Under normal operating conditions, a MicroGrid is interconnected with the medium voltage network; however, in order to deal with black start and islanded operation following a general blackout, an emergency operation mode must be envisaged. A sequence of actions and conditions to be checked during the restoration stage are identified and tested through numerical simulation. Voltage and frequency control approaches, inverter control modes, and the need of storage devices are addressed in this paper in order to ensure system stability, achieve robustness of operation, and not jeopardize power quality during service restoration in the low voltage area.

SUMMARYLarge scale integration of distributed generation of both medium and low voltage (LV) networks can be achieved by exploiting the Multi-MicroGrid (MMG) concept, a new distribution system architecture comprising a hierarchical control system, which allows the coordination among distributed generation units and MicroGrids (MGs) and therefore the operation of such a system in islanded mode. After a general blackout the MMG capabilities can also be used to provide service restoration in distribution systems. A new procedure for MMGs black start is then addressed in this paper. A sequence of control actions is defined and evaluated through numerical simulations. Fully automation of the entire MMG black start procedure is discussed along the paper. The results obtained demonstrate the feasibility of the proposed sequence of control actions and highlight some accomplishments that should be considered in order to successfully restore the MMG service, ensuring system stability and power quality.

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This paper proposes technical solutions that can be implemented in variable speed permanent magnet synchronous generators driven wind turbine systems aiming to mitigate high voltage problems in low voltage MicroGrids by controlling the active power output. Due to the limited control capability of these systems, controlling the output power to prevent voltage rise will require the local accommodation of the generation surplus. For this purpose, additional control functionalities are developed to be integrated in the control systems of the power electronic based interfaces. Their performance is evaluated through numerical simulations performed in Matlab ® /Simulink ® environment and considering the detailed models of the power electronic converters. The results obtained demonstrate the effectiveness of the proposed control functionalities.