Monday, March 30, 2009

Estimation of Induction Motor Parameters

Estimation of Induction Motor Parameters Based on
Field Test Coupled with Genetic Algorithm

This paper proposed a technique for estimating the
parameters of three-phase induction motor in order to conduct
on-site energy audits of existing motors, which are then used to
project a cost savings. This proposed technique uses only a few
sets of data (voltage, current, speed, power factor or torque if
possible) from the field test of motor (on-site), instead of the noload
and blocked rotor tests, coupled with the genetic algorithm
for evaluating the equivalent circuit parameters. Once these
parameters are known it is possible to obtain the operating
performances (50-100%) of the motor such as efficiency, current,
torque. This technique could be suitable for the general purpose
drive applications when the motor cannot operate at no-load
since its shaft is permanently connected to its load. To illustrate
how well the performances of the estimated model matches that
of the actual motor obtained from load test, the results of 3 HP
and 5 HP induction motors will be presented and compared.

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The paper deals with a simple estimation procedure of the
squirrel-cage induction motor parameters, like resistances and
inductances, considering the data from the machine nameplate.
First is presented the analytical calculation according to the
conventional steady-state per-phase equivalent circuit, neglecting
the ironcore losses. The magnitude of stator-, air-gap and rotor
fluxes, required as references by field-controlled scalar and vector
control systems, are also determined. For validation of the identified
parameters there are presented two simulation structures containing
the motor dynamic d-q model, based on the state equations related to
a stator-fixed and to a general oriented reference frame.
The simulation results are analyzed using the space-phasor theory.

Fig. 1. Steady-state electrical
(a) and magnetical
(b) equivalent circuits defined also for zero frequency

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The paper describes a method of parameter identification
of an equivalent circuit of an induction motor using fuzzy logic
controller. The method is based on the step-by-step approach in
which the parameters are calculated from an equivalent circuit and
real measured speed-torque characteristic. The displacement of
two characteristics as a complex input variable for a fuzzy logic
controller is used. In order to demonstrate the reliability of the
proposed methods, an example of speed-torque characteristic of
induction motors and parameter determination of an equivalent
circuit is discussed.

The algorithm of computer controlled determination of induction
motor characteristics and parameters

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