Nonlinear control of dc-dc bidirectional converters in stand-alone dc Microgrids

The direct current (dc) microgrids are an option to new demands for power quality and integration of renewable resources in developing regions, where the main network is unavailable. However, the dc architecture is based on multi-stage power converters where point-of-load converters can be seen by the feeder converter as constant power loads (CPLs). This nonlinear characteristic and the frequent change of the availability of energy sources and loads makes the linear control inadequate. This work addresses the nonlinear stability analysis of a stand-alone dc network. In addition, it is proposed a sliding mode controller based on a washout filter that is responsible for controlling the balance of power (load demand and generation) through a dc-dc bidirectional converter (DBC). This converter is connected to a storage device that plays the role of maintaining a constant dc bus voltage. Simulation results allow us to validate the proposed controller under variations in the availability of energy sources and loads.