Peak Current Mode Control - Phase shift

[engineer12]

Hi,

I am developing a peak current mode control of a H bridge dc converter. The output voltage of the converter is controlled by controlling the phase shift of leg B (Q3 & Q4). As it can be seen on the attached picture, the comparator is directly controlling the phase shift.

Since the comparator delivers 1 or 0 (On or Off state), I guess based on the On time I need to control the phase shift. What is the correlation (formula) of the On time vs phase shift?

Thank you. 

[Carlos_Mendoza]

Hi Ivan,

Could you tell us which MCU are you using?

Thanks in advance!

Best Regards,
Carlos Mendoza
Technical Support Engineer

[engineer12]

Hi Carlos,

I am using MC56F82748 chip (TWR-56F8200) and the CodeWarrior 11.0 software.

Thank you in advance.

Kind regards,

Ivan

[xiangjun_rong]

Hi, Ivan,

Pls refer to the application note of peak current mode of buck DC/Dc converter. The peak current control mode algorithms means that when the peak current reaches an adjustable threshold, the MOSFET turn off, obviously, the control mode does not apply for the phase-shift hardware architecture. If you use phase-shift architecture, you have to use PID and the PID output is the phase-shift angle for a H bridge.

Hope it can help you

BR

Xiangjun Rong

https://www.nxp.com/docs/en/application-note/AN4716.pdf 

[engineer12]

Hi Xiangjun,

In addition to my message, if you use a PID controller you still have the compensation ramp, DAC and comparator, so how that is different from the 2p2z control?

Thank you

[engineer12]

Hi Xiangjun,

Thank you for your reply.

I have read that document before, but still it is unclear to me what is the formula of the ON period in terms of time? I think that in order to control the second pair of MOSFETs at 50% duty cycle, we need to control the peak reference current or other parameter to make sure that the switching frequency is fixed and that the duty cycle is 50%. In theory, since the set/reset of PWM cycle happens at every peak current, that does not guarantee 50% duty cycle.

Does the peak current mode control controls the duty cycle instead of the phase shift?

Thank you.

Regards,

Ivan