A heuristic slow voltage control scheme for large power systems

Automatic control of transmission network voltage provides significant improvements in security, quality and efficiency of power system operation. In Europe, voltage control is traditionally organized in a three levels hierarchical structure. At the second level, the so called "secondary voltage control" divides the network into multiple control regions based on the pilot node concept and all generators in a given region are operated in an "aligned" mode. In North America, transmission grid voltage control is mostly achieved through manual switching of capacitor/reactor banks and LTC transformers by operators. Recently, an automatic discrete slow voltage controller is proposed to regulate voltage of the western Oregon area in the Pacific Northwest. The controller acts upon SCADA measurements and relies on state estimator model to evaluate the incremental effects of control device switching by running localized power flow.; This dissertation first proposes an alternate heuristic slow voltage controller, which can be easily integrated with the above controller and implemented under a common framework. Then the controller scheme is extended so that it is applicable to any large power systems. In view of a state estimator model maybe unavailable or unreliable because of topology errors under certain conditions, the proposed alternate controller operates independent of the state estimator model and can be either used as back-up controller under these conditions or used to reinforce the decision recommended by the model-based controller. A local voltage estimator is formulated based on linearized reactive power flow model to approximate switching effects by utilizing only the local SCADA measurements around the control devices.; For large power systems, several voltage problems may occur simultaneously in different areas, a multiple problematic area voltage control scheme is proposed to make simultaneous corrective control actions accordingly such that the system voltages are quickly brought back to normal range. This control scheme is quite open and can be easily extended to handle different objective functions. For many power systems, it is also necessary to consider generators as voltage control devices, which leads to the problem of coordinating generator controls and discrete device controls. A multi-phase hybrid voltage control scheme is proposed to deal with the problem by formulating generator and discrete device controls as continuous and discrete problems separately while taking reactive power security into consideration. The controller solves the problems in different operating phases using linear programming and integer programming algorithms respectively and sends alarms to operators if reactive power reserve limits are hit.