Research On Coordinated Operation Control And Energy Optimization Management Of DC Microgrid

With the widespread use of renewable energy sources based on clean energy,microgrid that can accept distributed energy have received extensive attention.DC microgrid has become a research direction in the field of microgrid due to the advantage of its power distribution method and its lower overall cost and total loss.The coordinated operation control and energy optimization management is the research emphases of DC microgrid.Considering the control targets of DC microgrid at different time scales,hierarchical control can solve the problem of mutual influence between different control targets.In this paper,the DC microgrid including photovoltaic and wind power generation units,energy storage units and grid-connected units is taken as the research object,and the hierarchical control method is used to solve the problem that the control targets interact with each other at different time scales.Two key issues of coordinated operation control and energy optimization management of DC microgrid are studied.Firstly,the topology and component of the DC microgrid are introduced.The mathematical model of the distributed power generation unit composed of wind power and photovoltaic power generation unit is established,and the respective output characteristics and the control strategy of the converter are analyzed.The mathematical model of the battery energy storage unit is established,and two operating states and control strategy of the energy storage converter are analyzed.The mathematical model of the grid-connected converter is established and its control strategy is introduced.Secondly,the significance of the hierarchical control of the DC microgrid is expounded,and the function and characteristics of each layer of control are introduced in detail.Corresponding to the two key problems of coordinated operation control and energy optimization management of the DC microgrid,the control objectives of each hierarchy ensure the stable operation of the DC microgrid and improve the economics of the DC microgrid.The related control of the converter is introduced.Then,for the coordinated operation control of the DC microgrid,its main purpose is to maintain the balance of active power in the DC microgrid,of which only indicator is the DC bus voltage.In order to maintain the stable operation of the DC microgrid,the power of the DC microgrids shall be adjusted to keep the DC bus voltage stable.The AC grid and battery energy storage unit with bidirectional power flow characteristics are selected as the voltage regulation unit for the primary control of the DC microgrid.The droop control and the voltage margin droop control method are adopted respectively to realize the automatic power distribution and improve the stability of the control.The secondary control solves the problem of voltage deviation by real-time updating the DC voltage and power reference value of the voltage regulator unit converter,so that the DC bus voltage is quickly recovered and runs at the rated voltage value.The simulation model is built to analyze and verify the control strategy.Finally,for the energy optimization management problem of DC microgrid,the power flow distribution of the DC microgrid is obtained from the power flow calculation,providing reference operation value of each unit in DC microgrid.Considering the economic optimization scheduling of DC microgrid with the minimum economic cost as the target,the charging and discharging control of the battery energy storage unit adopts the fuzzy control method,which reduces the damage of the battery due to frequent charging and discharging,and optimizes the economic dispatch under the time-of-use(TOU)price mechanism,and also improves the economy of the DC microgrid.The correctness of the method used was verified by analyzing two examples of a DC microgrid containing wind power,photovoltaic power generation,energy storage and grid connection,and a DC microgrid containing multiple micropower sources.