Predictive Control of Three Phase AC/DC Converters

UPα
Lα
Lα
3.5. VIRTUAL FLUX BASED CONTROL 31
On the basis of (3.39) and (3.40) virtual flux estimator with ideal integration
part has been built Fig. 3.18 (a).
(a)
UPα
(b)
I
200
0
ILαL
−200
(c)
2
1
0
I
−1
−2
0 0.1 0.2 0.3 0.4 0.5 0.6
ILβ
Figure 3.18: Virtual flux estimator with ideal integration: (a) block scheme,
(b) estimated line voltage U Lα [V], (c) estimated virtual flux Ψ Lα [Wb]
Lβ
UPβ
As it can be seen in Fig. 3.18 (c), ideal integration produce dc offset, because
it depends on unknown initial conditions Ψ Lαβ0 .
(a)
(b)
-
I
200
0
LPF
−200
ILαL
LPF
(c)
2
1
-
I
0
−1
−2
0 1 2 3 4 5 6
ILβ
Figure 3.19: Virtual flux estimator with low pass filter: (a) block scheme, (b) estimated
line voltage U Lα [V], (c) estimated virtual flux Ψ Lα [Wb]
Lβ
UPβ
To avoid initial condition problem, a low pass filter (LPF) has been implemented
in feedback loop as shown in Fig. 3.19 (a). In this case, even if initial
conditions of integral part are wrong, virtual flux dc offset is being removed after
about 3 seconds Fig. 3.19 (c). To speed up this process, an additional gain part
has been introduced into estimator Fig. 3.20 (a). In this case, dc offset removal
process takes about 300 ms Fig. 3.20 (c).