Note: Descriptions are shown in the official language in which they were submitted.
1084994
The present invention relates to a method of
regulating the electrical power delivered to a consumer
from an ~lternating current network by adjusting the current
flow angle by means of a power switching device connected in
the current path to the consumer, which is switched on at
the beginning of a half-wave of the network alternating
voltage at a phase angle of approximately zero degrees and
is switched off at a phase angle corresponding to the
desired current flow angle.
It is already known to effect power regulation of
the described type by simply using the so-called phase angle
control with thyristors or triacs as power switching devices.
In such method, during each half-wave of the network
alternating voltage after the zero passage the consumer is
connected thereto with such a phase angle delay that the
residual phase angle of the half-wave until the next
succeeding zero passage corresponds to the desired current
flow angle. In particular, if the connection of the consumer
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to the alternatin~ current network is effected at a rather
large phase angle, i.e., at a relatively high instantaneous
voltage of the networ~, considerable cuTrent peak values will
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occur at the instant of connection, especially for capacitive
consumers. ~hese current peaks excessively losd the network
and cause, in adjacent high-frequency consumers, for example
radio and televi~ion apparatu~, undesirable high-frequency
disturbances even when disturbance protective means are
provided ~or the power switching device.
~ ~ In the United States Patent Specification 3,525,882
¦ ~ and the British Patent Specification 1,047,904 there are
alread~ disclosed power switching devices which can be
connected to an alternating current network, which allow an
adjustable electrical power to be delivered to the consumer
~, by arranging that, in each half-wave of the rectified but not
smoothed network voltage, at the cro~s-over point of the net-
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work voltage ~semiconductor switchin~ element connected in
series with the consumer is switched to the on condition and,
at a predetermined, adjustable phase angle within the same
half-wave, i8 again switched off. By this method th0 result
i8 achieved that, upon connecting the consumer to the
rectifier arrangement, which is used for rectifying the net-
work alternating voltage, undesirable current peaks ars
avo ded durin~ the half-~ves of t~e recOi~ied networ~
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alternating voltage, and nevertheless a free choice o~ the
current flow angle is ensured during each half-wave.
For performing the above mentioned method it i8
possible, according to United States Patent ~pecification
3,525,882 to use thyristors or similar switching de~ices as the
power switching means, but this demands the arrangement of
~eries connected ~ectifiers, because these thyristors do not
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exhibit sufficient blocking capability under reversed polarit~
conditions. Moreover difficulties are encou~tered should a
parallel connection of the thyristors be necessary to effect
the power switching. Moreover, the use of thyristors as power
switching devices in the inventive method is a disadvantage
in 80 far as costly circuit arrangements must be provided for
producing the necessary cutting off pulses.
According to British Patent Specification 1,047~904 t~e
difficulties referred to can be avoided by providing as the
power switching device a transistor, which is controlled by a
bistable trigger circuit. Nevertheless this arrangement is not
suitable for the accurate switching of large ioads at predeter-
mined phase angles and with low losses because a considerable
control power must be brought into effect and an unacceptably
high level of heating of the transistor takes place in
conse~uence of the losses. Moreover these disadva~tages may
not be avoided in the known arrangement by connecting a plurality
of transistors in parallel; on the contrar~ difficulties
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84994
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enco~tered then become even greater, particularl~ in respect
of the control of the transistors. In addition ~he ~nown
arrangement doe~ not permit tne transistor, which is provided
as the power switching element, to switch off at a desired phase
~r~
i~ angle between 0 and 180 of the half-wave of the rectified
network alternating ~oltage.
The purpose of the present invention is to provide a
method of the fir~t mentioned type and a circuit arrangement for
its performance, which, by the use of transistors as power
switcbing elements for an alternating current delivered from
an alternating current network to the consumer, will allow a
loss-free and precisely timed control of.the transistors
whilst avoiding unacceptab~e heating effects, even for any
desired level of consumer currents, and to do this at any.
1 ~ desired time instant during each half-wave of the network
,i ~ alternatin~ ~oltage.
d ~ For solving this pro~lem, the method-of the above
mentioned type is characterized in that ~here iæ employed a
power switching device comprising at least two parallel connec-
ted mutually decoupled transiætors, the collector-emitter paths
.j; of which are connected in the current path to the consumer, and
which iare alternately switched in at a switching frequency which
~;,' i5 higher than the network frequency in such manner that the
time periods ol th ir IIOD~I CoDditioDs overlap and the alterrate
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switching in of the transistors t6~es place in each half
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cycle of the network alternating voltage from the beginning
of each half cycle until the desired current flow angle is
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reac~ed.
~he control of the transistors is ef*ected preferably
each case by a transformer in order that the control power
may be kept low, Advantageously each transistor is co~trolled
by a control voltage applied to the primary side of each
~;- transformer and having an at least approximately recta~gular
wave form of gated pulses and gated space intervals, ~aid
intervals each includine a wave segment, the polarity of which
- is opposite to that of the gated pulses iu order to render
- the remanence o$ the transformer ineffective.
According to a variant Or the method of the invention,
by the use of a second power switching device the consumer
- c~n be damped Pnd discharged in each half-wave of the net-
,
~ork alternating voltage, in which ca~e the second power
switching devico becomes effecti~e after each interruption of
the connection of the consumer to the networ~ has been
brought ~bout by switching out the first power switching
device, and said ~econd power switc~i~g de~ice becomes
inef~ective before every reconnectio~ of the consumer with the
networ~ brought ~bout by the switching in of the first power
switchi~g de~ice. -
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84994
This variation of the method makes it possible by
the periodic connection of the comsumer to the alternating
current network in the zero cross-over point of the network
alternating voltage, to bring about in the consumer at least
substantially complete discharge approximat~ng to the ideal
condition. By these means it becomes possible to avoid the
risk of formation of current peaks at the instant of connection,
this resulting on the one hand in the avoidance of high
frequency disturbance effects and furthermore the avoidance of
over-loading the netwark switching device effecting the
connection of the consumer to the network.
Accordingly, in the above described variant of the
method the second power switching device, which damps and
discharges the consumer, becomes effective when the first
power switching device, which connected the consumer to the
alternating current netw~rk, is ineffective. ~hus it is
possible for the energy stored in the consumer to be discha~ged
through the consumer and through the second power switching
device, whilæt said second device is effective, in the time
interval before the next reconnection of the first power
switching device at the next zero crass-over point of the
network alternating voltage, so that at the time instant of
the said reconnection not only is there no ~oltage at the
terminals of the consumerr but also there is no electrical
or mechanical energy stored in the consumer. m erefore no
current peaks can be established upon reconnection of the
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~ ~084994
consumer to the alternating current network.
An advantageous practical form of the described
variant of the m~thod provides that in the second power
switching device at least one transistor is used, whose
collector-emitter path is arranged in a current path lying
parallel to the consumer, which transistor is switched on and
switched off in a time interval occurring between the
interruption of the connection and the reconnection of the
consumer with the network, this switching being effected at
a switching frequency which is higher than the network
frequency, whilst the switching off period of the transistor
occurs during a time which is shorter than the storage time of
the transistor. Having regard to this storage time, it is
advantageous to employ a Darlington transistor, the cost of
which is, nevertheless, only slightly higher than that of a
conventional transistor. Darlington transistors exhibit at
the present time storage periods of about 15 to 20 microseconds,
80 that the storage effect of the Darlington transistor can
be utilized for bridging over the gated space intervals.
In order that the power applied in controlling the
transistor can be kept small, it is advantageous to employ for
controlling the transistor a control voltage having an at least
approximately rectangular characteristic, and to deliver this
to the transistor through a transformer.
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F~ 84994
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In the performance of the above defined inventive method
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there is employed a circuit arrangement characterized by the
feature that the first mentioned power switching device
comprises at least an arrangement of two transistors connected
in series to the consumer and having parallel coDnected
collector-emitter paths, together with an arrangement of
rectifiers ror correct polarity delivery of the network
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alternating voltage, wherein there iP connected in the base-
emitter circuit of-each transistor the secondar~ winding of
a~ associated transformer, the primar~ winding of which is
connected to a circuit arrangeme~t for generating the control
voltage for the transistors.
~or performing the above described variant of the method7
the inventive circuit arrangement may contain, connected in
parallel to the consumer, a second power switching device,
which comprises the series circuit of the collector-emitter
path of a transistor, e.e. a Darlington transistor~ further-
more an arrangement of rectifiers for correct polarity
delivery to the transistor of the voltage applied to the
consumer, and a load, whilst in the base-emitter circuit of
the transistor there is connected the secondary winding of a
transformer, the primary ~Ji~ding of which is connected to a
circuit arrangement for generating the control voltage for
the tra~sistor.
An advantageous practicaljform of this circuit
arrangement consists of rectifiers arranged in a rectifier
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84994
bridge, one diagonal of which is connected parallel to theconsumer, and to the other diagonal of which there is connected
the collector-emitter path of the transistorO
For the purpose of receiving the stored energy upon
discharge of the consumer, the load which is connected in
~ parallel to the consumer may be an ohmic resistance and a choke.
- ~he herein~described methods and circuit arrangements
can be applied for the regulat~on of any desired t~pes of
consumer driven by an alternating current network, in
particular those of a highly capacitive character or those
with exceptionally reflective characteristics, as well as
consumers with reactive load compensation.
An important application of the invention consists in
the regulation of the brilliance of an electrical li~hting
irlstallation. In particular the method can advantageously be
u~ed for the regulation of fluorescent tubes in a lighting
installation whilst having only the slightest interference with
an existing system, and bringing with it optimal compensation
of the reactive power and small regulating losses. In
particulax the above de~ined discharge of the total consumer
network pxo~ides constant conditions at the start of each
half-wave and diminishes the ris~ of extinction by the
suppression of random glow discharges through participating
starters during the transient decay process, such as would
occur in the a~sence of this switching device for discharge
~nd damping.
1~84994
A further field of application is the regulation of
the driving powers of electric motors. In this field the
ab.sence of high peak current values when employing the
inventive met~lod means that t~ere .is a reduction in the
~tressing of the internal motor insulation caused by parasitic
capacitances, in contrast to the conditions obtaining when the
known regulation b~ phase angle contrcl is employed, as well
as a reduction i~ the bearing ~tresses due to pe~k ~orques.
I~ particular, in consequence of the above defined discharge
of the consumer, there is achie~e~, on account of the absence
Or a change of current direction, ~Jh~ch wov.ld othelwise
inevitably result from the transient eff~cts following the
switching off of the network switching device for current
~upply, an optimal integration of the impressed current in the
motor and therefore an added improv~ment in the steady running
behaviour of the motor.
In accordance with one aspect of the present invention
there is provided a method of regulating electrical power supplied
via a current path to at least one consumer in an A.C. network
which involves setting desired current flow angle using a power
switching device connected in the current path to the consumer, the
improvement comprising providing as the switching device at least
two transistors, connected in parallel and mutually decoupled,
connecting collector-emitter leads of the transistors in the
current path to the consumer, switching the transistors alternately
at a switching frequency higher than the line frequency in such
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^` 1C~84~94
manner that the time intervals of their ON states overlap cutting
the switching device ON at the beginning of each half wave of
A.C. line voltage, at least approximately at a phase angle of
0 , and cutting the power switching device OFF at a phase
angle corresponding to the desired current flow angle; whereby
the alternate connection of the transistors takes place in each
half period of the A.C. line voltage beginning at its start and
lasting until the desired cuTrent flow angle is reached.
According to another aspect of the present invention,
there is provided a method of polarity-independent reduction of
feedback from a consuming means periodically connected to an
A.C, line which includes disconnecting the consuming means from
the line during a predetermined period in each half wave of the
A.C. line voltage, the improvement including damping and dis-
charging the consuming means during each half wave of the A.C,
line voltage using a power switching means during the predetermined
period when the consuming means is disconnected from the A.C,
line.
Further applications of the invention are possible in the
field of electrical ignition for combustion processes.
Practical examples of the inventive method and of circuit
arrangements for its performance will no~ be described in more
detail with reference to the accompanying drawing, in which:
Fig. 1 is a diagram of current plotted against time in a
consumer when using the known method of regulation
by phase angle control,
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Fig. 2 is a diagram of the current plotted against time
in a consumer when using the inventive method
o~ regulation,
Fig. 3 is a circuit diagram of a first practical form
of the power switching device for performing
the inventive method,
~ig~ 4 is a diagram of the control voltages as a
function of time i~ respect of the power switch-
ing device of fig. 3,
Fig. 5 i~ a circuit diagram of a second practical form
- of the power switching device,
Fig. 6 i~ a diagram of the current consumption plotted
with respect to time in a consumer with periodic
interruption of the consumer from the alternating
current network and respective reconnection of
the consumer with the network, when the consumer
has stored electrical energy, i.e. in the case
of a complex consumer,
Fi~. 7 is a diagram of the voltage established at a
complex consumer plotte~ as a function of time,
: Fig 8 i8 a diagram of the voltage established at a
complex consumer plotted as a ~unction with
- respect to time when using a variant of the
inventive method,
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J 1~084994
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Figo 9 is a circuit diagram of an arrangement for
regulating the brilliance of a lighting
installation having a second power switching
device for performin~ the variant o~ the met~od
of the invention,
Fig. 10 is a diagram showing the control pulses used
i~ the arrangement of fig. 9 plotted with
respect to time.
I~ fig. 1 there is shown as a function of time the
current flowing through a consu~er according to a known method
Or regulation by phase angle control. ~rom the first zero
cross-over point tO up to a later time instant tl the rele~ant
power switching device remains blocked, i.e. no current flows.
At the time instant tl the power switching device is switched
on, i.e. the consumer is connected to the network, so that a
sudden current increase takes place at a high velocity, which
c~uses the already described current peaks and high frequency
disturbances to occur. The current continues to flow until the
next zero cross-over point tO'.
` Fig. 2 show~ the correspo~ding current graph with
respect to time in a method of regulation in accordance with
the invention. ~he appertaining power switching device is here
already switched on at the time instant tO of the first zero
cross-over point, so that the network alternating current
already flows through the consumer from the instant o~ c~oæs-
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1084994
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over of the alternating voltage, and the sudden ~rrent surge
is avoided. At a later time instant t2, corresponding to
the desired current flow angle, the power switching device
i8 blocked so that the current flowing through the consumer
sinks to zero until the power switching device is again
switched on at the next zero transit.
In the practical e~ample represented in fig. 3 a
consumer V is connected through a power switching device L~l
to terminals N of an alternating current network. The power
switching device ~Sl comprises two transistors Tl and '~2,
which are mutually decoupled in parallel connection in that
the~ respective collectors and emitters are connected
together. The connected collectors and emitters of the
transistors Tl and T2 are conneçted across one diagonal of a
rectifier bridge Gl, which has in each branch a rectifier
Dl, D2, D3 and D4 respectively, for example one or more diodesO
~he other diagonal of the rectifier bridge i8 connected in
series with the consumer V. ~he rectifier bridge serves the
purpose of protecting the transistors from faulty poling and
to make possible the full-wave operation of thé power
switching device here shown.
For the purpose of controlling th~ tra~sistthrs ~ and
~2 the bases thereof are connected in each case / a current
limiting resistance Rl and ~2 to the secondary wind~ng of a
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driver transformer TRl and TR2 respectively. To the primary
windings of the respective transformers there are delivered
control voltages Ul and U2, which will be further described
herein, ~or which purpose the primary windings are connected to
~eparate output terminals of a control voltage generator SGl.
The control of the transistors ~1 and T2 throu~h the trans-
formers makes it pos~ible by the use of impedance matching to
keep the necessar~ control power low; this method of control
also makes possible a potential separation of the bases of
the two transistors. In~tead of using two transistors Tl a~d
~2 it i8 also possible, in accordance with the loading, to
pro~ide a greater number of transistors connected in parallel
in the same manner.
With the object firstly of obtaining precise switching
instant~ for the transistors Tl and T2, and thereby to achie~e
a precisely determined current flow angie, and secondly in
order to keep the dimensions of the driving tr~nsformers ~Rl
~nd TR2 small, the control voltage generator SGl i8 80 designed
that it delivers at it~ output terminals control signals, the
frequency of which is substantially higher than that of thé
network frequency, and amounts for example to around 10 k~z.
~he con~trol signals are also preferably ~t least approximately
rect~ngul~r, whilst the control signals delivered at the two
respecti~e output pairs of terminals of the control signal
generator SGl are mutually displaced in time but overlap each
other.
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1084994
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The control ~oltages Ul and U2, which are preferabl~
delivered by the control voltage generator SGl, are represented
schematically in fig. 4 as a function of the time.
~he control voltage Ul is a re~tangular voltage with gating
pulses I and spacing intervals L, in which the control voltage
falls to zero value~ However, within the space intervals L
there are provided~ additional pulses Z, the polarity of which'
is opposite to those of the gating pulses I. The control
voltage U2 exhibits the same time characteristic as the control
voltage Ul, but i8 time displaced with respect to it so that
the gating pulses I of the control voltage U2 occur at the same
time as the space intervals L of the control voltage Ul. As
will be seen from fig. 4 the gating p~lses I of the control
voltages Ul and U2 overlap ~ach other during the time period ~t.
~ he mode of operation of the power switching device of-
fig. 3 i8 as follows, assuming as a basis the signal voltages
~1 and U2 of fig. 4.
At the beginning of a half-wave of the ~etwork altern~-
ting voltage (phase angle e~ual to zero degree~) the control
~ generatorvoltage'~Gl i8 opened and delivers control voltages Ul and U2 to
the primary windings of the driving transl'ormers TRl and TR2
respectively. Initially there is delivered through the one
transformer, e.g. the transformer ~1, the control voltage Ul,
with the gating pulse I, to the transistor ~1, so that the
latter becomes current don'ducting. Before the beginning of the
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saturation of the tra~sformer T~l the gating pulse I of the
control voltage U2 is delivered by transformer TR2 and brings
the transistor T2 into the current conducting condition, and
indeed this happens during the time that the transistor Tl i8
still current conducting on account of the overlapping of the
control voltages Ul and U2, so that in the consumer V there i~
obtained a continuous current flow. The space interval L
of the control voltage Ul now blocks the transistor ~1, whilst
the additional pul~e Z of reverse polarity occurring within
that interval removes the remanent mag~etization in the
transformer, and thus increase~ the power capability for the
next succeeding current conducting phase of the transistor ~1.
This operation repeats itself alternately for the transistors
Tl and ~2, 80 that the loading distributes itself uniformly
over the two participating transistors Tl and T2, whilst the
current flowing through the consumer V ass~mes continuously the
course of the network alternating voltage in the respective
half-wave. For achieving the de~ired current flow angle, the
control voltage generator SGl is then blocked~at the correspon-
ding phase angle of the half-wave, 80 that a fuxther control of
the transistors ~1 and T2 into t e current conducting condition
is omitted until the beginning of the next half-wave of the
network alternating voltage. The diodes Dl to D4 of the
rectifier bridge Gl here provide for the correct poling in
accordance with the alternating sign of the half-waves.
17 ~ i~
F 1084994
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In an e~ample the pulse frequency of the control ~oltages
~1 and U2 was lO kHz, the voltage of the gated pulses +lOV,
the voltage of the additional pulses -lO V, and the transforma-
tion ratio of the transformers ~Rl and T~2 was 3 ~ l. The
,;"
~ generation of the control voltages Ul and U2 as well as the
.~,.................................................................... .
adjustment of the desired current flow angle by the starting
and bloc~ing of the control voltage generator SGl can quite
easil~ be effected with ~nown means, in particular by means of
digital circuit arrangements.
A further practical form Or the power switching de~ice,
which is capable of switching a larger current and which
generates a smaller thermal loss is represented in fig. 5.
In the power switching device LS2 here shown there are provided
two arrangements o~ decoupled parallel connected transistors
T3, T4 and T5, T6 respectively, ths control of which i~ effected,
as in the practical example of rig. 3, by the individually
allocated driving transformers TR3, TR4, TR5 and TR6, together
with current limiting resistances R3, R4, R5 and R6. For
achieving the correct poling for a full-wa~e d~i~ing operation,
a rectifier D5 and D6 respectively, e.g. a diode, i8 connected
in series to each arrangement T~3, TR4 and TR5, TR6 of parallel
connected transistors. ~hese two series circuits are connected
in parallel and are situated in the current path of the network
in series with the consumer V, so that the current ~low
directions of the arrange~ent~ of the transistors and the
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1084~9
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rectifier1 with reference to the network or consumer connection
side of the said parallel circuit, are opposite to each other
in the one branch and the other br~nch of the parallel circuit.
~he primary winding~ of the transformers TR3 to TR6 are
connected to suitable output terminals of a control ~oltage
generator SG2 *or delivering the appertaining control voltages
U3, U4, U5 and U6 The course taken b~ the control voltages
U3 to U6 aiffers from that of the control voltages U2 and ~3
of ~ig. 3 ~olely by reason of the fact that, in dependence upon
thé existing polarity of the network alternating voltage,
the control can be discontinued of that particular arrangement
of transistors T3, ~4 or ~5, ~6 respectively which happens to
be in the non-loaded condition.
In the practical example of fig. 5 thermal losses occur
only at two rectifiers D~, D6. Moreover the current loading
distributes itself over four transistors ~3 to T6.
! In the described methods and circuit arrangements it is
conceded that at the t~me instant of disconnection any stored
electrical or magnetic energy will cause transient oscillation
ahd will be dissipated in the consumer. In such a case it is
to be expected that a voltage pea~ will occur. Because in most
cases the consumer load will include both inducti~e and
capacitive components, it will also not be possible to avoid
change~ of curre~t direction in the consumer. ~urthermore it is
~ecessary to have regard to parit~ between the electrical
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condition in the consumer and in the network when the current
supply to the consumer iB renewed~ because otherwise it must
be expected that additional current peaks will result.
In fig. 6 there is shown, on a basis corresponding to
that of fig. 2, the time function of a current taken by a
consumer from a~ alternating current network, wherein the
consumer is connected to the network in each half-wave at
the zero cross-over point of the network alternating voltage,
i.e. at the time instants tO, t2, t4 etc, and/co~nected fro~
the network at a later time instant tl, t~, t5 etc. corres-
ponding to the desired current flow angle. It can be shown
that, in consequence of the storage of energy, strong current
peaks will occur at each reconnection of the consumer ~th the
network at the time instants tO, t2, t4 etc., as indicated in
fig. 6. Such current peaks cause considerable high frequency
disturbing voltages, and moreover place a load on the switch-
ing device which is used for effecting the discon~ection and
reconnection of the consumer with the network, the switching
element of said switching device usually being in the form of
a semiconductor arrangement which i8 sensitive to current a~d
voltage peaks.
The cause of the voltage peaks of fig. 6 is shown in
fig. 7, which indicates the corresponding time function o~ the
voltage at the consumer. ~he consumer is disconnected from
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1~84994
the network at the time point tl. In consequence of energy
storage, the voltage at the consumer then falls off, for
example in accordance with the full line of the curve and
tends to continue a course along the dashed line. Because,
at the time instant t2, at the zero cross-over point of the
net~rork alternating voltage a reco~nection of the consumer
with the networ~ iæ established, the decay process must ~e
interrupted and the voltage at the consumer must of necessity
follow the network voltage. The corresponding surge in the
consumer voltage indicated at the time instant t2 in fig. 7,
from a value differing from zero value to a practically zero
value in the zero cross-over point of the network alternating
voltage, gives rise to the current pea~ shown in fig.6 at the
time instant t2 as well as at the corresponding time instants
t4 etc. at the beginn;ng of a new commutation phase.
According to a variant of the inventive method, at all
of the time instants tl, t3~ t5 etc. or shortly thereafter,
i.e. after the disconnection of the consumer from the network,
the consumer i8 damped a~d its energy content substantiall~
short circuited. ~he mode of operating this method i8 shown
in fig.8. From this it ls clear that, as a result of the
imposed damping and discharge beginn~ng from the time i~stants
tl, t3, t5 etc., the voltage assumes a strongly attenuated
course, so that at the time insta~ts t2, t4 etc., at which
the consumer is reconnected to the network, the voltage has
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21.
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practicall~ assumed the zero value. The current taken by
the consumer from the network therefore no longer exhibit~
the current peaks at the time instants t2, t4 etc. shoh~ in
fig.6, but in other respects t~kes the form of fig.6.
In fig. 9 there is shown schematically an arrangement
for regulating the brilliance of a lighting installation. In
this arrangement the consumer, which is conn~cted through a
f~r~t power switching device to the terminals ~ of an
alternating current network comprises a plurality of ballast
devices V& and a pluralit~ of fluorescent tubes I~, of which
only one of which i8 shown in the drawing, as well as the
appertaining glow starter GS. ~he first power switching
device is the same as the ~ower switching device LSl of fig.3
and therefore contains the rectifier bridge Gl with the four
diodes Dl to D4 and the two transistors T1 and ~2, whose
respectively connected collectors and e~itters are connected
to one diagonal of the rectifier bridge Gl. ~he other
diagonal i8 connected through two windings Wl and W2 of a
choke D~ in series to the above mentioned con~umer. The choke
windings Wl and W2 together with the parallel connected
condensers Cl and C2 fu~ction both as disturbance protective
members as well as protective means for the sem~conductor
elements present in the illustrated arrangement.
For the purpose of controlling the transistors Tl and
~2, the ~ases thereof ar~, like those in fig. 3, connected
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through current limiting resistances Rl, R2 and driving
trans~ormers ~Rl, TR2 to a con~rol voltage generator SG3,
which delivers the control voltages Ul and U2. The graph o$
the control voltages ~1, U2 has already been described with
reference to fig.4 and is again shown in fig.10.
A second power switching device for periodically
damping and discharging the consumer contains, according to
fig.9, a ~urther rectifier bridge G2 with four diodes ~7 to
D10, one diagonal of which rectifier bridge is connected
through a limiting and load resistance R7, as well as through
a further winding W3 of the choke D~, parallel to the consumer
containing the ballast devices YG and the fluorescent tubes
~R. I~ the other diagonal of the rectifier bridge G2 there is
connected the collector-emitter path of a Darlington transis-
tor T7, whose base i8 connected through a current limiting
resistacce R8 to the secondary winding of a further driving
transformer TR7. ~o the primary winding Or the tr~nsformer
~7 there i8 delivered a control voltage U7, for which purpose
the ilatter is connected to further output terminals of the
control voltage generator SG3. ~he control voltage U7, like
the control voltages Ul and U2, i8 rectangular and has a sub-
stantially higher frequency as compared with the network
frequenc~. Preferably the control voltage U7 exhibits the ~ame
shape and frequency as the control voltages Ul and U2, as is
represented in fig.10, but the control voltage ~7 contains no
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108499~
additic-al pul~as of opposite polarity. As will be fieen in
fig.10 and will be further described later, the control
volta~e ~o~orator SG3 periodically delivers the control
voltage U7 at times when there is no delivery of control
voltage~ Ul and U2 from the control voltage generator SG3.
At the beginning of a half-wave of the network
alternatin~ vol~age (phase angle equal to zero degrees
corresponding to the time insta~ts tO, t2, t4 etc. in fig.8)
the control voltage generator SG3 delivers the control
voltages Ul and U2 to the primary windings of the driving
transformers TRl and TR2, as is alread~ described with
reference to fig. 3. For obtaining the desired current flow
angle, the control voltage generator SG3 then interrupts, at
the corresponding phase angle of the half-wave, corresponding
to the time instants tl, t3, t5 etc. in ~ig. 8, the delivery
of the control voltages Ul and ~2, 80 that a further control
Or the transistors Tl and T2 into the current conducting
condition is suspended until the beginning of the next half-
wave. The diodes Dl to D4 of the rectifier bridge Gl provide
in this case for the correct poling in correspondence with
the alternating sign of the half-waves.
~ llowing for a slight delay taking into aocount the
storage and discharge times of the semconductor eleme~ts,
the control voltage generator SG3 delivers, following the last
pulse of the control voltages ~1, U2, and within the same
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1(~84~94
half-wave, the rectangular control voltage U? (fig.10) so that
the Darlington transistor T7 becomes current conducting.
Because the pulse gap~ of the control voltage U7 are smaller
than the storage time of the Darlington transistor T7, the
current conducting condition o$ the transistor T7 is continuous.
~he time period during which the transistor T7 is in the
conducting condition provides, throu B the rectifier bridge G2,
i e. the diodes D7, D9 or D8, D10 according to the polarity
of the respective half-wave, the load resistance R7 and the
winaing W3 of the choke DR, a current path parallel to the
consumer. Accordingly it is possible for the electrical
energy stored in the consumer to diæcharge continuously through
the Darlington transistor ~7, th;s being i~dicated in fig.9
by the condenser C3 shown in dashed lines indicating a compen-
sating and parasitic capacitance.
: As is evident from fig.10, the control voltage generator
SG~ interrupts the delivery of the contro} volta~e U7 shortly
before the next zero cross-over point of the network alternating
voltage, i.e. shortly prior to the instant whe~ the control
voltage generator SG3 again brings the transistors Tl and T2
alternately into the conducting condition by mean~ of the
control ~oltages Ul and U2.
In the reconnection of the consumer to the network after
the completion of periodic separatio~ from the network, the
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1~84994
suppression of current peaks, which is effected by the
described discharge of the complex consumer for the purpose
of power regulation i8 indeed involved with losses, but the~e
are nevertheless acceptable and are not signific~nt as co~- -
pared with the achieved advantage of the avoidance of current
peaks ~or example the arrangement represented in fig.9 may
be for the regulation of a fluorescent tube lighting installa-
tion, which is designed for a nominal current of 35 A, and
which includes for complete compensation of the fluorescent
tubes a parallel capacitan¢e of 450 microfarads. This
capacitance will, in the most un*avourable case, be charged to
~ voltage of 300 V, 80 that for each half-wave an energy of
135 mWs i8 to be expended, because the residual component in
the *orm of non-capacitively ~tored energy is dis~ipated
through the ballast deYices and~the fluorescent tubeY. ~he
total efficiency of the arrangement shown in fig.9 is there-
fore degraded by only 1.7%.
~ he oontrol of the transistors Tl, T2, ~7 through trans-
rormers makes it possible to maintain the necessary control
power small by impeda~ce matching. Furthermore this method
makes po~sible the potential separation of the bases of the
transistors. ~he generation of rectangular control signals ~1,
~2, U7 having a substantially higher frequency than that of
the network can, as shown, be effected by a single control vol-
tage generator SG3, 80 that the latter can ~e of relatively
~imple design.
26.
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