advantages/disadvantages of square wave inverter vs modified sine wave inverte

[ch wazir]

Dear Alterlink,
Plz tell in detail the advantage of modified sine wave over square wave,Will it be possible to run the inductive load bit safely by modified sine wave inverter than sqare wave.Regards

 

[KerimF]

The main difference is in their peak voltages.

Let us assume we need Vrms=220V.

The peak voltage of the square wave would be 220V.

The peak voltage of the modified sine wave would be 220*SQRT(2) = 311V instead. But to get the same RMS, the duty cycle is made to be equal 50% (so the wave may be called rectangular instead). The advantage of the modified sine wave inverter is that it can supply the peak voltage needed by many old power supplies using the simple rectifier configuration. But since the currents are pulsed, thicker wires should be used than in case of the simple inverter.

Kerim

 

[ch wazir]

dear kerim,
you didn't follow my question,i enquired about the advantage of modified/quasi sine wave inverter over square wave inverter in detail.I already have the know how of your given explanation.I want to compare the both.

 

[KerimF]

Sorry... When I produced the modified sine wave inverters (that cost more than the square wave type) for sale, I did it just for the advantage I already mentioned.

The advantage of the modified sine wave inverter is that it can supply the peak voltage needed by many old power supplies that use the simple rectifier configuration

I hope some others know more than this main advantage

 

[ch wazir]

ok,Regards

 

[FvM]

When you're asking about inductive loads, you need to tell more about the intended implementation. If the zero phase in "modified sine wave" is actively switched, e.g. by a full bridge output stage, inductive loads won't be a problem. If you're just disconnecting the output transistors, there is a problem.

 

[ch wazir]

dear fvm,
The modified sine wave inverter having a full bridge and is to be used for feeding inductive load like fans/motor etc.I want to discuss on advantage of the same vs square wave inverter since the sine wave inverter is best but expensive.Regards

 

[KerimF]

If you're just disconnecting the output transistors, there is a problem.

In a push-pull inverter, there are also two flyback diodes when the two transistors are off. If they (diodes) are rated properly they can also disharge the inductive load current. But pehaps there is another important point that I missed.

Kerim

---------- Post added at 11:10 ---------- Previous post was at 11:02 ----------

A low cost CFL likely gets its current close to the voltage peaks. So to be sure that a bulb or a set works fine if supplied with a square wave inverter, one needs just testing it with a sinewave voltage at:
Vrms = 220 * 0.707 = 155 V

For instance, I tried adding more versions between these two extreme types. I found out that my best sales are for the type that uses 4/5 duty cycle (instead of the best one with 50% duty cycle). Obviously its peak voltage is SQRT (220^2 * 5 / 4) V . Actually I let it be a bit higher

 

[FvM]

As a disadvantage of flyback (free-wheeling) diodes versus true synchronous switching of modified sine, the former don't keep the waveform with inductive loads.

 

[ALERTLINKS]

A quality consideration that can be important in some applications is the output waveform of the UPS. This refers to the shape of the alternating current signal produced by the UPS.


Sine wave, Modified Sine wave, and Square wave.
There are 3 major types of inverters - sine wave (or "true" sine wave), modified sine wave (actually a modified square wave), and square wave.

Sine Wave

A sine wave is what you get from your local utility company and (usually) from a generator. This is because it is generated by rotating AC machinery and sine waves are a natural product of rotating AC machinery.
This is the best waveform, as it is the shape of an (ideal) AC electrical signal from the wall. The highest-quality UPSes produce a true sine wave output, which requires fairly expensive components in the inverter. This is especially important for online UPSes, since their loads are always running off the inverter. True sine wave UPSes are normally found only in higher-end models.
The major advantage of a sine wave inverter is that all of the equipment which is sold on the market is designed for a sine wave. This guarantees that the equipment will work to its full specifications.
Some appliances, such as motors and microwave ovens will only produce full output with sine wave power. Pure sine wave inverters are used to operate sensitive electronic devices that require high quality waveform with little harmonic distortion. In addition, they have high surge capacity which means they are able to exceed their rated wattage for a limited time. This enables power motors to start easily which can draw up to seven times their rated wattage during startup. Virtually any electronic device will operate with the output from a pure sine wave inverter.
A few appliances, such as bread makers, light dimmers, and some battery chargers require a sine wave to work at all.
Sine wave inverters are always more expensive - from 2 to 3 times as much.

Modified Sine Wave (quasi-sine)

A modified sine wave inverter actually has a waveform more like a square wave, but with an extra step or so. A modified sine wave inverter will work fine with most equipment, although the efficiency or power will be reduced with some.
Motors, such as refrigerator motor, pumps, fans etc will use more power from the inverter due to lower efficiency. Most motors will use about 20% more power. This is because a fair percentage of a modified sine wave is higher frequencies - that is, not 50 Hz - so the motors cannot use it.
Some fluorescent lights will not operate quite as bright, and some may buzz or make annoying humming noises.
Appliances with electronic timers and/or digital clocks will often not operate correctly. Many appliances get their timing from the line power - basically, they take the 50 Hz (cycles per second) and divide it down to 1 per second or whatever is needed. Because the modified sine wave is noisier and rougher than a pure sine wave, clocks and timers may run faster or not work at all. They also have some parts of the wave that are not 50 Hz, which can make clocks run fast.
Items such as bread makers and light dimmers may not work at all - in many cases appliances that use electronic temperature controls will not control. The most common is on such things as variable speed drills will only have two speeds - on and off.
This waveform is a compromise between the sine wave and the square wave. The positive and negative pulses of the square wave are thinned, separated and made taller, so the peak voltage is much closer to that of a sine wave, and the overall shape of the wave more closely resembles that of a sine wave. At the same time, the cost of the circuitry to produce a modified square wave output is much closer to the cost of a square wave's circuitry than that of a sine wave unit. (In fact, you can create a modified square wave by adding together two square waves that are shifted in phase slightly from each other.) Many fewer pieces of equipment have problems with modified square wave power than with straight square wave. Modified square wave output is used on many lower- to middle-range UPSes, and is also sometimes called "stepped approximation to a sine wave", "pulse-width modified square wave","Modified Square Wave"or even "modified sine wave". The last term is marketing cutesy-speak, since the output form isn't really a sine wave, modified or otherwise.
These inverters are capable of operating a wide variety of loads; electronic and household items including but not limited to TV, VCR, and satellite receiver, computers, and printers.
A modified sine wave inverter is probably OK for equipment that uses switch-mode power supplies, but for something like a pre-1990s stereo system or an analog TV set, you'd probably have more noise in the signal you are viewing/listening to. And don't get the energy to power a scope/spectrum analyzer's AC plug off an inverter like this...you'd probably get inaccurate readings on the measurements.

Square Wave

Very few but the very cheapest inverters any more are square wave. A square wave inverter will run simple things like tools with universal motors with no problem - but not much else. These are seldom seen any more except in the very cheap or very old ones.(In Pakistan, 99% of UPSes made are still based on sqare wave tropology)
The least desirable output waveform type, a square wave is sort of a "flattened-out" version of a sine wave. Instead of the voltage smoothly increasing from the negative maximum to the positive maximum and back again, it shifts suddenly from negative to positive, stays there for half a cycle, and then jumps to full negative and stays there for half a cycle, then repeats. Cheaper inverters are designed produce a square wave output primarily because the components required to do this are cheap. It wouldn't surprise you to learn that some equipment doesn't really like running on a square wave (it may be more surprising to learn that many types of equipment will run on it!) There are several reasons why square waves cause problems. For starters, the peak voltage of a square wave is substantially lower than the peak voltage of a sine wave, which causes issues with some types of equipment. In addition, while a sine wave has a single frequency in it--60 Hz in North America--a square wave contains many higher frequencies as well, called harmonics, which can cause buzzing or other problems with some equipment. Square wave output is found only in the cheapest equipment and should be avoided if possible. I would only use them for lighting or a power drill. Square wave inverters are simply worse than modified square wave inverters, that's why modified square wave inverters are advertised.You may have audio glitches and general touch pad funkiness when you charge from such an an inverter. It may not damage the laptop though.

It's safe to say any electronic device that requires sensitive calibration can only be used with pure sine wave inverters. For many electronic devices that don't require sensitive calibration, modified sine wave inverters are a more cost-effective option. Despite the drawbacks associated with modified sine wave inverters, they are the most commonly used inverters on the market.
Some electronic devices may pick up inverter noise while operating with modified sine waveform. Using fluorescent lighting can be problematic when using modified sine wave inverters. Most of the equipment on the market is designed for use with sine waves. Some appliances, such as microwaves, drills, clocks or speed motors will not produce full output if they don't use sine wave current, moreover they may damage the equipment. Some loads, such as light dimmers will not work without sine wave at all.
In practical terms, for a home PC UPS modified square wave output is fine. It will power a PC, monitor and similar equipment without any trouble. Of course, also remember that less expensive UPSes are normally running off line power anyway, and it is only when operating off the battery that the output waveform comes into play. I regularly use drill machine with a modified sine wave UPS (China made) in my wokshop during power blackouts with no problem. Ther is less noise from motors, fans than if run with square wave.

See the voltage difference as KerimF has stated ealier in this schematic representation of one cycle of a sine wave, square wave, and modified square wave
output. The area under each curve is the same, so they each carry the same amount of power.

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We need an inverter to change the direct current to alternating current (AC) in order to utilize the power being generated in a home. In order to maximize energy output, it is important to select an inverter with the following characteristics:

1.High efficiency
2.Low standby losses
3.High surge capacity
4.Low harmonic distortion

 

[ch wazir]

Many regards for detailed description