JP7542925B2 - Control device - Google Patents

Description

An embodiment of the present invention relates to a control device for a power converter.

Direct current (DC) transmission systems have been attracting attention for their efficient transmission of power and for connecting AC systems with different frequencies. A bipolar DC transmission system is known as a DC transmission method that can be operated with high availability.

In a bipolar DC transmission system, one of the two poles is selected for operation at the sending end or receiving end, allowing the system to continue operating without being shut down even during regular or irregular inspections or repairs in the event of a malfunction.

In addition, by operating two poles simultaneously, it becomes possible to transmit and receive large amounts of power, and by appropriately selecting the direction of the current in the two poles, it becomes possible to transmit and receive power over a wide range.

On the other hand, it is known that the transmitted and received power fluctuates transiently when one pole is started or stopped, or when the current direction is reversed. In order to reduce the power fluctuations when one pole is started or stopped, or when the current direction is reversed, transient fluctuation suppression measures are sometimes adopted, but there is an increasing demand to further suppress the fluctuations in order to respond to the increasing sophistication of power networks that come with disaster response and the diversification of local power sources.

Japanese Patent Application Publication No. 3-112322

The embodiment provides a control device that suppresses power fluctuations when starting, stopping, or reversing the power flow of one pole.

A control device according to an embodiment is used in a bipolar DC power transmission system having two DC systems provided between two AC systems, a first converter provided between one of the two DC systems and one of the two AC systems, and a second converter provided between the other of the two DC systems and one of the AC systems, and controls a total DC power output by the first converter which performs bidirectional power conversion between one of the DC systems and one of the AC systems, and the second converter which performs bidirectional power conversion between the other DC system and one of the AC systems , so as to follow a preset power setting value. This control device includes a bipolar common control circuit that generates a first power setting value for the first converter and a second power setting value for the second converter based on the power setting values; a first pole control circuit that controls the first converter so that a first DC power output by the first converter follows the first power setting value, calculates a measurement value of the first DC power by multiplying a line-to-line DC voltage of the one DC system detected by a first voltage detector by a current value of the one DC system detected by a first current detector, and transmits the measurement value of the first DC power to the bipolar common control circuit ; and a second pole control circuit that controls the second converter so that a second DC power output by the second converter follows the second power setting value, calculates a measurement value of the second DC power by multiplying a line-to-line DC voltage of the other DC system detected by a second voltage detector by a current value of the other DC system detected by a second current detector, and transmits the measurement value of the second DC power to the bipolar common control circuit . The bipolar common control circuit calculates the first power set value and the second power set value so that the sum of the first power set value and the second power set value becomes the power set value, changes the value of the first power set value , and at a first time when the first power set value is increased, decreased, or the flow direction is reversed , calculates a new second power set value by subtracting the measured value of the first DC power from the power set value, thereby calculating the new second power set value so that the sum of the first DC power and the second DC power becomes equal to the power set value, and transmits the calculated new second power set value to the second pole control circuit, thereby causing the second pole control circuit to control the second converter to make the second DC power follow the new second power set value .

In this embodiment, a control device is provided that suppresses power fluctuations when one pole is started, stopped, or the power flow is reversed.

FIG. 2 is a schematic block diagram illustrating a bipolar common control device according to an embodiment. FIG. 1 is a schematic block diagram illustrating a DC power transmission system. 3(a) and 3(b) are schematic block diagrams illustrating a comparative bipolar common control device. FIG. 11 is an operational waveform diagram illustrating a typical example for explaining the operation of a bipolar common control device of a comparative example. FIG. 4 is an operational waveform diagram illustrating a bipolar common control device according to the embodiment; FIG. 11 is an operational waveform diagram illustrating a typical example for explaining the operation of a bipolar common control device of a comparative example. FIG. 4 is an operational waveform diagram illustrating a typical example for explaining the operation of the bipolar common control device according to the embodiment. FIG. 11 is an operational waveform diagram illustrating a typical example for explaining the operation of a bipolar common control device of a comparative example. FIG. 4 is an operational waveform diagram illustrating a typical example for explaining the operation of the bipolar common control device according to the embodiment. FIG. 4 is an operational waveform diagram illustrating a typical example for explaining the operation of the bipolar common control device according to the embodiment.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
The drawings are schematic or conceptual, and the relationship between the thickness and width of each part, the size ratio between parts, etc. are not necessarily the same as in reality. Even when the same part is shown, the dimensions and ratios of each part may be different depending on the drawing.
In this specification and each drawing, elements similar to those described above with reference to the previous drawings are given the same reference numerals and detailed description thereof will be omitted as appropriate.

FIG. 1 is a schematic block diagram illustrating a bipolar common control device according to an embodiment.
1, a bipolar common controller (controller) 10 includes a smoothing control circuit 12. The smoothing control circuit 12 preferably includes a smoothing control inhibit circuit 14.

The bipolar common control device 10 is connected to the pole control devices 31 and 32. The bipolar common control device 10 is connected to a higher-level control device (not shown). The bipolar common control device 10 receives a power setting value Pdp from the higher-level control device. The bipolar common control device 10 receives data on DC power Pd1 transmitted or received (hereinafter referred to as "transmitted") by the first pole and data on DC power Pd2 transmitted by the second pole from the polarity control devices 31 and 32, respectively. The bipolar common control device 10 generates a power setting value Pdp1 for the first pole and a power setting value Pdp2 for the second pole according to the received power setting value Pdp, the output capacity of the converters 21 and 22, the current operating conditions, etc.

In the example described below, the power setting value Pdp is assumed to be supplied from a higher-level control device, but this is not limited to the above. For example, if a bipolar common control device for one terminal of a DC power transmission system is the master and a bipolar common control device for the other terminal is the slave, the master control device may generate a power setting value and transmit it to the slave control device.

The bipolar common control device 10 inputs the power setting values Pdp1, Ppd2 and the DC power Pd1, Pd2 to the smoothing control circuit 12. The smoothing control circuit 12 generates new power setting values Pdp1', Pdp2' based on the data of the power setting values Pdp1, Pdp2 and the DC power Pd1, Pd2.

The smoothing control circuit 12 generates a new power setting when the power setting of one pole changes and the DC power actually output by the converter of that pole changes due to other factors. Specifically, when the power setting of one pole is set to be lowered, increased, or the flow direction is reversed, the bipolar common control device 10 generates and outputs the power setting of the other pole as a new power setting. Needless to say, lowering the power setting includes a setting to stop the converter, and increasing the power setting includes a setting to start the converter.

The bipolar common control device 10 generates new power setting values Pdp1', Pdp2' when there is a change in the power setting value Pdp transmitted by the upper control device, and can generate power setting values Pdp1', Pdp2' at the discretion of the bipolar common control device 10 itself even when there is no change in the power setting value Pdp.

The power setting value Pdp transmitted by the upper control device is a command value having a constant value, and when the upper control device determines that a change in the power setting value Pdp is necessary, it transmits the power setting value Pdp to the bipolar common control device 10. The power setting values Pdp1, Pdp2 and new power setting values Pdp1', Pdp2' generated by the bipolar common control device 10 are generated as time function data that can change with time. The DC powers Pd1, Pd2 being transmitted, etc. are also time function data. The power setting values Pdp1'', Pdp2'' generated by the bipolar common control device 210 in the comparative example described below are also generated as time function data.

As will be described in more detail later, the smoothing control circuit 12 sets the power set value of a pole other than the pole that increases, decreases, or reverses the power set value so that the DC power Pd (= Pd1 + Pd2) output by the converters 21 and 22 becomes the power set value Pdp. The operating state of the other pole is determined according to the actual operating waveform when the power set value of the converter of the pole that increases, decreases, or reverses the power set value increases, decreases, or reverses the power flow direction. Therefore, the required new power set value can be generated by performing the same calculation regardless of the difference in the operation of increasing, decreasing, or reversing the power set value.

The bipolar common control device 10 transmits the generated new power setting values Pdp1' and Pdp2' to the pole control devices 31 and 32, respectively.

The pole control device 31 is connected to the one-pole converter 21 and controls the converter 21. In this example, the pole control device 31 is connected to voltage detectors 51a, 51b and a current detector 61. The voltage detector 51a is provided to detect the DC voltage of the one-pole bus 3F. The voltage detector 51b is provided to detect the DC voltage of the one-pole return line 3R. The current detector 61 detects the one-pole current. Based on the detection results of the voltage detectors 51a, 51b, the pole control device 31 inputs the line-to-line DC voltage Vd1 between the bus 3F and the return line 3R, and multiplies Vd1 by the current value Id1 detected by the current detector 61 to calculate the DC power Pd1. The pole control device 31 transmits the calculated DC power Pd1 data to the bipolar common control device 10.

The pole control device 32 is connected to the two-pole converter 22 and controls the converter 22. In this example, as in the case of one pole, the pole control device 32 is connected to voltage detectors 52a, 52b and a current detector 62. The voltage detector 52a is provided to detect the DC voltage of the two-pole bus 4F. The voltage detector 52b is provided to detect the DC voltage of the two-pole return line 4R. The current detector 62 detects the two-pole current. Based on the detection results of the voltage detectors 52a, 52b, the pole control device 32 inputs the line-to-line DC voltage Vd2 between the bus 4F and the return line 4R, and multiplies Vd2 by the current value Id2 detected by the current detector 62 to calculate the DC power Pd2. The pole control device 32 transmits the calculated DC power Pd2 data to the bipolar common control device 10.

The pole control devices (first control circuits) 31, 32 generate gate signals and the like for controlling the converters 21, 22 based on the new power setting values Pdp1', Pdp2' transmitted from the bipolar common control device 10, and supply them to the converters 21, 22, respectively.

The converters 21 and 22 are operated according to the new power set values Pdp1' and Pdp2' that have been supplied. Specifically, the converters 21 and 22 are operated so that the DC powers Pd1 and Pd2 they output follow the new power set values Ppdp1' and Pdp2'.

The one-pole converter 21 is connected to converter 41 via bus 3F and return 3R. The two-pole converter 22 is connected to converter 42 via bus 4F and return 4R. Although not shown, converters 41 and 42 are also connected to a pole control device and a bipolar common control device and are controlled by them.

Converters 21 and 22 are controlled by the bipolar common control device 10 and the pole control devices 31 and 32 to convert AC power to DC power and transmit it to converters 41 and 42. Converters 21 and 22 are also controlled by the bipolar common control device 10 and the pole control devices 31 and 32 to receive DC power transmitted from converters 41 and 42 and convert it to AC power.

In this example, converters 21, 22, 41, and 42 use a separately excited converter circuit using a thyristor as shown in FIG. 1, but they may also be converters that use a self-excited converter circuit, not limited to thyristor valves.

The smoothing control prohibition circuit 14 is provided to prevent smoothing control from being performed when the power setting values Pdp1 and Pdp2 change in the same direction. When the power setting values Pdp1 and Pdp2 change in the same direction, this refers to when both converters 21 and 22 are operating and the DC powers output by converters 21 and 22 are both increased or both decreased.

FIG. 2 is a schematic block diagram illustrating a DC power transmission system.
FIG. 2 shows the overall configuration of a DC power transmission system 100 including the configuration shown in FIG.
As shown in Fig. 2, the DC power transmission system 100 includes AC systems 1 and 2 and DC systems 3 and 4. The DC system 3 includes a bus 3F and a return line 3R. The DC system 4 includes a bus 4F and a return line 4R. The DC systems 3 and 4 are connected in parallel with each other, sharing the return lines 3R and 4R.

The DC systems 3 and 4 may include, for example, DC transmission lines. In this example, the bus bars 3F and 4F and the return lines 4F and 4R are DC transmission lines. The AC systems 1 and 2 are, for example, AC power systems, and may include generators, AC transmission lines, various AC loads, etc. The DC transmission system 100 converts AC power to DC power, transmits the converted DC power via the DC systems 3 and 4, and converts it back to AC power to connect to the AC system.

The converter 21 is provided between the AC system 1 and the DC system 3. The converter 22 is provided between the AC system 1 and the DC system 4. The converter 41 is provided between the DC system 3 and the AC system 2. The converter 42 is provided between the DC system 4 and the AC system 2. The converter 21 is connected to the AC system 1 via a transformer 5, and the converter 22 is connected to the AC system 1 via a transformer 6. The converter 41 is connected to the AC system 2 via a transformer 7, and the converter 42 is connected to the AC system 2 via a transformer 8.

Converters 21 and 22 can both operate and convert AC power from AC system 1 to DC power and transmit it to converters 41 and 42. Converters 21 and 22 can also both operate and convert DC power transmitted from converters 41 and 42 to AC power and connect it to the AC system.

When both converters 21 and 22 are operating, the power flow direction of converters 21 and 22 can be made the same to transmit power to converters 41 and 42. In this case, the power transmitted by converters 21 and 22 is the sum of the power transmitted by each converter 21 and 22.

When both converters 21 and 22 are operating, the power flow direction of converters 21 and 22 can be reversed to transmit power to converters 41 and 42. In this case, the power transmitted by converters 21 and 22 is the difference between the power transmitted by each converter 21 and 22. By reversing the power flow direction of converters 21 and 22, it is possible to set the transmitted power to zero without stopping converters 21 and 22, or to set the transmitted power to a value smaller than the minimum output power of converters 21 and 22.

One of the converters 21, 22 is in operation while the other is stopped, and the one in operation can convert AC power from the AC system 1 into DC power and transmit it to the converters 41, 42. The one in operation can also receive transmitted power from the converters 41, 42. In this way, in a bipolar DC transmission system, one of the converters can be stopped while the system is in operation, and inspection, repairs, etc. can be performed.

In the following, the case where the converters 21 and 22 are the sending end or the receiving end will be described. When the converter 21 is the sending end, the converters 41 and 42 are the receiving end, and when the converter 21 is the receiving end, the converters 41 and 42 are the sending end. Similarly, when the converter 22 is the sending end, the converters 41 and 42 are the receiving end, and when the converter 22 is the receiving end, the converters 41 and 42 are the sending end. In the following, the case where the converters 21 and 22 are operated, etc. will be described, and the converters 41 and 42 operate according to the operating conditions of the converters 21 and 22, etc., and detailed operation of the converters 41 and 42 will be omitted. The side where the converters 21 and 22 are provided may be referred to as the sending end or the receiving end with respect to the side where the converters 41 and 42 are provided. In addition, the transmitted power or received power of the converters 21 and 22 may be referred to as the transmitted power, etc.

In this embodiment, the operating state of the converters 21 and 22 can be in the following three cases. The operating state refers to a case where the bipolar common control device 10 generates a new power set value Ppdp1' or a power set value Pdp2' according to the timing when the power set value of either of the converters 21 and 22 increases, decreases, or reverses the power flow direction. As described above, the newly generated power set value is generated corresponding to the other pole different from the pole that increases, decreases, or reverses the power flow direction of the power set value.

In the first case, while one converter is operating, the power setting value of the other converter is increased to increase the transmission power at the sending end, etc. An example of a case in which the power setting value of the other converter is increased is when the other converter is started.

In the second case, while both converters are operating, the power setting value of one converter is lowered to reduce the transmission power at the sending end, etc. An example of a case in which the power setting value of one converter is lowered is when one converter is stopped.

The third state is when the direction of current flow in one converter is reversed while both converters are operating, reducing the transmission power at the sending end, etc.

In the second and third cases, both correspond to the case where the transmission power, etc. is reduced, but in the second case, the transmission power, etc. can be reduced to the minimum output power of the converter. In the third case, the transmission power, etc. can be set to a value smaller than the minimum output power of the converter.

The operation of the bipolar common control device 10 of this embodiment will now be described.
In order to facilitate understanding of the operation of the bipolar common control device 10 of this embodiment, the operation of a bipolar common control device of a comparative example will also be described below.
First, the configuration of a bipolar common control device of a comparative example will be described.
3(a) and 3(b) are schematic block diagrams illustrating a comparative bipolar common control device.
The bipolar common control device 210 of the comparative example is used in place of the bipolar common control device 10 of the embodiment shown in Fig. 1. However, in the bipolar common control device 210 of the comparative example, smoothing control is performed using only the power setting values Pdp1 and Pdp2 generated based on the power setting value Pdp from the higher-level control device, without using the DC powers Pd1 and Pd2 that are actually output.

As shown in FIG. 3(a), the bipolar common control device 210 of the comparative example includes an other-pole determination unit 211 and a smoothing control circuit 212. The bipolar common control device 210 is connected to a higher-level control device (not shown) and receives a power setting value Pdp from the higher-level control device. As in the case of the bipolar common control device 10 of the embodiment, the bipolar common control device 210 generates power setting values Pdp1 and Pdp2 based on the power setting value Pdp and the DC power that the converters 21 and 22 can output.

The other pole determination unit 211 inputs the power setting values Pdp1 and Pdp2. The other pole determination unit 211 determines which of the power setting values Pdp1 and Pdp2 will be started, stopped, or the current will be reversed, and supplies the power setting value to the smoothing control circuit 212 as the other pole, which is a pole other than the determined pole.

As shown in FIG. 3(b), the smoothing control circuit 212 includes first-order lag circuits 213a to 213c and switches 214a to 214c. The first-order lag circuits 213a to 213c are connected in parallel between the input and output of the smoothing control circuit 212. One of the first-order lag circuits 213a to 213c is selected by the switches 214a to 214c and outputs first-order lag response data of the input power setting value Pdp1 or Pdp2. New power setting values Pdp1'', Pdp2'' are generated as data that has passed through one of the first-order lag circuits 213a to 213c and are output.

The first-order lag circuit 213a (indicated as other pole start in the figure) inputs data on the power setting value Pdp1 or Pdp2 of the pole other than the pole to be started, and outputs a new power setting value Pdp1'' or Pdp2''. The first-order lag circuit 213b (indicated as other pole stop in the figure) inputs data on the power setting value Pdp1 or Pdp2 of the pole other than the pole to be stopped, and outputs a new power setting value Pdp1'' or Pdp2''. The first-order lag circuit 213c (indicated as other pole current reversal in the figure) inputs data on the power setting value Pdp1 or Pdp2 of the pole other than the pole whose current direction is reversed, and outputs a new power setting value Pdp1'' or Pdp2''.

Switch 214a is connected in series to first-order lag circuit 213a. Switch 214b is connected in series to first-order lag circuit 213b. Switch 214c is connected in series to first-order lag circuit 213c. Switches 214a to 214c are controlled to open and close by smoothing control enable signals C1 to C3. Switch 214a closes the circuit when smoothing control enable signal C1 is active and opens the circuit when it is inactive. Switch 214b closes the circuit when smoothing control enable signal C2 is active and opens the circuit when it is inactive. Switch 214c closes the circuit when smoothing control enable signal C3 is active and opens the circuit when it is inactive.

The smoothing control enable signals C1 to C3 are determined to be active or inactive, for example, by the bipolar common control device 210. The bipolar common control device 210 determines which smoothing control enable signal to activate based on the power setting values Pdp1 and Pdp2.

For example, when converter 22 is in operation and converter 21 starts up from a stopped state, smoothing control enable signal C1 is made active and switch 214a is closed.

For example, when both converters 21 and 22 are in operation, when the operating converter 21 stops, the smoothing control enable signal C2 is activated and switch 214b is closed.

For example, when both converters 21 and 22 are in operation, when the power flow direction of converter 21 is to be reversed, smoothing control enable signal C3 is made active and switch 214c is closed.

The first-order lag circuits 213a to 213c are set with a time constant according to the operating state described above, and when the power setting value for one converter suddenly changes, the power setting value for the other converter is gradually changed to suppress fluctuations in the transmission power at the sending end, etc.

A more specific description will be given while comparing the comparative example and the embodiment with reference to operation waveform diagrams.
FIG. 4 is an operational waveform diagram showing a schematic example for explaining the operation of the bipolar common control device of the comparative example.
Fig. 4 shows a schematic example of operational waveforms when the 2-pole converter 22 is operating at the minimum power setting value Pdpmin, the 1-pole converter 21 is started, and the power setting values of both the two converters 21 and 22 are set to Pdp/2. That is, Fig. 4 shows an operation corresponding to the first state in the case of the above-mentioned embodiment.

The top graph in FIG. 4 shows the time variation of the starting signal for the two-pole converter 22.
4 shows the time change of the start signal for the one-pole converter 21. For both converters 21 and 22, the L level indicates an inactive state, i.e., a stopped state, and the H level indicates an active state, i.e., an operating state (started).
4 shows the time variations in the power setting values Pdp1, Pdp2 for the one-pole and two-pole converters 21, 22. The dashed dotted line shows the total power setting value of the converters 21, 22.
The fourth graph in FIG. 4 shows the change over time of the DC voltage Vd output by the converters 21 and 22.
The fifth graph in FIG. 4 shows the change over time of the DC current Id output by the converters 21 and 22.
The sixth graph in FIG. 4 shows the change over time of DC powers Pd1 and Pd2 output by the converters 21 and 22, respectively.
The bottom graph in FIG. 4 shows the change over time in the total DC power Pd output by the two converters 21 and 22.
Although not shown, the smoothing control enable signals C1 to C3 described in relation to Fig. 3B are initially set to be inactive, for example, at level L. The configuration of the graphs is similar to that of Figs. 5 to 10 described later.

As shown in FIG. 4, at time t10, the start signal for the two-pole converter 22 becomes active. At time t11, the converter 22 starts up in response to the start signal and starts outputting the DC voltage Vd and the DC current Id. Note that in the period prior to time t10, the upper control device transmits the minimum power setting value Pdpmin that the converter can output to the bipolar common control device 210. The bipolar common control device 10 interprets the command from the upper control device and sets the two-pole converter 22 to operate at the minimum power setting value Pdpmin and sets the one-pole converter 21 to maintain a stopped state.

At time t12, the upper control device sends a command to the bipolar common control device 10 to change the power setting value from Pdpmim to Pdp. Here, the newly set power setting value Pdp is sufficiently larger than Pdpmin and slightly smaller than the maximum output power of one converter. In other words, to handle the new power setting value Pdp, either one of the converters 21 and 22 may be used, or the two may share the same. In this example, the bipolar common control device 10 interprets the command sent from the upper control device and sets the new power setting value Pdp to be shared between the converters 21 and 22, with half of the value shared.

The bipolar common control device 10 increases the power setting value for the two-pole converter 22 to a new setting value Pdp at a constant time increase rate from time t12 to time t13. The time increase rate of the power setting value is preset. The DC current Id2 output by the converter 22 increases in response to the increase in the power setting value.

At time t13, the start signal for the one-pole converter 21 becomes active. At this time, the bipolar common control device 10 sets the power setting values for the two converters 21 and 22 to Pdp/2, respectively, and inputs them to the other-pole determination unit 211. The other-pole determination unit 211 determines that the pole to be started is one pole, and inputs the power setting value Pdp2 for the other pole, two poles, to the smoothing control circuit 212.

The power set value Pdp1 of the converter 21 is set in a stepwise manner to Pdp/2 at time t13. The set power set value Pdp/2 is transmitted to the pole control device 31, and the converter 21 starts operating so as to follow the power set value Pdp/2.

Since the converter 21 starts from a stopped state, the DC voltage Vd1 that it outputs gradually rises from approximately 0 to the set voltage. The DC current Id1 that the converter 21 outputs rises according to the DC voltage that it outputs.

Also, at time t13, the bipolar common control device 210 activates the smoothing control enable signal C1 to close the circuit of the switch 214a. The first-order lag circuit 213a inputs the power setting value Pdp2 and outputs a new power setting value Pdp2''. The new power setting value Pdp2'' has a decreasing characteristic that asymptotically approaches Pdp/2 from Pdp, forming a downward convex curve.

The power setting value Pdp2'' for the two-pole converter 22 decreases with a first-order lag response waveform until time t14, and the bipolar power setting value becomes Pdp. In this figure, the bipolar power setting value Pdp is also shown by a dashed line.

The new power set value Pdp2'' generated by the smoothing control circuit 212 is sent to the pole control device 32, and the converter 22 outputs the DC current Id2 so as to follow the new power set value Pdp2''.

The converter 21 starts at time t13, and the DC voltage Vd2 rises from approximately 0. The DC current Id2 output by the converter 21 increases in accordance with the DC voltage Vd2. Here, the start-up time and maximum values of the DC voltage and DC current output when the converters 21 and 22 start are limited within the converters 21 and 22 to ensure safe operation of the converters 21 and 22. Therefore, it takes time until time t14 for the DC power Pd2 output by the converter 21 to follow the power setting value Pdp/2.

When the power setting value Pdp2 for the converter 22 is supplied to the pole control device 32 and the converter 22 without passing through the smoothing control circuit 212, the power setting value drops in a stepwise manner to the power setting value Pdp/2 at time t13, as shown by the dashed line in the figure. Therefore, the DC current output by the converter 22 also drops in a stepwise manner at time t13, and the DC power Pd2 output by the converter 22 also drops in a stepwise manner at time t13.

On the other hand, the DC power Pd1 output by the converter 21 has a startup waveform that is determined by the internal limitations of the converter 21 and the impedance of the line connected to the output, regardless of whether or not a smoothing control circuit 212 is present. Therefore, in the period from time t13 to time t14, the power setting value Pdp drops significantly in the first place, as shown by the dashed line.

When the single-pole converter 21 is started, the bipolar common control device 210 of the comparative example makes the fall of the power setting value Pdp2'' of the two-pole converter 22 gentler, suppressing the decrease in the bipolar power value Pd during the period from time t13 to time t14.

However, in the bipolar common control device 210 of the comparative example, the falling edge of the power setting value Pdp2'' at the time of the other pole start-up is generated by a first-order lag circuit 213a with a fixed constant, so if the magnitude of the change in the power setting values Pdp1 and Pdp2 is different, the bipolar power value Pd may further decrease. Also, in the example of Figure 4, a temporary decrease in the bipolar power value Pd occurs, and if it is desired to further suppress the impact on the grid, improvement is necessary.

FIG. 5 is a schematic diagram showing an example of an operation waveform for explaining the bipolar common control device according to the embodiment.
Fig. 5 shows a case where, as in the comparative example described above, converter 21 is started up in converter 22 during operation to increase the bipolar power setting value from Pdpmin to Pdp. In Fig. 5, the operation from time t10 to time t13 and the operation after time t14 are the same as those in Fig. 4. Therefore, the operation from time t13 to time t14 will be described.

As shown in FIG. 5, in the embodiment of the bipolar common control device 10, the power setting value Pdp2' of the two-pole converter 22, which is the other pole of the one pole that is activated, is calculated so that the DC power Pd (= Pd1 + Pd2) output by the converters 21 and 22 becomes the power setting value Pdp.

As shown in the figure, the power setting value Pdp2' and the DC powers Pd1 and Pd2 are functions of time, so data is acquired in time synchronization, the power setting value Pdp2' at that time is calculated, and the calculated power setting value Pdp2' is transmitted to the pole control device 32, for example, each time a calculation is performed.

In the case of FIG. 4, the first-order lag circuit 213a causes a temporary drop in the bipolar DC power Pdp due to the power set value Pdp2'', which has a downward convex time characteristic. In contrast, in this example of the embodiment, the power set value Pdp2' has an upward convex time characteristic, so the bipolar DC power Pd can be kept approximately constant after time t13.

In the embodiment of the bipolar common control device 10, the DC powers Pd1 and Pd2 are measured in real time, and the two-pole power setting value Pdp2' is calculated so that the bipolar DC power Pd, which is the sum of these data, becomes the bipolar power setting value Pdp. Therefore, even if the startup characteristics of the converters 21 and 22 differ depending on the conditions of the connected lines, the fluctuations in the transmission power at the sending end, etc. are suppressed, and the transition to the target power setting value can be made more smoothly.

FIG. 6 is an operational waveform diagram showing a schematic example for explaining the operation of the bipolar common control device of the comparative example.
Fig. 6 shows a schematic example of operating waveforms in the case where one-pole converter 21 is stopped while both converters 21, 22 are operating at the same power set value Pdp/2, and the transmission power, etc. are maintained the same before and after the stop. In this example, the upper control device commands the bipolar common control device 210 to operate at the same power set value Pdp, and it is assumed that one converter 21 is stopped at the transmitting end for inspection, repair, etc. Fig. 6 shows an operation corresponding to the second state in the case of the above-mentioned embodiment.

As shown in FIG. 6, before time t20, the bipolar common control device 210 receives the power setting value Pdp from the upper control device, and generates and sets the power setting values Pdp1 and Pdp2 (= Pdp/2) so that the two converters 21 and 22 share half of the power.

At time t20, the bipolar common control device 210 transitions the start signal to inactive so as to stop the one-pole converter 21. The bipolar common control device 210 transitions the power setting value Pdp1 of the one-pole converter 21 to 0 in a stepped manner. The DC voltage Vd1 output by the converter 21 gradually decreases to approximately 0. The DC current Id1 output by the converter 21 decreases according to the DC voltage Vd1. The change over time of the DC voltage Vd1 is determined by the impedance within the converter 21 and the impedance of the DC line connected to the converter 21, and is not controlled by control parameters such as the power setting value.

At the same time, at time t20, the bipolar common control device 210 changes the power set value Pdp2 to Pdp in a step manner so as to double the DC power Pd2 output by the two-pole converter 22.

The power setting values Pdp1 and Pdp2 are input to the other pole determination unit 211. The other pole determination unit 211 selects the power setting value Pdp2 and outputs it to the smoothing control circuit 212. The smoothing control circuit 212 inputs the power setting value Pdp2, activates the smoothing control enable signal C2, and closes the switch 214b. The power setting value Pdp2 passes through the first-order lag circuit 213b and is output from the smoothing control circuit 212 as a power setting value Pdp2'' that has an upwardly convex characteristic that gradually increases over time.

The bipolar common control device 210 transmits the power setting values Pdp1 and Pdp2 to the pole control devices 31 and 32, respectively, to set the operation of the converters 21 and 22.

The DC voltage Vd2 output by the converter 22 remains constant even after time t21. The converter 22 increases the DC current Id2 it outputs so as to follow the set power value Pdp2''. Therefore, the DC power Pd2 output by the converter 22 approaches the power set value Pdp according to a first-order lag response characteristic that is upwardly convex.

At time t20, the start-up signal of the converter 21 is made inactive, and the power setting value Pdp1 is set in a stepped manner to 0. The DC voltage Vd1 and DC current Id1 output by the converter 21 decrease according to the impedance within the converter 21 and the impedance of the DC line, and become approximately 0 at time t21.

As shown in the bottom graph, the DC power Pd2 output by the converter 22 has an upwardly convex characteristic due to its first-order lag response characteristic. The DC power Pd1 output by the converter 21 also does not have a downwardly convex characteristic, but may have an upwardly convex characteristic, because the charge stored in the capacitance components of the output capacitor, etc. in the converter 21 is discharged through the existing impedance. Therefore, the DC power Pd output by the sending end, etc., may be a value greater than the desired power setting value Pdp during the period from time t20 to time t21.

The dashed line in the figure represents the DC power Pd output by the sending end, etc., when the power setting value Pdp2 is not passed through the smoothing control circuit 212, and reaches twice the power setting value Pdp. The smoothing control circuit 212 of the comparative example can suppress the rise in DC power Pd by gradually changing the power setting value Pdp2'', but depending on the discharge waveform when the converter 21 is stopped, etc., the rise in DC power Pd may become even larger, and it is difficult to completely suppress the fluctuations in DC power Pd.

FIG. 7 is a schematic operational waveform diagram for explaining the operation of the bipolar common control device according to the embodiment.
As in the comparative example described above, Fig. 7 shows a case where, of converters 21 and 22 in operation, operation of converter 21 is stopped, the DC power output by converter 22 is doubled, and the transmission power at the sending end, etc. is kept constant. In Fig. 7, the operation before time t20 and the operation after time t21 are the same as those in Fig. 6. Therefore, the operation during the period from time t20 to time t21 will be described.

In the embodiment, the bipolar common control device 10 inputs the two-pole power setting value Pdp2 to the smoothing control circuit 12, and generates a new power setting value Pdp2' so that the DC power Pd (= Pd1 + Pd2) actually output by the converters 21 and 22 becomes the power setting value Pdp.

In this example, the DC power Pd2 after the converter 21 is stopped, which is determined by the internal and external impedances of the converter 21, etc., is upwardly convex, so to offset this, the bipolar common control device 10 generates a power setting value Pdp2' that is downwardly convex.

The power set value Pdp2' can be calculated in the same way as described in FIG. 5. That is, as shown in the figure, the power set value Pdp2' and the DC powers Pd1 and Pd2 are functions of time, so the data is acquired in time synchronization and transmitted to the pole control device 32 as the power set value Pdp2' at that time.

In this way, the DC power Pd output by the transmission end, including the converters 21 and 22, can be maintained at a constant value according to the power setting value Pdp.

FIG. 8 is an operational waveform diagram showing a schematic example for explaining the operation of the bipolar common control device of the comparative example.
Fig. 8 shows an example in which both converters 21, 22 are operated at the same magnitude of power setting value in different power flow directions to output a transmission power etc. smaller than the minimum output power of one converter. In this example, the upper control device sets the power setting value Pdp to 0, and then transitions it to a power setting value Pdp that is approximately the output power that one converter can output. The bipolar common control device 210 sets the converters 21, 22 to minimum power setting values ±Pdpmin in different power flow directions, respectively, and reverses the power flow direction of the converter 21 at the timing when the power setting value Pdp transitions from 0 to Pdp. Fig. 8 shows an operation corresponding to the third state in the above-mentioned embodiment.

As shown in FIG. 8, at time t30, the start-up signals of the converters 21 and 22 of both poles become active. The upper control device commands 0 as the power setting value Pdp, and the bipolar common control device 210 interprets this and sets ±Pdpmin so that the two converters 21 and 22 output the minimum DC power in different current directions.

At time t31, converters 21 and 22 start operating, and DC voltages Vd1 and Vd2 rise. Converters 21 and 22 output DC currents Id1 and Id2 in response to DC voltages Vd1 and Vd2.

At time t32, the bipolar common control device 210 increases the power setting value Pdp2. The time increase rate of the power setting value Pdp2 is preset. Time t32 is determined based on the initial power setting value Pdpmin and the increase rate of the power setting value Pdp2 so that at time t33, it becomes approximately the power setting value Pdp at the sending end, etc.

At time t33, the upper control device sends a command to transition the power set value from 0 to Pdp. The bipolar common control device 210 interprets the command and reverses the power flow direction of the converter 21 at time t33. The power set value Pdp1 after the power flow reversal is set to Pdp/2. In addition, the power set value Pdp2 of the converter 22 that does not reverse the power flow is also set to Pdp/2.

At time t33, Pdp1 and Ppd2 are input to the other pole determination unit 211. The other pole determination unit 211 determines that the converter 22 that does not reverse the power flow is the other pole, and outputs Pdp2 to the smoothing control circuit 212.

The smoothing control circuit 212 sets the smoothing control enable signal C3 to active. The power setting value Pdp2 is input to the first-order lag circuit 213c, and the smoothing control circuit 212 outputs the power setting value Pdp2''.

The power setting value Pdp2'' that passes through the first-order lag circuit 213c has a downward convex characteristic due to the first-order lag response.

At time t33, the converter 21 inverts the polarity of the DC voltage Vd1 to reverse the power flow direction. The period required for the reversal operation of the DC voltage Vd1 is set in advance, taking into consideration the characteristics of the DC line, etc. The DC current Id1 output by the converter 21 increases according to the power setting value Pdp1. Therefore, the DC power Pd1 output by the converter 21 increases according to the DC voltage Vd1.

In this example, if the DC power Pd1 output by the converter 21 changes almost linearly during the period from time t33 to time t34, and the DC power Pd2 output by the converter 22 shows a first-order lag response characteristic with a downward convexity, the transmission power, etc. will decrease slightly as shown. The dashed curve shows the transmission power, etc. when the power setting value Pdp2 is changed in a stepwise manner without passing through the smoothing control circuit 212, and compared to this, the power decrease in the transmission power, etc. in the comparative example is kept small. As in the cases corresponding to the first and second states described above, the rate of change of the DC voltage on the side where the power flow is reversed is internally fixed, and the DC power decrease may become even greater depending on the DC voltage values before and after the reversal.

FIG. 9 is an operational waveform diagram showing a schematic example for explaining the operation of the bipolar common control device according to the embodiment.
Fig. 9 shows a case where, as in the comparative example described above, the power flow direction of converter 21 of converters 21 and 22 in operation is reversed and the bipolar power setting value is increased from 0 to Pdp. In Fig. 9, the operation from time t30 to time t33 and the operation after time t34 are the same as those in Fig. 8. Therefore, the operation from time t33 to time t34 will be described.

As shown in FIG. 9, in the embodiment of the bipolar common control device 10, the power setting value Pdp2' of the converter 22 of the second pole, which is the other pole of the first pole that changes, is calculated and set so that the DC power Pdp (= Pd1 + Pd2) output by the converters 21 and 22 becomes the power setting value Pdp.

As shown in the figure, the power setting value Pdp2' and the DC powers Pd1 and Pd2 are functions of time, so the power setting value Pdp2' is calculated by acquiring data in time synchronization and transmitting it to the pole control device 32 as the power setting value Pdp2' at that time.

In this way, by calculating the power setting value of the other pole of the pole where the flow direction is reversed so that the actual output DC power Pd is equal to the power setting value Pdp, temporary changes in DC power at the time of flow reversal can be suppressed.

As described above, in the embodiment of the bipolar common control device 10, by calculating the power setting value of the pole other than the pole that is started, stopped, or reversed, it is possible to obtain the desired DC power without causing a drop or rise in DC power even during periods when changes occur.

In the bipolar common control device 210 of the comparative example, the degree of smoothing required differs depending on whether one pole is started, stopped, or the flow is reversed, so the time constant of the first-order lag circuit is set for each. Therefore, it is necessary to determine each time whether one pole is started, stopped, or the flow direction is reversed, and to switch the time constant of the first-order lag circuit. In contrast, the bipolar common control device 10 of the embodiment calculates the power setting value of the other pole so that the DC power Pd output from the sending end, etc. that is actually outputting, becomes the power setting value Pdp. Therefore, regardless of whether one pole is started, stopped, or the flow is reversed, the power setting value of the other pole can be calculated using the same circuit, algorithm, etc., so that the circuit configuration, program, etc. can be simplified.

As described above, the power setting value of one pole can be calculated regardless of the operating state of the other pole, so even if the behavior of one pole changes due to differences in the circuit constants in the converter or the impedance of the connected lines between systems, DC power can be output with reliably suppressed changes.

In the smoothing control circuit 12 of the bipolar common control device 10 of the embodiment, the power setting value Pdp2' (or Pdp1') is calculated using the DC power Pd (= Pd1 + Pd2) that is actually output. There is a delay associated with analog-to-digital conversion after the measurement of the electrical quantity, and a response delay of other circuits. Therefore, when calculating the power setting value Pdp2' (or Pdp1'), a correction value may be added or subtracted to account for these delays.

Next, the smoothing control inhibition circuit 14 will be described.
FIG. 10 is an operational waveform diagram showing a schematic example for explaining the operation of the bipolar common control device of the embodiment.
Fig. 10 shows a schematic example of an operational waveform when the power setting values of the two-pole converters 21 and 22 are increased simultaneously in the same direction when the two-pole converters 21 and 22 are operating at the minimum power setting value Pdpmin. In other words, Fig. 10 does not correspond to any of the first to third states in the above-mentioned embodiment.

In this case, as in the first to third states described above, the power setting value Pdp2' (or Pdp1') can be calculated so that the DC power Pd (= Pd1 + Pd2) actually output by the converters 21 and 22 follows the changed power setting value Pdp. However, when the outputs of the two converters 21 and 22 change simultaneously in the same direction, in order to make the DC power Pd follow the power setting value Pdp, it may be necessary to set it beyond the maximum output power of the converter of the pole that performs smoothing. Therefore, the smoothing control prohibition circuit 14 does not perform smoothing control of the power setting value when the power setting value changes in the same direction in this way.

As shown in FIG. 10, at time t40, the start signal of the converter 22 becomes active, and at time t41, the converter 22 starts operation and starts the DC voltage Vd2. The converter 22 outputs the DC current Id2 according to the DC voltage Vd2.

At time t42, the start signal for converter 21 becomes active, and converter 21 starts operating. Converter 21 starts up DC voltage Vd1 and outputs DC current Id2.

Here, the solid line shows the waveform when the power setting value Pdp2 is not passed through the smoothing control circuit 12. The DC power Pd1 output by the one-pole converter 21 has a waveform similar to that of the DC voltage Vd1 at startup, so the DC power Pd output by the sending end, etc., is lower than the desired power setting value Pdp during the period from time t42 to time t43.

At time t42, if the smoothing control circuit 12 generates the power setting value Pdp2' of the converter 22 so that it is convex downward, the DC power Pd output from the sending end, etc. can be made to follow the power setting value Pdp, but if the output capacity of the converter 22 is exceeded, the power setting value Pdp2' cannot be set. On the other hand, if the power setting value Pdp'' is generated by a first-order lag circuit as in the comparative example, the operating waveform becomes convex upward, and the DC power Pd output from the sending end, etc., will drop by a larger amount than in the case of the solid line, as shown by the dashed line.

Therefore, in the bipolar common control device 10 of the embodiment, when the power setting values are changed simultaneously in the same direction by the smoothing control prohibition circuit 14, the power setting values Pdp1 and Pdp2 are used directly without going through the smoothing control circuit 12, making it possible to output safe DC power with suppressed changes.

In the above, an example was described in which the operating state of each converter is controlled based on a power set value, but it goes without saying that a DC current set value can be used instead of a power set value.

In this way, a control device is realized that suppresses power fluctuations when one pole is started, stopped, or the power flow is reversed.

Although several embodiments of the present invention have been described above, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the gist of the invention. These embodiments and their variations are included within the scope and gist of the invention, as well as within the scope of the invention and its equivalents described in the claims. In addition, the above-mentioned embodiments can be implemented in combination with each other.

1, 2 AC system, 3, 4 DC system, 5-8 Transformer, 10 Bipolar common control device, 12 Smoothing control circuit, 14 Smoothing control inhibition circuit, 21, 22, 41, 42 Converter, 31, 32 Pole control device, 100 DC power transmission system

Claims (3)

A control device is used in a bipolar DC power transmission system having two DC systems provided between two AC systems, a first converter provided between one of the two DC systems and one of the two AC systems, and a second converter provided between the other of the two DC systems and the one of the AC systems, the control device controlling a total DC power output by the first converter performing bidirectional power conversion between the one of the DC systems and the one of the AC systems and the second converter performing bidirectional power conversion between the other of the DC systems and the one of the AC systems, to follow a preset power setting value,
a bipolar common control circuit that generates a first power setting for the first converter and a second power setting for the second converter based on the power settings;
a first pole control circuit that controls the first converter so that a first DC power output from the first converter follows the first power setting value, calculates a measurement value of the first DC power by multiplying a line-to-line DC voltage of the one DC system detected by a first voltage detector by a current value of the one DC system detected by a first current detector, and transmits the measurement value of the first DC power to the bipolar common control circuit ;
a second pole control circuit that controls the second converter so that a second DC power output from the second converter follows the second power setting value , calculates a measurement value of the second DC power by multiplying a line DC voltage of the other DC system detected by a second voltage detector by a current value of the other DC system detected by a second current detector, and transmits the measurement value of the second DC power to the bipolar common control circuit ;
Equipped with
The bipolar common control circuit includes:
calculating the first power setting value and the second power setting value such that a sum of the first power setting value and the second power setting value becomes the power setting value;
calculating a new second power set value by changing the value of the first power set value and subtracting the measured value of the first DC power from the power set value at a first time when the first power set value is increased, decreased, or the power flow direction is reversed, so that a sum of the first DC power and the second DC power is equal to the power set value;
A control device that transmits the calculated new second power setting value to the second pole control circuit, thereby causing the second pole control circuit to control the second converter so that the second DC power follows the new second power setting value . 2. The control device according to claim 1, wherein, when the first power setting value and the second power setting value increase or decrease in the same direction at the first time, the bipolar common control circuit does not calculate the new second power setting value, but outputs the second power setting value as is. A control device is used in a bipolar DC power transmission system having two DC systems provided between two AC systems, a first converter provided between one of the two DC systems and one of the two AC systems, and a second converter provided between the other of the two DC systems and the one of the AC systems, the control device controlling a total DC current output by the first converter performing bidirectional power conversion between the one of the DC systems and the one of the AC systems and the second converter performing bidirectional power conversion between the other of the DC systems and the one of the AC systems, to follow a preset DC current setting value,
a bipolar common control circuit that generates a first DC current setpoint for the first converter and a second DC current setpoint for the second converter based on the DC current setpoints;
a first pole control circuit that controls the first converter so that a first DC current output from the first converter follows the first DC current setting value , and transmits a measurement value of the first DC current detected by a first current detector to the bipolar common control circuit ;
a second pole control circuit that controls the second converter so that a second DC current output from the second converter follows the second DC current setting value , and transmits a measurement value of the second DC current detected by a second current detector to the bipolar common control circuit ;
Equipped with
The bipolar common control circuit includes:
calculating the first DC current set value and the second DC current set value such that a sum of the first DC current set value and the second DC current set value becomes the DC current set value;
calculating a new second DC current set value by changing a value of the first DC current set value and subtracting a measured value of the first DC current from the DC current set value at a first time when the first DC current set value is increased , decreased, or the power flow direction is reversed , so that a sum of the first DC current and the second DC current is equal to the DC current set value;
A control device that transmits the calculated new second DC current set value to the second pole control circuit, thereby causing the second pole control circuit to control the second converter so that the second DC current follows the new second DC current set value .

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