JP7050391B2 - Power converter - Google Patents

Description

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

At the time of maintenance and inspection of the power conversion device, it is necessary to stop the operation of the power conversion device. Power converters are often equipped with a capacitor with a large capacitance, and it is necessary to sufficiently discharge the electric charge stored in this capacitor in order to safely perform maintenance and inspection work after the operation is stopped. be.

As the converter of the power converter, various types are used or proposed depending on the power to be handled, the range of the input / output voltage, and the like. Modular Multilevel Converter (MMC) has been put into practical use as a power conversion method that can realize a large capacity while reducing the size by using a self-extinguishing semiconductor switching element. There is.

In the MMC type power converter, a large number of unit converters are connected in cascade to form an arm for each phase. Since the module including the unit converter is at a high potential with respect to the ground potential, each unit converter is used as the main circuit to generate a control power supply and operate the unit converter.

The MMC type power converter has a large-capacity capacitor for each unit converter, and it is necessary to confirm that the voltage across each capacitor has dropped to a safe voltage when the operation is stopped.

It is difficult to provide a monitoring device that supplies power to a high-voltage unit converter from the ground and checks whether the voltage of the capacitor is within the safe range. It is realistic to connect directly to each capacitor and check the voltage of the capacitor.

Therefore, a method of connecting a light emitting element such as a semiconductor light emitting element (LED) to both ends of the capacitor and confirming a decrease in the capacitor voltage depending on the presence or absence of light emission can be considered. In this method, when the voltage of the capacitor is high, it is necessary to connect a large number of light emitting elements in series. When one light emitting element fails and becomes an open state, all the light emitting elements are turned off, and it cannot be determined whether the voltage of the capacitor drops to the safe range and the light is turned off or the light is turned off due to the failure.

Japanese Unexamined Patent Publication No. 11-4534

The embodiment provides a power conversion device capable of reliably monitoring the voltage of a capacitor even if a light emitting element fails.

The power conversion device according to the embodiment includes a main circuit including a capacitor, a discharge circuit provided to discharge the charge of the capacitor, and a capacitor voltage monitoring circuit connected in parallel to the capacitor. Equipped with a vessel. The capacitor voltage monitoring circuit includes a first series circuit including a plurality of first light emitting elements connected in series, and a plurality of second light emitting elements connected in parallel to the first series circuit and connected in series. Includes a second series circuit. The magnitude of the voltage across the first series circuit when the current emitted by the first light emitting element flows is the magnitude of the voltage across the second series circuit when the current emitted by the second light emitting element flows. It is different from the magnitude of the voltage. The capacitor voltage monitoring circuit has a plurality of blocks including the first series circuit and the second series circuit, respectively. The plurality of blocks are connected in series and connected in parallel to the capacitor. The voltage across the capacitor is charged to 1000V or higher during normal operation of the power converter.

In the present embodiment, a power conversion device capable of reliably monitoring the voltage of the capacitor even if the light emitting element fails is realized.

It is a block diagram which illustrates the power conversion apparatus which concerns on 1st Embodiment. 2 (a) and 2 (b) are schematic circuit diagrams illustrating a part of the power conversion device of the first embodiment. It is a schematic diagram for demonstrating the operation of the power conversion apparatus of 1st Embodiment. It is a schematic diagram for demonstrating the use method of the power conversion apparatus of 1st Embodiment. 5 (a) to 5 (d) are block diagrams illustrating a power conversion device of a comparative example. 6 (a) and 6 (b) are schematic circuit diagrams illustrating a part of the power conversion device of the second embodiment. 7 (a) and 7 (b) are schematic circuit diagrams illustrating a part of the power conversion device of the third embodiment. 8 (a) and 8 (b) are schematic circuit diagrams illustrating a part of the power conversion device of the fourth embodiment.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
It should be noted that the drawings are schematic or conceptual, and the relationship between the thickness and width of each part, the ratio of the sizes between the parts, and the like are not necessarily the same as the actual ones. Further, even when the same part is represented, the dimensions and ratios may be different from each other depending on the drawing.
In addition, in the present specification and each figure, the same elements as those described above with respect to the above-mentioned figures are designated by the same reference numerals, and detailed description thereof will be omitted as appropriate.

(First Embodiment)
FIG. 1 is a block diagram illustrating an electric power conversion device according to the present embodiment.
As shown in FIG. 1, the power converter 10 includes a power converter 20. The power converter 20 is connected to the AC circuit 1 via the terminals 21a to 21c. The AC circuit 1 can include, for example, an AC power supply, an AC transmission line, an AC load, and the like. The AC circuit 1 is, for example, an AC power system. As in this example, the power conversion device 10 may be connected to the AC circuit 1 via the transformer 2. The power converter 20 is connected to the DC circuit 3 via the terminals 21d and 21e. The DC circuit 3 can include, for example, a DC power supply, a DC transmission line, a DC load, and the like. The DC circuit 3 is, for example, a DC transmission line, and a power conversion device capable of mutually converting AC and DC can be connected to the other end of the DC transmission line.

The power converter 20 includes an arm 22 corresponding to each phase of the AC circuit 1. The arm 22 is connected in series between the terminals 21d and 21e to form a leg.

A transformer 25 is connected in series to the arm 22 which is connected in series between the terminals 21d and 21e. A buffer reactor may be connected instead of the transformer 25.

The arm 22 includes a unit converter 30 connected in cascade. The unit converter 30 is connected to M units per arm 22. M may be 1, but preferably M is an integer of 2 or more.

2 (a) and 2 (b) are schematic circuit diagrams illustrating a part of the power conversion device of the present embodiment.
As shown in FIG. 2A, the unit converter 30 includes a main circuit 32 and a capacitor voltage monitoring circuit 34. The unit converter 30 includes terminals 31a and 31b. The unit converter 30 is connected to another unit converter 30 or the like by terminals 31a and 31b.

The main circuit 32 includes a switching element 32a, a diode 32b, a capacitor 32c, and a resistor 32d. The two switching elements 32a are connected in series. The two diodes 32b are connected to the two switching elements 32a in antiparallel. The capacitor 32c is connected in parallel to the series circuit of the switching element 32a. The resistor 32d is connected in parallel to the capacitor 32c.

The resistor 32d may be substantially connected in parallel to the capacitor 32c, and may be divided into two and connected in parallel to each of the two switching elements 32a, for example.

The unit converter 30 includes a main circuit 32, a capacitor voltage monitoring circuit 34, a control circuit (not shown), a gate drive circuit, and the like. In the unit converter 30, a control circuit receives a control signal generated by a control device (not shown). The control circuit and the gate drive circuit generate a gate drive signal for the switching element 32a based on the received control signal, turn the switching element 32a on and off to charge and discharge the capacitor 32c, and the voltage across the capacitor 32c ( Hereinafter referred to as capacitor voltage).

In MMC, in many cases, power is supplied for the operation of the control circuit of the unit converter 30, the gate drive circuit, and the like, using the power stored in the capacitor 32c.

The capacitor voltage monitoring circuit 34 is connected to both terminals of the capacitor 32c of the main circuit 32. That is, the capacitor voltage monitoring circuit 34 is connected in parallel to the capacitor 32c, and serves as a discharge path for the electric charge stored in the capacitor 32c together with the resistor 32d, the control circuit, and the like (discharge circuit).

The capacitor voltage monitoring circuit 34 includes a light emitting element 35 and a resistor 36. The light emitting element 35 and the resistor 36 are connected in series, and a current flows by the power supply from the capacitor 32c to light the light emitting element 35. The resistor 36 limits and sets the current flowing through the light emitting element 35.

The capacitor voltage monitoring circuit 34 includes a plurality of blocks, and each block is connected in series. In this example, N blocks are connected. The blocks connected in series are connected to both terminals of the capacitor 32c via the resistor 36.

Each block contains two series circuits. The two series circuits are connected in parallel. In this example, one series circuit includes two light emitting elements 35 connected in series, and the other series circuit includes three light emitting elements 35 connected in series.

When the operation of the power conversion device 10 is stopped, the capacitor voltage is continuously lowered by the discharge by the resistor 32d, the control circuit, the capacitor voltage monitoring circuit 34, and the like. When the capacitor voltage drops, the light emitting element 35 goes out. In the present embodiment, the capacitor voltage when the light emitting element is turned off is set to a value that allows safe work during maintenance and inspection, and is, for example, about 50V.

In this embodiment, the plurality of light emitting elements 35 have substantially the same current-voltage characteristics (hereinafter, also simply referred to as characteristics). The same characteristic means that when almost the same forward current is applied, almost the same forward voltage is output and light is emitted with almost the same brightness.

The number of light emitting elements 35 included in the two series circuits is not limited to the above example, and one may be one and the other may be two, or one may be three and the other may be four. Alternatively, as will be described later, one series circuit may include two light emitting elements 35 and the other series circuit may include four light emitting elements 35. It is sufficient that the magnitude of the voltage across the series circuit when a current flows through one series circuit is sufficiently lower than the magnitude of the voltage across the series circuit when a current flows through the other series circuit.

The operation of the power conversion device 10 of the present embodiment will be described.
2 (a) and 2 (b) also show the current path of the closed circuit by the capacitor 32c and the capacitor voltage monitoring circuit 34.
In FIG. 2A, the current path of the closed circuit by the capacitor 32c and the capacitor voltage monitoring circuit 34 when all the light emitting elements 35 are in a healthy state is shown by a thick solid arrow.

In this example, the characteristics of the light emitting elements 35 are almost the same, and the forward voltage Vf is almost the same. Therefore, when the capacitor voltage is sufficiently high, the light emitting element 35 is lit in the series circuit having the smaller number of series of the light emitting elements 35. However, in the series circuit having the larger number of light emitting elements 35 in series, the light emitting element 35 is turned off. That is, the current flowing out from one terminal of the capacitor 32c flows through the series circuit of the smaller number of light emitting elements 35 of each block through the resistor 36, and flows into the other terminal of the capacitor 32c.

In FIG. 2B, the current path when one of the two light emitting elements 35 of the series circuit of the block 2 which is the second block out of the N blocks fails and is opened is shown. It is indicated by a thick solid arrow. In the figure, it is assumed that the light emitting element 35 marked with x is out of order. As shown in FIG. 2B, in a series circuit having a smaller number of light emitting elements 35 connected in series, when one light emitting element 35 fails and becomes an open state, the entire series circuit becomes a capacitor 32c. The connection with is cut off.

On the other hand, all the light emitting elements 35 of the series circuit having the larger number of light emitting elements 35 are conductive. Therefore, in each block other than the block 2, a current flows in the series circuit having a smaller number of light emitting elements 35, and in the block 2, a current flows in the series circuit having a larger number of light emitting elements 35. Therefore, the current path of the closed circuit by the capacitor 32c and the capacitor voltage monitoring circuit 34 is maintained, and the light emitting element 35 can be turned on.

FIG. 3 is a schematic diagram for explaining the operation of the power conversion device of the present embodiment.
In FIG. 3, a characteristic graph when n light emitting elements 35 are connected in series is represented by a thick solid line. The characteristic graph when n + 1 light emitting elements 35 are connected in series is represented by a alternate long and short dash line. The horizontal axis of the graph is the forward voltage of n light emitting elements (LEDs) 35, and the vertical axis of the graph is the forward current flowing through the light emitting elements (LEDs) 35. The LED forward voltage in this case is the voltage across the series circuit of the n light emitting elements 35. In FIG. 3, the load line when the resistor 36 having the resistance value R is connected in series with the light emitting element 35 is shown by a broken line and a two-dot chain line. The dashed load line represents the case where n light emitting elements 35 are connected in series, and the two-dot chain line represents the case where n + 1 light emitting elements 35 are connected in series.

As shown in FIG. 3, assuming that the forward voltage of each light emitting element 35 is Vf, when n light emitting elements 35 are connected in series, the forward voltage is Vf1 = Vf × n as shown by the thick solid line. Until, the light emitting element 35 is in a cutoff state. After the forward voltage exceeds Vf1, the light emitting element 35 conducts and a forward current flows. The light emitting element 35 emits light when a forward current flows, and the brightness increases according to the forward current. Since the light emitting element 35 has an operating resistance, as shown in the figure, the larger the forward current, the higher the forward voltage.

In the broken line load line, the current intersecting the LED forward current axis represents the current flowing through the resistor 36 when the light emitting element 35 is in the short-circuited state. The slope of this load line is (−) 1 / R. The operating point OP1 is the point where the load line intersects with the characteristic curve of the light emitting element 35. The voltage at the operating point OP1 is determined according to the capacitor voltage when the power converter 20 is in normal operation.

As the capacitor voltage drops due to the shutdown of the power converter 20, the dashed load line moves in parallel, and the light emitting element 35 turns off when it intersects the voltage axis at Vf1.

As described with reference to FIG. 2B, when the light emitting element 35 of the series circuit having the smaller number of light emitting elements 35 is opened, the characteristic curve of the alternate long and short dash line in FIG. 3 is obtained. In the characteristic curve of the alternate long and short dash line, the light emitting element 35 conducts when Vf2 = Vf × (n + 1) or more, and the brightness increases as the forward current increases.

When the light emitting element 35 of the series circuit having the smaller number of light emitting elements 35 fails and a current flows through the series circuit having the larger number of light emitting elements 35, the operating point moves to OP2. The voltage at the operating point OP2 increases as the number of light emitting elements 35 increases, and the current at the operating point OP2 decreases as the LED forward voltage increases. The operating point moves downward along the characteristic curve of the alternate long and short dash line as the capacitor voltage drops, and the light emitting element 35 is turned off when the forward voltage reaches Vf2.

In this way, in the series circuit of the light emitting elements 35 connected in parallel, by making the number of series of the light emitting elements 35 different from each other, the current path in the other light emitting element 35 for the failure of one light emitting element 35. Can be made redundant. By making the current path redundant, it is possible to avoid turning off the light due to the failure of the light emitting element 35 and to determine that the light emitting element 35 is turned off sufficiently due to a decrease in the capacitor voltage.

FIG. 4 is a schematic diagram for explaining how to use the power conversion device of the present embodiment.
As shown in FIG. 4, the power converter 20 of the power converter is installed on the floor surface E of a substation or the like via an insulating frame 50. The insulating pedestal 50 is made of an insulating material, and each unit converter (denoted as a module in the figure) 30 of the power converter 20 is electrically insulated from the floor surface E.

Each unit converter 30 is arranged so as to be stacked upward from the floor surface E by an insulating columnar member or the like (not shown) on the insulating frame 50. The capacitor voltage monitoring circuit is provided in the vicinity of the outer peripheral surface of the unit converter 30, and the light emitting element 35 is arranged so as to face outward from the outer peripheral surface of the unit converter 30. Therefore, the lighting state or the extinguishing state of the light emitting element 35 can be visually recognized from the outside.

In MMC used for a backbone power system such as DC power transmission, the capacitor voltage of the unit converter 30 may reach several thousand V, and the voltage input / output by the power converter 20 may reach several tens of kV to several hundred kV. Therefore, during normal operation of the power converter 20, when the worker W approaches, the electric power converter 20 may be discharged and the worker W may receive an electric shock. A protective fence F is provided at a distance L1 from the power converter 20 so that the worker W does not approach the power converter 20 during operation. The distance L1 is determined based on the voltage handled by the power converter 20, and may reach several tens of meters in a high-voltage DC power transmission facility or the like.

When the capacitor voltage becomes several thousand V during normal operation, a considerable amount of time has elapsed since the operation was stopped, and after several hundred V have elapsed, the worker W approaches the power converter 20 rather than the protective fence F. can do. The worker W can approach the power converter 20 up to a distance L2 shorter than the distance L1. When the capacitor voltage is several hundred V, for example, L2 can be about 1 m.

When the capacitor voltage drops from several thousand V to several hundred V, the current flowing through the light emitting element 35 also drops to about 1/10 of the normal operation. Therefore, the brightness of the light emitting element 35 also decreases, so that the operator W needs to visually recognize the light emitting element 35 sufficiently close to the power converter 20 in order to confirm the presence or absence of light emission.

In order for the worker W to work safely for maintenance and inspection of the power converter 20, the capacitor voltage needs to be lowered to about 50V. When the capacitor voltage drops from several 100V to about 50V, the current flowing through the light emitting element 35 also drops further, and the worker W needs to be closer to the light emitting element 35 for each unit converter 30.

Therefore, after the voltage is lowered to a voltage that can approach the distance L2 that can be safely approached, the worker W uses a lifter LF or the like as in this example to generate a light emitting element corresponding to the upper unit converter 30. Close enough to 35 and visually check the presence or absence of light emission. When the presence or absence of light emission of the light emitting element 35 is visually confirmed after being sufficiently close to each other and it is confirmed that the light emitting element 35 is turned off, the operator W determines that the capacitor voltage has dropped to about 50 V.

The inspection work or the like may be started from the unit converter 30 in which the extinguishing of the light emitting element 35 is confirmed, or the inspection work or the like may be started after the extinguishing of all the light emitting elements 35 is confirmed.

The effect of the power conversion device 10 of the present embodiment will be described while comparing with the power conversion device of the comparative example.
5 (a) to 5 (d) are block diagrams illustrating a power conversion device of a comparative example.
5 (a) and 5 (b) show a case where a plurality of light emitting elements 35 are connected in series in one series circuit.
As shown in FIG. 5A, the unit converter 130a of the power conversion device of the comparative example includes a capacitor voltage monitoring circuit 134a. The capacitor voltage monitoring circuit 134a is connected to the capacitor 32c of the main circuit 32 in parallel with the resistor 32d.

The capacitor voltage monitoring circuit 134a has a plurality of light emitting elements 35 connected in series. When all the light emitting elements 35 are sound, a current flows according to the capacitor voltage, the resistance value of the resistor 36 and the number of series of the light emitting elements 35, the light emitting element 35 emits light, and when the capacitor voltage drops, the current flows. Is shut off and the light emitting element 35 is turned off.

As shown in FIG. 5B, when one light emitting element 35 in the series circuit of the light emitting element 35 fails and becomes an open state, the capacitor voltage monitoring circuit 134a itself is released and disconnected from the capacitor 32c. Therefore, the light emitting element 35 is turned off regardless of the capacitor voltage. Even though the capacitor 32c maintains a high capacitor voltage, it is dangerous for the operator to perform maintenance and inspection work by judging that the capacitor voltage has dropped below the safe voltage because the light emitting element 35 is turned off. Will be exposed to various conditions.

In FIGS. 5 (c) and 5 (d), the capacitor voltage monitoring circuit 134b includes two series circuits connected in parallel for redundancy. In the two series circuits, the same number of light emitting elements 35 are connected in series. The light emitting elements 35 all have the same characteristics, and output substantially the same forward voltage when a substantially same forward current is applied.

As shown in FIG. 5C, since the light emitting elements 35 of the two series circuits connected in parallel all have substantially the same forward voltage, the current flowing out from one terminal of the capacitor 32c is a resistance. After flowing into the vessel 36, the current is divided into two series circuits. That is, the forward current flowing through one series circuit becomes approximately ½ of the current flowing through the resistor 36 by dividing the current.

As described above, in order to be able to visually recognize the presence or absence of light emission of the light emitting element 35 in the range of several 1000 V to 50 V, it is necessary to make the capacitor voltage reach about 50 V near the visible limit immediately before turning off the light. be. Therefore, in the case of this comparative example, it is necessary to set the forward current during normal operation to be larger by the amount of the distribution to the two series circuits. Therefore, in the case of this comparative example, the power consumption in the capacitor voltage monitoring circuit 134b will increase.

In the present embodiment, the capacitor voltage monitoring circuit 34 includes two series circuits, the two series circuits are connected in parallel, and each series circuit includes a different number of light emitting elements 35 in series. Therefore, the current flowing out of the capacitor 32c flows to the series circuit of the two series circuits, which has the smaller number of light emitting elements 35 in series, without being divided. Therefore, even if the capacitor voltage drops to about 50 V, for example, the lighting state can be maintained.

When the light emitting element 35 of the series circuit having the smaller number in series fails, the lighting state of the light emitting element 35 can be maintained by flowing a current through the series circuit connected in parallel to the light emitting element 35.

In the capacitor voltage monitoring circuit 34, by connecting blocks in series, each block can monitor the capacitor voltage divided according to the number of blocks. Since the two series circuits are connected between the divided lower voltages, the difference in the forward voltage at the time of conduction can be increased when the number of series of the respective light emitting elements 35 is different. Therefore, it is possible to prevent the current from being divided into the two series circuits and the brightness of the light emitting element 35 from being lowered.

By dividing the series circuit of the light emitting element 35 into blocks, for example, one block can be formed on one substrate like a module. When the light emitting element 35 fails or the like, the replacement work can be performed in block units, and quick repair can be performed.

(Second embodiment)
The two series circuits connected in parallel are not limited to the case where one contains two light emitting elements 35 and the other contains three light emitting elements 35.
6 (a) and 6 (b) are schematic circuit diagrams illustrating a part of the power conversion device of the present embodiment.
In the present embodiment, the number of series of the light emitting elements 35 of one series circuit having a small number of series is two, and the number of series of the light emitting elements 35 of the other series circuit having a large number of series is four.
As shown in FIG. 6A, the unit converter 230 includes a capacitor voltage monitoring circuit 234 that is different from the other embodiments described above. The capacitor voltage monitoring circuit 234 includes a plurality of blocks, and these blocks are connected in series. The block contains two series circuits connected in parallel. One series circuit includes two light emitting elements 35, and the other series circuit includes four light emitting elements 35.

When all the light emitting elements 35 are sound, a current flows through the series circuit having the smaller number of series of the light emitting elements 35 as shown by the thick solid line arrow in the figure, and the light emitting element 35 lights up.

As shown in FIG. 6B, when the light emitting element 35 of the series circuit having a small number of light emitting elements 35 among the series circuits of the block 2 is released due to a failure, the current is generated by the light emitting element 35 of the block 2. It flows to the series circuit with the larger number of. Therefore, the current flowing out from the capacitor 32c continues to flow in the capacitor voltage monitoring circuit 234, and the light emitting element 35 can maintain the lighting state.

One series circuit is not limited to two, and the other series circuit is not limited to three (first embodiment) and four (second embodiment). When the characteristics of the light emitting elements 35 included in the two series circuits are the same, the current path can be made redundant by making the number of light emitting elements 35 in series different.

(Third embodiment)
Not limited to the case where the number of series of light emitting elements included in the series circuit connected in parallel is different, the voltage across the series circuit at the time of conduction of the light emitting elements may be different.

7 (a) and 7 (b) are schematic circuit diagrams illustrating a part of the power conversion device of the present embodiment.
As shown in FIG. 7A, the unit converter 330 includes a capacitor voltage monitoring circuit 334 that is different from the other embodiments described above. The capacitor voltage monitoring circuit 334 includes a plurality of blocks, and these blocks are connected in series. The block contains two series circuits connected in parallel. One series circuit includes two light emitting elements 35, and the other series circuit includes two light emitting elements 335. Here, the light emitting element 335 has a higher forward voltage than the light emitting element 35.

It is preferable that the difference in the magnitude of the forward voltage between the light emitting elements 35 and 335 is large. For example, the light emitting devices 35 and 335 are different types of semiconductor light emitting diodes. The different types are, for example, cases where the composition of the semiconductor material constituting the light emitting device is different. For example, the light emitting element 35 having the lower forward voltage is a general red light emitting diode, and the forward voltage is about 2V. The light emitting element 335 having the higher forward voltage is a general white diode, and the forward voltage is about 3.5V to 4V. Not limited to different types of semiconductor light emitting diodes, even if the same type of semiconductor light emitting diode is used, one having a low forward voltage and one having a high forward voltage may be selected in advance and used properly.

As shown in FIG. 7B, when the light emitting element 35 having the lower forward voltage of the series circuit of the block 2 is opened due to a failure, the current is the light emitted by the one having the higher forward voltage of the block 2. It flows to the element 335. Therefore, the current flowing out from the capacitor 32c continues to flow in the capacitor voltage monitoring circuit 334, and the light emitting elements 35 and 335 can maintain the lighting state.

If there is a sufficient difference between the voltage across the one series circuit when the current flows and the voltage across the other series circuit when the current flows, the two currents flowing out from the capacitor 32c will be two. Since the current is not divided into the series circuit, the light emitting elements 35 and 335 can be made to emit light with sufficient brightness.

8 (a) and 8 (b) are schematic circuit diagrams illustrating a part of the power conversion device of the fourth embodiment.
As shown in FIG. 8A, the unit converter 430 includes a capacitor voltage monitoring circuit 434 that is different from the other embodiments described above. The capacitor voltage monitoring circuit 434 includes a plurality of blocks, and these blocks are connected in series. The block contains two series circuits connected in parallel. One series circuit includes two light emitting elements 35, and the other series circuit includes two light emitting elements 35 and an impedance element 435. Here, in the two series circuits, the number of each light emitting element 35 may be the same or may be different. When the number of light emitting elements 35 is different, preferably, the number of light emitting elements 35 of the series circuit including the impedance element 435 is larger than the number of light emitting elements 35 of the series circuit not including the impedance element 435.

The impedance element 435 is a non-linear semiconductor element such as a rectifier (diode), a constant voltage diode (zener diode), or a DIAC. The impedance element 435 is not limited to a non-linear element but may be a linear element as long as the voltage across the series circuit becomes higher than the voltage across the series circuit on the other side when a current flows. .. The impedance element 435 is, for example, a resistor and has a resistance value sufficiently smaller than the resistance value of the resistor 36.

As shown in FIG. 8B, when the light emitting element 35 of the series circuit of the series circuit of the block 2 without the impedance element 435 is released due to a failure, the current is transferred to the impedance element 435 of the block 2. It flows to the series circuit of the one. Therefore, the current flowing out from the capacitor 32c continues to flow in the capacitor voltage monitoring circuit 434, and the light emitting element 35 can maintain the lighting state.

In this embodiment, it is sufficient that the magnitudes of the voltages across the series circuits generated when a current flows through each of the two series circuits are sufficiently different, so an impedance element is inserted in both of the two series circuits. Then, the number of the light emitting elements 35 may be adjusted appropriately.

In each of the above-described embodiments, in the two series circuits, the light emitting element included in one series circuit and the light emitting element included in the other series circuit may have different emission colors. It is possible to identify which series circuit light emitting element is lit by the emission color when the light emitting element of any series circuit is lit. For example, depending on the emission color of the lit light emitting element, it is possible to recognize in advance that the light emitting element of the series circuit with the lower voltage at both ends during conduction is out of order. It is possible to replace the light emitting element that has failed due to the above, and to realize reliable capacitor voltage monitoring.

In each of the above-described embodiments, the elements of a plurality of embodiments may be combined, not limited to the case of each alone. For example, the number of light emitting elements in the two series circuits may be different, and the characteristics of the light emitting elements may be different. Further, an impedance element may be inserted in either one series circuit or both series circuits.

In each of the above-described embodiments, one block includes two series circuits connected in parallel, but three or more series circuits may be connected in parallel. By increasing the number of parallels, the redundancy can be increased and the maintenance-free approach can be achieved. However, the voltage across the series circuit connected in parallel must be sufficiently different when a current flows through the series circuit.

In each of the above embodiments, it is preferable to apply to each unit converter of MMC, but the converter to be applied is not limited to MMC, and of course, it may be a power converter having a main circuit having a capacitor. not.

According to the embodiment described above, it is possible to realize a power conversion device that can reliably monitor the voltage of the capacitor even if the light emitting element fails.

Although some embodiments of the present invention have been described above, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other embodiments, and various omissions, replacements, and changes can be made without departing from the gist of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are also included in the scope of the invention and its equivalents described in the claims. In addition, each of the above-described embodiments can be implemented in combination with each other.

1 AC circuit, 2 transformer, 3 DC circuit, 10 power converter, 20 power converter, 22 arm, 30, 230, 330, 430 unit converter, 32 main circuit, 32a switching element, 32b diode, 32c capacitor, 32d resistor, 34,234,334,434 capacitor voltage monitoring circuit, 35,335 light emitting element, 36 resistor, 435 impedance element

Claims (5)

A power converter comprising a main circuit including a capacitor, a discharge circuit provided to discharge the charge of the capacitor, and a capacitor voltage monitoring circuit connected in parallel to the capacitor.
The capacitor voltage monitoring circuit is
A first series circuit including a plurality of first light emitting elements connected in series,
A second series circuit connected in parallel to the first series circuit and including a plurality of second light emitting elements connected in series, and a second series circuit.
Including
The magnitude of the voltage across the first series circuit when the current emitted by the first light emitting element flows is the magnitude of the voltage across the second series circuit when the current emitted by the second light emitting element flows. Unlike the magnitude of the voltage
The capacitor voltage monitoring circuit has a plurality of blocks including the first series circuit and the second series circuit, respectively.
The plurality of blocks are connected in series and connected in parallel to the capacitor.
A power converter in which the voltage across the capacitor is charged to 1000 V or higher during normal operation of the power converter. The first light emitting element and the second light emitting element have the same current-voltage characteristics, and the first light emitting element and the second light emitting element have the same current-voltage characteristics.
The power conversion device according to claim 1, wherein the number of series of the first light emitting element is different from the number of series of the second light emitting element. The power conversion device according to claim 1 or 2, wherein the first light emitting element has a current-voltage characteristic different from that of the second light emitting element. The first series circuit or at least one of the second series circuit according to any one of claims 1 to 3, which includes the first light emitting element and an impedance element having a current-voltage characteristic different from that of the second light emitting element. Power converter. The power converter according to any one of claims 1 to 4 , wherein the power converter includes a plurality of cascaded main circuits.

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