Maria Polikarpova

Evaluation of the Efficiency of Line-Start Permanent-Magnet Machines as a Function of the Operating Temperature

The standard squirrel-cage induction machine has nearly reached its maximum efficiency. In order to further increase the energy efficiency of electrical machines, the use of permanent magnets in combination with the robust design and the line start capability of the induction machine is extensively investigated. Many experimental designs have been suggested in literature, but recently, these line-start permanent-magnet machines (LSPMMs) have become off-the-shelf products available in a power range up to 7.5 kW. The permanent magnet flux density is a function of the operating temperature. Consequently, the temperature will affect almost every electrical quantity of the machine, including current, torque, and efficiency. In this paper, the efficiency of an off-the-shelf 4-kW three-phase LSPMM is evaluated as a function of the temperature by both finite-element modeling and by practical measurements. In order to obtain stator, rotor, and permanent magnet temperatures, lumped thermal modeling is used.

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.

Rotor surface ferrite magnet synchronous machine for generator use in a hybrid application — Electro-magnetic and thermal analysis

To reach a particular tangential stress in a PMSM the magnetic loading and the electric loading should have corresponding values. This means that if the magnetic loading is restricted by the characteristics of cheap and relatively weak ferrite permanent magnets, the electric loading should be increased to keep the tangential stress at desirable value. However, the latter is also limited because of the demagnetization risk of the permanent magnets by a high armature reaction. Therefore, surface ferrite PMSMs should have a low tangential stress in order to avoid the demagnetization risk, which consequently leads to a low torque density. This is one of the main drawbacks of ferrite magnets used in electric motor drives. This paper describes some possibilities for improving the torque density with surface ferrite PMSMs, describes the restrictions which one can meet while designing this type of the electric machines and observe the influence of temperature variation in the magnets on the electric machine performance. An example is done with the analytical and the FEM analyses of a 50 kW, 3000 rpm, permanent magnet generator for a series hybrid electric vehicle application.

Multidisciplinary Design of a Permanent-Magnet Traction Motor for a Hybrid Bus Taking the Load Cycle into Account

An electrical and mechanical design process for a traction motor in a hybrid bus application is studied. Usually, the design process of an electric machine calls for close cooperation between various engineering disciplines. Compromises may be required to satisfy the boundary conditions of electrical, thermal, and mechanical performances. From the mechanical point of view, the stress values and the safety factors should be at a reasonable level and the construction lifetime predicted by a fatigue analysis. In a vehicle application, the motor has to be capable of generating high torque when accelerating, and in normal operation, the losses of the machine should be low to be able to cool the machine. Minimization of the no-load iron losses becomes a very important electrical design requirement if the traction motor and the generator are mechanically connected with an internal combustion engine when it is operating as the only source of torque. The manufacturing costs of the motor are also taken into account in this paper.

Reliability analysis of a direct-liquid cooling system of direct drive permanent magnet synchronous generator

Wind turbines intended for electricity production are growing in power capacity with each new generation. At the same time, wind farm economics is demanding increased reliability to minimize costs and maximize productivity. These trends are driving a need for more powerful and more reliable energy conversion, and the DD-PMSG is quickly becoming the standard wind turbine generator. Larger DD-PMSGs must be liquid cooled to meet upcoming power capacity demands without exceeding practical limits for size, weight, and capital cost. However, liquid cooling is a new technology for wind turbines and its impact on reliability must be evaluated. This paper presents a reliability analysis for a liquid-cooled 8 MW DD-PMSG coupled with primary and secondary liquid coolant systems. Reliability has been calculated analytically and assessed based on the following reliability metrics: MTBF, MDT, MTTF, failure intensity, and availability.