Electric Loss Measurement Technique for Synchronous PM Brushless Machines

A novel technique to identify, by direct electric measurements, the total losses at full load in synchronous permanent-magnet brushless ac machines is here presented. The proposed procedure can anyway be extended to anisotropic machines. The procedure adopts a back-to-back electric and mechanic connection capable to use a single three-phase power converter to perform a full power test. The coupled motors are driven in speed as an equivalent electric machine at no load. The motor load can be regulated by the physical angular displacement in between the rotors of the two machines, and the converter will control the speed and equalize the current amplitude in the motors. In this condition, the motors exchange active power at the shaft in mechanical form and at the electric connections in electrical form. The active power supplied by the converter in steady state results in the total power dissipated by the two motors. A simple algorithm to identify the current-to-mechanical angle relationship at a given speed is proposed. The measurement technique is simulated and verified using an experimental test bench that adopts two low-power high-torque electric machines.