On the Unification of Optimal Current Reference Theory for Wound Rotor Synchronous Machines

TL;DR

This paper extends optimal current reference theory to Wound Rotor Synchronous Machines, incorporating complex effects and providing computationally efficient solutions validated on a physical prototype.

Contribution

It generalizes existing current reference methods to WRSMs by including additional degrees of freedom and nonlinear effects, with a tractable optimization framework.

Findings

The approach yields closed-form or polynomial solutions in various regimes.

It extends the unified theory beyond permanent-magnet machines.

Experimental results demonstrate effectiveness across the torque-speed range.

Abstract

Controllers for motor drives typically require a current reference which will satisfy the requested torque subject to system constraints. This work generalizes existing current reference theory to the case of the Wound Rotor Synchronous Machine (WRSM). By incorporating the additional rotor-current degree-of-freedom, along with magnetic saturation, cross-coupling, and speed-dependent core losses, the problem of finding an optimal current reference is formulated within affine flux regions as a quadratically constrained quadratic program using a piecewise-affine approximation derived from finite-element data. The solution is characterized according to the active constraint regime, yielding closed-form or low-dimensional polynomial solutions in several cases, and a small semidefinite program in the voltage constrained regime. The proposed framework extends unified optimal current reference theory beyond the permanent-magnet setting to three degree-of-freedom WRSMs while remaining computationally tractable. Results on a physical WRSM prototype illustrate the effectiveness of the approach across the torque-speed operating envelope.