Mikael C D Alatalo

Selecting IGBT module for a high voltage 5 MW wind turbine PMSG-equipped generating system

In this paper, a fairly high voltage generating system for a 5 MW generating system is investigated. The generating system consists of a surface mounted PMSG (Permanent Magnet Synchronous Generator) with a 2-level transistor converter. The focus is on utilizing three available high voltage IGBT-modules, and to investigate the resulting losses when using them to compose a converter, in order to observe the difference as well as the best choice. In addition, the ideal dc-link voltage for a certain module as well as for a certain main average wind speed is studied. It is found that the most suitable module to use from the loss point of view is the 1.7 kV module, the one with the lowest voltage rating. The difference towards using the 6.5 kV module is a loss increase in the converter at rated operation of 62 %. This is in spite of that a converter composed of the 6.5 kV module has less than half of the conduction losses compare to 1.7 kV module. Accordingly, it can be understood that the switching losses increase much stronger than the conduction losses decrease when using a module with higher voltage rating. When looking at the average annual energy efficiency difference, the best annual efficiency is also achieved when the converter is composed with the 1.7 kV modules.

Electric machine design for traction applications considering recycling aspects-review and new solution

With the expansion of the fleet of electric and hybrid electric vehicles worldwide, it is of interest to consider recycling aspects of the parts that are introduced in these new vehicles. This paper focuses on the design of electrical machines considering recycling of its components. The materials to consider are mainly copper, core materials such as lamination steel or iron, and permanent magnets. One design is suggested with a core material of soft magnetic composites which is very suitable for recycling as it is a brittle material and thus simplifies the access of the copper winding. The suggested design shows to have similar performance to a similar size and similar weight commercial permanent magnet electric machine made with steel lamination.

Comparison of a 5MW permanent magnet assisted synchronous reluctance generator with an IPMSG for wind application

This article presents a performance comparison of a 5MW interior permanent magnet synchronous generator (IPMSG) with a 5 MW permanent magnet assisted synchronous reluctance generator (PMa-SynRG) with the same stator, to be used for a wind energy application. It is found that PMa-SynRG has lower rotor weight as well as 14 % lower magnet weight with the same maximum torque performance. For wind speeds lower than 8.5 m/s the PMa-SynRG has less loss. Moreover, the machine annual energy efficiency for the PMa-SynRG is higher for average wind speeds between 5-10 m/s.

Torque Ripple Reduction Methods for an Interior Permanent Magnet Synchronous Generator

This article presents the effect of different torque ripple reduction methods on the average torque and back-emf harmonics. Two methods are compared. One is skewing the stator of the machine and the other method is using a fractional slot winding for the machine. It has been shown that both methods reduce the torque ripple of the IPMSM by 70% while the impact on the average torque is ignorable. The back-emf harmonics will be also reduced.

A segmented claw-pole motor for traction applications considering recycling aspects

With the expansion of the fleet of electric and hybrid electric vehicles worldwide, it is of interest to consider recycling aspects of the parts that are introduced in these new vehicles. This paper focuses on the design of an electrical machine, a claw-pole motor, considering recycling of its components. The suggested design has segmented core parts of soft magnetic composites which yield a design very suitable for recycling as the core material is brittle and it thus simplifies the access of the copper winding. The windings are pre-formed ring-coils with a high fill-factor and with no end-windings. Through the use of direct water cooling, employing space between the claws, the current density can be high, and the machine can be compact. The results of finite element simulations of the electromagnetic properties (previously validated against measurements) show that a high performance recyclable motor with ratings above 10 kW can be made. In comparison with a commercial motor, the claw-pole motor has similar performance, a higher core and magnet weight and a lower copper weight. It also has an expected advantage regarding manufacturing cost and cost of recycling and it has lower copper loss.

An electric machine design procedure that includes multiple cost scenarios

This paper presents a procedure to include different cost scenarios of raw materials into the design of electric machines. The ratio between performance and material cost is visualized over a number of different cost scenarios. It is thereby possible to see not only if a specific design is competitive under the current market circumstances, but also to compare the sensitiveness for fluctuations in the material prices.

Wireless Charging for vehicles-Some Key Elements

In this paper so called wireless charging is investigated, primarily considering applications such as charging hybrid or electric vehicles at stand-still. The base concept investigated is a sending and a receiving coil at various designs. The theory behind wireless energy transfer and the needed components are described and analyzed, showing how design aspects, frequencies, height and vertical displacement affect the results. Analytical expressions, measurements, as well as FEM analyses in 2D and 3D with two different FEM programs have been compared, with a reasonable agreement between methods.

DC-link voltage selection for a multi-MW wind turbine

Purpose – The purpose of this paper is to investigate how the dc-link voltage for the converter of a wind generator should be selected, i.e. to determine the losses in the generator and the converter when using various dc-link voltage levels. Design/methodology/approach – To presents the efficiency evaluation of 5MW wind turbine generating systems, two 5MW surface mounted permanent magnet synchronous generators (PMSG) with medium and low rated voltage is designed. A two-level transistor converter is considered for ac/dc conversion. Three different dc-link voltage levels are used. By using these voltage levels the PMSG is utilized in slightly different ways. Findings – It is found that the system with the lower voltage machine has slightly higher annual energy efficiency compare to the higher voltage system. Furthermore, it is shown that the best choice for the dc-link voltage level is a voltage between the minimum voltage which gives the desired torque and the voltage which gives Maximum Torque Per Ampere. Originality/value – A procedure as well as investigations with quantified results on how to find the highest complete drive system efficiency for a wind turbine application. Based on two given PMSG, the most energy-efficient dc-link voltage has been established.

Three traction motors with different magnet materials — Influence on cost, losses, vehicle performance, energy use and environmental impact

The aim of reducing both cost and environmental impact of automotive electric traction motors motivates the examination of motor performance when using magnets of varying strength and materials. Such investigations have attracted increasing interest in recent years. Given the same take-off torque capability, three motors are compared that have the same stator geometry but different magnet materials in the rotor; two PMSMs — one with Nd(Dy)FeB and one with SmCo magnets — and one PMaSynRM with strontium-ferrite magnets. To compensate the weaker magnets, their corresponding core stacks are prolonged. The resulting torque capability at high speed levels is lower for the SmCo PMSM and ferrite PMaSynRM compared to the Nd(Dy)FeB PMSM. The ferrite PMaSynRM has the poorest dynamic vehicle performance, but also the lowest energy losses over a wide range of drive cycles. In addition, the ferrite based motor option has the lowest environmental impact during manufacturing as well as the lowest material cost estimate. The SmCo motor has slightly lower losses than the Nd(Dy)FeB, but the highest material cost. Certainly, the result signals that further in-depth studies of the described PMaSynRM are of high relevance.

An LCL filter with an active compensation for a fast charger station

For the AC/DC stage of a 50 kW fast charger station which is a three-phase pulse width modulated (PWM) converter, an LCL filter is designed and constructed. As a PWM converter, the rectifier is a source of high frequency harmonics demanding filtering action to meet the grid regulations. Hence, the required filtering specification by the LCL filter is extracted using an appropriate harmonic model of the converter. The design procedure and the filter transfer function are presented. In addition, an active compensator is proposed to enhance the converter power factor by modification of the reference q current. Some simulation results are provided to show the effectiveness of the filter.