Power converter for railway vehicles

Description

Technical Field

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

Background Art

[0002] Power conversion devices include switching elements such as IGBTs (Insulated Gate Bipolar Transistors) and MOSFETs (Metal - Oxide - Semiconductor Field - Effect Transistors). In recent years' power conversion devices, with the increase in the breakdown voltage and frequency of switching elements, the switching voltage has increased and the switching operation has become faster.

[0003] Generally, the switching operation in a power conversion device is known to cause a common - mode current that is a zero - phase current. Also, the switching operation in a power conversion device is known to cause a leakage current flowing to the ground through the parasitic capacitance between the AC power line connecting the power conversion device and the load and the ground, and the parasitic capacitance between the load and the ground. Further, the switching operation in a power conversion device is known to cause a leakage current flowing to peripheral devices other than the load or the ground through the parasitic capacitance between the AC power line and the housing containing the power conversion device. These leakage currents are distinguished from the zero - phase current as common - mode currents flowing in the grounding system.

[0004] As described above, the increase in the switching voltage and the speeding up of the switching operation increase the leakage current, and as a result, increase the radiated noise, so there is a problem of adversely affecting peripheral communication devices and the like.

[0005] Patent Document 1 discloses a technique for reducing leakage current by preparing a common-mode current return line, which is a single electrical wire connecting the grounding terminal of a power converter and the grounding terminal of a load, and passing this common-mode current return line through the same magnetic core together with three AC power lines. When using the technique of Patent Document 1, the impedance of the return loop of the grounding system becomes larger than the impedance of the return loop of the common-mode current return line, so that the leakage current flowing through the return loop of the grounding system can be reduced. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2001-086734 [Overview of the project] [Problems that the invention aims to solve]

[0007] The technology described in Patent Document 1 utilizes the fact that the magnetic flux from the common-mode current flowing through the AC power line and the common-mode current flowing through the common-mode current return line cancels each other out when they flow in opposite directions. The degree to which the magnetic flux cancels out increases as the AC power line and the common-mode current return line get closer together, i.e., the closer they are to each other. However, in the case of power conversion devices for railway vehicles, extremely large currents flow through the AC power line, so the thickness of the AC power line, i.e., the cross-sectional area, becomes large. For this reason, when applying the technology of Patent Document 1 to power conversion devices for railway vehicles, it becomes difficult to wire one common-mode current return line in an evenly close manner to three AC power lines. Consequently, the technology of Patent Document 1 has the problem that the area of ​​the return loop, which is the path through which the current traveling between the AC power line and the common-mode current return line flows, cannot be sufficiently reduced, and the effect of reducing radiated noise is insufficient.

[0008] This disclosure has been made in view of the above, and aims to provide a power converter for railway vehicles that can enhance the effect of reducing radiated noise caused by common-mode current. [Means for solving the problem]

[0009] To solve the above-mentioned problems and achieve the objective, the power converter for railway vehicles according to this disclosure is a power converter for railway vehicles for driving a propulsion motor mounted on a railway vehicle. The power converter for railway vehicles comprises a three-phase inverter that converts DC power into AC power for the propulsion motor, a filter capacitor that smooths the DC voltage applied to the three-phase inverter, three AC power lines which are electrical wiring that electrically connects the three-phase inverter and the propulsion motor, and three common-mode current return lines, each of which is arranged along each of the three AC power lines. [Effects of the Invention]

[0010] The power converter for railway vehicles described herein has the effect of enhancing the reduction of radiated noise caused by common-mode current. [Brief explanation of the drawing]

[0011] [Figure 1] This figure shows an example of the electrical system configuration of a railway vehicle system including a power converter according to Embodiment 1. [Figure 2] This figure shows an example of mounting a power converter according to Embodiment 1 onto a railway vehicle. [Figure 3] A view from below of a railway vehicle equipped with the power converter according to Embodiment 1. [Figure 4] A diagram illustrating the method of arranging AC power lines and common-mode current return lines in a power conversion device according to Embodiment 1. [Figure 5] Figure 1 illustrates variations in the arrangement method of AC power lines and common-mode current return lines in the power conversion device according to Embodiment 1. [Figure 6]Figure 2 illustrates variations in the arrangement method of AC power lines and common-mode current return lines in the power conversion device according to Embodiment 1. [Figure 7] Figure 3 illustrates variations in the arrangement method of AC power lines and common-mode current return lines in the power conversion device according to Embodiment 1. [Figure 8] Figure 9 shows three electrical wiring models corresponding to each of the three electromagnetic field analysis results. [Figure 9] Figure 8 shows the results of electromagnetic field analysis performed on three electrical wiring models. [Figure 10] This figure shows an example of mounting a power converter according to Embodiment 2 onto a railway vehicle. [Figure 11] This figure shows the results of electromagnetic field analysis performed on the connection configuration of the power converter according to Embodiment 2. [Figure 12] Figure 1 shows an example of variations in the input circuit section. [Figure 13] Figure 12 shows an example of a filter capacitor configuration different from that of Figure 12. [Figure 14] Figure 13 shows a different example of grounding a filter capacitor. [Modes for carrying out the invention]

[0012] The power conversion device for railway vehicles according to the embodiment of this disclosure (hereinafter referred to as "power conversion device" as appropriate) will be described in detail below with reference to the attached drawings. Note that, for ease of understanding, the scale of each component in the attached drawings may differ from the actual scale. The same applies between drawings.

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

[0014] The input circuit section 2 is configured to include at least a circuit breaker and a filter reactor. One end of the input circuit section 2 is connected to the overhead wire 10 via the current collector 11. The other end of the input circuit section 2 is electrically connected to the rail 12 that imparts a ground potential, which is a ground potential, via the wheel 13. The DC power or AC power supplied from the overhead wire 10 is input to one end of the input circuit section 2 via the current collector 11. The DC voltage generated by the DC power at the output end of the input circuit section 2 is applied to the three-phase inverter 4. The filter capacitor 3 smoothes the DC voltage so that the ripple of the DC voltage applied to the three-phase inverter becomes small. The three-phase inverter 4 converts the DC power supplied via the input circuit section 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 connects the three-phase inverter 4 and the propulsion motor 15. One of the three AC power lines 5 is the U-phase electrical wiring, one of the remaining two is the V-phase electrical wiring, and the remaining one is the W-phase electrical wiring. Further, three common-mode current reflux lines 6 are drawn from the frame of the propulsion motor 15, and the three common-mode current reflux lines 6 are connected to a portion having the ground potential of the power conversion device 50. The common-mode current reflux line 6 is electrical wiring that electrically connects between the ground potential of the power conversion device 50 and the ground potential of the propulsion motor 15. In the propulsion motor 15, it is desirable that the portion where the common-mode circulation line 6 is drawn is near the portion where the AC power line 5 is drawn. Also, it is desirable that the grounding point of the common-mode circulation line 6 is near the portion where the filter capacitor 3 is grounded among several ground potentials. In the power conversion device 50 according to the first embodiment, it is assumed that the low-potential side DC bus 9 is grounded or the ground potential is applied to the DC bus 9.

[0016] The three-phase inverter 4 includes a plurality of switching elements 4a connected in a three-phase bridge. The switching element 4a has a freewheeling diode connected in antiparallel. The switching element 4a performs a switching operation according to a gate signal output from a drive circuit (not shown). By the switching operation of the switching element 4a, the current flowing through the switching element 4a is intermittently controlled. Thereby, the DC power supplied from the input circuit section 2 is converted into AC power to the propulsion motor 15. The propulsion motor 15 is driven by the AC power supplied from the three-phase inverter 4, and imparts a propulsion force to a train formed by one or more railway vehicles (not shown). The three-phase inverter 4 drives the propulsion motor 15 by converting the DC power supplied via the input circuit section 2 into AC power to the propulsion motor 15. In FIG. 1, the input circuit section 2 and the three-phase inverter 4 are shown as individual components, but these may be housed in the same housing.

[0017] Figure 2 shows an example of mounting the power converter 50 according to Embodiment 1 onto a railway vehicle. In Figure 2, components that are the same as or equivalent to those in Figure 1 are denoted by the same reference numerals. Figure 3 is a view from below of the railway vehicle on which the power converter 50 according to Embodiment 1 is mounted.

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

[0019] Each wheel 13 has an axle 22, and an earth brush 23 is provided on the axle 22. The earth brush 23 is electrically connected to the DC bus 9 by cable 28 and to the vehicle body 20 by cable 29. The earth brush 23 is also electrically connected to the rail 12 via the wheel 13. Furthermore, the earth brush 23 is electrically connected to the frame of the propulsion motor 15 by a voltage equalizing wire 30. Through these connections, the DC bus 9, vehicle body 20, earth brush 23, the frame of the propulsion motor 15, and the housing 24 housing the power converter 50 are all connected to the earth potential.

[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 section 31 for connecting the AC power line 5 and the common-mode current return line 6. The first terminal section 31 is electrically insulated from the motor housing (not shown).

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

[0022] One end of each of the three AC power lines 5 is connected to a first terminal section 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 section 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 section 31, and the other end of each of the three common-mode current return lines 6 is connected to a second terminal section 32 provided on the housing 24.

[0023] Furthermore, as shown in Figure 2, communication equipment 25 is located on the track where the rails 12 are laid, which facilitates communication between the ground and the railway vehicle. When 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. There are two types of current flow in the AC power line 5: normal mode current, in which the currents flowing through each of the three phases have a phase difference of 120 degrees, and common mode current, in which the same phase current flows through each of the three phases. Of these currents, the common mode current has a greater impact on the generation of radiated noise 26.

[0024] Therefore, in Embodiment 1, the three AC power lines 5 and the three common-mode current return lines 6 are covered with a metal duct 21 with a rectangular cross-section so as to reduce the radiated noise 26 directed toward the communication equipment 25. However, as shown in Figure 3, there are other devices 36 besides the power converter 50 housing 24 and the propulsion motor 15 in the lower part of the vehicle body 20. Due to the presence of the other devices 36, the AC power lines 5 and the common-mode current return lines 6 are forced to be arranged in a meandering manner as shown in Figure 3. For this reason, the metal duct 21 is made to cover the AC power lines 5 and the common-mode current return lines 6 in a portion of the section in which they are installed.

[0025] The cross-section of the metal duct 21 does not necessarily have to be square-shaped; it may also be a metal duct with a U-shaped or L-shaped cross-section. Needless to say, when using a metal duct with a U-shaped or L-shaped cross-section, the opening must not face the direction of the railway tracks.

[0026] In the power converter 50 according to Embodiment 1, the metal duct 21 is not necessarily an essential component. If the three common-mode circulating lines 6 are properly arranged and the radiated noise 26 is below a specified value, the metal duct 21 may be omitted.

[0027] Next, the method for arranging the three AC power lines 5 and the three common-mode current return lines 6 will be described. Figure 4 is a diagram illustrating the method for arranging the AC power lines 5 and the common-mode current return lines 6 in the power converter 50 according to Embodiment 1.

[0028] First, each of the three common-mode current return lines 6 is arranged to run alongside each of the three AC power lines 5. This arrangement allows each of the common-mode current return lines 6 to be in close contact with each of the AC power lines 5.

[0029] Furthermore, as shown in Figure 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 laid along 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 contact between the AC power line 5 and the common-mode current return line 6 in the twisted sections.

[0030] To create the electrical wiring shown in Figure 4, for example, the following procedure can be used. First, one of the three common-mode current return lines 6 is placed alongside each of the three AC power lines 5. Next, the centers of each end of the three AC power lines 5 are positioned approximately 120 degrees from the overall center, and similarly, the centers of each end of the three common-mode current return lines 6 are positioned approximately 120 degrees from the overall center. Then, the sets of electrical wiring consisting of one AC power line 5 and one common-mode current return line 6 are twisted together with the other two sets of electrical wiring. By following this procedure, the electrical wiring shown in Figure 4 can be constructed and installed.

[0031] Since the current flowing through the common-mode current return wire 6 is smaller than the current flowing through the AC power line 5, the diameter of the common-mode current return wire 6 can be made smaller than the diameter of the AC power line 5. For this reason, each of the three common-mode current return wires 6 can be easily placed 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 1 to 3, the diameter of the common-mode current return wire 6 can be reduced to 1 / √3 of the conventional diameter. As a result, the diameter of the common-mode current return wire 6 can be reduced, which increases the degree of contact between the AC power line 5 and the common-mode current return wire 6, and further facilitates the twisting of the AC power line 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 circulating wire 6 can be most easily explained by considering that a DC current flows through the common-mode circulating wire 6. The resistance of the common-mode circulating wire 6 is proportional to the cross-sectional area of ​​the common-mode circulating wire 6, so by using three wires, the cross-sectional area of ​​each wire can be reduced to 1 / 3, which translates to 1 / √3 in terms of diameter.

[0033] The common-mode current that causes radiated noise is an AC current with a frequency of approximately 100 kHz to 3 MHz. As the frequency increases, the AC resistance considering the thickness of the skin can be further reduced. Therefore, by using three common-mode circulating wires 6, the impedance can be reduced compared to using one wire.

[0034] Next, variations in the arrangement of the AC power line 5 and the common-mode current return line 6 will be explained with reference to Figures 5 to 7. Figures 5 to 7 are the first, second, and third figures, respectively, illustrating variations in the arrangement method of the AC power line 5 and the common-mode current return line 6 in the power converter 50 according to Embodiment 1.

[0035] Since the lower part of the vehicle body 20 is an environment where moisture tends to accumulate, a water drainage section 34 is provided near the first terminal section 31 of the propulsion motor 15, as shown in Figures 5 to 7. The first terminal section 31 has terminals 31a to 31f, to which terminals 31a to 31c are connected to each of the three AC power lines 5, and to which terminals 31d to 31f are connected to each of the three common-mode current return lines 6. The three sets of AC power lines 5 and common-mode current return lines 6 are arranged in the water drainage section 34 so as to bend downwards. Furthermore, if the three sets of AC power lines 5 and common-mode current return lines 6 are twisted together in the water drainage section 34, moisture will tend to accumulate, so they are arranged without twisting together as shown in Figure 5.

[0036] In addition, in the drainage section 34 of Figure 5, as shown in Figure 6, one AC power line 5 and one common-mode current return line 6, which is arranged along the AC power line 5, may be twisted together. If they are arranged in this way, the degree of contact between the AC power line 5 and the common-mode current return line 6 in the drainage section 34 can be increased. Also, since the diameter of the common-mode current return line 6 is smaller than the diameter of the AC power line 5, a gap can be secured between the AC power lines 5 even when they are twisted together. In this case, it is desirable to place terminals 31a and 31d adjacent to each other, terminals 31b and 31e adjacent to each other, and terminals 31c and 31f adjacent to each other.

[0037] Furthermore, in the twisted wire section 35 of Figure 6, as shown in Figure 7, one AC power line 5 and one common-mode current return wire 6 arranged along the AC power line 5 may be twisted together. If they are arranged in this way, it is possible to increase the degree of contact between the AC power line 5 and the common-mode current return wire 6 in the twisted wire section 35 as well.

[0038] Next, the effects of the power conversion device 50 according to Embodiment 1 will be explained with reference to Figures 8 and 9. Figure 8 is a diagram showing three electrical wiring models corresponding to each of the three electromagnetic field analysis results in Figure 9. Figure 9 is a diagram showing the electromagnetic field analysis results performed on the three electrical wiring models shown in Figure 8.

[0039] The lower part of Figure 8 shows the electrical wiring model of Embodiment 1, which corresponds to Figure 4. The upper and middle parts of Figure 8 show the electrical wiring models of Comparative Example 1 and Comparative Example 2, respectively. Comparative Example 1 is an electrical wiring model in which four electrical wires, each 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 more common-mode current return line 6 is twisted around the three twisted AC power lines 5. The diameter width of the common-mode current return line 6 in Embodiment 1 is assumed to be 1 / √3 of the diameter width of the common-mode current return line 6 in Comparative Examples 1 and 2.

[0040] Furthermore, as shown in Figure 8, the total wiring length of the three electrical wiring models is 5000 mm, and the pitch is 1000 mm. The total diameter width of the electrical wiring models in Comparative Example 1 and Embodiment 1 is 200 mm. In Comparative Example 2, the total 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 at a position 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, with an output port 42 provided at its output end. In addition, at the right end of each, three capacitors 43 with a capacitance of 30 nF, corresponding 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] In Figure 9, the horizontal axis represents the frequency of the signal input to the input port 41, and the vertical axis represents the transfer coefficient S21 from the input port 41 to the output port 42. In Figure 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] In communication equipment 25 placed on the transmission line, electromagnetic interference is a particular problem in the communication frequency band of 100kHz to 3MHz. In this communication frequency band, the analysis results in Figure 9 show that, with the exception of some resonant frequencies, the electrical wiring model of Embodiment 1 has the smallest transfer coefficient S21.

[0043] Comparing Comparative Examples 1 and 2, Comparative Example 1 has a smaller transfer coefficient S21 than Comparative Example 2. One possible reason for this is that Comparative Example 1 has a shorter overall diameter than Comparative Example 2, resulting in a smaller recirculation loop area. Reducing the recirculation loop area can reduce radiated noise for the same current value.

[0044] Furthermore, in Embodiment 1, the number of common-mode current return lines 6 is increased to three, thereby improving the tightness of the electrical wiring set consisting of one AC power line 5 and one common-mode current return line 6. For this reason, even though the total diameter width is the same in Comparative Example 1 and Embodiment 1, Embodiment 1 allows for a smaller return loop area, and therefore the transmission coefficient S21 is considered to be smaller.

[0045] As described above, the power conversion device for railway vehicles according to Embodiment 1 comprises a three-phase inverter that converts DC power into AC power for a propulsion 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 comprises three AC power lines, which are electrical wiring that electrically connects the three-phase inverter and the propulsion motor, and three common-mode current return lines, each of which is arranged along one of the three AC power lines. With a power conversion device configured in this way, the AC power lines and the common-mode current return lines can be arranged in close proximity. This makes it possible to reduce the area of ​​the return loop of current flowing between one AC power line and one common-mode current return line, thereby increasing the effect of reducing radiated noise caused by common-mode current.

[0046] In the power converter according to Embodiment 1, the three common-mode current return lines may be configured to connect to a first terminal provided on the propulsion motor and a second terminal provided on the housing housing the power converter. The three AC power lines and the three common-mode current return lines may be arranged in a twisted manner with the other two sets of electrical wiring in at least a portion of the section between the first and second terminals, where each set consists of one AC power line and one common-mode current return line laid along that AC power line. By twisting the three sets of electrical wiring together, the area of ​​the return loop of current flowing between the three AC power lines can be reduced, thereby further enhancing the effect of reducing radiated noise caused by common-mode current.

[0047] Furthermore, 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. By arranging them in this way, the degree of contact between the AC power line and the common-mode current return line can be increased, thereby further enhancing the effect of reducing radiated noise caused by common-mode current.

[0048] Furthermore, in the power conversion device according to Embodiment 1, the second terminal section may have three terminals for connecting each of the three common-mode current return lines. 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 reliable reduction in radiated noise.

[0049] Embodiment 2. The electromagnetic field analysis results described in Embodiment 1 assume that a potential fluctuation in the common-mode voltage due to the switching operation of the switching element 4a occurs relative to the ground potential. Here, the common-mode voltage is synonymous with the potential difference between the neutral point potential of the propulsion motor 15 and the ground potential. In the propulsion motor 15, if the U-phase voltage is represented as "Vu", the V-phase voltage as "Vv", and the W-phase voltage as "Vw", the common-mode voltage is expressed as (Vu + Vv + Vw) / 3.

[0050] On the other hand, if the switching operation of the switching element 4a causes a potential fluctuation in the common-mode voltage other than the ground potential, the leakage current flowing in the return loop of the grounding system will also flow through the stray capacitance between the part other than the ground potential and the vehicle body 20. The power converter 50 according to Embodiment 2 takes this into consideration and connects some of the three common-mode current return lines 6 to different locations than those in Embodiment 1.

[0051] Figure 10 shows an example of mounting the power converter 50 according to Embodiment 2 on a railway vehicle. The differences between the configuration in Figure 10 and the configuration in Figure 2 are the configuration of the second terminal section 32 and the connection destinations of the other ends of the three common-mode current return lines 6. Otherwise, it is the same as or equivalent to Embodiment 1 shown in Figure 2. In the following, we will omit content that overlaps with Embodiment 1 as appropriate and focus on the differences from Embodiment 1.

[0052] A part other than the ground potential where common-mode voltage potential fluctuations can occur is the housing 24 of the three-phase inverter 4. In the power converter 50 according to Embodiment 2, considering that common-mode voltage potential fluctuations occur with respect to the housing 24 of the three-phase inverter 4, one of the three common-mode current return lines 6 is connected to the housing 24. The other two of the three common-mode current return lines 6 are connected to terminals 32a and 32b of the second terminal section 32. Similar to Embodiment 1, terminals 32a and 32b are connected to the DC bus 9. Note that Figure 10 illustrates a configuration in which one of the three common-mode current return lines 6 is connected to the housing 24, but the device is not limited to this configuration. The power converter 50 according to Embodiment 2 may be configured such that two of the three common-mode current return lines 6 are connected to the housing 24.

[0053] Figure 11 shows the results of an electromagnetic field analysis performed on the connection configuration of the power converter 50 according to Embodiment 2. The electrical wiring model analyzed is the same as the electrical wiring model shown in Figure 4. In Figure 11, the analysis results for the connection configuration of Embodiment 2 shown in Figure 10 are shown by solid lines, and the analysis results for the connection configuration of Embodiment 1 shown in Figure 2 are shown by dashed lines. Similar to Figure 9, the horizontal axis of Figure 11 shows the frequency of the signal input to the input port 41, and the vertical axis shows the transfer coefficient S21 from the input port 41 to the output port 42. In the electromagnetic field analysis in Figure 11, a potential fluctuation of the common mode voltage is generated on the housing 24 of the three-phase inverter 4.

[0054] According to the analysis results in Figure 11, in the communication frequency band of 100 kHz to 3 MHz where electromagnetic interference is a problem, the connection configuration of Embodiment 2 shown in Figure 10 has a smaller transfer coefficient S21 than the connection configuration of Embodiment 1 shown in Figure 2, with the exception of some frequencies. The reason for this can be explained as follows.

[0055] When a potential fluctuation in the common-mode voltage occurs with respect to the housing 24 of the three-phase inverter 4, in the configuration of Embodiment 1 where the common-mode current return line 6 is not connected to the housing 24, a common-mode current flows through the AC power line 5, the stray capacitance of the propulsion motor 15, the equalizing line 30 connecting the housing of the propulsion motor 15 and the earth brush 23, the cable 29 connecting the earth brush 23 and the vehicle body 20, the bolts connecting the vehicle body 20 and 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 between the AC power line 5 and the common-mode current return line 6.

[0056] On the other hand, as mentioned above, in Embodiment 2, 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 could flow through the aforementioned path will mainly flow through the common-mode current return lines 6 connected to the housing 24. This is because the impedance of the return loop is smaller in the common-mode current return lines 6 than in the aforementioned path. Consequently, it is considered that the transfer coefficient S21 is smaller in the connection configuration of Embodiment 2 shown in Figure 10 than in the connection configuration of Embodiment 1 shown in Figure 2.

[0057] In Embodiment 2, a configuration in which one or two of the three common-mode current return lines 6 are connected to the housing 24 of the three-phase inverter 4 is illustrated, but the invention is not limited to this example. One or two of the three common-mode current return lines 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 lines 6 may be connected to a housing located at the bottom of the vehicle body 20 that houses equipment other than the three-phase inverter 4, and is a location where fluctuations in the common-mode voltage are likely to occur.

[0058] As described above, in the power converter 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 to which the other common-mode current return lines are connected. This configuration makes it possible to reduce radiated noise caused by common-mode current even when the potential fluctuation of the common-mode voltage due to the switching operation of the switching element occurs relative to a potential other than ground potential.

[0059] Embodiment 3. Although Embodiments 1 and 2 do not specifically mention the electrification system of the railway vehicle, the power converter 50 according to Embodiments 1 and 2 is applicable to both DC and AC electrification systems. Embodiment 3 describes an example of a configuration when applied to an AC electrified railway vehicle.

[0060] Figure 12 shows an example of a variation of the input circuit section 2 shown in Figure 1. Figure 12 shows the input circuit section 60 as an example when the overhead line 10 is an AC overhead line. The input circuit section 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 terminal of the converter 62. If the low-potential side of the filter capacitor 3 is grounded as in Figure 1, then, as in Figure 2, each terminal of the second terminal section 32 that connects the three common-mode current return lines 6 should be electrically connected to the potential of the ground side of the filter capacitor 3.

[0061] Figure 13 shows an example of a filter capacitor 3 configuration different from that shown in Figure 12. Figure 14 shows an example of grounding the filter capacitor 3 different from that shown in Figure 13. Figures 13 and 14 show a configuration consisting of filter capacitors 3A and 3B, where two filter capacitors 3 are connected in series. In Figure 13, the midpoint 3C, which is the connection point of filter capacitors 3A and 3B, is grounded, while in Figure 14, the midpoint 3C of filter capacitors 3A and 3B is not grounded, and the low-potential side of filter capacitor 3 is grounded. In the case of Figure 13, each terminal of the second terminal section 32, which connects the three common-mode current return lines 6, should be electrically connected to the midpoint 3C, which is the ground potential of the filter capacitor 3. In the case of Figure 14, similar to Figure 12, each terminal of the second terminal section 32, which connects the three common-mode current return lines 6, should be electrically connected to the ground potential of the filter capacitor 3. The same effects as in Embodiment 1 can be obtained with any of the configurations shown in Figures 12 to 14.

[0062] Furthermore, in the configurations shown in Figures 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 accommodates the converter 62. The same effects as in Embodiment 2 can be obtained with any of these configurations.

[0063] The configurations shown in the above embodiments are merely examples, and it is possible to combine them with other known technologies, combine different embodiments, and omit or modify parts of the configuration without departing from the gist of the invention. The various aspects of this disclosure are summarized below as an appendix. [Note 1] A power converter for railway vehicles, for driving a propulsion motor mounted on a railway vehicle, A three-phase inverter that converts DC power to AC power for the propulsion motor, A filter capacitor that smooths the DC voltage applied to the three-phase inverter, Three AC power lines, which are electrical wiring that electrically connects the three-phase inverter and the propulsion motor, Three common-mode current return lines are arranged, one for each of the three AC power lines, A power conversion device for railway vehicles, characterized by being equipped with the following features. [Note 2] One or two of the three common-mode current return lines are electrically connected to a potential different from the potential to which the other common-mode current return lines are connected. A power conversion device for railway vehicles as described in Appendix 1, characterized by the features described herein. [Note 3] The three common-mode current return lines are connected to a first terminal provided on the propulsion motor and a second terminal provided on the housing that houses the power converter. In at least a portion of the 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 arranged twisted together with two other sets of electrical wiring. A power conversion device for railway vehicles as described in Appendix 1 or 2, characterized by the features described herein. [Note 4] One of the aforementioned AC power lines and one of the aforementioned common-mode current return lines, which is arranged along the aforementioned AC power line, are arranged twisted together. A power conversion device for railway vehicles as described in Appendix 3, characterized by the features described herein. [Note 5] The second terminal section has three terminals for connecting each of the three common-mode current return lines, Each of the three terminals is electrically connected to the lower potential of the filter capacitor. A power conversion device for railway vehicles as described in Appendix 3 or 4, characterized by the features described herein. [Note 6] The second terminal section has three terminals for connecting each of the three common-mode current return lines, At least one of the three terminals is electrically connected to the low-potential side of the filter capacitor, and the remaining terminals are electrically connected to the housing that houses the power converter. A power conversion device for railway vehicles as described in Appendix 3 or 4, characterized by the features described herein. [Note 7] The second terminal section has three terminals for connecting each of the three common-mode current return lines, When the filter capacitor is composed of two capacitors connected in series, and the midpoint where the two capacitors are connected is grounded, The three terminals are electrically connected to the potential of the midpoint of the filter capacitor. A power conversion device for railway vehicles as described in Appendix 3 or 4, characterized by the features described herein. [Note 8] The second terminal section has three terminals for connecting each of the three common-mode current return lines, When the filter capacitor is composed of two capacitors connected in series, and the midpoint where the two capacitors are connected 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 terminals are electrically connected to the housing that houses the power converter. A power conversion device for railway vehicles as described in Appendix 3 or 4, characterized by the features described herein. [Note 9] The second terminal section has three terminals for connecting each of the three common-mode current return lines, When the filter capacitor is composed of two capacitors connected in series, and the lower 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 ground potential of the capacitor located on the low-potential side. A power conversion device for railway vehicles as described in Appendix 3 or 4, characterized by the features described herein. [Note 10] The second terminal section has three terminals for connecting each of the three common-mode current return lines, When the filter capacitor is composed of two capacitors connected in series, and the lower 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 ground potential of the capacitor located on the low-potential side, and the remaining terminals are electrically connected to the housing that houses the power converter. A power conversion device for railway vehicles as described in Appendix 3 or 4, characterized by the features described herein. [Explanation of symbols]

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

Claims

1. A power converter for railway vehicles, for driving a propulsion motor mounted on a railway vehicle, A three-phase inverter that converts DC power to AC power for the propulsion motor, A filter capacitor that smooths the DC voltage applied to the three-phase inverter, Three AC power lines, which are electrical wiring that electrically connects the three-phase inverter and the propulsion motor, Each comprises three common-mode current return lines, one of which is arranged along each of the three AC power lines, In at least a portion of the section where the three common-mode current return lines are installed, a set of electrical wiring consisting of one AC power line and one common-mode current return line installed along that AC power line is arranged twisted together with the other two sets of electrical wiring. A power conversion device for railway vehicles characterized by the following features.

2. One or two of the three common-mode current return lines are electrically connected to a potential different from the potential to which the other common-mode current return lines are connected. The power conversion device for railway vehicles according to feature 1.

3. One of the aforementioned AC power lines and one of the aforementioned common-mode current return lines, which is arranged along the aforementioned AC power line, are arranged twisted together. The power conversion device for railway vehicles according to feature 1.

4. The three common-mode current return lines are connected to a first terminal provided on the propulsion motor and a second terminal provided on the housing housing the power converter, The second terminal section has three terminals for connecting each of the three common-mode current return lines, Each of the three terminals is electrically connected to the lower potential of the filter capacitor. A power conversion device for railway vehicles according to claim 1 or 3.

5. The three common-mode current return lines are connected to a first terminal provided on the propulsion motor, and at least one or two of the three common-mode current return lines are connected to a second terminal provided on the housing housing the power converter. The second terminal section has three terminals for connecting each of the three common-mode current return lines, At least one of the three terminals is electrically connected to the low-potential side of the filter capacitor, and the remaining terminals are electrically connected to the housing that houses the power converter. A power conversion device for railway vehicles according to any one of claims 1 to 3.

6. The three common-mode current return lines are connected to a first terminal provided on the propulsion motor and a second terminal provided on the housing housing the power converter, The second terminal section has three terminals for connecting each of the three common-mode current return lines, When the filter capacitor is composed of two capacitors connected in series, and the midpoint where the two capacitors are connected is grounded, The three terminals are electrically connected to the potential of the midpoint of the filter capacitor. A power conversion device for railway vehicles according to claim 1 or 3.

7. The three common-mode current return lines are connected to a first terminal provided on the propulsion motor, and at least one or two of the three common-mode current return lines are connected to a second terminal provided on the housing housing the power converter. The second terminal section has three terminals for connecting each of the three common-mode current return lines, When the filter capacitor is composed of two capacitors connected in series, and the midpoint where the two capacitors are connected 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 terminals are electrically connected to the housing that houses the power converter. A power conversion device for railway vehicles according to any one of claims 1 to 3.

8. The three common-mode current return lines are connected to a first terminal provided on the propulsion motor and a second terminal provided on the housing housing the power converter, The second terminal section has three terminals for connecting each of the three common-mode current return lines, When the filter capacitor is composed of two capacitors connected in series, and the lower 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 ground potential of the capacitor located on the low-potential side. A power conversion device for railway vehicles according to claim 1 or 3.

9. The three common-mode current return lines are connected to a first terminal provided on the propulsion motor, and at least one or two of the three common-mode current return lines are connected to a second terminal provided on the housing housing the power converter. The second terminal section has three terminals for connecting each of the three common-mode current return lines, When the filter capacitor is composed of two capacitors connected in series, and the lower 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 ground potential of the capacitor located on the low-potential side, and the remaining terminals are electrically connected to the housing that houses the power converter. A power conversion device for railway vehicles according to any one of claims 1 to 3.

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