A two-level emergency control scheme against power system voltage instability

• An adaptive, two-level emergency scheme to prevent voltage instability is proposed.
• The upper level detects instability, relying on a wide-area monitoring system, through sensitivities computation and adapts threshold voltages used in the lower-level controllers.
• The lower-level closed-loop distributed controllers act on distribution transformers and/or curtail loads to restore transmission voltages at the threshold values.
• The proposed control scheme is robust with respect to controller and communication failures.
• It has minimal communication requirements between the two levels.

A two-level adaptive control scheme against power system voltage instability is proposed, to deal with emergency conditions by acting on distribution transformers and/or by curtailing some loads. The lower level includes distributed controllers, each acting once the voltage at a monitored transmission bus settles below a threshold value. The upper level benefits from wide-area monitoring and adjusts in real-time the voltage thresholds of the local controllers. Emergency detection is based on the sign of sensitivities. The proposed scheme is robust with respect to communication failures. Its performance is illustrated through detailed simulations of a small but realistic 74-bus test system.