Testing and Modelling of Electrical Traction Machines : Performance Characterisation with Measurements from Transient Operation

Abstract: This thesis presents methods to derive and model the performance characteristics of interior permanent magnet machines – a machine type which is commonly used for propulsion of electrical vehicles. The thesis divides the performance characteristics into three subcategories: The electromagnetic properties, the loss profile and the thermal behaviour of the machines. One separate characterisation method is presented for each subcategory. However, all three methods have in common that they use data solely from mechanical or thermal transient operation. The methods aim to derive the characteristics with as little and as cheap equipment as possible, and to minimise the duration of the tests.The procedure that derives the electromagnetic properties uses measurements from when the test objects accelerate and brake. The method obtains the relationship between the current and the linked magnetic flux in the stator windings with relatively small means, and it does not demand a brake machine or a power analyser. Furthermore, due to the low time duration of the tests, the method is well suited to derive the temperature dependence of the current/flux relationships. The loss profile of the machine is derived with a similar method as the magnetic model, but requires lower mechanical dynamics. Therefore, the method generally requires an increase of the moment of inertia of the rotating parts of the machines. This is typically achieved by mounting flywheels on the shafts of the test objects. The method yields results that are well suited to use as identification data for loss models of the machines. The thermal characteristics of the test objects are obtained from temperature measurements during transient thermal conditions. The measured data are used to derive an equivalent circuit that describes the thermal behaviour of the test objects well.