Evaluation of a newly proposed indirect efficiency determination method for permanent magnet synchronous machines

This paper evaluates the applicability of a newly proposed method for the indirect efficiency determination of permanent magnet synchronous machines by measuring individual losses. Similar methods are well-known and standardized for other kinds of electrical machines, but for permanent magnet synchronous machines, only the direct measurement of input and output power is standardized for efficiency determination according to IEC 60034-2-1. Measurements and finite element simulations are carried out for four selected test machines with a rated power range between 45 kW and 90 kW and with different stator and rotor topologies. It is shown that the proposed method is well applicable for permanent magnet synchronous machines with a distributed integer-slot stator winding. For machine designs with more rotor losses such as motors with tooth coil windings and open stator slots, larger deviations between the direct and indirect efficiency values of up to one percentage point are determined at rated load conditions.