Freddy Magnussen

Parasitic Effects in PM Machines With Concentrated Windings

Permanent-magnet machines using concentrated windings are gaining popularity at the expense of distributed windings in various applications, mainly due to cost savings. The result is often an increased amount of parasitic effects like ripple torque, alternating magnetic fields in the rotor, unbalanced radial forces, and magnetic noise. This paper describes the reasons for the parasitic effects, in which machine topologies are particularly sensitive, and suggests measures in order to reduce their importance. Both traditional and modular concentrated windings are analyzed, as well as double-layer and single-layer windings. Measurements on a prototype motor and three commercial servomotors have demonstrated that modular motors are favorable regarding ripple torque minimization.

Permanent-Magnet Optimization in Permanent-Magnet-Assisted Synchronous Reluctance Motor for a Wide Constant-Power Speed Range

A permanent-magnet (PM)-assisted synchronous reluctance (PMASR) machine exhibits both high efficiency and high flux-weakening (FW) range. However, the best performance is achieved after a machine design optimization. In industry applications, the design of PMASR machines requires to satisfy an increasing number of limitations. The key points are lamination geometry, material property, and control strategy. This paper analyzes the influence of PM volume (flux level) on the motor performance, although lamination geometry and stack length are kept fixed. Thus, the PM volume inset in the rotor is optimized. The considered PMASR motor is designed for a very high FW speed range. The study is based on a finite-element (FE) analysis. The accuracy of the FE simulations is verified comparing their results with measurements on a prototype. The FE model is then used to study the different cases.

Analysis and Tests of a Dual Three-Phase 12-Slot 10-Pole Permanent-Magnet Motor

In order to increase the fault tolerance of a motor drive, multiphase systems are adopted. Since custom solutions are expensive, machines with dual three-phase windings supplied by two parallel converters seem to be more convenient. In the event of a fault, one of the two three-phase windings (the faulty winding) is disconnected, and the motor is operated by means of the healthy winding only. A fractional-slot permanent-magnet (PM) motor with 12 slots and 10 poles is considered with two different rotor topologies: the interior PM (IPM) rotor and the surface-mounted PM rotor. Various winding configurations of dual three-phase windings are taken into account, comparing average torque, torque ripple, mutual coupling among phases, overload capability, and short-circuit behavior. Considerations are given regarding the winding arrangements so as to avoid excessive torque ripple and unbalanced radial forces in faulty operating conditions. An IPM motor prototype has been built, and experimental results are carried out in order to verify the numerical predictions.

Incorporating Lamination Processing and Component Manufacturing in Electrical Machine Design Tools

Measures to improve the modeling of steel-sheet laminations in electrical machine design tools are studied. Only the magnetic properties, namely, the permeability (BH curves) and the iron losses are addressed. The sensitivity of these properties upon dimensional, directional (anisotropy) and excitation variations, as well as upon the electrical machines manufacturing steps is evaluated. The studied electrical machines manufacturing step are: guillotine, laser-cutting, welding, pressing and punching. The properties of the delivered lamination coils and the various associated loss figures are also statistically benchmarked. The focus is on finding guidelines for incorporation of these sensitivities in design tools when needed. For this purpose, 5 Hz to 10 kHz tests are conducted on Epstein strips, on L-shaped segments and on standard stator laminations. Two different steel grades are studied. It is shown that the lateral dimension, anisotropy and welding influences are much more pronounced then those for punching, pressing and laser cutting and hence, need to be addressed in design tools. It is found that the commonly used Epstein test results of the coils are slightly inferior to the mean loss value of the online-testing (losses that are measured at every 1 m of the entire coil length). It is also noted that, the delivered laminations are almost always better than those ordered and the losses for each individual lamination coil are nearly constant.

Faulty Operations of a PM Fractional-Slot Machine With a Dual Three-Phase Winding

The permanent-magnet (PM) machine with dual three-phase windings is proposed for applications requiring continuous operating even under a partial fault. The two windings are supplied by two separate inverters. Thus, in the event of a fault of one winding, this is disconnected, and the machine continues to be operated by means of the healthy winding. This paper investigates the PM machine with dual three-phase windings and its capabilities during faulty operating conditions. A fractional-slot interior PM machine with 12 slots and 10 poles is taken into account. Its performance is investigated according to different winding configurations. The torque behavior, overload capability, and thermal limits are evaluated under open-circuit and short-circuit faults. A finite-element analysis as well as experimental tests is carried out on a prototype of such a machine.

Parasitic effects in PM machines with concentrated windings

PM machines using concentrated windings are gaining in popularity at the expense of distributed windings in various applications, mainly due to cost savings. The result is an increased amount of parasitic effects like ripple torque, alternating magnetic fields in the rotor, unbalanced radial forces and magnetic noise. This paper describes the reasons for the parasitic effects, which machine topologies that are especially sensitive and suggests measures in order to reduce their importance. Both traditional and modular concentrated windings are analyzed, as well as double layers and single layer windings. Measurements on a prototype motor and three commercial servomotors have demonstrated that modular motors are favorable regarding ripple torque minimization.

Six-Phase Supply Feasibility Using a PM Fractional-Slot Dual Winding Machine

The growing interest in fault-tolerant drives requires new solutions avoiding the adoption of custom and expensive configurations. The machine with a dual three-phase winding is an interesting candidate. It is provided with two windings, each of them fed by one converter of half power. With a proper mechanical and electrical arrangement, the machine can be exactly a six-phase machine, obtaining higher performance during healthy conditions. In the event of a fault, one of the two three-phase windings (the faulty one) is disconnected, and the machine is operated by means of the healthy winding only. This paper analyzes the feasibility of this dual winding configuration applied to a nonoverlapped-coil fractional-slot winding permanent-magnet machine. The star of slots is applied to highlight the proper winding candidates. The more interesting windings are deeply analyzed.

Rotor Flux-Barrier Geometry Design to Reduce Stator Iron Losses in Synchronous IPM Motors Under FW Operations

The interior permanent-magnet (IPM) synchronous motor is characterized by a high rotor anisotropy. Such an anisotropy is the cause of a high harmonic content of the air-gap flux density distribution, almost independent of the main flux. As a consequence, there are fluctuations of the flux density in the stator iron and, consequently, eddy-current iron losses. This aspect is prominently evident during flux-weakening operations, when the armature current weakens the permanent magnet flux and the motor runs above the base speed. This paper presents a complete study of such a phenomenon, including an analytical model and a finite element validation, as well as an experimental confirmation of the predicted stator tooth flux waveforms. Finally, some suggestions are given in order to design an IPM motor exhibiting reduced iron losses during all operating conditions.

Remarks on Torque Estimation Accuracy in Fractional-Slot Permanent-Magnet Motors

In permanent-magnet (PM) synchronous machines, when using integral-slot windings, the torque computed by using the d-q -axis theory is almost independent of the variation of the flux linkage with the rotor position. This is not verified when fractional-slot PM motors are used. The iron saturation greatly affects the torque behavior, increasing the torque ripple significantly. Particular care is necessary to determine the average torque and the torque ripple when dealing with fractional-slot PM motors. The analysis is carried out by means of a finite-element (FE) model. Since, in synchronous PM machines, the current control imposes constant d- and q-axis currents, the FE solutions are strictly related to the classical d- q-axis theory. The impact of iron saturation is taken into account, comparing a 24-slot 4-pole integral-slot machine and a 24-slot 20-pole fractional-slot-winding machine. Particular attention is given to the interior PM machines.

Design considerations to maximize performance of an IPM motor for a wide flux-weakening region

Interior permanent magnet (IPM) synchronous machines result to be a valid motor topology in case of both high efficiency and high flux-weakening range. In industry applications the design of interior permanent magnet (IPM) synchronous machines requires to satisfy an increasingly number of limitations. For an IPM machine the key parameters that can be used for a performance maximization refer to many aspects: geometry, material property, cost, control strategy. According to the size and geometry limitations of an IPM motor for a very high flux-weakening speed range is required, the paper analyzes how to maximize the performance modifying the PM quantity. FE simulations, are firstly verified comparing the results with measurements on a prototype, and then they are used to evaluate the tradeoffs of the different cases.