Predictive Control of Three Phase AC/DC Converters

80 CHAPTER 5. INVESTIGATIONS OF CONTROL METHODS PERFORMANCE
15
(a)
15
(b)
2 kW
1 kW
10
10
∆ S [%]
∆ S [%]
5
5
2 kW
1 kW
0
−100 −50 0 50 100
∆ R [%]
0
−100 −50 0 50 100
∆ R [%]
Figure 5.5: Power error ∆S versus line choke resistance value mismatch ∆R in:
(a) VSF-P-DPC, (b) CSF-P-DPC
10
9
8
7
(a)
10
9
8
7
(b)
2 kW
1 kW
THD i400
[%]
6
5
4
THD i400
[%]
6
5
4
3
2
1
2 kW
1 kW
3
2
1
0
−100 −50 0 50 100
∆ R [%]
0
−100 −50 0 50 100
∆ R [%]
Figure 5.6: Line current T HD i factor versus line choke resistance value mismatch
∆R in: (a) VSF-P-DPC, (b) CSF-P-DPC
5.2 On-line Choke Inductance Estimator
As shown in Section 5.1.1 and 5.1.2 the P-DPC algorithm is mainly sensitive to
mismatch of AC-side filter inductance L. Therefore, on-line choke estimation has
been introduced to improve accuracy and stability of the control.
Based on the input quantities (DC-link voltage U DC and transistor duty cycles
S a , S b and S c ), the converter AC-side voltage estimator (3.37), (3.38) calculates
U P αβ components, and next transforms into dq coordinates. The transformation
can be performed either with line voltage U L (Fig. 5.7 (b)) or with virtual flux
space vector Ψ L (Fig. 5.8 (b)). The measured line current vector I L is delivered
to the block, which computes its module |I L |. Signals U P q (or U P d ) and |I L |
after filtering in low-pass filter (LPF) blocks are delivered to the divider, which
calculates the actual value of choke inductance L est (Fig. 5.7 (a) and Fig. 5.8 (a)).
The estimated value is further used in VF estimator and predictive model. Note
that inductance is calculated under assumption of unity power factor condition