Estimation Method of Stator Winding Temperature for Dual Three-Phase Machines Based on DC-Signal Injection

Dual three-phase machines are becoming increasingly popular due to advantages such as inherent fault tolerant capability and lower current per phase for a given power. As in three-phase machines, it is important to provide thermal protection, in order to prevent reduction of the lifetime. Proposals specifically targeted to dual three-phase machines for estimating the stator winding temperature, and thus, avoiding the installation of thermal sensors, have not been reported so far. Concerning three-phase machines, previous publications have proposed techniques based on injecting a dc signal for estimating the stator winding temperature. However, a certain torque ripple is caused during the injection period, giving rise to a tradeoff between the magnitude of such ripple and the accuracy of the temperature estimation. This paper presents a method based on dc-signal injection for stator winding temperature estimation in dual three-phase machines with sinusoidally distributed windings and driven by field-oriented control. By applying the signal to the x-y plane, which is available in this type of machines and does not produce air-gap flux, no torque ripple is generated. Experimental results validate the proposed technique.