JP6411925B2 - Power converter - Google Patents

Description

  The present invention relates to a power converter, and more particularly, to a power converter suitable when the DC sides of a plurality of AC / DC converters are connected to each other.

  When transmitting a large amount of power over a long distance, it is known that DC transmission is more advantageous than AC transmission.

  For example, when power is transmitted from a first AC system to a second AC system, a first AC / DC converter connected to the first AC system and a second AC / DC converter connected to the second AC system are provided. Provided, and the DC side of the two AC / DC converters is connected by a DC transmission line.

  In the present specification, hereinafter, a configuration in which two AC / DC converters are connected by a DC power transmission line as described above is referred to as “two-terminal HVDC”.

  Similarly, a configuration in which the DC sides of n AC / DC converters are connected to each other by a DC power transmission line is referred to as “n terminal HVDC”.

  For example, in a three-terminal DC power transmission system, there may be an operating state in which the first and second AC / DC converters are operating and the remaining third AC / DC converter is stopped and disconnected from the DC power transmission line. .

  For example, in [Patent Document 1], when connecting the stopped third AC / DC converter to the operating first and second AC / DC converters, the DC / DC side of the third AC / DC converter is connected in parallel. Discloses a method of preventing an inrush current by dividing a capacitor into a plurality of capacitors connected in parallel and putting them in a time difference.

JP-A-2-164229

  In an HVDC having four or more terminals, the DC side of the four AC / DC converters is usually connected and operated.

  However, for example, four AC / DC converters are divided into two groups along with maintenance of the DC transmission line, that is, the first and second AC / DC converters are connected to the first two-terminal HVDC (first group). There may be a state where the third and fourth AC / DC converters are respectively operated while forming the second two-terminal HVDC (second group).

  From this state, when the DC sides of the four AC / DC converters are connected again and operated as one 4-terminal HVDC, the operating states of the first and second 2-terminal HVDCs are generally different. There is a possibility that the DC voltage across the switch connecting the first group and the second group is different.

  When a switch that connects the first and second groups is turned on when the DC voltage is different, an inrush current flows from one group to the other, and an AC / DC converter, a DC transmission line, a switch, etc. There is a problem that there is a risk of adversely affecting the environment.

In order to solve the above problems, the present invention provides a power conversion device in which the DC terminals of a plurality of AC / DC converters are connected, wherein the plurality of AC / DC converters are divided into at least first and second groups. And a switch is provided between the first group of DC transmission lines and the second group of DC transmission lines, and the first group of DC transmission lines and the second group of DC transmission lines. And a switch control means having a function of turning on the switch when it is detected that the voltages at both ends of the switch are substantially coincident with each other. At least one of the AC / DC converters is configured to control a DC voltage so as to detect the coincidence of voltages at both ends of the switch.
Alternatively, it is a power conversion device in which the DC terminals of a plurality of AC / DC converters are connected, and includes a switch that divides the AC / DC converters into at least a first group and a second group. A switch control means having a DC-DC converter in a DC circuit connecting the two groups, and having a function of turning on the switch when it is detected that the voltages at both ends of the switch substantially coincide with each other. And at least one of the AC / DC converters is controlled so that the switch control means detects the coincidence of voltages across the switch.
A power converter connected to the DC terminals of a plurality of AC / DC converters, comprising a switch for dividing the AC / DC converters into at least first and second groups, wherein the first and second A DC-DC converter in a DC circuit for connecting the groups, and a switch control means having a function of turning on the switch when it is detected that the voltages at both ends of the switch substantially coincide with each other. The DC-DC converter controls the DC voltage so that the switch control means detects the coincidence of the voltages at both ends of the switch.

  According to the present invention, it is possible to obtain an effect that two n-terminals HVDC in operation can be connected without causing an inrush current.

First embodiment of the present invention Detailed configuration example of AC / DC converter Bidirectional chopper type unit converter Full-bridge type unit converter Detailed configuration example of wind farm Timing chart example 1 Timing chart example 2 Another configuration example of the switch control means Another configuration example of the switch Another configuration example of AC / DC converter 1 Another configuration example of AC / DC converter 2 Another configuration example of AC / DC converter 3 Second embodiment of the present invention Third embodiment of the present invention Fourth embodiment of the present invention

  Hereinafter, a first embodiment of the present invention will be described.

  In the first embodiment, in the four-terminal HVDC in which the DC sides of four AC / DC converters are connected by a DC power transmission line, the four AC / DC converters are divided into two groups each having two two-terminal HVDCs. The switch is provided with a switch control means for switching on the voltage at both ends of the switch at the location where the two groups are connected from the operating state and then turning on the switch.

  Moreover, in Example 1, the operation control means which controls the operation mode of four AC / DC converters is provided.

  In the state where the switch is opened, one of the two AC / DC converters included in each of the two groups controls a DC voltage (AVR mode described later), and the other AC / DC converter. The DC / DC converter controls the DC current (APR mode described later), but after the switch is turned on, the operation control means promptly operates the AC / DC converter that controls the DC voltage included in one group. , Has a function to make a transition so as to control the direct current.

  In the first embodiment, when the two two-terminal HVDC are connected to operate as one four-terminal HVDC, no inrush current is generated, that is, the AC / DC converter and the DC transmission line are adversely affected. The effect of being able to connect without being obtained.

  The overall configuration of the first embodiment will be described below with reference to FIG.

  The power converter 103 is connected to three AC systems 101 a, b, c and one wind farm 102.

  AC / DC converters 107a, b, c, d are connected to the AC systems 101a, b, c, and the wind farm 102, respectively.

  The AC side of the AC / DC converter 107 a is connected to the AC system 101 a, and the DC side is connected to the DC bus 108 a via the switch 109.

  The AC side of the AC / DC converter 107 b is connected to the AC system 101 b, and the DC side is connected to the DC bus 108 b via the switch 109.

  Similarly, the AC side of the AC / DC converter 107c is connected to the AC system 101c, and the DC side is connected to the DC bus 108c via the switch 109.

  The AC side of the AC / DC converter 107 d is connected to the wind farm 102, and the DC side is connected to the DC bus 108 d via the switch 109.

  Although the wind farm 102 is composed of a plurality of wind power generators 113, in the following, each wind power generator 113 does not have a function of controlling the AC voltage amplitude and frequency of the wind farm 102. A description will be given assuming that the amplitude and the frequency are controlled by the AC / DC converter 107d. A detailed configuration of the wind farm 102 will be described later with reference to FIG.

  The DC buses 108a and 108b are connected to the switch 109 via the DC transmission line 110.

  The DC buses 108c and 108d are connected to the switch 109 via the DC power transmission line 110.

  Further, the DC buses 108a and 108d are connected via a switch 105x, a DC power transmission line 106, and a switch 105y.

  Here, FIG. 1 is drawn as a single line connection diagram on both the AC side and the DC side of the AC / DC converters 107a, b, c, and d. Therefore, the AC side is a three-phase or single-phase AC, and the DC side is a monopolar or bipolar power transmission. A detailed configuration example of the AC / DC converters 107a, b, c, and d will be described later with reference to FIG.

  Hereinafter, the state in which all the switches 109 are turned on and the switches 105x and 105y are opened is referred to as an “independent operation state”.

  In other words, the independent operation state means that the AC / DC converters 107a and 107b are operating as the first group 104x constituting the first two-terminal HVDC, and the AC / DC converters 107c and 107d are the second group 104y as the second group 104y. This is a state in which a two-terminal HVDC No. 2 is configured and operated.

  On the other hand, the state in which the switches 109, 105x, and y are turned on and the AC / DC converters 107a, b, c, and d are operated as one 4-terminal HVDC is referred to as “interconnection operation state”.

  In the present embodiment, as shown in FIG. 1, for example, two voltage detection means 111 for measuring the DC voltage across the switch 105y are provided.

  The switch control unit 112 has a function of calculating Verr, which is a difference between the measured values VDCd1 and VDCd2 of the two voltage detection units 111, and controlling on / off of the switch 105y.

  The switch control means 112 transmits the Verr to the AC / DC converter 107c, for example.

  The operation control means 113 gives the switch control means 112 a command signal Op for changing the operation state of the power converter 103 from the independent operation state to the connected operation state or vice versa.

  Further, the operation control means 113 transmits operation mode commands Opa, Opb, Opc, Opd to the AC / DC converters 107a, b, c, d, respectively. The operation mode will be described later.

  Hereinafter, an example of the detailed configuration of the AC / DC converter 107d and its vicinity will be described as an example of the AC / DC converters 107a, b, c, and d with reference to FIG.

  The AC side of the AC / DC converter 107 d is connected to the wind farm 102 via the transformer 201. More specifically, the primary winding 201 p of the transformer 201 is connected to the wind farm 102. The DC side of the AC / DC converter 107d is connected to the DC bus 108d via the switch 109.

  The secondary winding 201s of the transformer 201 and the u-phase leg 202u, the v-phase leg 202v, and the w-phase leg 202w are connected at the U point, the V point, and the W point, respectively.

  The u-phase leg 202u, the v-phase leg 202v, and the w-phase leg 202w are connected in parallel at the P point and the N point of the DC bus 108d.

  The u-phase leg 202u is a series circuit of the u-phase positive side arm 203up, the two reactors 204, and the u-phase negative side arm 203un, and the aforementioned U point is a connection point of the two reactors 204.

  The v-phase leg 202v is a series circuit of the v-phase positive arm 203vp, the two reactors 204, and the v-phase negative arm 203vn, and the above-described V point is a connection point of the two reactors 204.

  The w-phase leg 202w is a series circuit of a w-phase positive arm 203wp, two reactors 204, and a w-phase negative arm 203wn, and the aforementioned W point is a connection point of the two reactors 204.

  Each arm 203up, vp, wp, un, vn, wn is a series circuit of one or a plurality of unit converters 205, respectively. The detailed configuration of the unit converter 205 will be described later with reference to FIGS.

  In other words, the AC / DC converter 107d is H, Akagi, “Classification, terminology, and application of the modular multilevel cascade converter (MMCC),” IEEE Transactions on Power Electronics, vol. 26, no. 11, Nov. 2011 , MMCC-DSCC or MMCC-DSBC described in pp. 3119-3129.

  The AC / DC converter control means 206 transmits the gate signals guk, gvk, gwk to each unit converter 205 via the control communication line 207. Further, the capacitor voltages VCuk, VCvk, and VCwk of each unit converter 205 are received via the control communication line 208.

  For the sake of explanation, the voltage and current of each part in FIG. 2 are defined below.

  The AC phase voltage of the wind farm 102 is expressed as VFu, VFv, VFw.

  Currents flowing from the secondary winding 201s of the transformer 201 to the U point, the V point, and the W point are denoted as IU, IV, and IW, respectively.

  Further, the output voltages of the arms 203up, vp, wp, un, vn, wn are denoted as Vup, Vvp, Vwp, Vun, Vvn, Vwn, respectively.

  Further, the voltage between point P and point N of the AC / DC converter 107d is denoted as VDCd, and the current flowing out from point P is denoted as IDCd.

  The voltage of the DC bus 108d is expressed as VDCd1, and the DC voltage between the DC transmission line 106 and the switch 105y is expressed as VDCd2.

  When the switch 109 between the AC / DC converter 107d and the DC bus 108d is turned on, VDCd = VDCd1.

  The leakage inductance of the transformer 201 is denoted as Lt, and the inductance of the reactor 204 is denoted as LB.

  In FIG. 2, the detailed configuration of the switch 105y is illustrated. The switch 105y includes a single pole switch 209yp connected to the point P of the DC bus 108d and a single pole switch 209yn connected to the point N. .

  Similarly, a detailed configuration of the switch 105x is illustrated, and the switch 105x includes a single pole switch 209xp and a single pole switch 209xn.

  Hereinafter, the principle that the AC / DC converter 107d can supply the AC voltages VFu, VFv, and VFw to the wind farm 102 will be described.

Focusing on the U phase, VFu satisfies the equation (1).
[Equation 1]
VFu = (− Vup + Vun) / 2
+ (Lt + LB / 2) × d / dt × IU (1)

  Therefore, VFu can be controlled by controlling the output voltages Vup and Vun of the u-phase positive arm 203up and the u-phase negative arm 203un. Further, VFv and VFw can be controlled by the same principle.

  Hereinafter, the principle that the AC / DC converter 107d can supply the DC voltage VDCd to the DC bus 108d will be described.

VDCd satisfies the expression (2).
[Equation 2]
VDCd = (Vup + Vvp + Vwp + Vun + Vvn + Vwn) / 6
− (2/3) × Lb × d / dt × IDCd (2)

  Therefore, VDCd can be controlled by controlling the output voltage of each arm 203.

  Here, each arm 203 is a circuit in which one or more unit converters 205 are connected in series. Therefore, if the output voltage of the unit converter 205 included in each arm 203 can be controlled, the output voltage of the arm 203 can be controlled. Can be controlled.

  Hereinafter, with reference to FIG. 3, one example of the configuration of the unit converter 205 and its output voltage control principle will be described.

  FIG. 3 shows a configuration of a bidirectional chopper type unit converter 205c, which is one configuration example of the unit converter 205.

  A circuit in which the positive side switching element 301p and the positive side freewheeling diode 302p are connected in antiparallel and a circuit in which the negative side switching element 301n and the negative side freewheeling diode 302n are connected in reverse parallel form a series circuit. In addition, the series connection point is denoted as a point.

  The series circuit and the capacitor 303 are connected in parallel at points p and n. The voltage across the capacitor is denoted as VCjk. However, j = up, vp, wp, un, vn, wn, k = 1, 2,..., N, where N represents the number of unit converters 205 in each arm.

  The points a and n are used as output terminals of the bidirectional chopper type unit converter 205c, and the output voltage is expressed as Vjk.

  The voltage detector 304 detects the voltage VCjk of the capacitor 303 and transmits it to the unit converter controller 305.

  The unit converter control means 305 applies the gate-emitter voltage of the switching elements 301p, n based on the gate signal gjk received from the AC / DC converter control means 206 via the control communication line 207, and the switching elements 301p, n Controls on / off.

  Further, the voltage VCjk of the capacitor 303 is transmitted to the AC / DC converter control means 206 via the control communication line 208.

  Hereinafter, a method for controlling the output voltage Vjk of the bidirectional chopper type unit converter 205c will be described.

  When the positive side switching element 301p is turned on and the negative side switching element 301n is turned off, it can be controlled to approximately Vjk = VCjk.

  When the positive side switching element 301p is turned off and the negative side switching element 301n is turned on, it can be controlled to approximately Vjk = 0.

  Therefore, the output voltage of the bidirectional chopper type unit converter 205c can be controlled by controlling the on / off state of the switching elements 301p, n.

  Hereinafter, another example of the configuration of the unit converter 205 will be described with reference to FIG.

  FIG. 4 shows a configuration of a full bridge type unit converter 205 f which is one configuration example of the unit converter 205.

  A circuit in which the a-phase positive switching element 301ap and the a-phase positive circulating diode 302ap are connected in reverse parallel and a circuit in which the a-phase negative switching element 301an and the a-phase negative circulating diode 302an are connected in reverse parallel are the first series circuit. Is forming. In addition, the series connection point is denoted as a point.

  Similarly, a circuit in which the b-phase positive side switching element 301bp and the b-phase positive side free-wheeling diode 302bp are connected in reverse parallel and a circuit in which the b-phase negative side switching element 301bn and the b-phase negative side free-wheeling diode 302bn are connected in reverse parallel are the second. The series circuit is formed. The series connection point is denoted as b point.

  The first and second series circuits and the capacitor 303 are connected in parallel at points p and n. The voltage across the capacitor is denoted as VCjk. However, j = up, vp, wp, un, vn, wn, k = 1, 2,..., N, where N represents the number of unit converters 205 in each arm.

  The points a and b are used as output terminals of the full bridge unit converter 205f, and the output voltage is expressed as Vjk.

  The voltage detector 304 detects the voltage VCjk of the capacitor 303 and transmits it to the unit converter controller 305.

  The unit converter control means 305 applies the gate-emitter voltages of the switching elements 305ap, an, bn, bn based on the gate signal gjk received from the AC / DC converter control means 206 via the control communication line 207, and performs switching. The elements 305ap, an, bn, and bn are turned on and off.

  Further, the voltage VCjk of the capacitor 303 is transmitted to the AC / DC converter control means 206 via the control communication line 208.

  Hereinafter, a method for controlling the output voltage Vjk of the full bridge type unit converter 205f will be described.

  When the a-phase positive switching element 301ap is turned on, the a-phase negative switching element 301an is turned off, the b-phase positive switching element 301bp is turned on, and the b-phase negative switching element 301bn is turned off, Vjk = 0 Can be controlled.

  When the a-phase positive switching element 301ap is turned on, the a-phase negative switching element 301an is turned off, the b-phase positive switching element 301bp is turned off, and the b-phase negative switching element 301bn is turned on, Vjk = VCjk Can be controlled.

  When the a-phase positive switching element 301ap is turned off, the a-phase negative switching element 301an is turned on, the b-phase positive switching element 301bp is turned off, and the b-phase negative switching element 301bn is turned on, Vjk = 0 Can be controlled.

  When the a-phase positive switching element 301ap is turned off, the a-phase negative switching element 301an is turned on, the b-phase positive switching element 301bp is turned on, and the b-phase negative switching element 301bn is turned off, Vjk = − VCjk can be controlled.

  Therefore, the output voltage of the full-bridge unit converter 205f can be controlled by controlling the on / off states of the switching elements 301ap, an, bn, and bn.

  Hereinafter, a detailed configuration example of the wind farm 102 will be described with reference to FIG.

  One or more wind power generators 113 are connected to the current collector bus 508.

  In FIG. 5, three types of wind power generators 113a, 113b, and 113c are depicted as examples of the wind power generator 113.

  The wind power generator 113a includes, for example, a wind turbine 501, a gear box 502, a generator 503p, a generator side AC / DC converter 504, a capacitor 505, a current collecting bus side AC / DC converter 506, and a transformer 507.

  The generator side AC / DC converter 504 converts AC power from the generator into DC power. The current collector bus side AC / DC converter 506 converts the DC power into AC power and outputs the AC power to the current collector bus 508.

  Specifically, the current collecting bus side AC / DC converter 506 of each wind power generator 113 outputs a current in phase with the voltages VFu, VFv, and VFw supplied by the AC / DC converter 107d, whereby the wind turbine 501, The generated power obtained through the gear box 502 and the generator is output to the current collecting bus.

  The power output to the current collecting bus is converted to DC power by the AC / DC converter 107d via the transformer 201 of FIG.

  Unlike the wind power generator 113a, the wind power generator 113b does not use the gear box 502, and is a wind power generator in which the wind turbine 501 and the generator 503p are directly coupled.

  The wind power generator 113c includes, for example, a wind turbine 501, a gear box 502, a generator 503d, a generator side AC / DC converter 504, a capacitor 505, a current collecting bus side AC / DC converter 506, and a transformer 507.

  The stator winding of the generator 503d is connected to the current collecting bus 508 via the transformer 507, and the rotor winding of the generator 503d is the generator side AC / DC converter 504, the capacitor 505, and the current collecting bus side AC / DC. It is connected to the current collector bus via a converter 506 and a transformer 507.

  FIG. 5 shows an example of the configuration of the wind farm 102. The wind farm 102 may include at least one of the wind power generators 113a, 113b, 113c, and other types of wind power generators described above.

  Hereinafter, the operation of the switch control means 112 and the switch 105y, which is a feature of the present invention, will be described with reference to FIG.

  FIG. 6 is a schematic timing chart. When the group 104x formed by the AC / DC converters 107a and 107b and the group 104y formed by the AC / DC converters 107c and 107d are in an independent operation state, that is, the switch 105y is opened. It shows a period from when the switch 105y is turned on to when the four AC / DC converters 107a, b, c, d are changed to the connected operation state.

  Prior to time t = t1, the groups 104x and y were in an independent operation state.

  Prior to time t = t1, the operation mode commands Opa, Opb, Opc, Opd transmitted from the operation control means 113 to the AC / DC converters 107a, b, c, d are Opa = AVR, Opb = APR, OPc = AVR and OPd = APR.

  That is, in the group 104x, the AC / DC converter 107a operates as an automatic voltage regulator (AVR) and the AC / DC converter 107b operates as an automatic power regulator (APR).

  In the group 104y, the AC / DC converter 107c operates in the AVR mode, and the AC / DC converter 107d operates in the APR mode.

  Hereinafter, the AVR mode and the APR mode are collectively referred to as “operation mode”.

  In FIG. 6, it is assumed that the AC / DC converters 107a and 107c are operating in the AVR mode and the AC / DC converters 107b and 107d are operating in the APR mode before time t = t1.

  The AC / DC converter operating in the AVR mode performs control so that the voltage of the DC bus is substantially constant according to the given command value.

  The AC / DC converter operating in the APR mode controls the DC current according to the given command value, and as a result, controls the DC power.

  Hereinafter, the AVR mode and the APR mode are collectively referred to as “operation mode”.

  When the group 104x and the group 104y are in the independent operation state, the operation state of each group is naturally different. Therefore, the DC voltages VDCd1 and VDCd2 at both ends of the switch 105y that are input when transitioning to the interconnection operation state are not necessarily equal.

  At time t = t1, an interconnection operation command is given from the operation control means 113 to the switch control means 112. That is, a transition is made from OP = IS to Op = CN.

  The switch control unit 112 detects VDCd1 and VDCd2 via the voltage detection unit 111, calculates a difference Verr thereof, and transmits it to the AC / DC converter 107c operating as AVR.

  The AC / DC converter 107c controls the DC voltage VDCc of the DC bus 108c by controlling the output voltage of each arm 203 according to the principle shown in the equation (2).

As shown in equation (3), VDCd can be controlled by controlling VDCc.
[Equation 3]
VDCd1 = VDCc + 2 × IDCd × R (3)

  Here, R is the resistance value per line of the DC power transmission line 110y.

  The AC / DC converter 107c controls the VDCd1 through the control of the VDCc so that Verr = VDC1-VDC2 becomes substantially zero.

  At time t = t2, Verr can be controlled to almost zero, so that the switch control means 112 changes the switch control command SC to be given to the switch 105y from Off to On.

  According to the present invention, since VDCd1 = VDCd2 is substantially satisfied at time t = t2, an effect of preventing an inrush current when the switch 105y is turned on can be obtained.

  The switch 105y is turned on when SC = On is received. As a result, the AC / DC converters 107a, b, c, d are operated as one 4-terminal HVDC.

  At time t = t3, the operation control means 113 switches the operation mode command Opc of the AC / DC converter 107c from AVR to APR. As a result, the AC / DC converter 107c is switched from the AVR mode to the APR mode, and only the AC / DC converter 107a among the four AC / DC converters 107a, b, c, and d operates in the AVR mode.

  In other words, the AC / DC converter 107c changes the controlled object from the DC voltage VDCc to the DC current IDCc flowing between the AC / DC converter 107c and the DC bus 108c.

  By having only one AC / DC converter 107 in the AVR mode, it is possible to avoid a control conflict such that a plurality of AC / DC converters 107 attempt to control the DC voltage simultaneously.

  The AC / DC converters 107 that can be operated in the AVR mode are only the AC / DC converters 107a, 107b, and 107c. Since the AC / DC converter 107d needs to control the power output to the DC side according to the power generated by the wind farm 102, it cannot be operated in the AVR mode but must be operated in the APR mode.

  Therefore, the operation control means 113 is connected to the AVR mode from the AC / DC converter other than the AC / DC converter 107 connected to the system having no function of controlling the AC voltage amplitude and frequency, such as the wind farm 102. A function of selecting the AC / DC converter 107.

  From the above, according to the time chart of FIG. 6, it can be seen that the group 104x, y can be transitioned from the independent operation state to the connected operation state while preventing inrush current.

  FIG. 7 shows another example of a schematic timing chart.

  The difference between FIG. 7 and FIG. 6 is that at time t = t3, the AC / DC converter whose operation mode is AVR is not the AC / DC converter 107a but the AC / DC converter 107c.

  Even when the time chart of FIG. 7 is followed, the groups 104x and y can be transitioned from the independent operation state to the interconnection operation state while preventing inrush current.

  Hereinafter, another example of connection between the switch 105y and the voltage detection unit 111 will be described with reference to FIG.

  In FIG. 2, the voltage detection means 111 detects VDCd1 and VDCd2 separately, but in FIG. 8, the voltage detection means 111 detects the voltages across the switches 209yp and yn, respectively.

  When the group 104x, y is in an independent operation state, an inrush current when the switch 209yp, yn, that is, the switch 105y is turned on can be prevented if the voltage across the single pole switch 209yp, yn is zero.

  Therefore, the effects of the present invention can also be obtained using the configuration of FIG.

  Hereinafter, a detailed configuration example of the switch 105y will be described with reference to FIG.

  As described above, the switch 105y includes the monopolar switches 209yp and yn.

  The single pole switches 209 yp and yn have a configuration in which a series circuit composed of an auxiliary single pole switch 902 and a current limiting means 903 is connected in parallel with the main single pole switch 901. In addition, a switch timing control means 904 is provided to control the turning on / off of the main single pole switch 901 and the auxiliary single pole switch 902.

  With such a configuration, even when there is an error in the detection voltage by the voltage detection means 111 or the calculation result by the switch control means 112, an inrush current when the switch 105y is turned on can be prevented. can get.

  Hereinafter, the operation of the single pole switches 209 yp and yn will be described according to the timing chart on the right side of FIG. 9.

  At time t = t3, the switch control command SC is changed from Off to On.

  Then, at time t = t31, the switch timing control means 904 turns on the auxiliary single pole switch 902.

  As a result, the group 104x and the group 104y are connected via the current limiting means 903.

  Even when there is an error in the voltage detection means 111 and the switch control means 112, or when the DC voltage at both ends of the switch 105y is different, the current limiting means 903 can prevent the inrush current.

  Thereafter, at time t = t32, the switch timing control means 904 turns on the main single pole switch 901.

  As a result, the group 104x and the group 104y transition from the independent operation state to the connected operation state.

  Hereinafter, another configuration example of the AC / DC converters 107a, b, c, and d will be described with reference to FIG.

  An AC / DC converter 1001 shown in FIG. 10 is another configuration example of the AC / DC converters 107a, b, c, and d. The following description assumes that the AC / DC converter 107d is replaced with the AC / DC converter 1001. However, the AC / DC converter 1001 can be used for some or all of the AC / DC converters 107a, 107b, and 107c.

  A circuit in which u-phase positive switching element 1003up and u-phase positive-side freewheeling diode 1004up are connected in reverse parallel, and a circuit in which u-phase negative-side switching element 1003un and u-phase negative-side freewheeling diode 1004un are connected in reverse parallel are the first series circuit. Is forming. The series connection point is denoted as U point.

  A circuit in which the v-phase positive side switching element 1003vp and the v-phase positive side free-wheeling diode 1004vp are connected in reverse parallel and a circuit in which the v-phase negative side switching element 1003vn and the u-phase negative side free-wheeling diode 1004vn are connected in reverse parallel are the second series circuit. Is forming. The series connection point is denoted as V point.

  A circuit in which the w-phase positive side switching element 1003wp and the w-phase positive side free-wheeling diode 1004wp are connected in reverse parallel and a circuit in which the w-phase negative side switching element 1003wn and the w-phase negative side free-wheeling diode 1004wn are connected in reverse parallel are the third series circuit. Is forming. A series connection point is denoted as W point.

  The first, second, and third series circuits are connected in parallel with the capacitor 1005 at points P and N.

  The secondary winding 1002s of the transformer 1002 is connected to the U point, the V point, and the W point.

  In other words, the AC / DC converter 1001 has a configuration in which a transformer is connected to the AC side 1002 of the three-phase two-level converter.

  For example, when the AC / DC converter 1001 is the AC / DC converter 107 d, the primary winding 1002 p of the transformer 1002 is connected to the wind farm 102. Alternatively, for example, when the AC / DC converter 1001 is the AC / DC converters 107a, b, and c, the primary winding 1002p of the transformer 1002 is connected to the AC systems 101a, b, and c.

  The AC / DC converter control means 1007 transmits guk, gvk, and gwk to the switching elements 1003up, vp, wp, un, vn, and wn via the control communication line 207. Further, the voltage of the capacitor 1006, that is, the voltage VDCd between the point P and the point N is received via the control communication line 208.

  The AC / DC converter 1001 can control the voltage of the capacitor 1006 by exchanging power with the AC systems 101a, 101b, 101c, or the DC transmission lines 106, 110.

  Therefore, even if the AC / DC converter 1001 is used, the operation according to the timing chart of FIG. 6 or FIG. 7 is possible, so that the effect of the present invention can be obtained.

  Hereinafter, another configuration example of the AC / DC converters 107a, b, c, and d will be described with reference to FIG. In the following description, it is assumed that the AC / DC converter 107d is replaced with the AC / DC converter 1101. However, the AC / DC converter 1101 can be used for some or all of the AC / DC converters 107a, 107b, and 107c.

  An AC / DC converter 1101 in FIG. 11 has a configuration in which the transformer 201 is replaced with a three-winding transformer 1102 in the AC / DC converter 107d shown in FIG. In other words, the AC / DC converter 1101 is the AC / DC converter disclosed in FIG. 1 of JP2013-99054A.

  The AC / DC converter control means 1103 transmits the gate signals guk, gvk, and gwk to each unit converter 205 via the control communication line 207. Further, the capacitor voltages VCuk, VCvk, and VCwk of each unit converter 205 are received via the control communication line 208.

  The secondary winding 1102 s and the tertiary winding 1102 t of the three-winding transformer 1102 are Y-connected, and connect the neutral points of each other.

  The u-phase positive arm 203up is connected to the Up point of the secondary winding 1102s of the three-winding transformer 1102. Similarly, the u-phase negative arm 203un is connected to the Un point of the tertiary winding 1102t of the three-winding transformer 1102.

  The v-phase positive arm 203vp is connected to the Vp point of the secondary winding 1102s of the three-winding transformer 1102. Similarly, the v-phase negative arm 203 vn is connected to the Vn point of the tertiary winding 1102 t of the three-winding transformer 1102.

  The w-phase positive arm 203wp is connected to the Wp point of the secondary winding 1102s of the three-winding transformer 1102. Similarly, the w-phase negative arm 203wn is connected to the Wn point of the tertiary winding 1102t of the three-winding transformer 1102.

  Hereinafter, for the sake of explanation, the leakage inductance between the secondary winding 1102s and the tertiary winding 1102t of the three-winding transformer 1102 is denoted as Lt.

Here, the voltage VDCd between the point P and the point N satisfies the expression (3).
[Equation 3]
VDCd = (Vup + Vvp + Vwp + Vun + Vvn + Vwn) / 6
− (2/3) × Lt × d / dt × IDCd (3)

  Therefore, VDCd can be controlled by controlling the output voltage of each arm 203.

  Since the VDCd can be controlled, even if the AC / DC converter 1101 is used, the operation according to the timing chart of FIG. 6 or FIG. 7 is possible, so that the effect of the present invention can be obtained.

  Hereinafter, another configuration example of the AC / DC converters 107a, b, c, and d will be described with reference to FIG. The following description assumes that the AC / DC converter 107d is replaced with the AC / DC converter 1201. However, the AC / DC converter 1201 can be used for some or all of the AC / DC converters 107a, 107b, and 107c.

  The AC / DC converter 1201 shown in FIG. 12 has the same structure as the AC / DC converter 107d shown in FIG. 2 except that the transformer 201 is replaced with a staggered connection transformer 1202, and the arms 203u, v, and w are secondary windings of the staggered connection transformer 1202. 1202s is connected between the U point, V point, W point and P point.

  Further, the neutral point of the secondary winding 1202s of the staggered connection transformer 1202 is connected to the N point.

  In other words, the AC / DC converter 1101 is the AC / DC converter disclosed in FIG. 12 of Japanese Patent Application Laid-Open No. 2010-233411.

  For example, when the AC / DC converter 1201 is the AC / DC converter 107 d, the primary winding 1202 p of the transformer 1202 is connected to the wind farm 102. Alternatively, for example, when the AC / DC converter 1201 is the AC / DC converters 107a, b, and c, the primary winding 1202p of the transformer 1202 is connected to the AC systems 101a, b, and c.

  The AC / DC converter control means 1203 transmits the gate signals guk, gvk, and gwk to each unit converter 205 via the control communication line 207. Further, the capacitor voltages VCuk, VCvk, and VCwk of each unit converter 205 are received via the control communication line 208.

  The output voltages of the arms 203u, v, and w are denoted as Vu, Vv, and Vw, respectively.

  Hereinafter, for description, the inductance of the secondary winding 1202s of the staggered transformer 1202 with respect to the zero-phase current is denoted as L0.

Here, the voltage VDCd between the point P and the point N satisfies the equation (4).
[Equation 4]
VDCd = (Vu + Vv + Vw) / 3
− (1/3) × L0 × d / dt × IDCd (4)

  Therefore, VDCd can be controlled by controlling the output voltage of each arm 203.

  Since VDCd can be controlled, even if the AC / DC converter 1101 is used, the operation according to the timing timing chart of FIG. 6 or FIG. 7 is possible, so that the effect of the present invention can be obtained.

  In this embodiment, IGBT (insulated-gate bipolar transistor) symbols are used for the switching elements 301p, n, ap, an, bp, bn, and the switching elements 1003up, vp, wp, un, vn, wn. However, the semiconductor device is not limited to an IGBT, and is an on / off control semiconductor device such as a junction field-effect transistor (JFET), a metal-oxide-semiconductor field-effect transistor (MOSFET), a gate-commutated thyristor (GCT), and the like. The effect of the present invention can also be obtained by using a circuit in which these are connected in series, parallel, or series-parallel.

  The names “primary winding” and “secondary winding” used in the description of the transformers 201, 1102, and 1202 are for convenience of explanation, and “primary winding” The effects of the present invention can also be obtained when a name other than “secondary winding” is used.

  Hereinafter, a second embodiment of the present invention will be described.

  In the second embodiment, as in the first embodiment, in the four-terminal HVDC in which the DC sides of the four AC / DC converters are connected by the DC power transmission line, the four AC / DC converters are divided into two groups of two, A switch control means for switching on the switch after matching the voltages at both ends of the switch at the location where the two two-terminal HVDC are connected from the state of operating as two two-terminal HVDC. Is provided.

  In the second embodiment, as in the first embodiment, when the two two-terminal HVDCs are connected to operate as one four-terminal HVDC, no inrush current is generated, that is, an AC / DC converter, The effect of being able to connect without adversely affecting the DC power transmission line can be obtained.

  The overall configuration of the second embodiment will be described below with reference to FIG.

  However, only the differences between the AC / DC converter 103 of the first embodiment and the AC / DC converter 1301 of the second embodiment will be described.

  In the first embodiment, the switch control unit 112 detects the DC voltage across the switch 105y by the voltage detection unit 111, and the switch 105y is turned on when the difference becomes zero.

  On the other hand, in the second embodiment, switch control means 1301 is provided instead of the switch control means 112, and the switch control means 1302 receives the voltage coincidence detection signal VEQ from the AC / DC converter 107c, and VEQ = EQ If the operation command Op = CN from the operation control means 113, the switch 105y is turned on.

  The IDCc is detected by the current detection unit 1303.

  Further, the operation control means 113 transmits the voltage VDCa of the DC bus 108a to the AC / DC converter 107c.

  Hereinafter, the calculation when the AC / DC converter 107c outputs the voltage match detection signal VEQ will be described.

The AC / DC converter 107c determines the direct current of the switch 105y from the voltage VDCc of the direct current bus 108c controlled by itself in the AVR mode, the current IDCc flowing from the direct current transmission line 110 into the direct current bus 108c, and the resistance value of the direct current transmission line 110. The DC voltage VDCd on the bus 108d side is estimated based on the equation (5). Here, the estimated value of VDCd is expressed as <VDCd>.
[Equation 5]
<VDCd> = VDCc + R × IDCc (5)

When the absolute value of the difference between the estimated <VDCd> and the VDCa received from the operation control means 113 is below a certain threshold VDCth, VEQ = EQ, and when it exceeds, VEQ = UE. That is, VEQ is the expression (6).
[Equation 6]

  As VDCth, for example, a value of about 0.1% to 5% of VDCd is set.

  If the switch 105y is turned on while VEQ = EQ, an effect of preventing inrush current can be obtained.

  The third embodiment of the present invention will be described below.

  The third embodiment has a configuration in which a DC-DC converter is inserted in a DC power transmission line connecting two two-terminal HVDCs in the power conversion apparatus 103 of the first embodiment.

  In the third embodiment, as in the first embodiment, when the two two-terminal HVDCs are connected to operate as one four-terminal HVDC, no inrush current is generated, that is, an AC / DC converter, The effect of being able to connect without adversely affecting the DC power transmission line can be obtained.

  In addition, since a DC transmission line DC-DC converter is inserted into a DC transmission line connecting two two-terminal HVDCs, even when the two two-terminal HVDCs are operated at different voltages, Two two-terminal HVDC can be connected.

  The overall configuration of the third embodiment will be described below with reference to FIG. However, only differences from the first embodiment will be described.

  The power converter 1401 has a configuration in which a DC-DC converter 1402 is inserted into the DC power transmission line 106 of the power converter 103 of the first embodiment.

  As described in the first embodiment, the operation of the voltage detection unit 111, the switch control unit 112, and the AC / DC converter 107c detects that the DC voltages VDCd1 and VDCd2 at both ends of the switch 105y substantially coincide with each other, and then opens and closes. The container 105y is turned on.

  Hereinafter, with reference to FIG. 15, another example of a configuration in which a DC-DC converter is inserted in a DC power transmission line that connects two 2-terminal HVDCs will be described.

  The power converter 1501 in FIG. 16 includes a switch control unit 1502 instead of the switch control unit 112.

  The switch control unit 1502 calculates the difference Verr (= VDCd1−VDCd2) between the DC voltages VDCd1 and VDCd2 across the switch 105y, similarly to the switch control unit 112 of the first embodiment.

  However, unlike the switch control unit 112, the switch control unit 1502 transmits Verr to the DC-DC converter 1402.

  The DC-DC converter 1402 controls the direct-current voltage VDCd2 by controlling the electric power exchanged with the direct-current power transmission line 106, and controls the VDCd2 so that it substantially coincides with the VDCd1, that is, Verr becomes substantially zero.

  The switch control means 112 detects that Verr has become substantially zero, and changes the switch control command SC to be supplied to the switch 105y from Off to On.

  According to the present invention, since VDCd1 = VDCd2 before the switch 105y is turned on, the effect of preventing an inrush current when the switch 105y is turned on can be obtained.

  Further, with the configuration of FIG. 15, it is possible to connect the two two-terminal HVDC without affecting the voltage of the DC power transmission line in the group 104y.

101a, b, c ... AC system 102 ... Wind farm 103 ... Power conversion device 104x, y ... Group 105x, y ... Switch 106 ... DC transmission line 107a, b, c , D ... AC / DC converters 108a, b, c, d ... DC bus 109 ... Switch 110 ... DC transmission line 111 ... Voltage detection means 112 ... Switch control means 113 ..Operation control means 201: Transformer 201p: Transformer primary winding 201s: Transformer secondary winding 202u, v, w: Leg 203up, vp, wp, un, vn, wn ... arm 204 ... reactor 205 ... unit converter 205c ... bidirectional chopper type unit converter 205f ... full bridge type unit converter 206 ... AC / DC converter control means 207, 208 ... Control communication 209 yp, yn... Single pole switch 301 p, n, ap, an, bp, bn... Switching element 302 p, n, ap, an, bp, bn.・ Voltage detection means 305... Unit converter control means 501 .. wind turbine 502... Gear box 503 .. generator 504 .. generator side AC / DC converter 505 .. capacitor 506. Current collecting bus side AC / DC converter 507 ... Transformer 508 ... Current collecting bus 901 ... Main single pole switch 902 ... Auxiliary single pole switch 903 ... Current limiting means 904 ... Opening / closing Transformer timing control means 1001 ... AC / DC converter 1002 ... Transformer 1002p ... Transformer primary winding 1002s ... Transformer secondary winding 1003up, vp, wp, un, vn, wn .. switching element 1004up, vp, wp, un, vn, wn... Freewheeling diode 1005... Capacitor 1006... Voltage detection means 1007 .. AC / DC converter control means 1101. .. Three-winding transformer 1102p ... Transformer primary winding 1102s ... Transformer secondary winding 1102t ... Transformer tertiary winding 1103 ... AC / DC converter control means 1201 ... AC / DC converter 1202 ... Staggered connection transformer 1202p ... Staggered connection transformer primary winding 1202s ... Staggered connection transformer secondary winding 1203 ... AC / DC converter control means 1301 ... Power conversion Device 1302 ... Switch control means 1303 ... Current detection means 1401 ... Power converter 1402 ... DC-DC converter 1501 ... Power converter 15 02 ... Switch control means

Claims (8)

  A power converter connected to DC terminals of a plurality of AC / DC converters, wherein the plurality of AC / DC converters are divided into at least a first group and a second group, A switch is provided between the second group of DC transmission lines, and both the first group of DC transmission lines and the second group of DC transmission lines are in a power transmission state, and both ends of the switch A switch control means having a function of turning on the switch when it is detected that the voltages of the switches substantially match, so that the switch control means detects a match between the voltages at both ends of the switch. , At least one of the AC / DC converters controls a DC voltage.   2. The power conversion device according to claim 1, wherein the switch control unit has a function of turning on the switch when the switch control unit detects coincidence of voltages at both ends of the switch. 3. A power converter.   The power conversion device according to claim 1 or 2, wherein one of the AC / DC converters included in the first group controls a DC voltage when the switch is opened. The other AC / DC converter is operated to control DC current, and one of the AC / DC converters included in the second group is operated in AVR mode to control DC voltage. The other AC / DC converter is operating in the APR mode so as to control the direct current, and after the switch is turned on, one of the AC / DC converters operating in the AVR mode is switched to the APR mode. A power conversion device comprising operation control means having a function of changing to   4. The power converter according to claim 3, wherein the operation control means is an AC / DC converter that operates in an AVR mode after the switch is turned on, and has no means for controlling the AC voltage amplitude and frequency. A power converter having a function of selecting one of AC / DC converters other than the connected AC / DC converter.   A power converter connected to the DC terminals of a plurality of AC / DC converters, comprising a switch for dividing the AC / DC converters into at least first and second groups, wherein the first and second A DC-DC converter in a DC circuit for connecting the groups, and a switch control means having a function of turning on the switch when it is detected that the voltages at both ends of the switch substantially coincide with each other. And the switch control means controls at least one of the AC / DC converters so as to detect the coincidence of voltages at both ends of the switch.   A power converter connected to the DC terminals of a plurality of AC / DC converters, comprising a switch for dividing the AC / DC converters into at least first and second groups, wherein the first and second A DC-DC converter in a DC circuit for connecting the groups, and a switch control means having a function of turning on the switch when it is detected that the voltages at both ends of the switch substantially coincide with each other. And the DC-DC converter controls the DC voltage so that the switch control means detects the coincidence of the voltages at both ends of the switch.   The power converter according to any one of claims 1 to 6, wherein the switch includes a main single-pole switch, an auxiliary single-pole switch, and a current-limiting means, and the auxiliary single-pole switch and the current-limiting device. The means forms a series circuit, and the series circuit is connected in parallel to the main single pole switch. 8. The power conversion device according to claim 7 , further comprising switch timing control means having a function of turning on the main single-pole switch after the auxiliary single-pole switch is turned on. apparatus.