Load frequency control: Problems and solutions

Frequency control is one of the most profitable auxiliary services for the power systems through maintaining short-term balance of energy and frequency of the power systems. Frequency control is usually accomplished through generator governor response (primary frequency regulation) and Load Frequency Control (LFC). The goal of LFC is to reestablish primary frequency regulation capacity, return the frequency to its nominal value and minimize unscheduled tie-line power flows between neighboring control areas. This paper first formulates the LFC problem for single-area power systems as a disturbance rejection problem and discuss the effect of system parameters and the generation rate constraints (GRC) on the control performance. Then decentralized LFC for multi-area power systems is formulated and a result on checking the stability of the closed-loop system considering the inherent structure of the multi-area power systems is proposed. Finally, LFCs with communication delays and in deregulated market are formulated and a unified LFC-PID tuning method is discussed. It is shown that the load frequency control problem is a typical disturbance rejection problem with rate limit, parameter variations, structural uncertainties and communication delays. Advanced control techniques are expected to be applied to improve the control performance.