Welcome to this Yaskawa eLearning Video for The Benefits of Using the Yaskawa Matrix Drive
on Fans and Pumps.
I'm Paul Avery
In this video we will consider the financial and functional benefits of using
a Z1000U Matrix drive on a fan or pump application.
First we will establish the advantages of using any standard variable frequency drive
over running a fan or pump across-the-line with dampers or valves to adjust the performance
of the application.
Then we will compare how the Yaskawa Matrix drive compares to standard variable frequency
drive or even a VFD with an Active Front End package
Finally we will review the technology behind the matrix drive that makes it so unique.
Once we understand how the matrix works we can understand how both the ECO mode function
and the inherent regenerative capabilities can be beneficial to fan and pump applications.
Our first job is to consider and evaluate the use of a variable frequency drive, or
VFD, versus just running the fan or pump using an across-the-line starter.
An across-the-line starter can only apply full voltage and 60Hertz frequency to the
fan or pump motor.
Any changes to pressure or flow will need to be made using either dampers or inlet guide
vanes for fans or valves for pumps.
Conversely, the VFD can run the motor at whatever speed that the fan or pump system requires.
Fans and pumps run by VFDs do not need the dampers or valves.
The drive uses only the power needed to match the demand and the energy saved can provide
a return on your investment in less than three years.
The first issue we will consider is the power factor of a fan or pump application when using
either a VFD or across-the-line starter.
We will try to use a familiar visual aid to understand the ups and downs of power factor.
Power factor essentially designates how efficient the system is utilizing power.
The closer power factor is to unity (1), the more efficient the system is using power.
It turns out that some of the current does not actual generate the motor torque that
moves the air or water.
Some of the current is used to create the magnetic field in the motor, which is required
for the motor to generate torque.
This reactive current is necessary but doesn't directly move the load.
The aim is to minimize it.
One way to think of power factor is that the apparent power pulled from the utility is
partly real power, or power
used by the load, and partly reactive power necessary to produce magnetic fields.
The apparent power is defined as kilovolt-amps or kVA,
the real power
is defined as kilowatts or kW,
and the reactive power is defined as Kilovolt-amperes reactive or kVARS.
Now for our familiar visual aid.
How and why reactive power, or kVARS, are a reality when considering how power is drawn
by an induction motor or VFD can be thought of like pouring beer into a mug.
To get the beer from the keg into our mug we would prefer that most of the contents
stay in their drinkable liquid state but some of it will become a foam head.
We do our best to limit the foam some amount of foam is inevitable.
Equivalently, we would like all of the power drawn from the utility to go to driving the
load but unfortunately some of the power is lost to reactive elements in our system.
For some reason that last slide made me thirsty.
Anyway, lets put some numbers to this power factor discussion.
First lets consider a fully loaded variable torque application, like a fan or pump running
near full speed.
When a motor is running across-the-line the power factor is reasonable but the inductive
nature of the motor does tend to lower the power factor.
When we take the same fully loaded application and drive it with a VFD,
the VFD corrects for the motor's effect on the power factor.
The VFD will have its own effect on the power factor but the trade-off is clearly in favor
of using the VFD.
During low loads, proportionally more current is being used for magnetic fields than for
driving the load so the power factor drops pretty drastically.
However, with the VFD, the magnetic field can be feed from the drives DC Bus so from
the point of view of the utility there isn't quite such a drop in power factor.
Our next comparison will be in system efficiency which we already kind of tipped our hand about
when we discussed the VFD's ability to automatically regulate speed to meet actual demand.
If we want to compare the efficiency of using a VFD on a fan or pump versus running across-the-line,
then we need to look at the amount of energy used by each method across their
realistic operational range.
Our aid in this comparison is the set of Affinity Laws, which govern power usage for fan and
pump loads.
According to the affinity laws, if we drop the fan or pump speed by 10% we actually drop
the power used not by 10% but by 27%
So the slower the fan or pump runs, the greater the energy dollars saved.
Because the VFD has the ability to run the fan or pump only as fast as is necessary at
any moment, it can afford great savings in operation versus the single speed motor starter.
Although use of a inlet guide vane on an across-the-line installation can achieve some energy savings
as it reduces flow rates , it can not match the much lower power usage
afforded by the VFD being able to slow down the fan or pump
Let's take a look at an example that makes it easy to understand the savings you can
unlock by running your fan or pump with a VFD instead of across-the-line.
In this example we have two identical 5 horsepower fans.
When the cfm or cubic feet per minute of airflow required is equal to one of the two fans running
at full speed then the across-the-line solution will only run the one fan
while leaving the other fan off.
The energy usage is equal to the 5HP motor .
When both fans are run by VFDs and the cfm demand it equal to one fan running at full speed,
the option to achieve that flow by running both fans at half speed exists.
By running each fan at half speed you actually drop the power usage by a cube of the speed
reduction which leaves the power at 12.5% of rated power or 1.25 horsepower.
That yields a power savings of 75% while still achieving the system requirements.
Our next faceoff between VFD operation for fans and pumps versus across-the-line operation
will be over control options.
The features considered next will go directly to how easy it is to work with each technology.
When it comes to control options and capabilities it is really a one-sided battle.
The across-the-line installation has to run at full speed , starts with full voltage ,
which is stressful for both the mechanical , and electrical systems, , has no keypad, , and
won't talk on any network.
Conversely the VFD runs only as fast as is necessary and , can self regulate to match the systems flow or pressure needs.
The VFD will soft start the fan or pump which eliminates inrush current levels and
is far less stressful on the mechanical portions of the installation like fan belting and pump
valves which in turn lengthens their lifespans.
A VFD has the ability through it's keypad to give real-time information on everything
from the speed, to the pressure, to the amp draw of the motor.
This information provides peace of mind to the person in charge of making sure the pump
or fan is performing optimally.
Lastly, a VFD can be easily integrated into an automation network via option boards, or
hardwired I/O.
Most data acquisition is a cinch when the VFD can report details of its status in real-time
over the network.
The next step in evaluating the matrix drive on fan and pump applications is to compare
the unique capabilities of the matrix drive versus a standard six-pulse VFD.
As we have stated, any standard AC VFD has the ability to regulate a fan or pump to only
run at the speed that the system demands thereby eliminating the need for dampers, vanes, or
valves to regulate pressure or flow.
By automatically regulating speed to maintain demand the drive automatically optimizes the
systems operating efficiency.
The matrix can do all that as well but offers some distinct advantages not possible with
a standard VFD solution.
Let's begin our comparison with a look at the expected power factor performance of each
device.
What makes a standard VFD have better power factor than an across-the-line motor is that
the displacement power factor is so much better when a VFD is between the induction motor
and the line.
Now that our comparison involves drives in both cases, displacement power factor is not
really a differential.
This time the differential comes from how much current distortion is created.
Standard VFDs draw non-linear current, in other words, the current is not drawn in line
with the voltage.
The greater the current waveform differs from the voltage waveform the larger the current
distortion.
The true downside of the harmonics created by this distortion is that they also cause
extra heating in the cables and devices that are supplying the VFD with power, without
any real benefit.
In the left hand figure for the Matrix drive you can see that both the displacement power
factor is very good and the current distortion is very minimal.
Since we have brought up the topic of harmonics.
Let's try to give them a conceptual definition.
Harmonics are, in a simple sense, just multiples of some fundamental.
Since we are speaking of AC current, then harmonics are sine waves with frequencies
that are some multiple of the fundamental frequency.
In the graphic on this slide, the fundamental current frequency is 60 Hz.
Also depicted are representations of the 3rd, 5th, 7th, and 9th harmonic of a 60 Hz fundamental
waveform.
Of course standard VFDs and Matrix drives are not the only choices when it comes to
users concerned with mitigating harmonics and improving power factor.
Let's compare the Matrix to not only the Standard VFD but we will also add performance information
for a VFD with an added DC bus reactor and also a VFD with a multi-pulse front end .
Only by adding extra equipment such as the DC Bus reactors or the special transformer
and second rectifier bridge of the multi-pulse VFD harmonics
can we begin to eliminate the and improve the power factor.
But even in those cases we are still not reaching the harmonic mitigation and power factor improvements
offered by a standard Matrix drive.
To minimize the harmonic currents at the input of the drive, you need the Matrix drive.
The matrix drive can operate at full load with less than 5% iTHD (Total Harmonic Current Distortion).
Even an 18-pulse VFD won't necessarily meet 5% iTHD @ its input.
Our next comparison will be to compare the operational efficiency of a Yaskawa matrix
drive versus a VFD with a multi-pulse front end.
Here is an example of two 75 horsepower configurations, one an eighteen pulse matrix
and the other the drive.
Both are operating on a variable torque load.
You can see they both perform well at rated load.
Still, the matrix drive is at least 3% more efficient at rated power.
At lighter loads the 18 pulse drive's efficiency suffers greatly.
The matrix drive is still 94% efficient at 40% speed while the 18 pulse has dropped down
to 82% efficiency.
That is a 12% reduction in efficiency.
That's money out of your pocket.
Let's continue our comparison of the matrix drive and a standard VFD by considering their
control options.
Frankly there is no difference when it comes to control and convenience.
As a matter of fact, our matrix drives feature the same keypad, the same programming menus,
and the same option cards as our standard drive products.
If you know how to use and operate a standard Yaskawa fan and pump drive you can seamlessly
transition to using a Matrix drive.
The final section of our matrix drive discussion will cover two more matrix only functions
that put it in another class above standard VFDs.
We will present how the ECO mode function and the inherent regenerative capabilities
can be beneficial to fan and pump applications.
To truly understand how the ECO mode and regenerative capabilities work we must first understand
the technology behind the matrix drive.
The power section of the matrix is dominated by nine bi-directional switches.
Nine switches are required because we need to be able to connect any of the three input
phases to any of the three output phases .
Also included in the power section is an input filter.
The input filter is necessary to filter out the Pulse Width Modulation of any regenerated
power going back to the power supply.
Lets take a closer look at the nine switches.
By using the bi-directional switches, the matrix drive has the ability to allow motoring or regenerative power flow.
Now we can discuss the ECO mode.
Sometimes the benefits of being able to vary the speed of the fan or pump are lost because
the application is demanding full speed or near full speed operation.
During these conditions it would be nice if we could just open and close some contactors
in order to shunt around the drive bypassing it and run off line power.
The matrix drive takes the concept of a bypass and integrates it into its control to automatically
switch back and forth between drive control and operating the motor using line power directly.
This is called Eco-Mode.
Using the Eco-Mode function the Matrix can be programmed so that when it is running the
fan or pump near line frequency, it will simply pass the incoming sine wave power through
untouched.
When the application no longer needs to run up near line frequency the Matrix will transition
back to PWM switching and run the fan or pump at whatever speed the application calls for.
ECO mode eliminates audible motor noise, drive switching losses, and high frequency noise
like common mode and differential mode noise.
Going into Eco-Mode can improve drive efficiency by 19% on average.
Our final benefit of the matrix drive is the inherent regenerative operation of the matrix
drive technology.
Most fan and pump applications don't require motor braking during their normal operation.
However high inertia fans can cause a VFD to trip on a overvoltage condition as its
reaches set speed.
The inertia of the fan will want to keep the motor accelerating so the VFD will need to
deal with regenerated energy.
This causes a regenerative condition which sends energy from the motor back to the VFD
causing the overvoltage fault.
The Matrix drive with it's bi-directional switches will automatically send this regenerative
energy back to the line for triples operation.
The Matrix is also helpful to prevent OV faults caused by large supply fans overhauling smaller
return fans.
Everything necessary for regeneration is built right into the Matrix.
Thanks for joining me to cover the benefits of using Yaskawa's Matrix drive on fan and
pump applications.
If you have any questions about Yaskawa products or technology, please feel free to visit our
website at www.yaskawa.com or send us an email at training@Yaskawa.com
Thank you.