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an investigation of dual stator winding induction machines

an investigation of dual stator winding induction machines

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The most recent overview paper is given as [10.65], in which different sensorless<br />

methods have been <strong>an</strong>alyzed <strong>an</strong>d their merits <strong>an</strong>d drawbacks have been discussed. The<br />

mech<strong>an</strong>ism <strong>of</strong> the voltage model open loop flux observer <strong>an</strong>d its improved model have<br />

been clearly explained. The perform<strong>an</strong>ce improvement <strong>of</strong> the voltage model at the low-<br />

speed region including the effect <strong>of</strong> inverter nonlinearity has been addressed. For the<br />

closed loop observer, only the full-order flux observer <strong>an</strong>d the sliding model observer<br />

have been included in [10.65]. The basic ideas <strong>of</strong> those observers have been explained;<br />

however the shortcomings have not been noted. For the signal injection method, the<br />

injected signal excites the machine at a much higher frequency th<strong>an</strong> the fundamental.<br />

The resulting high frequency currents generate flux linkages that only pass through the<br />

leakage path <strong>of</strong> the machine <strong>an</strong>d do not influence the fundamental mutual flux linkage.<br />

The magnetic <strong>an</strong>isotropy, which is caused by the saturation <strong>of</strong> the leakage paths or the<br />

special rotor structure, serves to identify the rotor position <strong>an</strong>gle. It should be noted that<br />

the existing rotor <strong>an</strong>isotropies have different spatial orientations such as the actual<br />

<strong>an</strong>gular position <strong>of</strong> the fundamental field <strong>an</strong>d position <strong>of</strong> the rotor bars within a rotor bar<br />

pitch. The response to the injected signal reflects all <strong>an</strong>isotropies, so it is required to<br />

extract information on one particular <strong>an</strong>isotropy while the other <strong>an</strong>isotropies act as<br />

disturb<strong>an</strong>ces. The injection <strong>of</strong> a rotating carrier signal is the first method used. The<br />

useful information is separated by a b<strong>an</strong>dpass filter (BPF) from the fundamental current<br />

<strong>an</strong>d from the switching harmonics <strong>of</strong> higher frequency. However the axis leakage<br />

induct<strong>an</strong>ce ratio Lσ q Lσ<br />

d is so closed to unity value such that the <strong>an</strong>gular information is<br />

difficult to identify. A direct extraction <strong>of</strong> the current signal is also problematic since the<br />

characterizing components in current are very small <strong>an</strong>d being superimposed by the large<br />

41

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