Research On The Operation Modes Of Hybrid Micro-grid And Its Switching Control Strategy

The world-wide environmental problems and the petrochemical energy crisis have prompted us to focus on cleaner distributed energy and its power generation technologies.The distributed power supply with randomness and volatility has a great impact on the safe operation,protection control and monitoring and dispatching of the traditional distribution network.So the micro-grid technology which has a very strong ability to accept the distributed power came into being.According to different forms of power supply,micro-grid can be divided into AC micro-grid and DC micro-grid.The two kinds of micro-grids have advantages and disadvantages in terms of access cost and access loss for distributed power supply with different power generation characteristics,so hybrid micro-grid which contain both AC micro-grid and DC micro-grid rapid rise.The hybrid micro-grids formed by interconnection of AC micro-grids and DC micro-grids operate in a variety of modes,and its switching relationship is complicated.So it is very important to analyze the operation mode of hybrid micro-grids.In this paper,the current structure of hybrid micro-grid is divided into four basic topological types,and the characteristics of each topology,the classification of operation modes,the power balance relationship and the switching relationship among the operating modes are analyzed.Secondly,three operating modes switching rules are proposed,four kinds of state variables which describe the switching performance of the mode are defined,and the switching rules of the operating modes are analyzed theoretically by using the four variables,the third switching principle is simulated in PSCAD / EMTDC.In the end,the balance selection and transfer timing method is proposed in the AC-mixed hybrid network.Taking into account the delay between the switching of the control strategy and the hard switch,the switching between the AC and DC hybrid micro-grids is solved.It is possible to realize a smooth switching between operating modes.A method of voltage-power control is proposed to control the voltage stability and the smooth transmission power of AC-DC converters in different operation modes.The validity of the proposed method of balancing node selection and transfer timing and voltage-power control is verified in PSCAD / EMTDC.