The
function calculates the appropriate duty-cycle ratios, which are
needed for generation of the given stator-reference voltage vector using the general
sinusoidal modulation technique.
The
function for calculating of duty-cycle ratios is widely used in
modern electric drives. This function calculates the appropriate duty-cycle ratios, which
are needed for generating the given stator reference voltage vector using a special space
vector modulation technique called space vector modulation with O
000
nulls, where only
one type of null vector O
000
is used (all bottom switches are turned on in the invertor).
The derivation approach of the space vector modulation technique with O
000
nulls is in
many aspects identical to the approach presented in
. However, a
distinct difference lies in the definition of the variables t
1
, t
2
, and t
3
that represent
switching duty-cycle ratios of the respective phases:
Equation 47
where T is the switching period, and t_1 and t_2 are the duty-cycle ratios of the basic
space vectors that are defined for the respective sector in
.
The generally used center-aligned PWM is discussed briefly in the following sections.
Generating the center-aligned PWM pattern is accomplished practically by comparing the
threshold levels pwm_a, pwm_b, and pwm_c with the free-running up/down counter. The
timer counts up to 1 (0x7FFF) and then down to 0 (0x0000). It is supposed that when a
threshold level is larger than the timer value, the respective PWM output is active.
Otherwise it is inactive (see
).
GMCLIB_SvmU0n
GMCLIB User's Guide, Rev. 2, 10/2015
56
Freescale Semiconductor, Inc.
Содержание DSP56800E
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