Control device, power converter control method, and program

Abstract

The objective is to provide a control device, a control method for a power converter, and a program that can further improve the operational continuity of a power converter in a multi-terminal DC power transmission system. [Solution] The control device of the embodiment has a control unit. The control unit controls the power converters included in a multi-terminal DC power transmission system, which is configured by connecting the DC sides of a plurality of power converters that convert AC and DC to each other, so that the output voltage on the DC terminal side of the power converter to be controlled is output based on droop control using a predetermined droop characteristic. The control unit also controls the droop characteristic so that the operating point of the output voltage becomes lower than a reference when a fault occurs in the multi-terminal DC power transmission system or when the output of the power converter fluctuates.

Description

【Technical Field】 , , , 【0005】 【0001】 Embodiments of the present invention relate to a control device, a method for controlling a power converter, and a program. 【Background Art】 【0002】 In a multi-terminal HVDC (High Voltage Direct Current) system, there is a control method that can maintain the stable operation of the entire multi-terminal by each terminal having local control characteristics. One of them is the droop control (Pdc-Vdc droop control) in direct current power (Pdc) and direct current voltage output (Vdc). However, in the simulation verification of a multi-terminal HVDC system, in power converters other than the terminal where an accident has occurred, due to the influence of the accident and the droop characteristics, the balance of the cell capacitor voltages may be disrupted, and the operation of the power converter may not be able to continue. 【Prior Art Documents】 【Patent Documents】 【0003】 【Patent Document 1】 Japanese Patent Application Laid-Open No. 9-200952 【Patent Document 2】 Japanese Patent No. 7098416 【Summary of the Invention】 【Problems to be Solved by the Invention】 【0004】 The problem to be solved by the present invention is to provide a control device, a method for controlling a power converter, and a program that can further improve the continuity of operation of a power converter in a multi-terminal direct current power transmission system. 【Means for Solving the Problems】 【0005】 The control device of the embodiment has a control unit. The control unit controls the power converters included in a multi-terminal DC power transmission system, which is configured by connecting the DC sides of a plurality of power converters that convert AC and DC to each other, so that the output voltage on the DC terminal side of the power converter to be controlled is output based on droop control using a predetermined droop characteristic. The control unit also controls the droop characteristic so that the operating point of the output voltage becomes lower than a reference when a fault occurs in the multi-terminal DC power transmission system or when the output of the power converter fluctuates. [Brief explanation of the drawing] 【0006】 [Figure 1] A schematic diagram showing the usage environment of the multi-terminal DC power transmission system 1 according to an embodiment. [Figure 2] A diagram showing an example of the overall configuration of a multi-terminal DC power transmission system 1 including a control device 100 according to an embodiment. [Figure 3] A block diagram showing an example configuration of the control device 100 according to this embodiment. [Figure 4] A diagram showing an example configuration of the droop control unit 120 according to the embodiment. [Figure 5] A diagram illustrating the output characteristics of a power converter 10 controlled by a control device 100 according to an embodiment. [Figure 6] A flowchart showing an example of the processing flow executed by the control device 100 according to this embodiment. [Figure 7] A flowchart illustrating an example of adjusting and controlling droop characteristics. [Figure 8] A diagram showing an example of a control method for cases with two different droop characteristics according to the first embodiment. [Figure 9] This figure shows an example of control when only the first characteristic region is used. [Figure 10] A diagram illustrating the process of switching the DC voltage command value Vdc to a smaller value according to the second embodiment. [Figure 11] A figure showing an example of droop-specific control according to the third embodiment. [Modes for carrying out the invention] 【0007】 The control device, power converter control method, and program of the embodiment will be described below with reference to the drawings. 【0008】 (Overall structure) Figure 1 is a schematic diagram showing the operating environment of a multi-terminal DC power transmission system 1 according to an embodiment. The multi-terminal DC power transmission system 1 comprises, for example, multiple offshore substations T and one or more onshore substations S. In Figure 1, an example is shown in which there are three offshore substations T and two onshore substations S. The offshore substations T are connected to power generation equipment WF by AC transmission lines and to onshore substations S by DC transmission lines. In addition, the offshore substations T are interconnected with other offshore substations T by DC transmission lines. The power generation equipment WF is, for example, an offshore wind farm with multiple wind power generation systems. The offshore substations T collect the power generated by the power generation equipment WF, convert it to AC / DC, and transmit it as DC to the onshore substations S. The onshore substations S supply the power collected from the offshore substations T to consumers (not shown). 【0009】 Figure 2 is a diagram showing an example of the overall configuration of a multi-terminal DC power transmission system 1 including a control device 100 according to an embodiment. The substation unit TU shown in Figure 2 is installed, for example, in the offshore substation T shown in Figure 1. The substation unit TU is equipped with AC terminals and DC terminals. AC systems AC-1 to AC-3 are connected to the AC terminals, and DC transmission lines (DC transmission lines 40 to 42 or DC busbars 50-1 to 50-3) are connected to the DC terminals. The substation unit TU includes, for example, substation units TU-1 to TU-3. In the description of Figure 2, hyphens and the numbers and letters that follow them indicate which substation unit they correspond to. Hereafter, hyphens and the numbers that follow them will be omitted as appropriate in the description. 【0010】 Next, the configuration of substation unit TU-1 will be described, representing each substation unit TU of the multi-terminal DC power transmission system 1. Substation unit TU-1 includes, for example, a power converter 10-1 and a control device 100-1. The power converter 10-1 outputs power to the DC transmission line 40 via the DC bus 50-1. The control device 100-1 controls the output voltage value of at least the AC terminal of the power converter 10-1. The control device 100-1 is connected to, for example, a DC voltage detector 20-1 and a DC current detector 30-1. The control device 100-1 derives the output voltage value and power value of the power converter 10-1 by referring to the voltage value V (DC voltage detection value Vd) of the DC bus 50-1 detected by the DC voltage detector 20-1 and the current value I of the DC transmission line 40 detected by the DC current detector 30-1. 【0011】 Figure 3 is a block diagram showing an example configuration of a control device 100 according to an embodiment. The control device 100 in Figure 3 includes, for example, subtraction units 110 and 170, a droop control unit 120, an upper limit value derivation unit 130, a lower limit value derivation unit 140, a limiting unit 150, an addition unit 160, and a PI control unit 180. Some or all of these components are realized, for example, by a hardware processor such as a CPU (Central Processing Unit) executing a program (software). Some or all of these components may also be realized by hardware (including circuitry) such as an LSI (Large Scale Integration), ASIC (Application Specific Integrated Circuit), FPGA (Field-Programmable Gate Array), or GPU (Graphics Processing Unit), or by the cooperation of software and hardware. Note that among the configurations shown in Figure 3, the upper limit value derivation unit 130 and the lower limit value derivation unit 140 are examples of "derivation units". Furthermore, a configuration including subtraction units 110 and 170, a droop control unit 120, a limiting unit 150, an addition unit 160, and a PI control unit 180 is an example of a "control unit". 【0012】 The subtraction unit 110 subtracts the DC power (active power detection value) Pdc from the DC power command value Pdc* and outputs the subtraction result to the droop control unit 120. The DC power command value Pdc* may be set in advance by the administrator of the multi-terminal DC power transmission system 1, for example, or it may be input from a higher-level system of the multi-terminal DC power transmission system 1. The DC power Pdc is derived, for example, by multiplying the DC voltage detection value Vd detected by the DC voltage detector 20 and the current value I detected by the DC current detector 30. 【0013】 The droop control unit 120 sets a characteristic region having two different characteristics (droop characteristics) in the relationship between DC power Pdc and DC voltage Vdc, and outputs a value corresponding to the characteristics of the set characteristic region to the limiting unit 150. For example, the droop control unit 120 controls the power converter 10 to operate at an operating point corresponding to the characteristics of DC power and DC voltage, based on the droop characteristics consisting of the relationship between DC power and DC voltage. A specific example of the configuration of the droop control unit 120 will be described later. 【0014】 The upper limit value derivation unit 130 includes, for example, a subtraction unit 132, a PI control unit 134, and a limiting unit 136. The subtraction unit 132 subtracts the DC power output value Pdc from a predetermined DC power upper limit value Pdc_limH and outputs it to the PI control unit 134. The PI control unit 134 performs PI control on the value output by the subtraction unit 132 and outputs it to the limiting unit 136. PI control is, for example, feedback control based on calculations including proportional and integral terms. The limiting unit 136 limits the input value so that it falls within a first predetermined range and outputs the limited value as the output upper limit value Ulim. The first predetermined range is, for example, the range from the lower limit to the upper limit when the value obtained by subtracting the DC voltage command value Vdc* from a predetermined minimum DC voltage value Vdcmin (Vdcmin-Vdc*) is set as the lower limit and the value obtained by subtracting the DC voltage command value Vdc* from a predetermined maximum DC voltage value Vdcmax (Vdcmax-Vdc*) is set as the upper limit. For example, the limiting unit 136 may set the input value to the lower limit if it is less than the lower limit, and output the upper limit instead if it is greater than the upper limit. 【0015】 The lower limit value derivation unit 140 includes, for example, a subtraction unit 142, a PI control unit 144, and a limiting unit 146. The subtraction unit 142 subtracts the DC power Pdc from a predetermined DC power lower limit value Pdc_limL and outputs the result to the PI control unit 144. The PI control unit 144 performs PI control on the value output by the subtraction unit 142 and outputs the result to the limiting unit 146. The limiting unit 146 limits the input value so that it is included in a first predetermined range, and outputs the limited value as an output lower limit value Llim. The second predetermined range is the same as the first predetermined range described above. 【0016】 The limiting unit 150 limits the value output by the droop control unit 120 with an output upper limit value Ulim derived by the upper limit value derivation unit 130 and an output lower limit value Llim derived by the lower limit value derivation unit 140, and then outputs the result. Specifically, when the value output by the droop control unit 120 exceeds the output upper limit value Ulim, the limiting unit 150 outputs a value that is not less than the output lower limit value Llim and not more than the output upper limit value Ulim to the addition unit 160. When the value output by the droop control unit 120 is less than the output lower limit value Llim, the limiting unit 150 outputs a value that is not less than the output lower limit value Llim and not more than the output upper limit value Ulim to the addition unit 160. When the value output by the droop control unit 120 is not less than the output lower limit value Llim and not more than the output upper limit value Ulim, the limiting unit 150 outputs the value directly to the addition unit 160. 【0017】 The addition unit 160 adds the value output by the limiting unit 150 and the DC voltage command value Vdc*. The subtraction unit 170 subtracts the DC voltage detection value Vd from the value output by the addition unit 160 and outputs the result to the PI control unit 180. 【0018】 The PI control unit 180 performs PI control on the value output by the subtraction unit 170 and outputs a DC voltage control command value Vd*#. The control device 100 controls the output voltage (DC voltage Vdc) of the power converter 10 based on the DC voltage control command value Vd*#. 【0019】 [Droop control unit] Figure 4 shows an example of the configuration of the droop control unit 120 according to the embodiment. The droop control unit 120 in Figure 4 includes, for example, subtraction units 121, 125, and 127, setting units 122 and 124, limiting units 123, 126, and 128, and an addition unit 129. Figure 5 is a diagram for explaining the output characteristics of the power converter 10 controlled by the control device 100 according to the embodiment. In Figure 5, the horizontal axis represents DC power Pdc, and the vertical axis represents DC voltage Vdc. The configuration of Figure 4 will be described below with reference to Figure 5. 【0020】 The subtraction unit 121 subtracts the DC power command value Pdc* from the DC power Pdc and outputs the subtracted value to the setting units 122 and 124. The setting unit 122 and the limiting unit 123 perform processing to set the first characteristic region shown in Figure 5. Specifically, the setting unit 122 sets a first droop coefficient Kd1 corresponding to the characteristics of the first characteristic region. The droop coefficient Kd1 is information regarding the slope of the droop characteristic in the first characteristic region shown in Figure 5. The limiting unit 123 performs processing to set the range of the first characteristic region. The limiting unit 123 limits the input value so that it falls within a third predetermined range. The third predetermined range is the range from the lower limit to the upper limit, where the lower limit is the value obtained by subtracting the DC voltage command value Vdc* from a predetermined DC voltage lower limit Vdc_limL, and the upper limit is the value obtained by subtracting the DC voltage command value Vdc* from a predetermined DC voltage upper limit Vdc_limH. This sets the first characteristic region of the droop characteristic slope Kd1 shown in Figure 5. 【0021】 The setting unit 124, subtraction units 125 and 127, and limiting units 126 and 128 perform processing to set the second characteristic region. The second characteristic region is set to include at least one of the following: a characteristic region for power greater than the DC power corresponding to the first characteristic region (upper side), and a characteristic region for power less than the first characteristic region (lower side). In the examples in Figures 4 and 5, the second characteristic region is set above and below the first characteristic region. 【0022】 The setting unit 124, the subtraction unit 125, and the limiting unit 126 perform processing to set the second characteristic region (upper side) shown in Figure 5. Specifically, the setting unit 124 sets a second droop coefficient Kd2 corresponding to the characteristics of the second characteristic region. The droop coefficient Kd2 is information regarding the slope of the droop characteristic in the second characteristic region (upper side) shown in Figure 5. The slope Kd2 is less steep than the slope Kd1 (in other words, the change in DC voltage Vdc corresponding to the change in converter output Pdc in the second characteristic region is less than in the first characteristic region). 【0023】 The subtraction unit 125 subtracts the value calculated by the first calculation formula from the input value and outputs the subtracted value to the limiting unit 126. The first calculation formula is, for example, a formula for connecting the upper end of the first characteristic region and the lower end of the second characteristic region (upper side) shown in Figure 5. Specifically, it is the result of subtracting the DC voltage command value Vdc* from the DC voltage upper limit value Vdc_limH, dividing the result by the first droop coefficient Kd1, and then multiplying the result by the second droop coefficient Kd2 (Kd2*(Vdc_limH-Vdc*) / Kd1). 【0024】 The limiting unit 126 outputs a value that is positive (upper) than the range set for the first characteristic region, based on the value output by the subtracting unit 125. This sets the second characteristic region (upper) shown in Figure 5. 【0025】 Furthermore, the setting unit 124, the subtraction unit 127, and the limiting unit 128 perform processing to set the second characteristic region (lower side) shown in Figure 5. Specifically, the setting unit 124 sets the droop coefficient corresponding to the characteristics of the second characteristic region. The subtraction unit 127 subtracts the value calculated by the second calculation formula from the input value and outputs the subtracted value to the limiting unit 128. The second calculation formula is, for example, a formula for connecting the lower end of the first characteristic region and the upper end of the second characteristic region (lower side) shown in Figure 5. Specifically, it is obtained by subtracting the DC voltage command value Vdc* from the DC voltage lower limit value Vdc_limL, dividing the result by the first droop coefficient Kd1, and then multiplying the result by the second droop coefficient Kd2 (Kd2*(Vdc_limL-Vdc*) / Kd1). 【0026】 The limiting unit 128 outputs a value that is negative (lower) than the range set for the first characteristic region, based on the value output by the subtraction unit 127. As a result, the second characteristic region (lower side) shown in Figure 5 is set. 【0027】 The summing unit 129 outputs the combined output values ​​of the limiting units 123, 126, and 128. This allows the output characteristics of the power converter 10 (the operating point P1 of the DC voltage relative to the DC power) to be controlled by the characteristics of the first specific region and the second characteristic region in relation to the DC power Pdc and the DC voltage Vdc. In the above description, two second characteristic regions (upper and lower) were set, but in the embodiment, a configuration in which only one of the second characteristic regions is set may also be used. For example, if only the upper second characteristic region is set, the subtracting unit 127 and the limiting unit 128 are unnecessary in the configuration shown in Figure 4, and if only the lower second characteristic region is set, the subtracting unit 125 and the limiting unit 126 are unnecessary in the configuration shown in Figure 4. 【0028】 As described above, the value output by the droop control unit 120 is limited by the limiter control unit 150 using the upper limit value Ulim derived by the upper limit value derivation unit 130 and the lower limit value Llim derived by the lower limit value derivation unit 140, thereby limiting the DC power Pdc shown in Figure 5 to a range from the minimum output value Pdc_limL to the maximum output value Pdc_limH. This allows the operating point P1 to be controlled to lie on the DC power limiter (vertical line for the DC power lower limit value Pdc_limL and vertical line for the DC power upper limit value Pdc_limH shown in Figure 5) within the range of the Vdc limiter. In addition, in this embodiment, when the DC voltage Vdc limiter is reached, the control device 100 operates in such a way that the operating point P1 lies on the DC voltage Vdc limiter (horizontal line for the maximum DC voltage value Vdcmax and horizontal line for the minimum DC voltage value Vdcmin shown in Figure 5). In this way, by setting upper and lower limits on the DC voltage output by the power converter 10, as well as upper and lower limits on the output capacity, it is possible to accommodate a variety of grid operations. 【0029】 [Processing flow] Figure 6 is a flowchart showing an example of the processing flow performed by the control device 100 according to the embodiment. First, the control device 100 detects the DC power Pdc of the power converter 10 to be controlled (step S100). Next, the subtraction unit 110 subtracts the DC power Pdc by the DC power command value Pdc* (step S110). Next, the droop control unit 120 sets a first characteristic region and a second characteristic region in the relationship between the DC power Pdc and the DC voltage Pdc based on the DC power Pdc and the DC power command value Pdc* (step S130). Next, the upper limit value derivation unit 130 derives the upper limit value Ulim of the output voltage of the power converter 10 to be controlled (step S140). Also, the lower limit value derivation unit 140 derives the lower limit value Llim of the output voltage of the power converter 10 to be controlled (step S150). 【0030】 Next, the control unit performs droop control based on the first characteristic region, the second characteristic region, the upper limit, and the lower limit, and controls the power converter 10 to be controlled so that the output voltage (DC voltage Vdc) is output with a droop control that is different from that in the first characteristic region, at least in the second characteristic region (step S160). 【0031】 In addition, in the configuration of the control device 100 of this embodiment, an adder 160 may be placed after the droop control unit 120 shown in Figure 3, and the output of the adder 160 may be used as the input to the limiter 150. In this case, the output upper limit Ulim derived by the upper limit derivation unit 130 and the output lower limit Llim derived by the lower limit derivation unit 140 are also adjusted, taking into account the output result of the adder 160. 【0032】 For example, in conventional multi-terminal DC power transmission systems, the balance of cell capacitor voltages in power converters other than the one experiencing a fault may be disrupted due to the fault and droop characteristics, preventing the power converter from continuing operation. Furthermore, during large fluctuations such as DC faults at other terminals, the DC current of the converter at its own terminal fluctuates significantly due to the fault current, causing a large fluctuation in DC power Pdc. Consequently, the DC voltage Vdc at its own terminal may also fluctuate according to the slope of the droop. Additionally, although capacitor voltage control attempts to restore the capacitor voltage within the converter, which has been affected by the fault, to a normal value, the control performance of the capacitor voltage deteriorates when the DC voltage Vdc is fluctuating. This can lead to the capacitor voltage fluctuation exceeding the protection stop threshold, potentially causing the power converter to shut down. Therefore, in this embodiment, the control device 100 adjusts the droop characteristics (first characteristic region, second characteristic region) so that the operating range of the operating point P1 becomes a low voltage when a fault occurs in any of the multiple power converters included in the multi-terminal DC power transmission system 1, or when a large power fluctuation (converter output fluctuation) occurs in a power converter. 【0033】 Figure 7 is a flowchart showing an example of droop characteristic adjustment control. In the example shown in Figure 7, the control device 100 determines whether or not a fault or oscillation (such as power oscillation) has occurred in the power converter in the multi-terminal DC power transmission system 1 (step S200). In the process of step S200, for example, the determination of whether a fault or oscillation has occurred may be made based on a notification from the administrator of the multi-terminal DC power transmission system 1 or a notification from a higher-level system of the multi-terminal DC power transmission system 1, or it may be made based on a voltage value V (DC voltage detection value Vd) detected by the DC voltage detector 20 or a current value I detected by the DC current detector 30. 【0034】 If an accident or disturbance is detected, the droop control unit 120 controls the droop characteristics so that the voltage at the operating point (the operating point P1 for DC voltage relative to DC power) corresponding to the characteristics of DC power and DC voltage becomes lower than a reference value (an example of a reference) (step S210). The reference value may be, for example, the voltage value of the power converter 10 under normal conditions, or a predetermined value. 【0035】 Next, the droop control unit 120 determines whether the multi-terminal DC power transmission system 1 has returned to normal (whether the accident or disturbance has been resolved) (step S220). If it determines that it has returned to normal, the droop control unit 120 restores the droop characteristics to their original characteristics, or updates the droop characteristics to match the post-disturbance situation as the normal droop characteristics (step S230). Also, if it is determined in the process of step S200 that no accident or disturbance has occurred, it controls the system with the normal droop characteristics (step S240). This completes the process in this flowchart. Furthermore, if it is determined in the process of step S220 that it has not returned to normal, the process is terminated while maintaining the controlled (modified) droop characteristics. This contributes to maintaining the controllability of the capacitor voltage in the converter and further improves the operational continuity of the power converter. 【0036】 Next, the specific details of the process in step S210 will be explained in several examples. (First embodiment) In the first embodiment, for example, in the event of an accident or tremor, the droop characteristics (first characteristic region, second characteristic region) are manipulated so that the voltage at the operating point is lower than under normal conditions. 【0037】 Figure 8 shows an example of a control method for the case of having two different droop characteristics according to the first embodiment. In the example of Figure 8, the characteristic regions (first characteristic region, second characteristic region) of the two-stage droop control (droop coefficients Kd1, Kd2) as shown in Figure 5 above are extracted and shown. 【0038】 In the first embodiment, the control device 100 controls the operating point P1 of the DC voltage Vdc to be lower than before the switching by increasing the first droop coefficient (slope) Kd1 and decreasing the second droop coefficient (slope) Kd2 when an accident occurs or the converter output fluctuates. In the example of FIG. 7, the characteristics are switched such that "Kd1'>Kd1" in the first characteristic region and further "Kd2'<Kd2" in the second characteristic region (lower side). Thereby, for example, when an accident or a large fluctuation occurs, the droop characteristic can be adjusted so that the operating range of the DC power command value Vdc* becomes a lower voltage, which contributes to maintaining the controllability of the capacitor voltage and can further improve the operation continuity of the power converter. 【0039】 Note that the first embodiment may be applied only to, for example, the droop characteristic (first characteristic region) of one stage (first droop coefficient Kd1). FIG. 9 is a diagram showing an example of control in the case of only the first characteristic region. As shown in FIG. 9, even when the droop control unit 120 has only the characteristic region of the first droop coefficient Kd1, the same effect can be obtained by operating the droop characteristic so that the voltage of the operating point P1 becomes low (the slope becomes large) when an accident or a fluctuation occurs. 【0040】 (Second Embodiment) Next, the second embodiment will be described. In the second embodiment, in the droop characteristic, the DC voltage command value Vdc* is switched to be decreased when an accident occurs or the converter output fluctuates. FIG. 10 is a diagram for explaining the switching of decreasing the DC voltage command value Vdc according to the second embodiment. 【0041】 In the second embodiment, the droop control unit 120 reduces the DC voltage command value Vdc* when a fault occurs or when the converter output fluctuates, causing the first characteristic region and the second characteristic region (upper and lower sides) to drop from the solid line portion to the dotted line portion in Figure 10. As a result, the DC voltage Vdc output is based on the characteristics on the dotted line, as shown in the operating point P2. In this way, the control in the second embodiment makes it possible to lower the operating point of the DC voltage, which contributes to maintaining the controllability of the capacitor voltage and further improves the operational continuity of the power converter. 【0042】 (Third embodiment) Next, a third embodiment will be described. In the third embodiment, in the droop characteristics, the DC voltage operating point is controlled to be lowered by adjusting the limiter values ​​of the droop control output (maximum DC voltage Vdcmax, minimum DC voltage Vdcmin) when a fault occurs or when the converter output fluctuates. 【0043】 Figure 11 shows an example of droop-specific control according to the third embodiment. In the third embodiment, as shown in Figure 11, the control device 100 sets a DC voltage maximum value Vdcmax' which is at least smaller than the DC voltage maximum value Vdcmax when a fault occurs or when the converter output fluctuates. Note that the DC voltage maximum value Vdcmax' is set to a value smaller than the DC voltage command value. By adjusting the DC voltage maximum value Vdcmax' in this way, the normal operating point P1 can be operated at an operating point P2 where the DC voltage Vdc is smaller than the DC voltage maximum value Vdcmax'. 【0044】 In the third embodiment, the control device 100 sets a minimum DC voltage value Vdcmin', which is an increased value of the minimum DC voltage value Vdcmin, in addition to the maximum DC voltage value Vdcmax, and controls the device to narrow the range of DC power (output voltage). The minimum DC voltage value Vdcmin' is adjusted to be less than or equal to the maximum DC voltage value Vdcmax'. This makes it possible to further stabilize the operating point P2 in the event of a fault or when the converter output is unstable. 【0045】 As demonstrated in the above embodiment, by adjusting the droop characteristics to lower the operating voltage range of the DC voltage command value Vdc* in the event of an accident or significant shaking, it is possible to maintain the controllability of the capacitor voltage and further improve the continuity of operation of the power converter. 【0046】 In addition, in the first to third embodiments described above, the degree to which the DC voltage operating point is lowered may be adjusted, for example, depending on the type and scale of the fault, the scale of power fluctuations, etc., or it may be lowered by a predetermined rate or amount of reduction. 【0047】 Each of the first to third embodiments described above may be combined with some or all of the other embodiments. Furthermore, while the first to third embodiments described the case where the output voltage is positive, for the negative case, the magnitudes should be reversed. Although the first to third embodiments mainly described the case where there are characteristic regions (first characteristic region, second characteristic region) in a two-stage droop control (droop coefficients Kd1, Kd2), they can also be applied to a single-stage droop control (droop coefficient Kd1) with only a characteristic region (first characteristic region). In this case, the configuration of the droop control unit 120 shown in Figure 4 is applied, excluding the setting unit 124, subtraction units 125, 127, and limiting units 126, 128. 【0048】 According to the above-described embodiment, the control device 100 includes a control unit that controls a power converter, which is included in a multi-terminal DC power transmission system configured by connecting the DC sides of a plurality of power converters that convert AC and DC to each other, so that the output voltage on the DC terminal side of the power converter to be controlled falls within a predetermined range. The control unit sets a first characteristic region and a second characteristic region that have predetermined droop characteristics in the relationship between DC power and output voltage based on the DC power and DC power command value of the power converter to be controlled, and controls the power converter so that the voltage is output with a different droop control in the second characteristic region than in the first characteristic region. This makes it possible to control the operation of the power converter more appropriately in a multi-terminal DC power transmission system. 【0049】 Furthermore, according to the above-described embodiment, the control device 100 includes a control unit that controls a power converter among a plurality of power converters included in a multi-terminal DC power transmission system, which is configured by connecting the DC sides of a plurality of power converters that convert AC and DC to each other, so that the output voltage on the DC terminal side of the power converter to be controlled is output based on droop control using a predetermined droop characteristic. The control unit controls the droop characteristic so that the operating point of the output voltage becomes lower than a reference when a fault occurs in the multi-terminal DC power transmission system or when the output of the power converter fluctuates, thereby further improving the operational continuity of the power converter. 【0050】 While several embodiments of the present invention have been described, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These embodiments can be carried out in a variety of other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims and their equivalents. [Explanation of Symbols] 【0051】 1…Multi-terminal DC power transmission system, 10…Power converter, 100…Control device, 110, 132, 142, 170…Subtraction unit, 120…Droop control unit, 130…Upper limit derivation unit, 134, 144, 180…PI control unit, 136, 146, 150…Limiting unit, 140…Lower limit derivation unit, 160 Addition unit

Claims

[Claim 1] A multi-terminal DC power transmission system is configured by connecting the DC sides of multiple power converters that convert AC and DC to each other. The system includes a control unit that controls the power converters so that the output voltage on the DC terminal side of the power converter to be controlled is output based on droop control using predetermined droop characteristics. The control unit controls the droop characteristics such that the operating point of the output voltage becomes lower than the reference point when a fault occurs in the multi-terminal DC power transmission system or when the output fluctuation of the power converter occurs. Control device. [Claim 2] The control unit adjusts the value of the droop coefficient, which is associated with the droop characteristics, so that the operating point of the output voltage becomes lower than the reference when the fault occurs or when the output of the power converter is unstable. The control device according to claim 1. [Claim 3] The droop characteristics include a first characteristic region based on a first droop coefficient and a second characteristic region based on a second droop coefficient. The second characteristic region performs droop control differently from the first characteristic region. The control unit, in the event of the fault or when the output of the power converter fluctuates, adjusts the first droop coefficient to increase and the second droop coefficient to decrease, thereby controlling the operating point of the output voltage to be lowered. The control device according to claim 1. [Claim 4] The control unit adjusts the DC voltage command value to the power converter under control so that the operating point of the output voltage becomes lower when the fault occurs or when the output of the power converter is unstable. The control device according to claim 1. [Claim 5] The control unit adjusts the maximum value of the output voltage by the droop control when the fault occurs or when the output of the power converter fluctuates, so that the operating point of the output voltage is lowered. The control device according to claim 1. [Claim 6] The control unit adjusts the minimum value of the output voltage by the droop control to narrow the range of the output voltage. The control device according to claim 5. [Claim 7] Computers In a multi-terminal DC power transmission system, which is configured by connecting the DC sides of multiple power converters that convert AC and DC to each other, the power converters are controlled such that the output voltage of the DC terminal side of the power converter to be controlled is output based on droop control using a predetermined droop characteristic. The droop characteristics are controlled so that the operating point of the output voltage becomes lower than a reference point when a fault occurs in the multi-terminal DC power transmission system or when the output fluctuation of the power converter occurs. A control method for power converters. [Claim 8] On the computer, In a multi-terminal DC power transmission system, which is configured by connecting the DC sides of multiple power converters that convert AC and DC to each other, the power converters are controlled such that the output voltage of the DC terminal side of the power converter to be controlled is output based on droop control using a predetermined droop characteristic. The droop characteristics are controlled so that the operating point of the output voltage becomes lower than the reference point when a fault occurs in the multi-terminal DC power transmission system or when the output fluctuation of the power converter occurs. program.

Images