The influence of the inverter switching frequency on rotor losses in high-speed permanent magnet machines : an experimental study

Harmonic content of the output voltage of pulse width modulated voltage source inverters (PWM VSI) is determined by the switching frequency. On the other hand, rotor losses in high-speed permanent magnet (PM) machines are caused, among other factors, by harmonics in stator currents. These harmonics are determined by the harmonics in the inverter output voltage, and therefore dependent on the switching frequency. In high-speed PM machines, due to the high fundamental frequency, harmonics in the stator currents caused by PWM are located at very high frequencies. Measurement of rotor losses caused by these harmonics in a structure with a conductive retaining sleeve on the rotor which is prone to eddy currents might be very challenging. This paper investigates issues related to this measurement and presents a measurement method which results are compared with results from a 2D analytical model that takes into account eddy currents in the rotor.</p

Mechanical design of rotors for permanent magnet high speed electric motors for turbocharger applications

Realization of electrically boosted turbochargers requires electric motors capable of operating at very high speeds. These motors often use a permanent magnet rotor with the magnets retained within an interference fit external sleeve. Whilst it is possible to model such systems numerically, these models are an inefficient tool for design optimization. Current analytical models of rotors typically consider the stresses induced by the shrink fit of the sleeve separately from the stresses generated by centripetal forces due to rotation. However, such an approach ignores the frictional interaction between the components in the axial direction. This paper presents an analytical model that simultaneously accounts for interaction between the magnet and outer sleeve in both the radial and axial directions at designed interference and with the assembly subjected to centripetal and thermal loads. Numerical models presented show that with only moderate coefficients of friction and rotor lengths; axial load transfer between magnet and sleeve takes place over a short distance at the ends of the assembly. The paper then demonstrates how the analytical model aids definition of a feasible set of rotor designs and selection of an optimum design

Limits, modeling and design of high-speed permanent magnet machines

There is a growing number of applications that require fast-rotating machines; motivation for this thesis comes from a project in which downsized spindles for micro-machining have been researched (TU Delft Microfactory project). The thesis focuses on analysis and design of high-speed PM machines and uses a practical design of a high-speed spindle drive as a test case. Phenomena, both mechanical and electromagnetic, that take precedence in high-speed permanent magnet machines are identified and systematized. The thesis identifies inherent (physical) speed limits of permanent magnet machines and correlates those limits with the basic parameters of the machines. The analytical expression of the limiting quantities does not only impose solid constraints on the machine design, but also creates the way for design optimization leading to the maximum mechanical and/or electromagnetic utilization of the machine. The models and electric-drive concepts developed in the thesis are evaluated in a practical setup which includes a slotless PM motor with a short rotor supported by aerostatic bearings.Electrical Power EngineeringElectrical Engineering, Mathematics and Computer Scienc

Trade-offs in design of high-speed permanent magnet generators for gas-turbine-based micro-CHP systems

Micro CHP (combined heat and power) systems based on gas turbines represent a typical application which widely exploits high-speed permanent magnet machines. As an energy application which implies electromechanical conversion at high speeds, it sets high requirements with respect to power density and efficiency. In order to fulfill these requirements, high energy magnet materials have to be used. Significant drawbacks of high energy magnets are their thermal and structural vulnerabilities. This paper describes initial choices and trade-offs with the machine design in order to satisfy requirements for high power density and efficiency; at the same time such a design must ensure proper operating conditions for magnet materials from thermal and structural point of view

Trade-offs in design of high-speed permanent magnet generators for gas-turbine-based micro-CHP systems

Micro CHP (combined heat and power) systems based on gas turbines represent a typical application which widely exploits high-speed permanent magnet machines. As an energy application which implies electromechanical conversion at high speeds, it sets high requirements with respect to power density and efficiency. In order to fulfill these requirements, high energy magnet materials have to be used. Significant drawbacks of high energy magnets are their thermal and structural vulnerabilities. This paper describes initial choices and trade-offs with the machine design in order to satisfy requirements for high power density and efficiency; at the same time such a design must ensure proper operating conditions for magnet materials from thermal and structural point of view

Vector control of very-high-speed PM machines

Although demand for very-high-speed machines is steadily growing, closed-loop control of such machines is rarely reported in literature. Field-oriented control of high speed machines meets a number of challenges: strong crosscoupling between orthogonal components of the voltage and current vectors, great variation of machine parameters during operation, an exceptionally negative influence of a delay and dead-time on the control stability and a short switching period available for the execution of the digital control. This paper gives rigorous representation of a control system with a high-speed permanent magnet synchronous machine in the rotating reference system. Two different methods of decoupling the current control are analyzed; especially, the effects of parameter variation and delay in the control loop are taken into account. The paper uses the development of a vector controller for a high-speed micro-turbine generator as a test case