I. Introduction
With the development of the fractional calculus theory, the fractional-order systems (FSs) have attracted a lot of attention from engineering scholars in recent decades. Such systems have appeared in many practical applications, for instance, power systems [1], brushless DC motor (BLDCM) system [2], and chaotic systems [3]. In the meanwhile, two techniques are employed to research the stability of the FSs. The first technique is performed by estimating or calculating the solution of the FSs [1], [4], which is a conservative approach for the systems subject to time delays. Although the technique is not necessary to solve the complex linear matrix inequalities (LMIs), the obtained results using this technique are usually delay-independent, which results in a research defect for the delayed systems owing to the time delays are not reflected in the stability criteria. The second is carried out by utilizing Lyapunov functional technique [5]. Compared with the former, the latter can overcome this defect due to the stability criteria with time-delay dependence are obtained, and the conservatism of the results can be decreased by introducing some matrix variables. In addition, the delay margins can also be estimated through solving the LMIs.