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IGBT Dimmer - PWM AC Power Control for an Immersion Heater
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max_torque:
If the aim of the game is high efficiency, then going DC (solar) -> AC (inverter) - AC or DC resistive load (heater) is silly, when you'd be better off just putting the DC from the solar panels straight into a resistive load?  ie, don't pull the power from the inverter?
willz1200:

--- Quote from: max_torque on August 26, 2018, 01:51:40 pm ---If the aim of the game is high efficiency, then going DC (solar) -> AC (inverter) - AC or DC resistive load (heater) is silly, when you'd be better off just putting the DC from the solar panels straight into a resistive load?  ie, don't pull the power from the inverter?

--- End quote ---
Yes that would be the most ideal way, but thinking about it I can't intercept any power before my meter which is on the AC output of the inverter. This is because in the UK even if you consume the power you still get paid for it.
drussell:

--- Quote from: willz1200 on August 25, 2018, 10:59:58 pm ---I'm not very familiar with power factor correction controllers and haven't had much luck in finding a controller that accepts a control signal, can you point me in the right direction? Its worth considering if it will also allow for fine-grained control :)
--- End quote ---

I'm no PFC expert either but I did look into the early PFC control chips very closely (probably 15-20 years ago, when I was needing to build a large PFC'd battery charger for an off-grid set-up to pull more power from the generator than the stock 100A charger could) when they started to arrive on the market due to increasing requirements for PFC in more and more power supplies owing to the to various government regulations to help the power companies clean up their modern, messy power.  :)

Today, most typical PFC chips tend to be little 6-pin "do it all automatically" affairs for generic consumer power supplies rather than the uber-adjustable early stuff, though pretty much any a modern PFC chip could be used if you simply vary the divider voltage coming from your output (to the load) to the voltage sense input.  You could control it that way if needed by using some external circuitry to "fool" the VSENSE pin into thinking the output voltage is higher than it is.

However, while I don't recall any of the early ones that I saw that specifically had a "control" pin, some chips do still give you various kinds of additional inputs one way or another so you don't have to mess with the VSENSE divider itself from your output voltage.

For example, the TI UCC28180 would probably work in your application.  It has an integrated 1.5A source / 2A sink capable MOSFET driver built in, so can probably drive MOSFETs large enough for a few kW regulator circuit, plus it has access to the output side of the sense amplifier via the VCOMP pin which can be used to do soft-start, modify your output control loop sensed-voltage, pull the whole PFC regulator into standby, etc.  I would imagine that with simple external circuitry that could include input from your "excess solar power calculator" circuit.  :)

http://www.ti.com/lit/ds/symlink/ucc28180.pdf

I don't see why something like that wouldn't work.  I'm not sure it is the easiest or best way, it is just something to consider, since what you're trying to achieve is essentially what PFC regulator does in the first place anyway.  There must be Application Notes around for various PFC set-ups...  Anyone "in-the-know" want to chime in?  :)
Zero999:

--- Quote from: willz1200 on August 25, 2018, 06:21:08 pm ---
--- Quote from: David Hess on August 25, 2018, 04:59:56 pm ---For greater cost the MOSFET will always deliver lower static losses which will dominate in a low frequency switching application.
--- End quote ---
Yes after looking around I found these:
FMH30N60S1 - 106 mOhms (£1 each on aliexpress)
FDL100N50F  - 43 mOhms  (£2.50 each on aliexpress, £13.19 each on RS)
The only issue is that they could be counterfeit parts on aliexpress but probably worth a try. It might be best to just get a big heat sink and cheap out. After all it won't be running at high current for a great deal of the day.

Thanks for the information :)

--- End quote ---

Have you looked at Farnell?

They have the IPB60R060P7ATMA1, which has an on resistance of 49mOhms and is rated to 600V. It's £4.77 in single units or £4.06 each in packs of 10. More expensive than aliexpress but at least you can be sure it's genuine.
https://uk.farnell.com/infineon/ipb60r060p7atma1/mosfet-n-ch-600v-48a-to-263/dp/2841641

The problem then is driving the MOSFETs and designing a filter to prevent the EMI from going into the inverter and everything else connected to it.
jbb:

--- Quote from: willz1200 on August 25, 2018, 10:59:58 pm ---Yes I think the extra money I spend on the MOSFET will save money on the heatsink, So there's probably not a huge difference in the price point... Worth going for MOSFETs. Excellent and just RC snubbers will be sufficient? In some cases I've seen snubbers dedicated to the optocoupler is this necessary? I think the ball park recommendation is 100nF 100ohm but I've got an app note somewhere to find the proper values. Yes the immersion heater has a builtin thermostat. High voltage DC would be ideal my inverter is an ABB PVI-3.6-TL-OUTD-S unfortunately it looks like theres only AC out.

--- End quote ---

That should be a nice inverter (but I used to work for ABB so I might be biased :-) ).  It doesn't seem to have DC output, which isn't a surprise (DC outputs are more difficult to deal with safely).

I suspect that an RC snubber might need a little help to handle all conditions.  Exact values will need to be tweaked, depending on the situation.

The built-in thermostat could be a problem.  This is because a typical mechanical switch cannot break DC current - it just arcs and things catch fire.  But you don't want to remove it; it's an important safety device.  Can you reasonably get in between it and the element without making a mess?

And now I'm going to be the safety nut :D.  You're getting into some significant power and don't want to a) zap yourself, b) burn your house down or c) all of the above.  So, here are some comments:

* Have you worked with mains or power electronics before?
* An earthed metal box is your friend here.  It can keep you safe even if the internal circuitry cooks.
* An aluminium box can be a pretty good heatsink.
* Termination of incoming and outgoing wires needs to be secure (especially earth!!!) and this will take some room.  Soldering wires straight to a PCB is a bad plan because they tend to fatigue and break off.
* Ideally, you should consider what happens if the power semiconductors fail short-circuited.  A fuse is a good start.
* You should think about RF noise. Specifically, how not to spray it around the neighbourhood.
* Your switching controller may interact with the grid inverter.  Do you have an oscilloscope and probes to investigate this sort of thing?
* How are you planning to measure the grid tie power flow and communicate the results to this control box?  Do you have a measurement sorted out?
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