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      • ZHANG Hong, MA Hongjun, YAN He, SHI Hua, ZHANG Qian

        Available online:October 22, 2020  DOI: 10.7500/AEPS20200518002

        Abstract:In view of the high degree of autonomy of the microgrid and the uncertainty of renewable energy output, this paper proposes a two-stage day-ahead optimal scheduling framework of coordination of supply and demand from the perspective of a grid-connected microgrid operator. First of all, a bi-level optimization model of supply and demand collaborative scheduling is established based on the master-slave Stackelberg game. The upper operator’s problem includes two stages: day-ahead scheduling and real-time control. In the real-time control stage, the worst-case conditional value at risk is utilized to assess the cost risk caused by the uncertainty of renewable energy resources in the worst-case scenario. Then the Karush-Kuhn-Tucker condition,the Big-M method and strong duality theory of linear programming are used to transform the bi-level optimization problem into a mixed integer linear programming problem. Case analysis indicates that the proposed model can decide the optimal day-ahead scheduling scheme under the worst-case probability distribution of renewable energy output, simultaneously optimize the electricity price and load curve, and reduce the system operation cost and risk.

      • XIE Yuzheng, ZHANG Hengxu, LI Changgang, LI Wei, WANG Heng, CHANG Xiqiang

        Available online:October 22, 2020  DOI: 10.7500/AEPS20200511006

        Abstract:For the sending-end power grid where renewable energy accounts for a relatively high proportion and a large amount of power is sent out through multiple high-voltage direct current (HVDC) lines, HVDC blocking will cause over-frequency problems. Over-frequency generator tripping is an important control measure to restrain the frequency of the sending-end power grid. A setting method for the over-frequency generator tripping scheme is proposed based on considering the over-frequency protection of wind turbines and the active power change of transmission lines when HVDC blocking occurs. It is decomposed into the total generator tripping quantity submodel of the first round and the optimized setting submodel of generator tripping quantity of each basic round. The linear interpolation method and the perturbation method are used comprehensively to solve the generator tripping quantity of each round, and the two-element table is combined for the sensitivity analysis, thus the over-frequency generator tripping scheme is optimized. The effectiveness of the proposed over-frequency generator tripping scheme is verified by an example of a provincial power grid and the adaptability of the proposed scheme is checked in different operation modes.

      • CUI Yang, YAN Shi, WANG Zheng, HAN Chuanding, ZHAO Yuting

        Available online:October 22, 2020  DOI: 10.7500/AEPS20200420003

        Abstract:In an attempt to solve the joint clearing problem of integrated energy system and external grid under the environment of spot market and distribution side deregulation, a two-stage clearing method including day-ahead and real-time stages is proposed considering the mutual balance of interests between multi entities. In the day-ahead clearing stage, multiple rounds of iterative bidding are implemented considering the interest-driven of all entities, and incorporating factors into the day-ahead bidding process, such as mutual insurance, reserve and peak shifting. In the real-time clearing stage, a triple energy supply system from producers, superior power grid and spinning reserve providers is formed by coordinating internal and external reserve, energy supply refinement and interest distribution. Moreover, the clearing decision models for producers, operators, and load aggregators are built. Finally, the effective effects of demand response, mutual insurance contract and spinning reserve market on peak shifting and internal and external reserve are analyzed by case simulation, which shows that the method can realize the supply and demand balance and interest balance between each entity.

      • XU Chongbo, YANG Xiaodong, ZHANG Youbing, ZHANG Kaiyi, WANG Xiaozhong, TANG Ming

        Available online:October 22, 2020  DOI: 10.7500/AEPS20200331004

        Abstract:The soft open point (SOP) is used to connect two or more feeders. Its flexible reactive/active power adjustment capability can effectively mitigate the voltage deviation and improve the operation quality of the distribution network. The paper considers the coordination and optimization of multiple adjustment methods, including SOPs, on-load tap changers, switching capacitor banks, energy storage system (ESS) and demand response. On the basis of the control voltage amplitude within the safe operation range, the effective operation of the distribution network is realized. In order to cope with the multiple randomness of the system and properly avoid the actual operation risks caused by random factors, combined with the theories of the stochastic optimization and conditional risk at value (CVaR), this paper proposes a method for stochastic operation optimization of active distribution network considering risk management and control to achieve a balance between the expected operation cost and the operation risk. Then, the original model is transformed into a mixed-integer second-order cone programming model through the second-order cone transformation and linearization. It makes the model easier to solve. Finally, the test results on the modified IEEE 33-bus system verify the effectiveness of the proposed method.

      • ZHOU Xiaofa, SHI Hongjun, FU Jian, XIE Pan, YAN Quanquan, HUANG Yicheng

        Available online:October 22, 2020  DOI: 10.7500/AEPS20191007004

        Abstract:Converter valve is the core equipment of DC transmission, and its thyristor-level damping and voltage balancing element parameters need to be measured and tested regularly. Due to the large number of thyristors in the converter valve, traditional detection methods are inefficient and have certain safety risks. In this paper, a new detection method is proposed, which can apply voltage signals of different frequencies at both ends of the thyristor-level without disconnecting the wiring of the thyristor-level damping and voltage balancing element to generate a circuit network equation set, using the weighted least squares method to solve component parameters. The proposed method is applied to the rapid detection of thyristor-level damping and voltage balancing element parameters of converter valves in three technical routes. The results of simulation and field measurement verify that the proposed detection method is simple, efficient and highly accurate, and can meet engineering requirements

      • WANG Jiaming, ZHANG Jing, YANG Jianhua, WANG Guanzhong, ZHANG Feng, XIN Huanhai

        Available online:October 19, 2020  DOI: 10.7500/AEPS20191206002

        Abstract:Large-scale multi-infeed direct current systems (MIDCs) lead to the relatively weak voltage support capability in receiving AC systems, resulting in severe voltage stability issues. Although, it is critical to enhance the strength of the AC system, it may exacerbate the short-circuit current level. The structure of the receiving AC system affects both system strength and short-circuit current level. Since optimizing the grid structure of the MIDC can deal with the contradiction between system strength and short-circuit current level. This paper proposes a grid structure optimization method based on the sensitivity analysis of generalized short-circuit ratio (gSCR) and the branch addition method. Firstly, the relationship between the gSCR and the short-circuit current level are explored. Secondly, the impact of AC system structure adjustment on the two indicators is studied, and the comprehensive benefits of structure adjustment after coordination of the two indicators are analyzed. Finally, the receiving DC terminals are classified, and corresponding optimization methods for receiving AC system structures are given. Simulation results verify the validity and effectiveness of the proposed method.

      • XUE Yusheng, TAO Qi

        Available online:October 19, 2020  DOI: 10.7500/AEPS20200707002

        Abstract:The influence of operating conditions and fault scenarios on DC commutation security and synchronism stability are analyzed quantitatively. The idea of coordination and optimization between the equipment protection and the system protection are put forward. The quantitative index reflects the commutation security of DC system, and the extended equal-area criterion (EEAC) margin index reflects synchronism stability of power system. Based on these two quantitative indexes, the complex correlation between the two stability is revealed. According to the performance cost ratios of the control measures for improving commutation security and synchronism stability, the control strategy is coordinated and optimized to ensure the DC commutation security and system synchronism stability with the minimum control cost. Based on the simulations of AC/DC interconnected synchronous system and DC interconnected asynchronous system, the rationality of the commutation security margin index and the effectiveness of the coordinated optimization strategy are verified

      • CHEN Yuwei, WANG Bin, PAN Zhaoguang, SUN Hongbin, GUO Qinglai

        Available online:October 19, 2020  DOI: 10.7500/AEPS20200501004

        Abstract:This paper designs a functional framework of multi-time scale optimization dispatch module for multi-energy flow system, proposes a scheduling decision methods that takes into account the user's multi-energy demand response, and proposes a number of practical techniques including the model of multi-energy demand response and the model of energy storage that consider multiple types of actual constraints that can improve convergence. The multi-energy park dispatch system we developed supports multiple energy forms such as cold, heat, electricity, gas, etc., and fully exploits the adjustment capabilities in the user side, cooling system, heating system, and energy storage resources to improve the flexibility and economy of the parks. This dispatch system has been run online in actual parks in multiple cities. Based on the online optimization results in two actual parks, we analyze and verify the effect and adaptability of the dispatch system.

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      Volume 44,2020 Issue 20

      • ZHAO Shice, ZHAO Hongshan, SHOU Peiyao

        2020,44(20):1-10, DOI: 10.7500/AEPS20200303004

        Abstract:At present, the power grid introduces an agent based state monitoring management mode for some transmission equipment. However, this mode has a safety risk of single point failure and relies heavily on the high reliability of communication, which is not suitable for power distribution equipment widely distributed. That is, the power equipment currently still only performs functions without ‘intelligence’, which cannot realize intelligent perception of state, and does not meet the requirements of Energy Internet. To this end, the concept of ‘intelligent power equipment’ is elaborated, and its intelligent functions are comprehensively detailed, including self-sensing, self-alarming, self-state analysis, assessment of state of health, and self-protection. This equipment management mode is based on the intelligent perception, state analysis, and health management of the power equipment to operate autonomously and become an independent unit that can intelligently interact with the external environment. It realizes the efficient and comprehensive perception of power equipment, and adapts to the requirements of intelligent perception and flexible operation & maintenance of the power grid. In addition, the key technologies supporting this mode are studied, including sensing technologies, fault prediction algorithms, fault diagnosis algorithms, equipment degradation models, health assessment methods, communication methods and transmission protocols. Finally, the operation & maintenance management of the intelligent power equipment is discussed.

      • >Basic Research
      • ZHANG Yan, CHEN Qixin, GUO Hongye, WANG Yi, LU En

        2020,44(20):11-18, DOI: 10.7500/AEPS20200515004

        Abstract:In view of the difficulty in solving the fixed cost recovery problem of generating units in the energy-only market, the overseas power markets have launched the practice of establishing capacity markets, forming price signals for unit compensation with a market-based mechanism to ensure the sufficiency of generating capacity. From the perspective of capacity market mechanism design, this paper conducts modeling and equilibrium analysis of the power capacity market with investment decision on the premise of considering the strategic behavior of market members. Firstly, the basic mechanism of capacity markets is described, and a two-layer equilibrium model is established for the investment decision problem of capacity markets. The upper model is the optimal decision model of the oligarch and the lower model is the capacity market clearing model. Secondly, the two-layer model is transformed into a single-layer model by using the optimality condition. While the model is linearized by piecewise linearization, the mixed-integer linear programming problem is obtained. Finally, based on the actual data of one province in China, this paper makes a case study of the strategic behavior of market players, reveals the excessive investment behavior and its influencing factors of the oligarch during bidding period, proposes a strategic behavior regulation method based on limiting the freedom of project bidding, and verifies the effectiveness of this method.

      • LIU Dunnan, XU Erfeng, LIU Mingguang, ZHOU Baozhong, YING Yuhang, YU Qinbo

        2020,44(20):19-28, DOI: 10.7500/AEPS20200123004

        Abstract:In the background of Energy Internet, park operators firstly use distributed generators internally to meet the park electricity demand, and then exchange unbalanced energy externally. By formulating differentiated time-of-use (TOU) price packages, park operators can develop the demand response potential of park users, which can promote the local consumption of distributed generators and optimize the load exchange inside and outside the park. In this regard, a TOU pricing method for parks is proposed. Firstly, considering characteristics of electricity load and demand response, user groups in the park are clustered based on spectral clustering algorithm. Secondly, according to electricity load characteristics of user groups in the park, TOU periods are calculated based on k-means clustering algorithm. Finally, differentiated TOU price packages for different user groups in the park are formulated by constructing TOU pricing optimization model. According to the analysis of case examples, formulating TOU price in the park based on this method can effectively improve the local consumption rate and comprehensive utilization efficiency of the distributed generator in the park, as well as the friendliness with the external power grid and overall economy.

      • YAO Guangzeng, PENG Ke, LI Hairong, WEI Zhiyu, LI Xidong

        2020,44(20):29-36, DOI: 10.7500/AEPS20200412002

        Abstract:High-frequency oscillation is frequently occurs in flexible DC distribution systems, due to the influence of the interaction of multiple time scale control links and physical circuits. This paper studies the mechanism of high-frequency oscillation, and establishes a high-order mathematical model of the flexible DC distribution system. Sensitivity analysis of the key parameters affecting the system order has been conducted to realize the model order reduction. The analytical equation of high-frequency oscillation is deduced in time domain considering the influence of system parameters. This paper summarizes the influence law of the DC side filter capacitor, AC side equivalent inductance and controller parameters on high-frequency oscillation. Finally, based on Simulink, the simulation models of low-voltage and medium-voltage flexible DC distribution systems are built, and the simulation results verify the validity of the theoretical analysis.

      • CHEN Minquan, GAN Deqiang, KANG Zhuoran, ZHANG Qian, LI Shangyuan, LIU Junlei

        2020,44(20):37-45, DOI: 10.7500/AEPS20200115007

        Abstract:To some extent, power grid with increasingly complex structure can maintain long-term stable operation due to inherent system characteristics. As a qualitative characteristic of dynamic system, mixed monotonicity is derived from monotonicity, which can account for the inherent growth and decay mechanisms in the system structure. Jacobian matrices of dynamic electromechanical transient mathematical models of power grid generally exhibit constant sign patterns during different periods, which are consistent with the characteristics of the monotone system. Combined with the mixed monotone decomposition technique, the system parts with positive and negative effects on the key system state variables are decomposed. The growth and decay mechanisms among various state variables are studied and the dynamic response characteristics of the system in electromechanical transient scale are analyzed to explain some operation experiences of power grids. Finally, based on the result of the mixed monotone decomposition, a monotonic augmented system with bilateral comparison performance is constructed. Its vertex response gives a quick estimation of the interval response of the original system, which provides quantitative analysis results for uncertainty problems.

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

        2020,44(20):46-53, 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 becoming increasingly obvious. and the system frequency response is spatial and temporal distributed. 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 the inertia level of each area using the interconnector power and the 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 by 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 high accuracy in inertia assessment of power system with the large-scale integration of renewable energy resources.

      • LI Keqiang, HAN Xueshan

        2020,44(20):54-61, DOI: 10.7500/AEPS20200521002

        Abstract:This paper proposes a distributed algorithm of real-time optimal power flow for distribution systems with distributed energy resources (DERs). First, after obtaining the real-time data of the voltage state variables, the algorithm uses the second-order Taylor expansion of the original problem to correct the state variables, and uses the correction result in the calculation of control variables and the power control of DER. This paper gives the feasibility analysis of the proposed algorithm after continuous execution. Then, taking advantages of the sparse characteristics of the Hessian matrix, the decomposition and parallel calculation methods for the Hessian matrix elements and the distributed Gaussian elimination method for the correction equation are proposed to realize the distributed solution of the algorithm. Finally, the feasibility and effectiveness of the proposed algorithm are verified through the case analysis.

      • TAN Xiao, WANG Zhuding, SHU Dongsheng, SUN Jie

        2020,44(20):62-70, DOI: 10.7500/AEPS20200218004

        Abstract:With the increase of distributed generator (DG) penetration rates, the research on the impact of DG on the methods and results of distribution network planning has become more and more practical. A simplified optimization model for the number of substations and feeders with DGs is established by using a probabilistic planning method. The objective of the model is to minimize the related total cost of substations and medium-voltage lines, and the line capacity constraints are considered. An approximate calculation model of the length of medium-voltage trunk lines and branch lines is proposed, and the influence of load variation, DG randomness and line load transfer rate on the outage time and outage cost is considered. Based on the minimum total cost and the optimized number of substations and feeders obtained by model solution, three categories of credit variables are defined. The examples show the significance of probabilistic planning for the selection of the number of substations and feeders, and the substitution effects of DGs.

      • HAN Pingping, PAN Wei, ZHANG Nan, WU Hongbin, QIU Rujia, ZHANG Zhengkai

        2020,44(20):71-78, DOI: 10.7500/AEPS20200313003

        Abstract:It is found that adjusting the access phase sequence of the load can effectively reduce the line loss and three-phase load unbalance during the process of saving energy and reducing loss in 0.4 kV distribution network. This paper proposes an artificial phase sequence optimization method based on load forecasting and non-dominated sorting genetic algorithm (NSGA2). Firstly, the user load model is established by using the outlet current curve substitution method for distribution network. Secondly, based on the historical data, Elman neural network is used to predict the daily electricity consumption of each user and three-phase outlet current in distribution network on the day of phase modulation. Then, a multi-objective phase sequence optimization mathematical model of distribution network is established based on prediction data, taking the minimum line loss and the least number of phase modulation as the objective function. The NSGA2 is applied to solve the model to obtain the optimized phase sequence of each load. Finally, the effectiveness of the proposed method is verified by comparing the theoretical line loss before and after phase sequence adjustment in one distribution network of Anhui power grid of China.

      • >Application Research
      • DING Qia, YANG Junfeng, WANG Gang, ZHANG Yantao, CAO Rongzhang

        2020,44(20):79-85, DOI: 10.7500/AEPS20200421002

        Abstract:Transmission section limit (TSL) is an important boundary condition for the safe and reliable operation of power grid. As the scale of the power grid expands, the operation mode of the interconnected power grids is more and more complicated and variable, and many TSLs are only applicable under such conditions as certain unit start-up mode or related branch power flow level, and even these conditional transmission sections are interrelated. The traditional determination of the onset condition based on human experience requires repeated attempts of TSLs to optimize the power generation plan, which makes the optimization and decision-making process of power generation plan very complicated. Based on the traditional optimization model of power generation plan that considers fixed TSLs, and aiming at the characteristics of the conditional transmission section limits (C-TSLs) determined by the intervals which the relevant variables belong to, this paper proposes an optimization modeling technique by integrating power generation plans and C-TSLs. This model can achieve the automatic matching of C-TSL and power generation plan, and further tap the transmission potential of the power grid while ensuring the safety of the power grid. Finally, based on the proposed model, an example analysis is made on typical C-TSL scenarios such as cross section power flow ranges and the number of running and shut down units to verify the effectiveness of the model.

      • ZHOU Zhihang, SHI Libao, CHEN Yixuan

        2020,44(20):86-93, DOI: 10.7500/AEPS20191231006

        Abstract:After the Yunnan power grid of China and the China southern main power grid are interconnected asynchronously, the large amount of surplus power caused by the fault of sending DC lines makes the problem of system frequency stability more severe. Aiming at the DC blocking faults, the contribution factor of each generator unit to the surplus power caused by the fault is derived, and a tripping priority index with fault severity and probability taken into account is proposed. Furthermore, the configuration principles of the first-round and the last-round frequency settings for over-frequency generator tripping are discussed, and the dynamic cross-sequencing method is leveraged to meet the dispersion requirements of the tripped units. In order to improve the simulation efficiency, the approximate solution of over-frequency generator tripping is estimated by adjusting power first, and then the solution is modified by using the steady-state frequency constraint to complete the optimal configuration of the tripped units at each round. Finally, the generated typical faults are verified by using the clustering method. The simulation results demonstrate that the proposed method not only increases the minimum frequency but also reduces the maximum frequency during the transient process, which is more beneficial to the system stability and avoids the risk of under-frequency load shedding. At the same time, the overall tripping capacity is effectively reduced on the premise of ensuring that the steady state frequency is within the allowable range.

      • SHI Rongliang, ZHANG Lieping, WANG Wencheng, ZHANG Xing

        2020,44(20):94-102, DOI: 10.7500/AEPS20191130001

        Abstract:The renewable energy sources accessed to the power grid through fast-response power converters has received widespread attention, but they often cause frequency stability problems due to the reduction of power system equivalent inertia. This paper analyzes the effectiveness of two existing solutions. The direct differential operation method using phase-locked loop frequency has a slow dynamic response and causes noise amplifications. And the evaluation method of frequency differential signal using the second-order generalized integrator based frequency-locked loop (SOGI-FLL) can avoid the frequency differential operation. Nevertheless, the SOGI-FLL has a limited ability in suppressing the grid voltage disturbances. To solve this problem, this paper proposes a virtual inertia control strategy with the cascaded SOGI-FLL to accurately evaluate the frequency signal. The frequency self-adaptive filter based on SOGI is added to the SOGI-FLL control loop to enhance the disturbance suppression capabilities. Finally, both simulation and experimental platforms of the microgrid with diesel and energy storage system are established, and the simulation and experimental results verify the effectiveness of the proposed control strategy.

      • YU Guoxing, SONG Huihui, HOU Rui, GAO Le, QU Yanbin

        2020,44(20):103-111, DOI: 10.7500/AEPS20200116011

        Abstract:Flexible DC transmission is one of the best choices for solving the integration and aggregation problem of multiple microgrids. However, under the traditional control, DC transmission will cause frequency decoupling among microgrids, which makes them unable to form frequency support with each other. To solve this issue, based on the consistency theory, a new distributed frequency control structure is proposed. Then, a coordinated control strategy matching with the structure is designed. In this strategy, through the cooperation of interface converter stations, the objectives of frequency regulation among microgrids can be achieved. Meanwhile, with the cooperation between distributed generators in microgrids, the issues such as frequency restoration and accurate allocation of reserve capacity are effectively solved. The stability of the proposed control strategy in the system is demonstrated by the Lyapunov direct method. Finally, the simulation verifies the effectiveness and “plug and play” performance of the proposed strategy.

      • ZHANG Ruowei, QIN Boyu, LI Hengyi, LIU Wansong, CHEN Jiao

        2020,44(20):112-120, DOI: 10.7500/AEPS20200229002

        Abstract:Low voltage ride-through (LVRT) requires wind power generation systems to remain continuous operation during the sudden grid voltage sag and provide reactive power support for power grid. To enhance the LVRT capability of wind power generation systems using doubly-fed induction generators (DFIGs), this paper proposes a disturbance attenuation control (DAC) method based on state-dependent Riccati equation (SDRE) technique. The DAC objectives are as follows: the rotor side converter should provide required reactive power support for power grid during the transient period; the grid side converter should keep the DC-link voltage constant. Based on the above control objectives, the corresponding DAC problems are constructed, and the feedback control laws are obtained by using SDRE technique. The influence of control objectives, control effect and control cost are fully considered in the design of weighing matrices. To ensure the rotor current and DC-link voltage are within the safe range in the LVRT process, a rotor current limiting mechanism is proposed and a protection circuit using series dynamic resistor is adopted. Compared with the simulation results of the conventional proportional-integral (PI) control, the PI control based on particle swarm optimization (PSO), the sliding-mode control, and the exact linearization control, the proposed control strategy has better transient performance and can effectively improve the LVRT capability of wind power generation systems using DFIGs.

      • LI Jiazheng, ZENG Xiangjun, YU Kun, LI Li, WANG Zhan

        2020,44(20):121-126, DOI: 10.7500/AEPS20191203001

        Abstract:When the flexible grounding device is used to solve the problem of three-phase unbalanced overvoltage in the distribution network, the common current control method depends on the accurate measurement of phase-to-ground insulation parameters and harmonic current, so it is difficult to be applicated. To this end, the difference between voltage control and current control of unbalanced overvoltage suppression method is studied. An unbalanced overvoltage suppression method based on zero-sequence voltage is designed. The control strategy of inner loop proportional-integral (PI) plus outer loop first-order inertial link is adopted based on double closed-loop control. This method realizes unbalanced overvoltage suppression without measuring the phase-to-ground insulation parameters and harmonic current, and further improves the performance. Simulation results verify the dynamic and steady-state performance of the proposed method, and show that the unbalanced overvoltage could be suppressed quickly and precisely under various conditions.

      • WANG Ying, CHEN Chunlin, XIAO Xianyong, HE Hanyang, MA Ming, HU Wenxi

        2020,44(20):127-135, DOI: 10.7500/AEPS20200416012

        Abstract:The voltage sag tolerance capability of sensitive equipment is important information for formulating voltage sag suppression scheme and deciding equipment type to be purchased. The voltage tolerance curve (VTC) of sensitive equipment is usually obtained through test experiments of equipment voltage tolerance capability. The traditional test method has the problems of low automation, high work intensity, and low test efficiency. This paper proposes an automatic test method for the voltage sag tolerance capability of sensitive equipment, to integrate the processing of voltage, current and switch data of the voltage sag generator and the equipment under test. The criterion of voltage sag consequence and the threshold of switch and non-switch equipment are put forward to realize the synchronization of source and load data and automatic VTC drawing. This paper also proposes an improved dichotomy test method which can be applied to sensitive equipment with rectangular and non-rectangular VTCs. Finally, the proposed automatic test method and improved dichotomy test method are verified by an automatic test simulation system and an actual physical test platform. The simulation results show that the automatic test method can realize the automatic test for voltage sag tolerance capability of sensitive equipment with multi-dimensional voltage sag characteristics. Both the simulation and actual test results show the improved dichotomy test method has high accuracy and test efficiency.

      • WU Yanping, YAO Jianguo, CHANG Naichao, ZHANG Qibing, FAN Chen, DOU Renhui

        2020,44(20):136-141, DOI: 10.7500/AEPS20191126004

        Abstract:According to the wide-frequency characteristics of electric variables in the power electronized power grid, this paper designs a multi-functional wide-frequency measurement device. Based on high-speed synchronous sampling, the device is optimized to integrate such functions as wide-frequency oscillation detection, synchrophasor measurement and wide-frequency (inter)harmonics measurement. The algorithm models of transient variables, phasors and effective values are synthetically used to improve the monitoring and detection ability of wide-frequency electric variables with different signal structures. Considering both stable and non-stable conditions, the comprehensive detection of power frequency, non-power frequency components and oscillation power in the range of 0~2 500 Hz is realized, which provides targeted data for the research of generation mechanism, propagation path, analysis and control method of wide-frequency electric variables. The multi-functional wide-frequency measurement device realized in this paper has passed the test and been applied in pilot projects.

      • XU Bochao

        2020,44(20):142-147, DOI: 10.7500/AEPS20191229003

        Abstract:Aiming at distinguishing false data and abnormal state points in power plant parameters, a cleaning method based on association rule, density-based spatial clustering of applications with noise (DBSCAN) algorithm and improved Gauss kernel relevance vector machine (RVM) is proposed. Firstly, association rules are introduced to analyze the association among parameters and find out the combination of parameters with strong association. Secondly, the DBSCAN algorithm is used to detect the abnormal point preliminarily, and the cleaning procedure combined with the associated parameters is proposed to distinguish the false data and the system abnormal state points. Finally, RVM is used to clean the false data, and the time cost is reduced by improving the Gaussian kernel space sample point form. Test results show that the cleaning method based on parameter correlation can effectively improve the accuracy and timeliness of cleaning.

      • >Discussion
      • XIAO Yong, WANG Yan, QIAN Bin, JIANG Jing, GAO Ciwei

        2020,44(20):148-156, DOI: 10.7500/AEPS20200628013

        Abstract:Under the environment of power market, it is an important research topic how to make optimization strategy to maximize electricity benefits for electricity retailers according to electricity consumption characteristics of users. Aiming at the electricity retailers considering the coordination of power generation and consumption in medium- and long-term markets, the model of load combination optimization considering the benefits of electricity purchase and sale for electricity retailers is put forward. The demand response technology is further considered to optimize the integrated load characteristics of users. The benefits of electricity purchase and sale for electricity retailers is maximized in the market environment. At the same time, aiming at the load rebound problem of the demand response, a three-stage load rebound model is adopted. And a improved rolling optimization model considering load rebound is constructed to readjust the load value of demand response for users, which improves the load characteristics of demand response for combined users with the load rebound of demand response. Finally, the proposed model and strategy are simulated and analyzed based on the load data of industrial user group in a city of China in 2017, which verifies the effectiveness of the model

      • >Egineering Application
      • GUO Xianshan, LIU Bin, MEI Hongming, LIU Jie, YU Hualong, CAO Fengmei

        2020,44(20):157-164, DOI: 10.7500/AEPS20200211008

        Abstract:In December 2018, a 1 810 Hz resonance of AC voltage occurred during the open line test (OLT) of Hubei-side AC system in Chongqing-Hubei back-to-back HVDC project of China (referred to as “Chongqing-Hubei project”). After adopting the typical suppression measures for high-frequency resonance, a 700 Hz resonance of AC voltage occurred during OLT of Chongqing-side AC system. According to the Nyquist stability criterion, this paper adopts the Bode diagram based on impedance theory to study the resonance mechanism of the whole AC/DC system. The impedance characteristics of the flexible DC system and AC systems are analyzed. And the results show that there are risks of resonance near 1 780 Hz and 750 Hz in the flexible DC system and Hubei-side and Chongqing-side AC systems, which basically coincides with the field test. This paper proposes a control strategy based on the voltage feedforward link with the nonlinear filter, which changes impedance characteristics of flexible DC system in middle and high frequency bands to avoid its resonance with the AC system. An electromagnetic simulation model is established to simulate the flexible DC system and AC systems on both sides of Chongqing-Hubei project, and the resonance is reproduced. The simulation results verify the effectiveness of the proposed strategy for resonance suppression. Finally, the proposed strategy has been applied in Chongqing-Hubei project, and no resonance has been observed in typical operation modes.

      • WANG Yongli, WANG Shuo, ZHENG Yan, SONG Fuhao, MA Yuze, ZHANG Heng

        2020,44(20):165-172, DOI: 10.7500/AEPS20200202005

        Abstract:After the reform of transmission and distribution price, the demand for lean management of power grid companies is increasing. The cost of a project has direct impact on investment decisions, so the traditional rugged cost calculation method cannot meet the current demands. To this end, a cost accounting method is proposed. In this method, according to the efficiency idea, the operation and maintenance cost of project is allocated and calculated. Firstly, the Elastic Net algorithm is used to screen the factors affecting the operation and maintenance cost to determine the performance standards of key factors. Secondly, the criteria importance though intercrieria correlation (CRITIC) method is used to measure and calculate the weight. The cost allocation coefficient of a single project is obtained, and then the allocated cost of the project is calculated to realize the accurate measurement of the operation and maintenance cost of the project. Finally, the typical project data of a province in China is selected to verify the proposed model.The results show that the proposed model can more accurately calculate the operation and maintenance cost of the power grid project.

      • >Survey
      • SONG Guobing, WANG Ting, ZHANG Baohui, DONG Xinzhou, KANG Xiaoning

        2020,44(20):173-183, DOI: 10.7500/AEPS20191118005

        Abstract:The integration of a large number of power electronic devices into power system has changed the fault characteristics of power grid, which challenges the adaptability of the conventional relay protection excited by synchronous machines. The complex fault transient characteristics and short duration in power electronic system limit the application and development of passive detection protection technologies. The controllable ability of power electronic devices can improve the ability of fault identification of relay protection. The key technology of detective fault identification method is proposed based on the coordination of control and protection. Different types of power equipment that can realize the active detection are classified. Then the feasibility of the injection operation and the physical limitation of the injected detective signal are described. Finally, the application scenarios of the detective fault identification methods are discussed and the research prospect is given.