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an investigation of dual stator winding induction machines

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estimation. It has been claimed in [10.27] that the conventional MRAS scheme in [10.17]<br />

is a special case <strong>of</strong> operating point <strong>of</strong> a full-order flux observer. Most <strong>of</strong> the studies in<br />

sensorless control <strong>of</strong> <strong>induction</strong> <strong>machines</strong> utilized the full-order flux observer-based speed<br />

estimation scheme.<br />

From the error function point <strong>of</strong> view, the MRAS-based speed estimation schemes<br />

c<strong>an</strong> be divided into several categories. In the first type, q- <strong>an</strong>d d-axis rotor fluxes are<br />

estimated using two different machine models <strong>an</strong>d the error <strong>of</strong> the rotor fluxes from the<br />

two models are used to estimate the rotor speed [10.17-10.19]. The expression <strong>of</strong> the<br />

speed adaptive algorithm <strong>of</strong> the first type is expressed as;<br />

( λ ⋅ ˆ λ − λ ˆ )<br />

⎛ K i ⎞<br />

ˆ ωr<br />

= ⎜ K p + ⎟ ⋅ q d d ⋅ λq<br />

(1.9)<br />

⎝ S ⎠<br />

In the second type, the <strong>stator</strong> current is estimated <strong>an</strong>d compared with the measured<br />

<strong>stator</strong> current. The error between the estimated <strong>an</strong>d measured <strong>stator</strong> current is used to<br />

produce the speed adaptive scheme [10.20-10.23, 10.25-10.29, 10.31 -10.34]. This type<br />

<strong>of</strong> error function is the most popular one <strong>an</strong>d the speed estimation scheme is given as:<br />

( e ⋅ ˆ λ − e ˆ )<br />

⎛ K i ⎞<br />

ˆ ωr<br />

= ⎜ K p + ⎟ ⋅ iq d id ⋅ λq<br />

(1.10)<br />

⎝ S ⎠<br />

Another speed adaptive scheme has been proposed in [10.29] by adding a rotating<br />

<strong>an</strong>gle into the error function. It was claimed that the <strong>an</strong>gle c<strong>an</strong> ch<strong>an</strong>ge the direction <strong>of</strong> the<br />

error projection <strong>an</strong>d this <strong>an</strong>gle will be adjusted online to stabilize the regenerating-mode<br />

at low speed r<strong>an</strong>ge. The expression <strong>of</strong> this MRAS scheme is:<br />

⎛<br />

ˆ ωr<br />

= ⎜ K<br />

⎝<br />

p<br />

Ki<br />

⎞<br />

+ ⎟⋅<br />

Im<br />

S ⎠<br />

[ ˆ*<br />

− jφ<br />

λ ⋅(<br />

i − iˆ<br />

) ⋅e<br />

]<br />

qdr<br />

s<br />

s<br />

35<br />

(1.11)

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