| With the development of the smart metering technologies,demand response is participated in the frequency control of the power systems.By some kind of control method,demand response can response to the changes of the frequency of the power systems,and thus the frequency can be regulated real-time.Further research is needed on the mechanism of the demand response participation in frequency control as well as its control methods in order to utilize the demand response resources in the frequency control.Nowadays,increasingly penetration of renewable energies has brought lots of challenges to the power systems' stability and reliability.In such situation,there is much important practical significance in researching on the demand response for the frequency control.The mechanism of demand response in the power systems frequency control is analyzed under different circumstances in this thesis.The main contents are as follows.Firstly,a microgrid system which is consisted by a small hydropower and wind power is introduced.The principle of demand response participating in microgrid frequency control is analyzed,and a mathematical model is established based on it.Besides,the simulation model of demand response in microgrid frequency control is built by using MATLAB/Simulink,and the simulation analysis is carried out.Secondly,the operation principle and mathematical model of doubly-fed induction generator(DFIG),as well as the frequency adjustment principle and control method of DFIG participating in the power systems are analyzed.A simulation model containing demand response and wind power for microgrid system frequency control is established by using MATLAB/Simulink.The simulation results show that the frequency stability of microgrid can be improved obviously by the combination of demand response and wind power generation.Thirdly,the principle of demand response participating in multi-area power system frequency control is considered.The fuzzy principle based on the cloud model is given,and the fuzzy control is applied to the multi-area power system frequency control.The designed method of fuzzy controller is applied on the basis of the mathematical model.The program of demand response participating in three-area power system frequency is applied to various operation states.The simulation results show that the fuzzy controller can improve the frequency adjustment characteristic of multi-area power system effectively.Finally,considering the case of the communication delay,the networked control is used to control the demand response participating in the power system frequency control.A mathematical model of multi-area power system frequency control is established in the case of network delay.By using linear matrix inequality method,sufficient conditions for the H-infinity control of the system has been obtained and the state feedback gains can be obtained with the LMI tool box.The simulation shows that the robust controller can obtain better control effect even under possible network delay.From above analysis,it can be found that the control methods designed in this paper have a good effect and have a potential application in the field of demand response participating in power system frequency control. |
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