2017, 41(10):1-8. DOI: 10.7500/AEPS20160728017
Abstract:Energy Internet aims at breaking through the restriction of fossil energy, integrating complementary energy, exploring the energy production and consumption patterns. Power is taken as the main support energy of energy systems. Firstly, on the basis of the large-scale system decomposition-coordination and Pareto optimality of economics, the economic theory followed by Energy Internet is proposed. Then, compared with the traditional dispatching mechanism, Energy Internet dispatching mechanism is proposed and the micro balance transaction subjects, trading patterns and mechanism are analyzed. Finally, energy incentive allocation mechanism is established to coordinate the Energy Internet dispatching and trading plan and regional interests relationship. This work is supported by National Natural Science Foundation of China(No. 71401055), Beijing Social Science Foundation(No. 16GLC070)and Fundamental Research Funds for the Central Universities(No. 2016MS72).
2017, 41(10):9-15. DOI: 10.7500/AEPS20160923005
Abstract:Along with the deeper coupling between power system and information communication system, such traditional simulation methods as decoupling communication and ideal simulation can hardly satisfy the realistic demand because of the communication faults of time delay, bit error and interruption. Based on an analysis of existing modeling techniques of cyber physical system, a master-slave mode co-simulation platform supported by MATLAB and OPNET is proposed. Some key problems such as the co-simulation framework, the model in MATLAB and OPNET, software-based virtual measuring equipment and interactive interface are expounded, in which a hybrid time synchronization strategy is designed and analyzed. A microgrid case study is given to demonstrate the feasibility and availability of the co-simulation platform. This work is supported by National Natural Science Foundation of China(No. 51677025), Programs for New Century Excellent Talents in University(No. NCET-13-0129)and National Key Research and Development Program of China(No. 2016YFB0900400, No. 2016YFB09004004).
2017, 41(10):16-21. DOI: 10.7500/AEPS20160803007
Abstract:The energy router is an important device for the future Energy Internet. Based on an analysis of the energy sharing method using the energy router in the Energy Internet environment, the basic requirements of the energy router are analyzed, and a multi-interface energy router main circuit structure based on power electronic converters is proposed. The proposed energy router consists of energy storage and its converter, common DC bus and energy interface. According to the application, the energy interface can be divided into network energy interface and local energy interface. The control strategies of the modules in the energy router are briefly described. With the control strategies, an energy router can provide the access interface for the local distributed energy resources and supply the local load. Meanwhile, the energy router can control the exchange power of its network energy interface, and realize the point to point energy transmission between energy routers or between the energy router and the external power grid, which means the energy routing function is realized. An energy management strategy for energy storage and network energy interface is proposed. The energy router simulation model is established in the MATLAB/Simulink environment. The dynamic responses of the energy router and the energy management strategy are simulated, the simulation results verifying the correctness of the energy router main circuit and control strategy as well as the feasibility of the energy strategy proposed. This work is supported by National High Technology Research and Development Program of China(863 Program)(No. 2014AA052001)and Guangdong Provincial Natural Science Foundation of China(No. 2015A030310227).
2017, 41(10):22-28. DOI: 10.7500/AEPS20160721012
Abstract:The time-delay stability criterion based on the Lyapunov stability theory is commonly used to analyze the time-delay stability of power systems. Owing to the different Lyapunov functions and derivation processes adopted, different stability criteria tend to have different forms, computational efficiency and conservative properties. This paper tries to explain the difference in conservative properties by numerical calculation and a visualization method to provide guidance for seeking better criteria. First, four typical time-delay stability criteria are introduced based on a simple review of the time-delay system model. Furthermore, three kinds of indices reflecting the operational diversity of the power system are introduced by time-delay system simulation data. Then a numerical calculation method for evaluating the conservatism of time-delay stability criteria for power systems is presented. Finally, the application process of the evaluation method is shown by a typical first-order system. The effectiveness of the proposed method in multi-dimensional systems and multi-time-delay scenarios has been validated by a single-generator-infinite-bus system and a WSCC 3-generator 9-bus time-delay system. This work is supported by National Natural Science Foundation of China(No. 51277128)and National High Technology Research and Development Program of China(863 Program)(No. 2015AA050403).
2017, 41(10):29-36. DOI: 10.7500/AEPS20161108004
Abstract:The supplementary damping control(SDC)based on port energy is advantageous because of its simplicity, wide applicability and clear physical meanings. The SDC based on the real part of port energy(R-SDC)and the more advanced comprehensive SDC(C-SDC)are proposed. Compared with the existing SDC based on the imaginary part of port energy(I-SDC), the R-SDC is more suitable for resistance dominated networks. As the C-SDC can consider the coupling feature between the active/reactive power and the voltage magnitude/angle, it is better than the I-SDC in both resistance and reactance dominated networks. By applying the control strategies to the solar photovoltaic generators in modified IEEE benchmark systems, the effectiveness of the proposed control strategies is validated. This work is supported by National Basic Research Program of China(973 Program)(No. 2013CB228201).
2017, 41(10):37-43. DOI: 10.7500/AEPS20160729002
Abstract:For the control of virtual synchronous generator(VSG)of grid-connected inverter, an approach is proposed to estimate the produced inertia and damping of VSG. Thus, the capability of VSG to participate in power grid adjustment can be quantified. Based on the second-order nonlinear model of VSG and its small signal perturbation processing ability near the working point, a linearized model for VSG is proposed. The discrete model of the linearized model is derived and its relation with inertia and damping parameters of VSG is given. The error magnitude and effective range of the linearized model are proposed. Using the output power step disturbance of VSG, the modal information on power oscillation of VSG is energized. Then, the least-square method is utilized to estimate actual inertia and damping parameters of VSG. Finally, by taking the normal control and VSG control into account, simulated results and experimental measurements have confirmed the possibility and effectiveness of the proposed model and approach. This work is supported by Chongqing Research Program of Basic Research and Frontier Technology(No. cstc2016jcyjA0108), Fundamental Research Funds for the Central Universities(No. 106112015CDJXY150005)and State Grid Corporation of China(No. SGHADK00PJJS1500060).
2017, 41(10):44-50. DOI: 10.7500/AEPS20160602009
Abstract:The voltage stability margin of the weak grid is usually insufficient. While the fault ride-through(FRT)performance of the wind farm has significant effect on the transient voltage stability of power grid. The traditional FRT control method for doubly-fed induction generator(DFIG)based wind turbine is on the basis of constant power control which is suitable for strong grid. But it is difficult to support transient voltage stability of the weak grid. Therefore, a new FRT control method for DFIG-based wind turbine is proposed which can be applied to weak grids. The proposed control method based on synchronized control makes the wind turbine operate as controllable voltage source via active current and reactive current droop control. It not only enables the DFIG-based wind turbine to provide active and reactive currents, but also enhances the voltage stability during the transient re-exciting process after grid fault clearance. It is applicable for the DFIG-based wind turbine which needs seamless switching between grid connected and isolated networks as well. The effectiveness and advantages of the proposed control method is validated by the simulation cases of DFIG-based wind turbine connected to infinite bus, practical regional and islanded micro-grid. This work is supported by National Key Research and Development Program of China(No. 2016YFB0900104).
2017, 41(10):51-57. DOI: 10.7500/AEPS20160727013
Abstract:A multiport coordinated control strategy is proposed for multi-island grid converter station to participate in the main grid frequency stability regulation to heighten the frequency stability of voltage source converter based multi-terminal direct current(VSC-MTDC)system. According to the mathematical model of the interconnected system, this strategy has to design a control law for the direct current(DC)power regulatory amount of each island grid converter using the feedback linearization H∞ method in nonlinear robust control. Secondly, in consideration of the frequency fluctuations of each island grid, this strategy uses the simplex method to optimize the DC power distribution coefficient for the control rate of DC power adjustment amount, thereby obtaining the DC power adjustment amount of optimal allocation and ensuring coordinated participation by all island grids in the main grid frequency stability adjustment process with optimal DC voltage droop control. Finally, a three-terminal VSC-MTDC system is set up on PSCAD/EMTDC. Comparison of simulation results with those of conventional control strategy shows the correctness and superiority of the proposed control strategy. This work is supported by Post-doctoral Science Foundation of China(No. 2015M582543).
2017, 41(10):58-65. DOI: 10.7500/AEPS20160706008
Abstract:Aiming at enhancing the capability of the network frequency modulation supported by the doubly fed pumped storage unit(DFPSU), a kind of improved proportional-differential(PD)loop virtual inertia control strategy of DFPSU is proposed. First, based on the operation characteristics of DFPSU, the models of reversible pump turbine, doubly fed induction machine and control system of DFPSU are established. Then, according to the relationship between the virtual inertia, the rotational speed adjustment and the network frequency variation, a kind of improved PD loop virtual inertial control strategy of DFPSU is proposed. In addition, a control parameter calculating method in the improved PD virtual inertia control is also provided. Finally, a three-machine system with DFPSU is used to validate the proposed control strategy. The simulation results show that the proposed control strategy could effectively improve the frequency response ability of DFPSU in both the generator and motor mode and the frequency stability of the power system at the same time. This work is supported by National Natural Science Foundation of China(No. 51377184)and Fundamental Research Funds for the Central Universities(No. 106112016CDJZR158802).
2017, 41(10):66-71. DOI: 10.7500/AEPS20160930010
Abstract:As there are constraints such as the time delay and generation rate constraint(GRC)in the automatic generation control(AGC)regulation process, the frequency regulation characteristics of power systems cannot be reflected by the AGC control strategy based on linear models. For the saturation and the time delay in the AGC time-delay system, a genetic optimization strategy of AGC cascade control system based on the proportional-integral(PI)stability domain is proposed. AGC system is equivalent to cascade control system made up of load frequency control loop and unit control loop. The Hopf bifurcation algebraic criterion and the time-delay system stability criteria are used to compute the stability domain of the inner and outer loops, respectively. It is proved that the parameters of the saturation and the time delay will affect the PI stability domains. Then the PI stability domains are converted into constraints of controller parameter optimization. Optimization comparative researches for the inner loop have shown that the integral of the absolute error(IAE)index has better performance in suppressing disturbances while the integral of the time squared error(ITSE)index has smaller fluctuations for the outer loop. Genetic optimization results show that the proposed control strategy is able to effectively resist the impact of the saturation and the time delay on the AGC system. This work is supported by National Natural Science Foundation of China(No. 61074104).
2017, 41(10):72-81. DOI: 10.7500/AEPS20160915001
Abstract:Large scale charging load of electric vehicles will increase the degree of the deviation between node voltage and nominal voltage in a local distribution network, and the deviation which caused by the charging load is random on time and place, traditional reactive compensation method can solve the above problem, but the economy is bad. So a voltage control strategy based on reactive power compensation by electric vehicles is proposed, which aims at implementing reactive power compensation for distribution network and changing the charging active power at the same time through regulating the operating power factor of the chargers effectively. The strategy can ensure the security and stability of the node voltage and the efficiency of distribution network will not decrease. A strategy is proposed to calculate the controllable scope of operating power factors of chargers after analyzing the travel behavior characteristic in a working area of first-tier/second-tier city in China and the operating characteristic of charger. Then, the node voltage regulation model is used which considers all operating power factors of chargers as variables and considers the following conditions as the optimization objective: the deviation between node voltage and nominal voltage is minimum, the variance of the node voltage from current time to all time before is minimum, the state of charge charged in at unit duration is maximum. Finally, immune algorithm is used to get the values of variables. The rationality of the proposed node voltage regulation strategy can be validated through the simulation. This work is supported by National Natural Science Foundation of China(No. 51677004)and Fundamental Research Funds for the Central Universities(No. 2016JBM061).
2017, 41(10):82-91. DOI: 10.7500/AEPS20160803008
Abstract:With the large-scale application of microgrid, microgrids with single-phase/three-phase architecture geographically closer to one another can be interconnected to multi-microgrid systems with multi-phase architecture. For the regional autonomous multi-microgrid off the power distribution network, this paper proposes a distributed-coordinated hierarchical control strategy of multi-time scale, including second-level distributed real-time control, minute-level centralized coordinated control and hour-level dynamic island switching control. Distributed real-time control achieves power regulation with sources, loads and storages based on each microgrid's stability margin. Considering the three-phase unbalance factor as a constraint, centralized coordinated control achieves regulation of power with sources, loads and storages based on multi-objective mixed integer programming. Dynamic island switching realizes optimal resources allocation for the whole regional multi-microgrid through combined decision making. It is shown by simulation results that the proposed strategy can realize hierarchical control on multi-time scale for the regional autonomous multi-microgrid with single-phase/three-phase architecture and the coordinated control of the fluctuation of sources, loads and storages to help with the safe and efficient operation of the multi-microgrid off the distribution network. This work is supported by National Key Technologies R&D Program(No. 2015BAA06B02).
2017, 41(10):92-99. DOI: 10.7500/AEPS20160927006
Abstract:To compensate for the current inadequacy of large capacity rectifier transformers with only overcurrent protection but no longitudinal differential protection at home and abroad, the key contents of setting up longitudinal differential protection for rectifier transformer are proposed. First, the special treatment methods for the sampled secondary current values of current transformer on the valve side of the longitudinal differential protection are put forward and demonstrated. And it is also shown what value of effective three-phase current values on the grid and valve sides in the calculation of differential current and brake current for longitudinal differential protection should be adopted, i. e. , the best compensation(or angle)equation is demonstrated, which is different from the compensation equation of the conventional power transformer, converter transformer, electric furnace transformer, etc. A unique calculating method of phase and modulus value of grid-side current is proposed and demonstrated when a two-phase short circuit fault occurs on the valve side of the rectifier transformer. The action characteristics of differential protection for rectifier transformer are analyzed when a two-phase short circuit fault or a single-phase grounding fault occurs. The characteristics of setting calculation of differential protection can make the protection action sensitivity significantly increase during the internal short-circuit fault, and make the differential protection range significantly expand, while protecting the valve-side short-circuit of the rectifier bridge and the DC side short-circuit.
2017, 41(10):100-105. DOI: 10.7500/AEPS20160718008
Abstract:The accurate single terminal fault location can be realized by using data of two time sections to set up equations to describe the constant transmission line topology between two-terminal circuit breakers, the time after fault and that after single-phase circuit breaker tripping. But this method assumes that the impedance of opposite terminal and fault resistance in fault branch are constant between two time sections, which is untenable at the system side in transmission lines with wind farm connection. For this problem, the idea of operating fault location at the wind farm side is proposed to overcome the problem of equivalent system impedance variation between two time-sections. And then a new fault location equations direct calculation algorithm is proposed to resolve the problem of low fault location accuracy in the case of high impedance faults, which is usually produced by the previously adopted iterative searching algorithm. Fault distance and transitional resistance can thus be directly obtained using the new algorithm while subsequent research on adaptive reclosing is provided with a new line of thought. This work is supported by National Natural Science Foundation of China(No. 51477084)and State Key Laboratory of Power System(No. SKLD16Z07).
2017, 41(10):106-111. DOI: 10.7500/AEPS20160818002
Abstract:In view of the deficiency of the future model and historical model management in the smart grid dispatching and control system, this paper proposes a multi-version construction and management technology of power grid model based on application and time dimension. The method takes the use of lightweight file database and CIM/E files as the persistent storage medium of the multi-version model to implement security isolation among multiple versions. The different operational models are classified by logical model sets, and then the technical scheme of constructing and managing multi-temporal model versions among different transactions are realized. Furthermore, this paper proposes specific solutions for some key technologies, such as model comparison and consolidation between different versions, the model validation of future version and online process management. This technology has become a pilot application in the dispatching and control center for its ability to meet the demands of multiple business applications towards a multi-temporal version model, enhancing the supporting ability of the system control to construct the future model, backtrack historical model, model sharing and whatnot. This work is supported by State Grid Corporation of China.
2017, 41(10):112-116. DOI: 10.7500/AEPS20160915003
Abstract:With the rapid development of big data technology, the existing FNET/GridEye software system has been unable to adapt to future developments. As a result, a new distributed software architecture is designed and implemented based on phasor-oriented open-source and real-time big data projects: OpenPDC and OpenHistorian. The system is composed of three parts: the front cluster, the rear cluster and the system coordinator component, which has the characteristics of high system scalability and high reliability. Each OpenPDC server in the front cluster is responsible for the access to a certain number of phasor measurement unit(PMU)devices, and in which different power grid event triggers are run. When the power grid event is detected by the triggers, the system coordinator component will be notified by the multicast technology from the trigger, and the window data will be extracted from OpenHistorian by the system coordinator component, then the corresponding analysis application can be loaded to run in the application server. According to the throughput test results, stable operation for more than two years and increasing PMU devices and applications proves that the system design is advanced.
2017, 41(10):117-122. DOI: 10.7500/AEPS20160801005
Abstract:To solve the problems in high-voltage transmission line inspection, such as fixed-wing unmanned aerial vehicles(UAVs)are incapable of fine inspection and multi-rotor UAVs move slowly and require remote pilot which may pose safety risks, a scheme for inspecting high-voltage transmission lines with multiple cooperating autonomous multi-rotor UAVs is proposed. A cooperative method is discussed for inspecting high-voltage towers and transmission conductors by deploying two networked UAVs at both sides of the power line, respectively. Machine learning and multi-agent consensus control algorithms are employed to design the autopilot controller for the UAVs. According to the above work, four four-rotor UAVs and a ground station are built to validate the proposed methods. In the experiment, two pairs of UAVs are deployed to inspect the high-voltage transmission line in parallel with each other. The result shows that the UAV-station system can finish the inspection work as expected, and are free from misreported defects. Compared to the single remote-pilot multi-rotor UAV when inspecting high-voltage transmission lines, the two-UAV cooperation scheme features autopilot, and the average speed of inspection is even higher than the maximal speed of single UAV. Moreover, the average time of inspecting a transmission tower is less than half of single remote-pilot UAV's. This work is supported by Specialized Research Fund for the Doctoral Program of Higher Education of China(No. 20130185110023).
2017, 41(10):123-128. DOI: 10.7500/AEPS20160913004
Abstract:In view of the characteristics of the regional power grid, an analysis is made of the problem of long-term quit busbar automatic transfer switches(BATS)in the summer peaks or peak load periods. On this basis, a BATS strategy in real-time online analysis and closed-loop control system based on energy management system(EMS)system is developed. The system gest real-time operational information of the grid from EMS, creates the common model of BATS. The system uses a fast computing method of N-1 fault check in static safety analysis considering BATS, The Checking process takes into full account standby load sharing, action sequence, flow calculation convergence state, state estimation of bad data and other factors. and determines the optimal BATS combination according to a preset priority. After realizing the BATS strategy in real-time online analysis, the BATS closed-loop control using a secondary device remote control techique is achieved. Field application effect shows that the input rate of BATS and power supply reliability in reload transformer substation is dramatically increased.
2017, 41(10):129-134. DOI: 10.7500/AEPS20160826011
Abstract:Substation configuration description(SCD)file is important data for equipment operation, routine operation and maintenance, project management in smart substation. In view of the engineering application problems brought about by the high degree of coupling in the SCD model, the necessity and urgency of the decoupling technology about the SCD model is expounded. For the smart substation expansion project, the scheme of SCD bay physical decoupling is analyzed, and the bay modeling method based on the system specification description(SSD)model is put forward, which makes secondary devices grouped into the bay. The SCD model is decomposed into a number of bay files mainly by physical decoupling. And the unrelated bay, the correlation bay and the new bay are defined for the smart substation expansion project scenario. By means of physical isolation, automatic analysis of the relationship between the bay based on the SSD model, hierarchical signature comparison configuration modification, the unrelated bay is isolated and modification errors are avoided. The area of the configuration, debugging and testing, etc, is reduced for the smart substation expansion project. For engineering application requirements, the configuration process of SCD bay decoupling is given for the smart substation expansion project. Current main problems demanding prompt solu-tion for SCD bay decoupling are analyzed. This work is supported by State Grid Corporation of China.
2017, 41(10):135-140. DOI: 10.7500/AEPS20160925005
Abstract:In order to analyse the output characteristics, input impedance and system efficiency of series/series(S/S)compensated type wireless power transfer(WPT)system a model is set up based on transformer T-equivalent circuit. Then set the compensating capacitor as a variable to analyze the characteristics of system under the excitation of voltage source and current source, respectively. The conclusions are obtained from analysis. With respect to output, it is current source when input is voltage source and output is voltage source when input is current source under the condition the capacitor compensates for self-induction. But output is voltage source when input is voltage source and output is not voltage or current source when input is current source under the condition the capacitor compensates for leakage inductance. Input impedance is purely resistive when the capacitor compensates for self-induction. And input impedance is partially inductive when the capacitor compensates for leakage inductance. System efficiency is optimal when the capacitor compensates for self-induction. There is a corresponding load able to make the efficiency optimal whatever the compensation. Finally, the conclusions are verified by experiments. This work is supported by National Natural Science Foundation of China(No. 51307173).
2017, 41(10):141-147. DOI: 10.7500/AEPS20160802011
Abstract:For the present problems brought about by modular multilevel DC-DC converter topology and its AC balance control idea, a novel module multilevel DC-DC converter topology based on the DC control idea is proposed. By reconstructing the full-bridge submodules, each submodule capacitor contains two charging and discharging paths. The capacitors can perform power transfer and voltage self-balance through a local parallel branch formed between adjacent submodules, so as to avoid the voltage unbalance of the capacitors in the unidirectional DC power conversion. The analysis and simulation test of the balance mechanism and the basic principles of the converter show that the proposed converter can operate stably in the DC control mode, the capacitor voltage can be self-balanced, the conversion ratio is big and has the potential to be used in the different applications of DC transmission and distribution. This work is supported by National Natural Science Foundation of China(No. 51490681)and National Basic Research Program of China(973 Program)(No. 2015CB251004).
2017, 41(10):148-154. DOI: 10.7500/AEPS20160706001
Abstract:With the abrupt growth of installed capacity of wind and thermal power units in the northeast, northwest and North China, difficulties in power system operation and peak regulation are becoming increasingly outstanding. In 2014, the peak regulation ancillary service market in China was launched and run in the Northeast Grid. This market has made great effort to bring the initiative of thermal power enterprises into full play using the economic leverage and market means to further explore the potential of their peak regulation capabilities. And improvement of the accommodation of clean energy, while mitigating operation pressure and ensuring safe and stable operation of the power grid. The performance of the market shows that it has done an active exploration and played an exemplary role in enhancing the peak regulation of the power grid and improving the accommodation of the renewable energy. To further perfect the rules of the Northeast Grid peak regulation ancillary service market, this paper mainly focuses on the following topics: the historical background, design objectives, basic principles of this market, the specific rules, practical results and the operation problems, etc.
2017, 41(10):155-160. DOI: 10.7500/AEPS20160630002
Abstract:In view of the existence of illogical phenomenon of minimum energy consumption related to state shift path of load distribution of cascade hydropower plants in actual application, a study is made of the energy change relation of the cascade system and an analysis is made of the state shift path of cascade hydropower plants. Some improvements are made on the minimum energy consumption model based on a study of the energy change relationships between cascade reservoirs and an analysis of the influences of energy loss of inflow and head loss of tail water on energy consumption of the reservoir. The Wuqiangxi-Lingjintan cascade hydropower system is taken as an example to show that the optimal scheme of the improved model consumes 1. 61% less energy than that of the minimum energy consumption model, which demonstrates that the improved model can more accurately reflect the energy change relationships and laws of cascade reservoir system compared with the minimum energy consumption model. This work is supported by National Natural Science Foundation of China(No. 51379081)and State Grid Corporation of China(No. DKJS-13-00220).
2017, 41(10):161-169. DOI: 10.7500/AEPS20170109002
Abstract:The state-of-the-art development of spatial correlation based wind speed prediction is reviewed. And the concepts of conditional correlation and its corresponding confidence correlation are introduced to improve traditional spatial correlation. Based on big-data thinking, a framework of integrating data-driven with causality-driven wind speed prediction is proposed. In the framework, correlation is mined from historical data for wind speed prediction. Spatial correlation is employed to import data sources for wind speed prediction to overcome the shortage of historical data in part. Furthermore, spatial correlation with long time lag can be used to predict drastic and sudden change in downstream wind speed. Finally, suggestions for future research under the proposed framework can be made with confidence. This work is supported by the State Key Program of National Natural Science Foundation of China(No. 61533010), NSFC-NRCT(Sino Thai)Cooperation Research Project(No. 51561145011)and State Grid Corporation of China.