Sensorless Control of an IPM Synchronous Machine based Integrated Starter Generator

Interior Permanent Magnet (IPM) synchronous motors are today considered a viable solution to equip Integrated Starter Generator (ISG) systems for conventional and Mild Hybrid Electric Vehicles. They can take advantage from two key features: a strong armature reaction, that allows flux weakening operations, and a consistent reluctance torque, that allows to increase the total motor torque without introducing extra magnets. In this paper, a sensorless approach is introduced to drive an IPM based ISG system both in motoring and generating mode. In motoring mode the position of the rotor of the IPM machine is estimated exploiting the addition of a small high frequency sinusoidal signal to the stator voltage reference. Due to the rotor saliency, in fact, a stator voltage component is generated orthogonally to the spatial direction of the added signal, whose amplitude is a sinusoidal function of the rotor position. A robust rotor position tracking is then accomplished, by minimizing the amplitude of such an orthogonal voltage. The proposed technique is able to drive the machine in motoring mode (from 0 to 800 rpm) fully controlling the motor through a Maximum Torque per Ampere (MTPA) approach. In generating mode (from 800 to 5000 rpm) a sensorless flux weakening control is exerted where the estimation of the rotor position is obtained through the manipulation of the stator back EMF. The proposed approach has been successfully implemented on a DSP control board driving a four poles 5 HP IPM machine. Experimental results confirm the consistency of the proposed approach both in motoring and generating mode.