Robust Maximum Torque per Ampere (MTPA) Control of PM-Assisted SynRM for Traction Applications

Recently, permanent-magnet-assisted (PMa) synchronous reluctance motors (SynRMs) have been introduced as a possible traction motor in hybrid electric vehicle applications. In order to achieve maximum torque per ampere (MTPA), knowledge of the motor parameters is necessary. Due to the high ambient temperature inside the engine cavity as well as the saturation effect, variation of motor parameters such as inductances and permanent magnet (PM) flux density is not avoidable. Offline models for estimating the motor parameters are known as a computationally intensive method, particularly, when the effect of cross saturation and PM flux deterioration are included. In this paper, a practical MTPA control scheme, along with a simple parameter estimator for the PMa SynRM, is introduced. This method is capable of maintaining the MTPA condition and stays robust against motor parameter variations. To verify the validity and feasibility of the proposed controller, several simulations and experiments results on a low-power laboratory prototype PMa SynRM have been presented.

I. Introduction

Interior permanent magnet (IPM) synchronous motors are widely used in hybrid electric vehicles (HEVs) and vehicular applications, such as starters/alternators, power steering, and airconditioning motors [1]. These motors offer high efficiency by utilizing both magnetic torque and reluctance torque. However, drawbacks such as large -axis current at high speed during the flux-weakening region and the uncontrolled generator mode following unexpected inverter shutdowns are restricting factors. These problems are caused by the uncontrolled flux linkages that are produced by the permanent magnets (PMs). However, they can be eliminated in PMa SynRM, which is very similar to IPM. The amount of magnets and the magnet flux linkages are small in comparison with the conventional IPM, and the reluctance torque has the most contribution in the developed torque. With respect to the conventional synchronous reluctance machine, this motor offers better torque capabilities and power factors [2].