Research On Energy Storage System Based On SoC Balancing Control For DC Microgrid

Distributed generation can make full use of renewable energy,which is an important measure to achieve the goal of "Green Earth".As a small system that integrates distributed generation,power load units,energy storage system(ESS)and interface converter,microgrid has drawn more attention recently.But the power generation process of renewable energy has intermittent and fluctuant properties which has large impact on the safety and reliability of the system.The ESS in microgrid can suppress the power fluctuation,improve the power quality and ensure an uninterrupted power supply when a power failure happens.The power control strategies of ESS in DC microgrid were studied in this thesis.Firstly,the basic structure of the DC microgrid was introduced,and then each module unit of microgrid was analyzed.The modeling and control methods of interface converters including PV interface Boost converter and energy storage units(ESU)interface bidirectional DC/DC converter were researched,then compensators were designed by using the derived mathematical model,which ensures the stability of converters.Due to the two-way power flow characteristics in bidirectional DC/DC converter,complementary PWM and voltage current double-loop control strategy were adopted in this thesis.Only a set of control parameters was needed when working in different states,which simplifies the design of controller and the control methods were verified by simulation software.Secondly,the droop control strategy of DC microgrid was analyzed,and an improved droop control method based on SoC balancing was proposed.The SoC of each ESU may not be the same in ESS,so the SoC parameters were introduced to the droop variable,and different control expressions were adopted in the charging and discharging process,which make the ESU absorb and output power according to its own SoC and ultimately the output power and SoC of different ESUs were equalized.Then the detailed description of the selection of control parameters was given from the allowable bus voltage deviation and equilibrium rate requirements.In addition,a bus voltage compensation control strategy is proposed for the problem of bus voltage deviation caused by droop control.Finally,a DC microgrid energy storage system model was built in PSIM software,and the proposed control method was verified by simulation.Finally,based on theoretical research and simulation validation,the experimental platform of DC microgrid with ESU was built,and interface converters were constructed.On this experimental platform,experimental verification of MPPT and CVC control of photovoltaic power generation unit,charge and discharge control of energy storage unit and improved SoC droop control strategy were performed.The experimental results verify the correctness of theoretical analysis.