Vinícius Moraes de Albuquerque: On Storage and Harvesting: Applications in Ancillary Grid Services and a Novel Rectifier for Linear Generators

Abstract

Some of the main current challenges in electrical engineering can be described by the opposing forces of increased need of renewable generation and the stability requirements of a synchronous grid. This thesis describes works spread out on both fronts. Mainly, energy harvesting of hidden hydro potentials is seen as a possible innovative form of renewable generation. Among these potentials, water flows in open channels used for irrigation and drainage shows promising sources for powering sensors and small isolated loads. In order to capture the energy of vortex-induced vibrations (VIVs) in accordance with computational-fluid simulations (CFDs) results, two permanent-magnet linear generators and their respective rectification circuits were designed for different open channels. The first is a proof-of-concept small-scale device, with output on the mW scale, built with do-it-yourself techniques such as 3d printing and printed circuit board (PCB) coils in PAPER VI. The second is a large-scale device, with output in the hundreds of Watts, built for a larger channel. A novel solution based on power-factor correcting (PFC) converters as rectifiers for linear generator is also presented for both devices, and compared to conventional solutions such as passive rectification and three-phase voltagesource converters, respectively. The use of linear generators for harvesting of vortex-induced vibrations is not currently described in literature, and is more prominent on wave energy generation. The application of these generators suffers from given drawbacks due to its pulsed energy availability, and therefore, its grid-connection must also be further investigated. The use of energy storage and its uses on an isolated grid-forming control strategy as power-filtering of linear generators from wave energy are studied in PAPERS III to V, allowing for island electrification and support of weak isolated grids. It was shown that conventional controllers from wind and solar are applicable to wave applications in the grid-size inverter, and the energy storage if well designed can mitigate power deviations from wave energy. Furthermore, the use of energy storage for grid support is also further studied as means of increasing inertia reserves for renewable-rich grids. In PAPER I, a synthetic inertia method is developed by amplifying inertia response of synchronous machines during low frequency events, bypassing the frequency differentiation challenge. In PAPER II, a method for synthetic inertia is presented by differentiating the frequency through a moving least squares curve fit implemented in FPGA. In ongoing work, an experimentally-acquired model of this synthetic inertia is simulated on a grid model and compared to other fast frequency controllers that are viable fast-frequency reserve (FFR) services.