| With the increasing global energy and environmental crisis,the new energy will become an important part of the future energy system.As a small scale power system that integrates distributed generators(DGs),energy storage elements and loads together,the microgrid is the trend of the future new energy.Due to the randomness and the geographically distributed of the DGs in the microgrid,the traditional centralized control method becomes inappropriate to the microgrid cooperative control.The hieratical networked distributed cooperative control based on the wireless sensor networks(WSNs)has attracted wide attention.Combined with the recent research results at home and abroad,this paper proposed the distributed secondary cooperative control,secondary cooperative tracking control,secondary robust restoration control based on the WSNs for the microgrid output frequency and voltage.And the WSNs communication delay and reliability,the data sampling time's effects on the microgrid control system are obtained by theoretically analysis.Then,according to the microgrid control system communication requirements,an end-to-end performance optimization algorithm which can meet the requirements of the microgrid WSNs communication reliability and real-time property is presented.The main research work of this thesis is as follows:(1)A distributed cooperative secondary optimal control with packet loss for islanded microgrid is proposed.For the microgrid WSNs data packet loss,the communication information may be unavailable to the microgrid control system.Thus,we adopt a distributed consensus Kalman filter to evaluate the incomplete data,which has superiority in dealing with the communication packet loss.A small-signal model of the microgrid output voltage/frequency secondary control is proposed and a corresponding packet loss model is presented.Then,with the constraint of the quadratic cost function,an output feedback-like controller is eatablished to achieve optimal voltage/frequency restoration.Finally,combined with the communication quality problem to the control method,we obtained the microgrid networked closedloop system and the stability analysis.The simulation results show that the approach can restore the voltage and frequency with accurate performance.Compared to the distributed-averaging proportional-integral method(DAPI),our proposed microgrid secondary networked optimal method can achieve better robust performance when communication packet loss rate is 30%.(2)A distributed cooperative secondary tracking control for islanded microgrid with Markov time-varying delays is proposed.For the microgrid WSNs,the communication delay is usually stochastic and time-varying.Considering the congestion degree of the network channel,the delay of current transmission is usually related to the previous one.We model the microgrid WSNs stochastic time-varying delay with Markovian characteristics.Inspired by the stochastic theory,the global closed-loop stochastic model and the corresponding global stability analysis of the islanded microgrid networked control system with stochastic Markov time-varying delays are derived.And the control gain parameters margin and upper bound of communication delays for the distributed secondary control of the islanded microgrid can be derived from the stability theorem.The simulation results show that the approach has accurate regulations on voltage/frequency restoration to their reference and active power sharing in terms of load variations,plug-and-play capability,communication delays.In addiation,compared to other method,the approach has better control performance and faster convergence speed when the communication delays are 14 ms.(3)A distributed robust secondary voltage optimal control for islanded microgrid with nonuniform delays is proposed.Motivated by dealing with the microgrid WSNs nonuniform network-induced delay and investigating how sampling time affects the control performance,in this paper,we propose an energy-to-peak robust performance to quantitative analyze the robust performance of the microgrid voltage control system.Considering the tracking synchronization characteristic of the microgrid voltage control,inspired by the consensus algorithm,we model the microgrid output voltage secondary controller in the discrete-time model.A distributed secondary voltage control for microgrid with nonuniform delays is presented.Then,the global closed-loop stochastic model is eatablished,and the corresponding global stability and the energy-to-peak robust performance analysis theorems of the islanded microgrid are derived.Based on the above theorems,the feasible optimal voltage control gains can be obtained.The impact of sampling time on the secondary voltage control performance is also quantitative analyzed.The simulation results show that the voltage secondary robust approach can maintain accurate microgrid voltage restoration with communication delays.(4)An end-to-end delay optimization algorithm for distributed multi-hop wireless sensor networks in microgrid is proposed.For the WSNs communication quality and sampling time requirements in the microgrid distributed cooperative secondary control,by maximizing the packet arrival rate,an end-to-end delay optimization algorithm is presented to obtain the minimum sampling time in the microgrid control system which can obtain desirable soft Qo S guarantees.Inspired by IEEE 802.11 standards and the basic Probability theorem,combined with the M/M/1 queue theory,we derived the end-to-end delay model and the end-to-end delay distribution of the distributed multi-hop wireless sensor networks.An end-to-end delay optimization algorithm by maximizing the packet arrive rate is presented.The simulation results verify the wireless sensor networks parameters' effects,such as packet arrival rate,maximum backoff contention window size,hop number,and data packet size on the end-to-end delay performance.And the optimal packet arrive rate which meets desirable WSNs soft Qo S guarantees is obtained. |
PDF Full Text Request