EEVblog #449 - Absopulse VFC500 Variable Frequency Converter Teardown

[RobUSVI]

Neutral is connected to ground at one point, but treating it like a ground is reckless. It's just as "live" as phase. Saying ungrounded devices get connected to ground is technically correct but practically unsafe. Ungrounded devices are ungrounded.

Reckless and shocking when a careless electrician has reversed the white and black wire (neutral and hot) and you touch the "grounded" chassis.  (Where I live, anybody that can hold a screwdriver is an electrician... Sadly, I see hot neutrals all the time when troubleshooting.)

[staxquad]

Neutral is connected to ground at one point, but treating it like a ground is reckless. It's just as "live" as phase. Saying ungrounded devices get connected to ground is technically correct but practically unsafe. Ungrounded devices are ungrounded.

Reckless and shocking when a careless electrician has reversed the white and black wire (neutral and hot) and you touch the "grounded" chassis.  (Where I live, anybody that can hold a screwdriver is an electrician... Sadly, I see hot neutrals all the time when troubleshooting.)

which is why I plug in one of these anytime I work on the electricity in the house
identifies open ground, open neutral, open hot, hot&ground reversed, hot&neutral reversed and correct wiring
the button is to trip GFCI to test that it's functioning

[Rufus]

Neutral is connected to ground at one point, but treating it like a ground is reckless. It's just as "live" as phase. Saying ungrounded devices get connected to ground is technically correct but practically unsafe. Ungrounded devices are ungrounded.

Reckless and shocking when a careless electrician has reversed the white and black wire (neutral and hot) and you touch the "grounded" chassis

A device with neutral connected to the chassis becomes live if there is an open circuit fault in the neutral anywhere between the device and neutral/ground bonding point. It doesn't need an incompetent electrician to be dangerous.

[elgonzo]

Lovely ending with the sound demo. I'm curious though, what physical cause is there for why switching regulators emit this and surely it's not the direct switching frequency (usually betweeen 100KHz and 1Mhz?)?

Generally, it isn't the regulators, but the inductors or transformers that make the noise, the magnetic forces cause them to ever so slightly vibrate.


An interesting use of such an effect is in hobby grade brushless motor controllers, where the controller uses a winding as a speaker for notification sounds.

Another, quite famous example of such "coil whine" is the Siemens Taurus electric locomotive, also known as the musical loco.
Similar to what Dave demonstrated at the end of his video, you can hear the motor converters doing their work during the acceleration of the loco:

To achieve optimal traction on slippery rails, the power output of each motor on each axle is regulated individually to avoid wheel spin. With the right (bad) weather conditions and with a sufficiently heavy train the Taurus actually sounds like music:

[Paul Moir]

That's really neat elgonzo.  Thanks!

[Cognito]

we were still using 25Hz hydro electrical power in some parts of Ontario up until last year 

Three generating stations on the Upper Mattagami River – Wawaitin, Sandy Falls and Lower Sturgeon, built 100 years ago, were still generating electricity at 25Hz for the mines up until 2011.

What is the reason to use 25 Hz instead of 60 Hz? Could it generate a good speed for the pump in the mines?

Nice pictures =)

[elgonzo]

we were still using 25Hz hydro electrical power in some parts of Ontario up until last year 

Three generating stations on the Upper Mattagami River – Wawaitin, Sandy Falls and Lower Sturgeon, built 100 years ago, were still generating electricity at 25Hz for the mines up until 2011.

What is the reason to use 25 Hz instead of 60 Hz? Could it generate a good speed for the pump in the mines?

Nice pictures =)

Wikipedia says: https://en.wikipedia.org/wiki/Utility_frequency#25_Hz_origins

[Alana]

Another, quite famous example of such "coil whine" is the Siemens Taurus electric locomotive, also known as the musical loco.
Similar to what Dave demonstrated at the end of his video, you can hear the motor converters doing their work during the acceleration of the loco:

To achieve optimal traction on slippery rails, the power output of each motor on each axle is regulated individually to avoid wheel spin. With the right (bad) weather conditions and with a sufficiently heavy train the Taurus actually sounds like music:

I think they re-program those controllers for real music in some passenger locos during EURO 2012 football championships.

[KeithBrown]

Did any (other) sharp-eyed Canuks notice that there are actual components in the unit that are themselves made in Canada? At 28:38 we some resistors from http://www.renfrewelectric.com/index.html! Anybody spot anything else?

[elgonzo]

Another, quite famous example of such "coil whine" is the Siemens Taurus electric locomotive, also known as the musical loco.
Similar to what Dave demonstrated at the end of his video, you can hear the motor converters doing their work during the acceleration of the loco:

To achieve optimal traction on slippery rails, the power output of each motor on each axle is regulated individually to avoid wheel spin. With the right (bad) weather conditions and with a sufficiently heavy train the Taurus actually sounds like music:

I think they re-program those controllers for real music in some passenger locos during EURO 2012 football championships.

Well, there is a video on YT that presumably shows a German ICE 3 express train that plays the german national anthem while being in service mode.
If this video is indeed true, you can be certain that this is in no case part of the operating software of the train, but controlled through an external interface. Mind you, these trains do service speeds of 300 km/h with hundreds of passengers. In case such easter eggs would be discovered in the trains operating system, they would either be put out of service for safety-related investigations, or at least their allowed operational speed would be restricted severely and some serious complaints directed to the manufacturer...

[G7PSK]

25 HZ was also used by some train company's here in the uk as they said it was better for traction purposes, I have an old reed frequency meter from a power house of such a railway.
When Ferranti first started to push ac transmission he had a 96rpm 33 pole pair's alternator giving 100 amps at 1100 volts at 26.4 hz. He also had a co-ax power cable that he demonstrated the safty of by having his foreman knock a cold chisel through while live after the trips went he would simply replace the section of conductor and reset the trips. Ferranti was also a consultant on the first Niagara falls power plant in Canada.

[SeanB]

New ringtone done............

[staxquad]

we were still using 25Hz hydro electrical power in some parts of Ontario up until last year 

Three generating stations on the Upper Mattagami River – Wawaitin, Sandy Falls and Lower Sturgeon, built 100 years ago, were still generating electricity at 25Hz for the mines up until 2011.

What is the reason to use 25 Hz instead of 60 Hz? Could it generate a good speed for the pump in the mines?

Nice pictures =)

Wikipedia says: https://en.wikipedia.org/wiki/Utility_frequency#25_Hz_origins

Interesting read.

Japan is as f***ed up in frequencies as Australia is in rail gauge

In Japan, the western part of the country (Kyoto and west) uses 60 Hz and the eastern part (Tokyo and east) uses 50 Hz. This originates in the first purchases of generators from AEG in 1895, installed for Tokyo, and General Electric in 1896, installed in Osaka. The boundary between the two regions contains four back-to-back HVDC substations which convert the frequency; these are Shin Shinano, Sakuma Dam, Minami-Fukumitsu, and the Higashi-Shimizu Frequency Converter.

no use for the Absopulse whatsoever:

The 15 kV AC rail networks, used in Germany, Austria, Switzerland, Sweden and Norway, still operate at 16? Hz or 16.7 Hz

[Hypernova]

no use for the Absopulse whatsoever:

The 15 kV AC rail networks, used in Germany, Austria, Switzerland, Sweden and Norway, still operate at 16? Hz or 16.7 Hz

It's not likely that the designers at Absopulse had a locomotive in mind when they designed it.

[Ed.Kloonk]

no use for the Absopulse whatsoever:

The 15 kV AC rail networks, used in Germany, Austria, Switzerland, Sweden and Norway, still operate at 16? Hz or 16.7 Hz

It's not likely that the designers at Absopulse had a locomotive in mind when they designed it.

But if you were building a miniature model city like that one in Germany, you'll need to power the little miniature trains that should run on 16.7Hz if it's to be truly authentic.

[ConKbot]

Interesting that its AC->DC->DC->AC, instead of just AC->DC->AC,   I would have expected that The PFC rectifies and boosts to a ~380v ish voltage, feeds it to the h-bridge to drive your isolation transformer with high frequency, then your LC filters on the output. 


Anyone have any ideas on why the intermediate DC/DC step? 2250vdc isolation is doable with a double isolated transformer (special rated primary wire and tape etc...)   and then it would need a much smaller supply for internal functions and thats it.  2 separate transformers for hi-rel purposes? off the shelf transformers because it turns out they arent as custom wound as I would expect?

[tom66]

Possibly it drops the rail voltage for lower output voltages to improve efficiency (the switching transistors operate at a higher duty cycle.)

[Phoenix]

Interesting that its AC->DC->DC->AC
...
2 separate transformers for hi-rel purposes?

I think you missed an AC stage 

Rectifer+Boost PFC           ->           Push-Pull??+Rectifier                                       ->                                           Inverter
        AC-DC                                         DC-AC-DC                                                                                                     DC-AC
   1 Inductor                              1 Transformer, 1 Unknown Coupled Inductor                 2x Inductors, 1x Coupled Inductor (Common Mode Choke)

Anyone have any ideas on why the intermediate DC/DC step?

I'll take a stab - High frequency isolation requires a smaller transformer. If you were to put a transformer on the output of the H-bridge it would have to be big enough to operate at the 47Hz fundemental, but have little capacitive coupling to ensure blocking of the high frequency switching. You would also have to contend with the (less predictable?) leakage inductance, magnetising current and any transformer/magnetic nonlinearitries especially at low voltages - not sure exactly what effect that would have on the output quality, but it won't be good!

Possibly it drops the rail voltage for lower output voltages to improve efficiency (the switching transistors operate at a higher duty cycle.)

Don't think the efficiency benefit would be worth while (it's not very dependent on duty cycle - current will either flow in the FETs or antiparallel diodes), but the power quality benefit of runing at a higher duty cycle might be worthwhile. At a higher duty cycle there is greater ratio of fundemental voltage to switching harmonics. You may also drop pulses at very low duty cycle (when the FETs don't get a chance to fully switch on).

Could put a mutlimeter on to see if it's a constant 400VDC or variable? I would suggest it's a constant 400V as the PFC inductor and an output capacitor have 2x200V/1.5A each written on the side (22:19 and 26:33 in the video).

Perhaps one more reason -  the DC board looks like it's designed for mutliple uses as there are pads on the DC output that could be connected to parallel the two 200V transfomer outputs (27:04). As well as some pads to link to ground reference one of the rails.


The part that is confusing me is the purpose and arrangement of the magnetic component just before the DC output, after the high frequency isolation transformer, that has the flying torroidal component attached to it (28:32). It lookes like both the positive output rails of the transformer go through it, but share a common core (looking at the tracks)... but then some fly leads go off somewhere from the top...?

[ilanko]

Someone forget the DaveCade ... And what's PWD ?

[ilanko]

[ilanko]

Hi Dave, I hope to see a video testing common house electronic functioning under extreme frequency or low voltage.

[Yansi]

Hi
I've just seen this nice video. I was quite interested to see, what topology have they used. So I carefuly analyzed what I've seen in the video.

Mains input is rectified with a bridge, decoupled by the first 4u7 MKP cap gunked onto the first transformer - whcih is a choke actualy - from the PFC controller. Behind the choke, we can clearly see a TO247 mosfet and a diode. Then there is the filterbank.

The DC/DC converter then takes the PFC's  output of probably around 400-420 volts and produce 2x200Vdc in series on the two output caps. The main DC/DC is a standard halfbridge topology, with two secondaries, two bridge rectifiers and double output choke.

The rectangular cutouts in the board are for airflow cooling, not isolation gaps.

Now the more interesting part, the actual convertor: They've used H-bridge topology. Each half-bridge has its own output choke. Between the other ends of the two chokes, there's the second polypropylene capacitor. After that, commonmode choke was placed. The output is immediately after the commonmode choke, near ? a varistor. Seems there are no additional filtering caps. Pretty underestimated filtering. I expected somewhat better filtering there.

The most interesting part is, that the four mosfets in the H-bridge have all blocked the internal body diodes. The four TO220 two-legged diodes Dave showed in the video, are connected in series with drain electrodes of the mosfets. Then there are 8 small plastic diodes (like DO-41 ones) antiparallel with that. God why? I thought, that outblocking the mosfets internal diode is worth only for high switching frequencies, like 100+ kHz, which I think won't happen here, considering the quite bad board layout. Why have they did it? Your guess is good as mine. Maybe they have chased each miliwatt of heat and this helped a little to increase efficiency a little.

How do you think the current transducer works there? It is obviously connected on the plus side of the supply to the H bridge. Wtf? DC biasing the transformer / measuring DC current with it? No? I quite don't understand the location of the transformer. Very strange to me.  Source shunts would do much easier.

As I mentioned, the bord layout is not as good as I think it should be. Note the big curent loop, between the H-bridge stage and the electrollytic caps. Crazy. The cap connected after the output chokes is also connected via too long leads and traces. The layout should minimize stray inductances there to gain better HF suppression on the output.

The four PIC micros on the front panel are just funny touch to whole, as is the chassis grounding connection. Even if it would be connected (where?), it wouldn't respect the starpoint earthing - which is here important for reliability. It is not good to earth something somewhere to the chassis, and then elsewhere connect the chassis to the PE lead. There are to many interconnections in between, which could possibly make trouble.

I am also concerned, that the inverter's filter design is dodgy. There should be cap in between inverter supply ground and the choke output. The cap between the chokes only does not suppress the HF switching components between inverter ground and outputs. Oh yes, there's a commonmode choke there, but it is more like "how ya doing" than a properly designed filter. If there is enough capactity between inverter's ground and chassis (PE), it is something I would really be quite concerned about when testing the thing on EM compatibility. For more clearity, I redrawn the schematic of the inverter part of the circuit.

Here are some reverse-engineered pictures of the thing and its topology. Interesting to note, that one of the output post is labeled as "N" (neutral) on the front panel. Douesn't make any sense, if the whole inverter section is possibly floating, so both outputs symmetrical.

Edit: the last shot explains the labeling "PH N GND" quite well. grrrrrrrh.  They've just shorted one side of the floating output to PE with some crappy foil cap.

[NiHaoMike]

There are also asymmetrical inverter designs where one side is switched at a high frequency and the other side at the output frequency. That allows lower conduction loss (but higher switching loss) transistors to be used for one side, boosting efficiency.

[Yansi]

Think about it, twice. The topology you described is useless, because you would need the HF switching side to make sharp steps from V+ to V- side. This will introduce inherent distortion of the waweform around zero crossings and  problems with EMC, because both outputs of the inverter will jump at output frequency (50Hz or so) with square wave of 350Vpp. And you can't filter out this square wave component from the output. This asymmetrical approach is both unpractical and useless.

And I do not understand what other efficiency boost it will bring, than saving switching losses on one side. You still can use lower conduction loss transistors on both sides, regardles of the switching frequency.

The only assymetrical approach usable is to just ground one lead and have symmetrical supply of +-350Vdc. Then you will chop only one side in between these positive and negative rails. But this is not usually done, because as obvisous, you would need power switches designed for twice the voltage swing on them -> higher loss and EMI. This approach would require 1200V IGBTs and is not worthy for smaller output power, like these 500VA.

[bktemp]

Think about it, twice. The topology you described is useless, because you would need the HF switching side to make sharp steps from V+ to V- side. This will introduce inherent distortion of the waweform around zero crossings and  problems with EMC, because both outputs of the inverter will jump at output frequency (50Hz or so) with square wave of 350Vpp. And you can't filter out this square wave component from the output. This asymmetrical approach is both unpractical and useless.

You may be right with the fast edges around 50Hz when used at the output side, but this topology exist. I have seen it in some UPSs used at the low voltage side driving the primary winding of the transformer.

Another variant uses IGBTs for the low side switches and mosfets for the highside ones. Because IGBTs do not have a body diode, you can use faster external ones without the need to disable the internal ones. The IGBTs switch at ac frequency, the highside mosfets modulate the waveform. This may not be usefull for a universal ac supply, but it works well for loads like gas discharge lamps.