Key Branch Identification and Emergency Control Based on Wide Area Transient Response

High-volume synchrophasor data generated by the wide area measurement system (WAMS) present new challenges for the design of scalable and robust communication architectures suitable for the large-scale deployment in power grid monitoring and control applications. Features of information and communication technology (ICT) can be harnessed to devise a more flexible infrastructure than the conventional unicast-based hierarchical architecture. Multicast has been suggested as a potential solution for scalability issues in the current WAMS architecture. This article proposes a decentralized dynamic multicast routing management algorithm that manages network traffic efficiently, improves scalability, and makes the system resilient to component failures. The algorithm models the creation of alternate links as a stochastic process using the random-graph theory and manages connections between end hosts at the session layer. This protocol can be implemented using existing ICT protocols at a minimal cost. Numerical simulations and study of frequency control in an IEEE 39-bus system testbed show that the proposed algorithm improves the topological efficiency and resilience of the network.

WAMS (Wide Area Measurement System) is a newly developed technology, which can provide a reliable guarantee to the simultaneous measurement of power system. But PMU (Phasor Measurement Unit) can not be widely used in power grid now, so it is impossible that WAMS can replace SCADA (Supervisory Control And Data Acquisition) system presently. Hence, how to incorporate WAMS measuring data into other systems including SCADA has become a hot research topic currently especially the data exchange between them. In order to solve this problem, a CIM (Common Information Model)-based information model for WAMS is proposed in this paper according both to IEC 61970: EMS-API (Energy Management System Application Program Interface) part 303 and the principle and the application of WAMS. This paper establishes a new package named WAMS in the framework of CIM and then some extended classes and their attributes along with their relationships are also defined. Finally this paper briefly describes the application of this CIM-based information model by presenting a flow diagram about information integration and utilization between WAMS and SCADA.

It is very important to take into consideration time delay in wide area power system stability; the design of PSS (Power System Stabilizer) should consider global optimization with WAMS (Wide Area Measurement System) time delay. Newly designed PSS should be insensitive to time delay and suppress internal low frequency oscillations. It is used as feedback signal and is real-time synchronous that WAMS signal shows. Power system is modeled with the consideration of time delay. LMI (Linear Matrix Inequalities) is used to solve the stability condition of time delay system. Based on the time-delay effect of the wide-area measurement signals, this paper redesigned the PSS with global optimization of power system. The attached two-area-four-machine system simulation illustrates that wide-area PSS designed by global optimization with the consideration of time-delay can limit internal low frequency oscillation with time-delay insensitivity, and improve the stability of power system. It implements global optimization of PSS with WAMS time delay stability.

Wide Area Measurement System (WAMS) is technology to improve situational awareness and visibility within power system of today's and future grids. It uses real time synchro phasor data to measure the state of grid that enables improvement in stability and reliability of power grid. WAMS architecture plays an important role in these real time and data intensive systems. Proper selection of WAMS architecture helps immensely in achieving the benefits of WAMS technology namely increase in stability and reliability of grid. The factors like PMU data acquisition, decision making based on PMU data and the enactment of actions based on decision making determine the architecture details of WAMS. This paper discusses how different combinations of these factors lead to different realizable types of WAMS architectures. In addition, this paper also presents detailed comparison of all WAMS architectures to highlight the advantages and disadvantages of implementing each one of them based on WAMS features like WAMS data communication, data security, data storage, alarm/event management, system availability etc. The paper concludes with summarizing the architecture options and their possible use cases.

A new primary frequency controller in power grids undergoing massive wind power penetration is the focus of this paper. The inescapable problem in a largely wind penetrated power grid is to ensure the maintenance of its frequency in the nominal band prescribed by the power system operator (PSO). However, with the massive arrival of wind farms with conventional control schemes, the operation of maintaining and restoring the frequency to the regulatory regimes remains very complicated. In order to overcome the above problem, this paper proposes a new strategy for primary frequency control in power grids using model predictive control (MPC) for a multi-cluster doubly-fed induction generator (DFIG)-based wind farm (WF), with a main objective of reducing the frequency nadir (FN), eliminating the second frequency dip (SFD), and providing the optimal support during wind speed variations. In this approach, a rolling prediction and optimization control strategy is developed based on the dynamic power system model to ideally predict the additional power to be provided. Moreover, in order to avoid second frequency dips, the wind turbines (WTs) are not allocated to extract additional power from the grid during the frequency event, the rotor speeds are not recovered to the maximum power point tracking (MPPT) operating points during the primary frequency control. The performance of the proposed controller was evaluated using a two-zone electrical system in MATLAB/Simulink®. The obtained results disclose that the frequency nadir is enhanced with more than 6.1% compared to the conventional schemes. In addition, the frequency response settling time has been improved with more than 10.51 s.

In order to easily monitor the wide-area power system information covering many power producers, suppliers, and power companies, authors have been developed a PMU (phasor measurement unit) based WAMS (wide area measurement system). This WAMS momentarily gather information about the power oscillation affecting the stability of Japanese longitudinal power systems by signal processing of the power outlet phasor. This paper introduces the features of the PMU based WAMS, and an availability of the power outlet phasor is validated by comparing the measurements with actual power station. And as one of the applications, an estimation method of interconnected power system parameters from the monitored power oscillation information is proposed.

A wide-area measurement system (WAMS) consists of advanced measurementtechnology,thelatestcommunicationnetworkinfrastructure,andintegratedoperationalframework. The supervisory control and data acquisition (SCADA) infrastructure forenergy-management system (EMS) has been widely used in power systems for a longtime. Some of the functionalities of an EMS are system state monitoring, tie-line biascontrol,andeconomicdispatch[1].However,inrecentyears,variousdeficienciesoftheexisting SCADA-based EMS (such as quasi-steady-state calculation, non-synchronizeddataacquisition,andrelativelylowdatatransmissionrate)havebeenpointedout.Thesedefects make it impossible to sample the global state of a power system in real time.As more and more wide-area blackouts are reported, it is clear that acquiring real-timeor wide-area state information would be needed in the future. The state informationin terms of phasors of voltages and currents from a distributed wide area in real timeis therefore critical for avoiding large-area disturbances by effecting wide-area controlbased on wide-area measurements.The main enabler of WAMS is phasor measurement unit (PMU) technology. Withthe innovation of PMU, the problem of measuring the phasor quantities simultaneouslyfromawideareaofdistributedsubstations,alsocalled‘synchrophasor’,hasbeensolved.At present, the PMU technology is one of the essential enablers for WAMS. It utilizesthe availability of high-precision synchronized clock sources – extracted from globalpositioning system (GPS) receivers and samples the instantaneous analogue – quanti-ties of voltage and current magnitudes and phase angles. Many utilities are installingPMUs at very high voltage substations, but the trend is that eventually PMUs will beused to monitor all high-voltage transmission lines. There are debates as to whether thewide-area or long-distance communications that communicate phasor data, or controlaction messages, should only be done via proprietary networks, or the existing Inter-net infrastructure with quality-of-service (QoS) differentiated delivery could be used.These questions require further simulation studies as well as financial and policy deci-sions which are not considered in this chapter. We concentrate mostly on evaluatingthe network architecture, the specific network medium and technology, the appropriate

The wide application of WAMS (Wide Area Measurement System) provided a new thinking for transient stability analysis of power system. Based on real-time measurement information from WAMS, a method to quickly analysis power system transient stability that does not depend on network structure, model and parameters of power system is proposed in this paper. Firstly, the parameters of system are identified online by improved least squares method on basis of that the multi-machine power system is equivalently reduction to one machine infinity bus system. The equilibrium point and stability margin of equivalent system are rapidly computed, and then the stability of system is quickly judged. The simulation results show that the algorithm can accurately judge transient stability of system and has better antidisturbance ability and robustness. The issue of dependence of transient stability analysis on system model and parameter is solved. The adverse influences of data lose and measurement errors in actual measurement of the WAMS on analysis results are avoided effectively. Keywords-power system; wide-area measurement system; parameter identification; energy function; transient stability analysis

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).

Wide Area Measurement Systems (WAMS) use an underlying communication network to collect and analyze data from devices in the power grid, aimed to improve grid operations. For WAMS to be effective, the communication network needs to support low packet latency and low packet losses. Internet Protocol (IP), the pervasive technology used in today's communication networks uses loop-free best-paths for data forwarding, which increases the load on these paths causing delays and losses in delivery. Information-Centric Networking (ICN), a new networking paradigm, designed to enable a data-centric information sharing, natively supports the concurrent use of multiple transmission interfaces, in-networking caching, as well as per-packet security and can provide better application support. In this paper, we present iCASM, an ICN-based network architecture for wide area smart grid communications. We demonstrate through simulations that iCASM achieves low latency and 100% data delivery even during network congestion by leveraging multiple available paths; thus significantly improving communication resiliency in comparison to an IP-based approach. iCASM can be used immediately on today's Internet as an overlay.

The Study on the Communication Network of Wide Area Measurement System in Electricity Grid

Protection of power systems is important for stable and uninterrupted operation of power network. Maloperation of traditional back up protection schemes (e.g-Zone3 maloperation) causes many catastrophic phenomenon like cascaded tripping in power systems. So, some defensive mechanism are needed for taking care of such failures in power systems and to increase their security and reliability. Due to hugeness and complexity of Modern power systems, they are controlled, monitored and protected by Wide Area Measurement systems (WAMS). WAMS increases the efficiency and reliability of power networks and prevent the chance of blackouts and cascading failures in tandem. A synchronized phasor measurement-based wide-area backup protection scheme is presented in the paper where the magnitude of sequence voltages of buses at a system protection centre are used to identify the faulted area, bus closest to the fault and faulted line. The proposed method is tested for several faults including simultaneous faults in power systems with interconnections also. This technique is found to be Reliable, accurate and fast with contemporary synchronized measurement based technology. It is expected that numerous disastrous blackouts, cascaded tripping of power networks can be avoided and reliability and security of the power systems can be improved by the scheme. The study of new and improved back up protection scheme is done on a WSCC-3 machine-9 bus system. The data is simulated through EMTDC/PSCAD and MATLAB /SIMULINK software.

The distance for AC and DC dense transmission channels is very long, the transmission capacity is large, and the number of crossing points for 220kV and above are large. Multiple faults are prone to occur in extreme weather, natural disasters and so on, which seriously endangers the security of the power grid. The transmission sections are generally the weak links of power grid, and the rapid search of key transmission sections considering the influence of multiple faults is of great significance to the protection and control of power grid. The current research focuses on the influence of natural disasters on transmission equipment and transmission section search methods such as grid cut search and network contraction. But the impact of multiple faults on security and stability characteristics of power grid and the weak transmission sections haven’t been analyzed. In this paper, a key transmission section identification method considering multiple preconceived faults is proposed. Multiple faults are divided into three types, which are multiple AC line faults, multiple DC line faults and AC / DC line mixed faults. And the impact of the multiple faults on power grid security is analyzed. Then, the key section identification method considering multiple fault disturbances and the weak section identification method after topology changes due to multiple faults are studied. The validity of the proposed method is verified in scenarios with multiple expected faults by using AC/DC hybrid power grid data. Identification of critical sections under multiple faults is an important basis for on-line risk early warning and decision-making of multiple faults in large power grid, which has important practical value.

In this paper, we propose a novel excitation system for improvement of the transient stability. The proposed method controls the excitation voltage of synchronous generators (SGs) to promote decrease in an energy function after a disturbance. The abovementioned control action can be achieved by using wide area information obtained by a wide area measurement system (WAMS). Numerical simulations are carried out for a modified IEEE RTS-24 system with 23 generators. The numerical examples show the effectiveness of the proposed method for improvement of the first swing stability by comparing the proposed excitation system with a conventional automatic voltage regulator under three-line-to-ground faults. Impact of the communication latency in the WAMS-based method on the stabilizing effect is also investigated by setting various length of the latency in the numerical simulation.

With the wide application of synchronized phase measurement unit in power system, the wide-area measurement (WAM) system has enabled the use of a combination of measured information from remote location for improving transient stability. The paper focuses on a two-level hierarchical decentralized coordinated excitation control consists of multiple decentralized local fuzzy power system stabilizers (LFPSS) for each generator at the first level helped by a WAM based supervisory power system stabilizer (SPSS) at the secondary level for wide-area power system transient stability enhancement. In order to eliminate the inherent nonlinearities in the power system model and enable the model to be applicable to power system control, first, a direct feedback linearization compensator acting through the local excitation machine is proposed. Then, the T-S fuzzy model is employed to approximate the system model. Based on the T-S fuzzy model, the LFPSS is designed. And the SPSS is proposed to apply the remote signals from the WAM systems. For taking consideration of the time delays introduced by remote information’s transmission in WAM systems and overcoming their impacts on control performance, the authors develop a delay-independent H∞ robust control technique. Some new robust stability criteria in terms of LMI are derived by Lyapunov stability theory incorporating LMI techniques. Simulation examples demonstrate that the decentralized coordinated robust control has better transient stability performance in the face of transmission time delays, severe variations of operating point and faults in various locations.