Author Topic: IGBT Dimmer - PWM AC Power Control for an Immersion Heater  (Read 16560 times)

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Offline max_torque

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Re: IGBT Dimmer - PWM AC Power Control for an Immersion Heater
« Reply #25 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?
 

Offline willz1200Topic starter

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Re: IGBT Dimmer - PWM AC Power Control for an Immersion Heater
« Reply #26 on: August 26, 2018, 02:10:40 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?
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.
 

Offline drussell

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Re: IGBT Dimmer - PWM AC Power Control for an Immersion Heater
« Reply #27 on: August 26, 2018, 04:36:06 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 :)

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?  :)
 

Online Zero999

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Re: IGBT Dimmer - PWM AC Power Control for an Immersion Heater
« Reply #28 on: August 26, 2018, 11:40:52 pm »
For greater cost the MOSFET will always deliver lower static losses which will dominate in a low frequency switching application.
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 :)

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.
 

Offline jbb

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Re: IGBT Dimmer - PWM AC Power Control for an Immersion Heater
« Reply #29 on: August 27, 2018, 10:04:18 am »
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.

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?
 

Offline willz1200Topic starter

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Re: IGBT Dimmer - PWM AC Power Control for an Immersion Heater
« Reply #30 on: August 31, 2018, 02:43:08 am »
Apologies for the absence, I've had a busy few days.

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?  :)

Okay, I'll experiment with the idea of using PFC, even if its not the best way its probably still useful to understand these little 6 pin packages better :) I've got some on order, as well as some beefy MOSFETs.

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.


Great find thanks! It will be interesting heat-sinking a TO-263 package.

Yes that's the next task. I'm currently reading into filter design and will first have a go at incorporating a proper filter into the triac system.

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?

I've had it for several years now and its never let me down, so I can't complain.  :-+

Yes the thermostat can be intercepted quite easily, an extra live wire would have to be added. Ideally though the thermostat would be on the boards output so my controller is constantly powered.

  • Yes I've worked with mains and power electronics for a fairly long time, I don't have much industrial experience. But I'm in my final year at university studying Electrical and Electronic Engineering.
  • I'm just using a standard plastic hobby box, but I'm sure I'll upgrade in when everything is final.
  • I've got some thin aluminium boxes but I'll look out for a thicker one.
  • The current PCB has 20A terminal blocks which are working nicely.
  • I've got a fuse and metal oxide varistor for surge protection
  • I've got a big common mode choke on the system now but plan on reading properly into filter design.
  • Yes I certainly do. :)
  • Yes, that's already in place. I'm using an opto-isolator to obtain a voltage reference and CT clamps for current. I then look at the phase difference to obtain the direction of power transfer, and then communicate the data with an ESP8266



 

Offline Schneider.carl

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Re: IGBT Dimmer - PWM AC Power Control for an Immersion Heater
« Reply #31 on: October 28, 2018, 03:49:59 pm »
Hi there

Reading this with great interest. I’m looking to achieve the same end result, utilizing 'wasted' PV inverter capacity by controlling the load presented by the immersion heater element in the domestic hot water geyser. I’m running a Sunny Island and Sunny Boy AC coupled off-grid configuration and the element is around 3.5kW, so I’m looking for a gentle application of load, with variability in the amount of energy applied to the element. The grid forming Sunny Island uses Frequency Shift Power Control [FSPC] to throttle the Sunny Boy once the battery charging load and household loads have been met. I'm thinking along the lines of an Arduino Uno to measure the off-grid frequency, which will give me a measure of how hard the Sunny Boy is being throttled by the Sunny Island and then using the Arduino to present a suitable variable load to the off-grid to use some of the throttled capacity.

I notice that the frequency variation and Sunny Boy response to the FSPC is very damped, so there is nothing instantaneous about these variations. In my instance the Sunny Island uses the battery as the source and sink for rapid changes in load and in your system the grid would provide that function.

I agree with your sentiment of being gentle, but I’ve yet to find the gentle controller :) and it’s not the thermostat or any methodology which applies 3.5kW load no matter how short the duration. I did wonder if a small single phase 4kW VFD/VFC drive would do it, under some form of control from the Arduino, soft start and all those good features?

If you've come up with eating solution I would appreciate a pointer in the right direction.

 

Offline saabman

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Re: IGBT Dimmer - PWM AC Power Control for an Immersion Heater
« Reply #32 on: January 10, 2020, 12:55:00 am »
I realise this is an old thread but curious how the OP went with it?

 I have a similar setup with triac control of the heater element but looking to improve it.

The need to do it is to more closely match the surplus power from the inverter so no power is drawn from the grid which is what happens during the peaks of the cycle when using a phase control or pulse mode operation with triacs.
 

Offline nigelwright7557

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Re: IGBT Dimmer - PWM AC Power Control for an Immersion Heater
« Reply #33 on: January 10, 2020, 02:48:24 am »
I would control the heater from a triac on a heatsink.
I would burst control it (full cycles on and full cycles off depending on a pot setting.
Control all that from a PIC micro with an A2D input from a pot and output through an opto-coupler to the triac.

 

Offline saabman

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Re: IGBT Dimmer - PWM AC Power Control for an Immersion Heater
« Reply #34 on: February 06, 2020, 11:51:10 am »
That's currently how mine operates but uses a ESP8266 read the surplus power from the energy meter and to pulse the triac in a fashion to try and match the surplus power. Unfortunately it does not allow for a sufficiently fine control of the power delivered to the hotwater heater to track the solar generation effectively and results in surges of power and causes lights to flicker.

It does work, but not well enough.

 


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