An At-All Operating Points Highly Efficient PMSM for HEV

Average losses of the electric drive throughout a driving cycle are an important issue for hybrid electric vehicles. Permanent magnet synchronous electric motors (PMSM) are the most efficient electric drives under load conditions. However, they suffer from idle losses at high speed and low load, which is a typical operating condition in highway cycles. This leads, in some cases, to even higher fuel consumption of HEV vs. conventional vehicles.
As well designed permanent magnet machines for HEV usually have excellent efficiency at operating points close to their rating, the main focus of the presented work is achieving an improvement in no load and reduced load conditions. Such losses will occur at high speed and low load, because the PMSM creates an induced voltage exceeding the battery voltage, which must be compensated by an inductive voltage drop through the motor inductance by a purely reactive current causing losses.
A proposal for a special design for PMSM with regard to the ability of active reduction of those losses at high speeds is made in the following comment: The compensation current depends on the motor inductance. Obviously, a high inductance in the axis of magnetization needs a low compensation current, whereas a low inductance in the quadrature-axis results in a large constant power range. So a special design of an asymmetrical PMSM has been developed in order to achieve minimum idle losses.