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SENSORLESS FIELD ORIENTED CONTROL OF BRUSHLESS ...

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It must be emphasized that we have thus far only dealt with stator quantities; these were<br />

expressed in the stator and rotor reference frames. It is also possible to talk about rotor quantities<br />

and these may be described in either frame. Thus the distinction must be made between a quantity<br />

associated with the stator or rotor and one described in terms of the reference frame attached to<br />

the stator or rotor. When a stator (rotor) SV is described in terms of the stator (rotor) reference<br />

frame it is said to be in the natural reference frame [87], [35]. For example, a stator quantity is<br />

represented as S x ; a rotor quantity is represented as xR . But neither can be specified without a<br />

reference frame.<br />

S The stator and rotor quantities in the stator frame are xS S<br />

and xR<br />

, respectively.<br />

R The stator and rotor quantities in the rotor frame are x<br />

R<br />

and x , respectively. The<br />

S R<br />

transformations are given by Equation (3.113), where the boldface scripts correspond to the row<br />

and column labels.<br />

S R j r S R<br />

jr<br />

stator frame xS xS e xR xR e<br />

R S j r R S<br />

jr<br />

rotor frame x x e x x e<br />

(3.113)<br />

S S R R<br />

stator qtys rotor qtys<br />

Although there is a difference between a rotor and stator quantity, it is obvious that for either, the<br />

transformation between reference frames is the same (which we should expect), thus Equation<br />

(3.114).<br />

S R<br />

jr<br />

x x e<br />

R (3.114)<br />

S jr<br />

x x e<br />

It was earlier mentioned that the stator reference frame is assumed when no ‘S’ superscript is<br />

present, thus Equation (3.115), which was shown in the summary earlier.<br />

R<br />

jr<br />

x x e<br />

R (3.115)<br />

jr<br />

x xe Comparison with Phasor<br />

In concluding the presentation of space vectors it should be helpful to contrast it with the more<br />

familiar phasor analysis. Both the phasor and the SV map real quantities to the complex plane.<br />

The two largest differences between the two are that a phasor represents a single signal (a SV<br />

represents the combined action of all three phase variables) and that a phasor is technically a<br />

stationary variable in the phasor domain (a SV is an instantaneous variable in the complex<br />

domain; its magnitude and angle are functions of time).<br />

139

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