Variable speed operation of a hydraulic turbine using power electronics can prevent these events from occurring. Power electronics allow hydraulic turbine operating modes over a wide range of flow rates and heads outside design conditions, in addition to superior efficiency [19]. However, that the cost of the equipment needed for such a setup is high. Micro-hydropower plants operating at variable speed can have different topologies depending on the type of electrical generator. If the generator is a synchronous or asynchronous squirrel cage generator, a back-to-back converter can be used. If the generator is a wound rotor asynchronous generator, a double-feed can be used [20]. With both topologies, the main objective is to adjust the speed of the hydraulic turbine so that it operates at the maximum power point (_MPP_). There are two ways to find this operating point [21]:indirect and direct. For the former, the maximum power operating point is determined from sensor data and the characteristic curves of the hydraulic machine [22]. For the second, it is based on search algorithms (perturb and observe, artificial intelligent method) [23], which are usually independent of turbine parameters. Although they use sensors, they are not as expensive. Variable speed hydropower generation began to receive scientific attention several decades ago. Several projects showed the feasibility of variable speed operation in small hydropower plants [24]. Table 1 shows some of the hydropower plants using variable speed technology. The operating conditions of a micro-hydropower plant integrated into irrigation infrastructure can be highly variable. This flow instability reduces the overall efficiency of the micro-hydropower plant, and can even lead to the phenomenon of cavitation decreasing the lifetime thereof. By implementing a system that varies the rotational speed of the electric generator with respect to its synchronous speed, the turbine can better adapt to the hydrological regime of the river, and thus increase the overall efficiency of the micro-hydropower plant and extend its lifetime. If a micro-hydropower plant operates at synchronous speed, the turbine has a single operating point. In contrast, if it operates at variable speed, the hydraulic power transferred by the fluid can be modified and it can therefore operate at maximum power. This speed variation is made possible by the use of electronic power converters. This study focuses on the Rebolluelo micro-hydropower plant, located in the north of Spain as part of irrigation infrastructure. It is comprised of a semi-Kaplan turbine coupled to a squirrel-cage asynchronous generator. Both fixed-speed and variable-speed technologies are implemented at this micro-hydropower plant. The main contributions of this work are as follows:  
1. An analysis of the phenomenon of cavitation when using fixed-speed and variable-speed technologies;
2. An analysis of the investment costs for fixed-speed and variable-speed technologies;
3. An analysis of the power production for fixed-speed and variable-speed technologies;
4. An analysis of the economic benefit of fixed-speed and variable-speed technologies. In summary, the purpose of this work is to facilitate decision-making when considering future micro-hydropower plant installations. This paper is structured as follows: Section 2 presents the context of the Rebolluelo micro-hydropower plant with fixed-speed technology. Section 3 describes the Rebolluelo micro-hydropower plant operating at variable speed. The assessment indicators are shown in Section 4. The results are presented in Section 5. Finally, Section 6 summarises the main contributions and conclusions of the paper.