric arc furnaces, spot welders, starting of large ac motors, and the like. Converters based on Voltage Source technology (VSC) connected in shunt close to the fluctuating load are found to have the capability of reducing the voltage flicker level. Flicker control systems responsive to the active and reactive power components are used to exploit the capabilities of VSC in accordance with the invention. The flicker control systems reduce the voltage flicker observed at the point of common coupling by adapting, e.g., H-infinity, Linear Quadratic Gaussian, Minimum Variance Control, and self-tuning design methods for flicker control in power systems having fixed or self-tuning flicker controller parameters.

Flicker controllers using voltage source converters

A trigger control system for a thyristor-controlled series capacitor (TCSC) is disclosed. In one application, a power system 10 is coupled to a load 12 by a series capacitor 14 connected in parallel to a thyristor unit 16 and inductor 17. The thyristors are triggered by the control system 18, which includes a first circuit 20 that generates signals proportional to the peak of the line currents, a stabilizer circuit 22, an adder 24, a look-up table 26, a conversion circuit 28, a pulse generator 30, a phase-locked loop (PLL) 32, a ramp generator 34, a trigger window circuit 36, and a three input AND gate 38 the output of which is a grid pulse signal 40 that triggers the thyristor unit 16. The control system diminishes power swing oscillations and subsynchronous resonance oscillations.

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Cary, NC, United States of America

Hisham A Othman