CONTROL OF DC-DC CONVERTER USING MICROCONTROLLER

INTRODUCTION

• Satellites are man-made machines, that send radio waves down to Earth, and are used for communication and remote sensing applications.

• Various voltage levels are required for different types of payloads in the satellite.

• The various voltage levels are generated using DC-DC converters.

• The DC-DC Converters can be controlled either by pulse-width modulation or frequency modulation.

• The basic types of Converters are BUCK,BOOST,BUCK-BOOST and CUK.

DC-DC CONVERTERS

BUCK CONVERTER

BOOST CONVERTER

BUCK-BOOST

CUK CONVERTER

BUCK CONVERTER

OPERATION

CONTINUOUS MODE

MICROCONTROLLER

• A microcontroller is a small computer on a single integrated circuit .

• Microcontrollers are used in automatically controlled products and devices, such as remote controls, power tools, and toys.

PIC16F785 MICROCONTROLLER

FEATURES

• Operating Voltage Range : 2.0V-5.5V

• Frequency Range : 8 MHz to 32 MHz

• Uses HARVARD Architecture

• Two Operational Amplifiers

• Two Independent Analog Comparators

• Two-Phase PWM Module

CONTROL OF BUCK CONVERTER

BLOCK DIAGRAM

COMPARATOR

ALGORITHM

• PIC Microcontroller is configured to use built-in Internal Oscillator and code protect off, watchdog timer off, power up timer on and brown out detector off.

• Ports and module pins are configured as analog or digital input and output.• Port C is cleared.• Bit 6 and 7 of port C are configured as input using port C tristate register. Op-amp is enabled by setting bit 7 as 1.• Bit 3 and 0 of port A are configured as input using portA tristate register.• Comparator is on, non-inverted, normal speed, output present on pin 17, inputs

from op- amp and external ramp signal.• PWM auto-shutdown is disabled, SYNC pin acts as system slave, PH1 is driven by

PWM signal.• PWM outputs are configured active low, frequency of PWM set to 4MHz,time

period set to 100ksec.• PWM phase 1 is configured active low, PH1 resets when C1OUT goes high.

TEST RESULTS

PWM OUTPUT- Case1

Vin= 20V Duty Cycle= Ton/T = 0.624

MOSFET GATE DRIVE- Case1

Vin= 20V Duty Cycle = Ton/T= 0.237

Vout= Vin * Duty Cycle = 4.75V

OUTPUT OF BUCK- Case 1

Vout = 4.8 V

PWM OUTPUT – Case 2

Vin= 23V Duty Cycle= Ton/T = 0.564

MOSFET GATE DRIVE- Case2

Vin= 23V Duty Cycle = Ton/T= 0.209

Vout= Vin * Duty Cycle = 4.8V

OUTPUT OF BUCK – Case 2

Vout = 4.8 V

PROS AND CONS

ADVANTAGES

• In-Circuit Programmability of parameters– Code can be altered at any

stage of design

• Other control functions and communication interfaces can also be performed using Microcontroller.

• Less power consumption.

DISADVANTAGES

• Level shifting is required to Drive the MOSFET.– Can be overcome by using

Logic Level MOSFETs

• External SYNC pulse required– Can be generated using PIC

APPLICATIONS

• Used to generate various voltage levels required for different subsystems of a satellite.

• Can be used for Regulation of Satellite Power Bus.

• Can be used to generate Auxiliary Power Buses from Satellite Primary Power Bus.

CONCLUSION

• The successful control of a Buck Converter using PIC16F785 microcontroller was achieved.

• Future enhancements can be control of multiple DC-DC Converters with a single Microcontroller by using both the phases of PWM, control of Isolated Buck Converters, etc

THANK YOU