Open communication is an exigent need for future power systems, where time delay is unavoidable. In order to secure the stability of the grid, the frequency must remain within its limited range which is achieved through the load frequency control. Load frequency control signals are transmitted through communication networks which induce time delays that could destabilize power systems. So, in order to guarantee stability, the delay margin should be computed. In this paper, we present a new method for calculating the delay margin in load frequency control systems. The transcendental time delay characteristics equation is transformed into a frequency dependent equation. The spectral radius was used to find the frequencies at which the root crosses the imaginary axis. The crossing frequencies were determined through the sweeping test and the binary iteration algorithm. A one-area load frequency control system was chosen as a case study. The effectiveness of the proposed method was proven through comparison with the most recent published methods. The method shows its merit with less conservativeness and less computations. The impact of the proportional integral (PI) controller gains on the delay margin was investigated. It was found that increasing the PI controller gains reduces the delay margin.
The application of the phasor measurement units and the wide expansion of the wide area measurement units make the time delay inevitable in power systems. The time delay could result in poor system performance or at worst lead to system instability. Therefore, it is important to determine the maximum time delay margin required for the system stability. In this paper, we present a new method for determining the delay margin in the power system. The method is based on the analysis in the s-domain. The transcendental time delay characteristics equation is transformed to a frequency dependent equation. The spectral radius is used to find the frequencies at which the roots cross the imaginary axis. The crossing frequencies are determined through the sweeping test and the binary iteration algorithm. A single machine infinite bus system equipped with automatic voltage regulator and power system stabilizer is chosen as a case study. The delay margin is calculated for different values of the power system stabilizer (PSS) gain, and it is found that increasing the PSS gain decreases the delay margin. The effectiveness of the proposed method has been proved through comparing it with the most recent published methods. The method shows its merit with less conservativeness and fewer computations.
The fuel cell based heat and power co-generation is considered to be well qualified for a distributed energy system for residential and small commercial applications. A kW-scale system is under development in the New Energy Group in South China University of Technology. Natural gas is selected as fuel for hydrogen production. The system mainly consists of a fuel processing unit, a power generation unit and an auxiliary unit. The fuel processing unit includes a reformer (integrated with steam generation), two high and low temperature shift reactors, and a preferential oxidation reactor. The reformer integrated with steam generation is designed to produce hydrogen-rich syngas from natural gas and water. It can be operated under steam methane reforming or oxidative steam reforming modes. 800 grams of commercial nickel catalyst supported on gamma alumina are loaded in the reformer. The reactor performances under typical steam reforming and oxidative reforming modes are tested. Influences of reaction temperature, steam-to-carbon ratio and methane space velocity on reactor performance under steam reforming mode are experimentally investigated. Influences of oxygen-tocarbon ratio, steam-to-carbon ratio and methane space velocity on reactor performance under oxidative reforming mode are also studied. The reformer will be integrated with the other parts of the system to build a complete system.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.