Power oscillation damping control using wide-area signals: A case study on Nordic equivalent system
ABSTRACT Power oscillation damping (POD) control employing wide-area signals is illustrated in an equivalent system model representing key characteristics of Nordic power system. Phasor measurement units (PMUs) in Norway and Finland are used to obtain feedback signals for supplementary control of a large SVC unit located in the south-east of Norway. Comparison has been made between two control design approaches- (i) robust linear time invariant model based POD (MBPOD) - dependant on accurate system model and (ii) indirect adaptive POD (IAPOD) - which is fixed structure but time-varying and relies only on measurements. An optimization problem is formulated to design the controller parameters for MBPOD while the IAPOD is based on online Kalman filter estimation and adaptive pole-shifting control. Performances of both MBPOD and IAPOD are found to be quite similar even though IAPOD requires very little prior information about the system. A number of simulations are carried out under different tie-line outages to verify the performance.
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ABSTRACT: This article reports the results from the implementation and testing of a Wide-Area Power Oscillation Damper (WAPOD) controlling a 180 Mvar TCR Static Var Compensator (SVC) installed in the Hasle substation of Norwegian 420 kV transmission grid. The WAPOD uses voltage phase angle signals from two distant locations in the Norwegian grid as inputs to the damping controller. The damping controller modulates the voltage reference set point used by the SVC's voltage controller, thereby creating a damping effect. The WAPOD is an extension to the existing Power Oscillation Damping (POD) controller that uses local measurements. A switch-over logic allows for the use of no damping control, local damping control or wide-area control. Field tests were performed during November 2011, and involved the disconnection and re-connection of a 420 kV transmission line. The performance of the WAPOD is compared to that of state-of-the-art local Phasor POD, and when no damping control is enabled. The testing results show that the WAPOD performed satisfactorily and according to the design expectations. These results show that the potential flexibility of the WAPOD to choose, among the different PMU signals, those that have the good observability of inter-area modes can be an advantage to the use of local feedback signals for damping control, as it is current practice today. Further testing of this WAPOD with other PMU signals from locations with stronger observability will be helpful to illustrate the advantage of this flexibility.Power and Energy Society General Meeting, 2012 IEEE; 01/2012
Conference Paper: Introduction to wide-area control of power systems[Show abstract] [Hide abstract]
ABSTRACT: A key element in the development of smart power transmission systems over the past decade is the tremendous advancement of the Wide-Area Measurement System (WAMS) technology, also commonly referred to as the Synchrophasor technology. Sophisticated digital recording devices called Phasor Measurement Units or PMUs are currently being installed at different points in the North American grid, especially under the smart grid initiatives of the US Department of Energy, to record and communicate GPS-synchronized, high sampling rate (6-60 samples/sec), dynamic power system data. Significant research efforts have been made on techniques to useWAMS for monitoring and situational awareness of large power networks dispersed across wide geographical areas. In contrast, use of WAMS for automatic feedback control has received less attention from the research community. The objective of this paper is to bridge this gap by formulating wide-area control problems for oscillation damping, voltage control, wide-area protection, and disturbance localization. We present the main research challenges that need to be overcome to realize the benefits of wide area control in power systems. Our discussion begins with a review of the fundamental physical models of different characteristic components of a large transmission-level power grid such as synchronous generators, transmission lines, and loads, followed by a description of how these subsystem-level models can be integrated to form the overall system model. We pose ten distinct control-theoretic problems. The first two problems are on using PMU measurements from selected nodes in the system to identify such system models in different resolutions in real-time, and the remaining on how the identified models can be used for designing output-feedback based damping controllers, for understanding voltage fluctuations at different nodes of the network graph, and for detecting malicious inputs entering the system dynamics via faults or extraneous- attacks. We also propose two new control paradigms, namely a scheduling approach for appropriate controller selection based on online estimation of oscillation modes, and distributed phasor-based control using model estimation. We illustrate our ideas via representative examples, many of which are inspired by well-known power transfer paths in the US west coast grid, also referred to as the Western Electricity Coordinating Council (WECC).American Control Conference (ACC), 2013; 06/2013
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ABSTRACT: Low frequency inter-area oscillations are known stability issue of large interconnected electrical grids. It was demonstrated that additional control loop can be applied for static power sources, like FACTS, HVDC or modern Wind Power Plants, to modulate their power output and successfully attenuate these oscillations. Variety of control design methods were proposed for this service. In this paper focus is given to the most popular technique based on residues. Authors demonstrate on a small 4-machine 12-bus grid that residues may not provide sufficient information for effective damping control design. Hence, it is proposed to give more attention to additional indices like transfer function zero location and interactions between mode of interest and other system dynamics. Consequently, additional rules are proposed for residue based damping control design.Power and Energy Society General Meeting, 2012 IEEE; 01/2012