Wenzhong Gao

Energy Efficient Security Algorithm for Power Grid Wide Area Monitoring System

Modern power grid is the most complex human-made system, which is monitored by wide-area monitoring system (WAMS). Providing time-synchronized data of power system operating states, WAMS will play a crucial role in next generation smart grid protection and control. WAMS helps secure efficient energy transmission as well as reliable and optimal grid management. As the key enabler of a smart grid, numerous sensors such as PMU and current sensors transmit real-time dynamic data, which is usually protected by encryption algorithm from malicious attacks, over wide-area-network (WAN) to power system control centers so that monitoring and control of the whole system is possible. Security algorithms for power grid need to consider both performance and energy efficiency through code optimization techniques on encryption and decryption. In this paper, we take power nodes (sites) as platforms to experimentally study ways of energy consumptions in different security algorithms. First, we measure energy consumptions of various security algorithms on CrossBow and Ember sensor nodes. Second, we propose an array of novel code optimization methods to increase energy consumption efficiency of different security algorithms. Finally, based on careful analysis of measurement results, we propose a set of principles on using security algorithms in WAMS nodes, such as cryptography selections, parameter configuration, and the like. Such principles can be used widely in other computing systems with energy constraints.

Comparison and review of islanding detection techniques for distributed energy resources

The many different islanding detection methods for anti-islanding protection in power system are discussed. Passive, active and remote techniques are reviewed. Most of the ldquoactive methodsrdquo discussed are developed for photovoltaic (PV) as a distributed energy resource. Some recent methods can be use for any type of distributed generation. A final comparison of active islanding detection methods is presented later in this paper.

Optimal PMU Placement Considering Controlled Islanding of Power System

This paper proposes an optimal phasor measurement unit (PMU) placement model considering power system controlled islanding so that the power network remains observable under controlled islanding condition as well as normal operation condition. The optimization objectives of proposed model are to minimize the number of installed PMUs and to maximize the measurement redundancy. These two objectives are combined together with a weighting variable so that the optimal solution with minimum PMU number and maximum measurement redundancy would be obtained from the model. To reduce the number of required PMUs, the effect of zero-injection bus is considered and incorporated into the model. Furthermore, additional constraints for maintaining observability following single PMU failure or line loss are also derived. At last, several IEEE standard systems and the Polish 2383-bus system are employed to test the presented model. Results are presented to demonstrate the effectiveness of the proposed method.

Fault Detection, Identification, and Location in Smart Grid Based on Data-Driven Computational Methods

A fault detection, identification, and location approach is proposed and studied in this paper. This approach is based on matching pursuit decomposition (MPD) using Gaussian atom dictionary, hidden Markov model (HMM) of real-time frequency and voltage variation features, and fault contour maps generated by machine learning algorithms in smart grid (SG) systems. Specifically, the time-frequency features are extracted by MPD from the frequency and voltage signals, which are sampled by the frequency disturbance recorders in SG. A hybrid clustering algorithm is then developed and used to cluster the frequency and voltage signal features into various symbols. Using the symbols, two detection HMMs are trained for fault detection to distinguish between normal and abnormal SG operation conditions. Also, several identification HMMs are trained under different system fault scenarios, and if a fault occurs, the trained identification HMMs are used to identify different fault types. In the meantime, if the fault is detected by the detection HMMs, a fault contour map will be generated using the feature extracted by the MPD from the voltage signals and topology information of SG. The numerical results demonstrate the feasibility, effectiveness, and accuracy of the proposed approach for the diagnosis of various types of faults with different measurement signal-to-noise ratios in SG systems.

Mitigation of disturbances in DFIG-based wind farm connected to weak distribution system using STATCOM

DFIG (Doubly Fed Induction Generator) based wind farm is gaining popularity these days because of its inherent advantages like variable speed operation and independent controllability of active and reactive power over conventional Induction Generators. When interconnected into power grid, it brings voltage stability problems during grid-side disturbances. So integration of DFIG-based wind farm to power grid, especially to weak distribution system is major concern for power system engineers today with the recent grid code requirements. This paper examines the use of Static Synchronous Compensator (STATCOM) as a dynamic reactive power compensator at the point of common coupling to maintain stable voltage by protecting DFIG-based wind farm interconnected to weak distribution system from going offline during and after the disturbances. The developed system is simulated in MATLAB/Simulink and the results show that STATCOM mitigates the effects of transient disturbances viz., three phase fault, step load change, voltage swelling and sagging in the system and hence improves the stability and performance of wind farm.

Feedback Dynamic Algorithms for Preemptable Job Scheduling in Cloud Systems

An infrastructure-as-a-service cloud system provides computational capacities to remote users. Parallel processing in the cloud system can shorten the execution of jobs. Parallel processing requires a mechanism to scheduling the executions order as well as resource allocation. Furthermore, a preemptable scheduling mechanism can improve the utilization of resources in clouds. In this paper, we present a preemptable job scheduling mechanism in cloud system. We propose two feedback dynamic scheduling algorithms for this scheduling mechanism. We compare these two scheduling algorithms in simulations. The results show that the feedback procedure in our algorithms works well in the situation where resource contentions are fierce.An infrastructure-as-a-service cloud system provides computational capacities to remote users. Parallel processing in the cloud system can shorten the execution of jobs. Parallel processing requires a mechanism to scheduling the executions order as well as resource allocation. Furthermore, a preemptable scheduling mechanism can improve the utilization of resources in clouds. In this paper, we present a preemptable job scheduling mechanism in cloud system. We propose two feedback dynamic scheduling algorithms for this scheduling mechanism. We compare these two scheduling algorithms in simulations. The results show that the feedback procedure in our algorithms works well in the situation where resource contentions are fierce.

A Model for Assessing the Power Variation of a Wind Farm Considering the Outages of Wind Turbines

Most of the published models cannot properly incorporate the outages of wind turbines in estimating the stochastic variation of the wind power output. In reality, wind turbines are exposed to an open and uncontrolled environment, sometimes harsh, to harvest energy from wind. The environmental condition of wind turbines is thus worse than that of the conventional generators. This results in a relatively higher outage probability of the wind turbines, which significantly affects the power output from a wind farm. This paper proposes a model for including the outage probability of wind turbines in simulating the power output of wind farms. The contribution of this paper is in introducing a model to represent the relationship between the outage probabilities of wind turbines and wind speed and then integrating this model with a frequency-domain wind power output model. A numerical simulation approach based on the Monte Carlo method is then proposed to simulate the wind power variation including the outage probability of wind turbines. A validation study based on the field-measured data from a real wind farm shows that the simulated wind power variation matches well with the actual field measurements when the probability-based outage model is included in the calculations.

Wavelet-Based Disturbance Analysis for Power System Wide-Area Monitoring

This paper proposes a wavelet-based method to obtain the characteristics of frequency and voltage derivatives for disturbance analysis. Frequency and voltage derivatives are important indicators to reflect the degree of disturbances and manifest power system dynamics. However, current computational methods for the indicators have noticeable drawbacks with respect to the accuracy. Wavelet transform-based multiresolution analysis (WT-based MRA) is introduced to obtain the characteristics of the indicators by computed maximum wavelet coefficients (WCs). Results from numerical experiments show a superior performance of WT-based MRA over the existing methods. Generation loss and load change as two major types of disturbances are studied to verify the proposed method. The disturbances are simulated in PSS/E for IEEE New England 39-bus system. The relationship of maximum WCs and power variation is discussed. Maximum WCs can provide enough information to distinguish the location of generation loss and estimate the load power variation.

Adaptive Time Delay Compensator (ATDC) Design for Wide-Area Power System Stabilizer

Wide-area power system stabilizer (WPSS) is one of the most potentially effective approaches to damp interarea low frequency oscillations in power systems. When WPSS is implemented in a real project, emphasis should be put on feedback signal delay problem. In order to intensively study the delay of phasor measurement unit data, field tests have been carried out in Guizhou power grid (GZPG), and results show that, in the long-term, the delay might change remarkably under some circumstances, such as when route switches or communication load increases. Therefore, this paper proposes an adaptive time delay compensation method to deal with such kind of delay. Bounded random delay is divided into several intervals and compensators are designed for each delay interval. Then appropriate compensators will be selected according to the delay measured online, based on the switching rules that is also demonstrated in this paper. The delay used here is the average delay before the compensator switching. The proposed compensator is demonstrated in a two area power system. Numerical simulation results show the effectiveness and feasibility of the proposed adaptive compensator. A comparison with conventional methods is also presented. Finally, the proposed method is validated on GZPG based on real-time digital simulations.

Development of low voltage ride-through control strategy for wind power generation using real time digital simulator

With real time digital simulator (RTDS), new control strategy for low voltage ride through (LVRT) is developed for a doubly fed wind power induction generator (DFIG). Specifically, adaptive control method is proposed to limit high peak rotor current. Furthermore, current limiters are connected in three-phase rotor circuits, which are strategically controlled by thyristor switches to counter the effect of fault on DFIG operation. Simulation model is constructed in RTDS/RSCAD. Simulation results under various disturbances demonstrate the effectiveness of the new LVRT control strategies.