Converters have two modes of closed loop control. Either current mode or voltage mode control.current mode control has got an advantage of high band width. In this presentation i have included the digital mode of current controlling using PIC16f877a

1. CURRENT
PROGRAMMED MODE
OF BUCK CONVERTER
PRESENTED BY: SWATHI M NAIR
IDK18EEPC16
GUIDED BY : VISHAL M J

2. SYNOPSIS
•Current Programmed Mode(CPM)
•Buck converter
•Circuit and Design
•Closed loop control
•Bode plot
•Controlled waveform
•Advantages
•Conclusion
•Reference
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3. INTRODUCTION
•CPM : By limiting the inductor current or switch
current.
•Two control loops voltage mode control and current
mode control
•Inductor current is sensed and compared with
reference voltage.
•Switch off and switch on is based on this comparison.
•Voltage mode has a disadvantage of small frequency
band width.
•CPM is simple , robust and has wide frequency
band width output voltage.
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4. CIRCUIT AND DESIGN
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5. Contd..
• Power ,P =50W
• Input Voltage ,Vin =16-24V
• Output voltage, Vout=12V
• Switching Frequency =50kHz
• Output current Io=
50
12
= 4.125𝐴
• Load resistance R=
12
4.125
= 2.909𝑜ℎ𝑚
• ΔIL=10% of IL=0.4125A
• Δvo=1% of Vo=0.12V
• L=
𝑉𝑂 (1−𝐷)
Δ𝐼𝐿 𝑓𝑠
=300µH with ESR=0.1Ω
• C=
Δ𝐼𝐿
8𝑓𝑠 𝑉𝑜
=100µF with ESR=0.1Ω
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6. Contd..
• MOSFET- IRFZ44
• DIODE- STPS2045CT
• CURRENT SENSOR-ACS712 Hall effect current sensor
• PIC16F877A-Digital PID controller
• Transfer function
• A avg=
−𝑟𝑙+
𝑅 𝑟𝑐
𝑅+𝑟𝑐
𝐿
−𝑅
𝐿(𝑅+𝑟𝑐)
𝑅
𝑅+𝑟𝑐 𝐿
−1
𝐶(𝑟𝑐+𝑅)
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7. Contd..
• B avg= {[
1
𝐿
0]𝐷} 𝑇
• C avg = [
𝑅 𝑟𝑐
𝑅+𝑟𝑐
𝑅
(𝑅+𝑟𝑐)
]
• Transfer function =C[SI−A]−1
B
=
319.99𝑆+32192308.07
𝑆2+6235.8𝑆+40893466.6
=
319.9(𝑆+100604.10)
(𝑆+ 3117.9+5583𝑖 )(𝑆+(3117.9−5583𝑖))
• PI controller design
• Phase margin=29.2
• Kp=2
• Ki=2340*2
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8. INDUCTOR DESIGN
• L=300µH
• Area product=
𝐿𝐼2
2
• Ap=Aw Ac=
2𝐸
𝐾𝑤𝐾𝑐𝐵𝑚
=21039.6𝑚𝑚2
• Kw=0.3
• Kc=1.01
• J=4*106
A/MM^2
• B=0.2T For ferrite
• By choosing ferrite core characteristcs P 32/22
• Ac=201𝑚𝑚2
𝑎𝑛𝑑 𝐴𝑤 = 101𝑚𝑚2
• N=
𝐿𝐼
𝐴𝑐𝐵𝑚
=31 turns
• Wire gauge=
𝐼
𝐽
: SWG 16 is proper chice
• Air gap length=
µ0𝑁2 𝐴𝑐
𝐿
=0.809mm
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9. Bode plot
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10. Closed loop simulation
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11. Waveform
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12. Advantages
• Simple dynamics
• Simple compensation network,robust
• Wide band width output voltage control
• Output current is proportional to the control voltage, the
output current can be limited simply by clamping the control
voltage.
• Higher power applications, power stages can be connected
in parallel. Since the output currents are proportional to the
control voltages.
• Automatic feed forward from the line voltage
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13. Conclusion
• Current programmed mode is the simple model of control.
• Over current does not flow through the circuit, so the circuit never
gets damaged due to over current.
• The disadvantage of this circuit is susceptibility to noise, which can
be over comes by adding a artificial ramp signal.
• Turn on and turn off are determined by the times at which switch
current reaches threshold value.
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14. Reference
• Fundamentals of Power Electronics SECOND EDITION, Robert W.
Erickson University of Colorado
• Boulder, Colorado State Space Modelling of a BUCK Converter and
Designing a Controller A thesis report submitted to the department
of electrical engineering of BARC university .
• State Space Modelling Of Current-mode Control And Its Application
To Input Impedance Shaping Of Power Electronic Constant-power
Loads :Sean C. Smithson
• Course Material On Switched Mode Power Conversion --V.
Ramanarayanan
• VENABLE TECHNICAL PAPER : Current Mode Control
• Design of magnetic components for switch mode converters-
Umanand
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15. THANKYOU.!
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