Embedded Software and Motor Control Libraries for PXR40xx

It should be pointed out that, in the worst case, three simple comparisons are required to
precisely identify the sector of the stator reference voltage vector. For example, if the
stator reference voltage vector resides according to the one shown in Figure 4-71, the
stator reference voltage vector is phase-advanced by 30 ° from the α-axis, which results
in the positive quantities of u ref1 and u ref2 and the negative quantity of u ref3; refer to
Figure 4-76. If these quantities are used as the inputs to the Sector Identification Tree, the
product of those comparisons will be Sector I. Using the same approach identifies Sector
II, if the stator reference voltage vector is located according to the one shown in Figure
4-74. The variables t 1, t 2 and t 3, representing the switching duty-cycle ratios of the
respective three-phase system, are given by the following equations:
Equation GMCLIB_SvmStd_Eq25
Equation GMCLIB_SvmStd_Eq26
Equation GMCLIB_SvmStd_Eq27
where T is the switching period, t_1 and t_2 are the duty-cycle ratios (see Table 4-150) of
the basic space vectors, given for the respective sector. Equation
GMCLIB_SvmStd_Eq25, equation GMCLIB_SvmStd_Eq26 and equation
GMCLIB_SvmStd_Eq27 are specific solely to the Standard Space Vector Modulation
technique; consequently, other Space Vector Modulation techniques discussed later will
require deriving different equations.
The next step is to assign the correct duty-cycle ratios, t 1, t 2 and t 3, to the respective
motor phases. This is a simple task, accomplished in view of the position of the stator
reference voltage vector as shown in Table 4-151.
Table 4-151. Assignment of the duty-cycle ratios to motor phases
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
pwm a t 3 t 2 t 1 t 1 t 2 t 3
Table continues on the next page...
Embedded Software and Motor Control Libraries for PXR40xx, Rev. 1.0
Chapter 4 API References
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