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Embedded Software and Motor Control Libraries for PXR40xx

Embedded Software and Motor Control Libraries for PXR40xx

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Equation GMCLIB_SvmStd_Eq25<br />

Equation GMCLIB_SvmStd_Eq26<br />

Equation GMCLIB_SvmStd_Eq27<br />

where T is the switching period, t_1 <strong>and</strong> t_2 are the duty-cycle ratios (see Table 4-145) of<br />

the basic space vectors, given <strong>for</strong> the respective sector. Equation<br />

GMCLIB_SvmStd_Eq25, equation GMCLIB_SvmStd_Eq26 <strong>and</strong> equation<br />

GMCLIB_SvmStd_Eq27 are specific solely to the St<strong>and</strong>ard Space Vector Modulation<br />

technique; consequently, other Space Vector Modulation techniques discussed later will<br />

require deriving different equations.<br />

The next step is to assign the correct duty-cycle ratios, t 1, t 2 <strong>and</strong> t 3, to the respective<br />

motor phases. This is a simple task, accomplished in view of the position of the stator<br />

reference voltage vector as shown in Table 4-146.<br />

Table 4-146. Assignment of the duty-cycle ratios to motor phases<br />

Sector U 0, U 60 U 60, U 120 U 120, U 180 U 180, U 240 U 240, U 300 U 300, U 0<br />

pwm a t 3 t 2 t 1 t 1 t 2 t 3<br />

pwm b t 2 t 3 t 3 t 2 t 1 t 1<br />

pwm c t 1 t 1 t 2 t 3 t 3 t 2<br />

Chapter 4 API References<br />

The principle of the Space Vector Modulation technique consists in applying the basic<br />

voltage vectors U XXX <strong>and</strong> O XXX <strong>for</strong> the certain time in such a way that the mean vector,<br />

generated by the Pulse Width Modulation approach <strong>for</strong> the period T, is equal to the<br />

original stator reference voltage vector U S. This provides a great variability of the<br />

arrangement of the basic vectors during the PWM period T. Those vectors might be<br />

arranged either to lower switching losses or to achieve diverse results, such as centrealigned<br />

PWM, edge-aligned PWM or a minimal number of switching states. A brief<br />

discussion of the widely-used centre-aligned PWM follows. Generating the centrealigned<br />

PWM pattern is accomplished practically by comparing the threshold levels,<br />

<strong>Embedded</strong> <strong>Software</strong> <strong>and</strong> <strong>Motor</strong> <strong>Control</strong> <strong>Libraries</strong> <strong>for</strong> <strong>PXR40xx</strong>, Rev. 1.0<br />

Freescale Semiconductor, Inc. 525

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