99.5% Efficient Inverter Design

[HaldorEE]

Just for fun I checked my Dell Laptop. My Kill-a-Watt says it has a .91 Power factor. I suspect the switching power supplies on most modern electronics are going to be similar.

Active power factor correction is part of what is driving power supply designs to higher switching frequencies (in addition to the desire for lighter and cheaper magnetics).

Power Supply Design Basics: Active Power Factor Correction

Here’s the conclusion of our Power Supply Design Basics series! First we introduced the concept of the Power Factor, and then we discussed Power Factor Correction (PFC) and how to implement passive PFC. Here we’ll delve into active PFC, and when you would want to use it.

www.nuvation.com

EN61000-3-2 establishes four classes of equipment, each with their own limits for harmonic emissions.

Class D - T.V.’s, personal computers & monitors consuming ≤600 W
Class C - Lighting equipment
Class B - Portable tools
Class A - Everything else

Equipment Classes A & B have absolute limits for harmonics whatever the input power.
Equipment Class C and D have harmonic current limits that are a percentage (proportional) to the mains power consumed.

Power supplies for equipment Classes C & D will normally incorporate active power factor correction in order to meet the harmonic emissions regulations.

What this means is that pretty much any PC power supply sold in Europe that is <= 600W is going to have active power factor correction. Since manufactures hate making different power supplies for different markets, we are getting power factor correction in our PC power supplies whether it is required or not (the California affect).

Above information is from page 34 of this document.

http://www.xppower.ro/dwnd/Essential_Guide_to_Power_Supplies_full_pdf.pdf

 

[HaldorEE]

There is a power factor spec for Energy Star Rated LED lights > 5W.


For lamp power ≤5W and for low voltage lamps, no minimum power factor is required For lamp power >5W, power factor must be ≥ 0.70

Pertinent test specs are: ANSI C82.77 2002 and IES LM-79-08

https://www.energystar.gov/ia/partners/product_specs/program_reqs/Integral_LED_Lamps_Program_Requirements.pdf

 

[HaldorEE]

I just tried my comcast cable box.... It has a power factor of .61 and running ~ 20 Watts. Not only it is using up power when not in use, it is wasting 39% of what I pay for. I really need to do something about that wasted power. I am on grid and just throwing money away. The first thing is to put a timer on it so it is never running when I am never watching the TV. In fact, I have a whole stack of AV equipment that could go on such a timer. I just need to set it up so it is easy to turn on if I want to use it at times it would normally be off.

Is it transformer based or is it a switcher? If transformer (gets warm), the parasitic power loses could certainly add up.

 

[Factory400]

Is it transformer based or is it a switcher? If transformer (gets warm), the parasitic power loses could certainly add up.

Transformers do not mean it is not a switcher.

 

[Roswell Bob]

Thought someone DIY minded might be interested.
https://www.hackster.io/news/new-of...ign-reaches-99-5-peak-efficiency-75eb22fad017

 

[FilterGuy]

We have gone off topic with the power factor stuff..... I'll start a new thread.

Power factor energy savings

In a separate thread about inverter efficiency, @mandrews44 brought up the point that there is often a lot of power savings to be had by doing power factor correction on our equipment. We were getting way off topic on that thread so I thought I would start a new thread. the first problem I...

diysolarforum.com

 

[Roswell Bob]

Thought someone DIY minded might be interested.
https://www.hackster.io/news/new-of...ign-reaches-99-5-peak-efficiency-75eb22fad017

Looks like some DOE money being thrown at this.

 

[HaldorEE]

Transformers do not mean it is not a switcher.

Weight and heat is a big give away. Switching supplies are very light for their size.

 

[Factory400]

Weight and heat is a big give away. Switching supplies are very light for their size.

There are many switching power supplies that use transformers for isolation or voltage multiplication/division. All of them use inductors which is half of a transformer.

"Switching power supply" does not mean the absence of transformers and inductors.

 

[HaldorEE]

There are many switching power supplies that use transformers for isolation or voltage multiplication/division. All of them use inductors which is half of a transformer.

"Switching power supply" does not mean the absence of transformers and inductors.

Except switching power supplies are not using 60 Hz power transformers. Typically they are switching above 100 kHz which lets you use much lighter weight inductors and transformers.

The difference is not subtle. You can tell as soon as you pick up a power supply if it is an "old school" linear power supply or not.

 

[Factory400]

Agreed - which is why I am wondering why this design is switching so very slowly.

 

[HaldorEE]

Agreed - which is why I am wondering why this design is switching so very slowly.

Because the guy who created the website thinks that is the solution to higher efficiency. He didn't even invent this. I linked the 2006 paper by Hahn, that describes the same concept. Thing is, switching technology has gotten more efficient in the last 15 years. I seriously doubt if the switching frequency makes much real difference in overall efficiency when you are using current technology.

Direct PWM battery to line voltage conversion will give you the very highest efficiency because you don't have inductive losses, but doing that requires a 170VDC battery pack and the entire DC side has to meet elevated voltage ratings. The military very well could benefit from this, especially for aviation use (lighter weight being more attractive than efficiency gains) and being in an airplane or spaceship is about as off-grid as you can get.

 

[Keith C]

I'm with Factory on this. The efficiency improvement doesn't balance with the odd-ball design, the greater battery hazard, and the problems with solar charging the three different banks at different voltages and ground potentials. No thanks.

 

[MattiFin]

Because the guy who created the website thinks that is the solution to higher efficiency. He didn't even invent this. I linked the 2006 paper by Hahn, that describes the same concept. Thing is, switching technology has gotten more efficient in the last 15 years. I seriously doubt if the switching frequency makes much real difference in overall efficiency when you are using current technology.

Switching losses in the mosfets or IGBT's are quite often the limiting factor for upper frequency in high power SMPS or inverter.

There is work-arounds like resonant switching (added complexity, difficult to scale for large load variation) and faster semiconductors like SIC or GAN mosfet (lot more expensive)

Google inverter challenge is good example what is possible when you throw enough money and engineers to a problem:

https://pilawa.ece.illinois.edu/files/2016/05/Pilawa_PELS_webinar_may_25_2016_FINAL.pdf

98% efficiency with 200W/in^3 power density. 2kW inverter would be about the size of cigarette pack. But the complexity and cost is frightening. (multi-level inverter, fancy $$$ mosfets, fancy ceramic caps etc etc)

 

[MattiFin]

Victron on the other hand has opposite and really ancient design: generate the PWM sine wave at the low voltage side and use the heaviest 50/60hz toroid transformer you can find. But their end result is pretty good..

 

[Cal]

Direct PWM battery to line voltage conversion will give you the very highest efficiency because you don't have inductive losses, but doing that requires a 170VDC battery pack and the entire DC side has to meet elevated voltage ratings.

Aren't inductive losses limited to transformers, and not inductors? Inductors, which are part of the magnetics family are very efficient. I don't believe he can make an inverter without major emi problems without inductors. And, he admits the circuit requires inductors:

"It also may not be a bad idea to have a small inductor on the output of each of the 2 AC lines, and perhaps a small capacitance from one of the AC lines to the other, after the 2 inductors. The inductors would allow the current output to change a little more slowly, giving the hardware overcurrent protection a chance to trigger in the event of a short circuit."

There will be magnetics in the inverter.

 

[Roswell Bob]

Victron on the other hand has opposite and really ancient design: generate the PWM sine wave at the low voltage side and use the heaviest 50/60hz toroid transformer you can find. But their end result is pretty good..

I made a good living on the trailing edge of technology

 

[Factory400]

I made a good living on the trailing edge of technology

I purchased a bunch of Victron gear because it is anchient design topology and reliable. I did not want to be on the bleeding edge.

 

[HaldorEE]

Victron on the other hand has opposite and really ancient design: generate the PWM sine wave at the low voltage side and use the heaviest 50/60hz toroid transformer you can find. But their end result is pretty good..

I wouldn't call that ancient, I would call that robust and safe. Using a power transformer to boost the PWM AC waveform to line voltage is the very definition of a low frequency inverter. This is how pretty much every high quality inverter aimed at home, solar or RV applications does it. Xantrex makes about the only decent high frequency inverter I know of. It is cheaper than a Victron, but it is still not cheap.

Ancient would be using a ferroresonant transformer to convert a square wave into a sine wave. This is how sine wave inverters used to work. The ferroresonant approach does has a couple of real advantages. Automatic voltage regulation and increased surge capability makes them well suited for driving loads with bad power factors. Plus they are totally passive (no smarts), that is why they were the only game in town before modern digital electronics took over.

Ferroresonant also has significant disadvantages: they run hotter, are less efficient and both heat and efficiency are much worse at light loads. You aren't supposed to use them below 20% of rated capacity or they can burn themselves up. They are also audibly noisy, heavy and very expensive. Not being able to operate them in idle mode is fine for an industrial application where you have a fixed load, but that would be a real problem in the applications we use inverters for.

If you are interested, take a look at this discussion of ferroresonant and PWM inverters in UPS applications. It is from a vendor of ferroresonant based UPS so it is also a sales pitch. I used to use ferrorresonant supplies in industrial control applications back in the 80's and 90's, but I would never consider using one today in a solar power or RV application.

https://hrd1127ph3ye0og33luxdzon-wpengine.netdna-ssl.com/wp-content/uploads/2018/08/compferropwm.pdf

 

[HaldorEE]

Aren't inductive losses limited to transformers, and not inductors? Inductors, which are part of the magnetics family are very efficient. I don't believe he can make an inverter without major emi problems without inductors. And, he admits the circuit requires inductors:

"It also may not be a bad idea to have a small inductor on the output of each of the 2 AC lines, and perhaps a small capacitance from one of the AC lines to the other, after the 2 inductors. The inductors would allow the current output to change a little more slowly, giving the hardware overcurrent protection a chance to trigger in the event of a short circuit."

There will be magnetics in the inverter.

Filtering inductors in the output are not what I am talking about.

Any galvanically isolated inverter has to pass 100% (110% including losses) of the output power through a transformer. Low frequency inverters create the 60 Hz sine wave at battery voltage then step it up to line voltage with a 60 Hz power transformer. High frequency inverters use an isolated DC-DC boost converter to step battery voltage up to 170VDC then use PWM to convert that 170VDC into AC line voltage.

The high frequencies used in the DC-DC boost converter permits you to use much lighter and less expensive transformers. Unfortunately the vast majority of high frequency inverters are built by Chinese scam artists who will gladly cut every corner (including a number they really shouldn't) in order to be able to make a profit even when selling them for dirt cheap. Do you remember when PC audio first became a thing and you could buy a "200W" powered speaker for your PC for $20? And that "200W" speaker came with a 12V, 1A power supply. Same thing in the cheap end of the inverter marketplace. If you buy a "2000W" inverter for $400, consider yourself blessed if it is able to put out 1000W for more than a few seconds.

Ever wonder why a 12V, 2000W inverter would come with 6-AWG power wires? This is really common, check the description of any big inverter on Amazon that costs less than $500. 6 AWG wire is rated for a max of 65A (I wouldn't go above 55A). 12V x 65A = 780W. That would be appropriate wiring for a 700W inverter which is probably closer to what you really got, never mind the numbers printed on it.