Applying a Measurement-Based Iron Loss Model to an Efficiency Optimized Torque Control of an Electrically Excited Synchronous Machine

Electrically excited synchronous machines do not require expensive and temperature-dependent permanent magnets. Therefore they offer more safety, because there is no induced voltage when the excitation current has been turned off. For these reasons, electrically excited synchronous machines are getting interesting for different applications like electrical vehicles. For reaching higher torque and power density, an operation with high flux density is necessary. Hence, the behavior of the electrical machine is nonlinear. Through the possibility of varying the rotor excitation there is an additional degree of freedom for the determination of the operating point. For reaching high efficiencies at high speed, besides the copper losses, the iron losses have to be taken into account.Hence, this paper presents a method for calculating the iron losses based on nonlinear flux linkage maps. Based on this model, an efficiency optimized control strategy is introduced. The method is verified through measurements on the test bench and compared with the maximum torque per ampere control. The measurements show that the losses in partial-load operation can be significantly decreased, up to 20 %.