Power system inter-area oscillations can be damped using distributed control of multiple power injections within the interconnection. This type of control traditionally requires system-wide measurements which are transmitted from dispersed, sometimes remote, locations and are subject to delays. This paper evaluates the effect that delayed feedback signals have on the stability of a two-area power system and presents delay-dependent criteria for stability using two different implementations of a damping controller. The controllers are based on a uniform proportional control action and use two feedback signals one from each area of the two-area power system. Each of these signals is subject to an independent delay. Using a Lyapunov-based approach, sufficient conditions for stability that depend on each time delay are found for a range of proportional control gains. Numerical results show that the regions of time delays for which the system is stable are reduced as the proportional gain increases. Time domain simulations validate these stability regions and show the varying responses for the two control implementations and different values of the proportional gain.
This paper analyzes the effect of wind turbine integration (WT) on the inter-area oscillation mode of a test two-area power system. The paper uses a root-locus based design method to propose a pair of controllers to provide damping to the inter-area mode of the system. The controllers are selected from the best combination of feedback signal and WT control action. One of the controllers uses the active power control part of the WT while the other uses the reactive power part. The paper analyzes the impact that increases on the transmission line connecting the WT to the system have on the controllers' performance. Time domain simulations are provided to evaluate the effectiveness of the controllers under different conditions.
This paper focuses on a transmission system with a high penetration of converter-interfaced generators participating in its primary frequency regulation. In particular, the effects on system stability of widespread misconfiguration of frequency regulation schemes are considered. Failures in three separate primary frequency control schemes are analyzed by means of time domain simulations where control action was inverted by, for example, negating controller gain. The results indicate that in all cases the frequency response of the system is greatly deteriorated and, in multiple scenarios, the system loses synchronism. It is also shown that including limits to the control action can mitigate the deleterious effects of inverted control configurations.
This paper analyzes the effects on transient stability of integrating a wind power plant (WPP) on a single machine infinite bus (SMIB) test system. Wind penetration in the system was increased and the impact of this integration on the critical clearing time (CCLT) of the system is studied. This study is performed separately for different WPP reactive power control schemes. Additionally, the paper determines the reduction in power output of the conventional generator necessary to keep a constant CCLT in the face of increases in wind penetration. The results show that this reduction is smaller than the wind power integrated, which is reflected in an increase in the total power transfered across the transmission line. Hence, the total power of the transfer path can be increased without transient stability concerns.
This study describes the implementation of a tool to estimate latencies and data dropouts in communication networks transferring synchrophasor data defined by the C37.118 standard. The tool assigns a time tag to synchrophasor packets at the time it receives them according to a global positioning system clock and with this information is able to determine the time those packets took to reach the tool. The tool is able to connect simultaneously to multiple phasor measurement units (PMUs) sending packets at different reporting rates with different transport protocols such as user datagram protocol or transmission control protocol. The tool is capable of redistributing every packet it receives to a different device while recording the exact time this information is re-sent into the network. The results of measuring delays from a PMU using this tool are presented and compared with those of a conventional network analyzer. The results show that the tool presented in this paper measures delays more accurately and precisely than the conventional network analyzer.
This project explored coupling modeling and analysis methods from multiple domains to address complex hybrid (cyber and physical) attacks on mission critical infrastructure. Robust methods to integrate these complex systems are necessary to enable large trade-space exploration including dynamic and evolving cyber threats and mitigations. Reinforcement learning employing deep neural networks, as in the AlphaGo Zero solution, was used to identify "best" (or approximately optimal) resilience strategies for operation of a cyber/physical grid model. A prototype platform was developed and the machine learning (ML) algorithm was made to play itself in a game of 'Hurt the Grid'. This proof of concept shows that machine learning optimization can help us understand and control complex, multi-dimensional grid space. A simple, yet high-fidelity model proves that the data have spatial correlation which is necessary for any optimization or control. Our prototype analysis showed that the reinforcement learning successfully improved adversary and defender knowledge to manipulate the grid. When expanded to more representative models, this exact type of machine learning will inform grid operations and defense - supporting mitigation development to defend the grid from complex cyber attacks! This same research can be expanded to similar complex domains.
Inter-area oscillations are present in all power systems dispersed over large areas and can have detrimental effects limiting transmission capacity or even causing blackouts. The availability of wide-area measurements in power systems has enabled damping of inter-area oscillations using distributed control methods and system components, such as energy storage devices. We investigate the performance of damping control enabled by energy storage devices distributed throughout an example two-area power system assuming the availability of wide-area measurements of generator machine speeds. The energy storage devices are capable of injecting active power into the system in order to damp inter-area oscillations that occur after a fault in the system. An analysis of the linearized system and several simulations of the nonlinear system with multiple combinations of controlled power injections from energy storage devices are performed. From the results, we quantify and discuss how damping performance depends on the sizes and locations of injections.
A wide-area controller to damp inter-area oscillations in the North American Western Interconnection (WI) by modulating power transfers in a HVDC link is used in this paper to investigate the effects that latencies in its feedback signals have on its performance. This controller uses two feedback measurements to perform its control action. The analysis show that the stabilizing effect of the controller in transient stability and small signal stability is compromised as the feedback measurements experience higher delays. The results show that one of the feedback signals can tolerate more delay than the other. The analysis was performed with Bode plots and time domain simulations on a reduced order model of the WI from which a linear version was obtained.
This paper explores the controllability of power system oscillation modes by multiple high voltage DC (HVDC) transmission lines. The controllability exploration is performed in a reduced model of the Western Electricity Coordination Council (WECC) system, with added HVDC lines according to previously proposed lines. The exploration shows that various oscillation modes, across several system areas, can be simultaneously controlled by coordinating three or more HVDC lines. The degree of damping in each oscillation mode can be selected by designing a multi-input multi-output control system on the HVDC lines.
This report documents the use of wind turbine inertial energy for the supply of two specific electric power grid services; system balancing and real power modulation to improve grid stability. Each service is developed to require zero net energy consumption. Grid stability was accomplished by modulating the real power output of the wind turbine at a frequency and phase associated with wide-area modes. System balancing was conducted using a grid frequency signal that was high-pass filtered to ensure zero net energy. Both services used Phasor Measurement Units (PMUs) as their primary source of system data in a feedforward control (for system balancing) and feedback control (for system stability).