Wide Area Control Strategies for Improving Transient Stability in Multi-Machine Power Systems

Transient stability is the ability of synchronous machines in an interconnected power system to remain in synchronism after been subjected to a large disturbance. Transient instability is one of the less probable but severe events that a power system encounter in its daily operations. Historically, it has been the dominant stability problem in power systems and has been the focus of much of the power industry’s attention. Traditionally, when a generator or group of generators begin to lose synchronism with the rest of the system, they are tripped or islanded from the network to maintain transient stability and to prevent or limit cascaded outages. However, with the increase in the penetration of inverter-based generation, tripping schemes may become difficult to apply because of wide distribution of generation and loss of system inertia. This research presents control strategies that improves the transient stability of a power system without having to trip generators. This is achieved by modulating the active power absorbed or injected by distributed energy storage devices. These devices are located at the high voltage bus of several generators in a synchronous power system and are independently controlled. The strategy is based upon local and center-of-inertia frequency estimated in real time from wide-area measurements. It is shown that by absorbing or injecting real-power into a power system to remove as much kinetic energy gained during a disturbance as quickly as possible before it is converted to potential energy, synchronism can be maintained. The performance of the control strategy is evaluated on several multi-machine power system models. The result shows that this control strategy significantly improves the transient stability of power systems.