# Research and Development of a Large-Scale Axial-Flux Generator for Hydrokinetic Power System
## 1 Introduction  
The demand for energy and electricity has been rising at its fastest rate in recent years, driven by a growing population, robust economic growth, intense heatwaves, and the increasing uptake of technologies that run on electricity. The strong increase in global electricity consumption is set to continue into the next years, with growth of around 4%, according to a report by the International Energy Agency (IEA) [1]. Two major challenges, related to the energy demand increases, could be solved: equal energy access to all countries and people, and the need to reduce greenhouse gas emissions and environmental pollution [2]. It is known that renewable energy will play a key role in decarbonizing energy systems in the coming decades. Currently, the most popular energy sources are solar, wind, hydro, geothermal, and biomass energy. As a renewable energy resource, hydropower is one of the most commercially developed. Hydropower plants are currently the most contributory renewable energy source worldwide, and they continue to be installed, especially in emerging countries [3, 4]. Hydropower generation could be divided into the next major types: storage (and its variant--pumped storage), run-of-river (including in-stream), and tidal. A run-of-river hydropower plant draws energy for electricity production mainlyfrom the available flow of a river (sometimes called \"zero-head\" hydropower), sometimes with short-time storage [5]. In-stream solutions are a good alternative, having a lower environmental impact, in high-flow rivers since they use rivers' high kinetic energy. Generally, hydrokinetic systems convert the energy of moving water in rivers, oceans, or tidal currents into electricity without the use of a dam or barrage associated with conventional hydropower [6]. There are several kinds of hydrokinetic turbines of various sizes and different energy-capture principles. The major classification of hydrokinetic turbines is related to rotating axis positions with respect to the water flow: with a horizontal axis and a vertical axis. One of the constraints for the turbine power application is the low typical river current velocity [7]. The design philosophies of hydrokinetic turbines are similar to those of wind turbines, sharing the same working principles, which consist of converting the hydrokinetic power into mechanical power in the form of rotating blades [8]. Moreover, horizontal axis installations, with a buoyant mechanism, may allow a non-submerged generator to be placed closer to the water surface [9]. These specifics outline the major requirements concerning electricity generator design. An electricity generator for similar applications (including wind turbines) has also been subjected to active research [10; 11; 12; 13]. Traditionally, three main types of wind turbine generators can be considered for the various wind turbine systems, these being direct current (DC), alternating current (AC) synchronous, and AC asynchronous generators [14]. This is very similar when discussing generators for hydrokinetic power systems. For instance, a 2 MW turbine with a permanent magnet ring generator that measures 16 m in diameter was installed in the Bay of Fundy, Canada, in 2016 [15]. This study presents key points in the design development of an electricity generator for a hydrokinetic power system. In addition its specifics, similar to wind turbine generators, it also involves large dimensions and a high power output. The electrical generator is to be mounted on an in-stream installation of a buoyant type, as is shown in general in Figure 1.  
The floating nature of the system allows it to be easily anchored and unanchored in different water bodies, such as canals and rivers. This mobility enables the system to be deployed where needed, offering greater accessibility to remote areas or locations with varying water-flow conditions [16; 17]. This floating hydropower plant is intended to use a water wheel, with a relatively low rotational speed, that requires a gearbox [18].