A Study On Wireless Sensor Networks’ Theories And Methods For The Services And Applications Of Smart Grid

Smart grid is the upgraded version of traditional power grid.With the help of wireless sensor network,smart power grid can effectively improve its energy efficiency,energy economy,energy security and environmental harmony.Owning to the limitation of coverage and transmission rate,wireless sensor network usually working at the distribution part and the consumption part.WSNs mainly provide the communication to Advanced Metering Infrastructure(AMI),Demand side Response(DR)and Distribution Automation(DA),etc.Considering the limited resources of the WSN and the various characteristics of smart grid applications and communication requirements,theoretical analysis is often indispensable.Current theory researches of WSNs have some limitations and shortages applying to the specific services and applications of smart grid: 1)most of the traditional theoretical model and optimization algorithm didn’t provide specific application scenarios,and ignored the actual performance of wireless sensor devices,which is always not appropriate for smart grid services and applications.2)The addition of new applications and the replacement of old and new equipments will cause network changes,while most of the traditional parameter optimization algorithms cannot effectively distinguish whether the fluctuation of communication performance is caused by the randomness of channel access or the actual changes of network,so they barely can cope with the network changes in smart grid scenarios.3)Traditional theoretical models often assume the node with steady load state,while the traffic in many smart grid services and applications are generated periodically,which will lead to a unsteady load state of the node.Hence,the scenario of smart grid application is beyond the scope of traditional theoretical model.In addition,most of the traditional theoretical models and optimization algorithms for DR programs assume the utility function of the appliance as convex to ensure the optimization problem be convex.However,the utility functions of electrical appliances in real life are not always convex.So many traditional theoretical models are not rational and the corresponding optimization algorithm cannot obtain the actual optimal solution.To cope with these limitations and shortages,a series of theoretical researches are carried out based on the knowledge of WSNs,the characteristics of smart grid applications as well as the communication requirements.Major works and innovative points are as follows:1)To explore the applicability of WSNs in AMI system application,an accurate and comprehensive analytical model for AMI system application in Home Area Network(HAN)scenario has proposed based on IEEE802.15.4 standard.Without directly assuming the distribution of network traffic as previous works do,the network traffic on each channel is mathematically approximated as a Poisson process by characterizing the generation process of network traffic with a series of transformations among different stochastic processes.On the physical layer,we take both modulation way and handshake mechanisms into consideration.On the Medium Access Control(MAC)layer,by leveraging the properties of Poisson distribution,a simple but accurate analysis is obtained.With further analysis,the maximum backoff times and minimum backoff exponent are determined to be the most suitable parameters for optimization in the considered application scenario,which lays a theoretical foundation for the propose of channel access parameter optimization mechanism.2)Targeting smart grid applications with a higher monitoring frequency and the event of equipment replacement,this thesis has proposed a distributed adaptive parameter tuning algorithm for better coping with both stationary conditions and dynamic conditions.The Algorithm is based on the research result of previous chapter.The algorithm provides a different angle on network condition estimation.First,with the local measured information and current values of the key parameters,each sensor node can perform a conservative evaluation of the surrounding network’s condition.The result of the evaluation is presented as a synthetic value,called the equivalent node number.Then,considering the measured reliability and required reliability,as well as the equivalent node number,the phase of parameter tuning is considered regarding whether it will be active or not.Compared with traditional parameter optimization algorithms,the proposed algorithm can provide better the network with higher reliability,effectiveness and energy efficiency,and can provide nodes with better robustness.3)In order to analyze the channel access behavior of wireless sensor nodes in the fault detection and positioning applications for transmission line monitoring,an analytical model of slotted CSMA/CA mechanism has been proposed in the thesis.The proposed model focus on the network scenario when the time interval of node’ s packet generation is close to the time of sending a data packet.The model is unfolded from two perspectives,channel state and node state.By formulating the relationship between clear channel access(CCA)operation and its successful probability from both perspectives,the statistics of single node’s behavior and whole network’s performance under different network scales and traffic loads are carried out.The prosed model can support both single CCA mode and double CCA mode.According to the simulation results,double CCA mode is more suitable for the considered application scenario.By leveraging the distribution of backoff time,an approximate method of calculating the average transmission delay for a given network is proposed.4)Aiming at the goal of improving the power consumption’s(or power supply’s)welfare of whole grid system,a power network model with suppliers,utility companies,consumers with appliances and energy storage systems has been proposed in the thesis.Based on the concept of utility function,the proposed model formulates the relationship between the power consumption of different electric appliances and the welfare provided by them.The proposed model considers the behavior of consumers and the power consumption characteristics of the appliances.Concerning the power consumption limitation of consumers and electrical appliances,an optimization problem with power consumption constraint is constructed to maximize the total welfare of the power grid.By using Lagrange multiplier method,a distributed load scheduling algorithm for optimizing the total welfare of power grid is proposed,which can accurately calculate the optimal power consumption of electrical appliances and effectively improve the total welfare of power grid.Besides,this paper proposes a charging rate adjustment strategy for energy storage equipment according to the electricity price information,which can effectively improve the total welfare of the power grid while reduce the energy waste.