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an investigation of dual stator winding induction machines

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The rotor flux c<strong>an</strong> be obtained by:<br />

⎡ ⎛ ⎞ ⎤<br />

s Lˆ<br />

r s Lˆ<br />

2<br />

ˆ ⎢ ⎜ m s<br />

λ = ˆ − ⎟<br />

r λs<br />

⎜<br />

Lˆ<br />

s −<br />

⎟<br />

⋅i<br />

s ⎥<br />

(1.7)<br />

Lˆ<br />

m ⎢⎣<br />

⎝ Lˆ<br />

r ⎠ ⎥⎦<br />

Sensorless control <strong>of</strong> <strong>induction</strong> machine based on voltage model flux estimation has<br />

been proposed in [10.10], where two lag-circuits were inserted into the estimator for<br />

better estimation. The integration <strong>of</strong> (1.2) by pure integrator involves the drift <strong>an</strong>d<br />

saturation problems [10.12]. A Low Pass Filter (LPF) was proposed to solve the<br />

problems, the pure integrator is replaced by LPF <strong>an</strong>d the tr<strong>an</strong>sfer function becomes<br />

1<br />

compared with that <strong>of</strong> a pure integrator .<br />

s<br />

The current-based model is <strong>an</strong>other flux estimation method. The motor flux is<br />

identified by solving a set <strong>of</strong> equations where machine parameters <strong>an</strong>d rotor speed are<br />

required [10.13]. The estimation equation is given as:<br />

p ˆ<br />

⎛ rˆ<br />

⎜<br />

⎞<br />

⎟ ˆ + ˆ<br />

⎝ ⎠<br />

Lˆ<br />

s r<br />

s m s<br />

λ r = −<br />

⎜<br />

− jωr<br />

⋅ r rr<br />

is<br />

Lˆ<br />

⎟<br />

λ<br />

(1.8)<br />

r<br />

Lˆ<br />

r<br />

In [10.14], a clear classification <strong>of</strong> open loop flux observers has been given with the<br />

<strong>an</strong>alysis <strong>of</strong> their adv<strong>an</strong>tages <strong>an</strong>d disadv<strong>an</strong>tages. A design methodology based on the<br />

physical model <strong>of</strong> <strong>induction</strong> machine model has been presented. Four open loop flux<br />

observers <strong>an</strong>d a closed loop Gopinath flux observer are evaluated using Frequency<br />

Response Function (FRF) <strong>an</strong>alysis method. The voltage model flux observer utilizes the<br />

measured <strong>stator</strong> voltages <strong>an</strong>d currents, but not the rotor velocity. From FRF <strong>an</strong>alysis, the<br />

accuracy <strong>of</strong> this observer is sensitive to <strong>stator</strong> resist<strong>an</strong>ce at low rotor velocities, which is a<br />

well known limitation <strong>of</strong> this observer.<br />

31<br />

1<br />

s +<br />

a

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