Flux-Weakening (F-W) methods based on feedback voltage regulation are widely adopted in Interior Permanent Magnet Synchronous Motor (IPMSM) drives. Generally, the setpoint must be lower than maximum available voltage, to prevent saturation of current regulators during transients. However, the margin should be small, to exploit torque capability of the machine and avoid additional current magnitude during F-W operation. The trade-off between F-W control bandwidth and the necessity of voltage margin has not been analyzed in-depth in previous literature. In fact, F-W regulator design aiming at a certain bandwidth has been addressed by means of gain adaptation, but the choice of the target bandwidth remained as an open issue. In this paper, the crucial transient conditions which can cause the saturation of current regulators, specifically the reduction of input voltage, the fast acceleration of the drive and the transient torque demand, are considered. The input voltage reduction affects the available voltage, while fast acceleration and increase of torque demand push towards higher voltage, requiring disturbance rejection action by the F-W controller. All these conditions are analyzed in terms of worst-case requirement and the proposed analytical modeling is verified by means of simulations and experiments. The findings can be applied in the design of automatic tuning procedures and design for high-reliability or safety-critical applications.
