Performance Testing Results
For FlexMod Controller: Introduction
Executive Summary
| Introduction |
Conclusion
Electric Motor Energy Use
In 2005, the United States consumed more than four
million Gigawatt hours of electricity. Generating
this energy required millions of tons of coal and
thousands of pounds of processed nuclear fuel, and
released more than two billion tons of carbon
dioxide (CO2) into the atmosphere1. There is great
awareness that there are consequences to this level
of energy use and pollution. The U.S. Department of
Energy (DOE) and a myriad of other organizations
promote energy efficient products and behaviors to
help reduce the negative environmental and economic
impacts of our energy use. This project evaluated
one technology that could have a substantial impact
on the single largest consumer of electric energy:
the electric motor.
Government studies find that electric motor driven
systems consume nearly 70% of all industrial
electricity in the United States. According to the
Energy Efficiency and Renewable Energy Office of the
DOE, there are more than 13.5 million AC electric
motors greater than 1 horsepower (hp) operating in
U.S. industry2. Most of these motors are powered
directly from the 60 Hertz line voltage and operate
at a constant speed. If the load is constant and at
least 50% of the rated load, then these motors can
be very efficient. For example, 20 hp motors meeting
the National Electrical Manufacturers Association (NEMA)
Premium standards are at least 93% efficient, and
100 hp NEMA Premium motors are over 95% efficient3.
However, many motor loads are not constant, and many
motors drive equipment that does not operate
continuously. One common motor control scheme is the
on / off method. Examples of motor driven systems
using this control method include residential and
industrial heating and air conditioning fans, water
pumps tied to float level controls and many types of
blowers. In these systems, the control variable
(i.e., temperature set point, water level, etc.)
deviates from an allowed range and causes the motor
driven fan or pump to come fully on until the
control variable returns to an acceptable value.
Then the system powers off. A good example of this
control scheme is found in most residential heating,
ventilation and air conditioning (HVAC) systems. On
/ off control for motor driven systems results in
high startup currents and additional losses due to
fluid turbulence and overshoot of the control
variable. Such control schemes are simple and
inexpensive, but they can be inefficient.
Another method of controlling a motor driven system
is with a variable speed drive. A common type of
variable speed drive is known as a voltage /
frequency (V/F) controller. V/F controllers vary the
supplied voltage to match the speed and load
requirements, while attempting to maximize
efficiency over the full range of power. Some V/F
drives allow the user to program the exact
relationship between voltage and frequency. V/F
controllers are typically sized for moderate power
ranges like 5 to 10 hp, 10 to 20 hp and 20 to 50 hp.
For applications where dynamic performance is an
important consideration, vector drive motor
controllers may be used. These controllers are more
expensive than V/F controllers because of more
sophisticated electronics that allows control of
both frequency and current. Therefore, V/F drives
only adjust motor speed while vector drives adjust
motor speed and torque. Vector drives are usually
found in specialty applications where torque control
is important. For example, certain winding
applications have growing rotational inertias as
material is added to the roll. Examples include
thread in textiles, paper and printing, and
electrical wire winding on transformers. A vector
drive can replace inaccurate and inefficient brake
systems when torque control is required.
A relatively new application where electric motors
are subject to variable loads at variable speeds is
in hybrid electric vehicles. A hybrid electric
vehicle couples an internal combustion engine with
an electric motor in order to increase fuel economy.
The average increase in fuel economy of the hybrid
vehicle over its conventional equivalent is about
30%. The electric motor system in these vehicles
requires a sophisticated motor controller.
Currently, hybrid electric vehicles use relatively
expensive motors and controllers to achieve the
performance and efficiency expected by the market.
The initial cost of a hybrid vehicle is about $2,500
to $3,000 more than the traditional model.
Hybrid vehicles represented only 1.2 percent of the
total vehicles sold in 2005. However, hybrid vehicle
sales are projected to grow rapidly. Since the
introduction of the Toyota Prius in 2000, hybrid
vehicle sales have generally doubled each year. The
ABI Research & Automotive Technology Research Group
predicts that 5% to 6% of all vehicles sold in the
United States will be hybrids by 2013, assuming fuel
costs continue to increase following historic
trends4. Therefore, consumers should expect electric
motors used in more vehicle types in the future.
The purpose of this background information is to
clarify that electric motors are ubiquitous in
modern society. They are in our homes, our
businesses, our factories and our vehicles. Many of
these motor driven systems are operating at less
than maximum efficiency and could benefit from a
variable speed drive. Therefore, there is a clear
market need for a low cost, energy efficient
controller.
Potential Impact
As stated above, motor driven systems consume an
enormous amount of energy. Yet many of these systems
could be more efficient if they used a variable
speed drive. The U.S. Department of Energy estimates
that improved system controls including variable
speed drives could save more than 20% of
manufacturing motor system energy use in pump, fan
and compressed air systems5. This represents nearly
15,000 GWh per year and potentially $900 million per
year in energy savings.
In common fan applications like those in residential
HVAC systems, adding a variable speed drive can
reduce energy use in several ways. The power
required to turn a centrifugal fan is theoretically
proportional to the cube of the fan speed. So half
speed requires only one eighth the input power. In
reality, this is closer to a squared relationship,
i.e., half speed equals one fourth power. With an on
/ off control method, the motor operates at full
power for a brief period of time to move a certain
volume of air to adjust the temperature at the
thermostat. Therefore, the amount of heating or
cooling provided to the conditioned space is
proportional to the volume of air delivered to that
space. And volume is directly proportional to fan
speed. So if a house requires a certain volume of
air throughout the day then delivering that volume
at lower speeds consumes less power but still meets
the heating or cooling need of that space.
Continuously operating a fan at half speed uses one
quarter of the energy required to cycle the fan on
and off for the same airflow. This translates into
reduced operating costs for the same heating or
cooling load. Depending upon utility rates and
airflow requirements, adding a variable speed drive
to a home HVAC system could save several hundred
dollars each year in operating costs.
In addition to increased energy efficiency, a
modular motor drive platform can result in
substantial non-energy savings for industrial
facilities. Most manufacturing plants have multiple
brands and models of variable speed drives
throughout the facility. This increases their spare
parts inventory and increases their maintenance
training requirements (i.e., personnel need to learn
multiple systems). However, a modular drive platform
that used a common interface and only required
different power modules for different motor sizes
could decrease overall maintenance costs assuming
comparable maintenance requirements between the
modular system and other variable speed drives.
A low cost, modular drive system could clearly have
a very large impact on energy use and industrial
maintenance costs.
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