Hello my fellow engineers!!

I am currently working on my final year project that requires me to design a APFC single switch boost converter. I intend on using an average current mode control algorithm to ensure that the inductor current will emulate a scaled down full wave rectified DC signal (which will be captured from the input voltage sensor). I have designed my system such that the inductor operates in CCM. My progress has been unfortunately stumped due to the fact that my inductor seems to be working in DCM regardless of what duty ratio I operate in, as can be seen below.


My inductor size is 1.9mH and has been wound up using a toroidal core (DS740090). The measurements were further confirmed using an LCR meter.
And gives me a inductance of 1.939mH and a series resistance of 0.36ohms. Would anyone be able to give me guidance in this regard? Any help and suggestions will be highly appreciated.

 

A schematic would be nice. Pictures to.

 

A schematic would be nice. Pictures to.

Hello

Apologies for the lack of information. I have attached a rudimentary circuit schematic of my system.

The implementation is as follows:

 

Please find attached the MATLAB simulation of the system as well. With regards to the actual physical testing, I am using an STM32 Nucleo-F303re to generate a constant PWM signal at a switching frequency of 100kHz.

 

A MOSFET with no gate? What is that?

 

Are you operating in open loop?
If so, the current waveform is correct. A PFC only corrects the PF when operating in closed loop.

 

Are you operating in open loop?
If so, the current waveform is correct. A PFC only corrects the PF when operating in closed loop.

Yes sir I am operating in open loop conditions. My main worry is that to my knowledge I am required to ensure that the inductor works in CCM. But the question I have is that should the system automatically enter CCM under open loop conditions? Or is it normal for my system to enter DCM under open loop conditions?

 

A MOSFET with no gate? What is that?

Sorry sir, as it stands at this current stage I am using a constant PWM signal of 30%. I have increased the duty ratio to 40% and 50%, unfortunately my system is not able to enter CCM.

 

Are you operating in open loop?
If so, the current waveform is correct. A PFC only corrects the PF when operating in closed loop.

The waveform I have attached is the rectified full wave DC signal with respect to the inductor current as measured from the input of the inductor.

 

A MOSFET with no gate? What is that?

It is a poor imitation of a schematic with critical details missing. This is not a serious effort at communication.

 

Yes sir I am operating in open loop conditions. My main worry is that to my knowledge I am required to ensure that the inductor works in CCM. But the question I have is that should the system automatically enter CCM under open loop conditions? Or is it normal for my system to enter DCM under open loop conditions?

You are not operating in DCM. Note that the inductor's design is carried out to operate in CCM at the switching frequency. This will not occur at the mains frequency.
During the peak voltage of the mains, you switch the MOSFET numerous times, and the current does not drop to 0A between each switching, meaning it is operating in CCM.

Please observe that when the mains voltage is very low, the duty cycle must be increased to ensure the boost gain relationship: Vo/Vin = 1/(1-D). Your duty cycle should always be continuously corrected (closed-loop control) to ensure that the current waveform replicates the voltage waveform.