modelling and analysis of single-phase induction motor with external rotor uma. r edited by sarath s...

Modelling and Analysis of Single-Phase Induction Motor

with External Rotor

Uma. R

Edited By

Sarath S Nair

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Presentation Outline IntroductionWhy an external rotor?Equivalent circuit of rotorLumped parameter equivalent circuitMathematical modelRole of conducting shellSteady state and dynamic analysisSummaryReferences


Introduction

Many domestic appliances require low-power motors operating at constant speed that must start under load(compressors, pumps etc)

Because of the reliability in operation the single-phase induction motor is one of the most widely used types of AC machines

SPIM with external rotor is more advantageous for low power application

Constant speed at different load can be easily achieved by increasing the motor inertia, by using an external rotor


Why an external rotor?

Allows a higher stability in operation at different loads due to higher inertia

The fan blades can be attached directly to the outside of the rotor, making the motor more compact

Heat generated within the rotor, is on the outside and can be dissipated easily

The start-up and operating characteristics of single-phase induction motors with external rotor can be improved by covering the rotor with a conducting shell joining the two end rings


External rotor of an Induction motor

Fig1. axial half cross-section Fig2. Fluxes in longitudinal section

L – laminations Φσbx - leakage fluxes of bar

B - rotor cage bars Φδx - airgap flux

R - end rings Φex - leakage flux of shell S - conducting shell


Magnetic fluxes and Induced voltages

Φσbx= Lσb Ibx Φσrx= Lσr Irk

Σ Irk= kr Ibx kr =1/(2sin2(Πp/Z))

Φσrx= kr Lσr Ibx

The induced voltage by these fluxes equals the resistive voltage drops on the path г b

jω(Φδx + 2 Φσbx + 2Σ Φσrx )= 2Rb Ibx +2Rr Σ Irk

On the path г e- (a closed path, consisting from two "external bars“)

-jω(Φex + 2Σ Φσrx )= 2Re Iex +2Rr Σ Irk


Equivalent circuit of the Rotor

• U1, U2 etc -the bar e.m.f.sEach bar is represented by its complex impedance

Each ring by its ring-segment complex impedance


Contd…External shell

Due to the symmetry of the bar and ring segment currents, a star equivalent of impedance & for the ring segments can be established

equivalent impedance of a bar circuit is: without external conducting shell

with external conducting shell


Lumped parameter Equivalent Circuit

Assumptions

1. Only the fundamental space-harmonic component of the air-gap flux distribution is considered.

2. A nonlinear resistor that is associated with the total stator flux linkage models core loss in d and q axis.

3. Stray losses, temperature effects and rotational losses are neglected


Mathematical Model

Mathematical model is described by the following state-variable matrix equations:


Contd…

Where the inductance terms are calculated using the notations:

The induced voltages in the magnetising branch are readily determined with:


Contd…Where

Torque equation is:


Role of conducting shell

The ring impedance is especially high in small external rotor motors, because of the increased ring mean diameter

The external conducting shell ensures a parallel way for the ring currents diminishes the equivalent ring impedance decreases the rotor resistance and the leakage

reactanceincreases the cooling surface area


Steady state and Dynamic analysis

A split phase induction motor with following parameters are considered for analysis

o Rated output power: 60 Wo Rated frequency: 50 Hzo Rated speed: 2850 rpm o Rated voltage: 220 Vo Stator main winding resistance:37.57 ohmo Stator auxiliary winding resistance: 56.83 ohmo Rotor resistance: 76.23 ohm


Contd…

1) steady-state torque versus speed 2) steady-state torque versus for starting period speed for rated

operating period


Contd…

Fig(1) Fig(2) 1) instantaneous torque versus speed for motor with extemal rotor

and without conducting shell 2) instantaneous torque versus speed for motor with extemal rotor

with conducting shell


Contd…

Fig(1) Fig(2) 1)Start-up speed response for motor with external rotor and without

conducting shell 2)Start-up speed response for motor with external rotor with

conducting shell


SummaryThis paper focused on a new construction of SPIM

with external rotor and conducting shell

An equivalent circuit for analysis and modelling of the single-phase induction motor with external rotor is derived.

The torque and speed characteristics of the motor with and without the conducting shell is compared

A SPIM with external rotor and conducting shell finds its application in compressors, pumps, air conditioners etc


References

[l] M. Popescu, “Analysis and Modelling of Single-Phase Induction Motor with External Rotor for Domestic Applications”, IEEE Trans. Ind. Appl.,2000,pp463-470

[2]P.C. Krause, 0. Waszynchuk, S.D. Sudhoff: Analysis of Electrical Machinery, IEEE Press, New York, 1995

[3] S . D. Umans, “Steady-state, lumped-parameter model for capacitor-run, single-phase induction motors”, IEEE Trans. Ind. Appl., Vo1.32, no. 1, Jan/Feb 1996, pp.169-179

[4] E. Levi: “A unified approach to main flux saturation modelling in D-Q axis models of induction machines”, IEEE Trans. Energy Conv., Vol. 10, no.3, Sept. 1995,pp 455-461


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modelling and analysis of single-phase induction motor with external rotor uma. r edited by sarath s...

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