3.3.9 Controlling Zero Voltage Switched Full Bridge (ZVSFB) Converter
The example given in
assumes a static or constant phase relationship between legs (modules). In
such a case, control is achieved by modulating the duty cycle. It is also possible to dynamically change the
phase value on a cycle-by-cycle basis. This feature lends itself to controlling a class of power topologies known
as
phase-shifted full bridge
, or
zero voltage switched full bridge.
Here the controlled parameter is not duty cycle
(this is kept constant at approximately 50 percent); instead it is the phase relationship between legs. Such a
system can be implemented by allocating the resources of two PWM modules to control a single power stage,
which in turn requires control of four switching elements.
shows a master/slave module combination
synchronized together to control a full H-bridge. In this case, both master and slave modules are required to
switch at the same PWM frequency. The phase is controlled by using the slave's phase register (TBPHS). The
master's phase register is not used and therefore can be initialized to zero.
CTR=zero
CTR=CMPB
X
En
SyncOut
Phase reg
Ext SyncIn
(optional)
EPWM1A
EPWM1B
SyncOut
Phase reg
CTR=CMPB
CTR=zero
X
En
EPWM2B
EPWM2A
Slave
Master
V
out
EPWM1A
SyncIn
SyncIn
V
DC_bus
EPWM1B
EPWM2A
EPWM2B
Φ
=0
°
Φ
=Var
°
Var = Variable
Figure 3-66. Controlling a Full-H Bridge Stage (F
PWM2
= F
PWM1)
Enhanced Pulse Width Modulator (ePWM) Module
SPRUH18I – JANUARY 2011 – REVISED JUNE 2022
TMS320x2806x Microcontrollers
321
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Содержание TMS320 2806 Series
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