IGBT Dimmer - PWM AC Power Control for an Immersion Heater - Page 1
Forum section: electronics / projects

author: willz1200
author_rank: Contributor
timestamp: August 25, 2018, 01:43:32 pm
content: Hello,I'm currently in the process of building a solar power diverted to route surplus electricity to my 3kW immersion heater. So far I've made a triac phase cut dimmer which is wirelessly connected to CT clamps and AC voltage reference. It works okay but I'd like to implement a PWM IGBT dimmer to reduce EMI, acoustic noise and put a more uniform load on my inverter. There are two topologies I'm currently looking into, if you know of any other good ones please say.I found some schematics online which show a rough idea of what I mean. I also read that PWM dimming can be used in conjunction with zero crossing detection to slightly improve efficiency, I don't understand why this is true? Surely the constant switching will cause all the losses, what difference does the phase make?Topology 1)Rectified AC applied to the heater through one IGBT:It appears that this topology is more popular, but I'm concerned about the high power dissipation in the bridge rectifier.The schematic that I found shows a MOSFET instead of an IGBT, is there any significant benefits of using the IGBT besides its lower switching losses?Topology 2)Two anti series IGBTs applying the AC directly to the heater where each body diode allows the opposite cycle to pass:Will this topology result in an overall lower power dissipation?Will a separate rectified power source be needed to driver the gates and is a driving ic necessary?I'd also like to put more thought into the EMI filtering, is a single common mode choke sufficient?I came across this image of the 4-Noks Power Reducer which appears to be topology 1, looking at the top filtering PCB I see several common mode chokes and capacitors, why are so many different sized chokes used? How do you go about selecting them?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 25, 2018, 02:39:41 pm
content: First of all, did you try a zero crossing controller?Heaters don't need to turn on and off very fast. Skipping a line cycle every now and then is more than good enough for the purpose.Tim

author: willz1200
author_rank: Contributor
timestamp: August 25, 2018, 03:10:49 pm
content: Yes I'm currently using a MOC3021, AC Optocoupler and interrupts on an ATTINY44 to perform zero crossing detection which fires a triac. It works fairly well but its not ideal for controlling heavy loads. The idea is to finely tune the power consumption of the immersion heater to match the solar power surplus in real time. Which is why I'd quite like to build a PWM driver

author: David Hess
author_rank: Super Contributor
timestamp: August 25, 2018, 03:19:00 pm
content: Quote from: willz1200 on August 25, 2018, 01:43:32 pmIGBT switching losses are not lower than MOSFET switching losses except maybe at very high voltages where large MOSFET die size results in high capacitance. IGBTs like bipolar transistors have an advantage in cost at high voltages because MOSFETs have a die size which is proportional to the square of the voltage.QuoteYou will have one diode voltage drop instead of two from the bridge rectifier so losses will be slightly lower unless IGBTs can conduct in reverse? I have no idea; bipolar transistors can. One of a pair of MOSFETs would conduct in reverse so there would not even be the forward voltage drop of the diode making losses even lower.QuoteThe gate drive has to come from somewhere.QuoteMaybe.QuoteSometimes two or more common and differential mode suppression networks are used in series to provide enough suppression.

author: Richard Crowley
author_rank: Super Contributor
timestamp: August 25, 2018, 03:26:32 pm
content: The thermal mass of the water is like a humongous capacitor that is integrating your nice PWM back into a running average measured in seconds (or minutes). Using PWM for any kind of large-scale heating process is massive overcomplication.

author: willz1200
author_rank: Contributor
timestamp: August 25, 2018, 03:46:43 pm
content: QuoteWhen you say higher voltages do you mean in the kV range? Because briefly looking around 400V appear to be a similar price point.QuoteSo do you think MOSFETs are the way to go? I was thinking of trying the FDA24N40F which is 400V, 23A maybe a slightly higher voltage rating would be better? I'll pull some ideas together in LTspice.QuoteOf course, but what I mean is one of the schematics uses a zener diode to clamp the gate voltage and the other uses a drive IC.QuoteOkay, so is each individual suppression network tuned for different harmonics that can be expected?

author: Zero999
author_rank: Super Contributor
timestamp: August 25, 2018, 03:54:32 pm
content: A TRIAC is probably the most efficient option.A rectifier would drop too much voltage.Two IGBTs would drop more voltage than a TRIAC.Two MOSFETs connected back-to-back could theoretically drop less voltage, than a TRIAC, but it would work out very expensive. A TRIAC typically drops about 1.5V, so the MOSFET would need to drop under 0.75V in order to compete with that. The FDA24N40F has far too higher on resistance and will drop about 3.5V, at 13A with two devices back-to-back. The MOSFET needs to have an on resistance of under 0.75/13 = 58mOhms, to drop the same voltage as a TRIAC, which would not be cheap for a device rated to 400V.As mentioned above, there's no point in chopping the mains voltage up by PWM and powering a heater, because the thermal time constant will be enormous. It would also produce significantly more EMI, than your current configuration, a zero crossing TRIAC, which is already the most optimum solution.

author: willz1200
author_rank: Contributor
timestamp: August 25, 2018, 03:54:47 pm
content: QuoteBut won't this result in a running average of a lower voltage which will cause less power to be dissipated in the heater?QuoteYes it is a less traditional method, but in some ways it is less complicated, because in theory the driver doesn't need to perform zero crossing detection. Hence no interrupts or monostable circuit are needed.

author: Zero999
author_rank: Super Contributor
timestamp: August 25, 2018, 04:06:12 pm
content: Quote from: willz1200 on August 25, 2018, 03:54:47 pmI don't understand the question. The heater doesn't have any significant capacitance. It just stores heat, so the effect would be the same as measuring the power dissipation and passing the result through as low pass filter, i.e. RC circuit.The resistance of a water heater doesn't change much over its working temperature range and given the same duty cycle, the power dissipation should be the same whether the 230VAC is chopped up and PWMed at several kHz or PWMed with zero crossing, at a much lower frequency than the mains.QuoteYes it is a less traditional method, but in some ways it is less complicated, because in theory the driver doesn't need to perform zero crossing detection. Hence no interrupts or monostable circuit are needed.The additional complexity can be avoided by using an opto-coupler TRIAC with a built-in zero crossing circuit, such as the NTE3097 or MOC3042.http://exa.unne.edu.ar/ingenieria/sysistemas/public_html/Archi_pdf/HojaDatos/Optoelectronica/moc3041.pdfhttp://www.nteinc.com/specs/3000to3099/pdf/nte3097.pdf

author: drussell
author_rank: Super Contributor
timestamp: August 25, 2018, 04:16:55 pm
content: Quote from: Richard Crowley on August 25, 2018, 03:26:32 pmWell, from the controlling theheatingside of things, yes, of course it is over-complicated to have such "fine-grained control", but that isn't what the OP trying to accomplish. He is trying to (as precisely as possible) use up his extra solar capacity by heating the water. The fine-grained control is needed for thesupplyside, not the load, to be able to smoothly use only theexcessgenerated power.

author: Richard Crowley
author_rank: Super Contributor
timestamp: August 25, 2018, 04:21:38 pm
content: Quote from: Hero999 on August 25, 2018, 04:06:12 pmLook at the ENTIRE system (from solar energy to the temperature of the water). The water is a THERMAL "capacitor". It doesn't care whether you are powering the heater from a varying DC current, or from a PWM AC current, or from a slow on-off power (whether AC or DC). The "slow on-off" is the method used by the overwhelming majority of temperature control systems. Because of the massive integration of the energy sink (whether the water in your hot water tank, or the air temp in your house.)

author: drussell
author_rank: Super Contributor
timestamp: August 25, 2018, 04:23:22 pm
content: Quote from: Hero999 on August 25, 2018, 04:06:12 pmIt is true that it doesn't change the total amount of power drawn, but itdoesaffecthowthe power is drawn from his inverter.My understanding is that he is trying to make this load be a more consistent load to his inverter, so that it looks more like a varying resistive load instead of hacked-up pulse-here, pulse-there load. This makes perfect sense to me and seems that it could well be desirable in some cases like this so that the inverter is isn't having to supply random spikes of 3kW extra. Not that it shouldn't be able tohandleit but I think I understand the logic....

author: Richard Crowley
author_rank: Super Contributor
timestamp: August 25, 2018, 04:24:30 pm
content: Quote from: drussell on August 25, 2018, 04:16:55 pmPoint taken. From that perspective, then PWM seems justified.But then what difference does the efficiency of the switching methodology make when the ultimate point to the exercise is to simply waste power as heat energy? What difference does it make whether the energy is dissipated as heat in the switch vs in the load?

author: willz1200
author_rank: Contributor
timestamp: August 25, 2018, 04:28:18 pm
content: QuoteThanks for clearing that up, doesn't the unsymmetric nature of triac phase cutting, generate more noise than PWM?QuoteThat is very low, I think I'd struggle to even find that.QuoteAren't these drivers only suitable for burst mode control? Which would give me a small dimming window? Meaning less dimming levels.

author: willz1200
author_rank: Contributor
timestamp: August 25, 2018, 04:41:55 pm
content: QuoteYes that's my main aim, slowly increase power using a pid controller until the grid tie is on the edge of import/export.QuotePoint taken maybe I should bolt the FETs to the hot water tankI was just wondering how the use of IGBTs and MOSFETs compared and each PWM topology. But yes the main idea was to put a more uniform load on my inverter. The triac method causes some odd audible noises from my inverter, compared to boiling the kettle which doesn't produce the same noises.

author: David Hess
author_rank: Super Contributor
timestamp: August 25, 2018, 04:59:56 pm
content: Quote from: willz1200 on August 25, 2018, 03:46:43 pmVery few IGBTs are made for use below 600 volts because MOSFETs will generally be more economical. 600 volts and higher is where IGBTs become competitive.I actually did not know that they made any IGBTs below 600 volts until I just looked but there are a few for special applications.QuotePick a IGBT and then compare the price to that of a MOSFET with an on resistance which produces the same voltage drop. For greater cost the MOSFET will always deliver lower static losses which will dominate in a low frequency switching application.QuoteAC applications like this would usually use a TRIAC or MOSFET based solid state relay which do not support PWM faster than the line frequency. Higher frequency PWM requires more gate drive power so a different circuit is used to provide it.QuoteSomething like that. The lower frequency suppression network will not perform well at high frequencies so a separate high frequency suppression network is also used.

author: Zero999
author_rank: Super Contributor
timestamp: August 25, 2018, 06:19:53 pm
content: Quote from: Richard Crowley on August 25, 2018, 04:21:38 pmI understood your point. What I didn't get was the original poster's question.Quote from: willz1200 on August 25, 2018, 03:54:47 pmQuote from: willz1200 on August 25, 2018, 04:28:18 pmIf the PWM is at a much higher frequency, than the mains, then it will generate much more RFI, than a TRIAC with phase control.QuoteThe range of power control is the same with burst control as with phase control, the difference is it occurs over a much longer timescale.

author: willz1200
author_rank: Contributor
timestamp: August 25, 2018, 06:21:08 pm
content: Quote from: David Hess on August 25, 2018, 04:59:56 pmYes 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

author: Zero999
author_rank: Super Contributor
timestamp: August 25, 2018, 06:22:17 pm
content: Quote from: willz1200 on August 25, 2018, 04:41:55 pmOh I see what you're trying to do now: make a variable resistor. Yes PWM can probably be used to to that, but you'll nee a fairly large filter to get rid of the EMI.

author: willz1200
author_rank: Contributor
timestamp: August 25, 2018, 06:37:09 pm
content: Quote from: Hero999 on August 25, 2018, 06:19:53 pmOkay, Would the PWM noise be easier to suppress due to the uniform change in current?QuoteWouldn't that result in more difficulty in modulating the instantaneous power?Quote from: Hero999 on August 25, 2018, 06:22:17 pmSuper, Do you have any recommendations on what suppression network I should use?

author: drussell
author_rank: Super Contributor
timestamp: August 25, 2018, 08:36:49 pm
content: It just occurred to me that since the heating element doesn't care whether it is fed AC or DC, another possibility, in theory, is to use a "power factor correction" type circuit with a regulator controller designed for PFC, some of which have a way to vary the output voltage via a control signal.It is basically the same idea as the OP already has but it might be more easily implemented using components typically intended for PFC rather than rolling your own. PFC is designed to basically just make your load look resistive, even when it isn't, which is essentially what the OP is trying to do, in a general sense.Just a thought.

author: jbb
author_rank: Super Contributor
timestamp: August 25, 2018, 09:35:31 pm
content: I’m curious about what might be best for this...From the perspective of ‘don’t be mean to the inverter,’ a TRIAC is out (generates lots of harmonics in phase control or ‘lumpy’ waveforms in full wave mode).So it’s MOSFETs / IGBTs. For a given rating they behave in somewhat similar ways.For maximum efficiency, I would look at back-to-back connection (large MOSFETs would have lower losses that IGBTs and will make cooling easier and cheaper). An incoming line filter (e.g. 2x Y caps, common mode choke, filter inductor and X cap) will be required to keep the PWM out of your house wiring (and away from the inverter). A snubber will be required to eat voltage spikes across the power devices - and any inductance in the heater circuit will push more and more energy into the snubber.Is there a thermostat in the heater wiring? Or an over-temperature cutoff? These devices may not be able to switch off properly (I.e. arc over and catch fire) in some circuits.I don’t suppose you can get high voltage DC straight out of your inverter?

author: Richard Crowley
author_rank: Super Contributor
timestamp: August 25, 2018, 10:35:25 pm
content: I have an old reel-to-reel tape machine (Sony TC-850) that can operate at the user's selection of 3.75 or 7.5 or 15 inches per second (IPS) It uses a servo to maintain the selected speed. (Toothed gear and magnetic reluctance pickup to sense motor speed.) And a split-phase AC motor with the capacitor to generate the alternate "phase". Technology from the 1960s.But for the control element for the motor, I was amused that they just put an AC "resistor" in series with the motor. The "AC resistor" consisted of a bridge rectifier with a TO-3 transistor (2N3055 or equivalent?) on the DC side. Rather clever, I thought. With the pass transistor bolted to the center of a beefy aluminum plate around 100mm square. Certainly much quieter (electrically and acoustically) than some other alternatives. Of course, that configuration was only possible because the big power transformer had a dedicated secondary winding to power the capstan motor.

author: willz1200
author_rank: Contributor
timestamp: August 25, 2018, 10:59:58 pm
content: Quote from: drussell on August 25, 2018, 08:36:49 pmI'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 controlQuote from: jbb on August 25, 2018, 09:35:31 pmYes 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 anABB PVI-3.6-TL-OUTD-Sunfortunately it looks like theres only AC out.Quote from: Richard Crowley on August 25, 2018, 10:35:25 pmSo was the transistor just operating in its linear region to limit the speed? I bet the block of aluminium kept it cool, finding nice big PCB mounted heatsinks (For a decent price) has proven to be quite tricky, cpu heatsinks always work but they're not very nice to mount.

author: Richard Crowley
author_rank: Super Contributor
timestamp: August 25, 2018, 11:12:12 pm
content: Quote from: willz1200 on August 25, 2018, 10:59:58 pmYes. It seems rather crude in the 21st century, but it had some elegance to the basic concept.QuoteYeah, the heat-sink was larger than the motor.

author: max_torque
author_rank: Super Contributor
timestamp: August 26, 2018, 01:51:40 pm
content: 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?

author: willz1200
author_rank: Contributor
timestamp: August 26, 2018, 02:10:40 pm
content: Quote from: max_torque on August 26, 2018, 01:51:40 pmYes 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.

author: drussell
author_rank: Super Contributor
timestamp: August 26, 2018, 04:36:06 pm
content: Quote from: willz1200 on August 25, 2018, 10:59:58 pmI'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 muchanya 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" theVSENSEpin 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 theVSENSEdivider 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 theVCOMPpin 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.pdfI 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 beApplication Notesaround for various PFC set-ups... Anyone "in-the-know" want to chime in?

author: Zero999
author_rank: Super Contributor
timestamp: August 26, 2018, 11:40:52 pm
content: Quote from: willz1200 on August 25, 2018, 06:21:08 pmHave 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/2841641The 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.

author: jbb
author_rank: Super Contributor
timestamp: August 27, 2018, 10:04:18 am
content: Quote from: willz1200 on August 25, 2018, 10:59:58 pmThat 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 youreasonablyget in between it and the element without making a mess?And now I'm going to be the safety nut. 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?

author: willz1200
author_rank: Contributor
timestamp: August 31, 2018, 02:43:08 am
content: Apologies for the absence, I've had a busy few days.Quote from: drussell on August 26, 2018, 04:36:06 pmOkay, 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 betterI've got some on order, as well as some beefy MOSFETs.Quote from: Hero999 on August 26, 2018, 11:40:52 pmGreat 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.Quote from: jbb on August 27, 2018, 10:04:18 amI'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 protectionI'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

author: Schneider.carl
author_rank: Newbie
timestamp: October 28, 2018, 03:49:59 pm
content: Hi thereReading 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  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 controllerand 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.

author: saabman
author_rank: Newbie
timestamp: January 10, 2020, 12:55:00 am
content: 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.

author: nigelwright7557
author_rank: Frequent Contributor
timestamp: January 10, 2020, 02:48:24 am
content: 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.

author: saabman
author_rank: Newbie
timestamp: February 06, 2020, 11:51:10 am
content: 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.