Stability Control Strategy Of Bus Voltage For DC Microgrid

As an effective supplement to the modern power system,distributed power generation can significantly improve the utilization efficiency of new energy,and it has become one of the important trends about development of the power industry in the future.The increasing penetration rate of various renewable power generation units in the power grid may have many negative impacts on the safe operation of power systems.In order to improve environmental pollution problems and achieve local consumption of new energy sources,micro-grid technology emerges as the times require.At this stage,the application of AC micro grid in practical engineering is more common,but with the change of load type and the popularity of household PV,DC micro grid with simple structure and less loss has been widely recognized by scholars.At the same time,There is no problem of reactive power component and phase distribution in the DC micro grid.The DC bus voltage is an important indicator to measure the operation control of the system.Therefore,it is of great significance to study the bus voltage of the DC micro grid.In this context,this paper will focus on photovoltaic cells,battery energy storage and various types of power electronic converters,and analyze the control strategy of the island-type DC micro grid.Firstly,this paper briefly introduces the background of DC micro grid technology,and reviews the control strategies of the popular DC micro grid at the current stage,and it establishes the research method at the system level,and then it builds a photovoltaic cell,Battery storage and load unit based DC micro grid model.The mathematical model,output characteristic curve and maximum power control algorithm of photovoltaic cell are analyzed.The effectiveness of the algorithm in the change of external conditions is verified by MATLAB software simulation.Then the common DC micro grid energy storage form is introduced.The mathematical principle of battery energy storage is introduced,and the topology and operation principle of Boost converter and Buck-Boost converter in the system are analyzed in detail.Secondly,the control strategies of Boost converter and Buck-Boost converter are studied in depth.According to the power balance equation in the system and the output characteristics of the photovoltaic unit itself,the maximum power tracking control and constant voltage control are designed for the Boost converter.In the working mode,both use double closed-loop PI control strategy to eliminate system error.For the battery-side Buck-Boost converter,the nonlinear control method is used instead of the linear controller,and the nonlinear theory is introduced.The development and the limitations of thetraditional linear control strategy,the nonlinear sliding film control strategy is proposed,and the characteristics of the sliding mode controlled Buck-Boost converter are simulated.The results show that the control strategy has good dynamic characteristics.Compared with the traditional linear control method,it has obvious superiority.Finally,the coordinated control method of DC micro grid system is studied.Based on the power balance equation,the operating state of the system is divided into photovoltaic voltage regulator mode,energy storage converter voltage regulator mode and cut-off load voltage regulator mode.under different steady state,divide different working modes,and according to the power balance signal,make the system switch in each mode,respectively analyze the Boost converter and the nonlinear sliding film control Buck-Boost The simulation results of the converter in different operating modes show that the DC micro grid system shows good robustness to the output fluctuation of the photovoltaic unit and the load variation in the system.