Abstract
Multisector machines reveal a high fault-tolerant capability, since failure events can be isolated by de-energizing the faulty sector, while the healthy ones contribute in delivering the required power. This article is focused on the thermal analysis of multisector three-phase machines in healthy and faulty operations. First, a 3-D lumped parameter thermal network (LPTN) of a single sector is developed and finetuned against experimental data, through a genetic algorithm for identifying the uncertain parameters. According to the operating conditions, the varying housing surface temperature affects the heat exchanged to the ambient. Hence, an analytical formula is proposed to adjust the natural convection coefficient value depending on the operating condition. Then, the 3-D LPTN, modeling the whole machine, is built aiming at investigating the thermal behavior during faulty conditions. Finally, the complete 3-D LPTN is employed for predicting the machine thermal performance under several faulty conditions. Furthermore, the current overload experienced by the healthy sector (in order to keep the same torque level as during the pre-fault operation) is determined, in accordance with the magnet wire thermal class. The effectiveness of the 3-D LPTN in predicting the temperature is experimentally demonstrated.
Highlights
Multisector machines reveal a high fault-tolerant capability, since failure events can be isolated by de-energizing the faulty sector while the healthy ones contribute in delivering the required power
The thermal analysis on multiphase machines has been addressed in the existing literature [12]-[14], it is still difficult to find technical papers reporting the thermal behavior of multisector machines under faulted conditions
For fractional-slot concentrated winding (FSCW) permanent magnet (PM) machines employed in traction applications, the thermal benefits due to the proposed back-iron extension are assessed by using an lumped parameter thermal network (LPTN) in [18]
Summary
DUE to the intrinsic features such as fault tolerance, low torque ripple, and power splitting, multiphase machines are attracting a lot of research attention [1]-[3]. The most significant problem is that it is impossible to accurately determine some critical parameters of the LPTN, e.g. the equivalent thermal conductivity of winding, the interference gap between stator and housing, the heat transfer coefficient due to convection, etc. To compensate the output torque shortage arising from the sector opening (i.e. asymmetric-sector operation), the current flowing through the remaining sectors must be increased Such post fault strategy leads to overload operation of the healthy sectors, which might result in winding over heating. This peculiar working condition requires a detailed thermal analysis of the whole multisector machine in order to avoid the shortening of the insulation lifetime. The temperature prediction provided by the 3D-LPTN is experimentally validated
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