3
Control
The voltage-oriented control allows controlling the PFC behavior of the converter in the dq-axis synchronous
reference frame.
Table 6.
Control strategy comparison
Reference frame
Pros
Cons
3-axis stationary
reference frame (abc)
•
Simple implementation with PI
•
Avoids effort in the reference transformation
•
Best results with the PR regulator (no analog)
•
Best choice for the analog version
•
Poor in transient
•
Phase shifting (lag)
•
Needs three regulators (three-phase)
•
Necessary high bandwidth (noise)
•
Steady state error
2-axis stationary
reference frame (αβ)
•
Use two regulators instead of three
•
Simple implementation with PI
•
Best results with the PR regulator (no analog)
•
Poor in transient
•
Phase shifting (lag)
•
Digital version only
•
Necessary high bandwidth (noise)
2-axis synchronous
reference frame (dq)
•
Zero steady state error (DC reference)
•
Use of a simple PI (simple structure of the
regulator)
•
Low bandwidth is allowed (robust)
•
Best in transient (first order behavior)
•
Effort frame transformation
•
Digital version only
•
Necessary high bandwidth (noise)
•
Implementation
3.1
Control strategy
This reference design power converter can be represented as a second order dynamic system, which consists
of inductors and capacitors. The theoretical different dynamic behavior of this two-system element allows
considering two fully decoupling first order systems. For this reason, a current control and a voltage control
are taken into account.
Figure 45.
Cascaded control
Space
Vector
MODULATOR
V
αβ
*
ωL
Id
Iq
Controller
Controller
PLL
V
d
V
q
*
i
abc
L
i
abc
dq
dq
αβ
abc
dq
θ
Vabc
V
d
V
q
+
+
-
+
-
-
I
d
I
q
ωL
V
q
V
d
*
I
d
I
q
V
d
**
V
q
**
-
+
-
+
I
d
I
q
-
+
Voltage
Controller
V
dc
*
V
dc
I
q
*
I
d
*
3-Phases
Outer Loop
CO
N
VE
RT
ER
‘’Decoupling’’ Inner Loop
3.1.1
Current control strategy
A continuous conduction mode controls the reference design current.
UM2979
Control
UM2979
-
Rev 1
page 26/70
