Determination of efficiency of permanent magnet synchronous machines from summation of losses

Abstract

The determination of the efficiency of electrical machines by direct measurements is often too imprecise if the efficiency exceeds 95 %. For electrically excited synchronous machines a standardized method exists to determine the efficiency by summation of the individual losses. This method needs a variable excitation and therefore cannot be used for permanent magnet synchronous machines. As permanent magnet machines are increasingly used as wind turbine generators and traction motors, there is a large demand for an alternative method. In this project a new procedure is developed, which consists of a calculation of the losses at rated conditions via three different measurement series. The corresponding losses and circuit diagram parameters are determined from measurements at open circuit, measurements with removed rotor and measurements with pure reactive current. In addition to the theoretical calculations direct efficiency measurements are used to validate the efficiency calculation results. The two examined permanent magnet motors with fractional slot winding have a rated power of 45 kW.