Christian Carstensen

Temperature Rise Analysis of Switched Reluctance Motors Due to Electromagnetic Losses

We present a finite-element analysis of the temperature rise of switched reluctance motors (SRM) due to electromagnetic losses. We estimate the various components of electromagnetic losses, including core loss in the lamination as well as copper and eddy-current losses in windings, and then predict the temperature rise within the motor due to these losses. We present simulation results for an 8/6 SRM and discuss various aspects of thermal design of SRMs. To validate the procedure for the estimation of electromagnetic losses, we compare predicted and measured losses.

Flux Linkage Determination for Correct Modeling of Switched Reluctance Machines - Dynamic Measurement versus Static Computation

This paper presents a study on the determination of flux-linkage characteristics of switched reluctance machines. These characteristics are used to describe the behavior of individual machines for modeling as well as control purposes. Typically, the flux-linkage characteristics are either obtained by static FEM-calculations or by measurements. With the example of a 55 kW switched reluctance machine (SRM) it is shown that these two characterization methods do not inherently yield the same results but that they can differ more than 10%. FEM simulations are performed to analyze the dynamic processes occurring during flux-linkage measurements. It was found that current displacements due to winding eddy currents are responsible for a transient reduction of phase inductance and flux-linkage. Finally, it is investigated whether the results of static or dynamic flux- linkage determination are more accurate for look-up table based torque control.

Eddy currents in medium power switched reluctance machines

Switched reluctance machines are characterized by high local flux densities in the core, high current gradients in the windings and relatively large winding areas for the nondistributed windings. In particular, in medium-, high-power and high-speed machines these characteristics may lead to thermal problems. Hot spots in the windings are a result of losses, which originated from high-frequency alternating magnetic fields. It is identified that proximity effects situated at the pole tips and across the entire winding area are causing significant current displacements and in consequence for a considerable amount of copper losses. This paper reports the phenomenon of eddy currents in the windings of switched reluctance machines. Experimental verification and finite-element-simulation are presented for a 4-phase 55 kW switched reluctance machine.

Optimization of Predesign of Switched Reluctance Machines Cross Section Using Genetic Algorithms

Genetic algorithms (GA) have been applied in optimization of machine designs since the first publication in 1975 (J.H. Holland, 1992). In this paper, a practical implementation of this search technique in predesign of switched reluctance machines is presented. An optimized design was found by means of GA based on an objective function for maximizing an average torque of the machine, where dimensions and a thermal loading are specified. Moreover, an auxiliary objective for the most preferable geometries is utilized, well supporting a vector format of the model in GA. The simulation results verified and demonstrated the efficacy of the proposed strategy.