CA1056451A - Converter control apparatus for ac-dc parallel power transmission system - Google Patents
Converter control apparatus for ac-dc parallel power transmission systemInfo
- Publication number
- CA1056451A CA1056451A CA247,074A CA247074A CA1056451A CA 1056451 A CA1056451 A CA 1056451A CA 247074 A CA247074 A CA 247074A CA 1056451 A CA1056451 A CA 1056451A
- Authority
- CA
- Canada
- Prior art keywords
- voltage
- power transmission
- transmission system
- direct current
- current reference
- 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.)
- Expired
Links
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
- H02M7/66—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output with possibility of reversal
- H02M7/68—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output with possibility of reversal by static converters
- H02M7/72—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output with possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M7/75—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output with 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
- H02M7/757—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output with 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
- H02M7/7575—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output with 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 for high voltage direct transmission link
-
- 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
- H02J3/36—Arrangements for transfer of electric power between ac networks via a high-tension dc link
-
- 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
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/60—Arrangements for transfer of electric power between AC networks or generators via a high voltage DC link [HVCD]
Landscapes
- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Supply And Distribution Of Alternating Current (AREA)
- Direct Current Feeding And Distribution (AREA)
- Rectifiers (AREA)
Abstract
CONVERTER CONTROL APPARATUS FOR
AC-DC PARALLEL POWER TRANSMISSION SYSTEM
ABSTRACT OF THE DISCLOSURE
A phase locked oscillator in phase with the AC voltage at a connecting point between a direct current power transmission system and an alternating current power transmission system of an AC-DC parallel power transmission system is provided in order not to loss the phase signal of the AC voltage at the con-necting point at the time of occurrence of a fault in the power system. A firing signal continues to be applied to the converters of the direct current system during the presence of the fault on the basis of the phase signal produced from the oscillator.
With the elimination of the fault, the power trans-mitted through the direct current power transmission system is increased as far as possible to attain the greatest possible stability of the AC-DC parallel power transmission system. The transmitted power is restored to its steady state when the phase difference between the AC voltages at the ends of the AC-DC parallel power transmission system begins to be reduced.
AC-DC PARALLEL POWER TRANSMISSION SYSTEM
ABSTRACT OF THE DISCLOSURE
A phase locked oscillator in phase with the AC voltage at a connecting point between a direct current power transmission system and an alternating current power transmission system of an AC-DC parallel power transmission system is provided in order not to loss the phase signal of the AC voltage at the con-necting point at the time of occurrence of a fault in the power system. A firing signal continues to be applied to the converters of the direct current system during the presence of the fault on the basis of the phase signal produced from the oscillator.
With the elimination of the fault, the power trans-mitted through the direct current power transmission system is increased as far as possible to attain the greatest possible stability of the AC-DC parallel power transmission system. The transmitted power is restored to its steady state when the phase difference between the AC voltages at the ends of the AC-DC parallel power transmission system begins to be reduced.
Description
1 The present invention relates to a control nppara~us for a converter of an ~C-DC parallel power transmi~ion system in whlch an alternating current power transmission system is connected in parallel to a direct current power transmission system for trans-mission and receipt of power.
Most of the existing power systems are comprised of only an alternating current power trans-mission system. With the progress of the technologi-cal research into a large-power switching element such as a thyristor, on the other hand, a converter making use of such an element has almost reached a point of practical application. In line with this, transmission and receipt of power by means of a direct ~-current power transmission system was planned and being carried out in actual practice. In power trans-mission and receipt by a direct current power trans-mission, unlike the case of an alternating current power transmission, it is not required to pay atten-tion to the transient stability of the system involved.This leads to the advantage that the equipment of the direct current power transmission system can be used, for example, at the full current capacity of the trans-mission line of the direct current power transmission system. However, in view of the fact that a DC circuit ; breaker of large power is still under technological development, the freedom of system operation is lacking.
Therefore, the direct current power trans-mission system, if introduced into the present power , . ~ .
~,,,i~
105~4Si system, cannot entirely take the place of the ~ltcrnating cu~rent po~er transmission sy~tem. Rather, the future po~er system i9 most probably expected to be mainly com,prised of the alternating current power transmis-~ion system now used and a direct current powertransmission system arranged in parallel at strategic points.
One of the greatest technological problems encountered when operating the direct current power transmission system in parallel to the alternating current power transmission system is that of the effect that the fault, which may occur in the alter-nating current power transmission system, has on the converter in the direct current power transmission system. A typical one of such an effect is the reduction in the AC voltage at the AC-DC connecting point due to the fault. In other words, the large-power switching element such as a thyristor presently used for the converter is such that the timing at which it is turned on with a firing signal can be controlled, but the thyristor can not be turned off with a control signal. Thus it is exclusively by the use of the reverse voltage applied to the switch-ing element that the switching element turned on by the firing signal is turned off. Since the reverse ; voltage is given by the AC voltage at the AC-DC
connecting point to which the converter is connected, the reduction in the AC voltage at the AC-DC connect-ing point makes the operation of the converter impossible.
105~45~
1 For this reason, in the event that the AC
voltage at the AC-DC connecting point connected with the converter is reduced below a certain level, it has been customary to suspend the operation of the converter; and it is resumed at a later time when the fault of the alternating current power transmission system has been eliminated and the original AC voltage has been restored.
In this way, the AC-DC parallel power trans-mission system is operable. The control circuit forthe converter, however, incorporates a primary delay circuit and other various time delay factors. There-fore, it i~ some time later than the restoration of the AC voltage that the converter comes to perform its function to the full. This means that, apart ~rom the period during which the voltage of the power system is reduced by the fault of the alternating current power transmission system, transmission and receipt of the power by the direct current power transmission system is impossible for some time even after the elimination of the fault. From the viewpoint of the operation of the power system, however, it is desirable that the direct current power transmission system begins to display its full ability simultaneous-ly with the elimination of the trouble, thus contri-buting to stabilizing the power system.
Accordingly, it is an object of the pre-sent invention to provide a control apparatus for the converter so designed that the converter resumes ~0 its normal operation immediately after the elimination ~,, 105~451 of any f~ult of an alternating current powcr trans-mission system which may occur in a power system including an AC-DC parallel power transmission system.
Another object of the invention is to pro-vide a control apparatus for thé converter so design-ed that an optimum transmission power of the direct current power transmission system to enable the direct current power transmi-ssion system to contribute to the stable operation of the AC-DC parallel power transmission system is determinable at the time of elimination of a fault in the alternating current power transmission system.
Still another object of the invention is to provide a control apparatus for the converter so designed that the transmission po~lér of the direct current power transmission system is reduced to main-tain the voltage at the AC-DC connecting point of the AC-DC parallel power transmission system when the voltage at such a connecting point drops due to a fault in the alternating current power transmission system.
In order to achieve the above-mentioned objects, there is provided, according to the present invention, a control apparatus for the converter of the direct current power transmission system, com-prising first means for producing a first voltage signal corresponding to a required controlled delay angle for giving at least a minimum margin angle determined as a function ~f the voltate at the connecting point between the AC and DC
transmission lines and the current in the direct current power 105~4Sl 1 transmission line, second means for producing a second voltage signal as a function of the difference between a current reference value of the direct current power transmission system and an actual current value thereof, third means for selecting one of the first and second voltage signals, and f~21rth means for applying to the converter, in response to a phase signal in phase with the voltage at the AC-DC connecting point, a fir-ing signal adapted to fire the converter at a con-trolled delay angle corresponding to the selectedvoltage signal wherein the improvement comprises fifth means for maintaining the phase of the phase signal in phase with the voltage at the AC-DC connect-ing point even after the voltage at said AC-DC con-necting point drops transiently, and means for furthercontrolling the controlled delay angle given by the firing signal in response to the voltage drop at the AC-DC connection point.
~he above and other objects, features and advantages will be made apparent by the detailed des-cription taken in conjunction with the accompanying drawings, in which:
Figs. la, lb and lc show block diagrams for explaining the background of the present invention, in which Fig. la is a diagram schematically showing an example of the construction of the AC-DC parallel power transmission system, Fig. lb a schematic diagram showing an example of the fundamental construction of the control circuit for the converter of the direct current power transmission system, and Fig. lc a 1 diagram schematically showing an example of the phase locked oscillator used in the control circuit shown in Fig. lb;
Figs. 2a, 2b and 2c are diagrams for gene-rally explaining the effect of the present invention, in which Fig. 2a is a diagram showing the transmission power for the AC-DC parallel power transmission system, ~ig. 2b a diagram showing the transmission power at the time of occurrence of a fault in the alternating current power transmission system incorporating no means of the invention, and Fig. 2c a diagram showing the transmission power at the time of occurrence of the same fault as in Fig. 2b above in the presence of the means of the invention;
... ..
15 Pig. ~ is a diagram for explaining the fun-damental operating principle of the invention;
Fig. 4 is a block diagram showing an embodi-ment of the present invention;
Fig. 5 is a waveform diagram for explaining the operation of the embodiment of Fig. 4;
Fig. 6 is a diagram for explaining another effect of the embodiment shown in Fig. 4;
Fig. 7 is a block diagram showing an example of a circuit used in the embodiment of the invention;
25Figs. 8a to 8c show waveforms for explain-ing the operation of the circuit of Fig. 7;
Figs.-9 and 10 show a couple of partial modifications of the embodiment of Fig. 4; and Fig. 11 is a block diagram showing still another embodiment of the invention.
, 1 Prior to describing in detail the embodiments of the invention, explanation will be made of the background of the invention with reference to the drawing3 for facilitating the understanding of the invention.
; It i9 already explained that both the alter-nating current power transmission system and the direct current power transmission system have their own advantages respectively. Therefore, in order 10 to positively introduce the direct current power -~
transmission system into the power system, an effec-tive way will be to make use of the AC-DC parallel power transmission system as shown in Fig. la to lc.
An overall configuration of such a system 15 is schematically illustrated in Fig. la. Reference characters A and B show power stations, which have power supplies Gl and G2 respectively behind the reactances AC~ of the alternating current power ' transmission system. A couple of AC power trans-20 mission systems A~l and A~2 and a DC power trans-mission system D~ are interposed between the power stations A and B. The AC power transmission systems ; A~l and A~2 are connected to the bus bars AB and BB
through circuit breakers CBl; CB2 and CBl'; CB2' res-25 pectively. The DC power transmission system D~ is ~; connected to the bus bars AB and BB through converters 1 and 2 and transformers TRl and TR2 respectively.
By the way, the DC power transmission system D~ in-cludes a DC reactor DC~. High harmonics filters 30 Fl and F2 are inserted between the bus bar AB and A .. . . . .
. . . .
lOS6~51 the ~round and between the bus bar BB and the ground respectively.
The fundamental con~truction of the control apparatus 9 for the converter 1 of the above-mentioned system is shown in Fig. lb. The control apparatus 9' for the converter 2 is the same in construction a~ the control apparatus 9 and hence Fig. lb omits the detail of the apparatus 9'. Also the explanation will be made, hereinafter, of only the control apparatus 9.
The control apparatus 9 is impressed with voltage signal from the bus bar AB and current signal from the direct current power transmission line DL, res-pectively, through AC potential transformer 15 and DC current transformer 25 on the one hand, and cur-rent reference signal Idp for the converter 1 and a command for determining whether or not a current margin signal ~I should be given depending on the ope-ration mode, invertor- or rectifier-operated mode of the converter on the other. Reference numeral 4 shows a con3tant ext.i.nctJ.on angle control circuit which produces, in response to signals from the AC potential transformer 15 and the DC current transformer 25, an output voltage signal for giving a controlled delay angle corresponding to the constant margin angle whereby to assure the operation of the converter 1 without any commutation failure. Numeral 11 shows an adder which is impressed with a current refer-ence Idp, an actual current Idr of the direct current power transmission system obtained from the DC current transformer and the current margin signal ~I from the switch SWl turned on in response to a command to give ~OS~.451 1 ~he cu~rent margin si~nal ~ 11 of these signals are applied to the adder 11 a~ polarities shown in the drawing under consideration. Numeral 13 shows an amplifier for amplifying the output from the adder 11. Numeral 10 shows a voltage selector circuit for producing a control voltage Ec corresponding to a delay angle determined by the output of the constant extinction angle control circuit 4 or a delay angle determined by the output of the amplifier 13, whichever is smaller. Numeral 6 shows a phase locked oscillator which produces a phase signal in phase with the line voltage of the power station given by the AC potenti~l transformer, i.e., the AC . :
- voltage at the AC-DC connecting points tl and t2.
:: 15 Numeral 8 shows an automatic pulse pAase shifter for applying a firing signal to the converter 1 at the controlled delay angle a corresponding to the control ~ignal Ec. 'rhe automatic pulse phase shifter 8 has a controlled delay angle from amin to amaX as its characteristics are briefly illustrated in the draw-ing, even though it is not limited to the one shown in the drawing. As is well known, the various con-stants of each circuit are determined under the normal control conditions in such a manner that a takes an ; 25 appropriate value smaller than 90 (for example, 15) in the off state of the switch SW1, nameiy, in the rectifier-operated mode and larger than 90 (for instance, 140) in the on state of the switch SW1, namely, in the inverter-operated mode. In many cases, amin and amaX assume the values of about 5 and 160 _ g _ r~spectively.
When the converter 1 is operating as an inverter, the constant extinction angle control circuit 4 determines the controlled delay angle ~ corresponding to the minimum margin angl~e y for the converter to operate without commutation failure as a function of the voltage E2 at the connecting point t and the dc current Id by using the following equation:
~ = r + U = ~
cos y - cos B = XId where X = the commutating reactance and ~ = the control angle The constant extinction angle control circuit also provides a control voltage (first voltage signal) Ec which is determined from the controlled delay angle a by taking into consideration the phase-shift characteristics of the automatic pulse phase shi~ter 8.
~ig~ lc shows schematically an example of the phase locked oscillator 6, the detail of which is known from Proceedings of the IEEE Vol. 63, No. 2, ~ebruary 1975 pages 291 to 306, "Phase-Locked Loops"
by Someshwar C. Gupta. Symbols In and Out show input and output terminals respectively. Numeral 61 shows`
a phase difference detector circuit for producing an output voltage associated with the phase difference between the input In and the output Out. Numeral 62 shows a smoothing circuit which produces an output delayed by its time constant in response to the output of the phase difference detector 61. Numeral 6~ shows a voltage controlled oscillator which oscillates at a frequency corresponding to the output volt~ge of the smoothing circuit 62. By appropriately determining ~ - 10 -,~ .
:105~4Sl the constants of each circuit, it is possible to keep the sienals In and Out in the same phase and to produce a signal Out always, even in the transient absence of signal In, in phase with the signal In just before lt expires.
As will be understood from the foregoing description, by constant steady application of a phase signal from the ~C-DC connecting point to the control apparatus of the well-known converter, the operation of the direct current power transmission system becomes possible simultaneously with the restoration of the voltage which may have dropped transiently at the AC-DC connecting point.
The voltage drop at the AC-DC connecting - lOa ~
105~;451 1 point is attributable to various causes. Most of them are the grounding or short-circuiting faults of the alternating current power transmission line occurring at such points as f, ~' and f" as shown in Fig. la. These faults are eliminated by the operation of appropriate protective relays not shown in the drawing. In the case of the fault f in the alternating current power transmission line AL2, for instance, the circuit breakers CBl' and C~2' are opened, thereby restoring the voltages at the AC-DC
connecting points tl and t2.
In Figs. 2a, 2b and 2c, the difference angle e between the A~ voltages at the power stations A and ~ is plotted horizontally, and the transmission power P vertically. The graph of Fig. 2a concerns the normal condition; the result obtained by the control operation on the conventional principle is shown in Fig. 2b; and the effect of the control according to the invention is illustrated in Fig. 2c.
In the drawings, ~1, Q2 and ~3 show curves represent-ing transmissible power through the alternating cur-rent power transmission lines ALl and AI2 respectively.
In other words, the curve ~1 is associated with the case where both the alternating current power trans-mission lines AL1 and A~2 are operating normally;the curve Q2 the case where one of the alternating current power transmission lines ALl and AL2 is not operative; and the curve ~3 the case where the voltage has dropped due to a fault of the alternating current power transmission line. This transmissible power .
105f~4Sl in tl~e alternating current power transmission line, a~ well known, i~ 2xpressed as Vl - V2 X sin e where X is the reactance of the alternating current power transmission system; Vl and V2 the voltages at the terminals of the alternating current power trans-mission line; and ~ the phase difference between Vl and V2.
The graph of Fig. 2a shows the state where the transmission power Po i8 distributed under the normal condition between the alternating current power transmission line and the direct current power trans-mission line taking shares Pa and Pd respectively.
Under this condition, the phase difference between the power stations A and B is expressed as ~0. If a fault as shown by f occurs in the alternating current power transmission line AL2, the result of the con-2n ventional control is as shown in Fig. 2b. The voltageat the AC-DC connecting points tl and t2 drops. The transmission power Pd is reduced naturally to zero, while the power Pa is decreased also to the level b3.
The mechanical input to the rear power supplie~, on the other ~and, remains enough to supply-the transmission power Po, so that the power supplies are accelerated. The phase difference ~ begins to increase. If the fault is removed when 40 reaches ~1~ transmission power is restored to the level Q'2 but the direct current power transmission line has yet to begin 1 transmission. When ~2 is reached subsequently, the direct current power transmission line begins trans-mission of power Pd. The phase difference, however, continues to increase until transmission begins of the deceleration competitive wlth the acceleration occurred in the processes of changes from ~0 to ~1 to
Most of the existing power systems are comprised of only an alternating current power trans-mission system. With the progress of the technologi-cal research into a large-power switching element such as a thyristor, on the other hand, a converter making use of such an element has almost reached a point of practical application. In line with this, transmission and receipt of power by means of a direct ~-current power transmission system was planned and being carried out in actual practice. In power trans-mission and receipt by a direct current power trans-mission, unlike the case of an alternating current power transmission, it is not required to pay atten-tion to the transient stability of the system involved.This leads to the advantage that the equipment of the direct current power transmission system can be used, for example, at the full current capacity of the trans-mission line of the direct current power transmission system. However, in view of the fact that a DC circuit ; breaker of large power is still under technological development, the freedom of system operation is lacking.
Therefore, the direct current power trans-mission system, if introduced into the present power , . ~ .
~,,,i~
105~4Si system, cannot entirely take the place of the ~ltcrnating cu~rent po~er transmission sy~tem. Rather, the future po~er system i9 most probably expected to be mainly com,prised of the alternating current power transmis-~ion system now used and a direct current powertransmission system arranged in parallel at strategic points.
One of the greatest technological problems encountered when operating the direct current power transmission system in parallel to the alternating current power transmission system is that of the effect that the fault, which may occur in the alter-nating current power transmission system, has on the converter in the direct current power transmission system. A typical one of such an effect is the reduction in the AC voltage at the AC-DC connecting point due to the fault. In other words, the large-power switching element such as a thyristor presently used for the converter is such that the timing at which it is turned on with a firing signal can be controlled, but the thyristor can not be turned off with a control signal. Thus it is exclusively by the use of the reverse voltage applied to the switch-ing element that the switching element turned on by the firing signal is turned off. Since the reverse ; voltage is given by the AC voltage at the AC-DC
connecting point to which the converter is connected, the reduction in the AC voltage at the AC-DC connect-ing point makes the operation of the converter impossible.
105~45~
1 For this reason, in the event that the AC
voltage at the AC-DC connecting point connected with the converter is reduced below a certain level, it has been customary to suspend the operation of the converter; and it is resumed at a later time when the fault of the alternating current power transmission system has been eliminated and the original AC voltage has been restored.
In this way, the AC-DC parallel power trans-mission system is operable. The control circuit forthe converter, however, incorporates a primary delay circuit and other various time delay factors. There-fore, it i~ some time later than the restoration of the AC voltage that the converter comes to perform its function to the full. This means that, apart ~rom the period during which the voltage of the power system is reduced by the fault of the alternating current power transmission system, transmission and receipt of the power by the direct current power transmission system is impossible for some time even after the elimination of the fault. From the viewpoint of the operation of the power system, however, it is desirable that the direct current power transmission system begins to display its full ability simultaneous-ly with the elimination of the trouble, thus contri-buting to stabilizing the power system.
Accordingly, it is an object of the pre-sent invention to provide a control apparatus for the converter so designed that the converter resumes ~0 its normal operation immediately after the elimination ~,, 105~451 of any f~ult of an alternating current powcr trans-mission system which may occur in a power system including an AC-DC parallel power transmission system.
Another object of the invention is to pro-vide a control apparatus for thé converter so design-ed that an optimum transmission power of the direct current power transmission system to enable the direct current power transmi-ssion system to contribute to the stable operation of the AC-DC parallel power transmission system is determinable at the time of elimination of a fault in the alternating current power transmission system.
Still another object of the invention is to provide a control apparatus for the converter so designed that the transmission po~lér of the direct current power transmission system is reduced to main-tain the voltage at the AC-DC connecting point of the AC-DC parallel power transmission system when the voltage at such a connecting point drops due to a fault in the alternating current power transmission system.
In order to achieve the above-mentioned objects, there is provided, according to the present invention, a control apparatus for the converter of the direct current power transmission system, com-prising first means for producing a first voltage signal corresponding to a required controlled delay angle for giving at least a minimum margin angle determined as a function ~f the voltate at the connecting point between the AC and DC
transmission lines and the current in the direct current power 105~4Sl 1 transmission line, second means for producing a second voltage signal as a function of the difference between a current reference value of the direct current power transmission system and an actual current value thereof, third means for selecting one of the first and second voltage signals, and f~21rth means for applying to the converter, in response to a phase signal in phase with the voltage at the AC-DC connecting point, a fir-ing signal adapted to fire the converter at a con-trolled delay angle corresponding to the selectedvoltage signal wherein the improvement comprises fifth means for maintaining the phase of the phase signal in phase with the voltage at the AC-DC connect-ing point even after the voltage at said AC-DC con-necting point drops transiently, and means for furthercontrolling the controlled delay angle given by the firing signal in response to the voltage drop at the AC-DC connection point.
~he above and other objects, features and advantages will be made apparent by the detailed des-cription taken in conjunction with the accompanying drawings, in which:
Figs. la, lb and lc show block diagrams for explaining the background of the present invention, in which Fig. la is a diagram schematically showing an example of the construction of the AC-DC parallel power transmission system, Fig. lb a schematic diagram showing an example of the fundamental construction of the control circuit for the converter of the direct current power transmission system, and Fig. lc a 1 diagram schematically showing an example of the phase locked oscillator used in the control circuit shown in Fig. lb;
Figs. 2a, 2b and 2c are diagrams for gene-rally explaining the effect of the present invention, in which Fig. 2a is a diagram showing the transmission power for the AC-DC parallel power transmission system, ~ig. 2b a diagram showing the transmission power at the time of occurrence of a fault in the alternating current power transmission system incorporating no means of the invention, and Fig. 2c a diagram showing the transmission power at the time of occurrence of the same fault as in Fig. 2b above in the presence of the means of the invention;
... ..
15 Pig. ~ is a diagram for explaining the fun-damental operating principle of the invention;
Fig. 4 is a block diagram showing an embodi-ment of the present invention;
Fig. 5 is a waveform diagram for explaining the operation of the embodiment of Fig. 4;
Fig. 6 is a diagram for explaining another effect of the embodiment shown in Fig. 4;
Fig. 7 is a block diagram showing an example of a circuit used in the embodiment of the invention;
25Figs. 8a to 8c show waveforms for explain-ing the operation of the circuit of Fig. 7;
Figs.-9 and 10 show a couple of partial modifications of the embodiment of Fig. 4; and Fig. 11 is a block diagram showing still another embodiment of the invention.
, 1 Prior to describing in detail the embodiments of the invention, explanation will be made of the background of the invention with reference to the drawing3 for facilitating the understanding of the invention.
; It i9 already explained that both the alter-nating current power transmission system and the direct current power transmission system have their own advantages respectively. Therefore, in order 10 to positively introduce the direct current power -~
transmission system into the power system, an effec-tive way will be to make use of the AC-DC parallel power transmission system as shown in Fig. la to lc.
An overall configuration of such a system 15 is schematically illustrated in Fig. la. Reference characters A and B show power stations, which have power supplies Gl and G2 respectively behind the reactances AC~ of the alternating current power ' transmission system. A couple of AC power trans-20 mission systems A~l and A~2 and a DC power trans-mission system D~ are interposed between the power stations A and B. The AC power transmission systems ; A~l and A~2 are connected to the bus bars AB and BB
through circuit breakers CBl; CB2 and CBl'; CB2' res-25 pectively. The DC power transmission system D~ is ~; connected to the bus bars AB and BB through converters 1 and 2 and transformers TRl and TR2 respectively.
By the way, the DC power transmission system D~ in-cludes a DC reactor DC~. High harmonics filters 30 Fl and F2 are inserted between the bus bar AB and A .. . . . .
. . . .
lOS6~51 the ~round and between the bus bar BB and the ground respectively.
The fundamental con~truction of the control apparatus 9 for the converter 1 of the above-mentioned system is shown in Fig. lb. The control apparatus 9' for the converter 2 is the same in construction a~ the control apparatus 9 and hence Fig. lb omits the detail of the apparatus 9'. Also the explanation will be made, hereinafter, of only the control apparatus 9.
The control apparatus 9 is impressed with voltage signal from the bus bar AB and current signal from the direct current power transmission line DL, res-pectively, through AC potential transformer 15 and DC current transformer 25 on the one hand, and cur-rent reference signal Idp for the converter 1 and a command for determining whether or not a current margin signal ~I should be given depending on the ope-ration mode, invertor- or rectifier-operated mode of the converter on the other. Reference numeral 4 shows a con3tant ext.i.nctJ.on angle control circuit which produces, in response to signals from the AC potential transformer 15 and the DC current transformer 25, an output voltage signal for giving a controlled delay angle corresponding to the constant margin angle whereby to assure the operation of the converter 1 without any commutation failure. Numeral 11 shows an adder which is impressed with a current refer-ence Idp, an actual current Idr of the direct current power transmission system obtained from the DC current transformer and the current margin signal ~I from the switch SWl turned on in response to a command to give ~OS~.451 1 ~he cu~rent margin si~nal ~ 11 of these signals are applied to the adder 11 a~ polarities shown in the drawing under consideration. Numeral 13 shows an amplifier for amplifying the output from the adder 11. Numeral 10 shows a voltage selector circuit for producing a control voltage Ec corresponding to a delay angle determined by the output of the constant extinction angle control circuit 4 or a delay angle determined by the output of the amplifier 13, whichever is smaller. Numeral 6 shows a phase locked oscillator which produces a phase signal in phase with the line voltage of the power station given by the AC potenti~l transformer, i.e., the AC . :
- voltage at the AC-DC connecting points tl and t2.
:: 15 Numeral 8 shows an automatic pulse pAase shifter for applying a firing signal to the converter 1 at the controlled delay angle a corresponding to the control ~ignal Ec. 'rhe automatic pulse phase shifter 8 has a controlled delay angle from amin to amaX as its characteristics are briefly illustrated in the draw-ing, even though it is not limited to the one shown in the drawing. As is well known, the various con-stants of each circuit are determined under the normal control conditions in such a manner that a takes an ; 25 appropriate value smaller than 90 (for example, 15) in the off state of the switch SW1, nameiy, in the rectifier-operated mode and larger than 90 (for instance, 140) in the on state of the switch SW1, namely, in the inverter-operated mode. In many cases, amin and amaX assume the values of about 5 and 160 _ g _ r~spectively.
When the converter 1 is operating as an inverter, the constant extinction angle control circuit 4 determines the controlled delay angle ~ corresponding to the minimum margin angl~e y for the converter to operate without commutation failure as a function of the voltage E2 at the connecting point t and the dc current Id by using the following equation:
~ = r + U = ~
cos y - cos B = XId where X = the commutating reactance and ~ = the control angle The constant extinction angle control circuit also provides a control voltage (first voltage signal) Ec which is determined from the controlled delay angle a by taking into consideration the phase-shift characteristics of the automatic pulse phase shi~ter 8.
~ig~ lc shows schematically an example of the phase locked oscillator 6, the detail of which is known from Proceedings of the IEEE Vol. 63, No. 2, ~ebruary 1975 pages 291 to 306, "Phase-Locked Loops"
by Someshwar C. Gupta. Symbols In and Out show input and output terminals respectively. Numeral 61 shows`
a phase difference detector circuit for producing an output voltage associated with the phase difference between the input In and the output Out. Numeral 62 shows a smoothing circuit which produces an output delayed by its time constant in response to the output of the phase difference detector 61. Numeral 6~ shows a voltage controlled oscillator which oscillates at a frequency corresponding to the output volt~ge of the smoothing circuit 62. By appropriately determining ~ - 10 -,~ .
:105~4Sl the constants of each circuit, it is possible to keep the sienals In and Out in the same phase and to produce a signal Out always, even in the transient absence of signal In, in phase with the signal In just before lt expires.
As will be understood from the foregoing description, by constant steady application of a phase signal from the ~C-DC connecting point to the control apparatus of the well-known converter, the operation of the direct current power transmission system becomes possible simultaneously with the restoration of the voltage which may have dropped transiently at the AC-DC connecting point.
The voltage drop at the AC-DC connecting - lOa ~
105~;451 1 point is attributable to various causes. Most of them are the grounding or short-circuiting faults of the alternating current power transmission line occurring at such points as f, ~' and f" as shown in Fig. la. These faults are eliminated by the operation of appropriate protective relays not shown in the drawing. In the case of the fault f in the alternating current power transmission line AL2, for instance, the circuit breakers CBl' and C~2' are opened, thereby restoring the voltages at the AC-DC
connecting points tl and t2.
In Figs. 2a, 2b and 2c, the difference angle e between the A~ voltages at the power stations A and ~ is plotted horizontally, and the transmission power P vertically. The graph of Fig. 2a concerns the normal condition; the result obtained by the control operation on the conventional principle is shown in Fig. 2b; and the effect of the control according to the invention is illustrated in Fig. 2c.
In the drawings, ~1, Q2 and ~3 show curves represent-ing transmissible power through the alternating cur-rent power transmission lines ALl and AI2 respectively.
In other words, the curve ~1 is associated with the case where both the alternating current power trans-mission lines AL1 and A~2 are operating normally;the curve Q2 the case where one of the alternating current power transmission lines ALl and AL2 is not operative; and the curve ~3 the case where the voltage has dropped due to a fault of the alternating current power transmission line. This transmissible power .
105f~4Sl in tl~e alternating current power transmission line, a~ well known, i~ 2xpressed as Vl - V2 X sin e where X is the reactance of the alternating current power transmission system; Vl and V2 the voltages at the terminals of the alternating current power trans-mission line; and ~ the phase difference between Vl and V2.
The graph of Fig. 2a shows the state where the transmission power Po i8 distributed under the normal condition between the alternating current power transmission line and the direct current power trans-mission line taking shares Pa and Pd respectively.
Under this condition, the phase difference between the power stations A and B is expressed as ~0. If a fault as shown by f occurs in the alternating current power transmission line AL2, the result of the con-2n ventional control is as shown in Fig. 2b. The voltageat the AC-DC connecting points tl and t2 drops. The transmission power Pd is reduced naturally to zero, while the power Pa is decreased also to the level b3.
The mechanical input to the rear power supplie~, on the other ~and, remains enough to supply-the transmission power Po, so that the power supplies are accelerated. The phase difference ~ begins to increase. If the fault is removed when 40 reaches ~1~ transmission power is restored to the level Q'2 but the direct current power transmission line has yet to begin 1 transmission. When ~2 is reached subsequently, the direct current power transmission line begins trans-mission of power Pd. The phase difference, however, continues to increase until transmission begins of the deceleration competitive wlth the acceleration occurred in the processes of changes from ~0 to ~1 to
2' namely, until the power higher than the input begins to be transmitted. When ~3 is reached, the acceleration is finally balanced with the deceleration and the phase difference begins to decrease. In the conventional method of control, it will thus be seen that DC power transmission is not restored simultane-ously with the elimination of a fault and therefore the acceleration is increased as much.
The advantageæ of the present invention are illustrated in Fig. 2c. As in the case of Fig. 2b, a fault occurs under the transmission of the power Po (= Pa + Pd) at the phase difference of ~0 and the fault is eliminated at the phase difference ~1 In the case of the invented control shown in Fig. 2c, not only the direct current power transmission is restored but also the power Pd' begins to be trans-mitted simultaneously with the elimination of the fault at ~1 (Pd' is of course higher than Pd.) As a result, the acceleration is not uselessly increased on the one hand, and a great deceleration is obtained on the other. The phase difference is thus prevented from increasing more than ~3', greatly contributing to stabili~ing the system.
In Fig. 2c, the DC power is increased to - .
1 the level of Pd' only during the period of the in-crease in the phase difference and restored to Pd after ~3' is reached. In this way, a useless fluctuation of the phase difference can be avoided.
As will be easily understood without special reference to the drawings, in the face of the faults such as f' and f" occurring outside of the AC-DC
parallel power transmission system, a control opera-tion similar to that of Fig. 2c contributes to the stable operation if the place of occurrence of the fault is relatively near the system and the power transmission of the direct current power transmission line is stopped during the continuance of the fault.
In spite of the above-mentioned advantages, ; 15 the operation according to the invention may cause the transmission power to be transiently increased to Pd'. However, since the duration of this transient power increase is very short J it will not cause any trouble to operate the converters 1 and 2 and other elements under overload during such occasion. ~o implement this invention, therefore, it is not neces-sary to provide a direct current power transmission system with a rating capacity of Pd'.
~he diagram of Fig. ~ is for explaining 2~ to what degree the transmission power of the direct current power transmission line should be increased in eliminating a fault. In the drawing, the abscissa represents the current Id of the direct current power transmission line, while the ordinate shows the AC
voltage ET at the ~C-DC connecting point, the voltage ~056451 Vd of the direct current power transmission line, the DC power Pd, the operating power factor Pf of the converter~ and the phase difference ~ between the AC voltages of the power stations A and ~. The graphic presentation of Fig. ~ i9 bas~d on the calculations made assuming that the tap positions on the trans-formers TRl and TR2, hence the voltages of the rear power supplies, are fixed and that the resulting fixed power is shared by the alternating current power transmission lines A~l and AL2 and the direct current power transmission line D~ for the purpose of trans-mission. Assume that the systems are operated at Id (= Io). As will be seen ~rom the graph, in order to merely increase the DC power Pd, it will be effective to increase the DC current from Io to Idm. This, however, results in decreasing not only ET and Vd, but also Pf, thereby incretasing the!)phase difference ~. For the stable operation of the power system, a smaller phase difference ~ is desirable.
Therefore, any increase of current from Id (= Io) should be limited to Ido. The operation according to the invention may utilize the fact that ET, Vd and Pf assume their points of inflection at the point Ido of the DC current.
A block diagram of an embodiment of the invention covering only a power station is shown in Fig. 4. In the drawing, like reference numerals denote like component elements as in Fig. 1, and the other reference numerals and characters will be first described below.
10564Sl 1 . Numerals 21 and 23 8hoW ~C current trans-formers for detecting the currents flowing in the alternating current power transmission line~ ALl and AL2. Reference characters r and x show a resistance and a reactance respectively similating the alternat-ing current power transmission lines ALl and AL2.
By applying a sum of the outputs of the AC current transformers 21 and 23 to the resistance-reactance combination, a voltage simulating the phase signal of the AC voltage at the power station B is obtained thereacross. Numeral 20 shows a maximum difference detector circuit. A "1" signal is produced from this detector circuit 20 when the phase difference between the simulation voltage of the other power station obtained across the series-connected r and x and the voltage of the power station at this end obtained from the AC potential transformer 15 reaches a maximum point, i.e., when the phase difference which has so far been increased begins to decrease.
An example of the circuit under consideràtion will be described more in detail later. Numeral 17 shows a DC voltage transformer for introducing the voltage Vd of the direct current power transmission line.
Reference numerals 22 and 32 show rectifier circuits - 25 which rectify the voltages obtained at the AC potential transformers 15 and 17 and produce them in the form of DC voltages. Numeral3 24, 28 and 40 show comparator circuits for comparing the reference voltages Vcl, Vc2 and Vc3 with the input voltages el, e2 and e3 ~0 respectively. Specifically, it is assumed that the , , , l comparator 24 produces a "l" output when el is higher than Vcl, that the comparator 28 produces a "l" out-put when e2 is higher than Vc2, and that the comparator 40 produces a "l" signal when e3 is higher than Vc3.
Under the normal conditions of the power system, the voltages Vcl and Vc2 are as high as about 50~0 of the voltages el and e2 respectively while the voltage Vc~ takes a positive value almost zero. As a result, the comparators 24 and 28 naturally produce a "1"
signal when the voltage of the AC-DC connecting point is normal. ~umeral 26 shows a flip-flop circuit, which is set and produces a "1" signal in response to an input at the set terminal S when the output of the comparator circuit 24 change,s from "0" to "l", namely, when the voltage at the AC-DC connecting point less than 50% of the rating is restored to the rating.
The nip-flop circuit 26 is reset and produces a "0"
signal in response to an input to the reset terminal R when the output of the maximum phase difference detector circuit 20 changes from "0" to "1". ~umeral 34 shows a ramp voltage generator circuit which pro-duces a continuously increasing voltage in response to a "l" signal from the flip-flop circuit 26. ~Ihen the output of the flip-flop 26 changes to "0", on the other hand, the output of the circuit 34 is restored to ~ero immediately. Numeral 36 shows a tracking and holding circuit. When the flip-flop 38 produces a "0" output, the output'of the ramp voltage generator circuit 34 is followed by the output of the tracking and holding circuit 36; whereas when the output of 1 the flip-flop 38 chang 4sStlo "1" the tracki d holdin~ circuit 36 produce3 the same output as that produced by the ramp voltage ~enerator circuit ~4 immediately before the change of the state of flip-flop 38 to "1". Numeral 30 shows what is called aprimary delay circuit, or first order lag circuit, ~ith a comparatively short time constant. Numeral 27 shows an adder for taking a sum of the outputs of the primary delay circuit 30 and the rectifier circuit 32 at the shown polarities. As long as the voltage of the direct current power transmission line is constant for stable operation, the output voltage e3 of the adder 27 is maintained at zero. If the voltage of the direct current power transmission line sudden-ly drops, however, the voltage e3 changes to positive,and vice versa. Therefore, assuming that the compa-rator 40 compares the output of the adder 27 with a reference voltage Vc~ which is substantially zero and produces an output when e3 is higher than Vc3~
then the primary delay circuit 30, the adder 27 and the comparator 40 are able to detect a point of sudden voltage drop. Numeral 29 shows an AND circuit for producing a "1" output in the presence of both the outputs of the comparators 28 and 40 and an input "1"
applied to the input terminal 100. The "1" input is applied to the AND circuit 29 only when the direct current transmission system is under operation. By this, the output of the comparator 40 is rendered ineffective when the direct current transmission line is separated from the transmission system. The presence ~- 18 -Y~
. . , 1~56451 of any output from the ~ND circuit 29 means therefore that a voltage drop has occurred in the direct current power trans-missi~n line under a high voltage level operation.
Numeral ~8 shows a flip-flop, which is set to produce a "1" signal in response to a "1" signal from the AND circuit 29 and reset to produce a "O"
signal in response to a "1" signal from the maximum phase difference detector circuit 20. In this con-nection, take note of the output of the tracking and holding circuit 36 of the alternating current power transmission system. Once the voltage is restored(The DC current is also restored) after it is decreased (Of course, the voltage of the direct current power transmission line drops also at the same tLme), the tracking and holding circuit 36 produces the same out-put as the ramp voltage generator circuit 34. At a time point when the voltage of the direct current power transmission line begins to drop and the flip-flop 38 produces a "1" signal, the tracking and holding circuit 36 holds the value of the output of the ramp voltage generator 34 at that very instant. When thedifference reaches a maximum point, the maximum phase difference detector circuit 20 produces a "1" output, æo that the both the flip-flops 26 and 38 are reset and the tracking and holding circuit 36 produces a "O" output. The output of the tracking and holding circuit 36 is applied to the adder 31 at the shown polarity. In other words, the higher the output voltage of the tracking and holding circuit ~6, the 19 .
~. .
lOS~451 1 current reference value Idp of the converters becomes equivalently larger. It was already explained that when the current of the direct current power trans-mission line is increased to the level shown by Ido in ~ig. 3, the tracking and holding circuit 36 detects and holds the voltage drop of the direct current power transmission line. Thus the output of the con-verters 1 is controlled at an optimum value for stable operation. It will also be understood from the fore-eoing description that it is until the phase differencereaches ~3' in Fig. 2c that such an output is produced from the tracking and holding circuit 36.
Explanation will be made of the other parts of the circuit shown in Fig. 4. Numerals 33, 35, 37 and 39 show adders to which input signals are applied at shown polarities respectively. The adder 33 is impressed with the output of the adder 31 and, when the switch SWl is turned on with the converter 1 inverter-operated, impressed also with the current margin ~I. The adder 39 is impressed with the output of the rectifier circuit 32 and the bias voltage Vb. The bias voltage Vb is set at a level obtained at the output of the rectifier circuit 32 when the direct current power transmission line is in rated condition. The adder 39 therefore produces a posi-tive voltage as long as the direct current power transmission line is operated with its voltage reduced below a predetermined level. The adder 35 is impressed with the output of the adder 39 at the shown polarity.
When the voltage of the direct current power 1 transmission line i~ in the reduced condition, there-fore, the function is apparently is equivalent to that obtained when the current target of the converter is reduced. The operation characteristics under such a condition are shown in ~ig. 6. The solid lines in the drawing show the operations at ratings. Assuming that the system is operated at Vd and Idp and the voltage of the alternating current power transmission line drops to Vd', the current is also reduced to I'dp thus causing the system to operate under the characteristics shown by dashed lines.
' ~y reducing the current in accordance with the voltage drop in this way, the reactive power required of the converter l is also reduced, with the re~ult that the voltage drop at the AC-DC connecting - point is minimized. The adder 37 is for causing the reference value of the current corrected on the basis of various factors as mentioned above to be brought face to face with the actual current of the direct current power transmission line. Numerals 3 and 5, like numeral lO, show voltage selector circuits. The voltage selector circuit 3 compares the output of the voltage selector circuit lO with a positive voltage ' of Va90 applied'thereto through the switch SW2, and ' 25 produces a lower one of them. Numerals 41 and 43 show polarity-reversing circuits for producing a voltage of the same magnitude but of,different ~; polarity. The voltage selector circuit 5 is for comparing the output of the polarity-reversing circuit 41 with the negative voltage ~Va90 applied 105f~451 1 thereto through the switch SW3 and produces a signal more negative than the other. The polarity-reversing circuit 43 is for reversing the polarity of the output of the voltage selector 5 and applying it to the auto-matic pulse phase shifter 8. The voltages +V~gO and ~Va90 have an absolute value suitable for production of a firing signal by the automatic pulse phase shifter 8 at a = 90. When the switches SW2 and SW3 are turned on, therefore, a firing signal is produced from the automatic pulse phase shifter 8 at the timing of a = 90 regardless of the operation of each element, as described later.
The switches SW2 and SW3 are controlled by the ~witch drive circuit 18. The switch drive circuit 18 is impressed with the output of the polarity-reversing circuit 45 reversing the output of the com-parator 24. As long as the alternating current power transmission line is operating normally, the compa-rator 24 produces a "1" signal and therefore the output of the polarity reversing circuit 45 is in the state of "0", thus keeping the output of the switches SW2 and SW3 in the off state. When the voltage of the alternating current power transmission line is reduced and the output of the comparator 24 becomes zero, by contrast, the polarity reversing circuit 45 produces a "1" signal so that the switches SW2 and SW3 are turned on through the switch drive circuit 18. In other words, when the voltage of the alternating current power transmission line drops to such a degree as to make normal converter operation impossible, the .
- ~2 -1 control function is made ineffective and a firing signal continues to be applied to the converter.
In this way, voltage restoration is awaited.
The magnitude and variation of the signals of the respective parts related to the foregoing description are taken into consideration in the dia-gram of Fig. 5 in which time is plotted horizontally.
In the drawing, character a shows the controlled delay angle of the converter which is assumed to take the value of al under normal conditions.
During the period from tl to t2 when the AC voltage drops sharply, a is assumed to be 90. Until the time point t3 where the phase difference reaches its maximum, the delayed angle al is reduced by aO, thus increasing the transmission power. For subsequent periods such as between t4 and ts when the voltage - drop is small, aO' is added to al thereby to lessen the reactive component required by the converter.
An example of the maximum difference detector circuit 20 and an outline of the operating waveforms thereof will be explained with reference to Figs. 7 and 8 respectively showing a block diagram of the circuit 20 and waveforms of operation thereof.
' In Fig. 7, reference numerals 201 and 203 show zero voltage detectors which are impressed with the voltages Etl and Et2 at the AC-DC connecting points tl and t2 and produce a pulse at a point where the above-mentioned voltages are reduced to zero respectively.
The operation of the zero voltage detectors 201 and 203 is ~hown in Figs. 8a, 8b and 8c. Numeral 202 ~056451 1 shows a flip-flop circuit set and reset in response to output pulses from the zero voltage detectors 201 and 203 respectively. (The setting is rendered by a pulse associated with the zero value of the voltage at the AC-DC connecting point on the power station A side, while the resetting is accomplished by a pulse associated with the zero value of the simulation voltage at the AC-DC connecting point on the power station ~ side.) ~he signal waveforms for such operations are shown in Fig. 8d. Numeral 204 ' shows an integrator for integrating the output of the flip-flop 202. The output signal of the integrator 204 has a peak proportional to the phase difference, and the signal waveform thereof is,shown in ~ig. 8e.
Numeral 205 shows a smoothing circuit impressed with and smoothing the output of the integrator 204, the signal waveform thereof being shown in Fig. 8f.
Numeral 206 shows a memory comprised of the primary delay circuit which is impressed with the output signal from the smoothing circuit 204 and produces the same signal a predetermined time later. Numeral 207 shows an adder for adding the outputs of the primary delay circuit 206 and the smoothing circuit , 205 to each other at shown polarities. Numeral 208 shows a comparator which, in response to the output ', of the adder 207, produces an output signal. This ' output signal changes from "1" to "0" when the polarity of the output signal of the adder 207 changes from positive to negative, namely, when the phase difference is reduced. Numeral 209 shows a - 21~ -105~45~
1 differentiating circuit for applying reset signals to the flip-flops 26 and 38 at the time of change of the output of the circuit 209 from "1" to "0". In this way, the fact that the phase difference has reached ~3' is detected in Fig. 2, whereupon the DC transmission power is returned from Pd' to Pd.
The present invention is not limited to the embodiment of Fig. 4 but may be embodied in various modifications. As explained with reference to Fig. 3, when the current in the direct current power transmission line is increased beyond Ido, not only the DC voltage Vdl but also the voltage at the AC-DC connecting point and the power factor of the converter undergo a sudden change. It will be noted that this point of inflection may be detected to set the flip-flop circuit 38 in ~ig. 4. This concept is incorporated in the embodiments shown in Figs. 9 and 10. These circuits are built around the circuit elements used for setting the flip-flop 38, leaving the other parts identical with like elements in the other embodiments. Also, like numerals are attached to those elements whose functions are similar.
As will be obvious by comparing the output of the rectifier circuit 32 in Fig. 4 with that of the rectifier circuit 22 in Fig. 9, the circuit arrange-ment of this particular part is quite the same e~cepting the detection of the point of inflection of the voltage at the AC-DC connecting point. The circuit of Fig. 10 is configured with special emphasis on the change in the power factor of the converter 1 .
1 nnd ha~ an additional ~C current transformer 58.
The ou~puts V nnd I of the AC potential transformer 15 and AC current transformer 58 are applied to the Hall converter 72 and the multiplier 74 respectively for calculation of VIcos y and VI, where y is the phase difference between V and I. The outputs of the Hall converter 72 and the multiplier 74 are introduced to the divider 70 to obtain a power factor expressed by VIvIS ~ = c08 ~. This signal is applied to the primary delay circuit 28, the adder 27 and the comparator 40 thereby to detect a point of inflection.
The AND circuit 102 is provided to allow the output of the comparator 40 to be applied to the flip-flop 38 only when the direct current transmission line is under operation. In this case, if the voltage i9 zero, no power factor is calculated out and therefore the need for the comparator 28 and the AND gate 29 as in the circuit of Fig. 4 is eliminated.
Further, instead o4 starting the increase in the current reference value at the time of voltage re~toration at the AC-DC connecting point after shoot-ing the fault, the voltage restoration of the direct current power transmission system may of course be utilized, as illustratively shown in Fig. 11. By comparing Fig. 11 with Fig. 4, it will be obvious that in the case of Fig. 11 it sufficies if the out-put of the rectifier circuit 22 in Fig. 4 is replaced by that of the rectifier 32 as an input to the com-parator circuit 24. In Fig. 11, the AND circuit 104 ~ - 26 -: .
~OS~451 1 is corresponding to the AND circuit 102 in Fig. 10 and its input 105 receives a "1" si~nal only when the direct current transmission line is under operation.
It will thus be seen that according to the invention, in the event of a fault developed in the power system including an AC-DC parallel power trans-mission system and the resulting voltage drop at the AC-DC connecting point, the converter is rendered ready to enter into operation simultaneously with the voltage restoration, in response to the voltage drop. Also, when the converter resumes its operation, a transmission power most suitable for stable opera-tion of the power system is automatically determined.
Furthermore, if the voltage at the AC-DC connecting - point drops if not to such a degree as to make the converter ready for operation, the transmission power of the direct current power transmission line may be reduced accordingly. As a result, the use of the present invention is considered to enhance the value o~ the AC-DC parallel power transmission system among other parts of the power system.
The advantageæ of the present invention are illustrated in Fig. 2c. As in the case of Fig. 2b, a fault occurs under the transmission of the power Po (= Pa + Pd) at the phase difference of ~0 and the fault is eliminated at the phase difference ~1 In the case of the invented control shown in Fig. 2c, not only the direct current power transmission is restored but also the power Pd' begins to be trans-mitted simultaneously with the elimination of the fault at ~1 (Pd' is of course higher than Pd.) As a result, the acceleration is not uselessly increased on the one hand, and a great deceleration is obtained on the other. The phase difference is thus prevented from increasing more than ~3', greatly contributing to stabili~ing the system.
In Fig. 2c, the DC power is increased to - .
1 the level of Pd' only during the period of the in-crease in the phase difference and restored to Pd after ~3' is reached. In this way, a useless fluctuation of the phase difference can be avoided.
As will be easily understood without special reference to the drawings, in the face of the faults such as f' and f" occurring outside of the AC-DC
parallel power transmission system, a control opera-tion similar to that of Fig. 2c contributes to the stable operation if the place of occurrence of the fault is relatively near the system and the power transmission of the direct current power transmission line is stopped during the continuance of the fault.
In spite of the above-mentioned advantages, ; 15 the operation according to the invention may cause the transmission power to be transiently increased to Pd'. However, since the duration of this transient power increase is very short J it will not cause any trouble to operate the converters 1 and 2 and other elements under overload during such occasion. ~o implement this invention, therefore, it is not neces-sary to provide a direct current power transmission system with a rating capacity of Pd'.
~he diagram of Fig. ~ is for explaining 2~ to what degree the transmission power of the direct current power transmission line should be increased in eliminating a fault. In the drawing, the abscissa represents the current Id of the direct current power transmission line, while the ordinate shows the AC
voltage ET at the ~C-DC connecting point, the voltage ~056451 Vd of the direct current power transmission line, the DC power Pd, the operating power factor Pf of the converter~ and the phase difference ~ between the AC voltages of the power stations A and ~. The graphic presentation of Fig. ~ i9 bas~d on the calculations made assuming that the tap positions on the trans-formers TRl and TR2, hence the voltages of the rear power supplies, are fixed and that the resulting fixed power is shared by the alternating current power transmission lines A~l and AL2 and the direct current power transmission line D~ for the purpose of trans-mission. Assume that the systems are operated at Id (= Io). As will be seen ~rom the graph, in order to merely increase the DC power Pd, it will be effective to increase the DC current from Io to Idm. This, however, results in decreasing not only ET and Vd, but also Pf, thereby incretasing the!)phase difference ~. For the stable operation of the power system, a smaller phase difference ~ is desirable.
Therefore, any increase of current from Id (= Io) should be limited to Ido. The operation according to the invention may utilize the fact that ET, Vd and Pf assume their points of inflection at the point Ido of the DC current.
A block diagram of an embodiment of the invention covering only a power station is shown in Fig. 4. In the drawing, like reference numerals denote like component elements as in Fig. 1, and the other reference numerals and characters will be first described below.
10564Sl 1 . Numerals 21 and 23 8hoW ~C current trans-formers for detecting the currents flowing in the alternating current power transmission line~ ALl and AL2. Reference characters r and x show a resistance and a reactance respectively similating the alternat-ing current power transmission lines ALl and AL2.
By applying a sum of the outputs of the AC current transformers 21 and 23 to the resistance-reactance combination, a voltage simulating the phase signal of the AC voltage at the power station B is obtained thereacross. Numeral 20 shows a maximum difference detector circuit. A "1" signal is produced from this detector circuit 20 when the phase difference between the simulation voltage of the other power station obtained across the series-connected r and x and the voltage of the power station at this end obtained from the AC potential transformer 15 reaches a maximum point, i.e., when the phase difference which has so far been increased begins to decrease.
An example of the circuit under consideràtion will be described more in detail later. Numeral 17 shows a DC voltage transformer for introducing the voltage Vd of the direct current power transmission line.
Reference numerals 22 and 32 show rectifier circuits - 25 which rectify the voltages obtained at the AC potential transformers 15 and 17 and produce them in the form of DC voltages. Numeral3 24, 28 and 40 show comparator circuits for comparing the reference voltages Vcl, Vc2 and Vc3 with the input voltages el, e2 and e3 ~0 respectively. Specifically, it is assumed that the , , , l comparator 24 produces a "l" output when el is higher than Vcl, that the comparator 28 produces a "l" out-put when e2 is higher than Vc2, and that the comparator 40 produces a "l" signal when e3 is higher than Vc3.
Under the normal conditions of the power system, the voltages Vcl and Vc2 are as high as about 50~0 of the voltages el and e2 respectively while the voltage Vc~ takes a positive value almost zero. As a result, the comparators 24 and 28 naturally produce a "1"
signal when the voltage of the AC-DC connecting point is normal. ~umeral 26 shows a flip-flop circuit, which is set and produces a "1" signal in response to an input at the set terminal S when the output of the comparator circuit 24 change,s from "0" to "l", namely, when the voltage at the AC-DC connecting point less than 50% of the rating is restored to the rating.
The nip-flop circuit 26 is reset and produces a "0"
signal in response to an input to the reset terminal R when the output of the maximum phase difference detector circuit 20 changes from "0" to "1". ~umeral 34 shows a ramp voltage generator circuit which pro-duces a continuously increasing voltage in response to a "l" signal from the flip-flop circuit 26. ~Ihen the output of the flip-flop 26 changes to "0", on the other hand, the output of the circuit 34 is restored to ~ero immediately. Numeral 36 shows a tracking and holding circuit. When the flip-flop 38 produces a "0" output, the output'of the ramp voltage generator circuit 34 is followed by the output of the tracking and holding circuit 36; whereas when the output of 1 the flip-flop 38 chang 4sStlo "1" the tracki d holdin~ circuit 36 produce3 the same output as that produced by the ramp voltage ~enerator circuit ~4 immediately before the change of the state of flip-flop 38 to "1". Numeral 30 shows what is called aprimary delay circuit, or first order lag circuit, ~ith a comparatively short time constant. Numeral 27 shows an adder for taking a sum of the outputs of the primary delay circuit 30 and the rectifier circuit 32 at the shown polarities. As long as the voltage of the direct current power transmission line is constant for stable operation, the output voltage e3 of the adder 27 is maintained at zero. If the voltage of the direct current power transmission line sudden-ly drops, however, the voltage e3 changes to positive,and vice versa. Therefore, assuming that the compa-rator 40 compares the output of the adder 27 with a reference voltage Vc~ which is substantially zero and produces an output when e3 is higher than Vc3~
then the primary delay circuit 30, the adder 27 and the comparator 40 are able to detect a point of sudden voltage drop. Numeral 29 shows an AND circuit for producing a "1" output in the presence of both the outputs of the comparators 28 and 40 and an input "1"
applied to the input terminal 100. The "1" input is applied to the AND circuit 29 only when the direct current transmission system is under operation. By this, the output of the comparator 40 is rendered ineffective when the direct current transmission line is separated from the transmission system. The presence ~- 18 -Y~
. . , 1~56451 of any output from the ~ND circuit 29 means therefore that a voltage drop has occurred in the direct current power trans-missi~n line under a high voltage level operation.
Numeral ~8 shows a flip-flop, which is set to produce a "1" signal in response to a "1" signal from the AND circuit 29 and reset to produce a "O"
signal in response to a "1" signal from the maximum phase difference detector circuit 20. In this con-nection, take note of the output of the tracking and holding circuit 36 of the alternating current power transmission system. Once the voltage is restored(The DC current is also restored) after it is decreased (Of course, the voltage of the direct current power transmission line drops also at the same tLme), the tracking and holding circuit 36 produces the same out-put as the ramp voltage generator circuit 34. At a time point when the voltage of the direct current power transmission line begins to drop and the flip-flop 38 produces a "1" signal, the tracking and holding circuit 36 holds the value of the output of the ramp voltage generator 34 at that very instant. When thedifference reaches a maximum point, the maximum phase difference detector circuit 20 produces a "1" output, æo that the both the flip-flops 26 and 38 are reset and the tracking and holding circuit 36 produces a "O" output. The output of the tracking and holding circuit 36 is applied to the adder 31 at the shown polarity. In other words, the higher the output voltage of the tracking and holding circuit ~6, the 19 .
~. .
lOS~451 1 current reference value Idp of the converters becomes equivalently larger. It was already explained that when the current of the direct current power trans-mission line is increased to the level shown by Ido in ~ig. 3, the tracking and holding circuit 36 detects and holds the voltage drop of the direct current power transmission line. Thus the output of the con-verters 1 is controlled at an optimum value for stable operation. It will also be understood from the fore-eoing description that it is until the phase differencereaches ~3' in Fig. 2c that such an output is produced from the tracking and holding circuit 36.
Explanation will be made of the other parts of the circuit shown in Fig. 4. Numerals 33, 35, 37 and 39 show adders to which input signals are applied at shown polarities respectively. The adder 33 is impressed with the output of the adder 31 and, when the switch SWl is turned on with the converter 1 inverter-operated, impressed also with the current margin ~I. The adder 39 is impressed with the output of the rectifier circuit 32 and the bias voltage Vb. The bias voltage Vb is set at a level obtained at the output of the rectifier circuit 32 when the direct current power transmission line is in rated condition. The adder 39 therefore produces a posi-tive voltage as long as the direct current power transmission line is operated with its voltage reduced below a predetermined level. The adder 35 is impressed with the output of the adder 39 at the shown polarity.
When the voltage of the direct current power 1 transmission line i~ in the reduced condition, there-fore, the function is apparently is equivalent to that obtained when the current target of the converter is reduced. The operation characteristics under such a condition are shown in ~ig. 6. The solid lines in the drawing show the operations at ratings. Assuming that the system is operated at Vd and Idp and the voltage of the alternating current power transmission line drops to Vd', the current is also reduced to I'dp thus causing the system to operate under the characteristics shown by dashed lines.
' ~y reducing the current in accordance with the voltage drop in this way, the reactive power required of the converter l is also reduced, with the re~ult that the voltage drop at the AC-DC connecting - point is minimized. The adder 37 is for causing the reference value of the current corrected on the basis of various factors as mentioned above to be brought face to face with the actual current of the direct current power transmission line. Numerals 3 and 5, like numeral lO, show voltage selector circuits. The voltage selector circuit 3 compares the output of the voltage selector circuit lO with a positive voltage ' of Va90 applied'thereto through the switch SW2, and ' 25 produces a lower one of them. Numerals 41 and 43 show polarity-reversing circuits for producing a voltage of the same magnitude but of,different ~; polarity. The voltage selector circuit 5 is for comparing the output of the polarity-reversing circuit 41 with the negative voltage ~Va90 applied 105f~451 1 thereto through the switch SW3 and produces a signal more negative than the other. The polarity-reversing circuit 43 is for reversing the polarity of the output of the voltage selector 5 and applying it to the auto-matic pulse phase shifter 8. The voltages +V~gO and ~Va90 have an absolute value suitable for production of a firing signal by the automatic pulse phase shifter 8 at a = 90. When the switches SW2 and SW3 are turned on, therefore, a firing signal is produced from the automatic pulse phase shifter 8 at the timing of a = 90 regardless of the operation of each element, as described later.
The switches SW2 and SW3 are controlled by the ~witch drive circuit 18. The switch drive circuit 18 is impressed with the output of the polarity-reversing circuit 45 reversing the output of the com-parator 24. As long as the alternating current power transmission line is operating normally, the compa-rator 24 produces a "1" signal and therefore the output of the polarity reversing circuit 45 is in the state of "0", thus keeping the output of the switches SW2 and SW3 in the off state. When the voltage of the alternating current power transmission line is reduced and the output of the comparator 24 becomes zero, by contrast, the polarity reversing circuit 45 produces a "1" signal so that the switches SW2 and SW3 are turned on through the switch drive circuit 18. In other words, when the voltage of the alternating current power transmission line drops to such a degree as to make normal converter operation impossible, the .
- ~2 -1 control function is made ineffective and a firing signal continues to be applied to the converter.
In this way, voltage restoration is awaited.
The magnitude and variation of the signals of the respective parts related to the foregoing description are taken into consideration in the dia-gram of Fig. 5 in which time is plotted horizontally.
In the drawing, character a shows the controlled delay angle of the converter which is assumed to take the value of al under normal conditions.
During the period from tl to t2 when the AC voltage drops sharply, a is assumed to be 90. Until the time point t3 where the phase difference reaches its maximum, the delayed angle al is reduced by aO, thus increasing the transmission power. For subsequent periods such as between t4 and ts when the voltage - drop is small, aO' is added to al thereby to lessen the reactive component required by the converter.
An example of the maximum difference detector circuit 20 and an outline of the operating waveforms thereof will be explained with reference to Figs. 7 and 8 respectively showing a block diagram of the circuit 20 and waveforms of operation thereof.
' In Fig. 7, reference numerals 201 and 203 show zero voltage detectors which are impressed with the voltages Etl and Et2 at the AC-DC connecting points tl and t2 and produce a pulse at a point where the above-mentioned voltages are reduced to zero respectively.
The operation of the zero voltage detectors 201 and 203 is ~hown in Figs. 8a, 8b and 8c. Numeral 202 ~056451 1 shows a flip-flop circuit set and reset in response to output pulses from the zero voltage detectors 201 and 203 respectively. (The setting is rendered by a pulse associated with the zero value of the voltage at the AC-DC connecting point on the power station A side, while the resetting is accomplished by a pulse associated with the zero value of the simulation voltage at the AC-DC connecting point on the power station ~ side.) ~he signal waveforms for such operations are shown in Fig. 8d. Numeral 204 ' shows an integrator for integrating the output of the flip-flop 202. The output signal of the integrator 204 has a peak proportional to the phase difference, and the signal waveform thereof is,shown in ~ig. 8e.
Numeral 205 shows a smoothing circuit impressed with and smoothing the output of the integrator 204, the signal waveform thereof being shown in Fig. 8f.
Numeral 206 shows a memory comprised of the primary delay circuit which is impressed with the output signal from the smoothing circuit 204 and produces the same signal a predetermined time later. Numeral 207 shows an adder for adding the outputs of the primary delay circuit 206 and the smoothing circuit , 205 to each other at shown polarities. Numeral 208 shows a comparator which, in response to the output ', of the adder 207, produces an output signal. This ' output signal changes from "1" to "0" when the polarity of the output signal of the adder 207 changes from positive to negative, namely, when the phase difference is reduced. Numeral 209 shows a - 21~ -105~45~
1 differentiating circuit for applying reset signals to the flip-flops 26 and 38 at the time of change of the output of the circuit 209 from "1" to "0". In this way, the fact that the phase difference has reached ~3' is detected in Fig. 2, whereupon the DC transmission power is returned from Pd' to Pd.
The present invention is not limited to the embodiment of Fig. 4 but may be embodied in various modifications. As explained with reference to Fig. 3, when the current in the direct current power transmission line is increased beyond Ido, not only the DC voltage Vdl but also the voltage at the AC-DC connecting point and the power factor of the converter undergo a sudden change. It will be noted that this point of inflection may be detected to set the flip-flop circuit 38 in ~ig. 4. This concept is incorporated in the embodiments shown in Figs. 9 and 10. These circuits are built around the circuit elements used for setting the flip-flop 38, leaving the other parts identical with like elements in the other embodiments. Also, like numerals are attached to those elements whose functions are similar.
As will be obvious by comparing the output of the rectifier circuit 32 in Fig. 4 with that of the rectifier circuit 22 in Fig. 9, the circuit arrange-ment of this particular part is quite the same e~cepting the detection of the point of inflection of the voltage at the AC-DC connecting point. The circuit of Fig. 10 is configured with special emphasis on the change in the power factor of the converter 1 .
1 nnd ha~ an additional ~C current transformer 58.
The ou~puts V nnd I of the AC potential transformer 15 and AC current transformer 58 are applied to the Hall converter 72 and the multiplier 74 respectively for calculation of VIcos y and VI, where y is the phase difference between V and I. The outputs of the Hall converter 72 and the multiplier 74 are introduced to the divider 70 to obtain a power factor expressed by VIvIS ~ = c08 ~. This signal is applied to the primary delay circuit 28, the adder 27 and the comparator 40 thereby to detect a point of inflection.
The AND circuit 102 is provided to allow the output of the comparator 40 to be applied to the flip-flop 38 only when the direct current transmission line is under operation. In this case, if the voltage i9 zero, no power factor is calculated out and therefore the need for the comparator 28 and the AND gate 29 as in the circuit of Fig. 4 is eliminated.
Further, instead o4 starting the increase in the current reference value at the time of voltage re~toration at the AC-DC connecting point after shoot-ing the fault, the voltage restoration of the direct current power transmission system may of course be utilized, as illustratively shown in Fig. 11. By comparing Fig. 11 with Fig. 4, it will be obvious that in the case of Fig. 11 it sufficies if the out-put of the rectifier circuit 22 in Fig. 4 is replaced by that of the rectifier 32 as an input to the com-parator circuit 24. In Fig. 11, the AND circuit 104 ~ - 26 -: .
~OS~451 1 is corresponding to the AND circuit 102 in Fig. 10 and its input 105 receives a "1" si~nal only when the direct current transmission line is under operation.
It will thus be seen that according to the invention, in the event of a fault developed in the power system including an AC-DC parallel power trans-mission system and the resulting voltage drop at the AC-DC connecting point, the converter is rendered ready to enter into operation simultaneously with the voltage restoration, in response to the voltage drop. Also, when the converter resumes its operation, a transmission power most suitable for stable opera-tion of the power system is automatically determined.
Furthermore, if the voltage at the AC-DC connecting - point drops if not to such a degree as to make the converter ready for operation, the transmission power of the direct current power transmission line may be reduced accordingly. As a result, the use of the present invention is considered to enhance the value o~ the AC-DC parallel power transmission system among other parts of the power system.
Claims (13)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. In a control apparatus for converters in a power system including a direct current power transmission line connected in parallel to an alternating current power trans-mission line, said control apparatus comprising first means for producing a first voltage signal corresponding to a required controlled delay angle for giving at least a minimum margin angle determined as a function of the voltage at the connecting point between said AC and DC transmission lines and the current in said direct current power transmission line, second means for producing a second voltage signal as a function of the difference between a current reference value of said direct current power transmission system and an actual current value thereof, third means for selecting one of said first and second voltage signals, and fourth means for applying to said converter, in response to a phase signal in phase with the voltage at said AC-DC connecting point, a firing signal adapted to fire said converter at a controlled delay angle corresponding to said selected voltage signal; the improvement comprising fifth means for maintaining the phase of said phase signal in phase with the voltage at said AC-DC connecting point even after said voltage at said AC-DC connecting point drops transiently, and means for further controlling the delay angle given by said firing signal in response to the voltage drop at said AC-DC connection point.
2. The improvement according to Claim 1, wherein said delay angle controlling means comprises sixth means for forcibly fixing the controlled delay angle at a predetermined value when the voltage at said AC-DC connecting point drops below a predetermined level.
3. The improvement according to Claim 2, where-in said controlled delay angle is forcibly fixed at degrees.
4. The improvement according to Claim 1, wherein said delay angle controlling means comprises seventh means for reducing the apparent value of said current reference in accordance with said voltage drop at said AC-DC connecting point.
5. The improvement according to Claim 1, where-in said delay angle controlling means comprises eighth means for increasing said current reference value when the voltage at said AC-DC connecting point is restored from the voltage drop.
6. The improvement according to Claim 5, where-in said delay angle controlling means further com-prises ninth means in response to a predetermined operating condition in said power transmission system after said current reference value is caused to increase by said eighth means, to prevent said current reference value from being further increased.
7. The improvement according to Claim 5, in which the voltage restoration at said AC-DC connect-ing point is detected by monitoring the AC voltage at said AC-DC connecting point.
8. The improvement according to Claim 5, in which the voltage restoration-at said AC-DC connect-ing point is detected by monitoring the voltage of said direct current power transmission line.
9. The improvement according to Claim 6, where-in said delay angle controlling means further com-prises tenth means for resetting said eighth and ninth means to restore said current reference value to its original level when the phase difference between the voltages at the AC-DC connecting points at both sides of said power system reaches a maximum point.
10. The improvement according to Claim 6, in which said ninth means is responsive to a voltage drop exceeding a predetermined value, of said direct current power transmission line after restoration of the voltage of said direct current power transmission line derived from to the increase in said current reference value.
11. The improvement according to Claim 6, in which said ninth means is responsive to a drop of AC voltage, exceeding a predetermined value, at said AC-DC connecting point after restoration of the AC
voltage at said AC-DC connecting point derived from the increase of said current reference value.
voltage at said AC-DC connecting point derived from the increase of said current reference value.
12. The improvement according to Claim 6, in which said ninth means is responsive to a reduction exceeding a predetermined value in the power factor of said converter due to the increase of said current reference value by said eighth means.
13. The improvement according to Claim 2, wherein said delay angle controlling means further comprises seventh means for reducing the apparent value of said current reference in accordance with said voltage drop at said AC-DC connecting point, eighth means for increasing said current reference value when the voltage at said AC-DC con-necting point is restored from the voltage drop, ninth means in response to a predetermined operating condition in said power transmission system, after said current reference value is caused to increase by said eighth means, to prevent said current reference value from being further increased, and tenth means for resetting said eighth and ninth means to restore said current reference value to its original level, when the phase difference between the voltages at the AC-DC connecting points at both sides of said power system reaches a maximum value.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2595275A JPS5613099B2 (en) | 1975-03-05 | 1975-03-05 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1056451A true CA1056451A (en) | 1979-06-12 |
Family
ID=12180083
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA247,074A Expired CA1056451A (en) | 1975-03-05 | 1976-03-03 | Converter control apparatus for ac-dc parallel power transmission system |
Country Status (4)
| Country | Link |
|---|---|
| JP (1) | JPS5613099B2 (en) |
| CA (1) | CA1056451A (en) |
| DE (1) | DE2608973C2 (en) |
| SE (1) | SE419592B (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102496924A (en) * | 2011-12-12 | 2012-06-13 | 山东大学 | Modeling method and system for correcting and predicting arc extinguishing angle |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE3023698A1 (en) * | 1980-06-25 | 1982-01-14 | Brown, Boveri & Cie Ag, 6800 Mannheim | METHOD FOR COMMISSIONING ONE OF SEVERAL RANGE OF RECTIFIER GROUPS IN A HIGH VOLTAGE DC CURRENT TRANSMISSION SYSTEM |
-
1975
- 1975-03-05 JP JP2595275A patent/JPS5613099B2/ja not_active Expired
-
1976
- 1976-02-27 SE SE7602739A patent/SE419592B/en not_active IP Right Cessation
- 1976-03-03 CA CA247,074A patent/CA1056451A/en not_active Expired
- 1976-03-04 DE DE19762608973 patent/DE2608973C2/en not_active Expired
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102496924A (en) * | 2011-12-12 | 2012-06-13 | 山东大学 | Modeling method and system for correcting and predicting arc extinguishing angle |
Also Published As
| Publication number | Publication date |
|---|---|
| JPS5613099B2 (en) | 1981-03-26 |
| JPS51101838A (en) | 1976-09-08 |
| SE419592B (en) | 1981-08-10 |
| DE2608973A1 (en) | 1976-09-30 |
| DE2608973C2 (en) | 1984-11-15 |
| SE7602739L (en) | 1976-09-06 |
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