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      • XIAO Jinyu, HOU Jinming, DU Ershun, JIN Chen, ZHOU Yuanbing, KANG Chongqing

        Available online:August 03, 2020  DOI: 10.7500/AEPS20200407004

        Abstract:At present, the research on energy storage demand mostly focuses on the configuration of energy storage devices, such as electrochemical cells with short discharging time in specific application scenarios, and there is a lack of research on the planning method of system-level energy storage demand and the impact on the overall cost. Based on the characteristics of two different types of short-time and long-time energy storage, a quantitative analysis model and method with the optimization goal of the lowest system comprehensive cost are established. The system-level energy storage demand considering three key factors, namely, the capacity, the structure, and the cost is quantitatively analyzed. The energy storage planning is solved jointly with the power supply planning problem through the mixed integer optimization. Taking Europe, the world and China as examples, the energy storage type, installed capacity and acceptable cost of energy storage to support the clean transition of electric power system are analyzed. The results show that the short-time energy storage which is only represented by the lithium battery cannot meet all the system requirements of the scenario of renewable energy with high proportion in the future, and the long-time energy storage will gradually play a significant role in the deep clean transformation after 2035.

      • WEN Shiyang, YU Juan, DAI Wei, YANG Zhifang, YANG Gaofeng, YANG Maocha

        Available online:August 03, 2020  DOI: 10.7500/AEPS20200329003

        Abstract:With loads increasing and renewable source integrating, the operation security region of power grid is decreasing. For this reason, the operation flexibility space of power grid should be fully exploited to expand the security region of power grid operation , so as to achieve the optimal allocation of resources. In this paper, a concept of hydropower capacity flexibility space of reservoir is proposed, and the operation flexibility model for capacity of reservoir considering uncertainty of water inflow and risk cost is established. And on this basis, an economic dispatch model is proposed to evaluate the operation benefit of power grid considering the capacity flexibility of reservoir. In addition, based on Karush-Kuhn-Tucker (KKT) conditions, the sensitivity relationship between capacity flexibility of reservoir and operation state variables of power grid is deduced, and a sensitivity identification method for critical capacity flexibility space of reservoir is proposed to use the critical capacity flexibility space of reservoir preferentially in power grid operation. Finally, the effectiveness of the proposed method is verified on IEEE 30-bus system and an actual power grid of an area. The simulation results dedicate that on the basis of considering the demand of flood risk control of reservoir,the proposed method can effectively utilize the capacity flexibility of reservoir to adjust the reservoir water resources in stock flexibly, and promote the hydropower and wind power consumption, as well as reduce the operation cost of power grid.

      • CHEN Weinan, HU Zhijian, YUE Jingpeng, DU Yixing, QI Qi

        Available online:August 03, 2020  DOI: 10.7500/AEPS20200312005

        Abstract:Short-term load prediction is the basis for safe dispatch and smooth operation of the power grid. To further improve the accuracy of load prediction, a combined prediction model based on long-short-term memory (LSTM) network and light gradient boosting machine (LightGBM) is proposed. Firstly, according to the input structure of the LSTM network and LightGBM model, the pre-processed load data, temperature data, date data and holiday information are input into the two models, the respective prediction results are obtained after training. Then, the optimal weighted combination method is used to determine the weight coefficients, and the prediction value of the combined model is obtained. Finally, taking actual load data as examples for analysis, the results show that the proposed method can effectively combine the advantages of the two models, it takes the effective information of discontinuous features into account while preserving the overall perception of time-series data. Compared with other models, the proposed method has higher prediction accuracy.

      • HE Lezhang, HE Bingyuan, XU Junjie, XIE Yimiao, LI Zihao

        Available online:August 03, 2020  DOI: 10.7500/AEPS20200220007

        Abstract:In recent years, fault indicator is widely used in distribution network fault location because of its access flexibility and economy. However, the full coverage installation configuration scheme of fault indicator has high investment cost, and the planning scheme is not lean. In this paper, a distribution network reliability assessment model based on fault information variables is proposed, and an optimal placement method of distribution network fault indicator based on reliability constraints and mixed-integer linear programming is proposed. The reliability indices are put into the optimization model as a constraint to reduce the investment and maintenance cost of fault indicator under the premise of meeting the reliability requirements. The simulation based on IEEE 53-bus system shows that the proposed method takes into account the reliability and economy of fault indicator placement, and can accurately obtain the placement schemes under different reliability requirements.

      • LIU Fanglei, XU Guoyi, WANG Fan, YAN Jiaming, BI Tianshu

        Available online:August 03, 2020  DOI: 10.7500/AEPS20200219006

        Abstract:With the large-scale integration of renewable energy resources, the characteristics of decreasing and uneven distribution of the system inertia are increasingly obvious. The system frequency response has spatial and temporal distribution feature. An assessment method of system partition inertia based on differential calculation method is proposed. Firstly, the system is divided into several areas according to the similarity of frequency response characteristics and the dominant generator in each area is determined. Based on the partition and selection of dominate generators, a differential calculation method is proposed to assess inertia level of each area using the interconnector power and frequency of the dominant generators after disturbances. The proposed method requires only a few measurement data, which just needs to measure the data from regional interconnectors and dominate generators, and can be implemented to online estimation. The IEEE 10-machine 39-bus system is established in PSASP to verify the correctness of the proposed method in different operation conditions. The impact of the time period selection of disturbed data on inertia assessment is analyzed. The results show that the proposed method has a high accuracy in inertia assessment of power system with the large-scale integration of new energy resources.

      • YANG Shenbo, TAN Zhongfu, LIN Hongyu, DE Gejirifu, ZHOU Feng’ao

        Available online:August 03, 2020  DOI: 10.7500/AEPS20200218009

        Abstract:In order to balance system economic and environmental benefits, it is of great significance to study park integrated energy system (PIES) where clean energy units are employed. Firstly, considering the three main entities including external backup system, park users and PIES, the way for each entity to achieve cooperation alliance is designed. Secondly, a stochastic optimization model for PIES with independent and cooperative operation modes are constructed considering the uncertainty of clean energy. Thirdly, in order to stabilize the tripartite cooperation and reflect the contribution of different entities to the alliance income, an income allocation model based on the improved Shapley value method is constructed. Finally, a simulation analysis is carried out with an certain industrial park in Northern China as the research object to verify the effectiveness of the proposed model.

      • DU Xiaoli, LIANG Kairong, LI Dengfeng

        Available online:August 03, 2020  DOI: 10.7500/AEPS20200212007

        Abstract:As the priority industry embedded in the carbon trading system in China, the power industry has become an important subject to achieve carbon emission reduction. As a new distributed ledger technology, the blockchain technology can effectively solve the problems of data security and operation efficiency in the carbon trading system. Based on the blockchain technology, this paper builds the whole framework of the carbon trading system in the power industry. Based on the framework, this paper builds the carbon quota cost decision-making model, reward and penalty model of carbon emission reduction and carbon trading matching model, to realize safe and efficient carbon trading. The emission reduction effort index is introduced as the process promoter and the link bridge of the above three models. Finally, the effectiveness of the carbon trading system is verified by an example. The simulation design is also given, which shows that the carbon trading system based on blockchain can reduce costs, improve efficiency, and increase benefits.

      • CHEN Xiupeng, LI Gengyin, ZHOU Ming, XIA Yong

        Available online:August 03, 2020  DOI: 10.7500/AEPS20200116012

        Abstract:In view of the characteristics of heat-power coupling and multi-agents in regional energy network, and based on the space and time complementarity of energy production and consumption, a distributed trading market framework with multiple buyers and multiple sellers and a supply and demand interaction based joint heat-power price clearing strategy are proposed. Firstly, the framework and trading mechanism of heat-power interchanging market for the regional energy network are established, which is composed of energy trading platform, multi-energy microgrids and intelligent users. Secondly, the heat-power coupling price response models of multi-energy microgrids and intelligent users aiming to maximize their own interests are analyzed and established. Then, the joint heat-power price clearing strategy aiming at realizing the balance of energy supply and demand in the regional energy network is proposed. This strategy can not only realize the optimal resource allocation on the energy supply side and the rational consumption on the energy demand side, but also protect the privacy of market participants. Finally, the model is simulated on a regional energy network composed of 3 multi-energy microgrids and 6 intelligent users to verify its advantages in improving renewable energy consumption level, demand-side resource flexibility and heat-power complementary ability.

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      Volume 44,2020 Issue 15

        >Application of Blockchain Technology in Power System
      • CAI Yuanji, GU Yuxuan, LUO Gang, ZHANG Xuan, CHEN Qixin

        2020,44(15):1-9, DOI: 10.7500/AEPS20200222003

        Abstract:With the rapid development of renewable energy in China, the pressure on direct financial subsidies is increasing. The renewable portfolio standard (RPS) and tradable green power certificate (GPC) provide a market-oriented way to subsidize the renewable energy, which makes it a promising option to support the renewable energy industry in China. Chinese GPC market is still in the early stage and lacks a systematic design of circulation mechanism. This paper proposes a bilateral trading mechanism of GPC and designs the full life cycle of GPC circulation covering issuing, trading and inspection considering the needs of RPS. In the full life cycle of GPC, different entities need to track and update their status asynchronously. With the growth of GPC market, the consistency and security problems of the data ledger need to be tackled. Therefore, this paper proposes a solution for GPC trading platform based on Hyper-ledger Fabric1.1. The basic network and application environment of blockchain are built, and the functions and interfaces necessary for the trading are developed. The field verification is conducted based on “Internet Plus” Smart Energy Demonstration Project in Zhuhai, China. So far, more than 10 renewable generation enterprises and more than 30 power consumers have registered, and more than 100 simulated transactions have been completed, which verifies the practicability and effectiveness of the platform.

      • QIN Jinlei, SUN Wenqiang, LI Zheng, ZHU Youchan

        2020,44(15):10-18, DOI: 10.7500/AEPS20191218003

        Abstract:Compared with the traditional electricity market, the low barriers to entry of microgrid, strong profit-seeking tendency of individual users and unstable production capacity of distributed power equipment may make the microgrid transactions fall into a crisis of trust. Therefore, a credit consensus mechanism suitable for the microgrid energy trading blockchain is proposed. First, common consensus mechanisms and their defects in microgrid application scenarios are analyzed. Meanwhile, the node attributes of the microgrid energy trading blockchain account are designed, and the microgrid energy trading process based on the blockchain is improved. Then, the credit value evaluation mechanism is established for the microgrid node, and the open and fair evaluation of node credit value is completed. Finally, the consensus mechanism based on proof of credit and stake (PoCS) is proposed, which implements that the credit value affects the consensus process and economy factor encourages user nodes to maintain their credit values. The simulation results show that the proposed credit consensus mechanism suitable for microgrid energy trading blockchain and the smart contract for microgrid energy trading can stimulate high-credit nodes with economic benefits and restrain the dishonesty phenomenon of nodes in microgrid.

      • >Basic Research
      • FAN Shuai, JIA Kunqi, WANG Fen, WANG Zhihua, YANG Lin, HE Guangyu

        2020,44(15):19-27, DOI: 10.7500/AEPS20191107001

        Abstract:With the penetration of high-proportion renewable energy, the regulation capability of generation resources reduces significantly, and the curtailment of wind power and photovoltaic are huge if only relying on conventional controllable power sources. To solve the problems above, this paper proposes a power balancing scheme by regulating controllable resources to satisfy the uncontrollable resources, and coordinating large-scale demand-side resources in demand response (DR) mechanism. Firstly, the limitations of diverse DR mechanisms in large-scale DR are analyzed, especially several problems of customer baseline load (CBL). Secondly, the definition, model and response evaluation indices of the customer directrix load (CDL) are proposed together with the CDL-based DR implementation scheme. CDL is defined as a desired load profile that could effectively offset the uncontrollable fluctuations in power system. DR customers are incentivized to individually reshape their power usage ways to approach CDL considering their preferences, and the controllable resources will achieve real-time power balance with uncontrollable resources. Compared with the current DR mechanisms, CDL is more feasible to be deployed and more suitable for large-scale promotion, which fundamentally enhances the system regulation capability and greatly promotes the consumption of renewable energy. Based on the built test system, the results of the case study indicate that the proposed mechanism can significantly reduce the curtailment of wind power and photovoltaic.

      • GUO Kunjian, GAO Ciwei, LIN Guoying, LU Shixiang, FENG Xiaofeng

        2020,44(15):28-35, DOI: 10.7500/AEPS20190726002

        Abstract:Demand response is an important tool for the electricity retailer to manage risk in spot market. However, in previous studies, electricity retailers mostly adopt price-based demand response strategies, which cannot flexibly implement demand response according to the changing practical situation. The incentive-based demand response is lack of in-depth research. In this paper, a Stackelberg game model for the incentive-based demand response between a single electricity retailer and multiple users is established. In this model, the electricity retailer reduces the loss of electricity sales by formulating demand response subsidy strategies during the periods when the electricity price in spot market is higher than its selling price. In the corresponding period, users decide the response electricity quantity according to the subsidy price set by the electricity retailer to obtain additional profits. Moreover, the solution of game equilibrium is presented by analysis. A case study shows that electricity retailer and users can all benefit from the demand response. In addition, the influence of price fluctuations in spot market on the subsidy price of the electricity retailer, response electricity quantity of users and respective profits of each participant, as well as the impact of various users joining in demand response projects on the profits of the electricity retailer are analyzed.

      • XIAO Yong, WU Haowen, WANG Zongyi, WANG Yan

        2020,44(15):36-43, DOI: 10.7500/AEPS20191203006

        Abstract:The development of demand response (DR) normalization relies on highly reliable information interchange, especially in the applications of wireless transmission. In this paper, an adaptive space-time precoding strategy based on signal-to-noise ratio and channel gain is designed to improve the quality of communication channels for interruptible load control in current DR. The proposed strategy combines DR communication demands. While improving the reliability of information transmission, it adaptively avoids the extra computational overhead introduced by coding. Firstly, based on the DR information exchange specification of China, combined with the actual information transmission and control frequency requirements, the communication service levels for DR transmission are specified in different periods. Secondly, the Alamouti coding technology is introduced to optimize the channel gain and reduce the DR terminal calculation overhead. On this basis, the Alamouti coding strategy of the adaptive precoding mechanism is used to optimize the transmission quality of information. Simulation examples verify the effectiveness of the proposed algorithm.

      • XIAO Jun, LI Hang, WANG Bo, SONG Chenhui

        2020,44(15):44-51, DOI: 10.7500/AEPS20200210003

        Abstract:A large number of distributed generators (DGs) are integrated to the distribution network, which brings challenges to the safe operation of the distribution network and the reasonable interests of the transmission system. In order to ensure the security, efficiency of distribution network and the interests of transmission system while accommodating DG, this paper proposes a comprehensive matching evaluation and improvement method for urban distribution network integrated with DG. Firstly, the comprehensive matching evaluation indices are proposed, including load and DG matching, net load and feeder capacity matching, and transmission and distribution matching, which can evaluate the comprehensive matching level of distribution network integrated with DG from the aggregate perspective. Secondly, the influence factors of comprehensive matching are analyzed to find the dominant factors restricting the comprehensive matching. Thirdly, the sensitivity analysis between the comprehensive matching evaluation indices and the influence factor indices is used to find the cost-effective improvement factors and guide the improvement of load or DG power curve to achieve higher comprehensive matching level. Finally, a case study is presented to demonstrate the effectiveness of the proposed method and the proposals for distribution network planning are concluded. In order to achieve a high comprehensive matching level, the energy matching degree should be positive and the curve of net load should be stable.

      • JIN Weichao, HAN Chang, YANG Li, LIN Zhenzhi, GAO Qiang, YING Guode

        2020,44(15):52-61, DOI: 10.7500/AEPS20191015009

        Abstract:Constructing and differentially strengthening anti-disaster backbone power grids can guarantee the power grid security operation and power supply for important loads in extreme disasters. This paper proposes a multi-objective optimization model of backbone power grid considering multi-stage disaster resilience. In this model, the topology and operation importance of nodes and lines in power grids are evaluated quantitatively, and a comprehensive evaluation method based on kernel principal component analysis (KPCA) is proposed. The anti-disaster backbone power grid is optimized for maximizing the survivability, invulnerability and restorability of the power grids within investment constraints. Then, the graph repair strategy and the files learning strategy are embedded in the improved comprehensive learning particle swarm optimization (ICLPSO) algorithm to solve the optimization model, which expands the feasible solution space. Finally, the effectiveness of the proposed model is verified by the simulation results of a regional power grid.

      • WANG Jie, XU Chang, HAN Xingxing, XIN Ziyang, XUE Feifei, LI Linmin

        2020,44(15):62-69, DOI: 10.7500/AEPS20191024006

        Abstract:For micro-siting optimization of wind farms in the flat terrain, the meta-heuristic algorithms with random quantities are frequently used. These algorithms are hard to achieve a global optimization, and are relatively inefficient. Grids and constraints are usually needed to make a stable solution. To address these problems, this paper proposes an efficient meta-heuristic algorithm with stable optimization solution for the micro-siting of wind farms in the flat terrain, i.e., wind turbine wake repellency optimization algorithm. According to the principle of van der Waals force, the concept of wind turbine wake repulsive force is proposed, which is used to describe the mutual influence between wind turbines with wake effects. The greater the wake effect between two wind turbines, the greater the wind turbine repulsive force. During the process of optimization, the wind turbine will continuously move in the direction to reduce the wake under the action of the wind turbine wake repulsive force until the optimal solution is obtained. Simulation results show that the wind turbine wake repellency optimization algorithm does not need grid constraints, has a high optimization efficiency, and can obtain a certain optimal result, while the optimization results meet the actual engineering requirements.

      • LI Shenghu, JIANG Yitian

        2020,44(15):70-76, DOI: 10.7500/AEPS20190912001

        Abstract:The dynamic interaction of synchronous generators (SGs) and doubly-fed induction generators (DFIGs) changes the damping oscillation capability of the system. The system state matrix is decided by the parameters of the SGs and the DFIGs, which increases the difficulty of deriving the sensitivity of the oscillation modes to the control parameters. For the power system with the DFIGs, to quantify the control effect of reactive power adjustment on damping oscillation, the analytical expression of the sensitivity of the damping ratio to the reactive power output of the SGs is proposed. By introducing the constraint of the minimum damping ratio, the oscillatory stability constrained optimal power flow (OSC-OPF) model based on reactive power optimization is proposed. According to the Lagrange multiplier of the OSC-OPF, the sensitivity of the power loss to the reactive power capacity of the SGs under the stability constraint is proposed. The simulation results show that the proposed model helps to reduce the power loss and improve the damping capability of the wind power system.

      • TU Chunming, XIE Weijie, XIAO Fan, LAN Zheng

        2020,44(15):77-86, DOI: 10.7500/AEPS20190917002

        Abstract:The virtual synchronous generator (VSG) technology is a new technology to support new energy consumption, whose related issues of single-machine operation have been widely discussed. However, few literatures are based on the system level to comprehensively analyze the operation characteristics of multi-VSG parallel system. Therefore, this paper establishes a full-order model of multi-VSG parallel system, which clearly considers the action law of control parameters on the operation characteristics of VSG with system delay. Firstly, the operation principle of VSG and its parallel mode are briefly described. It is pointed out that the comprehensive model should take the line and load parameters into account. Then, the delay of the single-machine model of VSG is corrected, and the full-order small-signal state-space model of the multi-VSG parallel system is established based on the modified model. On this basis, this paper uses the participation analysis method to clarify the correspondence between different control parameters and high-frequency and low-frequency stability. By analyzing the eigenvalue trajectory, the influence trend of each parameter on the high-frequency and low-frequency stability of the system and its threshold are analyzed. Finally, the theoretical analysis is verified by simulation.

      • SONG Junying, CUI Yiwei, LI Xinran, ZHONG Wei, ZOU Xin, LI Peiqiang

        2020,44(15):87-94, DOI: 10.7500/AEPS20191016008

        Abstract:In order to improve the accuracy of similarity measurement and the quality of clustering results in current load modeling, a daily load curve clustering method based on Euclidean distance and dynamic time warping distance is proposed by using the principle of k-means and entropy weight method. Firstly, Euclidean distance and dynamic time warping distance are adopted to measure the overall distribution characteristics, local dynamic characteristics and overall dynamic characteristics of the daily load curves. Secondly, entropy weight method is introduced to adaptively configure the weight coefficients of these three characteristics. Finally, k-means clustering algorithm is used to cluster the daily load curves based on the proposed similarity measurement method. The clustering analysis of daily load curves of typical consumers in a provincial power grid is made. The results show that the similarity measurement indices selected in the proposed method are reasonable, and the method has certain advantages in clustering quality and robustness, which can truly reflect the power consumption characteristics of consumers in this area and meet the application requirements of online load modeling.

      • ZHOU Ning, ZHANG Zhang, LIANG Tao, WANG Ying, YUAN Bo, WU Hao

        2020,44(15):95-102, DOI: 10.7500/AEPS20200316007

        Abstract:In view of the existing unified power flow controller (UPFC) in actual operation and its fault control strategy, a short-circuit current (SCC) calculation method for near-end bus of UPFC is derived based on the electric network theory. The near-end bus of UPFC is described by transfer admittance of UPFC series line to faulty bus. Since the series side of UPFC is immediately protected through bypass after the near-end bus fault, the Thevenin equivalent potential of the faulty bus changes suddenly, which affects the calculation result of SCC. The relative change of the calculation result is related to both the operation voltage of UPFC before the fault and the current distribution coefficient. The effects of operation condition change and UPFC parameter change on the SCC are studied in the IEEE 9-bus system and verified by PSCAD. The influence of UPFC on the SCC in large-scale power grid is analyzed in the IEEE 118-bus system. The results show that UPFC has the opposite effect on the SCC of bus on two sides, and the effect on the SCC of the near-end bus decreases with the increase of electrical distance.

      • >Application Research
      • JIA Ke, YANG Zhe, WEI Chao, ZHENG Liming, LI Yanbin, BI Tianshu

        2020,44(15):103-111, DOI: 10.7500/AEPS20190630001

        Abstract:Renewable energy sources are directly or indirectly connected to the grid through power electronic devices. Their fault currents have limited amplitudes, controlled angles, rich harmonics and strong nonlinearity, which are significantly different from that of conventional synchronous generators. The performance of conventional percentage restrained differential protection is facing challenges. In order to solve this problem, this paper proposes a pilot protection method based on Spearman rank correlation coefficient for transmission lines. When the system operates normally or an external fault occurs, a traversing current is flowing through the transmission line, so the current waveforms on both sides are completely opposite. When an internal fault occurs, there are huge differences between the transient current waveforms on both ends. Therefore, the Spearman rank correlation coefficient can be used to measure the correlation degree between the current waveforms on two ends, to distinguish the faults inside and outside the zone. The method is suitable for all kinds of renewable energy power plants, and has good performance on tolerating transition resistance and noise. Compared with the existing protection based on fault characteristics of renewable energy sources, the proposed method also shows good operation performance when the output power of renewable energy sources is weak and the breaker recloses into a permanent fault. Both simulation results and field recording data verify the effectiveness of the proposed method.

      • ZHAO Chengyong, LYU Yu

        2020,44(15):112-119, DOI: 10.7500/AEPS20200218006

        Abstract:Accurately locating pole-to-pole short-circuit faults on DC side of multi-terminal flexible DC transmission system with modular multilevel converters (MMCs) is a key measure to ensure fast power recovery. In view of the problems of distance measurement for fault location and difficulties in obtaining the parameters of overhead lines, this paper proposes a location method of pole-to-pole short-circuit fault for the flexible DC grid based on a simplified R-L model of overhead lines. The unit resistance and inductance values in the fault state of overhead lines can be deduced through the presetting pole-to-pole short-circuit fault tests, so the R-L line model is obtained. Based on the model, the fault location formulas are derived, and the fault location can be calculated more accurately by using the measured voltage and current data from both ends of the short-circuit line. A four-terminal flexible DC system based on PSCAD/EMTDC is used to verify the effectiveness of the proposed location algorithm. The simulation results show that the proposed location algorithm has high precision and reliability, which is almost immune to the transition resistance and the transmission power of the system. At the same time, it also proves that the simplified R-L model has high precision.

      • XIE Huifan, TAN Bo, LIU Hongtao, LIU Paihong, SONG Yang, XU Guanghu

        2020,44(15):120-126, DOI: 10.7500/AEPS20200118002

        Abstract:In order to solve the bipolar commissioning problem of high voltage direct current (HVDC) transmission projects while the construction of conventional earth electrodes are not completed, the unconventional earth electrode operation schemes, including in-station deep electrodes and out-station simple electrodes, are introduced. Then the electrical performance of electrodes, human safety, electrode heating, DC bias of transformers and diverting potential are studied. The main conclusions are as follows: in-station deep electrode schemes are technically feasible, but isolating measures should be taken to avoid high induced DC potential of earthing grid endangering the safety of equipment and human, for out-station simple electrode schemes, the step voltage and electrode temperature rise requirements are difficult to meet in monopole operation mode. So unbalanced current control measures should be introduced to ensure the safety of equipment and human near electrodes.

      • XIONG Fei, NIE Chuanjie, LI Junchi, YAN Dong, CHEN Xiaolei

        2020,44(15):127-138, DOI: 10.7500/AEPS20191204003

        Abstract:In the power electronic transformer (PET), when the dynamic response of cascaded H-bridge (CHB) and dual active bridge (DAB) converters is quite different, the voltages of the high and low voltage DC buses will have large fluctuations. To solve this problem, this paper proposes a coordination control strategy for energy flow inside PET. The proposed strategy consists of the CHB control based on total DC bus energy adjustment and the model predictive control of DAB based on DC bus energy coordination. The fluctuations of total DC bus energy are quantitatively assigned to the DC bus on both high and low voltage sides. As a result, the quadratic sum of the relative deviation of DC bus energy on both sides can be minimized. The proposed strategy simplifies the closed-loop control system and the design method of control parameters while improves the dynamic response of DC voltage. Moreover, a compensation control method is presented to suppress second-order power transmission in DAB. The theoretical analysis shows that the proposed control strategy has strong robustness against the inconsistent circuit parameters. The correctness and effectiveness of the proposed method have been validated by simulations.

      • LI Ming, ZHANG Xing, GUO Zixuan, MA Mingyao, LI Fei, ZHAO Wei

        2020,44(15):139-147, DOI: 10.7500/AEPS20200120003

        Abstract:With the increase of installed capacity and penetration rate of renewable energy, the power grid gradually exhibits the characteristics of weakness with large equivalent grid impedance. Proportional-integral (PI) parameters of grid-connected inverter designed under the conventional strong grid often cause system resonance or other instability problems. To optimize the design of PI parameters for grid-connected inverter in a weak grid, the conventional method requires approximate processing or repeated trial and error, and cannot combine multiple performance indices for parameter setting. So, the stability region of PI parameters for the grid-connected inverter in a weak grid is obtained based on the D-partition method, which satisfies the multi-performance indices, such as phase margin, amplitude margin, current-loop bandwidth and short-circuit ratio, etc. And it can be visualized by graphics, so as to quickly and accurately obtain PI parameters of weak grid, avoiding repeated trial and error. Finally, it is concluded that even the bandwidth of phase-locked loop is set very low, the PI parameters of the grid-connected inverter need to be reasonably designed and selected to make the inverter operate stably and efficiently. The validity of this design method and conclusion is verified by 30 kW experimental platform.

      • YANG Xingwu, XU Yiming, YANG Fan, WANG Tao, YANG Shuai, XUE Hua

        2020,44(15):148-155, DOI: 10.7500/AEPS20191205003

        Abstract:Model predictive control is easy to control multiple parameters coordinately, which has significant advantages in the control of modular multilevel converter (MMC). However, the weighting factors of conventional finite-state model predictive control method are difficult to be designed accurately, which needs a large number of simulations and experimental tests. This paper proposes a hierarchical model predictive control method based on finite state. The number of inserted sub-modules of upper and lower arms is calculated through reverse prediction of AC voltage and the internal unbalanced voltage drop of arms, which achieves AC current control and circulating current suppression. In the proposed method, not only the complicated design process of weight factors is eliminated, but also all switching states need not be calculated circularly, which greatly simplifies the number of prediction cycle and can ensure output voltage levels of 2N+1. At the same time, a balance control method of sub-module capacitor voltage based on prediction group sorting is proposed, which effectively reduces the number of voltage sorting and switching frequency, thus relieving the computation burden of the controller. Finally, an MMC converter platform is built,and the correctness and effectiveness of the proposed method are verified.

      • ZOU Tonghua, GAO Yunpeng, YI Huijuan, XU Changbao, XIA Rui, WU Cong

        2020,44(15):156-162, DOI: 10.7500/AEPS20191231003

        Abstract:An abnormal data processing algorithm based on Thompson tau-quartile method and multi-point interpolation is proposed to solve the problems of long cleaning time and complex model in the processing of wind speed-active power abnormal operation data of traditional wind turbine. Firstly, the abnormal power data points between the cut-in wind speed and the cut-out wind speed that are equal to or less than zero are eliminated. By dividing the wind speed range, the Thompson tau-quartile method is used to segment and refine the abnormal operation data to reduce the complexity of the model for identifying abnormal points. Then, the cleaned abnormal data are reconstructed by four-point interpolation subdivision algorithm to obtain the complete effective wind speed-active power data. Finally, the actual wind speed-active power data of the wind turbine are used as an example for the comparative analysis. The results show that the proposed method is simpler and the cleaning efficiency is higher. In the case of data missing, abnormal and unavailable in the adjacent wind farm, the proposed reconstruction method can effectively improve the quality of reconstructed data and get better reconstruction results.

      • CHEN Qiang, WANG Jian, XIONG Xiaofu, WANG Qianggang, LONG Yi

        2020,44(15):163-171, DOI: 10.7500/AEPS20191214007

        Abstract:When large-scale wind power are integrated to the grid in a centralized way, an N-1 fault in the sending transmission channel may overload the transmission lines and step-up transformers. However, the existing overload protection and stability and control strategies cannot adapt to this short-term power flow overload, so a large number of wind turbines need to be cut off, which is not conducive to wind power consumption. The paper analyzes the key parameters and safety boundaries of safety overload capacity for power equipment , and determines the long-term and short-term overload zones of transmission lines and transformers. According to the safety overload capacity of the equipment, the emergency overload operation strategy of the transmission channel is proposed, which is suitable for the grid connection of the wind farm cluster, including the heavy overload alarm based on the long-term overload zone, the wind turbine cutting-off and the over-limit-tripping due to the temperature rising of the equipment based on the short-term overload zone. The test results show that the proposed strategy is feasible, which can fully tap the overload capacity of the transmission channel and improve the wind power transmission capacity on the premise of ensuring the safe operation of the transmission channel.

      • >Egineering Application
      • YUE Han, SHAO Guanghui, XIA Deming, SUN Mingze, LIU Yang, WANG Kefei

        2020,44(15):172-179, DOI: 10.7500/AEPS20200304004

        Abstract:The overvoltage of ultra-high voltage direct current (UHVDC) sending-end system caused by disturbances such as DC blocking has become the main constraint to the UHVDC transmission capacity and renewable energy consumption. Based on the ±800 kV Zhalute-Qingzhou UHVDC weak sending-end system and combined with the condenser project of Zhalute converter station and the system protection construction of northeast power grid in China, the paper puts forward the overvoltage suppressing strategy through coordinating converter station filters (capacitors), condensers, and the synchronous units near the converter station. On the one hand, during the steady-state operation of power grid, the converter station as well as the condensers and the synchronous units near the station is fully utilized to compensate the reactive power consumed by the valve groups, and reduces the input of filters (capacitors), thus reducing the transient overvoltage caused by the lagging removal of filters (capacitors) while DC blocking. On the other hand, the increase of the reactive power output of the condensers and the synchronous unit provides sufficient fall-back reactive power reserve for suppressing steady-state overvoltage caused by large-scale power retreat while DC blocking. Finally, the effectiveness of the strategy is verified based on the Zhalute-Qingzhou UHVDC sending-end system.

      • WANG Zhenzhen, SUN Dan, WEN Shufeng, WANG Yongfu, BU Qiangsheng

        2020,44(15):180-183, DOI: 10.7500/AEPS20191128005

        Abstract:Firstly, the definition and implementation of IEC 61850 control model are studied in conjunction with the standard. The practical application and the definition of the standard are compared and the necessity of testing is explained. Secondly, the control model contents in the second edition of IEC 61850-7-2 and IEC 61850-8-1 are compared with those in the first edition. Then this paper focuses on the analysis of test cases in the second edition of IEC 61850-10, which are quite different from those in the first edition and analyzes the new key points of the test cases. Finally, through the exploration of engineering application, aiming at typical problems, the relevant test requirements and solutions are discussed.