THE improvement of efficiency and power density in
an electric machine is a main issue on hybrid electric
vehicles (HEVs) because of their limited space, and hence,
interior permanent magnet synchronous motors (IPMSMs) are
suitable for HEV applications. However, an IPMSM requires
a rare-earth PM like neodymium and dysprosium known as
highly expensive materials leading to environment problems
during production. Hence, various studies on IPMSMs for an
HEV have received significant attention to eliminate PM from
the machine, such as a reluctance structure, or to replace rareearth
PM with rare-earth-free PM.