Variable-flux Permanent Magnet Machine Research Articles

Manufacturing and Characterization of Novel Multilayer Magnets for Electrical Machine Applications

This paper presents the potentialities of diverse kinds of permanent magnet materials in order to build and characterize multilayer magnets, as well as to investigate their prospective application in electrical machines. In particular, bonded magnet and hybrid magnet powders are used to build two-layer samples, which pave the way for constructing special electrical machines with complex magnetic structures, such as the variable flux permanent magnet machines. In this study, samples of innovative double-layer magnets are built through a single press and the following magnetization procedure. A particular electromagnetic circuit is adapted to experimentally achieve the demagnetization characteristic to estimate the air gap magnetic flux behaviour in electrical machines. The measurement system flexibility allowed the testing of two double-layer magnets: the so-called parallel and series arrangements.

Design of Variable Magnetization Pattern Machines for Dynamic Changes in the Back EMF Waveform

Variable magnetization pattern permanent magnet synchronous machines (VMP-PMSMs) capable of dynamic changes in the magnetization spatial distribution are discussed in this paper. VMP-PMSMs are able to change the harmonic components in the air gap magnetic flux density due to the magnet by intentional demagnetization; hence, they can effectively manipulate the torque ripples and losses according to the required operating points. The objective of this paper is to provide a procedure to design VMP-PMSMs that can have both the sinusoidal and the trapezoidal back EMF waveforms by switching magnetization pattern. The performance of the designed VMP-PMSM following the reported procedure is confirmed through experiments as well as finite element analysis (FEA) simulations in terms of the back EMF shaping, torque ripple reduction, and loss reduction. Loss analysis of VMP-PMSMs is also given as contrasting with variable flux permanent magnet machines (VF-PMSMs), showing that VMP-PMSMs can reduce more losses than VF-PMSMs with the same torque density.

Core Loss Calculation in a Variable Flux Permanent Magnet Machine for Electrified Transportation

The paper is focused on the modeling and measurement of core losses in an AlNiCo-based variable flux permanent magnet machine. The application of AlNiCo as a low coercivity magnet provides the ability of the magnet flux control using short-time $d$ -axis current pulses. This allows a reduction in the machine core losses under high-speed conditions, thus improving the machine efficiency. In order to identify the machine efficiency gains, the core losses have to be accurately modeled at different magnetization levels. An advanced core loss model for the variable flux machine (VFM) is first presented. This model is based on the calculation of an equivalent sinusoidal waveform of nonsinusoidal magnetic flux density. The model is then utilized to calculate the core losses in a tangentially magnetized VFM using finite-element simulation. In order to validate the developed model experimentally, a measurement method is developed to segregate the mechanical losses and the no-load core losses at different speeds and magnetization levels for a 5-hp VFM. Finally, the proposed model accuracy is verified through a comparison with the experimentally measured core losses under a no-load condition.

Characterization of a Variable Flux Machine for Transportation Using a Vector-Controlled Drive

Variable flux machines (VFMs) have one more dimension for the control and performance improvement of the drive. The magnet flux in the VFM can be controlled to optimize motor performance. Software packages used in the design and performance evaluation of variable flux permanent magnet (PM) machine use a single demagnetization curve and recoil the operating point based on a linear recoil line parallel to the original demagnetization curve. Since the magnets like AlNiCo that is used in VFM have a nonlinear demagnetization curve, performance prediction of a VFM designed using finite-element software needs experimental verification. This paper presents a method based on vector control for the characterization of a VFM. An existing drive is used to measure the dq inductances of the machine at several magnetization levels, including the cross-magnetization effects. The same technique is extended to measure the torque-ripple and the torque-angle characteristics of the machine at different magnetization levels. Experimental results are provided for a 5-hp variable flux PM machine. The proposed method uses an existing drive to perform the tests, requiring no additional test setup.

Review of Variable-flux Permanent Magnet Machines

Variable-flux permanent-magnet machines (VFPM) are of great interest and many different machine topologies have been documented. This paper categorizes VFPM machine topologies with regard to the method of flux variation and further, in the case of hybrid excited machines with field coils, with regard to the location of the excitation sources. The different VFPM machines are reviewed and compared in terms of their torque density, complexity and their ability to vary the flux.