JP2016100968A - Initial charging method of interconnection inverter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To avoid an excessive excitation rush current during initial charging of a DC capacitor and at the power-on of an interconnection transformer to a power system with an inexpensive charger that is as simple as possible and suppresses loss.SOLUTION: In an interconnection inverter, including a wattless power compensator that is constituted of a voltage inverter having a DC capacitor and interconnected to a power system via an interconnection transformer, an AC output side of a charger constituted of a switch, current limiting resistor, and isolating transformer is connected to an AC side of the interconnection inverter; an AC input side of the charger is connected to a charging AC power source; the charger is powered on to perform initial charging of the DC capacitor and excite the interconnection transformer from a secondary side; and the interconnection transformer is powered-on at the time of completion of charging of the DC capacitor.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a grid interconnection inverter such as a reactive power compensator which is constituted by a voltage source inverter having a DC capacitor and is linked to a power system through a linkage transformer, and an initial charging method for the grid connection inverter. About.

  A grid interconnection inverter including a DC capacitor and linked to a power system via a transformer is used as, for example, a reactive power compensator. It is known to perform initial charging of a DC capacitor by connecting a charger to a DC capacitor connected to the DC side of the inverter (see, for example, Patent Document 1 and Patent Document 2).

  FIG. 3 shows a conventional example of a grid interconnection inverter provided with this type of charger. For example, as shown in FIG. 4, the grid interconnection inverter 4 constituting the reactive power compensator includes an inverter bridge including semiconductor switching elements 8 a to 8 f and diodes 9 a to 9 f such as IGBT and GTO, and the inverter It consists of a DC capacitor 5 connected between the DC terminals of the bridge. The AC side of the inverter 4, that is, the inverter bridge three-phase AC terminal is connected to the secondary side of the interconnection transformer 3, and the primary side of the interconnection transformer 3 is connected to the power system 1 via the circuit breaker 2. Is possible. For the initial charging of the DC capacitor 4, a charger 6 is connected to the DC side of the inverter 4, and an input side of the charger 6 can be a charging power source 7 via a contactor 13. As shown in FIG. 5, the charger 6 can be composed of a current limiting resistor 10, an insulation transformer 11, and a rectifier including diodes 12 a to 12 f.

  When starting up the inverter 4, first, the contactor 13 is closed and the charger 6 is used to initially charge the DC capacitor 5 from the power supply 7. After completion of charging, the voltage is output from the inverter 4 to excite the interconnection transformer 3. When the interconnection transformer 3 is put into the power system 1 by the circuit breaker 2, an excessive magnetizing inrush current of the interconnection transformer 3 may occur. In order to suppress the excessive magnetizing inrush current, the primary side voltage Vi of the interconnection transformer 3 connected to the AC side of the inverter 4 and the voltage Vs of the power system 1 have the same amplitude and the same phase. At that time, the circuit breaker 2 is closed and the interconnection transformer 3 is put into the power system 1. This method is known, for example, from US Pat. When the circuit breaker 2 is closed and the interconnection transformer 3 is inserted into the electric power system 1, the contactor 13 is opened and the charging operation of the charger 6 is completed.

  However, in the case of this synchronous input method, since establishment of the synchronous input condition is performed by the control of the inverter 4, it takes time to establish the synchronous input condition. Therefore, during that period, the charger 6 charges the capacitor 5 by boosting the voltage from a power source 7 having a lower voltage (for example, 400V, 200V, etc.) than the power system 1 and converting it to DC, and the charged capacitor 5 until the inverter 4 outputs a voltage, and thus the loss of the inverter 4 and the interconnection transformer 3 is supplied until the interconnection transformer 3 is connected to the power system 1. Therefore, the capacity of the charger 6 must be designed in consideration of the maximum time required for establishing the synchronous input condition. For this reason, the device capacity of the charger 6 becomes large, and this becomes a factor of high cost.

  In addition, as a method of suppressing the magnetizing inrush current of the transformer, record the phase of the voltage when the circuit breaker is opened and the transformer is stopped. However, a method is known in which a transformer is inserted when the recorded phase is reached (see, for example, Patent Document 3). According to this method, if time has elapsed between the time when the transformer is opened and the next time it is turned on, the residual magnetic flux will change during that time, and even if it is turned on at the same phase, excessive excitation will occur. An inrush current may flow, and a sufficient suppression effect may not be obtained. Moreover, this patent document 3 does not disclose the technology relating to the initial charging of the grid interconnection inverter and the DC capacitor of the inverter.

  Further, as another method for suppressing the magnetizing inrush current of the transformer, a method of reducing the residual magnetic flux of the transformer by a magnetic flux control device including an inverter when the transformer is stopped is known (for example, patent document). 4). According to this method, since the residual magnetic flux of the transformer is reduced after the transformer is opened, an excessive excitation inrush current can be prevented even if the transformer is immediately turned on when the transformer is operated. However, for example, when the inverter protection function is activated, the transformer is cut off without any operation to reduce the residual magnetic flux. In such a case, in order to suppress the inrush current of the transformer at the time of reactivation, Another means, for example, the charger described in FIGS. 3 to 5 is required.

Japanese Patent Laid-Open No. 10-42475 JP 2008-125169 A Specification Japanese Patent Application Laid-Open No. 11-353969 JP 2012-196124 A

  An object of the present invention is to provide a grid connection that enables initial charging of a DC capacitor and suppression of an excessive excitation inrush current when an interconnection transformer is turned on to a power system by an inexpensive charger that is as simple as possible and has little loss. An object of the present invention is to provide an initial charging method for a system inverter.

  According to the first initial charging method of the grid interconnection inverter according to the present invention, the above-described problem is a reactive power composed of a voltage source inverter having a DC capacitor and linked to the power system via a grid transformer. In a grid interconnection inverter such as a compensation device, connect the AC output side of the charger composed of a switch, current limiting resistor, and insulation transformer to the AC side of the grid interconnection inverter, and connect the AC input side of the charger to Connect to the AC power supply for charging, charge the initial DC capacitor by turning on the charger, excite the interconnection transformer from the secondary side, and insert the interconnection transformer into the power system when the DC capacitor is fully charged This is solved by the initial charging method of the grid linking inverter.

  Further, according to the second initial charging method of the grid interconnection inverter according to the present invention, the above-described problem is constituted by a voltage source inverter having a DC capacitor, and is linked to the power system via the interconnection transformer. In a grid interconnection inverter such as a reactive power compensator, connect the AC output side of the charger, which is composed of a switch, current limiting resistor, and insulation transformer, to the AC side of the grid interconnection inverter. Connect the AC power supply to the AC power supply for charging, charge the DC capacitor initially by charging the charger, excite the interconnection transformer from the secondary side, and open the charger when the DC capacitor is fully charged. The voltage phase of the charger at the time of storage is stored, and when the voltage phase of the power system reaches the stored phase, the connection transformer is inserted into the power system. Also it solved.

  Further, according to the third initial charging method of the grid interconnection inverter according to the present invention, the above problem is constituted by a voltage source inverter having a DC capacitor and linked to the power system via a grid transformer. For grid interconnection inverters such as reactive power compensators, connect the AC output side of the charger composed of switches and voltage variable means to the AC output side of the grid interconnection inverter, and charge the AC input side of the charger for charging After connecting the AC power supply and performing the initial charging of the DC capacitor by turning on the charger, the output voltage of the charger is reduced to zero by the voltage variable means and then the charger is opened to power the interconnection transformer. It can also be solved by the initial charging method of the grid linking inverter.

  The voltage variable means can be composed of a slidac and an insulating transformer, or an insulating transformer with a tap, or can be composed of a rectifier, an inverter, and an insulating transformer.

  According to the initial charging method of the grid interconnection inverter according to the present invention, the AC output side of the charger is connected to the AC side of the grid interconnection inverter, that is, the secondary side of the grid transformer, and the AC input of the charger is connected. By connecting the side to the charging AC power supply, the connection transformer can be excited simultaneously with charging the DC capacitor from the charging AC power supply by turning on the charger. Since the charger is an AC input and an AC output, it is possible to use a charger having a simple configuration, particularly a charger constituted by a switch, a current limiting resistor, and an insulation transformer. When the voltage of the AC power supply for charging is synchronized with the voltage of the power system, according to the first initial charging method, when the initial charging of the DC capacitor is completed, there is no excessive excitation inrush current. Can be loaded. Therefore, since the interconnection transformer can be put into the power system in the shortest time after charging is completed, it is necessary for the charger to design the capacity of the charger in anticipation of power loss in the period until the synchronous charging condition is established as in the past. Therefore, it can be a particularly inexpensive charger.

  Furthermore, the advantage of the present invention is that, even if the charging power source and the power system are not synchronized, the charger is opened when the charging of the DC capacitor is completed according to the second initial charging method according to the present invention. By storing the phase of the charger voltage at the time of opening, and then inserting the interconnection transformer into the power system when the voltage phase of the power system reaches the stored phase, there is no excessive inrush current It is possible to carry out the input of the interconnection transformer. In this case, since the charger is opened when the charging of the DC capacitor is completed, there is no loss in the charger during the period from that point to the time when the interconnection transformer is turned on. Thus, unlike the conventional case, it is not necessary to design the capacity of the charger in consideration of the power loss in the period until the establishment of the synchronous input condition.

  Further, according to the third initial charging method of the present invention, the AC output side of the charger constituted by the switch and the voltage varying means is connected to the AC output side of the grid interconnection inverter, and the AC input side of the charger is used for charging. After connecting the AC power supply and performing the initial charging of the DC capacitor by turning on the charger, the output voltage of the charger is reduced to zero by the voltage variable means and then the charger is opened to power the interconnection transformer. By putting it in the system, it is possible to execute the connection transformer without excessive excitation inrush current. Also in this case, since the charger is opened when the charging of the DC capacitor is completed, there is no loss in the charger during the period from that point to the time when the interconnection transformer is turned on. Therefore, unlike the conventional case, it is not necessary to design the capacity of the charger in consideration of the power loss in the period until the establishment of the synchronous input condition, and thus a particularly inexpensive charger can be configured.

FIG. 1 is a circuit diagram showing a configuration example of an apparatus for carrying out an initial charging method according to the present invention. FIG. 2 is a circuit diagram showing another configuration example of an apparatus for carrying out the initial charging method according to the present invention. FIG. 3 is a circuit diagram showing a configuration example of an apparatus for carrying out a conventional initial charging method. FIG. 4 is a circuit diagram showing a configuration example of the grid interconnection inverter. FIG. 5 is a circuit diagram showing a conventional configuration example of a charger for initial charging.

  The invention is explained in more detail with reference to the drawings, in which embodiments of the invention are schematically shown. In the figure, constituent elements corresponding to each other are denoted by the same reference numerals.

  The grid interconnection inverter 4 according to the present invention shown in FIG. 1 is, for example, a reactive power compensator linked to the power grid 1 via the circuit breaker 2 and the grid transformer 3 or a part thereof. As shown in FIG. 4, similarly to the conventional example, the grid interconnection inverter 4 includes an inverter bridge composed of semiconductor switching elements 8a to 8f and diodes 9a to 9f such as IGBT and GTO, and a DC terminal of the inverter bridge. It is configured as a voltage source inverter having a DC capacitor 5 constituted by a connected DC capacitor 5.

  The charger 15 for initial charging of the DC capacitor 5 is connected to the charging AC power source 7 via the contactor 13 as in the conventional example shown in FIG. However, the output side of the charger 15 is not connected to the DC side of the inverter to which the DC capacitor 5 is connected as in the conventional charger 6 shown in FIG. It is connected to the secondary side of the system transformer 3. For this purpose, the charger 15 has a current limiting resistor 10 for limiting the charging current and an insulating transformer 11 for boosting, as in the conventional example shown in FIG. 5, but shown in the conventional example in FIG. It does not have the diode rectifiers 12a to 12f, but has a circuit breaker 14 instead.

  According to such a connection configuration of the charger 15, before the primary side of the interconnection transformer 3 is put into the power system 1 by the circuit breaker 2, the charger 15 is connected by the switch composed of the contactor 13 and the circuit breaker 14. When charging is performed, charging current is supplied from the AC power source 7 to the DC capacitor 5 via the current limiting resistor 10 and the insulating transformer 14 in the charger 15 and the diodes 9a to 9f in the inverter 4. At the same time, an exciting current is supplied to the secondary side of the interconnection transformer 3.

  If the charging AC power supply 7 is synchronized with the power grid 1 by, for example, taking out the charging AC power supply 7 from the power grid 1 through another transformer, the charging AC power supply 7 is connected from the secondary side. The primary voltage Vi of the interconnected transformer 3 to be excited can be in phase with the voltage Vs of the power system 1 and can have the same amplitude due to an appropriate transformation ratio of the insulating transformer 11. Therefore, in this case, when the initial charging of the intermediate capacitor 5 by the charging of the charger 15 is completed, the interconnection transformer 3 is input to the power system 1 by the circuit breaker 2 without causing an excessive magnetizing inrush current. The charger 15 can be opened by the circuit breaker 14. Thereafter, the grid interconnection inverter 4 is started to operate by a known grid control synchronized with the power system.

  In this way, when the charging is completed, it is not necessary to perform a control operation for establishing a synchronous charging condition as in the prior art, and the interconnection transformer can be immediately input to the power system. Therefore, it is not necessary for the charger 15 to design the capacity in consideration of the power loss in the period until the establishment of the synchronous input condition as in the conventional case, and only the charging current of the capacitor 5 and the exciting current of the interconnection transformer 3 are supplied. Therefore, it can be a particularly inexpensive charger.

  The above-described initial charging method according to the present invention can be developed so as to be applicable even when the charging AC power supply 7 is not synchronized with the power system 1. For this purpose, the conventional technique disclosed in Patent Document 3 shown in the background art can be used. That is, first, similarly to the above-described initial charging method, using the connection configuration of the charger 15 shown in FIG. Excited from the secondary side. Then, based on the prior art disclosed in Patent Document 3, the charger 15 is opened by the circuit breaker 14 when the charging of the DC capacitor is completed, and the voltage phase of the charger 15 (that is, the voltage of the interconnection transformer 3 when it is opened). (Phase of Vi) is recorded, and when the phase of the voltage Vs of the power system 1 becomes the stored phase, the interconnection transformer 3 is inserted into the power system 1 by the circuit breaker 2. Thereby, an excessive inrush excitation current at the time of turning on the interconnection transformer 3 can be avoided. After the interconnection transformer 3 is turned on, the operation of the grid interconnection inverter 4 is started.

  Also in this case, since the charger 15 is opened when the charging of the DC capacitor 15 is completed, no loss occurs in the charger 15 during the period from that time to the time when the interconnection transformer 3 is turned on. . Therefore, it is not necessary for the charger 15 to design the capacity in consideration of the power loss in the period until the synchronous input condition is established as in the conventional case, and only the charging current of the capacitor 5 and the exciting current of the interconnection transformer 3 are supplied. Therefore, it can be a particularly inexpensive charger.

  FIG. 2 shows another embodiment according to the present invention of an inverter for grid interconnection provided with a charger for initial charging. The charger 15 is composed of a switch and a voltage variable means. The switch comprises a circuit breaker 14 (and a contactor 13), and the voltage variable means is composed of a variable transformer 16 and an insulation transformer 11 here. The variable transformer 16 is also called a slidac and is a transformer capable of making the output voltage variable. This type of voltage varying means can be composed of a tapped insulation transformer, or can be composed of a rectifier, an inverter, and an insulation transformer.

  When starting up the grid interconnection inverter 4, the charger 15 is first turned on by closing the switches 13 and 14. The output voltage of the variable transformer 16 is changed from zero to the rated value, boosted by the insulation transformer 11, and the DC capacitor 5 is charged via the diodes 9 a to 9 f in the inverter 4. When the charging of the DC capacitor 5 is completed, the residual magnetic flux of the interconnection transformer 3 is decreased by reducing the output of the variable transformer 16 to zero, and then the switches 13 and 14 are opened to open the charger 15. After that, the circuit breaker 2 is closed and the interconnection transformer 3 is put into the power system 1. Thereby, an excessive inrush excitation current at the time of turning on the interconnection transformer 3 can be avoided. After the system transformer 3 is turned on, the operation of the grid interconnection inverter 4 is started.

  Also in this case, the charger 15 is opened when the charging of the DC capacitor 15 is completed and the output of the variable transformer 16 is reduced to zero. It is not necessary to design the capacity in anticipation of power loss in the period up to this time, and only the charging current of the capacitor 5 and the exciting current of the interconnection transformer 3 are supplied, so that a particularly inexpensive charger can be obtained.

DESCRIPTION OF SYMBOLS 1 Electric power system 2 Circuit breaker 3 Connection transformer 4 System connection inverter 5 DC capacitor 7 Charging AC power supply 8a-8f Semiconductor switch 9a-8f Diode 10 Current limiting resistance 11 Insulation transformer 13 Contactor 14 Circuit breaker 15 Charger 16 Variable transformer (Slidac)

Claims (6)

  Consists of a voltage-type inverter with a DC capacitor, and is connected to a power system via a connection transformer, such as a reactive power compensator, etc., and includes a switch, a current limiting resistor, and an insulation transformer Connect the AC output side of the charger to the AC side of the grid connection inverter, connect the AC input side of the charger to the AC power supply for charging, and perform initial charging of the DC capacitor by connecting the charger and connect An initial charging method for an inverter for grid connection, wherein the transformer is excited from the secondary side and the grid transformer is inserted into the power system when the charging of the DC capacitor is completed.   Consists of a voltage-type inverter with a DC capacitor, and is connected to a power system via a connection transformer, such as a reactive power compensator, etc., and includes a switch, a current limiting resistor, and an insulation transformer Connect the AC output side of the charger to the AC side of the grid connection inverter, connect the AC input side of the charger to the AC power supply for charging, and perform initial charging of the DC capacitor by connecting the charger and connect Energize the transformer from the secondary side, open the charger when the DC capacitor is fully charged, store the voltage phase of the charger when it is opened, and the voltage phase of the power system becomes the stored phase The initial charging method of the inverter for grid connection is to put the interconnection transformer into the power system at the moment.   In a grid-connected inverter, such as a reactive power compensator, which is composed of a voltage-type inverter having a DC capacitor and is linked to the power system via a grid transformer, the AC of the charger composed of a switch and voltage variable means Connect the output side to the AC output side of the grid interconnection inverter, connect the AC input side of the charger to the AC power supply for charging, and after charging the DC capacitor by turning on the charger, An initial charging method for an inverter for grid connection, in which the output voltage of the charger is lowered to zero and then the charger is opened, and the grid transformer is inserted into the power system.   4. The initial charging device for an inverter for system linkage according to claim 3, wherein said voltage varying means comprises a slidac and an insulating transformer.   4. The initial charging device for an inverter for system linkage according to claim 3, wherein said voltage varying means is constituted by a tapped insulation transformer.   4. The initial charging device for an inverter for system linkage according to claim 3, wherein said voltage varying means is constituted by a rectifier, an inverter, and an insulating transformer.

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