Initial allocation of carbon emission permits in power 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.

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.

Due to the maturity of wide area measurement technology, phasor measurement unit (PMU)-based dynamic equivalent modeling method (PDM) has been wildly used in large-scale power system modeling. However, traditional “event-based” PDM equivalent model may face serious robustness issues, such as although derived equivalent models show the good ability on reproduction of the system behaviors under recorded events where they derived from, they may not work well for other possible disturbances. In this article, to improve the robustness of equivalent model, a novel method on dynamic equivalent modeling of power system is proposed. Based on the result of coherency identification, generators inside the equivalent system can be aggregated into different coherent subgroups and represented by multimachine equivalent model. Key parameter selection, which can shrink the scale of identified parameters, is designed to avoid multiple solutions of the equivalent model. Moreover, a multiobjective parameter identification algorithm is developed to fully consider the PMU measurements in different system events. In addition, hybrid dynamic simulation is performed so that each equivalent submodel can be identified separately. Finally, the effectiveness of the proposed method is verified in an actual power grids in China.

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.

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.

After asynchronous operation, the Southwest Power Grid in China has the risk of ultra-low frequency oscillation, which seriously threatens the stable operation of the power grid. Based on the hydropower single-unit with load system, the extend Philips-Heffron model is built considering PSS/GPSS (Governor Power System Stabilizer). Then, the damping torque analysis is carried out in both prime mover and excitation side. The negative damping in the prime mover side is prominent in the ultra-low frequency band and the effect of damping ratio increase by PSS and GPSS is compared. After that, the small signal analysis of the whole system is conducted, the participation factors of the ULFO mode shows the high participation and controllability by GPSS control. At last, the proper GPSS parameters configured by small signal analysis are equipped in the hydro unit of asynchronous four-machine two-area system which reveals an obvious ULFO suppression effect. Furthermore, the practical ULFO identification algorithm based on feature points extraction and analysis which crossing the PFC (Primary Frequency Control) dead zone (49.95–50.05 Hz) is proposed, the GPSS control cubicle which embedded the practical ULFO identification algorithm is developed and the semi-physical simulation is conducted to verify the real ULFO suppression effect by GPSS control.

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.

In the analysis of cascading outages and blackouts in power systems, risky cascading fault chains should be accurately identified in order to do further block or alleviate blackouts. However, the huge computational burden makes online analysis difficult. In this paper, an online search method for representative risky fault chains based on reinforcement learning and knowledge transfer is proposed. This method aims at promoting efficiency by exploiting similarities of adjacent power flow snapshots in operations. After the “representative risky fault chain” is defined, a framework of tree search based on Markov Decision Process and Q-learning is constructed. The knowledge in past runs is accumulated offline and then applied online, with a mechanism of knowledge transition and extension. The proposed learning based approach is verified on an illustrative 39-bus system with different loading levels, and simulations are carried out on a real-world 1000-bus power grid in China to show the effectiveness and efficiency of the proposed approach.

Electric vehicles (EVs) as distributed storage devices have the potential to provide frequency regulation services due to the fast adjustment of charging/discharging power. In our previous research, decentralized vehicle-to-grid (V2G) control methods for EVs were proposed to participate in primary frequency control. In this paper, our attention is on bringing a large number of EVs into the centralized supplementary frequency regulation (SFR) of interconnected power systems. An aggregator is the coordinator between EVs and the power system control center. The aggregator calculates the total frequency regulation capacity (FRC) and expected V2G (EV2G) power of EVs based on the data communicated between the aggregator and individual EVs or EV charging stations. With FRC and EV2G power, a V2G control strategy is proposed for the aggregator to dispatch regulation requirements to EVs and EV charging stations. In individual EV charging stations, the FRC is calculated on the basis of the V2G power at present time, and EV2G power is presented considering both frequency regulation and charging demands. Besides, V2G control strategies are developed to distribute regulation requirements to each EV. Simulations on an interconnected power grid based on a practical power grid in China have demonstrated the effectiveness of the proposed strategies.

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.

Optimizing peak shaving operation in hydro-dominated hybrid power systems with limited distributional information on renewable energy uncertainty

The escalating frequency and intensity of wildfires, driven by extreme climate events and anthropogenic activities, pose severe threats to the security and reliability of electrical power systems. Wildfires in proximity to high-voltage transmission lines can lead to a critical reduction in air insulation strength, caused by elevated temperatures, smoke particulate matter, and highly conductive flames. These conditions often precipitate insulation breakdown, line tripping, and potentially widespread power outages. This paper proposes an integrated physical-Bayesian modeling framework for assessing the susceptibility of transmission lines to wildfire-induced tripping. The framework combines a Bayesian network model, which estimates wildfire ignition probability by incorporating geographic, meteorological, fuel, and anthropogenic variables, with a physics-based model that evaluates the risk of insulation failure under wildfire conditions, accounting for both flame bridging and smoke effects. Key influencing features are identified through the Relief algorithm for feature selection. Applied to the Guangdong Power Grid in China, the model identifies distance to settlements, vegetation type, and monthly rainfall as the dominant factors affecting ignition probability. Spatial analysis reveals strong agreement between high-risk zones and historical fire events, and predicted tripping risks are consistent with actual outage records. The approach supports differentiated wildfire prevention strategies and enhances grid resilience, offering a scientifically robust and practical tool for proactive risk management in power systems exposed to wildfire hazards.

This paper presents an efficient security assessment system for validating power system operation planning, which has been used in Henan provincial power grid in China. Daily operation planning is to schedule unit commitment and to dispatch generator output economically considering next day generators and transmission components' maintenance planning. The security assessment for validating the daily operation planning includes static security assessment and dynamic security assessment which are done for all the 96 power flow snapshots for next day. It is obviously a big challenge in reducing exhausting calculation burden. To speed up the calculation, a flexible and distributed parallel computing platform is designed which is based on a PC cluster and Multi-Agent system. The framework of the security assessment system for daily operation planning validation is introduced. And the technologies to implement the high performance computing are given. Some calculations for daily operation planning validation for control centre of Henan power grid are done and the results show that the parallel computing platform is efficient in computation.

Large geoelectric field generated in the ground during severe space weather events are sources of geomagnetically induced currents (GICs), which flow in power systems potentially causing damage to system component or failure of the system. In this paper, based on the H and D components of the recent geomagnetic storm data measured at 10 mid-to-low latitude geomagnetic observatories, we analyzed the variation characteristics of the amplitude of north-south and east-west geoelectric components with geographic latitudes. Furthermore, we discussed the possibilities of GIC problem occurrence in transmission lines in different directions at different latitude in China. The result shows that transmission lines in east-west direction at higher latitude are more susceptible to space weather hazard. And it will contribute to the assessment of geomagnetic hazard to power systems and the control of GIC in the current and future power grids in China.