JP2018014837A - Multiterminal dc power transmission system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To allow for continuous operation of the whole multiterminal DC power transmission system, in addition to continuous operation of a power converter unit, even upon occurrence of AC system failure.SOLUTION: A multiterminal DC power transmission system including more than one first AC system groups, more than one first power converter groups for converting the power of the first AC system groups, at least one second AC system groups, at least one second power converter groups for converting the power of the second AC system groups, and a DC power transmission network for linking the first and second power converter groups with DC, is further provided with effective power change means for changing the effective power transferred, respectively, from the first power converter groups for the DC power transmission network, according to the transmittable power of the first AC system groups.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a multi-terminal DC power transmission system, and in particular, an AC system and a renewable energy power source such as wind power generation or solar power generation are connected to an AC / DC converter, and the AC / DC converters are connected to each other by DC. The present invention relates to a multi-terminal DC power transmission system suitable for use in

  In order to improve the efficiency of long-distance power transmission and submarine power transmission, a DC power transmission system is often used. Since a general power system is an AC system, in a DC power transmission system, power from the AC system is converted into DC by a power converter for transmission.

  Conventionally, the DC power transmission system has been mainly used for one-to-one power transmission between two AC systems, but due to recent technological improvements, a multi-terminal that connects a plurality of AC systems by forming a DC power transmission network. The introduction of DC power transmission systems is increasing.

  A typical example of a multi-terminal DC power transmission system is an offshore wind farm in which a plurality of wind turbines are constructed on the ocean, and power generated by the wind turbines is transmitted to land using a DC power transmission network and a power converter.

  Further, as a configuration suitable for increasing the capacity of a power converter, a modular multilevel converter (MMC) in which outputs of a plurality of converters are cascade-connected has attracted attention (see Patent Document 1).

International Publication No. 2015/178376

  According to Patent Document 1 described above, when an MMC converter is used as a power converter, a DC capacitor voltage fluctuation of the MMC converter is detected at the occurrence of an AC system fault, and when the fluctuation exceeds a predetermined value, a direct current is detected. By changing the voltage command value, it is possible to continue the operation of the power converter while suppressing the voltage fluctuation of the DC capacitor voltage.

  However, in Patent Document 1, in the case of a multi-terminal DC power transmission system, a plurality of power converters are connected to the DC power transmission network, and each power converter is controlled in conjunction with each other, thereby stabilizing the entire multi-terminal DC power transmission system. It is necessary to operate.

  The same applies to the occurrence of an AC system fault, and it is desirable to enable continuous operation of the entire multi-terminal DC power transmission system in addition to continued operation of the power converter alone.

  The present invention has been made in view of the above points, and the object of the present invention is to continue operation of the entire multi-terminal DC power transmission system in addition to continuing operation of the power converter alone even when an AC system failure occurs. The object is to provide a multi-terminal DC power transmission system.

  In order to achieve the above object, a multi-terminal DC power transmission system according to the present invention includes at least two first AC system groups and at least two first power converters that convert the power of the first AC system group. A group, at least one second AC system group, at least one second power converter group that converts power of the second AC system group, the first power converter group, and the second Each of the first power converter groups includes a unit converter including a switching element and a power storage unit, and the unit converter The device is for charging and discharging the power storage unit by the operation of the switching element, and connecting a plurality of the unit converters in series as a unit converter group, connecting the unit converter group in parallel, Connect this parallel connection to the DC power grid, A multi-terminal DC power transmission system configured to connect each of the power converter groups to a power transmission network, wherein each of the first power converter groups corresponds to the transmittable power of the first AC system group. An active power changing means for changing the active power exchanged with the DC power transmission network is provided.

  According to the present invention, even when an AC system fault occurs, the operation of the entire multi-terminal DC power transmission system can be continued in addition to the continued operation of the power converter alone.

It is a conceptual diagram which shows Example 1 of the multi-terminal DC power transmission system of this invention. It is a figure which shows the structural example of the AC / DC converter employ | adopted as Example 1 of the multi-terminal DC power transmission system of this invention. It is a figure which shows the structural example of the unit converter which the AC / DC converter employ | adopted as Example 1 of the multi-terminal DC power transmission system of this invention comprises. It is a figure which shows the whole control block of the AC / DC converter employ | adopted as Example 1 of the multi-terminal DC power transmission system of this invention. It is a figure which shows the structure of the capacitor voltage control block which comprises the control block of the AC / DC converter shown in FIG. It is a figure which shows the structure of the DC voltage control block which comprises the control block of the AC / DC converter shown in FIG. It is a conceptual diagram which shows Example 2 of the multi-terminal DC power transmission system of this invention. It is a figure which shows the control block of the electric power absorption apparatus employ | adopted as Example 2 of the multi-terminal DC power transmission system of this invention.

  The multi-terminal DC power transmission system of the present invention will be described below based on the illustrated embodiments. In addition, in each Example, the same code | symbol is used for the same component.

  1 to 6 show a first embodiment of a multi-terminal DC power transmission system according to the present invention. FIG. 1 shows the overall configuration of Embodiment 1 of the multi-terminal DC power transmission system of the present invention.

  The multi-terminal DC power transmission system of the present embodiment shown in the figure includes two first AC systems A2a and a first AC system B2b, which are a first AC system group, and the first AC system A2a and the first AC system A1. The first AC / DC converter A1a and the first AC / DC converter B1b, which are the first power converter group that converts the power of the AC system B2b to AC or DC, and the regeneration that is the second AC system group A wind-powered converter that is a renewable energy-linked converter that constitutes one wind power plant 4 of a renewable energy power source and a second power converter group that converts the power of the wind power plant 4 into alternating current or direct current 3 and the first AC / DC converter A1a, the first AC / DC converter B1b, and the DC power transmission line 9 that is a DC power transmission network that links the wind-connected converter 3 with DC, Each of the converter A1a and the first AC / DC converter B1b The AC / DC converter A DC bus 8a of the first AC / DC converter A1a and the AC / DC converter B DC bus 8b of the first AC / DC converter A1b, which are DC terminals of the power converter group, are connected to the DC power transmission line 9. The AC / DC converter A AC bus 7a of the first AC / DC converter A1a, which is the other terminal of the first power converter group, and the AC / DC converter B AC bus 7b of the first AC / DC converter B1b are respectively The AC system A2a and the first AC system B2b are connected on a one-to-one basis.

  Each of the first AC / DC converter A1a and the first AC / DC converter B1b includes a unit converter 12 (see FIG. 2) including a switching element and a power storage unit. The unit converter 12 will be described later. However, the power storage unit is charged and discharged by the operation of the switching element, and a plurality of unit converters 12 are connected in series to connect the unit converter groups in parallel, and the parallel connection unit is connected to the DC power transmission line 9. To connect each of the unit converter groups to power transmission.

  In the present embodiment, each of the first AC / DC converter A1a and the first AC / DC converter B1b is connected to the DC power transmission line 9 according to the transmittable power of the first AC system A2a and the first AC system B2b. And active power changing means for changing the active power to be exchanged.

  More specifically, one end of the first AC / DC converter A1a is electrically connected to the AC / DC converter A AC bus 7a, and is electrically connected to the first AC system A2a via the AC power transmission line A5a. ing. The other end of the first AC / DC converter A1a is electrically connected to the AC / DC converter A DC bus 8a.

  One end of the first AC / DC converter B1b is electrically connected to the AC / DC converter B AC bus 7b, and is electrically connected to the first AC system B2b via the AC power transmission line B5b. The other end of the first AC / DC converter B1b is electrically connected to the AC / DC converter B DC bus 8b.

  One end of the wind-powered converter 3 is electrically connected to the wind-powered converter wind power station side bus 10 w and is electrically connected to the wind power station 4 via the wind power station transmission line 6. The other end of the wind power interconnection converter 3 is electrically connected to a wind power interconnection converter DC bus 11w which is a renewable energy interconnection converter DC bus.

  The wind power interconnection converter DC bus 11 w is electrically connected to the AC / DC converter A DC bus 8 a and the AC / DC converter B DC bus 8 b through the DC power transmission line 9.

  For the symbols in FIG. 1, the generated power of the wind power plant 4 is expressed as PW, the transmitted power from the wind-connected converter 3 to the wind-connected converter DC bus 11 w is expressed as PDCW, and the wind-connected converter The bus voltage of the DC bus 11w is expressed as VDCW. Further, regarding the current, voltage, and power of the first AC / DC converter A1a and the first AC / DC converter B1b, the AC / DC converter A DC bus 8a and the AC / DC converter B DC bus 8b to the first AC / DC converter A1a and The direct current flowing into the first AC / DC converter B1b is expressed as IDC, and the first AC / DC converter A1a and the first AC / DC converter B1b are connected to the AC / DC converter A AC bus 7a and the AC / DC converter B AC bus 7b. The inflowing AC current is expressed as IAC, the DC voltage of the wind power interconnection converter DC bus 11w is expressed as VDC, and the AC voltage of the AC / DC converter A AC bus 7a and AC / DC converter B AC bus 7b is expressed as VAC. The DC power flowing from the AC / DC converter A DC bus 8a and the AC / DC converter B DC bus 8b into the first AC / DC converter A1a and the first AC / DC converter B1b is expressed as PDC, and the first AC / DC converter A1a. as well as AC active power flowing from the first AC to DC conversion device B1b the AC-DC converter A ac busbars 7a and AC-DC converter B ac busbars 7b is indicated as PAC.

  In addition, for the current, voltage, and power described above, for each component related to the first AC / DC converter A1a, a suffix “A” is appended to each symbol, and for each component related to the first AC / DC converter B1b, A suffix “B” is added to the symbol. For example, a DC current flowing from the AC / DC converter A DC bus 8a into the first AC / DC converter A1a is denoted as IDCA.

  In addition, the power transmission form from the wind power plant 4 to the wind interconnection converter 3 and the configuration of the wind interconnection converter 3 are configured such that, when the power transmission form is AC transmission, the wind interconnection converter 3 has an alternating current therein. -A DC power converter is provided, and in the case of DC power transmission, a DC-DC power converter is provided inside.

  Next, a configuration example of the first AC / DC converter A1a and the first AC / DC converter B1b in the first embodiment of the multi-terminal DC power transmission system of the present invention will be described with reference to FIG.

  As shown in the figure, each of the first AC / DC converter A1a and the first AC / DC converter B1b employed in the multi-terminal DC power transmission system of this embodiment includes a unit converter 12, an arm 13, a reactor 14, and an A It consists of a phase AC connection end 15a, a B phase AC connection end 15b, a C phase AC connection end 15c, a DC positive side connection end 16a, and a DC negative side connection end 16b.

  In the first AC / DC converter A1a and the first AC / DC converter B1b, in addition to the power converter shown in FIG. A protective device may be provided.

  VARM in FIG. 2 is an output voltage of the arm 13. The arm 13 is a series connection circuit of the unit converters 12, and FIG. 2 shows an example in which N unit converters 12 are connected in series.

  Six sets of arms 13 are configured, and one end of each of the three sets is electrically connected to a different reactor 14, and the other end is electrically connected to the DC positive side connection end 16a. The three reactors 14 are referred to as a first reactor set.

  The remaining three sets of one ends are electrically connected to different reactors 14, and the other end is electrically connected to the DC negative side connection end 16b. These three reactors 14 are called the reactor second set.

  The first reactor set and the second reactor set described above are electrically connected in a one-to-one relationship, and the three connection points, the A-phase AC connection end 15a, the B-phase AC connection end 15b, and the C-phase AC connection end 15c are electrically connected to each other. Connected.

  Next, the structural example and operation | movement of the unit converter 12 in Example 1 of the multi-terminal DC power transmission system of this invention are demonstrated using FIG.

  First, a configuration example of the unit converter 12 will be described.

  FIG. 3 is a configuration example of the unit converter 12 used in the multi-terminal DC power transmission system of this embodiment. The unit converter 12 of this embodiment includes an H-side switching circuit 17, an L-side switching circuit 18, and a capacitor. (Or battery) 19, H side connection end 20 and L side connection end 21.

  3, i is the number of the unit converter 12 in the arm 13 and is an integer from 1 to N. VCi is a capacitor applied voltage of the i-th unit converter 12, VOi is an output voltage of the i-th unit converter 12, and SWHi and SWLi are the H-side switching circuit 17 in the i-th unit converter 12. And an ON / OFF signal of the L-side switching circuit 18.

  The H-side switching circuit 17 and the L-side switching circuit 18 have a function of switching both ends of the switching circuit to a short circuit or an open state in accordance with the on / off signals SWHi and SWLi.

  The switching circuit described above can be realized using a self-extinguishing element, a diode, or the like.

  Next, the operation of the unit converter 12 will be described.

  First, when the on-off signal SWHi is turned on to short-circuit the H-side switching circuit 17, and the on-off signal SWLi is turned off to open the L-side switching circuit 18, the H-side connection terminal 20 is connected to the H-side switching circuit 17, It is electrically connected to the L-side connection end 21 via a capacitor (or battery) 19. At this time, the output voltage VOi of the i-th unit converter 12 is approximately equal to the capacitor applied voltage VCi of the i-th unit converter 12.

  Next, when the on-off signal SWHi is turned off to open the H-side switching circuit 17 and the on-off signal SWLi is turned on to short-circuit the L-side switching circuit 18, the H-side connection end 20 is connected to the L-side switching circuit 18. The L-side connection end 21 is electrically connected. At this time, the output voltage VOi of the i-th unit converter 12 is substantially zero.

  Thus, in the unit converter 12, the output voltage VOi of the unit converter 12 outputs two voltages, that is, the capacitor applied voltage VCi and 0 of the unit converter 12 in accordance with the on / off signals SWHi and SWLi. Can do.

  Hereinafter, in this embodiment, a state where VOi = VCi is referred to as a “unit converter is on” state, and a state where VOi = 0 is referred to as a “unit converter is off” state.

  Next, the output voltage VARM of the arm 13 will be described.

  Since the arm 13 has a configuration in which the unit converters 12 are connected in series, VARM is the sum of the output voltages of the unit converters 12 and is expressed by Expression (1).

  In the formula (1), Mi is a value indicating the on / off state of the i-th unit converter 12, and is 1 if it is on and 0 if it is off. By changing the number of unit converters 12 with Mi = 1 according to the increase / decrease of the capacitor applied power VCi of the unit converter 12, the output voltage VARM of any arm 13 can be output as long as the configuration of the device permits. is there.

  By using 6 sets of arms 13 as shown in FIG. 2, the connection to the A phase AC connection end 15a, the B phase AC connection end 15b, the C phase AC connection end 15c, the DC positive side connection end 16a, and the DC negative side connection end 16b is performed. The output voltage can be arbitrarily controlled as long as the device configuration permits.

  4, 5 and 6 show control blocks of the first AC / DC converter A1a and the first AC / DC converter B1b employed in the first embodiment of the multi-terminal DC power transmission system of the present invention.

  FIG. 4 shows an overall configuration of control blocks of the first AC / DC converter A1a and the first AC / DC converter B1b employed in the first embodiment of the multi-terminal DC power transmission system of the present invention.

  As shown in the figure, the control blocks of the first AC / DC converter A1a and the first AC / DC converter B1b of this embodiment are a capacitor voltage control block 22, a DC voltage control block 23, an AC current control block 24, a DC current. It comprises a control block 25, an adder 26, and a modulation block 27.

  That is, the control blocks of the first AC / DC converter A1a and the first AC / DC converter B1b are the command values of the total capacitor voltage detection value (VC) of the unit converter 12 and the average value of all the capacitor voltages of the unit converter 12. (VCR), active power detection value (PDC) and AC / DC converter A that the first AC / DC converter A1a and the AC / DC converter B1b exchange with the AC / DC converter A DC bus 8a and AC / DC converter B DC bus 8b. Based on the AC voltage detection value (VAC) of the AC bus 7a and the AC / DC converter B AC bus 7b, the current command value that contributes to the active power output to the AC / DC converter A DC bus 8a and the AC / DC converter B DC bus 8b ( IPR) and the capacitor voltage control block 22 for calculating the DC current command value (IDCR1), the first AC / DC converter A1a and the first AC / DC converter B1b are connected to the AC / DC converter A DC bus 8a and the AC / DC converter. DC current command value (IDCR2) and first DC current command value (IDCR2) based on detected active power (PDC) exchanged with DC bus 8b and DC voltage detected value (VDC) of AC / DC converter A DC bus 8a and AC / DC converter B DC bus 8b DC voltage control block 23 for calculating the DC voltage command value (VDCR2) of the AC / DC converter A1a and the first AC / DC converter B1b, and AC voltage detection of the AC / DC converter A AC bus 7a and the AC / DC converter B AC bus 7b. Value (VAC), current command value (IPR) contributing to active power output to AC / DC converter A DC bus 8a and AC / DC converter B DC bus 8b, AC / DC converter A AC bus 7a and AC / DC converter B AC bus 7b The first AC / DC conversion based on the current command value (IQR) contributing to the reactive power output to AC and the AC current detection value (IAC) of the AC / DC converter A / AC bus 7a and AC / DC converter B / AC bus 7b The AC current control block 24 for calculating the AC voltage output command value (VACR) of the A1a and the first AC / DC converter B1b, the DC current command value (IDCR1) calculated by the capacitor voltage control block 22, and the DC voltage control block 23 The first AC / DC converter A1a and the first AC / DC are determined based on the DC current command value (IDCR2) calculated in step S1 and the DC current detection values (IDC) of the AC / DC converter A DC bus 8a and the AC / DC converter B DC bus 8b. DC current control block 25 for calculating DC voltage command value (VDCR1) of converter B1b, AC voltage output command value (VACR) of first AC / DC converter A1a and first AC / DC converter B1b, first AC / DC DC voltage command value (VDCR1) of converter A1a and first AC / DC converter B1b and DC voltage finger of first AC / DC converter A1a and first AC / DC converter B1b An adder 26 that adds the command value (VDCR2) and outputs the output voltage command value (VARMR) of each arm 13 of the first AC / DC converter A1a and the first AC / DC converter B1b, and the first AC / DC conversion Based on the output voltage command value (VARMR) of each arm 13 of the converter A1a and the first AC / DC converter B1b and the total capacitor voltage detection value (VC) of the unit converter 12, an on / off signal (SWHi, And a modulation block 27 for transmitting (SWLi).

  The command value (VCR) of the average value of all capacitor voltages of the unit converter 12 and the current command value (IQR) that contributes to the reactive power output to the AC / DC converter A / AC bus 7a and AC / DC converter B / AC bus 7b are It can be set for each of the first AC / DC converter A1a and the first AC / DC converter B1b according to the configuration and operating conditions of one AC / DC converter A1a and the first AC / DC converter B1b.

  Next, the capacitor voltage control block 22 will be described with reference to FIG.

  As shown in the figure, the capacitor voltage control block 22 of this embodiment is composed of a current command value calculation unit 28, a current command value selection signal generation unit 29, and a current command value selection unit 30, and the first AC / DC converter A1a. And each of 1st AC / DC converter B1b comprises the active power change means to change the active power exchanged with the DC power transmission line 9.

  That is, the capacitor voltage control block 22 of the present embodiment performs AC / DC conversion based on the total capacitor voltage detection value (VC) of the unit converter 12 and the command value (VCR) of the average value of all the capacitor voltages of the unit converter 12. A current command value calculation unit 28 for calculating a current command value (IPR0) that contributes to an active power output to the generator A AC bus 7a and the AC / DC converter B AC bus 7b, the first AC / DC converter A1a, and the first AC / DC Active power detection value (PDC) that converter B1b exchanges with AC / DC converter A DC bus 8a and AC / DC converter B DC bus 8b, AC voltage detection value of AC / DC converter A / AC bus 7a and AC / DC converter B / AC bus 7b (VAC) and the current command for calculating the current command value selection signal (VCLFLG) based on the maximum value (IACMAX) of the alternating current amplitude of the first AC / DC converter A1a and the first AC / DC converter B1b. Based on the selection signal generator 29 and the current command value (IPR0) and current command value selection signal (VCRFLG) that contribute to the active power output to the AC / DC converter A AC bus 7a and AC / DC converter B AC bus 7b A current command value (IPR) that contributes to an effective power output to the converter A DC bus 8a and the AC / DC converter B DC bus 8b and a current command value selector 30 that calculates a DC current command value (IDCR1); It constitutes an active power changing means.

  The current command value calculation unit 28 described above makes the average value of all capacitor voltage detection values (VC) of the unit converter 12 equal to the command value (VCR) of the average value of all capacitor voltages of the unit converter 12. The current command value (IPR0) that contributes to the active power output to the AC / DC converter A AC bus 7a and the AC / DC converter B AC bus 7b is calculated using proportional integral control and the like, and the current command value selection signal generator 29 is calculated. Then, the AC voltage detection value (VAC) of the AC / DC converter A AC bus 7a and AC / DC converter B AC bus 7b and the maximum AC current amplitude (IACMAX) of the first AC / DC converter A1a and the first AC / DC converter B1b. ) To calculate the effective power (PACMAX) that can be output to the AC / DC converter A AC bus 7a and the AC / DC converter B AC bus 7b, and the first AC / DC converter A1a and the first AC / DC converter B1b If the PACMAX is larger than the absolute value of the active power detection value (PDC) exchanged with the DC bus 8a and the AC / DC converter B DC bus 8b, VCRFLG = 1 is output, and if not, VCRFLG = 0. In the current command value selection unit 30, the current command value (IPR0) contributing to the active power output to the AC / DC converter A AC bus 7a and the AC / DC converter B AC bus 7b and the current command value selection signal (VCRFLG) If VCRFLG = 1, IPR = IPR0 and IDCR1 = 0 are output. If VCRFLG = 0, IPR = 0 and IDCR1 = KVCR × IPR0 are output. KVCR is a correction coefficient that can be set for each of the first AC / DC converter A1a and the first AC / DC converter B1b.

  Next, the above-described DC voltage control block 23 will be described with reference to FIG.

  As shown in the figure, the DC voltage control block 23 of this embodiment is composed of a DC voltage command value calculation unit 31 and a DC voltage upper / lower limit determination calculation unit 32.

  That is, the DC voltage control block 23 of the present embodiment detects the effective power that the first AC / DC converter A1a and the first AC / DC converter B1b exchange with the AC / DC converter A DC bus 8a and the AC / DC converter B DC bus 8b. The reference operating point of the value (PDC), the DC voltage (VDCR) of the first AC / DC converter A1a and the first AC / DC converter B1b, and the active power of the first AC / DC converter A1a and the first AC / DC converter B1b A DC voltage command value calculation unit 31 for calculating a DC voltage command value (VDCR0) based on the first AC / DC converter A1a and the first AC / DC converter B1b includes an AC / DC converter A DC bus 8a and an AC / DC converter B DC. Active power detection value (PDC) exchanged with bus 8b, DC voltage command value (VDCR0), DC voltage maximum value (VDCMAX) and minimum value (VDCV) of first AC / DC converter A1a and first AC / DC converter B1b DC voltage command value (IDCR2) based on CMIN) and a DC voltage upper / lower limit determination calculation unit 32 for calculating the DC voltage command value (VDCR2) of the first AC / DC converter A1a and the first AC / DC converter B1b. Has been.

  Note that VDCR, PDCR, VDCMAX, and VDCMIN are the first AC / DC converter A1a and the first AC / DC converter B1b depending on the configuration and operating conditions of the first AC / DC converter A1a and the first AC / DC converter B1b. Can be set for each.

  The DC voltage command value calculation unit 31 described above calculates VDCR0 according to the equation (2).

VDCR0 = VDCR-KVDC × (PDC-PDCR) (2)
Note that KVDC is a correction coefficient, and is determined for each of the first AC / DC converter A1a and the first AC / DC converter B1b according to the configuration and operating conditions of the first AC / DC converter A1a and the first AC / DC converter B1b. It can be set.

  The DC voltage upper and lower limit determination calculation unit 32 outputs IDCR2 = PDC / VDCMAX and VDCR2 = VDCMAX if VDCR0 is greater than VDCMAX, and IDCR2 = PDC / VDCMMIN and VDCR2 if VDCR0 is less than VDCMIN. = VDCMIN is output, and if none of the above, IDCR2 = 0 and VDCR2 = VDCR0 are output.

  Next, the above-described alternating current control block 24 will be described.

  In the AC current control block 24 of this embodiment, the AC current detection values (IAC) of the first AC / DC converter A1a and the first AC / DC converter B1b are the AC / DC converter A DC bus 8a and the AC / DC converter B DC bus. AC current determined from the current command value (IPR) contributing to the active power output to 8b and the current command value (IQR) contributing to the reactive power output to the AC / DC converter A / AC bus 7a and AC / DC converter B / AC bus 7b The AC voltage output command value (VACR) of the first AC / DC converter A1a and the first AC / DC converter B1b is calculated so as to be equal to the command value (IACR).

  Specific examples of the method include a method of performing feedback control for each of the three phases and a method of controlling by converting the three-phase alternating current into a direct current amount using coordinate conversion.

  Next, the DC current control block 25 described above will be described.

  The direct current control block 25 of this embodiment outputs VDCR1 = 0 if IDCR1 = 0 and IDCR2 = 0, and is proportional so that IDC is equal to IDCR1 + IDCR2 otherwise. VDCR1 is calculated using integral control or the like.

  The AC voltage output command value (VACR) of the first AC / DC converter A1a and the first AC / DC converter B1b, and the DC voltage command value (VDCR1) of the first AC / DC converter A1a and the first AC / DC converter B1b. The DC voltage command values (VDCR2) of the first AC / DC converter A1a and the first AC / DC converter B1b are added by the adder 26, and each arm of the first AC / DC converter A1a and the first AC / DC converter B1b is added. 13 output voltage command values (VARMR) are calculated.

  In the modulation block 27, the output voltage command value (VARMR) of each arm 13 of the first AC / DC converter A1a and the first AC / DC converter B1b and the total capacitor voltage detection value (VC) of the unit converter 12 are used as the basis. In addition, on / off of each unit converter 12 is determined by using pulse width modulation control or the like.

  Note that the control of the control block of the AC / DC converter shown in FIG. 4 is provided in both the first AC / DC converter A1a and the first AC / DC converter B1b, and each symbol in FIG. 4, FIG. 5 and FIG. In the description, when the first AC / DC converter A1a and the first AC / DC converter B1b are distinguished from each other, the subscript “A” is added to each symbol for each component relating to the first AC / DC converter A1a. The components relating to the first AC / DC converter B1b are described by adding the suffix “B” to each symbol.

  For example, in FIG. 4, VCR is the command value of the average value of all the capacitor voltages of the unit converter 12, but mentions the command value of the average value of all the capacitor voltages of the unit converter 12 of the first AC / DC converter A1a. In this case, it is written as VCRA.

  Next, operations of the first AC / DC converter A1a and the first AC / DC converter B1b in the multi-terminal DC power transmission system of the present embodiment will be described.

  Hereinafter, as an example, a case will be described in which a lightning strike occurs at the closest end of the AC / DC converter A AC bus 7a at time T1, Vaca and PACA decrease to 0, and the accident is removed and power is restored at time T2. .

  Note that the generated power PW of the wind power plant 4 is constant before and after the lightning strike and power recovery, and PW = PDCW (the bus voltage of the wind interconnection converter 3) by the wind interconnection converter 3. Is controlled as follows.

  Prior to time T1, PDCW, PACA, PACB, PDCA, and PDCB satisfy the relationships of Expressions (3), (4), and (5).

PDCW = PDCA + PDCG (3)
PDCA = PACA (4)
PDCB = PACB (5)
At this time, the wind interconnection converter 3 is controlled to make the active power constant, and the DC voltage of each DC bus is controlled to be constant by the first AC / DC converter A1a and the first AC / DC converter B1b. ing.

  Specifically, the VDCWF is expressed by an equilibrium point determined from the relational expression between the active power and the DC voltage of the formula (2) of the first AC / DC converter A1a and the first AC / DC converter B1b and the impedance of the DC transmission line 9. VDCA, VDCB, PDCA, and PDCB are determined.

  When VCA decreases to 0 at time T1, PDCA> PACA, and the active power of the difference between PDCA and PACA is stored in the capacitor 19 of the unit converter 12 of the first AC / DC converter A1a. To do.

  Since VCA becomes 0, IDCR1A is calculated in the capacitor voltage control block 22 so that VCA is equal to VCRA, VDCR1A is calculated in DC current control block 25 based on IDCR1A, and finally, the power converter The DC voltage output changes and VDCA changes.

  When VDCA changes, PDCA and PDCB change. At this time, the wind interconnection converter 3 controls to keep the active power constant, and the first AC / DC converter A1a controls the direct current to keep the capacitor voltage constant, and each DC bus Is controlled to be constant by the first AC / DC converter B1b.

  Specifically, the VDCWF, VDCA, VDCB, PDCA, and PDCB are expressed by the relational expression between the active power and the DC voltage of the formula (2) of the first AC / DC converter B1b and the equilibrium point determined from the impedance of the DC transmission line 9. Determined.

  PDCA is power for making the capacitor voltage constant, and if it is sufficiently smaller than PDCW, PDCB increases from time T1 and before and becomes approximately equal to PDCW. After the accident is removed and power is restored at time T2, VACA returns to the value before time T1, so VDCW, VDCA, VDCB, PDCA, and PDCB also return to the equilibrium point before the accident.

  As a renewable energy power source, a solar power plant can be used instead of the wind power plant described above.

  According to this embodiment, even when an AC system failure occurs, it is possible to continue operation of the entire multi-terminal DC power transmission system in addition to continuing operation of the power converter alone.

  Next, Example 2 of the multi-terminal DC power transmission system of the present invention will be described with reference to FIGS.

  In the first embodiment described above, it has been described that the operation of the multi-terminal power transmission system is continued even when an accident occurs in the AC system by interlocking the two AC / DC converters. In addition to the converter, a power absorbing device (described later) installed on the DC bus is also operated in an interlocked manner so that the operation of the multi-terminal power transmission system is continued.

  That is, in the multi-terminal DC power transmission system of this embodiment, as shown in FIG. 7, the first AC / DC converter B DC bus 8b is transferred from the connection end to the first AC / DC converter B DC bus 8b. A power absorption device 33 composed of a power storage device or a variable resistance device capable of controlling active power (PZ) is configured to be at least electrically connected. Other configurations are the same as those of the first embodiment.

  As shown in FIG. 8, the power absorbing device 33 is based on a DC voltage detection value (VDC) of the DC power transmission line 9 to which the power absorbing device 33 is connected and an upper limit value (VDCMAXZ) of the DC voltage of the DC power transmission line 9. An effective upper limit limiter 34 for calculating the DC voltage command value (VDCZ) and an effective power command value (PZR) based on the DC voltage detection value (VDC) and DC voltage command value (VDCZ) of the DC transmission line 9 And a power command value calculation block 35.

  The above-described upper limiter 34 compares the DC voltage detection value (VDC) of the DC transmission line 9 with the upper limit value (VDCMAXZ) of the DC voltage of the DC transmission line 9, and if VDC is larger than VDCMAXZ, VDCZ = VDCMAXAXZ. If not, VDCZ = VDC is output, and the active power command value calculation block 35 makes the DC voltage detection value (VDC) of the DC power transmission line 9 equal to the DC voltage command value (VDCZ). The active power command value (PZR) is calculated, and the power absorber 33 is controlled so that the active power (PZ) PZ is equal to the active power command value (PZR).

  Note that VDCMAXZ can be set according to the configurations and operating conditions of the power absorption device 33 and the multi-terminal DC power transmission system.

  It should be noted that the value of VDCMAXZ is preferably set to a value larger than VDCMAXB set by the DC voltage upper / lower limit determination unit 32 provided in the first AC / DC converter B1b.

  Next, as an example of the operation of the AC / DC converter according to the second embodiment of the present invention, a lightning strike accident occurs near the AC / DC converter A AC bus 7a at time T1, as in the first embodiment, and VCA and PACA. A case where the power supply decreases to 0, the accident is removed at time T2, and power is restored will be described.

  The configuration and control of the first AC / DC converter A1a and the first AC / DC converter B1b are the same as those in the first embodiment.

  Since VCA becomes 0 at time T1, IDCR1A is calculated so that VCA is equal to VCRA, VDCR1A is calculated by DC current control block 25 based on IDCR1A, and finally the DC voltage output of the power converter is VDCA changes. When VDCA changes, PDCA and PDCB change.

  At this time, the wind interconnection converter 3 controls to keep the active power constant, and the first AC / DC converter A1a controls the DC voltage output so as to keep the capacitor voltage constant. The DC voltage of the bus is controlled to be constant by the first AC / DC converter B1b.

  Specifically, the VDCWF, VDCA, VDCB, PDCA, and PDCB are expressed by the relational expression between the active power and the DC voltage of the formula (2) of the first AC / DC converter B1b and the equilibrium point determined from the impedance of the DC transmission line 9. Determined.

  PDCA is power for making the capacitor voltage constant, and if it is sufficiently smaller than PDCW, PDCB increases compared to before time T1 and tends to be approximately equal to PDCW.

  Hereinafter, a case where VDCCR0B = VDCMINB is set by the DC voltage command value calculation unit 31 and the DC voltage upper / lower limit determination calculation unit 32 of the first AC / DC converter B1b as a result of the increase in PDCB will be described.

  At this time, the wind interconnection converter 3 is controlled to keep the active power constant, and the first AC / DC converter A1a is controlling the direct current so as to keep the capacitor voltage constant. Since the AC / DC converter B1b controls the DC current so that the effective power flowing from the AC / DC converter B DC bus 8b to the first AC / DC converter B1b is constant, the DC voltage of each DC bus is constant. There are no AC / DC converters to keep the

  In this example, PDCW> (PDCA + PDCB).

  Since the difference between PDCW and (PDCA + PDCB) is charged to the capacitance of the DC power transmission line 9, the DC voltage of each DC bus rises. When the DC voltage of each DC bus rises and the DC voltage of AC / DC converter B DC bus 8b reaches VDCMAXAXZ, power absorption device 33 operates so as to keep the DC voltage of AC / DC converter B DC bus 8b constant. To do. By the operation of the power absorbing device 33, the DC voltage of each DC bus can be kept constant.

  After the accident is removed and power is restored at time T2, VACA returns to the value before time T1, so VDCW, VDCA, VDCB, PDCA, and PDCB also return to the equilibrium point before the accident.

  In the second embodiment, the power absorbing device 33 is connected to the AC / DC converter B DC bus 8b. However, the power absorbing device 33 may be connected to another DC bus. A plurality of power absorbing devices 33 may be connected.

  Even in the configuration of the present embodiment, the same effect as that of the first embodiment can be obtained. In addition to the AC / DC converter, the power absorbing device 33 installed in the AC / DC converter B DC bus 8b is also linked. The operation of the multi-terminal power transmission system can be continued by operating.

  In addition, this invention is not limited to an above-described Example, Various modifications are included. For example, the above-described embodiments have been described in detail for easy understanding of the present invention, and are not necessarily limited to those having all the configurations described. Further, a part of the configuration of one embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of one embodiment. Further, it is possible to add, delete, and replace other configurations for a part of the configuration of each embodiment.

  DESCRIPTION OF SYMBOLS 1a ... 1st AC / DC converter A, 1b ... 1st AC / DC converter B, 2a ... 1st alternating current system A, 2b ... 1st alternating current system B, 3 ... Wind power interconnection converter, 4 ... Wind power generation 5a: AC power transmission line A, 5b: AC power transmission line B, 6: Wind power plant power transmission line, 7a: AC / DC converter A AC bus, 7b ... AC / DC converter B AC bus, 8a ... AC / DC converter A DC bus , 8b ... AC / DC converter B DC bus, 9 ... DC transmission line, 10w ... Wind power interconnection converter, wind power station side bus, 11w ... Wind power interconnection converter DC bus, 12 ... Unit converter, 13 ... Arm, 14 Reactor, 15a ... A phase AC connection end, 15b ... B phase AC connection end, 15c ... C phase AC connection end, 16a ... DC positive side connection end, 16b ... DC negative side connection end, 17 ... H side switching circuit, 18 ... L side switching circuit, 19 ... capacitor, 20 ... H side connection end, 21 ... Side connection end, 22 ... capacitor voltage control block, 23 ... DC voltage control block, 24 ... AC current control block, 25 ... DC current control block, 26 ... adder, 27 ... modulation block, 28 ... current command value calculation unit, DESCRIPTION OF SYMBOLS 29 ... Current command value selection signal production | generation part, 30 ... Current command value selection part, 31 ... DC voltage command value calculation part, 32 ... DC voltage upper / lower limit determination calculation part, 33 ... Power absorption device, 34 ... Upper limiter, 35 ... Active power command value calculation block.

Claims (19)

At least two first AC system groups, at least two first power converter groups for converting the power of the first AC system group, at least one second AC system group, and the second At least one second power converter group for converting the power of the AC system group, and a DC power transmission network interconnected by DC between the first power converter group and the second power converter group. Prepared,
Each of the first power converter group includes a unit converter including a switching element and a power storage unit, and the unit converter charges and discharges the power storage unit by an operation of the switching element. And a plurality of the unit converters are connected in series to form a unit converter group, the unit converter groups are connected in parallel, the parallel connection portion is connected to the DC power grid, and each of the unit converter groups Is a multi-terminal DC power transmission system configured to connect to a power transmission network,
Each of the first power converter groups includes active power changing means for changing the effective power exchanged with the DC power transmission network according to the transmittable power of the first AC grid group. Multi-terminal DC power transmission system. The multi-terminal DC power transmission system according to claim 1,
In each of the first power converter groups, a DC side terminal of the first power converter group is connected to the DC power grid, and each other terminal of the first power converter group is the first power converter group. A multi-terminal DC power transmission system characterized in that the system is connected to an AC system group of No. 1 on a one-to-one basis. The multi-terminal DC power transmission system according to claim 2,
The first AC system group includes at least two AC systems, the first power converter group includes at least two AC / DC converters, and the second power converter group includes at least one renewable energy power source. The second power converter group is composed of at least one renewable energy interconnection converter, and the DC side terminal of the first power converter group is composed of an AC / DC converter DC bus, A multi-terminal DC power transmission system, wherein the other terminal of the power converter group is composed of an AC / DC converter AC bus. In the multi-terminal DC power transmission system according to claim 3,
The DC power transmission network is characterized in that one end is connected to the AC / DC converter DC bus and the other end is connected to a renewable energy interconnection converter DC bus. In the multi-terminal DC power transmission system according to claim 3 or 4,
One of the first power converter groups is a unit converter, an arm, a reactor, an A phase AC connection end, a B phase AC connection end, a C phase AC connection end, a DC positive side connection end, and a DC negative side connection end. Consisting of
Six sets of the arms are configured, and one end of each of the three sets is electrically connected to the different reactors, and the other end is electrically connected to the DC positive side connection end as a first set of reactors, and the remaining three One set of reactors is electrically connected to different reactors, and the other end is electrically connected to the DC negative side connection end. As a second set of reactors, the first set of reactors and the second set of reactors are electrically connected. The multi-terminal direct current is characterized in that three connection points are electrically connected to the A-phase AC connection end, the B-phase AC connection end, and the C-phase AC connection end, respectively. Power transmission system. The multi-terminal DC power transmission system according to claim 5,
The unit converter includes an H side switching circuit, an L side switching circuit, a capacitor or a battery, an H side connection end, and an L side connection end.
The H-side switching circuit and the L-side switching circuit are configured to match the on / off signal (SWHi) of the H-side switching circuit and the on-off signal (SWLi) of the L-side switching circuit in the i-th unit converter. A multi-terminal DC power transmission system comprising a switching element that switches both ends of the side and L side switching circuits to a short circuit or an open state.
(Where i is the number of the unit converter in the arm and is an integer from 1 to N) The multi-terminal DC power transmission system according to claim 6,
The on-off signal (SWHi) of the H-side switching circuit in the i-th unit converter is turned on, the H-side switching circuit is short-circuited by the switching element, and the L-side switching in the i-th unit converter An on / off signal (SWLi) of the circuit is turned off, the L side switching circuit is opened by the switching element, and the H side connection end is connected to the L side via the H side switching circuit, the capacitor or the battery. Electrically connected to the connection end,
On the other hand, an on / off signal (SWHi) of the H-side switching circuit in the i-th unit converter is turned off, the H-side switching circuit is opened by the switching element, and the L in the i-th unit converter is opened. The on-off signal (SWLi) of the side switching circuit is turned on, and the L-side switching circuit is short-circuited by the switching element. In this state, the H-side connection terminal is connected to the L-side switching circuit, the L-side connection terminal, A multi-terminal DC power transmission system characterized by electrical connection. The multi-terminal DC power transmission system according to claim 7,
The control block for controlling the AC / DC converter includes a total capacitor voltage detection value (VC) of the unit converter, an instruction value (VCR) of an average value of all the capacitor voltages of the unit converter, and the AC / DC converter includes the AC / DC converter. A current command value that contributes to an active power output to the AC / DC converter DC bus based on an active power detection value (PDC) exchanged with the converter DC bus and an AC voltage detection value (VAC) of the AC / DC converter AC bus (IPR) and a capacitor voltage control block for calculating a direct current command value (IDCR1);
The direct current command value (IDCR2) and the AC / DC conversion based on the active power detection value (PDC) exchanged with the AC / DC converter DC bus by the AC / DC converter and the DC voltage detection value (VDC) of the AC / DC converter DC bus. A DC voltage control block for calculating a DC voltage command value (VDCR2) of the detector;
AC voltage detection value (VAC) of the AC / DC converter AC bus, current command value (IPR) contributing to the active power output to the AC / DC converter DC bus, and reactive power output to the AC / DC converter AC bus An AC current control block that calculates an AC voltage output command value (VACR) of the AC / DC converter based on a current command value (IQR) and an AC current detection value (IAC) of the AC / DC converter AC bus;
The DC current command value (IDCR1) calculated by the capacitor voltage control block, the DC current command value (IDCR2) calculated by the DC voltage control block, and the DC current detection value (IDC) of the AC / DC converter DC bus A DC current control block for calculating a DC voltage command value (VDCR1) of the AC / DC converter based on
The AC voltage output command value (VACR) of the AC / DC converter, the DC voltage command value (VDCR1) of the AC / DC converter, and the DC voltage command value (VDCR2) of the AC / DC converter are added, and each of the AC / DC converters An adder for outputting an arm output voltage command value (VARMR);
A modulation block for transmitting an on / off signal of the all unit converter based on an output voltage command value (VARMR) of each arm of the AC / DC converter and a total capacitor voltage detection value (VC) of the unit converter. A multi-terminal DC power transmission system characterized in that The multi-terminal DC power transmission system according to claim 8,
The capacitor voltage control block is configured to supply the AC / DC converter AC bus to the AC / DC converter based on a command value (VCR) of an all capacitor voltage detection value (VC) of the unit converter and an average value of all capacitor voltages of the unit converter. A current command value calculation unit for calculating a current command value (IPR0) that contributes to the active power output;
Active power detection value (PDC) that the AC / DC converter exchanges with the AC / DC converter DC bus, AC voltage detection value (VAC) of the AC / DC converter AC bus, and maximum AC current amplitude of the AC / DC converter (IACMAX) ) Based on the current command value selection signal (VCRFLG), a current command value selection signal generator,
Based on the current command value (IPR0) and current command value selection signal (VCRFLG) that contribute to the active power output to the AC / DC converter AC bus, the current command value that contributes to the active power output to the AC / DC converter DC bus (IPR) and a current command value selection unit that calculates a DC current command value (IDCR1), and constitutes the active power changing means. The multi-terminal DC power transmission system according to claim 9,
The current command value calculation unit is configured so that an average value of all capacitor voltage detection values (VC) of the unit converter is equal to a command value (VCR) of an average value of all capacitor voltages of the unit converter. Calculate the current command value (IPR0) that contributes to the active power output to the AC / DC converter AC bus,
The current command value selection signal generation unit can output to the AC / DC converter AC bus from the AC voltage detection value (VAC) of the AC / DC converter AC bus and the maximum AC current amplitude of the AC / DC converter (IACMAX). Calculate the active power (PACMAX)
When the PACMAX is larger than the absolute value of the active power detection value (PDC) exchanged between the AC / DC converter and the AC / DC converter DC bus, the VCRFLG = 1 is output. VCLFLG = 0 is output, and the current command value selection unit, based on the current command value (IPR0) contributing to the active power output to the AC / DC converter AC bus and the current command value selection signal (VCRFLG), If VCRFLG = 1, the IPR = IPR0 and the IDCR1 = 0 are output, and if VCRFLG = 0, the IPR = 0 and the IDCR1 = KVCR × IPR0 are output. Terminal DC power transmission system.
(However, KVCR is a correction coefficient that can be set for each AC / DC converter) The multi-terminal DC power transmission system according to any one of claims 8 to 10,
The DC voltage control block includes an active power detection value (PDC) that the AC / DC converter exchanges with the AC / DC converter DC bus, a DC voltage (VDCR) of the AC / DC converter, and a reference operation of the active power of the AC / DC converter. A DC voltage command value calculation unit for calculating a DC voltage command value (VDCR0) based on the points;
Active power detection value (PDC) that the AC / DC converter exchanges with the AC / DC converter DC bus, the DC voltage command value (VDCR0), the maximum value (VDCMAX) and the minimum value (VDCMMIN) of the DC voltage of the AC / DC converter A multi-terminal DC power transmission system comprising: a DC voltage upper / lower limit determination calculation unit that calculates the DC current command value (IDCR2) and the DC voltage command value (VDCR2) of the AC / DC converter based on The multi-terminal DC power transmission system according to claim 11,
The DC voltage upper / lower limit determination calculation unit outputs the IDCR2 = PDC / VDCMMAX and the VDCR2 = VDCMAX if the VDCR0 is greater than the VDCMAX, and the IDCR2 = PDC / VDCMIN and VDCR2 = VDCMMIN are output, and if none of the above, IDCR2 = 0 and VDCR2 = VDCR0 are output. The multi-terminal DC power transmission system according to any one of claims 8 to 12,
The control block for controlling the AC voltage includes a current command value (IPR) in which an AC current detection value (IAC) of the AC / DC converter AC bus contributes to an active power output to the AC / DC converter DC bus and the AC / DC conversion. AC voltage output command value (VACR) of the AC / DC converter is calculated so as to be equal to an AC current command value (IACR) obtained from a current command value (IQR) contributing to reactive power output to the AC bus A multi-terminal DC power transmission system. The multi-terminal DC power transmission system according to any one of claims 8 to 13,
The DC current control block outputs the VDCR1 = 0 if the IDCR1 = 0 and the IDCR2 = 0, otherwise the VDCR1 is set so that the IDC is equal to the IDCR1 + IDCR2. A multi-terminal DC power transmission system characterized by calculating. The multi-terminal DC power transmission system according to any one of claims 1 to 14,
A multi-terminal DC power transmission system, wherein at least one power absorption device capable of controlling active power (PZ) transferred from a connection end to the DC power transmission network is electrically connected to the DC power transmission network. . The multi-terminal DC power transmission system according to claim 15,
The multi-terminal DC power transmission system, wherein the power absorbing device is composed of a power storage device or a variable resistance device. The multi-terminal DC power transmission system according to claim 15 or 16,
The power absorber includes a DC voltage command value (VDCZ) based on a DC voltage detection value (VDC) of the DC transmission network to which the power absorber is connected and an upper limit value (VDCMAXZ) of the DC voltage of the DC transmission network. An upper limiter to calculate
And an active power command value calculation block for calculating an active power command value (PZR) based on a DC voltage detection value (VDC) and a DC voltage command value (VDCZ) of the DC transmission network. Terminal DC power transmission system. The multi-terminal DC power transmission system according to claim 17,
The upper limiter compares the DC voltage detection value (VDC) of the DC transmission network with the upper limit value (VDCMAXZ) of the DC voltage of the DC transmission network, and if the VDC is larger than VDCMAXZ, the VDCZ = VDCMAXXZ. If not, the VDCZ = VDC is output, and the active power command value calculation block causes the DC voltage detection value (VDC) of the DC power grid to be equal to the DC voltage command value (VDCZ). The active power command value (PZR) is calculated, and the power absorber is controlled so that the active power (PZ) PZ is equal to the active power command value (PZR). Multi-terminal DC power transmission system. The multi-terminal DC power transmission system according to any one of claims 3 to 18,
At least one of the renewable energy power sources is wind power generation or solar power generation.

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