Hey there guys, Paul here from theengineeringmindset.com. In this video we're going
to be looking at inverters, their uses, and how they work Coming up, first of all
we'll look at the difference between alternating and direct current. Then we'll look at the
purpose of inverters and where they are used. And we'll move on and have
a look at a simple example of how they work. And finally we'll look
at at more advanced, pulse width modulation example. Guys, I just want to take a
quick moment to thank Danfoss, our sponsor for today's video. If you find inverters interesting, then you'll definitely want to check out the the Danfoss Optyma Plus
inverter condensing unit. The Optyma Plus inverter
leverages stepless technology to increase efficiency, and meet F-Gas and Ecodesign requirements. And it's a great fit for
applications in convenience stores, restaurants, et cetera. You can find out more
about this great product at optymaplusinverter.danfoss.com. So what is an inverter? Well let's start at the
basics first if all. So you probably know
that their are two types of electrical power in use. Which are direct current, or DC for short. Which is supplied by batteries,
and solar panels et cetera. Now this type of power is
mainly used by small digital goods with circuit boards et cetera. The other type of power is
alternating current, or AC. Now this is supplied from the
power sockets in your homes, and this will typically be used
to power larger appliances. Both of these types of power have their uses and limitations. So we'll often need to
convert between the two, to maximize their use. An inverter is a device
which is used to convert between direct current, DC,
and alternating current, AC. If you use an oscilloscope to look at the signal of these two types of power, you will see that direct
current sits at it's maximum voltage and continues in a straight line. That's because it's current flows directly in only one direction, which is why it's called direct current. Think of it a bit like a river or a canal. It's always at it's peak, and it flows in just one direction. If you looked at alternating current you'll see a wave like pattern, where the voltage alternates
between it's two peak voltages, in both the positive half, and then through to the
negative half of it's cycle. This is because the current
travels back and forth. It's a bit like the tide of the ocean, where it reaches it's maximum hight tide, and then transitions through
to it's maximum low tide. And in-between, the current of the sea water
will flow and change direction. So an inverter simply
converts from direct current, DC to alternating current, AC. And this is a very useful invention. You can also convert from
AC to DC, using a rectifier, and it's common to find both
of these in some devices. And we'll actually look at
this in just a moment also. If you want to learn more
on how electricity works, then start from the basics, with our previous video
on how electricity works. There's a link on the screen now, and there's also a link in
the video description below. So where are inverters used. Well a common, fairly simple
application of inverters, is within solar panels,
or photovoltaic arrays. As these generate DC power, but the appliances in your
home will use AC power. So this needs to be converted
for it to be of any use. You can also buy portable
inverters for you car, which allow you to use the cars battery, to power small household appliances. A slightly more complex way they are used, is when integrated into
variable frequency drives of variable speed drives, to control the speed, the torque, and the direction of AC motors, in order achieve very precise
control, which saves energy. You'll find these on fans,
pumps and compressors, and basically any equipment which rotates. They are used in all industries, but extensively within HVAC systems, for industrial and commercial properties. In this application the inverter is coupled with a rectifier, and the AC power which comes in, is converted to DC, and then back to AC. But the controllers will
change the frequency of the sine wave pattern. And by manipulating this, we can precisely control
how the motor behaves. And when you join this to a
fan, or a compressor et cetera, then you can precisely control
how that performs also. This is partly how the Danfoss Optyma Plus
inverter condensing unit works. It has a very clever control loop which is measuring the cooling load, and then changes the speed of the motor, which changes the speed
of the scroll compressor, and that increases or
decreased the cooling capacity, to match the load. Which results in precise
temperate control, as well as energy savings. So, how do they work? Well let's consider a simplified circuit, where the DC source is being
used to power an AC load, represented by the lamp. To convert the DC to the AC
we will use four switches. We will pair the switches together, so that switches two and three, only open when one and
four close, and vice versa. This will allow us to force the current through the AC load, in an alternating direction, so that the lamp will experience
an alternating current, even though it's from a DC source. So let's give that a try. If we leave switches two and three closed, and then open switches one and four, this will cause the
current to flow through the right-hand side of the lamp. If we then close switches one and four, and open switch two and three, this will force the current to flow through the left-hand side of the lamp. So you can see that there
is direct current source, that the lamp experiences
an alternating current. The lamp will not see this
as a sine wave however, as the sudden switching will
only result in a square wave. The sharp corners on the
square wave can be damaging to electrical equipment. So we need a way to
smooth the corners out. The switching is also far
too fast for a human to do. You can see that the
electricity you receive in the power socket of your home. This will be supplied at 50 or 60 Hertz, depending on where in the world you are. This means that the current needs to reverse direction
50 or 60 times per second. So to achieve this we'll use some special
electronic components, such as diodes, IGBTs MOSFETs et cetera. Now if you don't know how
these components work, don't worry about that for now, we'll cover this is another
video specifically for that. For now, just understand the circuits, and how the current is controlled. Let's look at a three-phase
example for a motor. You can see the circuit has
a DC source and an AC load, and to convert the direct
current into alternating current, there are bunch of these IGBTs which are connected to a controller. The controller will send
signal to each IGBT, telling it when to open and close. These IGBTs are paired together. So when the circuit is powered up you can see that the controller is switching pairs of IGBTs, to allow current to pass through them for a set amount of time. So that the motor will experience
an alternating current. In this example the alternating
current is in three phases. So this is used to power the motor. But how is it used to control the speed? Well, if we take a
closer look at the IGBTs, we'll see that they
actually open and close in a pulsating manner,
multiple times per cycle. This is known as pulse width modulation. What's happening is the
cycle has been broken up into multiple smaller segments, and the controller tells the IGBTs, how long to close for during each segment. I'm showing how this
works in just one cycle, for one phase of the three-phase circuit, just to keep it as simple as possible. By opening and closing the switches of varying lengths of time, during each segment, of each cycle, the IGBTs can allow
varying amounts of current to flow through the
circuit and into the motor. The result of this, is that the average
power over each segment, will result in a sine wave pattern The more segments the
cycle is broken into, the smother the sine wave will be, and the closer it will
mimic a real AC sine wave. So the motor will see the average value, and will therefore experience a sine wave alternating current. The controller can then change the amount of time the IGTs are open, to increase or decrease the
frequency and the wavelength, to control the motor's
speed, torque, and direction. And with a few additional control loops, it can be used to exactly
match the required loading, to provide precise control of a system and unlock energy savings. Okay that's it for today. Before I go, I just want to thank Danfoss one last time for sponsoring this video. Don't forget to check out
their Optyma Plus inverters by heading over to
optymaplusinverter.danfoss.com. Thanks for watching, I hope this has helped you
and you've learned from it. If you have then please
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theengineeringmindset.com Once again, thanks for watching.
