Power System Stability and Control

The electric power generation-transmission-distribution grid in developed countries constitutes a large system that exhibits a range of dynamic phenomena. Stability of this system needs to be maintained even when subjected to large low-probability disturbances so that the electricity can be supplied to consumers with high reliability. Various control methods and controllers have been developed over time that has been used for this purpose. New technologies, however, in the area of communications and power electronics, have raised the possibility of developing much faster and more wide-area stability control that can allow safe operation of the grid closer to its limits. This paper presents a conceptual picture of these new stability control possibilities.

Transmission power flow control
Most power systems have free flowing transmission lines. This means that although power injections and node voltages are controlled quite closely, the power flow on each transmission line is usually not controlled. However, such control is feasible.

A phase shifting transformer can control the power flow across it by changing the phase using taps. This has been used, especially on the Eastern interconnection in North America. The control is local, discrete and slow. A power electronic version of this is now under experimentation.