# Thermal Analysis of Inverter-Fed Induction Motor

Chapter
Part of the Lecture Notes in Electrical Engineering book series (LNEE, volume 436)

## Abstract

Reducing the size and cost and increasing the energy efficiency and optimal loading of the motor have a direct impact on the temperature rise of the motor. Motor needs to be operated such that its temperature rise is within the prescribed safe limit. Therefore, easy and precise temperature rise determination of motor becomes critical. Thermal models of motor are widely used for temperature determination. In this paper, a modified thermal model is proposed using which the temperature rise of induction motor fed from raw supply and inverter-fed supply is determined. The parameters of the thermal model are also determined.

## Keywords

Thermal analysis Induction motor Inverter Lumped parameter Temperature rise

## Nomenclature

$$R_{\text{csylf}}$$

Radial conduction thermal resistance of the stator yoke lower half part

$$R_{\text{csyuh}}$$

Radial conduction thermal resistance of the stator yoke upper half part

$$R_{\text{vstag}}$$

Convection thermal resistance between stator teeth and air gap

$$R_{\text{vrag}}$$

Convection thermal resistance between rotor and air gap

$$R_{\text{crst}}$$

Radial conduction thermal resistance of the stator teeth

$$R_{\text{csf}}$$

Axial conduction thermal resistance of the shaft

$$R_{\text{vswia}}$$

Convection thermal resistance between stator winding, external connection and inner air

$$R_{\text{cswec}}$$

Convection thermal resistance between stator winding, external connection and external case

$$R_{\text{viaec}}$$

Convection thermal resistance between internal air and end caps

$$R_{\text{cscss}}$$

Conduction thermal resistance between stator copper and stator slot

$$R_{\text{vcan}}$$

Natural convection thermal resistance between external case and ambient

$$P_{\text{rcu}}$$

Rotor copper loss

$$P_{\text{ir}}$$

Stator iron loss

$$P_{\text{scu}}$$

Stator copper loss

$$R_{\text{sc}}$$

Resistance in the stator conductor

$$R_{\text{sr}}$$

Resistance between stator and rotor

$$R_{\text{sy}}$$

Resistance between stator and yolk

$$R_{\text{rc}}$$

Resistance in the rotor conductor

$$R_{\text{re}}$$

Resistance between rotor and external case

$$P_{\text{scu}}$$

Stator copper loss

$$P_{\text{rcu}}$$

Rotor copper loss

$$P_{\text{ir}}$$

Stator iron loss

$$\theta_{\text{s}}$$

Temperature at outer stator surface

$$\theta_{\text{r}}$$

Temperature at outer rotor surface

$$\Delta P_{i}$$

Losses in the ith node (some are zero)

$$\theta_{i}$$

Temperature rise on the ith node

$$\propto_{ik }$$

Thermal conductivities between ith and the kth node (some are zero)

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