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SENSORLESS FIELD ORIENTED CONTROL OF BRUSHLESS ...

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Figure D.6 – Neutral voltage of load is common mode voltage of source.<br />

The common-mode voltage seen by the three-phase load is defined by Equation (D.16).<br />

1<br />

vcommon vAMvBM vCM<br />

(D.16)<br />

3<br />

Substituting Equation (D.12) into Equation (D.16) yields Equation (D.15), as before. Finally,<br />

comparing Equation (D.10) and Equation (D.12) in light of Equation (D.15) makes it<br />

exceptionally clear that since the ZS component of source voltage appears in the neutral, only the<br />

PS and NS components voltage appear across the load impedance. Since the ZS component does<br />

not appear across the load it cannot drive a current, thus from a current-control perspective it does<br />

not matter if a ZS component is present or not.<br />

Motor Load<br />

Most of the results for the passive load apply here, except the load’s line-neutral voltages are not<br />

required to sum to zero as they were in Equation (D.14) (several articles in the literature make<br />

grave mistakes regarding this). Each phase of the motor load is the bEMF in series with an<br />

impedance, Figure D.7.<br />

Figure D.7 – Motor load driven by source.<br />

315

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