Retrofit Control of Power Systems: Cooperation of Decentralized Controller and Global Controller

This paper develops a controller design method to improve the damping performance of frequency deviation caused by a fault in power systems, based on retrofit control. Retrofit control is a modular control approach for a stable network system whose subsystems are managed by their corresponding subsystem operators. The retrofit controller is designed only with a subsystem model that is available locally, and is activated only for local disturbance to the corresponding subsystem. This paper shows that the retrofit control cannot compensate an offset of the frequency, which is caused by system variation caused, e.g., by load variation. To address this problem, focusing on the fact that the offset can be compensated by a global controller that has an integrator, we propose a control method utilizing a retrofit controller in conjunction with a global controller. The proposed method provides a reasonable separation of the control to improve transient and steady state responses. The effectiveness of the proposed method is examined through a numerical simulation with the IEEE 68-bus, the 16-machine power system.