Study On Dc Micro-Grid For Distributed Power Access

As the distributed power access to the power grid in the form of large-scale, for the characteristics of large scale, strong intermittent, low-quality and so on, the traditional power grid structure, equipment and operation control have been challenged; In the contrast, as connect to the power grid in single form, because of the high cost, high requirements for grid technology and control difficultly, its large-scale application has been limited. On the other hand, currently, more and more electrical equipments work based on DC, more and more commonly communication equipment, the broad prospect of electric vehicle, LED lighting system and the demand for low power consumption and high speed performance of the motor, etc.The DC micro-grid for distributed power access is constructed. On one hand, combining and using the distributed power to improve energy utilization; On the other hand, supplying the DC load directly to decrease intermediate links to achieve the purpose of saving energy and reducing consumption. The main components are as follows.Firstly, basic elements of the DC micro-grid is determined. The DC micro-grid voltage grade is DC380V, single bus structure operation mode, unipolar two wiring form, interconnecting the 10kV distribution network with voltage source inverter, and then, using local PQ control strategy coordinately controlling micro-grid energy management.Secondly, photovoltaic array and wind turbines modules are built. Specificly:for the photovoltaic power generation, derives four parameters mathematical model for engineering use; adjusts the three typical compensation coefficient values; analyses the common three kinds of maximum power point tracking control method (the fixed voltage method, the disturbance observation method and the incremental conductance method), compares the advantages and disadvantages; writes Fortran program code to achieve maximum power point tracking control, builds the photovoltaic power generation system module. For the wind power generation, builds the wind turbine, transmission system and the permanent magnet synchronous generator modules; studies the maximum wind power tracking operation, constant speed operation and constant power operation three running state; analyses and compares the three kinds of maximum wind power tracking control method, builds the maximum wind power tracking control module based on the optimal power given; uses the vector control method based on rotor field orientation for machine side converter control, builds the machine side converter control module.Thirdly, in the condition of parallel operation, the grid side converter module with the vector control method based on grid voltage orientation and its control module are built. The DC micro-grid energy coordinated control strategy is proposed. Then, building the DC bus voltage control module. In the condition of islanding operation, the battery charge and discharge circuit model and its control model was established, controlling the battery charging and discharging to achieving energy balance in the micro-grid.Finally, simulation parameters are set up. Simulating and analysing the possible kinds of power supply modes in the condition of parallel operation and islanding operation which presents by the DC micro-grid on the PSCAD/EMTDC simulation platform. The effectiveness of the self-built modules and the feasibility of the control method have been verified.