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Power System Wide-area GPS Synchronized Monitoring with Phasor Measurements and Low-Frequency Oscillation Mitigation Analysis

Final Report Summary - PSWAMFOA (Power System Wide-area GPS Synchronized Monitoring with Phasor Measurements and Low-Frequency Oscillation Mitigation Analysis)

Electric power is essential to modern society. Economic prosperity, national security, and standard of living depend on reliable electric power systems. Currently power grids around the world are being challenged by very significant changes. Three main factors are at work, to different extents in different regions:

- Climate change concern is causing new uses of the existing network.
- Economic growth is driving expansion of the network.
- Long-life assets are falling due for replacement.

So, it's very important for the power systems to get the operating condition information of the electric grid state. The main focus of PSWAMFOA was on techniques that offer a reliable and sustainable energy system through increasing the efficiency, flexibility, security and quality of the network. Various application functions such as contingency analysis, corrective real and reactive power dispatch could not be executed without knowing the real-time operating conditions of the system. The presented synchronized phasor measurements in PSWAMFOA greatly elevated the availability as well as the quality of data and information useful to improve system monitoring, protection, control, and state estimation accurate and effectiveness.

Power system faults, line switching, generator tripping, load rejection and connection of large amount of load result in sudden changes in electromagnetic power. The unbalance between mechanical and electromagnetic powers causes oscillations in machine rotor angles and power flow swings. Therefore, power swings have to be monitored for safe operation of bulk power systems. Preventive control actions could be taken to mitigate severe power swings. Furthermore, emergency control actions, such as out-of-step (OOS) protection, could be taken to separate the system into several islands to prevent the propagation of severe disturbance and limit load outage. In this project, real-time swing curve and real-time extended equal area criteria (EEAC) based adaptive out-of-step protection schemes have been developed respectively, and numerical simulations was performed for validation of the proposed concepts.

Frequency is an important parameter for the monitoring and control of power systems. It is well known that any unbalance between generation and load is faithfully reflected by a change in the operating frequency. PSWAMFOA reviewed the frequency measurement techniques in power systems, and then proposed a method to accurately measure frequency under frequency-dynamic conditions. It calculated the positive sequence voltage phasor for a balanced system operating at off-nominal frequency, while still used the nominal frequency based DFT and samples, and then actual frequency was estimated by the inaccurate phasors. A laboratory experiment was performed to compare the frequency measured by the proposed method with those measured by PMUs.

With the assist of wide-area measurements provided by PMUs and FNET, more powerful tools are now at hands to help detect and analyse the oscillations in bulk power systems, discover new phenomena, and explore the working mechanism of interconnected power grid and its corresponding control methods. In PSWAMFOA, Low-frequency oscillation was studied in both time domain and frequency domain. Dynamic oscillation characteristics excited by different types of disturbances was illustrated. To explore the characteristics of low-frequency inter-area oscillations in frequency domain, several analysis tools such as the Matrix Pencil method was selected in power system mode analysis.

Knowledge transfer to university level through offering about ten talks or reports in Department of Electrical Engineering, Shanghai Jiao Tong University and other universities. Attended several seminars and conferences in subjects closely related to PSWAMFOA, thus offering transfer of knowledge to staffs and students of Shanghai Jiao Tong University, Fuzhou University, National Grid of China, and other Chinese academic research institutes.

Knowledge transfer to European, USA and China level through academic exchanges, talks and reports, or research collaboration with Alstom Grid Automation, Virginia Tech, Shanghai Jiaotong University, Fuzhou University, University of Electronic Science and Technology of China, Sichuan Electric Power Corporation, Chinese State Energy Smart Grid Research and Design Center, and so on.

The research results of PSWAMFOA will facilitate the launch of new projects aimed at to improve power system monitoring, protection, control, and state estimation accurate and effectiveness of Chinese power grid.