 |
Description  |
|
|
FIELD OF INVENTION
My invention relates to the field of ENERGY CONSERVATION through ENERGY
SAVINGS obtained by reducing the level of commercial electrical power
ordinarily WASTED in routine daily operation of hundreds of millions of
electric induction motors.
My invention pertains to the variable control of electrical power fed to
a.c. electric induction motors, and in particular to the instantaneous
modulation of the electrical power flow in proportion to changes in the
level of any load driven by the motor. My invention reduces the terminal
voltage and hence the power applied to a lightly loaded electric induction
motor, and increases the terminal voltage and applied power as the
induction motor load increases. My invention is fundamentally an ENERGY
CONSERVING apparatus which is intent on reducing energy losses in common
electric motors where such losses ordinarily are the result of excessive
eddy current and winding resistance losses, particularly when the motor is
less than fully loaded.
My invention finds particular utility with air conditioning and
refrigeration equipment, wherein induction motors operate over long
periods of time and under widely varying load conditions.
My invention is in particular an ENERGY SAVING contribution which lessens
the need for additional nuclear and conventional power generating plants
if the invention is implemented in mass-produced major appliances, such as
air conditioners and refrigerators in particular. For example, according
to the American Council for an Energy Efficient Economy (ACEEE)
"refrigerators alone use seven percent of the whole U.S. electricity
output. (Arthur Fisher, "How to Help Reduce Greenhouse Gases", Popular
Science magazine, October 1989, page 53). Therefore, a mere 20% reduction
in overall electric power consumption by the 125-million or so domestic
refrigerators in use today (whereby the reduction might be obtained over a
period of time through the inclusion of my invention as a feature in new
refrigerators, as old models are replaced with new models) which could
result in conservation of more electricity than what at least several
major nuclear power plants can produce, assuming the average refrigerator
now draws about 300 watts and runs about 20% of the time. More
particularly for example, merely during the month of May 1989 more than
686,200 refrigerators were "shipped" (Appliance Manufacturer magazine,
August 1989, Page 8) which, through simply using the ENERGY SAVINGS of my
invention could have saved through conservation more than eight megawatts
of on-line power generating capacity! Obviously, my invention can
contribute even greater savings in air conditioning power consumption,
etc. As a result, my invention may contribute significantly to the
reduction of atmospheric pollution, the attendent deleterious "greenhouse
effect" and the occurance of acid rain; all without the drawback of
causing any noticable change in public lifestyle.
BACKGROUND OF INVENTION
Alternating current electric motors, and particularly a.c. induction
motors, tend to waste a considerable amount of electric power when
operating with anything less than a full load coupled with their output
shaft. Induction motors are the mainstay of certain widespread
applications: in particular, they are almost universally used in
refrigerators and air-conditioners because they have many features which
make them attractive for inclusion in the usual unitized "hermetic"
motor/compressor assembly typical of such appliances. Such features
include proven reliability, absence of brushes, simple and cheap
construction, relatively quiet operation, and a good history of
predictable design performance. Induction motors also find widespread
application in other domestic and commercial appliances, such as washing
machines, clothes dryers, dishwashers, pumps, compressors, and so forth.
Again, their advantage is cheap, simple design and predictable
performance.
Induction motors are particularly prone to ENERGY LOSS when operating with
less than full load. A typical 1/3-horsepower induction motor, which might
be typified by a General Electric model H35JN30T, draws about 6.6 amperes
under full load and exhibits a power factor of about 80% or so. Under
light load, and particularly under no-load, this same motor exhibits
miserable actual efficiency because the internal losses remain high while
the output power demanded from the motor lessens. Although the power
factor may drop to 30% or so, the apparent current still remains high . .
. on the order of 4.9 amperes. As such, even though the 607 watts draw
under full load may drop to about 170 watts under no-load: it is the range
of operation between full load and this later no-load (or lightly loaded)
value which is the basis for considerable improvement in my invention. At
half-load, the power draw remains high, being nearly 360 watts. The
following BASIC computer routine may be used to determine not only running
efficiency, but also wasted power:
__________________________________________________________________________
10 REM MOTOR EFFICIENCY DETERMINATION
MOTEFF-1.BAS V1.01
20 REM MBASIC-80 (c) H. Weber K1VTW 9/9/89
30 PRINT CHR$(27) + "[2J"+ CHR$(27) + "[f"
' clear screen and home cursor
40 PRINT "Enter A.C. LINE VOLTAGE:
";:INPUT LV
50 PRINT " Motor OUTPUT (Decimal H.P.)
";:INPUT HP
60 PRINT " APPARENT Motor CURRENT
";:INPUT MI
70 PRINT " ACTUAL POWER FACTOR
";:INPUT PF
80 EF = ((74600!/(MI*LV*PF))*HP)*100
90 PWX = (MI*LV*PF*(100-EF))/10 4
100 PRINT:PRINT "MOTOR EFFICIENCY is:
"EF" percent"
110 PRINT "WASTED Motor POWER is:
" PWX "watts"
120 PRINT:PRINT:END
__________________________________________________________________________
Using this routine, you will obtain the following display when entering
full-load and half-load values:
______________________________________
Enter A.C. LINE VOLTAGE: ?
115
Motor OUTPUT (Decimal H.P.) ?
.333
APPARENT Motor CURRENT ? 6.6
ACTUAL POWER FACTOR (percent) ?
80
MOTOR EFFICIENCY is: 40.9121 percent
WASTED Motor POWER is: 358.782 watts
______________________________________
Enter A.C. LINE VOLTAGE ?
115
Motor OUTPUT (Decimal H.P.) ?
.167
APPARENT Motor CURRENT ? 5.8
ACTUAL POWER FACTOR (percent) ?
55
______________________________________
It is well known that eddy current losses and winding losses contribute
most of this power waste, particularly when operating under less than full
load. This power waste appears as heat, producing "temperature rise"
within the motor structure. Also known is that the apparent current (e.g.,
5.8 amperes at half-load) must circulate through the winding, and the
induced magnetic field must magnetize the core material of the stator. It
is only that the energy stored in the inductance of the core "returns"
energy to the system that some semblence of efficiency is obtained,
observable as low power factor manifested as phase lagging current flow.
Large power loss occurs because the apparent current flow must overcome
all the possible "friction" losses of the core material and the winding
resistance. In cheap commercial motors particularly, these losses can be
substantial. Economy motors are designed to operate with high current
density in their windings, and with near-saturation of the core material.
When an ordinary induction motor is lightly loaded, the rotor "speeds up"
with the result that the stator inductance actually tends to increase,
resulting in the low power factor intrinsic with unloaded or lightly
loaded induction motor operation. Clearly it would be better if the
motor's rotor did not speed-up, but instead that it would continue to slip
or drag by about the same amount under light load as what it does under
full load. By reducing the applied stator voltage, the field is weakened
and the rotor torque is lessened resulting in this desirable condition of
slip or drag. The benefit is that the current power factor remains high,
nearly that obtained under full load with full power applied. Mere
reduction of the applied stator voltage is, by itself, unacceptable in
most motor applications because any unexpected increase in motor loading
can result in stalling and unsatisfactory operating characteristics, and
can even lead to motor burnout.
Modern high-permeability core materials may also exhibit a somewhat more
abrupt "knee" where saturation occurs. With an economy design approach,
wherein the operating point for the core material making up the motor's
stator structure is established with a high flux density under normal line
voltage, it can be seen that an unsual increase in line voltage can bring
about a very serious decrease in efficiency as saturation of the core
material is approached. Under such a condition, the increased line voltage
contributes nothing except power waste to the overall operation of the
motor. Such losses tend to be regenerative, in that the mentioned increase
in losses produces more heating, which in turn increases the losses (i.e.,
winding resistance loss, etc.).
Electric utility companies frequently introduce "brown-out" conditions
during peak-usage periods or during unseasonable load demand periods (such
as most notably, during a hot and humid summer period when
air-conditioners are working hard). In the ordinary motor construction,
such a brown-out condition can cause failure of induction motors, with
stalling and overheating. My invention might be useful in overcoming these
brown-out attendant problems, at least in critical applications where the
stoppage of a motor can not be afforded. For example, in this kind of
"brown out resistant" configuration the motor may be designed to produce
its full torque (e.g., horsepower) at a reduced voltage level of say 100
volts and the control system of my instant invention will allow the motor
to still accomodate line voltage operating conditions of 117 or even 125
volts or more without undue electrical loss or malperformance.
Economy motor designs are not only found in motors like the mentioned major
appliance motor, but also they are ubiquitously found in the motors used
in hermetic sealed refrigeration and air conditioning motor/compressor
units. Induction motors of ordinary split-phase or capacitor start design
are known in hermetic units, such as a Whirlpool model S462544/H2269;
General Electric model PS-36-1/4; Americold model ML090-1; Tecumseh model
S4416; Matsushita model FN91F17R, and others.
In my prior U.S. Pat. No. 4,806,838 "A.C. Induction Motor Energy Conserving
Power Control Method and Apparatus" and U.S. Pat. No. 4,823,067 "Energy
Conserving Electric Induction Motor Control Method and Apparatus" I
particularly teach how motor losses may be greatly reduced through the use
of two separate parallel-acting RUN windings. One higher impedance RUN
winding supplies a sufficient portion of the field strength flux to
operate the motor under partial load, while the other lower impedance RUN
winding is modulated with a.c. power to increase the field strength flux
as the motor load increases. In the '838 patent, I sense the power factor
of the motor and as the power factor decreases when the motor loading
lessens, I reduce excitation to the modulated RUN winding thereby
increasing the apparent power factor. In my other '067 patent I utilize
load-related changes in sub-synchronous motor speed slip to establish
corresponding changes in the modulated RUN winding excitation.
In both of these prior patents a unique motor winding arrangement is needed
in order to obtain increased efficiency. It was not the purpose of these
prior inventions to necessarily be applicable to pre-existing motors, such
as found in refrigerators, air conditioners, and other appliances. It was
more the intent for the invention of these prior patents to provide a
convienent and effective arrangement for manufacturers to use in their new
motor designs in order to obtain a major increase in efficiency.
Older motors may also benefit from the kind of a.c. power control taught
under these prior patents, but in order to do so a motor controller is
needed which can operate to produce a virtual control effect which is
equivalent in ENERGY SAVINGS with that of my prior invention's unique
multiple RUN winding embodiment. I therefore conceived a controller that
produces such improvement, but requires no change in the older motor's
design: e.g., it operates well with merely a single RUN winding
arrangement in the motor.
The need for my current invention is to SAVE ENERGY in pre-existing motor
applications, particularly such as found in air conditioners and similar
equipment.
Manufacturer's of new equipment may also benefit from the ENERGY SAVING
contribution of my invention without having to re-engineer the electric
motor which may already be part of a proven product design, or consist of
considerable inventory.
SUMMARY
Hundreds of millions (say: billions!) of electric induction motors operate
daily, while supplying less than full rated load. Induction motors of
ordinary cheap commercial design (such as found in most consumer products,
like air-conditioners, refrigerators, washing machines, etc.) operate
under internally produced electromagnetic stress even when partially
loaded. Such stress brings about significant eddy current losses in the
stator (field) core structure, and "copper" winding losses in the RUN
windings. Even when operating with less than full load, very considerable
apparent current flow occurs through the windings and acts to magnetize
the stator core structure. Admittedly, power factor lessens when the motor
is lightly loaded, but such power factor decrease gains little in improved
operating efficiency of the windings and the core material since it is the
level of apparent current flow which determines eddy current and copper
losses. It is the net inductance of the winding arrangement which serves
to "return" power to the line, albeit of lagging phase. The magnetization
of the core by the apparent current flowing through the windings continues
to introduce considerable frictional losses which may be likened to
lowered "Q" of the inductive field (resulting in dissipation of power in
each the stator core material, and in the wire comprising the RUN winding.
Common economic practice dictates engineering the stator structure and the
associated RUN windings to operate near saturation. High a.c. magnetic
fields produce considerable losses as the core material nears saturation
during a portion of each cycle of the exciting a.c. waveform.
Additionally, the nearly-saturated core material gives a "shorted turn"
effect to the RUN winding (i.e., the stator winding inductance is
lessened), increasing circulating current through the RUN winding and
introducing substantial resistance loss.
Through the expedient of reducing the motor terminal voltage and resulting
excitation, the characteristics of an ordinary induction motor shift
considerably. Torque is of course reduced, as is horsepower potential.
More importantly though is that reduced peak excitation of the RUN winding
removes a considerable portion of the eddy current loss, because the
magnetizing field is less intense. In a like way, winding loss is reduced
because the reduction in near-saturation of the stator core results in a
higher "Q" of the RUN winding, resulting in more efficient energy use.
Merely reducing the applied motor voltage does not ordinarily work. The
reduced torque can cause stalling, or problems in start-up. What is needed
is an approach where full motor voltage is applied when the motor is
working hard, as when driving a full load. In less than full load
operation the motor voltage may be reduced in proportion to any load
decrease, with substantial advantage gained in motor efficiency and with
negligible change in operational performance.
In another earlier U.S. Pat. No. 4,052,648 (and U.S. Pat. No. 4,266,177)
issued to Frank Nola, phase-angle modulated a.c. power control of the full
applied motor current in proportion to motor loading (as determined by
a.c. power factor measurement) is taught as providing improvement in
efficiency. What resulted however was less than optimum realizable
performance because his phase-angle controlled power (delivered by mere
phase-angle thyristor control of the RUN winding power, much like the
control afforded by a "light dimmer") introduced severe a.c. power
waveform distortion and resulted in harmonic losses which adversely acted
to offset any gain proposed by the invention, when used in common
applications. Such abrupt pulsing of the a.c. power line caused all kinds
of losses in wiring, circuit capacitance, and in addition introduced noise
pulses into the utility line which could produce radio interference
(buzzing) and noticable light flicker. While these later shortfalls could
possibly be overcome by appropriate power line filtering, such additional
steps were both costly and bulky. More objectionably, the sudden pulsing
of the stator core of the motor (when the motor was of ordinary commercial
construction) appears to lead to increased losses introduced by the
"fast-rise" character of the leading edge of the thyristor controlled a.c.
power pulse. In effect, the eddy current losses increased. Quick turn-on
of substantial power as thyristor controlled pulses in the Nola controller
also leads to magnetostrictive forces of considerable magnitude in the
stator core material, which manifest as a "buzz" like noise. The triac
thyristor used by Nola also had to have substantial ratings, since it had
to handle the full motor current and the stress of the full peak line
voltage.
Now comes my instant invention which teaches an unprecedented approach
wherein a.c. power line distortion is kept to a minimum, in which
considerable a.c. power flow continues to flow over the full swing of each
a.c. power cycle, while the modulated portion of the controlled power flow
is cushioned by the greater full-cycle power flow and as a result
negligible harmonic losses occur and other related problems are
sidestepped.
In my invention most of the induction motor's operating current is drawn
over the full a.c. power cycle, and only a lesser portion of the a.c.
power is modulated by a semiconductor switch (such as a thyristor or power
transistor). As such, the substantial power draw obtained over the full
a.c. power cycle serves to efficiently swamp-out the lossy effects which
might otherwise occur due to phase angle modulated a.c. power control of a
lesser portion of each cycle of the a.c. power waveform as may be caused
to change between partial and full load operation of the motor. I have
obtained this improved more ENERGY EFFICIENT operation, without the
shortfalls of the prior apparatus of Nola and others known to me, and
without the separate dual RUN windings of my prior patents. I have
obtained this improvement mainly through the novel inventive act of
contriving a reactance in series with the motor's main RUN winding and
regularly changing the voltage dropping effect of the reactance in
proportion to changes in instant motor loading, as might be sensed through
changes in power factor or speed slip.
My invention provides reactive control of the power applied to the motor
RUN windings through a small inductor (i.e., a choke coil) coupled in
series between the a.c. power line and the windings. The inductance of the
choke is selected to provide a suitable voltage drop under minimum motor
load to maintain smooth motor operation: in practice for a 117 volt a.c.
motor, I have found that a choke that provides a voltage drop on the order
of 16 to perhaps about 34 volts can be used. The exact voltage drop is
best determined by selective tradeoff between the operating
characteristics of a particular motor design and the range of overall load
variation which it will drive. In practice, I have found it convenient to
operate the motor through a Variac, and to reduce the voltage until the
desired motor operating point is found. The difference between the reduced
voltage level and the normal line voltage may then be used to define the
voltage drop which is desired to be obtained across the choke. Through
measurement of current flow under the reduced 60 hertz power voltage
condition, the inductance may be (at least roughly) determined by:
L=EA/(IA.times.6.28.times.60)
where:
L=choke inductance, henries
EA=reduced voltage level
IA=current with reduced voltage
As a practical matter, I have found that a choke comprising about 100 turns
of 20 guage magnet wire wound on a 7/8".times.7/8" EI construction
transformer style iron core suits a particular 1/6 horsepower compressor
motor that is rated for 4 amperes under 115 volt a.c. operation.
The inductance afforded by the choke may also be provided by the low
impedance "primary" winding of a transformer, which includes an
inductively coupled higher impedance "secondary" winding. The higher
impedance secondary winding may then be shunted with a capacitor, with the
result that improved a.c. power waveform is had, and semiconductor switch
(e.g., thyristor) commutation is reliable.
A transformer having "step-up" configuration (either having separate
windings or of autotransformer configuration) may also be coupled to have
a relatively low impedance primary winding in series with the motor's RUN
winding, while the transformer's higher impedance secondary winding is
changably shunted (shorted out) by a thyristor or transistor switch. When
the secondary is shorted, most of the available a.c. power couples
directly through the primary winding as though it were a very low
impedance. The real impedance is mainly that of a smallish losses incurred
in the transformer primary and secondary winding resistance, and any
intrinsic leakage inductance. Some small portion of power loss may also
occur in the transformer, due to winding losses and eddy current losses in
the core material. In the usual practice of my invention, such winding and
eddy current losses are tiny compared to the magnitude of winding and eddy
current losses obtained in an un-controlled motor's operation. The
principal advantage of this hookup is that the semiconductor switch
(thyristor or transistor) handles less current, and therefore may be of
smaller construction.
A purpose of my invention is to teach ENERGY SAVING power reduction in the
operation of less-than-fully loaded electric induction motors.
Another purpose of my invention is to show how such ENERGY CONSERVATION may
be obtained from ordinary electric induction motors without re-engineering
the motor's construction.
My invention aims to improve the electrical efficiency of induction motors
through reduction of eddy-current and winding resistance losses when the
motor is less than fully loaded.
The fundamental essence of my invention involves the use of an inductor
which presents an impedance in electrical series with the current flow
coupled with an ordinary electric induction motor, together with a phase
angle controlled thyristor or transistor switch which shunts-out a portion
of any voltage drop developed across the inductor (during each a.c. power
half-cycle) in proportion to changes in motor loading.
My invention's embodiment is taught to use a transformer having a
relatively low-impedance primary inductance coupled in series with power
flow to the motor, and a higher inductance secondary the instant impedance
of which is continuously modulated by the phase-angle controlled switching
action of a thyristor or transistor.
My invention also aims to provide ENERGY SAVING improvement of ordinary
induction motor designs, including the split-phase, capacitor start,
permanent split capacitor, and shaded-pole configurations.
My invention serves to show particular adaptation to hermetic refrigeration
compressor motors, in which an induction motor operates in a sealed
environment over long periods of time and under widely varying load
conditions.
My invention further aims to obtain aftermarket application of ENERGY
SAVING electrical power consumption reduction to major appliances, such as
air-conditioners.
Importantly my invention divulges a method of operation and apparatus
suited for obtaining such operation which is stable and predictable,
preferably using digital circuit elements which may be predetermined to
have desired operating characteristics without requiring production-line
or field adjustment.
Furthermore my invention reduces a.c. power line distortions, including
deleterious harmonic energy, to negligible proportions unlike previously
known energy conserving motor control devices.
DESCRIPTION OF DRAWINGS
FIG. 1--Slip-speed load sensing control of appliance type induction motor.
FIG. 2--Waveforms of controllers for providing energy savings.
FIG. 3--Block diagram for slip-speed sensor type of energy controller.
FIG. 4--Schematic for circuit based upon FIG. 3 block diagram.
FIG. 5--Waveforms associated with circuit of FIG. 4 showing operating
levels.
FIG. 6--block diagram for alternate configuration of slip speed type of
energy controller.
FIG. 7--Schematic for circuit based upon FIG. 6 block diagram.
FIG. 8--Waveforms associated with circuit of FIG. 7 showing operating
levels.
FIG. 9--Circuit for slip-speed sensor type of energy controller providing
multilevel power modulation.
FIG. 10--Power control portion of circuit depicted in FIG. 9.
FIG. 11--Block diagram for controller employing power-factor changes as
load sensor.
FIG. 12--Schematic for circuit based upon FIG. 11 block diagram.
FIG. 13--Hermetic compressor motor having pressure or vibration sensors as
speed pickups.
FIG. 14--Circuit detail for vibration sensor connection with circuit of
FIG. 7.
FIG. 15--Three-phase motor having energy saving controller operation.
FIG. 16--Controller using MOSFET switch for power control.
FIG. 17--Waveforms which depict operation of circuit of FIG. 16.
FIG. 18--Controller having pre-programmed control by a timer which sets
motor operating level relative with predetermined load levels.
DESCRIPTION OF MY INVENTION
In FIG. 1, my invention is depicted in conjunction with a split-phase motor
10 such as used in a hermetically sealed refrigeration motor compressor
assembly. Such a hermetic motor unit may be typified by a model T37CN
motor/compressor found in certain Westinghouse refrigerators, or a
Kelvinator model A045 motor/compressor. The motor includes a RUN winding
12, and a START winding 14. A speed sensor 20 is coupled 18 with the motor
and is effective to determine the rotational speed of the motor's rotor.
The sensed speed information produces a signal on line 22 that couples
with the input of a performance computer 30, together with reference
frequency and power signals provided on lines 32-1 and 32-2 from an a.c.
power line that couples with terminals L1 and L2. The performance computer
performs to produce a gate turn-ON signal on line 42 whenever the motor
speed is less than a predetermined (usually full-load) speed value.
Conversely of course, the signal on line 42 is disabled for part or all of
the a.c. power cycle whenever the motor speed exceeds a predetermined
speed value, as it normally does under light load conditions. The gate
signal on line 42 couples with the gate of a semiconductor switch (e.g., a
thyristor such as a triac) 50, the power terminals MT-1 and MT-2 of which
couple in parallel with a power reactor 55. The inductance of the reactor
is preferably sized to produce about 10% to 20% voltage drop between its
terminals due to the current flow produced by the motor's RUN winding 14
which is drawn through the reactor. When the thyristor switch 50 is
turned-ON by the signal on line 42, the reactor's inductive voltage drop
is reduced almost to nil, being limited to merely the voltage drop
developed across the turned-ON thyristor. A motor starting relay 60 is
shown to have a coil (between terminals R1 and L2-1) coupled in series
between the motor's RUN winding 12 (line L2D) and the reactor 55 (line
L2C). When power is initially applied to the circuit, as might be done
when the control switch 70 (viz, a thermostat, timer, or other such
device) contacts CLOSE feeding power to line LZA, overcurrent is drawn by
the RUN winding due to the motor's rotor being stalled (or running at
substantially less than normal speed). The relay (as is usual practice) is
sized such that the motor's overcurrent condition produces pull-in of the
relay's armature, closing the normally-open contact sets 64 and 66.
Contact set 64 couples a.c. power to the START winding 14, thereby
producing the necessary rotational torque needed to "start" the motor. The
other contact set 66 shunts the power reactor and thyristor, thereby
bypassing the heavy starting current from flowing through the thyristor. A
snubber capacitor 57 serves to reduce any transient spiking which may be
produced by the thyristor 50 turn-ON, thereby improving the a.c. power
waveform and assuring more reliable operation of the thyristor.
FIG. 2 depicts electric power waveforms produced by the prior art as
compared with my instant invention. The uppermost waveform EA shows
waveforms characteristic of common 60-hertz commercial utility power. When
the invention taught by the mentioned Nola U.S. Pat. Nos. 4,052,648 and
4,266,177 is used to control a motor, the abruptly turned-ON waveforms MA
occur. For example, in Nola's '177 patent when the triac 16 turns-ON MAT
the partial waveform MAA is produced. As can be seen, the turn-ON is
abrupt and the waveform which results is highly distorted: the result is a
power switching circuit which is rich in harmonics and introduces
substantial losses into the load 14 which largely degrades any
power-conserving advantage which the circuit might otherwise afford. For
various phase-angle delays (i.e., power factor changes) which are sensed,
various duration power "pulses" MAB; MBA, MBB; MCA, MCB; MDA, MDB; MEA
result . . . each of which are highly distorted partial cycles of power
flow.
The waveform NA of FIG. | | |
