Research On Operation Control Of DC Microgrid

At the same time of energy shortage and environmental deterioration,technology and society are also making continuous progress and development,and the attention of the microgrid has gradually increased.Compared with the traditional distribution network,the microgrid has many advantages.Microgrid can improve the utilization rate of clean energy,integrate multiple distributed generators to coordinate work,and its structure is flexible and changeable.In microgrid,there are many types of DC units,such as photovoltaic cells,storage batteries,fuel cells,DC loads and so on.Compared with AC microgrid,DC microgrid has unique advantages,such as flexible control,simple structure,no need to consider the converter link,in addition to reactive power,frequency and other factors do not need to be considered,which can better improve the utilization of renewable energy.In this paper,the stable operation of islanded DC microgrid is studied.In this paper,the working characteristics and principles of photovoltaic power generation unit,battery unit and fuel cell unit are introduced,and the related converters are analyzed in detail.For photovoltaic cells,this paper studies two control methods,namely MPPT and CVC control,and simulates the two control modes through Matlab/Simulink under the condition of light intensity and temperature change.Considering the insufficiency of the control of the droop control on each unit,it is easy to cause the fluctuation of the DC bus voltage.This paper proposes a variable droop control strategy and applies it to the control of the battery and fuel cell.In addition,the simulation comparison analysis between the droop control and the variable droop control is also carried out by Matlab/Simulink.The results show that the variable droop control strategy proposed in this paper can make the DC bus voltage in a more stable state.Power balance and bus voltage stability are the two most important points in DC microgrid.Therefore,for the stable operation of the system,the bus voltage is divided into sections,which are divided into several modes.The control operation of each microgrid supply is studied in each mode.The microgrid control changes caused bythe conversion between various modes are also studied.The control strategy proposed in this paper is simulated by Matlab /Simulink.The results show that when the external conditions and loads change,the DC bus voltage can be maintained in a stable state through the coordinated control of the micro power supply.