Predictive Control of Three Phase AC/DC Converters

34 CHAPTER 3. CONTROL STRATEGIES FOR VSC
200
150
100
50
(a)
500
400
300
200
100
(c)
u P a
u La
0.1 0.105 0.11 0.115 0.12
0
−50
−100
−150
0
−100
−200
−300
−400
−200
0.1 0.105 0.11 0.115 0.12
15
10
(b)
−500
2500
2000
(d)
P Q
i La
0.1 0.102 0.104 0.106 0.108 0.11 0.112
5
1500
0
1000
−5
500
−10
0
−15
0.1 0.105 0.11 0.115 0.12
−500
Figure 3.22: Steady state operation of ST-DPC: (a) line voltage u La [V], (b) line
current i La [A], (c) VSC input voltage u P a [V], (d) referenced and measured
active P [W] and reactive power Q [var]
5
DPC-SVM
Fundamental (50Hz) = 7.873 , THD= 3.21%
5
ST-DPC
Fundamental (50Hz) = 7.926 , THD= 5.42%
4.5
4.5
4
4
Mag (% of Fundamental)
3.5
3
2.5
2
1.5
Mag (% of Fundamental)
3.5
3
2.5
2
1.5
1
1
0.5
0.5
0
0 50 100 150 200 250 300 350 400
Harmonic order
0
0 50 100 150 200 250 300 350 400
Harmonic order
Figure 3.23: Line current harmonics spectrum
In case of ST-DPC, switching frequency depends on switching table construction,
sampling frequency, hysteresis controllers band, DC-link voltage, and converter
load. For ST-DPC switching table has been designed in order to avoid
transistor switchings under maximum current conduction (Fig. 3.24 (b)).
Figure 3.23 shows line current i L harmonic spectrum up to 20 kHz. In case
of DPC-SVM harmonic spectrum is concentrated around multiple of sampling
frequency. For ST-DPC harmonic spectrum is spread over wide range of frequen-