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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



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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



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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


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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



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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


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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


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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



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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

i

c

i

e

n

c

y

E

f

f

i

c

i

e

n

c

y

R = 5

R = 20

R = 15

BUCK – BUCK BOOST – BOOST MODE

R= 5

R = 20

R = 15

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