Stability Analysis And Experimental Research Of Optical Storage DC Microgrid

With the increasing demand for emerging energy applications such as solar energy,distributed generation(DG)technology for microgrid has become more and more widely used.The Photovoltaic Energy Storage Microgrid have attracted widespread attention due to its flexible distribution and simple control.This paper focuses on the structural design,control strategy and system stability of optical storage DC microgrids.In addition,since the DC microgrid system is a simplified model of a optical storage system based on a photovoltaic power generation(PPG)system,this paper also studies the control strategy and mathematical modeling of the DC microgrid.The detailed research contents are as followings:(1)In this paper,each part of the optical storage DC microgrid is described in detail and related modeling is calculated.In order to cope with various complex working conditions in the actual environment,including changes in light intensity,changes in voltage reference values,and constant power load access,etc.,a set of optical storage DC microgrid system with a voltage level of 72 V was designed and built And the corresponding layered control method is designed.The bottom layer control realizes the stable work of each part;the top layer control is used to control the connection between each part system to ensure the reliable and stable operation of the whole system.The PLECS test fully shows the excellent effect of the layered control method of the optical storage DC microgrid,and it can also be seen that the system has a good dynamic response when responding to different conditions,and the response time is less than 0.5s.(2)This paper analyzes the two traditional control methods of droop control and frequency droop control and conducts related modeling and analysis of the two control methods.Finally,through PLECS,the relevant theories of the two control methods are verified under different working conditions,including control strategy switching,voltage reference value change,droop coefficient change,and load jump.In the DC microgrid system with a voltage level of 400 V,the droop control method cannot effectively control the DC bus voltage,and the bus voltage drop can reach 6.8%-21.5%.The control accuracy of the converter output current is low,and the current deviation reaches 1.5A-6.3A.The frequency droop control method has greatly improved thecontrol accuracy of the output current.The current deviation is about 0.1A,but the bus voltage cannot be effectively controlled.(3)After introducing two traditional control methods,this paper proposes a method to enhance frequency droop control.The control method can control the output voltage of the converter and recover the drop of the bus voltage through the secondary controller while ensuring the high standard of the output current sharing accuracy.The voltage level of the system in the simulation test is 400 V,and the test conditions include control strategy switching,voltage reference value change,droop coefficient change,and load jump,etc.,through system voltage recovery,current deviation,and response time and overshoot in the dynamic process Etc.shows the effect of the enhanced frequency droop control strategy on the microgrid.Compared with the traditional control test,it embodies the excellent performance of the enhanced frequency droop control strategy.The voltage drop is within 5%,the current deviation is 0.01 A,the response time is 0.2s,and the overshoot voltage is 1.5V and the current is 0.05 A.(4)After analyzing and explaining the enhanced frequency droop control strategy,a DC microgrid hardware experiment system is designed and constructed.The system is composed of Boost converters connected in parallel with the load,in which the system power level is 60 W,voltage level is 72 V,and load is 50?.At the same time,a set of software programs for enhanced frequency droop control method is designed.A series of experimental tests were conducted in the built DC microgrid hardware circuit system,and the dynamic characteristics and control effects of the system under different operating conditions were analyzed,including control strategy switching,voltage reference value changes,current distribution ratio changes,and converter cut-off access And load jump and so on.Finally,it is proved that the enhanced frequency droop control strategy can achieve the target requirements of current proportional distribution and bus voltage recovery,in which the voltage drop is 1V,the current deviation is 0.01 A,and the response time is 2s.