Operation And Control Of DC Micro-grid With Wind Power, Energy Storage And Seawater Desalination Load

Due to the remoteness of their geographic position,island regions are often faced with dual problem of both weak power grid construction and shortage of freshwater resources.Seawater desalination is a key technology to solve the problem of freshwater shortage in island regions.But due to its energy-intensive characteristic,it is hardly feasible to use the electricity from main power grid to desalinate seawater in such a special area with weak power grid construction.The establishment of a DC micro-grid with wind power,energy storage and seawater desalination unit is a possible way to solve the problem of weak power grid construction as well as the shortage of freshwater resources in island regions.Also,the coupled operation of wind power and seawater desalination can realize local consumption of wind power,which reduces the cost of raw material transportation and increases the utilization rate of wind power.Hence,it is of practical significance to study the operation and control of the DC micro-grid with wind power,energy storage and seawater desalination load.Firstly,this paper analyzed the overall structure of the DC micro-grid with wind power,energy storage and seawater desalination load and introduces the function of each micro unit.The mathematical model of wind turbine,energy storage system and desalination load is built emphatically.Secondly,the energy management system of the DC micro-grid is built and the energy management strategy after the connection of continuous-adjustable desalination load is proposed from a large time scale.The energy management strategy focuses on economical operation of the DC micro-grid.It takes into consideration the income of fresh water production and the life loss cost of battery caused by the decline of battery state of health as objective function,together with power balance and operation condition of each micro unit as constraints.With genetic algorithm to solve the problem,the output of battery and the total consumption of seawater desalination load are planned according to the predicted wind power.Case studies done in Matlab validate the effectiveness of the proposed energy management strategy.Finally,based on the analysis of operation and control method of each micro unit,power coordinated control strategies under grid-connected operation mode and isolated operation mode are proposed from second-level time scale.Under grid-connected operation mode,the AC power grid guarantees the voltage stability of the system when wind speed varies and desalination load operates at full capacity.Under isolated operation mode,the continuous-adjustable characteristic of seawater desalination load is taken full advantage of.It tracks the fluctuation of wind power under frequency conversion control and cut-in/out control.By adjusting load power consumption,the desalination load takes part in power exchange of the micro-grid and cooperates with battery to stabilize system voltage.The connection of continuous-adjustable desalination load significantly shared the power regulating pressure of battery under isolated operation mode.Simulation model of DC micro-grid with wind power,energy storage system and seawater desalination load is built in Matlab/Simulink.The simulation results validate the effectiveness of the proposed power coordinated control schemes.