Phase chopping.. bad?

Is chopping of a 240V rms AC-sinewave with ibgt (or mosfet..) with
5-30 kHz pwm and filter it to regulate power to pure resistance load a bad
idea?

RFI emission better or worse than forward/back phase chop regulation?

 

[legg]

On 07 Oct 2004 14:58:53 GMT,
pbdelete@spamnuke.ludd.luthdelete.se.invalid wrote:

Is chopping of a 240V rms AC-sinewave with ibgt (or mosfet..) with
5-30 kHz pwm and filter it to regulate power to pure resistance load a bad
idea?

RFI emission better or worse than forward/back phase chop regulation?

Buck regulating AC into any AC load with a common neutral will require
a bidirectional switch, which can get messy at higher frequencies.

Generally a 'pure resistance load' doesn't need fancy preregulation,
as all it can do is get hot.

If the aim is to make the load look resistive, then fancy
preregulation methods can have an application.

As all methods introduce switching frequency current into the line, a
topology allowing continuous current will tend to be easier to filter
at the switching fundamental and lower harmonics - required if these
are within the regulated bands in your application.

Buck topologies are discontinuous on input current, by definition and
will therefore require more filtering for the same current draw.

RL

 

Joel Kolstad <JKolstad71HatesSpam@yahoo.com> wrote:

pbdelete@spamnuke.ludd.luthdelete.se.invalid> wrote in message
news:416559ad$0$180$cc7c7865@news.luth.se...
Is chopping of a 240V rms AC-sinewave with ibgt (or mosfet..) with
5-30 kHz pwm and filter it to regulate power to pure resistance load a bad
idea?

There is very similar to how factor correction is done is power supplies --
when the instantaneous voltage of the AC sinewave is low, a large 'slice' is
switched on to the rest of the power supply followed by a short off-time.
At the peak of the waveform, a smaller slice is taken with a longer
off-time.

So... it's a 'reasonable enough' idea.

factor correction -> you mean power factor correction? (W vs VA etc..)

If so it's possible to build a adjustable powerfactor correction circuit
by an oversized capacitor that is connected through pwm cycles at varying
duty cycle?
And thus one can power correct a inductive load for use with ibgt if needed?

RFI emission better or worse than forward/back phase chop regulation?

It's worse in the sense that you'll have much higher frequency harmonics to
deal with. On the other hand, filtering out 5-30kHz signals is a easier (in
terms of component size and price) than 60Hz signals.

The same regulations that cajoled power supply manufacturers to add the
power factor correction circuitry also have plenty to say about emissions,
so it looks like controlling them is a reasonably solable problems (i.e.,
reasonably cheap).

* Any suggestion on filters?

* How to actually wire the IBGT?, is the below scheme ok?


___|\|____
| |/| |
| |
AC1 >----E IBGT C-----
|
G1 |
|
Load
|
G2 |
|
AC2 >----E IBGT C ----
| |
|___|\|____|
|/|

G1 would be sent a pwm pulse for the negative phase on AC1, and G2 for the
positive phase on AC1. This to take into account that IBGT works as an
"controlled" diode. The parallell diodes is to let the electric pass when
the ibgt of the other side is active.

 

[Joel Kolstad]

<pbdelete@spamnuke.ludd.luthdelete.se.invalid> wrote in message
news:4166ce3a$0$175$cc7c7865@news.luth.se...

Joel Kolstad <JKolstad71HatesSpam@yahoo.com> wrote:
pbdelete@spamnuke.ludd.luthdelete.se.invalid> wrote in message
news:416559ad$0$180$cc7c7865@news.luth.se...
Is chopping of a 240V rms AC-sinewave with ibgt (or mosfet..) with
5-30 kHz pwm and filter it to regulate power to pure resistance load a
bad
idea?

There is very similar to how factor correction is done is power
supplies --

factor correction -> you mean power factor correction? (W vs VA etc..)

Yes, sorry about dropping the word there.

If so it's possible to build a adjustable powerfactor correction circuit
by an oversized capacitor that is connected through pwm cycles at varying
duty cycle?
And thus one can power correct a inductive load for use with ibgt if
needed?

Yep. Power factor correctoin is a popular research topic, and important
enough commercially that you'll find the likes of On-Semi and others make
power factor correction chips. (Note that if you plan to do the same thing
and actually sell a product, there are a few patents out there to be aware
of. :-( )

I can't comment on the rest of your post in that I don't have any real
design experience with off-line (120V/240V) supplies other than having used
them and occasionally paying attention when they were discussed as part of
broader topic coverage (such as low voltage switchers, that I have design
experience with).

---Joel

 

[Joel Kolstad]

<pbdelete@spamnuke.ludd.luthdelete.se.invalid> wrote in message
news:416559ad$0$180$cc7c7865@news.luth.se...

Is chopping of a 240V rms AC-sinewave with ibgt (or mosfet..) with
5-30 kHz pwm and filter it to regulate power to pure resistance load a bad
idea?

There is very similar to how factor correction is done is power supplies --
when the instantaneous voltage of the AC sinewave is low, a large 'slice' is
switched on to the rest of the power supply followed by a short off-time.
At the peak of the waveform, a smaller slice is taken with a longer
off-time.

So... it's a 'reasonable enough' idea.

RFI emission better or worse than forward/back phase chop regulation?

It's worse in the sense that you'll have much higher frequency harmonics to
deal with. On the other hand, filtering out 5-30kHz signals is a easier (in
terms of component size and price) than 60Hz signals.

The same regulations that cajoled power supply manufacturers to add the
power factor correction circuitry also have plenty to say about emissions,
so it looks like controlling them is a reasonably solable problems (i.e.,
reasonably cheap).

---Joel Kolstad