Autonomous power management of series-cascaded and hybrid microgrids
Creators: name: Das, Siji Das
Publisher: name: RMIT University
Year: 2024
Subjects: classificationCode: 400803
subject: Electrical energy generation (incl. renewables, excl. photovoltaics)
classificationCode: 400899
subject: Electrical engineering not elsewhere classified
classificationCode: 400907
subject: Industrial electronics

description: Microgrids with power electronics interfaced Distributed Generation units are gaining high popularity due to its zero emission characteristics. Control and coordination of these generation units are the most crucial factors that will determine the effective utilisation and flexibility of microgrids. Conventional microgrid structure with droop controlled parallel distributed generation units are being replaced by the series-cascaded structure due to its reduced conversion stages and inherent harmonic sharing capability.<br><br>This research work first aims to develop a microgrid architecture integrating dispatchable and non-dispatchable distributed generation units in a series-cascaded manner. Existing control strategies for cascaded microgrids focus on dispatchable type generation only. However, adequate power sharing and voltage regulation of a microgrid containing mixed dispatchable and non-dispatchable cascaded generation units demand new control approaches to achieve operational performance and reliability comparable to the conventional parallel-topology microgrid. To ensure maximum utilisation of non-dispatchable units a novel microgrid architecture formed by a dispatchable master unit followed by a set of non-dispatchable slave photovoltaic units in a series-cascaded manner is developed. A fully decentralised control scheme is proposed, which achieves autonomous power balancing and voltage regulation, ensures full utilisation of non-dispatchable generation units, and allows surplus power curtailment under light load conditions.<br><br>Further, this research work aims to extend the series topological arrangement to form a hybrid microgrid, where low voltage converters are cascaded as a string unit to achieve rated output voltage, and these strings are then paralleled to obtain higher redundancy and power rating. The extension of the arrangement to a hybrid microgrid requires the development of new control strategies, since existing schemes cannot be applied in their original form. As of now hybrid microgrids are controlled using either distributed or centralised schemes to achieve accurate power sharing among the distributed generation units at the cost of complex communication infrastructure. Therefore, a new control scheme is proposed for the hybrid microgrid which aims to achieve accurate power sharing among the paralleled units while maintaining adequate synchronisation among the cascaded converters without any communication link.<br><br>Fundamental concepts as well as mathematical and simulation models of the existing and proposed control schemes are presented. All the proposed control strategies are validated through extensive simulation results and the series-cascaded microgrid control is validated through matching simulation and experimental results.