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EE136. STABILITY AND CONTROL LOOP COMPENSATION IN SWITCH MODE POWER SUPPLY Present By Huyen Tran. STABILITY AND CONTROL LOOP COMPENSATION IN SWITCH MODE POWER SUPPLY. potential risk for oscillation in a closed loop control system methods of stabilizing the loop .

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EE136

STABILITY AND CONTROL LOOP COMPENSATION IN SWITCH MODE POWER SUPPLY

Present By Huyen Tran


STABILITY AND CONTROL LOOP COMPENSATION IN SWITCH MODE POWER SUPPLY

potential risk for oscillation in a closed loop control system

methods of stabilizing the loop


Methods of stabilizing the loop

  • By Circuit and Mathematical Analysis

    -Required “fine tuning”

  • Interrogative Methods of Loop Stabilization

    -A “difference techniques” can be used to establish the required characteristics of the compensated control amplifier.


C1

R1

Vi

-

Vo

OUT

+

VREF

0

Methods of stabilizing the loop

Type 1 Compensation


Methods of stabilizing the loop

  • Type 2 Compensation


Methods of stabilizing the loop

  • Type 3 Compensation


Stability testing methods

  • One of these method is transient load testing

    -the transfer function changes under different loading conditions.


Set up the transient load test


Analysis for transient test


Analysis for transient test

  • For an under damped response, it will have a poor gain and phase margins and maybe only conditional stable. With this performance, the oscillation may occur.

  • For an over damped response, it is very stable, but does not give the best transient recovery performance.

  • For waveform c, it is stable transient response, and it will provide enough gain and phase margin for most application.


Measurement procedure for the closed- loop power supply systems


Measurement procedure for the closed- loop power supply systems

  • voltmeter V1 is used to measure the ac input of control amplifier

  • voltmeter V2 is used to measure the ac output voltage of power supply for each time changing the frequency


A typical Bode plot


Design example

Stabilizing a Forward Converter Feedback Loop with a Type 2 Error Amplifier

  • V0 = 5V

  • I0(nom) =10A

  • Minimum I0 = 1A

  • Switching frequency = 100 kHz

  • Minimum out put ripple = 50mV


Design example

  • calculate Lo and Co

And the cutoff frequency of the output LC filter Is


Design example

  • the frequency of the ESR zero is

Then the modulator gain :


Design example

  • Then the total open loop gain Gt = Glc + Gm +Gs is draw in fig.1


Design example

  • At very low frequency, it is a straight line with -1.5dB and then it hit 2 poles at the frequency which is 806 Hz and start rolling down with slope of -40dB/dec until it hit a zero at 2500 Hz, and the line still rolling down but the slope only -20dB/dec.


Design example

fz = 5kHz, fp =80 kHz, gain 40


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