JP2013192448A - Power conversion apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power conversion apparatus in which effective power can be transferred between CMC converters connected to a plurality of systems, respectively, without insulating a DC/DC converter or a transformer.SOLUTION: Effective power can be supplied from one system to another system by a power conversion system characterized by comprising: a first Y-connection cascade multilevel converter (CMC) linked through a first linkage reactor to a first power system; a second CMC linked through a second linkage reactor to a second power system; a first Y-connection reactor connected to the first power system; and a second Y-connection reactor linked to the second system, in which a neutral point of the first CMC and a neutral point of the second CMC are connected, a neutral point of the first Y-connection reactor and a neutral point of the second Y-connection reactor are connected, and the neutral points of the first and second CMCs and the neutral points of the first and second Y-connection reactors are made into DC link.

Description

  The present invention relates to a power conversion device interconnected with a power system.

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

  The CMC is a converter in which a full bridge circuit or a bidirectional chopper circuit is used as a unit cell and its input / output terminals are connected in cascade. The CMC is characterized in that the harmonics of the converter output by the CMC 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 reactive power output device or an active power storage device.

IEEJ Transactions D, Vol. 127, No. 8, pages 781-788 IEEJ Transactions D Division 126, No. 3, pages 211-217

  However, the CMC cannot exchange active power among a plurality of CMCs like HVDC and BTB. In [Non-Patent Document 2], CMC unit cells connected to different systems are connected by a DC / DC converter insulated by a transformer so that active power can be accommodated in a system using CMC. Is disclosed.

  However, the power conversion system disclosed in [Non-Patent Document 2] requires a DC / DC converter. Furthermore, since the DC / DC converter has different cell potentials, insulation by a transformer is essential, and the system becomes large.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a transformerless CMC converter system capable of accommodating active power between CMC converters connected to a plurality of systems without being insulated by a DC / DC converter or other transformers. For the purpose.

  In order to achieve the above object, a power conversion device of the present invention includes a first multi-level converter connected to a first power system via a first connection reactor, and a second power system. A second multi-level converter linked via two linked reactors, a first Y-connection reactor linked to the first power grid, and a second Y linked to the second power grid A connection reactor, a neutral point of the first multi-level converter and a neutral point of the second multi-level converter are connected; and a neutral point of the first Y-connection reactor and the second point A neutral point of the Y connection reactor is connected, and the neutral point of the first and second multi-level converters and the neutral point of the first and second Y connection reactors are DC-linked. It is characterized by that.

  Moreover, in order to achieve the said subject, the power converter device of this invention is connected to the 1st electric power system via the 1st interconnection reactor, The 1st multi-level converter, The 2nd electric power system A second multi-level converter linked to the second power reactor, a first Y-connection reactor linked to the first power system, and a second power level linked to the second power system. A Y-connection reactor, a neutral point of the first multi-level converter and a neutral point of the second Y-connection reactor, and a neutral point of the first Y-connection reactor and the second The present invention is characterized in that a configuration for connecting neutral points of two multi-level converters is provided.

  Furthermore, the power conversion device of the present invention is characterized in that the unit cell of the multilevel converter is constituted by a bidirectional chopper circuit.

  Furthermore, the power conversion device of the present invention is characterized in that the unit cell of the multilevel converter is configured by a full bridge circuit.

  According to the present invention, since a DC / DC converter and a transformer are not required in a power conversion device that accommodates active power, the system can be reduced in size and weight.

The circuit diagram which shows the 1st, 2nd embodiment of this invention. The circuit diagram which shows a part of 2nd, 4th embodiment of this invention. The circuit diagram which shows a part of 1st, 3rd embodiment of this invention. The circuit diagram which shows the 2nd, 4th embodiment of this invention.

[Example 1]
A first embodiment for carrying out the present invention will be described.

  In the first embodiment of the present invention, there is an effect that the DC / DC converter required in [Non-Patent Document 2] can be eliminated.

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

  The power conversion system of the present invention has two three-phase interconnected reactors 201a and 201b and two three-phase Y-connection reactors 202a and 202b. The three-phase connected reactors 201a and 201b are connected to CMCs 105a and 105b, respectively. On the other hand, the Y-connection reactor 202a and the Y-connection reactor 202b are configured such that the neutral points are connected at the connection point 300. Further, the neutral points of the CMC 105 a and the CMC 105 b are connected at the connection point 301.

  The CMCs 105a and 105b are converters in which a bidirectional chopper circuit 120C (see FIG. 3) and a full bridge circuit 120F (see FIG. 4) are used as unit cells 120 and their input / output terminals are connected in cascade. Each of the CMCs 105a and 105b connected to the systems 100a and 100b has a configuration in which three CMC legs are connected to the Y connection. Each of the CMC legs 103aU to 103bW has a configuration in which the unit cells 120 are connected in cascade.

  In the present embodiment, the circuit configuration of the unit cell 120 will be described with reference to FIG. 3 on the assumption that the unit cell is a bidirectional chopper 120C.

  The bidirectional chopper circuit 120C includes an IGBT leg 411 composed of an IGBT parallel body 402P and an IGBT parallel body 402N, and a DC capacitor 406 connected to the IGBT leg 411. The anode and cathode of the IGBT parallel body 402N function as the input / output terminal 400P and the input / output terminal 400N of the unit cell 120, respectively.

  The input / output terminals 400P and 400N of the unit cell 120 also function as the input / output terminals 500P (500aUP to 500bWP) and 500N (500aUN to 500bWN) of the CMC legs, and the unit cells 120 arranged at both ends of each CMC leg. Except for the input / output terminals 400P and 400N, the input / output terminal 400N of each unit cell 120 used in plurality is the input / output terminal 400P of the other unit cell 120, and the input / output terminal 400P of each unit cell is that of the other unit cell 120. The input / output terminal 400N is connected in cascade.

  The high-voltage input / output terminals 500P (500aUP to 500aWP) of the CMC legs 113 (113aU to 113aW) constituting the CMC 105a are electrically connected to the terminals of the three-phase interconnected reactor 201a, respectively. Similarly, each high-voltage input / output terminal 500P (500bUP to 500bWP) of each CMC leg 113 (113bU to 113bW) constituting the CMC 105b is electrically connected to each terminal of the three-phase interconnection reactor 201b. The low-voltage input / output terminals 500N (500aUN to 500bWN) of each CMC leg 113 (113aU to 113bW) are electrically connected to the low-voltage input / output terminals 500N (500aUN to 500bWN) of other CMC legs 113 at the neutral point 301. Is done.

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

  First, clarify the definition of each voltage. A voltage between the neutral point 301 and the neutral point 301 is defined as a neutral point voltage. Further, a voltage between the neutral point 300 and the high-voltage side input / output terminal 500P (500aUP to 500bWP) of each CMC leg 113 is defined as a CMC leg output voltage.

  Further, the phase voltage of each system 100a, 100b with respect to the neutral point 300 is defined as the system phase voltage.

  Further, as a neutral point 301 reference, the potential of the input / output terminal 500P (500aUP to 500bWP) on the high voltage side of each CMC leg 113 (113aU to 113bW), that is, between the input / output terminals 500P and 500N of the CMC leg 113. The voltage is defined as the CMC leg voltage.

  When the CMC converter system 101 exchanges power with the system 100, a current flows between the CMC converter system 101 and the system 100.

  Each phase output current flowing from the CMC converter system 101 to the system 100a has the relationship of the formula (1). Equation (1) shows the relationship between the output current and voltage of an arbitrary phase.

    Output current = (CMC leg output voltage−system phase voltage) / impedance of system interconnection reactor 201a (1)

  In Formula (1), since the impedance of the grid interconnection reactor 201a can be normally regarded as a fixed value, in order to control the output current, it is only necessary to detect the system phase voltage and control the CMC leg output voltage based on it. . The CMC leg output voltage of each phase has the relationship of Formula (2).

    CMC leg output voltage = neutral point voltage + CMC leg voltage (2)

  Among the terms of equation (2), the absolute value of the voltage between the neutral points can be calculated by using the legs of the CMCs 105a and 105b (113aU) if the impedances of the interconnection reactors 201a and 201b and the Y-connection reactors 201a and 201b are equal. , 113aV, 113aW, 113bU, 113bV, 113bW) equal to the average value of the CMC leg voltages. Each CMC leg voltage is the sum of the output voltages of the unit cells 120 constituting each CMC leg 113 and can be controlled by the output voltage of each unit cell 120. The output voltage of each unit cell 120 is controlled by so-called PWM control that compares the voltage command with a triangular wave to generate a gate pulse, and the input / output terminals 400P and 400N of the unit cell 120 correspond to the voltage command value voltage. Can output pulse voltage.

  Therefore, the output current can be controlled as follows from the equations (1) and (2).

  The CMC leg output voltage of the CMC leg 113 is detected by adjusting the CMC leg voltage of the target CMC leg 113 while detecting each system phase voltage and adjusting the total sum of the CMC leg voltages to be substantially constant. Can be controlled to output an arbitrary current to the system 100. (For example, an arbitrary U-phase current can be output to the system 100a by controlling the output voltage of the CMC leg 113aU).

  Even if the CMC leg output voltage of the CMC leg 113 is controlled by detecting each system phase voltage and the voltage between the neutral points and adjusting the CMC leg voltage of the target CMC leg 113, an arbitrary current is generated. It can be output to the system 100a (for example, an arbitrary U-phase current can be output by controlling the output voltage of the CMC leg). Thus, since the power converter of the present invention, that is, the CMC converter system 101 can output an arbitrary current, it is possible to realize the interchange of active power between the system 100a and the system 100b without a transformer.

[Example 2]
The configuration of the CMC converter system 101 of the second embodiment of the present invention can be represented in FIG. 1 as in the first embodiment. In the first embodiment, each unit cell is composed of the bidirectional chopper circuit 120C, whereas the second embodiment is different only in that each unit cell is composed of the full bridge circuit 120F.

  FIG. 4 shows a full bridge circuit 120F constituting the unit cell 120 according to the second embodiment of the present invention. 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 as in the first embodiment. 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 the input / output terminals 400 (400L, 400R) of each unit cell are cascade-connected.

  Next, the operation of the CMC converter system 101 of this embodiment will be described-. Since this embodiment is basically the same as the first embodiment except that each IGBT leg 411 can output positive and negative voltages, only the operation of the unit cell 120 will be described.

  The IGBT leg 411 of each full bridge circuit 120F constituting the unit cell 120 is controlled by so-called PWM control as in the first embodiment. Each of the IGBT leg 411L and the IGBT leg 411R constituting the full bridge performs PWM modulation by giving a voltage command value that is inverted between positive and negative. A pulse voltage corresponding to the voltage difference between the voltage command values is output to the terminal of the full bridge circuit 120F. Since the output voltage of the single cell is the difference voltage between the IGBT leg 411L and the IGBT leg 411R, in the first embodiment, the unit cell can output only zero or positive voltage, but outputs positive and negative voltage. Therefore, the power conversion device 101 using the CMC of this embodiment has an advantage of being able to output a neutral point voltage between both positive and negative polarities. When a short circuit accident occurs between the neutral points 300 and 301, the neutral point voltage can be reduced to zero to prevent the accident from expanding.

  Note that the terminal called the high voltage side input terminal 500P of the CMC leg 113 in the first embodiment is not necessarily the high voltage side in the present embodiment. In this case, 500P corresponds to a connection point between the interconnection reactor 201 and the CMC 105. Similarly, each terminal called the low voltage side input terminal 500N of the CMC leg 113 in the first embodiment is not necessarily the low voltage side in the present embodiment. 500 N corresponds to a connection point between the neutral point 301 and each CMC 105.

  Since the unit cell 120 according to the second embodiment has a higher degree of freedom in output voltage than the unit cell according to the first embodiment, the power conversion apparatus according to the present invention, that is, the power conversion 101 of the CMC, is arbitrary as in the first embodiment. A current can be output, and it is possible to realize the interchange of active power between the system 100a and the system 100b without a transformer.

Example 3
In the first embodiment, when the zero phase voltages of the two systems (100a and 100b) connected to the CMC converter system 101 are different, a zero phase current flows between the two systems. However, in the third embodiment, the flow of the zero-phase current can be suppressed.

  First, the configuration of the CMC converter system 101 of the third embodiment will be described with reference to FIG.

  Similar to the first embodiment, the CMC converter system 101 of the present invention has two interconnected reactors 201a and 201b and Y-connections 202a and 202b, and via the interconnected reactors, the systems 100a and 100b Connected. Of the interconnected reactors, interconnected reactors 201a and 201b are connected to CMC converters 105a and 105b, respectively. The point that the unit chopper cell 120 is composed of the bidirectional chopper 120C is the same as that of the first embodiment.

  On the other hand, the neutral point of each of the Y connection reactor 202a and the Y connection reactor 202b is connected to the neutral point of the CMC converter 105b and the neutral point of the CMC converter 105a, respectively, which is different from the first embodiment. .

  Hereinafter, the connection point between the Y connection reactor 202a and the CMC 105b is referred to as a neutral point 300b, and the connection point between the neutral point of the Y connection reactor 202b and the neutral point of the CMC converter 105a is referred to as a neutral point 300a.

  Next, the operation of the CMC converter system 101 of the third embodiment will be described.

  In the third embodiment, the potential of the neutral point 300b with respect to the neutral point 300a is defined as the neutral point voltage. Further, each potential of the CMC legs 113aU to 113aW of the CMC 105a with respect to the neutral point 300a and the connection points 500aUP to 500aWP of the interconnection reactor 201a is defined as a CMC leg output voltage A. Similarly, each potential at the connection points 500bUP to 500bWP between the CMC legs 113bU to 113bW of the CMC 105b and the interconnection reactor 201b is defined as a CMC leg output voltage B with the neutral point 300b as a reference.

  Further, a voltage generated at both ends of each CMC leg 113 (113aU to 113bW) is defined as a CMC leg voltage. In the third embodiment, the CMC leg output voltage is equal to the CMC leg voltage.

  Further, each phase potential at each connection point between the CMC conversion system 101 and the system 100a with the neutral point 300A as a reference is referred to as a system phase voltage A. Similarly, each phase potential at each connection point between the CMC conversion system 101 and the system 100b with the neutral point 300B as a reference is referred to as a system phase voltage B.

  The phase current flowing from the CMC converter system 101a to the system 100a has a relationship of the expression (3-1a) with each phase voltage.

    Phase current = (CMC leg output voltage A−system phase voltage A) / impedance of system interconnection reactor 201a (3-1a)

  Similarly, the phase current between the system 100b and the CMC converter system 101b has a relationship of Expression (3-1b).

    Phase current = (CMC leg output voltage B−system phase voltage B) / impedance of system interconnection reactor 201b (3-1b)

  In Formula (1), since the impedance of the grid interconnection reactor 201a can be normally regarded as a fixed value, in order to control the output current, it is only necessary to detect the system phase voltage and control the CMC leg output voltage based on it. .

  However, it is preferable to control the voltage between the neutral points so that no zero-phase current flows between the neutral point 300a and the system 100b and between the neutral point 300b and the system 100a. In order to prevent the flow of the zero-phase current, the average value of the CMC leg voltage of each CMC leg (113aU, 113aV, 113aW) of the CMC converter 105a is the difference voltage between the zero-phase voltages of the system 100a and the system 100b, the CMC converter The average value of the CMC leg voltage of each CMC leg (113bU, 113bV, 113bW) of 105b may be equal to the difference voltage between the zero-phase voltages of the system 100b and the system 100a.

  Therefore, if the average value of the CMC leg voltage is controlled to suppress the zero-phase current and the CMC leg voltage of any phase is individually controlled, the output current of the CMC can be controlled.

  Since the power conversion device, that is, the CMC converter system 101 of the present invention can output an arbitrary current, it is possible to realize the interchange of active power between the systems 100.

Example 4
The fourth embodiment is characterized in that each unit cell 120 of the third embodiment is constituted by a full bridge circuit 120F.

  In the third embodiment, each unit cell 120 is configured by a full bridge circuit 120F, whereas the fourth embodiment is different only in that each unit cell is configured by a bidirectional chopper circuit 120C. .

  The configuration of the CMC circuit 105 (105a and 105b) of the fourth embodiment is the same as that of the CMC circuit 105 of the second embodiment.

  In the third embodiment, the output voltage of the unit cell 120 can be zero or only a positive voltage can be output. On the other hand, the CMC converter system of the fourth embodiment can output both positive and negative voltages. As a voltage between the neutral points of the CMC converter system 101 that is a power converter, an effect of outputting positive and negative voltages can be obtained.

  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.

100a, 100b Three-phase power system 101 CMC converter system 105a, 105b CMC
113aU, 113aV, 113aW, 113bU, 113bV, 113bW CMC leg 120 Unit cell 201a, 201b Linked reactor 202a, 202b Y-connection reactor 300, 300a, 300b, 301 Neutral point 400L, 400R, 400P, 400N Unit cell input / output terminal 402P, 402N IGBT parallel body 406 DC capacitor 411, 411L, 411R IGBT leg 500aUP, 500aVP, 500aWP, 500bUP, 500bVP, 500bWP, 500aUN, 500aVN, 500aWN, 500bUN, 500bVN, 500bWN CMC leg input / output terminal

Claims (6)

A first multi-level converter connected to the first power system via a first connection reactor;
A second multi-level converter connected to the second power system via a second connection reactor;
A first Y-connection reactor connected to the first power system;
A second Y-connection reactor connected to the second power system;
Connecting a neutral point of the first multi-level converter and a neutral point of the second multi-level converter;
Connecting a neutral point of the first Y-connection reactor and a neutral point of the second Y-connection reactor;
A power conversion apparatus comprising: a DC link between a neutral point of the first and second multilevel converters and a neutral point of the first and second Y-connection reactors. In the power converter device of Claim 1,
A power conversion device, wherein a unit cell of the multi-level converter is formed of a bidirectional chopper circuit. In the power converter device of Claim 1,
A power conversion device, wherein a unit cell of the multilevel converter is constituted by a full bridge circuit. A first multi-level converter connected to the first power system via a first connection reactor;
A second multi-level converter connected to the second power system via a second connection reactor;
A first Y-connection reactor connected to the first power system;
A second Y-connection reactor connected to the second power system;
Connecting a neutral point of the first multi-level converter and a neutral point of the second Y-connection reactor,
A power conversion device comprising a configuration for connecting a neutral point of the first Y-connection reactor and a neutral point of the second multi-level converter. In the power converter of Claim 4,
A power conversion device, wherein a unit cell of the multi-level converter is formed of a bidirectional chopper circuit. In the power converter device of Claim 5,
A power conversion device, wherein a unit cell of the multilevel converter is constituted by a full bridge circuit.