POLITECHNIKA WARSZAWSKA

4. ANN based Current Controllers (CC)
On the other hand, rise time is mainly affected by the AC side inductances of the
converter. The optimization of the dynamic response usually requires a compromise,
which depends on the specific needs. This may also influence the choice of the CC
technique according to the application considered.
In general, the compromise is easier as the switching frequency increases. Thus,
with the speed improvement of today's switching components (e.g. IGBT's), the
peculiar advantages of different methods lose importance and even the simplest one
may be adequate. Nevertheless, for some applications with specific needs, like active
filters, which require very fast response, or high power inverters where the
commutations must be minimized, the most suitable CC technique must be selected.
4.2.2 Nonlinear Current Controllers
A. Hard Switched Converters
1) Hysteresis Current Controllers
Hysteresis control schemes are based on a nonlinear feedback loop with two-level
hysteresis comparators (Fig. 4.2a) [61]. The switching signals S A ,S B ,S C are produced
directly when the error exceeds an assigned tolerance band h (Fig. 4.2b).
U DC
i Ac
i Bc +
i Cc
+ -
+ -
-
S A
S B
S C
i A
i B
i C
Three-phase
Load
β
B
state 1
Hysteresis
band
state 0
A
500
N
250
(a)
a
b
c
i S
C
-h
+h
α
0 0 ms
40
(b)
(c)
Fig. 4.2. Two-level hysteresis controller: block scheme (a), switching trajectory (b) Number of inverter
switchings N (c) for: a) three two-level hysteresis comparators, b) three-level comparatos and lookup table
working in stationary and c) rotating coordinates
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