Wide Area Control Research Articles

A Lyapunov function based optimal hybrid power system controller for improved transient stability

In this paper, an intelligent power system stabilizer based on a stable and optimal hybrid learning-based adaptive control architecture is proposed which is evolved from approximate dynamic programming technique. The hybrid learning controller is based on two algorithms: (a) A reinforcement learning neural network controller implemented by adaptive critic design (ACD) and (b) A model reference adaptive controller (MRAC). The proposed method uses a novel value priority architecture for integrating these two algorithms. The designed ACD approximates nonlinear functional dynamics of the power system and interacts with the MRAC that adapts based on parametric changes. The value priority scheme developed based on a softmax network generates a hybrid control signal derived from a Lyapunov stability function that evaluates identification, performance, and stability of each controller. The overall hybrid control algorithm ensures convergence to an optimal control solution without using an explicit model of the system and at the same time ensures overall system stability. Theoretical results are validated by simulation studies for electric-generator stabilization on a 2-area 5-generator power system and as a wide-area controller on IEEE 68-bus system.

Decentralised wide‐area fractional order damping controller for a large‐scale power system

This study presents the design of wide-area fractional order damping controller for low frequency inter-area oscillations in Western Electricity Coordinating Council (WECC) system. The developed wide-area damping control scheme is implemented in a decentralised manner by examining the entire system through decentralised identification at the level of each generator bus and FACTS devices in large-scale system. The decentralised identification is done by applying n4sid (Subspace State Space System Identification) algorithm to the time-domain simulated response of WECC system. The main features of the proposed approach are: (a) measurement-based control which does not require complete model of WECC; (b) minimise the communicating signals required for damping controller and incorporate practical method of time-delay compensator (TDC) design to reduce the effect of time-varying delay. The performance of wide-area control (WAC) scheme is tested on the practical WECC system and verified by non-linear time-domain simulation. The proposed decentralised WAC scheme is compared with local and centralised control scheme, which enhances the damping of inter-area oscillation effectively compared to local control scheme and more reliable compared to centralised control scheme and its robustness is verified over a wide-range of operating conditions.

Adaptive inter-area oscillation damping controller for multi-machine power systems

The interconnection of multiple generation units in a power system can lead to inter-area oscillations that generally occur under critical operating conditions. To damp these oscillations, supplementary control can be provided by a wide area control (WAC) system using remote measurements from the power system. Wide area controllers designed with traditional approaches are non-adaptive and thus their control policy may not be optimal to nonlinear operation conditions and disturbances. In this paper, the concept of an artificial immune system (AIS) is applied in the development of an innate and adaptive controller to handle known, unknown and random disturbances in a power system. Furthermore, with synchronous generator coherency grouping, remote virtual generator measurements are used to generate supplementary control signals to a synchronous generator that is identified to have maximum controllability on a power system. Real-time simulation and frequency analysis results show the superior performance of AIS-based controller in damping inter-area oscillations for different power system conditions and disturbances.

Stability analysis and stabilization of delayed reduced-order model of large electric power system

Summary This paper discusses stability analysis using spectral discretization of time-delayed electric power system. The stability assessment is discussed in terms of influence of time delays on inter-area oscillation modes of the power system models: well-known 4-generator and 14-generator Southeast Australian power system. The three dominant inter-area modes available in full-order power system are retained in its equivalent representation, i.e., reduced-order model, obtained with the input–output variables of the generator that participates actively to low-frequency oscillation modes. The pseudospectrum analysis suggests the most dominant modes to be sensitive against time delay. The rightmost characteristic roots and the robust spectral abscissa are computed over a wide range of time delays in the input-output variables. The approach applied in study computes all the characteristic roots in the right half s-plane with the number of discretization points selected in such a way that rational approximation of the exponential functions remains accurate in this region. The effect of time delays on the computation of spectral abscissa is also investigated. Further, reduced-order time-delayed model is also used to design the wide-area controller by optimizing (minimizing) the robust spectral abscissa. Copyright © 2016 John Wiley & Sons, Ltd.

Local and Wide-Area PMU-Based Decentralized Dynamic State Estimation in Multi-Machine Power Systems

Accurate measurement of the rotor angle and speed of synchronous generators is instrumental in developing powerful local or wide-area control and monitoring systems to enhance power grid stability and reliability. Exogenous input signals such as field voltage and mechanical torque are critical information in this context, but obtaining them raises significant logistical challenges, which in turn complicates the estimation of the generator dynamic states from easily available terminal phasor measurement unit (PMU) signals only. To overcome these issues, the authors of this paper employ the extended Kalman filter with unknown inputs, referred to as the EKF-UI technique, for decentralized dynamic state estimation of a synchronous machine states using terminal active and reactive powers, voltage phasor and frequency measurements. The formulation is fully decentralized without single-machine infinite bus (SMIB) or excitation model assumption so that only local information is required. It is demonstrated that using the decentralized EKF-UI scheme, synchronous machine states can be estimated accurately enough to enable wide-area power system stabilizers (WA-PSS) and system integrity protection schemes (SIPS). Simulation results on New-England test system, Hydro-Quebec simplified system, and Kundur network highlight the efficiency of the proposed method under fault conditions with electromagnetic transients and full-order generator models in realistic multi-machine setups.

Stability Analysis and Controller Design of a Wide-Area Time-Delay System Based on the Expectation Model Method

Stochastic time delay is a new challenge for communication networks in wide-area damping control (WADC) systems. Uncertainties introduced by stochastic time delays increase the difficulty of modeling, analyzing the stability, and designing the controller. In this paper, a new approach for stability analysis and controller design through expectation modeling is proposed to solve for the uncertainty in wide-area controlled power systems introduced by the effect of a stochastic time delay. In the proposed method, the expectation model that considers the detailed stochastic time delay distribution is derived to accurately model the effect of a communication network on the wide-area control performance. Through a matrix transformation of the expectation model, the eigenvalue of the WADC system that considers time delay can then be calculated; this eigenvalue can be used for analyzing the system stability. A novel expectation model-based controller design procedure is established, through which traditional methods can be applied in the controller design of a power system with a stochastic time delay. Finally, the effectiveness of the stability analysis and controller design methods are validated through simulations in a power system of four generators and two areas with an HVDC link, and a power system with eight generators and 36 buses.

Multicast Delayed Authentication For Streaming Synchrophasor Data in the Smart Grid.

Multicast authentication of synchrophasor data is challenging due to the design requirements of Smart Grid monitoring systems such as low security overhead, tolerance of lossy networks, time-criticality and high data rates. In this work, we propose inf -TESLA, Infinite Timed Efficient Stream Loss-tolerant Authentication, a multicast delayed authentication protocol for communication links used to stream synchrophasor data for wide area control of electric power networks. Our approach is based on the authentication protocol TESLA but is augmented to accommodate high frequency transmissions of unbounded length. inf TESLA protocol utilizes the Dual Offset Key Chains mechanism to reduce authentication delay and computational cost associated with key chain commitment. We provide a description of the mechanism using two different modes for disclosing keys and demonstrate its security against a man-in-the-middle attack attempt. We compare our approach against the TESLA protocol in a 2-day simulation scenario, showing a reduction of 15.82% and 47.29% in computational cost, sender and receiver respectively, and a cumulative reduction in the communication overhead.

Design and Real-Time Implementation of Optimal Power System Wide-Area System-Centric Controller Based on Temporal Difference Learning

In this paper, a novel framework for designing and implementing a coordinated wide-area controller architecture for improved power system dynamic stability is presented and tested. The algorithm is an optimal wide-area system-centric controller and observer based on a hybrid reinforcement learning and temporal difference framework. It allows the system to deal with major concerns of wide-area monitoring problem: delays in signal transmission, the uncertainty of the communication network, and data traffic. The main advantage of this design is its ability to learn from the past using eligibility traces and predict the optimal trajectory of cost function through temporal difference method. The control algorithm is evolved from adaptive critic design (ACD) and performed online at a finite horizon through backward and forward view. The ACD controller's training and testing are implemented on the Innovative Integration Picolo card integrated to TMS320C28335 processor. Results on a real experimental test bed using a real power system feeder shows that this architecture provides better stability compared with conventional schemes.

A wide area synchrophasor-based load shedding scheme to prevent voltage collapse

Abstract This paper presents a new method based on wide area voltage stability index for optimal load shedding to prevent voltage instability phenomena. Phasor Measurement Units (PMUs) have widely been used in recent years due to their great advantages in power systems wide area monitoring, protection and control. The purpose of this paper is to provide a new optimal load shedding method, which disconnects the least possible amount of load from optimum buses. Not only the system stability is considered as main goal in this research, but also minimum load shedding is taken into account. Moreover, the problem of optimal load shedding is applied using modified Discrete Imperialistic Competition Algorithm (DICA) in mid-term and long-term voltage instability scenarios. In all investigations, certain limitations are considered to obtain practical answers. In addition, some modifications are applied to the conventional ICA, which make it proper for solving the optimal load shedding problem. New modifications result in fast convergence characteristic and less run time, which are crucial in dealing with power system instability problems.

Developing a Hybrid Intrusion Detection System Using Data Mining for Power Systems

Synchrophasor systems provide an immense volume of data for wide area monitoring and control of power systems to meet the increasing demand of reliable energy. The construction of traditional intrusion detection systems (IDSs) that use manually created rules based upon expert knowledge is knowledge-intensive and is not suitable in the context of this big data problem. This paper presents a systematic and automated approach to build a hybrid IDS that learns temporal state-based specifications for power system scenarios including disturbances, normal control operations, and cyber-attacks. A data mining technique called common path mining is used to automatically and accurately learn patterns for scenarios from a fusion of synchrophasor measurement data, and power system audit logs. As a proof of concept, an IDS prototype was implemented and validated. The IDS prototype accurately classifies disturbances, normal control operations, and cyber-attacks for the distance protection scheme for a two-line three-bus power transmission system.

Wide‐area control through aggregation of power systems

This study proposes a new method for stabilising disturbed power systems using wide-area measurement and controllable devices. A new control algorithm based on kinetic energy is proposed to be applied on the controllers to improve the first swing stability of power systems following large disturbances while also damping the subsequent inter-area oscillations. The wide-area controller is implemented by using the Kalman filter estimation of the area-based model of the system, to stabilise the inter-area dynamic and improve the stability margin of the system. The proposed approach is simulated on several test systems and the results show significant improvement in the first swing and damping stability of the test systems.

Analyzing the Cyber-Physical Impact of Cyber Events on the Power Grid

With ongoing smart grid activities, advancements in information and communication technology coupled with development of sensors are utilized for better situational awareness, decision support, and control of the power grid. However, it is critical to understand the complex interdependencies between cyber and power domains, and also the potential impacts of cyber events on the power grid. In this paper, the impact of three different possible cyber events on physical power grid have been analyzed using an integrated cyber-power modeling and simulation testbed. Real-time modeling of end-to-end cyber-power systems have been developed with hardware-in-the-loop capabilities. Real-time digital simulator, synchrophasor devices, DeterLab, and network simulator-3 are utilized in this developed testbed with a wide-area control algorithm and associated closed-loop control. DeterLab can be used to model real-life cyber events in the developed cyber-physical testbed. Man-in-the-middle and denial-of-service attacks have been modeled as specific cases for the IEEE standard test cases. Additionally, communication failure impact on the power grid has been analyzed using the testbed.

Sequential design and global optimization of local power system stabilizer and wide-area HVDC stabilizing controller

A sequential design and global optimization method is proposed to coordinately design local and wide-area controllers to enhance the overall stability of large-scale power system. The sequential design is used to assign the distributed local power system stabilizer (LPSS) and high-voltage direct current (HVDC) wide-area stabilizing controller (HVDC-WASC) to the concerned damping modes. The global optimization is used to simultaneously optimize all the overall control gains of LPSSs and HVDC-WASC. Moreover, the optimization model, which has an adaptive ability of searching and updating dominant oscillation modes, is established. Both the linear analysis and nonlinear simulation results verify the effectiveness of the proposed design method in enhancing the stability of large-scale power systems.

Transmission line fault detection and localisation methodology using PMU measurements

Rapid advancements pertaining to measurements and computational technology have brought a paradigm shift for operational architecture of power grids across the globe. Self-healing, a vital operational feature of emerging power grids, necessitates real-time identification and localisation of transmission line faults for the entire power network. This study proposes a novel support vector machine-based fault localisation methodology to precisely identify and localise all types of transmission line faults occurring at any location in the power grid based on phasor measurement unit (PMU) measurements. Detection of fault is achieved through PMU measurements only from a single generator bus for the entire grid. Bus associated with fault, faulty branch and location of fault in faulty branch are calculated using fast Fourier transform analysis of variations pertaining to equivalent voltage phasor angle (EVPA) and equivalent current phasor angle (ECPA). The proposed methodology has been validated through extensive case studies for Western System Coordinating Council (WSCC)-9 and IEEE-14 bus systems. The main contribution of the proposed methodology is that the fault location information can significantly contribute to system protection center for restoration of the line within shortest time span and initiate appropriate wide area control actions to maintain stability.

Predictive underfrequency load shedding scheme for islanded power systems with renewable generation

Underfrequency load shedding is one of the most important protection mechanisms in a power system. However, in the majority of power systems it has remained unchanged for decades, despite the advances in computer and communication technologies. Wide Area Monitoring System proved to be very useful and reliable in the last few years and this is why much effort is given into development of Wide Area Monitoring, Protection and Control concepts. Adaptive underfrequency load shedding is certainly a very suitable candidate for the task. In order to accelerate changes in this area, a proposal for an adaptive scheme has been developed, which is a good option from both the technical and economic points of view. In contrast to majority of adaptive schemes, it handles problems of active-power deficit estimation and its variations during the transient due to voltage dependent loads differently, i.e., by on-line forecasting the operating point trajectory in a phase space. The scheme has been tested on previously proven (by comparison to WAMS measurements) dynamic model of a part of a Slovenian power system and the results indicate a large improvement compared to the traditional scheme.

Mathematical Expectation Modeling of Wide-Area Controlled Power Systems With Stochastic Time Delay

Communication network brings new challenges such as time delay and data loss to wide-area damping control of power systems. The uncertainty caused by stochastic time delay of network communication increases the difficulty of wide-area control performance analysis. This paper proposes a mathematical expectation modeling approach to model and analyze wide-area controlled power systems considering the effect of stochastic time delay. In the proposed method, mathematical expectation of stochastic time delay distribution is derived to accurately model the impact of communication network on wide-area control performance. The theoretical frame of the proposed modeling approach is presented, and the effectiveness of the method is verified through the simulation of a power system with eight generators and 36 nodes.

Decentralized Communication and Control Systems for Power System Operation

Due to the rapid deployment of phasor measurement units (PMUs) on large power grids, the system operators now have access to high speed high resolution data. A new class of monitoring and control applications are made possible with the PMUs. Although PMU based monitoring systems have been well developed, implementations of PMU based fast acting closed loop wide area control systems are relatively rare. To meet the stringent latency requirements of a wide area controller the communication and power infrastructures have to collaborate strongly. In this paper, a combined process for design and simulation of both communication network and power network has been presented with the objective of damping interarea oscillations. A method to determine the optimal location of data routing hubs so as to minimize the volume of communications is also proposed. The IEEE 118 bus system is used to study the performance of communication system and the wide area power damping control system on both centralized and decentralized topologies, and the results are discussed. One of the conclusions of the paper is that the decentralized communication architectures involving data routing hubs are better suited for control applications requiring fast control actions.

Architecture Design for Integrated Wide Area Protection and Control Systems

This paper firstly reviews the recent development in power system protection and control, with special attention paid to the wide-area and integrated protection, in order to look into future development of integration of protection and control for smart grids. This paper mainly reports on the development of integrated wide area protection and control for power systems. The concept of integrated wide area protection and control is introduced, in which a hierarchical protection and control system provides the protection and control of wide area or regional power substations/ plants and their associated power network. The system is mainly divided into three levels, the local, the substation/plant and the wide area/regional protection and control. The integrated functions at each level are described in details with an aim to develop an optimal coordination mechanism between the levels. One of the core elements in the system is the synchronised wide area communication network between the substations and the protection and control system, in which latest communication technology is employed. Another important player in the system is the wide area synchronized protection and control information platform, which not only enables the fusion three line of defence for power system protection and control, but also provides a perfect tool for the application of cloud computing to substations and power networks.

Wide Area Control Systems (WACS) Implementation Based on Sensor Network Concepts

Wide Area Control Systems (WACS) are introduced to respond to the real time control requirements of a smart grid. The control messages in smart grid can be of different levels of criticality. Therefore priority based routing, depending on criticality of messages, is very essential in control message communication. The topology of the system considered, involves control units connected to five buses in a smart micro grid. The performance metrics are identified and threshold values are fixed. Different communication technologies are simulated and the performance is compared. Multi hopping communication is established between the nodes and heterogeneous communication architecture is implemented. The need for dynamic routing protocol in the grid, as the traffic on the network changes over time, is also met. A communication scenario which dynamically routes the control message from central station to control units depending on priority, through the shortest path available, is identified here.

Sensor Based Communication Network for WACS with DNP3

Smart grid is the emerging electricity network envisaged to connect the supplier and the consumer by two-way digital communication. One of the main attractions of the smart grid is the Wide Area Control System (WACS) with distributed controllers which actuate the instructions issued by the central controller. This paper focuses on the hardware implementation of a communication network for WACS in which ZigBee is used as the communication technology from the control station to the control unit. The control message sent should follow Distributed Network Protocol version 3 (DNP3), which is an IEEE standard for communication between central station and Intelligent Electronic Devices (IEDs). The simulation is done in network simulator (ns2), in which the number of packets follows the DNP3 format. Using mbed board a network topology is created for the WACS communication network and the control messages are communicated from the control station to the control units to validate a satisfactory performance.