Pavel Ponomarev

Effect of Slot-and-Pole Combination on the Leakage Inductance and the Performance of Tooth-Coil Permanent-Magnet Synchronous Machines

The influence of slot-and-pole-number combinations on the leakage inductance of double-layer fractional-slot concentrated nonoverlapping winding (i.e., tooth-coil winding) permanent-magnet synchronous machines is studied. A Fourier-analysis-based method for calculating the harmonic air-gap leakage inductance applied to the current-linkage waveform (winding function) in the air gap is suggested. Different slot-and-pole combinations are considered, and their influence, in particular, on the air-gap leakage inductance is indicated. In tooth-coil machines, the air-gap harmonic leakage can have a surprisingly large impact on the machine performance.

Unequal Teeth Widths for Torque Ripple Reduction in Permanent Magnet Synchronous Machines With Fractional-Slot Non-Overlapping Windings

Permanent magnet synchronous machines (PMSMs) with fractional-slot non-overlapping windings, also known as tooth-coil winding PMSMs (TCW PMSM), have been under intensive research during the latest decade. There are many optimization routines explained and implemented in the literature to improve the characteristics of this machine type. This paper introduces a new technique for torque ripple minimization in TCW PMSM. The source of torque harmonics is also described. The low-order torque harmonics can be harmful for a variety of applications, such as direct drive wind generators, direct drive light vehicle electrical motors, and for some high-precision servo applications. The reduction of the torque ripple harmonics with the lowest orders (6th and 12th) is realized by machine geometry optimization technique using finite element analysis. The presented optimization technique includes the stator geometry adjustment in TCW PMSMs with rotor surface permanent magnets and with rotor embedded permanent magnets. Influence of the permanent magnet skewing on the torque ripple reduction and cogging torque elimination was also investigated. It was implemented separately and together with the stator optimization technique. As a result, the reduction of some torque ripple harmonics was attained.

Influence of Travelling Current Linkage Harmonics on Inductance Variation, Torque Ripple and Sensorless Capability of Tooth-Coil Permanent-Magnet Synchronous Machines

This paper introduces an important source of torque ripple in permanent-magnet synchronous machines with tooth-coil windings (TC-PMSMs). It is theoretically proven that saturation and cross-saturation phenomena caused by the nonsynchronous harmonics of the stator current linkage cause a synchronous inductance variation with a particular periodicity. This, in turn, determines the magnitude of the torque ripple and can also deteriorate the performance of signal-injection-based rotor position estimation algorithms. An improved dq-inductance model is proposed. It can be used in torque ripple reduction control schemes and can enhance the self-sensing capabilities of TC-PMSMs.

Inductance Calculation of Tooth-Coil Permanent-Magnet Synchronous Machines

Analytical calculation methods for all the major components of the synchronous inductance of tooth-coil permanent-magnet synchronous machines are reevaluated in this paper. The inductance estimation is different in the tooth-coil machine compared with the one in the traditional rotating field winding machine. The accuracy of the analytical torque calculation highly depends on the estimated synchronous inductance. Despite powerful finite element method (FEM) tools, an accurate and fast analytical method is required at an early design stage to find an initial machine design structure with the desired performance. The results of the analytical inductance calculation are verified and assessed in terms of accuracy with the FEM simulation results and with the prototype measurement results.

Hybrid Cooling Method of Axial-Flux Permanent-Magnet Machines for Vehicle Applications

Thermal properties are a key issue in many applications associated with electrical machines. Because of its special configuration, an axial-flux electrical machine usually uses self-ventilation. However, this cooling method has a significant impact degrading the machine operating characteristics, and thus, an independent cooling system is desirable. The focus of this paper is on the steady-state thermal modeling and laboratory testing of an axial-flux permanent-magnet (AFPM) electrical machine intended for a traction application. The proposed hybrid cooling arrangement consists of a frame cooling circuit with a water flow inside, a set of copper bars inserted in the teeth, and a segment of potting material around the end windings. Computational fluid dynamics and finite-element analysis are applied for the preliminary design. This paper provides experimental verification of the simulation results on a 100-kW AFPM electrical machine.

Influence of wedge material on losses of a traction motor with tooth-coil windings

Permanent magnet (PM) machines with tooth-coil windings are designed and analyzed. We study how the slot wedge material affects the behaviour of losses when using tooth-coil windings. The losses of an interior permanent magnet rotor are studied over a wide speed range. A finite element analysis applying Cedrats Flux2D is made. Motors of this size can have high permanent magnet eddy current losses, and therefore, segmented magnets are often preferred even though interior magnets and semi-magnetic wedge materials are used. The study shows that tooth-coil windings may benefit from using a semi-magnetic material as a wedge material as it decreases the rotor iron losses and, especially, losses in the permanent magnets. The study shows also that wedges with relative permeabilities higher than 3 would not benefit this traction motor design, because of high losses and low maximum torque. Computations are compared to measurements of a 110 kW prototype traction motor.

Torque ripple reduction in double-layer 18/16 TC-PMSMs by adjusting teeth widths to minimize local saturation

The saturation in the stator teeth of an 18-slots 16-poles TC-PMSM with sinusoidal current supply caused by the interaction of armature reaction fluxes and rotor-PM-produced fluxes is studied. It is found that under load some teeth are saturated deeper than others. An increase in the width of these teeth reduces the oversaturation, which locally prevents the decrease in the inductance and back-EMF, and, consequently, reduces the torque ripple in the machine. The proposed technique can also be applied to other types of TC-PMSMs.

Selection of Geometric Design Variables for Fine Numerical Optimizations of Electrical Machines

This paper proposes an extended set of variables for numerical optimizations of tooth-coil permanent magnet synchronous machines (TC-PMSMs). The design variables for the extended set are chosen based on the magnetic asymmetries introduced by the saturated core under the loading conditions. The extended set allows to reach considerably higher values of torque density and significant reduction of torque ripple in comparison with a conventional set of optimization variables. The conventional and extended sets are compared on an example of an finite element method simulation of a double-layer winding surface permanent magnet-rotor TC-PMSM. A considerably better optimal machine is obtained when the extended set of variables is utilized. The paper showcases the design and the optimization of electrical machines using only free and open-source software.

Current linkage harmonics and air-gap harmonic leakage inductance of tooth-coil permanent-magnet synchronous machines

This paper emphasizes the importance of current linkage harmonics for tooth-coil permanent magnet synchronous machines (TC-PMSMs). In the literature the importance of the current linkage harmonics for the design of TC-PMSMs has so far been underestimated. It is shown that the current linkage harmonics affect a lot the performance and efficiency of this type of machines. The torque capability and field-weakening capability strongly depend on the harmonic spectra of the current linkage waveform. Losses in a TC-PMSM are also dependent on the spectrum of the current linkage waveform of the selected slot-and-pole combination. This paper presents a thorough analysis of the influence of the current linkage harmonics on the synchronous inductance of TC-PMSMs.

Torque ripple reduction in 12-slot 10-pole fractional slot permanent magnet synchronous motors with non-overlapping windings by implementation of unequal stator teeth widths

This paper describes an optimization of the stator geometry in a way that the torque ripple at particular load is reduced. The principle applied to the torque ripple reduction is based on the synchronous inductance variation suppression, caused by the non-linear steel saturation, which might be significant even in permanent magnet synchronous motors (PMSMs) with rotor surface permanent magnets. The design optimization, described in this paper, aims in reducing the armature reaction influence on the local steel saturation in fractional slot permanent magnet synchronous machines (FSPMSM) by rearranging of the stator teeth widths. The optimization was defined by means of magnetic equivalent circuit model (lumped model), and verified with finite element method (FEM).