Christof Zwyssig

Megaspeed Drive Systems: Pushing Beyond 1 Million r/min

The latest research in mesoscale drive systems is targeting rotational speeds toward 1 million r/min for a power range of 1-1 kW. Emerging applications for megaspeed drives (MegaNdrives) are to be found in future turbo compressor systems for fuel cells and heat pumps, generators/starters for portable nanoscale gas turbines, printed circuit board drilling and machining spindles, and electric power generation from pressurized gas flow. The selection of the machine type and the challenges involved in designing a machine for megaspeed operation such as the winding concepts, a mechanical rotor design capable of 1 000 000 r/min, the selection of magnetic materials for the stator, and the optimization concerning high-frequency losses and torque density are presented. Furthermore, a review of the advantageous inverter topologies, taking into account the extremely low stator inductance and possible high-speed bearing types such as ball bearings, air bearings, foil bearings, and magnetic bearings, are given. Finally, prototypes and experimental results originating from MegaNdrive research at Swiss Federal Institute of Technology Zurich are discussed and extreme temperature operation and power microelectricalmechanical system are identified as targets for future research.

An Ultrahigh-Speed, Low Power Electrical Drive System

New emerging applications in the areas of portable power generation, small turbocompressors and spindles require the development of ultrahigh-speed, low power electrical drives. A 500 000 r/min, 100 W electrical drive system is presented. Because of the ultrahigh-speed requirements, standard machine design and power electronic topology choices no longer apply and the complete drive system has to be considered. A permanent magnet machine with a slotless litz-wire winding is used, which results in a low motor inductance and a high fundamental machine frequency. Three different combinations of power electronic topologies and commutation strategies have been experimentally investigated. A voltage source inverter with block commutation and an additional dc-dc converter is selected as the most optimal choice for the power electronics interface as it results in the lowest volume of the entire drive system due to lower switching losses, no heat sink cooling required, a small number of semiconductor devices, and relatively simple control implementation in a low cost digital signal processor.

Design of a 100 W, 500000 rpm permanent-magnet generator for mesoscale gas turbines

Mesoscale gas turbine generator systems are a promising solution for high energy and power density portable devices. This paper focuses on the design of a 100 W, 500000 rpm generator suitable for use with a gas turbine. The design procedure selects the suitable machine type and bearing technology, and determines the electromagnetic characteristics. The losses caused by the high frequency operation are minimized by optimizing the winding and the stator core material. The final design is a permanent-magnet machine with a volume of 3.5 cm/sup 3/ and experimental measurements from a test bench are presented.

Efficiency Optimization of a 100-W 500 000-r/min Permanent-Magnet Machine Including Air-Friction Losses

This paper proposes a method for the efficiency optimization of ultrahigh-speed permanent-magnet machines. Analytical methods are applied for the modeling of the machine that is equipped with a diametrically magnetized rotor and a slotless stator. The outer dimensions of the machine are design constraints, and the internal dimensioning is optimized for minimum losses. The air-friction losses are taken into account in addition to the usual iron, copper, and eddy-current losses. Laminated silicon-iron or laminated amorphous iron is used as the stator core material. The results show that air-friction losses influence the optimum design considerably, leading to a small rotor diameter at high speeds. The loss minimization and the amorphous iron core make it possible to reduce the calculated losses by 63% as compared to a machine design not considering air-friction losses. The resulting efficiency is 95% for a 100-W 500 000-r/min machine excluding bearing losses. Experimental results are shown to illustrate the validity of the method.

An Ultra-High-Speed, 500000 rpm, 1 kW Electrical Drive System

New emerging micro gas turbine generator sets and turbocompressor systems push the speed limits of rotating machinery. To directly connect to these applications, ultra-high-speed electrical drive systems are needed. Therefore a 1 kW, 500000 rpm machine and the according power and control electronics are designed and built. This paper includes design considerations for the mechanical and electromagnetic machine design. Furthermore, a voltage source inverter with an additional dc-dc converter is described, and sensorless rotor position detection and digital control is used to drive the machine. Finally, the hardware and experimental results are presented.

Combined Radial-Axial Magnetic Bearing for a 1 kW, 500,000 rpm Permanent Magnet Machine

Ultra-high-speed and high-power-density drives are attracting much interest in todays industry. For instance, there are several investigations into mesoscale gas turbine generator systems and turbocompressors for fuel cells. In all ultra-high-speed machinery the bearing is a key technology. Therefore, this paper focuses on the design of a 500,000 rpm active magnetic bearing suitable for use in a 1 kW PM machine to complete an ultra-high-speed electrical drive system. The design procedure selects the suitable magnetic bearing type to keep the system compact and small. The electromagnetic characteristics are determined, the results for the rotor dynamic analysis are presented and the air friction losses caused by the high frequency operation are evaluated. The final design is a combined radial-axial magnetic bearing with a volume of 50 cm3.

Half-Controlled Boost Rectifier for Low-Power High-Speed Permanent-Magnet Generators

Literature reports several future portable and distributed power supplies in the watt-to-kilowatt range based on rotating machinery equipped with a variable-speed permanent-magnet generator. In order to generate a constant direct-current output voltage, an ultracompact highly efficient low-power rectifier is required. A suitable concept, i.e., the half-controlled three-phase pulsewidth-modulation boost rectifier (HCBR), is analyzed in this paper. In previous literature, there is only limited information available, particularly concerning current stresses, common-mode characteristics, and operating principles. Therefore, the HCBR topology analysis is completed in this paper. Furthermore, a novel modulation scheme improving the power electronics efficiency is proposed using space-vector analysis. The integration into a compressed-air-to-electric-power system with a generator rotating at 350 000 r/min is presented, and the measurements verify the theoretical results with an efficiency increase of 2% for the novel modulation scheme.

Modeling and Comparison of Machine and Converter Losses for PWM and PAM in High-Speed Drives

For variable-speed drives, the interaction of the machine and the converter is becoming increasingly important, especially for high-speed applications, mainly due to the effect of the converter modulation on the machine losses. The allocation of the losses to different components of the drive system needs to be known in order to choose the ideal machine and modulation combination. In this paper, individual models are introduced for calculating the rotor, copper, and core losses of the machine as well as the inverter losses, taking the modulation type into account. These models are developed by considering two typical high-speed permanent-magnet synchronous motor topologies (slotted and slotless machines) driven by pulse-amplitude modulation (PAM) and pulsewidth modulation (PWM) converters. The models are applied to two off-the-shelf machines and a converter operating with either PAM or PWM. The test bench used to experimentally verify the models is also described, and the model results are compared to the measurements. The results show that PAM produces a higher overall efficiency for the high-speed machines considered in this paper. However, PWM can be used to move the losses from the rotor to the converter at the expense of decreasing the overall drive efficiency. The possible benefits of these results are discussed.

Design considerations and experimental results of a 100 W, 500?000 rpm electrical generator

Mesoscale gas turbine generator systems are a promising solution for high energy and power density portable devices. This paper focuses on the design of a 100 W, 500 000 rpm generator suitable for use with a gas turbine. The design procedure selects the suitable machine type and bearing technology, and determines the electromagnetic characteristics. The losses caused by the high frequency operation are minimized by optimizing the winding and the stator core material. The final design is a permanent-magnet machine with a volume of 3 cm3 and experimental measurements from a test bench are presented.

Analytical and Experimental Investigation of a Low Torque, Ultra-High Speed Drive System

New application areas are demanding the development of ultra-high speed electrical machines. Significant challenges exist to produce a test bench that is capable of withstanding operating speeds exceeding 500,000 rpm and measuring very low torque values of mNm. This paper describes a purpose built test bench that is able to characterize the operation of an ultra-high speed drive system. Furthermore, the calculation of electromagnetic losses, air friction and critical speeds is presented and a comparison of analytical and experimental results is given. The ultra-high speed machine has an efficiency of 95%, however, in the upper speed ranges the frictional losses become dominant