Directly-Coupled Synchronous Generators With Converter Behavior in Islanded Microgrids

Because of the increasing share of distributed generation (DG) units, a coordinated approach for their integration in the electrical network is required. Therefore, the microgrid concept has been introduced. Most DG units use power-electronic interfaces, i.e., converters, for which control strategies have been developed such that these units can participate in the microgrid control. Because of the specific characteristics of low-voltage islanded microgrids, such as their resistive nature and lack of inertia, P/V and Q/f droops are often applied for the converter control. However, still some directly-coupled synchronous generators can be present in the microgrid. These generators have different characteristics compared to the converter-based DG units, such as the presence of rotating inertia. Also, their control is mostly based on P/f and Q/V droops. To integrate both synchronous generators and converter-based DG units in an islanded microgrid, their control strategies should be adjusted to each other. As the DG units form the major part of the generators in the islanded microgrid, in this paper, the control of the synchronous generators is changed to introduce converter behavior. The synchronous generators are equipped with P/V and Q/f droop controllers that are adjusted to take the rotating inertia into account. The converter controllers use a variant of P/V droop control to optimize the integration of renewable units in the microgrid.