Brushless rotor position estimation

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Joined Jun 17, 2009
How to estimate rotor position of a three phase brushless dc motor having trapezoidal shaped air gap flux distribution using flux-linkage based technique? The commonly used equation given in books and other technical resources to estimate the flux is given as Ψ = Ψp + Ψpm = ∫(U - Ri)dt , where Ψ denotes total flux linkage of the phase (consisting of self and mutual flux Ψp; and Ψpm due to permanent magnet rotor), U denotes phase voltage; R and i denote phase resistance and current. But how does this relation translate into rotor position? What electrical quantity do we actually measure to control the motor in this method?

Thank you.
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