JP3899446B2 - DC link system and operation method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a DC cooperative system and an operation method thereof, and in particular, a pair of power converters connected to each other with a DC main circuit interposed therebetween are connected to different AC systems, and one power converter is forward-converted. DC link system suitable for controlling the operation of each power converter at the time of failure of the AC system on the forward converter side in a DC link system that operates as a converter and the other power converter as an inverse converter and its operation Regarding the method.
[0002]
[Prior art]
As a DC link system for DC transmission, a pair of power converters (AC / DC converters) connected to each other with a DC main circuit having a DC reactor in between are connected to different AC systems, and one power conversion There is known a system in which a converter is operated as a forward converter (converter that converts alternating current into direct current) and the other power converter is operated as an inverse converter (converter that converts direct current into alternating current).
[0003]
Conventionally, when operating a DC linkage system, constant voltage control is performed to make the DC voltage constant on the reverse converter side, and the power converter has a higher potential on the forward converter side than on the reverse converter side. Constant current control is performed to make the DC current constant by controlling the firing angle, and power is exchanged from one AC system to the other AC system. When a ground fault due to lightning strike occurs in the AC system on the forward converter side, voltage control on the forward converter side becomes impossible as the alternating voltage on the forward converter side decreases, so the forward converter The bypass pair control is performed to simultaneously fire the upper and lower thyristors of the same phase among the three-phase switching elements that constitute the thyristor, the AC system and the DC main circuit are disconnected, and the operation of the forward converter is stopped. The forward converter is restarted after the system failure is recovered.
[0004]
[Problems to be solved by the invention]
In the prior art, when a fault occurs in the AC system on the forward converter side, when the AC voltage on the forward converter side decreases to a voltage that is not sufficient to ignite each thyristor of the forward converter, Since the operation cannot be continued, bypass pair control is performed on the forward converter to stop the operation of the forward converter, and the AC system and the DC main circuit are disconnected. If the AC system and the DC main circuit are disconnected when the forward converter stops operating, the DC current of the DC main circuit will be interrupted, and the inverter will stop operating using the DC power from the DC main circuit. Forced to do. For this reason, until the inverter is restarted after the operation of the inverter is stopped, power is not supplied to the AC system connected to the inverter.
[0005]
An object of the present invention is to provide a DC linkage system capable of continuing operation of equipment using DC power from a DC main circuit even when an AC system on the forward converter side fails, an operating method thereof, and a power converter. It is in.
[0006]
[Means for Solving the Problems]
In order to achieve the above object, the present invention converts a DC power from an AC system into a DC power and outputs it to a DC main circuit, and converts the DC power from the DC main circuit into an AC power. Forming a circuit connecting an inverter that outputs to an AC system different from the AC system, DC power generating means for generating DC power, the DC main circuit and the DC power generating means, and using this circuit as a command Switching means that opens and closes in response, forward converter control means for stopping the operation of the forward converter until the failure of the alternating current system recovers when the alternating current system on the forward converter side fails, and alternating current on the forward converter side Open / close command means for instructing the opening / closing means to close when a system failure occurs, and then opening the circuit, and a conversion output of the reverse converter according to the state of the DC main circuit when the AC system on the forward converter side fails Inverter control means for controlling It is obtained by constituting the DC link system comprising comprising a.
[0007]
In addition, the present invention operates one power converter as a forward converter among a pair of power converters connected to each other with mutually different AC systems and with a DC main circuit interposed therebetween, and the other power Opening and closing means connected to the DC main circuit and operating the converter as an inverse converter, stopping the operation of the forward converter until the failure of the AC system is recovered when the AC system on the forward converter side fails The DC power is supplied from the DC power source to the DC main circuit, and the conversion output of the inverse converter is controlled according to the current of the DC main circuit, and then the switching means is opened to open the DC power source. The operation method of the DC link system that stops the supply of DC power to the DC main circuit is adopted.
[0008]
The present invention also provides a forward converter that converts AC power from an AC system into DC power and outputs the DC power to a DC main circuit, and limits the DC power from the DC main circuit to a specified power and outputs it to a load. A limiter, DC power generating means for generating DC power, a circuit connecting the DC main circuit and the DC power generating means, and opening / closing means for opening and closing the circuit according to a command; Forward converter control means for stopping the operation of the forward converter until the failure of the AC system is recovered at the time of the failure of the AC system, and a closing circuit is instructed when the AC system on the forward converter side fails, and then an open circuit is instructed. The power conversion device comprises: an opening / closing command means for controlling and a limiter control means for controlling the output of the limiter according to the state of the DC main circuit when the AC system on the forward converter side fails. .
[0009]
According to the above-described means, when the AC system on the forward converter side fails, the operation of the forward converter is stopped until the failure of the AC system is recovered, and the switching means is closed and the DC power supply (DC power generating means) is used. When DC power is supplied to the DC main circuit and the conversion output of the reverse converter is controlled according to the state (current) of the DC main circuit, and the AC system failure on the forward converter side is recovered Since the DC power supply from the DC power supply (DC power generation means) to the DC main circuit is stopped by opening the switching means, the forward converter is shut down when the AC system on the forward converter side fails. Accordingly, even if the AC system on the forward converter side and the DC main circuit are separated, the DC power from the DC power source (DC power generating means) can be supplied to the DC main circuit, and the DC power from the DC main circuit can be supplied. Equipment using, for example, inverse converter, limiter Can be continuously operated, it is possible to restart without stopping at the same time system and clearing the AC system.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
[0011]
FIG. 1 is an overall configuration diagram of a system showing an embodiment of the present invention. In FIG. 1, an AC / DC converter (power converter) 16 is connected to a # 1 three-phase AC system 10 via an AC system link breaker 12 and a transformer 14, and a # 2 three-phase AC system 48 is connected. Is connected to an AC / DC converter (power converter) 40 via an AC system linkage breaker 46 and a transformer 44. Each of the AC / DC converters 16 and 40 includes six thyristors Q1 to Q6 as switching elements, for example, as shown in FIG. 2, and AC power is generated by a switching control signal from the control device 56 or 58. It is configured to be able to convert DC power to DC power or AC power. The AC / DC converters 16 and 40 are connected to each other with the DC main circuit 18 therebetween, and each AC / DC converter 16 and 40 receives the DC main circuit 18 from the AC system 10 as one element of the DC link system. When supplying power to the AC system 48 via the AC / DC converter 16, the AC / DC converter 16 is operated as a forward converter, the AC / DC converter 40 is operated as an inverse converter, and conversely, from the AC system 48 via the DC main circuit 18. When power is supplied to the AC system 10, the AC / DC converter 40 is operated as a forward converter, the AC / DC converter 16 is operated as an inverse converter, and mutual power exchange is performed between the AC system 10 and the AC system 48. Can be done.
[0012]
The DC main circuit 18 includes a DC reactor 30 as a main element, and both ends of the DC reactor 30 are connected to one ends of the AC / DC converters 16 and 40, respectively. The other ends of the AC / DC converters 16 and 40 are grounded. In addition, open / close circuit breakers 22 and 32 are connected to both sides of the DC reactor 30 as open / close means. The open / close circuit breaker 22 is connected to the open / close circuit breaker 28 via the capacitor 24 and the battery 26, and the open / close circuit breaker 32 is connected to the open / close circuit breaker 38 via the battery 34 and the capacitor 36. One end is grounded. The capacitor 24 and the battery 26 are connected in parallel to each other as a DC power source (DC power generating means), and the switching breakers 22 and 28 are connected in series to each other. The battery 34 and the capacitor 36 are connected to each other as a DC power source (DC power generation means), and the open / close circuit breakers 32 and 38 are connected to each other in series. The open / close circuit breakers 22 and 28 form a circuit connecting the DC main circuit 18 and the capacitor 24 and are configured to open and close the circuit in response to a command from the control device 58. The open / close circuit breakers 32 and 38 form a circuit connecting the DC main circuit 18 and the capacitor 36, and are configured to open and close the circuit in response to a command from the control device 56. That is, the open / close circuit breakers 22, 28, 32, and 38 each open the circuit during normal operation (open state), and when the AC system 10 fails, only the open / close circuit breakers 22 and 28 close the circuit (closed state), and the AC When the system 48 fails, only the switching breakers 32 and 38 close the circuit.
[0013]
The control device 56 is connected to a protection relay 54, and the protection relay 54 is connected to the primary side of the transformer 14 via a current transformer 50 and a transformer 52. When a fault such as a ground fault occurs in the AC system 10, a fault detection signal is input from the protection relay 54 to the control device 56. The control device 58 is connected to a protection relay 64, and the protection relay 64 is connected to the primary side of the transformer 44 through a current transformer 60 and a transformer 62. When a fault such as a ground fault occurs in the AC system 48, a failure detection signal is input from the protection relay 64 to the control device 58. Since the control devices 56 and 58 have the same configuration, only the specific configuration of the control device 58 will be described below.
[0014]
The control device 58 is connected to the control device 56 and is connected to a voltage sensor 20 that detects the voltage of the DC main circuit 18 and a current sensor 42 that detects the current of the DC main circuit 18. The control device 58 controls the conversion output of the AC / DC converter 40 according to the pair control signal 100 from the control device 56 and the signals from the voltage sensor 20 and the current sensor 42, and controls the opening / closing of the open / close circuit breakers 22 and 28. In order to achieve this, a voltage detection unit 66, an AND gate 68, a control calculation unit 70, an optimum call command value selection unit 72, a current detection unit 74, a switching unit 76, and an AND gate 78 are provided.
[0015]
The voltage detection unit 66 is based on the detection of the voltage sensor 20 on the condition that the current detected by the current sensor 42 is equal to or higher than the set level (provided that the current exceeding the set level flows in the DC main circuit 18). When the voltage drops below the set level, a signal “1” is output to the AND gate 68 assuming that an abnormality has occurred in the DC main circuit 18. Note that a dead band is provided in the setting level (setting value) of the DC voltage, and even if the DC voltage fluctuates during normal operation or when the AC / DC converters 16 and 40 are started up, the level varies with the fluctuation. It is designed to prevent false detection of changes.
[0016]
The AND gate 68 assumes that the AC system 10 has an accident when the pair of control signals 100 are input from the controller 56 when the voltage detection unit 66 outputs a signal “1”. An input command 80 is output to 28. That is, when a fault occurs in the AC system 10 and bypass pair control is performed on the AC / DC converter 16 from the control device 56, the input of the pair control signal 100 indicating that the bypass pair has been performed and voltage detection On condition that a signal “1” is generated from the unit 66, a closing command 80 is output to the circuit breakers 22 and 28.
[0017]
The control calculation unit 70 receives the detection voltage of the voltage sensor 20 and the detection current of the current sensor 42, and serves as an ignition command value (ignition angle) for each thyristor of the AC / DC converter 40 during normal operation (for the AC systems 10 and 48). The ignition command value at the time of soundness is generated, and the generated ignition command value is output to the switching unit 76. The optimum firing command value selection unit 72 selects an optimum firing command value (ignition angle) corresponding to the current detected by the current sensor 42 and outputs the selected firing command value to the switching unit 76. ing. For example, the optimum firing command value is set to a value that increases the firing angle as the current increases. During normal operation, the ignition command value from the control calculation unit 70 is selected by the switching unit 76, while the pair control signal 100 is input and the AND gate 68 outputs a signal "1". On the condition, the ignition command value selected by the optimum ignition command value selection unit 72 is selected, and the selected ignition command value 82 is output to each thyristor of the AC / DC converter 40.
[0018]
The current detection unit 74 outputs a signal “1” to the AND gate 78 when the level of the current detected by the current sensor 42 reaches a level at which each thyristor of the AC / DC converter 40 can be ignited. ing. The AND gate 78 predicts that the fault of the AC system 10 is recovered when the signal “1” is output from the current detection unit 74 on condition that the signal “1” is generated from the AND gate 68. Thus, an opening command 84 is output to the circuit breakers 22 and 28.
[0019]
In the above configuration, when power is supplied from the AC system 10 to the AC system 48, the AC / DC converter 16 is operated as a forward converter and the AC / DC converter 40 is operated as an inverse converter. At this time, the control device 56 functions as a forward converter control means, and the control device 58 functions as an inverse converter control means and also functions as an opening / closing command means.
[0020]
When the AC / DC converter 16 is operated as a forward converter and the AC / DC converter 40 is operated as an inverse converter, if a fault such as a ground fault 102 due to lightning strikes occurs in the AC system 10, the AC / DC converter 16 The supplied AC voltage decreases. When a failure detection signal is input from the protection relay 54 to the control device 56 by signals from the current transformer 50 and the transformer 52, bypass pair control is performed on the AC / DC converter 16 from the control device 56. In this case, as shown in FIG. 2, the upper and lower thyristors Q1 and Q2 of the same phase are simultaneously fired, and the AC side of the AC / DC converter 16 and the DC main circuit 18 are separated. Further, when the control device 56 performs bypass pair control, the control device 56 outputs a pair control signal 100 to the control device 58. When a signal “1” is output from the voltage detector 66 in the process of gradually decreasing the voltage and current of the DC main circuit 18 as the operation of the AC / DC converter 16 is stopped, the AND gate A signal “1” is output from 68. This signal is output as a closing command 80 to the circuit breakers 22 and 28. Accordingly, the circuit breakers 22 and 28 are turned on, and the discharge current Ic is supplied from the capacitor 24 charged by the battery 26 to the AC / DC converter 40 via the DC reactor 30.
[0021]
That is, the DC main circuit 18 is supplied with DC power from the battery 26 and the capacitor 24 after DC power from the AC / DC converter 16 is not supplied. Further, when a system failure is detected, the ignition command value 82 selected by the optimum ignition command value selection unit 72 is selected by the switching unit 76 instead of the ignition command value 82 calculated by the control calculation unit 70. Then, the selected firing command value 82 is output to the AC / DC converter 40. For this reason, although the current of the DC main circuit 18 is lower than that during normal operation, the firing angle of each thyristor is controlled based on the DC current from the battery 26 and the capacitor 24, and the AC / DC converter 40 to the AC system 48. Can be continuously supplied with power.
[0022]
Next, the current of the DC main circuit 18 is increased by the current from the battery 26 and the capacitor 24, and when this current exceeds a certain level, a signal “1” is output from the current detector 74, and the AND gate 78 A “1” signal is output. This signal is output to the circuit breakers 22 and 28 as an opening command 84, and the circuit breakers 22 and 28 are opened by the opening command 84. That is, after the operation of the AC / DC converter 16 is stopped, when the current of the DC main circuit 18 is restored to the set level, the current from the capacitor 24 and the battery 26 becomes unnecessary, so the circuit breakers 22 and 28 are replaced with the capacitor 24 and the battery 26. Control to disconnect from. Thereafter, when the failure is recovered, the AC / DC converter 16 is restarted by a command from the control device 56, and the control shifts to the normal operation.
[0023]
Thus, when an instantaneous failure such as the ground fault 102 occurs in the AC system 10, the DC power from the capacitor 24 and the battery 26 is supplied to the AC / DC converter 40 even if the operation of the AC / DC converter 16 is stopped. Thus, the operation of the AC / DC converter 40 can be continued. For this reason, in this embodiment, even if a failure occurs in the AC system 10, the operation of the AC / DC converter 40 can be continued, and power can be always supplied to the AC system 48. The system can be restarted without stopping at the same time as the failure removal (failure recovery).
[0024]
In the above-described embodiment, the breaker 22, 28, 32, 38 is used as the opening / closing means. However, a high-speed switching element may be used instead of the breaker 22, 28, 32, 38.
[0025]
Moreover, in the said embodiment, although the case where electric power was supplied from the alternating current system 10 to the alternating current system 48 was described, when driving | running the operation which supplies electric power from the alternating current system 48 to the alternating current system 10, Even when a failure occurs, the operation of the AC / DC converter 16 can be continued. In this case, the control device 56 functions as an inverse converter control means and an opening / closing command means, and the control device 58 functions as a forward converter control means. In this case, the opening / closing of the circuit breakers 32, 38 is controlled instead of the circuit breakers 22, 28, and the current from the battery 34 and the capacitor 36 is supplied to the AC / DC converter 16.
[0026]
In the above embodiment, the case where the present invention is applied to the DC cooperative system has been described. However, instead of the AC / DC converter 40, a limiter that limits the DC power from the DC main circuit 18 to a specified power and outputs it to the load is provided. It is also possible to configure a power converter that is provided and controls the output of the limiter by the controller 58. In this case, the control device 58 functions as a limiter control means, and the circuit breakers 32 and 38, the battery 34, and the capacitor 36 are removed from the DC main circuit 18. That is, the AC / DC converter 16, the circuit breakers 22, 28, the capacitor 24, the battery 26, the DC reactor 30, the limiter, the current transformer 50, the transformer 52, the protection relay 54, the control devices 56 and 58, the voltage sensor 20, and the current sensor. 42 constitutes a power converter.
[0027]
【The invention's effect】
As described above, according to the present invention, the operation of the forward converter is stopped until the failure of the AC system is recovered at the time of the failure of the AC system on the forward converter side, and DC power is supplied to the DC main circuit, Since the conversion output of the reverse converter is controlled according to the state (current) of the DC main circuit, the operation of the equipment using the DC power from the DC main circuit is continued when the AC system on the forward converter side fails. It is possible to restart the system without stopping it at the same time as removing the fault in the AC system on the forward converter side.
[Brief description of the drawings]
FIG. 1 is an overall configuration diagram of a system showing an embodiment of the present invention.
FIG. 2 is a diagram illustrating the configuration of an AC / DC converter.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 AC system 12 AC system cooperation circuit breaker 14 Transformer 16 AC / DC converter 18 DC main circuit 20 Voltage sensor 22 Circuit breaker 24 Capacitor 26 Battery 28 Circuit breaker 30 DC reactor 32 Circuit breaker 34 Battery 36 Capacitor 38 Circuit breaker 40 AC / DC converter 42 Current Sensor 44 Transformer 46 AC System Linkage Breaker 48 AC System 50 Current Transformer 52 Transformer 54 Protection Relay 56, 58 Control Device 60 Current Transformer 62 Transformer 64 Protection Relay 66 Voltage Detection Unit 68 AND Gate 70 Control Calculation Unit 72 optimum firing command value selection unit 74 current detection unit 76 switching unit 78 AND gate

Claims (2)

A forward converter that converts AC power from the AC system to DC power and outputs it to a DC main circuit, and converts DC power from the DC main circuit to AC power and outputs it to an AC system different from the AC system An inverter, a DC power generating means for generating DC power, a circuit connecting the DC main circuit and the DC power generating means, and an opening / closing means for opening and closing the circuit according to a command; and the forward converter Forward converter control means for stopping the operation of the forward converter until the failure of the AC system is recovered at the time of the failure of the AC system on the side, and the closing means is commanded to the switching means when the AC system on the forward converter side fails Thereafter, an open / close command means for instructing an open circuit, and an inverse converter control means for controlling the conversion output of the inverse converter according to the state of the DC main circuit when the AC system on the forward converter side fails. DC linkage system. One power converter of a pair of power converters connected to each other with different AC systems and connected to each other with a DC main circuit in between is operated as a forward converter, and the other power converter is an inverse converter And the operation of the forward converter is stopped until the failure of the AC system is recovered at the time of failure of the AC system on the forward converter side, and the switching means connected to the DC main circuit is closed and the DC power source is closed. DC power is supplied to the DC main circuit, and the conversion output of the inverter is controlled according to the current of the DC main circuit, and then the switching means is opened to switch the DC power source to the DC main circuit. A method for operating a DC link system that stops supplying DC power.

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