PMU Based RAS Report-1 - UTKweb.eecs.utk.edu/~hli31/CPS/May_RAS.pdf · Event-based RAS are designed...
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1. PMU Based RAS for a Hybrid AC/DC System 1.1. Project Team Primary Thrust: Modeling Secondary Thrust: Control Faculty: PI: Kevin Tomsovic (UTK) Graduate Student: Meimanat Mahmoudi (UTK) 1.2. Project Goals and Brief Abstract In current practice, RAS design is derived from off-line studies based on some performance criteria and response to events. Depending on the method of detection, existing RAS can be classified as event-based or response-based. Event-based RAS are designed to operate on the recognition of a particular combination of events (such as loss of several ties). Response-based RAS are based on real-time measurement and initiate control actions when the responses hit the trigger level. Event-based RAS can be fast since one need not wait for the response development. On the other hand, a response-based RAS has been mainly for slower phenomena, and can operate for unknown events and varying operating scenarios. The next generation of corrective controls requires fast detection of the system instability based on both events and responses from wide area monitoring. This has become possible with the deployment of real time phasor measurements (PMUs), as well as with modern communication systems. In addition, the PMUs may allow disturbances to be detected more quickly allowing less severe action. This effort focuses on PMU driven response-based RAS schemes. Specifically, we are investigating RAS schemes to prevent system separation based on information from PMU units. The project goals break down into three efforts: • Investigating the possibility of less disruptive supplementary inputs to existing controls rather than the more severe switching operations, such as, generation rejection, control blocking or other discrete operations, in today’s RAS. • Developing a framework to model the interaction among RAS schemes and understanding of the reliability implications. • Analyze the impact of the hybrid AC-DC system proposed in this project on the design of RAS. Initial effort stems from new distributed system modeling techniques to faithfully capture the "wave" like propagation of some disturbances. These new mathematical approaches lead us to propose new controls that seek to minimize the impact of disturbances. It is also an integration of various areas related to CPS, such as control, communications and computing, within the same framework.
Transcript of PMU Based RAS Report-1 - UTKweb.eecs.utk.edu/~hli31/CPS/May_RAS.pdf · Event-based RAS are designed...
1. PMU Based RAS for a Hybrid AC/DC System
1.1. Project Team Primary Thrust: Modeling Secondary Thrust: Control Faculty: PI: Kevin Tomsovic (UTK) Graduate Student: Meimanat Mahmoudi (UTK)
1.2. Project Goals and Brief Abstract
In current practice, RAS design is derived from off-line studies based on some performance criteria and response to events. Depending on the method of detection, existing RAS can be classified as event-based or response-based. Event-based RAS are designed to operate on the recognition of a particular combination of events (such as loss of several ties). Response-based RAS are based on real-time measurement and initiate control actions when the responses hit the trigger level. Event-based RAS can be fast since one need not wait for the response development. On the other hand, a response-based RAS has been mainly for slower phenomena, and can operate for unknown events and varying operating scenarios. The next generation of corrective controls requires fast detection of the system instability based on both events and responses from wide area monitoring. This has become possible with the deployment of real time phasor measurements (PMUs), as well as with modern communication systems. In addition, the PMUs may allow disturbances to be detected more quickly allowing less severe action.
This effort focuses on PMU driven response-based RAS schemes. Specifically, we are investigating RAS schemes to prevent system separation based on information from PMU units. The project goals break down into three efforts:
• Investigating the possibility of less disruptive supplementary inputs to existing controls rather than the more severe switching operations, such as, generation rejection, control blocking or other discrete operations, in today’s RAS.
• Developing a framework to model the interaction among RAS schemes and understanding of the reliability implications.
• Analyze the impact of the hybrid AC-DC system proposed in this project on the design of RAS.
Initial effort stems from new distributed system modeling techniques to faithfully capture the "wave" like propagation of some disturbances. These new mathematical approaches lead us to propose new controls that seek to minimize the impact of disturbances. It is also an integration of various areas related to CPS, such as control, communications and computing, within the same framework.
1.3. Support of the Strategic Plan
RAS schemes have proliferated in recent years as an attempt to delay needed transmission upgrades without compromising reliability or to address problems found during disturbances. The advantage is they may allow new generation to come on-line or identified problems to be addressed more quickly than waiting for the longer term planning cycle. Still, there is increasing concern with the numbers of these schemes, the effectiveness of their ad hoc designs [1] and the possibility that the interactions between RAS may create new system vulnerabilities [2]. This work is developing the foundation for designing these wide area protection schemes. Such schemes are essential to the strategic plan in enabling robustness in the face of disturbances for the developed wide area coordinated controls.
1.4. Challenges, Impacts and Methodology During the first stage of this research, we have focused on investigating the possibility of less disruptive supplementary inputs to existing controls rather than the more severe switching operations, such as, generation rejection, control blocking or other discrete operations, in today’s RAS [3]. By taking a continuum limit as generation is distributed over a grid, the classical power system model tends to a wave equation [4, 5]. The resulting model suggests that disturbances in power systems will propagate as traveling waves.
𝜕!𝛿𝜕𝑡! + 𝑣
𝜕𝛿𝜕𝑡 − 𝜗
!∇!𝛿 + 𝑢! ∇𝛿 ! = 𝑃 Eq.(1.1)
Using wave propagation speed along with wide area measurements provided by a communication network, one can design corrective controllers in order to respond to major disturbances before the time of arrival. In centralized control schemes, a single controller is able to measure all the system outputs, compute the optimal control solution, and applies that action to all actuators in the network, within one sampling period [6]. As power networks are large-scale systems, both computationally and geographically, a centralized wide- area controller is practically difficult to implement. Non-centralized control schemes can be divided into two categories: decentralized techniques, which do not allow for communication between local controllers and distributed techniques, where communication between different controllers is exploited to improve controller performance. We seek distributed control schemes that are equivalent to local feedback controllers plus neighboring controller’s adjustment with proportional gains.
Fig 1.1 Categories of Non-Centralized Control Schemes
A distributed excitation control scheme has been proposed based on [7] to mitigate electromechanical disturbance propagation in a large power network. The proposed controller consists of distinct LQR feedback controllers, one for each generator, where the inputs to each generator are computed only based on the states of the generator and its neighbors.
1.5. Achievements of First Stage
The proposed distributed controller is evaluated via numerical simulation using MATLAB for a mesh structure test system. A 30x30 mesh grid (total of 900) of identical generators connected through identical transmission lines is considered. A linearized fourth order generator model from [8] is used here as the model of 𝑖!! generator in the system. A power pulse perturbation (amplitude of 0.5 𝑝𝑢, 𝑡!"#$% = 0.1 𝑠 , and 𝑡!"#$%&'( = 0.5 𝑠) was applied to the generator in the middle of the mesh. Figures (1.4) to (1.8) illustrate the angle response of the system without using controller at time periods of t = 0.5, 1, 3, 5 and 10 seconds respectively. Comparing the results of controlled system in Figures (1.9) to (1.13) and the uncontrolled case illustrates that the proposed distributed controller improves the ability of the system to mitigate electromechanical disturbances.
Angle Response without Controller Angle Response with Proposed Distributed LQR Controller
Fig 1.4 Angle Response of the system at 𝑡 = 0.5 𝑠 Fig 1.9 Angle Response of the system at 𝑡 = 0.5 𝑠
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Fig 1.2 Information Exchange Block Diagram for the Proposed
Distributed LQR Controller
Fig 1.3 Two-Dimensional test system
Fig 1.5 Angle Response of the system at 𝑡 = 1 𝑠 Fig 1.10 Angle Response of the system at 𝑡 = 1 𝑠
Fig 1.6 Angle Response of the system at 𝑡 = 3 𝑠 Fig 1.11 Angle Response of the system at 𝑡 = 3 𝑠
Fig 1.7 Angle Response of the system at 𝑡 = 5 𝑠 Fig 1.12 Angle Response of the system at 𝑡 = 5 𝑠
Fig 1.8 Angle Response of the system at 𝑡 = 10 𝑠 Fig 1.13 Angle Response of the system at 𝑡 = 10 𝑠
1.6. Future Work
Along with the proposed research tasks in the area of modeling, control and communication, in future work there will be a special emphasis on new Remedial Action Schemes. Some of the main areas to be addressed are:
• Developing a framework to model the interaction among RAS schemes and understanding the reliability implications.
• Analyze the impact of the hybrid AC-DC system on the design of RAS.
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1.7. Milestones and Deliverables
TASK: PMU Based RAS for a Hybrid AC/DC System
Statement of Work Schedule Task Milestones and Deliverables
No. Task Description 2012 2013
Description A S O N D J F M A M J J
1 PMU based RAS design X X X X X X X X
Phase information used to for supplementary control design
2 Modeling framework for RAS interactions
X X X X X X X X X Wave model and distributed control models
3 RAS for hybrid architecture
X X X X X X X X X Possible switching actions in AC/DC hybrid network to stop propagation of disturbances
4 Testing and reports
X X X X X X Simulation and test
1.8. References
[1] Y. Zhang and K. Tomsovic, "Adaptive remedial action scheme based on transient energy analysis," Power Systems Conference and Exposition, 2004. IEEE PES, vol. 2, pp. 925- 931, Oct. 2004.
[2] K. Tomsovic, D. Bakken, V. Venkatasubramanian and A. Bose, "Designing the Next Generation of Real-Time Control, Communication, and Computations for Large Power Systems," Proceedings of the IEEE, vol. 93, no. 5, pp. 965-979, May 2005.
[3] J. McCalley and W. Fu, "Reliability of special protection systems," Power Systems, IEEE Transactions on, vol. 14, no. 4, pp. 1400-1406, Nov1999.
[4] J. Thorp, C. Seyler and A. Phadke, "Electromechanical wave propagation in large electric power systems," Circuits and Systems I: Fundamental Theory and Applications, IEEE Transactions on , vol. 45, no. 6, pp. 614-622, Jun 1998.
[5] R. Cresap and J. Hauer, "Emergence of a New Swing Mode in the Western Power System," Power Apparatus and Systems, IEEE Transactions on , Vols. PAS-100, no. 4, pp. 2037-2045, April 1981.
[6] R. M. Hermans, A. Jokić, M. Lazar, A. Alessio, P. P. vanden Bosch, I. A. Hiskens and A. Bemporad, "Assessment of non-centralised model predictive control techniques for electrical power networks," International Journal of Control, vol. 85, no. 8, pp. 1162-1177, Apr 2012.
[7] F. Borrelli and T. Keviczky, "Distributed LQR Design for Identical Dynamically Decoupled Systems," Automatic Control, IEEE Transactions on , vol. 53, no. 8, pp.
1901-1912, Sept 2008.
[8] P. Kundur, Power System Stability and Control, EPRI Power System Engineering, Series, McGraw-Hill, 1994.
