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an investigation of dual stator winding induction machines

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11.4 Per Unit Model<br />

For the fixed point DSP--TMS320LF2407A, a per unit model <strong>of</strong> the motor is always<br />

used to compromise both accuracy <strong>an</strong>d measurement r<strong>an</strong>ge. All the qu<strong>an</strong>tities <strong>of</strong> the<br />

model have to be referred to the base values. Generally speaking, the base values <strong>of</strong> the<br />

model c<strong>an</strong> be chosen arbitrary. However, the traditional method that the base values are<br />

determined from the nominal values <strong>of</strong> the machine is more me<strong>an</strong>ingful <strong>an</strong>d has been<br />

adopted in all the implementations. If the base values <strong>of</strong> voltage, current, electrical speed<br />

<strong>an</strong>d resist<strong>an</strong>ce are represented by V b , I b , ω b <strong>an</strong>d Z b respectively, the expressions for the<br />

calculations <strong>of</strong> base values are given as:<br />

V = 2 ⋅V<br />

(11.9a)<br />

b<br />

b<br />

p<br />

p<br />

I = 2 ⋅ I<br />

(11.9b)<br />

ω = 2π<br />

f<br />

(11.9c)<br />

b<br />

V<br />

p<br />

b Z b = (11.9d)<br />

Ib<br />

where, V p <strong>an</strong>d I p represent the RMS value <strong>of</strong> rated phase voltage <strong>an</strong>d rated phase current<br />

respectively; f p is the rated operating frequency.<br />

The real qu<strong>an</strong>tities that are implemented in the DSP s<strong>of</strong>tware are defined as:<br />

V<br />

real v = (11.10a)<br />

Vb<br />

I<br />

I<br />

real i = (11.10b)<br />

b<br />

ω<br />

ω<br />

real ω = (11.10c)<br />

b<br />

431

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