Two-stage oil-free centrifugal air compressors can bring significant advantages and open new market opportunities for compressor manufacturers. One of the core technologies behind this compressor type is the high-speed electrical machine supported by active magnetic bearings. In this paper, the requirements set by the compressor on the electrical machine design are presented. The design solutions aimed to satisfy these requirements are discussed. Two case studies illustrate possible design approaches for the target application with examples of a 120-kW, 60 000-r/min induction machine with a solid rotor and a 225-kW, 50 000-r/min permanent-magnet synchronous machine (PMSM) with a full cylindrical magnet. The system design and simulation results are confirmed by measurements of a PMSM prototype.

Design Aspects of High-Speed Electrical Machines With Active Magnetic Bearings for Compressor Applications

The successful industrial application of flexible rotors supported on active magnetic bearings (AMBs) requires careful attention not only to rotordynamic design aspects, but also to electromagnetic and feedback control design aspects. This paper describes the design, construction and modeling process for an AMB test rig which contains a 1.23m long flexible steel rotor, with a mass of 44.9 kg and two gyroscopic disks. The rotor typifies a small industrial centrifugal compressor designed to operate above 12,000 rpm and the first bending natural frequency. There are four AMBs — two AMBs at the shaft ends to support the shaft with a combined load capacity of 2600N and two additional AMBs at the mid and quarter spans to allow for the application of simulated destabilizing fluid or electromagnetic forces to the rotor. Simulated aerodynamic cross coupling stiffness values are to be applied to the rotor through these two internal AMBs with the goal of developing stabilizing robust controllers. The unique design allows multiple support and disturbance locations providing the ability to represent a variety of machine configurations, e.g., between bearing and overhung designs. The shaft transfer function in lateral movement has been developed with finite element model and then verified by experimental frequency response measurements. Models for the power amplifiers, position sensors, signal conditioning and data converter hardware were developed, verified experimentally and included in the overall system model. A PID controller was developed and tuned to levitate the rotor and enable further system characterization.Copyright © 2010 by ASME

Design, Construction and Modeling of a Flexible Rotor Active Magnetic Bearing Test Rig

This paper introduces electrically assisted turbocharging (EAT) together with the requirements and challenges in selecting an electrical machine for the application. In an effort to identify the most appropriate technology, a detailed, quantitative, multidomain comparison between induction, permanent magnet, and switched reluctance machines is conducted. The study presented puts equal weighing on the electromagnetic, thermal, and mechanical sciences, together with the all-important cost and provides clear guidelines on the pros and cons of each machine type for the application in hand. For a real case study, the induction machine (IM) is identified as the most suitable candidate due to its high-temperature withstand and equalizing capabilities, together with the lower volt-ampere (VA) requirements. A high-performance (10 kW, 120 krpm) IM is prototyped and specific suitability aspects demonstrated on actual system-representative tests.

Electrical Machines for Automotive Electrically Assisted Turbocharging

This paper demonstrates vibration reduction in a hollow rotating shaft by means of internal-stator active magnetic actuators, which are resiliently mounted This problem requires further consideration over and above classic rotor/magnetic bearing systems on account of the flexible behavior of the magnetic actuator support structure This paper presents an experimental facility conforming to the proposed topology, with a particular focus on the control problem such a system presents The unique challenges are discussed, and a solution is presented in the form of H $_\infty$ -based control Ultimately, experimental results demonstrate the system to be capable of substantial rotor vibration suppression, including while passing the rotor's first critical speed, which was not obtainable with simpler classical control techniques This means the top achievable rotor speed was increased from approximately 3000 r/min without magnetic actuator vibration suppression to over 9000 r/min with vibration suppression active At the rotor critical speed, the magnetic actuators affect a reduction in rotor vibration amplitude of over 70% compared to the rotor supported purely on mechanical bearings, while simultaneously avoiding excessive excitation of the flexible active magnetic actuator support structure

Active Vibration Control of a Flexible Rotor by Flexibly Mounted Internal-Stator Magnetic Actuators

This publication was made possible by Qatar University High Impact Research Grant # [QUHI-CENG-19/20-2] from the Qatar University. The publication charges are funded by the Qatar National Library, Doha, Qatar.

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Reduced order modeling and sliding mode control of active magnetic bearing

With the development of the magnetic bearing (MB) and its application in industry, the demands of high-speed MB are developing, which bring up new problems and requirement for the design. The motor with a high-speed rigid rotor requires that the axial length of MB is minimized to increase the critical speed, and the diameter of thrust disk is minimized to reduce the air friction loss. Also because of the high speed, the eddy currents induced in the iron cores have a significant influence on the dynamic characteristics of the MB. To design a high-performance MB for a high-speed motor, first an MB structure that has the feature of short axial length and small thrust disk is recommended for the high-speed motor. Next, the dynamic model, which takes into consideration eddy current effects, and leakage effects is developed. Then, an optimal design method with multiobjective of minimum length and air friction loss is presented. Design constraints are imposed, which includes the simultaneous consideration of material properties, load capacity, and power amplifier. Finally, a design example is given and a prototype is manufactured. The experimental results demonstrate that the proposed MB structure and the optimization method are feasible and valid in the application of a high-speed motor.

Kun Wang

Papers

Design and Optimization Method of Magnetic Bearing for High-Speed Motor Considering Eddy Current Effects