CA1128126A - Circuit arrangement for producing reactive currents rapidly variable in magnitude and curve shape, and control and regulating units therefor - Google Patents
Circuit arrangement for producing reactive currents rapidly variable in magnitude and curve shape, and control and regulating units thereforInfo
- Publication number
- CA1128126A CA1128126A CA306,630A CA306630A CA1128126A CA 1128126 A CA1128126 A CA 1128126A CA 306630 A CA306630 A CA 306630A CA 1128126 A CA1128126 A CA 1128126A
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- Prior art keywords
- current
- rated
- value
- converter
- circuit arrangement
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Classifications
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/18—Arrangements for adjusting, eliminating or compensating reactive power in networks
- H02J3/1821—Arrangements for adjusting, eliminating or compensating reactive power in networks using shunt compensators
- H02J3/1835—Arrangements for adjusting, eliminating or compensating reactive power in networks using shunt compensators with stepless control
- H02J3/1842—Arrangements for adjusting, eliminating or compensating reactive power in networks using shunt compensators with stepless control wherein at least one reactive element is actively controlled by a bridge converter, e.g. active filters
-
- 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
- H02M5/00—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases
- H02M5/02—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases without intermediate conversion into dc
- H02M5/04—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases without intermediate conversion into dc by static converters
- H02M5/22—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases without intermediate conversion into dc by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M5/25—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases without intermediate conversion into dc 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
- H02M5/27—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases without intermediate conversion into dc 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 for conversion of frequency
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
- Y02E40/20—Active power filtering [APF]
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- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Rectifiers (AREA)
- Control Of Electrical Variables (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
A circuit arrangement for producing rapidly variable reactive currents with a current-converter transformer applied to the three-phase alternating-current mains to be influenced, and a current-converter regulating unit having controllable current-converter valves by means of which similar secondary windings of the current-converter transformer are looped-in, with a three-phase battery of capacitors connected in parallel to the alternating-current mains, and with a control or regulating unit. Connected as the current-converter regulating unit, to the secondary windings of each secondary-winding system, are mains-controlled current-converter bridge circuits which, on the direct-current side, are connected in series with each other and with a smoothing choke coil, the direct-current circuits of all secondary systems being connected, in the same direction, in series, into a closed circuit.
A circuit arrangement for producing rapidly variable reactive currents with a current-converter transformer applied to the three-phase alternating-current mains to be influenced, and a current-converter regulating unit having controllable current-converter valves by means of which similar secondary windings of the current-converter transformer are looped-in, with a three-phase battery of capacitors connected in parallel to the alternating-current mains, and with a control or regulating unit. Connected as the current-converter regulating unit, to the secondary windings of each secondary-winding system, are mains-controlled current-converter bridge circuits which, on the direct-current side, are connected in series with each other and with a smoothing choke coil, the direct-current circuits of all secondary systems being connected, in the same direction, in series, into a closed circuit.
Description
~ ~ Z1~3 26 The invention relates to a circuit arrangement for producing reactive currents rapidly variable in magnitude and curve shape, with a current-converter -transformer applied to the three-phase alternating-current mains to be influenced, and a current-converter regulating unit having controllable current-converter valves by means of ~hich similar secondary windings of the current-converter transformer are looped-in or are bypassed in idle operation, with a three-phase battery of cap-acitors connected i.n parallel to the alternating-current mains for the purpose of readying a predetermined compensating reactive power; and with a control or regulating unit for regulating this circuit arrangement.
The invention is for use in power electronics, especially for drives, fed from current converters, with inductive load cir-cuits.
A ~nown circuit arrangement of this kind, for symmetri-zing asymmetrical real-power loading in supply mains and for compensating reactive~-power loading, has au-tomatically-commutated semi-conductor valves for connecting or disconnecting the sec-ondary windings of the current~converter transformer (GermanoS 23 28 287). The current-converter transformer is in the form of a stra~ transformer. In this known case it is therefore advantageous to convert the primary supply voltage, by means of stray transformer, into a voltage of relatively small magnitude controlled by the control element, the said stray transformer also serves to produce an inductive current component.
Also proposed for compensating and symmetri.zing rapidly variable reactive currents is an arrangement (P 26 44 682.2) consisting of an automatically controlled current converter, known as a four-quadrant control, and a three-phase capacitor, the size of the latter being such that the currents from the three cap-acitor phases are about half as large as the maximal load current , i.. . . . ...
The invention is for use in power electronics, especially for drives, fed from current converters, with inductive load cir-cuits.
A ~nown circuit arrangement of this kind, for symmetri-zing asymmetrical real-power loading in supply mains and for compensating reactive~-power loading, has au-tomatically-commutated semi-conductor valves for connecting or disconnecting the sec-ondary windings of the current~converter transformer (GermanoS 23 28 287). The current-converter transformer is in the form of a stra~ transformer. In this known case it is therefore advantageous to convert the primary supply voltage, by means of stray transformer, into a voltage of relatively small magnitude controlled by the control element, the said stray transformer also serves to produce an inductive current component.
Also proposed for compensating and symmetri.zing rapidly variable reactive currents is an arrangement (P 26 44 682.2) consisting of an automatically controlled current converter, known as a four-quadrant control, and a three-phase capacitor, the size of the latter being such that the currents from the three cap-acitor phases are about half as large as the maximal load current , i.. . . . ...
2~
to be compensatecl in the relevant phase. Accorcling to another proposal, the effective component of the currents from the current-converter-corllpensation regulating unit is determined by the rated value of the conductance thereof. The rated value for the reactive currents from the compensation-regulation unit is obtained by measuring directly, and wi-thout delay, the total transient values of the load currents and of a three-phase cap-acitor in parallel therewlth, and by reducing this by the effec-tive component of the joint system of load currents, the effec-tive component being generated by means of an effective-con-ductance converter by automatic multiplication of a factor, proportional to the effective conductance of the load, by factors proportional to the time curve of the three-phase mains voltages.
The magnitudes of the rated values for the effective conductance of the compensation-regulating unit, of those for the four-quadrant control used as the compensation-regulating unit, is determined by a device for regulating the average voltage on the direct-current side of the said four-quadrant control. The necessary measurement data for this circuit arrangement appears 20 in another earlier proposal (P 26 57 168.6).
The construction of an automatic current converter requires, as controllable current-converter valves, thyristors with specially low release times, a comparatively small number of which are obtained during production. For high-output com-pensating installations it may therefore be of advantage to use mains-controlled current converters, since in that case the requirements relating to thyristor release times are sub-stantially lower.
It is already known to release into the alternating-current mains a specific reactive output by means of two mains-commutated controllable bridge-current-converters which, on the direct-current side, are connected in series through two choke ... ... . .
coils, one of the said converters operating in the rectifying range, for example with a control angleo~of 75, while the other operates in the alternating-current range, for example with a control anyle~of 105, and thus also to reduce the harmonic content by supplying corresponding currents (German AS 22 01 800). Again in this known case, a three-phase battery of capacitors, connected in parallel with the alternating-current mains, makes a capacitative reactlve output available. In this known case, the current-converter valves are connec-ted directly to the alternating-current~
mains and are therefore sized accordingly.
It is the purpose of the invention, starting from a circuit arrangement having a current-converter transformer and the other characteristics described at the beginning hereof, -to be able to use current-converter valves, especially thyristors, the release times of which do not have to be extremely short. Further-more, this circuit arrangement is to make it possib]e to produce reactive currents of which the curve shape is adjustable.
This purpose is achieved, according to the invention, in that connected, as current-converter regulating units, to the secondary windings o~ each secondary winding system, are mains controlled current-converter bridge circuits w~ich, on the direct-current side, are connected in series with each other and and with a smoothing choke coil, the direct-current circuits of all secondary systems being connected, in the same direction, in series, into a closed circuit. Two designs of -this are possible.
According to the first design, a single-phase bridge circuit is connected to each secondary winding.
According to the second design, a set of current-con-verter valves is connected, in a three-phase bridge circuit, to the phase conductor of each secondary three-phase winding system, which are in star-connection per se, the said set of current-converter valves also comprising a fourth branch-pair of valves, 2~;
the alternating-current connection of which is connected to the zero point of the relevant winding system.
The advantage is that it is possible with both designs to deliver, with the current-converter bridge circuits in con-junction with the three-phase battery of condensers and an appropriate regulating unit, reactive currents which follow a predetermined rated value rapidly and with good approximation.
~ n order to deliver power oscillations at twice the mains frequency, it is desirable to insert a parallel-resonance circuit, which is tuned to this frequency and which consists of a choke coil and a capacitor, into the direct-current circuit.
It is also the purpose of the invention to provide a control and re~ulating unit for the aforesaid circuit arrange-ment whicll meets the above-mentioned conditions for the supply of reactive currents. This control and re~ulatin~ unit con-stitutes the weak-current-engineerinq component of the circuit arrangement, and it is to be stipulated as being already known that the device according to German OS 23 29 287 also comprises a control and regulating unit for compensating the reactive-output load.
In achieving this purpose reference is made to earlierpatent application P 26 44 682.2 already mentioned above.
According to the invention/ the said purpose is achieved in that a rated-value transmitter and a device for monitoring and controlling the valve(s) is provided, the three currents from the transformer primary windings being approximated, independ-ently of each other, by multi-stage control of predetermined rated values, in that the number of control stages of one polarity coincides with the number of secondary systems in the current-converter transformer, in that if a positive switching limit is exceeded, or if a negative switching limit is not reached, a valve section is ignited by the rated value .. , , .. ~ . . , of the current, through a device for monitoring and controlling the valve(s) which is connectecl to the transformex secondary winding of the relevant phase, and upon which the blocking voltage acts precisely in the forward direction when the sign of the mains voltage and that of the take-off of the rated-value of the current coincide.
In accordance with one embodiment, there is provided a circuit arrangement for producing reactive currents, rapidly variable in magnitude and curve shape, with a current-converter transformer applied to three-phase alternating-current mains to be influenced, and a cu;rent-converter regulating unit having controllable current converted valves by means of which similar secondary windings of the current-converter transformer are looped-in or are bypassed in idle operation, with a three-phase battery of capaci-tors connecte~ in parallel -to the alternating-current mains for the purpose of readying a pre-determined compensating reactive output; and with a control or regulating unit for regulating thls circuit arrangement, characterized in that connected, as the current-converter regulating unit, to the secondary windings of each secondary-winding system, are mains-controlled current-converter bridge circuits which, on the direct-current side, are connected in series with each other and with a smoothing choke coil, the direct-current circuits of all the secondary systems being connected, in the same direction, in series, into a closed circuit.
~ dditional configurations of the control and regulat-ing unit for the circuit-arrangement according to the invention are set forth in claims 6 to 11. It is desirable to provide a direct-current control circuit in addition to the prescribed reactive-current control~
- The invention is e~plained in greater detail herein-,.. i . ... .
8~ 6 after in conjunction wi-th the examples of embodiment illustrated in the drawing attached hereto, wherein:
Fig. 1 shows a circuit arrangement having a single~
phase bridge circuit and a control and regulating unit, one phase being shown;
Fig. 2 shows the time curves for currents and voltages in the circuit according to Fig. l;
Fig. 3 shows an example of the circuit arrangement with three~phase secondary windings in star-connection and with three-phase bridge circuits connected thereto, and Fig. 4 shows the time curves for currents and voltages in the circuit arrangement according to Fig. 3.
Fig. 1 shows one phase of the circuit arrangement in which a current-converter transformer comprises, for example, four similar secondary windings 1 to 4 and a primary winding 5.
Primary winding 5 is in delta connection with the other primary windings, not shown, of the current~converter transformer.
Located in parallel with primary winding 5 is a capacitor 6 which is of a size such that, upon connection to the mains voltage, a current is produced the peak value of which is approximately equal to the maximal instantaneous value of the current to be compensated. Connected to secondary windings 1 to 4, which are preferably similar, in a single-phase bridge circuit, are four sets of valves with current-converter valves in valve sections 11, 13, 14, 16 and 21, 23, 24, 26 and 31, 33, 34, 36 and 41, 43, 44, 46. Four similar smoothing choke wind-inys 10, 20, 30 and 40, connected on the direct-current side of the single-phase current converter, may be arranged on a common iron core. All four sin~le-phase current converters are connected in series on the direct-current side, and they ~.~Z~l26 form jointly a short circuit.
The control devlce for this circuit arrangement con-sists of a rated-value transmitter 50, the output 50a of which is connected to output signal iq50ll with a compara-tor sta-tion.
The output side of comparator station 51 is connected to a device 54 for monitoring and controlling -the valves. This device monitors the current and vol-tage in each valve section, e.g. inputs lla, llb, and also forms, through a corresponding set of controls, the control commands for valves 11, 13, 14, 16 and 21, 23, ?4, 26 and 31, 33, 34, 36, 41, 43, 44 and 46.
Devices of this kind are generally known in other connections, e.g. from German Og 24 4:L 962 which discloses a device for monitoring the blocking voltage, but this is entirely for the protection of thyris-tors in connection with an HGUe installation.
Also provided is a control circuit having a direct-current regulator 60 which keeps the direct current idl determined by a measurement-data pick-up 61, constant and which, in the event of differences between rated value Id and actual value id of the direct current, predetermines, in the form of a sign, an effective-current rated value i which is added to the rated value iqsol1 derived from the reactive current control, for the current in primary winding 5 of the current-converter transformer. The value of the direct current must be such that, with symmetrical control of all valve sections 11 .. 46, current iq in primary winding 5 is approximately equal to the peak value of the capacitor current.
The method of operation of the circuit arrangement as a whole is explained hereinafter in greater detail in connection with the production, by way of approximation, of the desired reactive-current pattern in the example illustrated in Fig. 2.
Curve 1 represents the sine-shaped voltage uRs, while curve 2 represents the rated value iqsoll of the curxent to ~e picked up by transformer winding 5, the ~aid ra-ted value being predetermlned by the superimposed compensation-con-trol device 50. In the case of a current-converter bridge, if direc-t-current id flows through two diametrically opposed valves, e.g. 13 and 11, then this current also flows through the relevant secondary winding, e.g. 1, of the transformer, and the result of this is a corresponding current iq in primary winding 5. Ifl on the other hand, direct current id flows, in so-called idle operation, through two adjacent valves, e.g. 13 and 14, connected to the same transformer connection, then the relevant transformer winding, e.g. 1, remains dead and therefore also contributes nothin~ to primary current iq. Thus if di~ect current id remains constant, then, bearing in mind the sign, nine different values frorn - lOO~o to -~ 100% are possible for current iq in primary winding 5, depending upon how many of the four bridge~s are actually in idl~e operation~ If in primary winding S the highest ~urrent, namely 100%, is to flow, none of the bridges must operate in idle. If, on the other hand, all of the brid~es operate in idle, the primary current is 0%.
Fig. 2 shows possible values of primary current iq in the form of thin lines running parallel with the time axis. At the beginning of the time period shown, rated value iqsoll is only small. The actual valua of the current (heavy stepped curve 3) is 0%; all bridges are operating in idle, and valves 13, 14 and 23, 24 and 33, 3~ and 43, and 44 are conductive.
In the lower part of Fig. 2, the conductive condition of a valve is identified by a continuous line. The beginning and end o the conductive condition are emphasized by dashes.
At moment a, rated value iqsoll of primary current iq exceeds the switching limit of -~ 12.5% lying between the possible actual values of 0% and 25% of primary current iq. This may be determined by compara-tor 51, to which the variable iqsoll is fed, or by variouq threshold-value unit~ (not shown). The fact that the switching value has been exceeded is pic]ced up in known fashion by control device 54 which then causes valve section 11 to ignite. With the aid of mains voltage iRS, which at this moment is positive, the direct current switches over from valve 14 to valve 11, direct current id now flows through secondary winding 1 of the transformer, primary current iq now has a value of 25%. Valves 21 and 31 are ignited accordingly at moments b and c and, after time c, primary current i~ has a value of 7~%. Since rated value iqsoll does not exceed the limit value oE 87.5%, the fourth bridge remains in idle operation. ~t moment d, rated value iqsoll fails to reach the 62.5% limit and the bridge connected to winding 1 is returned to idle by ignition of valve 16. At this time,`the direct current switches over, with the aid of voltage uRS which has in the meanwhile become negative, from valve 13 to valve 16.
The same occurs at moments e and f; from f to ~, all of the bridges are again in the idle condition. At moment q, ignition of valve 16 causes direct current id to flow th~ough winding in the negative direction, and the primary current assumes the value - 25%. The choice of valves 11 .. 46 to be i~nited is governed by the following rule: if primary current iq, bear-ing in mind the sign, is to be increased, i.e. if it is to rise in the positive direction, then a valve having an odd reference numeral must be ignited. If, at this time, several valves bearing odd reference numerals are dead, the one that has been dead longest is ignited. If the primary current is to be reduced, a valve bearing an even referenced numeral is ignited.
In order to keep direct current id constant, an effective-current rated value iWsoll is formed with the aid 2~
of direct-current regulator 60, and this is added to reactive-current rated value iqso~l of the primary current. As shown in Fig. 2, actual value iq of the primary current follows the resultant rated value iqsoll rapidly and with little error.
The effective component of primary current iq adjusts itself automatically in the arrangement described, in such a manner that all losses in transformers, chokes and valves are covered.
The method of operation explained in connection with the single-phase arrangement shown in Fig. 1 does not alter if the current-converter bridges in all three phases - of the usual th~-ee-phase arrangement - are connected in series into a single direct-current circuit. In this connection, it is desirable fir.st of all to connect directly in series three bridges located in different phases, so -that the total voltage becomes that of a six-pulse current converter. If the total voltage of all the current-converter bridges does not assume values that are too hlgh, division of the smoothing choke windings may be dispensed with. As already indicated, primary windings 5 in the three-phase arrangement, operate in delta connection.
In order to reduce the complexity of the three-phase arrangement, it is proposed, according to another concept of the invention, to use a special form of three-phase current converter instead of the single-phase current converter. This possibility is illustrated in Fig. 3. Arranged in parallel with a three-phase battery of capacitors 6 is the delta-connected primary winding of a three-phase transformer having four similar secondary windings 1 ... 4 in star connection. The conductors connected to the ends of the windings are marked R,S,T, while the zero-point conductor is marked N. Connected to the four conductors of each secondary winding 1 O.. 4, in four-phase bridge connection, is a set of current-converter valves. The .
~LZ~
circuit may also be regarded as a three-phase bridge with two controlled zero anodes. The relationship between the valves and the four different arms is indicated by the letters R, S, T and N, while the relationship to the eight different com-mutating groups is indicated by the numbers 11, 12, 21, 22, 31, 32, 41, ~2. On the direct-current side, all four bridge cir-cuits are connected in series, and the circuit also contains a smoothing cho~e coil 9 and a parallel-resonance circuit com-prising a choke coil 7 and a capacitor 8. The resonant frequency of the parallel oscillating circuit must be twice the mains fre-quency. The regulating unit corresponds to that described in connection with Fig. 1 but, in addition to measuring devices 55 used to determlne when the valves are dead, corresponding devices are provided for the zero valves.
Fig. 4 shows how, with this arrangemen-t, it is possible to adapt the currents from primary winding 5 to a predetermined rated value rapidly and with comparatively little error. In Fig. ~, the thin continuous curves represent rated values iRsoll, iSsoll an~ iTsoll of the winding currents on the primary side, whereas the stepped curves represent actual values iR, is, iT of these currents. The periods during which individual valves 12 ... ~1 are conductive are shown in the bottom part of Fig. 4. The four different arms R, S, T, ~ are identified by different combinations of dots and dashes, and the eight different commutating groups by numbers 11 ... 42. Ignition of the individual valves is in accordance with the following rules:
1. If the amount of a primary current having a positive instantaneous value is to be increased, then the valve to be ignited is one connected to a phase conductor in the relevant phase from a commu-tating group having an odd reference numeral.
If at this moment several such valves are dead, the valve 2~:~
ignited will be the one in the commutating group whose zero anode valve exhibits the longest ignition time, 2. If the amount of a primary current iR, is or iT
having a positive instantaneous value is to be reduced, the valve to be ignited is one connected to a zero conductor in a commutating group having an odd reference numeral. If at this moment several such valves are dead, the valve ignited will be the one in the commutating groups, associated with the relevant phase, which has the longest ignition time. The same rules apply to primary currents with negative instantaneous values, except that commutating groups having even reference numerals are to be selected, insteacl of those having odd refer-ence numerals. The example in Fig. 4 shows a highly asymmetric-al primary-winding system. If the voltage system is symmetrical, the joint components of the symmetrical current system produce a chronologically constant output, whereas the counter~components produce an alternating output oscillating at twice the mains frequency. m e parallel-resonance circuit makes it possible to take this alternating output from direct-current circuit 7, 8, without any appreciable pulsation in direct-current id.
to be compensatecl in the relevant phase. Accorcling to another proposal, the effective component of the currents from the current-converter-corllpensation regulating unit is determined by the rated value of the conductance thereof. The rated value for the reactive currents from the compensation-regulation unit is obtained by measuring directly, and wi-thout delay, the total transient values of the load currents and of a three-phase cap-acitor in parallel therewlth, and by reducing this by the effec-tive component of the joint system of load currents, the effec-tive component being generated by means of an effective-con-ductance converter by automatic multiplication of a factor, proportional to the effective conductance of the load, by factors proportional to the time curve of the three-phase mains voltages.
The magnitudes of the rated values for the effective conductance of the compensation-regulating unit, of those for the four-quadrant control used as the compensation-regulating unit, is determined by a device for regulating the average voltage on the direct-current side of the said four-quadrant control. The necessary measurement data for this circuit arrangement appears 20 in another earlier proposal (P 26 57 168.6).
The construction of an automatic current converter requires, as controllable current-converter valves, thyristors with specially low release times, a comparatively small number of which are obtained during production. For high-output com-pensating installations it may therefore be of advantage to use mains-controlled current converters, since in that case the requirements relating to thyristor release times are sub-stantially lower.
It is already known to release into the alternating-current mains a specific reactive output by means of two mains-commutated controllable bridge-current-converters which, on the direct-current side, are connected in series through two choke ... ... . .
coils, one of the said converters operating in the rectifying range, for example with a control angleo~of 75, while the other operates in the alternating-current range, for example with a control anyle~of 105, and thus also to reduce the harmonic content by supplying corresponding currents (German AS 22 01 800). Again in this known case, a three-phase battery of capacitors, connected in parallel with the alternating-current mains, makes a capacitative reactlve output available. In this known case, the current-converter valves are connec-ted directly to the alternating-current~
mains and are therefore sized accordingly.
It is the purpose of the invention, starting from a circuit arrangement having a current-converter transformer and the other characteristics described at the beginning hereof, -to be able to use current-converter valves, especially thyristors, the release times of which do not have to be extremely short. Further-more, this circuit arrangement is to make it possib]e to produce reactive currents of which the curve shape is adjustable.
This purpose is achieved, according to the invention, in that connected, as current-converter regulating units, to the secondary windings o~ each secondary winding system, are mains controlled current-converter bridge circuits w~ich, on the direct-current side, are connected in series with each other and and with a smoothing choke coil, the direct-current circuits of all secondary systems being connected, in the same direction, in series, into a closed circuit. Two designs of -this are possible.
According to the first design, a single-phase bridge circuit is connected to each secondary winding.
According to the second design, a set of current-con-verter valves is connected, in a three-phase bridge circuit, to the phase conductor of each secondary three-phase winding system, which are in star-connection per se, the said set of current-converter valves also comprising a fourth branch-pair of valves, 2~;
the alternating-current connection of which is connected to the zero point of the relevant winding system.
The advantage is that it is possible with both designs to deliver, with the current-converter bridge circuits in con-junction with the three-phase battery of condensers and an appropriate regulating unit, reactive currents which follow a predetermined rated value rapidly and with good approximation.
~ n order to deliver power oscillations at twice the mains frequency, it is desirable to insert a parallel-resonance circuit, which is tuned to this frequency and which consists of a choke coil and a capacitor, into the direct-current circuit.
It is also the purpose of the invention to provide a control and re~ulating unit for the aforesaid circuit arrange-ment whicll meets the above-mentioned conditions for the supply of reactive currents. This control and re~ulatin~ unit con-stitutes the weak-current-engineerinq component of the circuit arrangement, and it is to be stipulated as being already known that the device according to German OS 23 29 287 also comprises a control and regulating unit for compensating the reactive-output load.
In achieving this purpose reference is made to earlierpatent application P 26 44 682.2 already mentioned above.
According to the invention/ the said purpose is achieved in that a rated-value transmitter and a device for monitoring and controlling the valve(s) is provided, the three currents from the transformer primary windings being approximated, independ-ently of each other, by multi-stage control of predetermined rated values, in that the number of control stages of one polarity coincides with the number of secondary systems in the current-converter transformer, in that if a positive switching limit is exceeded, or if a negative switching limit is not reached, a valve section is ignited by the rated value .. , , .. ~ . . , of the current, through a device for monitoring and controlling the valve(s) which is connectecl to the transformex secondary winding of the relevant phase, and upon which the blocking voltage acts precisely in the forward direction when the sign of the mains voltage and that of the take-off of the rated-value of the current coincide.
In accordance with one embodiment, there is provided a circuit arrangement for producing reactive currents, rapidly variable in magnitude and curve shape, with a current-converter transformer applied to three-phase alternating-current mains to be influenced, and a cu;rent-converter regulating unit having controllable current converted valves by means of which similar secondary windings of the current-converter transformer are looped-in or are bypassed in idle operation, with a three-phase battery of capaci-tors connecte~ in parallel -to the alternating-current mains for the purpose of readying a pre-determined compensating reactive output; and with a control or regulating unit for regulating thls circuit arrangement, characterized in that connected, as the current-converter regulating unit, to the secondary windings of each secondary-winding system, are mains-controlled current-converter bridge circuits which, on the direct-current side, are connected in series with each other and with a smoothing choke coil, the direct-current circuits of all the secondary systems being connected, in the same direction, in series, into a closed circuit.
~ dditional configurations of the control and regulat-ing unit for the circuit-arrangement according to the invention are set forth in claims 6 to 11. It is desirable to provide a direct-current control circuit in addition to the prescribed reactive-current control~
- The invention is e~plained in greater detail herein-,.. i . ... .
8~ 6 after in conjunction wi-th the examples of embodiment illustrated in the drawing attached hereto, wherein:
Fig. 1 shows a circuit arrangement having a single~
phase bridge circuit and a control and regulating unit, one phase being shown;
Fig. 2 shows the time curves for currents and voltages in the circuit according to Fig. l;
Fig. 3 shows an example of the circuit arrangement with three~phase secondary windings in star-connection and with three-phase bridge circuits connected thereto, and Fig. 4 shows the time curves for currents and voltages in the circuit arrangement according to Fig. 3.
Fig. 1 shows one phase of the circuit arrangement in which a current-converter transformer comprises, for example, four similar secondary windings 1 to 4 and a primary winding 5.
Primary winding 5 is in delta connection with the other primary windings, not shown, of the current~converter transformer.
Located in parallel with primary winding 5 is a capacitor 6 which is of a size such that, upon connection to the mains voltage, a current is produced the peak value of which is approximately equal to the maximal instantaneous value of the current to be compensated. Connected to secondary windings 1 to 4, which are preferably similar, in a single-phase bridge circuit, are four sets of valves with current-converter valves in valve sections 11, 13, 14, 16 and 21, 23, 24, 26 and 31, 33, 34, 36 and 41, 43, 44, 46. Four similar smoothing choke wind-inys 10, 20, 30 and 40, connected on the direct-current side of the single-phase current converter, may be arranged on a common iron core. All four sin~le-phase current converters are connected in series on the direct-current side, and they ~.~Z~l26 form jointly a short circuit.
The control devlce for this circuit arrangement con-sists of a rated-value transmitter 50, the output 50a of which is connected to output signal iq50ll with a compara-tor sta-tion.
The output side of comparator station 51 is connected to a device 54 for monitoring and controlling -the valves. This device monitors the current and vol-tage in each valve section, e.g. inputs lla, llb, and also forms, through a corresponding set of controls, the control commands for valves 11, 13, 14, 16 and 21, 23, ?4, 26 and 31, 33, 34, 36, 41, 43, 44 and 46.
Devices of this kind are generally known in other connections, e.g. from German Og 24 4:L 962 which discloses a device for monitoring the blocking voltage, but this is entirely for the protection of thyris-tors in connection with an HGUe installation.
Also provided is a control circuit having a direct-current regulator 60 which keeps the direct current idl determined by a measurement-data pick-up 61, constant and which, in the event of differences between rated value Id and actual value id of the direct current, predetermines, in the form of a sign, an effective-current rated value i which is added to the rated value iqsol1 derived from the reactive current control, for the current in primary winding 5 of the current-converter transformer. The value of the direct current must be such that, with symmetrical control of all valve sections 11 .. 46, current iq in primary winding 5 is approximately equal to the peak value of the capacitor current.
The method of operation of the circuit arrangement as a whole is explained hereinafter in greater detail in connection with the production, by way of approximation, of the desired reactive-current pattern in the example illustrated in Fig. 2.
Curve 1 represents the sine-shaped voltage uRs, while curve 2 represents the rated value iqsoll of the curxent to ~e picked up by transformer winding 5, the ~aid ra-ted value being predetermlned by the superimposed compensation-con-trol device 50. In the case of a current-converter bridge, if direc-t-current id flows through two diametrically opposed valves, e.g. 13 and 11, then this current also flows through the relevant secondary winding, e.g. 1, of the transformer, and the result of this is a corresponding current iq in primary winding 5. Ifl on the other hand, direct current id flows, in so-called idle operation, through two adjacent valves, e.g. 13 and 14, connected to the same transformer connection, then the relevant transformer winding, e.g. 1, remains dead and therefore also contributes nothin~ to primary current iq. Thus if di~ect current id remains constant, then, bearing in mind the sign, nine different values frorn - lOO~o to -~ 100% are possible for current iq in primary winding 5, depending upon how many of the four bridge~s are actually in idl~e operation~ If in primary winding S the highest ~urrent, namely 100%, is to flow, none of the bridges must operate in idle. If, on the other hand, all of the brid~es operate in idle, the primary current is 0%.
Fig. 2 shows possible values of primary current iq in the form of thin lines running parallel with the time axis. At the beginning of the time period shown, rated value iqsoll is only small. The actual valua of the current (heavy stepped curve 3) is 0%; all bridges are operating in idle, and valves 13, 14 and 23, 24 and 33, 3~ and 43, and 44 are conductive.
In the lower part of Fig. 2, the conductive condition of a valve is identified by a continuous line. The beginning and end o the conductive condition are emphasized by dashes.
At moment a, rated value iqsoll of primary current iq exceeds the switching limit of -~ 12.5% lying between the possible actual values of 0% and 25% of primary current iq. This may be determined by compara-tor 51, to which the variable iqsoll is fed, or by variouq threshold-value unit~ (not shown). The fact that the switching value has been exceeded is pic]ced up in known fashion by control device 54 which then causes valve section 11 to ignite. With the aid of mains voltage iRS, which at this moment is positive, the direct current switches over from valve 14 to valve 11, direct current id now flows through secondary winding 1 of the transformer, primary current iq now has a value of 25%. Valves 21 and 31 are ignited accordingly at moments b and c and, after time c, primary current i~ has a value of 7~%. Since rated value iqsoll does not exceed the limit value oE 87.5%, the fourth bridge remains in idle operation. ~t moment d, rated value iqsoll fails to reach the 62.5% limit and the bridge connected to winding 1 is returned to idle by ignition of valve 16. At this time,`the direct current switches over, with the aid of voltage uRS which has in the meanwhile become negative, from valve 13 to valve 16.
The same occurs at moments e and f; from f to ~, all of the bridges are again in the idle condition. At moment q, ignition of valve 16 causes direct current id to flow th~ough winding in the negative direction, and the primary current assumes the value - 25%. The choice of valves 11 .. 46 to be i~nited is governed by the following rule: if primary current iq, bear-ing in mind the sign, is to be increased, i.e. if it is to rise in the positive direction, then a valve having an odd reference numeral must be ignited. If, at this time, several valves bearing odd reference numerals are dead, the one that has been dead longest is ignited. If the primary current is to be reduced, a valve bearing an even referenced numeral is ignited.
In order to keep direct current id constant, an effective-current rated value iWsoll is formed with the aid 2~
of direct-current regulator 60, and this is added to reactive-current rated value iqso~l of the primary current. As shown in Fig. 2, actual value iq of the primary current follows the resultant rated value iqsoll rapidly and with little error.
The effective component of primary current iq adjusts itself automatically in the arrangement described, in such a manner that all losses in transformers, chokes and valves are covered.
The method of operation explained in connection with the single-phase arrangement shown in Fig. 1 does not alter if the current-converter bridges in all three phases - of the usual th~-ee-phase arrangement - are connected in series into a single direct-current circuit. In this connection, it is desirable fir.st of all to connect directly in series three bridges located in different phases, so -that the total voltage becomes that of a six-pulse current converter. If the total voltage of all the current-converter bridges does not assume values that are too hlgh, division of the smoothing choke windings may be dispensed with. As already indicated, primary windings 5 in the three-phase arrangement, operate in delta connection.
In order to reduce the complexity of the three-phase arrangement, it is proposed, according to another concept of the invention, to use a special form of three-phase current converter instead of the single-phase current converter. This possibility is illustrated in Fig. 3. Arranged in parallel with a three-phase battery of capacitors 6 is the delta-connected primary winding of a three-phase transformer having four similar secondary windings 1 ... 4 in star connection. The conductors connected to the ends of the windings are marked R,S,T, while the zero-point conductor is marked N. Connected to the four conductors of each secondary winding 1 O.. 4, in four-phase bridge connection, is a set of current-converter valves. The .
~LZ~
circuit may also be regarded as a three-phase bridge with two controlled zero anodes. The relationship between the valves and the four different arms is indicated by the letters R, S, T and N, while the relationship to the eight different com-mutating groups is indicated by the numbers 11, 12, 21, 22, 31, 32, 41, ~2. On the direct-current side, all four bridge cir-cuits are connected in series, and the circuit also contains a smoothing cho~e coil 9 and a parallel-resonance circuit com-prising a choke coil 7 and a capacitor 8. The resonant frequency of the parallel oscillating circuit must be twice the mains fre-quency. The regulating unit corresponds to that described in connection with Fig. 1 but, in addition to measuring devices 55 used to determlne when the valves are dead, corresponding devices are provided for the zero valves.
Fig. 4 shows how, with this arrangemen-t, it is possible to adapt the currents from primary winding 5 to a predetermined rated value rapidly and with comparatively little error. In Fig. ~, the thin continuous curves represent rated values iRsoll, iSsoll an~ iTsoll of the winding currents on the primary side, whereas the stepped curves represent actual values iR, is, iT of these currents. The periods during which individual valves 12 ... ~1 are conductive are shown in the bottom part of Fig. 4. The four different arms R, S, T, ~ are identified by different combinations of dots and dashes, and the eight different commutating groups by numbers 11 ... 42. Ignition of the individual valves is in accordance with the following rules:
1. If the amount of a primary current having a positive instantaneous value is to be increased, then the valve to be ignited is one connected to a phase conductor in the relevant phase from a commu-tating group having an odd reference numeral.
If at this moment several such valves are dead, the valve 2~:~
ignited will be the one in the commutating group whose zero anode valve exhibits the longest ignition time, 2. If the amount of a primary current iR, is or iT
having a positive instantaneous value is to be reduced, the valve to be ignited is one connected to a zero conductor in a commutating group having an odd reference numeral. If at this moment several such valves are dead, the valve ignited will be the one in the commutating groups, associated with the relevant phase, which has the longest ignition time. The same rules apply to primary currents with negative instantaneous values, except that commutating groups having even reference numerals are to be selected, insteacl of those having odd refer-ence numerals. The example in Fig. 4 shows a highly asymmetric-al primary-winding system. If the voltage system is symmetrical, the joint components of the symmetrical current system produce a chronologically constant output, whereas the counter~components produce an alternating output oscillating at twice the mains frequency. m e parallel-resonance circuit makes it possible to take this alternating output from direct-current circuit 7, 8, without any appreciable pulsation in direct-current id.
Claims (12)
1. A circuit arrangement for producing reactive currents, rapidly variable in magnitude and curve shape, with a current-converter transformer applied to three-phase alternating-current mains to be influenced, and a current-converter regulating unit having controllable current-converter valves by means of which similar secondary windings of the current-converter transformer are looped-in or are bypassed in idle operation; with a three-phase battery of capacitors connected in parallel to the alternating-current mains for the purpose of readying a pre-determined compensating reactive output; and with a control or regulating unit for regulating this circuit arrangement, characterized in that connected, as the current-converter regulating unit, to the secondary windings of each secondary-winding system, are mains-controlled current-converter bridge circuits which, on the direct-current side, are connected in series with each other and with a smoothing choke coil, the direct-current circuits of all the secondary systems being connected, in the same direction, in series, into a closed cir-cuit.
2. A circuit arrangement according to claim 1, character-ized in that a single-phase bridge circuit is connected to each secondary winding.
3. A circuit arrangement according to claim 1, character-ized in that a set of current-converter valves is connected, in a three-phase bridge circuit, to the phase conductor of each secondary three-phase winding system, which are in star-connection per se, the said set of current-converter valves also comprising a fourth branch-pair of valves, the alternating-current connection of which is connected to the zero point of the relevant secondary winding system.
4. A circuit according to claim 1, characterized in that in order to deliver power oscillations at twice the mains fre-quency, a parallel-resonance circuit, which is tuned to this frequency and which consists of a choke coil and a capacitor, is inserted into the direct-current circuit.
5. A circuit arrangement according to claim 1, character-ized in that a rated-value transmitter, a comparator, and a device for monitoring and controlling the valves are provided, the three currents from the transformer primary windings being approximated, independently of each other, by multi-stage con-trol of the predetermined rated values; in that the number of control stages of one polarity coincides with the number of secondary systems of the current-converter transformer; in that if a positive switching limit is exceeded, or if a negative switching limit is not reached, a valve section is ignited, by the rated-value of the current, through the device for monitor-ing and controlling the valves which is connected to the trans-former secondary winding of the relevant phase, and to which the positive blocking voltage is applied at the comparison moment when the sign of the mains voltage, and that of the chronologic-al derivation of the rated-value of the current, coincide.
6. A circuit arrangement according to any one of claims 1, 2 or 3, characterized in that if a positive switching limit is not reached, or if a negative switching limit is exceeded, the rated value of the current, by means of a preceding com-parator, and through the control device, causes ignition of the valve section which is connected to a transformer winding of the relevant phase, and to which a positive blocking voltage is applied at the comparison moment, when the signs of the mains voltage, and of the chronological derivation of the rated-value of the current, coincide.
7. A circuit arrangement according to claims 4 or 5, characterized in that if a positive switching limit is not reached, or if a negative switching limit is exceeded, the rated value of the current, by means of a preceding comparator, and through the control device, causes ignition of the valve section which is connected to a transformer winding of the relevant phase, and to which a positive blocking voltage is applied at the comparison moment, when the signs of the mains voltage, and of the chronological derivation of the rated-value of the current, coincide.
8. A circuit arrangement according to claims 1, 2 and 5, characterized by measuring devices which determine the length of time during which each valve section is dead, and which ignite, through the control device, the valve section to which a positive blocking voltage has been applied, and which exhibits the highest measured value for the period during which it is dead.
9. A circuit arrangement according to claims 1, 3 and 5, characterized in that if a positive switching limit is not reached, or a negative switching limit is exceeded, ignition of the valve section is caused through the rated value of the current, by means of the comparator, through the relevant con-trol device, the said valve section being the one connected to a zero point of the transformer system and to which a positive blocking voltage has been applied, when the signs of the mains voltage and the chronological derivation of the rated-value of the current coincide.
10. A circuit arrangement according to claims 1, 3 and 5, characterized in that if a positive switching limit is not reached, or a negative switching limit is exceeded, ignition of the valve section is caused through the rated value of the current, by means of the comparator, through the relevant con-trol device, the said valve section being the one connected to a zero point of the transformer system and to which a positive blocking voltage has been applied, when the signs of the mains voltage and the chronological derivation of the rated-value of the current coincide, and further characterized by measuring devices which determine the length of time during which current flows in the valve branches connected to the phase conductors and which produce ignition of the valve section to which a positive blocking voltage has been applied and which belongs to the commutating group containing the valve having the high-est value of current flow of all valves in the relevant phase.
11. A circuit arrangement according to claims 1, 3 and 5, characterized in that if a positive switching limit is not reached, or a negative switching limit is exceeded, ignition of the valve section is caused through the rated value of the current, by means of the comparator, through the relevant con-trol device, the said valve section being the one connected to a zero point of the transformer system and to which a positive blocking voltage has been applied, when the signs of the mains voltage and the chronological derivation of the rated-value of the current coincide, and further characterized by measuring devices which determine the length of time during which current flows in the valve branches connected to the zero-point con-ductors, and which produce ignition of the valve section to which a positive blocking voltage has been applied, and which belongs to the commutating group containing the zero valve having the highest measured value of current flow.
12. A circuit arrangement according to claim 5, characterized by a direct-current regulator which keeps the direct current id constant and which, in the event of differences between the rated and actual values of the direct current, provides, in the form of a sign, an effective-current rated value iWsoll which is added to rated value iqsoll, derived from the reactive-current control, for the current in the primary winding of the current-converter transformer.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DEP2730010.3 | 1977-07-02 | ||
| DE2730010A DE2730010C2 (en) | 1977-07-02 | 1977-07-02 | Circuit arrangement for generating reactive currents that can be changed quickly according to size and curve shape |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1128126A true CA1128126A (en) | 1982-07-20 |
Family
ID=6013038
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA306,630A Expired CA1128126A (en) | 1977-07-02 | 1978-06-30 | Circuit arrangement for producing reactive currents rapidly variable in magnitude and curve shape, and control and regulating units therefor |
Country Status (3)
| Country | Link |
|---|---|
| CA (1) | CA1128126A (en) |
| DE (1) | DE2730010C2 (en) |
| SE (1) | SE438754B (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE2918299A1 (en) * | 1979-05-07 | 1980-11-20 | Bbc Brown Boveri & Cie | Rapidly changing reactive current producing system - uses three-phase transformer and compensation capacitors to perform given correction |
| EP0053413B1 (en) * | 1980-12-03 | 1984-10-24 | BBC Aktiengesellschaft Brown, Boveri & Cie. | Device for the continuous control of the phase angle in electric energy transmission installations |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE2247819C3 (en) * | 1972-09-29 | 1978-10-05 | Siemens Ag, 1000 Berlin Und 8000 Muenchen | Balancing device for a three-phase network |
-
1977
- 1977-07-02 DE DE2730010A patent/DE2730010C2/en not_active Expired
-
1978
- 1978-06-28 SE SE7807326A patent/SE438754B/en not_active IP Right Cessation
- 1978-06-30 CA CA306,630A patent/CA1128126A/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| DE2730010C2 (en) | 1985-05-30 |
| SE7807326L (en) | 1979-01-03 |
| DE2730010A1 (en) | 1979-01-18 |
| SE438754B (en) | 1985-04-29 |
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