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 synchronised 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.
-As a supplement of existing measurements, phasor measurements can extend measurement redundancy of the estimator. When state estimation is reformulated in terms of pure direct measurements of phasor voltages and currents, the resulting estimation problem would be a directly solvable problem, with the gain matrix constant, sparse, and in most cases real. A straightforward application of state estimation theory that treats phasor measurements of currents and voltages as additional measurements to be appended to traditional measurements is now being used in most energy management system (EMS) state estimators. The resulting state estimator is once again non-linear and requires significant modifications to existing EMS software. An alternative approach which leaved the traditional state estimation software in place was researched in PSWAMFOA. This novel method presented in this project incorporated the phasor measurements and the results of the traditional state estimator in a post-processing linear estimator, which largely reduced the scale of non-linear estimation problem as well as the number of iteration and the processing time per iteration. Experiments and simulations were used to verify the presented method and strategies.
-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 analyze 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 more than ten talks or reports in CAP Group, Dept. of Electrical & Electronic Engineering and attended several seminars in subjects closely related to PSWAMFOA, thus offering transfer of knowledge to staffs and students of Imperial College.
-Knowledge transfer to European and China level through academic visit, talks and reports, or research collaboration with University of Liverpool, Brunel University, 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 & Design Center, and so on
-The research results of PSWAMFOA will facilitate the launch of two new projects aimed at to improve power system monitoring, protection, control, and state estimation accurate and effectiveness of Chinese power grid.
-As a supplement of existing measurements, phasor measurements can extend measurement redundancy of the estimator. When state estimation is reformulated in terms of pure direct measurements of phasor voltages and currents, the resulting estimation problem would be a directly solvable problem, with the gain matrix constant, sparse, and in most cases real. A straightforward application of state estimation theory that treats phasor measurements of currents and voltages as additional measurements to be appended to traditional measurements is now being used in most energy management system (EMS) state estimators. The resulting state estimator is once again non-linear and requires significant modifications to existing EMS software. An alternative approach which leaved the traditional state estimation software in place was researched in PSWAMFOA. This novel method presented in this project incorporated the phasor measurements and the results of the traditional state estimator in a post-processing linear estimator, which largely reduced the scale of non-linear estimation problem as well as the number of iteration and the processing time per iteration. Experiments and simulations were used to verify the presented method and strategies.
-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 analyze 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 more than ten talks or reports in CAP Group, Dept. of Electrical & Electronic Engineering and attended several seminars in subjects closely related to PSWAMFOA, thus offering transfer of knowledge to staffs and students of Imperial College.
-Knowledge transfer to European and China level through academic visit, talks and reports, or research collaboration with University of Liverpool, Brunel University, 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 & Design Center, and so on
-The research results of PSWAMFOA will facilitate the launch of two new projects aimed at to improve power system monitoring, protection, control, and state estimation accurate and effectiveness of Chinese power grid.