High-speed Permanent Magnet Machines Research Articles

Eddy Current Reduction in High-Speed Machines and Eddy Current Loss Analysis With Multislice Time-Stepping Finite-Element Method

The significance of eddy-current in high-speed permanent magnet machines cannot be underestimated in that it has serious implications on the machine's efficiency or even demagnetizes the PMs because of an overheating problem. It is necessary to accurately estimate the eddy-current losses and find an optimal design to minimize the losses and improve the machine's performance. In this paper, the axial segmentation of the PMs is first employed to cut off the eddy-current axial paths. Then, a conductive shield is introduced to smooth the time varying magnetic field in the conductive sleeve and the PMs in order to reduce the eddy-current losses. A nodal method based network-field coupled multislice time-stepping finite element method (TS-FEM) is proposed to analyze the steady-state and dynamic characteristics of the high-speed PM machine; its merit is that sub-block matrixes of the circuit equations are more convenient to be established compared with that of mesh method. Analysis of eddy-current losses in the rotor is reported.

Thermal Analysis and Test for a High Speed PM Machine for Fan Application

For a give air flux, the higher speed the fanner is running, the smaller the fanner’s size is. It is also well known that for a given power, the higher the machine’s running speed, the smaller the machine’s size has. If the fanner is geared to a high speed machine directly, the fan set’s volume will be sharply decreased. However, the heat dissipation of the high speed machine becomes a serious problem also due to the small size and high power loss density. Therefore, how to estimate accurately the power losses and temperature rise is a key issue for the high speed machine design. In this paper, the power losses and temperature of high speed PM machine for a fanner application are thoroughly investigated. And the test results of a prototype fan set partly shown the validity of the calculation method.

Beyond IEEE Std 115 and API 546: Test Procedures for High-Speed Multimegawatt Permanent-Magnet Synchronous Machines

High-speed multimegawatt permanent-magnet (PM) machines have been proposed in the literature and offered for sale in a variety of petrochemical applications. Presently, the discussion of synchronous machines in both the IEEE Std 115 and American Petroleum Institute 546 excludes the consideration of PM synchronous machines. These machines pose special problems when attempting to apply the test procedures given for the wound-field synchronous machines in that many of the tests rely on the ability to adjust the field strength. In addition, a PM-rotor topology has different performance and robustness concerns than a wound-field machine, and those should be addressed. This paper attempts to outline a coherent method for evaluating high-speed PM machines by extending the test procedures outlined in IEEE Std 115 and presenting additional procedures specific to PM machines. Extended application guidelines will be discussed for high-speed multimegawatt machines. The differences between the risk profiles for the PM and wound-field machines will be highlighted with a particular emphasis on the risk mitigation via tests for the PM machine.

Study on Anti-Demagnetization of Magnet for High Speed Permanent Magnet Machine

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> Compared with common permanent magnet (PM) machine, the high speed PM machine has smaller size and larger power density. However, the heat dissipation of the high speed machine becomes a serious problem due to the small size and high power loss density. More attention should be paid to the protection of the PM rotor from overheating demagnetization. In this paper, the magnetic properties of high speed PM rotor for different machine structure and speed are studied based on the combined analysis of magnetic, temperature and fluid fields. In order to protect the PM rotor from overheating demagnetization, a new structure of high speed machine having PM rotor with nonmagnetic enclosure and stator with inner and outer cooling vents is proposed. The theoretical analysis and experiment result of high speed PM machine show the validity of the proposed anti-demagnetization approach. </para>

Analytical Computation of the Full Load Magnetic Losses in the Soft Magnetic Composite Stator of High-Speed Slotless Permanent Magnet Machines

This paper presents an analytical model for predicting the stator full load magnetic losses in high-speed slotless permanent-magnet machines with surface-mounted magnets on the rotor and a stator core made of isotropic and conductive soft magnetic composite material (SMC). The losses are derived from the computation of the two-dimensional magnetic field distribution created by the rotor magnets, the currents in the stator windings and the eddy currents that circulate in the SMC stator core, according to the time and space harmonics. Both eddy currents and hysteresis losses are computed. The model is cross-validated by 2-D FE analysis in terms of magnetic field distribution and eddy currents losses. 3-D FE simulations are also carried out to quantify the end-effect on the stator no-load eddy current losses. The developed model is an efficient machine design tool, used here to quantify the variations of both the eddy currents and hysteresis losses under full load operation when the control angle is modified.

Multiphysics thermal design of a high-speed permanent-magnet machine

In the paper, different methods for thermal design of a high-speed permanent-magnet machine are presented. The first implemented method is a numerical-multiphysics method which couples computational fluid dynamics and heat-transfer equations. The geometry of the machine in this method is considered to be 2D axi-symmetric. This method gives simultaneous solutions for the turbulent properties of the cooling fluid as well as for the temperature rise in the fluid and solid domains of the machine, but it is primarily intended for solving the fluid domain. The distribution of the temperature rise in the solid domain of the machine is estimated with a 3D numerical heat-transfer method that is the second one implemented in this paper. This method uses the properties of the turbulent flow from the 2D multiphysics method such as the temperature rise of the fluid and the coefficients of thermal convection and implements them as boundary conditions. Validation of the aforementioned methods is done using the traditional thermal-network method that is based on analytical and empirical equations and this is the third method implemented in this paper. The comparison of the results between the different methods shows a very good agreement.

Losses in High Speed Permanent Magnet Machines Used in Microturbine Applications

High speed permanent magnet (PM) machines are used in microturbine applications due to their compactness, robust construction, and high efficiency characteristics. These machines are integrated with the turbines and rotate at the same speeds. This paper discusses in detail the losses in high speed PM machines. A typical PM machine designed for microturbine application is presented with its detailed loss calculations. Various loss verification methods are also discussed.

A Design Approach to Reduce Rotor Losses in High-Speed Permanent Magnet Machine for Turbo-Compressor

In this paper, a design approach to reduce rotor losses in high-speed permanent magnet machines for turbo-compressor is discussed. In particular, the influence of materials chosen for the retaining sleeve is highlighted. The two topologies of high-speed permanent magnet machines with Inconel718 and Carbon-Fiber/Epoxy sleeves are employed for comparison of computed rotor losses by two-dimensional finite-element method and analytical field analysis. It is shown that the Carbon-Fiber/Epoxy is superior to Inconel718 in terms of reducing rotor losses

Steady-State Finite-Element Solver for Rotor Eddy Currents in Permanent-Magnet Machines Using a Shooting-Newton/GMRES Approach

This paper presents a two-dimensional steady-state finite-element solver, incorporating mechanical motion, that calculates eddy-current losses in the rotors of permanent-magnet machines. A shooting-Newton method is used to determine the periodic solution of the electromagnetics. Computation of the shooting-Newton Jacobian is avoided by using a generalized minimum residual (GMRES) linear solver. This method is more computationally efficient than performing transient analysis until convergence. The solver can be used to compare the rotor losses of different design choices for a high-speed permanent-magnet machine. Results show that rotor losses can be reduced significantly by laminating the rotor backiron, segmenting the permanent-magnet poles, increasing the number of stator slots, and closing the stator slots.

Analysis of unbalanced force for high-speed slotless permanent magnet machine with halbach array

This paper reports on the comparison of two types of high-speed slotless permanent magnet machines with the rotor eccentricity as the motor/generator for an electromechanical battery. Using a two-dimensional finite-element method, this paper deals with the magneto static field and unbalanced forces. Specifically, the advantages of Halbach array are discussed when the rotor has eccentricity.

Enhanced current control of high-speed PM machine drives through the use of flux controllers

This paper compares various types of current controllers, including a novel method based on flux control. A proportional integral (PI) control method is used initially, to control the current in a high-speed permanent-magnet synchronous machine. The performance of this simple PI loop is presented, Various improvements to the PI controller are investigated, and the change in performance examined. A new current control scheme based on a flux-linkage model of the machine is introduced. The performance of the model-based control is demonstrated and compared with the performance of the PI current controller. Factors affecting the accuracy of the model-based control are given. By incorporating these factors into the model, the performance of the flux controller is further enhanced.

Use of canned rotors in high-field permanent magnet machines

The design of high speed permanent magnet machines needs to address conflicting requirements arising from the requirements of high electromechanical efficiency and mechanical strength and smoothness of running. This paper investigates the use of canning material surrounding the rotor, to give it mechanical strength, and investigates its consequences with regard to the electromagnetic performance of the motor at high speeds. Two designs are investigated in detail. The performance of a high-field magnet configuration is assessed experimentally, and compares well with the results predicted from finite-element computations.