Poopak Roshanfekr

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.

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.

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.

Investigation of pole number selection in a synchronous reluctance generator for wind applications

Literature suggests that a number of poles over 6 is not recommended for Synchronous Reluctance Machines (SynRM) up to the kW-range. To investigate if this fact is also valid for multi-MW Synchronous Reluctance Generators (SynRG), this paper compares such a SynRG with 6, 8 and 12 poles. The effect of different pole numbers on average torque, loss, torque-ripple, d and q inductances is investigated. It is shown that, and explained why, the 8 pole machine has similar performance to the 6 pole machine but the 12 pole machine has worse performance.

Effect of magnet coverage on torque, loss and torque ripple in a PMSM

This paper address the effect of magnet coverage on the torque, iron and magnet loss components and torque ripple of two surface permanent magnet synchronous generators of 5MW. The values of torque, torque ripple, iron and magnet losses are calculated using a FEM program. It is concluded that the optimal magnet coverage can only be found by extensive investigations for each specific machine. However, an estimate value of magnet coverage can be found from recommendations and formulas, including only the number of phases and the number of slots per pole per phase. It is shown that by investigating each individual machine for a magnet coverage between 0.7-0.9, the torque ripple can be reduced up to 40% and magnet loss can be reduced up to 28%.