Microgrids, study and coordination of protections for the generators and the network

The liberalization of electricity markets associated with the integration of renewable energy has led to introduce the concept of local use of these new production sources. We can define the Microgrid paradigm as an aggregation of several distributed power sources that can supply their local charges. These microgrids may be islanded to ensure the continuity for supplying the loads in both operation modes. To provide these functions and, consequently, the reliability of the network, a strategy to protect the generators and the Microgrid itself has been proposed. In this thesis, we present, firstly, the similarities and differences between conventional generators and the generators connected to the network using the power electronics converter. Then we present the design of a voltage source connected by a power electronic converter and LC filter, the primary energy source considered controllable being a gas micro turbine. This type of generator is not naturally capable to support the high level fault currents. Moreover, the simultaneous disconnection of distributed generation in case of fault, could lead to a reduction in generated power and increase the instability of the system. Thus, we study the possibilities for the generator to remain connected in case of voltage sags (the fault-ride-through principle) while being protected against the overcurrents. We have proposed two different solutions to limit these generator currents. In addition, to ensure continuity of supply the loads in two operation modes, we presented an islanding detector based on the ROCOF (Rate Of Change Of Frequency) relay which switches the microgrid between the connected mode to the islanded mode. An experimental validation for this work was realized using PHIL (Power Hardware in the Loop) real-time simulation. The protection of generators based on the current limitation has a significant impact on the microgrid protection and its coordination. In this case, the principle based on a coordination of overcurrent protection is no longer applicable. Therefore, the last part of this thesis presents a coordinated protection plan valid in both operation modes and with different types of sources. This strategy was tested on a simulated example of microgrid on real-time simulator. (author)