Note: Descriptions are shown in the official language in which they were submitted.
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The present invention relates to a method and
to a static, three phase voltage regulator for adjusting
the electrical power supplied to a three phase load.
T~he subject invention is particularly suitable
for use in automatic equipments for the adjustment of tem-
perature and pressure or in electrical spot welding equip-
ments.
Three phase static contactors are presently used
to adjust the electrical power transmitted to a three phase
load. In response to a control signal, the contactor
connects the three phase load with the supply three phase
voltage. Such a contactor presents the drawback of starting
the load asynchronously, that is for a resistive load, the
first half-cycle of the supply voltage transmitted to the
load is not complete. This causes a high rate of
variation of the load voltage with respect to time, which
in some applicatnons, is not acceptable.
An object of the present invention is therefore
to eliminate the above discussed drawback of the prior
art contactorsby providing a method and a voltage regulator
for adjusting the electrical power supplied to a three phase
load which starts the latter load synchronously.
More specifically, in accordance with the in-
vention, there is provided a method of adjusting the
electric power supplied to a three phase load by an al-
ternating, three phase source having first, second and
third phases each supplying a single phase alternating
voltage and being each connected to a corresponding one
of the three phases of the load through an electronic
switching unit with a gate electrode, said adjusting
method comprising the steps of:
measuring the single phase voltage of the first,
second and third phases of the alternating source;
producing first, second and third pulse signals
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in response to the single phase voltage of said first,
second and third phases, respectively, each pulse signal
including a pulse produced upon each passage of the
corresponding single phase voltage by a zero
5 amplitude where the voltage amplitude changes from .
a value of a first polarity to a value of a second
polarity;
measuring an alternating, difference voltage
between the first and second phases of the alternating
source;
producing a fourth pulse signal in response
to said measured difference voltage, said fourth pulse
signal including a pulse produced upon each passage of
the difference voltageby a zero amplitude where the vol-
tage amplitude changes from a value of a first pola-
rity to a value of a second polarity; ~ -
generating, in response to the pulses of said
fourth signal, a periodic sawtooth signal of period
To and of increasing amplitude during each period To;
comparing, during each period To, the sawtooth
signal with a re~e.ence signal of adjustable amplitude
to produce a control pulse having a width varying with
the amplitude of the reference signal;
transmitting, at the beginning of the- control
pulse, the pulses of the fourth pulse signal to the gate
electrode of a first one of said switching units inter-
connecting one of the first and second phases of the
source with the corresponding one of the three phases of
the load, to turn said first switching unit on whereby
a voltage is applied to the load; and
detecting said voltage applied to the load,
and upon detection of the voltage applied to the load,
(a) interrupting transmission of the pulses of the
fourth signal to the gate electrode of the first swit-
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ching unit, and (b) transmitting the pulses of the first
pulse signal to the gate electrode of the switching unit
interconnecting said first phase of the source with the
corresponding phase of the load, the pulses of the second
pulse signal to the gate electrode of the switching
unit interconnecting said second phase of the source
with the corresponding phase of the load, and the pulses
of the third pulse signal to the gate electrode of the
switching unit interconnecting said third phase of the
source with the corresponding phase of the load, until
the control pulse ends, whereby the switching units are
turned on to supply electric power from the first, second
and third phases of the source to the three phase load
until said control pulse ends;
whereby, in operation, the electric power
supplied to the three phase load is adjusted by adjust-
ing the width of said control pulses through adjustment
of the amplitude of said reference signal.
According to the invention, there is also pro-
vided a static voltage regulator for adjusting the elec-
tric power supplied to a three phase load by an alter-
nating, three phase source having first, second and third
phases each supplying a single phase alternating voltage
and being each connected to a corresponding one of the
three phases of the load through an electronic switching
unit with a gate electrode, comprising:
means for measuring the single phase voltage
of the first, second and third phases of the said alter-
nating source;
means for producing first, second and third
pulse signals in response to the single phase voltage
of said first, second and third phases, respectively,
each pulse signal including a pulse produced upon each
passage of the corresponding single phase voltage by a
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zero amplitude where the voltage amplitude changes from
a value of a first polarity to a value of a second pola-
rity;
means for measuring an alternating, difference
voltage between the first and second phases of said alter-
nating source;
means for producing a fourth pulse signal in
response to said measured difference voltage, said fourth
pulse signal including a pulse produced upon each passage
of the differencevoltage by a zero amplitude where
the voltage amplitude changes from a value of
a first polarity to a value of a second pola-
rity;
means for generating, in response to the pulses
of said fourth signal, a periodic sawtooth signal of
period To and of increasing amplitude during each period
To;
. means for producing a reference signal~of
adjustable amplitude;
means for comparing, during each period To,
the sawtooth signal with said reference signal to produce
a control pulse having a width varying with the amplitude
of the reference signal;
means for transmitting, at the beginning of
said control pulse, the pulses of the fourth pulse signal
to the gate electrode of a first one of said switching
units interconnecting one of the first and second phases
of the source with the corresponding one of the three
phases of the load, to turn the first switching unit on
whereby a voltage is applied to the load;
means for detecting said voltage applied to
the load;
means responsive to said detection of the
voltage applied to the load for interrupting transmission
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of the pulses of the fourth signal to the gate electrode
of the first switching unit; and
means responsive to detection of the voltage
applied to the load for transmitting the pulses of the
first pulse signal to the gate electrode of the switching
unit interconnecting the first phase of the source with
the corresponding phase of the load, the pulses of the
second pulse signal to the gate electrode of the switching
unit interconnecting the second phase of the source with
the corresponding phase of the load, and the pulses of the
third pulse signal to the gate electrode of the switching
unit interconnecting the third phase of the source with
the corresponding phase of the load, until the control
pulse ends, whereby the switching units are turned on
to supply electric power from the first, second and
third phases of the source to the three phase load until
said control pulse ends;
whereby, in operation, the electric power
supplied to the three phase load is adjusted by adjusting
the width of said control pulses through adjustment of
the amplitude of said reference signal.
The objects, advantages and other features of
the present invention will become more apparent upon
reading of the following non restrictive description of
a preferred embodiment thereof, given in conjuction with
the accompanying drawings, in which:
Figure 1 is a schematic, block diagram of a
three phase static voltage regulator in accordance with
the present invention; and
: 30 Figure 2 presents waveforms related to the
operation of the voltage regulator of Figure 1.
As illustrated in Figure 1, the three phase
static voltage regulator comprises (a) a thyristor 1
mounted in parallel with a diode 2 between a phase ~ of
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a three phase, alternating supply source and a first phase
291 of a three phase load 29, (b) a thyristor 3 mounted
in parallel with a diode 4 between a phase S of the supply
source and a second phase 292 of the load 29, and (c) a
thyristor 5 mounted in parallel with a diode 6 between
the third phase T of the supply source and a third phase
293 of the three phase load 29. As can be noted, the
thyristors 1, 3 and 5 conduct in directions opposite to
that of their respective diodes 2, 4 and 6. In each
case, the thyristor has its anode electrode and the diode
its cathode electrode connected to the corresponding
phase of the supply source.
A three phase transformer 7 measures the single
phase, alternating voltage of each phase R, S and T of
the source. The three so measured voltages are separa-
tely amplified through amplifiers 8, 9 and 10, respectively,
which amplifiers have a very high amplification gain.
When the amplitude of the single phase voltage of the
phase R crosses zero, that is when this voltage passes
by a zero amplitude where the voltage amplitude changes
from a negative to a positive value, a monostable circuit
13 connected at the output of the amplifier 8 is triggered
to produce a positive pulse of a duration suitable to turn
the thyristor l on. Similarly when the amplitude of the
single phase voltages of the phases S and T crosses zero,
where the voltage amplitude changes from a positive to
a negative value, the monostable circuits 12 and ll
connected at the output of the amplifiers 9 and 10,
respectively, are triggered to produce a positive pulse
of the same duration as that produced by the monostable
circuit 13, suitable to turn the thyristors 3 and 5 on.
The pulses from the monostable circuits 11,
12 and 13 are respectively supplied to a first input of
AND gates 14~ 15 and 16. The pulses from the monostable
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circuits 13, 12 and 11 therefore turn the thyristors 1,
3 and 5 on synchronously, that is upon occurrence of the
above defined zero crossings of the amplitude of the
single phase voltages of the phases R, S and T, respectively,
when transmitted to the gate electrodes of these thyristors.
A single phase transformer 17 measures the al-
ternating voltage (voltage URs in Figure 2) between the
phases R and S of the source. The so measured voltage
is supplied to an amplifier 18 with a very high amplifi-
cation gain. Upon each zero crossing of the measured
voltage URs, that is when this alternating voltage
passes by a zero amplitude where the voltage amplitude
changes from a negative to a positive value, a monostable
circuit l9 connected at the output of the amplifier 18
is triggered to produce a positive pulse having the same
duration as the pulses from the monostable circuits 11,
12 and 13, that is suitable to turn the thyristor 1 on.
The pulses Ulg from the output of the monostable circuit
19 are illustrated by the curve a in Figure 2.
The pulses Ulg are counted by a 8-bit binary
counter 20 generating a digital pulse count output signal
converted into an analog signal by a 8-bit digital-to-
analog converter 21.
A periodic sawtooth signal U21 of period To
is produced at the output of the converter 21, which
signal U21 has an amplitude which increases linearly from
zero during each period To, for instance 3.56 seconds.
The sawtooth signal U21 is shown by curve _ in Figure 2.
The counter 20 is automatically reset after having counted
a predetermined number of pulses, that is at the beginning
of each period To. The period To therefore corresponds
to a multiple of the period T of the single phase, alter-
nating voltage of the phases R, S and T. The signal U
from the converter 21 is supplied to the inverting input
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of a comparator 22 having a non inverting input supplied
with a reference direct current voltage of adjustable ampli-
tude produced by a direct current voltage through a poten-
tiometer 23, During each period To, as long as the sawtooth voltage
U21 has an amplitude lower than that of the reference vol-
tage from the potentiometer 23, the output of the comparator
produces a positive, control pulse U22 (curve c in Flgure
2). The control pulses U22 from the output of the compa-
rator 22 are supplied to a second input of the AND gates 14,
15 and 16 whereby,the pulses from the monostable circuits
13, 12 and 11 can be transmitted to the gate electrodes of
the thyristors 1, 3 and 5, respectively, only when a pulse
U~2 is generated, to turn these thyristors on. Of course,
a control pulse U22 is produced only if a reference voltage
is produced through the potentiometer 23, and the width g
of the pulse U22 is adjusted through this potentiometer 23
by varying the amplitude of the reference voltage.
Each pulse transmitted to the thyristor 1
through the AND gate 16 is also supplied to an additional
monostable circuit 24 which extends when necessary the
width ~ of the control pulse U22 from the com~arator 22,
to ensure supply of a pulse to the gate electrodes of the
thyristors 3 and 5 through the AND gates 15 and 14 each
time a pulse is supplied to the gate electrode of the
thyristor 1. Accordingly, the thyristors 3 and 5 are
always turned on following turning on of the thyristor
1, even if the non extended control pulse U22 from the
comparator 22 ends just after transmission of a pulse
to the gate electrode of the thyristor 1 or thyristor 3
through the gate I6 or 15. A same number of complete
cycles of the single phase alternating voltages of the
phases R, S and T of the supply source is accordingly
supplied to the load 29 during each control pulse U22.
The three phase supply of the load 29 is accordingly
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balanced.
Any voltage applied to the load 26 is detected
by a three phase transformer 30, and the so detected
voltage is rectified through a three phase rectifier 31.
When no voltage applied to the load is detected, which
corresponds to turning off of the thyristors 1, 3 and
S, a threshold circuit 32, connected to the output of the
rectifier 31 supplying on its output a low logic level
signal. In response to the latter signal, an inverter 26
generates a high logic level signal.
When no voltage is detected by the transformer
30, the low logic level signal at the output of the thre-
shold circuit 32 is supplied to a third input of the
AND gates 14, 15 and 16 to prevent transmission of the
pulses from the monostable circuits 13, 12 and 11 to the
gate electrodes of the thyristors 1, 3 and 5, respectively.
Another AND gate 25 has a first input supplied
with the pulses Ulg from the monostable circuit 19, a
second input supplied with the pulses U22 from the compa-
rator 22, and a third input supplied with the output si-
gnal of the inverter 26. When no voltage is applied to
the three phase load 29 and when a control pulse U22
from the comparator 22 is supplied to the second input
of the AND gate 25 having its third input 3 supplied with
a high logic level signal from the inverter 26 as no
voltage is applied to the load, the pulses Ulg from the
monostable circuit 19 are transmitted to the gate of the
thyristor 1 through the AND gate 25, a pulse amplifier
27 and a pulse transformer 28 to turn the thyristor 1
on.
The thyristor 1 and the diode 4 then
: conduct and a voltage is applied to the load 29, which
voltage is detected through the transformer 30 and
rectified by the rectifier 31. me output of the threshold
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circuit 32 accordingly supplies a high logic level signal
applied to the third input of the AND gates 14, 15 and 16,
and to the input of the inverter 26 which then supplies a
low logic level signal to the third input of the gate 25 to
prevent this gate 25 to transmit the pulses from the
monostable circuit 19 to the pulse amplifier 27.
As a high logic level signal is supplied by the
threshold circuit 32 to the third input of the gates 14, 15
and 16 and the control pulse from the comparator 22 is
supplied to the second inpu-t of these three AND gates, the
pulses from the monostable circuit 13 are supplied to the
gate electrode of the thyristor 1 through the gate 16, the
pulse amplifier 27, and the pulse transformer 2~ to turn the
thyristor 1 on, the pulses from the monostable circuit 12
are supplied to the gate of the thyris-tor 3 through the AND
gate 15, a pulse ampli:Eier 34 and a pulse transformer 36 to
turn the thyristor 3 on, and the pulses from the monostable
circuit 11 are supplied to the gate electrode of the
thyristor 5 through the AND gate 14, a pulse amplifier 33
and a pulse transformer 35 to turn -the thyristor 5 on, and
that until the control pulse U22 from the comparator 22
having its width ~ eventually extended by the monostable
circuit 24 ends, as explained hereinabove. When the input c
of each pulse amplifier 33, 34 and 27 is connected to
ground, the control pulses of positive polarity from the
input a of the pulse amplifier 33 or 34, or the input a or b
of the pulse amplifier 27 determine the successive switching
of the corresponding output of each pulse amplifier, and the
pulses are transmitted to the secondary of the corresponding
pulse transformers 35, 36 and 28.
When the inpu-t c of each pulse amplifier 33, 34
and 27 is connected to a positive potential with respect to
the ground, the pulses from the inputs a and b are not
transmi-tted, as a consequence of i-t, in the secondary of the
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corresponding pulse transformers 35, 36 and 28 there is no
pulse.
This procedure is repeated for each of the
successive period T (see Figure 2) of the periodic sawtooth
voltage signal U21.
Accordingly, the number of cycles of the single
phase voltages of each phase R, S, T of the supply source
transmitted to the load 29 during each successive, basic
time period T of the sawtooth signal V2~1 is adjusted by
varying the width ~ of the pulses U22 of Figure 2, through
adjustment of the level of the reference voltage produced
through the potentiometer 23, which reference voltage is
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compared with the amplitude of the sawtooth voltage U
of Figure 2 by the comparator 22.
The above described switching procedure provides
for turning on of the thyristors 1, 3 and 5 synchronously
with the zero crossings of the alternating voltages of the
corresponding phases R, S and T, except for the short
period at the beginning of each pulse U22 during which
the pulses from the monostable circuit 19 are transmitted
to the gate of the thyristor 1 through the AND gate 25,
the pulse ampliier 27, and the pulse transformer 28.
Two current transformers 37 and 38 detect any
overcurrent supplied to the three phase load 29. In
response to sùch an overcurrent detection, a threshold
circuit 39 supplies a control input of the pulse ampli-
fiers 27, 34 and 33 with a pulse transmission interrup-
tion signal to block any pulses to the gate of the thy-
ristors 1, 3 and 5. Protection of the load 29 against
overcurrent is thereby obtained.
The three phase static voltage regulator pre-
sents in particular the following two advantages:
- it ensures supply of each phase of the load
29 with the same number of complete cycles of alternating
voltage; and
- variation in the amplitude of the source single
phase voltages does not influence the number of complete
cycles of alternating voltage supplied to the load.
Although the present invention has been des-
cribed hereinabove by way of a preferred embodiment
thereof, it should be pointed out that any modification
to this preferred embodiment, within the scope of the
appended claims, is not deemed to change or alter the
nature and scope of the subject invention.
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