Nonlinear Current Control of Reluctance Synchronous Machines With Analytical Flux Linkage Prototype Functions

The article proposes a nonlinear current control system of reluctance synchronous machines (RSMs) in combination with analytical flux linkage prototype functions. For highly nonlinear machines, such as RSMs, the magnetic characteristics change significantly throughout the whole operation range due to saturation and cross-coupling effects. Therefore, the current controller tuning must be adapted online to achieve a fast and accurate tracking performance. The proposed current controllers are derived based on the system theoretic concept of the exact input/output (I/O) linearization of the current dynamics. Thus, the nonlinear control system is simplified to an integrator which, in combination of proportional–integral controllers, can be tuned by means of pole placement similar to a phase-locked loop. For I/O linearization and control, the magnetic saturation and cross-coupling effects in the flux linkages and the differential inductances must be considered which is done by the utilization of analytical flux linkage prototype functions instead of lookup tables. The performance of the developed nonlinear current control system is validated by both, simulation and experimental results, for a highly nonlinear
$1.5 \,\mathrm{k}\mathrm{W}$
RSM. The results underpin 1) the very high approximation accuracy and the continuity and differentiability of the flux linkage prototype functions over the whole operation range and 2) the very fast and accurate tracking performance of the nonlinear I/O control system.