JP2014220966A - Self-excited converter charging method and power conversion system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the dimensions and cost of an apparatus for initial charging.SOLUTION: The self-excited converter charging method includes: stepping down electric power supplied from an AC system 1 by a first transformer 4; passing electric power output from the first transformer 4 through a resistor 7; stepping up electric power output from the resistor 7 by a second transformer 6; and inputting electric power output from the second transformer 6 into the AC side of a self-excited converter 21 to charge a capacitor 14 in the self-excited converter.

Description

  The present invention relates to a technique for performing initial charging of a self-excited converter.

  The self-excited converter includes a conversion transformer for connecting to an AC system, a converter that changes the power transmission direction at high speed, and a capacitor provided on the DC side. This self-excited converter controls active power and reactive power by changing the phase difference from the system voltage and the magnitude of the voltage. Self-excited converters also require initial charging of the capacitor.

  As a first technique for initial charging, a method of charging by directly attaching a charging device to the direct current side is known (for example, Patent Document 1). In this technology, the circuit breaker for connecting the converter to the AC system is opened, the capacitor is charged by connecting the initial charging circuit to the DC side, and after the charging is completed, the initial charging circuit is disconnected and disconnected. Turn on the unit and connect the DC system to the AC system.

  Further, as a second technique for initial charging, a method of charging a capacitor by charging a resistor from an AC system is known (for example, Patent Document 2). In this technique, a converter is connected to an AC system via a resistor, and after charging, the resistor is short-circuited.

JP 2011-172333 A Japanese Patent Laid-Open No. 8-130877

  The first technique requires a circuit for supplying electric power for initial charging in the self-excited converter, and thus has problems such as an increase in size and cost of the self-excited converter. The second technique requires a large resistance as the system voltage becomes higher, and therefore has a problem of increasing the size and cost of a circuit for initial charging.

  In order to solve the above problems, a self-excited converter charging method according to an aspect of the present invention is a method in which power supplied from an AC system is stepped down by a first transformer and is output from the first transformer. Is passed through a resistor, the power output from the resistor is boosted by a second transformer, and the power output from the second transformer is input to the AC side of the self-excited converter, Charging a capacitor in the self-excited converter.

  According to one embodiment of the present invention, the size and cost of equipment for initial charging can be reduced.

The structure of the power conversion system of the Example of this invention is shown. The first charging method is shown. The 1st state of a power conversion system is shown. The 2nd state of a power conversion system is shown. The 3rd state of a power conversion system is shown.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 shows a configuration of a power conversion system according to an embodiment of the present invention.

  This power conversion system is provided in a substation of the DC power transmission system, and performs power conversion between the AC system 1 and the DC system 31. The power conversion system has a bus 2 (first bus) and an Otobus 3 (second bus). Kobus 2 and Otobus 3 form a double bus. The Kobus 2 is connected to the AC system 1.

  The power conversion system further includes an in-house transformer 4 (first transformer), an emergency power source (EG) 5, a circuit breaker 8, a resistor 7 (resistor), and an in-house transformer 6 (second transformer). And have. The primary side (high-voltage side, input side) of the in-house transformer 4 is connected to the Kobaru 2. An emergency power source 5 and one end of a circuit breaker 8 are connected to the secondary side (low voltage side, output side) of the in-house transformer 4. One end of a resistor 7 is connected to the other end of the circuit breaker 8. The other end of the resistor is connected to the secondary side (low voltage side, input side) of the in-house transformer 6. The maiden bus 3 is connected to the primary side (high voltage side, output side) of the in-house transformer 6.

  The power conversion system further includes a circuit breaker 9 (first circuit breaker: bustie), a circuit breaker 10 (second circuit breaker: bustie), a circuit breaker 11, and a connection point 61. One end of a circuit breaker 9 is connected to the primary side of the in-house transformer 6 on the maiden bus 3. A connection point 61 is connected to the other end of the circuit breaker 9 on the maiden bus 3. One end of the circuit breaker 11 is connected to the connection point 61. A breaker 10 (bustie) is connected between the upper bus 2 and the connection point 61.

  The power conversion system further includes a self-excited converter 21. The other end of the circuit breaker 11 is connected to the AC side of the self-excited converter 21. A DC system 31 is connected to the DC side of the self-excited converter.

  The self-excited converter 21 includes a conversion transformer (converter transformer) 12, a converter 13, a capacitor 14, and a voltage measuring device 15. The primary side (high voltage side, input side) of the conversion transformer 12 is connected to the other end of the circuit breaker 11. The AC side of the converter 13 is connected to the secondary side (low voltage side, output side) of the conversion transformer 12. On the DC side of the converter 13, a capacitor 14, a voltage measuring device 15, and a DC system 31 are connected in parallel. The converter 13 changes the power transmission direction at high speed by using an IGBT (Insulated Gate Bipolar Transistor) as a switching element. The voltage measuring device 15 monitors the charge state of the capacitor 14 by measuring the voltage across the capacitor 14. Note that the self-excited converter 21 may include a plurality of sets of the converter 13, the capacitor 14, and the voltage measuring device 15.

  The power conversion system further includes a control device 41. The control device 41 displays information related to the voltage measured by the voltage measuring device 15 and sends an opening / closing instruction to the circuit breakers 8, 9, 10 and 11 based on an input from the operator.

  The in-house transformer 4 steps down the system voltage of the A bus 2 connected to the AC system 1 to the in-house voltage. The in-station voltage is a voltage used in the substation and is lower than the system voltage. The in-house transformer 6 boosts the in-house voltage to the system voltage. The in-house transformer 6 boosts the in-house voltage to a voltage in a predetermined voltage range including the system voltage. The predetermined voltage range is defined by, for example, an upper limit value and a lower limit value of the system voltage. In the following description, the section of the emergency power source 5, the circuit breaker 8, and the resistor 7 is referred to as internal wiring. The voltage of the in-house wiring becomes the in-house voltage. Inrush current can be avoided by applying resistance using the resistor 7.

  The emergency power source 5 supplies power having in-house voltage to the in-house wiring when power is not supplied from the AC system 1 to the in-house wiring due to an accident of the AC system 1 or the like. The emergency power supply 5 has a rechargeable battery, for example. In this case, the rechargeable battery in the emergency power source 5 is charged by the electric power supplied from the AC system 1 to the emergency power source 5 through the in-house transformer 4 at the normal time.

  FIG. 2 shows an initial charging method.

  First, the DC power transmission system enters an initial charging mode for charging the capacitor 14. In response to an instruction from the operator, the control device 41 turns on the breakers 8, 9, and 11 (in an “on” state) (S20). As a result, the power conversion system enters the first state, and the capacitor 14 is charged (S21).

  FIG. 3 shows a first state of the power conversion system.

  In the first state, the upper bus 2 and the in-house wiring are connected to the AC system 1. Since the circuit breakers 9 and 11 are turned on, the self-excited converter 21 is connected to the in-house wiring. An arrow 51 indicates a power flow in the first state. The circuit breakers 8, 9, 10, and 11 in this figure show an open / closed state. The in-house transformer 4 steps down the system voltage from the bus 2 to the in-house voltage. The electric power output from the in-house transformer 4 passes through the circuit breaker 8, passes through the resistor 7, and is input to the in-house transformer 6. The in-house transformer 6 boosts the in-house voltage from the resistor 7 to the system voltage. The electric power output from the in-house transformer 6 passes through the circuit breaker 9 on the second bus 3, passes through the circuit breaker 11, and is input to the self-excited converter 21. The electric power input to the self-excited converter 21 charges the capacitors 14 attached to all the converters 13 through the conversion transformer 12. Thereby, the capacitor | condenser 14 can be charged using the electric power from in-house wiring.

  Thereafter, when it is determined that charging of all the capacitors 14 is completed based on the voltage measured by the voltage measuring device 15, the control device 41 displays information indicating the completion (S22). For example, the control device 41 determines that the charging of all the capacitors 14 is completed when the voltages measured by all the voltage measuring devices 15 are equal to or higher than a predetermined voltage threshold.

  Thereafter, the control device 41 opens (breaks) the circuit breakers 9 and 11 in accordance with an instruction from the operator (S23). Thereby, between the in-house transformer 6 and the circuit breakers 10 and 11 in the maiden bus line 3 is disconnected. Further, the AC side of the self-excited converter 21 is disconnected from the Otobus 3. Note that the control device 41 may open the circuit breakers 9 and 11 when it is determined that charging of all the capacitors 14 has been completed.

  Then, the control apparatus 41 throws in the circuit breaker 10 according to the instruction | indication from an operator (S24). Thereby, a power conversion system will be in a 2nd state.

  FIG. 4 shows a second state of the power conversion system.

  In the second state, since the circuit breakers 9 and 11 are opened, the self-excited converter 21 is not linked to the in-house system. The upper bus 2 and the second bus 3 are connected via the circuit breaker 10, and the second bus 3 is connected to the AC system 1.

  Then, the control apparatus 41 throws in the circuit breaker 11 according to the instruction | indication from an operator (S25). Thereby, a power conversion system will be in a 3rd state. The DC power transmission system is in the normal operation mode (S26), and the control device 41 activates the converter 13.

  FIG. 5 shows a third state of the power conversion system.

  In the third state, the AC side of the self-excited converter 21 is connected to the Otobus 3 and is connected to the AC system 1. An arrow 53 indicates a tidal current in the third state. In the normal operation mode, the self-excited converter 21 converts AC power from the AC system 1 into DC power and supplies the DC power to the DC system 31. Thereby, self-excited converter 21 can receive the electric power from AC system 1 instead of the electric power from the in-house wiring after the capacitor 14 is completely charged. The above is the first charging method.

  In the conventional technique of charging a capacitor from an AC system, the power from the AC system is input to the self-excited converter through a resistor and a circuit breaker as the system voltage. Accordingly, a large resistance for avoiding an inrush current due to the system voltage, a circuit breaker that can withstand the system voltage, and the like are required, and the equipment is large and expensive. On the other hand, since the resistor 7 and the circuit breaker 8 of the present embodiment may be facilities corresponding to an in-house voltage lower than the system voltage, the size and cost can be reduced as compared with conventional facilities.

  In the initial charging method, the control device 41 may control the circuit breakers 9, 10, and 11 without receiving an instruction from the operator. For example, the control device 41 may execute S23 to S26 when it is determined in S22 that charging of all the capacitors 14 has been completed.

  According to the above-described initial charging method, the primary side of the in-house transformer 6 is connected to the AC side of the self-excited converter 21, thereby realizing the initial charging mode for charging the capacitor 14, and the AC system 1 is converted to the self-excited conversion. By being connected to the AC side of the device 21, a normal operation mode in which the converter 13 is operated is realized. Thus, the process in the initial charging method may be changed so that the normal operation mode is realized after the initial charging mode. For example, the control device 41 may open the circuit breaker 9 and turn on the circuit breaker 10 after completion of charging. Further, the power conversion system may not include the circuit breakers 8 and 11.

  In the initial charging mode, a circuit breaker (third circuit breaker) is connected in parallel with the resistor 7 and the capacitor 14 is charged or after the current flows through the resistor 7, the circuit breaker is turned on. The resistor 7 may be short-circuited. Thereby, inrush current can be avoided and power loss thereafter can be reduced.

  An initial charging method when power is not supplied from the AC system 1 will be described.

  When power is not supplied from AC system 1 due to an AC system 1 accident or the like, the power conversion system charges capacitor 14 with power from emergency power supply 5. The direct current power transmission system enters the initial charging mode, and the power conversion system enters the first state through S20 and S21 by the above-described initial charging method. In the first state, when power is not output from the on-site transformer 4, the emergency power source 5 outputs power. The electric power output from the emergency power supply 5 is boosted to the system voltage through the path indicated by the arrow 51 described above, and input to the self-excited converter 21. Thereby, the capacitor | condenser 14 is charged similarly to the above-mentioned initial charging method. When charging of all the capacitors 14 is completed and the AC system 1 is restored, the DC power transmission system enters the normal operation mode through S22 to S26.

  In the conventional technology for charging the capacitor from the AC system, the initial charging cannot be performed when the AC system power supply is lost due to a system fault or the like. On the other hand, in this embodiment, the capacitor 14 can be charged without the AC system power supply, and the converter 13 can be started. As a result, the self-excited converter 21 can be started (black start) in a state where there is no AC system power supply due to a load system without a power supply, a system failure, or the like.

  Further, when an emergency power source 5 that outputs electric power having an in-house voltage is prepared in the substation when the AC system power supply is lost, the in-house voltage is boosted and the capacitor 14 is charged for the first time. An emergency power source 5 can be used. This eliminates the need to prepare a power supply dedicated to the initial charge and a circuit dedicated to the initial charge for supplying power from the AC system, thereby reducing the size and cost of the power conversion system and reducing the number of devices. It can contribute to the improvement of reliability.

  At the time of charging, the power from the in-house wiring is boosted to the system voltage and input to the self-excited converter 21, and after charging, the power from the AC system 1 is input to the self-excited converter 21 while maintaining the system voltage. The operation in the initial charging mode and the normal operation mode can be executed without adding equipment such as a power source to the self-excited converter 21. Also, by using a double bus, during charging, power is supplied from the AC system 1 to the in-house wiring, and power is supplied from the in-house wiring to the self-excited converter 21. It is possible to supply power to the in-house wiring and to supply power from the AC system 1 to the self-excited converter 21.

The techniques described in the above embodiments can also be expressed as follows.
(Expression 1)
The power supplied from the AC system is stepped down by the first transformer,
The power output from the first transformer is passed through a resistor,
The power output from the resistor is boosted by a second transformer,
Charging the capacitor in the self-excited converter by inputting the power output from the second transformer to the AC side of the self-excited converter;
A self-excited converter charging method comprising:
(Expression 2)
By connecting the output side of the second transformer and the AC side of the self-excited converter during the charging, the power output from the second transformer is transferred to the AC side of the self-excited converter. input,
The self-excited converter charging method according to expression 1.
(Expression 3)
After the charging, the AC system is disconnected by cutting off the output side of the second transformer and the AC side of the self-excited converter and connecting the AC system and the AC side of the self-excited converter. The power supplied from is input to the AC side of the self-excited converter,
The self-excited converter charging method according to expression 2.
(Expression 4)
At the time of charging, the connection point provided between the output side of the second transformer and the AC side of the self-excited converter, between the output side of the second transformer and the connection point. By inputting the first circuit breaker provided, the power output from the second transformer is input to the AC side of the self-excited converter,
The self-excited converter charging method according to expression 3.
(Expression 5)
After the charging, the first circuit breaker is opened, and the second circuit breaker provided between the AC system and the connection point is turned on, whereby the electric power supplied from the AC system is self-excited. Input to the AC side of the converter,
The self-excited converter charging method according to expression 4.
(Expression 6)
At the time of charging, when power is not supplied from the AC system to the first transformer, power from a power supply device is input to the resistor,
The power output from the resistor is boosted by the second transformer,
The power output from the second transformer is input to the AC side of the self-excited converter.
The self-excited converter charging method according to expression 5.
(Expression 7)
The voltage on the output side of the second transformer is within a predetermined voltage range including the voltage of the AC system.
The self-excited converter charging method according to expression 6.
(Expression 8)
The input side of the first transformer is connected to the AC system via a first bus,
The first circuit breaker and the connection point are provided on a second bus;
The self-excited converter charging method according to expression 7.
(Expression 9)
During the charging, open the third circuit breaker connected in parallel with the resistor,
After the charging, the third circuit breaker is turned on.
The self-excited converter charging method according to expression 7.
(Expression 10)
A resistor that passes power supplied from the AC system and stepped down by the first transformer;
A self-excited converter including a capacitor and charging the capacitor with power output from the resistor and boosted by a second transformer;
A power conversion system comprising:

  In the above expression, the power supply device corresponds to the emergency power supply 5 or the like.

  The present invention is not limited to the above embodiments, and can be modified in various other forms without departing from the spirit of the present invention.

1: AC system, 2: Ko-bus, 3: Oto-bus, 4: In-house transformer, 5: Emergency power supply, 6: In-house transformer, 7: Resistance, 8, 9, 10, 11: Breaker, 12: Transformer for conversion, 13: Converter, 14: Capacitor, 15: Voltage measuring device, 21: Self-excited converter, 31: DC system, 41: Controller, 61: Connection point

Claims (10)

The power supplied from the AC system is stepped down by the first transformer,
The power output from the first transformer is passed through a resistor,
The power output from the resistor is boosted by a second transformer,
Charging the capacitor in the self-excited converter by inputting the power output from the second transformer to the AC side of the self-excited converter;
A self-excited converter charging method comprising: By connecting the output side of the second transformer and the AC side of the self-excited converter during the charging, the power output from the second transformer is transferred to the AC side of the self-excited converter. input,
The self-excited converter charging method according to claim 1. After the charging, the AC system is disconnected by cutting off the output side of the second transformer and the AC side of the self-excited converter and connecting the AC system and the AC side of the self-excited converter. The power supplied from is input to the AC side of the self-excited converter,
The self-excited converter charging method according to claim 2. At the time of charging, the connection point provided between the output side of the second transformer and the AC side of the self-excited converter, between the output side of the second transformer and the connection point. By inputting the first circuit breaker provided, the power output from the second transformer is input to the AC side of the self-excited converter,
The self-excited converter charging method according to claim 3. After the charging, the first circuit breaker is opened, and the second circuit breaker provided between the AC system and the connection point is turned on, whereby the electric power supplied from the AC system is self-excited. Input to the AC side of the converter,
The self-excited converter charging method according to claim 4. At the time of charging, when power is not supplied from the AC system to the first transformer, power from a power supply device is input to the resistor,
The power output from the resistor is boosted by the second transformer,
The power output from the second transformer is input to the AC side of the self-excited converter.
The self-excited converter charging method according to claim 5. The voltage on the output side of the second transformer is within a predetermined voltage range including the voltage of the AC system.
The self-excited converter charging method according to claim 6. The input side of the first transformer is connected to the AC system via a first bus,
The first circuit breaker and the connection point are provided on a second bus;
The self-excited converter charging method according to claim 7. During the charging, open the third circuit breaker connected in parallel with the resistor,
After the charging, the third circuit breaker is turned on.
The self-excited converter charging method according to claim 7. A resistor that passes power supplied from the AC system and stepped down by the first transformer;
A self-excited converter including a capacitor and charging the capacitor with power output from the resistor and boosted by a second transformer;
A power conversion system comprising:

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