inverterpower supplyrectifiersquare
Rectifying square wave voltage seems to give us DC directly without the need of a capacitor. so, why do we prefer sine wave over it?
What would change if I powered any adapter (laptop adapter as example) or any power supply with a square wave inverter instead of sine wave?
Edit: I understood from answers and comments that sine wave is better at generating and transmission, let's consider this a special case about "Powering power supplys (with input rectification) with inverters."
Some people claim that certain loads "may" not work as well, or "may" be damaged, with anything other than a pure sine wave.
Since the power coming out of my wall sockets is significantly different from a pure sinewave, I suspect these sincere and well-meaning people are merely repeating propaganda from the manufacturer of a pure sinewave inverter, much like people repeat urban legends.
There is only one kind of device that I know doesn't work as well with a non-sine-wave inverter: devices that use a "capacitive power supply" -- see How efficient is a capacitive power supply? for details.
Since a "capacitive power supply" has a power factor near 0, it is questionable whether any "capacitive power supply" meets EU-mandated power factor laws, such as EN61000-3-2.
I suspect that all products -- as long as they were designed after EU-mandated power factor laws went into effect -- should work just as well on "modified sine wave" as with "pure sine wave" inverters.
Of course, I can't possibly know about every product ever designed -- if there is any specific product (that was designed after those EU-mandated power factor laws went into effect) that can't work or doesn't work as well with "modified sine wave" power, I would be interested. If anyone can explain why it doesn't work, in enough detail that I can try to avoid that kind of failure, I would be fascinated and grateful.
This is a capture of the output of an APC 650 recorded by Jesse Kovach, while under load.
Notice the severe over-amplitude events at the extremes (the spikes at top and bottom). In reality they are actually much greater in amplitude, but the oscilloscope in the image was not fast enough to capture it.
Sharp edges in the time domain equate to broad-spectrum noise in the frequency domain. All of this high-frequency content represents additional energy that must be absorbed by protection circuits. If not, it can exceed isolation withstanding limits in the various input stage components and "burn through". If this doesn't burn out the input it will result in a cascading failure where it will cause something to fail on the secondary side from the resulting overvoltage.
...and that's just one failure mode. There are others. Psuedo-sine waves are poor matches to sine-wave inputs. :(
A much better (and much more efficient!) approach is to go DC-to-DC directly (note: you can't actually go DC-to-DC directly if your input voltage is lower than your output voltage, but the details of this are well contained inside a "DC-DC converter").
Self-contained switch-mode power supplies for Dell laptops that take DC inputs are available in the marketplace. Here's an example:
which I sourced from:
http://www.amazon.com/Adapter-Charger-Dell-Latitude-D630/dp/B002BK7JEC#
Please note that I have no personal experience with this particular product and many cheap DC converters are poorly designed internally. Be careful.
Best Answer
There are a number of crucial elements to consider when choosing an infrastructure
GENERATION
Generation is via electrical machines and almost all will generate Alternating current with a SINUS profile & the simplest is a wound-rotor sync machine & thus we have a source that is sinus [a]
TRANSMISSION
Let's assume we have generated a square-wave voltage source of a frequency suitable for SMPS... 50kHz-100kHz. We now need to move the power from generation to consumption USING the Tesla model.
During the Current wars Edison advocated DC & community generation. Tesla advocated AC & centralised generation.
With centralised generation the power stations are 10's of km away from consumption. To minimise losses this "squarewave" would need to be high-voltage (400kV) while also holding the characteristics of a squarewave (ie harmonics...).This would entail a dv/dt in excess of 400kV per us (assuming a pessimistic acceptable risetime...), likewise the inductance of the transmission line is quite significant. This will result in at least three things
Lets forget about this for a moment and accept that we have received a reasonable squarewave at 400kV with about 100kVA behind it... this needs to be transformed to a level that can be consumed. You are wanting to consider PSU's... You would not want to feed 400kV into a supply (Safety and other annoyances...) so this would need to be stepped down...
Could that be made? sure I guess but the power electronics involved isn't trivial BUT does exist. Take all the HVDC systems in existence. This square-wave would then need to be rectified to then be stepped down. Why bother with those extra diodes and just transmit in HVDC instead? Current wars... (see economics)
Even if an Edison generation model was considered the three named issues would still exist.
This only considers the bulks transmission of power. There is then the residential aspect as this 400kV is stepped down to 125kv down to 12kV .. 240V.
UTILISATION
In "modern society" we appear to use a lot of low-voltage DC fed equipment (chargers, PC, TV...) but they are not the high-power demanding devices (washers, heaters, vacuum...) and this is before considering industry.
One thing that is FANTASTIC about the UK is its unquenchable thirst for statistics, 2nd to none.
https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/546933/ECUK_user_guide_final.pdf
https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/541168/ECUK_Tables_2016.xlsx
In 2015
Home 9300 ktoe (ktoe = Thousands of tonnes of oil equiv)
Industry: 7940 ktoe
Commercial: 6402 ktoe
Some domestic is only 39% of electrical consumption
Concentrating PURELY on electrical power consumption, this is further split:
Those three highlighted account for 71% of all electrical consumption in the UK (motors alone are 51%)
The bulk require AC to function so with the blinkered view of SMPS driving a legitimate question "why not a squarewave" ignores what utilises it the most
ECONOMICS
To implement an electrical network takes a lot of time, money and resource & this was all initiated around the turn of the last century.
Edison: DC & Local generation
Tesla: AC & Centralised generation.
Tesla won in the end with AC mainly due to the economics of transformation. In the following decades many countries then started building their infrastructure around a wide variety of frequencies but eventually settling on 50Hz or 60Hz.
At the time what was capable of consuming electricity? Lighting (either AC or DC...) Heating (either AC or DC) Motors (low power at the time.. only AC or DC, not mixed.)
Why these frequencies? This is lost in time... but manufacturing capabilities would have had a large say in the matter... The laminations of a generators corepack could only reliably be made so thin, the same with XFMR laminations. Bearing only capable of withstanding a certain velocity...
And so we now have an electrical infrastructure built at a time of war, limited resource and technical ability. There was no power electronics todo any clever DC:DC conversion...
Today? if we were to rip up the entire system would we stick with 50Hz AC? probably... it is very convenient for transmission. HVDC is very economical over long distances and high powers.
Why would we want to transmit a high power square wave (if we could...) when high-voltage DC would be soo much simpler and HVAC is soo easy to manage.
In a domestic environment there could be an argument to have a LVDC ring as well as a LVAC ring due to all the additional DC-fed appliances and the "efficiencies of SMPS" but you have to be careful with a DC-bus ... they go unstable. Maybe there is a future in a 48V LVDC ring in each house but this LVDC ring is locally created rather than supplied by the local substation.
[a] Not all machines generate AC.. BrushedDC produces DC but you would not consider such machine topology anywhere near grid power-levels. SR machine+inverter will generate onto a DCbus but you will need an inverter to do this (additional cost, complexity etc...)