JP5719827B2 - Power converter - Google Patents

Description

  The present invention relates to a power converter and a DC power transmission system using the power converter.

  Non-Patent Document 1 discloses a schematic diagram with one line of the DC power transmission system shown in FIG.

  The DC power transmission system of FIG. 8 includes a three-phase AC power system 100, 170, a circuit breaker 124 installed to disconnect the DC power transmission system 800 from the AC system 100, 170, and a conversion transformer 805 for transforming AC voltage. A three-phase full-bridge power converter 801 using a plurality of semiconductor switching devices, capacitors 802 and 803 connected in parallel with the three-phase full-bridge power converter 801, and the capacitors 802 and 803 are connected. The sex point 806 is grounded. A DC power transmission cable 807, a DC reactor 804 connected in series with the power converter 801 and the DC power transmission cable 807 are provided.

  In general, the DC power transmission system transmits power from one three-phase AC power system to the other three-phase AC power system.

L Ronstrom, ML Hoffstein, R Pajo, M Lahtinen: “The Estlink HVDC Light Transmission System”, SECURITY AND RELIABILITY OF ELECTRIC POWER SYSTEMS, CIGRE Regional Meeting, June 18-20, 2007, Tallinn, Estonia, 21, rue d ' Artois, F-75008 PARIS

  In the direct current power transmission system shown in FIG. 8, a short circuit in a direct current section (hereinafter referred to as a direct current line) connecting the direct current output terminals of the three-phase full-bridge power converters 801 on both sides constituting the direct current power transmission system 800, for example, direct current A case where the connection point 901 between the reactor 804 and the DC power transmission cable 807 is short-circuited will be described with reference to FIG.

  When the connection point 901 is short-circuited, the electric charges of the DC capacitors 802 and 803 are discharged, and excessive current flows transiently through the DC power transmission cable 807, which may cause the DC power transmission cable 807 to burn out. The discharge path includes capacitor 802 -DC reactor 804 -connection point 901 -DC reactor 804 -capacitor 803 path, capacitor 802 -DC reactor 804 -DC transmission cable 807 -connection point 901 -DC transmission cable 807 -DC reactor 804- This is a capacitor 803.

  The discharge current is suppressed by the DC reactor 804. However, in order to increase the suppression effect, it is necessary to increase the inductance of the DC reactor, which increases the size and weight.

  The present invention relates to an overcurrent at the time of discharging from a DC capacitor (energy storage element) to a DC line in a DC power transmission system in which AC power is once converted into DC power and transmitted from one AC system to the other AC system. The present invention provides a power conversion device having a function to prevent, and a DC power transmission system.

In order to achieve the above object, the present invention has a plurality of circuits in which a plurality of unit converters are connected in series, and the unit converter includes a capacitor and a plurality of switching elements. The power conversion is performed by performing an operation of outputting the voltage of the capacitor to the terminal and an operation of storing the voltage from the terminal to the capacitor. When an abnormality occurs, the voltage of the capacitor is not output to the terminal. Is provided with a function of turning off at least a part of the switching elements of the unit converter .

  According to the power conversion device and the DC power transmission system of the present invention, when the DC line is short-circuited, the charge of the energy storage element of the power conversion device is not discharged, and an excessive current does not flow through the DC power transmission cable.

1 is a circuit diagram showing a first embodiment of the present invention. The transformer in the 1st Embodiment of the present invention. Unit chopper cell. The circuit diagram which shows the 2nd Embodiment of this invention. Unit full bridge cell. The circuit diagram which shows the 3rd Embodiment of this invention. The circuit diagram which shows the 4th Embodiment of this invention. 1 is a schematic diagram of a DC power transmission system shown in Non-Patent Document 1. FIG. The circuit diagram when a ground fault occurs in the direct-current power transmission system shown by the nonpatent literature 1. FIG. The cooling block diagram of the Example of this invention. An equivalent electrical circuit showing a thermal circuit of the cooling configuration of the present invention.

  Embodiments of the present invention will be described below with reference to the drawings.

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

  FIG. 1 is a circuit diagram of a DC power transmission system using the power conversion device of the present invention.

  First, the configuration of the DC power transmission system of the present invention will be described. The DC power transmission system includes three-phase AC power systems 100 and 170, two power converters 101 linked to the three-phase AC power systems 100 and 170, and the three-phase AC power systems 100 and 170, respectively. A DC power transmission cable 150 is connected to one of the two DC output terminals of each of the two power converters 101 linked to each other, and the other DC output terminal is grounded.

  The DC power transmission system of the present invention converts the AC power from the three-phase AC power systems 101 and 170 into DC power by each of the two power conversion devices 101 linked to the three-phase AC power systems, and the DC power transmission. Electric power is transmitted in one direction or in both directions by the cable 150.

  Next, the configuration of the power conversion device 101 will be described. The power conversion apparatus 101 includes a transformer 105, a positive side converter group 112, and a negative side converter group 116.

  In the present specification, each phase of the three-phase AC power system 100 is referred to as an R phase, an S phase, and a T phase. Furthermore, the current flowing through each phase of the three-phase AC power system 100 is referred to as a system current and is expressed as IR, IS, IT.

  Next, the configuration of the transformer 105 will be described with reference to FIGS. 1 and 2.

  The transformer 105 includes an R-phase terminal 102, an S-phase terminal 103, a T-phase terminal 104, a u-phase positive terminal 106, a v-phase positive terminal 107, a w-phase positive terminal 108, a u-phase negative terminal 109, v. A total of nine terminals including a phase negative terminal 110 and a w phase negative terminal 111 are provided.

  FIG. 2 shows the polarity of the magnetomotive force generated in each iron core by each winding of the transformer 105 and the connection of each winding. The transformer 105 has iron cores 131 to 133, and these iron cores constitute a tripod iron core. The primary winding 201 is delta-connected, and the windings 202 to 204 between the R phase and the S phase, between the S phase and the T phase, and between the T phase and the R phase are wound around the iron cores 131 to 133, respectively. The number of turns of the windings 202 to 204 is substantially equal.

  The u-phase positive side winding 134 and the u-phase negative side winding 137 are electrically connected in series. The u-phase positive side winding 134 is wound around the iron core 131, and the u-phase negative side winding 137 is wound around the iron core 133. Note that the magnetomotive force generated in the iron core 131 by the u-phase positive side winding 134 and the magnetomotive force generated in the iron core 133 by the u-phase negative side winding 137 are connected so as to have approximately the same size and opposite polarity. .

  The v-phase positive side winding 135 and the v-phase negative side winding 138 are electrically connected in series. The v-phase positive winding 135 is wound around the iron core 132, and the v-phase negative winding 138 is wound around the iron core 131. The magnetomotive force generated in the iron core 132 by the v-phase positive side winding 135 and the magnetomotive force generated in the iron core 131 by the v-phase negative side winding 138 are connected so as to have approximately the same size and opposite polarity. .

  The w-phase positive winding 136 and the w-phase negative winding 139 are electrically connected in series. The w-phase positive winding 136 is wound around the iron core 133, and the w-phase negative winding 139 is wound around the iron core 132. Note that the magnetomotive force generated in the iron core 133 by the w-phase positive winding 136 and the magnetomotive force generated in the iron core 132 by the w-phase negative winding 139 are connected so as to have approximately the same size and opposite polarity. .

  In this specification, the u-phase positive side winding 134 and the u-phase negative side winding 137 are collectively referred to as a u-phase winding. Further, the v-phase positive side winding 135 and the v-phase negative side winding 138 are collectively referred to as a v-phase winding. Similarly, the w-phase positive side winding 136 and the w-phase negative side winding 139 are collectively referred to as a w-phase winding.

  In this specification, the voltage across the u-phase positive winding 134 is VuH, the voltage across the v-phase positive winding 135 is VvH, the voltage across the w-phase positive winding 136 is VwH, and the u-phase negative winding. The voltage at both ends of 137 is expressed as VuL, the voltage at both ends of the v-phase negative winding 138 is expressed as VvL, and the voltage at both ends of the w-phase negative winding 139 is expressed as VwL.

  Also, the sum of VuH and VuL is called u-phase voltage Vu, the sum of VvH and VvL is called v-phase voltage Vv, and the sum of VwH and VwL is called w-phase voltage Vw.

  Further, a voltage applied between the positive side DC output terminal 121 and the negative side DC output terminal 122 of the power conversion device 101 is denoted as VD, and a current flowing through the positive side DC output terminal 121 is denoted as ID.

  Next, the configuration of the positive side converter group 112 and the negative side converter group 116 will be described.

  The positive-side converter group 112 includes a u-phase positive-side converter arm 113, a v-phase positive-side converter arm 114, and a w-phase positive-side converter arm 115. The negative-side converter group 116 includes a u-phase negative-side converter arm 117, a v-phase negative-side converter arm 118, and a w-phase negative-side converter arm 119.

  Each converter arm 113-115, 117-119 is provided with a terminal and b terminal. In this specification, the voltage up to the a terminal with respect to the b terminal is referred to as an arm voltage. Each of the converter arms 113 to 115 and 117 to 119 is a circuit in which one or a plurality of unit chopper cells shown in FIG. 3 are cascade-connected.

  The a terminal of the u-phase positive converter arm 113 is connected to the positive output terminal 121, and the b terminal is connected to the u-phase positive terminal 106 of the transformer 105. Further, in this specification, the arm voltage of the u-phase positive side converter arm 113 is expressed as VarmuH.

  The a terminal of the v-phase positive converter arm 114 is connected to the positive output terminal 121, and the b terminal is connected to the v-phase positive terminal 107 of the transformer 105. Further, in this specification, the arm voltage of the v-phase positive side converter arm 114 is expressed as VarmvH.

  The a terminal of the w-phase positive converter arm 115 is connected to the positive output terminal 121, and the b terminal is connected to the w-phase positive terminal 108 of the transformer 105. In this specification, the arm voltage of the w-phase positive converter arm 115 is denoted as VarmwH.

  The a terminal of the u phase negative converter arm 117 is connected to the u phase negative terminal 109 of the transformer 105, and the b terminal is connected to the negative output terminal 122. Further, in this specification, the arm voltage of the u-phase negative side converter arm 117 is expressed as VarmuL.

  The a terminal of the v phase negative converter arm 118 is connected to the v phase negative terminal 110 of the transformer 105, and the b terminal is connected to the negative output terminal 122. In this specification, the arm voltage of the v-phase negative converter arm 118 is denoted as VarmvL.

  The a terminal of the v-phase negative side converter arm 119 is connected to the w-phase negative side terminal 111 of the transformer 105, and the b terminal is connected to the negative side output terminal 122. Further, in this specification, the arm voltage of the w-phase negative converter arm 119 is expressed as VarmwL.

  In the first embodiment, the sum of VarmuH and VarmuL is expressed as u-phase arm voltage Varmu. Also, the sum of VarmvH and VarmvL will be expressed as v-phase arm voltage Varmu. Similarly, the sum of VarmwH and VarmwL will be expressed as w-phase arm voltage Varmu.

  In the first embodiment, the current flowing through the u-phase positive converter arm 113 and the u-phase negative converter arm 117 is the u-phase arm current Iu, the v-phase positive converter arm 114 and the v-phase negative converter arm. The current flowing through 118 is denoted as v-phase arm current Iv, and the current flowing through w-phase positive side converter arm 115 and w-phase negative side converter arm 119 is denoted as w-phase arm current Iw.

  Next, the configuration of the unit chopper cell 120 will be described with reference to FIG.

  The unit chopper cell shown in FIG. 3 includes a high side switching element 303, a low side switching element 304, and an energy storage element 305. The switching elements 303 and 304 are semiconductor switching elements represented by IGBT. The energy storage element 305 is a capacitor, a storage battery, or the like. In this specification, the voltage up to the x terminal 301 with the y terminal 302 as a reference is expressed as a cell voltage Vcell of the unit chopper cell.

Next, the operation of the power conversion device 101 will be described for the following two cases.
(1) When receiving active power from the three-phase AC power system 100 and supplying DC power to the DC power transmission cable 150 (2) Receiving DC power from the DC power transmission cable 150 and receiving power from the three-phase AC power system 100 Supply

  Hereinafter, an operation when the power conversion apparatus 101 receives active power from the three-phase AC power system 100 and supplies DC power to the DC power transmission cable 150 will be described.

  In the present specification, voltages obtained by converting the line voltages VRS, VST, VTR of the three-phase AC power system 100 to the secondary side of the transformer are expressed as aVRS, aVST, aVTR. Here, a is the turn ratio of the secondary winding to the transformer primary winding.

  Here, the voltages Vu, Vv, and Vw of the secondary winding of the transformer, the arm voltages Varmu, Varmv, and Varmw, and the voltage VD that is applied between the positive DC output terminal 121 and the negative DC output terminal 122 Explain the relationship.

  The relationship between Vu, Varmu, and VD is expressed by the following equation.

[Equation 1]
Vu = VD-Varmu
The relationship between Vv, Varmv, and VD is expressed by the following equation.

[Equation 2]
Vv = VD-Varmv
The relationship between Vw, Varmw, and VD is expressed by the following equation.

[Equation 3]
Vw = VD-Varmw

  As described above, the voltages Vu, Vv, and Vw of the secondary winding of the transformer can be controlled by controlling the u-phase arm voltage Varmu, the v-phase arm voltage Varmv, and the w-phase arm voltage Varmw from Equations 1 to 3.

  If the frequencies and amplitudes of Vu, Vv, and Vw are matched with the frequencies and amplitudes of aVRS, aVST, and aVTR, and only the phases of Vu, Vv, and Vw are slightly delayed from the phases of aVRS, aVST, and aVTR, three phases are obtained. Active power can be caused to flow from the AC power system 100 to the power converter 101.

  Next, it will be described that the arm voltage can be controlled by the switching state of the semiconductor switching elements constituting the unit chopper cell 120.

  When the high-side switching element 303 is on and the low-side switching element 304 is off, the cell voltage Vcell is approximately equal to the voltage VC of the DC capacitor 305 without depending on the current Icell.

  When the high-side switching element 303 is off and the low-side switching element 304 is on, the cell voltage Vcell is almost zero without depending on the current Icell.

  When both the high side switching element 303 and the low side switching element 304 are off, the cell voltage Vcell is determined depending on the polarity of the current Icell. When Icell is positive, the cell voltage Vcell is approximately equal to the voltage VC of the energy storage element 305. When Icell is negative, the cell voltage Vcell is approximately equal to zero.

  Next, a method for supplying power to the DC power transmission cable 150 will be described.

  The current ID flowing through the DC power transmission cable 150 is the sum (Iu + Iv + Iw) of the arm currents Iu, Iv, Iw. When the arm voltages Varmu, Varmv, and Varmw do not include a zero phase component, the arm currents Iu, Iv, and Iw also do not include a zero phase component. When the arm currents Iu, Iv, and Iw do not include a zero-phase component, Iu + Iv + Iw = ID = 0, and power cannot be transmitted to the DC power transmission cable 150.

  In this case, the active power flowing into the power conversion device 101 from the three-phase AC power system 100 is stored in an energy storage element (such as an electrolytic capacitor) inside each unit converter 120.

  In order to supply power to the DC power transmission cable, the zero phase components of the arm voltages Varmu, Varmv, and Varmv are adjusted, and the zero phase components of the arm currents Iu, Iv, and Iw are controlled. From Kirchhoff's current law, since ID = Iu + Iv + Iw, the current ID can be supplied by adjusting the zero-phase components of Iu, Iv, and Iw.

  In addition, when the active power flowing into the power converter 101 from the three-phase AC power system 100 and the active power transmitted to the DC power transmission cable 150 are equal, the energy flowing into and out of each unit chopper cell 120 is the power of the three-phase AC power system. It becomes almost zero in one cycle average.

  Further, as the current ID, a direct current, an alternating current, or a current in which both are superimposed can be passed.

  Hereinafter, an operation when the power conversion apparatus 101 receives active power from the DC power transmission cable 150 and supplies the active power to the three-phase AC power system 100 will be described.

  When the frequencies and amplitudes of Vu, Vv, and Vw are made to coincide with the frequencies and amplitudes of aVRS, aVST, and aVTR, and only the phases of Vu, Vv, and Vw are slightly advanced from the phases of aVRS, aVST, and aVTR, the power Effective power can be supplied from the converter 101 to the three-phase AC power system 100.

  Next, a method for receiving power from the DC power transmission cable 150 will be described.

  The current ID flowing from the DC power transmission cable is the sum (Iu + Iv + Iw) of the arm currents Iu, Iv, Iw. When the arm voltages Varmu, Varmv, and Varmw do not include a zero phase component, the arm currents Iu, Iv, and Iw also do not include a zero phase component. When the arm currents Iu, Iv, Iw do not include a zero-phase component, Iu + Iv + Iw = ID = 0, and power cannot be supplied from the DC power transmission cable 150.

  In this case, the active power flowing out from the power converter 101 to the three-phase AC power system 100 is supplied from an energy storage element (such as an electrolytic capacitor) inside each unit chopper cell 120.

  In order to allow power to flow from the DC power transmission cable 124 to the power converter 100, the zero phase components of the arm voltages Varmu, Varmv, and Varmv are adjusted to control the zero phase components of the arm currents Iu, Iv, and Iw. From Kirchhoff's current law, since ID = Iu + Iv + Iw, the current ID can be supplied by adjusting the zero-phase components of Iu, Iv, and Iw.

  In addition, when the active power flowing out from the power converter 101 to the three-phase AC power system 100 and the active power flowing into the power converter from the DC power transmission cable 150 are equal, the energy flowing into and out of each unit chopper cell 120 is three-phase. One cycle average of the AC power system becomes almost zero.

  In the present specification, the positive DC output terminal 121 and the negative DC output terminal 122 of each of the two power conversion devices 101 connected to the three-phase AC power systems 100 and 170 including the DC power transmission cable 150 are connected. The space is called a DC line.

  Moreover, in this specification, between the transformer 105 containing the alternating current output terminals 102-104 of each phase and the three-phase alternating current power systems 100 and 170 is called an alternating current line.

  Next, it will be described that the operation of the power converter 101 is different between when the AC line is short-circuited and when the DC line is short-circuited.

  When the AC line is short-circuited, a short-circuit current flows if the power conversion device 101 outputs a voltage to the AC line. In order to prevent the short-circuit current, both the high-side switching element 303 and the low-side switching element 304 constituting each unit chopper cell 120 are turned off, and an overcurrent flows in the AC line, as in a general power converter. prevent.

  When the DC line is short-circuited, the electric charge stored in the energy storage element 305 inside each unit chopper cell 120 is discharged to the DC line, and the current ID becomes an overcurrent. In order to prevent the overcurrent, the high-side switching element 303 and the low-side switching element 304 of each unit chopper cell are turned off. A diode is connected to the high side switching element 303 in antiparallel, and the diode has reverse current blocking characteristics. Therefore, the DC voltage of the energy storage element 305 is electrically insulated from the DC line, and the DC power transmission Overcurrent to the cable 150 can be suppressed.

  As described above, when the AC line is next short-circuited and when the DC line is short-circuited, the protection operation of the power conversion device 101 is different, so it is necessary to distinguish between the short-circuit between the DC line and the AC line.

  When the AC line is short-circuited, the current detected by the current sensor installed on the primary winding or secondary winding side of the transformer 105 increases. Therefore, when the current detected by the current sensor installed on the primary winding or secondary winding side of the transformer 105 exceeds the set threshold value, it is determined that the AC fault has occurred.

  Also, current sensors are installed in each phase of the positive converter group 112 and the negative converter group 116, and the current value detected by the current sensor installed in the positive converter group 112 and the negative converter group 116 are set. If the difference from the current value detected by the installed current sensor exceeds a set threshold value, it may be determined that an AC fault has occurred.

  When the DC line is short-circuited, if the current detected by the current sensor 123 installed in the DC line exceeds a set threshold value, it is determined that a DC fault has occurred.

  In addition, a current sensor may be installed at the a terminal or b terminal of each phase of the converter arm, and when the three-phase sum of the currents flowing through the respective converter arms exceeds a set threshold value, it may be determined that a DC fault has occurred.

  When it is determined that the AC line or the DC line has failed, the AC system 100 or 170 and the power converter 101 are disconnected by the circuit breaker 124 in a short time (usually after several tens of milliseconds to several hundred milliseconds).

  When the DC line is short-circuited, the short-circuit current Ish flows from the AC system 100 or 170 according to the leakage impedance of the transformer 105 for a short time until the AC system 100 or 170 and the power converter 101 are disconnected by the circuit breaker 124. . When the voltage of the three-phase AC power system 100 or 170 is Vs and the leakage impedance of the transformer 105 is Ztr, the short circuit current Ish is expressed by the following equation.

[Equation 4]
Ish = Vs / Ztr

  When the saturation current of the semiconductor switching element constituting the unit chopper cell 120 is Isa, the semiconductor switching element can be protected by adjusting the leakage impedance Ztr of the transformer 105 so that Isa> Ish.

  In addition, the junction temperature of the semiconductor switching element is equal to or higher than the set value until the three-phase AC power system 100 or 170 and the power conversion device 101 are disconnected by the circuit breaker 124 (usually several tens of milliseconds to several hundreds of milliseconds). Therefore, the semiconductor switching element can be protected by configuring a cooling system for the semiconductor switching element.

  Next, an example of the cooling system configuration will be described with reference to FIG.

  FIG. 10 is a diagram showing an example of a cooling configuration of the low-side switching element 304 constituting the unit chopper cell 120.

  The low side switching element 304 includes an IGBT 1000 and a diode 1001, and the IGBT 1000 and the diode 1001 are fixed to one cooling fin 1002.

  The heat P_IGBT and heat P_Diode generated from the IGBT 1000 and the Diode 1001 when the short-circuit current Ish flows are radiated from the cooling fins into the air.

  FIG. 11 is a diagram in which the thermal circuit in the cooling configuration of FIG. 10 is replaced with an equivalent electric circuit.

  The heat P_IGBT generated by the IGBT 1000 can be expressed by a current source 1100, and the heat P_Diode generated by the Diode 1001 can be expressed by a current source 1110.

  Further, the thermal resistance Rth (j−c) q and the thermal capacity Cth (j−c) q between the junction of the IGBT 1000 and the IGBT 1000 case can be represented by a resistor 1101 and a capacitor 1102.

  Further, the thermal resistance Rth (cf) q and the thermal capacity Cth (cf) q between the case of the IGBT 1000 and the cooling fin 1002 can be expressed by a resistance 1103 and a capacitor 1104.

  Further, the thermal resistance Rth (f−a) q and the thermal capacity Cth (f−a) q between the cooling fin 1002 and the air can be represented by a resistor 1105 and a capacitor 1106.

  The thermal resistance Rth (j−c) d and thermal capacity Cth (j−c) d between the junction of the diode 1001 and the diode 1001 case can be represented by a resistor 1111 and a capacitor 1112.

  Further, the thermal resistance Rth (cf) d and the thermal capacity Cth (cf) d between the case of the diode 1001 and the cooling fin 1002 can be represented by a resistance 1113 and a capacitor 1114.

  If the air temperature is assumed to be constant, the air temperature Ta can be set as the DC voltage source 1107.

  The high potential side potentials of the capacitors 1102 and 1112 correspond to the junction temperature of the IGBT and Diode.

  Therefore, by reducing the temperature Ta of the air, the junction temperature of the IGBT and the diode when the short-circuit current flows can be set to a set value or less.

  Also, the thermal resistance Rth (j−c) q between the junction of the IGBT 1000 and the IGBT 1000 case, or the thermal resistance Rth (c−f) q between the case of the IGBT 1000 and the cooling fin 1002, or the cooling fin 1002. By reducing the thermal resistance Rth (f−a) q between the air and the air, the junction temperature of the IGBT when the short-circuit current flows can be reduced to a set value or less.

  Also, the thermal resistance Rth (j−c) d between the diode 1001 junction and the diode 1001 case, the thermal resistance Rth (cf) d between the diode 1001 case and the cooling fin 1002, and the cooling fin 1002 and the air By reducing the thermal resistance Rth (f−a) q during the period, the junction temperature of the diode when the short-circuit current flows can be reduced to a set value or less.

  In addition, the short-circuit current flows only for a time (usually after several tens of milliseconds to several hundred milliseconds) of disconnecting the three-phase AC power system 100 or 170 and the power converter 101 by the circuit breaker 124. Heat capacity Cth (j−c) q between the junction and the IGBT 1000 case, or heat capacity Cth (cf) q between the case of the IGBT 1000 and the cooling fin 1002, or heat capacity Cth between the cooling fin 1002 and the air (f−a) By increasing q, the junction temperature of the IGBT can be set to a set value or less until the three-phase AC power system 100 or 170 and the power converter 101 are disconnected.

  Further, the heat capacity Cth (j−c) d between the junction of the Diode 1001 and the case of the Diode 1001, or the heat capacity Cth (cf) q between the case of the Diode 1001 and the cooling fin 1002, or the cooling fin 1002, By increasing the heat capacity Cth (f−a) q between the air, the junction temperature of the diode is kept below a set value until the three-phase AC power system 100 or 170 and the power converter 101 are disconnected. be able to.

  In this embodiment, the primary winding of the transformer is a delta connection, but it can also be applied to other connection methods such as a star connection.

  In this embodiment, two power converters are connected in series on both sides of the DC power transmission system, and the grounded two-wire DC power transmission system is grounded at the connection point. Is a two-wire DC power transmission system that uses only one power converter, or two power converters connected in series at both ends of the DC power transmission system, and each connection point is grounded and connected by a cable. It can also be applied to other DC power transmission systems such as a three-wire DC power transmission system.

  Moreover, although the present Example demonstrated using the direct-current power transmission system as an example, one end, such as a reactive power compensation apparatus and a power converter for motor drives, is connected to a three-phase alternating current power system, and alternating current power is converted into direct current power. Applicable to power converters.

  A second mode for carrying out the present invention will be described.

  In the first embodiment, the converter arm is configured by a chopper cell, but in the second embodiment, the converter arm is configured by a unit full bridge shown in FIG.

  Hereinafter, only the parts of the configuration of the second embodiment that are different from the configuration of the first embodiment will be described.

  FIG. 4 is a circuit diagram showing a second embodiment of the present invention. The power converter 401 is linked to the three-phase AC power systems 100 and 170 via the three-phase AC terminals 102 to 104, and exchanges active / reactive power with the three-phase AC power system 100. The power converter 401 includes a transformer 105, a positive converter group 112, and a negative converter group 116.

  Next, the configuration of the positive side converter group 112 and the negative side converter group 116 will be described.

  The positive-side converter group 112 includes a u-phase positive-side converter arm 113, a v-phase positive-side converter arm 114, and a w-phase positive-side converter arm 115. The negative-side converter group 116 includes a u-phase negative-side converter arm 117, a v-phase negative-side converter arm 118, and a w-phase negative-side converter arm 119.

  Each of the converter arms 113 to 115, 117, 118 is a circuit in which one or a plurality of unit full bridge cells 400 shown in FIG.

  The unit full bridge cell 400 is a two-terminal circuit having an x terminal 500 and a y terminal 501, and includes an x-phase high-side switching element 502, an x-phase low-side switching element 503, a y-phase high-side switching element 504, and a y-phase. The low-side switching element 505 and the energy storage element 506 are included. The switching elements 502 to 505 are semiconductor switching elements represented by IGBT. The energy storage element 506 is a capacitor, a storage battery, or the like. Also in this embodiment, the voltage up to the x terminal with respect to the y terminal is referred to as a cell voltage Vcell of the unit full bridge cell.

  Next, it will be described that the arm voltage can be controlled by the switching state of the switching elements constituting the unit full bridge cell 400.

  The x-phase high-side switching element 502 and the x-phase low-side switching element 503 are alternately turned on / off. Further, the y-phase high-side switching element 504 and the y-phase low-side switching element 505 are alternately turned on / off.

  When the x-phase high-side switching element 502 is on, the x-phase low-side switching element 503 is off, the y-phase high-side switching element 504 is off, and the y-phase low-side switching element 505 is on, it depends on the current Icell The cell voltage Vcell is substantially equal to the voltage VC of the energy storage element 506.

  When the x-phase high-side switching element 502 is on, the x-phase low-side switching element 503 is off, the y-phase high-side switching element 504 is on, and the y-phase low-side switching element 505 is off, it depends on the current Icell The cell voltage Vcell is almost zero.

  Depends on the current Icell when the x-phase high-side switching element 502 is off, the x-phase low-side switching element 503 is on, the y-phase high-side switching element 504 is off, and the y-phase low-side switching element 505 is on The cell voltage Vcell is almost zero.

  When the x-phase high-side switching element 502 is off, the x-phase low-side switching element 503 is on, the y-phase high-side switching element 504 is on, and the y-phase low-side switching element 505 is off, it depends on the current Icell In other words, the cell voltage Vcell is approximately equal to a voltage obtained by inverting the polarity of the voltage VC of the energy storage element 506.

  When the x-phase high-side switching element 502, the x-phase low-side switching element 503, the y-phase high-side switching element 504, and the y-phase low-side switching element 505 are all off, the cell voltage Vcell depends on the polarity of the current Icell. Determined. When Icell is positive, the cell voltage Vcell is approximately equal to the voltage VC of the energy storage element 506. When Icell is negative, the cell voltage Vcell is approximately equal to a voltage obtained by inverting the polarity of the voltage VC of the energy storage element 506.

  Next, operation | movement of the power converter device 401 when a DC line short-circuits is demonstrated.

  Moreover, since the protective operation of the power converter device 401 when the AC line and the DC line are short-circuited is different as in the first embodiment, it is necessary to distinguish the short-circuit between the DC line and the AC line.

  When the DC line is short-circuited, the charge stored in the energy storage element 506 inside each unit chopper cell 400 is discharged to the DC line, and the current ID increases. When the current ID is detected by the current sensor 123 and the set threshold is exceeded, it is determined that the DC fault has occurred, and the x-phase high-side switching element 502 and the y-phase high-side switching element 504 of each unit full bridge cell 400 are determined. OFF, x-phase low-side switching element 503 and y-phase low-side switching element 505 are on, or x-phase high-side switching element 502 and y-phase high-side switching element 504 are on, x-phase low-side switching element 503 and The y-phase low-side switching element 505 is turned off. Diodes are connected in antiparallel to the x-phase high-side switching element 502, the y-phase high-side switching element 504, the x-phase low-side switching element 503, and the y-phase low-side switching element 505, respectively. With reverse blocking characteristics. Therefore, the energy storage element 506 is electrically insulated from the DC line, and an overcurrent to the DC power transmission cable 150 can be suppressed.

  In addition, a current sensor may be installed at the a terminal or b terminal of each phase of the converter arm, and when the three-phase sum of the currents flowing through the respective converter arms exceeds a set threshold value, it may be determined that a DC fault has occurred.

  When it is determined that the DC line has failed, the circuit breaker 124 disconnects the three-phase AC power system 100 or 170 and the power converter 401 in a short time (usually after several tens to several hundreds of milliseconds). A short-circuit current Ish flows from the AC system 100 or 170 according to the leakage impedance of the transformer 105 for a short time until the three-phase AC power system 100 or 170 and the power converter 401 are disconnected. When the voltage of the three-phase AC power system 100 or 170 is Vs and the leakage impedance of the transformer 105 is Ztr, the short circuit current Ish is expressed by the following equation.

[Equation 4]
Ish = Vs / Ztr

  If the saturation current of the semiconductor switching elements constituting the unit full bridge cell 400 is Isa, the semiconductor switching elements can be protected by adjusting the leakage impedance Ztr of the transformer 105 so that Isa> Ish.

  Further, as in the first embodiment, the time for disconnecting the three-phase AC power system 100 or 170 and the power converter 401 by the circuit breaker 124 (usually after several tens of milliseconds to several hundred milliseconds) the junction temperature of the semiconductor switching element The semiconductor switching element can be protected by configuring a cooling system of the semiconductor switching element so that does not exceed the set value.

  When it is determined that there is a DC fault, the power conversion device 401 makes the voltage sum of the positive converter group 112 and the negative converter group 116 approximately equal to the reverse phase voltage of the three-phase AC power system 100 or 170. The DC terminal voltage can be made zero. Therefore, the current ID flowing through the DC output terminal can be reduced.

  In this embodiment, the primary winding of the transformer is a delta connection, but it can also be applied to other connection methods such as a star connection.

  In this embodiment, two power converters are connected in series on both sides of the DC power transmission system, and the grounded two-wire DC power transmission system is grounded at the connection point. Is a two-wire DC power transmission system that uses only one power converter, or two power converters connected in series at both ends of the DC power transmission system, and each connection point is grounded and connected by a cable. It can also be applied to other DC power transmission systems such as a three-wire DC power transmission system.

  Moreover, although the present Example demonstrated using the direct-current power transmission system as an example, one end, such as a reactive power compensation apparatus and a power converter for motor drives, is connected to a three-phase alternating current power system, and alternating current power is converted into direct current power. Applicable to power converters.

  A third embodiment for carrying out the present invention will be described. In the first embodiment, the voltage on the secondary side of the transformer is applied in the phase, but in the third embodiment, the voltage on the secondary side of the transformer is applied between the phases.

  In the following, only the parts of the configuration of the third embodiment that are different from the configuration of the first embodiment will be described.

  FIG. 6 is a circuit diagram showing a third embodiment of the present invention.

  AC power from the three-phase AC power systems 100 and 170 is converted into DC power by each of the two power converters 601 linked to each three-phase AC power system, and unidirectional or bidirectional by the DC power transmission cable 150 Power to

  The power converter 601 includes a transformer 600, a positive converter group 112, a negative converter group 116, a positive reactor group 602, and a negative reactor group 603.

  The positive-side converter group 112 has a configuration in which a u-phase positive-side converter arm 113, a v-phase positive-side converter arm 114, and a w-phase positive-side converter arm 115 are connected by star connection.

  The negative-side converter group 112 has a configuration in which a u-phase negative-side converter arm 113, a v-phase negative-side converter arm 114, and a w-phase negative-side converter arm 115 are connected by star connection.

  One terminal of the positive reactor group 602 is connected in series to the b terminal of the positive side converter group 112, and one terminal of the negative side reactor group 603 is connected in series to the other terminal of the positive side reactor group 602. This is a circuit in which the a terminal of the negative converter group 116 is connected in series to the other terminal of the reactor group 603.

  In this specification, one terminal of the positive reactor is connected in series to the b terminal of the positive converter arm, the other terminal of the positive reactor is connected in series to the other terminal of the negative reactor, and the positive reactor A circuit in which the a terminal of the negative converter arm is connected in series to the other terminal is called a leg.

  The a terminal of the positive converter group 112 is called a P terminal, the connection point of the two reactor groups is called an M terminal, and the b terminal of the negative converter group is called an N terminal.

  The two power converters 601 connect the DC power transmission cable 150 to the P terminal of one power converter 601 and the N terminal of the other power converter 601, and the N terminal of one power converter 601 and the other power The P terminals of the converter 601 are connected to each other, and the connection point 161 is grounded.

  The positive side reactor group 602 and the negative side reactor group 603 of the power conversion device 601 will be described.

  In the positive side converter group 112 and the negative side converter group 116, the voltage Vcell of the unit chopper cell can only output a voltage that is a multiple of the voltage VC of the energy storage element 305, and therefore the instantaneous value of the voltage for each leg is different.

  In the period in which the leg voltages of the three legs do not match, the difference in the leg voltage is shared only by the two reactors included in each leg. If the reactor does not exist, there is an overcurrent in the leg. Will flow.

  The positive side reactor group 602 and the negative side reactor group 603 have a role of preventing the overcurrent.

  Next, it will be described that the operation of the power converter 601 is different between when the AC line is short-circuited and when the DC line is short-circuited.

  When the AC line is short-circuited, if the power converter 601 outputs a voltage to the AC line, a short-circuit current flows. Therefore, when the AC line is short-circuited, both the high-side switching element 303 and the low-side switching element 304 constituting each unit chopper cell 120 are turned off in the same manner as a general power conversion device in order to prevent the short-circuit current. Thus, it is possible to prevent an overcurrent from flowing through the AC line.

  When the DC line is short-circuited, the electric charge stored in the energy storage element 305 inside each unit chopper cell 120 is discharged to the DC line, and the current ID becomes an overcurrent. In order to prevent the overcurrent, the high-side switching element 303 and the low-side switching element 304 of each unit chopper cell 120 are turned off. A diode is connected in antiparallel to the high-side switching element 303. Since the diode has reverse current blocking characteristics, the energy storage element 305 and the DC line are electrically insulated from each other. The overcurrent to can be suppressed.

  As described above, when the AC line is short-circuited and when the DC line is short-circuited, the protection operation of the power conversion device 601 is different, and therefore it is necessary to distinguish between the short-circuit between the DC line and the AC line.

  When the AC line is short-circuited, the current detection value detected by the current sensor installed on the primary winding or secondary winding side of the transformer 600 increases. Therefore, when the current detected by the current sensor installed on the primary winding or secondary winding side of the transformer 600 exceeds the set threshold value, it is determined that there is an AC failure.

  A current sensor is installed in each phase of the positive-side converter group 112 and the negative-side converter group 116, the current value detected by the current sensor installed in the positive-side converter group 112, and the negative-side converter group 116. When the difference from the current value detected by the current sensor installed in the battery exceeds the set threshold value, it may be determined that the AC fault has occurred.

  On the other hand, when the DC line is short-circuited, if the current detected by the current sensor 123 installed in the DC line exceeds a set threshold value, it is determined that a DC fault has occurred.

  In addition, if a current sensor is installed at the a terminal or b terminal of each phase converter arm, and the three-phase sum of the current detection values flowing through each converter arm exceeds a set threshold value, a DC fault may be determined. Good.

  When it is determined that the AC line or the DC line has failed, the AC system 100 or 170 and the power converter 601 are disconnected by the circuit breaker 124 in a short time (usually after several tens to several hundreds of milliseconds).

  Note that this embodiment can be applied not only to a three-phase AC power system but also to a power converter connected to a single-phase or multi-phase system by increasing or decreasing the number of converter arms.

  In the present embodiment, the transformer is a delta-connected transformer for both the primary winding and the secondary winding, but the present invention is not limited to the delta-connected winding configuration of the transformer.

  In this embodiment, two power converters are connected in series on both sides of the DC power transmission system, and the grounded two-wire DC power transmission system is grounded at the connection point. Is a two-wire DC power transmission system that uses only one power converter, or two power converters connected in series at both ends of the DC power transmission system, and each connection point is grounded and connected by a cable. It can also be applied to other DC power transmission systems such as a three-wire DC power transmission system.

  Moreover, although the present Example demonstrated using the direct-current power transmission system as an example, one end, such as a reactive power compensation apparatus and a power converter for motor drives, is connected to a three-phase alternating current power system, and alternating current power is converted into direct current power. Applicable to power converters.

  A fourth mode for carrying out the present invention will be described. The fourth embodiment is a modification of the third embodiment. In the third embodiment, unit chopper cells are used for the positive-side converter group and the negative-side converter group. However, the fourth embodiment is different in that unit full-bridge cells are used.

  In the following, only the parts of the configuration of the fourth embodiment that are different from the configuration of the third embodiment will be described.

  FIG. 7 is a circuit diagram showing a fourth embodiment of the present invention. The power conversion device 701 is linked to the three-phase AC power system 100 or 170 via the three-phase AC terminals 102 to 104, and exchanges active / reactive power with the three-phase AC power system 100 or 170. The power converter 701 includes a transformer 601, a positive converter group 112, and a negative converter group 113.

  Next, the configuration of the positive side converter group 112 and the negative side converter group 116 will be described.

  The positive-side converter group 112 includes a u-phase positive-side converter arm 113, a v-phase positive-side converter arm 114, and a w-phase positive-side converter arm 115. The negative-side converter group 116 includes a u-phase negative-side converter arm 117, a v-phase negative-side converter arm 118, and a w-phase negative-side converter arm 119.

  Each converter arm 113-115,117,118 is provided with a terminal and b terminal. In this specification, the voltage up to the a terminal with respect to the b terminal is referred to as an arm voltage. Each converter arm 113 to 115, 117, 118 is a circuit in which one or a plurality of unit full bridge cells 130 shown in FIG. 5 are cascade-connected.

  Next, it will be described that the operation of the power conversion device 701 differs between when the AC line is short-circuited and when the DC line is short-circuited.

  When the AC line is short-circuited, if the power converter 701 outputs a voltage to the AC line, a short-circuit current flows. Therefore, when the AC line is short-circuited, in order to prevent the short-circuit current, the x-phase high-side switching element 502, y-phase of each unit full-bridge cell 400 that constitutes each unit chopper cell 400 as in a general power converter. By turning off all of the high-side switching element 504, the x-phase low-side switching element 503, and the y-phase low-side switching element 505, it is possible to prevent an overcurrent from flowing through the AC line.

  When the DC line is short-circuited, the charge stored in the energy storage element 506 inside each unit full bridge cell 400 is discharged to the DC line, and the current ID increases. When the current ID is detected by the current sensor 123 installed in the DC line and the set threshold value is exceeded, it is determined that the DC fault has occurred, and the x-phase high-side switching element 502 and the y-phase high side of each unit full bridge cell 400 Switching element 504 is off, x-phase low side switching element 503 and y-phase low-side switching element 505 are on, or x-phase high-side switching element 502 and y-phase high-side switching element 504 are on, x-phase low-side The switching element 503 and the y-phase low side switching element 505 are turned off. Diodes are connected in antiparallel to the x-phase high-side switching element 502, the y-phase high-side switching element 504, the x-phase low-side switching element 503, and the y-phase low-side switching element 505, respectively. With reverse blocking characteristics. Therefore, the DC voltage of the energy storage element 506 is electrically insulated from the DC line, and overcurrent to the DC power transmission cable 150 can be suppressed.

  As described above, when the AC line and the DC line are short-circuited, the protection operation of the power conversion device 701 is different, so it is necessary to distinguish the short-circuit between the DC line and the AC line.

  When the AC line is short-circuited, the current detection value detected by the current sensor installed on the primary winding or secondary winding side of the transformer 600 increases. Therefore, when the current detected by the current sensor installed on the primary winding or secondary winding side of the transformer 600 exceeds the set threshold value, it is determined that an AC failure has occurred.

  A current sensor is installed in each phase of the positive-side converter group 112 and the negative-side converter group 116, the current value detected by the current sensor installed in the positive-side converter group 112, and the negative-side converter group 116. When the difference from the current value detected by the current sensor installed in the battery exceeds the set threshold value, it may be determined that the AC fault has occurred.

  On the other hand, when the DC line is short-circuited, it is determined that a DC fault has occurred when the current detected by the current sensor 123 installed in the DC line exceeds a set threshold value.

  In addition, if a current sensor is installed at the a terminal or b terminal of each phase converter arm, and the three-phase sum of the current detection values flowing through each converter arm exceeds a set threshold value, a DC fault may be determined. Good.

  When it is determined that there is a DC failure, the power conversion device 701 can set the DC terminal voltage to zero by outputting a voltage having a phase opposite to the voltage of the three-phase AC power system 100 or 170. Therefore, the current ID flowing through the DC output terminal can be reduced.

  When it is determined that the AC line or the DC line has failed, the AC system 100 or 170 and the power conversion device 701 are disconnected by the circuit breaker 124 in a short time (usually after several tens of milliseconds to several hundred milliseconds).

  Note that this embodiment can be applied not only to a three-phase AC power system but also to a power converter connected to a single-phase or multi-phase system by increasing or decreasing the number of converter arms.

  In the present embodiment, the transformer is a delta-connected transformer for both the primary winding and the secondary winding, but the present invention is not limited to the delta-connected winding configuration of the transformer.

  In this embodiment, two power converters are connected in series on both sides of the DC power transmission system, and the grounded two-wire DC power transmission system is grounded at the connection point. Is a two-wire DC power transmission system that uses only one power converter, or two power converters connected in series at both ends of the DC power transmission system, and each connection point is grounded and connected by a cable. It can also be applied to other DC power transmission systems such as a three-wire DC power transmission system.

  Moreover, although the present Example demonstrated using the direct-current power transmission system as an example, one end, such as a reactive power compensation apparatus and a power converter for motor drives, is connected to a three-phase alternating current power system, and alternating current power is converted into direct current power. Applicable to power converters.

  In addition to the direct current power transmission system (HVDC) that once converts alternating current power into direct current power and transmits the power, the present invention connects one end of a reactive power compensator and a power conversion device for motor drives to a three-phase alternating current power system. It can be applied to a power conversion device that converts AC power into DC power.

100, 170 Three-phase AC power systems 101, 401, 601, 701 Power converter 102 R phase terminal 103 S phase terminal 104 T phase terminals 105, 600, 805 Transformer 106 u phase positive side terminal 107 v phase positive side terminal 108 w phase positive side terminal 109 u phase negative side terminal 110 v phase negative side terminal 111 w phase negative side terminal 112 positive side converter group 113 u phase positive side converter arm 114 v phase positive side converter arm 115 w phase positive side Converter arm 116 Negative side converter group 117 u phase negative side converter arm 118 v phase negative side converter arm 119 w phase negative side converter arm 120 Unit chopper cell 121 Positive side DC output terminal 122 Negative side DC output terminal 123 Current Sensor 124 Circuit breaker 134 u-phase positive winding 135 v-phase positive winding 136 w-phase positive winding 137 u-phase negative winding 138 v-phase negative winding 139 w Phase negative side winding 150, 807 DC power transmission cable 161, 806 Neutral point 200 Secondary winding 201 Primary winding 202, 203, 204 Iron core 301 x terminal 302 y phase terminal 303 High side switching element 304 Low side switching element 305, 506 Energy storage element 400 Unit full bridge element 500 x-phase output terminal 501 y-phase output terminal 502 x-phase high-side switching element 503 x-phase low-side switching element 504 y-phase high-side switching element 505 y-phase low-side switching Element 602 Positive side reactor group 603 Negative side reactor group 604 Positive side u-phase reactor 605 Positive side v-phase reactor 606 Positive side w-phase reactor 607 Negative side u-phase reactor 608 Negative side v-phase reactor 609 Negative side w-phase reactor Toll 800 DC power transmission system 801 Three-phase full-bridge power converter 802, 803 Capacitor 804 DC reactor 901 Junction point 1000 IGBT
1001 Diode
1002 Cooling fin 1100 IGBT heat generation simulated current source 1101 IGBT junction-case thermal resistance 1102 IGBT junction-case thermal capacity 1103 IGBT case-cooling fin thermal resistance 1104 IGBT case-cooling fin thermal capacity 1105 IGBT cooling fin-air thermal resistance 1106 IGBT cooling fin-to-air heat capacity 1107 Air temperature simulated voltage source 1110 Diode heat generation simulated current source 1111 Diode junction-to-case thermal resistance 1112 Diode junction-to-case heat capacity 1113 Diode case-to-cooling heat resistance 1114 Diode case to cooling fin Heat capacity

Claims (6)

A plurality of series circuits each having a plurality of unit converters connected in series , the plurality of series circuits being connected in parallel between a DC terminal on one side and a DC terminal on the other side, each of the plurality of series circuits being an AC Having a terminal,
The unit converter includes a capacitor, a high-side switching element, and a low-side switching element, the high-side switching element and the low-side switching element are connected in series, and the high-side switching element connected in series is connected to the high-side switching element. It said switching element all SANYO connecting the capacitor in parallel to the low-side switching elements, each of the said high-side switching element low-side switching element includes a reverse connection diode, the high-side switching element the low-side switching elements are both a are those in which the capacitor under predetermined conditions when the OFF is connected to the terminal, the output voltage of said capacitor by said high-side switching element and the low-side switching element to the terminal Do Be from work with the terminal intended to power conversion by performing an operation of the power storage in the capacitor,
In the AC accident related to the AC terminal, both the high-side switching element and the low-side switching element are turned OFF, and in the DC accident related to the DC terminal, the high-side switching element and the low-side switching element A power conversion device comprising a function of turning on a switching element that conducts between the terminals and turning off the other . The power converter of claim 1, a power conversion apparatus characterized by detecting by distinguishing each short section of a short circuit the DC terminals of the ac terminals. The power conversion device according to claim 2, wherein a current detector is provided in a section of the DC terminal of the power conversion device, a short circuit in the section of the DC terminal is set, and a threshold value at which a current value detected by the current detector is set is set. The power converter device provided with the function to determine by exceeding. The power converter according to any one of claims 1 to 3, has a function of detecting and distinguishing each short section of a short circuit the DC terminals of the intersection upstream end terminal of the power conversion apparatus, and, power conversion A current detector for detecting the current state of the converter arm of the converter, and determining a short circuit in the section of the DC terminal by the fact that the three-phase sum of the current of each converter arm exceeds a set threshold value The power converter characterized by the above-mentioned. The power converter according to any one of claims 1 to 4, the current short circuit according to the exchange upstream end terminal of the power conversion apparatus is detected by a current detector installed in the transformer the primary side or the secondary side A power conversion device characterized in that determination is made when a set threshold value is exceeded. The power conversion device according to any one of claims 1 to 5, a short circuit of the ac terminal of the power conversion device, the installed current sensing transducer arm of positive converter group of the power converter And a difference current value of a current detected by a current detector installed in a converter arm of a negative converter group of the power converter is determined when a set threshold value is exceeded. Power converter.

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