Predictive Control of Three Phase AC/DC Converters

UPdqUDC
UDCSabc
uLab
iLab
4.4. CURRENT HARMONICS SPECTRUM CONTROL 47
7
P
PQ
Q
Power Model
Predictive Control
ULαβ ILαβ
(PQ)
αβ
abc
PPQP7
Qref Pref
Filter and
Cost Function
Minimization
VSC
PI
-
LOAD
Figure 4.4: Control scheme of Variable Switching Frequency Predictive Direct
Power Control with Current Spectrum Harmonics Control VSF-P-DPC
UDCref
where F is digital filter defined as:
F (z) = b 0z 0 + b 1 z 1 + . . . + b n z n
a 0 z 0 + a 1 z 1 + . . . + a n z n (4.17)
where n is filter order.
If we introduce band stop filter, the desired frequencies will be removed from
the cost function. It means that cost function will have lover value and control
will select more often vectors which produce desired frequencies. So, in order
to concentrate current spectrum at specified frequency an additional band stop
digital filter has to be introduced into the cost function. Figure 4.5 (a) shows
Bode diagram of band stop filter designed for 4 kHz.
On the contrary, to avoid specified frequency a band pass filter (see Fig. 4.5 (b))
has to be introduced into the cost function. In this situation cost function will
have higher value for desired frequency, so control will rarely select vectors, which
will generate that frequency. The cost function has to be modified as follow:
J = √ P 2 err + Q 2 err + K F BP [F (P 2 err) + F (Q 2 err)] (4.18)
where F is filter given by (4.17), K F BP is gain factor and P err , Q err are power