Framework of Smart Regulation System for Large-Scale Power Grid Based on Big Data and Artificial Intelligence

In power system operation, there are usually a few vulnerable lines (VLs) which are prone to exacerbate the propagation of cascading failures and lead to severe blackouts with high probability. To facilitate preventing the power grid from cascading blackouts, in this paper, a PageRank-based fast screening method is derived to identify VLs. To this end, we extend the concept of interaction graph to model cascading outages as a directed weighted graph, where impacts of hidden failures are first taken into account. Based on the graph, we modify the celebrated PageRank algorithm to derive an ultra-fast VLs screening algorithm for large-scale power grids. Simulations carried out on the IEEE 118-bus system show that the proposed method can achieve high-accuracy VLs screening while the speed can be enhanced for several orders of magnitude compared with cascading failure simulation methods. Tests on a 1122-bus real power grid in China demonstrate that it can discriminate the most VLs in a practical power grid within only several minutes, showing its great potential for on-line application.

This paper is the second part of a two-part paper on communication-failure-resilient architecture for distributed operation and control in smart grids with hybrid producer/consumer (prosumer) agents. Part I of this paper proposed the distributed architecture and algorithmic development, while this Part II provides the corresponding algorithmic implementation and simulations. We propose a general and scalable framework for implementing resilient distributed frequency regulation (DFR) on large-scale prosumer-based power grids, such as utilities, where each prosumer represents a frequency control area. We first develop a method to obtain quasi-steady state models of prosumers from the dynamic models of generators, loads, and power lines. This model allows demonstrating the dynamic evolution of prosumers under normal conditions and during communication failures. Next, we propose a framework to implement the resilient DFR algorithm on prosumer power grids. We show that under normal conditions prosumers need to solely communicate with their neighbors to obtain optimal control actions. But, during communication failures, prosumers need to extend the communication hops to maintain system-wide stability as well as fair power sharing. The resilient DFR algorithm is demonstrated on two real-world, large-scale power grids and the results show that it can indeed complement and enhance today's Automatic Generation Control systems.

With the UHV (Ultra High Voltage) power grid construction and the interconnection of regional power grids, the scale of power grids in China is increasing rapidly. At the same time, significant uncertainty and variability is being introduced into power grid operation with the integration of large-scale renewable energy in power systems. All of these pose an enormous challenge to the operation control of power systems in China. For a long time, online static security analysis, as an important part of EMS (Energy Management System), has been an effective tool for power grid operation. However, it is increasingly difficult for traditional static security analysis in serial computing mode to be online applied in bulk power grids in China. A new practical parallel approach for online static security analysis is put forward in this paper. A multithread parallelism is introduced into contingency screening, detailed contingency evaluation and decision support for reducing the execution time. By employing the multithread technology, the hardware resources of multi-processor/multi-core computer can be fully used and the program can be speeded up effectively. The performance of the parallel static security analysis is demonstrated by tests on two large-scale power systems. The test results show that the proposed method can be online applied in real bulk power grids.

Summary Low-frequency oscillations (LFOs) are inherent phenomena of modern interconnected electrical power systems, essentially caused by the continuous exchange of momentum among rotating masses. It is widely recognized that LFOs can be induced by both the occurrence of multiple disturbances and the existence of periodic disturbance sources. LFOs can be classified into negative damped oscillations and forced power oscillations. The former can be suppressed by standard controllers (e.g., power system stabilizers). The latter cannot be eliminated until the disturbance source is removed or isolated. Thus, locating the forced disturbance source promptly and accurately is crucial. In this paper, a traditional energy function, simplified and improved, with a new decomposition way to show the direction of energy flow is proposed. Energy associated with the LFO is decomposed into oscillating component and quasi-steady component at the aim of analyzing the inducing multiple disturbances. The branch energy is hence decomposed into periodic and aperiodic components. By identifying the direction along which the aperiodic component is propagated and dissipated, the periodic forced disturbance source could be located rapidly and accurately. The proposed energy decomposition method provides a novel idea to judge the direction along which the dissipated energy flows. The effectiveness and feasibility of the proposed method were verified by simulation results obtained on an actual large-scale interconnected power grid in China. Copyright © 2015 John Wiley & Sons, Ltd.

With the construction of northern and western wind power base, large-scale regional wind power grid connection begins to affect power system and several power grid accidents in Fuxin grid resulted in partial off-grid in recent years, causing certain damages on the security and stability of power system.The author takes Fuxin power grid as example to analyze on two problems existing in large-scale wind power centralized grid connection: frequent fluctuations and reactive voltage control, study on the effect of large-scale wind power centralized grid connection on the security and stability of power system and proposes countermeasures and suggestions. Basic Situation of Fuxin Wind Power BaseFuxin wind farm are mainly based in the northwest area of Fuxin and eastern Zhangwu.By the end of 2014, there has been a wind power capacity of 1,693,300 kilowatts in operation, among which there are 6 220 kV substation, 5 66 kV substation that delivers power to load centers like Jinzhou and Shenyang by 220 kV tie line.According to Fuxin City Plan, there will be an installed capacity of 16,167,000 kilowatts by 2015, among which 8.117 million kW are thermal power (increasing 6.3 million kilowatts) and 8.05 million kilowatts are new energy (increasing 6.25 million kilowatts); power generation will be as much as 58.1 billion kwh.

Based on an analysis of the misunderstanding and problems concerning wind power development, this paper summarizes the experiences of coordinated development of wind power and power grids in typical countries, proposes the principles and strategies for the coordinated development of wind power and power grids in China. Technically, bidirectional friendly technologies should be deployed to ensure the security of power system. In regulatory term, a complete and standardized regulatory strategy is key to harmonious interaction among different stakeholders concerning wind development. Incentive policies should be comprehensive, foreseeable and sustainable. Related measures and suggestions for large scale development of wind power in China are put forward.

In view of the need for stability analysis of large- scale new energy cluster connecting to large-scale power grid system, the existing electromagnetic transient simulation tools have certain limitations. At present, there is a lack of simulation platform that can uniformly establish large-scale new energy and large-scale power grid models. Based on two different simulation tools, RTLAB and CloudPSS, a large-scale new energy cluster and large-scale power grid electromagnetic transient co- simulation platform is built. A new energy station equivalence method based on single machine representation method is proposed, and the accuracy of the equivalence method is verified by comparing with detailed station model, which provides a basis for the modeling of large-scale new energy clusters. On the other hand, the electromechanical - electromagnetic model conversion tool based on CloudPSS is introduced, which provides a method for large-scale power grid modeling. At last, the decoupling principle and hardware implementation scheme of co-simulation model based on RTLAB and cloudPSS are presented and the comparison of simulation results verifies the accuracy of the simulation platform.

With integration of the large wind energy bases into power grid, wind energy has gradually become an important form of power supply. In order to ensure the stable operation and safe of the power grid after the large wind energy bases are connected, the operation control technology of the power grid after the large wind enengy bases are connected will become more and more important. Therefore, it is necessary to study the operating characteristics and control strategies of large wind energy bases based on the specific problems of power grids and the large-scale centralized connect to wind power grids, combined with the large wind energy bases already constructed and planned in the Northwest and North China power grids. The technical conditions for wind farms grid-connected operation study, the impact of large wind energy bases in North and Northwest China Power Networks on the system operation and stability modes, and the control measures would be include. Technical measures for optimal allocation of reserve capacity, auxiliary decision, power balancing and frequency regulation, suppression of low-frequency oscillation and reactive voltage control for large-scale wind power grid connected power systems would be studied.

With the large scale grid integration of renewable energy sources(RES) such as photovoltaic(PV) and wind power stations, new energy has become one of the main power sources, which has brought a series of challenges to the security, reliability and operation scheduling of the power grid system. There is an urgent need that these RES, especially the PV power generation system with IGBT-based inverters, supports the rapid power control, based on which the power grid system stability control system(PSCS) can realize "two-way regulating instead of one-way tripping/switching off ". A new scheme of system stability control based on photovoltaic rapid power control technology, and a station rapid power control device was also designed, supported by fast communication and rapid power execution of inverters. The scheme has been applied and tested in power grid of China. The test and operation results verify the effectiveness and advancement of the technology.

This study presents the analysis of debates on the future super grid in China. The rapid increase of power demands and the uneven distribution of energy bases and load demands in China require bulk‐capacity long‐distance power transmission. Two candidate solutions are thus proposed, that is, the ultra‐high‐voltage ac (UHVAC) synchronous power grid and the extra high‐voltage ac (EHVAC) asynchronous super power grid. The debates on the above two power grids are first reviewed. The two candidate power grids are then compared in detail in terms of security, economic and environmental aspects. Finally, this study provides a suggestion for the construction of UHV synchronous power grid in China as well as the future research direction. The research, discussion and conclusion related to UHVAC and EHVAC transmissions in China are expected to provide useful references for power system planning in other countries and to promote the development of the global power industry.

With the rapid development of the Chinese power grid, its dynamic behavior becomes increasingly complex. How to prevent voltage instability and voltage collapse at the receiving-end system has become an urgent problem at present. To prevent voltage collapse, the key is to determine the stability margin at the operating point of the power system, and the load margin is the most basic and widely accepted voltage stability margin indicator. Considering the role of medium and long-term slow-acting elements in the actual system that affect the system voltage stability, this paper combines the static voltage stability analysis with the transient, medium, and long-term dynamic voltage stability analysis based on whole process simulation, and uses time-domain simulation methods to evaluate the voltage stability of the actual system. By analyzing the various dynamic characteristics of generator overexcitation limits and transformer on-load regulation on the development process of voltage-collapsing accidents, this paper proposes an evaluation index for the whole process dynamic stability margin of the receiving-end system. On this basis, the whole process dynamic defense system of the power grid is also constructed. The proposed method is validated by using a provincial power grid in China as an example.

Studying the propagation of cascading failures through the transmission network is key to asses and mitigate the risk faced the energy system. As complex systems the power grid failure is often studied using some probability distributions. We apply 4 well-known probabilistic models, Poisson model, Power Law model, Generalized Poisson Branching process model and Borel-Tanner Branching process model, to a 14-year utility historical outage data from a regional power grid in China, computing probabilities of cascading line outages. For this data, the empirical distribution of the total number of line outages is well approximated by the initial line outages propagating according to a Borel-Tanner branching process. Also for this data, Power law model overestimates, while Generalized Possion branching process and Possion model underestimate, the probability of larger outages. Especially, the probability distribution generated by the Poisson model deviates heavily from the observed data, underestimating the probability of large events (total no. of outages over 5) by roughly a factor of 10-2 to 10-5. The observation is confirmed by a statistical test of model fitness. The results of this work indicate that further testing of Borel-Tanner branching process models of cascading failure is appropriate, and should be further discussed as it outperforms other more traditional models.

Wind damage is one of the common disaster that has serious influence on China’s power grid. The wind damage has a wide distribution and a low success rate of reclose, which makes the transmission line outage more likely. In this study, it is found that the 2016 wind damage of power grid in China’s major areas mainly distributed in the southeastern coast, southwest region, north China and its surrounding areas. In temporal distributions, wind damage mainly occurs in summer and afternoon. In 2016, the first reclose success rate of wind damage trip is only about 10% during 330 kV and above voltage level transmission lines. 220 kV is a voltage level threshold of trip line: tripps number increases with voltage level decreases when above the threshold, otherwise trips number decreases with voltage level decreases. Transmission line wind damage trip trend has a large interannual variation from 2010 to 2016. This study analyzes the characteristics of wind damage trips in 2016, which provides guidance for wind damage prevention work in windbreak-prone areas and windbreak-prone periods.

Performance and reliability of electrical power grids under cascading failures

Chinese energy resources and load are in reverse distribution, and it is necessary to vigorously develop UHV AC and DC technologies suitable for long-distance and large-power transmission. The pattern of UHV AC-DC hybrid power grid has been initially formed at present. However, the faults of UHV DC with large transmission power and complex fault forms have great impact on the power grid in both active and reactive power. In this paper, based on the analysis of the current situation and characteristics of UHV AC/DC power grids in China, the impact of UHV DC restart and commutation failure on the stability of the power grid is analyzed. The different types and triggering factors of DC commutation failures are analyzed, and the effects of single or multiple DC commutation failure types on the transient angle stability, the voltage stability and the transient overvoltage are simulated. The UHV DC restart fault time sequence is studied, and the effects of different restart modes on the system transient angle stability and transient overvoltage are demonstrated through simulation. The research results have laid the foundation for grasping the UHV DC fault morphology mechanism and the influence law on the stability of the power grid, and provided support for the safe and stable verification of the UHV AC/DC power grid.