06-08-2013, 01:57 PM
PULSE-WIDTH MODULATED CURRENT CONTROLLER
PULSE-WIDTH MODULATED.pptx (Size: 140 KB / Downloads: 22)
The current error is fed through the PI controller.
This current error gets amplified in the controller and emerges as a control voltage Vc.
The control voltage is equivalent to the duty cycle of the chopper.
Its realization is as follows.
The control voltage is compared with a ramp signal to generate on and off times.
On signal produced when Vc greater than ramp signal.
Off signal produced when Vc less than ramp signal.
Generation of base drive signals from current error
The duration for which the control signal exceeds the ramp signal determines the duty cycle of the chopper.
The on and off times signals are combined with control features like interlock, minimum on and off times and quadrant selection.
Interlock prevents turning on of the transistor in the same leg before the other transistor is completely turned off.
It is advantageous in that it has symmetry between the rising and falling sides of the waveform, unlike the ramp signal.
The voltage applied to the load is varied within one cycle of the carrier signal.
i*-ia ≥ carrier frequency saw tooth waveform magnitude. Tp = 1, Va =Vs