With large integration of plug-in hybrid electric vehicle (PHEV) and distributed generation (DG), a good regulation ability of the power grid is required for PHEVs random charging and DG's intermittency. Considering safe and economic operation of the power grid and charging cost of PHEV owners, vehicle-to-grid (V2G) is a multi-objective and multi-constrained optimization problem by nature. A multi-objective optimization coordination model is proposed for PHEV and DG integration. Objectives of this model are maximum synthetic load ratio, minimum node voltage deviation and power loss ratio, lowest V2G service cost of the grid and charging cost of PHEV owners. By dynamic regulating PHEV charging and discharging power, power fluctuation between load and DG can be matched well and the impact of DG intermittency on the power grid will be decreased. A real 10kV feeder is simulated.
With the increasing use of Variable Renewable Energy (VRE) resources and the recent advance of battery technologies, battery would likely become a non-generation alternative to participate in the deregulated electricity markets. This paper focuses on utilizing batteries for providing frequency regulation services and taking advantage of the short term price arbitrage (price spikes) in the spot market, because batteries have quick response time, and price spikes and frequency regulation services have similar time scales. Our experiment with real market data demonstrates that the proposed dynamic State of Charge (SoC) model makes much higher profits than a static SoC operation model.
The objective of power system restoration is to restore the load as soon as possible, while the successful start-up of generator is the precondition of load recovery and the emphasis of power system restoration. In this paper, both the generator start-up sequence and the restoration path are considered. A preference multi-objective model which considers the difference of the objectives' importance is proposed. To get the most preferred alternatives, a non-r-dominance sorting genetic algorithm II (r-NSGA-II) is used to solve the model. The reference point determination method and solution set scale controlling method are proposed to improve the algorithm, which makes the solution set scale controllable and the preference to be better expressed. Simulation results show that the proposed method has practical value when solving the generator start-up problem for network reconfiguration.
This paper discusses communication channel reconstruction based on wireless sensor network for pilot differential protection. Considering communication characteristic of WSN module, this paper further studies and analyzes redundant arrangement and communication performance under hazard from the perspective of practical application. A redundant arrangement algorithm of nodes based on reliability and optimal cost of the whole communication network is proposed. And the influence of communication distance, line span and hop counts to communication delay and is studied under ADOV routine by pilot differential protection digital simulation test. The results of pilot differential digital simulation test shows that emergency protection channel constructed by wireless sensor network which uses redundancy arrangement method to do network panning can achieve strong reliability and meet the need of pilot differential protection under extreme disaster.
The construction projects for distribution networks require good economy besides energy saving and voltage quality improvement. Thus the line loss rate and voltage qualification rate are the main assessment indices of construction projects for distribution networks. This paper proposes a comprehensive energy saving potential (ESP) evaluation system for distribution networks. The above basic indices and comprehensive ESP indices for each selected feeder are calculated under different improvement measures. Firstly, typical feeders are modeled using Power Factory software. Then power flow for distribution networks is calculated and weak networks can be found. Secondly, improvement measures for typical feeders can be chosen based on weak networks analysis to achieve the purpose of reducing the power loss rate. Thirdly, the paper gives the definition of loss reduction rate, voltage improvement rate and economic benefits. Furthermore, the implementation order of the measures is optimized according to the value of comprehensive ESP indices and the difficulty extent of implementation. The investment cost and the transformation effect are considered simultaneously for planning. Four measures which include replacing high-loss transformers and worn conductors, adding reactive power compensation devices and adjusting bus voltage are carried out on the IEEE 33-bus test system. The results of simulation calculation demonstrate the validity and superiority of the proposed system.
In this paper, we mainly focus on the problems of the data processing and data security in the environment of the electricity big data systems. Firstly, we focused on the security of big data storage, as well as the big data applications, including the classification, aggregation and data mining demands. We proposed several practicable schemes to the big data applications. After that, we studied on the problem of the privacy prevention in big data processing. In this paper, we analyzed the demands of the big data privacy prevention in smart grid, and also proposed several methods. Based on the previous researches, we put forward the outline of the research hotspots for the data protection.
In order to improve the measurement accuracy of synchronized phasor in the case of frequency offset, an adaptive DFT algorithm based on shifting window symmetrical was presented. First of all, sampling window length of DFT is determined by tracking the frequency of the power grid. Secondly, the composed phasor is calculated by utilizing three sampling windows which were away from a quarter sampling window length to each other. After compensating the fixed offset, the precise phasor measurement results can be computed. In addition, in order to quickly and accurately track the frequency, a zero-crossing algorithm based on three-phase signal for measuring frequency was proposed. The simulation results show that the proposed algorithm can meet the accuracy of synchronized phasor measurement, significantly decreases the computational complexity over the conventional method, and satisfies the requirements of real time applications for the smart grid.
According to the lack of unified, standardized testing methods for the feeder automation function of distribution automation system, this paper introduces a kind of simulation testing method realization of feeder automation function, which can provide technical reference for the bidding, and strengthen the quality control and operation management of power distribution automation system. This method setups testing environment by using the DATS-1000 distribution network automation master station injection testing system, simulates feeder and typical fault under the actual working condition and evaluates the feeder automation function conformed to the standard requirements. Through the actual products testing, this simply operated method was verified, it can reduce physical impact and testing cost effectively, which indicates that can be used for feeder automation function testing and also can be acceptance for the power distribution automation system simulation test and site.
With deep study of UHVDC, pure electromagnetic or electromechanical-electromagnetic hybrid simulation cannot meet the need of analysis of transient characteristics of UHVDC. In this paper, take ±800 kV Jinsu UHVDC project as background, Jiangsu power grid with Jinsu UHVDC accessing was built in RTDS, true-type device of UHVDC control and protection was taken. To ensure that the size of the grid while guaranteeing the DC system transient characteristics of the protection and control. Take an AC fault occurred in history of direct near placement as background, the simulation results of using the true-type simulation systems built and traditionally electromechanical-electromagnetic hybrid system were compared with the real fault recorder. The results shows the true-type device of UHVDC control and protection performance remain highly consistent with actual UHVDC project in protection functions, behavior and trends of steady-state operating conditions.
The paper studies the impact of power grid operation state and communication delay on current differential protection with a probabilistic method, and a false-trip probability model is proposed. First, the mechanism of false-trip of current differential protection is introduced and the quantitative relationship between differential current and power grid operation state and communication delay is derived. Then a false-trip probability model based on current differential protection action criterion is proposed with a probabilistic method. Simulations show the validity of the model. Based on the false-trip probability model, the key factors affecting false-trip of current differential protection are analyzed, and some useful conclusions are drawn.
As its sampling frequency is independent of the scale of the system, Monte-Carlo simulation is widely applied to reliability evaluation of generation and transmission system, which is a complex large system. However, it takes a relatively long period to obtain a higher accurate reliability index. This paper points out that, the combination of Importance sampling method and Discrete Latin Hypercube sampling method is able to reduce the variance of the sample space and uniformly sample it simultaneously, which improves the convergence of Monte-Carlo simulation. Besides, the combination of sensitivity analysis and linear programming in the process of overload correction is able to guarantee the solution optimality as well as improve the solving speed. Finally, the practicability of the proposed algorithm is verified with the case study in IEEE RTS79 and RTS96.
With the increasing of the new energy's permeability in the regional power network, the inherent characteristics of new energy output bring new challenges to the power network planning. In order to solve the problem that the traditional distribution network planning is too conservative for the new energy planning, a planning method for siting and sizing of distributed generation (DG) based on Chance-constrained programming is proposed in this paper. The method provides an approach to calculate the new energy's maximum installation capability and the optimal installation site for regional power network Basing on the analysis of stochastic models of wind power, solar output and load, the planning model has the objective function of maximizing renewable energy utilization with the considering of several constraint conditions such as node voltage constraint and branch transmission power constraint. The particle swarm optimization (PSO) algorithm and Monte-Carlo simulation method is used to solve the optimization problem. Taking a regional power network as an example, Power System Analysis Software Package (PSASP) is used to carry out transient and steady stability verification for the extreme scenario, and contingency plans for the accidents which is not satisfied with the verification requirement must be worked out to ensure the safe and stable operation of the network.
Combining switching characteristics of power electronic devices and state transitions in carrier phase-shifted SPWM (CPS-SPWM), this paper uses graphic Stateflow toolbox of Matlab/Simulink to design the process of CPS-SPWM. Then it is applied to STATCOM which is integrated with distribution transformer (DT-STATCOM) for PWM signal generation. Simulation results are presented to prove that the method is valid and effective for reactive power compensation. Meanwhile, software-in-loop (SIL) test and automatic code generation are also carried out. Results of experimental test with DSP TMSF28335 have validated the theoretical contributions of the paper. PWM signal comparison of both simulation and experiment result shows that this method has both the feasibility and effectiveness of software and hardware design. With this method, design of CPS-SPWM can be more rapid, efficient and convenient.
The regional security and stability control system is an important tool to ensure the safe and stable operation of modern power system. The communication system can provide information exchange among the stations for the regional security and stability control. Hence, the reliability of communication system is one of the important factors that need to be considered in the design of the control system. In this paper, firstly, the regional security and stability control system is divided into centralized control structure and distributed control structure using the decision-making method. Secondly, the evaluation index of the communication status for the control system is given. Thirdly, the differences of the communication networks based on centralized control and distributed control structure are analyzed comparatively. And finally, the design method of the control system based on centralized control as well as distributed control structure is proposed.
Load prediction is becoming difficult due to the larger, lighter and more flexible blades of large-scaled horizontal axis wind turbine (HAWT), which leads to the nonlinear aero-elastic responses. Based on geometrically exact beam (GEB) theory for blade structural dynamics, a free-vortex wake (FVW) model for the prediction of unsteady aerodynamic loads and a partitioned loosely coupled methodology to exchange the data at the interface, a nonlinear FSI model has been developed in this study. Through comparison of NREL UAE Phase VI experimental data and the load predicted by the nonlinear model, the capability to accurately predict the aerodynamic loads is validated. The nonlinear beam model is also validated by several cases which all show a good agreement with results obtained by other authors. Finally, dynamic responses for NREL 5 MW RWT are estimated and compared with results from linear model. The results show that the coupled method is capable of evaluating blade nonlinear responses for large-scaled HAWT.
Microgrid has played a crucial role in solving problems caused by integration of distributed generation and therefore be comes an effective and efficient means for promoting renewable energy utilization and improving power supply reliability. This paper summarizes the key technologies and standardization needs for microgrid development and applications, based on the market needs and industry status. Some key features of a microgrid that distinguish it from traditional power grid and smart grid are de scribed. After review of the relevant activities currently under going in IEEE and IEC, recommendations for microgrid standardization based on the existing work are proposed.
In order to enhance the frequency response capability of the power systems, the EV (electric vehicle) clusters and AC (air conditioner) clusters are used as response resources to maintain the system frequency within an acceptable range. The frequency control strategies of the EV clusters and AC clusters are given respectively. A load assessment index is proposed to evaluate the available response capability of the EV/AC loads in real time. Then an EV-AC coordination frequency control strategy is developed. The control sequence of the two controllable loads is determined by their impacts on the comfort level of EV/AC users. In the case study, a simplified frequency regulation model is used to investigate the effectiveness of the proposed strategy under two frequency events, the simulation results show that utilizing the EV/AC loads to stabilize the system frequency can reduce the frequency deviation to some extent without serious impact on the comfort level of users.
In this paper, Gini coefficient is introduced into the allocation of investments in electric power subsidiaries. First, three indicators including the return on total assets, future forecasted electricity consumption and the investment to electricity sales ratio are used to determine the initial allocation scheme of future grid investment in subsidiaries. The initial scheme ensures benefits (efficiency) priority. Then, control indicators such as the capacity-load ratio, power grid reliability are used in designing investment allocation model based on the Gini coefficient. The proposed model optimizes the initial allocation scheme from the perspective of improving the fairness. Finally, a provincial electric power company in China is taken as an example to verify the feasibility of the proposed model.
Power electronic transformer (PET), the key equipment for future smart grid, is vital for the whole power grid to be in normal operation. The mathematical relationship between the DC-link voltage and the system parameters for PET were analyzed in this paper. Based on the analysis, the optimal DC-link voltage for PET is obtained by mathematical deduction. Then, a novel adaptive voltage regulation method is proposed, in which the DC-link voltage reference value will be maintained in the required optimal voltage level, and it also can be adaptively changed according to different grid voltage levels and load levels. Therefore, PET can avoid the grid voltage and load level fluctuation impact on the input current distortion and output voltage stability. Finally, representative simulation results in PSCAD/EMTDC verify the validity and effectiveness of the optimal DC-link voltage design and the proposed adaptive voltage regulation method.
Research on interaction impacts on UHVDC after fault in receiving-end power grid is important for improving stability. In order to research the running stability of the receiving end grid under typical fault take Jinsu UHVDC project as background, the sending grid and also the entire main grid of Jiangsu outside Jinsu UHVDC were established base on ADPSS. In accordance with the actual project DC line, filters, converter transformer and other DC electromagnetic transient model. The influence of typical faults on the receiving end grid such as AC bus fault, three-phase short circuit on line and bipolar locking were analyzed. Finally, restart procedure of bipolar locking were studied. Simulation results shows that serious fault may lead to DC bipolar locking, bipolar blocking or typical fault in AC system; Jiangsu power grid can restart smoothly after bipolar blocking, but the receiving end power grid can keep stable operation after bipolar locking.
