DC power transmission systems, methods, and programs

Abstract

To reduce power loss in a bipolar DC power transmission system. [Solution] In the DC power transmission system 100, the higher-level control device 10 calculates a correction power 110C3 based on the control function 110C2 if the difference between the DC voltage 110A2P, 110A2N and the average value 110C1P, 110C1N exceeds the threshold 110C2T. It then calculates the distribution amount obtained by distributing the correction power 110C3 to the positive-side forward converter 111CP or negative-side forward converter 111CN connected to the positive-side forward converter 111CP or negative-side forward converter 111CN, which are connected to the positive-side forward converter 111CP or negative-side forward converter 40N, where the DC voltage 110A2P, 110A2N does not exceed the threshold 110C2T. The control amount of the positive-side forward converter 111CP and negative-side forward converter 111CN corrected by the distribution amount is calculated.

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 equipment. The frequency conversion equipment is equipment 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. Further, between the converter station on the power transmission side and the converter station on the power reception side, they are connected by 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 between the positive electrode and the negative electrode due to the control characteristics. The converter at the converter station on the power reception side is also controlled to receive power at a fixed ratio of 1:1 between the positive electrode and the negative electrode, similar to the converter at the converter station on the power transmission side. 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. When this happens, the reduction in the number of operating converters at the receiving-side converter station may cause some of the continuing-operating converters to become overloaded.

[0008] This invention has been made in view of the above problems, and aims to prevent the converter of the receiving side converter station in a bipolar DC power transmission system from becoming overloaded. [Means for solving the problem]

[0009] A DC power transmission system according to a typical embodiment of the present invention includes a transmission-side converter station comprising a positive-side forward converter that converts AC power to positive-electrode DC power according to a given control amount, and a negative-side forward converter that converts AC power to negative-electrode 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 positive-electrode main line, a negative-electrode main line, and a return line, each corresponding to the receiving-side converter station. The system comprises a DC transmission line connecting the transmitting converter and the receiving converter, and a higher-level control device that controls at least one of the transmitting converter and the receiving converter, the higher-level control device includes at least a storage unit that includes a control function which is a function representing the relationship between the DC voltage, which is the value of the voltage to ground of the positive main line and the negative main line of each DC transmission line, and the transmitted power, which is the power transmitted by the positive-side forward converter and the negative-side forward converter, and calculates the control amount of the positive-side forward converter and the negative-side forward converter, and the positive-side forward converter and the negative-side forward converter A control amount calculation unit that provides the control amount to the converter; a DC voltage measurement unit that measures the DC voltages and stores the measured results in the storage unit; an average DC voltage calculation unit that calculates the average value of the DC voltages over a certain period and stores the calculated results in the storage unit; a determination unit that determines whether the difference between the DC voltage of either the positive main line or the negative main line and the average value exceeds a threshold and stores the determination result in the storage unit; and based on the result determined by the determination unit, the control function is configured to apply the value of the positive main line or the negative line that exceeds the threshold. The control amount calculation unit calculates the received power obtained by inputting the value of the DC voltage of the main line as corrected power, and the control amount calculation unit calculates the amount obtained by distributing the corrected power to the positive-side forward converter or the negative-side forward converter connected [Effects of the Invention]

[0010] According to the present invention, it is possible to prevent the converter in the receiving-side converter station of a bipolar DC power transmission system from becoming overloaded. [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 is a graph showing the control function. [Figure 6] This diagram shows the controlled objects of a DC power transmission system. [Figure 7] This figure shows the control block of a higher-level control device according to an embodiment of the present invention. [Figure 8] This flowchart shows a method for controlling the distribution of power in a DC power transmission system using a higher-level control device. [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 in 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 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 a negative-side reverse converter that converts the DC power transmitted from the negative-side forward converter (111CN) to AC power (PNR). The system comprises a plurality of receiving-side converter stations (30) each equipped with a device (111IN), 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, 10A) that controls at least one of the transmitting-side converter station (20) and the receiving-side converter station (30), wherein the higher-level control device (10, 10A) is connected to the AC system to which the positive-side forward converter (111CP) and the negative-side forward converter (111CN) are connected. A memory unit (11) includes at least a control function (110C2) which is a function representing the relationship between the DC voltage (110A2P, 110A2N), which is the voltage value of each of the DC transmission lines (40P, 40N, 40G) calculated based on the voltage of the bus of the main unit (200), and the transmitted power (110A1P, 110A1N), which is the power transmitted by the positive-side forward converter (111CP) and the negative-side forward converter (111CN), and calculates the control amount of the positive-side forward converter (111CP) and the negative-side forward converter (111CN), and the positive-side forward converter (111CP) and the A control amount calculation unit (12) that provides the control amount to the negative forward converter (111CN), a DC voltage measurement unit (14) that measures and calculates the DC voltages (110A2P, 110A2N) respectively and stores the measured and calculated results in the storage unit (11), an average DC voltage calculation unit (15) that calculates the average value (110C1P, 110C1N) of the DC voltages (110A2P, 110A2N) over a certain period and stores the calculated results in the storage unit (11), and the DC voltage (110A2P, 110C1N) of either the positive terminal main line (40P) or the negative terminal main line (40N)A determination unit (16) determines whether the difference between 110A2N) and the average value (110C1P, 110C1N) exceeds a threshold (110C2T), and stores the determination result in the storage unit (11). A correction power calculation unit (17) calculates the power obtained by inputting the value of the DC voltage (110A2P, 110A2N) of the positive main line (40P) or the negative main line (40N) that exceeds the threshold (110C2T) into the control function (110C2) based on the determination result of the determination unit (16), as correction power (110C3). The system includes a corrected power distribution unit (18) that calculates a distribution amount obtained by distributing the corrected power (110C3) to the positive-side forward converter (111CP) or the negative-side forward converter (111CN) connected to the positive-side forward converter (40P) or the negative-side forward converter (40N) where the difference between the voltage (110A2P, 110A2N) and the average value (110C1P, 110C1N) does not exceed the threshold (110C2T), and the control amount calculation unit (12) calculates the control amount of the positive-side forward converter (111CP) and the negative-side forward converter (111CN) by correcting the command value of the control amount by the distribution amount.

[0014] [2] In the DC power transmission system (100) described in [1] above, the control function (110C2) has a first range (110C2R1) and a second range (110C2R2), the first range (110C2R1) is a range in which the absolute value of the difference between the DC voltage (110A2P, 110A2N) and the average value (110C1P, 110C1N) is less than or equal to the threshold (110C2T), and the transmitted power (110) due to the DC voltage (110A2P, 110A2N) The second range (110C2R2) is a range in which no change occurs in A1P, 110A1N), and it is preferable that the absolute value of the difference between the DC voltage (110A2P, 110A2N) and the average value (110C1P, 110C1N) exceeds the threshold (110C2T), and that the change in the transmitted power (110A1P, 110A1N) due to the DC voltage (110A2P, 110A2N) is determined by a predetermined slope (110C2S).

[0015] [3] A method according to one aspect of the present invention is a method for controlling a DC power transmission system (100). In this method, the DC power transmission system (100) includes a transmission-side converter station (20) which has 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, and a positive-side reverse converter (111CP) that converts the DC power transmitted from the positive-side forward converter (111CP) to AC power (PPR). The system comprises a plurality of receiving-side converter stations (30), each having a DC power (1IP) and a negative-side reverse converter (111IN) that converts DC power transmitted from the negative-side forward converter (111CN) to AC power (PNR), and a DC transmission line that includes a positive terminal main line (40P), a negative terminal main line (40N), and a return line (40G), and is provided corresponding to each receiving-side converter station (30), connecting the transmitting-side converter station (20) and the receiving-side converter stations (30). This method comprises a control amount calculation step (S7) which calculates the control amount for the positive-side forward converter (111CP) and the negative-side forward converter (111CN) and applies the control amount to the positive-side forward converter (111CP) and the negative-side forward converter (111CN), a DC voltage measurement step (S2) which measures the voltage of the busbar of the AC system (200) to which the positive-side forward converter (111CP) and the negative-side forward converter (111CN) are connected, and measures and calculates the DC voltages (110A2P, 110A2N) of each DC transmission line (40P, 40N, 40G) calculated based on the voltage of the busbar, and the DC voltage over a certain period of time ( Step (S3) calculates the average DC voltage (110C1P, 110C1N) of the DC voltages (110A2P, 110A2N), and Step (S4) determines whether the difference between the DC voltage (110A2P, 110A2N) of either the positive terminal main line (40P) and the negative terminal main line (40N) and the average value (110C1P, 110C1N) exceeds a threshold (110C2T). Based on the result determined in Step (S4), the DC voltage (110A2P, 110A2N) and the transmitted power (110A1P, 110C1N) transmitted by the positive-side forward converter (111CP) and the negative-side forward converter (111CN) are used.A correction power calculation step (S5) calculates the power obtained by inputting the value of the DC voltage (110A2P, 110A2N) of the positive main line (40P) or the negative main line (40N) that exceeds the threshold (110C2T) into a control function (110C2), which is a function representing the relationship between 110A2P and 110N, as the correction power (110C3). Based on the result determined in the determination step (S4), the difference between the DC voltage (110A2P, 110A2N) and the average value (110C1P, 110C1N) is the threshold (110C The process includes a correction power distribution step (S6) for calculating a distribution amount obtained by distributing the correction power (110C3) to the positive-side forward converter (111CP) or the negative-side forward converter (111CN) connected to the positive-side main line (40P) or the negative-side main line (40N) that does not exceed 2T, and the control amount calculation step (S7) includes a step of calculating the control amount of the positive-side forward converter (111CP) and the negative-side forward converter (111CN) by correcting the command value of the control amount by the distribution amount.

[0016] [4] A program (1021) according to one aspect of the present invention comprises a transmission-side converter station (20) equipped with 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, and 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 ( In a DC power transmission system (100) comprising: a plurality of receiving-side converter stations (30) each having 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), the control amount of the positive-side forward converter (111CP) and the negative-side forward converter (111CN) is calculated, and the positive A control amount calculation step (S7) in which the control amount is given to the side-forward converter (111CP) and the negative side-forward converter (111CN), a DC voltage measurement step (S2) in which the voltage of the busbar of the AC system (200) to which the positive side-forward converter (111CP) and the negative side-forward converter (111CN) are connected is measured, and the DC voltages (110A2P, 110A2N) which are the voltage values ​​of each of the DC transmission lines (40P, 40N, 40G) calculated based on the voltage of the busbar is measured and calculated respectively, and the average value (110C1P, Step (S3) is to calculate the average DC voltage (110C1N), and Step (S4) is to determine whether the difference between the DC voltage (110A2P, 110A2N) of either the positive terminal main line (40P) and the negative terminal main line (40N) and the average value (110C1P, 110C1N) exceeds a threshold (110C2T). Based on the result determined in Step (S4), the DC voltage (110A2P, 110A2N) and the transmitted power (110A1P, 110C1N) transmitted by the positive-side forward converter (111CP) and the negative-side forward converter (111CN) are calculated.A correction power calculation step (S5) of calculating, as correction power (110C3), the power obtained by inputting the value of the DC voltage (110A2P, 110A2N) of the main line (40P) of the positive electrode or the main line (40N) of the negative electrode that exceeds the threshold value (110C2T) into a control function (110C2) that is a function representing the relationship of (110A1N); and based on the result determined in the determination step (S4), the difference between the DC voltage (110A2P, 110A2N) and the average value (110C1P, 110C1N) does not exceed the threshold value (110C2T). A correction power distribution step (S6) of calculating the distribution amount obtained by distributing the correction power (110C3) to the positive-side converter (111CP) or the negative-side converter (111CN) connected to the main line (40P) of the positive electrode or the main line (40N) of the negative electrode. It is a program for causing the upper control device to execute. In this program, the control amount calculation step (S7) includes a step of calculating the control amounts of the positive-side converter (111CP) and the negative-side converter (111CN) by correcting the command value of the control amount by the distribution amount.,

[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, the same reference numerals are given to the common components in each embodiment, and repeated descriptions are omitted. Also, note that the drawings are schematic, and it is necessary to be aware that the dimensional relationships and ratios of each element may be different from reality. There may also be parts where the dimensional relationships and ratios are different between the drawings.,

[0018] <<Schematic Configuration of Power Conversion System>> FIG. 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 system 300 is an AC system that receives AC power output from the DC 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 one transmission-side converter station 20, but is not limited to this. That is, the DC transmission system 100 may have 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. The forward converter 111C and the inverse converter 111I (described later) are sometimes collectively referred to as converter 111.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] The receiving-side converter station 30 is a facility 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. In addition, the receiving-side converter station 30 is connected to other receiving-side converter stations 30 via a connecting line 50.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] 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, 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. In addition, the converter station protection control panel 112C 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. 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.

[0045] 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.

[0046] <<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 the first embodiment of the present invention. Figure 4 shows the hardware configuration of the higher-level control unit.

[0047] 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.

[0048] 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.

[0049] 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).

[0050] 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, and correction power calculation information 110C.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] Next, we will describe in detail each functional block of the higher-level control unit 10.

[0055] As shown in Figure 3, the higher-level control device 10 includes a control amount calculation unit 12, a converter station information monitoring unit 13, a DC voltage measurement unit 14, an average DC voltage calculation unit 15, a determination unit 16, a corrected power calculation unit 17, a corrected power distribution unit 18, and a storage unit 11 as functional blocks for realizing control of the DC power transmission system 100.

[0056] 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, converter information monitoring unit 13, DC voltage measurement unit 14, average DC voltage calculation unit 15, determination unit 16, corrected power calculation unit 17, corrected power distribution unit 18, and memory unit 11). At least one of the above functional blocks may be realized by a dedicated circuit.

[0057] 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 amount calculation unit 12 calculates the control amount by correcting the command value of the control amount with the distribution amount calculated by the corrected power distribution unit 18, which will be described later.

[0058] 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.

[0059] Similarly, when the AC power transmitted from the AC power system 200 on the transmission side is converted to DC power, the control amount calculation unit 12 calculates for each transmission-side converter station 20 a control amount that is less than or equal to the rated capacity of the negative-side forward converter 111CN and should be transmitted by the negative-side forward converter 111CN (hereinafter also referred to as "negative electrode transmitted power"), and assigns a control amount to each negative-side forward converter 111CN.

[0060] 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") by the distribution amount for correcting the control amount calculated by the correction power distribution unit 18, 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.

[0061] Similarly, the control amount calculation unit 12 corrects the command value of the control amount (hereinafter also referred to as "pre-correction negative electrode transmission power") by the distribution amount for correcting the control amount calculated by the correction power distribution unit 18, which will be described later, and then calculates the control amount of the negative-side forward converter 111CN (hereinafter also referred to as "corrected negative electrode transmission power") and assigns the control amount to each negative-side forward converter 111CN.

[0062] The converter station information monitoring unit 13 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 transmitted power, which is the power transmitted by the positive-side forward converter 111CP and the negative-side forward converter 111CN, and the received power, which is the power received by the positive-side inverse converter 111IP and the negative-side inverse converter 111IN.

[0063] The converter station information monitoring unit 13 stores the monitoring results of the operating status of the positive-side inverse converter 111IP and the negative-side inverse converter 111IN, the transmitted power of the positive-side forward converter 111CP and the negative-side forward converter 111CN, and the received power of the positive-side inverse converter 111IP and the negative-side inverse converter 111IN in the storage unit 11.

[0064] The converter information monitoring unit 13 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. The converter information monitoring unit 13 stores 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, in the storage unit 11.

[0065] The converter information monitoring unit 13 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.

[0066] 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 13 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.

[0067] 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.

[0068] 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.

[0069] Droop control state refers to the state in which the inverse converter 111I converts the transmitted power transmitted from the power transmission station 20 to AC power (hereinafter also referred to as "droop characteristic") while changing the received power of the positive inverse converter 111IP (hereinafter also referred to as "positive electrode received power") and the received power of the negative forward converter 111CN (hereinafter also referred to as "negative electrode received power") to follow the fluctuations in the power transmission system 500 when a fluctuation occurs in the power conversion system 500. The positive electrode received power and the negative electrode received power are changed as needed based on the gain value set in the inverse converter 111I. The gain value set for the inverse converter 111I is stored in the memory unit 11, which will be described later.

[0070] 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.

[0071] 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.

[0072] The DC voltage measurement unit 14 is a functional unit that measures the voltage of the busbar of the AC system to which the positive-side forward converter 111CP and the negative-side forward converter 111CN are connected, and based on the voltage of the busbar, measures and calculates the DC voltage 110A2P of the positive terminal main line 40P and the DC voltage 110A2N of the negative terminal main line 40N, which are the voltage values ​​of each DC transmission line. The DC voltage measurement unit 14 calculates, for example, the DC voltage 110A2P of the positive main line 40P and the DC voltage 110A2N of the negative main line 40N based on the measured RMS value of the AC power bus voltage. However, the DC voltage measurement unit 14 is not limited to this, and can calculate the DC voltage 110A2P of the positive main line 40P and the DC voltage 110A2N of the negative main line 40N from the AC power bus voltage based on known methods.

[0073] The DC voltage measurement unit 14 measures the voltage of the busbar of the AC system to which the positive-side forward converter 111CP and the negative-side forward converter 111CN are connected, and calculates the DC voltage 110A2P of the positive terminal main line 40P and the DC voltage 110A2N of the negative terminal main line 40N based on the voltage of the busbar. The DC voltage measurement unit 14 stores the measured DC voltages 110A2P of the positive terminal main line 40P and 110A2N of the negative terminal main line 40N in the storage unit 11.

[0074] The DC voltage measurement unit 14 may measure the voltage for each positive main line 40P and negative main line 40N connected to each power receiving converter station 30, and the measured voltages may be set as the DC voltage 110A2P of the positive main line 40P and the DC voltage 110A2N of the negative main line 40N. At this time, the DC voltage measurement unit 14 measures the DC voltage 110A2P of the positive terminal main line 40P and the DC voltage 110A2N of the negative terminal main line 40N for each positive terminal main line 40PA, 40PB, 40PC, 40PD (see Figure 6) and negative terminal main lines 40NA, 40NB, 40NC, 40ND (see Figure 6) connected to each power receiving converter station 30. However, when the DC voltage measurement unit 14 measures each positive main line 40P and negative main line 40N connected to each receiving side converter station 30, if there is only one receiving side converter station 30 connected to the transmitting side converter station 20, the distribution amount by the corrected power distribution unit 18, which will be described later, cannot be distributed. Therefore, it should be noted that when measuring each positive main line 40P and negative main line 40N connected to each receiving side converter station 30, it is necessary to connect multiple receiving side converter stations 30.

[0075] The average DC voltage calculation unit 15 is a functional unit that calculates the average value 110C1P of the DC voltage 110A2P and the average value 110C1N of the DC voltage 110A2N over a certain period of time for the main line 40P of the positive electrode and the main line 40N of the negative electrode, which are measured and calculated by the DC voltage measurement unit 14. Specifically, the average DC voltage calculation unit 15 calculates the average value 110C1P of the DC voltage 110A2P and the average value 110C1N of the DC voltage 110A2N for each positive terminal main line 40P and negative terminal main line 40N connected to each power receiving side converter station 30, as measured by the DC voltage measurement unit 14.

[0076] The average DC voltage calculation unit 15 may calculate the average values ​​110C1PA, 110C1PB, 110C1PC, 110C1PD, 110C1NA, 110C1NB, 110C1NC, and 110C1ND for each of the positive electrode main lines 40PA, 40PB, 40PC, and 40PD (see Figure 6), and the negative electrode main lines 40NA, 40NB, 40NC, and 40ND (see Figure 6). Alternatively, it may calculate the average value 110C1P for all of the positive electrode main lines 40PA, 40PB, 40PC, and 40PD (see Figure 6), and the average value 110C1N for all of the negative electrode main lines 40NA, 40NB, 40NC, and 40ND (see Figure 6).

[0077] Furthermore, the average DC voltage calculation unit 15 stores the average value 110C1P of the calculated DC voltage 110A2P and the average value 110C1N of the DC voltage 110A2N in the storage unit 11. Furthermore, the period set for calculating the average value 110C1P for DC voltage 110A2P and the average value 110C1N for DC voltage 110A2N can be determined arbitrarily.

[0078] The determination unit 16 is a functional unit that determines whether the difference between the DC voltage 110A2P, 110A2N of either the positive electrode main line 40P or the negative electrode main line 40N and the average value 110C1P, 110C1N exceeds the threshold 110C2T. Specifically, the determination unit 16 determines whether the difference between the DC voltage 110A2P and the average value 110C1P of the main line 40P of any positive electrode exceeds the threshold value 110C2T, which is set by the control function 110C2 described later.

[0079] Furthermore, the determination unit 16 determines whether the difference between the DC voltage 110A2N and the average value 110C1N of the main line 40N of either negative electrode exceeds the threshold 110C2T, which is set by the control function 110C2 described later. The determination unit 16 stores the result of the determination in the storage unit 11.

[0080] The corrected power calculation unit 17 is a functional unit that calculates the power obtained by inputting the DC voltage values ​​110A2P and 110A2N of the positive main line 40P or the negative main line 40N that exceed the threshold 110C2T into the control function 110C2, based on the result determined by the determination unit 16, as the corrected power 110C3. The corrected power calculation unit 17 stores the calculated corrected power 110C3 in the storage unit 11.

[0081] Specifically, if the determination unit 16 determines that the difference between the DC voltage 110A2P of the main line 40P of any positive electrode and the average value 110C1P exceeds the threshold 110C2T, which is set by the control function 110C2 described later, the correction power calculation unit 17 calculates the power obtained by inputting the value of the DC voltage 110A2P of the main line 40P of the positive electrode that exceeds the threshold 110C2T described later into the control function 110C2 described later, as the correction power 110C3P (see Figure 7).

[0082] Furthermore, if the determination unit 16 determines that the difference between the DC voltage 110A2N of the main line 40N of any negative electrode and the average value 110C1N exceeds the threshold 110C2T, which will be set by the control function 110C2 described later, the correction power calculation unit 17 calculates the power obtained by inputting the value of the DC voltage 110A2N of the main line 40N of the negative electrode that exceeds the threshold 110C2T described later into the control function 110C2 described later, as the correction power 110C3N (see Figure 7).

[0083] The corrected power distribution unit 18 is a functional unit that calculates the distribution amount obtained by distributing corrected power 110C3 to the positive-side forward converter 111CP or negative-side forward converter 111CN connected to the positive-side forward converter 111CP or negative-side forward converter 111CN, based on the result determined by the determination unit 16, where the difference between the DC voltage 110A2P, 110A2N and the average value 110C1P, 110C1N does not exceed the threshold 110C2T. Details on how to calculate the distribution amount will be described later.

[0084] 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, and the correction power calculation information 110C mentioned above.

[0085] The memory unit 11 includes at least the following: a control function 110C2 which is a function representing the relationship between the DC voltage, which is the value of the voltage to ground of the positive terminal main line 40P and the negative terminal main line 40N among the DC transmission lines 40P, 40N, and 40G, and the transmission power 110A1P and 110A1N, which are the power received by the positive-side forward converter 111CP and the negative-side forward converter 111CN; and the rated capacities of the positive-side forward converter 111CP, the negative-side forward converter 111CN, the positive-side reverse converter 111IP, and the negative-side reverse converter 111IN.

[0086] The transmission-side converter station information 110A includes information about the forward converter 111C stored in the memory unit 11 beforehand, 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, the positive electrode transmission power 110A1P and the negative electrode transmission power 110A1N, the DC voltage of the positive electrode main line 40P 110A2P (hereinafter also referred to as "positive electrode DC voltage 110A2P"), and the DC voltage of the negative electrode main line 40N 110A2N (hereinafter also referred to as "negative electrode DC voltage 110A2N").

[0087] 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.

[0088] 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, operating status, positive electrode power received, and negative electrode power received of the inverse converter 111I.

[0089] The operating state of the inverse converter 111I includes the gain values ​​of the droop control set for the positive inverse converter 111IP and the negative inverse converter 111IN, whose operating state is in the droop control state.

[0090] 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.

[0091] The corrected power calculation information 110C includes information related to the calculation of the corrected power 110C3 by the corrected power calculation unit 17. For example, the corrected power calculation information 110C includes, but is not limited to, the average value 110C1P of the DC voltage 110A2P and the average value 110C1N of the DC voltage 110A2N over a certain period of time measured by the DC voltage measurement unit 14 (hereinafter, the average value 110C1P and the average value 110C1N are collectively referred to as "average DC voltage 110C1"), the control function 110C2, and the corrected power 110C3.

[0092] The corrected power calculation 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.

[0093] The average DC voltage 110C1 includes the average value 110C1P (hereinafter also referred to as "positive electrode average DC voltage 110C1P") of the DC voltage 110A2P over a certain period measured by the DC voltage measurement unit 14, and the average value 110C1N (hereinafter also referred to as "negative electrode average DC voltage 110C1N") of the DC voltage 110A2N over a certain period measured by the DC voltage measurement unit 14.

[0094] The corrected power 110C3 is the power obtained when the corrected power calculation unit 17 inputs the values ​​of the DC voltages 110A2P and 110A2N of the positive main line 40P or the negative main line 40N that exceed the threshold 110C2T into the control function 110C2 based on the determination result of the determination unit 16.

[0095] Furthermore, the corrected power 110C3 is used by the corrected power distribution unit 18 when calculating the amount to be distributed to the positive-side forward converter 111CP or the negative-side forward converter 111CN.

[0096] <<Control function, threshold>> Figure 5 is a graph showing the control function.

[0097] The control function 110C2 represents the relationship between the DC voltage 110A2P and the positive electrode transmission power 110A1P. Furthermore, the control function 110C2 represents the relationship between the DC voltage 110A2N and the negative electrode transmission power 110A1N. The control function 110C2 includes a threshold value 110C2T.

[0098] In Figure 5, the vertical axis represents the magnitude of the positive electrode transmission power 110A1P or the negative electrode transmission power 110A1N (upward direction indicates increase, downward direction indicates decrease) (MW), and the horizontal axis represents the difference between the DC voltage 110A2P and the positive electrode average DC voltage 110C1P (at the 0 position on the horizontal axis) (V), or the difference between the DC voltage 110A2N and the negative electrode average DC voltage 110C1N (at the 0 position on the horizontal axis) (rightward direction indicates positive, leftward direction indicates negative) (V).

[0099] The control function 110C2 has a first range 110C2R1, a second range 110C2R2, and a third range 110C2R3.

[0100] The first range 110C2R1 includes a range where the absolute value of the difference between the DC voltage 110A2P and the average value 110C1P is less than or equal to the threshold 110C2T, and where no change in transmitted power 110A1P occurs due to the DC voltage 110A2P. Furthermore, the first range 110C2R1 includes a range where the absolute value of the difference between the DC voltage 110A2N and the average value 110C1N is less than or equal to the threshold 110C2T, and where no change in transmitted power 110A1N occurs due to the DC voltage 110A2N.

[0101] In the first range 110C2R1, the positive electrode transmission power 110A1P becomes the transmission power 110A1P1 that the positive-side forward converter 111CP is transmitting at that time. In the first range 110C2R1, the negative electrode transmission power 110A1N becomes the transmission power 110A1N1 transmitted by the negative forward converter 111CN at that time.

[0102] The second range 110C2R2 includes the range in which the absolute value of the difference between the DC voltage 110A2P and the average value 110C1P exceeds the threshold 110C2T and is less than or equal to the threshold 110C2T2, and in which the change in transmitted power 110A1P due to the DC voltage 110A2P is determined by a predetermined slope. Furthermore, the second range 110C2R2 includes the range in which the absolute value of the difference between the DC voltage 110A2N and the average value 110C1N exceeds the threshold 110C2T and is less than or equal to the threshold 110C2T2, and is the range in which the change in transmitted power 110A1N due to the DC voltage 110A2N is determined by a predetermined slope.

[0103] The third range, 110C2R3, includes the range where the absolute value of the difference between the DC voltage 110A2P and the average value 110C1P exceeds the threshold 110C2T2, and where no change in the transmitted power 110A1P occurs due to the DC voltage 110A2P.

[0104] Furthermore, the third range 110C2R3 includes the range where the absolute value of the difference between the DC voltage 110A2N and the average value 110C1N exceeds the threshold 110C2T2, and is the range in which no change in transmitted power 110A1N occurs due to the DC voltage 110A2N.

[0105] In the third range 110C2R3, the positive electrode transmission power 110A1P and the negative electrode transmission power 110A1N are set to values ​​110C2LP and 110C2LN, respectively, based on the rated capacity of the forward converter 111C.

[0106] The corrected power calculation unit 17 calculates a new transmission power 110A1P2 (corrected positive electrode transmission power 110A1P2) using the control function 110C2 if the absolute value of the difference between the DC voltage 110A2P and the average value 110C1P exceeds the threshold 110C2T. The value is determined by the absolute value of the difference between the current DC voltage 110A2P and the average value 110C1P and a preset slope 110C2S.

[0107] For example, if the difference between the DC voltage 110A2P and the average value 110C1P increases in the positive direction and exceeds the threshold 110C2T to the right, the corrected positive electrode transmission power 110A1P2 is determined by the difference between the DC voltage 110A2P and the average value 110C1P, and a preset slope 110C2S. In this case, the corrected positive electrode transmission power 110A1P2 will be a smaller value than the uncorrected positive electrode transmission power 110A1P1.

[0108] Furthermore, if the absolute value of the difference between the DC voltage 110A2N and the average value 110C1N exceeds the threshold 110C2T, the corrected power calculation unit 17 uses the control function 110C2 to calculate a new transmission power 110A1N2 (corrected negative electrode transmission power 110A1N2) as a value determined by the absolute value of the difference between the current DC voltage 110A2N and the average value 110C1N, and a preset slope 110C2S.

[0109] For example, if the difference between the DC voltage 110A2N and the average value 110C1N increases in the negative direction and exceeds the threshold 110C2T to the left, the corrected negative electrode transmission power 110A1N2 is determined by the difference between the DC voltage 110A2N and the average value 110C1N, and a preset slope 110C2S. In this case, the corrected negative electrode transmission power 110A1N2 will be a larger value than the uncorrected negative electrode transmission power 110A1N1.

[0110] The pre-set inclination 110C2S is information included in the control function 110C2 and is stored in the storage unit 11 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. The pre-set inclination 110C2S can be arbitrarily determined to match the characteristics of the forward converter 111C, particularly its rated capacity.

[0111] The corrected power 110C3 is calculated as the difference between the pre-correction positive electrode transmission power 110A1P1 and the post-correction positive electrode transmission power 110A1P2, or the difference between the pre-correction negative electrode transmission power 110A1N1 and the post-correction negative electrode transmission power 110A1N2.

[0112] The threshold value 110C2T is the value that separates the first range 110C2R1 from the second range 110C2R2. The threshold value 110C2T is determined by the absolute value of the difference between the DC voltage 110A2P and the average value 110C1P, or the absolute value of the difference between the DC voltage 110A2N and the average value 110C1N.

[0113] The threshold 110C2T is determined by information transmitted from an information processing device (not shown) connected via a network (not shown), or by information prepared in advance by a system administrator or the like. In other words, the threshold 110C2T can be set arbitrarily.

[0114] The threshold value 110C2T is preferably the absolute value of the difference between the DC voltage 110A2P and the average value 110C1P when the positive electrode transmission power 110A1P exceeds the rated capacity of the positive-side forward converter 111CP, or the absolute value of the difference between the DC voltage 110A2N and the average value 110C1N when the negative electrode transmission power 110A1N exceeds the rated capacity of the negative-side forward converter 111CN.

[0115] The threshold value 110C2T2 is the value that separates the second range 110C2R2 and the third range 110C2R3. The threshold value 110C2T2 is determined by the rated capacity of the positive forward converter 111CP or the rated capacity of the negative forward converter 111CN.

[0116] The threshold 110C2T2 is determined by information transmitted from an information processing device (not shown) connected via a network (not shown), or by information prepared in advance by a system administrator or the like. In other words, the threshold 110C2T2 can be determined arbitrarily.

[0117] The control function 110C2 shows that when the transmission power 110A1P and 110A1N of the forward converter 111C is controlled by the DC voltages 110A2P and 110A2N, there is a proportional relationship in the second range 110C2R2. On the other hand, the control function 110C2 shows that when the transmission power 110A1P and 110A1N of the forward converter 111C is controlled by the DC voltages 110A2P and 110A2N, the transmission power 110A1P and 110A1N are constant values ​​in the first range 110C2R1 and the third range 110C2R3. In other words, the control function 110C2 has a first range 110C2R1 and a third range 110C2R3, which are dead zones, and a second range 110C2R2, which is proportional to them.

[0118] <<Determination method, correction power calculation method, distribution amount calculation method, control amount calculation method>> Figure 6 shows the controlled objects of a DC power transmission system. Figure 7 shows the control block of a higher-level control device according to the first embodiment of the present invention. Figure 8 is a flowchart showing a method for controlling the distribution of power in a DC power transmission system by a higher-level control device.

[0119] Next, the details of the determination unit 16's method for determining whether the difference between the DC voltages 110A2P and 110A2N and the average values ​​110C1P and 110C1N exceeds the threshold 110C2T, the correction power calculation unit 17's method for calculating the correction power 110C3, the correction power distribution unit 18's method for calculating the distribution amount of the correction power 110C3, and the control amount calculation unit 12's method for calculating the control amount of the forward converter 111C after correcting the command value of the control amount based on the distribution amount calculated by the correction power distribution unit 18, and then assigning the control amount to each forward converter 111C will be explained.

[0120] First, we will explain the configuration of the power conversion system 500 in Figure 6 and the objects controlled by the DC power transmission system 100. The power conversion system 500 in Figure 6 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.

[0121] Specifically, the power conversion system 500 in Figure 6 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.

[0122] 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.

[0123] Furthermore, the positive electrode power received PPRA, positive electrode power received PPRB, positive electrode power received PPRC, and positive electrode power received PPRD are collectively referred to as the positive electrode power received PPR. Similarly, the negative terminal powers PNRA, PNRB, PNRC, and PNRD are collectively referred to as the negative terminal power PNR.

[0124] Note that the positive electrode transmission power PPS in Figure 6 refers to the same value as the positive electrode transmission power 110A1P in Figure 3. Furthermore, in Figure 6, the positive electrode transmission power PPS refers to the same value as the uncorrected positive electrode transmission power 110A1P1 in Figure 7 before the correction power distribution unit 18 distributes the amounts of correction powers 110C3P and 110C3N, and refers to the same value as the corrected positive electrode transmission power 110A1P2 after the correction power distribution unit 18 distributes the amounts of correction powers 110C3P and 110C3N.

[0125] Similarly, the negative electrode transmission power PNS in Figure 6 refers to the same power as the negative electrode transmission power 110A1N in Figure 3. Furthermore, in Figure 6, the negative electrode transmission power PNS refers to the same value as the uncorrected negative electrode transmission power 110A1N1 in Figure 7 before the correction power distribution unit 18 distributes the amounts of correction powers 110C3P and 110C3N, and refers to the same value as the corrected negative electrode transmission power 110A1N2 after the correction power distribution unit 18 distributes the amounts of correction powers 110C3P and 110C3N.

[0126] 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.

[0127] 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.

[0128] 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 gains set for the negative inverse converter 111IN are as follows: the gain KdNB set for the negative inverse converter 111INB 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.

[0129] Next, 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 will be described. 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.

[0130] 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.

[0131] 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.

[0132] Next, we will describe the control block of the higher-level control unit shown in Figure 7. The control block of the higher-level control device 10 shown in Figure 7 illustrates the detailed functions of the determination unit 16, the corrected power calculation unit 17, and the corrected power distribution unit 18.

[0133] The determination unit 16 calculates the difference between the positive electrode DC voltage 110A2P included in the power transmission side converter station information 110A and the positive electrode average DC voltage 110C1P included in the correction power calculation information 110C. Specifically, the determination unit 16 has a comparison unit 161P that calculates the difference between the positive electrode DC voltage 110A2P and the positive electrode average DC voltage 110C1P and compares it with a threshold value 110C2T. If the difference between the calculated positive electrode DC voltage 110A2P and the positive electrode average DC voltage 110C1P exceeds the threshold 110C2T, the comparison unit 161P transmits the calculated difference between the positive electrode DC voltage 110A2P and the positive electrode average DC voltage 110C1P to the correction power calculation unit 17.

[0134] Furthermore, the determination unit 16 calculates the difference between the negative electrode DC voltage 110A2N included in the power transmission side converter station information 110A and the negative electrode average DC voltage 110C1N included in the corrected power calculation information 110C. Specifically, the determination unit 16 has a comparison unit 161N that calculates the difference between the negative electrode DC voltage 110A2N and the negative electrode average DC voltage 110C1N and compares it with a threshold value 110C2T.

[0135] If the difference between the calculated negative electrode DC voltage 110A2N and the negative electrode average DC voltage 110C1N exceeds the threshold 110C2T, the comparison unit 161N transmits the difference between the calculated negative electrode DC voltage 110A2N and the negative electrode average DC voltage 110C1N to the correction power calculation unit 17.

[0136] The corrected power calculation unit 17 calculates the corrected power 110C3 based on the difference between the positive DC voltage 110A2P and the positive average DC voltage 110C1P, or the difference between the negative DC voltage 110A2N and the negative average DC voltage 110C1N, which is transmitted from the determination unit 16.

[0137] Specifically, the corrected power calculation unit 17 uses the control function 110C2 included in the corrected power calculation information 110C to calculate the corrected power 110C3 from the difference between the positive DC voltage 110A2P and the positive average DC voltage 110C1P or the difference between the negative DC voltage 110A2N and the negative average DC voltage 110C1N. The method for calculating the corrected power 110C3 using the control function 110C2 is as described above.

[0138] The corrected power distribution unit 18 calculates the amount to be distributed from the corrected power 110C3 calculated by the corrected power calculation unit 17 to the positive-side forward converter 111CP or the negative-side forward converter 111CN. The corrected power distribution unit 18 includes a positive electrode corrected power distribution unit 181P and a negative electrode corrected power distribution unit 181N.

[0139] The positive electrode correction power distribution unit 181P is a functional unit that, when the difference between the positive electrode DC voltage 110A2P and the positive electrode average DC voltage 110C1P exceeds the threshold 110C2T, adds the correction power 110C3 to the uncorrected negative electrode transmission power 110A1N1 and subtracts the correction power 110C3 from the uncorrected positive electrode transmission power 110A1P1.

[0140] The amount to be distributed to the positive-side forward converter 111CP is the value obtained by adding the correction power 110C3 to the uncorrected negative electrode transmission power 110A1N1 and subtracting the correction power 110C3 from the uncorrected positive electrode transmission power 110A1P1.

[0141] The negative electrode correction power distribution unit 181N is a functional unit that, when the difference between the negative electrode DC voltage 110A2N and the negative electrode average DC voltage 110C1N exceeds the threshold 110C2T, adds the correction power 110C3 to the pre-correction positive electrode transmission power 110A1P1 and subtracts the correction power 110C3 from the pre-correction negative electrode transmission power 110A1N1.

[0142] The amount to be distributed to the negative forward converter 111CN is the value obtained by adding the correction power 110C3 to the uncorrected positive electrode transmission power 110A1P1 and subtracting the correction power 110C3 from the uncorrected negative electrode transmission power 110A1N1.

[0143] In other words, the negative electrode correction power distribution unit 181N adds the correction power 110C3 to the uncorrected positive electrode transmission power 110A1P1, and the positive electrode correction power distribution unit 181P subtracts the correction power 110C3 from the uncorrected positive electrode transmission power 110A1P1, thereby calculating the corrected positive electrode transmission power 110A1P2.

[0144] Furthermore, the positive electrode correction power distribution unit 181P adds the correction power 110C3 to the uncorrected negative electrode transmission power 110A1N1, and the negative electrode correction power distribution unit 181N subtracts the correction power 110C3 from the uncorrected negative electrode transmission power 110A1N1, thereby calculating the corrected negative electrode transmission power 110A1N2.

[0145] Next, we will explain the operation of each functional unit when, for example, the positive-side inverter 111IPC and the negative-side inverter 111IND change from a powered state (droop control state) to a stopped state due to a fault in the operating state described above.

[0146] If the positive-side inverter 111IPC and the negative-side inverter 111IND change from a powered state (droop-controlled state) to a stopped state due to a fault, a change occurs in the power source of the positive terminal power PPRC received by the powered AC system 300C and the negative terminal power PNRD received by the powered AC system 300D.

[0147] In other words, the 300MW positive terminal power PPRC, which was being received by the positive-side inverter 111IPC (converting the transmitted power transmitted from the forward converter 111C into AC power), will now be received by the positive-side inverter 111IPD, which is in a droop-controlled state. Similarly, the 500MW negative terminal power PNRD, which was received by the negative inverter 111IND (converting the transmitted power transmitted from the forward converter 111C into AC power), will now be received by the negative inverter 111INC, which continues to be in a droop-controlled state.

[0148] At this time, the positive-side inverter 111IPD will receive not only the 500MW positive power PPRD that it had been receiving up to that point, but also the 300MW positive power PPRC that the positive-side inverter 111IPC had been receiving. Similarly, the negative inverter 111INC will receive not only the 300MW negative power PNRC that it had been receiving up to that point, but also the 500MW negative power PNRD that the negative inverter 111IND had been receiving.

[0149] Since the rated capacity of the positive-side inverter 111IPD is 1000MW, the positive-side inverter 111IPD can receive both the positive-side power PPRD and the positive-side power PPRC. However, since the rated capacity of the negative inverter 111INC is 600MW, if the negative inverter 111INC receives power from both the negative terminal (PNRC) and the negative terminal (PNRD), an overload of 200MW will occur.

[0150] Here, in order to prevent the negative inverse converter 111INC from becoming overloaded, the forward converter 111C is controlled. The processing flow by the higher-level control device 10 is explained below with reference to Figure 8.

[0151] Figure 8 is a flowchart showing the processing flow by the higher-level control device 10.

[0152] First, the converter station information monitoring unit 13 monitors the operating status of the positive-side inverse converter 111IP and the negative-side inverse converter 111IN, the transmission power 110A1P of the positive-side forward converter 111CP and the transmission power 110A1N of the negative-side forward converter 111CN (pre-correction positive-electrode transmission power 110A1P1 and pre-correction negative-electrode transmission power 110A1N1), the received power of the positive-side inverse converter 111IP and the negative-side inverse converter 111IN (pre-correction positive-electrode received power and pre-correction negative-electrode received power), and the droop control gain set for the positive-side inverse converter 111IP and the negative-side inverse converter 111IN (step S1).

[0153] The operating state of the positive-side inverse converter 111IPA is a constant power control state. Furthermore, the operating status of the positive-side inverse converter 111IPB is stopped. Furthermore, the operating state of the positive-side inverse converter 111IPC was droop-controlled before the accident and stopped after the accident. Furthermore, the operating state of the positive-side inverse converter 111IPD is in droop control mode.

[0154] The operating state of the negative inverter 111INA is a constant power control state. Furthermore, the operating status of the negative inverse converter 111INB is stopped. Furthermore, the operating state of the negative inverse converter 111INC is in droop control mode. Furthermore, the operating state of the negative inverter 111IND was droop control before the accident and stopped after the accident.

[0155] The pre-correction positive electrode transmission power 110A1P1 of the positive-side forward converter 111CP is 1050MW. The uncorrected negative electrode transmission power 110A1N1 of the negative forward converter 111CN is 1050MW.

[0156] The pre-correction positive electrode power received by the positive-side inverse converter 111IPA is 250 MW. Furthermore, the pre-correction positive electrode power received by the positive-side inverse converter 111IPB is 0 MW. Furthermore, the uncorrected positive electrode power received by the positive-side inverse converter 111IPC was 300 MW before the fault and 0 MW after the fault. Furthermore, the uncorrected positive electrode power received by the positive-side inverse converter 111IPD was 500 MW before the accident and 800 MW after the accident.

[0157] The uncorrected negative electrode power received by the negative inverse converter 111INA is 250 MW. Furthermore, the uncorrected negative electrode power received by the negative inverse converter 111INB is 0MW. Furthermore, the uncorrected negative electrode power received by the negative inverter 111INC was 300 MW before the accident and 800 MW after the accident. Furthermore, the uncorrected negative electrode power received by the negative inverter 111IND was 500 MW before the accident and 0 MW after the accident.

[0158] The gain KdPB set for the positive-side inverse converter 111IPB is 1. Furthermore, the gain KdPC set for the positive-side inverse converter 111IPC is 2. Furthermore, the gain KdPD set for the positive-side inverse converter 111IPD is 3.

[0159] The gain KdNB set for the negative inverse converter 111INB is 1. Furthermore, the gain KdNC set for the negative inverse converter 111INC is 2. Furthermore, the gain KdND set for the negative inverse converter 111IND is 3.

[0160] Next, the DC voltage measuring unit 14 measures the DC voltage 110A2P, which is the voltage to ground of the positive terminal main line 40P, and the DC voltage 110A2N, which is the voltage to ground of the negative terminal main line 40N (step S2).

[0161] Specifically, the DC voltage measurement unit 14 measures the voltage of the busbar of the AC system 200 to which the positive-side forward converter 111CP and the negative-side forward converter 111CN are connected, and calculates the DC voltage 110A2PA based on the busbar voltage. Furthermore, the DC voltage measurement unit 14 measures the voltage of the busbar of the AC system 200 to which the positive-side forward converter 111CP and the negative-side forward converter 111CN are connected, and calculates the DC voltage 110A2PB based on the busbar voltage. Furthermore, the DC voltage measurement unit 14 measures the voltage of the busbar of the AC system 200 to which the positive-side forward converter 111CP and the negative-side forward converter 111CN are connected, and calculates the DC voltage 110A2PC based on the busbar voltage. Furthermore, the DC voltage measurement unit 14 measures the voltage of the busbar of the AC system 200 to which the positive-side forward converter 111CP and the negative-side forward converter 111CN are connected, and calculates the DC voltage 110A2PD based on the busbar voltage.

[0162] Similarly, the DC voltage measurement unit 14 measures the voltage of the busbar of the AC system 200 to which the positive-side forward converter 111CP and the negative-side forward converter 111CN are connected, and calculates the DC voltage 110A2NA based on the busbar voltage. Furthermore, the DC voltage measurement unit 14 measures the voltage of the busbar of the AC system 200 to which the positive-side forward converter 111CP and the negative-side forward converter 111CN are connected, and calculates the DC voltage 110A2NB based on the busbar voltage. Furthermore, the DC voltage measurement unit 14 measures the voltage of the busbar of the AC system 200 to which the positive-side forward converter 111CP and the negative-side forward converter 111CN are connected, and calculates the DC voltage 110A2NC based on the busbar voltage. Furthermore, the DC voltage measurement unit 14 measures the voltage of the busbar of the AC system 200 to which the positive-side forward converter 111CP and the negative-side forward converter 111CN are connected, and calculates the DC voltage 110A2ND based on the busbar voltage.

[0163] Next, the average DC voltage calculation unit 15 calculates the average value 110C1P of the DC voltage 110A2P and the average value 110C1N of the DC voltage 110A2N for each positive terminal main line 40P and negative terminal main line 40N connected to each power receiving side converter station 30, which have been measured and calculated by the DC voltage measurement unit 14 (step S3).

[0164] Specifically, the average DC voltage calculation unit 15 measures the average value 110C1PA of the DC voltage 110A2PA over a certain period of time. Furthermore, the average DC voltage calculation unit 15 measures the average value 110C1PB of the DC voltage 110A2PB over a certain period. Furthermore, the average DC voltage calculation unit 15 measures the average value 110C1PC of the DC voltage 110A2PC over a certain period of time. Furthermore, the average DC voltage calculation unit 15 measures the average value 110C1PD of the DC voltage 110A2PD over a certain period of time.

[0165] Similarly, the average DC voltage calculation unit 15 measures the average value 110C1NA of the DC voltage 110A2NA over a certain period. Furthermore, the average DC voltage calculation unit 15 measures the average value 110C1NB of the DC voltage 110A2NB over a certain period of time. Furthermore, the average DC voltage calculation unit 15 measures the average value 110C1NC of the DC voltage 110A2NC over a certain period of time. Furthermore, the average DC voltage calculation unit 15 measures the average value 110C1ND of the DC voltage 110A2ND over a certain period.

[0166] Next, the determination unit 16 determines whether the difference between any of the DC voltages 110A2P, 110A2N and the average value 110C1P, 110C1N exceeds the threshold 110C2T set by the control function 110C2 (step S4).

[0167] Specifically, the determination unit 16 determines whether any of the following differences exceed the threshold 110C2T: the difference between DC voltage 110A2PA and the average value 110C1PA, the difference between DC voltage 110A2PB and the average value 110C1PB, the difference between DC voltage 110A2PC and the average value 110C1PC, the difference between DC voltage 110A2PD and the average value 110C1PD, the difference between DC voltage 110A2NA and the average value 110C1NA, the difference between DC voltage 110A2NB and the average value 110C1NB, the difference between DC voltage 110A2NC and the average value 110C1NC, and the difference between DC voltage 110A2ND and the average value 110C1ND.

[0168] If the difference between any of the DC voltages 110A2P, 110A2N and the average values ​​110C1P, 110C1N does not exceed the threshold 110C2T (step S4: NO), the correction power calculation unit 17 does not calculate the correction power 110C3, and the correction power distribution unit 18 does not calculate the distribution amount of the correction power 110C3. In this case, the control amount calculation unit 12 calculates the control amount without correcting the command values ​​of the control amounts for the positive-side forward converter 111CP and the negative-side forward converter 111CN (step S7). The control amount calculation unit 12 provides the control amount calculated in step S7 to the inverse converter 111I (step S8).

[0169] In other words, the control amount calculation unit 12 calculates the same control amounts as before for the positive inverse converters 111IPA, 111IPB, 111IPC, 111IPD and the negative inverse converters 111INA, 111INB, 111INC, 111IND, and assigns the same control amounts as before to the positive inverse converters 111IPA, 111IPB, 111IPC, 111IPD and the negative inverse converters 111INA, 111INB, 111INC, 111IND.

[0170] However, in this case, the positive inverter 111IPC and the negative inverter 111IND change from a droop control state to a stopped state due to a fault, and an overload occurs in the negative inverter 111INC. As a result, the difference between the DC voltage 110A2NC and the average value 110C1NC exceeds the threshold 110C2T (Step S4: YES). Therefore, in Steps S5 to S6, the correction power 110C3 and the distribution amount of the correction power 110C3 are calculated.

[0171] Next, the corrected power calculation unit 17 calculates the corrected powers 110C3P and 110C3N obtained by inputting the values ​​of the DC voltages 110A2P and 110A2N of the positive terminal main line 40P or the negative terminal main line 40N (DC voltages 110A2P and 110A2N and their average values ​​110C1P and 110C1N) of which the difference between any of the DC voltages 110A2P and 110A2N and their average values ​​110C1P and 110C1N exceeds the threshold 110C2T into the control function 110C2 (step S5).

[0172] In this case, since the difference between the DC voltage 110A2NC and the average value 110C1NC exceeded the threshold 110C2T, the correction power 110C3N is calculated by inputting the difference between the DC voltage 110A2NC and the negative electrode average DC voltage 110C1NC into the control function 110C2.

[0173] Specifically, by inputting the difference between the DC voltage 110A2NC and the negative electrode average DC voltage 110C1NC into the control function 110C2, the corrected power 110C3N is calculated to be 200MW.

[0174] Next, the corrected power distribution unit 18 calculates the distribution amount obtained by distributing the corrected power 110C3 to the positive-side forward converter 111CP or negative-side forward converter 111CN connected to the positive-side forward converter 111CP or negative-side forward converter 111CN, where the difference between the DC voltages 110A2P, 110A2N and the average values ​​110C1P, 110C1N does not exceed the threshold 110C2T (step S6).

[0175] Specifically, the positive electrode correction power distribution unit 181P adds the correction power 110C3 to the uncorrected negative electrode transmission power 110A1N1 and subtracts the correction power 110C3 from the uncorrected positive electrode transmission power 110A1P1 if the difference between the DC voltage 110A2P and the average value 110C1P exceeds the threshold 110C2T. Similarly, the negative electrode correction power distribution unit 181N adds the correction power 110C3 to the uncorrected positive electrode transmission power 110A1P1 and subtracts the correction power 110C3 from the uncorrected negative electrode transmission power 110A1N1 if the difference between the DC voltage 110A2N and the average value 110C1N exceeds the threshold 110C2T.

[0176] Specifically, the positive electrode correction power distribution unit 181P adds the correction power 110C3N to the pre-correction positive electrode transmission power 110A1P1.

[0177] Since the pre-correction positive electrode transmission power 110A1P1 of the positive-side forward converter 111CP is 1050 MW, when the positive electrode correction power distribution unit 181P adds the correction power 110C3N of 200 MW, the corrected positive electrode transmission power 110A1P2 becomes 1250 MW.

[0178] In this case, the amount of correction power 110C3N that the positive electrode correction power distribution unit 181P should distribute to the positive side forward converter 111CP is 200MW.

[0179] Furthermore, the negative electrode correction power distribution unit 181N subtracts the correction power 110C3N from the uncorrected negative electrode transmission power 110A1N1.

[0180] Since the uncorrected negative electrode transmission power 110A1N1 of the negative forward converter 111CN is 1050 MW, when the negative electrode correction power distribution unit 181N subtracts the correction power 110C3N of 200 MW, the corrected negative electrode transmission power 110A1N2 becomes 850 MW.

[0181] In this case, the amount of correction power 110C3N that the negative electrode correction power distribution unit 181N should distribute to the negative forward converter 111CN is -200MW.

[0182] Next, the control amount calculation unit 12 corrects the command value of the control amount based on the distribution amount calculated by the corrected power distribution unit 18, calculates the control amount for the forward converter 111C (step S7), and assigns the control amount to each forward converter 111C (step S8).

[0183] Specifically, the control quantity calculation unit 12 uses the corrected positive electrode transmission power 110A1P2, which is 1250MW, as the control quantity, which is obtained by adding the corrected power 110C3 of 200MW to the uncorrected positive electrode transmission power 110A1P1 of 1050MW, and provides the positive side forward converter 111CP with the control quantity, which is the positive electrode transmission power PPS 1250MW.

[0184] Similarly, the control quantity calculation unit 12 uses the corrected negative electrode transmission power 110A1N2, which is 6850MW, as the control quantity, obtained by subtracting the corrected power 110C3 of 200MW from the uncorrected negative electrode transmission power 110A1N1 of 1050MW, and provides the negative side forward converter 111CN with the control quantity, which is the negative electrode transmission power PNS850MW.

[0185] Through the above steps, the control amount calculation unit 12 provides the control amount based on the corrected positive electrode transmission power 110A1P2 and the corrected negative electrode transmission power 110A1N2 to the forward converter 111C. As a result, the corrected power 110C3N is distributed to the positive-side forward converter 111CP connected to the positive electrode (opposite electrode) main line 40P where the difference between the DC voltage 110A2NC and the average value 110C1NC does not exceed the threshold 110C2T (step S9).

[0186] Specifically, the positive-side forward converter 111CP transmits positive-electrode power PPS 1250MW, to which 200MW of correction power 110C3N is allocated, and the negative-side forward converter 111CN transmits negative-electrode power PNS 850MW, to which 200MW of correction power 110C3N is deducted.

[0187] As a result, the positive-side inverter 111IPA will receive 250 MW of power, and the positive-side inverter 111IPD will receive 1000 MW of power. Furthermore, the negative inverter 111INA will receive 250 MW of power, and the negative inverter 111INC will receive 600 MW of power.

[0188] In other words, the positive inverter 111IPD, which is in a droop-controlled state, will receive 1000 MW of power, which is below its rated capacity, and the negative inverter 111INC, which is in a droop-controlled state, will receive 600 MW of power, which is below its rated capacity, thus eliminating the overload on the negative inverter 111INC.

[0189] Following the steps in the flowchart above, the higher-level control device 10 determines whether the difference between the DC voltages 110A2P and 110A2N and the average values ​​110C1P and 110C1N exceeds the threshold 110C2T, calculates the correction power 110C3 and the distribution amount of the correction power 110C3, and distributes the calculated distribution amount of the correction power 110C3 to the positive-side forward converter 111CP and the negative-side forward converter 111CN, thereby preventing each inverse converter 111I from becoming overloaded.

[0190] In the DC power transmission system 100 according to the embodiment described above, the higher-level control device 10 calculates a correction power 110C3 based on the control function 110C2 if the difference between the DC voltages 110A2P and 110A2N and the average values ​​110C1P and 110C1N exceeds the threshold 110C2T, and calculates the distribution amount obtained by distributing the correction power 110C3 to the positive-side forward converter 111CP or negative-side forward converter 111CN connected to the positive-side forward converter 111CP or negative-side forward converter 111CN connected to the positive-side forward converter 40P or negative-side forward converter 40N where the DC voltages 110A2P and 110A2N do not exceed the threshold 110C2T, and calculates the control amount of the positive-side forward converter 111CP and negative-side forward converter 111CN corrected by the distribution amount.

[0191] According to this, in a DC power transmission system 100, if some positive-side inverters 111IP or negative-side inverters 111IN change from a power-receiving state to a stopped state due to an accident or inspection, the control amount of the positive-side inverter 111CP and the negative-side inverter 111CN can be calculated so as to distribute the correction power 110C3, which corresponds to the power-receiving power PPR and PNR that the positive-side inverter 111IP or negative-side inverter 111IN that changed from a power-receiving state to a stopped state was receiving before it changed to a stopped state, to the positive-side forward converter 111CP or negative-side forward converter 111CN, where the difference between the DC voltage 110A2P, 110A2N and the average value 110C1P, 110C1N does not exceed the threshold 110C2T.

[0192] Therefore, even if the number of operational positive-side inverters 111IP or negative-side inverters 111IN at the power receiving station 30 decreases, it is possible to prevent some of the operational positive-side inverters 111IP or negative-side inverters 111IN from becoming overloaded.

[0193] Furthermore, the DC power transmission system 100 according to this embodiment calculates a corrected power 110C3 based on a control function 110C2 which has a first range 110C2R1 in which no change occurs in the transmitted power 110A1P, 110A1N due to the DC voltages 110A2P, 110A2N, and a second range 110C2R2 in which the change in the transmitted power 110A1P, 110A1N due to the DC voltages 110A2P, 110A2N is determined by a predetermined slope 110C2S.

[0194] According to this, in the first range 110C2R1 where the absolute value of the difference between the DC voltages 110A2P, 110A2N and the average values ​​110C1P, 110C1N is the dead zone, no change is made to the control amount by the correction power 110C3. In the second range 110C2R2 which has a proportional characteristic, the correction power 110C3 is calculated such that the value determined by the preset slope 110C2S becomes the corrected positive electrode transmission power 110A1P2 or the corrected negative electrode transmission power 110A1N2, and the control amounts of the positive-side forward converter 111CP and the negative-side forward converter 111CN can be calculated based on the correction power 110C3.

[0195] In other words, depending on the magnitude of the absolute difference between the DC voltages 110A2P and 110A2N and the average values ​​110C1P and 110C1N, multiple control methods can be used.

[0196] <<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.

[0197] The flowcharts described above are examples and are not limited to the processing procedures shown in Figures 8 and 11. For example, other processes may be inserted between each step shown in Figures 8 and 11, or some processes may be parallelized.

[0198] For example, in the higher-level control device 10, the average DC voltage 110C1 and the correction power 110C3 are included in the correction power calculation information 110C, but the system is not limited to this, and the average DC voltage 110C1 and the correction power 110C3 may also be included in the transmission-side converter station information 110A. [Explanation of Symbols]

[0199] 10. Higher-level control unit 11 Storage section 12 Control variable calculation unit 13. Conversion Station Information Monitoring Department 14 DC Voltage Measurement Unit 15. Average DC Voltage Calculation Unit 16 Judgment section 17 Corrected Power Calculation Unit 18 Correction Power Distribution Unit 20 Power transmission side converter station 30 Power receiving conversion station 40 DC transmission lines 40N Negative electrode main line 40P Positive Main Line 40G return 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 110A1N negative electrode transmission power 110A1N1 Negative electrode transmission power before correction 110A1N2 Negative electrode transmission power after correction 110A1P Positive electrode power transmission 110A1P1 Pre-corrected positive electrode transmission power 110A1P2 Positive electrode transmission power after correction 110A2N Negative DC Voltage 110A2P Positive DC Voltage 110C corrected power calculation information 110C1 Average DC Voltage 110C1N Negative Average DC Voltage 110C1P Positive Average DC Voltage 110C2 control function Values ​​set based on the rated capacity of the 111C forward converter, such as 110C2LN and 110C2LP. 110C2R1 First range 110C2R2 Second range 110C2R3 Third range 110C2S tilt 110C2T threshold 110C2T2 threshold 110C3, 110C3N, 110C3P corrected power 111C Forward Converter 111I Inverse Converter 112 Converter Station Protection Control Panel 113 Converter control panel 114 Protective detection device 115 DC circuit breaker 161N, 161P comparison section 181N Negative electrode correction power distribution unit 181P Positive electrode correction power distribution unit 200 Transmission side AC system 300 Power receiving side AC system 500 Power Conversion Systems PPR positive electrode power reception 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 of the receiving-side converter stations, and connecting the transmitting-side converter station and the receiving-side 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 A storage unit that includes at least a control function which is a function representing the relationship between the DC voltage, which is the voltage value of each DC transmission line calculated based on the voltage of the busbar of the AC system to which the positive-side forward converter and the negative-side forward converter are connected, and the power transmitted by the positive-side forward converter and the negative-side forward converter, 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 DC voltage measurement unit measures and calculates the respective DC voltages and stores the measured and calculated results in the storage unit, An average DC voltage calculation unit calculates the average value of the DC voltage over a certain period and stores the calculated result in the memory unit, A determination unit that determines whether the difference between the DC voltage of either the positive electrode main line or the negative electrode main line and the average value exceeds a threshold, and stores the determination result in the storage unit, Based on the result determined by the determination unit, a corrected power calculation unit calculates the power obtained by inputting the value of the DC voltage of the positive main line or the negative main line that exceeds the threshold into the control function, and Includes a correction power distribution unit that calculates a distribution amount obtained by distributing the correction power to the positive-side forward converter or the negative-side forward converter connected The control amount calculation unit calculates the control amounts of the positive forward converter and the negative forward converter by correcting the command value of the control amount with the distribution amount. DC power transmission system.

2. The system according to claim 1, The control function has a first range and a second range, The first range is a range in which the absolute value of the difference between the DC voltage and the average value is less than or equal to the threshold, and in which no change in the transmitted power occurs due to the DC voltage. The second range is a range in which the absolute value of the difference between the DC voltage and the average value exceeds the threshold, and in which the change in the transmitted power due to the DC voltage is determined by a predetermined slope. DC power transmission system.

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 DC voltage measurement step involves measuring the voltage of the busbar of the AC system to which the positive-side forward converter and the negative-side forward converter are connected, and measuring and calculating the DC voltage of each DC transmission line, which is the voltage value calculated based on the voltage of the busbar. A step of calculating the average DC voltage over a certain period of time, A determination step of determining whether the difference between the DC voltage of either the positive electrode main line or the negative electrode main line and the average value exceeds a threshold, Based on the result determined in the determination step, a correction power calculation step is performed to calculate the power obtained by inputting the value of the DC voltage of the positive main line or the negative main line that exceeds the threshold into a control function which is a function representing the relationship between the DC voltage and the transmitted power which is the power transmitted by the positive-side forward converter and the negative-side forward converter, and the value of the DC voltage of the positive main line or the negative main line that exceeds the threshold, and the power obtained is calculated as the correction power. A correction power distribution step includes calculating a distribution amount obtained by distributing the correction power to the positive-side forward converter or the negative-side forward converter connected The control amount calculation step includes calculating the control amounts of the positive forward converter and the negative forward converter by correcting the command value of the control amount with the distribution amount. 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 DC power transmission system comprising: a plurality of receiving-side converter stations, each comprising a positive-side reverse converter for converting DC power transmitted from the positive-side forward converter to AC power, and a negative-side reverse converter for converting DC power transmitted from the negative-side forward converter to AC power; a DC transmission line including a positive main line, a negative main line, and a return line, provided corresponding to each receiving-side converter station and connecting the transmitting-side converter station and the receiving-side converter station; and a higher-level control device for controlling at least one of 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 DC voltage measurement step involves measuring the voltage of the busbar of the AC system to which the positive-side forward converter and the negative-side forward converter are connected, and measuring and calculating the DC voltage of each DC transmission line, which is the voltage value calculated based on the voltage of the busbar. A step of calculating the average DC voltage over a certain period of time, A determination step of determining whether the difference between the DC voltage of either the positive electrode main line or the negative electrode main line and the average value exceeds a threshold, Based on the result determined in the determination step, a correction power calculation step is performed to calculate the power obtained by inputting the value of the DC voltage of the positive main line or the negative main line that exceeds the threshold into a control function which is a function representing the relationship between the DC voltage and the transmitted power which is the power transmitted by the positive-side forward converter and the negative-side forward converter, and the value of the DC voltage of the positive main line or the negative main line that exceeds the threshold, and the power obtained is calculated as the correction power. A program for causing a higher-level control device to execute a correction power distribution step, which calculates a distribution amount obtained by distributing the correction power to the positive-side forward converter or the negative-side forward converter connected The control amount calculation step includes calculating the control amounts of the positive forward converter and the negative forward converter by correcting the command value of the control amount with the distribution amount. program.

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