POLITECHNIKA WARSZAWSKA

4. ANN based Current Controllers
The voltage vector state can be changed in the proposed method three times during
the sampling period, whereas in conventional approach only once. It means
increasing of the internal switching frequency, but the total number of switching in
period (and the mean switching frequency) does not change. Therefore, the harmonic
performance of this regulator is superior to the conventional NN since the zero vector
is being used to avoid ±1 transitions.
This regulator, however, cannot guarantee conformance to the PPCR because the
precise point in time where the line to line voltage fundamental crosses zero cannot
be estimated without the knowledge of the counter EMF.
4.3.2.4. Comparison with three hysteresis controllers
As has been suggested in [115] the input-output relation of three teaching signal is
similar to that of the hysteresis comparator with hysteresis width of δ. Note, that
introduction of such a similarity is false. The reasons of this conclusion is as follows:
• The feedforward ANN presented in this Section cannot implements
characteristic with hysteresis, because the system presented is without
memory;
• If the system is with symmetrical load, it does not choose zero vectors (i.e.
vector number 0 and 7), in spite of this, that we teach system such states.
The reason is, that it is not possible to obtain all values of error positive or
negative, because the sum of these errors has to be zero. So, this situation
is different as compared to hysteresis comparators;
• δ in Table 4.2 has no correlation with width of the hysteresis;
• The system presented is similar to delta modulator
In the next subsection ANN controller in α-β coordinates is introduced. The
considerations described in this subsection are explained and developed.
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