CA1168305A - Full wave frequency converter contractor structure and method - Google Patents
Full wave frequency converter contractor structure and methodInfo
- Publication number
- CA1168305A CA1168305A CA000360201A CA360201A CA1168305A CA 1168305 A CA1168305 A CA 1168305A CA 000360201 A CA000360201 A CA 000360201A CA 360201 A CA360201 A CA 360201A CA 1168305 A CA1168305 A CA 1168305A
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- Canada
- Prior art keywords
- phase
- full wave
- silicon controlled
- switching network
- rectifier
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Classifications
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
- H02M7/02—Conversion of ac power input into dc power output without possibility of reversal
- H02M7/04—Conversion of ac power input into dc power output without possibility of reversal by static converters
- H02M7/12—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M7/145—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a thyratron or thyristor type requiring extinguishing means
- H02M7/155—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a thyratron or thyristor type requiring extinguishing means using semiconductor devices only
- H02M7/162—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a thyratron or thyristor type requiring extinguishing means using semiconductor devices only in a bridge configuration
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- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Rectifiers (AREA)
- Arc Welding Control (AREA)
- Ac-Ac Conversion (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
A three-phase full wave bridge type rectifier utilizing silicon controlled rectifiers connected to receive a three-phase input electrical signal, a switch-ing network utilizing four silicon controlled rectifiers connected to receive and gate full wave rectified three-phase signals from the three-phase rectifier to provide desired positive and negative output signals, a trans-former having a single primary winding or multiple separate windings connected in parallel or series to receive the output of the switching network, and timing structure for timing the rectifier and switching network to produce alternate positive and negative full wave rectified three-phase signals at a selected frequency from the three-phase electrical energy input and gate them to the transformer primary, and the method of full wave frequency conversion comprising full wave rectifying three-phase electrical energy and gating the three-phase rectified electrical energy in alternate positive and negative electrical cycles to a transformer primary winding, or windings.
A three-phase full wave bridge type rectifier utilizing silicon controlled rectifiers connected to receive a three-phase input electrical signal, a switch-ing network utilizing four silicon controlled rectifiers connected to receive and gate full wave rectified three-phase signals from the three-phase rectifier to provide desired positive and negative output signals, a trans-former having a single primary winding or multiple separate windings connected in parallel or series to receive the output of the switching network, and timing structure for timing the rectifier and switching network to produce alternate positive and negative full wave rectified three-phase signals at a selected frequency from the three-phase electrical energy input and gate them to the transformer primary, and the method of full wave frequency conversion comprising full wave rectifying three-phase electrical energy and gating the three-phase rectified electrical energy in alternate positive and negative electrical cycles to a transformer primary winding, or windings.
Description
o s Title: "Full Wave Frequency Converter Contactor Structwre and Method"
BACKGROUND OF T~IE INVENTION
Field of the Invent.ion The invention relates to full wave frequency converter contactor structures a:nd methods~ and refers more specifically to structure for and a method o providing a transformer primary with an alternating electrical signal having substantially direct current electrical characteristics within the individual alter-nations thereof at selected frequencies, and the method of providing the selected frequency alternating signal~
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a schematic diagram of prior art frequency converter contactor structure utilizing con-ventional ignitron tubes.
Figure 2 is a schematic diagram of the full wave frequency converter contactor structure utilizing silicon controlled rectifiers constructed in accordance with the invention for performing the method of the invention.
Figure 3 is a diagram of the wave form of the signal from the full wave frequency converter contactor structure illustrated in Figure 2, useful in describing the structure and method of the invention.
Description of the Prior Art In the past, frequency converter contactors have generally taken the form of ignitron tubes connec-ted in the three separate phases of multi-part transformer primary windings, to produce half-wave rectified signals ,~
~ ~83~
through the separate parts of the primary windings~ One such prior art frequency converter contactor 10 i5 shown in E'igure 1.
The :Erequency converter contactor 10 is utilized in conjunction with or is part of the input circuit to the transformer 12. l'he fre~uency converter contactor 10 includes the inverse parallel connecked pairs of ignitron tubes 14,16 ancl 18 shown as switches in Figure 1 for simplicity, connected between the conduc-tors 20,22 and 2~ of a three-phase electrical power supply input line and the parts 26,28 and 30 of the primary winding 32 of transformer 12. The secondary winding 34 of the transformer 12 is then connected as shown in Figure 1 across the load 36.
With such structure, to generate a pulse of positive current in the secondary winding 34 of the transformer 12, the switch 14 is closed for a period during the time when the voltage between the conductors, 20 and 22 is positive. Switch 14 opens when the vol-tage between conductors 20 and 22 is no longer positive.
Sw.itch 16 is next closed while the voltage between the conductors 22 and 24 is positive and is opened when the voltage is no longer positive. Similarly, switch 18 is closed last while the voltage between conductors 24 and 20 is positive.
With such structure, the selecting o:E only the positive half cycles of the voltage across each phase of the three~phase power line 25 can continue until the transi~ormer core saturates. With such struc-ture the current of the secondary of the trans~ormer will be the half-wave of the three-phase primary current.
3~5 --3~
Such direct current wave form is useful where there i5 considerable inductance in the secondary cir-cuit of the transformerO The direct current wave~like form produced by the frequency converter contactor 10 is less affected by the inductance and allows more efficient use of the primary power.
However, the three interconnected windings of the transformer primary, that is, parts 26,28 and 30 thereof, present a problem to the contactor in the form of high voltage across the switches or ignitrons.
~ormally, with a 480 volt alternating current line 25, the peak voltage that a contactor has to wikhstand is approximately 680 volts. However, with the cross coupling effect of the three parimary windings 26,28 and 30, the peak voltage, that is, across the ignitron tubes or switches 14,16 and 18, is approximately 1280 volts.
Large voltage transients are generated by current cutoff at the end of each impulse due to the inductive nature of the transformer and its load. Like-wise, interruptions in t~e current due to weld blowouts in the case where transformer 12 is a welding trans-former and similar problems generate voltage transients across the primary windings 26,28 and 30 of the trans-former 12. These ~Ltage transients can reach amplitudes of 1000 volts and more.
secause of the combined problems indicated above, any contactor used for frequency converter ser-vice on a 480 volt line must be capable of withstanding, that is, have a withstanding voltage of at least 1800 volts. Experience has shown that a withstanding voltage substantially higher than this, that is, about 2500 volts is needed for truly reliable operation of a frequency converter.
~ ~;
~ ~83~
Until a few years ago, 2500 volt silicon con-trolled rectifiers of any size were unavailable. The technology to make them had not ~et been developed.
Even now, 2500 volt silicon controlled rectifiers with sufficient current handling capacity to control a large frequency converter transformer are prohibitively expensive when compared to ignitron tubes.
Further, with silicon controlled rectifiers in a traditional frequency converter contactor as disclosed in Figure 1, there is a tendency for them to turn on spuriously when a fast rise time voltage is applied across them. This is unac~ptable since i~ more than one silicon controlled rectifier is turned on at any give time, then a short circuit exists between two of the three phases in a three-phase power line through the transformer. The resultant high primary current, which may reach as high as 10,000 amperes, causes extreme stresses in a power transformer which will greatly shorten its life as a result of insulation failure.
SUMMARY OF THE INVE~TIOM
In accordance with the invention, a full wave frequency converter contactor, constructed as a three~
phase full wave bridge rectifier utilizing six silicon controlled rectifiers in conjunction with a switching network utilizing four additional silicon controlled rectifiers is provided between a three-phase electrical power supply line connected to the three-phase rectifier and a transfoxmer having a single primary winding or multiple separate primary portions connected with each other connected across the output of the switching net-work. Timing structure is also provided in accordance with the invention for turning the silicon controlled '`1 ' ~8~
rectifiers on and off ak selected times to provide full wave rectified electrical energy from the three-phase rectifier to the switching network and to gate the desired polarity pulses o rectified electrical energy through the switching net:wor~ to the transformer secondary winding.
In the full wave frequency conversion method of the invention, a three~phase alternating current signal is full wave rectified and the full wave rec-tified signal is gated to a u~i].izing transformer in pulses of selected polarity at selected times. The reswlting positive and negative substantially direct current pulses are fed into a single or multiple part transformer primary winding.
DESCRIPTION OF TEE: PREFÆRRED P~OI)IMEl!~T
As shown in Figure 2, the full wave fre~uency converter contactor structure 40 of the invention includes a three~phase full wave rectifier bridge cir-cuit ~2, a switching network 44 and a digital timer 46 connscted between a three-p~lase power line 4~ and a welding trans~ormer 50.
Electrical enargy from the three-phase elec-trical ener~y supply line 48 is connected to the three-phase rectifier 42 over the conductors 104, 106 and 108, as shown.
The three-phase rectifier 42 includes silicon controlled rectifiers 52, 54, 56, 58, 60 and 62. The silicon contxolled rectifiers are connected, as shown, in a full wave bridge rectifier circuit and have con-trol electxodes 64, 66r 68, 70, 72 and 74 connected to separate ones of the leads 76 from the digital timer 46 The silicon controlled rectifiers 52 through 62 are caused to conduct in pairs by signals through leads 76 from the timer 48 to provide rectified i~ree-phase alternating current of the polarity shown on the output conductors 78 and 80, as desired.
The switching ~etwork 44 includes the silicon controlled recti~iers 82, 84, 86 and 88 connected in a full wave brildge like circuit, as shown, having an input from the conductors 78 and 80 from the rectifier 42.
The silicon controlled rectifiers 82~ 84, 86 and 88 hav~ control electrodes 90, 92, 94 and 95 connected to separate ones of the leads 98 from the digital timer 46.
3 0 ~
The silicon controlled rectifiers 82,84,86 and 88 are caused to conduct in pairs by si.gnals over conductors 98 from the timer 48. The switching network 44 is oper-able to gate pulses of selected polarit~ from the rec-tifier 42 to the transformer 50 over the output conduc-tors 100 and 102.
~ he transformer 50, which may be a wel~ing transformer, includes the primary winding circuit 110 including the separate parts 112,114 and 116 and the secondary winding circuit 118. Parts 112,114 and 116 o~
the primary winding circuit 110 are connected in parallel with each other and receive the output of the switching network 44 over the conductors 100 and 102. It will be understood that the primary winding circuit 110 may be a single part winding or a multiple part winding with the parts connected in series as well as the multiple part winding 110 with the parts 112,114 and 116 connectad in parallel shown in Fig. 2.
In operation of the full wave frequency con-verter contactor structure 40 in accordance with the method of the invention, the three-phase electrical power signal from the electrical power line 48 is passed to the rectifier circui.t 42 over the conductors 104,106 and 108 and the rectifiers 52 through 62 are energized sequentially in pairs by signals from the digital timer 46 over conductors 76 to produce full wave rectifica-tion of the three-phase signal. A three-phase rectified, substantially direct current electrical signal polarized as shown is pxoduced on the conductors 78 and 80.
33~
With reference to Figure 3, wherein the electrical current from the conductors 104, 106 and 108 is indicated as wave orms 122, 124 and 126, respec-tively, the order of turning on the silicon controlled recti~iers ko rectify positive half~cyc:Les is as follows~
For phase one, 122, silicon comtrolled reckifiers 54 and 56 are turned on. For phase two, 124, silicon con-trolled rectifiers 58 and 60 will be turned on. For phase 3, 126, silicon controlled rectifiers 62 and 52 will be turned on.
For negative half-cycle rectification, shown.
in Figure 3, ~or phase one, 122 of the input electrical energy, rectifiers 52 and 58 would be turned on. For phase 2, 124, rectifiers 56 and 62 would be turned on.
For phase three, 1269 rectifiers 60 and 54 would be turned on Synchronized with the switching of the three-phase full wave ~ridge rectifier 42 by the digital tLmer 46 to produce pulses of electrical energy on conductors 100 and 10~Y the switching network ~4 is enexgized to apply voltage o the desired polarity at desired times to the transfo~mer primary winding 110. ~hus, if it is desired to pass a positive pulse to the transformer 50, the silicon controlled rectifiers 92 and 94 are energized, while if it is desired to pass a negative pulse through the transformer 50~ the silicon controlled rectifiers 90 and 96 are energized.
It wil]. ~e noted that the silicon controlled rectifiers are turned off for a short period o~ time ~ 16~0S
indicated 13* in Figure 3 between the production of the positive and negative pulses ga.ted to the transformer 50 to permit ths rectifiers to stabilize.
The digital timex 46 may be any of a n~nber of known digital controllers ca.pable o putting out pulses on the conductors 76 and 78 at selected t~nes to turn the silicon controlled rectifiers on in pairs as re~uired. Since such digital timers are within the skill of ths art to build or select or program in accordance wi~h the requirements of the invention, the digital timer 46 wi.ll not be considered in further detail herein.
Thus~ in operation, the three-phase bridge circuit is phase controlled to produce a substantially direct current voltage across the output conductors 78 and 80~ The switching network circuit is used to select which way the welding transformer 50 is connected to the positive and nesative output conductors 78 and 80~
In the full wave frequenc~ converter contactor 40, the silicon controlled rectifiers may be 140~ volt units, which are relatively inexpensive and quite avail-able. The reason that 1400 volt units are sufficien~
is that in the three-phase bridge circuit 42 there are two si~icon controlled rectifiers in series for each current path through the ~ridge, Thus, the withstanding voltage is the s~n of the two silicon controlled rec-tifiers withs~anding voltages, or 2800 voltsO
The sllicon controlled rectifiers in the switching networ~ circuit. 44 see the full ~80 volk line 10 -- .
voltage across them, that is, 680 volts peak. F~owever, they are not subject to any greater voltages than peaX
line voltage because there is no cross coupling effect between the primary parts of the transformer since the three parts of the primary winding 110 of the tran.s-former 50 are connected in parallel as shown~
Further, the transients caused by inductance of the transfoxmer and its load on turn-off are also dealt with effectively by the structure and method of the invention. Any voltage transients that appear across the tranqformer as its primary current is cut off are applied to at least two silicon controlled rectifiers in series, one of which will be reverse biased in accordance with the present invention.
Therefore, there is at least 2800 volts of withstanding capacity to withstand such transientsv In addition, any voltage transients generated in the txansformer circuit do not get coupled to the power line, becanse in order to do so the resulting current has to break down four silicon controlled rectifiers in series before ~uch coupling can occur.
The total withstanding voltage of the four silicon controlled rectifiers in series is approximately 5600 volts~
Thus, in accordance with the present structure an~ methoa~ silicon controlled rectifiers have been made available for fre~uency ~onverter service. In additionD the full wave frequency converter contactor of the invention has other advantages.
.
Because the transformer has full wave recti-fied direct current applied to its primaries, greater secondary welding currents are possible because any inductance in the primary wind-ings will no longer offer impedance to the applied direct current primary current.
In addition, primary resistanc~3 of a multiple-winding tran~ormer is reduced by the parallel connection of the three windings~
Also, the wave form of the current is much smoother, particularly at lower phase settingSo because the current wave form is full wave, not half wave rectified direct currentO The ripple frequency o~ 360 hz~
is very effectively filtered by secondary inductance, so that a standard strip chart recorder reading the voltage across a load shows almost no ripple, even at the lowest heat settings.
The power factor reflected back to the incom-ing power line is improved because there is no net direct current component to the current drawn. As a load, the contactor of Figure 2 much resembles a three-p~ase motor load.
When the current is off, the primary windings of the transformer are completely disconnected from the incoming power line. No voltage exists between the primary windings and ground~ This has favorable safety implications a~ ~.'721~ as isolating the transformer from the effects of very high voltage line surges due to lightning and other catastrophic events~
3~
~ 12 ~
Less expensive frequency converter trans-formers are possible with the contactor arrangement of the invention because they will only need one primary winding. Reliability and longevity o~ the transformer will likely be bette.r because of greater simplicity.
While one embodLment o~ the present invention has been considered in detail~ it will be understood that other embodiments and modi~ications thereo~ are contemplated by the inventor. It is the intention to include all embodiments and modifications as are de~ined ~y the appended claims within the scope o~ the invention.
. ' .
BACKGROUND OF T~IE INVENTION
Field of the Invent.ion The invention relates to full wave frequency converter contactor structures a:nd methods~ and refers more specifically to structure for and a method o providing a transformer primary with an alternating electrical signal having substantially direct current electrical characteristics within the individual alter-nations thereof at selected frequencies, and the method of providing the selected frequency alternating signal~
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a schematic diagram of prior art frequency converter contactor structure utilizing con-ventional ignitron tubes.
Figure 2 is a schematic diagram of the full wave frequency converter contactor structure utilizing silicon controlled rectifiers constructed in accordance with the invention for performing the method of the invention.
Figure 3 is a diagram of the wave form of the signal from the full wave frequency converter contactor structure illustrated in Figure 2, useful in describing the structure and method of the invention.
Description of the Prior Art In the past, frequency converter contactors have generally taken the form of ignitron tubes connec-ted in the three separate phases of multi-part transformer primary windings, to produce half-wave rectified signals ,~
~ ~83~
through the separate parts of the primary windings~ One such prior art frequency converter contactor 10 i5 shown in E'igure 1.
The :Erequency converter contactor 10 is utilized in conjunction with or is part of the input circuit to the transformer 12. l'he fre~uency converter contactor 10 includes the inverse parallel connecked pairs of ignitron tubes 14,16 ancl 18 shown as switches in Figure 1 for simplicity, connected between the conduc-tors 20,22 and 2~ of a three-phase electrical power supply input line and the parts 26,28 and 30 of the primary winding 32 of transformer 12. The secondary winding 34 of the transformer 12 is then connected as shown in Figure 1 across the load 36.
With such structure, to generate a pulse of positive current in the secondary winding 34 of the transformer 12, the switch 14 is closed for a period during the time when the voltage between the conductors, 20 and 22 is positive. Switch 14 opens when the vol-tage between conductors 20 and 22 is no longer positive.
Sw.itch 16 is next closed while the voltage between the conductors 22 and 24 is positive and is opened when the voltage is no longer positive. Similarly, switch 18 is closed last while the voltage between conductors 24 and 20 is positive.
With such structure, the selecting o:E only the positive half cycles of the voltage across each phase of the three~phase power line 25 can continue until the transi~ormer core saturates. With such struc-ture the current of the secondary of the trans~ormer will be the half-wave of the three-phase primary current.
3~5 --3~
Such direct current wave form is useful where there i5 considerable inductance in the secondary cir-cuit of the transformerO The direct current wave~like form produced by the frequency converter contactor 10 is less affected by the inductance and allows more efficient use of the primary power.
However, the three interconnected windings of the transformer primary, that is, parts 26,28 and 30 thereof, present a problem to the contactor in the form of high voltage across the switches or ignitrons.
~ormally, with a 480 volt alternating current line 25, the peak voltage that a contactor has to wikhstand is approximately 680 volts. However, with the cross coupling effect of the three parimary windings 26,28 and 30, the peak voltage, that is, across the ignitron tubes or switches 14,16 and 18, is approximately 1280 volts.
Large voltage transients are generated by current cutoff at the end of each impulse due to the inductive nature of the transformer and its load. Like-wise, interruptions in t~e current due to weld blowouts in the case where transformer 12 is a welding trans-former and similar problems generate voltage transients across the primary windings 26,28 and 30 of the trans-former 12. These ~Ltage transients can reach amplitudes of 1000 volts and more.
secause of the combined problems indicated above, any contactor used for frequency converter ser-vice on a 480 volt line must be capable of withstanding, that is, have a withstanding voltage of at least 1800 volts. Experience has shown that a withstanding voltage substantially higher than this, that is, about 2500 volts is needed for truly reliable operation of a frequency converter.
~ ~;
~ ~83~
Until a few years ago, 2500 volt silicon con-trolled rectifiers of any size were unavailable. The technology to make them had not ~et been developed.
Even now, 2500 volt silicon controlled rectifiers with sufficient current handling capacity to control a large frequency converter transformer are prohibitively expensive when compared to ignitron tubes.
Further, with silicon controlled rectifiers in a traditional frequency converter contactor as disclosed in Figure 1, there is a tendency for them to turn on spuriously when a fast rise time voltage is applied across them. This is unac~ptable since i~ more than one silicon controlled rectifier is turned on at any give time, then a short circuit exists between two of the three phases in a three-phase power line through the transformer. The resultant high primary current, which may reach as high as 10,000 amperes, causes extreme stresses in a power transformer which will greatly shorten its life as a result of insulation failure.
SUMMARY OF THE INVE~TIOM
In accordance with the invention, a full wave frequency converter contactor, constructed as a three~
phase full wave bridge rectifier utilizing six silicon controlled rectifiers in conjunction with a switching network utilizing four additional silicon controlled rectifiers is provided between a three-phase electrical power supply line connected to the three-phase rectifier and a transfoxmer having a single primary winding or multiple separate primary portions connected with each other connected across the output of the switching net-work. Timing structure is also provided in accordance with the invention for turning the silicon controlled '`1 ' ~8~
rectifiers on and off ak selected times to provide full wave rectified electrical energy from the three-phase rectifier to the switching network and to gate the desired polarity pulses o rectified electrical energy through the switching net:wor~ to the transformer secondary winding.
In the full wave frequency conversion method of the invention, a three~phase alternating current signal is full wave rectified and the full wave rec-tified signal is gated to a u~i].izing transformer in pulses of selected polarity at selected times. The reswlting positive and negative substantially direct current pulses are fed into a single or multiple part transformer primary winding.
DESCRIPTION OF TEE: PREFÆRRED P~OI)IMEl!~T
As shown in Figure 2, the full wave fre~uency converter contactor structure 40 of the invention includes a three~phase full wave rectifier bridge cir-cuit ~2, a switching network 44 and a digital timer 46 connscted between a three-p~lase power line 4~ and a welding trans~ormer 50.
Electrical enargy from the three-phase elec-trical ener~y supply line 48 is connected to the three-phase rectifier 42 over the conductors 104, 106 and 108, as shown.
The three-phase rectifier 42 includes silicon controlled rectifiers 52, 54, 56, 58, 60 and 62. The silicon contxolled rectifiers are connected, as shown, in a full wave bridge rectifier circuit and have con-trol electxodes 64, 66r 68, 70, 72 and 74 connected to separate ones of the leads 76 from the digital timer 46 The silicon controlled rectifiers 52 through 62 are caused to conduct in pairs by signals through leads 76 from the timer 48 to provide rectified i~ree-phase alternating current of the polarity shown on the output conductors 78 and 80, as desired.
The switching ~etwork 44 includes the silicon controlled recti~iers 82, 84, 86 and 88 connected in a full wave brildge like circuit, as shown, having an input from the conductors 78 and 80 from the rectifier 42.
The silicon controlled rectifiers 82~ 84, 86 and 88 hav~ control electrodes 90, 92, 94 and 95 connected to separate ones of the leads 98 from the digital timer 46.
3 0 ~
The silicon controlled rectifiers 82,84,86 and 88 are caused to conduct in pairs by si.gnals over conductors 98 from the timer 48. The switching network 44 is oper-able to gate pulses of selected polarit~ from the rec-tifier 42 to the transformer 50 over the output conduc-tors 100 and 102.
~ he transformer 50, which may be a wel~ing transformer, includes the primary winding circuit 110 including the separate parts 112,114 and 116 and the secondary winding circuit 118. Parts 112,114 and 116 o~
the primary winding circuit 110 are connected in parallel with each other and receive the output of the switching network 44 over the conductors 100 and 102. It will be understood that the primary winding circuit 110 may be a single part winding or a multiple part winding with the parts connected in series as well as the multiple part winding 110 with the parts 112,114 and 116 connectad in parallel shown in Fig. 2.
In operation of the full wave frequency con-verter contactor structure 40 in accordance with the method of the invention, the three-phase electrical power signal from the electrical power line 48 is passed to the rectifier circui.t 42 over the conductors 104,106 and 108 and the rectifiers 52 through 62 are energized sequentially in pairs by signals from the digital timer 46 over conductors 76 to produce full wave rectifica-tion of the three-phase signal. A three-phase rectified, substantially direct current electrical signal polarized as shown is pxoduced on the conductors 78 and 80.
33~
With reference to Figure 3, wherein the electrical current from the conductors 104, 106 and 108 is indicated as wave orms 122, 124 and 126, respec-tively, the order of turning on the silicon controlled recti~iers ko rectify positive half~cyc:Les is as follows~
For phase one, 122, silicon comtrolled reckifiers 54 and 56 are turned on. For phase two, 124, silicon con-trolled rectifiers 58 and 60 will be turned on. For phase 3, 126, silicon controlled rectifiers 62 and 52 will be turned on.
For negative half-cycle rectification, shown.
in Figure 3, ~or phase one, 122 of the input electrical energy, rectifiers 52 and 58 would be turned on. For phase 2, 124, rectifiers 56 and 62 would be turned on.
For phase three, 1269 rectifiers 60 and 54 would be turned on Synchronized with the switching of the three-phase full wave ~ridge rectifier 42 by the digital tLmer 46 to produce pulses of electrical energy on conductors 100 and 10~Y the switching network ~4 is enexgized to apply voltage o the desired polarity at desired times to the transfo~mer primary winding 110. ~hus, if it is desired to pass a positive pulse to the transformer 50, the silicon controlled rectifiers 92 and 94 are energized, while if it is desired to pass a negative pulse through the transformer 50~ the silicon controlled rectifiers 90 and 96 are energized.
It wil]. ~e noted that the silicon controlled rectifiers are turned off for a short period o~ time ~ 16~0S
indicated 13* in Figure 3 between the production of the positive and negative pulses ga.ted to the transformer 50 to permit ths rectifiers to stabilize.
The digital timex 46 may be any of a n~nber of known digital controllers ca.pable o putting out pulses on the conductors 76 and 78 at selected t~nes to turn the silicon controlled rectifiers on in pairs as re~uired. Since such digital timers are within the skill of ths art to build or select or program in accordance wi~h the requirements of the invention, the digital timer 46 wi.ll not be considered in further detail herein.
Thus~ in operation, the three-phase bridge circuit is phase controlled to produce a substantially direct current voltage across the output conductors 78 and 80~ The switching network circuit is used to select which way the welding transformer 50 is connected to the positive and nesative output conductors 78 and 80~
In the full wave frequenc~ converter contactor 40, the silicon controlled rectifiers may be 140~ volt units, which are relatively inexpensive and quite avail-able. The reason that 1400 volt units are sufficien~
is that in the three-phase bridge circuit 42 there are two si~icon controlled rectifiers in series for each current path through the ~ridge, Thus, the withstanding voltage is the s~n of the two silicon controlled rec-tifiers withs~anding voltages, or 2800 voltsO
The sllicon controlled rectifiers in the switching networ~ circuit. 44 see the full ~80 volk line 10 -- .
voltage across them, that is, 680 volts peak. F~owever, they are not subject to any greater voltages than peaX
line voltage because there is no cross coupling effect between the primary parts of the transformer since the three parts of the primary winding 110 of the tran.s-former 50 are connected in parallel as shown~
Further, the transients caused by inductance of the transfoxmer and its load on turn-off are also dealt with effectively by the structure and method of the invention. Any voltage transients that appear across the tranqformer as its primary current is cut off are applied to at least two silicon controlled rectifiers in series, one of which will be reverse biased in accordance with the present invention.
Therefore, there is at least 2800 volts of withstanding capacity to withstand such transientsv In addition, any voltage transients generated in the txansformer circuit do not get coupled to the power line, becanse in order to do so the resulting current has to break down four silicon controlled rectifiers in series before ~uch coupling can occur.
The total withstanding voltage of the four silicon controlled rectifiers in series is approximately 5600 volts~
Thus, in accordance with the present structure an~ methoa~ silicon controlled rectifiers have been made available for fre~uency ~onverter service. In additionD the full wave frequency converter contactor of the invention has other advantages.
.
Because the transformer has full wave recti-fied direct current applied to its primaries, greater secondary welding currents are possible because any inductance in the primary wind-ings will no longer offer impedance to the applied direct current primary current.
In addition, primary resistanc~3 of a multiple-winding tran~ormer is reduced by the parallel connection of the three windings~
Also, the wave form of the current is much smoother, particularly at lower phase settingSo because the current wave form is full wave, not half wave rectified direct currentO The ripple frequency o~ 360 hz~
is very effectively filtered by secondary inductance, so that a standard strip chart recorder reading the voltage across a load shows almost no ripple, even at the lowest heat settings.
The power factor reflected back to the incom-ing power line is improved because there is no net direct current component to the current drawn. As a load, the contactor of Figure 2 much resembles a three-p~ase motor load.
When the current is off, the primary windings of the transformer are completely disconnected from the incoming power line. No voltage exists between the primary windings and ground~ This has favorable safety implications a~ ~.'721~ as isolating the transformer from the effects of very high voltage line surges due to lightning and other catastrophic events~
3~
~ 12 ~
Less expensive frequency converter trans-formers are possible with the contactor arrangement of the invention because they will only need one primary winding. Reliability and longevity o~ the transformer will likely be bette.r because of greater simplicity.
While one embodLment o~ the present invention has been considered in detail~ it will be understood that other embodiments and modi~ications thereo~ are contemplated by the inventor. It is the intention to include all embodiments and modifications as are de~ined ~y the appended claims within the scope o~ the invention.
. ' .
Claims (10)
1. Full wave frequency converter contactor structure comprising a three-phase rectifier adapted to be connected to a source of three-phase electrical energy for supplying a full wave rectified substantially direct current energy to a switching network, a switching network connected directly to the three phase rectifier with substantially no impedance therebetween to receive the rectified direct current energy for gating the direct current energy in pulses directly to a transformer pri-mary winding in accordance with desired polarity and timing means connected to the three-phase rectifier and switching network for synchronizing the operation of the three-phase rectifier and the switching network to provide pulses of alternate positive and negative polarity of substantially direct current electrical energy from the switching network directly to the transformer at a selected fre-quency.
2. Structure as set forth in claim 1, wherein the three-phase rectifier includes six silicon controlled rectifiers connected in a full wave three-phase bridge rectifier circuit and the silicon controlled rectifiers are connected to the timing means so that the silicon controlled rectifiers are turned on in pairs to provide full wave rectification of the three-phase electrical energy from the three-phase electrical energy source.
3. Structure as set forth in claim 1, wherein the switching network includes four silicon controlled rectifiers connected in a full wave single-phase bridge-like switching network circuit and the silicon controlled rectifiers are connected to the timing means so that the silicon controlled rectifiers are turned on in pairs to gate the direct current energy from the three-phase full wave rectifier through the switching network to the transformer primary winding with the desired polarity.
4. Structure as set forth in claim 1, and further including the transformer primary winding and wherein the transformer primary winding is a single coil.
5. Structure as set forth in claim 1, and further including the transformer primary winding and wherein the transformer primary winding has multiple separate coils and the separate coils are connected in parallel with each other and across the switching net-work.
6. Structure as set forth in claim 1, where-in the timing means includes means for turning off the rectifier and switching network for a brief period be-tween each alternate positive and negative pulse.
7. A full wave frequency conversion method comprising converting three-phase alternating electri-cal energy into full wave rectified direct current energy and directly gating the direct current electri-cal energy in pulses of alternate positive and negative polarity directly to a transformer primary winding at a selected frequency.
8. The method as set forth in claim 7, wherein the three-phase electrical energy is rectified in a full wave bridge type rectifier including six silicon control-led rectifiers by alternatively energizing selected pairs of the silicon controlled rectifiers.
9. The method as set forth in claim 7, wherein the gating is accomplished by a switching network inclu-ding four silicon controlled rectifiers by alternately energizing pairs of the rectifiers.
10. The method as set forth in Claim 7, wherein the converting of the three-phase alternating energy and the gating of the direct current electrical energy in pulses is briefly halted between pulses of positive and negative polarity.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US7498179A | 1979-09-13 | 1979-09-13 | |
| US074,981 | 1979-09-13 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1168305A true CA1168305A (en) | 1984-05-29 |
Family
ID=22122811
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000360201A Expired CA1168305A (en) | 1979-09-13 | 1980-09-12 | Full wave frequency converter contractor structure and method |
Country Status (5)
| Country | Link |
|---|---|
| JP (1) | JPS5688674A (en) |
| CA (1) | CA1168305A (en) |
| DE (1) | DE3034151A1 (en) |
| FR (1) | FR2465356B1 (en) |
| GB (1) | GB2061032B (en) |
Family Cites Families (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2129834B1 (en) * | 1971-03-16 | 1974-04-26 | Jeumont Schneider | |
| GB1290810A (en) * | 1971-06-28 | 1972-09-27 | ||
| GB1467447A (en) * | 1974-02-22 | 1977-03-16 | Westinghouse Brake & Signal | Inverters |
| JPS5117532A (en) * | 1974-08-03 | 1976-02-12 | Yaskawa Denki Seisakusho Kk | |
| DE2541661C3 (en) * | 1975-09-18 | 1981-08-13 | Siemens Ag, 1000 Berlin Und 8000 Muenchen | Device for controlling the ignition angle of a resonant circuit inverter |
| DE2704347A1 (en) * | 1977-02-02 | 1978-08-03 | Siemens Ag | DEVICE FOR THE POWER SUPPLY OF AN OZONIZER |
| JPS5425430A (en) * | 1977-07-29 | 1979-02-26 | Toshiba Corp | Overvoltage protective system for current-type inverter |
-
1980
- 1980-09-11 DE DE19803034151 patent/DE3034151A1/en not_active Withdrawn
- 1980-09-12 CA CA000360201A patent/CA1168305A/en not_active Expired
- 1980-09-12 FR FR8019769A patent/FR2465356B1/en not_active Expired
- 1980-09-12 GB GB8029479A patent/GB2061032B/en not_active Expired
- 1980-09-13 JP JP12785480A patent/JPS5688674A/en active Pending
Also Published As
| Publication number | Publication date |
|---|---|
| DE3034151A1 (en) | 1981-04-02 |
| JPS5688674A (en) | 1981-07-18 |
| FR2465356B1 (en) | 1985-07-26 |
| GB2061032A (en) | 1981-05-07 |
| FR2465356A1 (en) | 1981-03-20 |
| GB2061032B (en) | 1984-01-25 |
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