Re: Active PFC multiphase output question

Scott,

The duty cycle of each boost converter must vary between almost 100% at the
zero crossings of the mains voltage and almost zero at the peak of the mains
voltage, when it is close to the output voltage.
So, when switching at 100KHz, the gate pulses for each boost FET must vary
between 0-10us.
To have optimum benefit (ripple current reduction at the input and the
output) from the three boost converters, they must be interleaved: the
pulses must be shifted by 120°, in other words, the leading edge of the
pulses must be delayed by 3.33us.

Best regards,

Gerhard

"Scott Ronald" <scottm361@xxxxxxxxx> schreef in bericht
news:bjBHj.5627$Cj7.3559@xxxxxxxxxxxx
I am looking at a multiple boost converter active power factor correction
circuit like below:

vin = 160*|sin(2pi*60*t)|
input filter is a LC lowpass, with cutoff somewhere between 60Hz and F_PWM


|-------------[input filter]-|---[inductor1]--|-[diode]-|---|----|
| | | | | |
| | [PWM1]--[fet1]-[gnd] | | [load]
[vin] | | | |
| |---[inductor2]--|-[diode]-| [cap] |
| | | | | |
| | [PWM2]--[fet2]-[gnd] | | |
| | | | |
| |---[inductor3]--|-[diode]-| | |
| | | | | |
| | [PWM3]--[fet3] | | |
| | | | | |
|----------------------------|----------------|---------|---|----|
|
[gnd]

My question is about the PWM controllers. My sampling rate is 100kHz so I
make my adjustments to the duty cycle at 100kHz.

should I run the PWMs separately and possibly have overlap so
in the 10us period:
PWM1 can be on from 0 to 5us
PWM2 can be on from 2.5us to 7.5us
PWM3 can be on from 5us to 10us
(each PWM has the same duty %)

or

A single multiplexed 300kHz PWM so that with no overlap
in the 10us period:
PWM1 can be on from 0 to 3.333us
PWM2 can be on from 3.333us to 6.666us
PWM3 can be on from 6.666us to 10us
(each PWM has the same duty%)

Scott


.

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