about loop compensation in dc-dc converter

[huangjw]

hi,
I enconter following problem when I simulated a dc-dc buck converter.
1. when i change the load,the stability situation changed. could you please tell me the relation between load and stability?
2. also input voltage
3. The output of the error amplifier changes with the change of load and input voltage,is it normal?
4.how compensate the loop?

 

[johnsmith101]

Are you using voltage-mode or current-mode control?

 

[jwfan]

1. when i change the load,the stability situation changed. could you please tell me the relation between load and stability?
2. also input voltage
The Zeros and Poles of the loop will change with the load. and the Duty cycle will change with your input voltage, so the transfer function will also change. The "fundamentals of power electronics" talk about it in details.

3. The output of the error amplifier changes with the change of load and input voltage,is it normal?
The output of the error amplifier determined the duty cycle. So it changes with the output current and the input voltage.

4.how compensate the loop?
firstly, you should derive the transfer function of the uncompensated loop using small-signal model to replace the switch. and then using compensator to make sure you have enough phase margin and band width.