Research On Variable Droop Control Of Indrpendent PV DC Microgrid

With the progress of human society,people's demand for non-renewable energy such as petroleum and coal has gradually increased,causing it to face a depletion crisis.However,environmental friendly and clean renewable energy power generation is receiving widespread attention.The DC microgrid can solve the impact of distributed generation on the power grid and thus make more efficient use of new energy.But the power generated by the distributed power supply is greatly affected by the environment,and the stability of the bus voltage and the power quality are also affected.Through a well-designed control method,the DC microgrid can operate stably in different conditions.The PV DC micro-grid designed in this paper mainly supplies power to residents in remote mountainous areas.Therefore,the studies have been conducted on the energy management and coordination control of the isolated grid system as follow:The overall structure of the independent PV DC microgrid is analyzed.The structural characteristics and working principle of photovoltaic cells,batteries and fuel cells are explained.Each unit is modeled and the corresponding interface converter is introduced.The relevant factors that affect the stability of the DC bus voltage are clarified.The droop control method is used to control each power generation unit,and the deficiencies of the control method are analyzed.The variable droop control of photovoltaic cells,batteries,and fuel cells was proposed.In order to prevent degradation of the operating characteristics of the fuel cell as the output current increases,constant current discharge control is used to make it operate in an economical operating area.The power generation priority of each power supply is set,and a multi-source coordinated control strategy is proposed.The bus voltage is designed to be divided into a plurality of voltage ranges.Each unit has a corresponding control mode in different intervals.Bus voltage is used as the control signal.In order to coordinate the mutual switching of power control modes,voltage is finally controlled within a reasonable range,and the control mode of each power supply is designed.The MATLAB/Simulink simulation platform is used to build a model of an independent PV DC microgrid.The results show that under the change of light intensity and load power,the variable droop control of photovoltaic cells achieves that the output power of different capacity sizes PV are proportional distribution in parallel,and the stability of the bus voltage is also improved;the variable droop control of the battery makes the voltage output is stable and the volatility is reduced;the variable droop control of the fuel cell makes its discharge process flexible.The multi-source coordinated control strategy enables the PV DC microgrid to operate safely and reliably in different operating conditions.