Power conversion device for railway vehicle

Abstract

A power conversion device (50) for a railway vehicle for driving a propulsion motor (15) mounted on the railway vehicle comprises: a three-phase inverter (4) for converting DC power to AC power supplied to the propulsion motor (15); a filter capacitor (3) for smoothing a DC voltage applied to the three-phase inverter (4); three AC power lines (5) that are electric wires for electrically connecting the three-phase inverter (4) and the propulsion motor (15); and three common mode current back-flow lines (6), each of which is disposed along each of the three AC power lines (5) one by one.

Description

Power conversion equipment for railway vehicles

[0001] The present disclosure relates to a power conversion device for a railway vehicle for driving a traction motor mounted on the railway vehicle.

[0002] Power conversion devices include switching elements such as IGBTs (Insulated Gate Bipolar Transistors) and MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors). In recent power conversion devices, switching elements have become higher in voltage resistance and higher in frequency, leading to increased switching voltages and faster switching operations.

[0003] It is generally known that switching operations in power conversion devices cause common-mode currents, which are zero-phase currents. It is also known that switching operations in power conversion devices cause leakage currents to flow to the ground via parasitic capacitances between the AC power lines connecting the power conversion device to the load and the ground, and between the load and the ground. It is also known that switching operations in power conversion devices cause leakage currents to flow to peripheral devices other than the load or to the ground via parasitic capacitances between the AC power lines and the housing that houses the power conversion device. These leakage currents are common-mode currents that flow in the grounding system and are distinguished from zero-phase currents.

[0004] As described above, an increase in the switching voltage and an increase in the speed of the switching operation increase the leakage current, which in turn increases the radiation noise, causing a problem of adversely affecting surrounding communication devices and the like.

[0005] Patent Document 1 below discloses a technology for reducing leakage current by preparing a common-mode current return line, which is a single electrical wiring that connects the ground terminal of a power conversion device and the ground terminal of a load, and passing this common-mode current return line together with three AC power lines through the same magnetic core.When the technology in Patent Document 1 is used, the impedance of the return loop of the ground system is larger than the impedance of the return loop of the common-mode current return line, so the leakage current flowing in the return loop of the ground system can be reduced.

[0006] Japanese Patent Application Laid-Open No. 2001-086734

[0007] The technology of Patent Document 1 utilizes the fact that the magnetic fluxes generated by the common-mode currents flowing in the AC power lines and the common-mode current return lines cancel each other out when the common-mode currents flow in opposite directions. The degree of magnetic flux cancellation increases the closer the AC power lines and the common-mode current return lines are to each other. However, in the case of a power conversion system for a railway vehicle, the AC power lines carry extremely large currents, so their thickness, i.e., cross-sectional area, increases. Therefore, when applying the technology of Patent Document 1 to a power conversion system for a railway vehicle, it is difficult to route one common-mode current return line in evenly close contact with three AC power lines. Therefore, the technology of Patent Document 1 has a problem in that it is not possible to sufficiently reduce the area of ​​the return loop, which is the path through which current flows between the AC power lines and the common-mode current return lines, resulting in insufficient radiation noise reduction.

[0008] The present disclosure has been made in view of the above, and has an object to provide a power conversion device for a railway vehicle that can enhance the effect of reducing radiation noise caused by common mode currents.

[0009] To solve the above-mentioned problems and achieve the object, a power conversion device for a railway vehicle according to the present disclosure is a power conversion device for a railway vehicle for driving a traction motor mounted on the railway vehicle, and includes a three-phase inverter that converts DC power into AC power for the traction motor, a filter capacitor that smoothes the DC voltage applied to the three-phase inverter, three AC power lines that are electrical wiring that electrically connect the three-phase inverter and the traction motor, and three common-mode current return lines that are arranged one alongside each of the three AC power lines.

[0010] The power conversion device for a railway vehicle according to the present disclosure has the effect of being able to enhance the effect of reducing radiation noise caused by common mode current.

[0011] FIG. 1 is a diagram showing an example of the configuration of an electrical system of a railway vehicle system including a power conversion device according to embodiment 1. FIG. 2 is a diagram showing an example of mounting a power conversion device according to embodiment 1 on a railway vehicle. FIG. 3 is a diagram showing a railway vehicle on which a power conversion device according to embodiment 1 is mounted, viewed from below. FIG. 4 is a diagram used to explain a method of arranging AC power lines and common mode current return lines in a power conversion device according to embodiment 1. FIG. 5 is a first diagram used to explain variations in the method of arranging AC power lines and common mode current return lines in a power conversion device according to embodiment 1. FIG. 6 is a second diagram used to explain variations in the method of arranging AC power lines and common mode current return lines in a power conversion device according to embodiment 1. 13 is a diagram illustrating an example of a grounding configuration of a filter capacitor different from that of FIG. 12.

[0034] FIG. 14 is a diagram illustrating an example of a grounding configuration of a filter capacitor different from that of FIG. 13.

[0035] FIG. 15 is a diagram illustrating an example of a grounding configuration of a filter capacitor different from that of FIG. 13.

[0012] A power conversion device for a railway vehicle (hereinafter, abbreviated as "power conversion device" as appropriate) according to an embodiment of the present disclosure will be described in detail below with reference to the accompanying drawings. Note that in the accompanying drawings, the scale of each component may differ from the actual scale for ease of understanding. The same applies to each of the drawings.

[0013] First Embodiment Fig. 1 is a diagram showing an example of the configuration of an electrical system of a railway vehicle system including a power conversion device 50 according to a first embodiment. The power conversion device 50 according to the first embodiment includes a filter capacitor 3 and a three-phase inverter 4. In Fig. 1, an input circuit unit 2 is present at the input end of the three-phase inverter 4. The input circuit unit 2 and the three-phase inverter 4 are connected by a high-potential DC bus 8 and a low-potential DC bus 9. The filter capacitor 3 is connected between the DC bus 8 and the DC bus 9. At least one traction motor 15 is connected to the output end of the three-phase inverter 4. The traction motor 15 is a three-phase motor that provides propulsive force to the railway vehicle.

[0014] The input circuit unit 2 is configured to include at least a circuit breaker and a filter reactor. One end of the input circuit unit 2 is connected to an overhead line 10 via a current collector 11. The other end of the input circuit unit 2 is electrically connected via wheels 13 to a rail 12 that applies a ground potential, which is a ground potential. DC power or AC power supplied from the overhead line 10 is input to one end of the input circuit unit 2 via the current collector 11. A DC voltage generated by the DC power at the output end of the input circuit unit 2 is applied to a three-phase inverter 4. A filter capacitor 3 smoothes the DC voltage applied to the three-phase inverter 4 so that ripples in the DC voltage are reduced. The three-phase inverter 4 converts the DC power supplied via the input circuit unit 2 into AC power for the propulsion motor 15.

[0015] The three-phase inverter 4 is connected to the propulsion motor 15 by three AC power lines 5. The AC power lines 5 are electrical wiring that electrically connect the three-phase inverter 4 and the propulsion motor 15. One of the three AC power lines 5 is a U-phase electrical wiring, one of the remaining two is a V-phase electrical wiring, and the remaining one is a W-phase electrical wiring. Three common-mode current return lines 6 are drawn from the frame of the propulsion motor 15 and connected to a portion of the power conversion device 50 that is at ground potential. The common-mode current return lines 6 are electrical wiring that electrically connect the ground potential of the power conversion device 50 and the ground potential of the propulsion motor 15. It is preferable that the portion of the propulsion motor 15 from which the common-mode return lines 6 are drawn is near the portion from which the AC power lines 5 are drawn. It is also preferable that the ground point of the common-mode return lines 6 be near the portion of several ground potentials to which the filter capacitor 3 is grounded. In the power conversion device 50 according to the first embodiment, the DC bus 9 on the low potential side is grounded, or a ground potential is applied to the DC bus 9 .

[0016] The three-phase inverter 4 includes multiple switching elements 4a connected in a three-phase bridge configuration. The switching elements 4a have freewheeling diodes connected in anti-parallel. The switching elements 4a perform switching operations in response to gate signals output from a drive circuit (not shown). The switching operations of the switching elements 4a intermittently control the current flowing through the switching elements 4a. This converts DC power supplied from the input circuit unit 2 into AC power for the traction motor 15. The traction motor 15 is driven by AC power supplied from the three-phase inverter 4 and provides propulsion power to a train composed of one or more railway cars (not shown). The three-phase inverter 4 drives the traction motor 15 by converting DC power supplied via the input circuit unit 2 into AC power for the traction motor 15. Note that while FIG. 1 illustrates the input circuit unit 2 and the three-phase inverter 4 as separate components, they may also be housed in the same housing.

[0017] Fig. 2 is a diagram showing an example of mounting the power conversion device 50 according to the first embodiment on a railway vehicle. In Fig. 2, components that are the same as or equivalent to those in Fig. 1 are denoted by the same reference numerals. Fig. 3 is a diagram showing the railway vehicle on which the power conversion device 50 according to the first embodiment is mounted, as viewed from below.

[0018] The filter capacitor 3 and the three-phase inverter 4 that constitute the power conversion device 50 are housed in an aluminum or iron housing 24. The housing 24 is attached to the lower part of the vehicle body 20 by fastening members (not shown). Although not shown, the housing 24 also houses a drive circuit for driving the switching elements 4a, a control device including a waveform generation circuit for generating a signal to operate the switching elements 4a, and the like.

[0019] The wheels 13 have axles 22, and earth brushes 23 are provided on the axles 22. The earth brushes 23 are electrically connected to the DC bus 9 by cables 28 and to the car body 20 by cables 29. The earth brushes 23 are also electrically connected to the rails 12 via the wheels 13. The earth brushes 23 are also electrically connected to the frame of the traction motor 15 by equalizing wires 30. Through these connections, a ground potential is applied to the DC bus 9, the car body 20, the earth brushes 23, the frame of the traction motor 15, and the housing 24 that houses the power conversion device 50.

[0020] The propulsion motor 15 is mounted on a bogie (not shown) and installed under the car body 20. The bogie is electrically insulated from the car body 20. The propulsion motor 15 is provided with a first terminal portion 31 for connecting the AC power line 5 and the common mode current return line 6. The first terminal portion 31 is electrically insulated from the motor housing (not shown).

[0021] The housing 24 that houses the power conversion device 50 is provided with a second terminal 32 for connecting the common-mode current return line 6 and a third terminal 33 for connecting the AC power line 5. The second terminal 32 and the third terminal 33 are electrically insulated from the housing 24. The second terminal 32 has terminals 32a to 32c, and the third terminal 33 has terminals 33a to 33c. The terminals 32a to 32c are connected to the DC bus 9, and the terminals 33a to 33c are connected to AC output terminals for each phase in the main circuit of the three-phase inverter 4. The second terminal 32 and the third terminal 33 may be configured as a single terminal.

[0022] One end of each of the three AC power lines 5 is connected to a first terminal 31 provided on the propulsion motor 15, and the other end of each of the three AC power lines 5 is connected to a third terminal 33 provided on the housing 24. In addition, one end of each of the three common mode current return lines 6 is connected to the first terminal 31, and the other end of each of the three common mode current return lines 6 is connected to a second terminal 32 provided on the housing 24.

[0023] 2, communication equipment 25 that performs required communication between the ground side and the railway vehicle side is present on the track on which the rails 12 are laid. When a current flows through the AC power line 5, radiated noise 26 is generated, and this radiated noise 26 affects the communication of the communication equipment 25. The current that flows through the AC power line 5 can be either a normal mode current in which the currents flowing through each of the three phases have a phase difference of 120 degrees, or a common mode current in which the currents flowing through each of the three phases are in phase. Of these currents, it is the common mode current that has the greatest impact on the generation of radiated noise 26.

[0024] Therefore, in the first embodiment, the three AC power lines 5 and the three common mode current return lines 6 are covered with a metal duct 21 having a square cross section so as to reduce the radiation noise 26 directed toward the communication equipment 25. However, as shown in FIG. 3 , other equipment 36 other than the housing 24 that houses the power conversion device 50 and the traction motor 15 is present under the vehicle body 20. Due to the presence of the other equipment 36, the AC power lines 5 and the common mode current return lines 6 are forced to be arranged in a serpentine manner as shown in FIG. 3 . For this reason, the metal duct 21 is arranged to cover the AC power lines 5 and the common mode current return lines 6 in a portion of the section in which the AC power lines 5 and the common mode current return lines 6 are installed.

[0025] The cross section of the metal duct 21 does not necessarily have to be square-shaped, and may be a metal duct with a U-shaped or L-shaped cross section. It goes without saying that when a metal duct with a U-shaped or L-shaped cross section is used, the opening should not face the direction of the tracks.

[0026] It should be noted that the metal duct 21 is not necessarily an essential component of the power conversion device 50 according to the first embodiment. When the three common mode return wires 6 are appropriately arranged and the radiation noise 26 is equal to or less than a specified value, the metal duct 21 may be omitted.

[0027] Next, a description will be given of a method for arranging the three AC power lines 5 and the three common mode current return lines 6. Fig. 4 is a diagram illustrating a method for arranging the AC power lines 5 and the common mode current return lines 6 in the power conversion device 50 according to the first embodiment.

[0028] First, each of the three common mode current return lines 6 is arranged along each of the three AC power lines 5. By arranging them in this manner, each of the common mode current return lines 6 can be closely attached to each of the AC power lines 5.

[0029] 4, an even more desirable electrical wiring configuration would be one in which a set of electrical wiring consisting of one AC power line 5 and one common mode current return line 6 arranged alongside this AC power line 5 is twisted together with two other sets of electrical wiring. By twisting the AC power line 5 and the common mode current return line 6, it is possible to further increase the degree of adhesion between the AC power line 5 and the common mode current return line 6 in the twisted portion.

[0030] The electrical wiring shown in Figure 4 can be constructed, for example, by the following procedure. First, three common mode current return wires 6 are arranged so that one wire is parallel to each of the three AC power wires 5. Next, the three AC power wires 5 are arranged so that the center position of each end of the three AC power wires 5 is offset by approximately 120 degrees from the overall center position, and the three common mode current return wires 6 are similarly arranged so that the center position of each end of the three common mode current return wires 6 is offset by approximately 120 degrees from the overall center position. Then, an electrical wiring set consisting of one AC power line 5 and one common mode current return wire 6 is twisted together with two other electrical wiring sets. Using this procedure, the electrical wiring shown in Figure 4 can be constructed and installed.

[0031] Because the current flowing through the common mode current return wire 6 is smaller than the current flowing through the AC power lines 5, the diameter of the common mode current return wire 6 can be smaller than the diameter of the AC power lines 5. Therefore, each of the three common mode current return wires 6 can be easily arranged along each of the three AC power lines 5. Furthermore, in the technology of embodiment 1, by changing the number of common mode current return wires 6 from one to three, the diameter of the common mode current return wire 6 can be reduced to 1 / √3 of the conventional diameter. This allows the diameter of the common mode current return wire 6 to be reduced, thereby improving the degree of adhesion between the AC power lines 5 and the common mode current return wire 6 and facilitating the twisting of the AC power lines 5 and the common mode current return wire 6. The reason why the diameter of the common mode current return wire 6 can be reduced to 1 / √3 of the conventional diameter is as follows.

[0032] First, the resistance of the common mode return wire 6 can be most simply explained by considering a direct current flowing through the common mode return wire 6. The resistance of the common mode return wire 6 is proportional to the cross-sectional area of ​​the common mode return wire 6, so by using three wires, the cross-sectional area per wire can be reduced to 1 / 3, which can be converted to a diameter of 1 / √3.

[0033] The common mode current that causes radiated noise is an AC current with a frequency of about 100 kHz to 3 MHz. As the frequency increases, the AC resistance can be further reduced, taking into account the skin thickness. Therefore, if there are three common mode return wires 6, the impedance can be reduced compared to when there is only one.

[0034] Next, variations in the arrangement of the AC power line 5 and the common mode current return line 6 will be described with reference to Fig. 5 to Fig. 7. Fig. 5 to Fig. 7 are first, second, and third diagrams respectively used to explain variations in the arrangement method of the AC power line 5 and the common mode current return line 6 in the power conversion device 50 according to the first embodiment.

[0035] Because the lower part of the vehicle body 20 is an environment where moisture is likely to accumulate, a drain 34 as shown in Figures 5 to 7 is provided near the first terminal portion 31 of the propulsion motor 15. The first terminal portion 31 has terminals 31a to 31f, with three AC power lines 5 connected to terminals 31a to 31c, and three common mode current return lines 6 connected to terminals 31d to 31f. The three sets of AC power lines 5 and common mode current return lines 6 are arranged so as to bend downward in the drain 34. Furthermore, because moisture is likely to accumulate if the three sets of AC power lines 5 and common mode current return lines 6 are twisted in the drain 34, they are arranged without twisting, as shown in Figure 5.

[0036] In the draining portion 34 of Fig. 5 , one AC power line 5 and one common mode current return line 6 arranged along the AC power line 5 may be twisted together as shown in Fig. 6 . This arrangement can increase the degree of adhesion between the AC power line 5 and the common mode current return line 6 in the draining portion 34. Furthermore, because the diameter of the common mode current return line 6 is smaller than the diameter of the AC power line 5, gaps can be secured between the AC power lines 5 even when they are twisted together. In this case, it is desirable to arrange the terminals 31a and 31d adjacent to each other, the terminals 31b and 31e adjacent to each other, and the terminals 31c and 31f adjacent to each other.

[0037] 6, one AC power line 5 and one common mode current return line 6 arranged along the AC power line 5 may be twisted together as shown in FIG. 7. Arranged in this manner, the degree of adhesion between the AC power line 5 and the common mode current return line 6 can be increased even in the twisted line section 35.

[0038] Next, the effects of the power conversion device 50 according to the first embodiment will be described with reference to Fig. 8 and Fig. 9. Fig. 8 is a diagram showing three electrical wiring models corresponding to the three electromagnetic field analysis results in Fig. 9. Fig. 9 is a diagram showing the results of electromagnetic field analysis performed on the three electrical wiring models shown in Fig. 8.

[0039] The lower part of Fig. 8 shows an electrical wiring model of embodiment 1, which corresponds to Fig. 4 . The upper and middle parts of Fig. 8 show electrical wiring models of comparative examples 1 and 2, respectively. Comparative example 1 is an electrical wiring model in which four electrical wirings, consisting of three AC power lines 5 and one common mode current return line 6, are twisted together. Comparative example 2 is an electrical wiring model in which three AC power lines 5 are twisted together and one common mode current return line 6 is further twisted around the three twisted AC power lines 5. The radial width of the common mode current return line 6 in embodiment 1 is assumed to be 1 / √3 of the radial width of the common mode current return line 6 in comparative examples 1 and 2.

[0040] As shown in FIG. 8 , the wiring length of the three electrical wiring models is 5000 mm, and one pitch is 1000 mm. The overall diameter width of the electrical wiring models in Comparative Example 1 and Embodiment 1 is 200 mm. In Comparative Example 2, the overall diameter width of the electrical wiring model is 300 mm, and the diameter width of the three AC power lines 5 is 200 mm. An input port 41 is provided at the left end of each electrical wiring model, and a loop antenna is installed 2500 mm from the left end, which is the center position between the left and right ends, and 700 mm away from this center position, and an output port 42 is provided at its output end. Furthermore, at the right end of each model, three capacitors 43 each having a capacitance of 30 nF, equivalent to the stray capacitance of the propulsion motor 15, are connected between the AC power line 5 and the common-mode current return line 6.

[0041] 9, the horizontal axis represents the frequency of the signal input to input port 41, and the vertical axis represents the transfer coefficient S21 from input port 41 to output port 42. In Fig. 9, the analysis results for the electrical wiring model of embodiment 1 are shown by a solid line, the analysis results for the electrical wiring model of comparative example 1 are shown by a dashed line, and the analysis results for the electrical wiring model of comparative example 2 are shown by a dashed line.

[0042] For communication equipment 25 placed on the line, electromagnetic interference is a problem particularly in the communication frequency band of 100 kHz to 3 MHz. In this communication frequency band, the analysis results in Fig. 9 show that, except for some resonant frequencies, the electrical wiring model of embodiment 1 has the smallest transfer coefficient S21.

[0043] Comparing Comparative Examples 1 and 2, the transmission coefficient S21 is smaller in Comparative Example 1 than in Comparative Example 2. One of the reasons for this is thought to be that the overall diameter width is shorter in Comparative Example 1 than in Comparative Example 2, and the area of ​​the return loop is smaller in Comparative Example 1 than in Comparative Example 2. If the area of ​​the return loop is reduced, it is possible to reduce the radiation noise for the same current value.

[0044] Furthermore, in the first embodiment, the number of common mode current return wires 6 is increased to three, thereby increasing the degree of adhesion between the pair of electrical wirings consisting of one AC power line 5 and one common mode current return wire 6. For this reason, even though the overall diameter widths of both comparative example 1 and the first embodiment are the same, the area of ​​the return loop can be made smaller in the first embodiment, which is thought to result in a smaller transfer coefficient S21.

[0045] As described above, the power conversion device for a railway vehicle according to the first embodiment includes a three-phase inverter that converts DC power into AC power for a traction motor mounted on the railway vehicle, and a filter capacitor that smooths the DC voltage applied to the three-phase inverter. The power conversion device also includes three AC power lines that are electrical wiring that electrically connect the three-phase inverter and the traction motor, and three common-mode current return lines that are arranged one alongside each of the three AC power lines. With this power conversion device configured in this manner, the AC power lines and the common-mode current return lines can be arranged in close contact with each other. This reduces the area of ​​the return loop of the current traveling between one AC power line and one common-mode current return line, thereby enhancing the effectiveness of reducing radiation noise caused by common-mode current.

[0046] In the power conversion device according to the first embodiment, the three common-mode current return lines may be configured to be connected to a first terminal provided on the propulsion motor and a second terminal provided on a housing that accommodates the power conversion device. The three AC power lines and the three common-mode current return lines may be configured such that, in at least a portion of a section between the first terminal and the second terminal, a set of electrical wiring consisting of one AC power line and one common-mode current return line arranged along the one AC power line is twisted together with the other two sets of electrical wiring. Twisting the three sets of electrical wiring together reduces the area of ​​the return loop of the current traveling between the three AC power lines, thereby further enhancing the effect of reducing radiation noise caused by the common-mode current.

[0047] In the power conversion device according to embodiment 1, one AC power line and one common mode current return line arranged along the AC power line may be twisted together. This arrangement increases the degree of adhesion between the AC power line and the common mode current return line, thereby further improving the effect of reducing radiation noise caused by common mode currents.

[0048] In the power conversion device according to the first embodiment, the second terminal unit may have three terminals for connecting the three common-mode current return lines, respectively. By electrically connecting each of these three terminals to the low-potential side of the filter capacitor, the potential of the low-potential side of the filter capacitor can be stably applied to the three common-mode current return lines, thereby ensuring a configuration that is effective in reducing radiation noise.

[0049] Embodiment 2 The electromagnetic field analysis results described in embodiment 1 are based on the assumption that potential fluctuations in the common-mode voltage caused by the switching operation of the switching element 4a occur relative to the ground potential. The common-mode voltage referred to here is synonymous with the potential difference between the neutral point potential of the propulsion motor 15 and the ground potential. If the U-phase voltage of the propulsion motor 15 is represented by "Vu," the V-phase voltage by "Vv," and the W-phase voltage by "Vw," then the common-mode voltage can be expressed as (Vu + Vv + Vw) / 3.

[0050] On the other hand, if a potential fluctuation in the common mode voltage due to the switching operation of switching element 4 a occurs at a potential other than the ground potential, the leakage current flowing in the return loop of the grounding system will also flow via stray capacitance between the portion other than the ground potential and vehicle body 20. Taking this into consideration, the power conversion device 50 according to the second embodiment has different connections to some of the three common mode current return lines 6 from those in the first embodiment.

[0051] Fig. 10 is a diagram showing an example of mounting a power conversion device 50 according to embodiment 2 on a railway vehicle. The differences between the configuration of Fig. 10 and the configuration of Fig. 2 are the configuration of the second terminal unit 32 and the connection destinations of the other ends of the three common mode current return lines 6. The rest is the same as or equivalent to embodiment 1 shown in Fig. 2. The following description will omit content that overlaps with embodiment 1 as appropriate, and will focus on content that differs from embodiment 1.

[0052] An example of a location other than the ground potential where potential fluctuations of the common-mode voltage may occur is the housing 24 of the three-phase inverter 4. In the power conversion device 50 according to the second embodiment, one of the three common-mode current return lines 6 is connected to the housing 24 in consideration of the potential fluctuations of the common-mode voltage occurring with respect to the housing 24 of the three-phase inverter 4. The other two of the three common-mode current return lines 6 are connected to the terminals 32a and 32b of the second terminal unit 32. As in the first embodiment, the terminals 32a and 32b are connected to the DC bus 9. Note that while FIG. 10 illustrates an example configuration in which one of the three common-mode current return lines 6 is connected to the housing 24, this configuration is not limiting. The power conversion device 50 according to the second embodiment may be configured such that two of the three common-mode current return lines 6 are connected to the housing 24.

[0053] FIG. 11 is a diagram showing the results of an electromagnetic field analysis performed on the connection configuration of the power conversion device 50 according to the second embodiment. The electrical wiring model to be analyzed is the electrical wiring model shown in FIG. 4. In FIG. 11, the solid lines indicate the analysis results performed on the connection configuration of the second embodiment shown in FIG. 10, and the dashed lines indicate the analysis results performed on the connection configuration of the first embodiment shown in FIG. 2. As in FIG. 9, the horizontal axis of FIG. 11 indicates the frequency of the signal input to the input port 41, and the vertical axis indicates the transfer coefficient S21 from the input port 41 to the output port 42. The electromagnetic field analysis in FIG. 11 was performed by generating a potential fluctuation of the common-mode voltage in the housing 24 of the three-phase inverter 4.

[0054] According to the analysis results of Fig. 11, it can be seen that, with the exception of some frequencies, in the communication frequency band of 100 kHz to 3 MHz where electromagnetic interference becomes a problem, the transfer coefficient S21 of the connection configuration of the second embodiment shown in Fig. 10 is smaller than that of the connection configuration of the first embodiment shown in Fig. 2. The reason for this can be explained as follows.

[0055] In the case of the configuration of embodiment 1 in which the common mode current return line 6 is not connected to the housing 24, when a potential fluctuation in the common mode voltage occurs with respect to the housing 24 of the three-phase inverter 4, a common mode current flows through the AC power lines 5, the stray capacitance of the propulsion motor 15, the equalizer 30 connecting the housing of the propulsion motor 15 to the earth brushes 23, the cable 29 connecting the earth brushes 23 to the car body 20, the bolts connecting the car body 20 to the housing 24, and the stray capacitance between the housing 24 and the three-phase inverter 4. The area of ​​the return loop of the current flowing through this path is larger than the area of ​​the return loop of the current traveling back and forth between the AC power lines 5 and the common mode current return line 6.

[0056] On the other hand, as described above, in the second embodiment, one or two of the three common mode current return lines 6 are connected to the housing 24 of the three-phase inverter 4. As a result, the common mode current that may flow through the aforementioned paths flows mainly through the common mode current return line 6 connected to the housing 24. This is because the impedance of the return loop is smaller in the common mode current return line 6 than in the aforementioned paths. As a result, it is believed that the transfer coefficient S21 is smaller in the connection configuration of the second embodiment shown in FIG. 10 than in the connection configuration of the first embodiment shown in FIG. 2.

[0057] Although the second embodiment has been described with reference to a configuration in which one or two of the three common mode current return wires 6 are connected to the housing 24 of the three-phase inverter 4, the present invention is not limited to this example. One or two of the three common mode current return wires 6 may be connected to a location at the same potential as the housing 24. Alternatively, one or two of the three common mode current return wires 6 may be connected to a housing that houses devices other than the three-phase inverter 4 and is located below the vehicle body 20, where potential fluctuations in the common mode voltage are likely to occur.

[0058] As described above, in the power conversion device for railway vehicles according to embodiment 2, one or two of the three common-mode current return lines are configured to be electrically connected to a potential different from the potential of the connection destination of the other common-mode current return lines. This configuration makes it possible to reduce radiation noise caused by common-mode currents even when the switching operation of the switching elements causes a potential fluctuation in the common-mode voltage relative to a potential other than ground.

[0059] Embodiment 3. Although the first and second embodiments do not specifically mention the electrification method of the railway vehicle, the power conversion device 50 according to the first and second embodiments is applicable to both DC and AC electrification systems. In the third embodiment, a configuration example when applied to an AC-electrical railway vehicle will be described.

[0060] Fig. 12 is a diagram showing a variation of the input circuit unit 2 shown in Fig. 1. Fig. 12 shows an input circuit unit 60 as an example when the overhead line 10 is an AC overhead line. The input circuit unit 60 includes a main transformer 61 that steps down the AC voltage received via the current collector 11, and a converter 62 that converts the AC voltage stepped down by the main transformer 61 into a DC voltage. A filter capacitor 3 is connected to the output end of the converter 62. When the low-potential side of the filter capacitor 3 is grounded as in Fig. 1, the terminals of the second terminal unit 32 to which the three common-mode current return lines 6 are connected can be electrically connected to the potential on the ground side of the filter capacitor 3 as in Fig. 2.

[0061] FIG. 13 is a diagram showing a configuration example of the filter capacitor 3 different from that shown in FIG. 12 . FIG. 14 is a diagram showing a grounding example of the filter capacitor 3 different from that shown in FIG. 13 . FIGS. 13 and 14 show configurations in which the filter capacitor 3 is composed of two filter capacitors 3A and 3B connected in series. FIG. 13 shows a configuration in which the midpoint 3C, which is the connection point between the filter capacitors 3A and 3B, is grounded. FIG. 14 shows a configuration in which the midpoint 3C between the filter capacitors 3A and 3B is not grounded, but the low-potential side of the filter capacitor 3 is grounded. In the case of FIG. 13 , each terminal of the second terminal unit 32 connecting the three common-mode current return lines 6 is electrically connected to the midpoint 3C, which is the potential on the ground side of the filter capacitor 3. In the case of FIG. 14 , similar to FIG. 12 , each terminal of the second terminal unit 32 connecting the three common-mode current return lines 6 is electrically connected to the potential on the ground side of the filter capacitor 3. The same effects as those of the first embodiment can be achieved with any of the configurations shown in FIGS. 12 to 14 .

[0062] 12 to 14 , one or two of the three common mode current return lines 6 may be connected to the housing 24 of the three-phase inverter 4 as described in embodiment 2. Alternatively, one or two of the three common mode current return lines 6 may be connected to the housing that houses the converter 62. With any of these configurations, the same effects as in embodiment 2 can be obtained.

[0063] The configurations shown in the above embodiments are merely examples, and may be combined with other known technologies, or different embodiments may be combined with each other. It is also possible to omit or modify parts of the configurations as long as they do not deviate from the gist of the invention.

[0064] 2, 60 Input circuit section, 3, 3A, 3B Filter capacitor, 3C Neutral point, 4 Three-phase inverter, 4a Switching element, 5 AC power line, 6 Common mode current return line, 7 Grounding wire, 8, 9 DC bus bar, 10 Overhead line, 11 Current collector, 12 Rail, 13 Wheel, 15 Propulsion motor, 20 Car body, 21 Metal duct, 22 Axle, 23 Earth brush, 24 Housing, 25 Communication equipment, 26 Radiated noise, 28, 29 Cable, 30 Equalizing wire, 31 First terminal section, 31a to 31f, 32a to 32c, 33a to 33c Terminal, 32 Second terminal section, 33 Third terminal section, 34 Water drain section, 35 Stranded section, 36 Equipment, 41 Input port, 42 Output port, 43 Capacitor, 50 Power conversion device, 61 Main transformer, 62 converter.

Claims

1. A power conversion device for a railway vehicle for driving a traction motor mounted on the railway vehicle, comprising: a three-phase inverter that converts DC power into AC power for the traction motor; a filter capacitor that smoothes the DC voltage applied to the three-phase inverter; three AC power lines that are electrical wiring that electrically connect the three-phase inverter and the traction motor; and three common mode current return lines that are arranged one alongside each of the three AC power lines.

2. The power conversion device for railway vehicles according to claim 1, characterized in that one or two of the three common mode current return lines are electrically connected to a potential different from the potential of the connection destination of the other common mode current return lines.

3. A power conversion device for a railway vehicle as claimed in claim 1 or 2, characterized in that the three common mode current return wires are connected to a first terminal unit provided on the propulsion motor and a second terminal unit provided on a housing that houses the power conversion device, and in at least a portion of the section between the first terminal unit and the second terminal unit, a set of electrical wiring consisting of one AC power line and one common mode current return wire arranged along the one AC power line is twisted together with the other two sets of electrical wiring.

4. The power conversion device for railway vehicles according to claim 3, characterized in that one of the AC power lines and one of the common mode current return lines arranged along the one of the AC power lines are twisted together.

5. A power conversion device for railway vehicles according to claim 3 or 4, characterized in that the second terminal section has three terminals for connecting each of the three common mode current return lines, and each of the three terminals is electrically connected to the potential on the low potential side of the filter capacitor.

6. A power conversion device for a railway vehicle as described in claim 3 or 4, characterized in that the second terminal unit has three terminals for connecting each of the three common mode current return lines, at least one of the three terminals being electrically connected to the potential on the low potential side of the filter capacitor, and the remaining terminal being electrically connected to a housing that houses the power conversion device.

7. A power conversion device for railway vehicles as described in claim 3 or 4, characterized in that the second terminal unit has three terminals for connecting each of the three common mode current return lines, and when the filter capacitor is composed of two capacitors connected in series and the midpoint which is the connection point of the two capacitors is grounded, the three terminals are electrically connected to the potential of the midpoint of the filter capacitor.

8. A power conversion device for railway vehicles as described in claim 3 or 4, characterized in that the second terminal unit has three terminals for connecting each of the three common mode current return lines, and when the filter capacitor is composed of two capacitors connected in series and the midpoint which is the connection point of the two capacitors is grounded, at least one of the three terminals is electrically connected to the potential of the midpoint of the filter capacitor, and the remaining terminal is electrically connected to a housing that houses the power conversion device.

9. A power conversion device for railway vehicles as described in claim 3 or 4, characterized in that the second terminal unit has three terminals for connecting each of the three common mode current return lines, and when the filter capacitor is composed of two capacitors connected in series and the low potential side of the capacitor located on the lower potential side of the two capacitors is grounded, the three terminals are electrically connected to the potential of the ground side of the capacitor located on the lower potential side.

10. A power conversion device for a railway vehicle as described in claim 3 or 4, characterized in that the second terminal section has three terminals for connecting each of the three common mode current return lines, and when the filter capacitor is composed of two capacitors connected in series and the low potential side of the capacitor located on the lower potential side of the two capacitors is grounded, at least one of the three terminals is electrically connected to the potential on the ground side of the capacitor located on the lower potential side, and the remaining terminal is electrically connected to a housing that houses the power conversion device.

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