2014, 38(6):1-5. DOI: 10.7500/AEPS20130826005
Abstract:Under the condition of unbalanced economic progress and geographical distribution of natural resources in China, high voltage direct current (HVDC) transmission is playing a more and more important role in energy saving, emission reduction, and optimization of resource allocation. To steadily improve the reliability of the operating HVDC systems and provide a full view of the operating HVDC conditions in State Grid Corporation of China (SGCC), this paper takes the HVDC systems, ultra high voltage direct current (UHVDC) systems and back-to-back HVDC systems as the research objects, and a statistical analysis is made of the forced outages using the yearly operation data. An assessment is made of the systems’ operating conditions from the perspective of the extreme weather, equipment fault, and external damages. By referring to typical case studies of faults, the security situation the SGCC is in is made clear. The weak links in the systems available are analyzed and relevant suggestions are made.
2014, 38(6):6-13. DOI: 10.7500/AEPS20131009012
Abstract:In light of the significance of the random characteristics of photovoltaic (PV) power generation to research on power system planning and operation involving PV, an analytic method is proposed for assessing the stochastic characteristics of PV power stations by separating the certainty and uncertainty stochastic parts of PV output time series. The global solar radiation model is adopted first to model the certainty part of the PV output, while the concept of PV output shedding factor is introduced to assess the uncertainty part of PV output to form a complete model description. By means of empirical analysis of real data of PV, the stochastic characteristics of the PV output shedding factor, in terms of the probabilistic distribution and the intermittency are investigated along with the spatial correlation of PV output.
2014, 38(6):14-19. DOI: 10.7500/AEPS20130830010
Abstract:An ultra-short-term wind power prediction method based on an online sequential extreme learning machine (OS-ELM) is proposed. Firstly, the OS-ELM is utilized to correct the predicted wind speed sequence so as to amend and improve the accuracy of predicted wind speed. Then, by combining batch processing with successive iteration, real-time prediction of wind turbine power output is accomplished with the help of the advantages of OS-ELM’s fast learning speed and strong generalization ability. Finally, a Bootstrap method is adopted to estimate the predicted intervals by resampling data. Analysis results show that, compared with the back propagation (BP) network and support vector machine (SVM) method, this prediction method can better meet the demand of online application and has good application prospects, while its forecasting accuracy is comparable to BP network and SVM method.
2014, 38(6):20-25. DOI: 10.7500/AEPS20130504002
Abstract:In order to maximize the match between the output of the hybrid wind/photovoltaic/energy storage system and the scheduling curve, the energy storage device is optimized and controlled one day ahead. Owing to the fuzziness of the wind and photovoltaic output, an optimal control method of energy storage is proposed based on a fuzzy correlated-chance programming theory. This method considers the constraints of the energy storage device including the power output and energy constraints, and the matching degree of each time is represented by the credibility value. So the final goal is to maximize the mean value of the total credibility within a day of 96 periods. By using the fuzzy simulation based genetic algorithm, the different periods of energy storage charge and discharge power corresponding to the credibility of the maximum mean value can be obtained. Numerical results analysis shows that the proposed optimal control strategy is valid for maximizing the match between the output of the hybrid wind/photovoltaic/energy storage system and the scheduling curve.
2014, 38(6):26-32. DOI: 10.7500/AEPS20130701001
Abstract:The ability of absorbing the disturbance of wind power generation has become a bottleneck to the development of the wind power. Because of the lower load response rate, traditional thermal power units cannot meet the requirement. The pipe line, heat exchanger and radiator in the heat supply network of heat supply units have huge capacity of thermal storage, which can be used to improve the load response rate within a short time. Based on the idea of experimental verification, by nonlinear multi scale decomposing of automatic generation control (AGC) load order, the load order of heat supply units is constructed. According to the simplified nonlinear dynamic model of typical heat supply units, the optimization control scheme for units is designed. The scheme can take full advantage of the thermal storage in the heat supply network, which can improve the load response rate of the units drastically and can compensate the stochastic disturbance of wind power generation without the influence on the heat consumer.
2014, 38(6):33-37. DOI: 10.7500/AEPS20130418012
Abstract:Two new bifurcations in time-delayed power systems, the oscillation disappearance bifurcation (ODB) and oscillation emergence bifurcation (OEB) found in a previous study, are explored and discussed. Their definitions are given first according to the transform of the system eigenvalues. Further, an approach to determining the occurrence of ODB and OEB in time-delayed dynamic systems is proposed. It uses the information on the disappearance and emergence of the real solution branches of the Lambert W function. A typical one-dimensional time-delayed system and WSCC 3-machine-9-bus system with time delay are then selected to show the mechanism of two bifurcations and to validate the given approach. Since OEB and ODB are closely related to the emergence and disappearance of the system oscillation modes, the study under discussion is helpful to power system stability analysis with time delays.
2014, 38(6):38-42. DOI: 10.7500/AEPS20130712018
Abstract:In order to further study the operation mechanism of the Central-North China AC synchronous power grid, this paper simplified this power grid into a 7-machine 48-node equivalent system. The equivalent system well retains the power flow static characteristics, tie-line power dynamic characteristics, the impact of large disturbance characteristics and short-circuit current characteristics of the original power grid. By the simulation analysis of the equivalent system, this paper preliminarily proves that the system UHV AC line splitting resulting from the serious fault occurring in Sichuan power grid is an angle instability problem. Based on this, a practical measure is proposed to improve the system stability.
2014, 38(6):43-48. DOI: 10.7500/AEPS20130724001
Abstract:Development of the smart grid technology requires fast electromagnetic transient simulation, which is provided with a highly-efficient simulation environment and platform by ever-increasing widely-used graphic processing unit (GPU). First, this paper puts forward two fine-grained parallel operational-level strategies, which are parallelisms based on single instruction multiple data (SIMD) and shared memory. Next, fine-grained parallel electromagnetic transient simulation algorithms for GPU are designed, and simulation procedures are implemented by adopting the two strategies in the improved electromagnetic transient algorithm. Test results of pulse-width modulation (PWM) converters show that, the fine-grained parallel simulation algorithm for GPU enhances simulation efficiency enormously while maintaining accuracy. It's also shown that the algorithm is especially useful when dealing with large system simulation problems.
2014, 38(6):49-54. DOI: 10.7500/AEPS20130802005
Abstract:A substation topology error identification method based on uncertainty reasoning is proposed. Topology error identification rules are divided into four categories according to different data types and relationships used by each rule. An inaccurate model for each of the data in substation and topology error identification rules is developed. The integrated certainty factor value of each circuit breaker and switch is calculated by using the transfer algorithm and synthetic algorithm of uncertainty reasoning. The results are used to determine the status of each circuit breaker and switch. This substation topology error identification method has high redundancy using the three-phase multi-source data in substation and has improved the ability of identifying the switch status and solved the problem of conflicts between rules. Simulation for the multiple topology errors with multiple bad data has validated its effectiveness and high reliability.
2014, 38(6):55-60. DOI: 10.7500/AEPS20130618011
Abstract:Avoiding infeasible solutions is essential for fast reconstruction of a distribution network. A coding method without infeasible solutions is put forward by automatically generating the basic ring matrix, and an improved harmony search algorithm is used for solving the networks reconfiguration mathematical model. In order to make full use of the information in the harmony memory bank, the considering probability and trimming probability of the harmony memory bank are improved by imitating the fuzzy clustering method, so both probabilities can adaptively vary with the variation of particle information of the memory bank. Results of simulation on 33-node and 119-node networks show that the improved harmony algorithm has a faster optimization and a better convergence. The validity of this algorithm is also proved by the results.
2014, 38(6):61-67. DOI: 10.7500/AEPS20130505006
Abstract:A method of responsibility proration among multiple three-phase unbalanced sources based on the reference impedance method is proposed． A mathematical model of responsibility proration among multiple three-phase unbalanced sources is developed， four quantitative indices are defined， and the detailed implementation steps are given． The validity and rationality of the method are proved by a simulation system model with three users and the measured data of a 10 kV power system in a steel plant． Finally， the sensitivity analysis between reference impedance and quantitative indices shows that the error of the method is small owing to the improved accuracy of the responsibility proration among multiple three-phase unbalanced sources.
2014, 38(6):68-74. DOI: 10.7500/AEPS20130629002
Abstract:The security protection system of the secondary power system has no central management and auditing, and the public key algorithm of existing security systems is RSA algorithm. So a design and implementation scheme for security supporting platform based on domestic SM2 cryptosystem is proposed. First, the difficulty in making the security supporting platform upgraded to support the SM2 algorithm is pointed out. Then a scheme of building the self-developed security encrypted channel with the component technology is proposed to ensure the SM2 algorithm can be realized in the security supporting platform. Finally, the application function of integrated security supporting platform is tested and analyzed. The results show that this platform can achieve smooth integration among the applications of the secondary power system, while providing safe identity authentication, effective access control and authorization management, safety auditing logging, and user management. What’s more, the security support platform can centralize the identity authentication and the access control. The platform has been applied in a certain provincial power grid, which has proved its availability in actual projects.
2014, 38(6):75-79. DOI: 10.7500/AEPS20130704011
Abstract:In the background of “large operation”, the wide area distributed prefecture-county integrated dispatching automation system can greatly conform to the construction need of prefecture-county smart grid dispatching automation. But the wide area distribution of data acquisition, various applications and the computer nodes is bound to bring about the risks of more faults and lower reliability as well as the data inconsistency caused by the network faults. The design of network division/recovery mechanism is intended to solve the problems of the prefecture-county dispatching operation due to the network faults. The wide area distributed prefecture-county integrated dispatching automation system is briefly described, with emphasis on the key technology and principles of the network division/recovery mechanism. It is proved that the communication network division/recovery mechanism can effectively safeguard the operation of the wide area distributed prefecture-county integrated dispatching automation system as can be seen from field projects in operation.
2014, 38(6):80-84. DOI: 10.7500/AEPS20130622006
Abstract:The permanent magnet synchronous motor (PMSM) used in wind turbine and electric vehicle situations usually has to directly track the torque command issued by the main control system. As a matter of fact, however, no torque test components such as a torque sensor is available in an actual system. So the exact acquisition of the observed torque is of utmost importance for the torque control system. To enhance the torque observer performance, this paper proposes a real-time stator flux linkage observation method based on a minimum extended flux linkage observer, through which the stator flux linkage and the electrical torque are calculated. The proposed stator flux linkage observer is not only free from the flaws of the traditional pure integral strategy, such as saturation, phase shift, amplitude deviation, and so on, but also, as a pure integral strategy, is robust for parameter deviation, namely, the precision of the observed torque is basically unaffected by the direct- and quadrature- axis inductance and the rotor flux linkage. Simulations and experiments on an 11 kW PMSM have validated the performance of the proposed method.
2014, 38(6):85-90. DOI: 10.7500/AEPS20130613013
Abstract:An implementation method for hysteresis-band current tracking for active power filter (APF) based on digital over-sampling is proposed, which enables precise compensation of harmonic current and stabilizes the switching-frequency. This method can meet different dynamic response demands of control and operation modules by utilizing different extraction factors of digital chip over-sampling. And it fully coordinates two kinds of operations in the digital signal processor (DSP), the sampling interrupt operation and main loop operation, which ensures real-time harmonic current detection and synchronous tracking for the compensating current.The same reference will be tracked N times and the change of power switching device status depends only on the parameters of the preceding switching-period, resulting in high precision tracking for current. Compared with the traditional hysteresis-band current control method, the proposed method has 0the advantage of not only stabilized switching-frequency but precise harmonic compensation as well, proving its applicability and reliability. A 65 kVA experiment system for three-phase three-wire APF is built for verification and the validity of the proposed method is confirmed by experimental results.
2014, 38(6):91-97. DOI: 10.7500/AEPS20130411011
Abstract:Frequency response analysis is an important method of detecting transformer winding deformation. Experienced professionals are able to judge winding deformation accurately by qualitative analysis of the frequency response data atlas. Firstly, the qualitative analysis methods for frequency response data are summarized. Secondly, according to the characteristics of the qualitative analysis, the mathematical morphology is introduced and the quantitative analysis for the amplitude difference is researched. The frequency domain is defined to divide the extreme points of the frequency response data into matched extreme point, shifted extreme point, lost extreme point, excess extreme point and the quantitative analysis for the extreme points is researched. Finally, the block frequency point method is proposed. The main points of the qualitative analysis for frequency response data atlas are mathematically presented with the block frequency point method, and the quantitative analysis for frequency response data is realized. The effectiveness of the method is proved by verification of an example.
2014, 38(6):98-105. DOI: 10.7500/AEPS20130531012
Abstract:Currently the analysis of sympathetic inrush mechanism is usually based on no-load operating transformers. The complex sympathetic inrush when a transformer operates with load is studied less often. The analytical expressions for the transformers flux linkages, the source and load current, when one no-load transformer is energized and the other is operating with load, are derived to obtain the influencing factors and key characteristics of the complex sympathetic inrush. Besides, the impact of sympathetic inrush on the current differential protection for generators is analyzed. Digital simulation, dynamic simulation test, and the on-site recorded data have proved the validity.
2014, 38(6):106-111. DOI: 10.7500/AEPS20130717010
Abstract:Real-time synchronous acquisition of wide-area information is the key technology of realizing panoramic information acquisition in the intelligent substation. Based on a study of global positioning system (GPS) sampling data synchronization, a method of realizing closed-loop calibration system of synchronous sampling clock based on the field programmable gate array (FPGA) is proposed to make up for the inadequacy of synchronous sampling clock’s high dependence on the oscillator clock in conventional merging unit and relatively larger output error in the case of aging of the oscillator and reduced accuracy of frequency. By analyzing the output errors of two synchronous sampling clocks quantitatively, it is revealed that the output error can be reduced by software compensation using this method, which ensures accordance of the output phase as well as improves accuracy of the synchronous sampling pulse output. It is verified that the synchronous sampling value of the merging unit can meet the 0.2 s class accuracy standard when an ordinary quartz oscillator is used, reflecting good synchronization.
2014, 38(6):112-116. DOI: 10.7500/AEPS20130601003
Abstract:Proceeding from the hardware structure and software configuration of smart substation design, the function distribution and structure characteristics of the secondary system are analyzed. The implementation process and software configuration of an information model of the IEC 61850 standard are investigated. In light of the demand for design expression method of the secondary system, a simultaneous design method based on standardized virtual terminals and virtual secondary circuits is proposed. Based on the virtual terminals and traditional secondary circuits, the design drawings and the data model configuration for the IEC 61850 standard are integrated, and the logic connections implicit in the information model are expressed in the form of visual working drawings. Network connection charts, sampling value (SV)/generic object-oriented substation event (GOOSE) information flow charts and virtual secondary circuit charts are employed to fully reflect the information connections of devices. The design expression is conducive to a clear understanding and mastery of the mutual information of the smart equipment by construction and debugging personnel, and will improve the operation efficiency on the spot.
2014, 38(6):117-122. DOI: 10.7500/AEPS20130624005
Abstract:To further save the energy and reduce the system power generation cost, a real-time generation scheduling model is proposed. In this model, different models and different distribution strategies for the positive and negative power deviations generated by unit power output regulation can be adopted. The piecewise regulation cost of unit power regulation is introduced, then the different control and distribution strategies can be realized by setting different regulation costs. An actual provincial power system in China is tested. The results show that the model can adjust the unit power in a rational way according to the planned principle, and well track the day-ahead schedule. The model also satisfies the limit values of network constraints.
2014, 38(6):123-127. DOI: 10.7500/AEPS20130606007
Abstract:In a nuclear power plant, between the generator terminal and the step-up transformer, generator circuit breakers are installed, and generator circuit breaker failure protection is also installed. This paper analyzes the protections and the value settings of the nuclear power plant generator, and points out the problems in the generator circuit breaker failure protection design. First, in the protection of some jump starter generator circuit breakers, de-excitation, and the main valve closing, as the current criteria are not satisfied, the starter generator circuit breaker failure protection cannot be directly activated. Secondly, during the turbo-generator program tripping process, the generator circuit breakers break down and cannot trip, neither can the generator circuit breaker failure protection be activated. Based on the harm caused by these problems, this paper proposes some improvements on the nuclear power plant generator breaker failure protection design, further improving the generator circuit breaker failure protection design in the nuclear power plant.
2014, 38(6):128-135. DOI: 10.7500/AEPS20130819007
Abstract:Based on an analysis of the cause and developing process of blackouts in a super megacity power system, the key factors endangering the security of the system are pointed out. The power system intrinsic physical characteristic is expounded that in the overload condition of a power transmission grid in the receiving-end grid, the interactions between various electrical variables can cause the system state to deteriorate gradually during the adjustment process of the generator units in the receiving-end grid. By referring to the characteristics of the receiving-end grid in a long distance power transmission system with large capacity and the problems from increasing penetration of intermittent generation sources, the weak links of the security analysis, security assessment and security defense system are discussed in terms of power grid planning and operation control, respectively. Countermeasures to reduce blackout risk are presented. A new expatiation and recommendation on the configuration of three-precautionary lines for insuring the security of the power system is put forward.