| Microgrids offer a means of improving the efficiency and reliability of the power system. A microgrid is an electrical power distribution circuit that can operate in isolation and can optionally exchange power with other circuits through power electronic gateways. Although three-phase networks are used to deliver power from sources at higher power levels, single-phase microgrids provide an attractive framework to incorporate low power (≤ 20 kW) energy sources and ensure reliable power supply in single-phase residential distribution systems. Additionally, it may be economically advantageous to operate a residential microgrid at higher frequencies (≥ 400 Hz). Microgrids, thus, can have different phase numbers or operate at different frequencies. This thesis addresses issues concerning the integration of two or more disparate single-phase microgrids. All the problems considered are related to the design of the power electronic gateway converters.;In this thesis, dynamic phasors are used for state space analysis. Spiral vectors are introduced to study pulsating power in single-phase systems. Various power converter topologies are analyzed for suitability as a gateway between a single-phase microgrid and an asynchronous single- or three-phase microgrid; the back-to-back (BTB) voltage source converters (VSCs) topology is identified as the most suitable. The stability of a VSC connected to a stiff grid is shown to depend on the voltage control method and the filter parameters. Although voltage waveform control methods achieve better transient response, voltage magnitude control methods are more robust in terms of stability.;Regulation of the dc bus voltage of the BTB gateway by a PI controller driving the power set point of each VSC is shown to effect autonomous power exchange between asynchronous microgrids. A control-Lyapunov-function-based relative voltage angle controller is proven to minimize the power pulsations at the dc bus of a gateway between asymmetric single-phase circuits and a three-phase circuit. Results from computer simulations and laboratory experiments corroborate the theoretical predictions. |
