JP5145124B2 - Power converter - Google Patents

Description

  The present invention relates to a multiplex power converter.

  For example, when driving a high-power motor that drives a large-capacity fan, pump, blower, etc. at a variable speed, a plurality of one cell unit consisting of an inverter circuit in which a bridge circuit is formed by a plurality of switching elements are connected in series. Multiple-type power converters that are connected to increase the voltage are used. However, if one of the switching elements in the cell unit fails during the operation of the apparatus, the cell unit having the failed switching element is opened, and the operation of the apparatus in which the cell units are connected in series cannot be continued.

  As a means for solving such a problem, for example, a control method described in Patent Document 1 is known. According to this, when one of the switching elements constituting the inverter circuit of the cell unit has an open failure, the current is bypassed by forcibly turning on or off the other switching element corresponding to the open failure. The route to do is secured. Thereby, it is possible to prevent the failed cell unit from being opened, and to continue the operation of the apparatus.

JP 2004-357427 A

  However, according to Patent Document 1, the switching elements that are forcibly turned on or off differ depending on the direction of current and which switching element has failed. For this reason, a control circuit for specifying a switching element to be forcibly turned on or off becomes complicated, so that the configuration of the apparatus becomes complicated, and there is a concern that the reliability is lowered accordingly.

  The problem to be solved by the present invention is to continue operation with a control circuit having a simpler configuration even if a cell unit fails.

  In order to solve the above-mentioned problem, the power conversion device of the present invention is formed by connecting the outputs of a plurality of cell units that convert input alternating current into arbitrary voltage and frequency in series, and each cell unit rectifies the input alternating current. A switching control circuit for controlling on / off of each switching element of each cell unit, comprising an inverter circuit having a circuit, a plurality of switching elements connected in a single-phase bridge, and a return diode connected in parallel to each switching element In the power conversion device, each cell unit includes a switch that detects an overcurrent of the input alternating current and interrupts the input alternating current, and a failure detection circuit that detects a failure of the cell unit, and the switching control circuit includes: Outputs a command to turn on all the switching elements of the cell unit according to the failure detection signal of the failure detection circuit. It is characterized in.

  That is, for example, when the switching element is short-circuited, all the switching elements of the short-circuited inverter circuit are turned on, so that current paths in both positive and negative directions passing through the switching element and the return diode are formed. The current path is formed even if any switching element is short-circuited. On the other hand, when an open circuit failure occurs in the switching element, all the switching elements except the open circuit switching element of the inverter circuit in the open circuit failure are turned on. A path is formed. The current path is formed even if any switching element has an open failure. Thereby, even if the switching element of the inverter circuit in the cell unit is short-circuited or opened, the operation of the power conversion device can be continued. In any case, the switch is opened and the input AC is cut off due to the overcurrent caused by the failure or the overcurrent caused by turning on all the switching elements. Since such a current path is formed, it is possible to operate the power conversion apparatus with a cell unit other than the failed cell unit without providing a circuit for bypassing the cell unit and without specifying a failed switching element. Can continue.

  In this case, the input alternating current is a three-phase alternating current, and it is also possible to configure a power conversion system in which cell unit groups connected in series are provided for three phases and the cell unit groups are star-connected.

  In addition, the failure detection circuit detects the output voltage of the cell unit, and detects a failure when the deviation between the output voltage and the voltage preset in the cell unit (set voltage) exceeds the set value. It can also be configured to generate a signal. In addition to the failure of the switching element of the inverter circuit described above, the failure of the cell unit includes the failure of the rectifier circuit and the freewheeling diode. Thus, any failure can be detected. Regardless of which failure occurs, current paths in both positive and negative directions can be formed according to the present invention.

  According to the present invention, even if a cell unit fails, the operation can be continued by a control circuit having a simpler configuration.

  Hereinafter, the Example of the power conversion system 1 of this invention is described. In the following description, the same functional parts are denoted by the same reference numerals, and redundant description is omitted.

  FIG. 1 is a configuration diagram of a power conversion system 1 of the present embodiment. As shown in FIG. 1, the power conversion system 1 converts a three-phase lead-in wire 2, a multiple transformer 4, and a three-phase alternating current into an arbitrary target voltage and frequency (single-phase alternating current in this embodiment). A plurality (15 in this embodiment) of cell units 6 and a load 8 are provided. The multiplex transformer 4 has a plurality (15 in this embodiment) of secondary windings, the primary windings are connected to the three-phase lead-in wires 2, and the secondary windings are connected to each cell unit 6. It is connected. In the cell unit 6, a plurality of (in this embodiment, five) outputs are connected in series to constitute a cell unit group 10. The cell unit group 10 is star-connected as U-phase, V-phase, and W-phase, and includes a load 8 at one end.

  FIG. 2 is a configuration diagram of the cell unit 6. The cell unit 6 is connected in a single-phase bridge with a rectifier circuit 12 formed by bridge-connecting a plurality of diodes, a smoothing circuit 13 connected in parallel to the output of the rectifier circuit 12 and connected in series with a plurality of smoothing capacitors. The inverter circuit 19 includes switching elements 14 a, 14 b, 14 c, 14 d and free-wheeling diodes 18 a, 18 b, 18 c, 18 d connected in parallel to the switching elements 14, and is connected in parallel to the output of the smoothing circuit 13. Moreover, the power conversion system 1 has a switching control circuit 20, and the switching control circuit 20 performs on / off control of the switching element 14 of each cell unit 6.

  Here, the structure which concerns on the characteristic of the present Example in the cell unit 6 is demonstrated. The cell unit 6 is connected to each phase and detects a fault of the cell unit 6 by a plurality of (three in this embodiment) fuses 21 that detect an input AC overcurrent and cut off the input AC. 22. The fuse 21 is opened when an overcurrent flows. The failure detection circuit 22 detects the output voltage of the cell unit 6, and generates a failure detection signal by determining a failure when a deviation between the output voltage and a voltage preset in the cell unit 6 exceeds a set value. Then, it is transmitted to the switching control circuit 20.

  The operation of this embodiment configured as described above will be described with reference to FIGS. The three-phase alternating current drawn by the three-phase lead-in wire 2 is changed to a desired voltage by the multiple transformer 4 and supplied to each cell unit 6. The supplied three-phase alternating current is input to the rectifier circuit 12 through the fuse 21 and rectified, and is smoothed by the smoothing circuit 13 to become direct current and flows to the inverter circuit 19. The switching control circuit 20 that controls the inverter circuit 19 performs on / off control of each switching element 14 by PWM control, converts the direct current flowing through the inverter circuit 19 into single-phase alternating current, and outputs the single-phase alternating current. The output single-phase alternating current is supplied to the load 8. The above-described operation is performed for each cell unit 6 based on a command from the switching control circuit 20. In this way, a voltage that is five times the voltage that can be output from one cell unit 6 can be supplied to the load 8 from each of the U, V, and W phases. In this embodiment, the required power is 12 cell units 6 and each cell can be rated output by 4 cell units 6, but normally the rated output is maintained by 5 cell units 6. Yes. When one cell unit 6 fails, the switching control circuit 20 switches control so that the other four normal cell units 6 in the same phase can perform rated output.

  Here, the operation according to the feature of the present embodiment will be described with reference to FIGS. FIG. 3 is a circuit diagram showing an example of a current path when the switching element 14a has a short-circuit fault. FIG. 4 is a circuit diagram showing an example of a current path when the switching element 14a has an open fault. FIG.

  When one cell unit 6 fails, the failure detection circuit 22 provided in the cell unit 6 detects the failure and outputs a failure detection signal to the switching control circuit 20. The switching control circuit 20 continues to output a command to turn on all the switching elements 14 of the failed cell unit 6 in accordance with the failure detection signal. As a result, a current path is formed, and the output of the inverter circuit 19 is not opened. Since the fuse 21 is opened due to an overcurrent due to a failure or an overcurrent caused by turning on all the switching elements, the power of the multiple transformer 4 is not supplied to the failed cell unit 6.

  Here, an example of the formed current path will be described separately for a short circuit failure and an open failure. In order to simplify the description, only one example of current paths is shown, but the number of current paths is not limited to one. When the short-circuit failure occurs in the switching element 14a, the current path shown in FIG. 3 is formed. The current path A is a flow from the terminal 24b to the terminal 24a through the freewheeling diode 18b and the short-circuited switching element 14a. The current path B is a flow from the terminal 24a to the terminal 24b through the free wheeling diode 18a and the switching element 14b in the on state. In this way, it is possible to deal with currents in both positive and negative directions from the terminal 24b to the terminal 24a and from the terminal 24a to the terminal 24b. In addition, even if any of the switching elements 14 causes a short circuit failure or a plurality of switching elements 14 cause a short circuit failure, a current path is formed.

  Next, when the switching element 14a has an open failure, the current path shown in FIG. 4 is formed. The current path C is a flow from the terminal 24b to the terminal 24a through the switching element 14d in the on state and the free wheeling diode 18c. The current path D is a flow from the terminal 24a to the terminal 24b via the ON switching element 14c and the freewheeling diode 18d. In this way, it is possible to deal with currents in both positive and negative directions from the terminal 24b to the terminal 24a and from the terminal 24a to the terminal 24b. Even if any switching element 14 causes an open failure, a current path is formed. Furthermore, even if the switching element 14a and the switching element 14c or the switching element 14b and the switching element 14d cause an open failure, a current path is formed.

  Further, the same applies to the case where the rectifier circuit 12 fails. By turning on all the switching elements 14, current paths in both positive and negative directions are formed.

  Further, in the case where the free-wheeling diode 18 is short-circuited, for example, if the free-wheeling diode 18a is short-circuited, a current path similar to that in FIG. 3 when the switching element 14a is short-circuited is formed. In the case where the freewheeling diode 18 has an open failure, for example, if the freewheeling diode 18a has an open failure, a current path similar to that in FIG. 4 when the switching element 14a has an open failure is formed.

  When both the switching element 14a and the freewheeling diode 18a are short-circuited, a current path similar to that in FIG. 3 is formed. Further, when both the switching element 14a and the freewheeling diode 18a fail to open, a current path similar to that in FIG. 4 is formed. When the switching element 14a is short-circuited and the freewheeling diode 18a is open, the current path is a flow from the terminal 24b to the terminal 24a via the freewheeling diode 18b and the shorted switching element 14a. One current path is a flow from the terminal 24a to the terminal 24b through the ON switching element 14c and the freewheeling diode 18d. When the switching element 14a has an open failure and the free wheel diode 18a has a short circuit failure, a current path similar to that of FIG. 4 is formed.

  As described above, when the switching element 14 is short-circuited, all the switching elements 14 of the short-circuited inverter circuit 19 are turned on, so that a current path in both positive and negative directions passing through the switching element 14 and the freewheeling diode 18 is formed. . The current path is formed even if any of the switching elements 14 is short-circuited, and is formed even if a plurality of switching elements 14 are short-circuited. On the other hand, when the switching element 14 has an open failure, similarly, all the switching elements 14 except the open failure switching element of the inverter circuit 19 in which the open failure has occurred are turned on. Current paths in both positive and negative directions are formed. The current path is formed even if any of the switching elements 14 has an open failure, and is formed even if a plurality of switching elements 14 have an open failure. Thereby, even if the switching element 14 of the inverter circuit 19 in the cell unit 6 is short-circuited or opened, the operation of the power conversion system 1 can be continued. In any case, the fuse 21 is opened due to an overcurrent caused by the failure or an overcurrent caused when all the switching elements 14 are turned on, and the input AC is cut off. Since such a current path is formed, a circuit for bypassing the cell unit 6 is not provided, and a faulty switching element is not specified. Driving can be continued.

  Even when a failure occurs in the rectifier circuit 12 and the freewheeling diode 18, current paths in both positive and negative directions can be formed according to the present invention.

  The power conversion system 1 according to the present embodiment has been described above, but the present invention is not limited to this embodiment, and can be applied by appropriately changing the configuration. For example, in this embodiment, the rated output is maintained by the five cell units 6 for each phase in preparation for the case where the cell unit 6 breaks down. The cell unit 6 may be a standby system. In this case, the standby cell unit 6 is not normally operated, and only passes any voltage and frequency output from the other cell units 6.

  Further, in this embodiment, when two in-phase cell units 6 fail, the output of the phase becomes three cell units 6. In this case, the switching control circuit 20 can be configured to control the output of the other phases to be equal to that of the three cell units 6, and the operation can be continued by balancing the outputs of the respective phases.

  Further, in the present embodiment, the failure is detected from the output of the cell unit 6, but the failure of each circuit may be detected by the change in the output of the rectifier circuit 12 or the inverter circuit 19. Moreover, you may comprise so that the failure of each element may be detected by the change of the voltage of the switching element 14 or the free-wheeling diode 18.

It is a block diagram of the power conversion system of a present Example. It is a block diagram of a cell unit. It is an example of the circuit diagram which shows the electric current path when a switching element raise | generates a short circuit failure. It is an example of the circuit diagram which shows the electric current path when a switching element raise | generates an open failure.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Power conversion system 2 Three-phase lead-in line 4 Multiple transformer 6 Cell unit 8 Load 10 Cell unit group 12 Rectifier circuit 13 Smoothing circuit 14a, 14b, 14c, 14d Switching element 18a, 18b, 18c, 18d Free-wheeling diode 19 Inverter circuit 20 Switching control circuit 21 Fuse 22 Fault detection circuit 24a, 24b Terminal

Claims (3)

Outputs of a plurality of cell units that convert input alternating current into arbitrary voltage and frequency are connected in series, and each cell unit includes a rectifier circuit that rectifies the input alternating current, and a plurality of switching elements connected in a single-phase bridge. And an inverter circuit having a free-wheeling diode connected in parallel to each switching element, and a power conversion device including a switching control circuit that controls on / off of each switching element of each cell unit,
Each of the cell units includes a switch that detects an overcurrent of the input alternating current and interrupts the input alternating current, and a failure detection circuit that detects a failure of the cell unit, and the switching control circuit includes: A power converter that outputs a command to turn on all the switching elements of the cell unit in accordance with a failure detection signal. In claim 1,
The input alternating current is a three-phase alternating current, and includes a series of cell unit groups connected in series for three phases, and the cell unit group is a star-connected power conversion system. In claim 1,
The failure detection circuit detects an output voltage of the cell unit, and determines a failure when a deviation between the output voltage and a voltage preset in the cell unit exceeds a set value, and outputs the failure detection signal. A generated power conversion device or power conversion system.

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