An Islanded Hybrid AC/DC Microgrid with Seamless Transition Capabilities

This work focusses on the design and control implementation of a wind-solar based hybrid AC/DC microgrid, aimed to guarantee an uninterruptible power supply to the loads located in remote areas. The off-grid system consists of a doubly fed induction generator (DFIG) for wind energy conversion, and a solar photovoltaic (SPV) array for solar energy conversion. The renewable energy sources are aided by a battery energy storage (BES), for powering the AC and DC loads in the microgrid. In this configuration, the stator terminals of the DFIG are connected with the point of common coupling (PCC) of the AC loads through a solid state transfer switch (SSTS). The coordinated control strategy for the power converters in this hybrid AC/DC microgrid, is designed to seamlessly disconnect and reconnect the DFIG stator with the PCC terminals, without interrupting the power to the loads. The disconnection of the stator terminals is required in the event of prolonged period of no generation from the WECS. The controller is synthesized to ensure no or low transient effect during disconnection and reconnection. The presented control strategy additionally provides other complementary functionalities such as optimal generator utilization through unity power factor operation at the stator, maximum power tracking from the WECS and the SPV array, unbalance, reactive power and harmonics compensation for AC loads, and regulated supplies for DC loads. The effectiveness of this system is verified through obtained results in different operating conditions.