Research On Control Of Frequency And Voltage For A Microgrid

As the shortage of traditional energy,the new energy has become the focus of future development.The technology of the microgrid has become an effective way to make use of the new energy.The intermittent and uncertainty of the natural internal power output power and the random load fluctuations lead to imbalance of power in the internal microgrid,and further affects the frequency and voltage stability of the microgrid.So it is necessary to control the frequency and voltage effectively.There are three operating states in the microgrid,that is,grid-connected state,islanded state and switching state.In this paper,frequency and voltage regulation in the grid-connected state and islanded state is studied.The third chapter studies the frequency control of the microgrid,and the frequency regulation scheme based on microgrid power manage system is proposed.Frequency control is realized through microgrid power manage system.The regulation power is calculated,corrected and distributed among DGs by microgrid power manage system.And the rolling average method and the segmental average method are used to correct the link of microgrid power manage system.Though both the two methods can realize the stability of the frequency,the rolling average method can realize the more control effort.The fourth chapter studies the voltage control of the microgrid,and the secondary voltage regulation scheme of the islanded microgrid is proposed.As the relationship between the voltage control and reactive power control is similar,three voltage control objects are proposed.Voltage control,reactive power control and voltage-reactive power control are analyzed in detail and simulation studies are carried out.The results of simulation show that the effects of three voltage control strategies are obvious differences.Suitable control target should be choosed according to the request for the actual system.The fifth chapter studies the frequency control and the voltage control of the grid-connected microgrid.A new control strategy based on the back-to-back converters as connection device is proposed.The USC of the public side takes the direct current control,and the control objective is to maintain the stability of voltage of the dc link.The constant power control is adopted for the MSC of the microgrid side,and the control objective is to output a constant power.The control of the frequency and voltage is achieved by active and reactive power control,and the microgrid power manage system be designed active power management subsystem and reactive power management subsystem.The microgrid power manage system collects the real-time signal of thefrequency and voltage,generatse and distributes the power regulation,and realize the power control on the PCC.Simulation is carried out during the heavy load cutting and the switch between the grid-connected state and the islanded state by the proposed control strategy.The results shows that the microgrid can maintain the stability of frequency and voltage under the above cases.