Control system for excitation of synchronous machine

Abstract: An excitation control system (200) for a synchronous machine and configured from automatic voltage regulators (6a, 6b, 6c) that output control signals (CA, CB, CC) so as to regulate a terminal voltage of a synchronous machine (1), phase controllers (8a, 8b, 8c) that output phase signals (PA, PB, PC) so as to control the phase of an arc pulse (PL) of a thyristor rectifier that supplies a field current to a field winding (2) of the synchronous machine (1), intermediate pulse selectors (14) provided with three pairs of pulse outputters (11a, 11b, 11c) that output the arc pulses (PL) on the basis of the phase signals (PA, PB, PC) and which are provided between aforementioned three pairs of pulse outputters (11a, 11b, 11c) and phase controllers (8a, 8b, 8c) provided between pulse outputters (11a, 11b, 11c) and the three pairs of phase controllers (8a, 8b, 8c), with a logical sum of the three arc pulses being supplied to said thyristor rectifier. Furthermore, the intermediate pulse selectors (14) selects phase signals of an intermediate phase from the three phase signals (PA, PB, PC), phase signals from one of another two pairs being selected and output when one pair of the three pairs of automatic voltage regulators (6a, 6b, 6c) and phase controllers (8a, 8b, 8c) fails, with phase signals output from the unfailed pair being selected and output when two of the three pairs of automatic voltage regulators (6a, 6b, 6c) and phase controllers (8a, 8b, 8c) fails.

Description: The present invention relates to an excitation control system provided to a synchronous machine such as a synchronous generator or a synchronous electric motor or the like, and more particularly, to an excitation control apparatus according to the preamble of claim 1. Such a control apparatus provides an excitation control system for synchronous machines that are duplicated so as to increase their reliability. An excitation control apparatus of this type is known from the prior art JP-A-1 315 300 and will be discussed below. In general, excitation control systems for synchronous machines have a basic function to perform automatic voltage regulation functions so as to control a terminal voltage of the synchronous machines to be constant, with ancillary functions being an overexcitation limit function and an underexcitation limit function so that the operation of the synchronous machine is stable and within the critical limits. Furthermore, there is also a control system provided with many complex functions such as secondary regulation functions so that the performance and the ineffective power are stable. However, when there is the generation of a failure in such an excitation control system, a control abnormality generates and the control operation stops so that it is no longer possible to continue the operation of the synchronous machine. Accordingly, it is required that there be a high reliability of excitation control systems. In particular, in cases when there is a large-capacity synchronous generator provided to operating power facilities, it is necessary that there always be an extremely high reliability from the point of view of the public nature and the social importance of power supply. Control systems for which such extremely high reliability is demanded are generally such that there is duplicated configuration of control systems so that the reliability of the control system itself is increased so as to prevent the generation of failures and so that it is possible to continue the operation of the machines that are the object of control even if a failure should generate. FIG. 1 is a view showing the configuration of a conventional example of an excitation control system for synchronous machines that have a duplicated configuration. In the figure, a field winding 2 of a synchronous machine 1 is supplied via a field circuit breaker 3, with an excitation current from a thyristor rectifier apparatus 4 that has three-phase uniform bridge wiring, and the AC power EA from this thyristor rectifier apparatus 4 is supplied via an excitation transformer 5 from the output of the synchronous machine 1. As shown in FIG. 1, a control system 100 comprises an A group control unit 100A, a B group control unit 100B and a C group control unit 100C, for respectively controlling an excitation of A-C groups. Automatic voltage regulators 6a, 6b and 6c detect the terminal voltage of the synchronous machine 1 via the potential transformer 7 and perform control calculations so that this terminal voltage becomes equal to the objective value (set value), and outputs the control signals CA, CB and CC. Phase controllers 8a, 8b and 8c input the AC power voltage EA via the transformer 9 and this AC power voltage is output as the reference phase as the phase signals PA, PB and PC that change in accordance with the control signals CA, CB and CC. Intermediate pulse selectors 10a, 10b and 10c select the phase signals of the intermediate phase from the phase signals PA, PB and PC, and output the phase signals PLA, PLB and PLC. Pulse outputters 11a, 11b and 11c output arc pulses in the phase indicated by the phase signals PLA, PLB and PLC and the configuration is such that this output is connected by logical sum, and so that the firing pulses PL are supplied to the thyristor rectifier apparatus 4. When there is normal operation, the automatic voltage regulators 6a, 6b and 6c and the phase controllers 8a, 8b and 8c operate in the same manner, respectively. However, the terminal voltage detection error of the automatic voltage regulators 6a, 6b and 6c, and the reference phase detection error of the phase controllers 8a, 8b and 8c cause there to be operation having a slight difference in the control signals CA, CB and CC, and the phase signals PA, PB and PC. The intermediate pulse selectors 10a, 10b and 10c select the phase signals of the intermediate phase from amongst the phase signals PA, PB and PC and so the phase signals PLA, PLB and PLC become the same signals. Accordingly, the firing pulses that are output by the pulse outputters 11a, 11b and 11c become the same signals and the firing pulse PL which is the logical sum of them is also the same signal. FIG. 2 is a view showing the configuration of the intermediate pulse selector 10a and is a majority circuit comprising an AND circuit (logical product) 12A, 12B and 12C and an OR circuit (logical sum) 13a and so the phase signals PLA become the majority result of the phase signals PA, PB and PC. Moreover, the other intermediate pulse selectors 10b and 10c have the same configuration as the intermediate pulse selector 10a. FIG. 3 is a view showing the waveform indicating the operation of a conventional excitation control system. The thyristor rectifier apparatus 4 has a three-phase uniform bridge wiring and so the firing pulses PL and the phase PA, PB, PC, PLA, PLB and PLC are each signals of the six phases but in FIG. 3, only one phase portion of there is indicated. In addition, the phase signals PLA, PLB and PLC become the same signal and so only the phase signal PLA is shown. A cycle t 1 of the AC power EA shows the normal operation and the phase signals PA, PB and PC shown in FIG. 3(a) each become signals that are proportional to the control signals CA, CB and CC with each of the phases of the AC power EA being the reference, as shown in FIG. 3(b) through (d). As shown in FIG. 3(e), the phase signals PLA become the majority result of the phase signals PA, PB and PC and so for the cycle t 1 , become the same signal as the phase signals PA. More specifically, the phase signal PLA selects the phase signal PA that indicates the intermediate phase of the three phase signals PA, PB and PC. The firing pulse PL becomes the pulse signal of a predetermined width from the rise of the phase signal PLA. Then, the cycle t 2 shows the operation when either or both of the automatic voltage adjuster portion 6a or the phase control portion 8a fails and the phase signal PA is no longer output. In this case, the phase signal PLA is the result of the logical product of the phase signals PB and PC and so becomes the same signal as the phase signal PC. Furthermore, the cycle t 3 shows the operation for the status where the phase signal PA is no longer output and either or both of the automatic voltage regulator 6b and the phase control portion 8b has failed and the phase signal PB is no longer output. In this case, the phase signal PLA is no longer output and so the firing pulse PL is also not output. In such a conventional excitation control apparatus, even if there is a failure on one system of the automatic voltage regulators 6a, 6b and 6c and the phase control portions 8a, 8b and 8c which are both triplicated, the action of the intermediate pulse selector portions 10a, 10b and 10c selects the normal phase signals from the phase signals PA, PB and PC, and outputs the corresponding firing pulses PL but there is the disadvantage that normal operation is no longer possible when there is a failure in two of the systems. SUMMARY OF THE INVENTION The present invention has as an object the provision of an excitation control system that has an extremely high reliability and that can continue normal operation even if two of the triplicated control svstems fail. This object is solved by an excitation control apparatus comprising the features of claim 1. By this, normal phase signals are always selected even if one or two of the systems of the triplicated phase control portions and automatic voltage regulator portions fails. As has been described above, according to the present invention, it is possible to select and output normal phase signals even if one or two of the systems of the triplicated phase control portions and automatic voltage regulator portions fails and to use this output as the basis for the supply of firing pulses to a thyristor rectifier apparatus and therefore enable provide an excitation control system for synchronous machines and that has an extremely high reliability and that enables the continuous operation of the synchronous machines. BRIEF DESCRIPTION OF THE DRAWINGS In the appended drawings, FIG. 1 is a view showing the configuration of a conventional excitation control system; FIG. 2 is a view showing the configuration of a conventional intermediate pulse selector portion; FIG. 3 is a waveform diagram showing the operation of a conventional excitation control system; FIG. 4 is a view showing the configuration of a first embodiment of the excitation control system according to the present invention; FIG. 5 is a view showing the configuration of an intermediate pulse selector portion of a first embodiment of the excitation control system according to the present invention; FIG. 6 is a view describing the truth value table of the intermediate pulse selector portion described above; and FIG. 7 is waveform diagram showing the operation of a control system relating to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 4 is a view showing the configuration of a first embodiment of the excitation control system according to the present invention. In the figure, those portions that correspond to portions of FIG. 1 are indicated with corresponding numerals and the corresponding descriptions of them are omitted. A control system 200 shown in FIG. 4 comprises an A group control unit 200A, a B group control unit 200B, a C group control unit 200C, and a failure detection unit 20 which detects each failure of A-C groups. Intermediate pulse selectors 14a, 14b and 14c input each of the phase signals PA, PB and PC, and the failure signals DA, DB and DC, and output the phase signals PLA, PLB and PLC. The failure signal DA is turned on (hereinafter referred to as the "H" signal level) when there is a failure in either of the automatic voltage regulator 6a or the phase controller 8a of the A group, as detected by the OR circuit 20a of the failure detection unit 20. In the same manner as for the failure signal DA, the failure signals DB and DC become "H" when there is a failure in either or both of the automatic voltage regulators 6b and 6c and the phase controllers 8b and 8c, and are turned off (hereinafter referred to as the "L" signal level) when there is no failure, as detected by the OR circuits 20b and 20c provided to each group, respectively. As shown in FIG. 4, in each A group control unit 200A, B group control unit 200B and C group control unit 200C, the automatic voltage regulator 6a, 6b or 6c comprises a failure detector 30a, 30b or 30c for outputting a detection signal FA, FB or FC, respectively, after detecting a failure of the regulator 6a, 6b or 6c. Moreover, the phase controller 8a, 8b or 8c also comprises a failure detector 31a, 31b or 31c for outputting a detection signal GA, GB or GC, respectively, when it detects a failure of the controller 8a, 8b or 8c. The failure detection unit 20 comprises the OR circuit 20a for outputting the failure signal DA which is a logical sum of the detection signals FA and GA respectively output from the failure detectors 30a and 31a, the OR circuit 20b for outputting the failure signal DB which is a logical sum of the detection signals FB and GB respectively output from the failure detectors 30b and 31b, and the OR circuit 20c for outputting the failure signal DC which is a logical sum of the detection signals FC and GC respectively output from the failure detectors 30c and 31c. All these failure signals DA, DB and DC are supplied to all of the intermediate pulse selectors 14a, 14b and 14c of A , B and C group control units. FIG. 5 is a view showing the configuration of an intermediate pulse selector portion 14a, and in the figure, those portions that correspond to portions of FIG. 2 are indicated with corresponding numerals and the corresponding descriptions of them are omitted. A switching portion 15 outputs the phase signals PHA, PHB and PHC corresponding to the phase signals PA, PB and PC, and when the failure signals DA, DB and DC are all "L", the phase signals PHA, PHB and PHC are all the same value as the phase signals PA, PB and PC. More specifically, this switching portion 15 is configured from inverters 16A, 16B and 16C that invert the failure signals DA, DB and DC, AND circuits 17A, 17B and 17C that determine the logical product of the inverted signals and the aforementioned failure signals DA, DB and AC, AND circuits 18A, 18B and 18C that respectively determine the logical product of the inverted signals of the signal DC with respect to the failure signal DA, the inverted signals of the signal DA with respect to the failure signal DB, and the inverted signals of the signal DB with respect to the failure signal DC, and OR circuits 19A, 19B and 19C that respectively determine the logical sum of the aforementioned AND circuits 17A and 18A, 17B and 18B, and 17C and 18C. Accordingly, when one of the failure signals DA, DB and DC is at the "H" level, one of the corresponding phase signals PHA, PHB and PHC becomes "H". When two of the failure signals DA, DB and DC are at the "H" level, one of the corresponding phase signals PHA, PHB and PHC becomes the "H" level and the other becomes the "L" level. When all of the failure signals DA, DB and DC are at the "H" level, the phase signals PHA, PHB and PHC all become the "L" level. The phase signals PLA shows the majority result of the phase signals PHA, PHB and PHC. FIG. 6 is a view describing the truth value table of the intermediate pulse selector portion 14a with respect to the failure signals DA, DB and DC. As can be seen from the diagram, the phase signals PLA become the majority result of the phase signals PA, PB and PC when all of the failure signals DA, DB and DC are the "L" level. In addition, when either of the failure signals DA, DB and DC is at the "H" level, the logical sum of the two that of the phase signals PA, PB and PC that do not correspond to a failures is taken. Furthermore, when two of the failure signals DA, DB and DC are at the "H" level, the one of the phase signals PA, PB and PC that does not correspond to a failure becomes the phase signal PLA. FIG. 7 is a waveform diagram showing the operation of the control system 200 relating to the embodiment of the present invention. The cycle t 1 of the AC power shown in FIG. 7(a) shows normal operation, and the phase signals PA, PB and PC become signals that are proportional to the control signals CA, CB and CC, with the phases of the each of the AC power EA being the reference. In FIG. 7(b) through (d), each of the failure signals DA, DB and DC show the "L" level and so the phase signals PHA, PHB and PHC becomes the same as each of the phase signals PA, PB and PC as shown in FIG. 7(e) through (g). Accordingly, the phase signals PLA become the same signals as the phase signals PA at the cycle t 1 . The arc pulse PL becomes the pulse signal with a predetermined width from the rise of the phase signal PLA. Then, the cycle t 2 shows the operation for the case when either or both of the automatic voltage regulator 6a and the phase controller 8a fails, and the phase signal PA is not output. In this case, the failure signal DA becomes the "H" level as shown in FIG. 7(b) and so the phase signal PHA becomes "H" irrespective of the status of the phase signal PA and as shown in FIG. 7(h), and the phase signal PLA becomes the result of the logical sum of the phase signals PB and PC, as shown in FIG. 7(k). Accordingly, at the cycle t 2 , the phase signals PLA become the same signal as the phase signal PB. Furthermore, cycle t 3 shows the operation for the status where the phase signal PA is not output, and either or both of the automatic voltage regulator 6b and phase controller 8b fails, and the phase signal PB is no longer output. In this case, as shown in FIG. 7(b) and (c), the failure signals DA and DB become the "H" level and so the phase signals PHA become the "H" level irrespective of the status of the phase signal PA, as shown in FIG. 7(h), and the phase signals PHB of FIG. 7(i) become the "L" level irrespective of the status of the phase signal PB, and at the cycle t 3 , the phase signal PLA of FIG. 7(k) becomes the same signal as the phase signal PC of FIG. 7(g). As has been described above, even if one or two systems of the triplicated automatic voltage regulators 6a, 6b and 6c and the triplicated phase controllers 8a, 8b and 8c fail, the intermediate pulse selectors 14a, 14b and 14c select the phase signals of the normal system output of the phase signals PA, PB and PC and so the synchronous machine 1 can continue to operate normally.

Claims: An excitation control apparatus for a synchronous machine comprising three automatic voltage regulator portions (6a, 6b, 6c) that output control signals so as to regulate the terminal voltage of a synchronous machine (1); three phase control portions (7a, 7b, 7c) that output phase signals (Xa, Xb, Xc) so as to control the phase of an arc pulse of a thyristor rectifier apparatus (3) that supplies a field current to a field winding (2) of said synchronous machine (1); three intermediate pulse selector portions (14a, 14b, 14c) each connected to the outputs (Xa, Xb, Xc) of said phase control portions and outputting intermediate signals (Xm) three pulse output portions (11a, 11b, 11c) connected to the corresponding output of said intermediate pulse selector portions and outputting said arc pulse (PL) on the basis of said phase signals (PA, PB, PC) such that, when none of the automatic voltage regulator portions or the phase control portions has failed, the majority result of the outputs of the phase control portions is selected as arc pulse, and when one of the automatic voltage regulator portions or the phase control portions has failed, the logical sum of the outputs of the two other phase control portions is selected as arc pulse, characterized by the following features: each of said intermediate pulse selector portions (14a, 14b, 14c) receives the supply of failure signals (DA, DB, DC) output from a failure detector circuit (20) that detects whether or not each (6a and 8a, 6b and 8b, 6c and 8c) of said three of automatic voltage regulator (6a, 6b, 6c) and phase control portions (8a, 8b, 8c) has failed on the basis of detection signals (FA, FB, FC and GA, GB, GC) respectively ouptut from respective failure detectors (30a-30c and 31a-31c); such that, when said failure detector circuit (20) detects that a pair of said three of automatic voltage regulator (6a, 6b, 6c) and phase control portions (8a, 8b, 8c) has failed, the output of the phase control portions which has not failed is selected as arc pulse (PL). The control apparatus of claim 1, wherein: said failure detection circuit (20) comprises a first OR circuit (20a) that takes a logical sum of said detection signal (GA) from said detector (31a) of said first phase control portion (8a) and said detection signal (FA) from said detector (30a) of a first automatic voltage regulator portion (6a) and outputs the first failure signal (DA) to first through third intermediate pulse selector portions (14a, 14b, 14c), a second OR circuit (20b) that takes a logical sum of said detection signal (GB) from said detector (31b) of said second phase control portion (8b) and said detection signal (FBA) from said detector (30b) of said second automatic voltage regulator (6b) and outputs the second failure signal (DB) to first through third intermediate pulse selector portions (14a, 14b, 14c), and a third OR circuit (20c) that takes a logical sum of said detection signal (GC) from said detector (31c) of said third phase control portion (8c) and said detection signal (FC) from said detector (30c) of said third automatic voltage regulator (6a) and outputs the third failure signals (DC) to first through third intermediate pulse selector portions (14a, 14b, 14c). The control apparatus of claim 1, wherein: one intermediate pulse selector of said intermediate pulse selector portions (14a, 14b, 14c) of A to C groups comprises a switching portion (15) that outputs phase signals (PHA, PHB, PHC) on the basis of said failure signals (DA, DB, DC) that indicate failure of any of said pairs of entometic voltage regulator and phase controller (6a and 8a, 6b and 8b, 6c and 8c) and said phase signals (PA, PB, PC), and a plural number of logical elements (12A, 12B, 12C) that by the logical calculation of said phase signals (PHA, PHB, PHC) output phase signals (PLA, PLB, PLC) that are majority result of said signals (PHA, PHB, PHC). The control apparatus of claim 3, wherein: said switching portion (15) comprises first, second and third inverters (16A, 16B, 16C) that invert said first, second and third failure signals (DA, DB, DC), first through third AND circuits (17A, 17B, 17C) that take the logical product of said signals output from said first, second and third inverters with respect to said first, second and third phase signals (PA, PB, PC), fourth through sixth AND circuits (18A, 18B, 18C) that take the logical product between a signal output from said third inverter (16C) and said first failure signal (DA), between a signal output from said first inverter (16A) and said second failure signal (B), and between a signal output from said second inverter (16B) and said third failure signal (DC), respectively, and first through third OR circuits (19A, 19B, 19C) that respectively take the logical sum of outputs of first and fourth AND circuits (17A, 17B), second and fifth AND circuits (17B, 18B) and third and sixth AND circuits (17C, 18C) and respectively output said phase signals (PHA, PHB, PHC). The control apparatus of claim 3, wherein: said logical elements (12A, 12B, 12C and 13) comprise first through third AND circuits (12A, 12B, 12C) that respectively take the logical sum of first and second signals (PHA, PHB), second and third signals (PHB, PHC), and third and first signals (PHC, PHA) of said phase signals, and an OR circuit (13) that inputs all of the outputs of said first through third AND circuits (12A, 12B, 12C), takes the logical sum, and outputs said phase signals (PLA, PLB, PLC) that indicate a majority result of said phase signals (PHA, (PHA, PHC).

Inventors: MURAKAMI HITOSHI, MURAKAMI, HITOSHI
Applicants: TOSHIBA KK, KABUSHIKI KAISHA TOSHIBA
Application year: 1991
Main classification: H02H7
IPC codes: H02P9, H02H7, G05B9