DC power transmission systems, methods, and programs

Abstract

To reduce power loss in a bipolar DC power transmission system. [Solution] When the higher-level control device 10 in the DC power transmission system 100 detects that the operating state of at least one of the positive-side inverter converter 111IP and the negative-side inverter converter 111IN has changed from a constant power control state or a droop control state to a stopped state, it calculates the reference electrode transmission power Ps so as to distribute the total value of the power received by the positive-side inverter converter 111IP and the negative-side inverter converter 111IN before they changed to a stopped state to the positive-side inverter converter 111CP or the negative-side inverter converter 111CN, which has been determined to be the reference electrode, based on the gain ratio, calculates a correction value to modify the reference electrode transmission power Ps, and calculates the control amount by correcting the command value of the control amount with the correction value.

Description

Technical Field

[0001] The present invention relates to a DC power transmission system, method, and program, and more particularly, to a bipolar DC power transmission system, method, and program.

Background Art

[0002] The bipolar DC power transmission system is used to connect solar power generation facilities, wind power generation facilities, etc. to the commercial power system (see, for example, Patent Document 1).

[0003] In addition, the bipolar DC power transmission system is used as one element constituting the frequency conversion facility. The frequency conversion facility is a facility for connecting commercial power systems with different frequencies.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The bipolar DC power transmission system has a converter for the positive electrode and a converter for the negative electrode at the converter station on the power transmission side and the converter station on the power reception side, respectively. In addition, between the converter station on the power transmission side and the converter station on the power reception side, there are three DC power transmission lines: the main line for the positive electrode, the main line for the negative electrode, and the return line.

[0006] Generally, the converter at the converter station on the power transmission side is controlled to transmit power at a fixed ratio of 1:1 or the like between the positive electrode and the negative electrode due to the control characteristics. Similarly, the converter at the converter station on the power reception side is also controlled to receive power at a fixed ratio of 1:1 or the like between the positive electrode and the negative electrode. Therefore, normally, no current flows through the return line.

[0007] In a bipolar DC power transmission system, multiple receiving-side converters may be connected to a single transmitting-side converter station. In this case, due to accidents or inspections, some converters at the receiving-side converter stations may be shut down while others continue to operate. At this time, the ratio of the number of operating positive-electrode converters to the number of operating negative-electrode converters at the receiving-side converter station (hereinafter also referred to as the "number ratio") changes. This change in the number ratio causes a power difference between the positive-electrode converters and the negative-electrode converters, even in receiving-side converter stations where converters are not shut down. When a power difference occurs between the positive-electrode converters and the negative-electrode converters, current flows in the return line, resulting in significant power loss.

[0008] This invention has been made in view of the above problems, and aims to reduce power loss in a bipolar DC power transmission system. [Means for solving the problem]

[0009] A DC power transmission system according to a typical embodiment of the present invention includes a transmitting-side converter station comprising a positive-side forward converter that converts AC power to positive-side DC power according to a given control amount, and a negative-side forward converter that converts AC power to negative-side DC power according to a given control amount; a plurality of receiving-side converter stations comprising a positive-side reverse converter that converts DC power transmitted from the positive-side forward converter to AC power, and a negative-side reverse converter that converts DC power transmitted from the negative-side forward converter to AC power; and a DC transmission line that includes a positive-side main line, a negative-side main line, and a return line, is provided corresponding to each of the receiving-side converter stations, and connects the transmitting-side converter station and the receiving-side converter station. The system includes a power-side converter and a power-receiving converter, the higher-level control device which controls at least one of them, the higher-level control device which includes a storage unit, a control amount calculation unit which calculates the control amount for the positive-side forward converter and the negative-side forward converter and provides the control amount to the positive-side forward converter and the negative-side forward converter, a reference electrode determination unit which determines either the positive electrode or the negative electrode as a reference electrode and stores reference electrode determination information, which is information about the determined reference electrode, in the storage unit, and the operating state of the positive-side reverse converter and the negative-side reverse converter which is a stopped state, a constant power control state and a droop control state. A converter station information monitoring unit that monitors whether the state is as described above, monitors the power received by the positive-side inverse converter and the negative-side inverse converter, and the value of the droop control gain set for the positive-side inverse converter and the negative-side inverse converter when the operating state is the droop control state, and stores the monitoring results in the storage unit; a reference pole power calculation unit that calculates the reference pole power that the positive-side forward converter or the negative-side forward converter, which has been determined as the reference pole of the power transmission side converter station, should transmit, and stores the calculation results in the storage unit; and the reference pole power calculation unit The converter information monitoring unit includes a correction value calculation unit which calculates a correction value for correcting the control amount based on the calculation result calculated by the converter information monitoring unit which detects that the operating state of at least one of the positive-side inverter and the negative-side inverter has changed from the constant power control state or the droop control state to the stopped state and stores the monitoring result in the storage unit, and the reference pole power calculation unit which calculates the total value of the received power of the positive-side inverter and the negative-side inverter before they changed to the stopped state based on the monitoring result, Based on the gain ratio, the reference electrode transmission power is calculated to be distributed to the positive-side forward converter or the negative-side forward converter determined as the reference electrode. If the correction value calculation unit modifies the transmission power of the positive-side forward converter or the negative-side forward converter based on the calculation result of the reference electrode power calculation unit, it calculates a correction value based on the transmission power of the positive-side forward converter or the negative-side forward converter before modification and the calculation result. The control amount calculation unit calculates the control amount by correcting the command value of the control amount with the correction value. [Effects of the Invention]

[0010] According to the present invention, it is possible to reduce power loss in a bipolar DC power transmission system. [Brief explanation of the drawing]

[0011] [Figure 1] This figure shows a schematic configuration of a power conversion system including a DC power transmission system according to an embodiment of the present invention. [Figure 2] This figure shows a detailed configuration of the area around the converter shown in Figure 1. [Figure 3] This figure shows the functional block configuration of a higher-level control device according to an embodiment of the present invention. [Figure 4] This diagram shows the hardware configuration of the higher-level control unit. [Figure 5] This diagram shows the controlled objects of a DC power transmission system. [Figure 6] This flowchart shows a method for controlling the distribution of power in a DC power transmission system using a higher-level control device. [Figure 7] This graph shows an example of how the power that a converter that has stopped operating was receiving is distributed to the positive and negative electrode converters that are still in operation. [Modes for carrying out the invention]

[0012] 1. Overview of the Embodiment First, a general overview of a typical embodiment of the invention disclosed in this application will be provided. In the following description, as an example, the reference numerals on the drawings corresponding to the components in each embodiment are indicated in parentheses.

[0013] [1] A DC power transmission system (100) according to one aspect of the present invention includes a positive-side forward converter (111CP) that converts AC power (PPS) to DC power at the positive electrode according to a given control amount, A transmitting converter station (20) is provided with a negative forward converter (111CN) that converts AC power (PNS) to DC power on the negative terminal according to a controlled amount; a plurality of receiving converter stations (30) are provided with a positive reverse converter (111IP) that converts DC power transmitted from the positive forward converter (111CP) to AC power (PPR); and a negative reverse converter (111IN) that converts DC power transmitted from the negative forward converter (111CN) to AC power (PNR); and the receiving converter station (30) includes a positive main line (40P), a negative main line (40N), and a return line (40G). Each unit is provided with a corresponding DC transmission line connecting the transmitting converter (20) and the receiving converter (30), and a higher-level control device (10) that controls at least one of the transmitting converter (20) and the receiving converter (30), wherein the higher-level control device (10) includes a storage unit (11), a control amount calculation unit (12) that calculates the control amount for the positive-side forward converter (111CP) and the negative-side forward converter (111CN) and provides the control amount to the positive-side forward converter (111CP) and the negative-side forward converter (111CN), and a reference electrode which is either the positive or negative electrode A reference pole determination unit (13) determines the reference pole and stores the determined reference pole information, which is the reference pole determination information (110C), in the storage unit (11), and monitors whether the operating state of the positive side inverter (111IP) and the negative side inverter (111IN) is a stopped state, a constant power control state, or a droop control state, and also monitors the power received by the positive side inverter (111IP) and the negative side inverter (111IN), which is the power received by the positive side inverter (111IP) and the negative side inverter (111IN), and the operating state of the positive side inverter (111IP) and the negative side inverter (111IN) is the droop control state. The converter station information monitoring unit (14) monitors the gain value of the droop control set to IN) and stores the monitoring result in the storage unit (11); the reference pole power calculation unit (15) calculates the reference pole power transmission power (Ps), which is the power to be transmitted by the positive-side forward converter (111CP) and the negative-side forward converter (111CN) determined as the reference pole of the power transmission side converter station (20), and stores the calculation result in the storage unit (11); and the correction value calculation unit (16) calculates a correction value for correcting the control amount based on the calculation result calculated by the reference pole power calculation unit (15).The converter information monitoring unit (14) detects that the operating state of at least one of the positive inverse converter (111IP) and the negative inverse converter (111IN) has changed from the constant power control state or the droop control state to the stopped state, and stores the monitoring result in the storage unit (11). The reference pole power calculation unit (15), based on the monitoring result, calculates the total value of the received power of the positive inverse converter (111IP) and the negative inverse converter (111IN) before they changed to the stopped state, and uses the gain ratio to determine the positive forward converter (111CP) as the reference pole. Alternatively, the reference electrode transmission power (Ps) is calculated to be distributed to the negative forward converter (111CN). The correction value calculation unit (16), when correcting the transmission power (PPS) of the positive forward converter (111CP) or the transmission power (PNS) of the negative forward converter (111CN) based on the calculation result of the reference electrode power calculation unit (15), calculates a correction value based on the transmission power (PPS) of the positive forward converter (111CP) or the transmission power (PNS) of the negative forward converter (111CN) before correction and the calculation result. The control amount calculation unit (12) then calculates the control amount by correcting the command value of the control amount with the correction value.

[0014] [2] In the DC power transmission system (100) described in [1] above, it is preferable that the reference pole power calculation unit (15) calculates the reference pole power transmission power (Ps) according to a function that includes the following function (A), the following function (B), the following function (C), and the following function (D), which are included in the function information (110E) stored in the storage unit (11). Prca=ΣKdnS / (ΣKdnP+ΣKdnN)×(Pall−Papr+Pla)…(A) (In the above function (A), Prca is calculated from the total power received by either the positive reverse converter (111IP) or the negative reverse converter (111IN) before the operating state of either of the positive reverse converters (111IP) or the negative reverse converter (111IN) changes from the constant power control state or the droop control state to the stopped state. ΣKdnS represents the total power received by the positive-side inverse converter (111IP) or the negative-side inverse converter (111IN) of the reference electrode, taking into account the effect of the received power of the positive-side inverse converter (111IP) or the negative-side inverse converter (111IN) in a constant power control state, when the operating state of either the positive-side inverse converter (111IP) or the negative-side inverse converter (111IN) changes from the constant power control state or the droop control state to the stopped state and then changes to the droop control state. ΣKdnS represents the total gain of the reference electrode, ΣKdnP represents the total gain of the positive-side inverse converter (111IP), and ΣKdnN represents the total gain of the negative-side inverse converter (111IN). Pall represents the total transmitted power of the positive forward converter (111CP) and the negative forward converter (111CN), Papr represents the total received power of the positive reverse converter (111IP) and the negative reverse converter (111IN) whose operating state is the constant power control state, and Pla represents the received power of the positive reverse converter (111IP) or the negative reverse converter (111IN) before it changed to the stopped state, in the case where the operating state of either the positive reverse converter (111IP) or the negative reverse converter (111IN) changes from the constant power control state to the stopped state. Prcd={1−(ΣKdnS−ΣKddS) / (ΣKdnP+ΣKdnN−ΣKdd)}×(PddS−PddNS)…(B) (In the above function (B), Prcd represents the total power received by the positive reverse converter (111IP) or negative reverse converter (111IN) before the operating state of either the positive reverse converter (111IP) or the negative reverse converter (111IN) changes from the droop control state to the stop state, which should be subtracted from the total power transmitted by the positive forward converter (111CP) or the negative forward converter (111CN) of the reference pole after the operating state of either the positive reverse converter (111IP) or the negative reverse converter (111IN) changes from the droop control state to the stop state; ΣKdnS represents the total gain of the reference pole; and ΣKddS represents the total gain of the positive reverse converter (111IP) or the negative reverse converter (111IN) at the reference pole after the operating state changes from the droop control state to the stop state. ΣKdnP represents the total gain of the positive inverse converter (111IP), ΣKdnN represents the total gain of the negative inverse converter (111IN), ΣKdd represents the total gain of the positive inverse converter (111IP) or the negative inverse converter (111IN) when the operating state changes from the droop control state to the stopped state, PddS represents the total power received by the positive inverse converter (111IP) or the negative inverse converter (111IN) before the operating state changes from the droop control state to the stopped state at the reference electrode, and PddNS represents the total power received by the positive inverse converter (111IP) or the negative inverse converter (111IN) before the operating state changes from the droop control state to the stopped state at an electrode different from the reference electrode. Pdr = Prca - Prcd ... (C) (In the above function (C), Pdr represents the power that the positive-side inverter (111IP) or the negative-side inverter (111IN) of the reference pole, whose operating state is the droop control state, should receive. Prca is the total received power of the positive-side inverter (111IP) or the negative-side inverter (111IN) before any one of their operating states changes from the constant power control state or the droop control state to the stop state, minus the influence of the received power of the positive-side inverter (111IP) or the negative-side inverter (111IN) whose operating state is the constant power control state. Considering this value, Prca represents the total received power of the positive-side inverter (111IP) or the negative-side inverter (111IN) of the reference pole in the droop control state after any one of their operating states changes from the constant power control state or the droop control state to the stop state. Prcd represents the total received power of the positive-side inverter (111IP) or the negative-side inverter (111IN) before changing to the stop state, which should be subtracted from the total transmitted power of the positive-side converter (111CP) or the negative-side converter (111CN) of the reference pole after any one of their operating states changes from the droop control state to the stop state.) (Among the above-mentioned positive-side inverter (111IP) or negative-side inverter (111IN), after any one of their operating states changes from the constant power control state or the droop control state to the stop state, the total transmitted power of the positive-side converter (111CP) or the negative-side converter (111CN) of the reference pole should be subtracted by the total received power of the positive-side inverter (111IP) or the negative-side inverter (111IN) before changing to the stop state when their operating state changes from the droop control state to the stop state.) Ps = Pdr + Psapr…(D) (In the above function (D), Ps represents the reference pole transmitted power, Pdr represents the power that the positive-side inverter (111IP) or the negative-side inverter (111IN) of the reference pole, whose operating state is the droop control state, should receive, and Psapr represents the total received power of the positive-side inverter (111IP) and the negative-side inverter (111IN) of the reference pole whose operating state is the constant power control state.)

[0015] [3] A method for reducing power loss according to one aspect of the present invention is a method for controlling a DC power transmission system (100), the DC power transmission system (100) comprising: a transmission-side converter station (20) comprising: a positive-side forward converter (111CP) that converts AC power (PPS) to positive DC power according to a given control amount; a negative-side forward converter (111CN) that converts AC power (PNS) to negative DC power according to a given control amount; a positive-side reverse converter (111IP) that converts the DC power transmitted from the positive-side forward converter (111CP) to AC power (PPR); and the negative-side forward converter The system comprises a plurality of receiving-side converter stations (30), each equipped with a negative-side reverse converter (111IN) that converts DC power transmitted from a device (111CN) to AC power (PNR), and a DC transmission line that includes a positive main line (40P), a negative main line (40N), and a return line (40G), provided corresponding to each receiving-side converter station (30), and connecting the transmitting-side converter station (20) and the receiving-side converter stations (30), and calculates the control amount of the positive-side forward converter (111CP) and the negative-side forward converter (111CN). A control amount calculation step (S9, S10) to give the control amount to the positive electrode and the negative electrode, a reference electrode determination step (S1) to determine which of the positive electrode and the negative electrode is the reference electrode, and monitoring whether the operating state of the positive side inverter (111IP) and the negative side inverter (111IN) is a stopped state, a constant power control state and a droop control state, and the power received by the positive side inverter (111IP) and the negative side inverter (111IN) is the power received by the positive side inverter (111IP) and the negative side inverter (111IN), and the operating state of the positive side inverter (111IP) and the negative side inverter is the droop control state. The converter information monitoring step (S2, S3, S4) includes monitoring the gain value of the droop control set in the converter (111IN), a reference pole power calculation step (S7) which calculates the reference pole power transmission power (Ps) which is the power to be transmitted by the positive-side forward converter (111CP) or the negative-side forward converter (111CN) determined to be the reference pole of the power transmission side converter (20), and a correction value calculation step (S8) which calculates a correction value for correcting the control amount based on the result calculated in the reference pole power calculation step (S7), and the converter information monitoring step (S2, S3,S4) includes a step of detecting that the operating state of at least one of the positive-side inverter (111IP) and the negative-side inverter (111IN) has changed from the constant power control state or the droop control state to the stop state. The reference-pole power calculation step (S7) is based on the results of the conversion location information monitoring steps (S2, S3, S4), and calculates the reference-pole transmission power (Ps) so as to distribute the total value of the received power before the change to the stop state of the positive-side inverter (111IP) and the negative-side inverter (111IN) that have changed to the stop state, based on the ratio of the gains, to the positive-side forward converter (111CP) or the negative-side forward converter (111CN) determined as the reference pole. The correction value calculation step (S8) includes a step of calculating a correction value based on the transmission power (PPS) of the positive-side forward converter (111CP) or the transmission power (PNS) of the negative-side forward converter (111CN) before correction and the calculation result when correcting the transmission power of the positive-side forward converter (111CP) or the negative-side forward converter (111CN) according to the calculation result of the reference-pole power calculation step (S7). The control quantity calculation step (S9) includes a step of calculating the control quantity by correcting the command value of the control quantity with the correction value. PNS) and calculating a correction value based on the calculation result. The control quantity calculation step (S9) includes a step of calculating the control quantity by correcting the command value of the control quantity with the correction value.

[0016] [4] A program (1021) according to one aspect of the present invention includes a power transmission converter (20) comprising a positive-side forward converter (111CP) that converts AC power (PPS) to positive DC power according to a given control amount, and a negative-side forward converter (111CN) that converts AC power (PNS) to negative DC power according to a given control amount, a positive-side reverse converter (111IP) that converts DC power transmitted from the positive-side forward converter (111CP) to AC power (PPR), and a negative-side reverse converter (111I) that converts DC power transmitted from the negative-side forward converter (111CN) to AC power (PNR). A DC power transmission system (100) comprising: a plurality of receiving-side converter stations (30) each having N), a positive terminal main line (40P), a negative terminal main line (40N), and a return line (40G), a DC transmission line provided corresponding to each receiving-side converter station (30) and connecting the transmitting-side converter station (20) and the receiving-side converter station (30), and a higher-level control device (10) that controls at least one of the transmitting-side converter station (20) and the receiving-side converter station (30), wherein a program (1021) to be executed by the higher-level control device (10) is provided, wherein the positive-side forward converter (111CP A control amount calculation step (S9) calculates the control amount for the positive forward converter (111CP) and the negative forward converter (111CN) and provides the control amount to the positive forward converter (111CP) and the negative forward converter (111CN), a reference electrode determination step (S1) determines which of the positive or negative electrode is the reference electrode, and monitors whether the operating state of the positive reverse converter (111IP) and the negative reverse converter (111IN) is stopped, constant power control, or droop control, and when the positive reverse converter (111IP) and the negative reverse converter (111IN) receive power Converter station information monitoring steps (S2, S3, S4) monitor the received power, which is the power being transmitted, and the droop control gain values ​​set for the positive-side inverse converter (111IP) and the negative-side inverse converter (111IN), whose operating state is the droop control state; a reference pole power calculation step (S7) calculates the reference pole transmitted power (Ps), which is the power to be transmitted by the positive-side forward converter (111CP) or the negative-side forward converter (111CN) determined to be the reference pole of the transmitting-side converter station (20); and based on the results calculated in the reference pole power calculation step (S7),The converter information monitoring step (S2, S3, S4) includes a correction value calculation step (S8) for calculating a correction value to correct the control amount, and the converter information monitoring step (S2, S3, S4) includes detecting that the operating state of at least one of the positive-side inverse converter (111IP) and the negative-side inverse converter (111IN) has changed from the constant power control state or the droop control state to the stopped state, and the reference pole power calculation step (S7) calculates the total value of the power received by the positive-side inverse converter (111IP) and the negative-side inverse converter (111IN) before they changed to the stopped state, based on the gain ratio, and the positive side determined as the reference pole. The steps include calculating the reference pole transmission power (Ps) to be distributed to the forward converter (111CP) or the negative forward converter (111CN), the correction value calculation step (S8) includes, if the transmission power (PPS) of the positive forward converter (111CP) or the transmission power (PNS) of the negative forward converter (111CN) is corrected based on the calculation result of the reference pole power calculation step (S7), calculating a correction value based on the transmission power (PPS) of the positive forward converter (111CP) or the transmission power (PNS) of the negative forward converter (111CN) before correction and the calculation result, and the control amount calculation step (S9) includes calculating the control amount by correcting the command value of the control amount with the correction value.

[0017] 2. Specific Examples of Embodiments Hereinafter, specific examples of embodiments of the present invention will be described with reference to the drawings. In the following description, common components in each embodiment will be denoted by the same reference numerals, and repeated explanations will be omitted. Also, the drawings are schematic and do not show the dimensional relationships of each element or the ratios of each element. It is important to note that ratios and other figures may differ from reality. Even within drawings, there may be discrepancies in the relationships and proportions of dimensions between them.

[0018] <<First Embodiment>> <<Outline Configuration of the Power Conversion System>> Figure 1 is a diagram showing a schematic configuration of a power conversion system including a DC power transmission system according to the first embodiment of the present invention.

[0019] The power conversion system 500 shown in Figure 1 comprises a transmitting AC system 200, a receiving AC system 300, and a DC transmission system 100. The transmitting AC system 200 is connected to the DC transmission system 100. The receiving AC system 300 is connected to the DC transmission system 100. The power conversion system 500 is a system in which the AC power transmitted by the transmitting AC system 200 is converted into DC power by the DC transmission system 100, the DC power converted by the DC transmission system 100 is converted back into AC power, and then the AC power is transmitted to the receiving AC system 300.

[0020] The transmission-side AC system 200 is an AC system that inputs AC power to the DC transmission system 100. The transmission-side AC system 200 is, for example, a power generation facility that does not have a synchronizing force, such as a solar power generation facility or a wind power generation facility, or a commercial power system with a constant frequency. In this embodiment, the transmission-side AC system 200 includes a wind turbine generator 201 and a transformer 202. The receiving AC power system 300 is an AC power system that receives AC power output from the DC power transmission system 100. The receiving AC system 300 is, for example, a commercial power system, and in particular a commercial power system having a different frequency from the commercial power system connected to the transmitting AC system 200.

[0021] The DC power transmission system 100 is a system that converts AC power transmitted from the transmitting AC system 200 into DC power, converts the converted DC power back into AC power, and transmits the converted AC power to the receiving AC system 300.

[0022] For example, if the transmitting AC system 200 is a power generation facility that does not have synchronizing power, such as a solar power generation facility or a wind power generation facility, and the receiving AC system 300 is a commercial power system, the DC transmission system 100 functions as a power converter.

[0023] Furthermore, for example, if the transmitting AC system 200 is a commercial power system with a constant frequency, and the receiving AC system 300 is a commercial power system with a different frequency from the commercial power system connected to the transmitting AC system 200, the DC transmission system 100 functions as a frequency conversion device. Note that the transmitting AC system 200 and the receiving AC system 300 are not limited to the examples described above.

[0024] Specifically, the DC power transmission system 100 comprises a higher-level control device 10, a power transmission converter station 20, a power receiving converter station 30, and a DC power transmission line 40.

[0025] The higher-level control device 10 is an information processing device that monitors and controls the operating status and transmitted power of the power transmission station 20, as well as the operating status and received power of the power receiving station 30. Further details will be described later.

[0026] The transmission-side converter station 20 is equipment that converts AC power input from the transmission-side AC system 200 into DC power. The transmission-side converter station 20 is connected to the receiving-side converter station 30 via the DC transmission line 40. In Figure 1, the DC transmission system 100 has the transmission-side converter station 20 as 1 It has, but is not limited to, one or more transmission-side converter stations 20.

[0027] The power transmission side converter station 20 includes a forward converter 111C, a converter station protection control panel 112C, and a converter control panel 113C. Note that the forward converter 111C and the inverse converter 111I, which will be described later, are sometimes collectively referred to as converter 111. Figure 2 shows a detailed configuration of the area around the converter in Figure 1. As shown in Figure 2, the forward converter 111C is a semiconductor power converter that converts AC power input from the transmission AC system 200 to DC power according to a control amount given by the higher-level control device 10. The forward converter 111C comprises a positive forward converter 111CP and a negative forward converter 111CN. The positive-side forward converter 111CP is a semiconductor power converter that converts AC power input from the transmission AC system 200 to positive DC power according to a control amount provided by the higher-level control device 10. The negative-side forward converter 111CN is a semiconductor power converter that converts AC power input from the transmission AC system 200 to negative DC power according to a control amount provided by the higher-level control device 10.

[0028] The converter station protection control panel 112C is a device that constitutes the converter control device 120C, and controls the operating status of the forward converter 111C and the power transmission in accordance with commands input from the higher-level control device 10. The converter station protection control panel 112C comprises a converter station control panel and a converter station protection panel. The converter station protection control panel 112C outputs signals (hereinafter also referred to as "control signals") to the converter control panel 113C for controlling the operating status of the forward converter 111C and the power transmission in response to commands input from the higher-level control device 10 via the converter station control panel. In addition, the converter station protection control panel 112C outputs signals (hereinafter also referred to as "monitoring signals") to the higher-level control device 10 via the converter station control panel 113C that transmit the operating status of the forward converter 111C and the status of the power transmission.

[0029] The converter station protection panel outputs protection detection device operation information, which is input from a protection detection device (not shown), to the converter station control panel and the converter control panel 113C. The converter control panel 113C is a component of the converter control device 120C and controls the operating state and power transmission of the forward converter 111C in accordance with control signals input from the converter station control panel. The converter control panel 113C also outputs monitoring signals to the converter station control panel. Furthermore, the converter control panel 113C controls the operating state and power transmission of the forward converter 111C in accordance with protection detection device operation information input from the converter station protection panel.

[0030] The receiving-side converter station 30 is equipment that converts the DC power transmitted from the transmitting-side converter station 20 into AC power, and then transmits the AC power to the receiving-side AC system 300. The receiving-side converter station 30 is connected to the transmitting-side converter station 20 via a DC transmission line 40. Furthermore, the receiving-side converter station 30 is connected to other receiving-side converter stations 30 via a connecting line 50. In Figure 1, the DC power transmission system 100 has two receiving-side converter stations 30, but it is not limited to this. That is, the DC power transmission system 100 may have one or more receiving-side converter stations 30. The power transmission converter station 20 and the power receiving converter station 30 may be installed together at one location, or they may be installed at different locations.

[0031] The power receiving side converter station 30 includes an inverse converter 111I, a converter station protection control panel 112I, and a converter control panel 113I.

[0032] The inverse converter 111I is a semiconductor power converter that converts the DC power transmitted from the forward converter 111C into AC power and then transmits the AC power to the receiving AC system 300. The inverse converter 111I comprises a positive inverse converter 111IP and a negative inverse converter 111IN. The positive-side inverse converter 111IP is a semiconductor power converter that converts the DC power transmitted from the positive-side forward converter 111CP into positive-side AC power and then transmits the AC power to the receiving-side AC system 300. The negative-side inverse converter 111IN is a semiconductor power converter that converts the DC power transmitted from the negative-side forward converter 111CN into negative-side AC power and then transmits the AC power to the receiving-side AC system 300.

[0033] The converter station protection control panel 112I is a device that constitutes the converter control device 120I, and controls the operating status of the inverse converter 111I and the power transmission in accordance with commands input from the higher-level control device 10. The converter station protection control panel 112I comprises a converter station control panel and a converter station protection panel. The converter station protection control panel 112I outputs signals (hereinafter also referred to as "control signals") to the converter control panel 113I for controlling the operating status of the inverse converter 111I and the power transmission in response to commands input from the higher-level control device 10 via the converter station control panel. In addition, the converter station protection control panel 112I outputs signals (hereinafter also referred to as "monitoring signals") to the higher-level control device 10 via the converter station control panel 113I that transmit the operating status of the inverse converter 111I and the status of the power transmission.

[0034] The converter station protection panel outputs protection detection device operation information, which is input from a protection detection device (not shown), to the converter station control panel and the converter control panel 113I. The converter control panel 113I is a component of the converter control device 120I and controls the operating status and power transmission of the inverse converter 111I in accordance with control signals input from the converter station control panel. The converter control panel 113I also outputs monitoring signals to the converter station control panel. Furthermore, the converter control panel 113I controls the operating status and power transmission of the inverse converter 111I in accordance with protection detection device operation information input from the converter station protection panel.

[0035] The DC transmission line 40 is a transmission line that transmits DC power generated by the forward converter 111C to the reverse converter 111I. The DC transmission line 40 connects the power transmission station 20 on the transmitting side and the power reception station 30 on the receiving side. The DC transmission line 40 is, for example, an OF cable (Oil-Filled Cable) or a CV cable (Cross-Linked Polyethylene Insulated Vinyl Sheath Cable). The DC transmission line 40 can be installed in any location, such as underground or underwater. The DC transmission line 40 connects the transmitting converter station 20 and the receiving converter station 30. The DC transmission line 40 is provided in correspondence to each of the multiple receiving converter stations 30 connected to the transmitting converter station 20. The DC transmission line 40 comprises a positive main line 40P, a negative main line 40N, and a return line 40G.

[0036] The positive terminal main line 40P is a transmission line that transmits the DC power generated by the positive forward converter 111CP to the positive reverse converter 111IP. The negative terminal main line 40N is a transmission line that transmits the DC power generated by the negative forward converter 111CN to the negative reverse converter 111IN. The return line 40G is a transmission line that transmits the power that flows when there is a difference between the power transmitted between the positive forward converter 111CP and the positive reverse converter 111IP and the power transmitted between the negative forward converter 111CN and the negative reverse converter 111IN (hereinafter also referred to as "return line power") between the forward converter 111C and the reverse converter 111I.

[0037] Furthermore, the power transmission converter station 20 may also be equipped with a protection detection device and a DC circuit breaker in addition to the above-described configuration. For example, a protective detection device has a protective relay that detects abnormal conditions such as overvoltage and overcurrent. It outputs and, if necessary, instructs the DC circuit breaker to open. In addition, the converter station protection control panel 112C outputs information regarding the operation of the protection detection device input from the converter station protection panel to the higher-level control device 10 via the converter station control panel. For example, the DC circuit breaker performs closing and opening operations based on instructions from the converter control panel 113C. The DC circuit breaker also performs opening operations based on instructions from the protection detection device. The protective detection device and DC circuit breaker may be installed upstream or downstream of the point where the positive main line 40P, the negative main line 40N, and the return line 40G branch off toward the converter station 30 on each receiving side.

[0038] Similarly, the power receiving converter station 30 may also include a protection detection device and a DC circuit breaker in addition to the above-described configuration. The protection detection device has a protective relay that detects abnormal conditions such as overvoltage and overcurrent, and instructs the DC circuit breaker to open as needed. The converter station protection control panel 112I outputs information regarding the operation of the protection detection device, which is input from the converter station protection panel, to the higher-level control device 10 via the converter station control panel. The DC circuit breaker performs closing and opening operations based on instructions from the converter control panel 113I. The DC circuit breaker also performs opening operations based on instructions from the protection detection device.

[0039] <<Configuration of the higher-level control unit>> Figure 3 is a diagram showing the functional block configuration of a higher-level control device according to an embodiment of the present invention. Figure 4 shows the hardware configuration of the higher-level control unit.

[0040] The higher-level control unit 10 is a program processing unit that performs data processing according to programs stored in a storage device such as a PC (Personal Computer), server, tablet terminal, and smartphone. The higher-level control unit 10 includes hardware resources such as an arithmetic unit 101, a storage device 102, an input device 103, an I / F (Interface) device 104, an output device 105, and a bus 106.

[0041] The arithmetic unit 101 is composed of processors such as a CPU (Central Processing Unit) and a DSP (Digital Signal Processor). The storage device 102 has a storage area for storing programs that cause the arithmetic unit 101 to perform various data processing operations, and data such as parameters and calculation results used in the data processing by the arithmetic unit 101, and is composed of, for example, ROM (Read Only Memory), RAM (Random Access Memory), HDD, and flash memory.

[0042] Here, program 1021 includes a program for causing the computer to function as a higher-level control unit 10. For example, program 1021 is a program for realizing the control (native application) of the DC power transmission system 100 according to this embodiment, and may be downloaded in advance from an external device (e.g., an external storage medium) and stored in the storage device 102 within the higher-level control unit 10, or it may be stored on an external server (including on the internet).

[0043] Furthermore, data 1022 includes data such as various parameters necessary for controlling the DC power transmission system 100 by program 1021, and data such as the control results of the DC power transmission system 100 by the higher-level control device 10. For example, data 1022 includes transmission-side converter station information 110A, receiving-side converter station information 110B, reference pole determination information 110C, reference pole transmission power information 110D, function information 110E, etc.

[0044] Furthermore, program 1021 and data 1022 may be distributed via a network, or they may be written to a computer-readable storage medium such as a CD-ROM and distributed therein.

[0045] The input device 103 is a functional unit that detects information input from the outside and consists of, for example, a keyboard, mouse, pointing device, buttons, or touch panel. The I / F device 104 is a functional unit that sends and receives information to and from the outside and consists of a communication control circuit, input / output ports, antenna, etc., for wired or wireless communication.

[0046] The output device 105 is a functional unit that outputs information obtained through data processing by the arithmetic unit 101. Examples of output devices 105 include external storage devices such as SSDs (Solid State Drives) and HDDs (Hard Disk Drives), and display devices such as console units. The bus 106 is a functional unit that interconnects the arithmetic unit 101, storage device 102, input device 103, I / F device 104, and output device 105, enabling data exchange between these devices.

[0047] Next, we will describe in detail each functional block of the higher-level control unit 10.

[0048] As shown in Figure 3, the higher-level control device 10 includes a control amount calculation unit 12, a reference pole determination unit 13, a converter station information monitoring unit 14, a reference pole power calculation unit 15, a correction value calculation unit 16, and a storage unit 11 as functional blocks for realizing control of the DC power transmission system 100.

[0049] These functional blocks are realized through the cooperation of the aforementioned hardware resources and software that constitute the higher-level control unit 10. Specifically, in the higher-level control unit 10, the arithmetic unit 101 performs various calculations according to the program 1021 and data 1022 stored in the memory device 102, and controls the memory device 102, input device 103, I / F device 104, output device 105, and bus 106 in the higher-level control unit 10, thereby realizing the above functional blocks in the higher-level control unit 10 (control quantity calculation unit 12, reference pole determination unit 13, converter information monitoring unit 14, reference pole power calculation unit 15, correction value calculation unit 16, and storage unit 11). At least one of the above functional blocks may be realized by a dedicated circuit.

[0050] The control variable calculation unit 12 is a functional unit that calculates the control variables for the positive-side forward converter 111CP and the negative-side forward converter 111CN, and provides these control variables to the positive-side forward converter 111CP and the negative-side forward converter 111CN. The control variable calculation unit 12 can also calculate the control variables for the positive inverse converter 111IP and the negative inverse converter 111IN, and provide these control variables to the positive inverse converter 111IP and the negative inverse converter 111IN. Furthermore, the control variable calculation unit 12 calculates the control variable by correcting the command value of the control variable with a correction value calculated by the correction value calculation unit 16, which will be described later.

[0051] As a specific example, when the AC power transmitted from the AC power transmission system 200 is converted to DC power, the control amount calculation unit 12 calculates for each positive-side forward converter 111CP a control amount that is less than or equal to the rated capacity of the positive-side forward converter 111CP and should be transmitted by the positive-side forward converter 111CP (hereinafter also referred to as "positive electrode transmitted power"), and assigns a control amount to each positive-side forward converter 111CP. Similarly, when the control amount calculation unit 12 converts AC power transmitted from the AC power transmission system 200 to DC power, the control amount is less than or equal to the rated capacity of the negative-side forward converter 111CN. The negative forward converter 111CN calculates the power to be transmitted (hereinafter also referred to as "negative electrode transmitted power") for each converter station 20 on the transmission side and provides a control amount to each negative forward converter 111CN.

[0052] Furthermore, the control amount calculation unit 12 corrects the command value of the control amount (hereinafter also referred to as "pre-correction positive electrode transmission power") using a correction value calculated by the correction value calculation unit 16, which will be described later, and then calculates the control amount of the positive-side forward converter 111CP (hereinafter also referred to as "corrected positive electrode transmission power") and assigns the control amount to each positive-side forward converter 111CP.

[0053] Similarly, the control amount calculation unit 12 corrects the command value of the control amount (hereinafter also referred to as "negative electrode transmission power before correction") using the correction value calculated by the correction value calculation unit 16, which will be described later, and then calculates the control amount of the negative-side forward converter 111CN (hereinafter also referred to as "negative electrode transmission power after correction") and assigns the control amount to each negative-side forward converter 111CN.

[0054] The reference electrode determination unit 13 is a functional unit that determines either the positive electrode or the negative electrode as the reference electrode of the power conversion system 500. For example, by determining the positive electrode as the reference electrode, the reference electrode power calculation unit 15, which will be described later, can calculate the reference electrode transmission power Ps using the positive electrode as the reference electrode. In this embodiment, the following explanation will proceed assuming that the reference electrode determination unit 13 has determined the positive electrode as the reference electrode. However, the reference electrode determination unit 13 may also determine the negative electrode as the reference electrode.

[0055] The reference pole determination unit 13 may determine the reference pole based on information transmitted from an information processing device (not shown) connected via a network (not shown), or information prepared in advance by a system administrator or the like. Furthermore, the reference pole determination unit 13 stores the reference pole determination information 110C, which is the information of the determined reference pole, in the storage unit 11.

[0056] The converter station information monitoring unit 14 is a functional unit that monitors whether the operating state of the positive-side inverse converter 111IP and the negative-side inverse converter 111IN is stopped, constant power control, or droop control, and also monitors the received power, which is the power received by the positive-side inverse converter 111IP and the negative-side inverse converter 111IN. Furthermore, the converter information monitoring unit 14 stores the operating status of the positive-side inverse converter 111IP and the negative-side inverse converter 111IN, as well as the monitoring results of the received power, in the storage unit 11.

[0057] Furthermore, the converter information monitoring unit 14 monitors the gain values ​​of the droop control set for the positive inverse converter 111IP and the negative inverse converter 111IN, which are operating in a droop control state. Furthermore, the converter information monitoring unit 14 stores in the storage unit 11 the monitoring results of the droop control gain values ​​set for the positive inverse converter 111IP and the negative inverse converter 111IN, which are operating in a droop control state.

[0058] Furthermore, the converter information monitoring unit 14 detects when the operating state of at least one of the positive-side inverse converter 111IP and the negative-side inverse converter 111IN changes from a constant power control state or a droop control state to a stopped state.

[0059] Furthermore, if the operating state of at least one of the positive inverse converter 111IP and the negative inverse converter 111IN changes from a constant power control state or a droop control state to a stopped state, the converter information monitoring unit 14 stores in the storage unit 11 the monitoring result that the operating state of at least one of the positive inverse converter 111IP and the negative inverse converter 111IN has changed from a constant power control state or a droop control state to a stopped state.

[0060] A stopped state refers to a condition in which the inverse converter 111I is unable to convert the positive or negative power transmitted from the forward converter 111C into AC power due to an accident, inspection, or other reasons. The power receiving state refers to the state in which the inverter 111I can convert the positive and negative power transmitted from the forward converter 111C into AC power. The power receiving state includes the constant power control state and the droop control state.

[0061] The constant power control state refers to a state in which the inverse converter 111I always converts the transmitted power transmitted from the power transmission station 20 on the transmission side into a constant AC power (active power), even if a disturbance occurs in the power conversion system 500. The droop control state refers to the state in which the inverter 111I converts the transmitted power transmitted from the power transmission station 20 to AC power while adjusting the positive and negative power received to follow the fluctuations in the power conversion system 500 when fluctuations occur in the power conversion system 500 (hereinafter also referred to as the "droop characteristic"). The positive and negative power received are changed as needed based on the gain value set in the inverter 111I. The gain value set for the inverse converter 111I is stored in the memory unit 11, which will be described later.

[0062] The gain, in particular, is the reciprocal of the slope of the droop control, which is the value that determines the change in DC voltage corresponding to the change in transmitted power. When the positive-side inverter 111IP and the negative-side inverter 111IN are in a constant power control state or a droop control state, they control the positive-electrode power and negative-electrode power themselves according to these states, so there is no need for the control amount calculation unit 12 to calculate the control amount.

[0063] The reference pole power calculation unit 15 is a functional unit that calculates the reference pole transmission power Ps, which is the power that the positive-side forward converter 111CP or negative-side forward converter 111CN, which has been determined to be the reference pole of the power transmission station 20, should transmit. Furthermore, the reference pole power calculation unit 15 stores the calculation result of the reference pole transmission power Ps in the storage unit 11.

[0064] Furthermore, the reference pole power calculation unit 15 calculates the reference pole transmission power Ps based on the monitoring results, so as to allocate the total value of the received power of the positive-side inverse converter 111IP and the negative-side inverse converter 111IN before they changed to a stopped state to the positive-side forward converter 111CP or the negative-side forward converter 111CN, which has been determined to be the reference pole, based on the gain ratio.

[0065] Specifically, when the converter station information monitoring unit 14 detects that the operating state of one or more of the inverse converters 111I has changed from a power receiving state to a stopped state, the reference pole power calculation unit 15 calculates the reference pole power transmission power Ps, which is the total power that the reference pole forward converter 111CP should transmit, based on the function information 110E described later. The reference pole power calculation unit 15 calculates the reference pole transmission power Ps according to a function that includes function (A), function (B), function (C), and function (D), which are included in the function information 110E stored in the memory unit 11. Details about functions (A), (B), (C), and (D) will be provided later.

[0066] Furthermore, the reference pole power calculation unit 15 calculates the non-reference pole transmission power Pn, which will be described later, according to a function that includes function (E) and function (F), which are included in the function information 110E stored in the memory unit 11. Details about functions (E) and (F) will be discussed later. Furthermore, the reference pole power calculation unit 15 stores the calculated non-reference pole transmission power Pn in the storage unit 11.

[0067] The correction value calculation unit 16 is a functional unit that calculates a correction value for correcting the control variable based on the calculation result calculated by the reference pole power calculation unit 15.

[0068] When the correction value calculation unit 16 corrects the transmission power PPS (see Figure 5) of the positive-side forward converter 111CP and the transmission power PNS (see Figure 5) of the negative-side forward converter 111CN based on the reference pole transmission power Ps calculated by the reference pole power calculation unit 15, it calculates a correction value based on the calculation results of the transmission power PPS of the positive-side forward converter 111CP and the transmission power PNS of the negative-side forward converter 111CN before correction, as well as the reference pole transmission power Ps.

[0069] Furthermore, when the correction value calculation unit 16 corrects the transmission power PPS of the positive-side forward converter 111CP and the transmission power PNS of the negative-side forward converter 111CN based on the non-reference pole transmission power Pn calculated by the reference pole power calculation unit 15, it calculates a correction value based on the calculation results of the transmission power PPS of the positive-side forward converter 111CP, the transmission power PNS of the negative-side forward converter 111CN, and the non-reference pole transmission power Pn before correction. Details on how to calculate the correction value will be described later.

[0070] The memory unit 11 is a functional unit for storing various data such as parameters necessary for controlling the DC power transmission system 100 and the control results of the DC power transmission system 100 by the higher-level control device 10. For example, the memory unit 11 stores the transmission-side converter station information 110A, the receiving-side converter station information 110B, the reference pole determination information 110C, the reference pole transmission power information 110D, and the function information 110E, as described above.

[0071] The transmission-side converter station information 110A includes information about the forward converter 111C that has been stored in the memory unit 11 in advance, and information included in the monitoring signal input from the converter control device 120C. For example, the transmission-side converter station information 110A includes, but is not limited to, information about the rated capacity and operating status of the forward converter 111C, as well as information about the positive electrode transmission power and negative electrode transmission power.

[0072] The power transmission side converter station information 110A stored in the memory unit 11 may include information transmitted from an information processing device (not shown) connected via a network (not shown), or information prepared in advance by a system administrator or the like.

[0073] The receiving-side converter station information 110B includes information about the inverse converter 111I that has been stored in the memory unit 11 in advance, and information included in the monitoring signal input from the converter control device 120I. For example, the receiving-side converter station information 110B includes, but is not limited to, information about the rated capacity and operating status of the inverse converter 111I, as well as the positive electrode power received and the negative electrode power received. The operating state of the inverse converter 111I includes the droop control gain values ​​set for the positive inverse converter 111IP and the negative inverse converter 111IN, whose operating state is in droop control mode.

[0074] The power receiving converter information 110B stored in the memory unit 11 may include information transmitted from an information processing device (not shown) connected via a network (not shown), or information prepared in advance by a system administrator or the like.

[0075] The reference pole determination information 110C includes information about the reference pole of the power conversion system 500, which has been determined by the reference pole determination unit 13. In this embodiment, the reference pole determination information 110C includes information that the reference pole of the power conversion system 500 is the positive pole.

[0076] The reference pole determination information 110C stored in the memory unit 11 may include information transmitted from an information processing device (not shown) connected via a network (not shown), or information prepared in advance by a system administrator or the like.

[0077] The reference pole transmission power information 110D includes the reference pole transmission power Ps, which is the power that the reference pole, the positive-side forward converter 111CP, should transmit, calculated by the reference pole power calculation unit 15 according to the function included in the function information 110E described later. Furthermore, the reference pole transmission power information 110D includes the non-reference pole transmission power Pn, which is the power that the negative-side forward converter 111CN (not the reference pole) should transmit, calculated by the reference pole power calculation unit 15 according to the function included in the function information 110E described later.

[0078] The function information 110E includes functions used by the reference pole power calculation unit 15 when calculating the reference pole transmission power Ps and the non-reference pole transmission power Pn. Specifically, the function information 110E includes functions (A) to (F).

[0079] Function (A) is a function that calculates Prca, which is the total power received by the reference electrode inverter 111I in a droop control state after one of the inverters 111I changes from a power-receiving state to a stop state. This calculation takes into account the effect of the power received by the inverter 111I in a constant power control state, which is obtained by subtracting the effect of the power received by the inverter 111I in a constant power control state from the total power received by the inverters 111I before the operating state of any of the inverters 111I changes from a power-receiving state to a stop state.

[0080] The above Prca can be calculated using the following function (A), where ΣKdnS is the sum of the gains of the reference poles, ΣKdnP is the sum of the gains of the positive inverse converter 111IP, ΣKdnN is the sum of the gains of the negative inverse converter 111IN, Pall is the sum of the transmitted power of the forward converter 111C, Papr is the sum of the received power of the inverse converters 111I whose operating state is constant power control, and Pla is the received power of the inverse converter 111I before it changed to the stopped state when the operating state of any of the inverse converters 111I changes from constant power control to stopped.

[0081] Prca=ΣKdnS / (ΣKdnP+ΣKdnN)×(Pall−Papr+Pla)…(A)

[0082] Function (B) is a function that calculates Prcd, which is the sum of the received power before the reverse converter 111I changed from a droop-controlled state to a stopped state, to be subtracted from the transmitted power of the reference pole forward converter 111C after the operating state of any of the reverse converters 111I changes from a power-receiving state to a stopped state.

[0083] The above Prcd can be calculated by the following function (B), where ΣKdnS is the sum of the gains of the reference pole, ΣKddS is the sum of the gains of the inverse converter 111I whose operating state has changed from a droop control state to a stopped state at the reference pole, ΣKdnP is the sum of the gains of the positive inverse converter 111IP, ΣKdnN is the sum of the gains of the negative inverse converter 111IN, ΣKdd is the sum of the gains of the inverse converter 111I whose operating state has changed from a droop control state to a stopped state, PddS is the sum of the received power before the inverse converter 111I whose operating state has changed from a droop control state to a stopped state at the reference pole, and PddNS is the sum of the received power before the inverse converter 111I whose operating state has changed from a droop control state to a stopped state at a pole other than the reference pole.

[0084] Prcd={1−(ΣKdnS−ΣKddS) / (ΣKdnP+ΣKdnN−ΣKdd)}×(PddS−PddNS)…(B)

[0085] Function (C) is a function that calculates Pdr, which is the power that the reference electrode inverter 111I should receive when its operating state is in droop control mode.

[0086] The above Pdr can be calculated by the following function (C), where Prca is the total power received by the reference electrode inverter 111I in a droop control state after one of the inverters 111I changes from a power-receiving state to a stop state, taking into account the effect of the power received by the inverter 111I in a constant power control state, which is calculated by the above function (A) from the total power received by the inverter 111I before one of the inverters 111I changes from a power-receiving state to a stop state, and Prcd is the total power received by the inverter 111I before one of the inverters 111I changes from a droop control state to a stop state, which should be subtracted from the power transmitted by the reference electrode forward converter 111C after one of the inverters 111I changes from a power-receiving state to a stop state, which is calculated by the above function (B).

[0087] Pdr = Prca - Prcd ... (C)

[0088] Function (D) is a function that calculates Ps, which is the reference electrode transmission power.

[0089] The above Ps can be calculated using the following function (D), where Pdr is the power that the reference electrode inverter 111I should receive when its operating state is droop control, and Psapr is the total power received by the reference electrode inverter 111I when its operating state is constant power control.

[0090] Ps = Pdr + Psapr ... (D)

[0091] Function (E) is a function that calculates RATEs, which is the ratio of the reference pole transmission power Ps to Pall, which is the total transmission power of the forward converter 111C.

[0092] The above RATEs can be calculated using the following function (E).

[0093] RATEs=Ps / Pall…(E)

[0094] Function (F) is a function that calculates RATEn, which is the ratio of the non-reference pole transmission power Pn to Pall, which is the total transmission power of the forward converter 111C.

[0095] The above RATEn can be calculated using the following function (F).

[0096] RATEn=Pn / Pall=(1―Ps) / Pall…(F)

[0097] In the above functions (A) through (F), the gain value may be the reciprocal of the slope of the droop control set in the inverse converter 111I.

[0098] The function information 110E stored in the memory unit 11 may include information transmitted from an information processing device (not shown) connected via a network (not shown), or information prepared in advance by a system administrator or the like.

[0099] <<Method for calculating correction values, method for calculating control variables>> Figure 5 shows the controlled objects of a DC power transmission system. Figure 6 is a flowchart showing a method for controlling the distribution of power in a DC power transmission system by a higher-level control device. Figure 7 shows the power that the stopped converter was receiving just before the operation stopped, and the positive electrode that is still in operation. This graph shows an example of how the signal is distributed between a converter for the negative electrode and a converter for the negative electrode.

[0100] Next, we will describe in detail the method by which the correction value calculation unit 16 calculates the correction value, and the method by which the control amount calculation unit 12 corrects the command value of the control amount using the correction value calculated by the correction value calculation unit 16, calculates the control amount for each forward converter 111C, and assigns the control amount to each forward converter 111C.

[0101] First, we will describe the configuration of the power conversion system 500 and the controlled objects of the DC power transmission system 100 in Figure 5. The power conversion system 500 in Figure 5 differs from the power conversion system 500 in Figure 1 in that it comprises one transmitting AC system 200, four receiving AC systems 300, and a DC transmission system 100. The DC transmission system 100 comprises one transmitting converter station 20, four receiving converter stations 30, four positive main lines 40P, four negative main lines 40N, and four return lines 40G. Specifically, the power conversion system 500 in Figure 5 comprises one transmitting AC line 200, one positive forward converter 111CP, one negative forward converter 111CN, four receiving AC lines 300A, 300B, 300C, and 300D, four positive reverse converters 111IPA, 111IPB, 111IPC, and 111IPD, four negative reverse converters 111INA, 111INB, 111INC, and 111IND, four positive main lines 40PA, 40PB, 40PC, and 40PD, four negative main lines 40NA, 40NB, 40NC, and 40ND, and four return lines 40GA, 40GB, 40GC, and 40GD.

[0102] In this description, the DC power transmission system 100 controls the following: the positive power transmission power PPS and negative power transmission power PNS transmitted by the transmitting AC system 200; the positive power reception power PPRA and negative power reception power PNRA received by the receiving AC system 300A; the positive power reception power PPRB and negative power reception power PNRB received by the receiving AC system 300B; the positive power reception power PPRC and negative power reception power PNRC received by the receiving AC system 300C; and the positive power reception power PPRD and negative power reception power PNRD received by the receiving AC system 300D. The sum of the positive electrode transmission power PPS and the negative electrode transmission power PNS is the transmission power P.

[0103] Next, the specific rated capacities and operating conditions of the forward converter 111C and the reverse converter 111I will be described. The rated capacities of the forward converters 111C are 1700 MW for the positive forward converter 111CP and 1700 MW for the negative forward converter 111CN. Furthermore, the rated capacities of the inverse converters 111I are as follows: positive inverse converters 111IPA and 111IPB have a capacity of 250 MW, positive inverse converter 111IPC has a capacity of 600 MW, positive inverse converter 111IPD has a capacity of 1000 MW, negative inverse converters 111INA and 111INB have a capacity of 250 MW, negative inverse converter 111INC has a capacity of 600 MW, and negative inverse converter 111IND has a capacity of 1000 MW.

[0104] The operating state of the inverse converters 111I is such that the positive inverse converter 111IPA and the negative inverse converter 111INA are in a constant power control state, while the positive inverse converters 111IPB, 111IPC, and 111IPD, and the negative inverse converters 111INB, 111INC, and 111IND are in a droop control state.

[0105] The gains set for the positive-side inverse converter 111IP are as follows: the gain KdPB set for the positive-side inverse converter 111IPB is 1, the gain KdPC set for the positive-side inverse converter 111IPC is 2, and the gain KdPD set for the positive-side inverse converter 111IPD is 3. Furthermore, the gain set in the negative inverse converter 111IN is set in the negative inverse converter 111INB. The set gain KdNB is 1, the gain KdNC set for the negative inverse converter 111INC is 2, and the gain KdND set for the negative inverse converter 111IND is 3.

[0106] Next, we will describe the specific positive electrode transmission power, negative electrode transmission power, positive electrode reception power, and negative electrode reception power of the forward converter 111C and the reverse converter 111I. The positive terminal transmission power of the positive-side forward converter 111CP is 1500 MW, given that the positive terminal transmission power PPS transmitted by the transmission-side AC system 200 is 1500 MW, and the rated capacity of the positive-side forward converter 111CP is 1700 MW. The negative terminal power transmitted by the negative forward converter 111CN is 1500 MW, given that the negative terminal power PNS transmitted by the transmission AC system 200 is 1500 MW, and the rated capacity of the negative forward converter 111CN is 1700 MW.

[0107] The positive terminal power received by the positive-side inverter 111IPA is 250 MW, because the positive terminal power received by the receiving AC system 300 A is 250 MW, and the rated capacity of the positive-side inverter 111IPA is 250 MW. Furthermore, the positive terminal power received by the positive-side inverter 111IPB is 200 MW, given that the positive terminal power received by the receiving AC system 300B is 200 MW, and the rated capacity of the positive-side inverter 111IPB is 250 MW. Furthermore, the positive terminal power received by the positive-side inverter 111IPC is 300MW, given that the positive terminal power received by the receiving AC system 300C is 300MW, and the rated capacity of the positive-side inverter 111IPC is 600MW. Furthermore, the positive terminal power received by the positive-side inverter 111IPD is 750 MW, given that the positive terminal power received by the receiving AC system 300D is 750 MW, and the rated capacity of the positive-side inverter 111IPD is 1000 MW.

[0108] The negative terminal power received by the negative inverter 111INA is 250 MW, since the negative terminal power PNRA received by the receiving AC system 300 A is 250 MW, and the rated capacity of the negative inverter 111INA is 250 MW. Furthermore, the negative terminal power received by the negative inverter 111INB is 200 MW, given that the negative terminal power received by the receiving AC system 300B is 200 MW, and the rated capacity of the negative inverter 111INB is 250 MW. Furthermore, the negative electrode power received by the negative inverter 111INC is 300 MW, given that the negative electrode power received by the receiving AC system 300C is 300 MW, and the rated capacity of the negative inverter 111INC is 600 MW. Furthermore, the negative electrode power received by the negative inverter 111IND is 750 MW, given that the negative electrode power received by the receiving AC system 300D is 750 MW, and the rated capacity of the negative inverter 111IND is 1000 MW.

[0109] Next, we will explain the operation of each functional unit when, for example, the positive-side inverter 111IPB changes from a powered state (droop control state) to a stopped state due to a fault in the operating state described above.

[0110] If the positive-side inverter 111IPB changes from a power-receiving state (droop-controlled state) to a stopped state due to a fault, a change occurs in the destination of the positive terminal power PPRB that the power-receiving AC system 300B had been receiving. In other words, the 200MW positive terminal power PPRB that the positive-side inverter 111IPB had been receiving (converting the transmitted power transmitted from the forward converter 111C into AC power) will now be received by the positive-side inverters 111IPC and 111IPD, which are still in a droop-controlled state.

[0111] At this time, the positive terminal power PPRC received by the receiving AC system 300C and the receiving AC The magnitude of the positive terminal power PPRD received by system 300D becomes greater than before the positive-side inverter 111IPB changed to the stopped state. Therefore, a difference arises between the positive terminal power PPRC received by the receiving AC system 300C and the negative terminal power PNRC received by the receiving AC system 300C, causing a return current to flow through the return line 40GC. At the same time, a difference arises between the positive terminal power PPRD received by the receiving AC system 300D and the negative terminal power PNRD received by the receiving AC system 300D, causing a return current to flow through the return line 40GD.

[0112] Here, by setting the difference between the positive terminal's received power PPRC and the negative terminal's received power PNRC to 0, and the difference between the positive terminal's received power PPRD and the negative terminal's received power PNRD to 0, it becomes possible to prevent power loss due to return current. Therefore, the higher-level control device 10 controls the forward converter 111C and the reverse converter 111I so that the difference between the positive terminal's received power PPRC and the negative terminal's received power PNRC is 0, and the difference between the positive terminal's received power PPRD and the negative terminal's received power PNRD is 0. The processing flow by the higher-level control device 10 will be explained below with reference to Figure 6. Figure 6 is a flowchart showing the processing flow by the higher-level control device 10.

[0113] First, the reference electrode determination unit 13 determines either the positive or negative electrode of the power conversion system 500 as the reference electrode (step S1). In this embodiment, the reference electrode determination unit 13 determines the positive electrode as the reference electrode.

[0114] Next, the converter station information monitoring unit 14 monitors the operating status of the positive-side inverse converter 111IP and the negative-side inverse converter 111IN, as well as the power received (step S2). The positive-side inverse converter 111IPA is in a constant power control state, and the positive electrode power PPRA is 250 MW. The positive-side inverse converter 111IPB is in a droop-controlled state, and the positive terminal power PPRB is 200 MW. The positive-side inverse converter 111IPC is in a droop-controlled state, and the positive terminal power PPRC is 300 MW. The positive-side inverse converter 111IPD is in a droop-controlled state, and the positive terminal power PPRD is 750 MW. The negative inverse converter 111INA is in a constant power control state, and the power received by the negative terminal, PNRA, is 250 MW. The negative inverse converter 111INB is in a droop-controlled state, and the negative terminal power PNRB is 200 MW. The negative inverse converter 111INC is in a droop-controlled state, and the negative terminal power PNRC is 300 MW. The negative inverse converter 111IND is in a droop-controlled state, and the negative terminal power PNRD is 750 MW.

[0115] Furthermore, the converter station information monitoring unit 14 monitors the positive terminal power PPS transmitted by the positive forward converter 111CP and the negative terminal power PNS transmitted by the negative forward converter 111CN. The positive terminal power PPS transmitted by the positive-side forward converter 111CP is 1500 MW. The negative terminal power PNS transmitted by the negative forward converter 111CN is 1500 MW.

[0116] Next, the converter information monitoring unit 14 checks whether the operating status of the positive-side inverse converter 111IP and the negative-side inverse converter 111IN are all in a constant power control state or a droop control state (step S3). If the operating states of both the positive-side inverse converter 111IP and the negative-side inverse converter 111IN are constant power control or droop control (step S3: YES), the correction value calculation unit 16 does not calculate the correction value. In this case, the control amount calculation unit 12 calculates the positive-side forward converter 111CP and the negative-side inverse converter 111IN. The control amount is calculated without correcting the command value of the control amount of the forward converter 111CN (step S10). As a result, the control amount calculated in step S10 is given to the forward converter 111C (step S11). That is, the control amount calculation unit 12 gives the same control amount to the forward converter 111C as before, and as a result, the control amounts of the positive inverse converters 111IPA, 111IPB, 111IPC, 111IPD and the negative inverse converters 111INA, 111INB, 111INC, 111IND do not change from the previous control amounts.

[0117] However, in this case, since the positive inverse converter 111IPB changed from a droop control state to a stopped state (step S3: NO), the correction value is calculated according to the contents of steps S4 to S9.

[0118] Based on the monitoring results, the converter information monitoring unit 14 extracts the positive inverse converters 111IPC, 111IPD, 111INB, 111INC, and 111IND from the positive inverse converters 111IPA, 111IPB, 111IPC, 111IPD and the negative inverse converters 111INA, 111INB, 111INC, and 111IND that are in a droop control state (step S4). Furthermore, the converter information monitoring unit 14 detects, based on the monitoring results, that the positive-side inverse converter 111IPB has changed from a droop control state to a stopped state (step S4).

[0119] Next, the converter information monitoring unit 14 refers to the gain values ​​KdPC, KdPD, KdNB, KdNC, and KdND set for the positive inverse converter 111IPC, positive inverse converter 111IPD, negative inverse converter 111INB, negative inverse converter 111INC, and negative inverse converter 111IND, which are in a droop control state. Furthermore, the converter information monitoring unit 14 refers to the gain KdPB value that was set before the positive inverse converter 111IPB changed from the droop control state to the stopped state. At this time, the converter information monitoring unit 14 checks whether the gain KdPC of the positive inverse converter 111IPC and the gain KdNC of the negative inverse converter 111INC are equal, since both the positive inverse converter 111IP and the negative inverse converter 111IN are in a droop control state (step S5). The converter information monitoring unit 14 also checks whether the gain KdPD of the positive inverse converter 111IPD and the gain KdND of the negative inverse converter 111IND are equal, since both the positive inverse converter 111IP and the negative inverse converter 111IN are in a droop control state (step S5).

[0120] If either the gain KdPC of the positive inverse converter 111IPC and the gain KdNC of the negative inverse converter 111INC are not equal, or the gain KdPD of the positive inverse converter 111IPD and the gain KdND of the negative inverse converter 111IND are not equal (Step S5: NO), the converter information monitoring unit 14 adjusts the gains KdPC and KdNC so that the gains KdPC of the positive inverse converter 111IPC and KdNC of the negative inverse converter 111INC match (Step S6). The converter information monitoring unit 14 also adjusts the gains KdPD and KdND so that the gains KdPD of the positive inverse converter 111IPD and KdND of the negative inverse converter 111IND match (Step S6).

[0121] In this case, the gain KdPC of the positive inverse converter 111IPC and the gain KdNC of the negative inverse converter 111INC are equal to 2, and the gain KdPD of the positive inverse converter 111IPD and the gain KdND of the negative inverse converter 111IND are equal to 3 (Step S5: YES). Therefore, the converter information monitoring unit 14 proceeds to the next step without adjusting the gains KdPC, KdNC, KdPD, and KdND.

[0122] Next, the reference pole power calculation unit 15 calculates the reference pole transmission power Ps and the non-reference pole transmission power Pn based on the function information 110E (step S7). Specifically, the reference pole power calculation unit 15 calculates the reference pole transmission power Ps according to functions (A) to (D) included in the function information 110E.

[0123] Furthermore, the reference pole power calculation unit 15 calculates RATEs, which is the ratio of the reference pole transmission power Ps to the total transmission power of the forward converter 111C, according to the function (E) contained in the function information 110E.

[0124] Furthermore, the reference pole power calculation unit 15 calculates the non-reference pole transmission power Pn according to the function (F) included in the function information 110E. Furthermore, the reference pole power calculation unit 15 calculates RATEn, which is the ratio of the non-reference pole transmission power Pn to the total transmission power of the forward converter 111C, according to the function (F) included in the function information 110E.

[0125] In this case, the total gain of the reference electrode (positive inverter 111IP) ΣKdnS is 6, the total gain of the positive inverter 111IP ΣKdnP is 6, the total gain of the negative inverter 111IN ΣKdnN is 6, the total transmitted power of the forward converter 111C Pall is 3000MW, the total received power of the positive inverter 111IPA and negative inverter 111INA, which are operating in a constant power control state, Papr is 500MW, and if the operating state of any of the inverters 111I changes from a constant power control state to a stopped state... In the combined case, since the received power Pla of the inverter 111I before it changed to the stopped state was 0MW, according to function (A), the total received power Prca of the reference pole inverter 111I, which is in a droop control state after the operating state of any of the inverters 111I changes from the received power state to the stopped state, is calculated to be 1250MW, taking into account the effect of the received power of 500MW of the positive inverter 111IPA and negative inverter 111INA, which are in a constant power control state, from the total transmitted power of the forward converter 111C, which is 3000MW.

[0126] Furthermore, the total gain ΣKdnS of the reference electrode (positive inverse converter 111IP) is 6, the total gain ΣKddS of the positive inverse converter 111IPB when the operating state at the reference electrode changes from a droop control state to a stopped state is 1, the total gain ΣKdnP of the positive inverse converter 111IP is 6, the total gain ΣKdnN of the negative inverse converter 111IN is 6, the total gain ΣKdd of the positive inverse converter 111IPB when the operating state changes from a droop control state to a stopped state is 1, and the positive inverse converter 111IPB when the operating state at the reference electrode changes from a droop control state to a stopped state The total power received before the change PddS is 200 MW, and the total power received before the change to the stopped state of the inverter 111I, whose operating state changed from a droop control state to a stopped state on a pole different from the reference pole, is 0 MW. Therefore, according to function (B), the total power received before the change to the stopped state of the positive-side inverter 111IPB, whose operating state changed from a droop control state to a stopped state, which should be subtracted from the transmission power of the forward converter 111C of the reference station after the operating state of any of the inverters 111I changes from a power received state to a stopped state, is calculated to be 109.1 MW.

[0127] Furthermore, considering the effect of the 500MW received power of the positive-side inverse converter 111IPA and negative-side inverse converter 111INA, which are in a constant power control state, subtracted from the total transmitted power of the forward converter 111C, calculated using function (A) above, the total received power Prca of the reference pole inverse converter 111I, which is in a droop control state after the operating state of any of the inverse converters 111I changes from a received state to a stopped state, is 1250MW. Also, the total received power Prcd of the positive-side inverse converter 111IPB, which is in a droop control state after the operating state of any of the inverse converters 111I changes from a droop control state to a stopped state, which should be subtracted from the transmitted power of the reference station's forward converter 111C after the operating state of any of the inverse converters 111I changes from a received state to a stopped state, calculated using function (B) above, is 109.1MW. Therefore, according to function (C), the operating state is droop control The power Pdr that the reference electrode inverter 111I should receive is calculated to be 1140.9 MW.

[0128] Furthermore, the power Pdr that the reference electrode inverter 111I, operating in a droop control state, should receive, calculated using function (C), is 1140.9 MW, and the total power Psapr received by the reference electrode positive side inverter 111IP, operating in a constant power control state, is 250 MW. Therefore, according to function (D), the reference electrode transmission power Ps is calculated to be 1390.9 MW.

[0129] Furthermore, since the total power transmission value Pall of the forward converter 111C is 3000MW and the reference pole transmission power Ps is 1390.9MW, according to function (E), the ratio RATEs, which is the ratio of the reference pole transmission power Ps to the total power transmission value of the forward converter 111C, is calculated to be 0.464. Furthermore, according to function (F), RATEn, which is the ratio of the non-reference pole transmission power Pn to the total transmission power of the forward converter 111C, is calculated to be 0.536.

[0130] Here, since the transmission power of the forward converter 111C is 3000 MW, the non-reference pole transmission power Pn is calculated by multiplying the ratio of the non-reference pole transmission power Pn to the total transmission power of the forward converter 111C, RATEn 0.536, by the total transmission power of the forward converter 111C, which is 3000 MW, resulting in 1609.1 MW.

[0131] Next, the correction value calculation unit 16 calculates a correction value for correcting the control amount based on the reference pole transmission power Ps and non-reference pole transmission power Pn calculated by the reference pole power calculation unit 15 (step S8).

[0132] Before the positive-side inverse converter 111IPB changes from a droop control state to a stopped state, the converter station information monitoring unit 14 stores in the storage unit 11 the monitoring results that the positive terminal transmission power PPS transmitted by the positive-side forward converter 111CP is 1500 MW and the negative terminal transmission power PNS transmitted by the negative-side forward converter 111CN is 1500 MW. In step S7, the reference pole power calculation unit 15 newly calculated the reference pole transmission power Ps and the non-reference pole transmission power Pn because the positive-side inverter 111IPB changed from a droop control state to a stopped state.

[0133] Therefore, when the correction value calculation unit 16 corrects the transmission power PPS of the positive-side forward converter 111CP or the transmission power PNS of the negative-side forward converter 111CN based on the reference pole transmission power Ps calculated by the reference pole power calculation unit 15, it calculates a correction value based on the calculation results of the transmission power PPS of the positive-side forward converter 111CP or the transmission power PNS of the negative-side forward converter 111CN and the reference pole transmission power Ps before correction. Furthermore, when the correction value calculation unit 16 corrects the transmission power PPS of the positive-side forward converter 111CP or the transmission power PNS of the negative-side forward converter 111CN based on the non-reference pole transmission power Pn calculated by the reference pole power calculation unit 15, it calculates a correction value based on the calculation results of the transmission power PPS of the positive-side forward converter 111CP or the transmission power PNS of the negative-side forward converter 111CN and the non-reference pole transmission power Pn before correction.

[0134] Specifically, the correction value calculation unit 16 calculates the correction value of the transmission power PPS of the corrected positive-side forward converter 111CP as -109.1MW, based on the difference between the calculated reference pole transmission power Ps of 1390.9MW and the transmission power PPS of the uncorrected positive-side forward converter 111CP, which is 1500MW. Similarly, the correction value calculation unit 16 calculates the transmission power PNS of the corrected negative forward converter 111CN as 1609.1MW, which is the result of the calculation of the non-reference pole transmission power Pn, and the negative forward converter 11 before correction. Based on the difference of 1500MW in the transmission power PNS of 1CN, the correction value is calculated to be 109.1MW.

[0135] Next, the control variable calculation unit 12 corrects the command value of the control variable using the correction value calculated by the correction value calculation unit 16, then calculates the control variable for the forward converter 111C (step S9), and provides the control variable to the forward converter 111C (step S10).

[0136] Specifically, the control amount calculation unit 12 calculates a control amount of 1390.9 MW by correcting the command value of the control amount of the positive-side forward converter 111CP, which is 1500 MW, by the correction value of -109.1 MW, and provides the positive electrode transmission power PPS 1390.9 MW, which is the control amount, to the positive-side forward converter 111CP. Similarly, the control amount calculation unit 12 calculates a control amount of 1609.1MW by correcting the command value of the control amount of the negative forward converter 111CN, which is 1500MW, with the correction value of 109.1MW, and provides the negative electrode transmission power PNS 1609.1MW, which is the control amount, to the negative forward converter 111CN.

[0137] Through the above steps, the control amount calculation unit 12 provides the forward converter 111C with a control amount based on the reference electrode transmission power Ps and the non-reference electrode transmission power Pn. As a result, the received power that the positive-side inverse converter 111IPB, which has changed from a droop-controlled state to a stopped state, received before changing to a stopped state is distributed to the positive-side inverse converter 111IPC, positive-side inverse converter 111IPD, negative-side inverse converter 111INB, negative-side inverse converter 111INC, and negative-side inverse converter 111IND, which are in a droop-controlled state, based on the ratio of gains KdPC, KdPD, KdNB, KdNC, and KdND (step S11).

[0138] Specifically, the power received by each inverter 111I before the positive inverter 111IPB changed to a stopped state is distributed based on a ratio obtained by dividing the gains KdPC, KdPD, KdNB, KdNC, and KdND set for each inverter 111I by the sum of the gains KdPC, KdPD, KdNB, KdNC, and KdND of each inverter 111I.

[0139] More specifically, the received power of 200 MW that the positive-side inverter converter 111IPB was receiving before it changed to a stopped state is divided by the sum of the gains, which is 11. The resulting quotient is 18.18 (≒200 / 11) MW. This product is then multiplied by the gain KdPC set for the positive-side inverter converter 111IPC, which is 2. The resulting product, 36.36 MW, is then allocated to the positive-side inverter converter 111IPC.

[0140] Similarly, the received power of 200 MW that the positive inverse converter 111IPB was receiving before it changed to the stopped state is divided by the sum of the gains, which is 11. The resulting quotient is 18.18 (≒200 / 11) MW. This product, 54.54 MW, obtained by multiplying this quotient by the gain KdPD set for the positive inverse converter 111IPD, which is 3, is then allocated to the positive inverse converter 111IPD.

[0141] Similarly, the quotient obtained by dividing the received power of 200 MW that the positive inverse converter 111IPB was receiving before it changed to the stopped state by the sum of the gains, which is 11, is 18.18 (≒200 / 11) MW. This quotient is then multiplied by the gain KdNB, which is 1, set for the negative inverse converter 111INB, resulting in a product of 18.18 MW, which is then allocated to the negative inverse converter 111INB.

[0142] Similarly, the quotient obtained by dividing the received power of 200 MW that the positive-side inverse converter 111IPB was receiving before it changed to the stopped state by the sum of the gains is 18.18 (≒20 The product obtained by multiplying 0 / 11 MW by the gain KdNC, which is set for the negative inverse converter 111INC and is 2, is 36.36 MW, which is then allocated to the negative inverse converter 111INC.

[0143] Similarly, the product 54.54 MW, obtained by multiplying the quotient 18.18 (≒200 / 11) MW, which is the received power of 200 MW that the positive inverter 111IPB received before changing to the stopped state, by the total gain, by the gain KdND of 3 set for the negative inverter 111IND, is allocated to the negative inverter 111IND.

[0144] As a result, the positive electrode power PPRC of the positive-side inverse converter 111IPC is 336.36 MW. Similarly, the positive terminal power PPRD of the positive-side inverse converter 111IPD is 804.54 MW. Similarly, the power received at the negative terminal of the negative inverse converter 111INB, PNRB, is 218.18 MW. Similarly, the power received at the negative terminal of the negative inverse converter 111INC, PNRC, is 336.36 MW. Similarly, the negative electrode power PNRD, which is the controlled variable of the negative inverse converter 111IND, is 804.54 MW.

[0145] Following the steps in the flowchart above, for each receiving-side converter station 30 where both the positive-side inverse converter 111IP and the negative-side inverse converter 111IN are in a droop-controlled state, the power received by the positive-side inverse converter 111IP and the power received by the negative-side inverse converter 111IN are equal, and the return power approaches zero, so that the power received by the positive-side inverse converter 111IP and the power received by the negative-side inverse converter 111IN are equal, and the return power approaches zero.

[0146] Next, we will explain the process by which the return power becomes zero, using the graph shown in Figure 7. In Figure 7, the horizontal axis represents time (s), and the vertical axis represents the change (absolute value) (MW) of the positive terminal transmission power PPS and the negative terminal transmission power PNS from the reference value.

[0147] Curve 601A in Figure 7 shows the change in return power from time 0 to time t. Curve 601B in Figure 7 also shows the change in the amount of positive electrode transmission power PPS and negative electrode transmission power PNS from time 0 to time t, starting from the state immediately after the positive side inverter 111IPB changed from the power receiving state (droop control state) to the stopped state due to a fault.

[0148] The standard values ​​for positive electrode power transmission power PPS and negative electrode power transmission power PNS shall both be 1500 MW.

[0149] At time t0, immediately after the positive-side inverter 111IPB changes from a powered state (droop-controlled state) to a stopped state due to an accident, it has not yet been achieved that the return power can be distributed to the inverter 111I, which is in a droop-controlled state. At this time, the positive terminal's transmission power PPS is 1300 MW, which is the sum of the positive terminal's receiving power PPRA of 250 MW, the positive terminal's receiving power PPRC of 300 MW, and the positive terminal's receiving power PPRD of 750 MW. Furthermore, the negative terminal transmission power PNS is 1500 MW, which is the sum of the negative terminal reception power PNRA (250 MW), the negative terminal reception power PNRB (200 MW), the negative terminal reception power PNRC (300 MW), and the negative terminal reception power PNRD (750 MW).

[0150] In other words, at time t0, curve 601A is 200MW. Similarly, curve 601 B will be 0MW.

[0151] Following the steps in the flowchart described above, when the received power (return power) that the positive-side inverter 111IPB received before changing to the stopped state is distributed to the inverter 111I, which is in a droop-controlled state, at time t1, the positive-side transmission power PPS will be the sum of the positive-side received power PPRA received by the receiving-side AC system 300A, the positive-side received power PPRC received by the receiving-side AC system 300C, and the positive-side received power PPRD received by the receiving-side AC system 300D. Similarly, at time t1, the negative terminal transmission power PNS is the sum of the negative terminal received power PNRA received by the receiving AC system 300A, the negative terminal received power PNRB received by the receiving AC system 300B, the negative terminal received power PNRC received by the receiving AC system 300C, and the negative terminal received power PNRD received by the receiving AC system 300D.

[0152] At this time, since the positive-side inverter 111IPA and the negative-side inverter 111INA continue to maintain a constant power control state, the positive terminal power PPRA and the negative terminal power PNRA received by the receiving AC system 300A continue to be 250MW each. Therefore, the positive terminal's transmitted power PPS at time t1 is 1390.9 MW, which is the sum of the positive terminal's received power PPRA of 250 MW, the positive terminal's received power PPRC of 336.36 MW, and the positive terminal's received power PPRD of 804.54 MW. Furthermore, the negative terminal transmission power PNS at time t1 is 1609.1 MW, which is the sum of the negative terminal reception power PNRA (250 MW), the negative terminal reception power PNRB (218.18 MW), the positive terminal reception power PPRC (336.36 MW), and the positive terminal reception power PPRD (804.54 MW).

[0153] At time t1, the positive terminal transmission power PPS is 1390.9MW, which is a change of 109.1MW in the negative direction from the reference value of 1500MW. Also, at time t1, the negative terminal transmission power PNS is 1609.1MW, which is a change of 109.1MW in the positive direction from the reference value of 1500MW. As a result, as shown in Figure 7, curve 601A is 0 MW at time t1. Similarly, curve 601B is 109.1 MW at time t1.

[0154] In other words, the return power is distributed by the higher-level control device 10 to the positive-side forward converter 111CP and the negative-side forward converter 111CN by providing a control amount corrected by the correction value calculation unit 16, so that for each receiving-side converter station 30 where both the positive-side inverse converter 111IP and the negative-side inverse converter 111IN are in a droop control state, the power received by the positive-side inverse converter 111IP and the power received by the negative-side inverse converter 111IN are equal, and the return power is zero. This makes it possible to reduce the return power (power loss) generated in the return line 40GB while preventing the generation of return power (power loss) in the return lines 40GC and 40GD.

[0155] In the DC power transmission system 100 according to the embodiment described above, when the higher-level control device 10 detects that the operating state of at least one of the positive-side inverse converter 111IP and the negative-side inverse converter 111IN has changed from a constant power control state or a droop control state to a stopped state, it calculates the reference electrode transmission power Ps so as to distribute the total value of the power received by the positive-side inverse converter 111IP and the negative-side inverse converter 111IN before they changed to a stopped state to the positive-side forward converter 111CP or the negative-side forward converter 111CN, which has been determined as the reference electrode, based on the gain ratio, calculates a correction value to modify the reference electrode transmission power Ps, and calculates the control amount by correcting the command value of the control amount with the correction value.

[0156] According to this, when the positive-side inverter 111IP and negative-side inverter 111IN in the DC power transmission system 100 change to a stopped state, a correction value can be calculated that minimizes the return power of the received power that they were bearing until immediately before the change. Based on the calculated correction value, the positive-side forward converter 111CP or the negative-side forward converter 111CN can be controlled. Therefore, it becomes possible to reduce power loss in a bipolar DC power transmission system.

[0157] Furthermore, in the DC power transmission system 100 according to this embodiment, the higher-level control device 10 calculates the reference pole transmission power Ps according to functions (A) to (D), and calculates a correction value to distribute the reference pole transmission power Ps so that the power received by the positive side inverter 111IP and the power received by the negative side inverter 111IN of the receiving side converter station 30, which is in a droop control state, are equal.

[0158] According to this, when the operating state of at least one of the positive-side inverter 111IP and the negative-side inverter 111IN changes from a constant power control state or a droop control state to a stopped state, the reference electrode transmission power Ps can be calculated based on the parameters before and after the change in operating state, and the calculated reference electrode transmission power Ps can be distributed so that the power received by the positive-side inverter 111IP and the power received by the negative-side inverter 111IN of the receiving-side converter station 30, which is in a droop control state, are equal.

[0159] <<Extension of the Embodiment>> Although the present inventors have described the invention in detail based on embodiments, it goes without saying that the present invention is not limited thereto and can be modified in various ways without departing from its essence.

[0160] The flowchart described above is a specific example and is not limited to the processing procedure shown in Figure 6. For example, other processes may be inserted between each step shown in Figure 6, or some processes may be parallelized.

[0161] For example, if both the positive-side inverter 111IP and the negative-side inverter 111IN are in a droop-controlled state at the same power receiving station 30, the gains of the positive-side inverter 111IP and the negative-side inverter 111IN are usually set to the same value. Therefore, steps S5 and S6 may be omitted in the flowchart shown in Figure 6. [Explanation of symbols]

[0162] 10. Higher-level control unit 11 Storage section 12 Control variable calculation unit 13 Reference pole determination section 14. Conversion Station Information Monitoring Department 15 Reference pole power calculation section 16 Correction Value Calculation Unit 20 Power transmission side converter station 30 Power receiving conversion station 40 DC transmission lines 40P Positive Main Line 40N Negative electrode main line 40G return line 50 Connecting Line 100 DC power transmission systems 101 Arithmetic equipment 102 Storage device 1021 Program 1022 data 103 Input device 104 I / F device 105 Output device 106 Bus 110A Transmission Side Converter Station Information 110B Receiving Side Converter Station Information 110C Reference pole determination information 110D Reference pole transmission power information 110E Function Information 111C Forward Converter 111I Inverse Converter 112 Converter Station Protection Control Panel 113 Converter control panel 114 Protective detection device 115 DC circuit breaker 200 Transmission side AC system 300 Power receiving side AC system 500 Power Conversion Systems Power received by the positive electrode of the PPR PNR negative terminal power Power transmission from the positive electrode of the PPS PNS negative electrode power transmission

Claims

1. A power transmission station comprising a positive-side forward converter that converts AC power to positive-side DC power according to a given control amount, and a negative-side forward converter that converts AC power to negative-side DC power according to a given control amount, A plurality of receiving-side converter stations comprising a positive-side inverse converter that converts DC power transmitted from the positive-side forward converter to AC power, and a negative-side inverse converter that converts DC power transmitted from the negative-side forward converter to AC power, A DC transmission line including a positive terminal main line, a negative terminal main line, and a return line, provided corresponding to each power receiving converter station, and connecting the power transmitting converter station and the power receiving converter station, The system includes a higher-level control device that controls at least one of the power transmission side converter station and the power receiving side converter station, The aforementioned higher-level control device is Memory unit and, A control amount calculation unit calculates the control amount for the positive forward converter and the negative forward converter, and provides the control amount to the positive forward converter and the negative forward converter, A reference electrode determination unit that determines either the positive electrode or the negative electrode as the reference electrode and stores the information of the determined reference electrode, which is the reference electrode determination information, in the storage unit, A converter information monitoring unit monitors whether the operating state of the positive and negative inverters is stopped, constant power control, or droop control, and also monitors the power received by the positive and negative inverters, which is the power received by the positive and negative inverters, and the gain value of the droop control set for the positive and negative inverters when their operating state is the droop control state, and stores the monitoring results in the storage unit. A reference pole power calculation unit calculates the reference pole power transmission power, which is the power to be transmitted by the positive-side forward converter or the negative-side forward converter determined to be the reference pole of the power transmission station, and stores the calculation result in the storage unit. A correction value calculation unit calculates a correction value for correcting the control amount based on the calculation result calculated by the reference pole power calculation unit, Includes, The converter information monitoring unit detects that the operating state of at least one of the positive-side inverse converter and the negative-side inverse converter has changed from the constant power control state or the droop control state to the stopped state, and stores the monitoring result in the storage unit. The reference electrode power calculation unit calculates the reference electrode power transmission power so as to distribute the total value of the received power of the positive reverse converter and the negative reverse converter before they changed to the stopped state, based on the gain ratio, to the positive forward converter or the negative forward converter determined as the reference electrode. When the correction value calculation unit modifies the transmission power of the positive-side forward converter or the transmission power of the negative-side forward converter based on the calculation result of the reference pole power calculation unit, it calculates a correction value based on the transmission power of the positive-side forward converter or the transmission power of the negative-side forward converter before modification and the calculation result. The control amount calculation unit calculates the control amount by correcting the command value of the control amount with the correction value. DC power transmission system.

2. The system according to claim 1, The reference pole power calculation unit calculates the reference pole transmission power according to a function that includes the following functions (A), (B), (C), and (D) included in the function information stored in the memory unit. DC power transmission system. Prca=ΣKdnS / (ΣKdnP+ΣKdnN)×(Pall−Papr+Pla ) ... (A) (In the above function (A), Prca represents the total power received by the positive or negative inverter of the reference electrode, which is in the droop control state after the operating state of either the positive or negative inverter changes from the constant power control state or the droop control state to the stop state, taking into account the effect of the power received by the positive or negative inverter when the operating state is in the constant power control state, from the total power received by the positive or negative inverter before the operating state of either the positive or negative inverter changes from the constant power control state or the droop control state to the stop state, and ΣKdnS is ΣKdnP represents the total gain of the reference electrode, ΣKdnN represents the total gain of the positive-side inverse converter, ΣKdnN represents the total gain of the negative-side inverse converter, Pall represents the total transmitted power of the positive-side forward converter and the negative-side forward converter, Papr represents the total received power of the positive-side inverse converter and the negative-side inverse converter whose operating state is the constant power control state, and Pla represents the received power of the positive-side inverse converter or the negative-side inverse converter before it changed to the stopped state when the operating state of either the positive-side inverse converter or the negative-side inverse converter changes from the constant power control state to the stopped state. Prcd={1-(ΣKdnS-ΣKddS) / (ΣKdnP+ΣKdnN-ΣKdd)}×(PddS-PddNS)...(B) (In the above function (B), Prcd represents the total power received before the positive or negative reverse converter changed to the stop state after the operating state of either the positive or negative reverse converter changed from the constant power control state or the droop control state to the stop state, which should be subtracted from the power transmitted by the positive or negative forward converter of the reference electrode after the operating state of either of the positive or negative reverse converter changed from the droop control state to the stop state, ΣKdnS represents the total gain of the reference electrode, ΣKddS represents the total gain of the positive or negative reverse converter at the reference electrode after the operating state changed from the droop control state to the stop state, Σ KdnP represents the total gain of the positive inverse converter, ΣKdnN represents the total gain of the negative inverse converter, ΣKdd represents the total gain of the positive or negative inverse converter when its operating state changes from the droop control state to the stopped state, PddS represents the total power received by the positive or negative inverse converter before it changes to the stopped state when its operating state changes from the droop control state to the stopped state at the reference electrode, and PddNS represents the total power received by the positive or negative inverse converter before it changes to the stopped state when its operating state changes from the droop control state to the stopped state at an electrode different from the reference electrode. Pdr=Prca-Prcd...(C) (In the above function (C), Pdr represents the power that the positive or negative inverter of the reference electrode should receive when the operating state is the droop control state, and Prca is a value obtained by subtracting the influence of the power received by the positive or negative inverter of the reference electrode when the operating state is the constant power control state from the total power received by the positive or negative inverter of the reference electrode before either of the positive or negative inverters changes from the constant power control state or the droop control state to the stopped state, and is calculated based on the function (C) above, where Pdr represents the power that the positive or negative inverter of the reference electrode should receive when the operating state is the droop control state, and Prca represents a value obtained by subtracting the influence of the power received by the positive or negative inverter when the operating state is the constant power control state from the total power received by the positive or negative inverter of the reference electrode before either of the positive or negative inverters changes from the constant power control state or the droop control state to the stopped state. The value of the operating state of the positive or negative reverse converter of the reference electrode represents the total power received by the positive or negative reverse converter when the operating state changes from the constant power control state or the droop control state to the stopped state, and Prcd is the value to be subtracted from the power transmitted by the positive or negative forward converter of the reference electrode when the operating state of either the positive or negative reverse converter changes from the constant power control state or the droop control state to the stopped state, before the change in the operating state of the positive or negative reverse converter from the droop control state to the stopped state. (This represents the total value of the recorded power received.) Ps=Pdr+Psapr…(D) (In the above function (D), Ps represents the power transmitted to the reference electrode, Pdr represents the power that the positive or negative inverter of the reference electrode should receive when the operating state is the droop control state, and Psapr represents the sum of the power received by the positive and negative inverters of the reference electrode when the operating state is the constant power control state.)

3. A method for controlling a DC power transmission system, The aforementioned DC power transmission system is A power transmission station comprising a positive-side forward converter that converts AC power to positive-side DC power according to a given control amount, and a negative-side forward converter that converts AC power to negative-side DC power according to a given control amount, A plurality of receiving-side converter stations comprising a positive-side inverse converter that converts DC power transmitted from the positive-side forward converter to AC power, and a negative-side inverse converter that converts DC power transmitted from the negative-side forward converter to AC power, A DC transmission line is provided corresponding to each of the receiving-side converter stations, and includes a positive terminal main line, a negative terminal main line, and a return line, connecting the transmitting-side converter station and the receiving-side converter station. A control amount calculation step of calculating the control amount of the positive forward converter and the negative forward converter, and assigning the control amount to the positive forward converter and the negative forward converter, A reference electrode determination step in which either the positive electrode or the negative electrode is determined as the reference electrode, Converter station information monitoring step: Monitors whether the operating state of the positive and negative inverters is stopped, constant power control, or droop control, and also monitors the power received by the positive and negative inverters, which is the power received by the positive and negative inverters, and the gain value of the droop control set for the positive and negative inverters when their operating state is the droop control state. A reference pole power calculation step for calculating the reference pole power, which is the power to be transmitted by the positive-side forward converter or the negative-side forward converter determined to be the reference pole of the converter station on the transmission side, A correction value calculation step is performed to calculate a correction value for correcting the control amount based on the result calculated in the reference pole power calculation step, Includes, The converter information monitoring step includes detecting that the operating state of at least one of the positive-side inverse converter and the negative-side inverse converter has changed from the constant power control state or the droop control state to the stopped state. The reference pole power calculation step includes a step of calculating the reference pole transmission power such that, based on the results of the converter station information monitoring step, the total value of the received power of the positive reverse converter and the negative reverse converter before they changed to the stopped state is distributed to the positive forward converter or the negative forward converter determined as the reference pole, based on the gain ratio. The correction value calculation step includes, when correcting the transmission power of the positive-side forward converter or the transmission power of the negative-side forward converter based on the calculation result of the reference pole power calculation step, a step of calculating a correction value based on the transmission power of the positive-side forward converter or the transmission power of the negative-side forward converter before correction and the calculation result, The control amount calculation step includes a step of calculating the control amount by correcting the command value of the control amount with the correction value. method.

4. A power transmission station comprising a positive-side forward converter that converts AC power to positive-side DC power according to a given control amount, and a negative-side forward converter that converts AC power to negative-side DC power according to a given control amount, A forward converter that converts the DC power transmitted from the forward converter to AC power, and A DC power transmission system comprising: a plurality of receiving-side converter stations each having a negative-side reverse converter that converts DC power transmitted from a negative-side forward converter to AC power; a DC transmission line connecting the transmitting-side converter station and the receiving-side converter station, each line being provided in correspondence with the receiving-side converter station and including a positive main line, a negative main line, and a return line; and a higher-level control device that controls at least one of the transmitting-side converter station and the receiving-side converter station, wherein the program to be executed by the higher-level control device is as follows: A control amount calculation step of calculating the control amount of the positive forward converter and the negative forward converter, and assigning the control amount to the positive forward converter and the negative forward converter, A reference electrode determination step in which either the positive electrode or the negative electrode is determined as the reference electrode, Converter station information monitoring step: Monitors whether the operating state of the positive and negative inverters is stopped, constant power control, or droop control, and also monitors the power received by the positive and negative inverters, which is the power received by the positive and negative inverters, and the gain value of the droop control set for the positive and negative inverters when their operating state is the droop control state. A reference pole power calculation step for calculating the reference pole power, which is the power to be transmitted by the positive-side forward converter or the negative-side forward converter determined to be the reference pole of the converter station on the transmission side, A correction value calculation step is performed to calculate a correction value for correcting the control amount based on the result calculated in the reference pole power calculation step, Includes, The converter information monitoring step includes detecting that the operating state of at least one of the positive-side inverse converter and the negative-side inverse converter has changed from the constant power control state or the droop control state to the stopped state. The reference pole power calculation step includes a step of calculating the reference pole transmission power such that, based on the results of the converter station information monitoring step, the total value of the received power of the positive reverse converter and the negative reverse converter before they changed to the stopped state is distributed to the positive forward converter or the negative forward converter determined as the reference pole, based on the gain ratio. The correction value calculation step includes, when correcting the transmission power of the positive-side forward converter or the transmission power of the negative-side forward converter based on the calculation result of the reference pole power calculation step, a step of calculating a correction value based on the transmission power of the positive-side forward converter or the transmission power of the negative-side forward converter before correction and the calculation result, The control amount calculation step includes a step of calculating the control amount by correcting the command value of the control amount with the correction value. program.

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