Criterion for reverse control action of TCUL controls and their deactivation timings

The dynamic behaviors of the TCUL controls are investigated from the viewpoint of the effect of control actions on voltage stability as well as on voltage regulations, taking into account the interference among the multiple control actions of TCULS. The Liapunov stability theorem is applied to a system having nonlinear voltage-dependent loads to derive conditions for stability. We define the term 'reverse control action for multiple TCULS' to indicate undesirable tap operations, where multiple controls as a whole cause the decrease in voltages of specific nodes, leading to voltage collapse, in spite of normal individual operations. A criterion to detect the phenomena is derived and then a new control strategy based on this criterion is demonstrated. In this demonstration, unsuitably acting TCULs are individually deactivated at their most effective timings to improve voltage stability. The effectiveness of the proposed criterion and its application to the deactivation control have successfully been confirmed through numerical simulations in a radial network with three cascaded TCUL transformers, where a specific area of a real system is reduced to form the example system.