POLITECHNIKA WARSZAWSKA

4. ANN based Current Controllers (CC)
Based on work [34] (where it has been demonstrated that is possible to perform
current vector control in an arbitrary coordinates), a synchronous controller working
in the stationary coordinates α-β with ac components has been presented [33]. As
shown in Fig.4.8b by the dashed line, the inner loop of the control system (consisting
of two integrators and multipliers) is a variable frequency generator, which always
produces reference voltages uαc , u βc for the PWM modulator, even when in the
steady state the current error signals are zero.
In general, thanks to the use of PWM modulators, the linear controllers make a well
defined harmonic spectrum available, but their dynamic properties are inferior to
those of bang-bang controllers.
C. State Feedback Controller
The conventional PI compensators in the current error compensation part can be
replaced by a state feedback controller working in stationary [29] or synchronous
rotating coordinates [13,25,27,28,30].
Feedforward
K f
K d
Disturbance
U DC
i sc
+
-
K 2
u sc
PWM
modulator
Integral part
K 1
State
feedback
i s
Three-phase
Load
Fig. 4.9. State feedback Current controller
The controller of Fig. 4.9 works in synchronous rotating coordinates d-q and is synthesised
on the basis of linear multivariable state feedback theory. A feedback gain
matrix K=[K 1 ,K 2 ] is derived by utilising the pole assignment technique to guarantee
sufficient damping. While with integral part (K 2 ) the static error can be reduced to
zero, the transient error may be unacceptably large. Therefore, feedforward signals for
the reference (K f ) and disturbance (K d ) inputs are added to the feedback control law.
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