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an investigation of dual stator winding induction machines

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ase values <strong>of</strong> voltage/current. The maximum voltage/current h<strong>an</strong>dled by the hardware is<br />

represented by 512 in digital format <strong>an</strong>d 1.65V in <strong>an</strong>alog circuits. The voltage/current<br />

conversion into the Q12 format is achieved by multiplying the sensed voltage/current<br />

with the following const<strong>an</strong>ts:<br />

K<br />

K<br />

K<br />

V<br />

I<br />

dc<br />

4096<br />

= (11.12)<br />

Vb<br />

512 ⋅<br />

V<br />

max<br />

4096<br />

= (11.13)<br />

Ib<br />

512 ⋅<br />

I<br />

max<br />

4096<br />

= (11.14)<br />

Vb<br />

1024 ⋅<br />

V<br />

max<br />

It should be noticed that in one single multiplication, this const<strong>an</strong>t performs not only<br />

the per unit modeling but also the numerical conversion into Q12 format.<br />

11.7 Position/Speed Measurement<br />

A 4096 pulse absolute encoder with binary code is used to measure the rotor speed in<br />

this application. Twelve digital I/O ports <strong>of</strong> the TMS320LF2407A are used for reading<br />

the outputs <strong>of</strong> the encoder. Generally speaking, the mech<strong>an</strong>ical time const<strong>an</strong>t is much<br />

lower th<strong>an</strong> the electrical one, so the frequency <strong>of</strong> the speed regulation loop c<strong>an</strong> be lower<br />

th<strong>an</strong> the frequency <strong>of</strong> the current loop. This c<strong>an</strong> be achieved by me<strong>an</strong>s <strong>of</strong> a s<strong>of</strong>tware<br />

counter. This counter takes the clock <strong>of</strong> PWM interrupt as the input <strong>an</strong>d the speed is<br />

calculated every 50 cycles. If the gray code encoder is used, a logic conversion code that<br />

435

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