POWER CONVERSION DEVICE

Unit converters each comprises a capacitor, a switching element having a flat surface on one side, a P-pole connection conductor where a second terminal hole at one end for fixing an electrode corresponding to a P-pole of the switching element and a first terminal hole at the other end for fixing a terminal of the capacitor are formed, and an N-pole connection conductor where a second terminal hole at one end for fixing an electrode corresponding to a N-pole of the switching element and a first terminal hole at the other end for fixing a terminal of the capacitor are formed. The unit-converters each including the connection conductors arranged to overlap in the thickness direction with their insulation maintained make the cooling surfaces of the switching elements be opposed to each other with a cooling device therebetween.

TECHNICAL FIELD

The present application relates to a power conversion device.

BACKGROUND ART

As a power conversion device used for DC power transmission or the like, a modular multilevel converter (hereinafter referred to as MMC) is known. MMC is a power conversion device including a plurality of unit-converters, each of which includes a pair of switching elements, such as an insulated gate bipolar transistor (IGBT) or a metal oxide semiconductor field effect transistor (MOSFET), and a DC capacitor.

In addition, a multi-level power conversion device is known for use in a distributed power supply and a motor drive. Even in the multi-level power conversion device, there is a case where the multi-level power conversion device is composed of a plurality of unit-converters, and a power conversion device has been proposed, aiming to equalize duties of a plurality of DC capacitors (for example, refer to Patent Document 1).

CITATION LIST

Patent Document

SUMMARY OF INVENTION

Problems to be Solved by Invention

On the other hand, in a power conversion device used for DC power transmission or the like, a high voltage and a large current are often handled, and a switching element, a DC capacitor, and wiring are increased in size, and a structure supporting these components is also increased in size. Therefore, in the power conversion device used for DC power transmission or the like, size reduction thereof is an important issue.

The present application discloses a technique for solving the above-described problem, and an object of the present application is to obtain a compact power conversion device used for DC power transmission or the like.

Means for Solving Problems

A power conversion device disclosed in the present application includes a pair of unit-converters, and a cooling device. Each of the pair of unit-converters includes a capacitor, a switching element in which a cooling surface and a connecting surface opposite to the cooling surface are provided and two electrodes through which main power flows are formed in the connecting surface and by which a leg for power conversion is formed by forming a pair, a first conductive plate in which a second terminal hole is formed at one end for fixing an electrode of the switching elements forming the pair, the electrode corresponding to a first pole in the leg, and a first terminal hole is formed at the other end for fixing an electrode of the capacitor corresponding to the first pole, and a second conductive plate in which a second terminal hole is formed at one end for fixing an electrode of the switching elements forming the pair, the electrode corresponding to a second pole in the leg, and a first terminal hole is formed at the other end for fixing an electrode of the capacitor corresponding to the second pole, the second conductive plate being arranged to overlap with the first conductive plate in a thickness direction, maintaining insulation from the first conductive plate. In the pair of unit-converters, the cooling surfaces of the switching elements forming the pair in one unit-converter is opposed to the cooling surfaces of the switching elements forming the pair in the other unit-converter with the cooling device interposed therebetween.

Advantageous Effect of Invention

According to the power conversion device disclosed in the present application, since the power conversion device can be configured by sharing the cooling device of the switching element, the number of components is reduced, and a compact power conversion device used for DC power transmission or the like can be obtained.

MODE FOR CARRYING OUT INVENTION

FIG.1AtoFIG.8Care for describing a configuration and an operation of the power conversion device according to Embodiment 1, andFIG.1Ais a perspective view showing the configuration of the power conversion device when viewed obliquely from above,FIG.1Bis a circuit diagram showing a configuration of an unit-converter, andFIG.2is a perspective view showing the unit-converter when viewed obliquely from above.FIG.3Ais a perspective view showing a structure of a P-pole connection conductor inFIG.2that is turned upside down, andFIG.3Bis a perspective view showing a structure of an N-pole connection conductor inFIG.2that is turned upside down.

FIG.4is a circuit diagram showing a configuration of legs in which three switching elements are connected in parallel,FIG.5Ais a schematic diagram of a P-pole connection conductor portion for describing wiring lengths for switching elements connected in parallel in a power conversion device according to a comparative example, andFIG.5Bis a schematic diagram of the P-pole connection conductor portion for describing wiring lengths for switching elements connected in parallel in the power conversion device according to Embodiment 1. Further,FIG.6is a perspective view corresponding toFIG.3Aof the P-pole connection conductor for describing positions of terminals for electrical connection to a capacitor.

On the other hand,FIG.7Ais a perspective view of the power conversion device corresponding toFIG.1Afor describing electrical connection between the unit-converters, andFIG.7Bis a plan view when it is viewed from above. In addition,FIG.8AtoFIG.8Care plan views of connection objects for electrically connecting the unit-converters to each other or wiring members having different shapes.

The power conversion device disclosed in the present application is used for DC power transmission and is assumed to be an MMC system to be described later in detail in Embodiment 3. As shown inFIG.1A, the power conversion device9is configured such that a cooling device4is interposed between the two unit-converters3(details will be described later). The unit-converter3is constituted by a capacitor1as a power storage element and two or more switching elements2. Here, prior to the description of a characteristic configuration of the present application, a basic configuration as a premise will be described.

More specifically, as shown inFIG.1B, the unit-converter3is constituted by a half-bridge circuit by a leg20in which two or more switching elements2are connected in series and a capacitor1is connected in parallel to the leg20. Here, the middle of the leg20in which two or more switching elements2are connected in series is an AC-pole20p3. One end of the leg20serves as a P-pole20p1, and the other end opposite to the P-pole20p1serves as an N-pole20p2. A drain terminal or a collector terminal of the switching element2is connected to the P-pole20p1. A source terminal or an emitter terminal of the switching element2is connected to the N-pole20p2.

As the capacitor1, various power storage elements such as a film capacitor, an electrolytic capacitor, and an electric double-layer capacitor can be applied. Various semiconductor elements such as an insulated gate bipolar transistor (IGBT) and a metal oxide semiconductor field effect transistor (MOSFET) can be applied to the switching element2. However, the present application is not directed to the press-packed semiconductor element disclosed in Patent Document 1 in which electrodes through which electric power flows are separately formed on both surfaces, but is directed to the switching element2in which two electrodes through which electric power flows are formed by dividing a region in one surface in a package to be described later. A form in which the electrode, for example, can be mechanically fixed and electrically connected by a bolt or the like, such as a screw hole over the surface of an insulating package, is assumed.

Here, in order to actually form the unit-converter3described with reference toFIG.1B, in addition to the element constituting the half-bridge circuit, the P-pole connection conductor5serving as P-pole wiring, the N-pole connection conductor6serving as N-pole wiring, an AC-pole connection conductor7serving as AC-pole wiring, and a cooling device4for cooling the switching element2are required.

When assembling of the element constituting the half-bridge circuit is performed together with metal plates used for the conductors such as the P-pole connection conductor5, the N-pole connection conductor6, and the AC-pole connection conductor7, and a thick plate-shaped cooling device4, the unit-converter3as shown inFIG.2can be structured. InFIG.2, three legs20are connected in parallel to each other (refer toFIG.6). InFIG.1B, a 2-in-1 package in which two switching elements2are integrated is assumed, and a package forming the leg20is drawn as a single switching element2, but this is not a limitation. For example, two 1-in-1 packages each including the single switching element2may be arranged in the series connection direction to constitute the leg20, and then three legs20may be arranged in the parallel connection direction.

Note that, as the cooling device4, an example of a structure assuming a water-cooled fin is shown, and the cooling device4is provided with a water-cooled valve port4v, which is an inlet and an outlet of refrigerant, and is supported by a structural component4s. The structural component4sis connected and fixed to a housing (not shown) in which the unit-converter3is built in. Although not described in detail in the present application, if necessary, the capacitor1and various conductors are also fixed to the housing by some structural parts such as bolts and metal fittings.

The P-pole connection conductor5and the N-pole connection conductor6are arranged to overlap each other in the thickness direction. However, a certain gap or an insulating member is provided between the P-pole connection conductor5and the N-pole connection conductor6, and they are electrically separated from each other. In addition, the capacitor1includes a P-pole terminal1p1and an N-pole terminal1p2. The P-pole terminal1p1and the N-pole terminal1p2of the capacitor1are provided on the same surface of the capacitor1. A first terminal hole5t1formed at one end of the P-pole connection conductor5shown inFIG.3Aand a first terminal hole6t1formed at one end of the N-pole connection conductor6shown inFIG.3Bare fixed to the surface by a mechanism such as a bolt. In order to avoid interference between the terminal1p1and the terminal1p2, the P-pole connection conductor5and the N-pole connection conductor6are formed with through holes5hand6hin alignment with the positions of the first terminal hole6t1of the N-pole connection conductor6and the first terminal hole5t1of the P-pole connection conductor5, respectively.

Second terminal holes5t2(hidden and invisible inFIG.2) formed at an end portion of the P-pole connection conductor5on the opposite side to the first terminal hole5t1in the plane are connected to the P-poles20p1of the legs20by a mechanism such as a bolt. Second terminal holes6t2formed at an end portion of the N-pole connection conductor6on the opposite side to the first terminal hole611in the plane are connected to the N-poles20p2of the legs20by a mechanism such as a bolt.

Note that, inFIG.2, three bolts that are not denoted by reference numerals at the connection points between the N-pole connection conductor6and the legs20correspond to the respective three legs20. Similarly, there are three bolts at the connection points between the P-pole connection conductor5and the P-poles20p1of the legs20, but these bolts are hidden by the N-pole connection conductor6and cannot be seen. The P-pole connection conductor5is bent by an angle of 90 degrees at the middle portion (bent portion5b) between the first terminal hole5t1and the second terminal holes5t2. The N-pole connection conductor6is also bent by an angle of 90 degrees at the middle portion (bent portion6b) between the first terminal hole6t1and the second terminal holes6t2. The reason to have the bent portions will be described later.

Further, the P-pole connection conductor5is provided with third terminal holes5t3at positions different from the first terminal hole5t1and the second terminal holes5t2(details will be described later), and the third terminal holes are used for connection between the unit-converter3and the outside. Similarly, the N-pole connection conductor6is provided with third terminal holes6t3at positions different from the first terminal hole6t1and the second terminal holes6t2, and the third terminal holes are used for connection between the unit-converter3and the outside.

First terminal holes7t1provided at one end of the AC-pole connection conductor7are connected to the AC-poles20p3of the legs20by a mechanism such as a bolt, and the three bolts at connection points between the AC-pole connection conductor7and the legs20correspond to the respective three legs20. A second contact hole7t2of the AC-pole connection conductor7, which is located at an end portion opposite to the first terminal holes7t1in the plane, is connected to the outside of the unit-converter3and used as an input/output terminal.

The switching element2, including the 2-in-1 package, has a plate shape, and electrodes to be connected to various conductors (the P-pole connection conductor5, the N-pole connection conductor6, and the AC-pole connection conductor7) are formed in separate regions on one of the two main surfaces. Although it is described that the P-pole connection conductor5and the N-pole connection conductor6are bent by 90 degrees in the middle, it is a simple example that the P-pole connection conductor5and the N-pole connection conductor6are bent by an angle of 90 degrees. The angle is not necessarily 90 degrees and may be another angle as in a variation example to be described later. As an extreme example, in a case where the thickness of the capacitor1is equal to or less than the thickness of the switching element2, the P-pole connection conductor5and the N-pole connection conductor6do not need to be bent in the middle for the reason to be described later.

The surface of the switching element2opposite to the surface on which various electrodes are provided is flat and is used as a cooling surface without electrical connection. When the switching element2is energized, various losses such as a switching loss and a conduction loss occur, which causes a temperature rise of the switching element2. The temperature rise of the switching element2causes a decrease in the performance of the switching element2or a failure of the switching element2, and thus needs to be suppressed.

Therefore, in order to suppress the temperature rise of the switching element2, the unit-converter3is provided with the cooling device4. The cooling device4needs to have a cooling capability to deal with the amount of heat generated owing to the loss that occur in the switching element2. As an index of the cooling capability, for example, thermal resistance (K/W) is used, which represents a temperature difference (K) necessary for heat transfer per 1 watt (W), and as the thermal resistance is smaller, heat transfer can be performed with a smaller temperature difference, that is, the reaching temperature of a cooling target can be suppressed to be low.

On the premise of the above-described basic configuration, a characteristic part of the power conversion device9of the present application configured such that two unit-converters3share one cooling device4will be described. In the power conversion device9using the two unit-converters3, the two unit-converters3are arranged so as to be opposed to each other as shown inFIG.1A. At this time, the cooling surface of the switching element2in each of the unit-converters3is arranged such that they are opposed to each other. By disposing the two unit-converters3so as to be opposed to each other in this manner, the cooling device4, which is originally required to be provided for the respective unit-converters3, can be unified (shared).

Here, for the unification of the cooling device4provided for each of the unit-converters3, the cooling surfaces of the switching elements2or of the packages in the unit-converters3need to be placed close to each other. Therefore, among the components constituting the unit-converter3, a component exceeding the height of the switching element2or the package needs to be disposed in a direction different from that of the switching element2.

For example, in the unit-converter3shown inFIG.2, the capacitor1has a higher mounting height than the switching element2. Therefore, the P-pole connection conductor5and the N-pole connection conductor6are bent by 90 degrees at the middle portions (bent portion5band bent portion6b) between the region connected to the switching element2and the region connected to the capacitor1. The mounting direction of the switching element2(horizontal direction in the figure) is different from the mounting direction of the capacitor1(vertical direction in the figure) by 90 degrees. As a result, with respect to the two unit-converters3, the cooling surfaces of the respective switching elements2can be brought close to and opposed to each other.

As described above, the bent portion5band the bent portion6bare required when there are a component exceeding the height of the switching element2or the package among the components constituting the unit-converter3. Therefore, when the capacitor1does not exceed the height of the switching element2, it is not necessary to bend the P-pole connection conductor5and the N-pole connection conductor6in the middle. Accordingly, the P-pole connection conductor5and the N-pole connection conductor6may be flat plates that are not bent. In addition, the switching element2may be connected to one side in the surfaces of the P-pole connection conductor5and the N-pole connection conductor6, and the capacitor1may be connected to the other side in the surfaces opposite to the one side. In such an arrangement, the P-pole connection conductor5and the N-pole connection conductor6do not need to be bent even when the capacitor1is larger in mounting height than the switching element2.

On the other hand, the cooling device4shared by the two unit-converters3is required to have the cooling capability corresponding to the amount of heat generated by the switching elements2of the two unit-converters3. Compared with a case where an independent cooling device4is provided for each of the unit-converters3, in the cooling device4unified in the two unit-converters3, it is necessary to cool down the temperature rise caused by the loss that is twice as much in a simple calculation. When the cooling device4is an air-cooled fin, the thermal resistance thereof may be reduced by increasing the amount of air or changing the shape of the fin.

When the cooling device4is a water-cooled fin, the thermal resistance thereof may be reduced by improving the thermal conductivity by changing the composition of the cooling water in addition to the increase in the flow rate, the change in the fin shape, or the like. An example of a method for improving the thermal conductivity of the cooling water is to utilize the fact that the thermal conductivity typically depends on the temperature. By using cooling water having a composition in which the thermal conductivity increases as the cooling water temperature increases, when the amount of heat generation increases and the cooling water temperature increases, it is possible to compensate for the decrease in the temperature difference to maintain the cooling capability.

The cooling device4used in the unit-converter3according to Embodiment 1 is illustrated, assuming the water-cooled fin. In the case of improving the cooling capability of the cooling device4, it is not always necessary to increase the size of the outer shape of the cooling device4itself as long as the cooling capability is improved by the conditions of the refrigerant such as the cooling air and the cooling liquid. Then, the outer shape of the cooling device4unified in the two unit-converters3is not always necessary to be changed from that of the one independent cooling device provided for each unit-converter3.

Therefore, in the power conversion device9of the present application, the cooling device4having the same outer shape as the cooling device having the specifications provided for each of the unit-converters3as originally intended is used, and one cooling device4is installed for the two unit-converters3. Accordingly, the number of cooling devices installed on the power conversion device9can be reduced by half. Note that, in a case where the press-packed semiconductor element described in Patent Document 1 is used, it is necessary to install cooling devices on both sides of the semiconductor element, and even if one cooling device is shared between the unit-converters, it is necessary to further install cooling devices in accordance with the number of the elements and use at least three cooling devices. In other words, more cooling devices than the number of unit-converters are required.

As a material of the cooling device, typically, aluminum (Al), copper (Cu), or an alloy mainly containing these is often used. When copper is used, the cooling capability is excellent, but the weight tends to be high, and when aluminum is used, the weight is lower than that of copper. In order to incorporate such a cooling device4into the power conversion device9, the structural component4sfor fixing is required. The structural component4sis, for example, a metal framework (frame), and is connected and fixed to a housing (not shown) in which the power conversion device9is built in.

As the housing, for example, a rectangular parallelepiped box made of metal or resin is used. The thickness and strength of the structural component4sneed to be adjusted in accordance with weights of objects to be supported, and the number of structural components needs to be increased in accordance with the number of the objects to be supported. Therefore, halving the weight and the number of the cooling devices4not only means the reduction of the number of the cooling devices4, but also obtains the effect of reducing the number of structural components4s.

Opening

In the above configuration, the wiring lengths in a case where a plurality of switching elements2are connected in parallel will be described. The switching element2is plate-shaped, in which two electrodes for passing a current as a half bridge are formed in separate regions on one side. For example, a semiconductor chip is sealed in a resin case having a rectangular parallelepiped shape, and electrodes for connection are provided on it's upper surface. The number of switching elements2connected in parallel and used in the power conversion device9may be changed in accordance with the rated current of the power conversion device9.

When a desired current can be reached by using one switching element2for the rated current of the power conversion device9, one or more switching elements2are used. For the rated current of the power conversion device9, for example, when the desired current can be eventually reached by using three switching elements2, three or more switching elements2are used.

A problem related to the wiring lengths in the case where the switching elements2are connected in parallel as described above will be described. The magnitude of the current flowing through the switching elements2changes depending on the case of the current flow in the switching elements2and the ease of the current flow in the path through which the current flows. In the plurality of switching elements2connected in parallel, the magnitude of the current flowing through each of the switching elements2varies depending on the variation in the ease of the current flow in each switching element2and the variation in the ease of the current flow in each current path.

For example, as shown inFIG.4, a case where three switching elements2are connected in parallel will be examined. In the case above, when a current easily flows in a case where an impedance R2of a current path P2of the switching element2located at the center is smaller than impedances R1and R3of the other current paths P1and P3, the current concentrates on the switching element2located at the center. For example, the situation above corresponds to a case where wiring is performed for each switching element2at the current paths P1to P3divided into three at the branch point Ps for the respective three switching elements2arranged side by side. In this case, the length of the wiring required for the current path P2of the central switching element2is physically shorter than the length of the wiring required for the current paths P1and P3of the switching elements2on both sides. As a result, the impedances R1and R3are larger than the impedance R2.

On the other hand, in the case where two switching elements2are arranged side by side, the current path is divided into two paths, and the two current paths are wired to the respective two switching elements2, the wiring of the two current paths tends to be symmetrical and equal in length. Therefore, when three or more switching elements2are connected in parallel, it is more difficult to equalize the currents flowing to the switching elements2than when two switching elements2are connected in parallel.

If the switching element has a shape for a module type for high current applications, a metal plate may be used for the wiring and bolted to the switching element. When three or more switching elements are connected in parallel using metal plates, the wiring length in the current path of each switching element depends on the physical arrangement.

For example, a description will be made using a comparative example shown inFIG.5A. In the comparative example, three switching elements2arranged side by side are connected by terminal holes5t2C at the lower end of a metal conductor5C corresponding to the P-pole connection conductor5of the present application, and are electrically connected to the outside through a terminal hole5t1C (corresponding to the first terminal hole5t1of the present application and the branch point Ps inFIG.4) at the upper end central portion. Note that the corresponding portions of the comparative example to those in the embodiment are distinguished by adding “C” to the end of the reference numerals. In this case, the wiring length varies depending on the positional relationship between the arrangement of the switching elements2and the terminal hole5t1C, and a wiring length L2C becomes short (mismatch) relative to wiring lengths L1C and L3C, and the current flowing to each switching element2cannot be equalized.

In contrast, in the power conversion device9of the present application, as shown inFIG.5B, an opening (slit5s) is provided in the metal plate (P-pole connection conductor5) to be connected to three or more switching elements2. Although not specified, the slit5sserves as an insulating portion of air or the like, and a current path from the first terminal hole5t1to each switching element2(second terminal holes5t2) is formed so as to avoid the slit5s. As a result, a wiring length L1(=Lm+Ls1) to the switching element2on the outer side is equal to a wiring length L2(=Lm+Ls2) to the switching element2in the center. This also applies to the N-pole connection conductor6provided with the slit6s.

Therefore, among the variations in the currents flowing through the switching elements2, the variation caused by the difference in the wiring length is to be suppressed. The method of providing an opening such as the slit5sin the metal plate can be performed by a typical method such as press working or laser-beam machining. In the metal plates (the P-pole connection conductor5and the N-pole connection conductor6) used for connecting the switching elements2connected in parallel in this way, current equalization is achieved by simple processing such as providing the opening (slit5s, slit6s).

The current equalization of each switching element2provides an effect of uniformly improving a current utilization factor of each switching element2. Here, the current utilization factor is a ratio when the rated current value of the switching element2is used as a denominator and the maximum flowing current value is used as a numerator. When the currents of the switching elements2are not uniform, the current utilization factor of the switching element2through which the current flows most easily is restricted so as not to exceed 1. As a result, the current utilization factor of the switching element2through which the current tends to flow less becomes lower than 1, which means that the switching element2is not fully utilized. In contrast, the equalization achieved by providing the opening allows for each switching element2to be fully utilized.

End Shape

As shown inFIG.2, the AC-pole connection conductor7used in the power conversion device9of the present application has a shape in which two of the four corners of a rectangle are diagonally cut out. There are no conductors in the portions of the two corners cut from the rectangular conductor, so it is no longer a current path. The two corners cut out from the rectangular conductor are located closer to the two switching elements2that are located on the outer side among the three switching elements2than to the switching element2that are arranged in the center. Therefore, the cutting of the two corner portions from the rectangular conductor is likely to affect the ease of the current flow to the two switching elements2arranged on the outer side, and is unlikely to affect the ease of the current flow to the switching elements2arranged on the center. Therefore, by adjusting the shape in the cut portion of the corner with respect to the rectangular shape, that is, by narrowing the width of the end portion where the number of terminal holes formed is smaller, it is possible to adjust the ease of the current flow to the switching elements2on the outer side.

On the other hand, the opening (slits5s,6s) provided inside the rectangular shape make it difficult for the current of the switching element2at the center to flow. As described above, by combining the adjustment of the outer peripheral shape of the conductor used for the electrical connection and the adjustment of the shape of the opening provided inside, the ease of the current flow to each switching element2is adjusted. As a result, an effect of equalizing the current utilization factor of each switching element2is obtained.

Here, although the AC-pole connection conductor7is taken as an example, this is not limited to the AC-pole connection conductor7. Although it has been described that the ease of the current flow to the switching element2is adjusted, it can also be used to adjust the ease of current flow to the capacitor1. Although the shape in which the corner of the conductor is diagonally cut out is shown, the shape to be cut out is not limited to a triangle, and the same effect can be obtained by cutting it out in a square shape or other shape.

<Current Path to Capacitor>

In addition to the wiring lengths of the current paths between the branch point Ps and the switching elements as described above, as the current paths to the capacitors each of the positions of third ends in the P-pole connection conductor and the N-pole connection conductor will be described. In the P-pole connection conductor5, the first terminal hole5t1connected to the electrode of the capacitor1, the second terminal holes5t2connected to the switching elements2, and the third terminal holes5t3connected to the outside are formed. A steep voltage change and a steep current change generated by the switching operation of the switching element2are absorbed by the smoothing action of the capacitor1, which is a power storage element. In order for the smoothing action to be smoothly performed, it is necessary to lower the impedance of the current paths between the switching elements2and the capacitor1.

However, in the third terminal holes5t3of the P-pole connection conductor5formed of the metal plate, since electrical connection is formed to a mounting hole by bolting, a contact resistance is generated. Therefore, it is desirable that positions of the third terminal holes5t3of the P-pole connection conductor5avoid paths connecting the first terminal hole5t1to the second terminal holes5t2. In contrast, if the third terminal holes5t3of the P-pole connection conductor5are provided on the paths connecting the first terminal hole5t1to the second terminal holes5t2, the steep voltage change and the steep current change generated by the switching operation are easily transferred to the outside through the third terminal holes5t3. Note that, when the impedance formed by connection to the outside is sufficiently high, they are not transferred to the outside.

Therefore, in the P-pole connection conductor5of the power conversion device of the present application, the third terminal holes5t3are arranged so as to avoid the paths connecting the first terminal hole5t1to the second terminal holes5t2, as shown inFIG.6. Paths indicated by arrows P1and P2inFIG.6are those connecting the first terminal hole5t1to the second terminal holes5t2. The third terminal holes6t3of the N-pole connection conductor6are also arranged so as to avoid the paths connecting the first terminal hole6t1to the second terminal holes612, as in the case of the P-pole connection conductor5. By thus setting the positions of the third terminal holes5t3and6t3, it is possible to stabilize the switching operation of the power conversion device9.

In addition to the current paths in the P-pole connection conductor and the N-pole connection conductor in the unit-converter described above, an electrical connection method for forming a current path between the unit-converters will be described. In the P-pole connection conductor5, two third terminal holes5t3, which are arranged in consideration of the positional relationship between the first terminal hole5t1and the second terminal holes5t2described above and are used for connecting the unit-converter3to the outside, are provided on the side of a portion51(FIG.3A) where the first terminal hole5t1is formed. Similarly, in the N-pole connection conductor6, two third terminal holes6t3, which are arranged in consideration of the positional relationship between the first terminal hole6t1and the second terminal holes612described above and are used for connecting the unit-converter3to the outside, are provided on the side of a portion61(FIG.3B) where the first terminal hole6t1is formed.

The two third terminal holes5t3of the P-pole connection conductor5extend toward a side of a portion52(downward direction inFIG.3A), and are arranged at positions symmetrical with respect to the center of the P-pole connection conductor5(in the left-right direction in the same figure (direction in which the bent portion5bextends)). Similarly, the two third terminal holes6t3of the N-pole connection conductor6also extend toward a side of a portion62(downward direction inFIG.3B), and are arranged at positions symmetrical with respect to the center of the N-pole connection conductor6in the left-right direction (in the left-right direction in the same figure (direction in which the bent portion6bextends)).

When incorporated into the unit-converter3, as shown inFIG.7AandFIG.7B, the third terminal holes5t3of the P-pole connection conductor5and the third terminal holes6t3of the N-pole connection conductor6are placed into two positions apart in the unit-converter3and arranged adjacent to each other in the left-right direction at each position. At this time, as described above, since the third terminal holes5t3are disposed at positions symmetrical (equidistant) with respect to the center, when the switching elements2of the two unit-converters3are disposed so as to be opposed to each other, two tip portions of the third terminal holes5t3in the respective P-pole connection conductors5come close to each other in the extending direction. Similarly, two tip portions of the third terminal holes6t3of the respective N-pole connection conductors6come close to each other in the extending direction.

Further, the third terminal holes5t3of the P-pole connection conductor5and the third terminal holes6t3of the N-pole connection conductor6in the unit-converter3are provided at positions adjacent to each other in the left-right direction as described above. Therefore, the third terminal holes5t3of the P-pole connection conductors5facing each other is located close to each other and the third terminal holes6t3of the N-pole connection conductors6facing each other is located close to each other in the two unit-converters3incorporated as the power conversion device9. Therefore, the connection between the two unit-converters3can be made with short wiring.

The connection between the third terminal holes5t3of the P-pole connection conductor5to each other and the third terminal holes6t3of the N-pole connection conductor6to each other in the two unit-converters3can be achieved, for example, with a wiring member10in a linear shape having terminal holes10tformed at both ends, as shown inFIG.8A. The connection between the third terminal holes5t3of the P-pole connection conductor5of one unit-converter3and the third terminal holes6t3of the N-pole connection conductors6of the other unit-converter3can be achieved with an L-shaped wiring member10as shown inFIG.8Bor an S-shaped wiring member10as shown inFIG.8C. As described above, the two unit-converters3are connected using the wiring member10for the connection, and can be connected in series or in parallel by selecting the shape of the wiring member10. Only by selecting the shape of the wiring member10for the connection, a serial connection application and a parallel connection application can be easily selected.

Further, in the power conversion device9of the present application, the two unit-converters3constituting the power conversion device9have the same shape in the P-pole connection conductors5and the same shape in the N-pole connection conductors6for component sharing. That is, the two unit-converters3constituting the power conversion device9each use the P-pole connection conductor5having the same shape (FIG.3A) and the N-pole connection conductor6having the same shape (FIG.3B).

As a result, the P-pole connection conductor5and the N-pole connection conductor6each in the two unit-converters3constituting the power conversion device9can be made common. Therefore, it is possible to obtain effects such as a reduction in the number of component manufacturing lines by the component sharing and simplification of the manufacturing of the power conversion device9.

Variation

In the example described above, the capacitor has a cubic shape, and the P-pole connection conductor and the N-pole connection conductor are provided with the bent portions of 90 degrees. In the present variation, a case where a capacitor having a triangular prism shape is used will be described.FIG.9is a schematic side view for describing a configuration of a power conversion device according to the present variation. The configuration other than the shapes of the P-pole connection conductor and the N-pole connection conductor in accordance with the shape of the capacitor is basically the same as that of the above-described embodiment, and the description of the same portions will be omitted.

In the power conversion device9according to the present variation, the capacitor1having a triangular prismatic shape is used and is mounted such that the axes of the column are set parallel to a grounding surface (for example, the surface on which the first terminal hole5t1is formed) and a certain side surface faces the grounding surface, instead of the end surfaces of the column such as the top surface and the bottom surface. In this case, as shown inFIG.9, the P-pole connection conductor5and the N-pole connection conductor6are formed with bent portions5band6b, which are bent in an angle range of more than 0 degree and less than 90 degrees in accordance with the angle of a corner of the triangular prism. Thus, the capacitor1can be placed on the front side relative to the switching element2in each of the unit-converters3(for example, on the portion62side relative to an extension line of the portion52), and the switching elements2can be opposed to each other to share the cooling device4.

In this case, portions for the third terminal holes5t3in the P-pole connection conductor5and the third terminal holes613in the N-pole connection conductor6in the two unit-converters3are bent to be perpendicular to the portions52and62in the middle so as not to extend in parallel to the portions51and61, for example. In this way, two of the third terminal holes5t3of the respective P-pole connection conductors5in the two unit-converters3come close to each other in the extending direction. Similarly, two of the third terminal holes6t3of the respective N-pole connection conductors6come close to each other in the extending direction. As a result, the unit-converters3can be easily electrically connected to each other by the wiring member10described inFIG.8AtoFIG.8C.

Alternatively, the portions for the third terminal holes5t3in the P-pole connection conductor5and the third terminal holes6t3in the N-pole connection conductor6of the two unit-converters3are left extending in parallel to the portions51and61. Even in this case, for example, by bending the middle portion of the wiring member10described inFIG.8AtoFIG.8Cin the thickness-wise direction, electrical connection between the unit-converters3can be easily achieved.

In Embodiment 1, the case where one capacitor is provided for each unit-converter has been described. In Embodiment 2, a case where a plurality of capacitors are provided for each unit-converter will be described.FIG.10andFIG.11are for describing a configuration and an operation of a power conversion device and the unit-converter according to Embodiment 2.FIG.10is a perspective view corresponding toFIG.2for describing a configuration of the unit-converter of the power conversion device, andFIG.11is a perspective view corresponding toFIG.1Afor describing the configuration of the power conversion device. The configuration other than the shapes of the P-pole connection conductor and the N-pole connection conductor in accordance with an arrangement of the capacitors are basically the same as those of the above-described embodiment, and the description of the same portions will be omitted, andFIG.1B,FIG.4, andFIG.9, etc., used in Embodiment 1 will be referred to.

In the power conversion device9according to Embodiment 2, as shown inFIG.10, two capacitors1having the same specifications (when two capacitors are distinguished from each other, one capacitor1is referred to as a capacitor1A, and the other capacitor1is referred to as a capacitor1B) are provided in the unit-converter3. The two capacitors1are arranged symmetrically with respect to a plane including a center line X3in the left-right direction of the unit-converter3. Then, a center position PX1(a distance L2A coincides with a distance L2B) between the center position between a P-pole terminal1p1A and a N-pole terminal1p2A in the capacitor1A (equally divided by a distance LIA) and the center position between a P-pole terminal1p1B and a N-pole terminal1p2B in the capacitor1B (equally divided by a distance L1B) is located on the center line X3.

Note that, in the unit-converter3including a single capacitor1, the center position PX1between the P-pole terminal1p1and the N-pole terminal1p2is on the center line X3because the capacitor1is placed on the center line X3. Therefore, current paths between a capacitor1and the switching elements2are equivalent between the unit-converter3including the two capacitors1A and1B and the unit-converter3including the single capacitor1. Note that, when the unit-converters3each including the two capacitors1A and1B and the shared cooling device4are combined, a power conversion device9as shown inFIG.11is obtained.

In Embodiment 3, for a power conversion device in which one cooling device is shared and two unit-converters are combined, which is described in each of the above-described embodiments, an example provided with a bypass switch serving as a device protection means and an MMC combined with those described above will be described.FIG.12toFIG.15are diagrams for describing configurations and an operation of a power conversion device and an unit-converter according to Embodiment 3,FIG.12is a schematic circuit diagram for describing a configuration of a power conversion device of an MMC system, andFIG.13is a schematic circuit diagram of a power conversion device including a bypass mechanism suitable for the MMC system.

FIG.14is a perspective view of the power conversion device including the bypass mechanism, corresponding toFIG.1A, andFIG.15is a side view of the power conversion device including the bypass mechanism. Note that the configuration except that the bypass mechanism is provided is basically the same as in Embodiment 1 and Embodiment 2 described above, and the description of the same portions will be omitted, andFIG.2toFIG.11used in Embodiment 1 or Embodiment 2 will be referred to.

As shown inFIG.13, the power conversion device9according to Embodiment 3 is configured such that the AC-poles20p3of two unit-converters3are connected to each other via a bypass switch14. The N-pole connection conductor6of one unit-converter3and the P-pole connection conductor5of the other unit-converter3are connected with the wiring member10described in Embodiment 1. The unit-converters3of the power conversion device9having the bypass switch14is used as a cell, and a P-pole connection conductor5of a unit-converter3on the P-pole side of a certain power conversion device is connected to an N-pole connection conductor6of a unit-converter3on the N-pole side of an adjacent power conversion device9. Then, as shown inFIG.12, an arm30in which cells of a plurality of the power conversion devices9are connected in series is formed, and a power conversion device9M of the MMC system is formed.

The power conversion device9M of the MMC system includes a plurality of the arms30, and the arms30are divided into first arms30connected to a positive voltage terminal9Mt2side and second arms30connected to a negative voltage terminal9Mt3side, and places where the first arms30and the second arms30are connected to each other are AC terminals9Mt1.

At this time, when a specific power conversion device9is brought into a disabled condition of an energization operation due to occurrence of an anomaly or the like, the power conversion device9brought into the disabled condition of the energization operation is bypassed in order to continue the operation in the entire power conversion device9M of the MMC system. An example of the bypass mechanism is the bypass switch14. As another example, an element that is to be short-circuited by application of a voltage equal to or higher than a predetermined voltage may be used. Or in a case where a short-circuit accident occurs outside a power conversion device9, the power conversion device9concerned is bypassed in order to avoid a failure caused by an overcurrent flowing through the power conversion device9. An example of the bypass mechanism in this case is a commutation diode or a bypass switch.

Then, in the power conversion device9according to the present embodiment, by bypassing between the AC-poles20p3of the two respective unit-converters3, it is possible to bypass their own unit-converters3when the power conversion device9is brought into a loaded condition of the energization operation. In addition, for example, when a rectangular parallelepiped bypass switch14is used as the bypass mechanism, as shown inFIG.14andFIG.15, the bypass switch14can be fixed in a form interposed between the AC-pole connection conductors7of the two respective unit-converters3.

The bypass mechanism is fixed by a mechanism such as a bolt together with an external connection wire15connected to the first terminal hole7t1of the AC-pole connection conductor7. That is, since the unit-converters3are configured such that the capacitors1do not protrude in front of the switching element2, the single bypass switch14can be shared by the two unit-converters3as in the cooling device4.

As a result, the number of bypass mechanisms required in the entire power conversion device9M of the MMC system can be reduced by half as compared with the case where one bypass mechanism is provided for each of the unit-converters3. Further, by fixing the bypass mechanism (bypass switch14) and the external connection wire15by a common mechanism, the number of structural components can be reduced.

Although various exemplary embodiments and examples are described in the present application, various features, aspects, and functions described in one or more embodiments are not inherent in an application of the contents disclosed in a particular embodiment, and can be applicable alone or in their various combinations to each embodiment. Accordingly, countless variations that are not illustrated are envisaged within the scope of the art disclosed herein. For example, the case where at least one component is modified, added or omitted, and the case where at least one component is extracted and combined with a component disclosed in another embodiment are included.

For example, the positional relationship between the switching element2and the capacitor1is not limited to the exemplified embodiments, and the capacitors1for the pair of unit-converters3may be integrally provided as long as the cooling device4is shared. In addition, the shapes, etc., of the capacitor1, the P-pole connection conductor5, and the N-pole connection conductor6can be variously modified.

As described above, the power conversion device9in the present application includes the pair of unit-converters3, and the cooling device4. Each of the pair of unit-converters3includes the capacitor1, the switching element2in which the cooling surface and the connecting surface opposite to the cooling surface are provided and two electrodes through which main power flows are formed in the connecting surface and by which the leg20for the power conversion is formed by forming a pair, the first conductive plate (for example, P-pole connection conductor5) in which the second terminal hole5t2is formed at one end for fixing an electrode of the switching elements2forming the pair, the electrode corresponding to the first pole (for example, P-pole20p1) in the leg20, and the first terminal hole5t1is formed at the other end for fixing the electrode (terminal1p1) of the capacitor1corresponding to the first pole (P-pole20p1), and the second conductive plate (for example, N-pole connection conductor6) in which the second terminal hole6t2is formed at one end for fixing an electrode of the switching elements2forming the pair, the electrode corresponding to the second pole (for example, N-pole20p2) in the leg20, and the first terminal hole6t1is formed at the other end for fixing the electrode (terminal1p2) of the capacitor1corresponding to the second pole (N-pole20p2), the second conductive plate being arranged to overlap with the first conductive plate (P-pole connection conductor5) in the thickness direction, maintaining insulation from the first conductive plate. In the pair of unit-converters3, the cooling surfaces of the switching elements2forming the pair in one unit-converter3is opposed to the cooling surfaces of the switching elements2forming the pair in the other unit-converter3with the cooling device4interposed therebetween. That is, the power conversion device9is configured such that the cooling surfaces of the switching elements2are opposed to each other with the single cooling device4interposed (shared) therebetween. Therefore, the number of components is reduced, and it is possible to obtain a compact power conversion device9.

At this time, each of the pair of unit-converters3is configured such that the capacitor1is placed on the front side relative to the cooling surface of the switching element2in a direction away from the second terminal hole5t2(and the second terminal hole6t2). Therefore, the capacitors1do not interfere with each other, (the flat surfaces of) the switching elements2are opposed to each other, and the power conversion device9can be configured by interposing (sharing) one cooling device4.

In particular, the first conductive plate (P-pole connection conductor5) and the second conductive plate (N-pole connection conductor6) each are formed with the bent portion (bent portions5b,6b) in the middle portion so as to have an angle between the portion (portions51,61) where the first terminal hole (5t1,6t1) is formed and the portion (portions52,62) where the second terminal hole (5t2,6t2) is formed. Therefore, the capacitor1, which is bulkier than the switching element2, can be easily placed on the front side.

When the pair of unit-converters3are configured such that the first conductive plates (P-pole connection conductor5) have the same shape and the second conductive plates (N-pole connection conductor6) have the same shape to each other, the productivity is further improved by the component sharing.

When each of the first conductive plate (P-pole connection conductor5) and the second conductive plate (N-pole connection conductor6) is configured such that three or more of the second terminal holes (5t2,6t2) are arranged along the one end, and the opening (slits5s,6s) is formed on the line connecting a centrally arranged terminal hole thereof and the first terminal hole (5t1,6t1), the length L2(=Lm+Ls2) of the current paths between the switching element2connected to the central terminal hole and the capacitor1and the length L1(=Lm+Ls1) of the current paths between the switching element2connected to the outer terminal hole and the capacitor1are adjusted to be equal by the position and size of the opening, and thus the current utilization factor of each of the switching elements2connected in parallel can be uniformly improved.

The first conductive plate (P-pole connection conductor5) and the second conductive plate (N-pole connection conductor6) are respectively provided with third contact holes5t2and6t2for electrical connection to the outside at positions away from the shortest paths (current paths5t1and6t1) connecting the second contact holes P1and P2and the first contact holes5t3and6t3.

In one of the first conductive plate (P-pole connection conductor5), the second conductive plate (N-pole connection conductor6), and the third conductive plate (AC-pole connection conductor) whose one end is formed with a terminal hole (first terminal hole711) corresponding to the AC pole (AC-pole20p3) in the leg20and whose other end is formed with a terminal hole (second terminal hole7t2) for electrical connection to the outside, when the number of terminal holes formed at one end portion is larger than the number of terminal holes formed at the other end portion and the width of the other end portion is narrower than the width of the one end portion, the length of the current paths from the elements connected in parallel through the conductor plate concerned can be equalized.

In particular, by providing the bypass mechanism (bypass switch14) that bypasses between the pair of unit-converters3, it is possible to form a power conversion device9of the MMC system that can operate normally even if an anomaly occurs in a specific power conversion device9.

DESCRIPTION OF REFERENCE NUMERALS AND SIGNS