Discussion on the Control of Wound-Rotor Synchronous Motors for Variable Speed Drives

For wound-rotor synchronous machines, one has four degrees of freedom to set a particular torque-speed operation point: Excitation current, phase current, phase current frequency and the current angle. It is desirable to set these parameters according to a particular strategy (e.g. Maximum Torque per Ampere). When the motor design is changed, the optimal combination of the four parameters at an operation point might change as well. To ensure a fair comparison of variants in the design process, it is desirable to assess them using their respective adapted control. This paper presents a workflow to calculate the best control parameters numerically and compute results for performance assessment. The calculation of the torque-speed envelope curve is used as exemplary means of performance evaluation. The suggested procedure is based on Finite-Element models without, however, becoming prohibitively computational expensive. Consideration of eddy-currents and core saturation is possible. Finally, torque-optimal control of wound-rotor synchronous machines is discussed in more detail.