What Is A Pure Sine Wave Inverter?

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Although Tesla’s AC beat out Edison’s DC in the race to power our homes, solar technology is undoubtedly DC’s wheelhouse, which poses a problem…

How can we use our DC solar energy to power our overwhelmingly AC lives?

What Is A Pure Sine Wave Inverter?

Well, you can holster that calculator and return those books on electrical engineering, as this conundrum has already been solved by the amazing pure sine wave inverter, a nifty gadget with a remarkable superpower.

These contraptions can transform DC (direct current) into AC (alternating current) and back again if necessary, so whatever our green energy goals are, we can work towards achieving them.

But how exactly do they accomplish this miraculous metamorphosis? Read on and all will be revealed.

Why Do We Need Pure Sine Wave Inverters?

Okay, so we’ve established that we need pure sine wave inverters to power our AC appliances with a current that started things out on the other side of the tracks, but why is this the case?

What would happen if we tried to use a DC current to power an AC appliance?

To put it bluntly, the appliance would die a horrible death, and if it survived the incident, it would certainly be damaged.

These energy formats are just too different; if an appliance is designed to accept one, it cannot receive the other.

What’s The Difference Between AC & DC Current?

DC current is composed of electrons that travel continuously in one direction, from the negative to the positive electrode.

AC current, by contrast, is composed of electrons that flow one way, and then, periodically, bring it around and head back where they came from, hence why it’s called alternating current.

So, as you see, inter-current compatibility isn’t really a thing.

How Do Pure Sine Wave Inverters Work?

To understand how inverters work, first it’s important to know that we use waveforms as a visual reference of the behavior of electrons in a current — Our DC current is represented simply by a straight line, as it only moves from negative to positive, while our AC current is represented by a sine wave, as it has peaks that oscillate back and forth between negative and positive.

Sine waves look like the smooth ups and downs of a rollercoaster.

It’s the job of the pure sine wave inverter to change that boring DC line, into our AC rollercoaster, but that’s not all.

AC runs with a much higher voltage, so the inverter also has to amplify the volts of an incoming DC current.

Converting The Waveforms

Converting The Waveforms

To complete the primary duty of modifying the behavior of electrons, an inverter uses an automated switch system called an H-Bridge.

A basic H-Bridge is composed of four switches and a central load.

Two of the switches send a voltage through the load in one direction, while the other two reverse the polarity, sending it in the other direction.

These switches simply take turns switching on, then switching off.

The resulting waveform representation is a square wave, which is still very much different from a sine wave, as the peaks and troughs of these waves don’t come close to aligning.

To get things a little more in sync, before the active and inactive switches trade duties, all of them take a small break, producing a square wave interspersed by short sections of the straight DC current.

Now the peaks and troughs of the current vaguely follow those of an AC sine wave, but it’s still not close enough.

The current travels in a very jagged and robotic way from negative to positive and back again, whereas the pure sine wave flows between the poles smoothly.

To continue this transition, first, the inverter hits the modified square wave with another layer of modification, essentially placing an identical, smaller square wave on the peaks of each original wave.

This looks more jagged, but there are actually more points of contact with a flowing sine wave.

This waveform is also known as a quasi-sine wave, as it gets so close to the real deal, but again, it’s just not enough.

To iron out those remaining kinks in the waveform, our inverter uses pulse width modulation (PWM) to generate a bunch of high-frequency triangle waves as well as a new sine wave for the triangle waves to use as an amplitude guide.

These triangle waves oscillate back and forth between poles remarkably quickly, overlapping the sine wave a number of times, allowing an output that closely resembles the general movement of a sine wave, albeit with a saw-tooth line.

All that’s left for our inverter to do now is to feed the rough sine wave through a low-pass filter to smooth out all those teeth, and voilà — We’re left with an almost perfect pure sine wave AC current.

Boosting Voltage

You’ll be happy to hear that the process of boosting the voltage of a DC current to AC standards is way simpler than the waveform conversion.

All it takes is a transformer, an electromagnetic device composed of an iron core hooked up to a couple of copper wire coils. One is the primary coil, the other is the secondary coil.

The low voltage current arrives via the primary coil, which magnetizes the iron core, allowing it to, as if by magic, induce a much higher voltage in the secondary coil.

Are There Any Alternatives To Pure Sine Wave Inverters?

You have two options when it comes to inverters…

  • A pure sine wave inverter
  • A modified sine wave inverter

… the difference being the quality of the waveform.

As discussed, the line that forms the sine wave of a pure sine wave inverter is almost entirely smooth, but the line that forms the sine wave of a modified waveform is composed of many tiny square waves that take the form of steps.

But what does this mean in practical terms?

Well, due to the reduction in current quality, modified sine wave inverters aren’t very efficient and cannot be used for all AC devices, especially sensitive electronics such as computers.

Conversely, pure sine inverters, such as this one from the folks over at Renogy, create a high-quality replica AC current that works with all AC electronics.

Final Thoughts

To sum up, a pure sine wave inverter utilizes intelligent switching and pulse wave modulation to turn a DC current into one that closely resembles an AC current so we can use our DC solar energy to power our AC appliances.

Modified sine wave inverters do the same job but not as well, as the sine wave produced is composed of small steps rather than a smooth line.