BUS BAR MODULE AND POWER CONVERSION SYSTEM

A bus bar module is disposed over a plurality of housings to distribute DC power to smoothing capacitors and power conversion units. The bus bar module includes a first conductor and a second conductor. The first conductor is applied to either a first electrode or a second electrode of direct current. The second conductor is connected in parallel to the first conductor. The first conductor includes a first flat plate portion formed to have a first thickness in a cross section perpendicular to an extension direction. The second conductor includes a second flat plate portion having a cross section bent at a predetermined angle in a cross section perpendicular to the extension direction and formed with a second thickness thinner than the first thickness.

TECHNICAL FIELD

The present invention relates to a bus bar module and a power conversion system.

BACKGROUND ART

A power conversion system in which a plurality of power conversion units are divided and disposed in a plurality of housings and are connected by a common DC bus bar is known. A lower limit of a cross-sectional area S of a DC bus bar is determined by an output capacity of the power conversion system, and the like. Reducing the cross-sectional area S of the DC bus bar or increasing a length of the DC bus bar may increase a wiring inductance L and may cause resonance in the circuit. Therefore, it was not easy to reduce the total amount of conductors in the DC bus bar.

CITATION LIST

Patent Document

SUMMARY OF INVENTION

Technical Problem

A problem to be solved by the present invention is to provide a bus bar module and a power conversion system capable of reducing the total amount of conductors in a DC bus bar.

Solution to Problem

A bus bar module according to one aspect of an embodiment is disposed over a plurality of housings to distribute DC power to smoothing capacitors and power conversion units. The bus bar module includes a first conductor and a second conductor. The first conductor is applied to either a first electrode or a second electrode of direct current. The second conductor is connected in parallel to the first conductor. The first conductor includes a first flat plate portion formed to have a first thickness in a cross section perpendicular to an extension direction. The second conductor includes a second flat plate portion having a cross section bent at a predetermined angle in a cross section perpendicular to the extension direction and formed with a second thickness thinner than the first thickness.

DESCRIPTION OF EMBODIMENTS

Hereinafter, a bus bar module and a power conversion system according to embodiments will be described with reference to the drawings. The drawings are schematic or conceptual, and the distribution of functions of each part is not necessarily the same as the actual one.

In the specification and drawings of the present application, the same reference numerals are given to components having the same or similar functions. Duplicate descriptions of the configurations may be omitted.

In the embodiments, the term “connection” includes electrical connection. The terms “based on XX” mean “based on at least XX” and may include “based on other elements in addition to XX.” The terms “based on XX” are not limited to the case in which XX is used directly, but can also include the case based on that XX is calculated or processed. The terms “XX or YY” are not limited to either one of XX and YY, and may include both of XX and YY. This is also the case in which there are three or more selective elements. The “XX” and “YY” are arbitrary elements (for example, arbitrary information).

Also, first, a +X direction, a −X direction, a +Y direction, a −Y direction, a +Z direction, and a −Z direction are defined. The +X direction, the −X direction, the +Y direction, and the −Y direction are directions along a floor surface on which a power conversion system is placed. The +X direction is, for example, a direction along which devices related to the power conversion system are arranged. The −X direction is a direction opposite to the +X direction. When the +X direction and the −X direction are not distinguished, they are simply referred to as an “X direction.” The +Y direction and −Y direction are directions that intersect (for example, substantially perpendicular to) the X direction and may be referred to as a depth direction of each device related to the power conversion system. The +Y direction and the −Y direction are opposite to each other. When the +Y direction and the −Y direction are not distinguished, they are simply referred to as a “Y direction.” When each device related to the power conversion system is seen in the +Y direction, it is called the front, and when it is seen in the −Y direction, it is called the rear. The +Z direction and −Z direction are directions that intersect (for example, substantially perpendicular to) the X direction and the Y direction and are, for example, a vertical direction. The +Z direction is an upward direction. The −Z direction is a direction opposite to the +Z direction. When the +Z direction and the −Z direction are not distinguished, they are simply referred to as a “Z direction.”

First Embodiment

FIG.1is a schematic configuration diagram of a power conversion system1according to a first embodiment.

The power conversion system1includes, for example, a transformer group2(FIG.2), a forward converter group3, an inverse converter group5, and a controller40. The power conversion system1steps down three-phase AC power supplied from an AC power supply PS (FIG.2), forward-converts the stepped-down AC power to produce DC power, inversely converts the DC power to produce three-phase AC power, and supplies the three-phase AC power to an electric motor8(FIG.2).

The power conversion system1generates U-phase, V-phase, and W-phase AC power to be supplied to the electric motor8using separate transformers of the transformer group2, forward converters of the forward converter group3, and inverters of the inverse converter group5, respectively.

For example, the forward converter group3includes forward converters3U,3V, and3W.

The inverse converter group5includes a set of inverters5U and5X, a set of inverters5V and5Y, and a set of inverters5W and5Z.

The power conversion system1generates U-phase AC power to be supplied to the electric motor8using a transformer20U of the transformer group2, the forward converter3U, and the set of the inverters5U and5X. Similarly, the power conversion system1generates V-phase AC power to be supplied to the electric motor8using a transformer20V of the transformer group2, the forward converter3V, and the set of inverters5V and5Y. The power conversion system1generates W-phase AC power to be supplied to the electric motor8using a transformer20W of the transformer group2, the forward converter3W, and the set of the inverters5W and5Z.

The transformers20U,20V, and20W may be disposed on the AC input panels3UI,3VI, and3WI shown inFIG.1, respectively.

For example, an AC input panel3UI, a forward converter3U, an inverter5X, and an inverter5U are arranged in the stated order in the +X direction. An AC input panel3VI, a forward converter3V, an inverter5Y, and an inverter5V are arranged in the stated order in the +X direction. An AC input panel3WI, a forward converter3W, an inverter5Z, and an inverter5W are arranged in the stated order in the +X direction. The controller40is arranged in the −X direction with respect to the AC input panel3UI, and an output panel5OUT is arranged in the +X direction with respect to the inverter5W. The output panel5OUT is connected to load power lines58U,58V, and58W (FIG.2), and is connected to the electric motor8via the load power lines58U,58V, and58W (FIG.2).

DC bus bars are respectively provided between the AC input panel3UI and the inverter5U, between the AC input panel3VI and the inverter5V, and between the AC input panel3WI and the inverter5W. Neutral lines65U,65V, and65W which will be described later are examples of the DC bus bars. Positive electrode bus bars60U,60V, and60W and negative electrode bus bars70U,70V, and70W which are not shown are also examples of the DC bus bars. In the following description, the neutral line65U, the positive electrode bus bar60U, and the negative electrode bus bar70U may be collectively called a DC bus bar.

FIG.2is a configuration diagram of the power conversion system1according to the first embodiment.

FIG.2shows an AC power supply PS and the electric motor8in addition to the power conversion system1.

For example, the AC power supply PS is a commercial power grid, a generator, or the like and supplies three-phase AC power to the power conversion system1. The electric motor8is, for example, an AC variable speed electric motor such as an induction motor. The electric motor8is driven by AC power supplied from the power conversion system1and outputs a rotational driving force to an output shaft (not shown).

Next, each part of the power conversion system1will be described in order.

The transformer group2includes the transformers20U,20V, and20W, for example. Each of the transformers20U,20V, and20W is a three-winding transformer with a different connection system on the secondary side. Since each of the transformers20U,20V, and20W has the same configuration, the transformer20U will be described below as a representative.

The transformer20U includes, for example, a primary winding22U, a secondary winding24UP, and a tertiary winding24UN. The transformer20U receives supply of three-phase AC power from the AC power supply PS at the primary winding22U, transforms the received three-phase AC power, and outputs three-phase AC power transformed from the secondary winding24UP and the tertiary winding24UN. The three-phase AC power output from the secondary winding24UP and the tertiary winding24UN is supplied to the forward converter3U via transformer output lines25UPRST and25UNRST. The transformer output lines25UPRST and25UNRST are shown in a single line diagram. Each R-phase, S-phase, and T-phase current flows through the transformer output line25UPRST as a line current. The transformer20V and the transformer20W are also configured in the same manner as the transformer20U. As for the transformer20V and the transformer20W, the description of the transformer20U is incorporated herein by replacing U in the reference numerals of the components with each of V and W.

Since each of the forward converters3U,3V, and3W of the forward converter group3has the same configuration, the forward converter3U will be described below as a representative.

The forward converter3U includes, for example, a rectifier32UP and a rectifier32UN.

Each of the rectifiers32UP and32UN includes a three-phase full-bridge diode rectifier circuit. The AC side of the rectifier32UP is connected to the secondary winding24UP via the transformer output line25UPRST. The AC side of the rectifier32UN is connected to the tertiary winding24UN via the transformer output line25UNRST. The load sides of the rectifiers32UP and32UN are connected in series with each other. DC power rectified by the rectifiers32UP and32UN connected in series with each other is output from a rectifier positive electrode terminal33UP and a rectifier negative electrode terminal33UN.

One end of the positive electrode bus bar60U is connected to the rectifier positive electrode terminal33UP. A positive electrode input terminal52U of the inverter5U and a positive electrode input terminal52X of the inverter5X are connected to an extension destination of the positive electrode bus bar60U. The one end of the positive electrode bus bar60U does not necessarily have to be a structural end portion of the positive electrode bus bar60U.

One end of the negative electrode bus bar70U is connected to the rectifier negative electrode terminal33UN. A negative electrode input terminal54U of the inverter5U and a negative electrode input terminal54X of the inverter5X are connected to an extension destination of the negative electrode bus bar70U. The one end of the negative electrode bus bar70U does not necessarily have to be a structural end portion of the negative electrode bus bar70U.

Since the rectifiers32UP and32UN are supplied with AC power having different potentials from the secondary winding24UP and the tertiary winding24UN of the transformer20U, each of rectifiers32UP and32UN outputs a total value (referred to as a total voltage) of an output voltage of the rectifier32UP and an output voltage of the rectifier32UN from the rectifier positive electrode terminal33UP and rectifier negative electrode terminal33UN by connecting the respective outputs of the rectifiers32UP and32UN in series. The total voltage is smoothed by a capacitor provided in the subsequent stage.

Thus, the forward converter3U supplies DC power to a capacitor and an inverter (a power converter) provided in the subsequent stage.

Since each of the inverters5U,5V, and5W and the inverters5X,5Y, and5Z of the inverse converter group5has the same configuration, in the following, the set of inverters5U and5X will be described as a representative.

The set of inverters5U and5X is formed to be operable as a full-bridge neutral-point-clamped (NPC) five-level inverter by, for example, a combination of legs including power switching devices such as an insulated gate bipolar transistor (IGBT), a metal-oxide-semiconductor field effect transistor (MOSFET), a gate commutated turn-off thyristor (GCT).

For example, the inverter5U includes a leg50U, a capacitor55UP, and a capacitor55UN. The inverter5X includes a leg50X, a capacitor55XP, and a capacitor55XN.

The leg50U and the leg50X have the same configuration. The legs50U and50X are respectively pulse width modulation (PWM)-controlled to convert the DC power supplied from the forward converter3U via the positive electrode bus bar60U and the negative electrode bus bar70U into three-phase AC power having a variable frequency and a variable voltage.

The capacitor55UP and the capacitor55UN are connected in series with each other and are connected to the positive electrode bus bar60U and the negative electrode bus bar70U, respectively. The capacitor55UP and the capacitor55UN are connected between the positive electrode bus bar60U and the negative electrode bus bar70U to smooth the DC power output from the forward converter3U.

A connection point65UA between the capacitor55UP and the capacitor55UN is connected to the neutral line65U. The capacitor55UP and the capacitor55UN have substantially the same capacitance so that a potential of the connection point65UA becomes an intermediate potential between the positive electrode bus bar60U and the negative electrode bus bar70U.

The capacitor55XP and the capacitor55XN are connected in series with each other and are connected to the positive electrode bus bar60U and the negative electrode bus bar70U, respectively. The capacitor55XP and the capacitor55XN are connected between the positive electrode bus bar60U and the negative electrode bus bar70U to smooth the DC power output from the forward converter3U.

A connection point65XA between the capacitor55XP and the capacitor55XN is connected to the neutral line65U. The capacitor55XP and the capacitor55XN have substantially the same capacitance so that a potential of the connection point65XA becomes an intermediate potential between the positive electrode bus bar60U and the negative electrode bus bar70U.

As described above, the set of capacitors55UP and55UN and the set of capacitors55XP and55XN smooth a pulsating current output from the rectifiers32UP and32UN of the forward converter3U. The smoothed DC power is supplied to the inverters5U and5X.

The inverter5U supplies U-phase AC power converted by the leg50U to the electric motor8via the load power line58U. The output of the inverter5X is connected to the neutral point N on the AC side. The inverter5X shifts a DC level of the U-phase with a potential of the neutral point N as a reference using X-phase AC power converted by the leg50X.

The forward converters3V and3W are configured similarly to the forward converter3U. As for the forward converters3V and3W, the description of the forward converter3U is incorporated herein by replacing U in the reference numerals of the components with each of V and W.

A set of inverters5V and5Y and a set of inverters5W and5Z are configured similarly to the set of inverters5U and5X. For the set of inverters5V and5Y and the set of inverters5W and5Z, the description of the pair of inverters5U and5X is incorporated herein by replacing U and X in the reference numerals of the components with V and Y, and W and Z, respectively.

Further, in the following description, the capacitors55UP,55UN,55VP,55VN,55WP, and55WN will be referred to as a capacitor55unless otherwise distinguished. In the following description, the legs50U,50V,50W,50X,50Y, and50Z will be referred to as a leg50unless otherwise distinguished. The leg50is an example of a power conversion unit.

The controller40PWM-controls the switching devices by outputting a gate pulse signal to the switching device of the leg50due to feedback control based on a detected value of a current detector (not shown) that detects a load current flowing through two or more of the load power lines58U,58V, and58W.

As described above, in the power conversion system1, the capacitor55is provided to suppress fluctuations in the DC voltage due to switching of the leg50. However, the DC voltage in the inverse converter group5may fluctuate according to a magnitude and balance of the current flowing through the electric motor8.

For example, when the inverter5U outputs the highest five-level voltage, a current flows through the positive electrode bus bar60U in a direction from the forward converter3U toward inverter5U. At this time, the potential of the positive electrode input terminal52X of the inverter5X also becomes a high potential.

Further, when the inverter5U outputs the lowest five-level voltage at another timing, a current flows through the negative electrode bus bar70U in a direction from the inverter5U toward the forward converter3U. At this time, the potential of the positive electrode input terminal52X of the inverter5X becomes a potential close to the potential of the neutral point N.

In this way, the potential of each of the positive electrode bus bar60U, the negative electrode bus bar70U, and the neutral line65U fluctuates with respect to the potential of the neutral point N when the power conversion system1is operating.

Incidentally, when the capacity (scale) of the power conversion system increases, this may lead to fluctuations in the potential that exceed an allowable range of the DC bus bar and may become a factor in destabilizing the operation of the power conversion system.FIG.3is a diagram for describing factors that destabilize the operation of the power conversion system according to a comparative example.

A configuration in which the forward converter group3and the inverse converter group5are connected by a DC bus bar of a comparative example and a smoothing capacitor is provided therebetween is shown as a model.

For example, when a size of the power conversion system is increased and thus the DC bus bar is simply extended in an extension direction without changing the cross-sectional area thereof, a wiring inductance L increases according to a respective extension amount. Furthermore, a capacitance of a smoothing capacitor C needs to be increased in proportion to an output capacity of the power conversion system1(a capacity of the inverse converter group5). A closed circuit including the wiring inductance L and the smoothing capacitor C is formed as shown inFIG.3. A resonance frequency of the closed circuit may decrease as the capacity of the power conversion system increases.

In the case of such a comparative example, when the closed circuit vibrates and resonates due to switching noise when the power conversion system is operated, a current larger than a rated current may be generated in the DC bus bar.

Further, as another comparative example, in order to suppress the occurrence of such resonance, resonance may be suppressed by providing a reactor, which is a lumped constant type circuit element, in the closed circuit, adjusting the inductance of the closed circuit and shifting the resonance frequency of the closed circuit. However, since the size of a reactor that can pass a relatively large current becomes larger, it may be difficult to mount the reactor. In response thereto, there has been a need for a coping method that does not use a lumped constant type circuit element such as a reactor.

FIGS.4A and4Bare diagrams for describing the DC bus bar according to the first embodiment.FIG.5is a layout diagram of the DC bus bar according to the first embodiment.FIGS.6A and6Bare overhead views of the DC bus bar portion according to the first embodiment.FIG.7is a cross-sectional view of the DC bus bar according to the first embodiment.

The description of the DC bus bar shown inFIGS.4A to7can be applied to the positive electrode bus bar60U, the negative electrode bus bar70U, and the neutral line65U. The neutral line65U will be described below as an example of the DC bus bar.

The neutral line65U includes a first conductor65UB, a second conductor65UU, and a third conductor65UD.

FIG.4Ashows an example of the first conductor65UB of the neutral line65U.

(a) inFIG.4Ashows a front view of the first conductor65UB, (b) inFIG.4Ashows a top view of the first conductor65UB, and (c) inFIG.4Ashows a side view of the first conductor65UB.

The first conductor65UB is made of, for example, a plate-shaped metal having a length x, a width a, and a thickness b. The first conductor65UB extends in the X direction and is disposed so that a normal to a surface thereof is directed in the Y direction. A width direction of the surface is the Z direction. The first conductor65UB is supported by a frame (not shown) of a housing via a plurality of insulators (FIG.6B) disposed at predetermined positions, and is fixed in a state in which the first conductor65UB is insulated from the frame of the housing by each of the insulators. The length x of the first conductor65UB is longer than a width of the housing of each device related to the power conversion system. For example, the width a is sufficiently long with respect to the thickness b.

For example, in the surface of the first conductor65UB normal to the Y direction, a plurality of through holes (not shown) are provided at predetermined positions in the extension direction (the X direction). For example, a nut (FIG.6B) having a predetermined thread diameter may be press-fitted into each of the through holes. The plurality of through holes are used to respectively fix the second conductor65UU and the third conductor65UD.

FIG.4Bshows an example of the second conductor65UU of the neutral line65U.

The second conductor65UU is formed to have a plate shape, extends in the X direction, and is disposed so that a normal to a surface is directed in the Z direction. A width direction of the surface is the Y direction. A flange for fixing to the first conductor65UB is provided at an end portion of the second conductor65UU in the +Y direction. The flange may be provided over the entire length of the second conductor65UU in the extension direction, and may be formed to have a predetermined length (a bending width) shorter than the total length in the extension direction and may be disposed at a plurality of locations within the total length in the extension direction. The flange shown inFIG.4Bis an example of the latter. A plurality of through holes FH are formed in the flange at predetermined intervals in the extension direction. The plurality of through holes FH are used to fix the second conductor65UU to the first conductor65UB. A plurality of through holes WC for ventilation may be provided in the surface of the second conductor65UU.

The third conductor65UD may be formed to have the same shape as the second conductor65UU.

The layout diagram ofFIG.5is a plan view showing schematic positions of the DC bus bars in each of the housings of the power conversion system1. A plurality of rectangular frames inFIG.5indicate housings of each device of the forward converter3U, the inverter5X, and the inverter5U. As shown in the layout diagram ofFIG.5, the neutral line65U is disposed over each of the housings of the forward converter3U, the inverter5X, and the inverter5U.

The overhead view ofFIG.6Ais a view of the inside of the housing of the inverter5U from a position closer to the front. The overhead view ofFIG.6Bis a view of the inside of the housing of the inverter5U from a position closer to the rear. As shown inFIG.6A, the neutral line65U is disposed at a position lower than the capacitor55UP. The neutral line65U is mounted within a limited range in a height direction without protruding beyond the width of the first conductor65UB. As shown inFIGS.6A and6B, the neutral line65U can be mounted from the front side of the housing of the inverter5U. For example, the first conductor65UB is fastened to a nut (not shown) of the frame by a bolt from the front side. The second conductor65UU and the third conductor65UD are fastened to a nut of the first conductor65UB with a bolt from the front side.

The cross-sectional view ofFIG.7shows the mutual positional relationship when the first conductor65UB, the second conductor65UU, and the third conductor65UD of the neutral line65U are combined. The same applies to any one of a positive electrode, a negative electrode, and a neutral point-electrode of direct current. An arbitrary two of the positive electrode, the negative electrode, and the neutral point-electrode of the direct current are an example of a first electrode and a second electrode of direct current.

The first conductor65UB is applied to a bus bar of a pole that becomes a U-phase DC reference potential (a midpoint potential of direct current).

The first conductor65UB includes a first flat plate portion having a width a and a thickness b (a first thickness) in a cross section perpendicular to the X direction (the extension direction).

The second conductor65UU and the third conductor65UD are connected in parallel to the first conductor65UB so as to be electrically equipotential to the first conductor65UB. The cross sections of the second conductor65UU and the third conductor65UD are bent in an L shape. The second conductor65UU and the third conductor65UD extend in a direction away from the first conductor65UB (for example, the −y direction). The extension direction of the second conductors65UU and the third conductors65UD may be the Z direction when there is no reduction in mounting.

The DC bus bar according to the first embodiment will be described with reference toFIGS.8to9D.

FIG.8is a diagram for describing the distribution of the current flowing through the DC bus bar and the generated magnetic flux φ according to the first embodiment.

Due to a surface effect of a conductor (a metal), a component having a high frequency flows near the surface of the conductor, and a component having a low frequency and a DC component flow with a uniform current density over the entire cross section of the conductor. Therefore, since only the DC component flows in a portion relatively deep from the surface of the metal, the conductor may not be effectively used.

In the present embodiment, the component having the lower frequency and the DC component are caused to flow through the first conductor65UB, the second conductor65UU, and the third conductor65UD, and the component having the higher frequency is caused to flow near the surfaces of the second conductor65UU, the third conductor65UD, and the first conductor65UB. A range in which the component having the higher frequency flows is indicated by hatching in the cross-sectional view ofFIG.8. In this case, a magnetic flux generated in the neutral line65U due to a current i flowing in the extension direction of the neutral line65U forms a magnetic path along the outer periphery of the cross section of each of the first conductor65UB, the second conductor65UU, and the third conductor65UD. This is indicated by a dashed line.

In this way, the second conductor65UU and the third conductor65UD are provided on the first conductor65UB. Thus, it is clear that the magnetic path formed in the first conductor65UB is longer than the comparative example formed only by the first conductor65UB. In the present embodiment, the second conductor65UU and the third conductor65UD are used to increase the length of the magnetic path.

Hereinafter, the neutral line65U will be described in more detail with reference toFIGS.9A to9D.FIGS.9A and9Bare diagrams for describing the DC bus bar according to a comparative example.FIGS.9C and9Dare diagrams for describing the DC bus bar according to the embodiment.

FIG.9Cshows an overhead view of the neutral line65U.

FIG.9Dshows a cross-sectional view of the second conductor65UU in a surface perpendicular to the X direction. The second conductor65UU includes a second flat plate portion which has a cross section bent at a predetermined angle in a cross section perpendicular to the X direction (the extension direction) and is formed to have a thickness 2d (a second thickness) that is thinner than the thickness b (the first thickness). For example, a cross section of the second flat plate portion is bent in an L shape. The predetermined angle is an example of a substantially right angle. A length e of the flange may be determined as appropriate.

The thickness 2d of the second flat plate portion of the second conductor65UU is at least twice a surface depth δ1 at a reference frequency HFref higher than a carrier frequency for PWM control of the power conversion unit (hereinafter, simply referred to as a carrier frequency). The reference frequency HFref may be determined based on a harmonic frequency in the carrier frequency. For example, the reference frequency HFref may be an integer multiple of the carrier frequency and may be aligned with a harmonic frequency of a particular order.

The thickness 2d of the second flat plate portion of the second conductor65UU is thinner than a surface depth δ2 of a fundamental frequency of an alternating current generated by the power conversion unit. When the thickness 2d of the second flat plate portion is reduced to such a thickness, the impedance in the fundamental frequency component of the alternating current increases, and thus it is difficult for the alternating current to flow through the second flat plate portion. Further, the reference frequency HFref is associated with frequency components (the carrier frequency and the harmonic frequency thereof) generated by the carrier frequency.

In the above description, the second conductor65UU is exemplified for description, but the same applies to the third conductor65UD. For example, the third conductor65UD includes a third flat plate portion which has a cross section bent at a predetermined angle in a cross section perpendicular to the X direction (the extension direction) and is formed to have a thickness 2d (a third thickness) thinner than the thickness b (the first thickness). For example, a cross section of the third flat plate portion is bent in an L shape.

The thickness (the third thickness) of the third flat plate portion of the third conductor65UD may be the same as the thickness (the second thickness) of the second flat plate portion of the second conductor65UU and may vary according to conditions.

As shown inFIG.9C, a surface of a flange portion on the +Y direction side (on the first end portion side of the second flat plate portion) that is formed on the second flat plate portion of the second conductor65UU is in contact with a surface of the first conductor65UB on the −Y direction side. The second flat plate portion (the second end portion) of the second conductor65UU connected to the flange portion extends in a direction away from the first conductor65UB (the −Y direction).

The first conductor65UB, the second conductor65UU, and the third conductor65UD are configured to cause the current i to flow in the X direction, which is the extension direction thereof, so that DC power can be supplied across the panels of the power conversion system1. In addition to the DC component of the current i, the AC component also flows through the DC bus bar. The shape and area of the cross section of the first conductor65UB and the shape and area of the cross section of each of the second conductor65UU and the third conductor65UD may be determined based on a magnitude of the DC component and a magnitude of the AC component of the current i.

For example, the surface of the first conductor65UB orthogonal to the X direction has a cross section having a width a and a thickness b. An area S of the cross section is the product of the width a and the thickness b. When the current i flows through the first conductor65UB, a magnetic path is formed along the periphery of the cross section of the first conductor65UB. Electrical relationships are shown in the following Equations (1) to (4).

The “magnetic path1” in Equation (3) is the length of the magnetic path.

The inductance L can be calculated using the following Equation by arranging Equations (1) to (4).

According to Equation (5), when the area S is unchanged, the length of the magnetic path1and the inductance L are in an inversely proportional relationship. In other words, when the area S is unchanged, the inductance L can be reduced by increasing the magnetic path1. Conversely, when the magnetic path1is unchanged, the inductance L will also decrease by reducing the area S.

Here, the total amount of conductors in the comparative example ofFIGS.9A and9Bwill be examined. The comparative example shown here has a rectangular cross section with a length of perimeter substantially equal to the length of the perimeter of the cross section of the neutral line65U shown inFIG.9C. Here, the length of the perimeter of the cross section of the neutral line65U is regarded as the length of the magnetic path1.

In the first comparative example shown inFIG.9A, the first conductor65UB is widened in the width direction (the Z direction). This conductor includes a flat plate portion having a width (a+2c+2d) and a thickness b (the first thickness) in a cross section perpendicular to the X direction (the extension direction). The area of the cross section is (ab+2bc+2bd).

In the second comparative example shown inFIG.9B, the first conductor65UB is widened in the thickness direction (the Y direction). This conductor includes a flat plate portion having a width a and a thickness (b+2c+2d) in a cross section perpendicular to the X direction (the extension direction). The area of the cross section is (ab+2ac+2ad).

In the case that the shape of the cross section of the first conductor65UB is formed so that the thickness b is sufficiently thinner than the width a (for example, a>>b), when the areas of the first comparative example and the second comparative example are compared with each other, the area of the first comparative example is smaller. The first comparative example is an example in which the total amount of conductors in the DC bus bar can be reduced with respect to the same amount of magnetic path1.

Therefore, in analyzing the area S of the cross section of the neutral line65U according to the embodiment, the area of the cross section of the second conductor65UU is approximated to (2cd) by focusing on the first flat plate portion of the second conductor65UU. Thus, the area S of the cross section of the neutral line65U can be approximated to (ab+4cd) including the third conductor65UD.

Further, according to the above conditions, the thickness 2d of the second conductor65UU is thinner than the thickness b of the first conductor65UB (2d<b).

When comparing (ab+4cd) as the area S of the cross section of the neutral line65U with (ab+2bc+2bd) as the area of the first comparative example, the area S of the cross section of the neutral line65U is narrower, and thus the neutral line65U can be configured with a smaller total amount of conductors in the DC bus bar than in the first comparative example (and the second comparative example) for the same amount of magnetic path1. Along with this, the inductance L of the neutral line65U also decreases, and thus the neutral line65U is less likely to resonate than in the first comparative example (and the second comparative example).

According to the above embodiment, the bus bar modules applied to the DC bus bar are disposed over a plurality of housings and distribute DC power to the connected smoothing capacitors and power conversion units. The DC bus bar includes a first conductor applied to either a first electrode or a second electrode of DC, and a second conductor connected in parallel to the first conductor. The first conductor includes a first flat plate portion having a thickness b (the first thickness) in a cross section perpendicular to the extension direction that follows the X direction. The second conductor includes a second flat plate portion which has a cross section bent at a predetermined angle in a cross section perpendicular to the extension direction following the X direction and has a thickness 2d (the second thickness) thinner than the thickness b (the first thickness). Thus, the total amount of conductors in the DC bus bar can be reduced.

The power conversion system1may be formed to include a DC bus bar, a first smoothing capacitor disposed in a first housing among a plurality of housings, and a second power converter disposed in a second housing among the plurality of housings.

The power conversion system1may include a capacitor55UP (a first smoothing capacitor) disposed in a housing (a first housing) of the inverter5U, a leg50U (a first power conversion unit), a capacitor55XP (a second smoothing capacitor) disposed in a housing (a second housing) of the inverter5X, and a leg50X (a second power conversion unit).

Modified Example of First Embodiment

A modified example of the first embodiment will be described.

The flanges of the second conductor65UU and the third conductor65UD in the first embodiment are divided into predetermined lengths (bending widths). On the other hand, the flanges of the second conductor65UUa and the third conductor65UDa in the modified example are continuous over the length in the extension direction (the X direction) of the second conductor65UU. This will be described below.

FIG.10is a diagram for describing a DC bus bar according to a modified example of the first embodiment.FIG.11is an overhead view of the DC bus bar portion of the modified example of the first embodiment.FIGS.10and11replaceFIGS.4B and6Bdescribed above.

The flange of the second conductor65UUa shown inFIGS.10and11is continuous over the entire length of the second conductor65UU in the extension direction (the X direction). When the length of the flange in the extension direction increases in this way, it may be difficult to bend the flange, but since a contact area between the second conductor65UUa and the first conductor65UB can be increased, contact resistance between the second conductor65UUa and the first conductor65UB can be reduced.

In the case of the modified example of the first embodiment as well, although the amount of conductors in the flange portion is somewhat increased, the total amount of conductors in the DC bus bar can be reduced in the same manner as in the first embodiment.

Second Embodiment

A second embodiment will be described with reference toFIGS.12and13.

The first embodiment has described the structural example which reduces the total amount of the conductor and the inductance in a DC bus bar. In the present embodiment, the DC bus bar is used as a branch circuit. This application will be described.

FIG.12is a diagram showing a branch circuit from the DC bus bar to the capacitor55according to the second embodiment.FIG.13is an overhead view of a DC bus bar portion of the second embodiment.FIGS.12and13replaceFIGS.5and6Adescribed above.

As shown inFIGS.12and13, a connection conductor55UPN is provided between each of the capacitors55and the second conductor65UU. The connection conductor55UPN connects the electrode of each of the capacitors55to the second conductor65UU. In other words, the electrode of each of the capacitors55is connected to the second conductor65UU via the connection conductor55UPN. Thus, each of the capacitors55is connected to the first conductor65UB via the connection conductor55UPN and the second conductor65UU.

FIGS.12and13show an example of connection to one electrode of each of the capacitors55, but the other electrode may also be connected to the DC bus bar in the same manner.

According to the second embodiment, the second conductor65UU can be used in a part of the branch circuit from the DC bus bar. Thus, the connection conductor55UPN and the second conductor65UU are configured to be used together rather than separated, and as in the first embodiment, in addition to reducing the total amount of conductors of the DC bus bar, the total amount of conductors in a range including the connection conductor55UPN and the second conductor65UU can be reduced.

According to at least one embodiment described above, the bus bar module distributes DC power to the smoothing capacitors and power conversion units disposed in a plurality of housings. The bus bar module includes a first conductor and a second conductor. The first conductor is applied to either a first electrode or a second electrode of direct current. The second conductor is connected in parallel to the first conductor. The first conductor includes a first flat plate portion having a first thickness in a cross section perpendicular to the extension direction. The second conductor includes a second flat plate portion having a cross section bent at a predetermined angle in a cross section perpendicular to the extension direction and having a second thickness thinner than the first thickness. As a result, the total amount of conductors in the DC bus bar can be reduced.

Although several embodiments of the present invention have been described, the embodiments have been presented by way of example and are not intended to limit the scope of the invention. The embodiments can be implemented in various other forms, and various omissions, replacements, and modifications can be made without departing from the scope of the invention. The embodiments and the modifications thereof are included in the scope and spirit of the invention, as well as the scope of the invention described in the claims and equivalents thereof.

The leg50of the inverse converter group5may be a full-bridge 3-level inverter instead of the full-bridge NPC type 5-level inverter.

REFERENCE SIGNS LIST