NXP Semiconductors DSP56800E, Руководство пользователя

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Using these equations, and also considering that the normalized magnitudes of the basic
space vectors are |U
120
| = |U
60
| = 2 / √3 , the equations expressed for the unknown duty-
cycle ratios of basic space vectors T
120
/ T and T
60
/ T can be expressed as follows:
Equation 38
The duty-cycle ratios in the remaining sectors can be derived using the same approach.
The resulting equations will be similar to those derived for sector I and sector II.
Equation 39
To depict the duty-cycle ratios of the basic space vectors for all sectors, we define:
• Three auxiliary variables:
Equation 40
• Two expressions - t_1 and t_2, which generally represent the duty-cycle ratios of the
basic space vectors in the respective sector (for example, for the first sector, t_1 and
t_2), represent duty-cycle ratios of the basic space vectors U
60
and U
0
; for the second
sector, t_1 and t_2 represent duty-cycle ratios of the basic space vectors U
120
and
U
60
, and so on.
The expressions t_1 and t_2, in terms of auxiliary variables X, Y, and Z for each sector,
are listed in
Table 2-10 .
Table 2-10. Determination of t_1 and t_2 expressions
Sectors U
0
, U
60
U
60
, U
120
U
120
, U
180
U
180
, U
240
U
240
, U
300
U
300
, U
0
t_1 X Z -X Z -Z Y
t_2 -Z Y Z -X -Y -X
For the determination of auxiliary variables X, Y, and Z, the sector number is required.
This information can be obtained using several approaches. The approach discussed here
requires the use of modified Inverse Clark transformation to transform the direct-
α
and
quadrature-
β
components into balanced three-phase quantities u
ref1
, u
ref2
, and u
ref3
, used
for straightforward calculation of the sector number, to be shown later.
Chapter 2 Algorithms in detail
GMCLIB User's Guide, Rev. 2, 10/2015
Freescale Semiconductor, Inc. 45