WO1994017586A1

WO1994017586A1 - Single-phase induction motor safety controller

Info

Publication number: WO1994017586A1
Application number: PCT/US1993/000394
Authority: WO
Inventors: Gary C. Heath
Original assignee: Condyne Technology Inc
Current assignee: Condyne Technology Inc
Priority date: 1993-01-19
Filing date: 1993-01-19
Publication date: 1994-08-04
Anticipated expiration: 1995-07-19
Also published as: AU3584293A

Abstract

An electronic control apparatus to operate an alternating current induction motor (10) protecting same from power line blackouts, brownouts and providing self-adjusting, linearized, non-stepped reduced voltage output coinciding to work load to enhance efficiency, thereby reducing electrical energy used by the motor (62). This apparatus can be utilized in conjunction with a refrigerator (58), air conditioner or almost any home appliance to yield substantial savings in electrical use.

Description

SINGLE-PHASE INDUCTION MOTOR SAFETY CONTROLLER

Background of the Invention

This invention relates to motor control system and more particularly to

single-phase alternating current induction motors.

Although pulse-width modulated motor control systems are well known

for control of single-phase motors and their fluctuating loads, such systems

require field adjustments to satisfy varying applications. Moreover, the erratic

operation from stepped function gate control used by prior motor controllers,

along with loading excursions beyond field adjustability, degrades system

performance and can damage motor and adjacent mechanical apparatuses.

Important considerations for any motor control should also involve means of

sensing and reacting to existing power line conditions and load side

characteristics to protect the motor from catastrophic failure and extend the life

of same. Also, a motor controller should protect air-conditioning and

refrigeration motors when a short power outage brings a compressor on under

high lead pressure, which could cause damage and reduce motor life.

The prior patented art includes the following patents related to motor

control apparatuses.

U.S. Patent No. Inventor Issue Date

4,052,649 Nola 10/04/77 3,307,084 Ogle 02/28/67 4,788,485 Kawagishi 11/29/88 3,124,734 Sampietro 03/10/64 3,105,180 Burnett 09/24/63 3,775,652 Bowler 11/27/73 4,186,334 Hirata 01/29/80 3,758,836 Shibata 09/11/73 3,763,417 Johnston 10/02/73

Although the Nola patent provides a motor control, the Nola device must

be set manually in the field for each motor application, as does the other prior

art, because the devices do not automatically adjust to the AC motor as does the

present invention. Field adjustment requires that an amp meter be used to set

the prior devices each time when it is in the field.

In addition, the Nola patent operates differently in that it utilizes a step-

function approach to the control of the motor, whereas the present invention

operates linearly in real time. Moreover, none of the above patents provide

protection to the motor in a brownout situation, which could cause a motor to

churn and thereby malfunction. On the other hand, the present invention shuts

off the motor in voltage situations which are less than that required by the

motor. Furthermore, the present invention provides for a delayed start-up of

the motor once power is returned.

Thus, none of the prior patented inventions provides the full range of

controlling a motor in an automatically-adjustable manner as does the present

invention. Summary of the Invention

The primary object of the present invention is to provide an electronic

means to automatically adjust input power to a single-phase induction motor.

A corollary object of the present invention is to provide the most efficient

means of adjusting electrical power input in conjunction with varying input

voltages and loading.

Another object is to provide an on-delay for full power in blackout

conditions or initial start-ups.

A further object is to provide a means of shutting off power to a motor

in low voltage brownout conditions.

An even further object is to provide an over-current detection means

which overrides reduced voltage runs to supply a full voltage source for a

motor.

An additional object of the present invention is to provide an auxiliary

circuit means to act as an off delay to stop power to the motor to relieve high

head pressure start-ups in refrigeration or air conditioning applications.

The present invention accomplishes the above and other objects by

providing an electronic controller apparatus for alternating current induction

motors which provides means for sampling voltage and current inputs from an

electrical source to the motor, said means being connected to the input line, the sampled voltage is rectified and compared to reference voltage provided by a

regulator. At the same time, the sample current is also compared to pre-set

reference currents to determine if the current is proper to operate the motor.

If the volt age and current are within acceptable limits, then they are provided

to the motor. After the motor is operating, the load requirements of the motor

are continuously monitored and the voltage and current are continuously

adjusted in accordance with the load requirements of the motor, whereby the

motor uses a lower average voltage and current, thereby consuming less

electrical p owe r. The present invention further provides optional means for

delay and re-commencement of electrical power from the electrical power

source after a voltage interruption caused by the power source dropping below

a pre-set voltage. The latter is accomplished by means of an auxiliary time-

delay circuit built into the present invention.

The above objects and advantages of the present invention will become

more readily apparent when a preferred embodiment is discussed in detail in

conjunction with the drawings.

Brief Description of the Drawings

The drawings used in conjunction with the detailed description of the

preferred embodiments in order to provide a complete understanding of the

present invention and its advantages are as follows:

FIG. 1 is a block diagram of the system of the invention;

FIG. 2 is an electronic schematic diagram of the invention;

FIG. 3 illustrates the various signals produced in the invention shown

in FIGS. 1 and 2 as follows:

FIG. 3a shows the AC sine wave voltage supplied to the invention;

FIG. 3b shows the full wave rectified signal present at point 3b of FIG.

2;

FIG. 3c shows the zero-crossing voltage detector output present at point

3c of FIG. 2;

FIG. 3d shows the current of the motor being controlled by the

invention;

FIG. 3e shows the zero-crossing detector input and output current into

the monstable circuit at point 3e of FIG. 2 and out of the Nonstable at point 3f

of FIG. 2.;

FIG. 3g shows the signal when the triac 12 of FIG. 2 is on, which is

also the input to the opto-coupler 23 of FIG. 2 and at point 3g of FIG. 2; FIG. 3h shows the time periods when the triac gate is conducting;

FIG. 3i shows the auxiliary time delay 50 in FIG. 2 which, with its

signal preset 3h of FIG. 2 to inhibit the nor gate 24 of FIG. 2;

FIG. 3j shows the action of the current surge detection circuit with a

superimposed high current wave form which engages the one-shot 26 of FIG.

2;

FIG. 4 shows the apparatus in use with a refrigerator or other appliance;

and

FIG. 5 shows a hand-wired version of, the apparatus as it would be

connected to an induction motor for various applications, such as air

conditioning, compressors, pumps and industrial applications.

Description of the Preferred Embodiments

Referring to FIGS. 1 and 2 of the drawings, an AC induction motor 10

is powered by input voltage 11 through a triac 12. Alternatively, the motor

10 can also be powered through back-toback Scrs rather than the triac 12. A

step-down type transformer 20 reduces the line voltage to approximately 8

VRMS. A full wave bridge rectifier 21 then provides a rectified full wave

signal of approximately 11 volts peak to the input of a 5-volt direct current

(DC) regulator 22 and to one input of a voltage input comparator 14 and also to two variable inputs, input 15 of the over-voltage comparator 16, and input

37 of the over-current comparator 40. The DC regulator 22 also provides

regulated +5VDC for the rest of the electronic components. The +5VDC is

also divided down to provide reference voltages 17, 18, 33, and 34 for

comparators 16, 14, 31 and 32, respectively.

The under-voltage comparator 16 and auxiliary time delay circuit 50 will

cause the input to the opto-coupler 23 to remain off whenever the input line

voltage 11 drops below the level preset by resistor 15 or when the output of

comparator 16 is adapted to the auxiliary time delay circuit 50 through output

51. The latter is accomplished by providing a logic high to the NOR 24 to

prevent its output from going high.

Then the rectified output of the full-wave bridge rectifier 21 is compared

to a reference voltage 18 at the input of comparator 14. The output of

comparator 14 is a pulse every half cycle of the input voltage. This pulse

occurs centered around the zero crossing of the input voltage 11. These pulses

are used to set a Bistable 25 and prevent an output from the NOR 24 circuit.

The power on one-shot astable 26 and over-current comparator 40 with

its preset resistor 37 gives a logic high to the input of opto-coupler 23 for a

period of approximately 45 seconds. This holds the triac 12 fully on for this

period to provide full electrical power and allows the motor 10 to come up to speed with full power applied. The motor 10 could be the AC motor in a

refrigerator, air-conditioning or other appliance.

A sample of the voltage across the triac 12 which represents the current

through it and the motor 10 is fed through the dual comparators 31 and 32 to

monitor both polarities of the current. These comparators function to determine

the zero-crossing points of the current. When the current wave form crosses

through zero, a pulse is output from the OR 35 circuit. This occurs 8.33

milliseconds for a 60Hz input voltage.

Then these pulses are used to trigger a monstable or one-shot circuit 36.

The duration of the one-shot signal output is present at the manufacturing of the

system, but is nominally set to be 1-3 milliseconds wide. This output pulse (a

logic high) resets the Bistable 25 and provides a logic high to NOR 24. This

output high, even though the other two inputs are now at logic low, outputs a

logic low to the opto-coupler 23. This means the triac 12 is not turned on for

this duration (nominally 2 milliseconds). The result is a 2 millisecond delay

from the time the motor current drops to zero (and the triac turned off) and the

triac 12 turns on and applies voltage to the motor 10. This, in turn, means a

lowered average voltage and current and less power consumed by the motor.

As illustrated in FIG. 3, a-h, when the load of the motor increases, the

zero-crossing of the current approaches the zero-crossing of the voltage and the delay has less and less effect as the 2-millisecond delay now represents less and

less voltage being missed before turn on of the triac 12.

In actual application and operation, the circuitry described hereinabove

is incorporated into a compact, motor-control plug-in device 52 as illustrated

in FIG. 4. The device 52 can be plugged into a regular household wall socket

next to the appliance on which the device is being used. For instance, in FIG.

4, the device 52 is shown being utilized for a refrigerator 58. The electric cord

57 from the refrigerator 58 is plugged into the bottom or side of the device 52.

In this particular application, of the device 52 will also contain a heat sink 53

on the back thereof for cooling purposes. In the hand-wired version, a heat

sink may be contained on the side of the device. On its face 54, the device 52

may contain an indicator light 55 which would be illuminated when the unit is

engaged or to show a fault. An additional light 56 may also be included on the

face to indicate when the unit is actually saving energy. An on/off or override

switch 41 may also be optionally provided to shut off the unit when its use is

not desired, particularly in the hand-wired version of FIG. 5.

Although the device 52 is illustrated as a stand-alone unit when utilized

with refrigerator 58 in FIG. 4, in some motor applications, such as in an air-

conditioner, the circuitry of the device 52 incorporating the circuitry would be

hard-wired into the appliance before or after market rather than being plugged into an electric socket as shown in FIG. 4. FIG. 5 shows a hardwire version

of the invention. A barrier strip 66 interconnects the controller circuitry 67 and

the motor 62 via the AC input voltage lines 11. The motor 62 is connected to

the original AC input from external power supply 59 via an electrical line 61

and tie in 61. The hot input line 59 is also tied into the barrier strip 66 at 68.

The original neutral line 63 is disconnected from the motor and the neutral

electrical line 64 is tied in at 65 to the neutral input line to barrier strip 69.

The motor 62 connects directly to the barrier strip at 70 from which the motor

receives its input from the controller circuitry 67. An optional override switch

41 is provided for shutting of f the circuit. The barrier strip 66 is connected

to the triac 12 which is in turn connected to the controller circuitry 67.

It should be apparent from the above-detailed description of the preferred

embodiment of this invention that there has been provided a novel and non-

obvious AC induction motor control device which offers numerous advantages

and benefits. Among the advantages and benefits provided by the present

invention, is that it continually adjusts to the minimum current necessary to run

a particular motor with no loss of motor function, thereby providing maximum

savings in electricity. Tests have shown the savings range anywhere from ten

to forty percent, depending on the particular appliance to which the invention

is applied. Also, as the motor is provided only the minimum voltage it needs, the motor will run cooler thereby extending the life of the motor. A further

advantage is that the device protects motors from brownout situations which

eliminates motor damage due to low input voltage. Air conditioning units,

refrigerators and other devices utilizing the invention thus run more efficiently.

A further advantage is that this device provides surge and lightning protection

which extends the life of the appliance. An even further advantageous feature

is that this motor controller provides overcurrent protection to an AC induction

motor. A further optional feature is that the device incorporates a start-up

delay to insure maximum starting torque and minimizes surges after a voltage

interruption. This "soft-start" feature enhances the life of the appliance.

Although the above-detailed description has dealt with only one preferred

embodiment of the device, this invention incorporates any and all modifications

within the scope or equivalent of the claims.

Claims

ClaimsHaving thus described my invention, I claim the following:

1. An electronic control apparatus for an alternating

current (AC) induction motor comprising:

a means for sampling voltage input provided by an electrical source

to the motor, said means being connected to an input line from the electrical

source;

a means for sampling current input and detecting over-current

conditions being provided by an electrical source to the motor, said means also

being connected to an input line from the electrical source;

a means for rectifying the sample voltage input taken from the

electrical source to yield a rectified output voltage;

a means for camparing the rectified voltage to a reference voltage

provided by a regulator;

a means for camparing the sampled current input to a preset

reference current from the electrical power source; and

a means for continuously monitoring the voltage and current loads

of the motor, said means connected to the input line of the motor, whereby the

motor uses a lower average voltage and current so that less power is consumed

by the motor.

2. The electronic control apparatus of claim 1 , further comprising:

a means for delaying re-cornmencement of electrical power from

the electrical power source after a voltage interruption caused when the voltage

from the power source drops below a pre-set voltage.

3. The electronic control apparatus of claim 1 or 2 wherein the means

for sampling voltage input compromises a transformer which reduces line

voltage through a full wave range rectifier, which in turn provides a rectified

full wave signal to a direct current regulator.

4. The electronic control apparatus of claim 3 wherein the means for

sampling current input and detecting over-current conditions comprises a

comparator connected between the motor and electrical power source which

compares the current input to a reference current preset by a variable resistor.

5. The electronic control apparatus of claim 4 wherein the means for

rectifying the sampled voltage input consists of a transformer which reduces line

voltage to provide same to a fullwave bridge rectifier to yield a rectified full-

wave signal.

6. The electronic control apparatus of claim 5 wherein the means for

comparing the rectified voltage output consists of a comparator that compares

voltage output from the rectifier to a reference voltage.

7. The electronic control apparatus of claim 6 wherein the means for

comparing the current input to preset reference current consists of a comparator which compares the current input to the preset current provided by a resistor

network.

8. The electronic control apparatus of claim 1 wherein the means for

continuously monitoring the current and voltage loads of the motor consists of

a set of comparators in line with the input to the motor which, when the voltage

drops below a set value, a preset monstable is triggered to reset a Bistable and

turn off a triac so that the electrical power source to the motor is interrupted.

9. The electronic control apparatus of claim 3 wherein the means for

delaying re-commencement of electrical power consists of a time delay circuit

connected between an undervoltage detector and logic circuit.

10. A method of continuously monitoring the mini-mum voltage and

current requiements of an AC motor and providing those requirements to the

motor, comprising:

sampling incoming voltage and current provided by an electrical

source to the motor;

determining by comparison to a preset reference voltage and

current whether the incoming voltage and current is within limits for the motor;

if voltage and current are determined to be within limits, then

providing said voltage and current to the motor;

automatically continuously checking a load on the motor during its

operation after the voltage and current are provided; and

\ A automatically continuously resetting the voltage and current

provided to the motor according to the load on the motor during its operation.