8/13/2019 Simulation of Buck Boost Converter

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SIMULATION OF BUCK-BOOST CONVERTER 

AIM

To simulate a buck-boost converter using Matlab simulink model.

SOFTWARE USED

Matlab 2010

SIMULINK LIBRARY BROWSER

SL

NO. COMPONENT LIBRARY FILE

1. DC voltage source Simpower system- electrical sources

2. MOSFET Simpower system- power electronics

3. Series RLC branch Simpower system- elements

4. Pulse generator Simulink - sources

5. Voltage measurement Simpower system- measurement

6. Scope Simulink - sink

7. Diode Simpower system – power electronics

8. To workspace Simulink - sink

9. Display Simulink - sink

10. Power gui Simpower system

THEORY

A buck converter produce an average output voltage less than the input voltage and a boost

converter produce an average output voltage greater than input voltage. In a buck-boost

converter an output voltage that may be less or greater than input voltage is produced, hence

the name buck-boost converter; the output voltage polarity is opposite to that of input voltage.

The circuit operation can be divided into two modes. Continuous mode and discontinuous

mode. During mode 1,transistor Q1is turned ON and diode Dm is reverse biased. The input

current, which rises, flows through inductor L and transistor Q1. During mode 2, transistor Q1 isswitched off and the current which was flowing through inductor L, would flow through L, C,

Dm and the load. The energy stored in the inductor L would be transferred to the load and the

inductor current would fall until transistor Q1 is switched on again in the next cycle. 

A buck-boost converter provides output voltage polarity reversal without a transformer. It has

high efficiency.

8/13/2019 Simulation of Buck Boost Converter

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CIRCUIT DIAGRAM 

The ratio of output voltage to input voltage is given by,

Vo/Vin= D/(1-D)= I/Io

Where Vo & Vin are output & input voltages, I & Io are input and output currents, D is the duty ratio

defined as the ratio of ON time of switch to the total switching period.

CONTINUOUS MODE OF OPERATION 

If the current through the inductor never falls to zero during a commutation cycle, the

converter is said to operate in continuous mode. The current and voltage waveforms in an ideal

converter is shown in figure. From t=0 to t=DT,the converter is in ON state, so the switch S is

closed.

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DISCONTINUOUS MODE OF OPERATION 

In some cases, the amount of energy required by the load is small enough to be transferred in a

time smaller than the whole commutation period. In this case, the current through the inductor

falls to zero during part of the period. The only difference in the principle described above is

that the inductor is completely discharged at the end of the commutation cycle, in

discontinuous operation, the output voltage not only depends on the duty cycle, but also on the

inductor value, the input voltage and the output current. 

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SIMULINK MODEL

RESULT

Buck-boost converter is simulated using MATLAB simulink model.