V. SIMULATION AND EXPERIMENTAL RESULTS AND
DISCUSSION
The closed-loop system comprising of the boost converter
and the 2 DOF controller designed above is simulated in
MATLAB-SIMULINK environment. The converter, supplying
designed load, is considered to be operating at 5 kHz . A load
perturbation of 60% is introduced at 0.12 sec and it is
withdrawn at 0.16 sec. The nature of the load perturbation is
shown in Figure 6 and 7.
The nature of load current during these increment and
decrement are shown in Fig. 6 and Fig. 7. The figures show
that the load current changes from its nominal value of 0.5
Amp to 0.8 Amp, and on withdrawal of the load perturbation
of same amount at 0.16 sec, the load current settles down at its
nominal value of 0.5 amp. In both the cases, the load current
takes about 6 msec to settle down.
Fig. 6: Load Current Perturbation of 60% introduced at 0.12 sec
Fig. 7: Load Current perturbation withdrawn at 0.16 sec
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As a result of these load perturbations, the output voltage
responses are shown in Fig. 8 and Fig. 9. The controller takes
approximately 6 msec to settle the output voltage again to its
nominal value 24 Volts. Therefore, the simulation results
depict that the controller can efficiently sustain a high amount
of perturbation in load current.
Fig. 8: Output voltage response under the load perturbation
Fig. 9: Output voltage Response on withdrawn of load perturbation
The real-time implementation of 2 DOF controller is done in
dSPACE 1104 environment. The scheme of the experimental
setup of the boost converter is shown in Fig. 10.
Fig. 10: Experimental control scheme of the Boost Converter
The experimental setup of the boost converter has been
realized by IGBT based switch, to be controlled through the
dSPACE controller. The 2 DOF controller requires only one
voltage feedback and hence is as advantageous as control.
The controller shown in Fig. 2 is implemented in the block of
Fig. 10. Here the reference voltage is set at 24 Volts. The
output of the controller is the control voltage ( ). The control
voltage is used to generate the PWM gate signal by comparing
with saw tooth wave of 5 kHz. The scaling is done according
to the nominal choices of variables of the converter. The two
current sensors however are placed for observation of the
intermediate and output variable. They are never coming in the
design and implementation loop of the control scheme. The
PWM buffer and isolator circuit receives the signals from
PWM port of the dsp controller board, and then produces
PWM signals of required level for the IGBT used as the switch
of the boost converter. The gate driver circuit is thus not
utilizing the power from the dsp control board. The switching
frequency for the experiment has been fixed at 5 kHz. The load
ensures continuous conduction modes at the initial level.
Hence the CCM is also there with higher load (at 60%
perturbation).
The real-time results are in good agreement with that
obtained in simulation as discussed above.
A load perturbation of 60% is introduced at 3.4837 sec. The
load current changes from its nominal value of 0.5 Amp to 0.8
Amp. The perturbation is withdrawn at 7.665 sec. The
controller exhibits a fast recovery in output voltage within
approximately 7.5 msec. On addition of load perturbation, the
output voltage reduces to minimum 23 Volts, and it again
attains its nominal value 24 Volts after 7.5 msec. On the other
hand, on withdrawal of perturbation, the output voltage
undergoes a change and increases to 25 Volts maximum. In
this case also the voltage settles down to 24 Volts within 7.5
msec. The load current, output voltage response and the
behavior of the inductor current during addition and withdrawn
of the load perturbation are shown, respectively, in Fig. 11 and
Fig. 12. The pattern of inductor current is showing the obvious
sluggish response in both increasing and decreasing scenarios.
Moreover, the inductor current is confirming the continuous
conduction mode by showing that the current never goes to
zero.
Fig. 11(a): Load perturbation of 60% introduced at 3.48 sec.
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