Brushless Permanent Magnet Motor Design- P4 docx

Brushless Motor Operation because the layout of the end turns is subject to few restrictions and a set magnetic field distribution is impossible to define As a result, the end turn inductance is often roughly approximated, e.g., LiwschitzGarik and Whipple (1961) The approach followed here for computing end turn leakage inductance is to use the coenergy approach, expressed by (4.17), and to assume that the magnetic field is distributed about the end turns in the same way that it is about an infinitely long cylinder having a surface current/, as illustrated in Fig 4.19 If the current I is equal to ni, then from (4.17) the inductance of a section of the cylinder of length Z out to a radius R is \r 77 (4.20) Application of this expression to find the end turn leakage inductance requires finding appropriate values for Z, R, and r If the end turns are semicircular as shown in Fig 4.20, then these parameters can be approximated by Z = R 77" 7"n - Ì cLqw r, = V IT r