JP2019208337A - Control device for dc converter - Google Patents

Abstract

To solve a problem in which, in a DC system, voltage of a terminal converter deviates from upper limit voltage.SOLUTION: A control device for a DC converter is provided with: an obtaining part that obtains output current of a plurality of terminal converters linked to a terminal of a DC cable in the DC system; an output-current assumption part that sets a combination pattern of output current to be assumed for every terminal converter for every time cross section; a current-distribution calculation part that calculates distribution of passing current for every section of the DC cable; a voltage difference calculation part that calculates voltage difference in rise or drop for every section from the distribution for every combination pattern; a voltage-distribution determination part that determines voltage distribution in the DC system so as to match voltage in a highest point with the upper limit voltage in the DC system by extracting the highest point having the highest voltage from the voltage difference for every combination pattern; a voltage-dispersion calculation part that calculates dispersion of voltage values for every terminal converter from the voltage distribution in all the combination patterns; a constant-voltage-control determination part that determines one terminal converter for constant voltage control by using a value of the dispersion; and a target-voltage distribution part that distributes target voltage to the other terminal converters.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a control device for a DC converter that determines a control mode of a terminal converter linked to a terminal of a DC system.

  A DC system that has less power loss than an AC system and can efficiently transport electric power has attracted attention. The direct current system includes a direct current cable, at least one terminal converter connected to a terminal of the direct current cable, a load facility and a power generation facility connected to an arbitrary place of the direct current cable.

  Here, as the terminal converter, a DC / DC converter (DC / DC converter) that mutually interchanges power with another adjacent DC system of a voltage class, a DC load facility, and a DC power generation facility, or adjacent to each other. An AC / DC converter (AC / DC converter) that interchanges power with an AC system, AC load equipment, and AC power generation equipment can be used.

  Each terminal converter maintains the voltage in the DC system properly and controls the output current so that the sum of the current values flowing into and out of the DC system becomes zero, that is, the power supply-demand balance is maintained. However, it is basically divided into either constant voltage control or constant current control.

  In the terminal converter with constant voltage control, the output voltage is controlled so that the connection point voltage with the DC system matches the given target voltage. For the current in the constant voltage control, a current value obtained by inverting the sign of the sum of the output currents of the other terminal converters in the DC system is output in succession. In the terminal converter with constant current control, the output current is controlled so as to match the given target current.

  In general, one terminal converter performs constant voltage control, and the other terminal converter performs constant current control. Conventionally, a method of setting whether to perform constant voltage control or constant current control for each terminal converter has been disclosed (for example, Patent Document 1 and Patent Document 2).

  In Patent Document 1, among a plurality of terminal converters, a forward converter (converter that converts AC to DC direction) having the largest transmission power for flowing current into the DC system, or received power for extracting current from the DC system is minimum. The inverse converter (converter that converts from direct current to alternating current) is controlled at a constant voltage. A terminal converter that performs the control to maintain the voltage at a predetermined value to maintain the voltage in the DC system, and the other terminal converter performs constant current control, so that the burden of power interchange performs constant voltage control. To avoid concentrating on.

  Moreover, in patent document 2, when the terminal converter of constant voltage control fails, it is the system which determines the terminal converter made into constant voltage control in order of a capacity | capacitance. As described above, the conventional terminal system is basically selected as the terminal converter for constant DC voltage control depending on the capacity.

  This is because when the sum of currents flowing into and out of the DC system is not zero, and when there is power shortage or power surplus, the constant current control terminal converter changes the output and absorbs it during the control delay. The terminal converter with constant voltage control temporarily bears all power shortages and power surpluses. For this reason, if a terminal converter having a margin of output as much as possible is selected for constant voltage control, the risk of a converter overload output is reduced and the stability of the DC system is improved.

  Further, in Non-Patent Document 1, the output voltage of the terminal converter for constant voltage control is not fixed, and the converter rated current does not increase in the vicinity of the upper limit voltage and lower limit voltage of the target voltage as shown in FIG. A method has been proposed in which a V-I characteristic (voltage-current characteristic) is set and an output voltage value is determined in accordance with its own output current.

  In the DC system, the current flows according to Ohm's law V = I × R (V is the voltage difference between the two points, I is the current flowing between the two points, and R is the resistance value of the DC cable between the two points). System voltage drops in the direction. Therefore, in general, when the output current from the terminal converter is in the forward direction (positive direction in FIG. 20) in which current flows into the DC system, the voltage is expected to gradually decrease as viewed from the terminal converter. Therefore, the target voltage is set higher. Conversely, in the case where the main current is in the reverse direction in which the current is extracted (negative direction in FIG. 20), the voltage is expected to gradually increase when viewed from the terminal converter, so the target voltage is set lower.

JP-A-60-241716 JP-A-7-131936

W. Wang, M. Barnes, O. Marfanovic, “Droop Control Modeling and Analysis of Multi-terminal VSC-HVDC for Offshore Wind Farms”, AC and DC Power Transmission (ACDC 2012) 10th IET International Conference on IET, 2012, pp .1-6.

  If a terminal converter is selected that is controlled at a constant voltage only by the magnitude of the power to be converted or the converter capacity, the power loss consumed in the DC system is not minimized.

  In other words, the power loss that occurs in the DC system mainly consists of the converter loss that occurs when power is converted by the terminal converter, and the line loss that occurs when current flows through the DC cable. It is proportional to the square of the current.

  Here, normally, the magnitude of the power transmission current that flows current from each terminal converter of constant current control into the DC system or the power reception current that extracts the current is determined by the power that each terminal converter intends to transmit and receive power . In a DC system, it is defined as power = voltage × current. For this reason, the current flowing through the terminal converter and the DC cable, which keeps the voltage of the DC system generally high, can be small, and therefore the power loss can be reduced.

  However, if the target voltage of the terminal converter voltage with constant voltage control is fixed, the target voltage is set so that the voltage distribution is always within the upper and lower limits of the regulation no matter how the current distribution in the DC system changes. Therefore, it cannot always be kept high.

  In addition, even if the control is performed using the VI characteristic as shown in FIG. 20, in the multi-terminal DC system in which the number of terminal converters connected to the DC system is three or more and the current distribution is diversified, the output current of constant voltage control is used. Even if are the same, the current / voltage distribution in the DC system cannot be uniquely determined.

  22 and 23 are diagrams showing the output current of the terminal converter in the DC system and the voltage distribution of the DC system. For example, in a DC system consisting of four terminals as shown in FIG. 21, the terminal converter a has constant voltage control and the other terminal converter b to terminal converter d has constant current control as shown in FIGS. Think about the case. 22 and 23, the output current of the terminal converter a is 900A. In FIG. 22, when the output voltage of the terminal converter a is V1, the current is minimized, but when it is V2, the current of the DC system increases because the same power is transmitted, and the converter loss and line loss increase. On the other hand, in FIG. 23, if the output voltage of the terminal converter a is V1, the terminal converter d deviates from the upper limit voltage, so the output voltage needs to be V2. In order not to cause voltage deviation in both cases, the output voltage of the terminal converter needs to be V2. As a result, even if the VI characteristic is used, the voltage cannot always be kept high and the power loss cannot be reduced.

  The control device for a DC converter according to the present invention is assumed for each terminal converter for each time converter and an acquisition unit that acquires output currents of a plurality of terminal converters connected to terminals of a DC cable in a DC system. Output current assumption unit that sets the combination pattern of output current, current distribution calculation unit that calculates distribution of passing current for each section of DC cable, and calculation of voltage difference of rise or fall for each section from distribution for each combination pattern Voltage distribution calculation unit that determines the voltage distribution of the DC system so that the highest point with the highest voltage is extracted from the voltage difference for each combination pattern and the voltage at the highest point matches the upper limit voltage of the DC system Voltage distribution calculation unit that calculates the variance of the voltage value for each terminal converter from the voltage distribution of all the combination patterns, and a constant voltage that determines one terminal converter that performs constant voltage control using the variance value Control decision And parts, which is the control device of the DC converter, characterized in that a target voltage distribution unit that distributes the target voltage to the remaining terminals converter.

  Further, the control device for the DC converter according to the present invention assumes an acquisition unit that acquires output currents of a plurality of terminal converters connected to terminals of a DC cable in a DC system, and each terminal converter for each time section. Output current assumption unit that sets a combination pattern of output currents, a current distribution calculation unit that calculates the distribution of passing current for each section of the DC cable, and a voltage difference that rises or falls from distribution to section for each combination pattern The voltage difference calculation unit that calculates the voltage, and the voltage that determines the voltage distribution of the DC system so that the highest point with the highest voltage is extracted from the voltage difference for each combination pattern and the voltage at the highest point matches the upper limit voltage of the DC system A distribution determination unit, a voltage distribution calculation unit that calculates the variance of the voltage value for each terminal converter from the voltage distribution of all combination patterns, and one terminal converter that performs constant voltage control using the value of the variance are determined. Constant voltage A V-I characteristic determining unit that determines a V-I characteristic from a combination of a connection point voltage of the terminal converter in the voltage distribution for each combination pattern and an assumed output current of the terminal converter; A DC converter control device comprising: a VI characteristic distribution unit that distributes a target voltage obtained from a VI characteristic according to an output current of the terminal converter.

  According to the control device for a DC converter of the present invention, the voltage distribution in the DC system can be kept high.

FIG. 2 is a block diagram showing a configuration of a DC converter control device according to Embodiment 1 and its periphery. 4 is a flowchart illustrating an example of an operation of a data acquisition process flow according to the first embodiment. It is a figure which shows the example of the data structure of output performance DB which concerns on Embodiment 1. FIG. 6 is a flowchart illustrating an example of an operation of a constant voltage control converter determination processing flow according to the first embodiment. It is a figure which shows the example of the assumed electric current of a terminal converter for every combination pattern which concerns on Embodiment 1. FIG. It is a figure which shows the example of the data structure of system equipment DB which concerns on Embodiment 1. FIG. 6 is a diagram illustrating an example of a calculation result of a current distribution calculation unit in the first embodiment. FIG. 6 is a diagram illustrating an example of a calculation result of a voltage difference calculation unit according to Embodiment 1. FIG. 6 is a diagram illustrating an example of a calculation result of a voltage distribution determination unit according to Embodiment 1. FIG. It is a figure which shows the example of the calculation result of step S208 which concerns on Embodiment 1. FIG. It is a figure which shows the example of the voltage dispersion | distribution calculation result which concerns on Embodiment 1. FIG. It is a figure which shows the example of the voltage distribution determination result which concerns on Embodiment 1. FIG. FIG. 5 is a block diagram showing a configuration of a DC converter control device according to a second embodiment and its periphery. 10 is a flowchart illustrating an example of an operation of a constant voltage control converter determination processing flow according to the second embodiment. It is a figure which shows the example of the example of the result of the voltage distribution calculation which concerns on Embodiment 2, and a current likelihood calculation. FIG. 10 is a block diagram illustrating a DC converter control device according to a third embodiment and its peripheral configuration. 12 is a flowchart illustrating an example of an operation of a constant voltage control converter determination processing flow according to the third embodiment. It is a figure which shows the example of the combination of the electric current and voltage which were set for every terminal converter which concerns on Embodiment 3. FIG. It is an image figure which shows the example of the combination of the assumption electric current which concerns on Embodiment 3, and a connection point voltage, and a VI characteristic. It is a figure which shows an example of a VI characteristic. It is a figure which shows an example of a DC system. It is a figure of an example which shows the output current of a terminal converter, and the voltage distribution of a DC system. It is a figure of an example which shows the output current of a terminal converter, and the voltage distribution of a DC system.

Embodiment 1 FIG.
<Configuration>
FIG. 1 is a block diagram illustrating an example of a configuration of a DC converter control device 2 according to the first embodiment and its periphery. In the direct current system to be monitored and controlled, the direct current cable 1 has an AC / DC converter that mutually interchanges power with another alternating current system, and a DC / DC that mutually interchanges power with another direct current system. The converter is linked. In addition, the DC cable 1 is linked to at least one terminal converter that interchanges power with the load facility. Further, at least one terminal converter for mutual interchange of electric power with the power generation facility is linked to the DC cable 1. For this reason, in FIG. 1, although it is set as four units | sets, the terminal converter A to the terminal converter D, it is not restricted to this.

  The control device 2 of the DC converter is connected to each terminal converter via a communication network such as optical communication, metal communication, and wireless communication. In the control device 2 of the DC converter, for example, a database expressed as DB is a storage device, and a portion expressed as the remaining part is an arithmetic device, and inputs and outputs via a communication network. .

  The output record acquisition unit 12 receives the output current record (output current value) sent from each terminal converter and records it in the output record DB 13.

  The weather condition acquisition unit 11 acquires weather information such as weather, temperature, and humidity as factors related to the current value flowing in or out of the load facility and power generation facility connected to the DC system, and records them in the output result DB 13.

  The output current assumption unit 14 extracts a plurality of time sections of the season, time zone, weather, temperature, and humidity that are the same or similar conditions as the current condition from the output record DB 13, and records each terminal in each time section. The output current value of the converter is set as one combination pattern of output currents that can be assumed from the present. Therefore, combination patterns are generated by the number of extracted time sections.

  For each combination pattern of the output current assumption unit 14, the current distribution calculation unit 15 determines each DC cable section (terminal converter and unit) from the output current value of each terminal converter and the system topology recorded in the system facility DB 16. The value of the current that flows for each unit) is calculated.

  The voltage difference calculation unit 17 determines the DC cable according to Ohm's law from the current value set for each combination pattern and each DC cable section and the line impedance value for each DC cable section recorded in the system facility DB 16. The voltage change width that occurs in the section (voltage rise width / voltage drop width at both ends of the section) is calculated.

  For each combination pattern, the voltage distribution determination unit 18 makes the voltage at the point (terminal converter or system branch point) in the DC system determined to have the highest voltage as a result of the voltage difference calculation match the upper limit voltage. Next, the voltage distribution of the DC system is determined.

  The voltage dispersion calculation unit 19 recalculates the voltage values for each terminal converter from the voltage distribution for each combination pattern determined by the voltage distribution determination unit 18, and calculates the variance of the frequency distribution. Therefore, the voltage value for each point is totaled by the number of combination patterns.

  The constant voltage control determination unit 20 selects a terminal converter having the narrowest distribution, that is, the smallest statistical variance value among the distributions calculated by the voltage frequency calculation unit. In the example of FIG. 1, the terminal converter D is selected.

  The target voltage determination unit 21 selects a minimum voltage value from the voltage frequency distribution of the terminal converter selected by the constant voltage control determination unit 20 and uses the minimum voltage value as a constant voltage control (FIG. 1). In the example, it is set as the target voltage value of the terminal converter D).

  For the terminal converter (terminal converter D) selected for the constant voltage control, the control mode / target voltage distribution unit 22 is set to the target voltage set by the target voltage determination unit 21 in the constant voltage control mode. Send a command to control. Other terminal converters (terminal converters A to C in the example of FIG. 1) are not controlled by the present invention, and are controlled so as to have a separate target current (regardless of the control method). ) Send a command to control in constant current control mode.

<Operation>
FIG. 2 is a flowchart showing an example of the operation of the data acquisition processing flow by the output record acquisition unit 12 and the weather condition acquisition unit 11 in the control device 2 of the DC converter. The operation of the process shown in FIG. 2 starts at a constant cycle that matches a communication cycle (for example, a 10-minute cycle) between the terminal converter in the DC system and the control device 2 of the DC converter.

  In step S11, the output record acquisition unit 12 receives the current output current value (output current record) for each terminal converter measured by each terminal converter.

  In step S12, the output record obtaining unit 12 stores the received individual output current values in the output record DB 13. When the output current value is stored in the output record DB 13, the output current value is stored at the time corresponding to the reception time and the location of the terminal converter ID corresponding to the terminal converter of the reception source. In other words, the output record acquisition unit 12 stores the output current value and the measurement time in the output record DB 13 for each terminal converter ID. Note that the ID is an identification number.

  In step S13, the weather condition acquisition unit 11 includes, for example, current weather (sunny, cloudy, rain, snow, etc.), current temperature, current humidity, and the like from an external weather information providing system (not shown). Receive current weather information. Here, the present is the latest information available. The weather information may be obtained by installing a sunshine meter, a pyranometer, a temperature / humidity meter or the like in the vicinity of the DC system, not from the weather information providing system.

  In step S <b> 14, the weather condition acquisition unit 11 stores the received weather information in the time corresponding to the reception time and the location of the corresponding weather condition item in the output record DB 13.

  FIG. 3 is a diagram illustrating an example of the data structure of the output result DB 13. Along with weather conditions such as weather, temperature, and humidity, these are current values measured for each terminal converter ID in time series. The output current and phase condition from the terminal converter are accumulated as time series data. The output current is expressed with positive and negative signs. In this example, the direction in which current flows into the DC system is positive, and the direction in which current is extracted from the DC system is negative.

  FIG. 4 shows an output current estimator 14, a current distribution calculator 15, a voltage difference calculator 17, a voltage distribution determiner 18, a voltage dispersion calculator 19, a constant voltage control determiner 20, in the DC converter controller 2. 10 is a flowchart showing an example of an operation of a constant voltage control converter determination processing flow by the target voltage determination unit 21 and the control mode / target voltage distribution unit 22. This flow processing operation may be performed in a predetermined cycle (for example, one hour cycle), or triggered by a change in current weather conditions or a significant change in the output current of each terminal converter. It may be activated.

  In step S201, the output current assumption unit 14 acquires the latest weather information from the output record DB 13.

  In step S202, the output current assumption unit 14 selects the output current assumption unit 14 from the series of time sections recorded in the output record DB 13 in the same season, day of the week, and time zone (for example, 10: 0 to 100). 11:00) and a time section corresponding to the weather condition (meteorological state) similar to the latest weather information is selected.

  Whether the weather condition is similar, for example, in the weather, if the present is clear, the clear and cloudy with the same amount of sunshine is similar, and if the current is cloudy, the clear, cloudy and rain are similar, and the present is In the case of rain, it can be considered that clouding with little sunlight and rain are considered similar. Further, regarding the temperature, for example, it is conceivable that the current temperature is within ± 3 ° C. In terms of humidity, for example, it may be considered that the current humidity is within ± 10% as similar.

  In step S203, the output current assumption part 14 sets the combination pattern of the output current values of each terminal converter of the selected time section as the assumed current. In other words, the output current assumption unit 14 acquires the output current value of each terminal converter from the output record DB 13 for each selected time section, and sets the assumed current of each terminal converter as a set of combination patterns.

  For example, the current time is immediately before 10:00, the weather is sunny or cloudy as the latest weather situation, the temperature is 5 ° C., the humidity is 30%, and the voltage is constant between 10:00 and 11:00. When it is desired to determine the terminal converter and its target voltage, all the time sections that meet the conditions are extracted from the output record DB 13 illustrated in FIG. 3, and the output current of the terminal converter of each time section is calculated. It is set as a set of combination patterns as shown in FIG. In FIG. 5, the assumed current of the terminal converter ID (A to D in this example) is obtained for each combination pattern ID.

  In step S <b> 204, the current distribution calculation unit 15 acquires one set of unprocessed assumed current combination patterns.

  In step S205, the current distribution calculation unit 15 determines each section of the DC cable (delimited by the terminal converter and the system branch point) from the output current of the terminal converter of the acquired combination pattern and the system topology recorded in the system facility DB 16. The value of the current that flows for each unit of the direct current cable 1 is calculated. In other words, the current distribution calculation unit 15 calculates the passing current from the output current of the terminal converter and the system topology for each DC cable section.

  FIG. 6 is a diagram illustrating an example of the data structure of the system facility DB 16. The DC system is expressed as a node corresponding to a terminal converter or a system branch point and a branch connecting the nodes, that is, a DC cable section. In each node, the ID of the equipment, the upper limit voltage, the lower limit voltage, and the rated current of the converter in the case of a terminal converter are recorded. In each branch, node IDs and line impedances at both ends are recorded in the system facility DB 16.

  FIG. 7 is a diagram illustrating an example of a calculation result of the current distribution calculation unit 15. 6 is a result of calculating a branch ID (each branch), that is, a current flowing in a DC cable section, from the node / branch data representing the system topology of FIG. 6 for each combination pattern ID of FIG. Here, the current flowing in the opposite direction to the node 1 (terminal converter A) is a positive value, and the current flowing toward the node 1 is a negative value.

  The current flowing through each branch is calculated by adding and subtracting the output current of each terminal converter. For example, in the case of the combination pattern 1, since only the output current + 900A from the terminal converter A flows in the branch 1, (+ 900A). Only the output current −300 A of the terminal converter B flows through the branch 2 (+300 A). In branch 3, (+ 900A) from branch 1 is diverted to branch 2 (+ 300A), so (+ 900A) − (+ 300A) = (+ 600A) is calculated.

  In step S206, the voltage difference calculation unit 17 determines the voltage change width generated in the branch, that is, the direct current, from the current flowing in each branch calculated in step S25 and the line impedance value of the branch recorded in the system facility DB 16. Calculate the voltage rise width or voltage drop width at both ends of the cable section. In other words, the voltage difference calculation unit 17 calculates the voltage change width from the passing current and the line impedance for each DC cable section.

  FIG. 8 is a diagram illustrating an example of a calculation result of the voltage difference calculation unit 17. The voltage difference was calculated for each branch in FIG. 7 according to Ohm's law, with “voltage difference between two points (V) = current flowing between two points (A) × resistance between two points (Ω)”. The voltage difference is calculated by multiplying the current value by the line impedance value of FIG. Here, based on the voltage value of node 1 (terminal converter A), the direction in which the voltage increases is a positive value, and the direction in which the voltage decreases is a negative value. For example, since the current flowing in the branch 1 of the combination pattern 1 is (+900 A) from the node 1 to the node and the impedance is 10Ω, the voltage drops by 900 × 10 = 9000 V = 9 kV when viewed from the node 1. Therefore, it is −9 kV.

  In step S207, the voltage distribution determination unit 18 calculates a voltage difference between each node and the reference point for each node from the calculation result in step S206 using any node as a reference point. In other words, the voltage distribution determining unit 18 calculates a voltage difference between the reference point in the direct current and each point.

  FIG. 9 is a diagram illustrating an example of a calculation result of the voltage distribution determination unit 18. Node 1 is the reference point. It is obtained by adding the voltage difference (calculation result in FIG. 8) in each branch of the path from the node 1 to each node. For example, since the terminal converter D (branch 5) in the combination pattern 1 passes through the branch 1, branch 3, and branch 5 from the terminal converter A, the voltage difference with the terminal converter A is (−9 kV) + (−12 kV) + (− 6 kV) = − 27 kV.

  In step S208, the voltage distribution determination unit 18 specifies the node with the highest voltage (the highest voltage node) from the calculation result of the voltage difference between each node and the reference node in step S207, and the node with the highest voltage (the highest voltage node). The voltage value of each node is calculated by the following calculation formula so that the voltage of) matches the upper limit voltage. In other words, the voltage distribution determining unit 18 determines the voltage distribution so that the voltage at the highest voltage matches the upper limit voltage.

  That is, each node voltage = (voltage difference from the reference node) + (upper limit voltage−voltage difference between the highest voltage node and the reference node).

  FIG. 10 is a diagram illustrating an example of the calculation result of step S208. For example, in the combination pattern 1, in the result of FIG. 9, since the voltage of the node 1 is the highest, the highest voltage node is the node 1. Therefore, the voltage at each node is calculated so that the voltage at node 1 matches the upper limit voltage 700 kV in FIG. For example, in the node 2, (−9 kV) + (700 kV−0 kV) = 691 kV. As another example, in the combination pattern 2, the node 6 has the highest voltage in the result of FIG. Therefore, the voltage of the node 2 is (−9 kV) + (700 V − (+ 19 kV)) = 672 kV.

  In step S209, it is determined whether or not the process has been completed for all the assumed current combination patterns set in step S203. If completed, the process proceeds to step S210, and if not completed, the process proceeds to step S204.

  In step S210, the voltage dispersion calculation unit 19 acquires the voltage value of the voltage distribution calculation result determined in step S208 from all the combination patterns set in step S203 for each node corresponding to the terminal converter, A standard deviation (or a variance value that is a square value thereof) is obtained as the degree of spread of the frequency distribution. In other words, the voltage dispersion calculating unit 19 calculates and ranks the voltage distribution through all combination patterns for each terminal converter.

  For example, from the result of FIG. 10, the voltages of the node 1 corresponding to the terminal converter A are 700 kV, 681 kV, 685 kV,..., And the voltage of the node 5 corresponding to the terminal converter C is 678. Voltages of .7 kV, 683.7 kV, 688 kV,.

  FIG. 11 is a diagram illustrating an example of a voltage dispersion calculation result. It is replaced with a frequency distribution graph, and the standard deviation is obtained for each terminal converter as an indicator of the extent of dispersion. In this example, since the standard deviation of the terminal converter C is the smallest at 2.5V, the peak of frequency is the sharpest. On the other hand, since the standard deviation of the terminal converter D is the largest at 9.5V, the frequency peak is the smoothest.

  FIG. 12 is a diagram illustrating an example of a voltage distribution determination result in which the terminal converters are ordered in ascending order of the standard deviation and the standard deviation of the distribution and the minimum voltage (minimum voltage) in the distribution are listed.

  In step S211, the constant voltage control determining unit 20 determines that the terminal converter having the smallest spread of the voltage frequency distribution, that is, the standard deviation or the smallest variance value as a result of step S210, is the constant voltage control. Select as In other words, the constant voltage control determining unit 20 selects the converter having the smallest distribution spread as the constant voltage control.

  In step S212, the target voltage determination unit 21 extracts the voltage distribution of the constant voltage control selected in step S211 from the voltage distribution obtained in step S210, and sets the minimum voltage of the selected constant voltage control distribution as the target voltage. Set as. In other words, the target voltage determination unit 21 sets the voltage distribution minimum value of the terminal converter (the terminal converter) selected for the constant voltage control as the target voltage.

  In this way, the input / output current of each terminal converter and the current distribution case of the DC system are comprehensively assumed, and the voltage maximum point is obtained by calculating the voltage difference between the terminals for each assumed case. The voltage distribution of the assumed case is set so that the voltage at that point is in contact with the upper limit voltage value, and the terminal converter in which the connection point voltage is concentrated to the most arbitrary voltage value through all the assumed cases It will be selected as a converter.

  In step S213, the control mode / target voltage distribution unit 22 uses the constant voltage control mode so that the terminal converter selected for constant voltage control in step S211 has the target voltage set in step S212. It transmits so that it may drive | operate, and it transmits so that it may drive | operate with a constant electric current control mode with respect to another terminal converter. In other words, the control mode / target voltage distribution unit 22 transmits the control mode to each terminal converter and the target voltage to the terminal converter of constant voltage control.

  As a result, by fixing the maximum value of the voltage frequency distribution as the target voltage, it is possible to maintain as high a voltage as possible and reduce power loss as much as possible without causing an upper limit deviation in any assumed case.

  In the example of the present embodiment, the current and voltage difference flowing in each branch are simply calculated by simple four arithmetic operations. For example, the line loss, ground capacitance, terminal conversion of the DC cable 1 is more accurately performed. You may calculate by the convergence calculation etc. which considered the change of the electric current and voltage by the conversion loss etc. of a device.

  In this way, the DC converter control device selects a terminal converter for constant voltage control and determines its target voltage in a DC system including at least two terminal converters linked to the terminals of the DC cable. Output current assumption part that sets the combination pattern of output current that can be assumed for each terminal converter, and current distribution calculation part that calculates the passing current for each DC cable in the DC system from the result of the output current assumption for each pattern And the voltage difference calculation part that calculates the voltage rise / drop width for each DC cable from the result of current distribution calculation for each pattern, and the point where the voltage is highest in the DC system from the voltage difference calculation result for each pattern, A voltage distribution determining unit that determines the voltage distribution of the DC system so that the voltage at that point matches the upper limit voltage of the DC system, and the voltage value for each terminal converter from the voltage distribution of all patterns. Voltage distribution calculation unit that calculates the spread of the number distribution, and terminal converters in order of narrow voltage frequency distribution, that is, the spread of the frequency distribution is as small as possible, and terminal converter candidates with the higher terminal converter as constant voltage control Since the selection is made, it is possible to select a terminal converter that performs constant voltage control so that the voltage distribution can be maintained as close to the upper limit as possible in various assumed current distributions. Further, as a result of maintaining the voltage at a high level, when the same power is sent, the current can be reduced, so that the power loss substantially proportional to the square of the current can be reduced.

  In addition, an output result DB for accumulating the output current results of the respective terminal converters for each time section is provided, and the output current assumption unit determines the combination of the output currents of the respective terminal converters in one time section of the past predetermined period as one. Since it is set as a combination pattern of two output currents, a current distribution can be easily assumed from past results.

  Furthermore, the output current assumption unit matches weather conditions such as weather, temperature, and humidity that are expected between the start time and the end time, which are targets for determining the terminal converter to be controlled at a constant voltage from the output record DB or Similar, select only the time section that matches the time conditions such as season, day of the week, and time of day, and combine the output current of each terminal converter in the selected individual time section with one output current combination pattern Therefore, it is possible to assume a highly accurate current distribution according to weather conditions and time.

  As described above, the control device for the DC converter is assumed to be an acquisition unit that acquires output currents of a plurality of terminal converters connected to terminals of a DC cable in the DC system, and to each terminal converter for each time section. Output current assumption unit that sets a combination pattern of output currents, a current distribution calculation unit that calculates the distribution of passing current for each section of the DC cable, and a voltage difference that rises or falls from distribution to section for each combination pattern The voltage difference calculation unit that calculates the voltage, and the voltage that determines the voltage distribution of the DC system so that the highest point with the highest voltage is extracted from the voltage difference for each combination pattern and the voltage at the highest point matches the upper limit voltage of the DC system A distribution determination unit, a voltage distribution calculation unit that calculates the variance of the voltage value for each terminal converter from the voltage distribution of all combination patterns, and one terminal converter that performs constant voltage control using the value of the variance are determined. Constant voltage A control determination unit, and a target voltage distribution unit that distributes the target voltage to the remaining terminals converter.

  In addition, the control device for the DC converter includes an output record database that stores the output current record for each terminal converter for each time section. Further, the output record database stores the record in association with the weather condition, and the output current assumption unit outputs the output current for each terminal converter using at least one of the weather condition and the time section condition in the output record database. The combination pattern is set.

  Further, the constant voltage control determining unit determines the terminal converter having the smallest dispersion value for the constant voltage control.

  According to this embodiment, in the current distribution assumed in the DC system, the voltage distribution of the entire DC system can be maintained high. As a result, when the same power is interchanged between the terminal converters, the value of the current flowing through the DC system can be reduced, so that power loss can be reduced.

Embodiment 2. FIG.
<Configuration>
FIG. 13 is a block diagram illustrating an example of a control device for a DC converter according to the second embodiment and a peripheral configuration thereof. The difference from the first embodiment is that a current likelihood calculation unit 23 is added. Since the other configuration is the same as that described in the first embodiment, the description thereof is omitted.

  The current likelihood calculation unit 23 extracts a maximum current value having the maximum absolute value from the output current values for each terminal converter among all the combination patterns assumed by the output current assumption unit 14. Compared with the rated current recorded in the system facility DB 16, the current likelihood of the terminal converter is calculated.

  In the drawings, the same reference numerals denote the same or corresponding parts, and this is common to the entire text of the specification and all the drawings. Furthermore, the forms of the constituent elements appearing in the entire specification are merely examples and are not limited to these descriptions. Only differences from the first embodiment will be described below.

<Operation>
Since the operation of the data acquisition processing flow by the output record acquisition unit 12 and the weather condition acquisition unit 11 in the control device 2 of the DC converter is the same as that of the first embodiment, the description thereof is omitted.

  FIG. 14 shows an output current assumption unit 14, a current likelihood calculation unit 23, a current distribution calculation unit 15, a voltage difference calculation unit 17, a voltage distribution determination unit 18, a voltage dispersion calculation unit 19, in the DC converter control device 2. 10 is a flowchart showing an example of an operation of a constant voltage control converter determination processing flow by the constant voltage control determination unit 20, the target voltage determination unit 21, the control mode / target voltage distribution unit 22, and the current likelihood calculation unit 23. Steps S212 to S210, step S212 and step S213 are the same as the steps in FIG.

  In step S301, the current likelihood calculation unit 23 outputs an output current value having the maximum absolute value for each terminal converter from among a plurality of output current values for each terminal converter assumed by the output current estimation unit 14. To extract. The difference between the extracted maximum current value and the absolute value of the rated current recorded in the system facility DB 16 is calculated as the current likelihood of the terminal converter, assuming that there is an additional output margin from the assumed current.

  Further, a value obtained by dividing the difference between the maximum current value and the absolute value of the rated current recorded in the system facility DB 16 by the absolute value of the rated current may be used as the current likelihood. In this case, it becomes an index of what percentage of output margin is further in the rated ratio. In any case, the current likelihood calculation unit 23 calculates the current likelihood from the maximum value of the assumed current for each terminal converter.

  In step S302, the voltage constant control determining unit 20 determines that the current likelihood is equal to or greater than a predetermined value and the spread of the voltage frequency distribution is the smallest, that is, the standard deviation or the variance value is the smallest, based on the results of steps S210 and S301. The selected terminal converter is selected as a terminal converter with constant voltage control. It is conceivable that the predetermined value of the current likelihood is calculated based on an expected off track record from a past assumed current. In other words, the constant voltage control determination unit 20 selects a converter having a current likelihood equal to or greater than a predetermined value and the smallest spread of distribution for the constant voltage control.

  FIG. 15 is a diagram illustrating an example of calculation results of the voltage dispersion calculation unit 19 and the current likelihood calculation unit 23. In this example, since the terminal converter C having the highest rank has a sufficient current likelihood, the terminal converter C is selected for constant voltage control. However, if the current likelihood of the terminal converter C is small (for example, 100A or less), the terminal converter B which is the next order is selected for constant voltage control.

  As described above, the current value having the maximum current absolute value is extracted from the plurality of output currents for each terminal converter assumed by the output current assumption unit 14 and compared with the rated current of the terminal converter, thereby converting the terminal conversion. A current likelihood calculation unit 23 for calculating a current likelihood up to a rated current for each unit, and the voltage constant control determination unit 20 has a current likelihood of a predetermined value or more and a narrow voltage frequency distribution, that is, a frequency distribution. Since a terminal converter with a small spread is selected as a terminal converter candidate for constant voltage control, it is possible not only to reduce power loss but also to avoid converter overload.

  As described above, the control device for the DC converter is assumed to be an acquisition unit that acquires output currents of a plurality of terminal converters connected to terminals of a DC cable in the DC system, and to each terminal converter for each time section. Output current assumption unit that sets a combination pattern of output currents, a current distribution calculation unit that calculates the distribution of passing current for each section of the DC cable, and a voltage difference that rises or falls from distribution to section for each combination pattern The voltage difference calculation unit that calculates the voltage, and the voltage that determines the voltage distribution of the DC system so that the highest point with the highest voltage is extracted from the voltage difference for each combination pattern and the voltage at the highest point matches the upper limit voltage of the DC system A distribution determination unit, a voltage distribution calculation unit that calculates the variance of the voltage value for each terminal converter from the voltage distribution of all combination patterns, and one terminal converter that performs constant voltage control using the value of the variance are determined. Constant voltage A control determination unit, and a target voltage distribution unit that distributes the target voltage to the remaining terminals converter.

  Also, the DC converter controller extracts the maximum current value with the maximum absolute value from the output current for each terminal converter, and compares the rated current and maximum current of the terminal converter to convert the terminal. A current likelihood calculating unit for calculating a current likelihood up to a rated current for each unit; Further, the constant voltage control determining unit determines the terminal converter having the smallest variance value in the current likelihood being equal to or greater than a predetermined value for the constant voltage control.

  According to this embodiment, even when a current exceeding the current distribution assumed in the DC system flows through the terminal converter, the voltage distribution of the entire DC system is reduced without causing an overload to the terminal converter. Highly maintainable.

Embodiment 3 FIG.
<Configuration>
FIG. 16 is a block diagram showing an example of the DC converter control device 2 according to the third embodiment and its peripheral configuration. The difference from the first embodiment is that a voltage / current correspondence setting unit 24 is added, the VI characteristic determining unit 25 is replaced with the target voltage determining unit 21, and the control mode / target voltage distributing unit 22 is replaced with the control mode. The V-I characteristic distribution unit 26 is. Only differences from the first embodiment will be described below.

  The voltage / current correspondence setting unit 24 determines, for each combination pattern, the connection point voltage value for each terminal converter and the assumed output of the terminal converter in the combination pattern from the voltage distribution determined by the voltage distribution determination unit 18. The current value is extracted.

  The V-I characteristic determination unit 25 outputs a voltage and a voltage to the terminal converter selected by the constant voltage control determination unit 20 among the connection point voltage and the assumed output current extracted by the voltage / current correspondence setting unit 24. An approximate line indicating a correlation with the current is calculated as a VI characteristic (relationship between voltage and current).

  The control mode / VI characteristic distribution unit 26 outputs the output voltage to the terminal converter selected for the constant voltage control in the constant voltage control mode according to the VI characteristic set by the VI characteristic determination unit 25. A command is sent to control other terminal converters, and the command is sent to control in a constant current control mode in which the current is controlled to be the target current by some method regardless of the present invention. . The terminal converter other than the terminal converter selected for the constant voltage control is not limited as long as it is a control method for controlling the terminal current to be the target current. Since the configuration other than these is the same as that of the first embodiment, the description thereof is omitted.

<Operation>
Since the operation of the data acquisition processing flow by the output record acquisition unit 12 and the weather condition acquisition unit 11 in the control device 2 of the DC converter is the same as that of the first embodiment, the description thereof is omitted.

  FIG. 17 shows an output current assumption unit 14, a current likelihood calculation unit 23, a current distribution calculation unit 15, a voltage difference calculation unit 17, a voltage distribution determination unit 18, a voltage dispersion calculation unit 19, in the control device 2 for the DC converter. An example of the operation of the constant voltage control converter determination processing flow by the constant voltage control determining unit 20, the voltage / current correspondence setting unit 24, the VI characteristic determining unit 25, and the control mode / VI characteristic distributing unit 26 is shown. It is a flowchart. Steps S201 to S208 and steps S209 to S21 1 are the same as the steps in FIG.

  In step S401, the voltage / current correspondence setting unit 24 extracts the connection point of the terminal converter, that is, the voltage value of the corresponding node in the voltage distribution determined in step S208, and the same terminal in the combination pattern at that time. The output current value of the converter is set as one voltage / current combination. Therefore, finally, the combination of voltage and current extracted for each terminal converter is the same as the number of combination patterns. In other words, the voltage / current correspondence setting unit 24 sets the combination of the voltage and current of each terminal converter.

  FIG. 18 is a diagram illustrating an example of combinations of current and voltage set for each terminal converter in step S401. For example, in the combination pattern 1, as a result of trying to maintain the DC system voltage as high as possible in Step S208, the voltage of the terminal converter C becomes 678.7 kV, and the assumed output current at that time is -300A. Means that.

  In step S403, the VI characteristic determination unit 25 obtains an approximate line from the current / voltage combination set in step 401 for the terminal converter determined in step S211 to be constant voltage control, and determines the VI. Set as a characteristic. In other words, the VI characteristic determining unit 25 determines an approximate line from a plurality of current / voltage combinations of the terminal converter selected for the constant voltage control, and sets the VI characteristic.

  FIG. 19 is an image diagram showing an example of a combination of an assumed current and a connection point voltage and a VI characteristic. The horizontal axis represents current, the vertical axis represents voltage, and each small point represents the one set of currents.・ It means voltage. For all points, an approximate line with the converter rated current at both ends is obtained, and this is taken as the VI characteristic of the converter. The approximate line may be linear approximation or linear approximation as shown in FIG.

  For example, the target voltage of the terminal converter for constant voltage control is, for each pattern, the connection point voltage of the terminal converter in the voltage distribution determined by the voltage distribution determining unit 18 and the output current of the converter assumed at that time. In addition, the combination of the connection point voltage and the output current of all patterns is plotted on a two-dimensional graph of voltage and current, and the VI characteristic is determined by the approximate line. 25. The target voltage is not fixed, but is variable according to the output current.

  In step S404, the control mode / VI characteristic distributing unit 26 applies the constant voltage control mode to the terminal converter selected for constant voltage control in step S211 according to the VI characteristic set in step S403. It transmits to drive | operate with, and it transmits so that it may drive | operate with a constant electric current control mode with respect to another terminal converter. In other words, the control mode / VI characteristic distribution unit 26 transmits the control mode to each terminal converter and the VI characteristic to the terminal converter with constant voltage control.

  As described above, the control device for the DC converter is assumed to be an acquisition unit that acquires output currents of a plurality of terminal converters connected to terminals of a DC cable in the DC system, and to each terminal converter for each time section. Output current assumption unit that sets a combination pattern of output currents, a current distribution calculation unit that calculates the distribution of passing current for each section of the DC cable, and a voltage difference that rises or falls from distribution to section for each combination pattern The voltage difference calculation unit that calculates the voltage, and the voltage that determines the voltage distribution of the DC system so that the highest point with the highest voltage is extracted from the voltage difference for each combination pattern and the voltage at the highest point matches the upper limit voltage of the DC system A distribution determination unit, a voltage distribution calculation unit that calculates the variance of the voltage value for each terminal converter from the voltage distribution of all combination patterns, and one terminal converter that performs constant voltage control using the value of the variance are determined. Constant voltage A V-I characteristic determining unit that determines a V-I characteristic from a combination of a connection point voltage of the terminal converter in the voltage distribution for each combination pattern and an assumed output current of the terminal converter; A VI characteristic distribution unit that distributes a target voltage obtained from the VI characteristic according to the output current of the terminal converter.

  According to the present embodiment, the voltage distribution of the DC system can be maintained higher depending on the situation by changing the target voltage of the terminal converter of constant voltage control up and down according to the output current.

  The present invention is not limited to the embodiments described so far, and can be variously modified within the scope of the present invention. That is, the configuration of the embodiment described so far may be improved as appropriate, and at least a part of the configuration may be replaced with another configuration. Furthermore, the constituent elements that are not particularly limited with respect to the arrangement are not limited to the arrangement disclosed in the embodiment, and can be arranged at positions where the functions can be achieved. Further, the present invention may be formed by appropriately combining a plurality of constituent elements disclosed in the embodiments described above. Further, the present invention is shown not by the scope of the embodiments described so far but by the scope of the claims, and includes all modifications within the meaning and scope equivalent to the scope of the claims.

  DESCRIPTION OF SYMBOLS 1 DC cable, 2 Control apparatus, 11 Weather condition acquisition part, 12 Output results acquisition part, 13 Output results DB, 14 Output current assumption part, 15 Current distribution calculation part, 16 System equipment DB, 17 Voltage difference calculation part, 18 Voltage Distribution determination unit, 19 voltage dispersion calculation unit, 20 constant voltage control determination unit, 21 target voltage determination unit, 22 control mode / target voltage distribution unit, 23 current likelihood calculation unit, 24 voltage / current correspondence setting unit, 25 V− I characteristic determination unit, 26 control mode / VI characteristic distribution unit.

Claims (6)

An acquisition unit for acquiring output currents of a plurality of terminal converters connected to terminals of a DC cable in the DC system;
An output current assumption unit that sets a combination pattern of the output current assumed for each terminal converter for each time section;
A current distribution calculation unit for calculating a distribution of passing current for each section of the DC cable;
A voltage difference calculation unit for calculating a voltage difference of ascending or descending for each of the sections from the distribution for each combination pattern;
A voltage distribution determining unit that extracts the highest point of the highest voltage from the voltage difference for each combination pattern and determines the voltage distribution of the DC system so that the voltage at the highest point matches the upper limit voltage of the DC system; ,
A voltage dispersion calculation unit for calculating a dispersion of voltage values for each of the terminal converters from the voltage distribution of all the combination patterns;
A constant voltage control determining unit for determining one of the terminal converters to be a constant voltage control using the value of the dispersion;
A control apparatus for a DC converter, comprising: a target voltage distribution unit that distributes a target voltage to the remaining terminal converters. An acquisition unit for acquiring output currents of a plurality of terminal converters connected to terminals of a DC cable in the DC system;
An output current assumption unit that sets a combination pattern of the output current assumed for each terminal converter for each time section;
A current distribution calculation unit for calculating a distribution of passing current for each section of the DC cable;
A voltage difference calculation unit for calculating a voltage difference of ascending or descending for each of the sections from the distribution for each combination pattern;
A voltage distribution determining unit that extracts the highest point of the highest voltage from the voltage difference for each combination pattern and determines the voltage distribution of the DC system so that the voltage at the highest point matches the upper limit voltage of the DC system; ,
A voltage dispersion calculation unit for calculating a dispersion of voltage values for each of the terminal converters from the voltage distribution of all the combination patterns;
A constant voltage control determining unit for determining one of the terminal converters to be a constant voltage control using the value of the dispersion;
A VI characteristic determination unit that determines a VI characteristic from a combination of the connection point voltage of the terminal converter in the voltage distribution for each combination pattern and the output current of the terminal converter assumed;
A control device for a DC converter, comprising: a VI characteristic distribution unit that distributes a target voltage obtained from the VI characteristic according to the output current of the terminal converter. A control device for a DC converter according to claim 1 or 2,
A control device for a DC converter, comprising an output record database for storing the record of the output current for each of the terminal converters for each time section. A control device for a DC converter according to claim 3,
The output results database accumulates the results in association with weather conditions,
The output current assumption unit sets the combination pattern of the output current for each of the terminal converters using at least one of the weather condition and the time section condition in the output record database. Control device for DC converter. A control device for a DC converter according to claim 1,
The maximum current value having the maximum absolute value is extracted from the output current for each terminal converter, and the rated current for each terminal converter is compared with the rated current of the terminal converter and the maximum current. A current likelihood calculation unit for calculating the current likelihood until
The constant voltage control determination unit determines the terminal converter that has the smallest value of the variance as the current likelihood is equal to or greater than a predetermined value as the constant voltage control device. . A control device for a DC converter according to any one of claims 1 to 5,
The constant voltage control determination unit determines the terminal converter having the smallest value of the variance as the constant voltage control.

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