Delay-dependent stability of load frequency control with adjustable computation accuracy and complexity

Cyber-physical power systems (CPPS) utilize wide-area measurement system, where communication networks employed in the control loop introduce time delays inevitably. The existing studies focus on either computation accuracy or efficiency for investigating the delay-dependent stability of large-scale delayed CPPS. Whereas, the requirements for calculation accuracy and efficiency vary from the demand for online stability analysis and offline controller design. This paper investigates the demand-oriented stability of the delayed CPPS and takes load frequency control (LFC) systems as typical examples. Novel regulation schemes have been proposed with adjustable conservatism and computation complexity. Different from existing studies, this paper establishes regulated stability criteria by constructing variable Lyapunov-Krasovskii functionals and using compatible integral inequalities for estimations. Then, an algorithm is designed by introducing a threshold parameter to calculate accurate delay margins or to realize high computation efficiency flexibly. Case studies are complemented on the two-area LFC scheme and IEEE 39-bus system. It is illustrated that the proposed method can realize on-demand adjustments for real power systems, i.e., setting the threshold parameter to zero achieves almost accurate delay margins like the frequency-domain method, which guides the offline controller design with desired performance; less computation complexity is achieved with a relatively large threshold parameter, and thus, the proposed method is applicable for online stability analysis.

Automated summary

This paper investigates the demand-oriented stability of delayed CPPS and proposes novel regulation schemes using variable Lyapunov-Krasovskii functionals and compatible integral inequalities. An algorithm is designed to calculate accurate delay margins or achieve high computation efficiency flexibly. Case studies on load frequency control systems and IEEE 39-bus system demonstrate the effectiveness of the proposed method.