JP2014207728A - Power conversion device, direct current power transmission system, and power conversion device control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stop a plurality of unit converters in a short time when it was detected that overcurrent flowed through a group of the unit converters.SOLUTION: A power conversion device 102a comprises a plurality of groups of unit converters 106 in each of which groups a plurality of unit converters 108 each comprising a switching element allowing the voltage of a capacitor to output are connected in series, and converts system current, which is alternate current, into direct current or direct current into alternate current. The power conversion device comprises: an arm voltage command value generating unit 311 for generating and outputting a command value to the unit converters 108; an overcurrent detection unit 117 for detecting overcurrent flowing through the group of unit converters 106; and a communication interface unit 118 that transmits an operation command frame to each unit converter 108 at a prescribed cycle on the basis of the command value generated by the arm voltage command value generating unit 311, and that transmits a stop command frame for emergency stop to each unit converter 108 not depending on the prescribed cycle if the overcurrent detection unit 117 detected overcurrent.

Description

  The present invention relates to a power conversion device including a plurality of unit converter groups in which a plurality of unit converters each including a semiconductor switching element and a capacitor are connected in series, a DC power transmission system, and a method for controlling the power conversion device.

  In recent years, power converters that convert alternating current to direct current or direct current to alternating current have been widely used. Such a power conversion device is also applied to the field of high voltage, and for example, there is one configured by connecting a plurality of unit converters each including a semiconductor switching element and a capacitor in series.

  In a power converter applied to the field of high voltage, for example, an arm is constituted by a unit converter group in which unit converters are connected in series. The power conversion device connects one end of each arm to each phase of the AC terminal, connects the other end of each arm to the positive DC terminal or the negative DC terminal, and controls each unit converter. By controlling the current flowing through each arm, power is mutually converted between the AC terminal and the DC terminal.

  The summary of Patent Document 1 states that “when a power converter configured by connecting a plurality of cells using semiconductor switching elements in a cascade configuration is controlled, communication between the plurality of cells and the central controller is necessary. However, the increase in the number of cells increases the amount of communication information and the load of information processing. An object of the present invention is to reduce the amount of information communicated between each cell and the central controller. As a means for solving the problem, “the power conversion device of the present invention includes a plurality of arms configured by connecting a plurality of cells in cascade, and communicates with a central control device configuring the cells. As a result, “In the power conversion device of the present invention, the power of the cell control device of each cell is supplied from the main circuit, thereby providing each cell with the function of supplying power from the main circuit.” By major component is no longer able to communicate with the cell controller of the corresponding cell when failed, the central control unit that the corresponding cell has failed is described as possible. "Recognition.

  When an overcurrent occurs in any of the arms due to a system fault or the like, the power conversion device needs to immediately stop the semiconductor switching element of each unit converter in order to prevent its own failure. In the conventional low-voltage power converter, each unit converter is arranged at a medium / low-voltage potential with respect to the ground potential. The unit converter controller that controls the unit converter is disposed in or near the control device that detects overcurrent. The control device and the unit converter controller are connected by an electric cable. Therefore, since the control device can transmit an electrical signal to a large number of unit converter controllers at a time, it can quickly transmit a stop command for the semiconductor switching element to each unit converter.

JP2011-193615A

However, in a power converter of a system in which unit converters for high voltage or extra high voltage are connected in series, each unit converter and unit converter controller are at a high voltage potential with respect to the ground potential. The unit converter controller for controlling the detector is arranged at a distance from the control device for detecting overcurrent and is electrically insulated. The controller and the unit converter controller are connected by an optical fiber. The control device transmits a control command value at a predetermined control cycle to each of the many unit converter controllers, and each unit converter controller controls the semiconductor switching element of each unit converter. Therefore, since the control device cannot command each unit converter at a high speed, it is difficult to promptly transmit a stop command for the semiconductor switching element.
In other words, power converters with a high-voltage or extra-high-voltage unit converter connected in series will cause a stop command to be sent to all unit converters at a high speed due to communication and control delays, just like low-voltage power converters. I can't tell you. Therefore, there is a possibility that the power conversion device of the system in which unit converters for high voltage or extra high voltage are connected in series may take time to stop all the unit converters even if it detects that an overcurrent has flowed. there were.

  Therefore, the present invention provides a power conversion device, a DC power transmission system, and a power conversion capable of stopping a plurality of unit converters in a short time when it is detected that an overcurrent flows through the unit converter group. It is an object of the present invention to provide a method for controlling an apparatus.

In order to solve the above-mentioned problem, in the invention according to claim 1 of the present invention, a plurality of unit converters each having a plurality of switching elements capable of outputting the stored energy accumulated by the electrical energy storage means are connected in series. A plurality of unit converter groups, which convert power from a system current that is alternating current into direct current, or direct current into alternating current, generate a command value for each of the unit converters, and the unit Based on the command value generated by the command value generated by the command value generation unit and the overcurrent detection unit that detects the overcurrent flowing through the converter group, the operation command frame is transmitted to each unit converter at a predetermined period, and the overcurrent detection is performed. A communication interface unit that transmits a stop command frame to each of the unit converters when the unit detects an overcurrent, the power conversion device comprising: .
Other means will be described in the embodiment for carrying out the invention.

  According to the present invention, when it is detected that an overcurrent flows through the unit converter group, the power converter, the DC power transmission system, and the power conversion capable of stopping a plurality of unit converters in a short time An apparatus control method can be provided.

1 is a schematic configuration diagram showing a DC power transmission system in a first embodiment. It is a figure which shows the circuit structure of the bidirectional | two-way chopper type unit converter in 1st Embodiment. It is a figure which shows the logic structure of the control part in 1st Embodiment. It is a figure which shows the logic structure of the command value distribution part in 1st Embodiment. It is a figure which shows the logic structure of the overcurrent detection part in 1st Embodiment. It is a state transition diagram of the communication interface unit in the first embodiment. It is a sequence diagram at the time of the overcurrent detection in 1st Embodiment. It is a sequence diagram at the time of overcurrent detection and resumption in the first embodiment. It is a sequence diagram at the time of overcurrent detection in a comparative example. It is a figure which shows the circuit structure of the full bridge type | mold unit converter in 2nd Embodiment.

Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings.
(First embodiment)
FIG. 1 is a schematic configuration diagram showing a DC power transmission system 100 according to the first embodiment.
The DC power transmission system 100 includes a power conversion device 102a and a power conversion device 102b. In the DC power transmission system 100, a power conversion device 102a and a power conversion device 102b are connected between an AC system 101a and an AC system 101b. The power converter 102a includes a positive DC terminal Pa and a negative DC terminal Na. The power converter 102b includes a positive DC terminal Pb and a negative DC terminal Nb. Between the power converter 102a and the power converter 102b, a positive DC terminal Pa and a positive DC terminal Pb are connected, and a negative DC terminal Na and a negative DC terminal Nb are connected. ing. The connection of the positive DC terminals Pa and Pb and the connection of the negative DC terminals Na and Nb constitute a DC system (DC transmission line). Here, it is assumed that the voltages of the positive DC terminals Pa and Pb are higher than the voltages of the negative DC terminals Na and Nb.

The DC power transmission system 100 supplies, for example, power of an AC system 101a that is a first AC system to an AC system 101b that is a second AC system. The DC power transmission system 100 converts alternating current into direct current in the power conversion device 102a that is the first power conversion device, and converts direct current in the power conversion device 102b that is the second power conversion device via the direct current system. Convert to alternating current.
The DC power transmission system 100 includes a power conversion device 102a as a first power conversion device connected to one end side of the DC power transmission line, and as a second power conversion device connected to the other end side of the DC power transmission line. A power converter 102b is provided. The DC power transmission system 100 converts an alternating current input to the power conversion device 102a into a direct current, reconverts the alternating current into an alternating current by the power conversion device 102b, and outputs the alternating current or outputs an alternating current input to the power conversion device 102b. It converts into direct current, reconverts it into alternating current with the power converter 102a, and outputs.
These power conversion devices 102a and 102b are connected to the control devices 150a and 150b through various signal lines. The control devices 150a and 150b include similar control units 112a and 112b, respectively.
Next, the configuration of the power converters 102a and 102b will be described. Since these are almost the same configuration, here, the power converter 102a will be mainly described.

  The power conversion device 102a includes an AC voltage sensor 110, an initial charging device 120, a circuit breaker 121, a transformer 130, an arm 105 for each phase (an R-phase arm 105R, an S-phase arm 105S, and a T-phase arm). 105T), an AC current sensor 140, a control device 150a, a capacitor voltage detection line 114, a DC voltage sensor 115, and an operation command signal line 116.

  The power converter 102a is connected to the AC system 101a via an internal circuit breaker 121. In the first embodiment, the AC system 101a side of the transformer 130 is a primary side, and each line is a primary side terminal R, S, T. Further, the secondary side positive side of each phase of the transformer 130 is set as the secondary side positive terminals Ra, Sa, Ta, and the secondary side negative side of each phase of the transformer 130 is set as the secondary side negative terminal Nx. (Negative DC terminal Na). The power conversion device 102a converts AC system currents IR, IS, IT to DC, or DC to AC.

The R-phase arm 105R includes a unit converter group 106R and an arm current sensor 111, which are connected in series. In the unit converter group 106R, M (M is a natural number of 2 or more) bidirectional chopper type unit converters 108 are connected in series.
The S-phase arm 105S includes a unit converter group 106S and an arm current sensor 111, which are connected in series. In the unit converter group 106S, M unit converters 108 are connected in series.
The T-phase arm 105T includes a unit converter group 106T and an arm current sensor 111, which are connected in series. In the unit converter group 106T, M unit converters 108 are connected in series. The unit converter 108 may have other configurations such as a full bridge type (see FIG. 10) instead of the bidirectional chopper type.

The output side of the arm current sensor 111 is connected to the control unit 112a. The arm current sensor 111 measures the current flowing through each arm 105 and outputs it to the control unit 112a.
The output side of the DC voltage sensor 115 is connected to the control unit 112a. The DC voltage sensor 115 measures a voltage applied between the positive DC terminal Pa and the negative DC terminal Na and outputs the voltage to the control unit 112a as the voltage VDC.

  The operation command signal line 116 is, for example, an optical fiber, and connects the control unit 112a and each unit converter 108, respectively. The control unit 112a controls the operation of each unit converter 108 by the operation command signal line 116.

  The capacitor voltage detection line 114 is, for example, an optical fiber, and connects each unit converter 108 and the control unit 112a. Each unit converter 108 converts the voltage signal of the capacitor 203 (see FIG. 2) into a digital signal, and transmits the digital signal to the control unit 112a via each capacitor voltage detection line 114. The control unit 112a detects the state of the unit converter 108 by the capacitor voltage detection line 114. The capacitor voltage detection line 114 and the operation command signal line 116 may be physically the same optical fiber.

  The AC voltage sensor 110 is connected to the AC system 101a. The output side of the AC voltage sensor 110 is connected to the control unit 112a. The AC voltage sensor 110 measures the system voltages VGR, VGS, VGT of the AC system 101a and outputs them to the control unit 112a.

Next, the internal configuration of the transformer 130 will be described.
The transformer 130 includes iron cores 131R, 131S, and 131T, windings 132RA, 132RB, and 132RC, windings 132SA, 132SB, and 132SC, and windings 132TA, 132TB, and 132TC, and further includes primary side terminals R and S. , T, secondary side positive terminals Ra, Sa, Ta, a secondary side negative terminal Nx, and an internal terminal Ny. The secondary negative terminal Nx is connected to a negative DC terminal Na that is a second DC terminal.

  A winding 132RB that is the first secondary winding and a winding 132TC that is the second secondary winding are wound around the iron core 131R by the same number of turns. Further, a winding 132RA, which is a primary winding, is wound around the iron core 131R in the same direction as the winding 132TC.

  A winding 132SB that is a first secondary winding and a winding 132RC that is a second secondary winding are wound around the iron core 131S by the same number of turns. Further, a winding 132SA, which is a primary winding, is wound around the iron core 131S in the same direction as the winding 132RC.

A winding 132TB that is a first secondary winding and a winding 132SC that is a second secondary winding are wound around the iron core 131T by the same number of turns. Further, a winding 132TA, which is a primary winding, is wound around the iron core 131T in the same direction as the winding 132SC.
The transformer 130 includes the plurality of iron cores 131R, 131S, and 131T.

  Hereinafter, when the iron cores 131R, 131S, and 131T are not particularly distinguished, they are simply referred to as the iron core 131. When the windings 132RA to 132TC are not particularly distinguished, they are simply referred to as windings 132. These windings 132 are wound in the same direction around the iron cores 131R, 131S, and 131T.

  In each iron core 131, the terminals in the direction of the secondary positive terminals Ra, Sa, Ta in the figure are called positive terminals. A terminal in the direction of the secondary negative terminal Nx (negative DC terminal Na) in the drawing is referred to as a negative terminal.

  Positive terminals of windings 132RA, 132SA, and 132TA are connected to primary terminals R, S, and T, respectively. The negative terminals of the windings 132RA, 132SA, 132TA are connected to each other and are star-connected (Y-connected). That is, the windings 132RA, 132SA, and 132TA, which are primary windings, are Y-connected to the AC system 101a.

  The positive terminals of the windings 132RB, 132SB, and 132TB that are the first secondary windings are the positive terminals of the windings 132RC, 132SC, and 132TC that are the second secondary windings wound around the iron cores 131 of different phases. Connected to the side terminal. The negative terminals of the windings 132RC, 132SC, 132TC, which are the second secondary windings, are all connected to the secondary negative terminal Nx (negative DC terminal Na).

One end of each phase arm 105R, 105S, 105T is connected to the positive DC terminal Pa, and the other end thereof is connected to the secondary positive terminals Ra, Sa, Ta.
The negative side terminals of the windings 132RB, 132SB, and 132TB, which are the first secondary windings, are connected to the secondary side positive terminals Ra, Sa, and Ta, respectively, and are connected to the other ends of the respective arms 105R, 105S, and 105T. It is connected.

Here, let us consider a case where the same DC current flows from the secondary positive terminals Ra, Sa, Ta to the secondary negative terminal Nx (negative DC terminal Na). In the iron core 131R, the magnetic flux generated in the winding 132RB and the magnetic flux generated in the winding 132TC are in the opposite direction and have the same strength, and thus cancel each other. In the iron core 131 </ b> S, the magnetic flux generated in the winding 132 </ b> SB and the magnetic flux generated in the winding 132 </ b> RC have opposite directions and the same strength, and thus cancel each other. In the iron core 131T, the magnetic flux generated in the winding 132TB and the magnetic flux generated in the winding 132SC are in opposite directions and have the same strength, and thus cancel each other.
Thereby, the power converters 102a and 102b can flow the current Idc of the DC system independently of the system currents IR, IS, and IT of the AC systems 101a and 101b.

  In the first embodiment, the windings 132RA, 132SA, and 132TA are respectively connected to the internal terminal Ny and are star-connected (Y-connected). However, the present invention is not limited to this, and the windings 132RA, 132SA, and 132TA may be configured as a delta connection (Δ connection).

  Between both terminals of the circuit breaker 121, the initial charging device 120 is connected in parallel. The initial charging device 120 is a device for initially charging the DC unit capacitor 203 (see FIG. 2) of the unit converter 108 constituting the power conversion device 102a. The initial charging device 120 is constituted by, for example, a series circuit of a resistor and a circuit breaker, operates before the circuit breaker 121 is turned on, and initially charges the capacitor 203 (see FIG. 2) of the unit converter 108. .

  One end of the R-phase arm 105 </ b> R is connected to the secondary side positive terminal Ra of the transformer 130. The other end of the R-phase arm 105R is connected to the positive DC terminal Pa (first DC terminal). The voltage output from the unit converter group 106R in the arm 105R is the output voltage VRa. An arm current IRa flows through the arm 105R in the direction from the secondary positive terminal Ra to the positive DC terminal Pa. In the output voltage VRa and the arm current IRa, the direction from the secondary positive terminal Ra to the positive DC terminal Pa is positive.

  One end of the S-phase arm 105 </ b> S is connected to the secondary side positive terminal Sa of the transformer 130. The other end of the S-phase arm 105S is connected to the positive DC terminal Pa (first DC terminal). The voltage output from the unit converter group 106S in the arm 105S is the output voltage VSa. An arm current ISa flows through the arm 105S in the direction from the secondary positive terminal Sa to the positive DC terminal Pa. In the output voltage VSa and the arm current ISa, the direction from the secondary positive terminal Sa to the positive DC terminal Pa is positive.

  One end of the T-phase arm 105T is connected to the secondary positive terminal Ta of the transformer 130. The other end of the T-phase arm 105T is connected to the positive DC terminal Pa (first DC terminal). The voltage output from the unit converter group 106T in the arm 105T is assumed to be the output voltage VTa. An arm current ITa flows through the arm 105T in the direction from the secondary positive terminal Ta to the positive DC terminal Pa. In the output voltage VTa and the arm current ITa, the direction from the secondary positive terminal Ta to the positive DC terminal Pa is positive.

  In the first embodiment, the turns ratio of the transformer 130 (windings 132RA, 132RB, 132TC), (windings 132SA, 132SB, 132RC), and (windings 132TA, 132TB, 132SC) are 2: 1: 1, respectively. It is. However, the present invention is not limited to this, and the turn ratio may be (X: 1: 1).

  Hereinafter, the structure of the control apparatus 150a with which the power converter device 102a is provided is demonstrated. In addition, the control apparatus 150b with which the power converter device 102b is provided is comprised similarly to the control apparatus 150a. Hereinafter, when the control devices 150a and 150b are not particularly distinguished, they may be simply referred to as the control device 150.

  The control device 150a receives signals from the AC voltage sensor 110, the DC voltage sensor 115, each arm current sensor 111, and the AC current sensor 140.

  The control device 150a takes in the capacitor voltage VCjkl (j = R, S, T, k = 1, 2,..., M, l = a, b) of the unit converter 108 via the capacitor voltage detection line 114. Yes. In the first embodiment, j indicates the type of arm 105 (j = R, S, T) among the symbols jkl attached to the capacitor voltage VC and the like. k indicates the order 1, 2,..., M in the arm 105. l indicates which of the power conversion devices 102a and 102b belongs to.

The control device 150 includes a control unit 112a that controls the power conversion device 102a. The control unit 112a includes an overcurrent detection unit 117, a communication interface unit 118, and an arm voltage command value generation unit 311. The output sides of the overcurrent detection unit 117 and the arm voltage command value generation unit 311 are connected to the communication interface unit 118. The output side of the communication interface unit 118 is connected to each unit converter controller 312 (see FIG. 2) that controls each unit converter 108 via the operation command signal line 116.
The arm voltage command value generation unit 311 (command value generation unit) calculates a command value for each unit converter 108 at a predetermined control cycle, generates a voltage command frame, and transmits it to the communication interface unit 118.

Based on the measured values of the arm currents IRa, ISa, and ITa, the overcurrent detection unit 117 detects an overcurrent that flows through any of the arms 105R, 105S, and 105T, and transmits the detection to the communication interface unit 118. Is.
The communication interface unit 118 transmits an operation command frame to each unit converter 108 at a predetermined control cycle based on the voltage command frame received from the arm voltage command value generation unit 311, and the overcurrent detection unit 117 detects the overcurrent. If detected, a stop command frame for emergency stop is transmitted to each unit converter 108 regardless of a predetermined control cycle. The configuration and operation of the control unit 112a will be described in detail with reference to FIG.

The physical distance from the control device 150 to the unit converter controller 312 of each unit converter 108 is separated, and is connected by an optical fiber for electrical insulation. For this reason, the control unit 112a serially transmits a command to each unit converter controller 312 for each control period, and thus it takes a predetermined time.
The power conversion device 102 a includes three arms 105 including M unit converters 108. The control device 150 calculates a command value for the 3M unit converters 108 at a predetermined control cycle, and transmits and controls an operation command frame. Therefore, these unit converters 108 are controlled in a predetermined control cycle in principle. Therefore, when an overcurrent flows through the arm 105 and the operation of the unit converter 108 has to be stopped urgently, if the emergency stop is transmitted at the timing of each control cycle, the switching elements 201H and 201L are broken. Therefore, it is necessary to control with a sequence different from the normal control sequence. This control sequence will be described in detail with reference to FIGS.

FIG. 2 is a diagram showing a circuit configuration of the unit converter 108 in the first embodiment.
Here, as a representative of each arm 105, the unit converter 108 in the arm 105R will be described. The unit converters 108 included in the arms 105S and 105T are configured in the same manner as the unit converters 108 in the arm 105R.
The unit converter 108 includes a plurality of switching elements 201H and 201L that can output the stored energy stored by the electric energy storage means. The power conversion device 102a includes a plurality of unit converter groups 106 in which a plurality of unit converters 108 are connected in series, thereby converting the system currents IR, IS, and IT, which are alternating currents, into direct current or power from direct current into alternating current. . Further, the unit converter 108 of the first embodiment is configured to stop the operation in a short time when a stop command frame for emergency stop is transmitted from the control unit 112a.

  The arm 105R includes a unit converter group 106R and an arm current sensor 111 that detects an arm current IRa that flows through the unit converter group 106R. One end of the arm 105R is connected to the positive DC terminal Pa. The other end of the arm 105R is connected to the secondary side positive terminal Ra. The unit converter group 106R includes a plurality of unit converters 108, which are configured to be connected in series.

The unit converter 108 includes a parallel circuit of a high-side switching element 201H and a free-wheeling diode 202H, a parallel circuit of a low-side switching element 201L and a free-wheeling diode 202L, a capacitor 203 serving as an electric energy storage unit, a voltage sensor 204, And a gate driver 205 for driving the switching elements 201H and 201L. The gate driver 205 is connected to the unit converter controller 312 via the signal line 113. The command value distribution unit 313 includes each unit converter controller 312.
The positive terminal 208 (first terminal) of the unit converter 108 is connected to the negative terminal 209 (second terminal) of the other unit converter 108 or the positive DC terminal Pa. . The negative terminal 209 (second terminal) of the unit converter 108 is connected to the positive terminal 208 of the other unit converter 108 or one end of the arm current sensor 111.

A parallel circuit of the switching element 201H and the freewheeling diode 202H and a parallel circuit of the switching element 201L and the freewheeling diode 202L are connected in series.
The collector of the switching element 201H is connected to one end of the capacitor 203. The collector of the switching element 201H is further connected to the cathode of the freewheeling diode 202H. The emitter of the switching element 201H is connected to the anode of the freewheeling diode 202H, and is further connected to the collector of the switching element 201L.

  The collector of the switching element 201L is connected to the emitter of the switching element 201H and the cathode of the freewheeling diode 202L. The emitter of the switching element 201L is connected to the anode of the freewheeling diode 202L, and is further connected to the other end of the capacitor 203. A voltage sensor 204 is connected to both ends of the capacitor 203.

  The negative terminal 209 of the unit converter 108 is connected to the emitter of the switching element 201L. A positive-side terminal 208 of the unit converter 108 is connected to a connection node between the collector of the switching element 201L and the emitter of the switching element 201H.

  The switching element 201H and the switching element 201L can output the energy stored in the capacitor 203 between the terminal 208 (first terminal) and the terminal 209 (second terminal). That is, the switching element 201H and the switching element 201L can output the voltage across the capacitor 203 between the terminal 208 (first terminal) and the terminal 209 (second terminal).

  The gate driver 205 (switching element driving unit) is connected to the unit converter controller 312 via the signal line 113. The output side of the gate driver 205 is connected to the gate and emitter of the switching element 201H, and is further connected to the gate and emitter of the switching element 201L.

  The gate driver 205 is a switching element driving unit of the unit converter 108, and is controlled by the unit converter controller 312 that receives the operation / stop command of the control unit 112a. The gate driver 205 can output the voltage of the capacitor 203 between the positive terminal 208 and the negative terminal 209 by switching the switching element 201H and the switching element 201L on and off. The output voltage Vjk between the terminal 208 and the negative terminal 209 is controlled.

  The freewheeling diode 202H and the freewheeling diode 202L are connected in series in a direction in which no current flows with respect to the capacitor voltage VCjk. The switching element 201H connected in parallel to the freewheeling diode 202H and the switching element 201L connected in parallel to the freewheeling diode 202L are attached in the direction of discharging the capacitor voltage VCjk when the respective switching states are on.

  In the first embodiment, the element connected to the capacitor 203 having the higher voltage is on the high side, and “H” is added to the end of the reference numeral. The element connected to the lower voltage of the capacitor 203 is the low side, and is indicated by adding “L” to the end of the symbol.

  When switching element 201L is off and switching element 201H is on, output voltage Vjk output from unit converter 108 is applied between the collector and emitter of switching element 201L.

  In the first embodiment, an IGBT (Insulated Gate Bipolar Transistor) is employed for the switching element 201H and the switching element 201L. However, the present invention is not limited to this, and switching elements 201H and 201L include MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors), GCTs (Gate Commutated Turn-off thyristors), GTOs (Gate Turn Off thyristors), and others. An element capable of on / off control may be employed.

The unit converter controller 312 receives the operation command frame or the stop command frame transmitted from the communication interface unit 118 (see FIG. 1) via the operation command signal line 116. When the unit converter controller 312 receives the operation command frame, the unit converter controller 312 receives the gate signals GHjk, GLjk (j = R, S, T, k = 1, based on the arm voltage command values VRa *, VSa *, VTa *. 2,..., M). When the unit converter controller 312 receives the stop command frame, each of the gate signals GHjk, GLjk (j = R, S, T, k = 1, 2,..., M so as to turn off the switching elements 201H and 201L. ) Is generated. The unit converter controller 312 generates the gate signals GHjk and GLjk based on the information for instructing to stop the short frame of 1 bit instead of the arm voltage command values VRa *, VSa *, and VTa *. The switching elements 201H and 201L can be controlled to be turned off over time.
The unit converter controller 312 further measures the voltage of the capacitor 203 by the voltage sensor 204 and transmits it to the control unit 112a (see FIG. 1) via the capacitor voltage detection line 114.

  The gate driver 205 of the unit converter 108 is based on the gate signal GHjk (j = R, S, T, k = 1, 2,..., M) generated by the unit converter controller 312 and the gate / emitter of the switching element 201H. A gate voltage is applied between them, and a gate voltage is applied between the gate and emitter of the switching element 201L based on the gate signal GLjk (j = R, S, T, k = 1, 2,..., M).

  Hereinafter, the relationship between the output voltage Vjk of the unit converter 108 and the on / off states of the switching element 201H and the switching element 201L will be described.

  When the switching element 201H is on and the switching element 201L is off, the output voltage Vjk is approximately equal to the capacitor voltage VCjk regardless of the arm current Ij (j = R, S, T) of the unit converter 108. Will be equal.

When the switching element 201H is in the off state and the switching element 201L is in the on state, the output voltage Vjk is substantially equal to zero regardless of the arm current Ij.
By controlling the switching element 201H and the switching element 201L in this way, the unit converter 108 can output the stored energy stored in the capacitor 203 which is an electrical energy storage unit.

FIG. 3 is a diagram illustrating a logical configuration of the control unit 112a in the first embodiment.
The control unit 112a includes an arm voltage command value generation unit 311, communication interface units 118R, 118S, and 118T, and an overcurrent detection unit 117. The control unit 112a is configured to transmit an overcurrent detection signal to the communication interface units 118R, 118S, and 118T and the host control system 119. The control unit 112a calculates a command value of each unit converter 108 and transmits a frame based on the command value to each unit converter 108 (unit converter controller 312). The control unit 112a is configured to detect that an overcurrent has flowed through one of the arms 105, and transmit a stop command frame to each unit converter 108 (unit converter controller 312) in a short time.
The host control system 119 transmits / receives information to / from the control unit 112a in order to confirm whether or not each unit converter 108 is stopped based on the overcurrent detection information of the overcurrent detection unit 117. .

The arm voltage command value generation unit 311 generates arm voltage command values VRa *, VSa *, and VTa * for the arms 105R, 105S, and 105T. The output side of the arm voltage command value generation unit 311 is connected to the communication interface unit 118. In the present invention, the arm voltage command value generation unit 311 is not limited to the configuration of the first embodiment.
The overcurrent detection unit 117 receives the arm currents IRa, ISa, ITa indicated by the nodes R to T, and the failure reset signal output by the host control system 119. When the overcurrent detection unit 117 detects an overcurrent, the overcurrent detection unit 117 operates to continuously output the overcurrent detection signal until a reset signal is input. The overcurrent detection unit 117 monitors each arm current IRa, ISa, ITa, and detects that an overcurrent has flowed to any one of the arms 105R, 105S, 105T. The output side of the overcurrent detection unit 117 is electrically connected to the communication interface unit 118 and the host control system 119, and transmits an overcurrent detection signal using an H level voltage signal. The configuration and operation of the overcurrent detection unit 117 will be described in detail with reference to FIG.

  The communication interface units 118R, 118S, and 118T transmit an operation command frame including arm voltage command values VRa *, VSa *, and VTa * to the unit converter controller 312 of the arm 105. Further, if the overcurrent detection unit 117 detects an overcurrent, the communication interface units 118R, 118S, and 118T transmit a stop command frame for stopping the operation of each unit converter 108 to the unit converter controller 312. To do. Hereinafter, when the communication interface units 118R, 118S, and 118T are not particularly distinguished, they are simply referred to as the communication interface unit 118.

The communication interface units 118R, 118S, and 118T are connected to the output side of the overcurrent detection unit 117 and the output side of the host control system 119.
Further, a voltage command frame including the arm voltage command value VRa * calculated by the arm voltage command value generation unit 311 is output to the input side of the communication interface unit 118R. The output side of the communication interface unit 118R is connected to the unit converter controller 312 of each unit converter 108 constituting the arm 105R via M operation command signal lines 116.
Further, a voltage command frame including the arm voltage command value VSa * calculated by the arm voltage command value generation unit 311 is output to the input side of the communication interface unit 118S. The output side of the communication interface unit 118S is connected to the unit converter controller 312 of each unit converter 108 constituting the arm 105S via M operation command signal lines 116.
Further, a voltage command frame including the arm voltage command value VTa * calculated by the arm voltage command value generation unit 311 is output to the input side of the communication interface unit 118T. The output side of the communication interface unit 118T is connected to the unit converter controller 312 of each unit converter 108 constituting the arm 105T via M operation command signal lines 116.

  The arm voltage command value generation unit 311 includes a phase detector 306, an arm current regulator 330, an AC power calculator 340, an active power regulator APR, and a reactive power regulator AQR. The arm voltage command value generation unit 311 calculates the arm voltage command values VRa *, VSa *, and VTa * at a predetermined control cycle Tc, generates a voltage command frame, and outputs the voltage command frame to the communication interface unit 118. The power control function of the arm voltage command value generation unit 311 is realized by the AC power calculator 340, the active power adjuster APR, the reactive power adjuster AQR, and the arm current adjuster 330.

  The AC side power calculator 340 has a function of obtaining active power P and reactive power Q. AC power calculator 340 receives power from AC system 101a with system currents IR, IS, IT indicated by nodes A to C and system voltages VGR, VGS, VGT indicated by nodes G to I as inputs. The active power P and the reactive power Q flowing into the conversion device 102a are calculated and output to the active power adjuster APR and the reactive power adjuster AQR. The active power P is indicated by node O. The reactive power Q is indicated by a node M.

  The active power adjuster APR includes an adder / subtracter 361 and a proportional-plus-integral adjuster 362. The active power adjuster APR performs feedback control so that the active power P indicated by the node O matches the active power command value P *. The active power adjuster APR subtracts the active power P from the active power command value P * by the adder / subtractor 361, calculates the d-axis current command value Id * by the proportional-plus-integral adjuster 362, and Output to the current regulator 330.

  The reactive power adjuster AQR includes an adder / subtracter 363 and a proportional-integral adjuster 364. The reactive power adjuster AQR performs feedback control so that the reactive power Q indicated by the node M matches the reactive power command value Q *. The reactive power adjuster AQR subtracts the reactive power Q from the reactive power command value Q * by the adder / subtracter 363, calculates the q-axis current command value Iq * by the proportional-plus-integral regulator 364, and Output to the current regulator 330.

  System voltage VGR, VGS, VGT of AC system 101 a measured by AC voltage sensor 110 is input to phase detector 306. The phase detector 306 detects the phase angle θ of the system voltages VGR, VGS, VGT and outputs it to the arm current regulator 330.

  The arm current adjuster 330 includes a voltage coordinate conversion circuit 333, a current coordinate conversion circuit 334, an arm current adjustment circuit 335, an arm voltage command value coordinate inverse conversion circuit 336, an adder 331, and an adder 332. It has. The arm current adjuster 330 includes system voltages VGR, VGS, VGT indicated by nodes G to I, a d-axis current command value Id * indicated by node K, and a q-axis current command value Iq * indicated by node L. The arm voltage command values VRa *, VSa *, and VTa * are calculated using the arm currents IRa, ISa, ITa measured by the arm current sensor 111 and the phase angle θ as inputs. The arm current regulator 330 is realized by, for example, reading an arm voltage control program into a RAM (Random Access Memory) (not shown) and executing it by a CPU (Central Processing Unit) (not shown). The arm current regulator 330 is configured to calculate the arm voltage command values VRa *, VSa *, and VTa * for each predetermined control period because the amount of calculation in each unit is large.

The voltage coordinate conversion circuit 333 receives the system voltages VGR, VGS, VGT and the phase angle θ thereof, calculates system voltages Vd, Vq by coordinate conversion (α-β conversion and dq conversion), and an adder 331. And output to the adder 332.
The current coordinate conversion circuit 334 receives the arm currents IRa, ISa, ITa and the phase angle θ of the system voltages VGR, VGS, VGT as inputs, and performs d-axis current Id by coordinate conversion (α-β conversion and dq conversion). , Q-axis current Iq is calculated and output to arm current adjustment circuit 335.

  The arm current adjustment circuit 335 receives the d-axis current command value Id *, the q-axis current command value Iq *, the d-axis current Id, and the q-axis current Iq as input, and the d-axis current Id becomes the d-axis current command value Id *. The voltage command values Vd * and Vq * are calculated by feedback control so as to converge and the q-axis current Iq matches the q-axis current command value Iq *, and output to the adder 331 and the adder 332.

  The arm voltage command value coordinate inverse transformation circuit 336 receives the value (Vd + Vd *) added by the adder 331, the value (Vq + Vq *) added by the adder 332, and the phase angle θ as input, and performs coordinate inverse transformation ( Arm voltage command values VRa *, VSa *, VTa * are calculated by inverse α-β conversion and inverse dq conversion.

  The arm voltage command value generation unit 311 transmits a voltage command frame including the arm voltage command values VRa *, VSa *, and VTa * as electrical signals to the communication interface units 118R, 118S, and 118T.

If the overcurrent detection unit 117 detects no overcurrent, each communication interface unit 118R, 118S, 118T converts the voltage command frame received as an electrical signal into an operation command frame that is an optical signal, which will be described later. It transmits to each unit converter controller 312R, 312S, 312T of command value distribution part 313R, 313S, 313T shown in FIG.
If the overcurrent detection unit 117 detects an overcurrent, the communication interface unit 118 sends a stop command frame that is an optical signal to the unit converter controllers 312R, 312S, and 312T of the command value distribution units 313R, 313S, and 313T. Send.
The mode transition of the communication interface unit 118 will be described in detail with reference to FIG.

FIG. 4 is a diagram illustrating a logical configuration of the command value distribution units 313R, 313S, and 313T according to the first embodiment.
The command value distribution units 313R, 313S, and 313T distribute the command value included in the operation command frame transmitted by the control unit 112a to each unit converter 108. Each command value distribution unit 313R, 313S, 313T has (3 × M) unit converter controllers 312R, 312S, 312T for controlling each unit converter 108 constituting each arm 105R, 105S, 105T. doing. In FIG. 4, unit converter controllers 312R, 312S, and 312T representing the arms 105R, 105S, and 105T are shown, respectively, but actually M unit conversions that constitute the arms 105R, 105S, and 105T, respectively. Each unit converter controller 312 is provided in each unit 108. Note that the command value distribution units 313R, 313S, and 313T are simply described as the command value distribution unit 313 when not particularly distinguished.

  M operation command signal lines 116 are input to the command value distribution units 313R, 313S, and 313T, respectively. The output side of the command value distribution unit 313R is connected to each unit converter 108 constituting the arm 105R via the signal line 113. The output side of the command value distribution unit 313S is connected to each unit converter 108 constituting the arm 105S via a signal line 113. The output side of the command value distribution unit 313T is connected to each unit converter 108 constituting the arm 105T via a signal line 113.

  Unit converter controller 312R outputs gate signals GHRk and GLRk to each unit converter 108 of arm 105R based on arm voltage command value VRa * and the operation command or stop command included in the received frame. When the unit converter controller 312R receives the operation command, the unit converter controller 312R modulates the arm voltage command value VRa * by, for example, a pulse width modulation method (PWM method: Pulse Width Modulation) to generate the gate signals GHRk and GLRk. The unit converter controller 312R turns off the gate signals GHRk and GLRk when receiving the stop command.

  The unit converter controller 312S outputs the gate signals GHSk and GLSk to each unit converter 108 of the arm 105S based on the arm voltage command value VSa * and the operation command or stop command included in the received frame. When the unit converter controller 312S receives the operation command, the unit converter controller 312S modulates the arm voltage command value VSa * by, for example, a pulse width modulation method, and generates gate signals GHSk and GLSk. When unit converter controller 312S receives the stop command, unit converter controller 312S turns off gate signals GHSk and GLSk.

  Unit converter controller 312T outputs gate signals GHTk and GLTk to each unit converter 108 of arm 105T based on the arm voltage command value VTa * and the operation command or the stop command included in the received frame. When the unit converter controller 312T receives the operation command, the unit converter controller 312T modulates the arm voltage command value VTa * by, for example, a pulse width modulation method, and generates gate signals GHTk and GLTk. When unit converter controller 312T receives the stop command, unit converter controller 312T turns off gate signals GHTk and GLTk.

FIG. 5 is a diagram showing a logical configuration of the overcurrent detection unit 117 in the first embodiment.
The overcurrent detection unit 117 includes absolute value circuits 401R, 401S, and 401T, overcurrent determination units 402R, 402S, and 402T, an OR circuit 403, and a holding circuit 404. The overcurrent detection unit 117 detects that an overcurrent has flowed through any of the arms 105.
Hereinafter, when the absolute value circuits 401R, 401S, and 401T are not particularly distinguished, they are simply referred to as an absolute value circuit 401. When the overcurrent determination units 402R, 402S, and 402T are not particularly distinguished, they are simply referred to as an overcurrent determination unit 402.
The arm currents IRa, ISa, ITa on the input side of the overcurrent detection unit 117 are input to absolute value circuits 401R, 401S, 401T. The output sides of the absolute value circuits 401R, 401S, 401T are connected to the overcurrent determination units 402R, 402S, 402T, respectively. The output sides of the overcurrent determination units 402R, 402S, and 402T are output to the holding circuit 404 via the OR circuit 403. The output side of the holding circuit 404 is the output side of the overcurrent detection unit 117.

  The absolute value circuits 401R, 401S, and 401T calculate the absolute values of the arm currents IRa, ISa, and ITa, and thus calculate the amplitudes of the arm currents IRa, ISa, and ITa. The absolute value circuits 401R, 401S, 401T output the calculated absolute values (amplitudes) of the arm currents IRa, ISa, ITa to the overcurrent determination units 402R, 402S, 402T, respectively.

The overcurrent determination units 402R, 402S, and 402T compare the preset overcurrent determination values IRref, ISref, and ITref with the absolute values (amplitudes) of the arm currents IRa, ISa, and ITa. It is determined whether or not an overcurrent has passed through 105S and 105T. The overcurrent determination units 402R, 402S, and 402T output an H level signal to the OR circuit 403 when an overcurrent flows through the arms 105R, 105S, and 105T.
The logical sum circuit 403 outputs a logical sum of input signals. Here, the input signal is a signal indicating whether or not an overcurrent has passed through each of the arms 105R, 105S, and 105T. Therefore, the OR circuit 403 outputs an H-level overcurrent detection signal to the holding circuit 404 when it is determined that an overcurrent has flowed in at least one of the arms 105R, 105S, and 105T.

  The holding circuit 404 is a latch circuit, and holds the ON state until the failure reset signal is input when the overcurrent detection signal is turned ON. If the failure reset signal is input in the ON state (the failure reset signal changes to H level), the holding circuit 404 resets the ON state and sets the output signal to L level.

  The control unit 112a operates the arm voltage command value generation unit 311 and the overcurrent detection unit 117 in parallel. Since the arm voltage command value generation unit 311 has a complicated process and a large amount of calculation, the arm voltage command value generation unit 311 can generate a command value only every predetermined control cycle. However, since the overcurrent detection unit 117 is simple in processing and has a small amount of calculation, it can output an overcurrent detection signal in a short time when an overcurrent flows through any of the arms 105.

FIG. 6 is a state transition diagram of the communication interface unit 118 in the first embodiment. In addition, (1)-(3) shown beside each transition is the priority of the state transition from each state, and has shown that a priority is so high that the number in a parenthesis is small.
First, the state transition route R23 during normal operation will be described. In FIG. 6, the state transition route R23 is indicated by a broken line.
The communication interface unit 118 transitions from the initial state S1 immediately after startup to the reception wait state S2 as shown in transition T12 upon completion of initialization.
In the reception waiting state S2, the communication interface unit 118 holds this state as shown in transition T22 if no frame or signal is received.

  In the reception waiting state S2, when receiving the voltage command frame from the arm current regulator 330, the communication interface unit 118 transitions to the normal transmission state S3 as shown in transition T23.

  In the normal transmission state S3, the communication interface unit 118 generates an operation command frame for the unit converter controller 312, transmits the generated operation command frame, and unconditionally waits for reception S2 as shown in transition T32. Transition to.

  During normal operation, the arm current regulator 330 creates a voltage command frame for each control cycle Tc and transmits it to the communication interface unit 118. The communication interface unit 118 receives this voltage command frame every control cycle Tc, and repeats the transition T23 from the reception waiting state S2 to the normal transmission state S3 and the transition T32 to the reception waiting state S2.

Next, the state transition route R24 when overcurrent is detected will be described. In FIG. 5, the state transition route R24 is indicated by a one-dot chain line.
In the reception waiting state S2, if there is no reception of a frame or a signal, the communication interface unit 118 maintains the state as shown in transition T22.

  In the reception waiting state S2, when receiving the overcurrent detection signal, the communication interface unit 118 transitions to the emergency stop transmission state S4 as shown in transition T24.

  In the emergency stop transmission state S4, as shown in transition T44, the communication interface unit 118 generates a stop command frame for emergency stop for the unit converter controller 312 and uses the generated stop command frame as the unit converter controller 312. Send to repeatedly. Since the stop command frame only needs to include 1-bit stop command information, the frame length of the stop command frame can be shortened. Since the stop command frame to be transmitted is short, the communication interface unit 118 can repeatedly transmit to a large number of unit converter controllers 312 in a short time.

  When the specified time Tx has elapsed since the transition to the emergency stop transmission state S4 and the stop command signal is received from the host control system 119, the communication interface unit 118 receives the failure reset waiting state as indicated by transition T45. Transition to S5.

  In the emergency stop transmission state S4, the communication interface unit 118 repeatedly transmits a stop command frame for emergency stop for a specified time Tx. As a result, each unit converter 108 can stop its own operation if it successfully receives one of the stop command frames, so that it does not continue to operate erroneously due to a communication error. Note that the communication interface unit 118 may repeatedly transmit the stop command frame a specified number of times in the emergency stop transmission state S4.

  Furthermore, the communication interface unit 118 repeatedly transmits a stop command frame until a stop command signal from the host control system 119 is received. Thereby, the host control system 119 can suppress the occurrence of inconsistency in the operation of the DC power transmission system 100 without recognizing the stop of the power conversion apparatus 102a.

  In the failure reset waiting state S5, when the communication interface unit 118 receives a failure reset signal from the host control system 119, the communication interface unit 118 transitions to the reception waiting state S2 as shown in transition T52. At this time, the overcurrent detection unit 117 can simultaneously receive the failure reset signal, reset the holding of the overcurrent detection signal, and stop the output. As a result, the host control system 119 simultaneously initializes the communication interface unit 118 and the overcurrent detection unit 117, and resumes the operation of each unit converter 108 while matching the states of the respective units of the power converter 102a. be able to.

Further, the transition T34 in which the communication interface unit 118 has received the overcurrent detection signal in the normal transmission state S3 will be described.
In the normal transmission state S3, when the communication interface unit 118 generates an operation command frame, if the communication interface unit 118 receives an overcurrent detection signal, the communication interface unit 118 is generating as shown in transition T34. The operation command frame is discarded, and the state transits to the emergency stop transmission state S4. The subsequent transition is the same as the state transition route R24.

  In the first embodiment, if the communication interface unit 118 receives an overcurrent detection signal while generating an operation command frame, the communication interface unit 118 discards the operation command frame being generated. However, the present invention is not limited to this, and the communication interface unit 118 may transmit the operation command frame being generated with a stop command added thereto.

FIG. 7 is a sequence diagram at the time of overcurrent detection in the first embodiment.
Sequences Q10 to Q15 show sequences during normal operation. At the start of these sequences, the communication interface unit 118 is in the reception waiting state S2 (see FIG. 6).
In sequence Q <b> 10, the host control system 119 transmits an operation command signal to the communication interface unit 118.

In the sequence Q11, the arm voltage command value generation unit 311 acquires the values of the arm currents IRa, ISa, ITa and the system voltages VGR, VGS, VGT for each control cycle Tc, and the arm voltage command value VRa *, VSa * and VTa * are calculated and transmitted to the communication interface unit 118 as a voltage command frame. As a result, the communication interface unit 118 transitions to the normal transmission state S3 (see FIG. 6).
In sequence Q12, the communication interface unit 118 generates an operation command frame at this time and transmits it to the unit converter 108 (unit converter controller 312). In the following sequence, “transmit to unit converter 108” means that the communication interface unit 118 transmits a frame to the unit converter controller 312 and the unit converter controller 312 executes control based on the frame. Say.

This operation command frame includes arm voltage command values VRa *, VSa *, and VTa *. When the communication interface unit 118 transmits the operation command frame, the communication interface unit 118 transitions to a reception waiting state S2 (see FIG. 6).
In sequence Q13, the host control system 119 transmits an operation command signal to the communication interface unit 118.

In sequence Q14, the arm voltage command value generation unit 311 acquires the values of the arm currents IRa, ISa, ITa and the system voltages VGR, VGS, VGT, and the arm voltage command values VRa *, VSa *, VTa *. Is transmitted to the communication interface unit 118 as a voltage command frame. In the sequence Q14, the control cycle Tc has elapsed with respect to the time of the sequence Q11. When the communication interface unit 118 transmits the operation command frame, the communication interface unit 118 transitions to a reception waiting state S2 (see FIG. 6).
In sequence Q15, the communication interface unit 118 generates an operation command frame at this time and transmits it to the unit converter 108 (unit converter controller 312). When the communication interface unit 118 transmits the operation command frame, the communication interface unit 118 transitions to a reception waiting state S2 (see FIG. 6).

Sequences Q20 to Q23 show sequences at the time of emergency stop.
In the sequence Q20 in which the sequence Q15 is being executed, the overcurrent detection unit 117 detects that an overcurrent has flowed through any of the arms 105.
In sequence Q21a, the overcurrent detection unit 117 transmits an overcurrent detection signal to the communication interface unit 118, and transmits an overcurrent detection signal to the arm voltage command value generation unit 311 in sequence Q21b. When receiving the overcurrent detection signal, the communication interface unit 118 transitions to the emergency stop transmission state S4 (see FIG. 6).

In sequence Q22, the communication interface unit 118 generates a stop command frame for emergency stop without waiting for the next control cycle Tc, and transmits it to the unit converter 108 (unit converter controller 312). Thereby, the communication interface unit 118 can stop the plurality of unit converters 108 in a short time regardless of the control cycle Tc.
In the sequence Q23, the unit converter 108 stops its operation. That is, the unit converter controller 312 receives and interprets the stop command frame, and turns off the switching element 201H and the switching element 201L of the unit converter 108.
The power conversion device 102a controls each communication interface unit 118 as in sequences Q20 to Q23, so that the arrival time T0 of the stop command frame to the unit converter 108 than the comparative example (see FIG. 9) described later (see FIG. 9). 9)) can be processed in a short time.

FIG. 8 is a sequence diagram at the time of overcurrent detection and at the time of resumption in the first embodiment.
At the start of these sequences, the communication interface unit 118 is in the reception waiting state S2 (see FIG. 6).
Processing of sequences Q20 to Q23 is the same as sequences Q20 to Q23 shown in FIG.
In sequence Q24, the host control system 119 transmits a stop command signal to the communication interface unit 118. At this time, since the specified time Tx has not yet elapsed from the sequence Q22, the communication interface unit 118 maintains the emergency stop transmission state S4, and repeats the stop command frame to the unit converter 108 without depending on the control cycle Tc. Send.
In sequence Q25, the arm voltage command value generation unit 311 acquires the values of the arm currents IRa, ISa, ITa and the system voltages VGR, VGS, VGT, and the arm voltage command values VRa *, VSa *, VTa *. And a voltage command frame is generated and transmitted to the communication interface unit 118. In the sequence Q25, the control cycle Tc has elapsed with respect to the time of the sequence Q14 (see FIG. 7).

In sequence Q26, the host control system 119 transmits a stop command signal to the communication interface unit 118. At this time, since the specified time Tx has elapsed since the sequence Q22, the communication interface unit 118 stops transmitting the stop command frame and transitions to the failure reset waiting state S5 (see FIG. 6).
The processing of sequence Q27 is the same as that of sequence Q25.
In this way, the communication interface unit 118 continuously transmits the stop command frame for at least the specified time Tx, so that it is possible to prevent the unit converter 108 from erroneously continuing operation due to a communication error. it can.

Sequences Q30a to Q33 show a reset after stopping due to overcurrent. At the start of these sequences, the communication interface unit 118 is in the failure reset waiting state S5 (see FIG. 6).
In sequence Q30a, the host control system 119 transmits a failure reset signal to the communication interface unit 118. As a result, the communication interface unit 118 transitions to the reception waiting state S2 (see FIG. 6).
In sequence Q30b, the host control system 119 also transmits a failure reset signal to the overcurrent detection unit 117.

In sequence Q31, the host control system 119 transmits an operation command signal to the communication interface unit 118.
In sequence Q32, the arm voltage command value generation unit 311 obtains the values of the arm currents IRa, ISa, ITa and the system voltages VGR, VGS, VGT, and outputs the arm voltage command values VRa *, VSa *, VTa *. Is transmitted to the communication interface unit 118 as a voltage command frame. As a result, the communication interface unit 118 transitions to the normal transmission state S3 (see FIG. 6).
In sequence Q33, the communication interface unit 118 generates an operation command frame at this time and transmits it to the unit converter 108 (unit converter controller 312). When the communication interface unit 118 transmits the operation command frame, the communication interface unit 118 transitions to a reception waiting state S2 (see FIG. 6).

  By doing in this way, the power converter device 102a can perform the restart after an overcurrent stop, matching the state of the high-order control system 119, the communication interface part 118, and the overcurrent detection part 117.

FIG. 9 is a sequence diagram when overcurrent is detected in the comparative example.
The comparative example is an example in which the control device 150a communicates with the unit converter controller 312 only for each control cycle Tc.
In sequence Q40, the host control system 119 transmits an operation command signal to the communication interface unit 118.
In sequence Q41, the arm voltage command value generation unit 311 acquires the arm currents IRa, ISa, ITa and the system voltages VGR, VGS, VGT and outputs the arm voltage command values VRa *, VSa * for each control cycle Tc. , VTa * are calculated and transmitted to the communication interface unit 118 as a voltage command frame.

  In sequence Q42, the communication interface unit 118 generates an operation command frame at this time and transmits it to the unit converter 108 (unit converter controller 312). This operation command frame includes arm voltage command values VRa *, VSa *, and VTa *.

In sequence Q43, the host control system 119 transmits an operation command signal to the communication interface unit 118.
In sequence Q44, the arm voltage command value generation unit 311 acquires the values of the arm currents IRa, ISa, ITa and the system voltages VGR, VGS, VGT, and the arm voltage command values VRa *, VSa *, VTa *. Is transmitted to the communication interface unit 118 as a voltage command frame. In the sequence Q44, the control cycle Tc has elapsed with respect to the time of the sequence Q41.

In sequence Q45, the communication interface unit 118 generates an operation command frame at this time and transmits it to the unit converter 108 (unit converter controller 312).
In the sequence Q50 in which the sequence Q45 is being executed, the overcurrent detection unit 117 detects that an overcurrent has flowed through any of the arms 105.
In sequence Q51, the overcurrent detection unit 117 transmits an overcurrent detection signal to the host control system 119.

In sequence Q52, the host control system 119 transmits a stop command signal to the communication interface unit 118.
In sequence Q53, the arm voltage command value generation unit 311 acquires the values of the arm currents IRa, ISa, ITa and the system voltages VGR, VGS, VGT, and the arm voltage command values VRa *, VSa *, VTa *. Is transmitted to the communication interface unit 118 as a voltage command frame. In the sequence Q53, the control cycle Tc has elapsed with respect to the time of the sequence Q44.

In sequence Q54, the communication interface unit 118 generates a stop command frame and transmits it to the unit converter 108 (unit converter controller 312).
In sequence Q55, the unit converter 108 stops operating. The sequence Q55 is delayed from the sequence Q51 by the arrival time T0.
In the comparative example, as shown in sequences Q52 to Q54, the host control system 119 has to wait for the next control cycle Tc in order to transmit a stop command frame for emergency stop to the unit converter controller 312. there were.

  As shown in FIG. 7, when detecting an overcurrent, the control unit 112a of the first embodiment transmits a stop command frame for emergency stop without waiting for communication every control cycle Tc. Thereby, the power converter device 102a can shorten the time from detection of an overcurrent to an emergency stop.

(Effects of the first embodiment)
The first embodiment described above has the following effects (A) to (F).

(A) When the physical distance from the control device 150 to the unit converter controller 312 of each unit converter 108 is long and connected by an optical fiber for electrical insulation, this power Even when the number of unit converters 108 included in the conversion device 102a is large, the time required to stop all the unit converters 108 can be shortened. Thereby, since the overcurrent which flows into each unit converter 108 can be suppressed small, destruction of the element by overcurrent can be controlled.

(B) The control unit 112a repeatedly transmits a stop command frame for emergency stop over a specified time Tx. As a result, it is possible to prevent the unit converter 108 from continuing erroneous operation due to a reception error of the unit converter controller 312.

(C) The control unit 112a operates the arm voltage command value generation unit 311 and the overcurrent detection unit 117 in parallel. Since the overcurrent detection unit 117 is simpler and requires less computation than the processing of the arm voltage command value generation unit 311, an overcurrent detection signal is output in a short time when an overcurrent flows through any of the arms 105. can do.

(D) In the first embodiment, a stop command signal for the unit converter 108 is also transmitted from the host control system 119. As a result, the host control system 119 and the control unit 112a can prevent a state mismatch with the unit converter 108, and can safely stop the entire system.

(E) When the power conversion apparatus 102a returns to the normal operation from the stop due to the overcurrent, the host control system 119 transmits a failure reset signal to the communication interface unit 118 and the overcurrent detection unit 117 to initialize It has become. As a result, the power conversion device 102a can prevent the inconsistency of the state of each unit, and can safely return the entire system to normal operation.

(F) The stop command frame for emergency stop transmitted by the control unit 112a includes 1-bit stop command information and does not include arm voltage command values VRa *, VSa *, and VTa *. Thereby, the control part 112a can transmit to many unit converters 108 in a short time. Furthermore, the unit converter controller 312 has only to interpret the 1-bit stop command information included in the stop command frame, so that the switching elements 201H and 201L can be turned off in a short time.

(Second Embodiment)
The DC power transmission system 100 of the second embodiment includes the unit converter 108A different from the unit converter 108 (see FIG. 2) of the first embodiment, except that the first embodiment shown in FIG. The DC power transmission system 100 is configured in the same manner and operates in the same manner.
FIG. 10 is a diagram illustrating a circuit configuration of a full-bridge type unit converter 108A according to the second embodiment.
Here, as a representative of each arm 105, the unit converter 108A in the arm 105R will be described. The unit converter 108A included in the arm 105S and the arm 105T is configured similarly to the unit converter 108A in the arm 105R.
Similarly to the unit converter 108 of the first embodiment, the unit converter 108A of the second embodiment includes a plurality of switching elements that can output the stored energy stored by the electric energy storage means. .

Unit converter 108A includes a parallel circuit of high-side switching element 201HL and free-wheeling diode 202HL, a parallel circuit of low-side switching element 201LL and free-wheeling diode 202LL, a parallel circuit of high-side switching element 201HR and free-wheeling diode 202HR, A parallel circuit of a low-side switching element 201LR and a free-wheeling diode 202LR, a capacitor 203 serving as electric energy storage means, a voltage sensor 204, and a gate driver 205 that drives the switching elements 201HL, 201LL, 201HR, and 201LR are provided. The gate driver 205 is connected to the unit converter controller 312 via the signal line 113 as in the first embodiment. The command value distribution unit 313 includes each unit converter controller 312.
The positive side terminal 208 (first terminal) of the unit converter 108A is connected to the negative side terminal 209 (second terminal) of the other unit converter 108A or the positive side DC terminal Pa. . The negative terminal 209 (second terminal) of the unit converter 108A is connected to the positive terminal 208 of the other unit converter 108A or one end of the arm current sensor 111.

The parallel circuit of switching element 201HL and freewheeling diode 202HL and the parallel circuit of switching element 201LL and freewheeling diode 202LL are connected in series. The parallel circuit of the switching element 201HR and the freewheeling diode 202HR and the parallel circuit of the switching element 201LR and the freewheeling diode 202LR are connected in series. Further, these two series connection circuits are connected in parallel.
The collector of the switching element 201HL is connected to one end of the capacitor 203. The collector of the switching element 201HL is further connected to the cathode of the freewheeling diode 202HL. The emitter of the switching element 201HL is connected to the anode of the freewheeling diode 202HL, and is further connected to the collector of the switching element 201LL.

  The collector of the switching element 201LL is connected to the emitter of the switching element 201HL and the cathode of the freewheeling diode 202LL. The emitter of the switching element 201LL is connected to the anode of the freewheeling diode 202LL, and is further connected to the other end of the capacitor 203.

  The collector of the switching element 201HR is connected to one end of the capacitor 203. The collector of the switching element 201HR is further connected to the cathode of the freewheeling diode 202HR. The emitter of the switching element 201HR is connected to the anode of the freewheeling diode 202HR, and is further connected to the collector of the switching element 201LR.

The collector of the switching element 201LR is connected to the emitter of the switching element 201HR and the cathode of the freewheeling diode 202LR. The emitter of the switching element 201LR is connected to the anode of the freewheeling diode 202LR, and is further connected to the other end of the capacitor 203.
A voltage sensor 204 is connected to both ends of the capacitor 203.

  The positive side terminal 208 of the unit converter 108A is connected to a connection node between the emitter of the switching element 201HL and the collector of the switching element 201LL. The negative terminal 209 of the unit converter 108A is connected to a connection node between the emitter of the switching element 201HR and the collector of the switching element 201LR.

  The switching elements 201HL, 201LL, 201HR, and 201LR can output the accumulated energy accumulated in the capacitor 203 between the terminal 208 (first terminal) and the terminal 209 (second terminal). That is, the switching elements 201HL, 201LL, 201HR, and 201LR can output the voltage across the capacitor 203 between the terminal 208 (first terminal) and the terminal 209 (second terminal).

  The gate driver 205 (switching element driving unit) is connected to the unit converter controller 312 via the signal line 113. The output side of the gate driver 205 is connected to the gates and emitters of the switching elements 201HL, 201LL, 201HR, and 201LR, respectively.

  The gate driver 205 is a switching element driving unit of the unit converter 108A, and is controlled by the unit converter controller 312 that receives the operation / stop command of the control unit 112a. The gate driver 205 can output the voltage of the capacitor 203 between the positive terminal 208 and the negative terminal 209 by switching the switching elements 201HL, 201LL, 201HR, and 201LR on and off. The output voltage Vjk between the terminal 208 on the side and the terminal 209 on the negative side is controlled.

  The freewheeling diodes 202HL, 202LL, 202HR, 202LR are connected in series in a direction in which no current flows with respect to the capacitor voltage VCjk. A switching element 201HL connected in parallel to the freewheeling diode 202HL, a switching element 201LL connected in parallel to the freewheeling diode 202LL, a switching element 201HR connected in parallel to the freewheeling diode 202HR, and a parallel connection to the freewheeling diode 202LR The switching element 201LR is attached in a direction in which the capacitor voltage VCjk is discharged when each switching state is ON.

The unit converter controller 312 receives the operation command frame or the stop command frame transmitted from the communication interface unit 118 (see FIG. 1) via the operation command signal line 116. When the unit converter controller 312 receives the operation command frame, the unit converter controller 312 receives the gate signals GHLjk, GLLjk, GHRjk, GLRjk (j = R, S, T, k = 1, 2,..., M). When the unit converter controller 312 receives the stop command frame, each of the gate signals GHLjk, GLLjk, GHRjk, GLRjk (j = R, S, T, k) so as to turn off the switching elements 201HL, 201LL, 201HR, 201LR. = 1, 2, ..., M). The unit converter controller 312 generates gate signals GHLjk, GLLjk, GHRjk, GLRjk based on information for instructing to stop a short frame of 1 bit instead of the arm voltage command values VRa *, VSa *, VTa *. Therefore, the switching elements 201HL, 201LL, 201HR, and 201LR can be controlled to be turned off in a short time.
The unit converter controller 312 further measures the voltage of the capacitor 203 by the voltage sensor 204 and transmits it to the control unit 112a (see FIG. 1) via the capacitor voltage detection line 114.

  The gate driver 205 of the unit converter 108A is based on the gate signal GHLjk (j = R, S, T, k = 1, 2,..., M) generated by the unit converter controller 312 and the gate / emitter of the switching element 201HL. A gate voltage is applied between them, and a gate voltage is applied between the gate and emitter of the switching element 201LL based on the gate signal GLLjk (j = R, S, T, k = 1, 2,..., M). Further, the gate driver 205 applies a gate voltage between the gate and the emitter of the switching element 201HR based on the gate signal GHRjk (j = R, S, T, k = 1, 2,..., M), and the gate signal GLRjk ( j = R, S, T, k = 1, 2,..., M), and a gate voltage is applied between the gate and the emitter of the switching element 201LR.

  Since the unit converter 108A of the second embodiment includes a circuit having a full bridge configuration, electric energy can be efficiently stored in the capacitor 203A compared to the unit converter 108 of the first embodiment. At the same time, the energy stored in the capacitor 203 can be output efficiently. Thereby, the energy efficiency of the power converters 102a and 102b and the energy efficiency of the DC power transmission system 100 can be improved.

(Modification)
The present invention is not limited to the embodiments described above, and includes various modifications. For example, the above-described embodiment has been described in detail for easy understanding of the present invention, and is not necessarily limited to the one having all the configurations described. A part of the configuration of one embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of one embodiment. Moreover, it is also possible to add, delete, and replace other configurations for a part of the configuration of each embodiment.

  A part or all of the above-described configurations, functions, processing units, processing means, and the like may be realized by hardware such as an integrated circuit. Each of the above-described configurations, functions, and the like may be realized by software by a processor interpreting and executing a program that realizes each function. Information such as programs, tables, and files for realizing each function may be stored in a recording device such as a memory, a hard disk, or an SSD (Solid State Drive), or a recording medium such as a flash memory card or a DVD (Digital Versatile Disk). it can.

In each embodiment, the control lines and information lines indicate what is considered necessary for the explanation, and not all the control lines and information lines on the product are necessarily shown. Actually, it may be considered that almost all the components are connected to each other.
Examples of modifications of the present invention include the following (a) to (d).

(A) In the power conversion device 102a of the above embodiment, each arm 105 is connected to a three-phase transformer 130. However, the present invention is not limited to this, and the power conversion device of the present invention only needs to include a plurality of unit converters 108 and 108A, and may include a plurality of legs to which two arms are connected in series, for example.

(B) The unit converters 108 and 108A of the present invention only need to have a plurality of switching elements and can output the stored energy stored by the electric energy storage means represented by the capacitor 203. The form is not limited.

(C) The overcurrent detection unit 117 of the above embodiment includes a holding circuit 404 that holds an overcurrent detection state. However, the present invention is not limited to this, and the communication interface unit 118 may be configured to hold this overcurrent detection information when detecting the rising edge of the overcurrent detection signal. As a result, the initialization target of the host control system 119 can be the communication interface unit 118 only, and wiring from the host control system 119 to the overcurrent detection unit 117 can be omitted.

(D) The communication interface unit 118 of the above embodiment transmits the operation command frame and the stop command frame as optical signals having the same wavelength to the unit converter controller 312 of each unit converter 108, 108A. However, the present invention is not limited to this, and the communication interface unit generates an operation command frame including a voltage command and a stop command frame when an overcurrent is detected using optical signals of different wavelengths, and generates these two optical signals. You may comprise so that it may multiplex and transmit. Thereby, the mode transition of the communication interface unit can be simplified.

100 DC power transmission system 101a, 101b AC system 102a, 102b Power converter 105, 105R, 105S, 105T Arm 106, 106R, 106S, 106T Unit converter group 108 Unit converter 110 AC voltage sensor 111 Arm current sensor 112a, 112b Control Unit 113 Signal line 114 Capacitor voltage detection line 115 DC voltage sensor 116 Operation command signal line 117 Overcurrent detection unit 118 Communication interface unit 119 Host control system 120 Initial charging device 121 Circuit breaker 130 Transformer 131, 131R, 131S, 131T Iron core 132 , 132RA, 132SA, 132TA Winding 132RB, 132SB, 132TB Winding 132RC, 132SC, 132TC Winding 140 AC current sensor 150, 150a, 150b Controller 201H switching element 201L switching element 201HL switching element 201HR switching element 201LR switching element 202LR freewheeling diode 202L freewheeling diode 202HL freewheeling diode 202HR freewheeling diode 202LL freewheeling diode 202LR freewheeling diode 203 capacitor 205 gate driver 208, 209 terminal 306 phase detector 311 Arm voltage command value generator (command value generator)
312, 312 R, 312 S, 312 T Unit converter controller 313, 313 R, 313 S, 313 T Command value distribution unit 330 Arm current regulator 340 AC side power calculator 401, 401 R, 401 S, 401 T Absolute value circuit 402, 402 R, 402 S, 402 T Overcurrent determination unit 403 OR circuit 404 holding circuit

Claims (8)

A plurality of unit converter groups in which a plurality of unit converters each having a plurality of switching elements capable of outputting the stored energy stored in the electric energy storage means are connected;
A command value generator for generating a command value for each of the unit converters;
An overcurrent detector for detecting an overcurrent flowing through the unit converter group;
Based on the command value generated by the command value generation unit, an operation command frame is transmitted to each unit converter at a predetermined cycle, and if the overcurrent detection unit detects an overcurrent, it does not depend on the predetermined cycle. A communication interface unit for transmitting a stop command frame to each of the unit converters;
A power conversion device comprising: The communication interface unit
If the overcurrent detector detects an overcurrent, it repeatedly transmits a stop command frame to each of the unit converters over a specified time.
The power conversion apparatus according to claim 1. The communication interface unit
If the overcurrent detection unit detects an overcurrent, it repeatedly transmits a stop command frame to each unit converter a specified number of times.
The power conversion apparatus according to claim 1. If the overcurrent detection unit detects an overcurrent in any of the plurality of unit converter groups, it outputs overcurrent detection information to the communication interface unit.
The power conversion apparatus according to claim 1. Based on the overcurrent detection information of the overcurrent detection unit, a host control system that commands the stop of each unit converter is connectable via the communication interface unit,
The communication interface unit transmits a stop command frame to each unit converter based on the command of the host control system.
The power conversion apparatus according to claim 1. The host control system restarts driving of each unit converter by initializing the overcurrent detection unit and the communication interface unit.
The power conversion device according to claim 5. The first power converter connected to one end of the DC power transmission line includes the power converter according to claim 1 and a second power converter connected to the other end of the DC power transmission line. As a power converter according to claim 1,
The alternating current input to the first power conversion device is converted into direct current, and the second power conversion device reconverts the alternating current to output, or is input to the second power conversion device. Converting alternating current to direct current, reconverting to alternating current with the first power conversion device, and outputting,
DC power transmission system characterized by A plurality of unit converters each having a plurality of unit converters each having a plurality of switching elements capable of outputting the stored energy accumulated by the electrical energy storage means are provided, and a system current that is alternating current is converted to direct current, or A power conversion device that converts direct current to alternating current
A command value generator for generating a command value for each of the unit converters at a predetermined period;
An overcurrent detector for detecting overcurrent;
A communication interface unit for transmitting a signal to the unit converter;
With
The communication interface unit
Based on the command value generated by the command value generation unit, an operation command frame is transmitted to each unit converter at the predetermined period,
If the overcurrent detector detects an overcurrent, a stop command frame is transmitted to each unit converter regardless of the predetermined period.
A method for controlling a power conversion device.

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