2021, 45(22):1-8. DOI: 10.7500/AEPS20210302001
Abstract:Along with the increasing demand for energy transition and rapid development of renewable energy, the energy structure and the power system structure are under reform in China. In order to adapt to the requirement of large-scale renewable energy transmission and construct a novel power system with renewable energy as the main body, research and application of flexible transmission technologies are in urgent demand. The significance of high voltage direct current (HVDC) technology based on power electronic equipment is getting more and more prominent. At present, practical HVDC technologies in China include line commutated converter based HVDC (LCC-HVDC) technology, voltage source converter based HVDC (VSC-HVDC) technology and hybrid HVDC technology. Based on the development and engineering practice of HVDC technologies in China, the key problems of HVDC transmission technologies for large-scale renewable energy in engineering application are summarized, and several technology directions are discussed, which provide reference for the development of renewable energy transmission technology.
2021, 45(22):9-18. DOI: 10.7500/AEPS20210221003
Abstract:A reasonable system capacity configuration scheme is an important basis for the development and utilization of renewable energy. An optimal capacity configuration method for the grid-connected wind-photovoltaic-pumped-storage joint operation system is proposed. The method establishes a system model with the optimization objectives of the minimum cost, the maximum economic benefit and the minimum carbon emission. Based on the real data of a coastal island in southeast China, the model is solved by fast and elitist non-dominated sorting genetic algorithm-Ⅱ (NSGA-Ⅱ). Then, grey relational analysis (GRA) is introduced to achieve an unbiased trade-off strategy to obtain the optimal capacity configuration scheme. The results show that the joint operation system can achieve continuous and stable operation on the basis of maximum utilization of wind and solar energy. It is feasible to introduce GRA to determine the optimal capacity configuration scheme, and the carbon emission of the joint operation system in the whole project cycle decreases with the increase of the grey correlation degree. Increasing the access rate of wind and photovoltaic power appropriately can reduce the system cost, improve economic benefits and reduce carbon emission.
2021, 45(22):19-28. DOI: 10.7500/AEPS20210303011
Abstract:The siting and sizing for the hydrogen producing and refueling station (HPRS) and wind farms in the wind-hydrogen-electricity coupled network are studied with the intent of realizing the scientific layout of HPRS and wind farms. Firstly, a full-process model for HPRS including hydrogen production, compression, storage and injection into hydrogen fuel vehicles is proposed to simulate the hydrogen production and consumption of HPRS with on-site water electrolysis. Secondly, the hydrogen refueling logic rules and network expansion technique in the traffic network are introduced. Finally, a wind-hydrogen-electricity coupled network planning model considering traffic flow capture is developed by simultaneously taking into account the traffic network constraints, power network constraints and equipment operation constraints. Taking the IEEE 33-bus electricity network and 25-bus traffic network as case systems, the research results verify the effectiveness of the proposed model.
2021, 45(22):29-37. DOI: 10.7500/AEPS20210208006
Abstract:Global increase in large-scale outages caused by small-probability and high-impact extreme events has attracted extensive academic attention to the disaster response capability of multi-microgrid systems. In order to improve the ability of multi-microgrid systems to cope with extreme events, this paper proposes a two-stage energy management and scheduling method based on the system of systems (SoS) architecture. By making full use of various power generation resources in the systems, the power supply capacity of multi-microgrid systems can be maximized when it is disconnected from the main grid. Meanwhile, this paper also proposes a resilience index system to evaluate the ability of multi-microgrid systems to cope with the extreme events. The effectiveness of the proposed method is verified by comparing with the traditional multi-microgrid energy management method.
2021, 45(22):38-46. DOI: 10.7500/AEPS20210421009
Abstract:With the large-scale access of distributed generators, the strategy of the traditional distribution network fault recovery is gradually difficult to adapt to the actual needs. Therefore, the coordinated optimization strategy of fault emergency recovery and repair for distribution networks with distributed generators is proposed. Firstly, the typical load time-varying demand model is introduced into the fault emergency recovery model to restore the load with high demand first, and the fault repair model is obtained by taking the shortest time and the minimum social and economic loss of distribution network restoration as the objective function. Then, the coordinated optimization strategy of fault emergency recovery and repair is researched. The main network and island coordination control are used for recovery and the improved particle swarm optimization algorithm is used to obtain the optimal repair sequence. In the emergency repair process, considering the changes of load and time-varying demand, the optimal scheme of emergency recovery and repair is adjusted to ensure that the distribution network is reliable and quickly restored to normal operation. Finally, the IEEE 33-bus system is used for example analysis, and the results verify the effectiveness of the proposed strategy.
2021, 45(22):47-54. DOI: 10.7500/AEPS20201116001
Abstract:The large-scale interconnection of distributed generators (DGs) makes the medium- and low-voltage distribution network have the ability to participate in optimal dispatching, but the randomness of DG output and the complexity of power flow distribution bring new challenges to the reactive power optimization of medium- and low-voltage distribution networks. Considering the practical problem of incomplete station area topology information and the limitations of traditional cooperative optimization, a distributed cooperative reactive power optimization strategy for medium- and low-voltage distribution networks is proposed in this paper. Firstly, the feeder physical model and station area fitting model are established for the feeder and station area, respectively. Then, the master-slave splitting method is used to decompose the global reactive power optimization model, and the power flow fitting model of uncontrollable station area is introduced into the feeder reactive power optimization model, so as to make full use of feeder resources, improve the voltage quality of each node in the uncontrollable station area, solve the limitations of cooperative optimization based on physical model, and improve the level of cooperative reactive power optimization. The simulation results of an example verify the effectiveness and superiority of the proposed strategy.
2021, 45(22):55-64. DOI: 10.7500/AEPS20210423011
Abstract:A regional short-term load forecasting method based on virtual similar days and dual-stage attention-based long and short time pattern network (DA-LSTPNet) is proposed for the demand of the refinement of short-term load forecasting. To obtain the fine-grained real-time meteorological data matching the load, a meteorological virtual similar day containing fine-grained meteorological data is firstly obtained using gray correlation and correlation weighting method based on the coarse-grained meteorological data. Then, the maximum information coefficient (MIC) is used to analyze the nonlinear correlation between meteorological feature information and load. And the MIC-weighted selection algorithm for the load virtual similar day is constructed to solve the problem of excessive local similarity or even non-similarity caused by selecting historical days as traditional load similar days. Finally, in order to address the problem that the relationship between characteristic factors and local load fine-grained variation, the DA-LSTPNet is constructed to effectively explore the characteristics of long-term macroscopic and short-term local variation of load feature data for the day-ahead short-term load forecasting. Based on the actual load data of the power grid in a certain area of southern China, the various forms of simulation are used to demonstrate the higher prediction accuracy and universality of the proposed forecasting method.
2021, 45(22):65-73. DOI: 10.7500/AEPS20210207002
Abstract:In a wind farm where the wind turbines are arranged irregularly, the distribution of many wind turbines in different spatial locations forms a point cloud instead of a regular rectangular grid. The point cloud is irregular and unordered, which can represent the geographical location distribution of multiple wind turbines in any wind farm. However, the point cloud data cannot constitute the input of the highly regular grid for the convolutional neural network (CNN). It is difficult for the convolution operator to learn the spatial local correlation in the point cloud. If the irregular point cloud is directly mapped to a grid arrangement for regular convolution, the original spatial information of the point cloud will be lost. Therefore, the point CNN is used for spatial correlation extraction, then the simple recurrent unit is used to extract the temporal correlation information. And then the spatio-temporal correlation of point cloud data can be obtained. At the same time, the spatial features on multiple scales are extracted and integrated when designing the point CNN. Finally, the simulation results of multiple wind turbines with actual point cloud distribution show the effectiveness of the proposed forecasting model.
2021, 45(22):74-82. DOI: 10.7500/AEPS20210126009
Abstract:Short-circuit ratio (SCR) is an important indicator to measure the grid-connected strength of power access points. The probability of oscillation and voltage instability for renewable energy power plants connected to the grid with low SCR is higher. First, for the scenario of the grid-connected renewable energy cluster, this paper analyzes the applicability and deficiencies of calculation methods of weighted SCR, composite SCR and equivalent SCR that are commonly used. An improved equivalent SCR calculation method for the renewable energy cluster considering reactive power output of renewable energy, static var generators, impedance angle and initial phase angle is proposed. Then, based on a simple network, the relationship between the proposed calculation method and the conventional SCR is proven, and the influence of the reactive power compensation method on the equivalent SCR is analyzed. Finally, combined with typical calculation examples and actual renewable energy base with ultra-high voltage DC transmission project, assessment and application study of power grid strength based on improved equivalent SCR is carried out, and the effect of distributed condensers on strengthening the grid-connected point strength of renewable energy power plants is further analyzed.
2021, 45(22):83-94. DOI: 10.7500/AEPS20210311006
Abstract:The integration of high proportion of renewable energy makes security, stability and economic operation of power system face great challenges. As an important adjustment method, demand response (DR) plays an increasingly important role in the balance of power supply and demand. However, the response of demand-side resources has great uncertainty, which leads to a limited demand side market and insufficient economic motivation. In order to effectively guide the demand side to provide high-quality response services, this paper designs a transaction mechanism considering the response rate difference, puts forward the evaluation index of resource quality, and formulates a dynamic reward and punishment mechanism based on the principle that “resource with high response rate has high reward price”. Under this mechanism, in order to avoid the economic risk caused by low response quality, the form of generalized energy storage aggregator (GESA) is proposed on the demand side, and the generalized energy storage operation decision model is constructed, which combines the narrow energy storage of “high response precision and high cost” with the virtual energy storage of “low response precision and low cost” to cooperatively participate in the market transaction. The influence of the improved mechanism on its operation decision is also discussed. The calculation example based on the US PJM market data shows that the improved mechanism can provide economic benefit motivation for aggregators, effectively guide them to actively improve the response rate, provide better service for the power grid, and achieve a win-win situation.
2021, 45(22):95-104. DOI: 10.7500/AEPS20200905002
Abstract:Forced oscillations are mainly caused by oscillation sources of generators. The fundamental way to eliminate the forced oscillation is to locate the oscillation source generator and remove it. A method based on differentiated design of observer signal sensitivity is proposed to locate the oscillation source. According to the
2021, 45(22):105-114. DOI: 10.7500/AEPS20210414004
Abstract:The application of Ethernet technology has promoted the development of information sharing in smart substations, but the transmission of information faces many risks. Smart substations based on the IEC 62351 standard have new requirements for the security of information transmission. At present, there are security threats such as illegal theft, tampering, denial of service, denial and replay attacks on communication messages in smart substations. To solve this problem, a security communication strategy based on multi-stage transmission is proposed. The strategy realizes the two-way authentication of the identity of the communication subject through the double sequence function, uses the random factor generated by the double sequence function to check the freshness of the message, and combines the digital signature algorithm to verify the integrity of the message and solve the subject’s denial threat. Furthermore, the delay of the proposed strategy is quantitatively calculated and validated by the OPNET simulation in two cases that the bus faults occur in the star network and ring network in the D2-1-type substation, and the end-to-end communication delays of the multi-stage transmission of secure messages in the two network structures are obtained. The simulation results show that the proposed communication strategy can effectively improve the security of communication messages while meeting the real-time communication requirements in smart substations.
2021, 45(22):115-123. DOI: 10.7500/AEPS20210308002
Abstract:In order to accurately evaluate the reliability of the main electrical connection for the sending-end converter station for Kunliulong hybrid DC project of China, the equivalent two-state models of static components, dynamic components and auxiliary components in the main electrical connection of Kunbei converter station are built. In order to reduce the computational complexity, the sending-end converter station is partitioned according to the fault consequence and location of the components. Then, the GO method and fuzzy dynamic Bayesian network are combined to built the reliability model of the system. The proposed model can directly reflect the time-sequential change process of the system reliability, and can use the posterior probability to analyze the vulnerability of the main electrical connection. The feasibility and effectiveness of the proposed model and method are proven through the analysis of simulation results.
2021, 45(22):124-133. DOI: 10.7500/AEPS20210302010
Abstract:Aiming at the problem of poor transient stability and unclear instability mechanism of the voltage source converter (VSC) that adopts the grid-forming control strategy (take the virtual synchronous generator control as an example) with a current limiting loop, this paper starts with the transient stability analysis of the traditional synchronous generator, and qualitatively analyzes the transient process of the grid-forming VSC. Through the nonlinear differential equation analysis method based on the phase portrait, the quantitative analysis of the transient instability mechanism of the grid-forming VSC is implemented. Moreover, a new synchronization method (called hybrid synchronization control) that combines the swing equation of the traditional synchronous generator and the phase-locked loop is proposed, which makes the VSC not only has the ability of frequency response, but also greatly improve its transient stability margin. Finally, the simulation model built in MATLAB/Simulink verifies the accuracy of the analysis method and the effectiveness of the proposed control scheme.
2021, 45(22):134-145. DOI: 10.7500/AEPS20210403002
Abstract:To improve the power quality of the integration point of hybrid cascaded high voltage direct current (HVDC) transmission system and reduce the project occupied area and cost, this paper proposes an active harmonic compensation method based on modular multilevel converter (MMC). Firstly, the topology and harmonic characteristics of hybrid cascaded HVDC transmission system are introduced. The high-voltage valve adopts the line commutation converter (LCC), and the low-voltage valve adopts multiple MMCs. Then, the harmonic equivalent circuit of the system and the active harmonic compensation control strategy are described. In the strategy, the harmonics of LCC will be compensated by MMCs. Furthermore, the influence of active harmonic compensation on the steady-state operation of MMC are analyzed. Finally, a simulation model of hybrid cascaded HVDC transmission system is built in PSCAD/EMTDC simulation software, which verifies the availability of the active harmonic compensation control strategy in the steady-state operation, power change and time delay conditions of the system.
2021, 45(22):146-156. DOI: 10.7500/AEPS20210226001
Abstract:Aiming at the three-phase voltage unbalance problem of the interconnected power supply system of traction substation groups, a negative sequence centralized compensation scheme and control strategy based on three-phase transformer and static var generator (SVG) are proposed. First, according to the power transformation relation of the traction transformer and different load conditions, general power compensation expressions of compensation devices for the traction load in two modes are deduced. According to the power quality standards in China, a double-limit compensation scheme is proposed aiming at satisfactory negative sequence compensation, which includes mode selection method, SVG capacity configuration method and SVG operation method. According to the compensation scheme, the SVG double closed-loop compensation control strategy with mode discrimination is designed. Then, the compensation scheme is validated with measured data of traction substations, which proves that the scheme has good compensation effect. Compared with the complete compensation scheme, the proposed scheme requires smaller device capacity. Finally, it is proven through simulations that the control strategy is effective in negative sequence compensation and has fast response speed.
2021, 45(22):157-166. DOI: 10.7500/AEPS20210121007
Abstract:Aiming at the problem that the accuracy of traditional intelligent optimization algorithms in fault section location of distribution networks will greatly decrease with the expansion of the scale of distribution networks, a fault section location method for distribution networks based on improved electromagnetism-like mechanism (IELM) algorithm is proposed. Firstly, the integrated structure of the traditional fault location method is optimized based on the idea of hierarchical processing and global optimization. By changing the algorithm structure, the hierarchical processing of single-fault and multiple-fault is realized, and the solution space of multiple-fault location is reduced. Based on the structure optimization, the electromagnetism-like mechanism (ELM) is improved. Therefore, the impact of the global electric charge on the single electric charge is ignored; the learning ability of the single electric charge to the optimal electric charge is highlighted; and the global optimization ability and operation efficiency are improved. Finally, the IEEE 13-bus radiation distribution network with single power source and the modified 119-bus distribution network with four power sources are employed as simulation test systems. The test results demonstrate that the proposed fault section location method has the advantages of high accuracy, good fault tolerance, fast location speed and good dimension reduction effect for the distribution networks with different structures and scales and it also has a good application prospect in large-scale distribution networks.
2021, 45(22):167-173. DOI: 10.7500/AEPS20210127002
Abstract:The drivetrain is responsible for the energy transfer from rotor hub to generator in wind turbines. If any part of the drivetrain, such as gears and bearings, is abnormal, the wind turbine will face a huge safety hazard. Now most of the current wind turbine fault diagnosis based on the deep learning need to select target parameters artificially, and the identified fault has a close correlation with the selected variables, resulting in insufficient versatility. Wasserstein generative adversarial network-gradient penalty (WGAN-GP) uses Wasserstein distance between the generated data and the real data as a measurement for the cost function, which has the advantage of stable training results. This paper proposes a two-step data preprocessing method for data screening based on the supervisory control and data acquisition (SCADA) system, and designs anomaly state score of the wind turbine drivetrain based on the WGAN-GP model to identify the drivetrain faults. The proposed method uses common SCADA parameters, does not need to manually select target variables, and can stably identify non-specific faults in the wind turbine drivetrain, which has the advantages of accurate identification results and strong generalization ability. The status identification results of nine doubly-fed wind turbines verify the effectiveness of the proposed method, which can assist in guiding the operation and maintenance of wind farms.
2021, 45(22):174-182. DOI: 10.7500/AEPS20200601005
Abstract:With the comprehensive deepening of China's power system reform and the roll-out of the spot market construction, insufficiency of power capacity, massive stranding cost of power resources or other problems have been exposed in several regions. There is an urgent need to improve the capacity market mechanism and the electricity market system to promote unit investment and ensure the sufficiency of power generation capacity. This paper proposes a capacity market mechanism adapting to the clean energy development and spot market operation. On the one hand, the proposed mechanism takes the elements of spot electric energy trading into account, which mobilizes the competitiveness of capacity resources in terms of constant costs and operation costs, strengthens the connection between capacity investment/construction and system operation. This is conducive to the formation of a more practical capacity investment and construction plan. On the other hand, to meet the goal of "carbon peak and carbon neutral", the embedded energy structure constraints are considered to be compatible with industrial structure adjustments so as to obtain the most economical capacity combination that meets the requirements of low-carbon transition for the clean energy. Finally, a bi-level optimal model is established to realize the centralized clearing of capacity bidding considering the spot market operation. The simulation calculations of the modified IEEE 24-bus and other systems show that the proposed mechanism can not only encourage market players' active participation and adaptation to the replacement effect of clean energy costs in the future, but also realize the effective improvement of the overall economic efficiency of the market.
2021, 45(22):183-190. DOI: 10.7500/AEPS20201122001
Abstract:In order to fully stimulate the peak regulation willingness of thermal power units and promote the local consumption of clean energy such as hydropower, China Southern Power Grid pilots the first provincial peak regulation ancillary service market of the region in Guangxi, China. This paper focuses on the transaction types, transaction organization forms, clearing models and methods, settlement allocation mechanism, engineering problems and treatment methods of the peak regulation ancillary service market in Guangxi. The clearing model considers not only the conventional deep peak regulation and start-stop peak regulation resources, but also the dispatch of start-stop peak regulation of units on hot standby, which fully exploits the peak regulation potential of thermal power units. Meanwhile, the constraints consider the startup and shutdown processes of the units, which better matches with the actual peak regulation characteristics of thermal power units. The developed technical support system based on the proposed model and method has been put into the practical operation of the peak regulation ancillary service market in Guangxi. The case analysis and operation practice show that the proposed model and method are effective, and the developed technical support system can meet the actual engineering needs.
2021, 45(22):191-207. DOI: 10.7500/AEPS20200828012
Abstract:The observable and controllable capabilities of modern power distribution and consumption systems have been significantly improved. A large number of distributed energy resources such as flexible loads, energy storage devices and renewable energy generations have the ability of flexible control. The operation reliability of power distribution and consumption systems is affected by multiple uncertain factors. In order to effectively improve the reliability level in the operation stage, it is necessary to identify and suppress system operation risks. In this paper, the research on the operation reliability of power distribution and consumption systems with multiple distributed energy resources is deeply analyzed and summarized. The new research progress of the existing operation reliability evaluation and improvement technologies of power distribution and consumption systems are summarized. Development trends of operation reliability research are analyzed, and the research connotation and main research routes of operation reliability of modern power distribution and consumption systems are refined. In this paper, the key technologies of typical new equipment, new loads, new forms and support platforms in the power distribution and consumption systems are summarized, and the ideas for further research is given, so as to make the operation reliability evaluation and improvement fit the current development characteristics.