Electronic – Output capacitance effect on stability of DC/DC Buck Converter

buckdc/dc converterpower supplystability

How does having more or less capacitance at the output of a DC/DC buck converter contribute to the location of the poles and zeros. Is there a way to crudely make this calculation.

Best Answer

It depends on many factors. The load (ohmic or others), the state variables, the operation mode (CCM/DCM) and others. After you decide these factors you can formulate the state matrices (A,B,C,D).

Following is a simple Matlab code may help you studying any converter poles position with different capacitor values. The state formulation is taken from this paper. The capacitor varies between \$5 \mu F\$ and \$50 \mu F\$ with step change of \$5 \mu F\$.

L=1e-3;  
R=10;    
c=5e-6;   
d=0.5;
B=[d/L;0];
C=[1 0;0 1];
D=[0;0];
hold on
for i=1:10
    A=[0 -1/L;1/c -1/(R*c)];  
    sys=idss(A,B,C,D);
    pzmap(sys);
    c=c+5e-6;
end

And the result for this particular case,

enter image description here

So for this particular formulation, the increment of capacitor drag the poles of the system to the right hand side of the poles map.

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