Ralph Barone
Guest
Wed Jan 18, 2012 7:18 am
Do PFC circuits inherently result in unity power factor or can they be
"fudged" to produce a leading or lagging power factor?
John Larkin
Guest
Wed Jan 18, 2012 4:07 pm
On Wed, 18 Jan 2012 06:18:26 GMT, Ralph Barone
<address_is_at_invalid.invalid> wrote:
Quote:
Do PFC circuits inherently result in unity power factor or can they be
"fudged" to produce a leading or lagging power factor?
The common flyback PWM can't output current to the AC line, so can't
accurately fake a capacitance or inductance. Their positive peak
current could be shifted in time, which would technically be a power
factor shift.
Other circuits could, given adequate reservoir capacitance, really sim
an L or C over the whole cycle.
John
Tim Williams
Guest
Thu Jan 19, 2012 1:37 am
You can take the line in through an inductor and chop it with a bridge (so
it looks like you're driving the line with the bridge's output), and
operate with PWM in a current loop so that the line current is always
proportional to the line voltage, or some phase shift thereof. This is
scaled by the DC error voltage on the output rail, so the voltage remains
regulated while 120Hz ripple (or 360Hz if you do this with a three phase
chopper for industrial use) appears on the filter cap.
You're basically running a VFD in reverse. Two of these, back to back,
would do a great job running motors; unsurprisingly, this is often done.
Tim
--
Deep Friar: a very philosophical monk.
Website:
http://webpages.charter.net/dawill/tmoranwms
"John Larkin" <jjlarkin_at_highNOTlandTHIStechnologyPART.com> wrote in
message news:qmndh7pjbcs1d17r5c9drceu0arsla3k3t_at_4ax.com...
Quote:
On Wed, 18 Jan 2012 06:18:26 GMT, Ralph Barone
address_is_at_invalid.invalid> wrote:
Do PFC circuits inherently result in unity power factor or can they be
"fudged" to produce a leading or lagging power factor?
The common flyback PWM can't output current to the AC line, so can't
accurately fake a capacitance or inductance. Their positive peak
current could be shifted in time, which would technically be a power
factor shift.
Other circuits could, given adequate reservoir capacitance, really sim
an L or C over the whole cycle.
John
Ralph Barone
Guest
Thu Jan 19, 2012 3:34 am
John Larkin <jjlarkin_at_highNOTlandTHIStechnologyPART.com> wrote:
Quote:
On Wed, 18 Jan 2012 06:18:26 GMT, Ralph Barone
address_is_at_invalid.invalid> wrote:
Do PFC circuits inherently result in unity power factor or can they be
"fudged" to produce a leading or lagging power factor?
The common flyback PWM can't output current to the AC line, so can't
accurately fake a capacitance or inductance. Their positive peak
current could be shifted in time, which would technically be a power
factor shift.
Other circuits could, given adequate reservoir capacitance, really sim
an L or C over the whole cycle.
John
Darn. I guess that approach won't work then. Thanks for the info.
