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Claims  |
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What is claimed is:
1. A system for starting an electric motor having a main winding and a
start winding comprising,
a solid state switch having a gate and having a first and second main
terminals connectable in series with the start winding to control
energization thereof,
control apparatus comprising
a power supply for providing a DC bias voltage,
trigger means coupled to the gate for providing a signal to the gate to
turn on the switch and energize the start winding, the trigger means
turning on the switch upon energization of the motor from an at rest
condition,
measuring means to continuously measure a wave form of one of the main
winding current and start winding voltage, the measuring means integrating
the entire value of each half cycle of one polarity, the measuring means
including an operational amplifier, a transfer gate having an output
connected to an input of the operational amplifier, a first capacitor
coupled to the transfer gate, means to take a plurality of differential
samples of one half cycle of the wave form and apply the samples to the
first capacitor, a second capacitor connected between an input of the
operational amplifier and its output and means after each differential
sample to turn on the gate connecting the first capacitor to the second
capacitor to transfer the charge on the first capacitor to the second
capacitor while the wave form is of one polarity so that at the end of the
half cycle the output of the operational amplifier equals the integration
of the entire half cycle,
calibration means for storing a first integrated value as a calibration
value, and
comparison means for comparing the continuing integrated values to the
calibration value, the trigger means interrupting the signal to the gate
to turn off the switch and de-energize the start winding when the
continuing integrated values reaches a threshold value which is a selected
proportion of the calibration value.
2. A system according to claim 1 including means to derive the first
integrated value by averaging the integrated values of at least two entire
half cycles of the same polarity to minimize the effects of any spurious
wave form.
3. A system for starting a single phase, capacitor start motor having a
main winding and a start winding comprising,
a triac having a gate and having first and second main terminals
connectable in series with the start winding to control energization
thereof,
control apparatus comprising
a power supply for providing a bias voltage,
trigger means coupled to the gate for providing a signal to the gate to
turn on the triac and energize the start winding, the trigger means
turning on the triac upon energization of the motor from an at rest
condition,
measuring means to measure the start winding voltage integrating a
plurality of samples of values of a given half cycle of the wave form,
calibration means for storing a first value of start winding voltage as a
calibration value,
comparison means for comparing subsequent values of start winding voltage,
the trigger means interrupting the signal to the gate to turn off the
triac and de-energize the start winding when the subsequent start winding
voltage values reach a threshold value which is a selected proportion of
the calibration value.
4. A system according to claim 3 in which the calibration value is derived
by averaging the values of at least two entire half cycles to minimize the
effects of any spurious wave form.
5. A system according to claim 3 further including means for maintaining
the calibration value for a selected period of time in the event that
power to the motor is interrupted whereby upon resumption of power to the
motor within the selected period of time the comparison means will compare
the renewed subsequent values of start winding voltage to the calibration
value existing before the power interruption.
6. A system according to claim 3 in which the threshold value of start
winding voltage is approximately 150% of the calibration value of start
winding voltage.
7. A system according to claim 3 in which the trigger means, subsequent to
turning off the triac to de-energize the start winding, will provide a
signal to the gate to turn on the triac and re-energize the start winding
upon the decrease of start winding voltage to a selected re-energization
value.
8. A system according to claim 7 in which the selected re-energization
value is approximately 40% of the calibration value.
9. A system according to claim 3 further including means to disable the
triac after a selected period of on time.
10. A system according to claim 9 in which the means to disable the triac
includes a counter means and further including means to decrement the
counter during normal running conditions of the motor.
11. A system according to claim 3 further including resistance means
adapted to be coupled across the start capacitor of the motor to improve
restart characteristics.
12. A system for starting one of a split phase,
capacitor start and capacitor start, capacitor run motors having a main
winding and a start winding comprising:
a triac having a gate and having first and second main terminals connected
in series with the start winding to control energization thereof,
control apparatus comprising
a power supply for providing a bias voltage, trigger means coupled to the
gate for providing a signal to the gate to turn on the triac and energize
the start winding, the trigger means turning on the triac upon
energization of the motor from an at rest condition,
measuring means to measure the main winding current and integrate a
plurality of samples of values of a given half cycle of the main winding
current wave form,
calibration means for storing a first integrated value of main winding
current as a calibration value,
comparison means for comparing subsequent values of main winding current,
the trigger means interrupting the signal to the gate to turn off the
triac and de-energize the start winding when the subsequent main winding
current values reach a threshold value which is a selected proportion of
the calibration value.
13. A system according to claim 12 in which the measuring means integrates
a plurality of samples of values of a given half cycle for each half cycle
of one polarity of the current wave form.
14. A system according to claim 13 in which the calibration value is
derived by averaging the values of at least two half cycles to minimize
the effects of any spurious wave form.
15. A system according to claim 13 including means for maintaining the
calibration value for a selected period of time in the event that power to
the motor is interrupted whereby upon resumption of power to the motor
within the selected period of time the comparison means will compare the
renewed subsequent values of main winding current to the calibration value
existing before the power interruption.
16. A system according to claim 13 in which the threshold value of main
winding current is approximately 70% of the calibration value.
17. A system according to claim 13 in which the trigger means, subsequent
to turning off the triacs to de-energize the start winding, will provide a
signal to the gate to turn on the triac and re-energize the start winding
upon the increase of main winding current to a selected re-energization
value.
18. A system according to claim 17 in which the selected re-energization
value is approximately 85% of the calibration value.
19. A method for starting a single phase electric motor having a main
winding and a start winding and a triac serially connected to the start
winding comprising the steps of turning on the triac concomitantly with
energizing the motor when starting from an at rest condition, measuring as
a characteristic one of the locked rotor main winding current and start
winding voltage and storing it as a calibration value, on a continuous
basis measuring subsequent values of the same characteristic at least each
half cycle of one polarity, comparing the subsequent values with the
calibration value and turning off the triac when the subsequent values of
the characteristic reach a selected proportion of the calibration value
and maintaining the stored value of the calibration value for a selected
period of time following an interruption of power to the motor
sufficiently long to ensure that the motor has come to a complete stop.
20. A method according to claim 19 wherein the selected period of time is
approximately twenty seconds or greater.
21. A method for starting a single phase electric motor having a main
winding and a start winding and a triac serially connected to the start
winding comprising the steps of turning on the triacs concomitantly with
energizing the motor when starting from an at rest condition, measuring as
a characteristic one of the locked rotor main winding current and start
winding voltage, integrating an entire half cycle of a wave form
converting converting the measurement into a low level voltage, inputting
the low level measured value into an amplifier, increasing the gain of the
amplifier until the output voltage equals a selected calibration voltage,
loading the gain value into a register and comparing later low level
measured values to determine when the triac should be disabled and
enabled.
22. A method according to claim 21 in which the measurements are taken
every other half cycle.
23. A method according to claim 22 in which a plurality of samples of a
given half cycle is integrated to obtain a measurement value.
24. A method according to claim 23 in which the measurement used as a
calibration value is derived from an average of at least two half cycles
following an initial inrush cycle.
25. A method for starting a single phase electric motor having start and
run winding and a triac serially connected to the start winding to control
energization of the start winding comprising the steps of measuring one of
the main winding current and start winding voltage as a motor performance
characteristic, converting the measurement into a calibration voltage
within a selected range, inputting the calibration voltage into one input
of an amplifier, inputting a reference voltage into another input of the
amplifier, increasing the gain of the amplifier until the output level of
the amplifier equals the reference voltage, storing the resulting gain,
taking later measurements of the same characteristic, resulting voltage
into the one input of the amplifier using the same gain, inputting a
selected cut out reference voltage into the said another input of the
amplifier and de-energizing the start winding by turning off the triac
when the resulting voltage equals the cut out reference voltage.
26. A method for starting a single phase electric motor having a main
winding and a start winding and a triac serially connected to the start
winding comprising the steps of turning on the triac concomitantly with
energizing the motor when starting from an at rest condition, measuring as
a characteristic the wave form of one of the locked rotor main winding
current and start winding voltage by integrating the entire value of a
given half cycle of the wave form, storing the value to provide a
calibration value, continuing to measure the wave form by integrating the
entire value of following half cycles of one polarity and comparing the
resulting value with the calibration value and de-energizing the start
winding when the measured value reaches a selected value relative to the
calibration value. |
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Claims |
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Description |
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BACKGROUND OF INVENTION
This invention relates generally to starting single phase motors and more
particularly to starting capacitor start, capacitor start-capacitor run
and split phase motors using solid state apparatus and techniques.
Such motors conventionally have been started using electromechanical relays
or centrifugal switches. These devices are generally effective and are of
relatively low cost but they suffer from certain inherent limitations. For
example, since these devices have moving parts their longevity is limited
thereby. Further, they are generally susceptible to being affected by dirt
and chemical substances which may happen to be in their environment and
they may also be sensitive to vibration. The most serious limitation
however is the need to select and calibrate such devices for each motor
rating.
It is an object of the present invention to provide a starting system and
method for a single phase induction motor which can be used with a wide
range or motor ratings, for example, from a tenth of horsepower up to
approximately five horsepower.
Yet another object is the provision of a starting system and method which
can be used with split phase motors as well as capacitor start and
capacitor start-capacitor run motors.
Another object of the invention is the provision of a system which is
reliable and long lasting.
Still another object of the invention is the provision of a starting system
which will provide restart capability, prevent overloading of the start
winding and be insensitive to line voltage variations.
Another object of the invention is the provision of a system that can
readily replace existing systems, as a service part of as an original
component, without significant modifications of the motor.
Various additional objects and advantages of the present invention will
become readily apparent from the following detailed description and
accompanying drawings.
SUMMARY OF THE INVENTION
Briefly, the above objects are realized by using a triac serially connected
to the start winding of a single phase motor of any of a capacitor start,
capacitor start-capacitor run or split phase type, and controlling the
conduction of the triac and concomitantly energization of the start
winding based on measuring ratiometric changes of either the start winding
voltage or main winding current and comparing these changes to a value
obtained during a calibration sequence.
According to a feature of the invention, a negative DC bias voltage is
provided for the control module so that the triac can be driven in the
second and third quadrants to minimize the required gate current. A powe
supply detect circuit measures the value of the bias voltage and provides
either a bias OK (BOK) signal indicative that the power supply is fully on
or a system clear (SYSCLR) signal indicative that the bias voltage has
decayed to a point where the data retained in the digital latches are
considered not to be valid.
A triac enable (TENA) signal is issued by a state controller to a triac
control circuit which turns on the triac and returns data to the
controller when the actual command has been executed (TEXE). The triac
control on the initial cycle always turns on the triac at a zero crossing
of the triac voltage in order to protect the triac.
According to a feature of the invention an input signal processor is
adapted to measure either start winding voltage or main winding current as
selected and convert that into a DC level usable by comparators in the
system. Every other half cycle is integrated and held for the following
half cycle with decisions being processed during the following half cycle.
The input signal processor is self timed to obviate phase relationship
problems. The output of the input signal processor is a DC value
proportional to the integration which, during a calibration sequence, is
entered into a register as a calibration value with continuing
measurements then compared to the calibration cut-in and cut-out constants
that have been previously selected.
According to an alternative embodiment data measurements can be taken using
multiple half cycles, for example two consecutive half cycles of the same
polarity in order to improve the reliability of the data.
According to another feature of the invention, a start timeout counter is
provided to prevent thermal overloading of the triac in the event that the
motor fails to start after a selected period of time which, if desired,
may be decremented during normal run time of the motor to avoid possible
nuisance stalling of the motor.
According to a feature of the invention should the motor be overloaded
during its normal run state, the start winding will be re-energized at a
selected start winding voltage or main winding current value. If the power
to the motor is interrupted the system enters a so called sleep state in
which energy consuming portions of the system are turned off so that the
calibration value can be retained for a selected period of time. If the
motor is restarted within the selected period of time the recalibration
sequence will be bypassed with the previous calibration value being
employed.
BRIEF DESCRIPTION OF THE DRAWINGS
In the accompanying drawings in which several of the preferred embodiments
of the invention are illustrated:
FIG. 1 is a schematic diagram showing the system used with a capacitor
start motor;
FIG. 1a is a graph showing torque and start winding voltage as a percent of
locked rotor versus slip for a typical capacitor start motor;
FIG. 2 is a schematic diagram showing the system used with a split phase
motor;
FIG. 2a is a graph showing torque and main winding current as a percent of
locked rotor versus slip for a typical split phase motor;
FIG. 3 is a block diagram of a control module used in the FIGS. 1, 2
system;
FIG. 4 is a state table showing the several states of operation and their
sequence;
FIG. 5 shows the relationship of FIGS. 5a-5g to one another;
FIGS. 5a-5g together comprise a schematic circuit diagram of the control
module of the instant invention selected to measure start winding voltage;
FIG. 6 shows a toroid for use in the control module when main winding
current measurement is selected;
FIG. 7, a block diagram and FIG. 7a, a schematic circuit diagram, show a
modification of the FIG. 5d portion of the system to provide decrement
means for the triac time out counter; and
FIG. 8 is a schematic circuit diagram showing a modification of the
measurement portion of the system.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now to the drawings; FIG. 1 shows a control module made in
accordance with the invention used to start a capacitor start motor. An
integrated circuit 10 is mounted on board 12 which is provided with
terminals 1 through 4. Terminals 3 and 4 are connected to opposite sides
of a start capacitor C.sub.a which in turn is connected to the start
winding of a capacitor start motor. Terminals 1 and 2 are connected
respectively to power lines L1 and L2. The power supply for integrated
circuit 10 comprises a filter capacitor C.sub.b, dropping resistor R.sub.a
and half wave rectifier diode D.sub.a serially connected between terminals
1 and 2. A zener diode Z.sub.a is connected on one side between the
junctions of capacitor C.sub.b and resistor R.sub.a and IC 10 and on the
other side to terminal 2. Zener diode Z.sub.a provides and regulates the
supply to a selected level, e.g., 5 volts. An auxiliary power supply
capacitor C.sub.c is shown connected between IC 10 and terminal 2 to
provide power for the sleep feature to be explained below. Dropping
resistor R.sub.b is connected between terminal 1 and IC 10 and dropping
resistor R.sub.c is connected between terminal 4 and IC 10 to provide a
suitable low voltage for the start winding voltage measurement.
Triac 14 is connected between terminals 3 and 2 with a gate control circuit
comprising resistors R.sub.d and R.sub.e providing gating voltage for the
triac. Zero voltage crossing to keep the voltage across the triac below
approximately 20 volts to permit turn on the triac without deleterious
effects is accomplished by sensing voltage across the triac through
resistors R.sub.f and terminal 2.
Resistor R.sub.f connected between IC 10 and terminal 3 forms part of a
zero voltage crossing turn on circuit also to be discussed below. An RC
circuit comprising resistor R.sub.g and capacitor C.sub.d provides a
snubbing function minimizing the rate of change of voltage over time to
prevent triac misfiring. Resistor R.sub.h, connected between terminals 3
and 4, is a bleeder resistor for the start capacitor of the motor to
provide shorter restart times. It should be noted that resistors R.sub.b
and R.sub.c used in measuring the start winding voltage do not need to be
expensive low tolerance resistors since the measurement technique employed
is ratiometric, as will be described in detail below, and therefore the
cost of the circuit is considerably reduced compared to direct measurement
techniques.
FIG. 1a depicts motor characteristics of a capacitor start motor showing
torque and start winding voltage with start winding both in and out of the
current as a percent of locked rotor versus slip. The cut-in and cut-out
values for the start winding are shown by the horizontal lines labeled In
and Out at approximately 40% and 150% respectively. Upon initial starting
of the motor the start winding is energized with the start winding voltage
increasing along with torque, and at approximately 150% of locked value
the start winding is de-energized with its voltage dropping to slightly
under 60%. If an overload should occur the start winding voltage will
decrease and upon reaching approximately 40% of the locked rotor value the
system re-energizes the start winding to significantly increase the
torque. The circuit provides a desired amount of hysteresis (differential
between cut-out and cut-in values) to provide increased torque for such
overloads.
FIG. 2 shows the system used with a split phase motor. IC 10 is provided
with a current sensing toroid or current transformer T.sub.a with one or
few turns connected between terminals 2 and 4 to carry main winding
current and an output resistor R; coupled across the secondary winding
connected to IC 10.
FIG. 2a shows the motor characteristics of a single phase motor showing
torque and main winding current as a percentage of locked rotor with the
start winding energized and de-energized versus slip. The system
de-energizes the start winding when the main winding current decreases to
approximately 70% of the locked rotor value and re-energizes the start
winding upon an overload which causes the main winding current to increase
to approximately 85% of locked rotor value.
With reference to FIG. 3, the block diagram of the electronics (IC 10)
includes a Power Supply, a Power Supply Detect (PSD), a Triac Control
(TRC), a State Controller (STC), an Input Signal Processor (ISP), an
Internal Clock (IC), a Programmable Level Comparator (PLC) and a Start
Time-Out Counter (TOC). A system built in accordance with the invention
comprises discrete components on a circuit board but is suitable for
reducing to an integrated circuit. The IC package would have fourteen pins
including; (1) COM, AC1-common for the power supply, (2) AC2-a power
supply, (3) V.sub.ee -a negative bias supply, (4) VS1-a positive sense
analog input-voltage/current, (5) VS2-a negative sense analog
input-voltage/current, (6) VS3-a triac sense analog voltage, (7) Gate-the
triac trigger source, (8) V.sub.Cal -a reference calibration voltage, (9)
V.sub.CO -triac cut-out voltage, (10) V.sub.CI -triac cut-in voltage, (11)
MT-select voltage or current operation (motor type), (12) DISA-disable
triac-timeout counter and pins 13 and 14 not used.
The Power Supply converts 115 or 230 volts into a negative DC bias voltage
used by the electronics in the system and the triac drive.
The Power Supply Detect circuit generates two logic control signals, a bias
OF (BOK) indicative that the power supply is fully on, and a system clear
(SYSCLR) indicative that the bias voltage has decayed to a point where the
data retained in the digital latches is no longer considered to be valid.
The Triac Control circuit determines, under the control of the State
Controller, when to trigger the triac that is driving the start winding.
The Triac Control outputs either an enable signal that can be used by a
zero crossing optical coupler or a direct triac drive based on second and
third quadrant triac operation, as desired.
The Triac Control Circuit receives enable signals from the State Controller
and returns data to the Controller when the actual command has been
executed. The Triac Control insures when the triac is turned on the
initial cycle always occurs at a zero crossing of the triac voltage to
thereby prevent any large surge currents which can occur with capacitor
start motors and avoid triac overloading.
The Input Signal Processor is adapted to measure either start winding
voltage or main winding current and convert that into a DC level usable by
the comparators in the system. The method used in determining the value
involves integration of every other half cycle. Integration obviates
spurious noise peaks which could otherwise affect the accuracy of the
measurement. Every other half cycle is used to process the previous half
cycle integration. The input signal processor is self timed by using the
input voltage zero crossings to derive a clock signal called Z clock (ZCK)
which is used to time the rest of the logic of the system. This results in
avoiding phase problems regarding timing and signal processing. The output
of the Input Signal Processor is a DC value proportional to the
integration of the input data which is inputted to the Programmable Level
Comparitor which compares the value to the calibration cut-in and cut-out
constants which are ratiometrically programmed by the manufacturer of the
system.
Since the system employs ratiometric comparisons the absolute value of any
of the programming constants is not determinative but rather the division
of one by another is determinative. This results in a system which is
relatively independent of bias, voltage and temperature extremes.
The Internal Clock is a two phase high frequency clock used for switched
capacitor circuits to insure that phase a and phase b have no overlapping
edges.
The Start Time-Out Counter is a simple eight bit counter used to prevent
the triac from thermal overload, that is, to turn off the triac if the
motor cannot be started during a selected period of time.
TABLE 1
__________________________________________________________________________
SYN. CLOCKED BY ZCK DFF
CURRENT ST
INPUTS OUTPUTS VARIABLES
STATE NAME
CODE
S0
S1
S2
TEXE
DCMP
BOK
TC1
TENA
RST
NXS
D0 D1 D2
__________________________________________________________________________
RESET 0 0 0 0 X X X 0 0 1 1 0 0 1
INITIALIZE
1 0 0 1 0 X X 1 1 0 l 0 0 1
INITIALIZE
1 0 0 1 1 X X 1 1 0 2 0 1 0
CALIBRATE
2 0 1 0 X 0 X 1 1 0 2 0 1 0
CALIBRATE
2 0 1 0 X 1 X 1 1 0 3 0 1 1
RUN DETECT
3 0 1 1 X 0 X 1 1 0 3 0 1 1
RUN DETECT
3 0 1 1 X 1 X 1 1 0 4 1 0 0
RUNNING 4 1 0 0 X 0 X 0 0 0 4 1 0 0
RUNNING 4 1 0 0 X 1 X 0 0 0 5 1 0 1
LS RESTART
5 1 0 1 0 X X 0 1 0 5 1 0 1
LS RESTART
5 1 0 1 1 X X 0 1 0 3 0 1 1
ERROR 6 1 1 0 X X X 0 0 0 6 1 1 0
SLEEP 7 1 1 1 X X 0 0 0 0 7 1 1 1
SLEEP 7 1 1 1 X X 1 0 0 0 3 0 1 1
__________________________________________________________________________
STATE NAME OPERATIONAL SEQUENCE
__________________________________________________________________________
RESET THE NULL STATE, SYSTEM RESET
INITIALIZE START TRIAC, WAIT FOR OK
INITIALIZE RECEIVE OK FROM (TRC)
CALIBRATE RUN CALIBRATION SEQUENCE, WAIT FOR RESULT
CALIBRATE RECEIVED CALIBRATION COMPLETE
RUN DETECT WAIT FOR CUT-OUT DETECT, INC (TOC)
RUN DETECT CUT-OUT DETECTED
RUNNING NORMAL RUN STATE
RUNNING CUT-IN DETECTED, GO TO LS RESTART
LS RESTART WAIT FOR TRIAC "ON"
LS RESTART TRIAC "ON", GO BACK TO RUN DETECT
ERROR TIME OUT ERROR STATE
SLEEP POWER SUPPLY HOLD-UP
SLEEP POWER BACK, RETURN TO FLOW
__________________________________________________________________________
NAME/DEFINITION
__________________________________________________________________________
BOK = T IF VEE IS VALID
TEXE = T IF TRIAC HAS BEN ENABLED
DCMP = T IF COMPARE RESULT
TCOF = T IF TOC HAS TIMED OUT
DV = SUCCESSFUL CALIBRATION DATA VALID LATCH
TCI = INDEX TOC
TENA = REQUEST TRIAC ON
RST = RESET SYSTEM
NXS = NEXT STATE CODE
__________________________________________________________________________
With reference to FIG. 4 and Table 1 the operational sequence will be
described. In the Null State the power is off and the motor will be at
rest. When the power switch is turned on the system must first obtain a DC
bias necessary to run the electronics and then perform several operations
based on the conditions that are measured. As soon as a power valid signal
(BOK) is detected the motor start switch system will reset all
programmable parameters in the electronics. As mentioned above the circuit
is self timed with respect to the measurements that it is making on the
input. If valid data transitions are detected on the input, the system
will then proceed to initialize the triac. These states are coded as noted
in FIG. 4 and TABLE 1.
In the normal sequence when the power is high enough to run the electronics
all the registers will be initialized and the triac will be turned on.
This allows time for the in-rush current of the motor to stabilize.
This is labeled state code 1 which has a binary equivalent to 001. The
system outputs a triac enable system to the triac control and waits for
the triac control to tell the state controller that the zero crossing of
the triac voltage has been detected, and the triac in now being triggered
on every half cycle of the 60 cycle input wave form. At this point the
motor start winding voltage or main winding current can now be calibrated
for the purpose of measuring ratiometric change. After the first zero
crossing of the triac voltage, the system will enter state code 2 which
has a binary equivalent of 010. In this state the triac is still on and
the measurement system will now measure locked rotor start winding voltage
or main winding current. The Input Signal Processor and Programmable Level
Comparator are now directed by the State Controller to integrate, hold and
detect a reference calibration level to be used in determining when the
motor is at proper speed and when the motor needs to be restarted.
The method used requires that the calibration voltage in the electronics be
normalized by a digitally controlled, data control circuit, to be
discussed infra, which takes the calibration measurement and increases the
gain of an amplifier until the output level of the amplifier equals the
voltage that has been previously programmed as the calibration voltage
labeled V-CAL. In this way, the total equivalent gain between the motor
start winding voltage or main winding current is modified during the
calibration cycle so that the gain constants can be used to determine
ratiometric changes regarding cycles that occur later. When this gain is
found, the system automatically loads the value of the gain into a
register which can not be changed unless the circuit is completely reset.
The data valid latch set to true tells the electronics that there is a
valid locked rotor calibration of either start winding voltage or main
winding current available to detect when the motor has started or when it
has been stalled. When the data valid latch has been set, the system is
ready to detect when the motor is actually run. This state is labeled run
detect has a state code of 3 or a binary equivalent of 011.
In this state the triac is still energized while the system is detecting
the start winding voltage or main winding current of every cycle then
comparing that to the voltage used to determine when the triac should be
cut-out.
As mentioned supra, the motor characteristic of capacitor start motors and
split phase motors are different in that capacitor start motors have a
start winding voltage that increases with increasing rotor RPM. In split
phase motors, the start winding voltage does not change with speed.
However, since main winding current decreases with increasing speed in
both types of motors, split phase motors may use main winding current to
sense speed changes. The MT input (motor type input) tells the
programmable level comparator whether the system is to detect start
winding voltage or main winding current. The run detect state simply waits
until the start winding voltage has increased to the cut-out constant or
main winding current has decreased to the cut-out constant. When this is
detected it is represented by a signal from the Programmable Level
Controller called the data compare (DCMP). When this occurs the controller
knows that the start winding voltage has risen to a constant equal to the
cut-out constant divided by the calibration constant, or in the main
winding current mode that the cut-out constant divided by the calibration
constant has been reached.
Once the system is running this state is labeled state code 4 which has a
binary equivalent to 100.
The triac enable signal, labeled TENA, is now returned to zero and the
triac controller disables the triac. The running state is the normal
operating mode for the motor. From this state if a stall occurs, which
means the motor is overloaded, the system is still detecting start winding
voltage or main winding current. In the running state and if the so called
cut-in constant is detected for either operating mode then the system will
attempt an automatic restart similar to the initial start of the motor.
This occurs when the State Controller receives the data compare signal
from the programmable level Comparator. The transition between running and
stall level or drop out state has a state code 5, a binary equivalent of
101.
The drop out state causes a triac enable signal to be sent to the triac
controller, however, the triac controller will not attempt to turn on the
triac until the voltage on the triac has been reduced to a selected value
typically in the range of twenty to forty volts. This prevents the triac
from turning on with relatively high DC voltage on its anodes and enhances
the reliability of the system.
The Statee Controller receives confirmation from the Triac Control that the
zero crossing has been detected and the triac is now being triggered. It
will make the transition back to the run-detect state and the run-detect
to run sequence is reinitiated. Should for any reason, however, the motor
be permanently stalled, the function of the Start Time-Out Counter comes
into play. This counter is intended to prevent thermal overloading of the
triac. This is a simple eight bit counter that is cleared in the
initialization state and indexed whenever the triac is enabled. In the
state transition table these increments are labeled TCI and there is one
increment for every transition or zero positive crossing of the
measurement clock. This feature could be disabled at the discretion of the
user. This describes the normal operating sequence of the motor start
switch, however, there are several other conditions that can occur that
the motor start switch system will properly handle. These include loss of
power due to a momentary interruption of the power line or a triac timeout
which occurs when the time counter overflows. This is represented in the
state table as TCOF is true. Most of the transitions in the normal
sequence are synchronized, that is, they trigger on the leading edge of
the sixty (of fifty) cycle clock. However, other substates of the system
are asynchronous since they can occur at any point in time. These
asynchronous transitions are triggered when the triac time overflow
counter has overflowed indicating that the triac should be turned off
permanently or at least until the system is reset completely or by loss or
bias, which occurs when the power has been interrupted to the system.
These states are labeled error and sleep recover state, respectively. The
error state code is 6 which has a binary equivalent of 110 and the sleep
recover state is 7 with a binary equivalent of 111.
The error state can only be entered via the Start Time-Out Counter
overflowing. This occurs when the triac has been on for a selected time,
for example at least eight seconds which is at least seven or eight times,
depending on the motor application, the amount of time required to start a
motor. Once the time-out error state is entered the system will not
re-energize the triac until the system is cleared. This requires that the
bias voltage to the system diminish below the point at which any of the
data can be successfully held by the latches and flip flops.
The sleep recover mode eliminates potential calibration errors during a
brief loss of power. This state is entered when the bias is detected to be
not valid and the system has a valid set of calibration data. If the
system loses power before the motor has been successfully calibrated then
no attempt to recover can be attempted and the system must be driven back
to the reset stage. If the system does enter the sleep state then a motor
restart without a calibration can be attempted. As soon as the bias is
detected to be valid again, as long as the bias has not decayed to the
value set as a system clear, the detection of a valid bias will cause the
system to enter the run detect state, again, a normal start sequencing is
re-enabled. The sleep-recover feature avoids the situation of using
calibration data based on a motor which is still rotating due to a large
moment of inertia, even though power has been interrupted.
Referring now to FIG. 5a which shows an implementation employing discrete
components, the Power Supply comprises a step down transformer shown at
pins 1 and 2 needed due to the relatively large number of IC's employed.
This would not be used when the system is reduced an IC. The line from pin
2 is the reference common for the entire electronics system and is
connected to the power busing, a 60 (or 50) cycle AC wave form derived
from the input power line. This is rectified by diode D.sub.1 into a
negative half cycle sine wave. Capacitor C.sub.1 and C.sub.22 filter that
wve form into an RMS value plus the AC harmonics.
Transistor Q.sub.1, and Diodes D.sub.4, D.sub.3, D.sub.2, Z.sub.1 coupled
to the base of Q.sub.1 form a voltage reference that defines the value of
-V. Diode D.sub.5 coupled to the emitter of Q.sub.1 prevents flow of
current from -V.sub.ee through Q.sub.1 in its reverse direction. Resister
R.sub.2 biases D.sub.4, R.sub.3, D.sub.2 & Z.sub.1 and reistor R.sub.1
limits the current through transitor Q.sub.1 to protect Q.sub.1. Capacitor
C.sub.2 is used to filter the output of the regulator and is the sleep
function holdup capacitor.
The power supply detect circuit comprise two sections, the first generates
a bias status logic signal--this logic signal is detected from the input
bias signal V.sub.ee. Zener diode Z.sub.2, resistors, R.sub.3 and R.sub.4
are placed in series between common and -V.sub.ee with transistor Q.sub.2
coupled between from V.sub.ee and the center tap of R.sub.3 and R.sub.4.
Transistor Q.sub.2, in collector is pulled up to common through resistor
R.sub.5. This forms a voltage switch which will send the collector voltage
of Q.sub.2 which is labeled BOK low whenever the voltage on Vee is greater
than the zener voltage of Z.sub.2 plus the base emitter voltage of Q.sub.2
multiplied by the factor 1+R.sub.3 /R.sub.4.
It will be seen that the BOK signal can be programmed to different values
by the selection of Z.sub.2, and R.sub.3 and R.sub.4. The output of
Q.sub.2 is then inputted into a logic gate labeled Z.sub.3C which is a two
input NOR gate connected as an inverter. This provides a logic true value
for BOK. The system clear function is derived from transistors Q.sub.3 &
W.sub.4 which form a resistively coupled latch that detects the relative
value of V.sub.ee. Collector pull ups for the latch are resistor R.sub.33
and R.sub.38. The feedbacks resistors are R.sub.34, R.sub.37, R.sub.35 and
R.sub.36. Capacitor C.sub.10 is used to decouple any RF interference from
the latch. During normal operations with all the capacitors initially
discharged as V.sub.ee begins to rise the output of the latch labeled
SYSCLR would normally be low because of the different resistor ratios of
R.sub.34, R.sub.36, R.sub.37, R.sub.35. This would clear all the latches.
Once V.sub.ee is greater than approximately 4 volts, the voltage at which
a flip flop will hold its data properly, the latch resets into the non
clear mode. Thus if V.sub.ee is below the lower threshold all the data is
cleared from the system but for any voltage above that threshold it is
not. In the normal sequence, when power is lost, as V.sub.ee decays the
BOK signal is used to eliminate all major power drain but the latches are
not cleared unless V.sub.ee decays to the lower limit voltage.
The triac control (see FIGS. 5c and 5f) senses the voltage across the triac
and depending upon logic control from the State Controller determines
proper triggering for the triac. As seen in FIG. 5c, the triac voltage is
sensed through two comparators labeled X.sub.1A and X.sub.1C. The resistor
string formed by R.sub.12, R.sub.13, R.sub.14 & R.sub.16 and R.sub.15 is
used to set thresholds for when the triac voltage is above or below its
zero value. Diode D.sub.10, D.sub.11, D.sub.12 & D.sub.13 are reverse
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