Portable equipment as well as propulsion of small airplanes (UAV) and robots have enhanced the need for portable power supplies of large energy density (kWh/kg). This has resulted in a growing interest in micro-gasturbines as they should be capable of delivering 20 times more energy than batteries for the same weight. The need for high performance and the specific problems are at the origin of a worldwide increase of research on micro-gasturbines and the motivation for the present paper.
In micro-gasturbines, high-speed and compact motors and generators are highly required. These electrical machines can be directly connected to high-speed gas turbines without mechanical gears. The machines have to operate at the same high-speed as turbines.
This paper study on new electrical machine capable of operating at the very high rotational speed and the related power control for micro-gasturbine. The permanent-magnet synchronous machine can be used as high-speed electrical generator. A 400,000 rpm, 800 W electrical generator is developed. First of all, rotor dynamics analysis was performed to design a new rotor for ultra high rotational speed. A two-pole rotor consists of a cylindrical samarium-cobalt permanent-magnet encased in an Inconel-817 sleeve. The permanent-magnet diameter of 6.4mm and the retaining sleeve thickness of 0.8mm are selected from a considered critical speed. In the next, a new material, amorphous alloy, was imposed on stator core due to minimize the iron losses. Three-phase six-slot stator has been selected to reduce the electric frequency. The diameter of the stator is 44mm with a length of 15mm. Numerical models were developed to analyze the performance of the machine. These numerical models were verified with experimental results.
The generator can be used as a startup motor because it is connected to the compressor and the turbine. So that the motor drive requires digital signal processor for the implementation of rotor position sensorless control strategy. This paper describes a sensorless controller that will operate at speeds up to 200,000 rpm for the startup motor.
The two ceramic ball bearings sustained the rotor for initial development. The back-to-back tests are performed. The ceramic ball bearing has been tested in electrical machine, and stably operated at 100,000rpm. The air foil bearing test will be continued until 400,000rpm is achieved.