JP6541155B2 - Power converter and control method thereof - Google Patents

Description

  Embodiments of the present invention relate to a power converter and a control method thereof.

  There is known a multistage power converter in which a plurality of converters are connected in series. A multistage power conversion device is used, for example, in a DC power transmission system that converts AC voltage into DC voltage and transmits the converted power. Each converter includes a plurality of switching elements and a charge storage element connected in parallel to each switching element. In the power converter, on / off of each switching element is controlled. Thus, the AC voltage is converted to a DC voltage. Alternatively, the DC voltage is converted to an AC voltage.

  In the multistage power conversion device, when the charge storage element of each converter is in an overvoltage state, there is a possibility that the charge storage element or the switching element may be damaged. For this reason, in the multistage power conversion device, a discharge device is connected to the charge storage element of each converter. The overvoltage state of the charge storage element is detected, and the operation of each switching element is stopped in response to the detection of the overvoltage, and the charge stored in the charge storage element is discharged to the discharge device. Thereby, damage to the charge storage element and each switching element can be suppressed.

  However, in the configuration in which the discharge device is provided for each of the converters, the number of parts is increased, which leads to an increase in size and cost of the power converter. For this reason, in the multistage power conversion device, it is desirable to suppress the damage of the element due to the overvoltage of the charge storage element without increasing the number of parts, and to improve the reliability.

  Moreover, in the structure which discharges to discharge apparatus, for example, it may take several minutes for discharge. When the charge storage element is naturally discharged without using a discharge device, it may be considered that the discharge may take several hours. While discharge is being performed, power conversion can not be performed, and the operability of the power conversion device is degraded. For this reason, in the multistage power conversion device, it is desirable to discharge the charge storage element in the overvoltage state in a shorter time to improve operability.

  Thus, in the multistage power converter, it is desirable to improve the reliability and operability without increasing the number of parts.

JP, 2014-57488, A

  An embodiment of the present invention provides a power converter and its control method with improved reliability and operability without increasing the number of parts.

  According to an embodiment of the present invention, a power converter including a main circuit unit and a control circuit is provided. The main circuit unit has a plurality of arm units in which a plurality of converters are connected in series, and the plurality of converters perform at least conversion of AC power to DC power and conversion of DC power to AC power. Perform AC / DC conversion on one side. The control circuit controls the operation of the main circuit unit. The plurality of converters include a plurality of switching elements in a half bridge connection or a full bridge connection, and a charge storage element connected in parallel to the plurality of switching elements. The main circuit unit includes a plurality of voltage detectors that detect voltages of the charge storage elements of the plurality of converters. The control circuit causes the alternating current and direct current flowing into and out of the main circuit unit to follow the alternating current command value and the direct current command value based on the alternating current command value and the direct current command value input in advance. Thus, while controlling the AC / DC conversion by the main circuit unit by controlling on / off of the plurality of switching elements, the voltage detected by any of the plurality of voltage detectors is equal to or higher than the upper limit value. When it becomes, the alternating current command value and the direct current command value are made smaller than usual, to control the on / off of the plurality of switching elements.

  A power converter and its control method with improved reliability and operability without increasing the number of parts are provided.

FIG. 1 is a block diagram schematically showing a power conversion device according to an embodiment. It is a block diagram which represents a converter typically. It is a graph which represents typically an example of operation | movement of a control circuit. FIG. 2 is a block diagram schematically showing an example of a control circuit. It is a block diagram showing typically an example of a common control block. It is a block diagram showing an example of an individual control block typically. FIG. 3 is a block diagram schematically showing an example of an overvoltage detection circuit. It is a graph which represents typically an example of the characteristic of a switching element. FIGS. 9A to 9E are graphs schematically showing an example of a simulation result. It is a flowchart which represents typically an example of operation | movement of the power converter device which concerns on embodiment. It is a block diagram which represents the modification of a converter typically. It is a block diagram which represents the modification of a main circuit part typically. FIG. 7 is a block diagram schematically showing a modification of the overvoltage detection circuit. FIG. 7 is a block diagram schematically showing a modification of the overvoltage detection circuit.

Hereinafter, each embodiment will be described with reference to the drawings.
The drawings are schematic or conceptual, and the relationship between the thickness and width of each part, the ratio of sizes between parts, and the like are not necessarily the same as the actual ones. In addition, even in the case of representing the same portion, the dimensions and ratios may be different from one another depending on the drawings.
In the specification of the present application and the drawings, the same elements as those described above with reference to the drawings are denoted by the same reference numerals, and the detailed description will be appropriately omitted.

FIG. 1 is a block diagram schematically showing the power conversion device according to the embodiment.
As shown in FIG. 1, the power conversion device 10 includes a main circuit unit 12 and a control circuit 14. The power converter 10 is used, for example, in a DC power transmission system. Power conversion device 10 is connected to AC power system 2 (AC circuit) and a pair of DC power transmission lines 3 and 4 (DC circuit) in a DC power transmission system.

  The power conversion device 10 converts alternating current power supplied from the alternating current power system 2 into direct current power, and supplies the direct current power after conversion to the direct current transmission lines 3 and 4. In addition, the power conversion device 10 converts the DC power supplied from the DC power transmission lines 3 and 4 into AC power, and supplies the AC power after conversion to the AC power system 2. Thus, the power conversion device 10 performs AC-DC conversion from AC to DC and AC-DC conversion from DC to AC.

  The AC power of AC power system 2 is, for example, three-phase AC power. The power converter 10 performs, for example, conversion from three-phase AC power to DC power and conversion from DC power to three-phase AC power. The AC power of the AC power system 2 may be single phase AC power or the like.

  For example, the DC transmission line 3 is a transmission line on the high voltage side of DC power, and the DC transmission line 4 is a transmission line on the low voltage side of DC power. The power conversion device 10 outputs DC power after conversion to the DC power transmission lines 3 and 4 so that the DC power transmission line 3 side is high voltage and the DC power transmission line 4 side is low voltage.

  The power conversion device 10 is not limited to a DC power transmission system, and may be applied to any other system that requires AC to DC conversion and DC to AC conversion. The AC / DC conversion by the power conversion device 10 is not limited to both AC to DC and DC to AC, and may be only AC to DC or DC to AC. The power conversion device 10 may be capable of performing AC-DC conversion of at least one of AC to DC and DC to AC. Further, in this example, the AC power system 2 is shown as an AC circuit, and the DC power transmission lines 3 and 4 are shown as DC circuits. 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.

  The main circuit unit 12 is provided between the AC power system 2 and the DC power transmission lines 3 and 4. The main circuit unit 12 performs conversion of AC power to DC power and conversion of DC power to AC power. The main circuit unit 12 is connected to the AC power system 2 via, for example, a transformer 16. The transformer 16 converts AC power of the AC power system 2 into AC power corresponding to the main circuit unit 12. The transformer 16 changes the effective value of the AC power in accordance with the main circuit unit 12. The transformer 16 is provided as needed and can be omitted. The main circuit unit 12 may convert AC power supplied directly from the AC power system 2 into DC power.

  For example, a modular multilevel converter (MMC) power converter is used for the main circuit unit 12. The MMC type main circuit unit 12 has a plurality of converters connected in series. Each converter has a plurality of switching elements 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 AC / DC conversion by switching of each switching element.

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

  Power converter 10 further includes current detectors 17 a, 17 b, 17 c, 18 and a voltage detector 19. The current detectors 17 a, 17 b, 17 c detect alternating current (phase current) of each phase of the alternating current power system 2 and input a detected value to the control circuit 14. The current detector 18 detects a direct current flowing through the DC transmission lines 3 and 4, and inputs a detected value to the control circuit 14. The voltage detector 19 detects an AC voltage (phase voltage) of each phase of the AC power system 2 and inputs a detected value to the control circuit 14.

  The main circuit portion 12 includes first and second pairs of DC terminals 20a and 20b, first to third three AC terminals 21a to 21c, and first to sixth six arm portions 22a to 22f. And.

  The first DC terminal 20 a is connected to the DC power transmission line 3 on the high voltage side. The second DC terminal 20 b is connected to the DC transmission line 4 on the low voltage side. Thus, the DC power converted by the main circuit unit 12 is supplied to the DC power transmission lines 3 and 4, and the DC power supplied from the DC power transmission lines 3 and 4 is input to the main circuit unit 12. In other words, the current detector 18 detects a direct current flowing through each of the direct current terminals 20a and 20b.

  The first arm portion 22a is connected to the first DC terminal 20a. The second arm 22b is connected between the first arm 22a and the second DC terminal 20b. The first arm 22a and the second arm 22b are connected in series between the DC terminals 20a and 20b.

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

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

  In the main circuit portion 12, a first leg LG1 is constituted by the first arm portion 22a and the second arm portion 22b, and a second leg LG2 is constituted by the third arm portion 22c and the fourth arm portion 22d. The third leg LG3 is configured by 22e and the sixth arm portion 22f. That is, in this example, the main circuit unit 12 is a three-leg, six-arm three-phase inverter. The first arm 22a, the third arm 22c, and the fifth arm 22e are upper arms. The second arm 22b, the fourth arm 22d, and the sixth arm 22f are lower arms. The main circuit unit 12 may be, for example, a two-leg, four-arm single-phase inverter. That is, the main circuit portion 12 may have at least the first arm portion 22a to the fourth arm portion 22d.

The first arm portion 22a has a plurality of transducers UP1, UP2 ... UPM ₁ connected in series. The second arm unit 22b includes a plurality of transducers UN1, UN2 ... UNM ₂ connected in series. The third arm portion 22c has a plurality of transducers VP1, VP2... VPM ₃ connected in series. The fourth arm unit 22 d includes a plurality of transducers VN 1, VN 2,..., VNM ₄ connected in series. The fifth arm portion 22 e has a plurality of transducers WP 1, WP 2 to WPM ₅ connected in series. The sixth arm unit 22 f includes a plurality of transducers WN 1, WN 2 to WNM ₆ connected in series.

However, in the following, each converter UP1, UP2 ... UPM ₁ , UN1, UN2 ... UNM ₂ , VP1, VP2 ... VPM ₃ , VN1, VN2 ... VNM ₄ , WP1, WP2 ... WPM ₅ , WN1, WN2 ... WNM ₆ When collectively called, it is called "converter CEL".

In each of the arm units 22a to 22f, M ₁ , M ₂ , M ₃ , M ₄ , M ₅ , and M ₆ represent the number of serially connected converters CEL. The number of converters CEL connected in series in each of the arm units 22a to 22f is, for example, about 100 to 120. However, the number of converters CEL connected in series is not limited to this, and may be any number.

  The number of converters CEL provided in each of the arm portions 22a to 22f is substantially the same. For example, in the case where a large number of converters CEL are connected, the number of converters CEL provided in each of the arm units 22a to 22f may be different within a range that does not affect the operation of the main circuit unit 12. For example, in the case where 100 transducers CEL are connected in series to one arm unit, the number of transducers CEL provided on another arm unit may be different from one to two.

  Each of the arm portions 22a to 22f further includes buffer reactors 23a to 23f. Each buffer reactor 23a-23f is connected in series to each converter CEL in each of each arm part 22a-22f. The buffer reactor 23a of the first arm 22a is provided between the converter UP1 and the second arm 22b. The buffer reactor 23b of the second arm 22b is provided between the converter UN1 and the first arm 22a. The buffer reactor 23c of the third arm 22c is provided between the converter VP1 and the fourth arm 22d. The buffer reactor 23d of the fourth arm unit 22d is provided between the converter VN1 and the third arm unit 22c. The buffer reactor 23e of the fifth arm 22e is provided between the converter WP1 and the sixth arm 22f. The buffer reactor 23f of the sixth arm unit 22f is provided between the converter WN1 and the fifth arm unit 22e.

  In the main circuit portion 12, a connection point between the first arm 22a and the second arm 22b, a connection point between the third arm 22c and the fourth arm 22d, and a fifth arm 22e and a sixth arm Each of connection points with 22f becomes an AC output point.

  The first AC terminal 21a is connected to a connection point between the first arm 22a and the second arm 22b. The second AC terminal 21b is connected to a connection point between the third arm 22c and the fourth arm 22d. The third AC terminal 21c is connected to a connection point of the fifth arm 22e and the sixth arm 22f. Each of the AC terminals 21 a to 21 c is connected to, for example, a transformer 16. In other words, each of the current detectors 17a, 17b, and 17c detects alternating current (phase current) of each phase flowing through each of the alternating current terminals 21a to 21c.

  Each converter CEL is connected to the control circuit 14 via signal lines 24 and 25. The control circuit 14 controls the operation of the converter CEL by inputting a control signal to the converter CEL via the signal line 24. The converter CEL inputs control and protection signals for control and operation protection of the converter CEL to the control circuit 14 via the signal line 25.

FIG. 2 is a block diagram schematically showing a converter.
As shown in FIG. 2, the converter CEL includes a first connection terminal 40 a, a second connection terminal 40 b, a first switching element 41, a second switching element 42, a charge storage element 45, and a driver circuit 46. And a voltage detector 47.

  Each of the switching elements 41 and 42 includes a pair of main terminals and a control terminal. The control terminal controls the current flowing between the pair of main terminals. For each switching element 41, 42, for example, a self arc extinguishing element such as an IGBT is used. The pair of main terminals is, for example, an emitter and a collector, and the control terminal is, for example, a gate. For each of the switching elements 41 and 42, for example, a normally-off semiconductor element is used.

  The pair of main terminals of the second switching element 42 is connected in series to the pair of main terminals of the first switching element 41. The charge storage element 45 is connected in parallel to the first switching element 41 and the second switching element 42. The charge storage element 45 is, for example, a capacitor. The first connection terminal 40 a is connected between the first switching element 41 and the second switching element 42. The second connection terminal 40 b is connected to the main terminal opposite to the main terminal connected to the second switching element 42 of the first switching element 41.

  Further, in the first switching element 41, a rectifying element 41d is connected in antiparallel to the pair of main terminals. The forward direction of the rectifying element 41 d is opposite to the direction of the current flowing between the pair of main terminals of the first switching element 41. Similarly, in the second switching element 42, a rectifying element 42d is connected in antiparallel to the pair of main terminals. The rectifying elements 41d and 42d are so-called reflux diodes.

  The supply of power to the converter CEL takes place via the respective connection terminals 40a, 40b. In the converter CEL, each switching element 41, 42 is half bridge connected. In other words, the converter CEL is a bi-directional chopper. The first switching element 41 is a so-called low side switch, and the second switching element 42 is a so-called high side switch.

  Control terminals of the switching elements 41 and 42 are input to the driver circuit 46. The driver circuit 46 is connected to the control circuit 14 via the signal line 24. The control circuit 14 transmits a control signal for controlling on / off of the switching elements 41 and 42 to the driver circuit 46 via the signal line 24. The driver circuit 46 switches on / off of the switching elements 41 and 42 based on the input control signal. Thus, on / off of the switching elements 41 and 42 is controlled according to the control signal from the control circuit 14. The control circuit 14 generates a control signal for each converter CEL, and controls on / off of each switching element 41, 42 of each converter CEL. Thus, the control circuit 14 controls the conversion of power by the main circuit unit 12.

  The voltage detector 47 detects the voltage of the charge storage element 45. The voltage detector 47 is connected to the control circuit 14 via the signal line 25. The voltage detector 47 inputs the detected voltage value of the charge storage element 45 to the control circuit 14 as a control signal and a protection signal. Thus, the voltage value of the charge storage element 45 of each converter CEL is input to the control circuit 14.

FIG. 3 is a graph schematically showing an example of the operation of the control circuit.
As shown in FIG. 3, the control circuit 14 controls switching of the switching elements 41 and 42 based on the voltage reference VR and the carrier signal CW. The control circuit 14 sets a voltage reference VR for each converter CEL. When M converters CEL are connected in series to one arm unit, the control circuit 14 sets M voltage references VR for each converter CEL. The carrier signal CW may be commonly used for each of the converters CEL, or M carrier signals CW for each converter CEL may be set.

  The voltage reference VR is, for example, sinusoidal. The control circuit 14 adjusts the amplitude and phase of the voltage reference VR for each converter CEL. The frequency of voltage reference VR is set according to the frequency of the AC voltage of AC power system 2. That is, the frequency is set according to the actual use situation. The frequency of the voltage reference VR is, for example, 50 Hz or 60 Hz. The carrier signal CW has, for example, a triangular waveform. The carrier signal CW may be a sawtooth wave or the like. The frequency of the carrier signal CW is higher than the frequency of the voltage reference VR.

  The control circuit 14 shifts the phase of the voltage reference VR of each converter CEL. The control circuit 14 sets, for example, for each converter CEL, a voltage reference VR shifted in phase by 360 / M (degrees) in one arm unit.

  The control circuit 14 compares the voltage reference VR with the carrier signal CW. The control circuit 14 turns on the first switching element 41 and turns off the second switching element 42 when the voltage reference VR is less than the carrier signal CW in the upper arm. In this case, the connection terminals 40a and 40b are short-circuited by the first switching element 41, and the voltage between the connection terminals 40a and 40b is substantially 0V. Then, when the voltage reference VR is equal to or higher than the carrier signal CW, the control circuit 14 turns off the first switching element 41 and turns on the second switching element 42. In this case, the voltage Vc of the charge storage element 45 appears between the connection terminals 40a and 40b.

  Further, the control circuit 14 inverts the determination of each of the switching elements 41 and 42 in the lower arm. That is, in the converter CEL of the upper arm, when the first switching element 41 is on and the second switching element 42 is off, the first switching element 41 is turned off in the converter CEL having the same number of stages in the lower arm. The switching element 42 is turned on.

  Thus, the converter CEL outputs two levels of power, + Vc and 0, by the switching of the switching elements 41 and 42. The converter CEL may be called, for example, a power cell.

  In power converter 10, the total of the output voltage of each converter CEL connected in series turns into voltage of each arm part 22a-22f. Thereby, the power conversion apparatus 10 can perform multi-level power conversion according to the number of series connections of the converters CEL.

FIG. 4 is a block diagram schematically showing an example of the control circuit.
As shown in FIG. 4, the control circuit 14 includes a common control block 50, an individual control block 51, an adder 52, a comparator 53, AND circuits 54 and 55, a NOT gate 56, and an overvoltage detection circuit. And 58. In FIG. 4, for convenience, only one arm in each of the arm portions 22 a to 22 f is shown.

  The common control block 50 is provided, for example, corresponding to each of the legs LG1 to LG3. Therefore, although only one common control block 50 is illustrated in FIG. 4, actually, three common control blocks 50 corresponding to each of the legs LG1 to LG3 are provided in the control circuit 14. The common control block 50 may be provided for each of the arms 22a to 22f.

  On the other hand, each of individual control block 51, adder 52, comparator 53, AND circuits 54, 55, and NOT gate 56 corresponds to each of M stages of converters CEL included in one arm of the corresponding leg. M are provided.

  The voltage detection value of the charge storage element 45 detected by the voltage detector 47 of each converter CEL in the first to Mth stages is input to the overvoltage detection circuit 58. Further, the upper limit value of the voltage of the charge storage element 45 of each converter CEL is input to the overvoltage detection circuit 58. The overvoltage detection circuit 58 detects the overvoltage of the charge storage element 45 of each converter CEL based on the voltage detection value and the upper limit value of the charge storage element 45 of each converter CEL which are input. Then, the overvoltage detection circuit 58 inputs an overvoltage detection signal SOV representing the detection result of the overvoltage to the common control block 50. For example, the overvoltage detection signal SOV becomes Lo (for example, OV) when the overvoltage is not detected, and becomes Hi (for example, +5 V) when the overvoltage is detected.

In the common control block 50, the detection values of the alternating current of each phase detected by the respective current detectors 17a to 17c, the detection value of the direct current detected by the current detector 18, and the voltage detector 19 are detected. The detected value of the AC voltage of each phase is input. The common control block 50 is included in one leg based on the detection results of each of the current detectors 17a, 17b, 17c, 18 and the voltage detector 19 and the over voltage detection signal SOV input from the over voltage detection circuit 58. A voltage reference VR _BASE is generated to control the operation of each converter CEL. Then, the generated voltage reference VR _BASE is input to each of the adders 52.

In each individual control block 51, the voltage detection value of the charge storage element 45 detected by the voltage detector 47 of the converter CEL of the corresponding stage among the first to Mth stages of the converters CEL It is input. Each individual control block 51 calculates correction values V _{CRT1 to} V _CRTM of the voltage reference VR _BASE for each converter CEL based on the detection result of the voltage detector 47 of each converter CEL. Then, each individual control block 51 _inputs the calculated correction values V _{CRT1 to} V _CRTM to the corresponding adder 52.

Each adder 52 adds the correction value V _{CRT1 to} V _CRTM calculated at each corresponding individual control block 51 to the voltage reference VR _BASE generated at the common control block 50. In other words, each adder 52 corrects the voltage reference VR _BASE for each converter CEL based on the correction values V _{CRT1 to} V _CRTM . Thus, the voltage reference _VR 1 _{to VR} M of each transducer for each CEL from the underlying voltage reference _{VR BASE} (VR) is generated. Each adder 52 inputs the generated voltage reference _VR 1 to VR _M to the comparator 53 corresponds.

Each comparator 53, together with the voltage reference _VR 1 to VR _M generated by the adder 52 is input, the carrier signal CW is inputted. Each comparator 53, as described above, compares the voltage reference _VR 1 to VR _M and the carrier signal CW. Then, each comparator 53 inputs the comparison result to one input terminal of the corresponding AND circuit 54 and also inputs the comparison result inverted through the NOT gate 56 to one input terminal of the corresponding AND circuit 55. Do.

  The output terminal of each AND circuit 54 is connected to the control terminal of the switching element 42 of the corresponding converter CEL. The output terminal of each AND circuit 55 is connected to the control terminal of the switching element 41 of the corresponding converter CEL. Thereby, according to the comparison result of the comparator 53, on / off of each switching element 41 and 42 is switched as mentioned above.

  A gate OFF signal is input to the other input terminal of each of the AND circuits 54 and 55. When the gate OFF signal is set to Hi, on / off of each switching element 41, 42 is controlled as described above. On the other hand, when the gate OFF signal is set to Lo, each switching element 41, 42 is held in the OFF state. That is, each switching element 41 and 42 is gate-blocked. Thus, the gate OFF signal is negative logic that is set to Lo at the time of gate block.

FIG. 5 is a block diagram schematically showing an example of the common control block.
As shown in FIG. 5, the common control block 50 includes command value switching units 61 and 62, an alternating current control unit 63, a direct current control unit 64, and an adder 65.

  An alternating current command value at a normal time and an alternating current command value at the time of detection of an overvoltage are input to a command value input terminal of the command value switching unit 61. The command value switching unit 61 outputs an alternating current command value at normal time when the switching signal input terminal is at Lo level, and outputs an alternating current command value at over voltage detection when the switching signal input terminal is at Hi level. It is configured to An overvoltage detection signal SOV is input to the switching signal input terminal. Based on the overvoltage detection signal SOV, the command value switching unit 61 switches between an alternating current command at a normal time and an alternating current command value at the time of overvoltage detection.

  The alternating current command value at the time of overvoltage detection is smaller than the effective value of the alternating current command value at the normal time. The alternating current command value at the time of detecting the overvoltage is, for example, equal to or less than 0.1 times the normal alternating current command value. The alternating current command value at the time of overvoltage detection may be, for example, zero. The alternating current command value is a signal of the effective value level (DC conversion level).

  The command value input terminal of the command value switching unit 62 receives a normal DC current command value and a DC current command value at the time of detection of an overvoltage. The command value switching unit 62 outputs a normal DC current command value when the switching signal input terminal is at Lo level, and outputs a DC current command value at over voltage detection when the switching signal input terminal is at Hi level. It is configured to An overvoltage detection signal SOV is input to the switching signal input terminal. Based on the overvoltage detection signal SOV, the command value switching unit 62 switches between a normal DC current command and a DC current command value at the time of overvoltage detection.

  The DC current command value at the time of detection of the overvoltage is smaller than the DC current command value at the normal time. The direct current command value at the time of detection of the overvoltage is, for example, equal to or less than 0.1 times the normal direct current command value. The DC current command value at the time of overvoltage detection may be, for example, zero. The direct current command value at the time of overvoltage detection may be the same as or different from the AC current command value at the time of overvoltage detection.

  The four command values may be changed, for example, in the case where the power is supplied from the AC side to the DC side and in the case where the power is supplied from the DC side to the AC side. Also, each command value may be changed, for example, according to an instruction from the outside.

  In FIG. 5, switch-like command value switching units 61 and 62 are shown. The command value switching units 61 and 62 are not limited thereto, and may have any configuration that can switch the command value to be input. For example, each command value is stored in advance in AC current control unit 63 and DC current control unit 64, and each command value is stored in AC current control unit 63 and DC current control unit 64 in accordance with the level of overvoltage detection signal SOV or the like. It is possible to switch selectively in. That is, AC current control unit 63 selects the AC current command value stored in advance when the overvoltage detection signal SOV is Lo, and stores the voltage when the overvoltage detection signal SOV is Hi in advance. An alternating current command value may be selected. The direct current control unit 64 selects the normal direct current command value stored in advance when the overvoltage detection signal SOV is Lo, and the direct current in the case of the overvoltage detection stored in advance when the overvoltage detection signal SOV is Hi. The command value may be selected.

  The alternating current command value from the command value switching unit 61 is input to the alternating current control unit 63, and the detection value of the alternating current of one phase detected by one of the current detectors 17a, 17b, and 17c, And the detection value of the alternating voltage of one phase detected by the voltage detector 19 is input. The AC current control unit 63 switches, for example, from an AC current command value at normal time to an AC current command value at over voltage detection, and switches from an AC current command value at over voltage detection to an AC current command value at normal time. Slowly change each command value due to, for example, primary delay. Thereby, for example, it is possible to suppress an abrupt change of the alternating current. The time constant of the first-order lag is either when switching from an alternating current command value at normal time to an alternating current command value at detecting over voltage, and when switching from an alternating current command value at detecting over voltage to an alternating current command value at normal time. You may change it.

The alternating current control unit 63 performs, for example, PI (Proportional-Integral) control on the input alternating current command value, alternating current detection value, and alternating voltage detection value, to thereby perform alternating current according to the command value. To generate an AC voltage reference VR _BASE-0 to flow to the AC output point of the power conversion device 10. The alternating current control unit 63 generates, for example, a voltage reference VR _BASE-0 for controlling the switching elements 41 and 42 such that the alternating current detection value follows the alternating current command value. The alternating current control unit 63 inputs the generated voltage reference VR _BASE-0 to the adder 65.

The generation of the voltage reference VR _BASE-0 by the AC current control unit 63 is not limited to PI control, but may be P control, Proportional-Integral-Derivative (PID) control, etc., using other modern control theory etc. May be

  The direct current control unit 64 receives the direct current command value from the command value switching unit 62 and also receives the detected value of the direct current detected by the current detector 18. The DC current control unit 64 switches, for example, from the normal DC current command value to the DC current command value at the overvoltage detection time, and the DC current control value at the overvoltage detection time from the DC current command value to the normal DC current command value. Slowly change each command value due to, for example, primary delay. Thereby, for example, it is possible to suppress a rapid change in direct current. The time constant of the first-order lag is either when switching from the normal DC current command value to the DC current command value when the overvoltage is detected or when switching from the DC current command value when the overvoltage is detected to the DC current command value when normal. You may change it.

The DC current control unit 64 causes a DC current corresponding to the command value to flow to the DC output point of the power conversion device 10, for example, by performing PI control on the inputted DC current command value and DC current detection value. The correction value V _CRT0 of the voltage reference VR _BASE-0 is calculated. The DC current control unit 64 calculates, for example, a correction value V _CRT0 of a voltage reference VR _BASE-0 for controlling the switching elements 41 and 42 such that the DC current detection value follows the DC current command value. The calculated correction value V _CRT0 is, for example, a DC component of the voltage reference VR _BASE-0 . The direct current control unit 64 inputs the calculated correction value V _CRT0 to the adder 65. The correction value V _CRT0 may be calculated by P control or PID control.

The adder 65 adds the correction value V _CRT0 calculated by the DC current control unit 64 to the voltage reference VR _BASE-0 generated by the AC current control unit 63. The adder 65 adds a DC component to, for example, a sinusoidal voltage reference VR _BASE-0 . Thereby, the adder 65 generates the corrected voltage reference VR _BASE from the voltage reference VR _BASE-0 . The adder 65 inputs the voltage reference VR _BASE after the addition of the correction value to each adder 52 as described above.

FIG. 6 is a block diagram schematically showing an example of the individual control block.
As shown in FIG. 6, the individual control block 51 includes a subtractor 71 and a controller 72. The voltage target value of the charge storage element 45 of each converter CEL and the voltage detection value of the charge storage element 45 detected by the voltage detector 47 are input to the subtractor 71. The subtractor 71 calculates the difference between the voltage target value and the voltage detection value, and inputs the calculated difference to the controller 72.

The controller 72 calculates the correction value of the voltage reference VR _BASE for setting the voltage of the charge storage element 45 to the target value from the input difference. The controller 72 calculates the correction value by performing P control on the difference, for example. The calculation of the correction value by the controller 72 may be PI control or PID control. The correction value calculated by the controller 72 is, for example, a correction value for adjusting the phase and amplitude of the voltage reference VR _BASE . The controller 72 thus calculates the correction value for each converter CEL, and inputs the calculated correction value to the corresponding adder 52.

  Thus, based on the alternating current command value and the direct current command value input in advance, the control circuit 14 converts the alternating current and direct current flowing into and out of the main circuit unit 12 into the alternating current command value and the direct current command value. By controlling ON / OFF of each switching element 41, 42 so as to follow, the AC / DC conversion by the main circuit unit 12 is controlled, and the voltage detected by any of the voltage detectors 47 is the upper limit value or more When it becomes, the alternating current command value and the direct current command value are made smaller than usual, and the on / off of each switching element 41, 42 is controlled. The normal time, that is, the case where the voltage detected by each of the voltage detectors 47 is less than the upper limit value.

FIG. 7 is a block diagram schematically showing an example of the overvoltage detection circuit.
As shown in FIG. 7, the overvoltage detection circuit 58 includes a plurality of comparison circuits 75 a to 75 f and an OR circuit 76. Each of the comparison circuits 75a to 75f is provided corresponding to each of the arm portions 22a to 22f. The comparison circuit 75 a includes a plurality of comparators COMP _{1 to} COMP _M and an OR circuit 77.

The comparators COMP _{1 to} COMP _M are provided corresponding to the respective converters UP ₁ to UPM ₁ of the first arm portion 22 a. The signal input terminal of the comparators COMP ₁ ~COMP _M, voltage detection values of the respective charge storage elements 45 of each transducer UP1～UPM ₁ is inputted.

On the other hand, the upper limit value of the voltage of the charge storage element 45 of each converter CEL is input to the set value input terminal of each of the comparators COMP _{1 to} COMP _M. Each of the comparators COMP _{1 to} COMP _M compares the input voltage detection value with the upper limit value. That is, each of the comparators COMP _{1 to} COMP _M compares whether the input voltage detection value is equal to or more than the upper limit value. Each of the comparators COMP _{1 to} COMP _M may have a hysteresis.

For example, when the signal at the signal input terminal is equal to or less than the set value input signal, the outputs of the comparators COMP _{1 to} COMP _M are Lo. When the signal level at the signal input terminal rises and exceeds the signal at the set value input terminal, the outputs of the comparators COMP _{1 to} COMP _M become Hi.

Further, the signal of the signal input terminals of the comparators COMP ₁ ~COMP _M is greater than the signal of the setting value input terminals of the comparators COMP ₁ ~COMP _M, outputs of the comparators COMP ₁ ~COMP _M is a Hi after the signal level of the signal input terminals of the comparators COMP ₁ ~COMP _M is decreased, even equal to the signal of the set value input terminals of the comparators COMP ₁ ~COMP _M, the comparators COMP ₁ ~ The output of COMP _M maintains the Hi level. Then, the signal level further reduction of the signal input terminals of the comparators COMP ₁ ~COMP _M, further that there is only a low signal level hysteresis level α from the signal of the setting value input terminals of the comparators COMP ₁ ~COMP _M, each The output terminals of the comparators COMP _{1 to} COMP _M become Lo level.

  The upper limit value is, for example, a predetermined constant value. The upper limit value is, for example, 1.1 PU of the rated voltage of the charge storage element 45 of each converter CEL. Alternatively, the upper limit value is set based on, for example, the safe operation area of each switching element 41, 42.

The outputs of the comparators COMP _{1 to} COMP _M are input to the OR circuit 77. As a result, the output of the OR circuit 77 becomes Hi level when one of the outputs of each of the comparators COMP _{1 to} COMP _M becomes Hi. The output of the OR circuit 77 is input to the OR circuit 76.

  The configuration of each of the other comparison circuits 75b to 75f is substantially the same as the configuration of the comparison circuit 75a described above, and thus the detailed description will be omitted. The outputs of the OR circuits 77 of the respective comparison circuits 75 a to 75 f are input to the OR circuit 76.

  The overvoltage detection circuit 58 inputs the output of the OR circuit 76 to the common control block 50 as the overvoltage detection signal SOV. Therefore, the overvoltage detection signal SOV becomes Hi level when an overvoltage is detected in any one of the charge storage elements 45 of each converter CEL.

FIG. 8 is a graph schematically showing an example of the characteristics of the switching element.
FIG. 8 schematically shows an example of the characteristic of the safe operation area SOA of each switching element 41, 42 of the converter CEL. The vertical axis in FIG. 8 is the current flowing between the pair of main terminals of each of the switching elements 41 and 42, and the horizontal axis is the voltage applied between the pair of main terminals.

  As shown in FIG. 8, the voltage that can be applied between the main terminals of the switching elements 41 and 42 is in inverse proportion to the current flowing between the main terminals. Therefore, as described above, when any of the voltage detection values of the charge storage elements 45 becomes equal to or more than the upper limit value, the command values of the alternating current and the direct current are reduced. For example, the command values of the alternating current and the direct current are reduced to a current value that falls within the range of the safe operation area SOA with respect to the voltage value set to the upper limit value. For example, when any of the voltage detection values of each charge storage element 45 becomes equal to or higher than the upper limit value, alternating current and direct current so as to change from the normal current control maximum level in FIG. Decrease the command value of. In this case, the voltage that can be applied to each of the switching elements 41 and 42 can be raised from the normal voltage maximum level to the overvoltage detection voltage level. As a result, even when each charge storage element 45 is in an overvoltage state, breakage or the like of each switching element 41, 42 can be suppressed. For example, the command values of the alternating current and the direct current are reduced to about 1/10 of the normal time. Thereby, the relationship between the voltage of the upper limit value and the current of the command value can be properly contained within the range of the safe operation area SOA.

  Then, with the outflow and inflow currents to the AC power system 2 side and the DC transmission lines 3 and 4 reduced, the switching elements 41 and 42 are operated such that the voltage of the charge storage element 45 follows the voltage target value. As a result, the voltage rise of the charge storage element 45 in the overvoltage state can be equalized by the charge storage element 45 of each converter CEL, and the overvoltage state of the charge storage element 45 can be eliminated.

  For example, the information of the characteristic of the safe operation area SOA of each switching element 41, 42 is stored, and the AC current command value and the DC current command value at the time of overvoltage detection according to the voltage detection value compared with the upper limit value or more. May be changed. That is, as the voltage detection value becomes higher, the current command value is made smaller. Thereby, when the voltage detection value is relatively low, the time required for the discharge can be further shortened.

FIGS. 9A to 9E are graphs schematically showing an example of a simulation result.
Fig.9 (a)-FIG.9 (e) represent an example of the simulation result when overvoltage generate | occur | produces in one converter CEL contained in the 1st arm part 22a (upper arm).
FIG. 9A shows the voltage of the charge storage element 45 of the normal converter CEL (normal CELL) and the voltage of the charge storage element 45 of the converter CEL (abnormal CELL) in which the overvoltage occurs.
FIG. 9B shows the alternating current of one phase of the alternating current power system 2 flowing to the first leg LG1.
FIG. 9C shows direct current flowing in the direct current transmission lines 3 and 4.
FIG. 9D shows the upper arm current flowing to the first arm portion 22a which is the upper arm of the first leg LG1.
FIG. 9E shows the lower arm current flowing to the second arm portion 22b which is the lower arm of the first leg LG1.

  As shown in FIGS. 9A to 9E, in the simulation, an overvoltage occurs in the abnormal CELL at time t1. And in simulation, according to detection of overvoltage, operation of each converter CEL is made to stop temporarily (time t1-t2). However, as shown in FIGS. 9A to 9E, even if the operation of each converter CEL is stopped, the voltage of the abnormal CELL does not immediately decrease.

  In the simulation, at time t2, the operation of each converter CEL in which the alternating current command value at the time of overvoltage detection and the DC current command value at the time of overvoltage detection are set is started.

  As shown in FIGS. 9A to 9E, after the voltage increase, the current flowing into and out of the AC power system 2 side and the DC transmission lines 3 and 4 is reduced, and the voltage of each charge storage element 45 is reduced. The current is supplied to the AC side, the DC side, and the main circuit portion 12 so as to balance the two. As a result, the voltage increase is reduced, and then the operation can be resumed. In the simulation, at time t3, the operation of each converter CEL in which the normal alternating current command value and the normal direct current command value are set is resumed.

  In Drawing 9 (a)-Drawing 9 (e), since it is a wave form of tidal current conditions which electric power has flowed into main circuit part 12 from the direct-current side, arm current is a wave form of a direct current ingredient of negative. Even if the flow direction is reversed, balance is possible as well. For example, when an overvoltage state is detected, part of the charge stored in each charge storage element 45 may be output to the AC power system 2 as reactive power. Further, although only one converter CEL is shown in the figure, the voltage of each charge storage element 45 can be similarly balanced even when the voltage of a plurality or one arm rises. As a result, since a discharge device for the charge storage element 45 is not required, it is possible to suppress an increase in the number of parts, and to realize size reduction and cost reduction of the power conversion device 10.

  Further, as shown in FIGS. 9A to 9E, in this example, the charge storage element 45 in the overvoltage state can be discharged to an appropriate value (less than the upper limit value) in about 0.1 seconds. When the voltage of the charge storage element 45 is discharged using a discharge device, the discharge may take several minutes. On the other hand, in the power conversion device 10, the charge storage element 45 in the overvoltage state can be discharged to an appropriate value in several seconds. As described above, in the power conversion device 10, the charge storage element 45 in the overvoltage state can be discharged in a short time, and operability can be improved, as compared with the case where the discharge device is used. For example, the time from the operation stop to the restart of the operation due to the detection of the overvoltage can be suppressed to about several seconds. Thus, in the power conversion device 10, the reliability and operability can be improved without causing an increase in the number of parts.

  In the simulation, for the convenience of description, the operation of each converter CEL is temporarily stopped at time t1 to t2. In practice, it is not necessary to stop each converter CEL. When an overvoltage is detected, the operation at the time of overvoltage detection may be performed continuously to the normal operation.

FIG. 10 is a flowchart schematically illustrating an example of the operation of the power conversion device according to the embodiment.
In the control circuit 14 of the power conversion device 10, the voltage detection value of the charge storage element 45 of each converter CEL is input to the overvoltage detection circuit 58. As described with reference to FIG. 7, the overvoltage detection circuit 58 compares each input voltage detection value with the upper limit value, and inputs an overvoltage detection signal SOV according to the comparison result to the common control block 50 (see FIG. 10 steps S11).

  When the voltage detection value of the charge storage element 45 of each converter CEL is less than the upper limit value, the common control block 50 (when the overvoltage detection signal SOV is Lo) instructs the alternating current command value at the normal time to the command value switching unit 61 From the above, the alternating current control unit 63 is input, and a normal direct current command value is input from the command value switching unit 62 to the direct current control unit 64. That is, the common control block 50 selects a normal alternating current command value and a normal direct current command value when each voltage detection value is less than the upper limit value (step S12 in FIG. 10). Thus, as described above, the control circuit 14 generates the voltage reference VR for each converter CEL based on each current command value at the normal time. Then, the control circuit 14 operates the switching elements 41 and 42 of the converters CEL based on the generated voltage references VR (step S13 in FIG. 10). Thereby, while an alternating current according to the alternating current command value at the normal time flows between the AC power system 2 and the main circuit portion 12, a direct current according to the normal command value for the normal time flows the DC transmission line 3, 4 and the main circuit section 12, and conversion of AC power to DC power or conversion of DC power to AC power is performed.

  On the other hand, when any of the voltage detection values of the charge storage element 45 of each converter CEL is equal to or more than the upper limit (when the overvoltage detection signal SOV is Hi), the common control block 50 performs AC current command value at the time of overvoltage detection. Is inputted from the command value switching unit 61 to the alternating current control unit 63, and a direct current command value at the time of detection of an overvoltage is inputted from the command value switching unit 62 to the direct current control unit 64. That is, the common control block 50 selects the alternating current command value at the time of the overvoltage detection and the direct current command value at the time of the overvoltage detection, when any of the voltage detection values is equal to or more than the upper limit (step S14 in FIG. 10). . Thereby, the control circuit 14 reduces each current command value when any of the voltage detection values of the charge storage element 45 of each converter CEL is equal to or more than the upper limit value.

  As described above, the control circuit 14 makes the voltage of the charge storage element 45 of each converter CEL follow the voltage target value in a state where the outflow and inflow currents to the AC power system 2 and the DC transmission lines 3 and 4 are reduced. The switching elements 41 and 42 are operated so as to (step S15 in FIG. 10). As a result, the voltage rise of the charge storage element 45 in the overvoltage state can be equalized by the charge storage element 45 of each converter CEL, and the overvoltage state of the charge storage element 45 of each converter CEL can be eliminated. Reliability and operability can be improved without increasing the number of parts.

  When the control circuit 14 starts the operations of the switching elements 41 and 42 based on the current command values at the time of overvoltage detection, the control circuit 14 sets each current command value at the time of overvoltage detection until the voltage detection value becomes less than the upper limit. The operations of the switching elements 41 and 42 based on the above are continued (step S16 in FIG. 10). More specifically, the operation of each switching element 41, 42 based on each current command value at the time of overvoltage detection is continued until each voltage detection value becomes smaller than a value obtained by subtracting the hysteresis α from the upper limit value.

  The control circuit 14 returns the current command value input from the command value switching unit 61 to the alternating current control unit 63 to the alternating current command value at the normal time when each detected voltage value becomes smaller than the upper limit value -α. The current command value input from the command value switching unit 62 to the DC current control unit 64 is returned to the normal DC current command value, and the normal operation is restarted. The control circuit 14 repeatedly executes the above processing.

FIG. 11 is a block diagram schematically showing a modification of the converter.
As shown in FIG. 11, in this example, the converter CEL further includes a third switching element 43 and a fourth switching element 44. For the third switching element 43 and the fourth switching element 44, elements substantially the same as the first switching element 41 and the second switching element 42 are used.

  The pair of main terminals of the fourth switching element 44 is connected in series to the pair of main terminals of the third switching element 43. The third switching element 43 and the fourth switching element 44 are connected in parallel to the first switching element 41 and the second switching element 42. The charge storage element 45 is connected in parallel to the first switching element 41 and the second switching element 42, and is connected in parallel to the third switching element 43 and the fourth switching element 44.

  In the third switching element 43, a rectifying element 43d is connected in antiparallel to the pair of main terminals. In the fourth switching element 44, a rectifying element 44d is connected in antiparallel to the pair of main terminals.

  The first connection terminal 40 a of the converter CEL is connected between the first switching element 41 and the second switching element 42. The second connection terminal 40 b is connected between the third switching element 43 and the fourth switching element 44. In this example, the second connection terminal 40 b is connected to the main terminal on the opposite side to the main terminal connected to the second switching element 42 of the first switching element 41 via the third switching element 43. That is, in this example, the switching elements 41 to 44 are connected in a full bridge. In this example, the converter CEL is a full bridge circuit.

  Thus, the converter CEL used in the MMC main circuit unit 12 may be a half bridge circuit or a full bridge circuit.

FIG. 12 is a block diagram schematically showing a modification of the main circuit portion.
As shown in FIG. 12, in the main circuit portion 12a of this example, the transformer 16 and the buffer reactors 23a to 23f shown in FIG. 1 are omitted, and instead, three winding transformers 81 to 83 are provided. It is done.

  The three-winding transformer 81 is provided between the first arm 22a and the second arm 22b. The triple winding transformer 81 has a primary winding 81a, a secondary winding 81b, and a tertiary winding 81c. The primary winding 81 a of the three-winding transformer 81 is connected to the AC power system 2. The secondary winding 81b is connected to the negative terminal of the first arm 22a which is the upper arm. The tertiary winding 81c is connected to the positive terminal of the second arm 22b which is the lower arm.

  The three-winding transformer 82 is provided between the third arm 22c and the fourth arm 22d. The triple winding transformer 82 has a primary winding 82a, a secondary winding 82b, and a tertiary winding 82c. The primary winding 82 a of the three-winding transformer 82 is connected to the AC power system 2. The secondary winding 82b is connected to the negative terminal of the third arm 22c which is the upper arm. The tertiary winding 82c is connected to the positive terminal of the fourth arm portion 22d which is the lower arm.

  The three-winding transformer 83 is provided between the fifth arm 22e and the sixth arm 22f. The triple winding transformer 83 has a primary winding 83a, a secondary winding 83b, and a tertiary winding 83c. The primary winding 83 a of the three-winding transformer 83 is connected to the AC power system 2. The secondary winding 83b is connected to the negative terminal of the fifth arm 22e which is the upper arm. The tertiary winding 83c is connected to the positive terminal of the sixth arm 22f which is the lower arm.

  Further, in each three-winding transformer 81 to 83, the neutral point of the secondary winding 81b and the tertiary winding 81c, the neutral point of the secondary winding 82b and the tertiary winding 82c, and the secondary winding 83b And the neutral point of the tertiary winding 83c are connected to each other.

  The main circuit unit 12a shown in FIG. 12 can also perform the AC / DC conversion by the same operation as the main circuit unit 12 shown in FIG. When one of the voltage detection values of the charge storage element 45 of each converter CEL exceeds the upper limit value, reliability and operability can be achieved without causing an increase in the number of parts by reducing each current command value. Can be improved. Further, in the main circuit unit 12a of this example, the buffer reactors 23a to 23f and the like can be omitted compared to the main circuit unit 12, and the number of parts can be further reduced. For example, the increase in size and cost of the power conversion device 10 can be further suppressed.

FIG. 13 is a block diagram schematically showing a modification of the overvoltage detection circuit.
As shown in FIG. 13, in the overvoltage detection circuit 58 a of this example, the comparison circuit 75 a includes the maximum value selection circuit 100 and the comparator 102. The signal input terminal of the maximum value selection circuit 100, a voltage detection value of each of the charge storage elements 45 of each transducer UP1～UPM ₁ is inputted. The maximum value selection circuit 100 selects the maximum value of each input detected value, and inputs the selected maximum value to the signal input terminal of the comparator 102.

The upper limit value of the voltage of the charge storage element 45 of each converter CEL is input to the setting value input terminal of the comparator 102. The comparator 102 compares the input maximum value with the upper limit value. That is, the comparator 102 compares whether the input maximum value is equal to or more than the upper limit value. Note that, similarly to the comparators COMP _{1 to} COMP _M described in the above embodiment, the comparator 102 may have hysteresis. The output of the comparator is input to the OR circuit 76.

  The configuration of each of the other comparison circuits 75b to 75f is substantially the same as the configuration of comparison circuit 75a, so detailed description will be omitted. The output of the comparator 102 of each of the comparison circuits 75 a to 75 f is input to the OR circuit 76.

  The overvoltage detection circuit 58a inputs the output of the OR circuit 76 to the common control block 50 as the overvoltage detection signal SOV. As described above, in the overvoltage detection circuit 58a, in each of the arm portions 22a to 22f, whether or not the maximum value of the element voltage detection value is equal to or more than the upper limit value is compared. Also in this case, as in the case of the overvoltage detection circuit 58 of the above embodiment, when the charge storage element 45 of any of the converters CEL becomes an overvoltage, the overvoltage detection signal SOV can be set to the Hi level. In the overvoltage detection circuit 58a, the number of comparators can be reduced compared to the overvoltage detection circuit 58. In the overvoltage detection circuit 58a, for example, the circuit configuration can be simplified, and the number of parts can be reduced, and the manufacturing cost can be reduced accordingly.

FIG. 14 is a block diagram schematically showing a modification of the overvoltage detection circuit.
As shown in FIG. 14, the overvoltage detection circuit 58 b of this example includes a maximum value selection circuit 110 and a comparator 112. Voltage detection values of the charge storage elements 45 of all the converters CEL included in the main circuit unit 12 are input to the signal input terminal of the maximum value selection circuit 110. The maximum value selection circuit 110 selects the maximum value of each input detected value, and inputs the selected maximum value to the signal input terminal of the comparator 112.

  The upper limit value of the voltage of the charge storage element 45 of each converter CEL is input to the setting value input terminal of the comparator 112. The comparator 112 compares the input maximum value with the upper limit value. That is, the comparator 112 compares whether the input maximum value is equal to or more than the upper limit value. The comparator 112 may have hysteresis.

  The overvoltage detection circuit 58b inputs the output of the comparator 112 to the common control block 50 as the overvoltage detection signal SOV. Thus, in the overvoltage detection circuit 58b, it is compared whether or not the maximum value of the element voltage detection values of all the converters CEL is equal to or more than the upper limit value. Also in this case, as in the above embodiments, when the charge storage element 45 of any of the converters CEL becomes an overvoltage, the overvoltage detection signal SOV can be set to the Hi level. In the overvoltage detection circuit 58b, for example, the circuit configuration can be further simplified. For example, the number of parts and the manufacturing cost can be further suppressed.

  In each of the above embodiments, an MMC type power converter is used for the main circuit unit 12. The main circuit unit 12 is not limited to the MMC type, and may be another type of power converter in which a plurality of converters CEL are connected in series.

  While certain embodiments of the present invention have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and the gist of the invention, and are included in the invention described in the claims and the equivalent scope thereof.

DESCRIPTION OF SYMBOLS 2 AC power system 3, 4 DC power transmission line 10 Power converter 12, 12a Main circuit part 14 Control circuit 16 Transformer 17a-17c 18 Current detector 19 Voltage detectors 20a, 20b: DC terminals, 21a to 21c: first to third AC terminals 22a to 22f: first to sixth arm portions 23a to 23f: buffer reactors 24, 25: signal lines, 40a 40b: first and second connection terminals 41 to 44: first to fourth switching elements 45: charge storage elements 46: driver circuits 47: voltage detectors 50: common control block 51: individual control Block 52 52 Adder 53 Comparator 54 54 55 AND circuit 56 NOT gate 58 58a 58b Overvoltage detection circuit 61 62 Command value switching unit 63 AC Control part 64: DC current control part 65: Adder 71: Subtractor 72: controller 75a to 75f: comparison circuit 76, 77: OR circuit 81 to 83: 3 winding transformer 81a, 82a, 83a: primary winding, 81b, 82b, 83b: secondary winding, 81c, 82c, 83c: tertiary winding, 100, 110: maximum value selection circuit, 102, 112: comparator, CEL: converter, COMP _{1 to} COMP _M ... Comparator

Claims (5)

A plurality of converters have a plurality of arm parts connected in series, and the plurality of converters perform AC / DC conversion of AC power to DC power and / or DC power to AC power conversion. Main circuit section,
A control circuit that controls the operation of the main circuit unit;
Equipped with
The plurality of transducers are
A plurality of switching elements connected in a half bridge connection or a full bridge connection,
A charge storage element connected in parallel to the plurality of switching elements;
Have
The main circuit unit includes a plurality of voltage detectors that detect voltages of the charge storage elements of the plurality of converters,
The control circuit causes the alternating current and direct current flowing into and out of the main circuit unit to follow the alternating current command value and the direct current command value based on the alternating current command value and the direct current command value input in advance. Thus, while controlling the AC / DC conversion by the main circuit unit by controlling on / off of the plurality of switching elements, the voltage detected by any of the plurality of voltage detectors is equal to or higher than the upper limit value. When it becomes, the power conversion device which controls the on / off of a plurality of switching elements by making the alternating current command value and the direct current command value smaller than usual.   The power conversion device according to claim 1, wherein the plurality of voltage detectors are provided in each of the plurality of converters, and detect a voltage of the charge storage element of each of the plurality of converters.   The power conversion device according to claim 2, wherein the control circuit operates the plurality of switching elements such that the voltage of the charge storage element follows a voltage target value based on detection values of the plurality of voltage detectors.   The control circuit performs a safety operation of the plurality of switching elements with respect to the voltage value set to the upper limit value when the voltage detected by any of the plurality of voltage detectors becomes the upper limit value or more. The power converter according to any one of claims 1 to 3, wherein the alternating current command value and the direct current command value are reduced to a current value which falls within the range of the range. A plurality of converters have a plurality of arm parts connected in series, and the plurality of converters perform AC / DC conversion of AC power to DC power and / or DC power to AC power conversion. Main circuit section,
A control circuit that controls the operation of the main circuit unit;
Equipped with
The plurality of transducers are
A plurality of switching elements connected in a half bridge connection or a full bridge connection,
A charge storage element connected in parallel to the plurality of switching elements;
Have
The main circuit unit is a control method of a power conversion device having a plurality of voltage detectors for detecting a voltage of the charge storage element of the plurality of converters,
The plurality of alternating currents and direct currents flowing into and out of the main circuit unit follow the alternating current command values and the direct current command values based on the alternating current command values and the direct current command values input in advance. Controlling the AC / DC conversion by the main circuit unit by controlling the on / off of the switching element of
When the voltage detected by any of the plurality of voltage detectors becomes equal to or higher than the upper limit value, the alternating current command value and the direct current command value are made smaller than in a normal state to turn on the plurality of switching elements. The control method of the power converter device which controls OFF.

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