fixed frequency boundary control of Buck Converter with 2nd order switching surface

8/9/2019 fixed frequency boundary control of Buck Converter with 2nd order switching surface

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- The advanced digitalized control in SMPS..

Fixed-Frequency Boundary Control of Buck ConverterWith Second-Order Switching Surface

Under The Guidance-

Mr. JAY KUMAR,

SENIOR LECTURER,

TOCE, EEE Dept, VTU.

Seminar presentation by-Mr. PAPANNA DHANANJAY,

M.TECH-POWER ELECTRONICS,

2nd SEMESTER, TOCE, EEE Dept,

VTU11


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INTRODUCTION:

The control of Buck converter is done by BOUNDARY

CONTROL TECHNIQUES with linear switching

surfaces, such as Hysteresis control and Sliding-mode

control , or nonlinear switching surfaces have been proposed

to be alternatives to pulse width-modulated control strategies

in dc/dc switching regulators.

22Fixed Frequency Boundary Control


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o achieve an ideal switching surface . That leads tolobal and large signal stability.

ood large-signal operation.

ast Dynamics.

etter steady-state and transient behaviors.

Reduce the hardware & software design complexity.

Immune to Chaos due to Electro magnetic Interference fro

outside source

AIM:



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xisting System:

CONTROL TECHNIQUES FORTHE BUCK CONVERTER

ndary control withing Controller

PWMController

Boundary control withHysteresis Controller

Fuzzy logic alongPID controller



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PROBLEM STATEMENT:

In conventional DC/DC controllers we are facing the following

problems:

q Deterred steady-state behaviors.

q The Transient Dynamics is not optimized.

q Chattering as a result of imperfect control switchings

qWhen a converter is operated in the discontinuous

conduction mode, an additional boundary due to the

zero inductor current is created which forms an unstable

combination.



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The Challenge:

To design the universally acceptable DC/DC controller that satisfies

the aims and Overcomes the problems specified.



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PROPOSED SOLUTION:

Use Fixed Frequency Boundary Control technique with

Second- Order Switching Surface to design theDC/DCcontroller.



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ELABORATING OF THE TOPIC

q Fixed Frequency: The output power is controlled by

making Frequency as constant even under variation in the input

voltage.

q Boundary Control: controlling of on & off state trajectory for

maintaining large-signal stability.

q Buck Converter: Its a fixed DC to variable DC converter, where

output voltage is always less than or equal to input voltage. The

output voltage can be varied by varying the duty cycle.

i.e., Vo/Vs= D continue


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Fixed Frequency Boundary Control99

Continue

q2nd order Switching Surface:

It consists of two poles

It controls the hysteresis band by generating upper and lower

bands together.

It helps in determining the switching times of the main switch S.

It exhibit better steady-state and transient behaviors than the one

with a first-order switching surface.


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1010 Fixed Frequency Boundary Control

Figure 1: System Block Diagram.

WORKING OF THECONTROLLER:


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Figure 2: System Implementation1111

Fixed Frequency Boundary Control


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1212

Figure 3: Small-signal block diagram of the control loop.



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Figure 4: Key time-domain waveforms of the converter.



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In Mode 1 (t1 t < t3), Sis ON andD is OFF.

In Mode 2 (t3 t < t5 ), Sis OFF andD is ON.



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As the load variation is small, vCis relatively constantover a switching cycle. Thus

Then, by substituting equation (4.6) into (4.2), the Mode-1 state trajectorcan be shown to be

Where,


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Assume that iCvaries linearly in Mode 2. Bysubstituting (4.5) into (4.3)

Thus, by substituting (4.8) into (4.4), the Mode-2 state trajectory can beshown to be

Where,


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Thus, by substituting (4.10) and (4.11) into (4.7), Swill be switched ONwhen

and 4.12

The criteria for switching SOFF is based on considering that

and

Thus, by substituting (4.13) and (4.14) into (4.9), Swill be switched OFFwhen

CRITERIA FOR TURN ON & OFF:

The criteria for switching SON is based on consideringthat


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FIGURE 5: STATE-PLANE TRAJECTORIES (SOLID LINES: MODE-1TRAJECTORIES, DOTTED LINES: MODE-2 TRAJECTORIES).

SWITCHING FREQUENCY AND


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SWITCHING FREQUENCY ANDOUTPUT VOLTAGE RIPPLE:

By substituting (4.5) into (4.1) and (4.3), it can beshown that

and

Equations (4.12) and (4.15) will then give

and

Where


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Thus, by substituting (4.18) and (4.19) into (4.16) and(4.17), the switching frequencyfSis equal to

Where and


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MALL-SIGNAL MODELING:

Based on (4.20), the small-signal frequency-to-rippletransfer function GSBC of SBC is

Where , = >The steady-state value of the hysteresis band.

KT => The total gain including the gain of the transducers.

The transfer function of FVC is, GFVC = KFVC

The transfer function of the low-pass filter at the output ofFVC is

Wh


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Where

is the cutoff frequency of the low-pass filter.

Transfer unction of a non inverting EA is

Where is the cutoff frequency of the EA.

The loop gain TOL of the frequency control loop is

SIMPLIFIED DESIGN PROCEDURES


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SIMPLIFIED DESIGN PROCEDURES:

The system is designed by considering the followingspecifications:

a) Input voltage vi: [Vin,min, Vin,max];b) Output voltage vo: Vo;c) Maximum output voltage ripple: Vo;d) Maximum inductor current ripple: IL;e) Switching frequency:fS.

The design procedures are described as follows.qThe minimum values ofL and Cin the power stage are designed by the

formulas of

and

th l f K1 d K2 h t b


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qthe values ofK1 andK2 are chosen to be

and

Where

The values ofRLP, CLP,RC, and CCare chosen so that LP = 2 C= (2fS), where


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TABLE 1: COMPONENT VALUES OF THE PROTOTYPE

FIGURE 6.B: CIRCUIT IMPLEMENTATION OF THE SYSTEM SHOWN INFIGURE 2.


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FIGURE 6.A: CIRCUIT IMPLEMENTATION OF THE SYSTEM SHOWN IN

FIGURE 2.

RESULTS AND DISCUSSION


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RESULTS AND DISCUSSION:

A 140 W buck converter has been designed and

tested and the specifications are given as follows:a) Input voltage, vi: 2030 V;b) Output voltage, vo: 12 V;c) Maximum output voltage ripple, 2: 160 mV;

d) Maximum inductor current ripple: 7 A;e) Switching frequency: 25 kHz;


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Sudden change of the output current iofrom 11A (132 W) to 2.5A (30 W).(VO: 1V/div, io: 5A/div, vg: 2V/div)(Time base: 100s/div).

Transient response ofvfand when current changed from 11A to2.5 A and 2.5A (30 W) to 11A(132 W).


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Fixed Frequency Boundary Controlof Buck Converter with 2nd order

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Sudden change of the input voltagevi from 20Vto 30V.

Sudden change of the input voltagevi from 30V to 20V

Switching frequency and outpu


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Switching frequency and outpuvoltage ripples without theproposed control method.

Switching frequency and output


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Switching frequency and outputvoltage ripples with theproposed control method.

Characteristics of the


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Characteristics of thecontrol loop shown inFigure (a) Gain

curve. (b) Phase curve.


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:An improved boundary control technique with

second-order switching surface for buck converters has

been presented which provides-

q By using of SBC the converter can reach the steady state in two

switching actions after large-signal disturbances.

q The switching frequency can be kept at a relatively constant value and

the implementation of the frequency control loop only requires

simple circuitry.


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Finally, I Thank to novel Boundary control method

That as boosted the performance of the control

system in

DC/DC converter system.



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Q/A

Questions and answer time



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THANK YOU

Documents

fixed frequency boundary control of Buck Converter with 2nd order switching surface