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Design >> High-Power Design >> Boost Converter Right Half-Plane Zero Physical Manifestations and Solution Limit
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Message started by kanmaedex on Aug 4^th, 2013, 4:12am

Title: Boost Converter Right Half-Plane Zero Physical Manifestations and Solution Limit
Post by kanmaedex on Aug 4^th, 2013, 4:12am

Hello I just learned about the inherent Right Half-Plane Zero (RHPZ) problem that is found in some power supply topologies such as the boost converter and the flyback converter. As I've seen in the website, http://powerelectronics.com/power-ma...alf-plane-zero , Christopher Basso says that the effect of the Right Half-Plane Zero can be seen for instance in a boost converter when you apply a large step increase in load current, the output voltage dips down before going back up again into steady-state. The solution stated in the site is that we reduce the rate of change of the duty ratio through proper compensation. I have some questions regarding this.

1.) Are there other physical manifestations resulting from this?
2.) When compensated properly, is it possible that the RHPZ could be eliminated completely, as in no onset of the dip during the occurrence of the step load could be seen? Or is it only possible to reduce this 'dip' but not completely remove it.
3.) As far as I understand, the RHPZ increases gain but reduces phase, which greatly reduces the phase margin. This is what causes the instability effects. So the RHPZ could also cause physical manifestations such as oscillations that occur forever? maybe small amplitude ripple that goes on and on causes by imbalance of charging the output capacitor and charging the inductor current.
4.) Would you know of a good source which says how to compensate for the RHPZ in a boost converter in current-mode control? The link I provided discusses it for Voltage mode control but for current-mode control the equations seem very complicated hence I rely on my simulator to tweak the gain and phase margins. In the first place, I do not even know the limitation of solving this problem as seen in the time domain hence my question number 2. Or would you know how?

Thanks!

Title: Re: Boost Converter Right Half-Plane Zero Physical Manifestations and Solution Limit
Post by AnilReddy on Sep 12^th, 2013, 4:03am

Hello,

I don't understand the following...

"the effect of the Right Half-Plane Zero can be seen for instance in a boost converter when you apply a large step increase in load current, the output voltage dips down before going back up again into steady-state".

Any -ve feedback circuit of limited BW will have the same effect. Why RHP zero in particular? In addition, if you have a forward path (RHP zero) then output tries to rise initially rather than dip.

As far as i know, we can't completely remove the affect of that zero by compensation. what we can do is that increase the current loop gain (in current-mode control) to a value that pushes the inductor pole beyond UGB and compensate the phase shift of RHP zero. rhp zero location is determined predominantly by inductor itself.

Bye
Anil Reddy