The interconnected electrical power grids are operated by multilevel control centers with hierarchical architecture. Since large-scale renewables are integrated in different voltage levels, the traditional isolated operation of interconnected power grids is uneconomical and meets operational risk due to lack of coordination. Therefore, the coordination between control centers in different levels and areas are indispensable. However, existing distributed approaches may either encounter numerical problems or converge slowly when the nonlinear AC optimal power flow (ACOPF) models are applied. Moreover, the total iteration number presents an exponential increase with the levels of hierarchical grids. In order to improve computational efficiency, this paper proposes a nested decomposition method for the coordinated operation of multilevel ACOPF problem, which has superlinear convergence and can achieve the optimal solution (KKT point). During each iteration, a projection function, which embodies the optimal objective value of a lower level power grid projected onto its boundary variable space, is computed with second-order exactness. Thus, the proposed method can be applied to nonlinear continuous optimizations with high efficiency. The paper also provides a rigorous proof for its convergence under the condition that the lower level optimization problems are convex with continuously differentiable objectives and constraints. Numerical tests are conducted with three trilevel power grid of different scales, which verify that the computational efficiency and scalability of the proposed algorithm are superior to those of existing methods.

Considering that more and more large-scale renewable energy is connected to the bulk power system, the fluctuation and uncertainty of its output make it difficult to make day-ahead dispatching plan. On the basis of historical data of wind power output, this paper proposed a day-ahead scheduling strategy for bulk power system based on accurate prediction of wind power output. Firstly, an improved Long-Short Term Memory (LSTM) neural network prediction model is proposed to predict the wind power output accurately, then a day-ahead scheduling model is established. Finally, the proposed mothed is tested on modified IEEE-30 system to verify the effectiveness.

Virtual Power Plant (VPP) aggregates and coordinates community-owned renewable distributed generations (DGs) and flexibility resources for participating in power system operation. In this paper, the coordinated operation problem of VPPs and the distribution system operator (DSO) is formulated as minimizing the total operational cost constrained by linearized three-phase power flow equations and operational constraints. To preserve the VPPs’ privacy, the DSO needs to coordinate the VPPs in a distributed manner. However, conventional synchronous distributed methods may suffer from communication delays or failures because of the flimsy communication conditions between DSO and VPPs. We propose an asynchronous distributed algorithm that is robust against communication uncertainties. Firstly, a hybrid alternative direction method of multipliers (ADMM) algorithm is developed, which can be applied to convex problems with promising convergence performance. In the hybrid ADMM framework, the delayed or missing data that transmitted from VPPs are compensated by a novel predicting algorithm combining the multi-parameter quadratic programming (MPQP) and autoregressive integrated moving average model (ARIMA). We prove that the proposed algorithm can converge under imperfect communication condition with some mild assumptions. Numerical tests on IEEE 33-bus and IEEE 123-bus systems indicate that the proposed method has more reliable and faster convergence performance than existing asynchronous methods in all cases.

With the increasing penetration rate of new energy in power grid, the uncertainty of new energy has a certain impact on power grid dispatching operation. Therefore, some new requirements are put forward for scheduling operation control technology. In order to directly express the real-time accommodation capacity of new energy in the power grid, and guide the maximized accommodation of new energy and the stable operation of the power grid, the main factors affecting the accommodation of new energy are analyzed in this paper firstly. On this basis, an optimization model of new energy real-time accommodation capacity considering the security constraints of network and sources is established. At the same time, an assessment method of new energy real-time accommodation capacity considering the uncertainty of new energy is proposed as well. The results of example show that the proposed method can reduce the influence of new energy uncertainty effectively and evaluate the maximum real-time accommodation capacity of new energy reasonably on the premise of ensuring the safe operation of power grid.

In recent years, repeated voltage fluctuations frequently occur in the actual operation of large-scale wind power integration system, which has the characteristics of large voltage fluctuation range and second fluctuation period. This kind of abnormal voltage fluctuation is significantly different from the voltage fluctuation caused by the randomness of wind energy. Owing to the voltage fluctuations, the wind turbines can be disconnected from the grid by continuous low voltage ride through (LVRT) failures, which seriously threatens the safe and stable operation of the power grid. Such a kind of operating accident involves the coupling between wind turbine fault ride through strategy and the characteristics of weak power grids, which is difficult to be explained directly by traditional power system voltage stability analysis methods. In this paper, an analysis method for integration system active power and voltage curve, i.e. PV curve, is proposed to accurately describe the system operating point moving trajectory during the repeated voltage fluctuation, considering the LVRT characteristics of wind turbines. Furthermore, the optimized control strategy for wind turbine LVRT is proposed to suppress the repeated voltage fluctuation. The simulation analysis based on the actual power system data shows that increasing the wind turbine LVRT exiting threshold and adopting the strategy of maintaining active power during LVRT can effectively suppress the repeated voltage fluctuation.

模块化多电平换流器（MMC）可独立解耦调节有功、无功功率，使得柔性直流换流站具有在交流系统电压跌落工况下提供无功支撑的潜能.提出了MMC 柔性直流换流站无功级联的控制策略，即将定交流电压控制和定无功控制级联，其中定交流电压控制包括桥臂电流辅助控制环节，并在故障清除后瞬间进行积分环节清零重置控制.以中国张北±500 kV 四端柔性直流电网工程为例进行了仿真验证，结果表明相对于传统的定无功或定交流电压控制方式，柔性直流换流站无功级联控制方式可以兼顾电网稳态无功调节和暂态无功支撑等需求，快速平稳地输出无功功率，能在保证MMC 设备安全的前提下提供暂态无功支撑，并缓解故障清除瞬间可能发生的暂态交流过电压.

With the rapid development of economy, more and more nonlinear loads are connected to the national power grid system, and the nonlinear load will bring a large number of harmonics to the complex power grid structure, thus affecting the power quality. To solve this problem, it is proposed to add active filter equipment (APF) on the power grid side to eliminate harmonics, design the mathematical model of three-phase parallel voltage source active filter, and build a simulated power grid system containing power grid side APF and a variety of nonlinear loads using MATLAB to verify the effect of adding power grid side APF on eliminating harmonics. The test results show that after the active filter is connected, the current distortion of each phase has been greatly reduced to a degree that cannot be easily detected by the naked eye, and the current distortion rate has been reduced from 22.47% to 0.01%, which is significantly improved compared with that when the active filter is not put into operation.

With the rapid increase of distributed generation resources, transmission grids and distribution grids have become more closely coupled, especially in respect of voltage problems. This paper presents a coordinated reactive power optimization (RPO) method for integrated transmission networks and distribution grids in distributed manner, which is based on a distribution-objective-projection framework. The power flow model in polar coordinates is adopted in both the transmission and distribution networks. The quadratic convex (QC) relaxation technique is used to make the distribution network model convex, which can guarantee the convergence of the proposed decentralized algorithm. The numerical tests on the actual Jibei system are conducted to validate the advance of the proposed method.

with a variety of new energy access to the power grid, its frequency control is facing many new challenges, and the demand response resources play an increasingly important role in FM (frequency modulation). In this paper, the intermittent characteristics of demand response resource is described, which is determined by the user's comfort and the physical characteristics of the demand response resources themselves. For example, air conditionings are disconnected for a period of time to maintain constant room temperature. Electric vehicle need to charge themselves after participating in the frequency response. The intermittent characteristics will reduce the performance of frequency control without coordination. Thus the coordination strategy will be designed for diffident demand response resources based on switch control method. And the simulation results show the effectiveness of the coordination strategy.

VSC-HVDC transmission technology is an effective technology to realize large-scale renewable energy transmission under the condition of weak power grid. For large-scale renewable energy cluster with the VSC-HVDC transmission system as the only transmission path, active power control system is essential to guarantee the operating status of sending terminal converter station within its feasible PQ range. Aiming at the rigid constraint of sending terminal converter station, a radical active power control strategy and a conservative one are proposed in this paper, based on the understanding of the over load risk and operation demand. Ultra-short term power prediction is introduced as a classification index in order to improve the accuracy of generation right dynamic redistribution. On this basis, a method to determine the active power control margin of large-scale renewable energy cluster based on sequential production simulation is proposed. The simulation analysis is carried out based on the example of Zhangbei VSC-HVDC power grid and its renewable energy collection. Results show that the radical active power control strategy needs to reserve more control margin, but the generation space is more fully utilized under this strategy, making the utilization hours of renewable energy stations much higher. The research results of this paper may provide an important reference for the active power control and safety margin setting of Zhangbei VSC-HVDC power grid.

In the context of global energy transformation, it is particularly important to tap the potential of flexible loads on the distribution network side to participate in the regulation and operation of the power grid. Effective and reliable load aggregation technology is the basis and prerequisite for flexible loads to participate in the power grid dispatching and control. In order to better understand the current research level of flexible load aggregation technology and make full use of existing research results for further research, this paper summarizes the application of distribution network flexible load aggregation technology in power systems and models various flexible load aggregation. The method and principle are systematically summarized and analyzed, and the future research directions of flexible load aggregation technology are prospected.

The "source-grid-load" interaction involving three major types of entities which are obviously source, gird and load, will have an important impact on the entire power system. In order to evaluate the interaction effect, this paper designs an overall evaluation framework and proposes a comprehensive indicator system respectively related to each participant. The research results can help to guide the positive interaction among source, grid and load, and promote the optimal allocation of power system resources.

Voltage stability is one of the key factors to ensure the stable operation of power systems. The study of Short-Term Voltage Stability (STVS) is necessary when the complexity of the dynamic response of the power system is increased. In order to reduce the probability of short-term voltage instability and the consequences caused by short-term voltage instability, it is necessary to predict the STVS of power systems before the faults have cause serious consequences. In this paper, a STVS prediction method based on pre-fault operation status and anticipate faults is proposed. A Support Vector Machine (SVM) model is constructed and trained based on the samples generated using numerical simulation software. The effectiveness of the proposed method is presented based on an actual power grid model of China. The prediction accuracy of the SVM model can reach over than 96%, so it has the potential to use practically.

With energy shortages and environmental pollution becoming increasingly prominent, the power industry is inevitably facing enormous challenges. Distributed power supplies are reliable, flexible, economical and environmentally friendly, while they are widely distributed in number and have great volatility and randomness. The virtual power plant (VPP) helps to integrate a large amount of distributed energy in the smart grid, providing a proven solution to the above from a new perspective. Based on the virtual power plant with large-scale distributed wind power, this paper studies the optimal configuration model of energy storage system(ESS). According to economy, load shifting and safety norms in the energy storage system, the optimal objective function of the energy storage system is established. The model is solved by particle swarm optimization algorithm, and the feasibility of the proposed model is verified by an example. It is concluded that optimization result is affected by weight factors and to the three roles of energy storage system.

在电力传输过程中,存在输电线路、变压器、母线等电气设备出现损耗从而降低供电效率的情况,目前常用无功补偿的方式来解决此问题.因此无功补偿装置的性能对电力系统安全稳定运行具有十分重要的作用.但是目前对于无功运行管理方面缺乏高效的手段,亟需完整科学的方法进行指导.针对上述问题和需求,本文首先应用大数据技术构建了支撑评价指标计算和分析的数据层,根据发电机组无功运行考核的实际业务需求分析提出了完整的评价指标体系,包括设备可用率、设备折旧率和设备故障率三个二级指标,最后提出了层次分析法与熵权值法相结合的综合评价方法.应用本文提出的指标对并网发电机组的无功运行情况进行考核评价,能够从客观角度反映机组的实际运行情况,为电网运行专业管理人员提供辅助决策.

An emergency control strategy is proposed to solve the problem caused by station fault blocking in DC grid. The aim of this strategy is to make full use of the ability of regulating unbalanced power in DC grid of non-fault converter stations with different control modes. Firstly, the value of unbalanced power in DC grid is determined. Secondly, the adjustable power of nonfault converter stations in voltage control, voltage margin control and power control are calculated respectively. Thirdly, the method of adjusting the reference power of non-fault converter station in power control mode is put forward. Finally, a simulation model based on Zhangbei ±500 kV DC grid demonstration project in China is built in PSCAD/EMTDC for validating the effectiveness of the proposed emergency control strategy. The simulation results show that the proposed control strategy can not only reduce the impact on ac system but also improve the safe and stable operation of DC grid.

The change regulation of power load could be obtained by the analysis and classification of power load characteristics,and the important load extraction could be applied to the optimiza-tion decision of black-start scheme.In order to make the important load recover quickly,the load recovery model during the black-start was presented in this paper.Power load characteristics were classified with the fuzzy clustering in the black-start scheme.A load characteristics classification method was thus presented and the various substation load could be sorted.Finally,an actual black-start scheme was provided,and the analysis results verified the feasibility of the proposed classification method.

主要介绍了冀北电网利用跨区、跨省通道恢复全停主网架黑启动方案相关研究工作的背景、意义,针对冀北电网各区域地理位置相对分散的特点,按照地缘分布情况并结合冀北各地区电网结构现状对区域网架结构进行了研究梳理,利用联络线将黑启动工作分解为唐承秦、张家口、廊坊3个地区的黑启动问题,在研究分析的基础上提出了3个推荐方案.

变电站中自动化设备的运行状态对变电站的正常运行有着至关重要的作用.因此,开发一套变电站自动化设备的远程维护管理系统势在必行.首先提出了一种新型变电站集控模型,介绍了站控层设备的开发、传输规约,并在其基础上实现了自动化设备的远程维护管理.

交直流混合微电网中的接口变换器对于系统的稳定运行和功率的协调分配有着重要的作用。提出了一种接口变换器的双向下垂控制方法,分别采用变换器两侧的交流母线频率和直流母线电压对交流、直流微电网的电能需求程度进行衡量,确定变换器传输功率的大小与方向。控制架构中包括直流电压-有功功率和交流频率-有功功率两个下垂环节,并将二者输出之差作为接口变换器的功率参考值。同时,为了减缓下垂控制导致的电压或频率的跌落,在下垂控制基础上设计了恢复控制策略,以提高交直流混合微电网的电能质量和可靠性。这种双向下垂控制可以更精确地协调交流与直流微电网之间的能量传输,实现分布式能源的充分利用。利用Dig SILENT软件搭建系统仿真模型,验证了控制方法的正确性。