Special features of ultrahigh-speed induction generators are analyzed, that are applied in a system developed to generate electric energy by utilizing renewable and waste energy resources. The solution is based on a system that consists of a high-speed turbine, coupled to a three-phase induction generator, an AC/AC converter and a supervisory control unit. The function of the system is to utilize the energy content of some working medium by a special high speed turbine that converts the energy content of the working medium into electric energy by the generator and the AC/AC converter. Various waste energy sources can also be utilized by applying the system, eg. energy that can be obtained during the process of pressure reduction in steam, gas and fluid networks. The electric power generated by the system can be fed back to the utility mains or it can be used in stand-alone mode to supply a selected group of loads. The paper considers the special properties of the system mainly in connection with the unusual behavior of the ultrahigh-speed induction generator. The requirements against the AC/AC converter are also overviewed. Control strategies of the system to ensure optimum and reliable performance are compared.