JP2012050163A - Protective device of power conversion device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To discriminate an internal short circuit from a commutation failure which is an abnormality with an external cause, with a simple device configuration.SOLUTION: In a protective device of a power conversion device, an AC side of a first converter is connected to a first AC system, and an AC side of a second converter is connected to a second AC system. A DC reactor is provided to a DC circuit between the first converter and the second converter, and one of the converters is operated as a forward converter while the other converter is operated as a reverse converter. Current of the first AC system and current of the second AC system are compared with a DC current reference value respectively. Based on positiveness or negativeness of its differential current, the abnormality of the power converter is determined as an internal short circuit or as a commutation failure.

Description

  The present invention relates to a protection device for a power conversion device, and more particularly to a protection device for a power conversion device that can discriminate between an internal abnormality and an abnormality caused by the outside.

  Although power conversion devices having various configurations are used in various fields, a power conversion device to which the present invention is applied includes a forward converter and an inverse converter, and a direct current is interposed between these converters. It is the type that forms the circuit. As a system that employs such a power conversion device, there are a direct current power transmission system of a power system, a pumping starter of a pumped storage power generation system, and the like.

  In FIG. 2, the structure of the pumping start apparatus of a pumped-storage power generation system is shown as an example to which the power converter device provided with a forward converter and an inverse converter is applied. In this figure, 1 is a three-phase power system of R, S, and T, and 2 is a starting transformer. On the other hand, 6 is a generator motor, and a pump turbine 9 is directly connected to a rotating shaft thereof. The generator motor 6 side is a three-phase AC system of U, V, and W. Reference numeral 10 denotes a power conversion device provided between the power system 1 and the generator motor 6, and includes a forward converter 3, an inverse converter 5, and a DC reactor 4 on a DC circuit.

  According to this device configuration, at the start of pumping of the pumped storage power generation system, the AC power of the power system 1 is converted to DC by the forward converter 3, and this DC is smoothed by the DC reactor 4 and then passed to the inverse converter 5. Entered. The inverse converter 5 supplies AC power having a frequency corresponding to the rotational speed of the generator motive 6 to be driven. Non-Patent Document 1 is known as an application of a power conversion device including a forward converter and an inverse converter to a pumping starter of a pumped storage power generation system.

  For the forward converter 3 and the inverse converter 5, semiconductor switches such as thyristors and IGBTs are used. For example, thyristors are connected in series to form upper and lower arms, and the upper and lower arms are connected to each phase of the AC system. Also, both ends of the arm are connected to a DC circuit. Furthermore, for the purpose of controlling and protecting the power converter, the alternating current on both sides of the power converter is detected and used by the current transformers CTA and CTB.

  In the following description, the semiconductor switches constituting the forward converter 3 and the inverse converter 5 may be referred to, but the individual semiconductor switches connected to the three-phase arm are represented by the forward converter 3 and the inverse converter 5. Symbols (3, 5) representing AC, symbols (UVW, RST) representing AC phases, and symbols (1, 2) for distinguishing the upper arm and lower arm are distinguished and represented by a three-digit symbol. .

  In a power converter, various abnormal states are caused mainly in association with the use of a semiconductor switch. This is an internal short circuit, for example, commutation failure that is an abnormality caused by the outside. The previous Non-Patent Document 1 shows that an alternating current on both sides of the power converter is input and an abnormality is detected by the difference current. Japanese Patent Application Laid-Open No. H10-228561 discloses a method for detecting a commutation failure using an AC side current and an arm current of a converter as inputs.

Japanese Patent Laid-Open No. 62-262670

Magazine "Hitachi Review" February 2007 "Start of operation of 525 MVA power generation motive and thyristor starter for Tokyo Electric Power Company's Kanagawa Power Station"

  Of the abnormal states in the power converter, the system should be shut down quickly in the case of an internal short circuit, but in many cases, commutation failure, which is an abnormality caused by the outside, may recover within several AC cycles. It is not always necessary to stop the system because it is expensive.

  If it is determined that the system is stopped during the pumping start, the apparatus is stopped by the operation sequence, so that the power generation motive that has been accelerated halfway is naturally decelerated thereafter. Then, after the complete shutdown, the equipment is used again after confirming that there are no suspected internal abnormalities, and until then it will not be possible to operate, adversely affecting the operation of the power system in terms of lost pumping opportunities. In addition, there is a problem that it takes time to identify the phenomenon.

  Also, if the system is shut down, in the case of the pumping starter of the pumped storage power generation system, the operation returns to the initial stage and the electric circuit operation such as the AC system and the power converter, the mechanical system such as the pump turbine, or the water system operation is performed again. In this sense, too much time and labor are required.

  For this reason, it is desirable to distinguish between internal short circuit and commutation failure, which is an abnormality caused by the outside, and to adopt post-measures suitable for each. However, in Patent Document 1 or Non-Patent Document 1, these cannot be clearly distinguished. .

  FIG. 4 is a diagram illustrating an accident situation when an internal short circuit occurs. For example, in the forward converter 3, it is assumed that the semiconductor switch 3S1 has an internal short circuit at the timing when the semiconductor switches 3R1 and 3T2 are conductive. . In this case, a short circuit is formed from the R phase of the starting transformer 2 to the S phase of the starting transformer 2 via the semiconductor switches 3R1, 3S1.

  On the other hand, commutation failure that is an abnormality caused by the outside is a state in which the upper and lower semiconductor switches are simultaneously turned on because the commutation of the direct current Id is not successful due to some reason in the forward converter 3 and the reverse converter 5. It is a phenomenon. This commutation failure is often a problem especially when the semiconductor switch is a thyristor, but the reason why it is considered as “a transient abnormality caused by the outside” is due to the following two circumstances. However, it is often possible to recover after that and continue operation again.

  First, the first case is when a disturbance occurs in the power system 1. For example, when a ground fault occurs due to a lightning strike to the power system, the voltage of the power system is lower than that during normal operation. This abnormal condition is usually temporary. Usually, the fault point is removed by opening the circuit breakers at both ends of the ground fault occurrence point, and the voltage is recovered in several cycles. However, since the commutation voltage is insufficient for the forward converter during the voltage drop period, normal commutation may not be achieved and commutation may fail.

  The second case is a case where the synchronization signal that is the basis of the ignition command of the inverse converter fluctuates due to noise or the like. When the synchronization signal fluctuates and the ignition command for the semiconductor switch of the inverse converter is delayed, the reverse voltage period for extinguishing the semiconductor switch that has been in a conductive state may be insufficient. In that case, the semiconductor switch cannot be extinguished, and becomes conductive again when the forward voltage is applied next. Since this re-conduction is not conduction by control, the DC circuit is short-circuited with another semiconductor switch fired by control.

  In both the first and second cases, the state to be reached as a result is a commutation failure as shown in FIG. 5 (in the example shown in the figure, the upper and lower arms are short-circuited in the reverse converter 5, between 5V1 and 5V2), and abnormal energization Although it is in a state, it is not an internal abnormality of the device. In addition, the event that causes the problem may be a temporary event caused by the outside of the apparatus. Therefore, when the voltage of the AC system is stabilized or the noise of the synchronization signal is eliminated, the commutation operation can be stably resumed after returning to the old one.

  With respect to these abnormal events, the technique of Patent Document 1 or Non-Patent Document 1 can detect commutation failure and internal short circuit, respectively. However, in the method of Non-Patent Document 1 that monitors the difference between the alternating currents on both sides of the power conversion device, the measurement event that the difference in alternating current occurs in both the commutation failure in FIG. 5 and the internal short circuit in FIG. Is the same, and as a result, it is determined as an internal short circuit.

  In the method of Patent Document 1 that uses an AC current and each arm current, it cannot be distinguished from an internal short circuit by itself (it cannot be distinguished even if the same event occurs due to a short circuit). It is necessary to judge comprehensively by combination.

  In view of the above, an object of the present invention is to provide a protection device for a power conversion device that can distinguish between an internal short circuit and an external commutation failure with a simple device configuration.

  In order to solve the above problems, the protection device for a power converter according to the present invention is configured such that the AC side of the first converter is connected to the first AC system, and the AC side of the second converter is connected to the second AC system. In a power conversion apparatus in which a DC reactor is provided in a DC circuit between the first converter and the second converter, and one of the converters operates as a forward converter and the other converter operates as an inverse converter. The current of the first AC system and the current of the second AC system are respectively compared with the DC current reference value, and the abnormality of the power converter is determined to be an internal short circuit and a commutation failure based on the sign of the difference current.

  In addition, the output of the direct current transformer provided in the direct current circuit is used as the direct current reference value to be compared with the current of the alternating current system.

  In addition, the first converter connected to the first AC system controls the DC current of the DC circuit to the set value to a constant value, and sets the DC current reference value as a DC current reference value to be compared with the AC system current. Use the value.

  In order to solve the above problems, the protection device for a power converter according to the present invention is configured such that the AC side of the first converter is connected to the first AC system, and the AC side of the second converter is connected to the second AC system. In a power conversion apparatus in which a DC reactor is provided in a DC circuit between the first converter and the second converter, and one of the converters operates as a forward converter and the other converter operates as an inverse converter. A first subtraction circuit for obtaining a difference between the absolute value of the maximum value of the current of the first AC system and the DC current reference value; and an absolute value of the maximum value of the current of the second AC system and the DC current reference value A second subtraction circuit for obtaining a difference, a first comparison circuit for determining whether the output of the first subtraction circuit is positive or negative and discriminating and determining a commutation failure and an internal short circuit of the converter on the first AC system side; Determine whether the output of the second subtractor circuit is positive or negative and identify the commutation failure and internal short circuit of the converter on the second AC system side. And a second comparator circuit to determine.

  In addition, it is good to use the output of the direct current transformer provided in the direct current circuit as a direct current reference value compared with the electric current of an alternating current system.

  In order to solve the above problems, the protection device for a power converter according to the present invention connects the AC side of the first converter to the first AC system, and connects the AC side of the second converter to the second AC system. And a DC reactor is provided in the DC circuit between the first converter and the second converter, one of the converters is operated as a forward converter, and the other converter is operated as an inverse converter. In the power converter configured to control the DC current of the DC circuit to its set value constantly by the first converter connected to the AC system, the current of the AC system and the set value of the DC current are compared, When the difference is equal to or greater than a predetermined value, it is determined that an internal short circuit has occurred in the converter connected to the AC system, and when the AC system current becomes zero, the commutation of the converter connected to the AC system Judge as failure.

  When comparing the current of the AC system and the set value of the DC current and determining that the difference is equal to or greater than a predetermined value, it is preferable to provide a time characteristic according to the magnitude of the difference.

  When it is determined that the internal short circuit has occurred, the apparatus is stopped. When it is determined that the commutation has failed, the operation is resumed after the recovery.

  According to the present invention, since it is possible to distinguish between an internal accident and a commutation failure, there is no need to stop the system. Since it is possible to determine the abnormality, it is possible to prevent losing the opportunity to start pumping.

The figure which shows the 1st Example of the protective device which distinguishes an internal short circuit and commutation failure. The figure which shows the application example of a power converter device provided with a forward converter and an inverse converter. The figure which shows the input current which a power converter device and its protection device require. The figure which shows the accident aspect when the forward converter side internal short circuit generate | occur | produced. The figure which shows the accident aspect when the reverse converter side commutation failure generate | occur | produces. The figure which shows each part current waveform at the time of normal driving | operation. The figure which shows each part signal of the circuit of FIG. 1 at the time of normal driving | operation. The figure which shows each part current waveform at the time of a forward converter side internal short circuit. The figure which shows each part signal of the circuit of FIG. 1 at the time of a forward converter side internal short circuit. The figure which shows each part current waveform at the time of a reverse converter side commutation failure. The figure which shows each part signal of the circuit of FIG. 1 at the time of reverse converter side commutation failure. The figure which shows the combination of a driving | running state, abnormality classification, or an abnormal location. The figure which shows the signal of each part of FIG. 1 in each case of FIG. The figure which took the electric current IA on the horizontal axis and showed the abnormal area | region of the electric power system side converter. The figure which took the electric current IB on the vertical axis | shaft and showed the abnormal area | region of the generator motive side converter. FIG. 17 is a diagram in which the abnormal regions in FIG. 14 and FIG. 16 are superimposed. The figure which shows the 2nd Example of the protective device which distinguishes an internal short circuit and commutation failure. FIG. 18 is a diagram showing an output region of the comparison circuit C1 of FIG. FIG. 18 is a diagram showing an output region of the comparison circuit C2 of FIG. FIG. 18 is a diagram showing an output region of the comparison circuit C3 of FIG. FIG. 18 is a diagram showing an output region of the comparison circuit C4 of FIG. FIG. 18 is a diagram showing an output region of the comparison circuit C5 of FIG. The figure which shows the output area | region of AND circuit AND1 of FIG. The figure which shows the output area | region of AND circuit AND2 of FIG. The figure which shows the output area | region of AND circuit AND3 of FIG. The figure which shows the 3rd Example of the protective device which distinguishes an internal short circuit and commutation failure. FIG. 20 is a diagram illustrating a time characteristic of the determiner in FIG. 19. The figure which shows the driving | operation sequence when employ | adopting the protection apparatus of this invention. The figure which shows the driving | operation restart after a stop at the time of commutation failure detection.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  In the present invention, not the difference current between the alternating currents at both ends of the power converter, but the positive / negative of the difference signal between each alternating current and the reference value of the direct current is evaluated. In this case, an embodiment in which the reference value of the direct current to be compared is a direct current derived from a direct current circuit is shown in FIG. 3 as the first embodiment. Examples in which the reference value of the direct current is a current set value when the converter is controlled at a constant direct current are shown in FIGS. 17 and 18 as second and third embodiments.

FIG. 3 is a diagram showing an input signal required by the power conversion device and the protection device according to the first embodiment of the present invention for this protection. The configuration of the power conversion device is the same as that in FIG. 2, but for the protection, the AC current IA (I _R , I _S , I _T ) on the forward converter 3 side is taken in from the current transformer CTA, and the current is converted. AC current IB (I _U , I _V , I _W ) on the inverse converter 5 side is taken in from the converter CTB. Furthermore, in the first embodiment of the present invention, a direct current transformer CTD is provided, and a direct current ID is input.

FIG. 1 shows an internal short circuit and commutation failure using two sets of alternating currents IA (I _R , I _S , I _T ), IB (I _U , I _V , I _W ) and one DC current ID. 1 shows an embodiment of a protective device to be distinguished. In this figure, MXA is forward converter side AC current _{IA (I R, I S,} I T) the first maximum value detection circuit for detecting a maximum value of, MXB is inverter-side alternating current IB (I _U , I _V , I _W ) is a second maximum value detection circuit for detecting the maximum value, and ABA and ABB are absolute value circuits for obtaining the absolute value.

MN1 and MN2 are first and second subtraction circuits, respectively, in which the output of the maximum value detection circuit is a positive input and the direct current ID is a negative input, and C10, C11, C12, and C13 are determined by the positive / negative of the subtraction circuit output It is a comparison circuit that provides an output. The outputs of the comparison circuits C10, C11, C12, and C13 are X _R , Y _R , X _I , and Y _I , respectively. When the inputs of the comparison circuits C10 and C12 are positive (the maximum value of the alternating current IA or IB is larger than the direct current ID), the outputs X _R and X _I are set to “1”, and the comparison circuits C11 and C13 are When the input is negative (the maximum value of the alternating current IA or IB is smaller than the direct current ID), the outputs Y _R and Y _I are set to “1”.

  Hereinafter, the operation of the circuit of FIG. 1 will be described. Here, the description will be made on the assumption that electric power is supplied from the starting transformer 2 side to the generator motivator 6 side. Furthermore, in the following description of the present invention, the converter 3 (when operating as a forward converter or when operating as an inverse converter) controls the DC current of the DC circuit to its set value Id. The explanation is based on the assumption that Further, the operation at each time will be described in order by dividing into normal operation, forward converter side internal short circuit, and reverse converter side commutation failure.

  In the regenerative operation state, electric power is supplied from the generator motive 6 side to the starting transformer 2 side. Moreover, there may be various combinations such as forward converter side commutation failure and reverse converter side internal short circuit. Here, detailed operation explanations according to these operating states, abnormality types, or combinations of abnormal parts will be collectively performed using FIG. 12 after the explanation in the above case is completed.

  First, FIG. 6 shows each part current waveform as an input when the power is normally supplied from the starting transformer 2 side to the generator motive 6 side. As shown in FIG. 6, the AC currents IA and IB are generally different in frequency because the current transformer CTA side is synchronized with the frequency of the power system 1 and the current transformer CTB side is synchronized with the rotational speed of the generator motivator 6. Become. However, since the current flows as a result of commutation of the common direct current, the peak value is Id, which is the same value. This peak value Id is a DC current settling value generally determined by the current control function of the forward converter. In addition, each current of the three phases changes to positive and negative, but the current that flows into the converter from one phase (for example, the positive direction) flows out from the other phase (in this case, the negative direction) It is always flowing in two of the three phases.

As a result, even if the sum of the alternating currents is taken at an arbitrary timing t1 in FIG. That is, the sum of the forward converter side AC currents IA (I _R , I _S , I _T ) and the sum of the reverse converter side AC currents IB (I _U , I _V , I _W ) are zero. Further, the forward converter side AC current _{IA (I R, I S,} I T) Maximum value of inverter side AC current _{IB (I U, I V,} I W) a maximum value of, also the DC current value ID is It is the same value and this is Id. In a normal device, the magnitude of the direct current is set to a constant value Id determined by the current control function in the forward converter.

  FIG. 7 illustrates the magnitude of the signal of each part of the circuit of FIG. 1 at this time, and shows the situation at the timing t1 of the waveform of FIG. In this case, the output of the maximum value detection circuits MXA and MXB, the output of the absolute value circuits ABA and ABB, and the magnitude of the direct current ID are both the same value (Id), without needing to be described again. . As a result, the outputs of the subtraction circuits MN1 and MN2 are 0, and the outputs of the comparison circuits C10, C11, C12, and C13 are also 0.

  Using the fact that the relationship as shown in FIG. 6 is established at the normal time, it is possible to detect a circuit abnormality between the forward converter 3 and the inverse converter 5 using this circuit. The case of the forward converter 3 side internal short circuit accident of FIG. 4 will be described. However, in FIG. 4, when the semiconductor switches 3R1 and 3T2 are conducting in the forward converter 3, the semiconductor switch 3S1 is short-circuited, and the short-circuit current Ic is the starting transformer R phase, the semiconductor switches 3R1, 3S1 starting transformer. It flowed in the path of the vessel S phase.

  As shown in FIG. 8, the current waveform of each part in this state is as follows. In the current transformer CTA on the forward converter side after the internal short-circuit occurrence time t1, the rapidly increasing short-circuit current IA = Ic (−Ic) Observed in the S phase. At this time, the forward converter 3 becomes unable to control the direct current Id as its output, so that the ID becomes 0. Accordingly, the output current of the inverse converter 5 is also zero. This is shown in FIG. 8, and FIG. 9 shows circuit signals of the respective parts of the circuit of FIG. 1 at time t2 after time t1 when the internal short circuit occurs.

In FIG. 9, at time t2, I _R = Ic, I _S = −Ic, and all other currents are 0. Therefore, the output of the subtraction circuit MN1 becomes Ic, and the output X _R = 1 of the comparison circuit C10 It becomes.

  The respective currents when the V-phase arm is short-circuited due to the commutation failure of the switching element of the inverse converter 5 described in FIG. 5 are as shown in FIG. That is, on the forward converter 3 side, the conversion operation can be performed at the same timing as before, and the commutation operation is continued. On the reverse converter 5 side, current does not flow to the generator motive 6 side due to the arm short circuit. FIG. 11 shows the signals of the respective parts of the circuit in FIG. 1 at the timing t1 in FIG.

As shown in FIG. 11, at time t1, I _R = Id and I _T = −Id, and the direct current ID is Id. Since all other currents are 0, the output of the subtraction circuit MN2 becomes −Ic, and the output Y _I of the comparison circuit C12 becomes 1.

  The operation of the circuit of FIG. 1 has been described for normal operation, forward converter side internal short circuit, and reverse converter side commutation failure. As a result, all the comparison circuits did not output during normal operation, and the comparison circuit C10 provided an output when the forward converter side internal short circuit occurred, and the comparison circuit C13 provided an output when the reverse converter side commutation failed. As can be inferred from this, the circuit of FIG. 1 functions so that the comparison circuit C12 provides an output in the case of an internal short circuit on the reverse converter side, and the comparison circuit C11 provides an output in the case of a forward converter side commutation failure.

  In addition, it has been described above that there are a plurality of states corresponding to the combination of the operating state, the abnormality type, or the abnormal part, and these combinations are shown in FIG.

  The side of FIG. 12 shows the operation state such as the pumping start operation state on the left side, the regenerative operation state on the right side, and the normal state on the center. Moreover, among these operation states, the pumping start operation state and the regenerative operation state are subdivided by abnormality types such as internal short circuit and commutation failure, respectively. Further, the vertical lines indicate abnormal points such as the power system side and the power generation motivation side. This is a plurality of states depending on the operating state, abnormality type, or combination of abnormal parts, and they are distinguished by attaching symbols A to I respectively.

  Hereinafter, it will be described in detail that the circuit of the first embodiment of the present invention shown in FIG. 1 operates correctly and can distinguish between an internal short circuit and a commutation failure with a simple device configuration in all possible combinations. To do. However, the firing angle of the forward converter is 90 degrees or less, and the firing angle of the reverse converter is 90 degrees or more. Note that IA is an AC current on the power system side, IB is an AC current on the generator motivation side, ID is a DC current of the DC circuit, and Id is a DC current settling value.

A: Normal state (including both start and regenerative states)
Regarding the movement of the normal state in the starting stage, the current of each part has been described with reference to FIG. In short, all the currents of the respective parts become the DC current settling value Id, and no difference signal is generated in the subtraction circuits MN1 and MN2. Since the movement in the normal state of the regenerative state is also the same, the description is omitted.

B: Internal short circuit occurred in power system side converter at start-up stage FIG. 4 describes the event, FIG. 8 shows each part current, and FIG. 9 explains each part signal magnitude. In short, IA (AC current on the power supply side) increases to Ic equal to or higher than the DC current set value Id, and all other currents become zero. As a result, a positive difference signal is generated in the subtraction circuit MN1, and the comparison circuit C10 outputs (X _R = 1).

C: Commutation failure generated in the power system side converter in the starting stage In this case, the AC current IA on the power system side instantaneously becomes 0 due to the short circuit between the arms. In addition, since the forward converter has a current control function, when the forward converter loses the current control function due to its abnormality, the alternating current IB and the direct current ID on the generator motivation side also attenuate to zero. .

  At this time, the reason why the alternating current IB on the generator motivation side and the direct current ID are attenuated to 0 will be described. First, the generator motivation 6 lost the power supply from the conversion device side, but the rotation does not stop, so a counter electromotive force is generated. Moreover, in this state, the reverse converter continues the commutation operation according to the rotation speed of the generator motivator 6, and a series circuit is formed on the forward converter side by an arm short circuit. As a result, the generator motivation 6 is used as a power source, a closed circuit is formed by the reverse converter and the short circuit point between the arms, and the current due to the counter electromotive force of the generator motivator 6 continues to flow while being attenuated. The current due to the counter electromotive force circulates through the short circuit between the arms and is measured by the current transformers CTB and CTD.

In the subtraction circuit MN2 of FIG. 1, this attenuation current is canceled and does not appear as a difference, but is extracted as a negative signal in the subtraction circuit MN1. As a result, the comparison circuit C11 provides an output (Y _R = 1).

  In the above example, the generator motivation is installed in the AC system on the reverse converter side, and the attenuation current due to the back electromotive force flows from here, but in the case of a DC power transmission system, there is a power source. It goes without saying that an indefinite current (current value is determined by an abnormal aspect and is not uniquely determined) flows in through the same route as described above, resulting in the same determination result.

D: Internal short circuit generated in the generator-motive side converter at the starting stage In this case, the forward converter is sound. The reverse converter has an internal short circuit in a part thereof, but the ignition operation can be continued as the converter. For this reason, the current flowing from the forward converter side is held at the set value Id by its current control function and circulates through the upper and lower arms formed by the ignition operation of the reverse converter. This current is detected as IA = ID = Id. On the other hand, since the reverse converter is performing the reverse conversion operation, a short-circuit current is generated between the power generation motive and the short-circuit point. Although the short-circuit current does not become an excessive current, the current value Ie detected as IB at this time is a value larger than the DC current set value Id.

As a result, in the subtraction circuit MN1 of FIG. 1, this current is canceled and does not appear as a difference, but in the subtraction circuit MN2, since Ie is larger than Id, it is extracted as a positive signal, and the comparison circuit C12 outputs (X _I = 1).

E: Commutation failure generated in the generator-motive-motor-side converter in the starting stage FIG. 5 illustrates the event, FIG. 10 illustrates each part current, and FIG. 11 illustrates the magnitude of each part signal. In short, Id flows in IA (AC current on the power supply side) and DC current ID, but the AC current IB on the generator motivation side is all zero. As a result, a negative difference signal is generated in the subtraction circuit MN2, and the comparison circuit C13 outputs (Y _I = 1).

  As described above, the operations and determination results for all combinations in the starting stage have been described. However, as shown in FIG. 13, the magnitude of each part signal in each case and the determination results are correctly determined. I can understand that.

  Next, the operation at the time of so-called regenerative operation is performed by operating the converter on the generator motivation side as a forward converter and operating the converter on the power system side as an inverse converter to send power from the generator motivation side to the power system side. The determination results will be described according to cases F, G, H, and I. However, the DC current control function of the DC circuit is assumed to be carried by the converter on the power system side, as in the starting stage.

F: Internal short circuit generated in the power system side converter at the regeneration stage At this time, in the power system 1 side converter 3 performing the reverse conversion operation, the current control function is lost due to the internal short circuit, and the short circuit current is generated at the short circuit point. Although it flows, it does not become a large current as in the case B because the reverse conversion operation has been performed until just before, but increases. Let the short-circuit current at this time be Ic. On the other hand, in the generator-motive-motor-side converter performing the forward conversion operation, a circuit is formed on the direct current side, so that the current Ie is fed by the forward conversion operation. Since the current control function of the power system side converter is lost, the current at this time is determined by the circuit conditions at that time.

As a result, power system side current IA = Ic, DC circuit current ID = Ie, and generator motivation side current IB = Ie are detected. At this time, the input of the subtraction circuit MN2 of the protection circuit in FIG. 1 becomes the same value (Ie), and no difference is generated. Ic + Ie is generated in the subtraction circuit MN1, and since it is larger than Ic, this value becomes positive and the comparison circuit C10 outputs (X _R = 1).

G: Commutation failure generated in the power system side converter in the regeneration stage At this time, the power system 1 side converter 3 that was performing the reverse conversion operation can perform the reverse conversion operation due to the arm short circuit formed by the commutation failure. First, the current IA = 0. On the other hand, the generator-motive 6-side converter 5 performs a forward conversion operation, and a current Ie from the generator-motive 6 toward the DC circuit flows as in the case C. Since the current Ie is not current controlled, it is determined by the circuit conditions at this time.

As a result, power system side current IA = 0, DC circuit current ID = Ie, and generator motivation side current IB = Ie are detected. At this time, the input of the subtraction circuit MN2 of the protection circuit in FIG. 1 becomes the same value (Ie), and no difference is generated. -Ie is generated in the subtraction circuit MN1, and the comparison circuit C11 provides an output (Y _R = 1).

H: Internal short-circuit generated in the generator-motive side converter at the regeneration stage In this case, the appearance is almost the same as in Case D. First, the power system side converter performs an inverse conversion operation, but since it has a current control function, it operates to set the DC current ID to the set value Id. The generator-motive side converter performs a forward conversion operation and supplies a short-circuit current Ic.

As a result, power system side current IA = Id, DC circuit current ID = Id, and generator motivation side current IB = Ic are detected. At this time, the input of the subtraction circuit MN1 of the protection circuit in FIG. 1 becomes the same value (Id), and no difference is generated. Although Ic−Id is generated in the subtraction circuit MN2, the short circuit current Ic is larger and thus becomes positive, and the comparison circuit C12 gives an output (X _I = 1).

I: Commutation failure generated in the power generation motive side converter at the regeneration stage In this case, the appearance is almost the same as in Case E. First, the power system side converter performs reverse conversion operation, but since it has a current control function, it operates to set the DC current ID to the set value Id, and the arm short circuit point due to the commutation failure is closed circuit. A current IA = Id is passed through the circuit to be operated. The generator-motive side converter performs forward conversion, but no current flows because it does not form a closed circuit due to an arm short circuit.

As a result, power system side current IA = Id, DC circuit current ID = Id, and generator motivation side current IB = 0 are detected. At this time, the input of the subtraction circuit MN1 of the protection circuit in FIG. 1 becomes the same value (Id), and no difference is generated. -Id is generated in the subtraction circuit MN2, and the comparison circuit C13 outputs (Y _I = 1).

  As described above, the operations and determination results for all combinations in the regeneration stage have been described. However, as shown in FIG. 13, the magnitude of each part signal in each case and the determination results are all correctly determined. I can understand that.

  As described above, according to the first embodiment shown in FIG. 1, it is possible to correctly determine abnormality in all combinations regardless of the operation state, abnormality type, and abnormality location. In the embodiment of FIG. 1, this is realized by using a DC current transformer CTD. Next, a method not using the DC current transformer CTD will be described.

For this reason, the following will become clear when the results of FIG. 13 are first examined in detail. First, in FIG. 13, regarding the normal state of case A and the abnormal cases B, C, F, and G in the converter 3 on the power system 1 side, the current IA flowing through the converter 3 on the power system side is Each case can be organized as follows. Here, the converter 3 on the power system side is a converter that controls the DC current of the DC circuit to the set value Id as described above. As described above, the evaluation is focused on the AC current on the terminal side that is controlled at a constant current.
During normal operation (Case A): IA = Id (DC current setting value)
When commutation fails (cases C and G): IA = 0
Internal short circuit (cases B and F): IA = Ic (short circuit current)
This means that when the current IA flowing through the converter 3 on the power system 1 side takes a value other than Id or 0, it is an internal short circuit. That is, if it can be detected that IA is a predetermined value (0 or DC current set value Id), it can be distinguished from an internal short circuit that takes other values.

  Here, when it is detected that the detected value is the DC current set value Id or 0, it is often performed to have a certain detection range, but here, for detecting the DC current set value Id. Consider the detection width of δ for detecting ± ε, 0.

  FIG. 14 shows the above relationship with the current IA on the horizontal axis, and the range from 0 to the detection width δ is the commutation failure detection range R1 of the power system 1 side converter 3. Similarly, the range of ± ε from the DC current set value Id is the normal operation detection range R2 of the power system side converter. Therefore, a range other than this range can be set as a short-circuit current detection range R3 at the time of an internal short circuit.

When the same analysis as described above is attempted for the normal state of case A and the abnormal cases D, E, H, and I in the converter 5 on the generator motive 6 side in FIG. 13, the converter on the generator motive 6 side The current IB flowing through 5 can be organized as follows for each case. Here, the converter 5 on the generator motivation 1 side is a converter on the side where the DC current of the DC circuit is not controlled to be constant at its settling value Id (the other party is controlling the constant current). .
During normal operation (Case A): IB = Id (DC current setting value)
When commutation fails (cases E and I): IB = 0
Internal short circuit (cases D and H): IB = Ic, Ie
This means that when the current IB flowing through the converter 5 on the power generation motivator 6 side also takes a value other than Id or 0, it is an internal short circuit. That is, if it can be detected that IB is a predetermined value (0 or a direct current set value), it can be distinguished from an internal short circuit that takes other values.

  Again, let us consider the detection width of δ for detecting ± ε and 0 for detecting that the detected value is Id.

  FIG. 15 describes the above relationship with the current IB on the vertical axis, and the range from 0 to the detection width δ is the commutation failure detection range R4 of the generator-motive side converter. Similarly, the range of ± ε from the DC current set value Id is the normal operation detection range R5 of the generator-motive side converter. Therefore, a range other than this range can be set as a short-circuit current detection range R6 at the time of an internal short circuit.

  In the detection system of FIG. 1, when the power system side converter side becomes abnormal because the power system side converter 3 performs constant current control, the current of the generator-motive side converter also becomes an irregular value. Conversely, if the power system side converter side is healthy, ID and IA are maintained at Id. From the above examination results, if FIG. 15 is integrated into the region R2 in which the power system side converter is normal in FIG.

  FIG. 16 is a two-dimensional display with the current axis IA on the power system side on the horizontal axis and the current on the generator motivation side on the vertical axis, with the IA side as the main component, where D0 is the normal region and D1 is the power System side converter commutation failure area, D2 means power system side converter internal short circuit area, D3 means commutation failure area of generator motivator side converter, D4 means internal short circuit area of power generator motivator side converter Yes.

  As is apparent from the illustrations of FIGS. 14, 15 and 16, if the magnitudes of the alternating currents IA and IB are 0 or Id, the direct current is detected from the direct current transformer CTD, The commutation failure region, the internal short-circuit region, and the normal region can be distinguished for both the power system side converter 3 and the generator-motive side converter 5 (without input). Even if the detected value of the direct current is not used, the information necessary for the area division can be obtained only by the set value.

  In the second embodiment of the present invention, the circuit configuration of the protection device is performed based on the above analysis and knowledge, and an example thereof is shown in FIG. The second embodiment shown in FIG. 17 is essentially different from the first embodiment shown in FIG. 1 except that the alternating currents IA and IB are detected currents from the alternating current transformers CTA and CTB. Others are those given in advance as predetermined set values (fixed values). In particular, there is a clear difference in that the DC current setpoint Id is used and the DC current transformer CTD is not used.

  The idea of FIG. 17 is to determine where the input currents IA and IB are located in each area of FIG. 16, and the areas where the five comparison circuits C are established and their meanings are as follows.

  Comparison circuit C1: Current IA from current transformer CTA is a region smaller than set value δ, and corresponds to R1 in FIG. 14 and D1 in FIG. 16, as shown in FIG. 18a. This output means the commutation failure of the power system side converter.

  Comparison circuit C2: Current IB from current transformer CTB is a region smaller than set value δ, and corresponds to R4 in FIG. 15 as shown in FIG. 18b. This output means the commutation failure of the generator-motive side converter.

  Comparison circuit C3: The absolute value of the difference (MN4) between the current IA from the current transformer CTA and the DC current set value Id is larger than the set value ε. As shown in FIG. 18c, R2 in FIG. All areas except This area is all areas showing an abnormality of the power system side converter.

  Comparison circuit C4: The absolute value of the difference (MN4) between the current IA from the current transformer CTA and the DC current set value Id is smaller than the set value ε, and as shown in FIG. 18d, R2 in FIG. It is an area. This area means a normal area of the power system side converter.

  Comparison circuit C5: The area where the absolute value of the difference (MN4) between the current IB from the current transformer CTB and the DC current set value Id is larger than the set value ε, and as shown in FIG. All areas except This area is all areas showing an abnormality in the generator-motive side converter.

  Each comparison circuit C in FIG. 17 outputs in the above state. The outputs of these comparison circuits are finally detected as a short circuit or commutation failure detection signal by a logic circuit using a NOT circuit NOT or an AND circuit AND. Hereinafter, the detection logic of each abnormality detection signal will be described.

AC system commutation failure: Y _R
As the output of the comparator circuit C1, utilized as the AC mains commutation failure detection signal Y _R.

AC system side internal short circuit: X _R
The region D1 of FIG. 18a is excluded from the operation region of the comparison circuit C3 (FIG. 18c), and the region of FIG. 18f that operates only in the region D2 is obtained. The region D2 is obtained by the negative circuit N1 and the AND circuit AND1.

Power generation motive side commutation failure: Y _I
If the output of the comparison circuit C2 (region of FIG. 18b) is used as the commutation failure detection signal of the generator-motive side converter as it is, IB is almost zero, so whether this is due to the abnormality of the AC side converter, Since it cannot be distinguished whether it is due to the commutation failure on the generator side or the like, the commutation failure detection signal of the generator-motive side converter is used under the matching condition that the AC system side converter is normal (FIG. 18d). This coincidence is obtained by the AND circuit AND2, and the resulting operation area is represented as shown in FIG. This region is D3 in FIG.

Power generation motive side internal short circuit: _XI
Here, it is assumed that the operation finally takes place in the region D4 in FIG. 18h. For this purpose, the D0 region is excluded by matching the region of the comparison circuit C5 (FIG. 18d) and the region of the comparison circuit C4 (FIG. 18e), and further, by matching with the inverted output of the AND circuit AND2. , D3 region is excluded. The AND circuit AND3 excludes the areas D0 and D3 by taking the coincidence of these signals so that only the area D4 is obtained.

  As described above, in the second embodiment of the present invention shown in FIG. 17, the DC current transformer CTD is not used, and the determination is made using the current set value. However, the third embodiment of the present invention shown in FIG. In the embodiment, a transient phenomenon is used for discrimination of an abnormal event. The use of the transient phenomenon is performed by the determiners J1 and J2 in FIG.

  The idea of FIG. 19 also determines where the input currents IA and IB are located in each region of FIG. 16, and the establishment of two comparison circuits C, two determination devices J, and a negative circuit N3. The following areas and their meanings are as follows. In conclusion, the determination units J1 and J2 output in the same region as the comparison circuits C3 and C5, respectively, and the negation circuit N3 corresponds to the comparison circuit C4.

  Comparison circuit C1: Current IA from current transformer CTA is a region smaller than set value δ, and corresponds to R1 in FIG. 14 and D1 in FIG. 16, as shown in FIG. 18a. This output means the commutation failure of the power system side converter.

  Comparison circuit C2: Current IB from current transformer CTB is a region smaller than set value δ, and corresponds to R4 in FIG. 15 as shown in FIG. 18b. This output means the commutation failure of the generator-motive side converter.

  Judgment device J1: The difference (MN4) between the current IA from the current transformer CTA and the DC current set value Id is input. As will be described in detail later, the determiner J1 determines that this difference is large and outputs it after a predetermined time determined by the magnitude of the difference. Although there is a time delay until the output, this output is basically the entire region other than R2 in FIG. 14, as shown in FIG. 18c. This area is all areas showing an abnormality of the power system side converter.

  Negation circuit N3: The output region of the determiner J1 is negated, and this is the R2 region of FIG. 14, as shown in FIG. 18d. This area means a normal area of the power system side converter.

  Judger J2: The difference (MN4) between the current IB from the current transformer CTB and the DC current set value Id is input. As will be described in detail later, the determiner J1 determines that this difference is large and outputs it after a predetermined time determined by the magnitude of the difference. Although there is a time delay until the output, this output is basically the entire region other than R5 in FIG. 15, as shown in FIG. 18e. This area is all areas showing an abnormality in the generator-motive side converter.

  The circuit of each part of the circuit in FIG. 19 outputs in the above state. This output is the same as the output area of each comparison circuit C in FIG. 17, and is different only in that it has a time characteristic.

  The outputs of these circuits are finally detected as a short circuit or commutation failure detection signal by a negative circuit NOT in the subsequent stage or a logic circuit using an AND circuit AND. Since the conclusion derived as a result is the same as that described with reference to FIG.

  Hereinafter, the function of the determiner J will be described in detail. Of these, the input of the determiner J1 is first the difference (MN4) between the current IA from the current transformer CTA and the DC current set value Id. This input is used for the purpose of discriminating the internal short circuit of the AC system side converter. As shown in FIG. 8, the transient phenomenon at the time of the internal short circuit causes the short circuit current to increase and flow. . In the classification shown in FIGS. 12 and 13, this corresponds to cases B and F.

  The input of the judgment device J2 is a difference (MN6) between the current IB from the current transformer CTB and the DC current set value Id. This input is used for the purpose of determining an internal short circuit of the generator-motive side converter, and the short circuit current increases due to the internal short circuit and flows. In the classification shown in FIGS. 12 and 13, this corresponds to cases D and N. In these events, the magnitude of the short-circuit current is not uniquely determined to be a fixed value, and is accompanied by a transient phenomenon.

  FIG. 20 is for determining an abnormality by capturing this transient phenomenon. The horizontal axis represents the time from the occurrence of a short circuit abnormality, and the vertical axis represents the magnitude of the difference current (IA-Id) or (IB-Id). taking it.

  Of these, regarding the determination device J1 that inputs the difference current (IA−Id), for example, due to an internal short circuit of the AC system side converter, the AC current IA becomes excessive as shown in case D of FIG. 8 or FIG. , ΔI1 = IA−Id> 0 occurs. The determiner J1 generates an output t1 after the generation of ΔI1 based on the magnitude of ΔI generated and its own time characteristic f1. By setting the characteristic f1 to the right as shown in FIG. 20 (providing an inverse time characteristic), the output is output in a short time if the generated IA is large, and the output is delayed if the value is close to Id. This characteristic is determined according to the overcurrent withstand capability of the circuit sound part.

  Further, for example, it is assumed that, due to an internal short circuit of the generator-motive side converter, IB becomes insufficient as shown in Case H of FIG. 12, and ΔI2 = IB−Id <0 occurs. The determiner J2 generates an output after tc as described above. If the characteristic f2 of 0 or less in FIG. 20 is set to a delay of a certain time or a characteristic close to it, the malfunction during the IIB <Id period at the current rising at the time of starting the apparatus is avoided, and it does not become excessive. Short circuit current can be detected.

  In the third embodiment of FIG. 19, the operation of the other logic circuit portions can be easily understood in the above description, and the description thereof is omitted. However, if a determiner J as shown in FIG. It is possible to distinguish between an internal short circuit that really needs to be stopped and a commutation failure that can be suspended.

  FIG. 21 shows an operation sequence in the case where an abnormality is detected according to the first to third embodiments. First, when an abnormality is detected in step S100, the type is determined in step S101, and an internal short circuit is detected. If there is, the apparatus immediately stops in step S102. If the commutation has failed, the operation is temporarily suspended in step S103, and the operation is resumed in step S104 after the recovery.

  By making it as FIG. 21, it can drive | operate, without stopping a power converter device completely. That is, for example, if the power generation motivation is being accelerated, the acceleration can be resumed after a temporary stop period has elapsed as shown in FIG.

  The present invention can be widely used for power conversion devices provided between AC systems.

1: Power system 2: Start transformer 3: Forward converter 4: DC reactor 5: Reverse converter 6: Generator motivation CTA, CTB: Current transformer CTD: DC current transformer 9: Pump turbine 10: Power converter Id: DC current settling value IA: Power system side AC current IB: Generator-motive side AC current ID: DC current MX: Maximum value detection circuit AB: Absolute value circuit MN: Subtraction circuit C: Comparison circuit J: Determinator

Claims (8)

The AC side of the first converter is connected to the first AC system, the AC side of the second converter is connected to the second AC system, and between the first converter and the second converter. In the power conversion device in which a DC reactor is provided in the DC circuit and one of the converters is operated as a forward converter and the other converter is operated as an inverse converter,
The current of the first AC system and the current of the second AC system are respectively compared with the DC current reference value, and the abnormality of the power converter is determined to be an internal short circuit and commutation failure by the positive / negative of the difference current. A protective device for a power conversion device. In the protection apparatus of the power converter device of Claim 1,
An apparatus for protecting a power converter, wherein an output of a DC current transformer provided in the DC circuit is used as a DC current reference value to be compared with a current of the AC system. In the protection apparatus of the power converter device of Claim 1,
The first converter connected to the first alternating current system controls the direct current of the direct current circuit to a constant value thereof, and sets the direct current setting as a direct current reference value to be compared with the current of the alternating current system. A protective device for a power converter, characterized by using a value. The AC side of the first converter is connected to the first AC system, the AC side of the second converter is connected to the second AC system, and between the first converter and the second converter. In the power conversion device in which a DC reactor is provided in the DC circuit and one of the converters is operated as a forward converter and the other converter is operated as an inverse converter,
A first subtraction circuit for obtaining a difference between the absolute value of the maximum value of the current of the first AC system and the DC current reference value; and an absolute value of the maximum value of the current of the second AC system and the DC current reference value A second subtraction circuit for obtaining a difference; and a first comparison circuit for discriminating and determining a commutation failure and an internal short circuit of the converter on the first AC system side by judging whether the output of the first subtraction circuit is positive or negative And a second comparison circuit that judges whether the output of the second subtracting circuit is positive or negative and discriminates and judges the commutation failure and internal short circuit of the converter on the second AC system side. Device protection device. In the protection apparatus of the power converter device of Claim 4,
An apparatus for protecting a power converter, wherein an output of a DC current transformer provided in the DC circuit is used as a DC current reference value to be compared with a current of the AC system.   The AC side of the first converter is connected to the first AC system, the AC side of the second converter is connected to the second AC system, and the first converter and the second converter are connected to each other. A direct current reactor is provided in the direct current circuit, one of the converters is operated as a forward converter, the other converter is operated as an inverse converter, and the first converter connected to the first alternating current system is used to In a power converter that is configured to control the DC current to its set value constantly, the current of the AC system is compared with the set value of the DC current, and when the difference is a predetermined value or more, the AC system A protection device for a power conversion device, characterized in that it is determined as an internal short circuit of a connected converter, and when the current of the AC system becomes 0, it is determined that commutation of the converter connected to the AC system has failed. . In the protection apparatus of the power converter device of Claim 6,
Compared with the current of the AC system and the set value of the DC current, and when it is determined that the difference is equal to or greater than a predetermined value, it has a time characteristic according to the magnitude of the difference Protection device for the conversion device. In the protection apparatus of the power converter device in any one of Claims 1 thru | or 7,
A protection device for a power converter, characterized in that when the internal short-circuit is determined, the device is stopped, and when it is determined that the commutation has failed, the operation is resumed after the recovery.

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