JP5675152B2 - Power converter - Google Patents

Description

  The present invention relates to a power conversion system. Specifically, the present invention relates to a power conversion system linked to an AC system through a transformer.

  Non-Patent Document 1 uses a switching element (Insulated-gate bipolar transistor: IGBT, etc.) capable of on / off control, and cascades as one method of a power converter that can output a high voltage exceeding the withstand voltage of the switching element. -A multi-level converter (CMC) is proposed.

  The CMC is a converter in which a bidirectional chopper circuit or a full bridge circuit connected to a DC capacitor is used as a unit cell and its input / output terminals are connected in cascade. The CMC has a feature that the output voltage harmonic can be suppressed by shifting the phase of the PWM control carrier wave of the unit cell for each unit cell. It is known that the CMC can be used as a grid-connected voltage converter such as a reactive power output device and a power storage device.

  When the DC capacitor of each unit cell is not charged when the multi-level converter is connected to the system, the unit capacitor enters the DC capacitor via a diode constituting a bidirectional chopper circuit or full bridge circuit of the unit cell. An excessive current flows in as a current. As a countermeasure, there is an initial charging method in which each DC capacitor is charged from the AC system via a resistor as a method for safely charging the first DC capacitor.

  On the other hand, there is a method of charging the DC capacitor by connecting a variable voltage source to the DC capacitor of the second converter and gradually boosting the voltage of the voltage source.

  As described above, in the first initial charging method, the DC capacitor of each unit cell is charged from the AC system via the resistor. In this case, a loss occurs in the resistor, which is not preferable from the viewpoint of energy saving. Further, the resistor generates heat and becomes high temperature, which is not preferable from the viewpoint of safety.

  On the other hand, in the second initial charging method, as described above, the variable voltage source is connected to the DC capacitor of the converter, and the DC capacitor is charged by gradually increasing the voltage of the voltage source. Since it is not necessary to connect a resistor between the variable voltage source and the DC capacitor, the DC capacitor can be charged efficiently. However, when this method is applied to a CMC, a variable voltage source must be connected for each DC capacitor, so that the initial charging circuit becomes large, which is not preferable from the viewpoint of miniaturization.

  An object of the present invention is to provide a cascade converter in which unit cells such as bidirectional choppers and full bridges are connected in cascade to perform initial charging of each unit cell to a DC capacitor with high efficiency and to provide a small initial charging circuit. It aims at providing CMC which has.

  In a cascade converter system having a configuration in which unit cells composed of bidirectional chopper circuits or the like are connected in cascade, an initial charging circuit is connected in parallel with the main circuit of the cascade converter to the AC output of the cascade converter The problem can be solved by the cascade converter system characterized in that. By connecting an initial charging circuit to the cascade in parallel with the converter, the initial charging can be performed without connecting to the AC system.

  Furthermore, in the cascade converter system, the problem can be solved by the cascade converter system characterized in that the output voltage of the initial charging circuit is lower than the AC voltage connected to the cascade converter.

  If the input / output of another unit cell is short-circuited, only a predetermined unit cell can be initially charged. In order to initially charge only a predetermined cell, the initial charging circuit only needs to output a voltage for charging the DC voltage of the cell, and can be lower than the voltage of the AC system.

  In cascade converters with unit cells such as bidirectional choppers and full bridges connected in cascade, the initial charge to the DC capacitor of each unit cell is performed with high efficiency and a cascade converter with a small initial charge circuit is realized. it can.

The circuit diagram which shows embodiment of the power conversion system of this invention. 1 is a circuit diagram showing a part of a first embodiment of the present invention. The circuit diagram which shows a part of 2nd Embodiment of this invention. The circuit diagram which shows embodiment of the power conversion system of this invention. The circuit diagram which shows embodiment of the power conversion system of this invention. The circuit diagram which shows embodiment of the power conversion system of this invention. The circuit diagram which shows embodiment of the power conversion system of this invention. The circuit diagram which shows embodiment of the power conversion system of this invention. The circuit diagram which shows embodiment of the power conversion system of this invention. The circuit diagram which shows embodiment of the power conversion system of this invention. The circuit diagram which shows embodiment of the power conversion system of this invention. The circuit diagram which shows embodiment of the initial charging circuit among the power conversion systems of this invention. The circuit diagram which shows embodiment of the initial charging circuit among the power conversion systems of this invention.

  In each embodiment, the semiconductor switching element is described as an IGBT, but other semiconductor switching elements such as a GTO and a MOSFET may be used.

  A first embodiment for carrying out the present invention will be described.

  In the first embodiment, an embodiment of the present invention will be described using a CMC (cascade multilevel converter) as an example.

  FIG. 1 is a circuit diagram showing a first embodiment of the present invention. First, the structure of the power converter system 101 of this invention is demonstrated using FIG.

  The power converter system 101 of the present invention includes a power converter 105, an arm reactor 201 (201U to 201W), a breaker 202, and an initial charging circuit 252. The arm reactor 201 functions as an interconnection impedance, and the interconnection transformer 102 may be substituted as shown in FIG.

  The power converter 105 includes three cascade arms 113 (113U to 113W).

  The cascade arm 113 has a structure in which the unit cells 120 are connected in cascade, and the unit cell 120 includes a full bridge circuit 120F as shown in FIG. The unit cell 120 may be composed of a bidirectional chopper 120C as shown in FIG. 2. However, since the full bridge circuit has a higher degree of control freedom, hereinafter, the unit cell 120 has a full bridge circuit configuration. Will be described as an example.

  The full bridge circuit 120F has a configuration in which two IGBT legs 411 (411L, 411R) are connected in parallel and connected to a DC capacitor 406. Each IGBT leg 411 has a configuration in which IGBT parallel bodies 402 (402P, 402N) are connected in series. An input / output terminal 400 (400L, 400R) is provided at a connection portion between the IGBT parallel body 402P and the IGBT parallel body 402N, and in principle, the input / output terminals 400 of each unit cell are cascade-connected.

  More specifically, the output terminal 400N of each unit cell 120 other than the terminals (602U to 602W, 603U to 603W) at both ends of the cascade arm 113 (113U, 113V, 113W) is connected to the output terminal 400P of another unit cell. The output terminal 400P of each unit cell is connected to the output terminal 400N of another unit cell.

  One terminal 602 (602U to 602W) of each cascade arm 113 (113U, 113V, 113W) is star-connected to each other at the connection point 600N. The other terminal 603 (603U to 603W) of each cascade arm 113 (113U, 113V, 113W) is electrically connected to the arm reactor 201 (201U, 201V, 201P) and also connected to the initial charging circuit 252. The The initial charging circuit 252 includes a variable DC voltage source 250 and a contactor 251.

  Also, the arm reactor 201 (201U, 201V, 201P) is connected to the three-phase power system 100. A connection point between the arm reactor 201 and the three-phase power system 100 is referred to as a connection point 650 (650U, 650V, 650W). The initial charging circuit 252 may be connected to the system side of each arm reactor 201, for example, the connection point 650.

  Next, the operation of the power converter system 101 of the present invention will be described.

  First, the output voltage of each phase of the power converter 105 constituting the power converter system 101 will be described. However, unless otherwise specified, the connection point 600N of the power converter system 101 is set as a reference potential. The potential at the interconnection point 650 (650 U, 650 V, 650 W) is defined as each phase output voltage of the power converter 105.

  Further, the potential of the connection point 603 (603U, 603V, 603W) is defined as the inner cascade voltage V113 (V113U, V113V, V113W).

  The normal operation of the power converter system 101 of the present invention will be described.

  The interchanged power between the power converter system 101 and the three-phase power system 100 can be controlled by adjusting the amplitude and phase of the inner cascade voltage V113 of the power converter system 101 based on the system voltage.

  On the other hand, the inner cascade voltage can be controlled as follows.

  The voltage applied between the input / output terminals (between 600N and 603U, between 600N and 603V, and between 600N and 603W) of each cascade arm 113U, 113V, 113W of the power converter system 101 is the cascade arm 113U, 113V, 113W. Is a combined voltage of the output voltages of the unit cells 120 constituting the. Therefore, the inner cascade voltages V113U, V113V, and V113W can be controlled by the output voltage of each unit cell 120 of each cascade arm.

  Since the inner cascade voltages V113U, V113V, and V113W correspond to the output voltage of the power converter 105, the inner cascade voltages V113U, V113V, and V113W are controlled to control the connection between the three-phase power system 100 and the converter system 101. The amount of power interchange can be controlled. Since the output voltage of the unit cell 120 is controlled by PWM control of each IGBT leg 411, it is necessary to control the DC capacitor 406 of each unit cell to a predetermined voltage.

  Next, a sequence before operation of the power converter system 101 will be described.

  First, all the IGBTs 451 of each IGBT parallel body 402 (402P, 402N) of one unit cell 120 are all turned off, and all the IGBTs 451 of each IGBT parallel body 402N of the other remaining unit cells 120 are turned on.

  Next, all the contactors 251 of the initial charging circuit 252 are turned on.

  The voltage of the variable DC voltage source 250 of the initial charging circuit 252 in the phase having the unit cells 120 in which all the IGBTs 451 of the IGBT parallel bodies 402 are all turned off is gradually increased. Since the output terminal of the unit cell 120 in which the IGBT of each IGBT parallel body 402N is turned on is short-circuited by the turned on IGBT 451, the DC capacitor 406 of the unit cell is not charged. On the other hand, in the unit cell 120 in which all the IGBTs 451 of each IGBT parallel body 402 are all turned off, when the potential of the output terminal 400L is higher than the potential of 400R, the DC capacitor 406 and the IGBT leg 411R via the diode 452 of the IGBT leg 411L. The current flows in the order of the diode 452 and the DC capacitor 406 is charged. When the potential of the unit cell output terminal 400R is higher than the potential of 400L, a current flows in the order of the DC capacitor 406 and the diode 452 of the IGBT leg 411L through the diode 452 of the IGBT leg 411R, and the DC capacitor 406 is charged. The

  That is, if a voltage is applied between the IGBT leg 411L and the IGBT leg 411R of the unit cell 120 in which all the IGBTs 451 of the IGBT parallel bodies 402 are all turned off, the voltage of the unit cell 120 DC capacitor 406 can be charged. Therefore, even if a voltage is applied to the initial charging circuit of the other phase, if the voltage is applied to the DC capacitor 406, it is possible to charge the DC capacitor.

  In order to prevent charging of DC capacitor 406, IGBT 451 of two IGBT parallel bodies 402P of each unit cell 120 may be turned on instead of IGBT parallel body 402N.

  In FIG. 1, the initial charging circuit 252 of the initial charging circuit 252 is a variable AC voltage source 252A (252AU to 252AW), but may be a variable DC voltage source 252D (252DU to 252DW) as shown in FIG.

  Moreover, in FIG. 1, although connected to the three-phase electric power system 100 via the arm reactor 201, you may connect to the three-phase electric power system 100 via the interconnection transformer 102 like FIG. The leakage inductance of the interconnection transformer 102 functions in the same way as the interconnection reactor 201.

  Further, as shown in FIG. 6 and FIG. 7, the interconnection reactor 201 may be installed between the initial charging circuit 252 and the power converter 105.

  Further, as shown in FIG. 8, the power converter 105 may be delta-connected.

  Further, as shown in FIG. 9, the connection of the initial charging circuit 252 may be a delta connection.

  Further, as shown in FIG. 10, the neutral point of the star-connected initial charging circuit 252 and the neutral point of the cascade-connected cascade arm may be connected.

  Further, as shown in FIG. 10, the initial charging circuit 252 may be connected in parallel to each cascade arm 113 of the power converter 105 connected in delta connection.

  In any case, since there is no resistor between the initial charging circuit 252 and the DC capacitor 406 of the initial charging circuit 252, the initial charging can be performed efficiently, and the initial charging circuit can be miniaturized.

  Next, the DC capacitors 406 of all the unit cells 120 can be initially charged by turning off all the IGBTs 451 of the IGBT parallel bodies 402 of the unit cells not initially charged and repeating the initial charging operation described above. .

  In this embodiment, the variable DC voltage source 250 shown in FIGS. 1, 2, 4, 4, 5, 6, 7, 8, 9, 10, and 11 of the first embodiment is replaced with that shown in FIG. .., And a voltage source 750 as shown in FIG. Since the output voltage of the voltage source 750 may be a voltage for charging only the DC capacitor 406 of the unit cell 120 for the first time, it is sufficiently smaller than the voltage of the three-phase power system 100. Therefore, the voltage applied to the resistor 766 can make the initial charging more efficient and reduce the size of the initial charging circuit compared to the conventional example in which the voltage of the three-phase power system 100 is applied to the resistor.

  The present invention can be used for a reactive power compensator (STATCOM), a back-to-back system (frequency converter, etc.), a direct current power transmission system (HVDC), a motor drive, and the like.

100 three-phase power system 101 power converter system 102 interconnection transformer 102C variable voltage transformer 105 power converter 113Up, 113Vp, 113Wp, 113Un, 113Vn, 113Wn cascade leg 120 unit cell 121C bidirectional chopper 121F full bridge circuit 201Up, 201 Vp, 201 Wp, 201 Un, 201 Vn, 201 Wn Arm reactor 202 Breaker 250 Variable DC voltage source 251 Contactor 252 Initial charging circuit 400P, 400N, 400L, 400R Unit cell output terminal 402P, 402N IGBT parallel body 406 DC capacitors 411, 411L, 411R IGBT leg 451 IGBT
452 Diode 600U High voltage side terminal 600V of cascade leg 113Up High voltage side terminal 600W of cascade leg 113Vp High voltage side terminal 602U of cascade leg 113Wp Low voltage side terminal 602V of cascade leg 113Up Low voltage side terminal 602W of cascade leg 113Vp Low voltage side terminal of cascade leg 113Wp 603U Cascade leg 113Un high voltage side terminal 603V Cascade leg 113Vn high voltage side terminal 603W Cascade leg 113Wn high voltage side terminal 604U Cascade leg 113Un low voltage side terminal 604V Cascade leg 113Vn low voltage side terminal 604W Cascade leg 113Wn low voltage side terminal 650U, 650V, 650W U phase input / output terminal 750AU, 750AV, 75 of power converter 105 AW's first charging AC voltage source 750DU, 750DV, 750DW's first resistor of the charging DC voltage source 766 initial charge for

Claims (9)

In the power conversion system having a configuration in which unit cells are connected in cascade, the unit cell includes a terminal, a capacitor, and a switching element that controls a connection state between the capacitor voltage and the terminal, and is connected to the cascade. unit cell constitutes a cascade arms, the cascade arms provided corresponding to a plurality of phases, the plurality of cascaded arms are connected to each other, one side and the different sides from one side of the other side of the cascade arm voltage with respect to the system to compensate for the reactive power between line and by controlling the respective unit cells of the plurality of cascaded arm to the capacitor of each cell in the current flowing through each unit cell is charged and discharged to and a performs the normal power conversion is to convert the phase electrodeposition for initial charge electrically connected to the AC output Have the initial charging time to prior to normal power conversion, said through one side and the other side the unit cells to a different side from the one side of the cascade arm in a predetermined phase from the power source for the initial charge first wherein when the charging current flows, so that does not flow to the capacitor of the other unit cells in the predetermined phase the initial charging current to the capacitor of the selected predetermined unit cells flows out of the cascade arm A power conversion system having a function of controlling a switching element of each unit cell.
  2. The power conversion system according to claim 1, wherein the voltage source for initial charging is a DC voltage source.   2. The power conversion system according to claim 1, wherein the initial charging voltage source is a DC variable voltage source.   2. The power conversion system according to claim 1, wherein the voltage source for initial charging is an AC voltage source.   2. The power conversion system according to claim 1, wherein the initial charging voltage source is an AC variable voltage source.   2. The power conversion system according to claim 1, wherein the initial charging voltage source is a combination of an AC voltage source and a resistor.   2. The power conversion system according to claim 1, wherein the initial charging voltage source is a combination of a DC voltage source and a resistor. In any of the power conversion system of claim 1乃 optimum 7, the power conversion system, wherein the first charging power supply is connected in parallel with the power converter.
The power conversion system according to any one of claims 1 to 8, wherein the power conversion system is a power conversion system connected to an AC voltage source such as an AC system, and the power is higher than the voltage of the AC voltage source. A power conversion system characterized in that the output voltage of the voltage source for initial charging is lower .

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