Winding MMF Research Articles

Research on Winding MMF Harmonics of the PMSM with the Same Number of Poles and Slots

Research on Winding MMF Harmonics of the PMSM with the Same Number of Poles and Slots

Investigation of Doubly Salient Structure for Permanent Magnet Vernier Machines Using Flux Modulation Effects

Recently, the permanent magnet vernier machine (PMVM) is studied extensively because of its merits such as the high torque density. Similar to the magnetic gears, the PMVM operates on the principle of flux modulation. However, there is a distinct difference in between the two as unlike the magnetic gear, in case of PMVM, the winding MMF harmonics rotates with different speed as that of the fundamental. As a result, these harmonics are capable of making a working magnetic field by interacting with different permeance harmonics. Therefore, this paper aims to provide an analytical explanation of this whole process, which is helpful to understand the effect of the flux modulation on the output torque. Furthermore, using the analytical formulation, this work finds the optimal geometric parameters which maximize the working magnetic field and hence the torque. A detailed analysis of the PMVM with the doubly salient structure is studied and the performance is analyzed using the finite element method (FEM) and the experimental setup. The FEM and experimental results verify the maximum torque production by using the optimal geometric parameters in the PMVM modeling, obtained using the analytical formulation.

Потери от вихревых токов в массиве постоянных магнитов магнитоэлектрических вентильных двигателей

Higher harmonic components of magnetic field in the air gap of permanent-magnet electrical machines cause eddy currents to occur in the bodies of permanent magnets, due to which the latter become heated and partially demagnetized. Expressions for the coordinate components of magnetic induction and eddy current density in the magnet body (given the known value of the n-th harmonic component of magnetic inductance on the magnet external surface) are obtained proceeding from analytical solution of the well-known Maxwell equations for the n-th harmonic component of magnetic field. It is shown that the electromagnetic wave energy enters into the magnet through the external cylindrical surface and lateral radial flat edges. It is also found that the power flux surface density in the first channel is constant, whereas that in the two other channels decreases exponentially in the radial direction. Therefore, it is not expedient to subdivide the pole magnet into elementary tiles in the transverse direction from the viewpoint of losses, because the losses in the first channel remain unchanged (i.e., they are invariant to decomposition), whereas the losses in the second channel increase (the total number of tile lateral edges increases in decomposing the magnet). The article presents a quantitative assessment of losses in samarium-cobalt magnets of a switched motor with a capacity of 15 kW due to a slotted stator surface outline, a non-sinusoidal waveform of the frequency converter voltage, and higher harmonic components of the stator winding MMF.

Harmonic Winding Factors and MMF Analysis for Five-phase Fractional-slot Concentrated Winding PMSM

To enhance torque density by harmonic current injection, optimal slot/pole combinations for five-phase permanent magnet synchronous motors (PMSM) with fractional-slot concentrated windings (FSCW) are chosen. The synchronous and the third harmonic winding factors are calculated for a series of slot/pole combinations. Two five-phase PMSM, with general FSCW (GFSCW) and modular stator FSCW (MFSCW), are analyzed and compared in detail, including the stator structures, star of slots diagrams, and MMF harmonic analysis based on the winding function theory. The analytical results are verified by finite element method, the torque characteristics and phase back-EMF are also taken into considerations. Results show that the MFSCW PMSM can produce higher average torque, while characterized by more MMF harmonic contents and larger ripple torque.

Hydro Generator High Voltage Stator Windings: Part 2 - Design for Reduced Copper Losses and Elimination Of Harmonics

Hydro generator stator winding design is one of the key factors when considering machine upgrades and uprates. The hydro generators built 30-50 years ago employed stator insulation systems with lower voltage stresses and correspondingly larger insulation allowances. Modern insulation systems use thinner, more homogenous insulations, which permit higher voltage stresses, while providing much improved thermal conductivity and better heat dissipation. There is therefore quite a scope for the high voltage (HV) stator winding designer to increase overall coil copper content by between 20-40%, which often provides copper losses at increased output not much higher than the losses produced by the existing winding at pre-uprate machine rating. In conjunction with the new insulation improved thermal dissipation, it is possible to design uprated windings with temperature rises similar to the existing ones. The main focus of the HV coil design for hydro generator upgrades and uprates is therefore reduction of copper losses, and optimisation of thermal characteristics for best dissipation of heat losses. The loads connected to the hydro generator terminals (transformers, transmission lines, switchgear, etc.) are all designed to operate with pure sinusoidal EMF (Walker, 1981). The purity limits of the generators’ open circuit wave are prescribed by the standards (AEMC, 2008). Given the salient pole construction of hydro generator rotor with large variation of magnetic permeance in direct and quadrature axes, and the concentrated nature of rotor field pole windings, special measures are implemented on the geometry of rotor pole face. They include pole face shaping for sinusoidal approximation of rotor MMF, and adjustment of damper winding geometry relative to the slotted periphery of stator bore for reduction of the slot ripples (Walker, 1981). Given the relatively slow hydro generator operational speeds and necessarily large number of poles, the stator winding consists of large numbers of pole phase groups having only a few coils (typically 1 to 3). The stator winding MMF will therefore be rather coarse, and special measures must be implemented to achieve the output waveform as close to a pure sinusoid as possible. This second of four papers on hydro generator stator windings (refer to Znidarich, 2008a, Znidarich, 2009b, and Znidarich, 2009c) describes some tools at the hydro generator stator winding designer’s disposal for effective reduction of harmonics and optimisation of output waveform purity. They include skewing of stator core slots, fractional (short) pitching of stator winding coils and fractional slot windings.

AN ANALYSIS OF ROTOR DOUBLE POINT GROUND FAULTS

ABSTRACT This paper analyses the second harmonic component which appears in stator emf during rotor double point ground faults or interturn faults. The second harmonic component can be used to realize rotor double point ground protection for large generators. Starting from basic physical concepts, the paper discusses the rotor winding mmf and gap flux density distribution during normal and fault conditions as well as corresponding stator harmonic emf. A method of “calculate flux density curve” is proposed, so that analysis process is simplified and more convenient.

Three-Dimensional Finite Element Analysis of Slitted Reaction Plate in Linear Induction Motor.

While a solid plate is usually adopted to the reaction plate of the linear induction motor (LIM), slits are often introduced to the plate in order to obtain the higher thrust force by enforcing eddy currents effectively. In this paper, we investigate the slit effect to find a suitable configuration of slits by the three-dimensional finite element analysis with A-φ method, and we propose a face-elements procedure with double nodes for φ at the slit to express its infinitesimal width. We also adopt a current-sheet expression, which consists of three regions for primary winding MMF, that is given by diamond coils. Based on above approaches, we evaluate the slit effect in the LIM, and compare it with the experimental data to conform the validity of the methods, resulting follows; (1) Number of slit per slot-pitch is required more than 4 for obtaining sufficient performances. (2) Preferable slit length is a little bit longer than the stator width. (3) A belt of no slit region in the middle part of the reaction plate is proposed from the structural point of view. However, its width should be less than 40% of the stator width to enforce eddy currents effectively.

STRAY LOSSES IN A SINGLE‐SIDED LINEAR INDUCTION MOTOR

The paper deals with the method of the stray losses calculation in single‐sided linear induction motors. The stray losses produced by the higher space harmonics of the primary winding MMF and by the primary slots have been discussed.

Theory of the Three Phase Salient Pole Type Generator with Bridge Rectified Output-Part I

The theoretical equations, describing the characteristics of a three phase salient pole type AC generator with asymmetrical damperwindings and bridge rectified output are derived. All resistance and rectifier drops are neglected; only the first winding MMF's and the first two permeance harmonics are considered. All winding inductances are defined in detail in App. I and are expressed in absolute and per-unit values. A set of equations is derived, defining the mutual relations between DC output voltage and current, start and duration of commutation, commutation current, constant and variable field current, damper circuit currents and instantaneous DC voltage fluctuations. By the use of two simplifying assumptions, this set is converted into explicit equations for the above values. These show that the inductance, determining the length of the commutation period is the equivalent of the average between the direct and quadrature subtransient inductances. Both a Star as well as a Delta connected stator winding is discussed. All equations can be expressed in generalized machine parameters. A numerical example is included.

An Accurate Method of Calculation or Subtransient Reactances of Synchronous Machines

A rigid method of estimation of the subtransient reactances for the direct and quadrature axes of synchronous machines is presented in this paper. The field and damper winding mmf (magneto-motive forces) are evaluated from the field forms and the rotor circuit leakage permeances for the two axes. Equations for the subtransient reactances in the most general form are derived in Appendix III.