Fault Characteristic Analysis And Fault Control Of Microgrid

Microgrid can organize distributed generators (DGs) efficiently, suppress the adverse effects caused by fluctuations and intermittent of DGs and improve the reliability and flexibility of the power system. Generally, DGs in a microgrid are interfaced through power electronic devices, so the fault characteristic of microgrid is very different from that of traditional distribution network. Therefore, the research on fault characteristic and fault control of microgrid is a work of high theoretical and practical value.Firstly, the structure and parameters of a microgrid are designed, the model of microgrid is built to lay the foundation for fault analysis and fault control. The mathematical models of photovoltaic (PV) arrays, wind turbines and energy storage batteries are established. The control strategies of PV system and wind power generation system are described. For the energy storage system, the droop control strategy with line impedance compensation is proposed. The control strategies of DGs, the operation and mode switching of microgrid are verified in PSCAD/EMTDC.Based on the model of microgrid, the fault characteristic of microgrid is analyzed. Theoretical analysis of fault characteristics of PV system and wind power generation system is conducted and verified by simulation. The fault characteristic of energy storage system is analyzed by simulation and the results show that voltage drop will cause over current, so extra control measures should be taken. The fault characteristic of the microgrid in different operating modes is analyzed by simulation. When the fault occurs in main grid, the voltage of microgrid drops and the tie line current increases with a serious distortion. Because of the current limitation of DGs, the fault current in isolated operation mode is much smaller than that in grid-connected operation mode.Finally, the control strategy of microgrid in faulty conditions is studied. With asymmetric fault, PV system and wind power generation system take double current closed loops control to achieve symmetrical output current. To deal with the over current of energy storage system in faulty conditions, the control strategy of adding a virtual resistor to limit the current is put forward. It is proposed that a fault current limiter should be installed to improve the fault ride-through capability of microgrid and weaken the harm caused by main grid. The proposed control strategies are verified by simulation in PSCAD/EMTDC.