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CHAPTER 5
HARDWARE IMPLEMENTATION OF THE POSITIVE
BUCK BOOST CONVERTER USING A NOVEL
TRIGGERING METHOD
5.1 INTRODUCTION
In this chapter, the proposed method of the PBBC is fabricated as
per the simulation model, and the results are analyzed and discussed. The
hardware circuit is fabricated based on the parameters collected in the table
and the various modes of operation are implemented in the circuit by varying
the duty cycle and control parameter. In addition, the duty cycle variations for
different pulses of the buck, boost and buck-boost operating modes are
explained, with suitable tables and graphs. The ripple contents and efficiency
are analyzed for each mode of operation.
5.2 DESCRIPTION OF THE HARDWARE CIRCUIT WITH FUZZY
LOGIC CONTROLLER
The hardware of a positive buck–boost converter is designed, based
on the parameters listed in Table 3.1. The converter operates at 100 kHz
switching frequency. Two n-type MOSFET switches and two Schottky barrier
diodes are used for the positive buck–boost converter configuration. The
MOSFET switches and diodes are IRF540 and 1N5817, respectively. The
Controller has been implemented using a Texas Instruments digital signal
processor (DSP) (320F2812). The output voltage reference is set to 12 V, and
the input voltage varies from 15 to 8 V (31-62).
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Figure 5.3 DSP Processor
Figure 5.4 Driving Circuit
5.3 HARDWARE RESULT ANALYSIS
Hardware results had been obtained for various modes of operation
with respect to various input conditions. The various models are explained.
5.3.1 Mode 1 (Buck – Boost)
The PBBC is operated in the Buck to Boost mode. The output
voltage has considerable variations during the transition from the buck to
boost. Figures 5.5 and 5.6 demonstrate the output voltage of the converter,
buck pulses, and boost pulses during a direct transition from the buck mode to
the boost mode. Here, the ripple content is about 12%. The voltage ripple is
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defined as the peak to peak ripple as a percentage of the output voltage of the
converter.
Figure 5.5 Output Voltage –Transition from Buck – Boost
Figure 5.6 Enlarged view of Output Voltage Transition from Buck –
Boost Mode
5.3.2 Mode 2 (Buck – Buck Boost – Boost)
In this case, the transition from the buck to the boost is carried out
through a transition from the buck to buck boost mode, followed by a
transition from buck boost to boost mode. The input voltage is decreased from
BUCK MODE BOOST MODE
BUCK PULSE Output Voltage BOOST PULSE
BUCK MODE BOOST MODE
BUCK PULSE Output Voltage BOOST PULSE
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15 to 8 V while the output voltage is tightly regulated at 12 V. Figures from
5.7 to 5.10 present the output voltage of the converter, buck pulses and boost
pulses, for an indirect transition from the buck to boost. In this experiment,
the transition is from the buck to the buck boost to the boost mode with a
ripple content of 10% to 12% as shown in the Figure 5.7 to 5.10.
Figure 5.7 Output Voltage –Transition from the Buck – Buck Boost
Mode
Figure 5.8 Enlarged View of Output Voltage Transition from Buck –
Buck Boost Mode
BUCK MODE BUCK BOOST MODE
BUCK MODE BUCK BOOST MODE
BUCK PULSE Output Voltage BOOST PULSE
BUCK PULSE Output Voltage BOOST PULSE
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Figure 5.9 Output Voltage Transition from Buck Boost –Boost Mode
Figure 5.10 Enlarged View of Output Voltage Transition from Buck
Boost – Boost Mode
5.3.3 Mode 3 (Buck – Combination A – Buck Boost – Combination B
– Boost)
In order to improve the efficiency of the converter in addition to
improving the output voltage transients, the dynamic behavior of the system
BUCKBOOST MODE BOOST MODE
BUCKBOOST MODE BOOST MODE
BUCK PULSE Vout BOOST PULSE
BUCK PULSE V out BOOST PULSE
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for a direct transition from the combination mode A to the combination mode
B is investigated. Figure 5.11 presents the output voltage, buck pulses, and
boost pulses in a direct transition from the combination mode A to the
combination mode B through the buck boost mode. The ripple content in this
mode is 6% as shown in Figure 5.11.
Figure 5.11 Input and Output Voltages for the Transition from Buck –
Boost using the Proposed Method Including Buck Boost
Mode
Figure 5.12 demonstrate the output voltage variation as well as the
buck and boost pulses in transition from the buck to the combination mode A.
Figure 5.13 demonstrate the buck and boost pulses in the transition from
combination mode A to buck boost mode, where each three buck pulses are
associated with one boost pulse. Figure 5.14 demonstrates the buck, boost,
and buck–boost pulses in transition from the buck–boost mode to combination
mode B and the buck, boost, and buck–boost pulses are used to triggering the
converter. In addition, Figure 5.15 illustrates the buck and boost pulses in the
combination mode B before the transition to boost mode is complete. In the
combination mode B, each buck pulse is associated with two boost pulses.
Output Voltage Input Voltage
BUCK MODE BOOST MODE
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The each mode of triggering pulses are analyzed and the average triggering
ripple content is varying from 9% to 11%.
Figure 5.12 Output Voltage Transition from Buck – Combination A
Mode
Figure 5.13 Output Voltage Transition from Combination A – Buck
Boost Mode
BUCK MODE COMBINATION A
COMBINATION A BUCK BOOST MODE
BUCK PULSE Vout BOOST PULSE
BUCK PULSE Vout BOOST PULSE
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Figure 5.14 Output Voltage Transition from Buck Boost – Combination
B Mode
Figure 5.15 Output Voltage Transition from Combination B – Boost
Mode
BUCK BOOST MODE COMBINATION B
COMBINATION B BOOST MODE
BUCK PULSE Vout IL BOOST PULSE
BUCK PULSE Vout BOOST PULSE
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Table 5.1 summarizes the output voltage ripple during transients
through different modes of operation.
5.3.4 Mode 4 (Buck – Boost Through Combination A and
Combination B)
Figures 5.16 to 5.18 shows the transients of converter from buck to
boost through the proposed method without the buck boost mode .The ripple
contents are obtained at 5% as shown in the Table 5.1. The Figure depicts the
output voltage of the converter, buck pulses, boost pulses, for an indirect
transition from the buck to boost through combination A and Boost mode.
Figure 5.16 Output Voltage Transition from Buck Mode – Combination
A Mode
BUCK MODE COMBINATION A
BUCK PULSE Vout BOOST PULSE
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Figure 5.17 Output Voltage Transition from Combination Mode A –
Combination Mode B
Figure 5.18 Output Voltage Buck and Boost Pulses in Transition from
Combination B Mode – Boost Mode
COMBINATION A COMBINATION B
COMBINATION B BOOST MODE
BUCK PULSE Vout IL BOOST PULSE
BUCK PULSE Vout IL BOOST PULSE
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Table 5.1 Summary of the Output Voltage Transients During
Transition Through Different Modes of Operation
Transition Output VoltageRipple (%)
Direct Buck - Boost 12
Buck to Buck - Boost 4
Buck - Boost to Boost 9
Buck to Combination mode A
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method has increased the efficiency by about 17 % to 20% respectively, in the
cases of R = 5 , R=15 and R = 20 as shown in Figures 5.19 and 5.20.
Figure 5.19 Mode of Transition from Buck – Buck Boost – Boost Mode
Figure 5.20 Mode of Transition from Buck – Boost through Buck Boost
and Combination Modes
BUCK --- COMBINATION A – COMBINATION B – BOOST MODE
E
f
f
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c
i
e
n
c
y
E
f
f
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R = 5
R = 20
R = 15
BUCK – BUCK BOOST – BOOST MODE
R= 5
R = 20
R = 15
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