Power converter

Abstract

The present invention provides a power conversion device that can properly cool the converter and suppress unnecessary power consumption in the cooling device. [Solution] A power conversion device is provided that includes a main circuit section having a converter for converting power, a control device for controlling the operation of power conversion by the main circuit section, and a cooling device for cooling the converter. The converter can convert power and change the magnitude of the power output from the main circuit section by switching a switching element, the loss of the converter changes according to the magnitude of the power output from the main circuit section, the cooling device can change the cooling capacity of the converter and reduce power consumption in accordance with the decrease in the cooling capacity of the converter, and acquires a converter status signal representing the state of the loss of the converter, and based on the converter status signal, reduces the cooling capacity of the converter in accordance with the decrease in the loss of the converter, thereby reducing power consumption.

Description

Technical Field

[0001] Embodiments of the present invention relate to a power conversion device.

Background Art

[0002] There is a power conversion device including a converter that performs power conversion, a control device that controls the operation of the converter, and a cooling device that cools the converter. The cooling device cools the converter by driving a pump, for example, to circulate a cooling medium.

[0003] The converter has switching elements, performs power conversion by switching the switching elements, and can change the magnitude of the output power by adjusting the switching interval of the switching elements. The converter varies its output according to, for example, the situation on the load side such as the power grid. Therefore, the converter does not always output the maximum power, and the timing when the output of the converter becomes maximum is limited.

[0004] The cooling capacity of the cooling device is set according to the maximum loss (heat generation of the converter) assumed in the converter so that the converter can be appropriately cooled even when the converter is outputting the maximum power. In this case, even during low-output operation in which the converter outputs power of a magnitude lower than the maximum power magnitude, or during standby operation in which the converter has stopped power output, the cooling device performs a constant operation according to the maximum loss of the converter. Therefore, during low-output operation or standby operation of the converter, the cooling capacity of the cooling device becomes excessive, resulting in unnecessary power consumption in the cooling device.

[0005] For this reason, in a power conversion device, it is desirable to be able to appropriately cool the converter while suppressing unnecessary power consumption in the cooling device.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

[0007] Embodiments of the present invention provide a power conversion device that can properly cool the converter and suppress unnecessary power consumption in the cooling device. [Means for solving the problem]

[0008] According to an embodiment of the present invention, a power conversion device is provided that includes a main circuit section having a converter for converting power, a control device for controlling the operation of power conversion by the main circuit section, and a cooling device for cooling the converter, wherein the converter has a switching element, and by switching the switching element, it can convert power and change the magnitude of the power output from the main circuit section, the loss of the converter changes according to the magnitude of the power output from the main circuit section, the cooling device can change the cooling capacity of the converter and reduce power consumption in accordance with the decrease in the cooling capacity of the converter, and a converter status signal representing the loss state of the converter is acquired, and based on the converter status signal, the cooling capacity of the converter is reduced in accordance with the decrease in the loss of the converter, thereby reducing power consumption. [Effects of the Invention]

[0009] A power conversion device is provided that can properly cool the converter and suppress unnecessary power consumption in the cooling device. [Brief explanation of the drawing]

[0010] [Figure 1] This is a schematic block diagram showing a power conversion device according to the first embodiment. [Figure 2] This is a schematic block diagram showing the converter and cooling device according to the first embodiment. [Figure 3]This is a schematic block diagram showing a modified example of the converter and cooling device according to the first embodiment. [Figure 4] This is a schematic block diagram showing a modified example of the converter and cooling device according to the first embodiment. [Figure 5] This is a schematic block diagram showing the converter and cooling device according to the second embodiment. [Figure 6] This is a schematic block diagram showing a converter and cooling device according to the third embodiment. [Figure 7] This is a schematic block diagram showing the converter and cooling device according to the fourth embodiment. [Figure 8] This is a schematic block diagram showing the converter and cooling device according to the fifth embodiment. [Figure 9] This graph schematically illustrates an example of the operation of a control device. [Modes for carrying out the invention]

[0011] Each embodiment will be described below with reference to the drawings. Please note that the drawings are schematic or conceptual, and the relationships between the thickness and width of each part, as well as the ratios of the sizes of the parts, are not necessarily identical to those of reality. Furthermore, even when representing the same part, the dimensions and ratios may differ between drawings. In this specification and in each figure, elements similar to those described above are denoted by the same reference numerals, and detailed explanations are omitted as appropriate.

[0012] (First Embodiment) Figure 1 is a schematic block diagram showing a power conversion device according to the first embodiment. As shown in Figure 1, the power converter 10 comprises a main circuit section 12 and a control device 14. The power converter 10 is used, for example, in a DC power transmission system. In the DC power transmission system, the power converter 10 is connected to the AC power system 2 and a pair of DC transmission lines 3 and 4.

[0013] The DC power transmission system has, for example, a transformer 6. The main circuit section 12 of the power conversion device 10 is connected to the AC power system 2 via the transformer 6. The AC power of the AC power system 2 is three-phase AC power. More specifically, it is symmetric three-phase AC power. The transformer 6 converts the three-phase AC power of the AC power system 2 into AC power corresponding to the main circuit section 12. The transformer 6 changes the effective value of each phase of the three-phase AC power according to the main circuit section 12. The transformer 6 is a three-phase transformer. The transformer 6 is provided as required and can be omitted. The three-phase AC power of the AC power system 2 may be directly supplied to the main circuit section 12.

[0014] The power conversion device 10 converts the three-phase AC power supplied from the AC power system 2 into DC power and supplies the converted DC power to the DC transmission lines 3 and 4. Also, the power conversion device 10 converts the DC power supplied from the DC transmission lines 3 and 4 into three-phase AC power and supplies the converted three-phase AC power to the AC power system 2. Thus, the power conversion device 10 performs AC-DC conversion and DC-AC conversion. Also, in this example, the AC power system 2 is shown as an AC circuit, and each DC transmission line 3 and 4 is shown as a DC circuit. The AC circuit may be, for example, an AC load or an AC power source. The DC circuit may be, for example, a DC load or a DC power source.

[0015] For example, the DC transmission line 3 is a transmission line on the high-voltage side of the DC power, and the DC transmission line 4 is a transmission line on the low-voltage side of the DC power. The power conversion device 10 outputs the converted DC power to the DC transmission lines 3 and 4 such that the DC transmission line 3 side is high voltage and the DC transmission line 4 side is low voltage.

[0016] The main circuit unit 12 is provided between the AC power system 2 and each of the DC transmission lines 3 and 4. The main circuit unit 12 performs the conversion from three-phase AC power to DC power and the conversion from DC power to three-phase AC power. The main circuit unit 12 is, for example, a multilevel power converter having a plurality of converters connected in series. The main circuit unit 12 is, for example, a power converter of the MMC (Modular Multilevel Converter) type. The MMC-type main circuit unit 12 has a plurality of converters connected in series. Each converter has a plurality of switching elements connected in a half-bridge connection or a full-bridge connection, and a charge storage element connected in parallel to each switching element. The main circuit unit 12 performs power conversion by the operation of the plurality of converters. The main circuit unit 12 performs AC-DC conversion, for example, by switching each switching element of the plurality of converters. The plurality of converters have a plurality of switching elements and perform power conversion by switching the plurality of switching elements.

[0017] The control device 14 is connected to the main circuit unit 12. The control device 14 controls the conversion from three-phase AC power to DC power and the conversion from DC power to three-phase AC power by the main circuit unit 12 by controlling the on / off of each switching element.

[0018] The main circuit unit 12 has a pair of first and second DC terminals 20a and 20b, three AC terminals 21a to 21c from the first to the third, and six arm portions 22a to 22f from the first to the sixth.

[0019] The first DC terminal 20a is connected to the high-voltage side DC transmission line 3. The second DC terminal 20b is connected to the low-voltage side DC transmission line 4. Thereby, the DC power converted by the main circuit unit 12 is supplied to the DC transmission lines 3 and 4, and the DC power supplied from the DC transmission lines 3 and 4 is input to the main circuit unit 12.

[0020] The first arm section 22a is connected to the first DC terminal 20a. The second arm section 22b is connected between the first arm section 22a and the second DC terminal 20b. The first arm section 22a and the second arm section 22b are connected in series between the respective DC terminals 20a and 20b.

[0021] The third arm section 22c is connected to the first DC terminal 20a. The fourth arm section 22d is connected between the third arm section 22c and the second DC terminal 20b. The third arm section 22c and the fourth arm section 22d are connected in parallel to the first arm section 22a and the second arm section 22b.

[0022] The fifth arm section 22e is connected to the first DC terminal 20a. The sixth arm section 22f is connected between the fifth arm section 22e and the second DC terminal 20b. That is, the fifth arm section 22e and the sixth arm section 22f are connected in parallel to the first arm section 22a and the second arm section 22b, and also in parallel to the third arm section 22c and the fourth arm section 22d.

[0023] In the main circuit section 12, the first leg LG1 is formed by the first arm section 22a and the second arm section 22b, the second leg LG2 is formed by the third arm section 22c and the fourth arm section 22d, and the third leg LG3 is formed by the fifth arm section 22e and the sixth arm section 22f. In other words, in this example, the main circuit section 12 is a three-phase inverter with three legs and six arms. To put it another way, the main circuit section 12 has multiple bridge-connected arm sections 22a to 22f. In this example, the main circuit section 12 has six three-phase bridge-connected arm sections 22a to 22f.

[0024] The first arm section 22a, the third arm section 22c, and the fifth arm section 22e are upper arms. The second arm section 22b, the fourth arm section 22d, and the sixth arm section 22f are lower arms. Thus, the main circuit section 12 has multiple arm sections and multiple legs, each composed of multiple switching elements. The main circuit section 12 may be, for example, a single-phase inverter with 2 legs and 4 arms. The number of arm sections and legs is not limited to those described above and may be any number.

[0025] The first arm section 22a has a plurality of converters UP1, UP2...UPM1 connected in series. The second arm section 22b has a plurality of converters UN1, UN2...UNM2 connected in series. The third arm section 22c has a plurality of converters VP1, VP2...VPM3 connected in series. The fourth arm section 22d has a plurality of converters VN1, VN2...VNM4 connected in series. The fifth arm section 22e has a plurality of converters WP1, WP2...WPM5 connected in series. The sixth arm section 22f has a plurality of converters WN1, WN2...WNM6 connected in series.

[0026] However, in the following, when referring to each converter UP1, UP2...UPM1, UN1, UN2...UNM2, VP1, VP2...VPM3, VN1, VN2...VNM4, WP1, WP2...WPM5, WN1, WN2...WNM6 collectively, they will be referred to as "Converter CEL".

[0027] In each arm section 22a to 22f, M1, M2, M3, M4, M5, and M6 represent the number of series-connected converter CELs. In each arm section 22a to 22f, the number of series-connected converter CELs is, for example, around 100 to 120 units. However, the number of series-connected converter CELs is not limited to this and can be any number.

[0028] The number of converter CELs provided in each arm section 22a to 22f is substantially the same. For example, if a large number of converter CELs are connected, the number of converter CELs provided in each arm section 22a to 22f may differ to the extent that it does not affect the operation of the main circuit section 12. For example, if 100 converter CELs are connected in series to one arm section, the number of converter CELs provided in other arm sections may differ by 1 to 2.

[0029] Each of the arm sections 22a to 22f further comprises buffer reactors 23a to 23f and a plurality of current detectors 24a to 24f. The power conversion device 10 also further comprises a voltage detection unit 25.

[0030] Each buffer reactor 23a to 23f is connected in series to each converter CEL in each of the arm sections 22a to 22f. The buffer reactor 23a of the first arm section 22a is provided between the AC terminal 21a and the connection point between the first arm section 22a and the second arm section 22b and converter UP1. The buffer reactor 23b of the second arm section 22b is provided between the AC terminal 21a and the connection point between the first arm section 22a and the second arm section 22b and converter UN1. The buffer reactor 23c of the third arm section 22c is provided between the AC terminal 21b and the connection point between the third arm section 22c and the fourth arm section 22d and converter VP1. The buffer reactor 23d of the fourth arm section 22d is provided between the AC terminal 21b and the connection point between the third arm section 22c and the fourth arm section 22d and converter VN1. The buffer reactor 23e of the fifth arm section 22e is provided between the connection point between the AC terminal 21c and the fifth arm section 22e and the sixth arm section 22f and the converter WP1. The buffer reactor 23f of the sixth arm section 22f is provided between the connection point between the AC terminal 21c and the fifth arm section 22e and the sixth arm section 22f and the converter WN1.

[0031] The current detector 24a is installed on the first arm portion 22a and detects the current flowing through the first arm portion 22a. That is, the current detector 24a detects the arm current of the first arm portion 22a. The current detector 24a is connected to the control device 14 via wiring, etc., which is not shown in the figure. The current detector 24a inputs the detected current value of the first arm portion 22a to the control device 14. As a result, the control device 14 receives the current value of the first arm portion 22a.

[0032] Similarly, current detector 24b detects the current flowing through the second arm section 22b and inputs the detected current value to the control device 14. Current detector 24c detects the current flowing through the third arm section 22c and inputs the detected current value to the control device 14. Current detector 24d detects the current flowing through the fourth arm section 22d and inputs the detected current value to the control device 14. Current detector 24e detects the current flowing through the fifth arm section 22e and inputs the detected current value to the control device 14. Current detector 24f detects the current flowing through the sixth arm section 22f and inputs the detected current value to the control device 14.

[0033] The voltage detection unit 25 detects the AC voltage (phase voltage) of each phase of the AC power system 2 and inputs the detected value to the control device 14. The voltage detection unit 25 may be connected to the primary side or the secondary side of the transformer 6.

[0034] In the main circuit section 12, the connection points between the first arm section 22a and the second arm section 22b, the connection points between the third arm section 22c and the fourth arm section 22d, and the connection points between the fifth arm section 22e and the sixth arm section 22f each serve as AC output points.

[0035] The first AC terminal 21a is connected to the connection point between the first arm section 22a and the second arm section 22b. The second AC terminal 21b is connected to the connection point between the third arm section 22c and the fourth arm section 22d. The third AC terminal 21c is connected to the connection point between the fifth arm section 22e and the sixth arm section 22f. Each of the AC terminals 21a to 21c is connected to, for example, the transformer 6.

[0036] Each converter CEL is connected to the control device 14, for example, via a signal line 26. The control device 14 controls the operation of the converter CEL by inputting control signals to the converter CEL via the signal line 26. The converter CEL also inputs control signals and protection signals related to the control and operation protection of the converter CEL to the control device 14 via another signal line (not shown).

[0037] The communication method between the control device 14 and each converter CEL is not limited to the above. For example, multiple converter CELs connected in series may be daisy-chained, and the control device 14 may communicate only with the converter CEL at one end of the daisy-chained connection and the converter CEL at the other end. The communication method between the control device 14 and each converter CEL may be any communication method that allows for appropriate communication between the control device 14 and each converter CEL.

[0038] Figure 2 is a schematic block diagram showing the converter and cooling device according to the first embodiment. As shown in Figure 2, the converter CEL has a plurality of switching elements 41, 42, a plurality of rectifier elements 51, 52, a charge storage element 60, and a pair of connection terminals 61, 62.

[0039] Each switching element 41, 42 has a pair of main terminals and a control terminal. The control terminal controls the current flowing between the pair of main terminals. Self-extinguishing elements such as IGBTs are used for each switching element 41, 42. The pair of main terminals are, for example, an emitter and a collector, and the control terminal is, for example, a gate.

[0040] Each switching element 41, 42 switches between an ON state, which allows current to flow between the pair of main terminals, and an OFF state, which blocks the current flowing between the pair of main terminals. The OFF state is not limited to a state in which no current flows at all between the pair of main terminals; for example, it may be a state in which a very weak current flows between the pair of main terminals, such that it does not affect the operation of the converter CEL. In other words, the OFF state is a state in which the current flowing between the pair of main terminals is sufficiently small.

[0041] Each switching element 41, 42 is, for example, a normally-off semiconductor element. Each switching element 41, 42 is turned on when the voltage at the control terminal is high, and turned off when the voltage at the control terminal is low. Each switching element 41, 42 is turned off when the voltage at the control terminal is lower than the voltage at the ON state. Each switching element 41, 42 is, for example, turned on when a positive voltage is applied to the control terminal, and turned off when the voltage at the control terminal is set to 0V or when a negative voltage is applied to the control terminal.

[0042] The pair of main terminals of switching element 42 are connected in series with the pair of main terminals of switching element 41. In this example, the converter CEL has two switching elements 41 and 42 connected in series. In other words, the converter CEL has two switching elements 41 and 42 connected in a half-bridge configuration. In this example, the converter CEL is a converter with a half-bridge configuration.

[0043] The rectifier element 51 is connected in antiparallel to the pair of main terminals of the switching element 41. The forward direction of the rectifier element 51 is opposite to the direction of the current flowing between the pair of main terminals of the switching element 41. Similarly, the rectifier element 52 is connected in antiparallel to the pair of main terminals of the switching element 42. The rectifier elements 51 and 52 are so-called freewheeling diodes.

[0044] The connection terminal 61 is connected between the switching element 41 and the switching element 42. The connection terminal 62 is connected to the main terminal of the switching element 41 on the opposite side of the main terminal connected to the switching element 42.

[0045] Multiple converters CEL within the same arm are connected in series via a pair of connection terminals 61 and 62. Power is supplied to the converters CEL via each connection terminal 61 and 62. Switching element 41 is a so-called low-side switch, and switching element 42 is a so-called high-side switch.

[0046] The converter CEL communicates with the control device 14 via signal line 26 and a transmission circuit (not shown in the figure). The control device 14 transmits control signals to each converter CEL via signal line 26 to switch the on and off states of each switching element 41, 42.

[0047] The converter CEL switches the on and off states of each switching element 41 and 42 based on the control signal received from the control device 14. This controls the on / off state of each switching element 41 and 42 in accordance with the drive command from the control device 14. The control device 14 generates a control signal for each converter CEL and controls the on / off state of each switching element 41 and 42 in each converter CEL. In this way, the control device 14 controls the power conversion by the main circuit unit 12.

[0048] The charge storage element 60 is connected in parallel to the switching elements 41 and 42. The charge storage element 60 is, for example, a capacitor.

[0049] When switching element 41 is in the off state and switching element 42 is in the on state, the voltage of the charge storage element 60 appears between the connection terminals 61 and 62. When switching element 41 is in the on state and switching element 42 is in the off state, the connection terminals 61 and 62 conduct, and the voltage between the connection terminals 61 and 62 becomes virtually zero.

[0050] In this way, the converter CEL switches between an output state in which the voltage of the charge storage element 60 is output between the connection terminals 61 and 62, a bypass state in which the connection terminals 61 and 62 are conductive, and a stopped state in which the switching elements 41 and 42 are turned off, by switching the switching elements 41 and 42 based on the control signal from the control device 14. The converter CEL enters the bypass state by turning on the lower switching element 41 of the two half-bridge connected switching elements 41 and 42.

[0051] In each arm section 22a to 22f, the total voltage of the converter CELs in the output state becomes the voltage of each arm section 22a to 22f. The main circuit section 12 and the control device 14 perform multi-level power conversion by controlling the number of converter CELs that are in the output state.

[0052] Furthermore, the main circuit unit 12 and the control device 14 can change the magnitude of at least one of the AC power and DC power output from the main circuit unit 12 by controlling the number of converter CELs that are in the output state. The loss of the converter CEL changes according to the magnitude of the power output from the main circuit unit 12. The loss of the converter CEL decreases as the magnitude of the power output from the main circuit unit 12 decreases.

[0053] When both switching elements 41 and 42 are in the off state (when the converter CEL is stopped), the voltage between each connection terminal 61 and 62 is determined by the direction of the arm current. For example, when the arm current flows from connection terminal 62 to connection terminal 61, the rectifier element 51 turns on, and the voltage between each connection terminal 61 and 62 becomes virtually zero. Conversely, when the arm current flows from connection terminal 61 to connection terminal 62, the rectifier element 52 turns on, the charge storage element 60 is charged, and the voltage of the charge storage element 60 appears between each connection terminal 61 and 62.

[0054] As shown in Figure 2, the power converter 10 further includes a cooling device 80 for cooling the converter CEL. The power converter 10 includes, for example, multiple cooling devices 80 corresponding to multiple converter CELs. Multiple cooling devices 80 are provided, for example, for each of the multiple converter CELs. However, the number of multiple cooling devices 80 does not necessarily have to be the same as the number of multiple converter CELs.

[0055] One cooling device 80 may be used in common for multiple converter CELs. The power converter 10 may, for example, have six cooling devices 80 provided for each arm section 22a to 22f. The cooling devices 80 may, for example, cool multiple converter CELs connected in series in each arm section 22a to 22f. Alternatively, the power converter 10 may cool all converter CELs with a single cooling device 80. The number of cooling devices 80 provided in the power converter 10 can be any number.

[0056] The cooling device 80 includes a cooling pipe 81, a pump 82, a cooler 83, a drive circuit 84, and a control unit 85.

[0057] The cooling tube 81 constitutes a path for cooling the converter CEL by circulating a cooling medium such as water. At least a portion of the cooling tube 81 is installed inside the converter CEL. At least a portion of the cooling tube 81 is installed in close proximity to each of the elements, for example, the switching elements 41, 42, the rectifier elements 51, 52, and the charge storage element 60. In this way, the cooling tube 81 cools each of these elements of the converter CEL.

[0058] The pump 82 is located along the path of the cooling pipe 81 and circulates the cooling medium in the cooling pipe 81 by applying pressure to it.

[0059] The cooler 83 is installed along the path of the cooling pipes 81 and cools the cooling medium circulating within the cooling pipes 81 in response to the drive of the pump 82. The cooler 83 is, for example, a heat exchanger. If the cooling medium can be adequately cooled, for example, by exposing the cooling pipes 81 to the outside air, the cooler 83 may be omitted. The cooler 83 is provided as needed and can be omitted.

[0060] The drive circuit 84 drives the pump 82. The drive circuit 84 controls the rotational speed of the pump 82, for example, by controlling the amount of power supplied to the pump 82. In this way, the cooling device 80 can control the flow rate of the cooling medium circulating in the cooling pipes 81 per unit time by controlling the rotational speed of the pump 82. In other words, in the cooling device 80, increasing the rotational speed of the pump 82 increases the flow rate of the cooling medium circulating in the cooling pipes 81 per unit time, and decreasing the rotational speed of the pump 82 decreases the flow rate of the cooling medium circulating in the cooling pipes 81 per unit time.

[0061] As a result, the cooling device 80 can change the cooling capacity of the converter CEL by controlling the rotation speed of the pump 82. The cooling device 80 can increase the cooling capacity of the converter CEL by increasing the rotation speed of the pump 82 and increasing the flow rate of the cooling medium circulating in the cooling pipe 81 per unit time, and decrease the cooling capacity of the converter CEL by decreasing the rotation speed of the pump 82 and decreasing the flow rate of the cooling medium circulating in the cooling pipe 81 per unit time.

[0062] Furthermore, in the cooling device 80, the power consumption of the cooling device 80 (pump 82) can be changed by controlling the rotation speed of the pump 82. In the cooling device 80, increasing the rotation speed of the pump 82 increases the power consumption of the cooling device 80, while decreasing the rotation speed of the pump 82 decreases the power consumption of the cooling device 80. In other words, the power consumption of the cooling device 80 can be reduced by lowering the cooling capacity of the converter CEL.

[0063] The maximum rotational speed of the pump 82 (the maximum flow rate per unit time of the cooling medium circulating in the cooling tube 81) is set according to, for example, the maximum loss of the converter CEL (the maximum heat generated by the converter CEL) when the main circuit unit 12 outputs the maximum amount of AC and DC power. This ensures that the converter CEL is properly cooled even when the main circuit unit 12 outputs the maximum amount of AC and DC power, thereby suppressing failures of the converter CEL.

[0064] The control unit 85 controls the operation of the pump 82 by controlling the operation of the drive circuit 84. The control unit 85 controls the driving and stopping of the pump 82, as well as the rotational speed of the pump 82, by controlling the operation of the drive circuit 84. In other words, the drive circuit 84 switches between driving and stopping the pump 82, and changes the rotational speed of the pump 82, based on the control of the control unit 85.

[0065] The control unit 85 acquires a converter status signal representing the loss state of the converter CEL and controls the operation of the pump 82 based on the converter status signal. Based on the converter status signal, the control unit 85 controls the operation of the pump 82 to lower the cooling capacity of the converter CEL in accordance with the decrease in the loss of the converter CEL. As a result, the cooling device 80 can reduce its power consumption when the loss of the converter CEL is low.

[0066] The converter CEL has a current detector 65. The current detector 65 detects the magnitude of the current flowing through the converter CEL and outputs a current detection signal representing the magnitude of the detected current. For example, the current detector 65 detects the magnitude of the current flowing between a pair of connection terminals 61 and 62 of the converter CEL. In other words, the current detector 65 detects the magnitude of the arm current flowing through the arm section.

[0067] The control unit 85 acquires the current detection signal output from the current detector 65 as a converter status signal. The control unit 85 may, for example, acquire the current detection signal from the current detector 65. The control unit 85 may also acquire the current detection signal from, for example, the control device 14.

[0068] The control unit 85 controls the operation of the pump 82 so that its rotational speed becomes the first rotational speed when the magnitude of the current detected by the current detector 65 is greater than or equal to a threshold, and controls the operation of the pump 82 so that its rotational speed becomes the second rotational speed, which is lower than the first rotational speed, when the magnitude of the current detected by the current detector 65 is less than the threshold. As a result, the cooling device 80 can reduce the cooling capacity of the converter CEL in accordance with the decrease in the loss of the converter CEL, thereby reducing the power consumption of the cooling device 80.

[0069] The first rotational speed is set to, for example, the maximum rotational speed of the pump 82. This allows for proper cooling of the converter CEL even when the main circuit section 12 outputs the maximum amount of AC and DC power, as described above.

[0070] As described above, in the power conversion device 10 according to this embodiment, the cooling device 80 can change the cooling capacity of the converter CEL, and can reduce power consumption in accordance with the decrease in the cooling capacity of the converter CEL. It acquires a converter status signal and, based on the converter status signal, reduces power consumption by decreasing the cooling capacity of the converter CEL in accordance with the decrease in the loss of the converter CEL. As a result, in the power conversion device 10 according to this embodiment, the converter CEL can be properly cooled and unnecessary power consumption in the cooling device 80 can be suppressed.

[0071] Furthermore, in the power conversion device 10 according to this embodiment, the cooling device 80 has a pump 82 and a drive circuit 84, and changes the cooling capacity of the converter CEL by controlling the rotational speed of the pump 82. The cooling device 80 reduces the cooling capacity of the converter CEL by reducing the rotational speed of the pump 82 in accordance with the decrease in the losses of the converter CEL. This makes it possible to appropriately change the cooling capacity of the converter CEL in accordance with the rotational speed of the pump 82, and to appropriately reduce power consumption in accordance with the decrease in the rotational speed of the pump 82.

[0072] Furthermore, in the power converter 10 according to this embodiment, the cooling device 80 acquires the current detection signal output from the current detector 65 as a converter status signal. When the converter CEL is under low load, the magnitude of the current flowing through the converter CEL decreases, and the heat generated in the converter CEL also decreases. Therefore, by acquiring the current detection signal from the current detector 65 as a converter status signal, the cooling device 80 can appropriately determine the magnitude of the loss in the converter CEL. The cooling device 80 reduces the cooling capacity of the converter CEL in accordance with the decrease in the magnitude of the current flowing through the converter CEL (magnitude of the current detection signal). This allows the cooling device 80 to set an appropriate cooling capacity according to the magnitude of the loss in the converter CEL.

[0073] In the above embodiment, one threshold is set for the current detection signal, and the rotation speed of the pump 82 is changed in two stages. In other words, one threshold is set for the current detection signal, and the cooling capacity of the cooling device 80 is changed in two stages. However, the embodiment is not limited to this, and for example, by setting multiple thresholds of different magnitudes for the current detection signal, the rotation speed of the pump 82 (cooling capacity of the cooling device 80) may be changed in three or more stages. For example, the rotation speed of the pump 82 (cooling capacity of the cooling device 80) may be arbitrarily changed in response to the current detection signal by using a predetermined calculation formula or the like.

[0074] Figure 3 is a schematic block diagram showing a modified example of the converter and cooling device according to the first embodiment. As shown in Figure 3, the cooling device 80a has multiple pumps 82. More specifically, the cooling device 80a has two pumps 82. On the other hand, the drive circuit 84 is omitted in the cooling device 80a. Components that are substantially the same in function and configuration as those in the above embodiment are denoted by the same reference numerals, and detailed explanations are omitted.

[0075] In the cooling device 80a, the control unit 85 individually controls the operation of multiple pumps 82. For example, the control unit 85 individually controls the driving and stopping of two pumps 82. The two pumps 82 switch between driving and stopping based on the control of the control unit 85. When the two pumps 82 are driving, they operate at a preset constant rotation speed.

[0076] The rotational speeds of the two pumps 82 (the flow rate per unit time of the cooling medium circulating in the cooling pipe 81 when the two pumps 82 are operating) are set, for example, according to the maximum loss of the converter CEL (the maximum amount of heat generated by the converter CEL) when the main circuit unit 12 outputs the maximum amount of AC power and DC power.

[0077] In the cooling system 80a, the flow rate of the cooling medium circulating in the cooling pipes 81 per unit time can be controlled by controlling the number of operating pumps 82. In other words, in the cooling system 80a, the flow rate of the cooling medium circulating in the cooling pipes 81 per unit time can be increased by increasing the number of operating pumps 82, and the flow rate of the cooling medium circulating in the cooling pipes 81 per unit time can be decreased by decreasing the number of operating pumps 82.

[0078] As a result, the cooling system 80a can change the cooling capacity of the converter CEL by controlling the number of operating pumps 82. In the cooling system 80a, the cooling capacity of the converter CEL can be increased by increasing the number of operating pumps 82 and increasing the flow rate of the cooling medium circulating in the cooling pipes 81 per unit time, and the cooling capacity of the converter CEL can be decreased by decreasing the number of operating pumps 82 and decreasing the flow rate of the cooling medium circulating in the cooling pipes 81 per unit time.

[0079] Furthermore, in the cooling system 80a, the power consumption of the cooling system 80a can be changed by controlling the number of operating pumps 82. In the cooling system 80a, the power consumption of the cooling system 80a can be increased by increasing the number of operating pumps 82, and the power consumption of the cooling system 80a can be decreased by decreasing the number of operating pumps 82.

[0080] The control unit 85 controls the operation of the two pumps 82, for example, by operating both pumps 82 when the magnitude of the current detected by the current detector 65 is greater than or equal to a threshold, and operating one pump 82 when the magnitude of the current detected by the current detector 65 is less than the threshold. As a result, the cooling device 80a can reduce the cooling capacity of the converter CEL in accordance with the decrease in the loss of the converter CEL, thereby reducing the power consumption of the cooling device 80a.

[0081] Thus, the cooling capacity of the converter CEL is not limited to controlling the rotational speed of the pump 82, but may also be controlled by controlling the number of operating pumps 82. The cooling device 80a reduces the cooling capacity of the converter CEL by reducing the number of operating pumps 82 in accordance with the decrease in losses of the converter CEL. As a result, the cooling device 80a can appropriately change the cooling capacity of the converter CEL in accordance with the number of operating pumps 82, as in the above embodiment, and can also appropriately reduce power consumption in accordance with the decrease in the number of operating pumps 82.

[0082] The cooling device 80a is equipped with two pumps 82. However, the number of pumps 82 is not limited to two; it may be three or more. By providing three or more pumps 82, the cooling capacity of the converter CEL may be changed in three or more stages. In addition, the cooling device 80a is equipped with two pumps 82 in parallel. Multiple pumps 82 are not limited to being in parallel; they may be equipped in series.

[0083] Figure 4 is a schematic block diagram showing a modified example of the converter and cooling device according to the first embodiment. As shown in Figure 4, in the cooling device 80b, the cooling pipes 81, pump 82, and cooler 83 are omitted, and a fan 86 is provided. The fan 86 cools the converter CEL by blowing cooling air onto it. In the cooling device 80b, the drive circuit 84 drives the fan 86. The drive circuit 84 controls the rotational speed of the fan 86 by controlling, for example, the amount of power supplied to the fan 86.

[0084] Thus, the cooling method for the converter CEL is not limited to a so-called water-cooling method using a cooling tube 81, pump 82, and cooler 83, but may also be a so-called air-cooling method using a fan 86.

[0085] The cooling device 80b changes the cooling capacity of the converter CEL, for example, by controlling the rotational speed of the fan 86. The cooling device 80b reduces the cooling capacity of the converter CEL by lowering the rotational speed of the fan 86 in accordance with the decrease in the losses of the converter CEL. As a result, in this example as well, the cooling capacity of the converter CEL can be appropriately changed in accordance with the rotational speed of the fan 86, and the power consumption can be appropriately reduced in accordance with the decrease in the rotational speed of the fan 86.

[0086] The cooling device 80b may, for example, provide multiple fans 86 and change the cooling capacity of the converter CEL by controlling the number of fans 86 in operation. The cooling device 80b may also reduce the cooling capacity of the converter CEL by decreasing the number of fans 86 in operation in accordance with the decrease in losses of the converter CEL.

[0087] (Second embodiment) Figure 5 is a schematic block diagram showing the converter and cooling device according to the second embodiment. As shown in Figure 5, in this example, the current detector 65 is omitted in the converter CEL. In the cooling device 80c, the control unit 85 acquires a current command value, which represents the magnitude of the current to flow through the converter CEL, as a converter status signal. The control unit 85 acquires the current command value from the control device 14 by communicating with the control device 14, for example.

[0088] However, the method by which the control unit 85 obtains the current command value is not limited to this. The control unit 85 may, for example, obtain the current command value from a higher-level controller by communicating with it. The method by which the control unit 85 obtains the current command value may be any method that is capable of appropriately obtaining the current command value.

[0089] The current command value represents, for example, the magnitude of the current flowing between the pair of connection terminals 61 and 62 of the converter CEL. In other words, the current command value represents the magnitude of the arm current flowing through the arm section. The current command value is a command value used within the control device 14 to control the operation of each converter CEL.

[0090] The control unit 85 controls the operation of the pump 82 so that its rotational speed becomes a first rotational speed when the current command value is above a threshold, and controls the operation of the pump 82 so that its rotational speed becomes a second rotational speed lower than the first rotational speed when the current command value is below a threshold. As a result, in the cooling device 80c, as in the above embodiment, the cooling capacity of the converter CEL can be reduced in accordance with the reduction in the loss of the converter CEL, thereby reducing the power consumption of the cooling device 80c.

[0091] Thus, the converter status signal is not limited to a current detection signal, but may also be a current command value. The cooling device 80c acquires the current command value as the converter status signal. As described above, when the converter CEL is under low load, the magnitude of the current flowing through the converter CEL decreases, and the heat generated in the converter CEL also decreases. Therefore, even when the current command value is acquired as the converter status signal, the cooling device 80c can appropriately determine the magnitude of the loss in the converter CEL, similar to the first embodiment described above. The cooling device 80c reduces the cooling capacity of the converter CEL in accordance with the decrease in the current command value. This allows the cooling device 80c to set an appropriate cooling capacity according to the magnitude of the loss in the converter CEL.

[0092] In addition, in the cooling device 80c, as in the first embodiment described above, the configuration for changing the cooling capacity of the converter CEL may be control of the rotational speed of the pump 82, control of the number of operating pumps 82, control of the rotational speed of the fan 86, or control of the number of operating fans 86.

[0093] (Third embodiment) Figure 6 is a schematic block diagram showing the converter and cooling device according to the third embodiment. As shown in Figure 6, in this example, the converter CEL further includes a voltage detector 66. The voltage detector 66 detects the magnitude of the voltage of the charge storage element 60 and outputs a voltage detection signal representing the magnitude of the detected voltage.

[0094] In the cooling device 80d, the control unit 85 acquires the voltage detection signal output from the voltage detector 66 as a converter status signal. The control unit 85 acquires the voltage detection signal from the voltage detector 66, for example. The control unit 85 may also acquire the voltage detection signal from the control device 14, for example.

[0095] The control unit 85 controls the operation of the pump 82 so that its rotational speed becomes the first rotational speed when the magnitude of the voltage detected by the voltage detector 66 is greater than or equal to a threshold, and controls the operation of the pump 82 so that its rotational speed becomes the second rotational speed, which is lower than the first rotational speed, when the magnitude of the voltage detected by the voltage detector 66 is less than the threshold. As a result, in the cooling device 80d, as in the above embodiment, the cooling capacity of the converter CEL can be reduced in accordance with the reduction in the loss of the converter CEL, thereby reducing the power consumption of the cooling device 80d.

[0096] Thus, the converter status signal may also be a voltage detection signal. The cooling device 80d acquires the voltage detection signal as the converter status signal. When the voltage of the charge storage element 60 of the converter CEL decreases, the loss in the converter CEL decreases, and the amount of heat generated decreases. Therefore, even when the voltage detection signal is acquired as the converter status signal, the cooling device 80d can appropriately determine the magnitude of the loss in the converter CEL, similar to the embodiments described above. The cooling device 80d reduces the cooling capacity of the converter CEL in accordance with the decrease in the voltage detection signal. This allows the cooling device 80d to set an appropriate cooling capacity according to the magnitude of the loss in the converter CEL.

[0097] In addition, in the cooling device 80d, as in the embodiments described above, the configuration for changing the cooling capacity of the converter CEL may be control of the rotational speed of the pump 82, control of the number of operating pumps 82, control of the rotational speed of the fan 86, or control of the number of operating fans 86.

[0098] (Fourth embodiment) Figure 7 is a schematic block diagram showing the converter and cooling device according to the fourth embodiment. As shown in Figure 7, in this example, the converter CEL further includes multiple temperature detectors 71 and 72, each corresponding to one of the multiple switching elements 41 and 42. Temperature detector 71 detects the temperature of the switching element 41 and outputs a temperature detection signal representing the detected temperature. Temperature detector 72 detects the temperature of the switching element 42 and outputs a temperature detection signal representing the detected temperature.

[0099] In the cooling device 80e, the control unit 85 acquires the temperature detection signals output from the temperature detectors 71 and 72 as converter status signals. The control unit 85 acquires the temperature detection signals from, for example, the temperature detectors 71 and 72. The control unit 85 may also acquire the temperature detection signals from, for example, the control device 14.

[0100] The control unit 85 may, for example, control the operation of the pump 82 so that the rotation speed of the pump 82 becomes a first rotation speed when any of the temperatures detected by the multiple temperature sensors 71 and 72 are above a threshold, and control the operation of the pump 82 so that the rotation speed of the pump 82 becomes a second rotation speed lower than the first rotation speed when any of the temperatures detected by the multiple temperature sensors 71 and 72 are below a threshold. The control unit 85 may, for example, control the operation of the pump 82 so that the rotation speed of the pump 82 becomes a first rotation speed when any of the temperatures detected by the multiple temperature sensors 71 and 72 are above a threshold, and control the operation of the pump 82 so that the rotation speed of the pump 82 becomes a second rotation speed lower than the first rotation speed when any of the temperatures detected by the multiple temperature sensors 71 and 72 are below a threshold. In this way, in the cooling device 80e as well, similar to the embodiment described above, the cooling capacity of the converter CEL can be reduced in accordance with the reduction in the loss of the converter CEL, thereby reducing the power consumption of the cooling device 80e.

[0101] Thus, the converter status signal may also be a temperature detection signal. The cooling device 80e acquires the temperature detection signal as the converter status signal. When the loss in the converter CEL decreases, the heat generated by the multiple switching elements 41 and 42 decreases. Therefore, even when the temperature detection signal is acquired as the converter status signal, the cooling device 80e can appropriately determine the magnitude of the loss in the converter CEL, similar to the embodiments described above. The cooling device 80e reduces the cooling capacity of the converter CEL in accordance with the decrease in the temperature detection signal. This allows the cooling device 80e to set an appropriate cooling capacity according to the magnitude of the loss in the converter CEL.

[0102] In addition, in the cooling device 80e, as in the embodiments described above, the configuration for changing the cooling capacity of the converter CEL may be control of the rotational speed of the pump 82, control of the number of operating pumps 82, control of the rotational speed of the fan 86, or control of the number of operating fans 86.

[0103] (Fifth embodiment) Figure 8 is a schematic block diagram showing the converter and cooling device according to the fifth embodiment. As shown in Figure 8, in the cooling device 80f, the control unit 85 acquires the carrier frequency signal as a converter status signal. The control unit 85 acquires the carrier frequency signal from the control device 14 by communicating with the control device 14, for example.

[0104] However, the method by which the control unit 85 acquires the carrier frequency signal is not limited to this. The control unit 85 may, for example, acquire the carrier frequency signal from a higher-level controller by communicating with it. The method by which the control unit 85 acquires the carrier frequency signal may be any method that is capable of appropriately acquiring the carrier frequency signal.

[0105] Figure 9 is a schematic graph illustrating an example of the operation of the control device. As shown in Figure 9, the control device 14 generates a control signal to control the switching of the multiple switching elements 41 and 42 based on the voltage reference VR and the carrier signal CW. For example, the control device 14 sets a voltage reference VR for each converter CEL. If M converter CELs are connected in series to one arm, the control device 14 sets M voltage reference VRs for each converter CEL. The carrier signal CW may be used in common for each converter CEL, or M carrier signals CW may be set for each converter CEL.

[0106] The voltage reference VR is, for example, sinusoidal. The control device 14 adjusts the amplitude and phase of the voltage reference VR for each converter CEL. The frequency of the voltage reference VR is set according to the frequency of the AC voltage of the AC power system 2. That is, it is set to a frequency appropriate for the actual usage conditions. The frequency of the voltage reference VR is, for example, 50Hz or 60Hz. The carrier signal CW is, for example, triangular wave. The carrier signal CW may also be a sawtooth wave or the like. The frequency of the carrier signal CW is higher than the frequency of the voltage reference VR.

[0107] The control device 14 shifts the phase of the voltage reference VR for each converter CEL. For example, in one arm section, the control device 14 sets a voltage reference VR for each converter CEL with a phase shift of 360 degrees.

[0108] The control device 14 compares the voltage reference VR with the carrier signal CW. For example, the control device 14 generates a pulse signal as a control signal that is Low when the voltage reference VR is less than the carrier signal CW, and High when the voltage reference VR is equal to or greater than the carrier signal CW. However, the relationship between the High and Low of the control signal may be the opposite of the above.

[0109] The converter CEL turns on switching element 41 and off switching element 42 when the control signal is low. In this case, the connection terminals 61 and 62 are short-circuited by switching element 41, and the voltage between the connection terminals 61 and 62 becomes effectively 0V. Then, the converter CEL turns off switching element 41 and on switching element 42 when the control signal is high. In this case, the voltage of the charge storage element 60 appears between the connection terminals 61 and 62. That is, when the control signal is high, the converter CEL is in an output state that outputs a predetermined voltage, and when the control signal is low, the converter CEL is in a stopped state that stops outputting the predetermined voltage. When the control signal is high, in other words, it is the first state for putting the converter CEL into an output state, and when the control signal is low, in other words, it is the second state for putting the converter CEL into a stopped state. In this way, the converter CEL outputs two levels of voltage, +Vc and 0, by switching the switching elements 41 and 42.

[0110] The control device 14 adjusts the amplitude and phase of the voltage reference VR so that, for example, the current and voltage values ​​on the DC side and the AC side of the main circuit section 12 approach the command values. This allows the operation of the main circuit section 12 to be controlled based on the command values.

[0111] Furthermore, the control device 14 changes the frequency of the carrier signal CW according to, for example, the conditions of the three-phase AC power of the AC power system 2 and the DC power of the DC transmission lines 3 and 4. By increasing the frequency of the carrier signal CW, for example, the tracking ability of the three-phase AC power output from the main circuit unit 12 to the voltage reference VR can be improved. On the other hand, increasing the frequency of the carrier signal CW increases the switching loss in the switching elements 41 and 42. For this reason, the control device 14 increases the frequency of the carrier signal CW when high tracking ability to the voltage reference VR is required, such as when the voltage reference VR is changed, and decreases the frequency of the carrier signal CW when high tracking ability to the voltage reference VR is not required, such as when the three-phase AC power output from the main circuit unit 12 is already sufficiently tracking the voltage reference VR. This makes it possible to improve the tracking ability of the three-phase AC power output from the main circuit unit 12 to the voltage reference VR while suppressing the switching loss in the switching elements 41 and 42.

[0112] In the cooling device 80f, the control unit 85 acquires a carrier frequency signal, which represents the height of the carrier signal CW, as a converter status signal. For example, based on the carrier frequency signal, the control unit 85 controls the operation of the pump 82 so that the rotation speed of the pump 82 becomes the first rotation speed when the height of the carrier signal CW is above a threshold, and controls the operation of the pump 82 so that the rotation speed of the pump 82 becomes a second rotation speed, which is lower than the first rotation speed, when the height of the carrier signal CW is below the threshold. As a result, in the cooling device 80f, as in the above embodiment, the cooling capacity of the converter CEL can be reduced in accordance with the reduction in the loss of the converter CEL, and the power consumption of the cooling device 80f can be reduced.

[0113] Thus, the converter status signal may also be a carrier frequency signal. The cooling device 80f acquires the carrier frequency signal as the converter status signal. When the frequency of the carrier signal CW decreases, the switching loss in the switching elements 41 and 42 decreases, and the heat generated in the converter CEL also decreases. Therefore, even when the carrier frequency signal is acquired as the converter status signal, the cooling device 80f can appropriately determine the magnitude of the loss in the converter CEL, similar to the embodiments described above. The cooling device 80f reduces the cooling capacity of the converter CEL in accordance with the decrease in the frequency of the carrier signal CW. This allows the cooling device 80f to set an appropriate cooling capacity according to the magnitude of the loss in the converter CEL.

[0114] In addition, in the cooling device 80f, as in the embodiments described above, the configuration for changing the cooling capacity of the converter CEL may be control of the rotational speed of the pump 82, control of the number of operating pumps 82, control of the rotational speed of the fan 86, or control of the number of operating fans 86.

[0115] The first to fifth embodiments described above can be combined in any way. The cooling device 80 acquires at least one of the current detection signal, current command value, voltage detection signal, temperature detection signal, and carrier frequency signal, and may reduce the cooling capacity of the converter CEL in accordance with the decrease in the loss of the converter CEL, based on at least one of the current detection signal, current command value, voltage detection signal, temperature detection signal, and carrier frequency signal.

[0116] In each of the above embodiments, a half-bridge configuration of the converter CEL is represented. The configuration of the converter CEL is not limited to this, and may also be a full-bridge configuration in which multiple switching elements are connected in a full bridge.

[0117] Furthermore, in each of the above embodiments, an MMC-type main circuit section 12 is shown in which multiple converter CELs are connected in series. The configuration of the main circuit section 12 is not limited to this. The number of converter CELs provided in the main circuit section 12 may be as few as one. The configuration of the main circuit section 12 (converter CEL) may be any configuration that has at least one switching element, can perform power conversion by switching the switching element, can change the magnitude of the output power, and can change the loss in the converter CEL by changing the magnitude of the output power. The configuration of this embodiment is applicable to all power converters that are cooled by water cooling.

[0118] This embodiment includes the following aspects. (Note 1) A main circuit section having a converter that performs power conversion, A control device that controls the power conversion operation by the main circuit section. A cooling device for cooling the converter, Equipped with, The converter has a switching element, and by switching the switching element, it can convert power and change the magnitude of the power output from the main circuit section. The loss of the converter changes according to the magnitude of the power output from the main circuit section. The cooling device can change the cooling capacity of the converter, reduce power consumption in accordance with the decrease in the cooling capacity of the converter, acquire a converter status signal representing the loss state of the converter, and based on the converter status signal, reduce power consumption by reducing the cooling capacity of the converter in accordance with the decrease in the loss of the converter.

[0119] (Note 2) The cooling device, A cooling pipe that constitutes a path for the cooling medium to cool the converter by circulating the cooling medium, A pump provided along the path of the cooling pipe, which circulates the cooling medium in the cooling pipe by applying pressure to the cooling medium in the cooling pipe, A drive circuit that drives the pump and controls the rotational speed of the pump, The power conversion device according to Appendix 1, which has a pump rotation speed that changes the cooling capacity of the converter, and reduces the cooling capacity of the converter and reduces power consumption by reducing the rotation speed of the pump in accordance with the reduction in the losses of the converter.

[0120] (Note 3) The cooling device, A cooling pipe that constitutes a path for the cooling medium to cool the converter by circulating the cooling medium, Multiple pumps are provided along the path of the cooling pipes and apply pressure to the cooling medium within the cooling pipes, thereby circulating the cooling medium within the cooling pipes. The power conversion device described in Appendix 1, which has the following characteristics, and changes the cooling capacity of the converter by controlling the number of operating pumps, and reduces the number of operating pumps in accordance with the decrease in losses of the converter, thereby reducing the cooling capacity of the converter and reducing power consumption.

[0121] (Note 4) The converter has a current detector that detects the magnitude of the current flowing through the converter and outputs a current detection signal that represents the magnitude of the detected current. The power conversion device according to any one of the appendices 1 to 3, wherein the cooling device acquires the current detection signal output from the current detector as the converter status signal, and reduces the cooling capacity of the converter in accordance with the decrease in the magnitude of the current represented by the current detection signal.

[0122] (Note 5) The power conversion device described in any one of the appendices 1 to 4, wherein the cooling device acquires a current command value representing the magnitude of the current flowing through the converter as a converter status signal, and reduces the cooling capacity of the converter in accordance with the decrease in the magnitude of the current represented by the current command value.

[0123] (Note 6) The aforementioned converter is A charge storage element connected in parallel to the switching element, A voltage detector that detects the magnitude of the voltage of the charge storage element and outputs a voltage detection signal representing the magnitude of the detected voltage, It has, The power conversion device according to any one of the appendices 1 to 5, wherein the cooling device acquires the voltage detection signal output from the voltage detector as the converter status signal, and reduces the cooling capacity of the converter in accordance with the decrease in the magnitude of the voltage represented by the voltage detection signal.

[0124] (Note 7) The converter has a temperature detector provided in correspondence with the switching element, which detects the temperature of the switching element and outputs a temperature detection signal representing the detected temperature. The power converter according to any one of the appendices 1 to 6, wherein the cooling device acquires the temperature detection signal output from the temperature detector as the converter status signal, and reduces the cooling capacity of the converter in accordance with the decrease in temperature represented by the temperature detection signal.

[0125] (Note 8) The control device generates a control signal to control the switching of the switching element by comparing a sinusoidal voltage reference with a carrier signal having a higher frequency than the voltage reference. The cooling device is a power converter according to any one of the appendices 1 to 7, which acquires a carrier frequency signal representing the height of the carrier signal as the converter status signal, and reduces the cooling capacity of the converter in accordance with the decrease in the frequency represented by the carrier frequency signal.

[0126] 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 novel 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 of the invention and its equivalents. [Explanation of Symbols]

[0127] 2…AC power system, 3, 4…DC transmission line, 6…Transformer, 10…Power converter, 12…Main circuit section, 14…Control device, 20a, 20b…DC terminals, 21a~21c…1st~3rd AC terminals, 22a~22f…1st~6th arm sections, 23a~23f…Buffer reactor, 24a~24f…Current detector, 25…Voltage detection section, 26…Signal line, 41, 42…Switching element, 51, 52…Rectifier element, 60…Charge storage element, 61, 62…Connection terminal, 65…Current detector, 66…Voltage detector, 71, 72…Temperature detector, 80, 80a~80f…Cooling device, 81…Cooling pipe, 82…Pump, 83…Cooler, 84…Drive circuit, 85…Control unit, 86...fan, CEL...converter

Claims

1. A main circuit section having a converter that performs power conversion, A control device that controls the power conversion operation by the main circuit section. A cooling device for cooling the converter, Equipped with, The converter has a switching element, and by switching the switching element, it can convert power and change the magnitude of the power output from the main circuit section. The loss of the converter changes according to the magnitude of the power output from the main circuit section. The cooling device can change the cooling capacity of the converter, reduce power consumption in accordance with the decrease in the cooling capacity of the converter, acquire a converter status signal representing the loss state of the converter, and based on the converter status signal, reduce power consumption by reducing the cooling capacity of the converter in accordance with the decrease in the loss of the converter.

2. The cooling device, A cooling pipe that constitutes a path for the cooling medium to cool the converter by circulating the cooling medium, A pump provided along the path of the cooling pipe, which circulates the cooling medium in the cooling pipe by applying pressure to the cooling medium in the cooling pipe, A drive circuit that drives the pump and controls the rotational speed of the pump, The power conversion device according to claim 1, comprising: having a pump rotation speed control thereby changing the cooling capacity of the converter; and reducing the rotation speed of the pump in accordance with the reduction in the loss of the converter, thereby reducing the cooling capacity of the converter and reducing power consumption.

3. The cooling device, A cooling pipe that constitutes a path for the cooling medium to cool the converter by circulating the cooling medium, Multiple pumps are provided along the path of the cooling pipes and apply pressure to the cooling medium within the cooling pipes, thereby circulating the cooling medium within the cooling pipes. The power conversion device according to claim 1, which has a plurality of pumps, and changes the cooling capacity of the converter by controlling the number of pumps in operation, and reduces the number of pumps in operation in accordance with the decrease in losses of the converter, thereby reducing the cooling capacity of the converter and reducing power consumption.

4. The converter has a current detector that detects the magnitude of the current flowing through the converter and outputs a current detection signal that represents the magnitude of the detected current. The power conversion device according to claim 1, wherein the cooling device acquires the current detection signal output from the current detector as the converter status signal, and reduces the cooling capacity of the converter in accordance with the decrease in the magnitude of the current represented by the current detection signal.

5. The power conversion device according to claim 1, wherein the cooling device acquires a current command value representing the magnitude of the current flowing through the converter as a converter status signal, and reduces the cooling capacity of the converter in accordance with the decrease in the magnitude of the current represented by the current command value.

6. The aforementioned converter is A charge storage element connected in parallel to the switching element, A voltage detector that detects the magnitude of the voltage of the charge storage element and outputs a voltage detection signal representing the magnitude of the detected voltage, It has, The power conversion device according to claim 1, wherein the cooling device acquires the voltage detection signal output from the voltage detector as the converter status signal, and reduces the cooling capacity of the converter in accordance with the decrease in the magnitude of the voltage represented by the voltage detection signal.

7. The converter has a temperature detector that is provided in correspondence with the switching element, detects the temperature of the switching element, and outputs a temperature detection signal representing the detected temperature. The power conversion device according to claim 1, wherein the cooling device acquires the temperature detection signal output from the temperature detector as the converter status signal, and reduces the cooling capacity of the converter in accordance with the decrease in temperature represented by the temperature detection signal.

8. The control device generates a control signal to control the switching of the switching element by comparing a sinusoidal voltage reference with a carrier signal having a higher frequency than the voltage reference. The power conversion device according to claim 1, wherein the cooling device acquires a carrier frequency signal representing the height of the carrier signal frequency as the converter status signal, and reduces the cooling capacity of the converter in accordance with the decrease in the frequency represented by the carrier frequency signal.

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