Patent Description:
To identify a failure of a power electronic device early, the currents flowing to and from the device may be monitored. It is oftentimes preferred in high-power applications to monitor the currents contactlessly, such as by providing connection lines of the device with a Rogowski coil or Hall-effect sensor, both of which utilize inductive phenomena. For examples, see [<NUM>] <NPL> and [<NUM>] <NPL>.

To connect power-electronic building blocks (PEBBs), a busbar <NUM> with the example structure shown in <FIG> may be used. The depicted busbar <NUM> is composed of two planar conductors or conductive layers, shown as parallel plates <NUM>, <NUM> separated by a distance d of the order of hundreds of micrometers. For visibility, the distance d has been enlarged in <FIG>. The external side of each plate comprises an input area <NUM>, <NUM> and an output area <NUM>, <NUM>, within which it is suitable to connect a current source or current consumer, e.g., by welding, soldering, clamping means or mechanical connectors of the fixed or detachable type.

In one example use case, a source-side device (not shown) is connected at the input areas <NUM>, <NUM> at the left-hand edge of the busbar and a load-side device (not shown) is connected at the output areas <NUM>, <NUM> at the right-hand edge of the busbar. A first current A<NUM> flows through the upper plate <NUM>, and a second current A<NUM> flows through the lower plate <NUM>; the orientation of the hollow arrows representing these currents refer to a reference polarity of each current rather than suggesting that the current is unidirectional at all times. Conventionally, a busbar is designed to have small resistance, so as to limit thermal losses, and very small inductance. A reduced inductance means that the inductive response to a sudden change in the circuit characteristics - as may result from an overvoltage, discharge, short-circuit or the like - is less pronounced, and will thereby protect the connected PEBBs. This is also valid for busbars designed to transfer direct current. <CIT> discloses a junction box apparatus for a vehicle. The junction box apparatus comprises a shunt busbar and test points. The shunt busbar, which may be manu-factured by stamping an electrical conductor from flat copper or brass stock, comprises a body portion, two pairs of male terminals for coupling the shunt busbar in a current loop. A load and a power supply can be placed in the current loop. A comparator is connected to the terminals across the shunt busbar. Shunt-based current monitoring is available for some low-power applications but has not been successfully upscaled to the high-power case. It would be desirable to generalize this robust and relatively simple monitoring technique to PEBB applications.

One objective is to make available shunt-based current monitoring for PEBB applications. It is a particular objective to propose a busbar allowing such current monitoring.

In the invention according to independent claim <NUM>, there is provided a busbar comprising a first conductive layer with an input area and an output area, wherein the conductive layer has a machined pattern defining a meandering conductive path between the input area and output area.

Because the meandering conductive path is longer than a straight conductive path directly from the input to the output area, the machined pattern increases the resistance of the conductive path in a controlled fashion. The increase in resistance is achieved without increasing the outer dimensions of the busbar. For comparison, the conductive path from the input area <NUM> to the output area <NUM> of the upper plate <NUM> of the busbar <NUM> shown in <FIG> is straight and therefore less resistive than an imaginary meandering conductive path in the same plate <NUM>. By providing the busbar with a desired resistance, it becomes possible to monitor the current flowing through the busbar by monitoring a voltage drop along the conductive path.

A further advantage of the invention is that the busbar can be manufactured in a simple fashion by manipulation of a conventional planar busbar for PEBBs. A still further advantage in comparison with the use of a Rogowski coil that no delicate measuring components, such as an integrator circuit, are needed for the measurement as such.

In the invention, power electronics circuitry is provided, which comprises: the busbar; a direct-current capacitor connected at the input area of the busbar; a semiconductor device connected at the output area of the busbar; and a current monitoring arrangement adapted to sense a voltage drop over said meandering conductive path.

The conductive path is one through which the current from the input area to the output area must pass; alternatively, the conductive path is one of several paths in a group which represents all possible paths from the input area to the output area. To render an input or output area suitable for its purpose of connecting a current source or current consumer, the necessary structural modification may be very limited or even non-existent; in fact, the identification of an input/output area in the sense of the claims may refer to an intended use. In the sense of the claims, moreover, the conductive path is meandering if it comprises at least one meandering section or portion. The machined pattern, if it penetrates all the way through the busbar layer, may alternatively be referred to as a slot pattern.

The aspects of the present disclosure will now be described more fully with reference to the accompanying drawings, on which certain embodiments of the invention are shown. These aspects may, however, be embodied in many different forms and should not be construed as limiting; rather, the disclosed embodiments are provided by way of example so that this disclosure will be thorough and complete, and to fully convey the scope of all aspects of invention to those skilled in the art.

<FIG>, which has been briefly discussed in a previous section of this disclosure, shows a two-layer busbar <NUM> according to the state of the art. Busbars according to the present invention, which differ from the state of the art mainly by the presence of the machined pattern, may have same or similar generic properties as the busbar shown in <FIG>. In terms of possible further differences, busbars according to the present invention may include one, two or more conductive layers. The layers may be separated by a void (e.g., air, insulating gas, pressurized or at atmospheric pressure) or an insulating layer. Alternatively or additionally, the placement of the input and output areas <NUM>, <NUM>, <NUM>, <NUM> may be different, such as on the edge side (i.e., laterally) or extending around the edge of the plate. The width-to-length ratio of the busbar may differ from that suggested in <FIG>.

<FIG> is a top view of a conductive layer <NUM> in a busbar with a machined pattern, according an embodiment of the present invention. The machined pattern <NUM> is composed of six slots (vertically oriented in <FIG>) in a baffle-like arrangement. It may be said to define a meandering conductive path, in which five vertical segments can be discerned between nearby slots of the machined pattern <NUM>. The conductive path is therefore noticeably longer than the distance from the input area <NUM> to the output area <NUM>. In approximate terms, the machined pattern <NUM> in <FIG> defines a conductive path that is at least twice as long as said distance, which in itself may double the resistance compared to a conductive layer without any machined pattern. Additionally, the conductive path is narrower for the most part than the straight current path on a pattern-free conductive layer, which normally increases the resistance.

The machined pattern <NUM> may be a chemically or photochemically machined pattern, preferably an etched pattern, a laser-cut pattern or a waterjet-cut pattern. The machined pattern <NUM> may penetrate through the first conductive layer. In particular, it may be composed of cut-through slots. The width of the machined pattern <NUM> may be approximately <NUM> or less; in other embodiments, the width of the machined pattern <NUM> may be less than <NUM> or less than <NUM>.

Machined patterns which define a conductive path with parallel adjacent opposite sections may be advantageous since they avoid an uncontrolled inductance increase when the resistance is brought to increase by the addition of the machined pattern. For example, consecutive vertical segments of the conductive path according to <FIG> will convey oppositely directed currents. Preferably, the provision of the machined pattern increases the resistance between the input area <NUM> and the output area <NUM> by a factor greater than or equal to a concomitant inductance increase. Expressed in mathematical notation, if the resistance increases by a factor kR and the inductance increases by a factor kL when the machined pattern is added, then preferably kR ≥ kL applies. It is recalled that the factors kR, kL can be determined by theoretical calculation or simulation. Likewise, while it is clearly possible to manufacture a busbar according to the invention by starting from a pattern-free busbar layer and adding the machined pattern subsequently, the invention does not require this specific sequencing; rather, the pattern may be present from the earliest stages of the manufacturing process.

Other embodiments of the invention may be adapted for different use cases, with different requirements for the resistance increase. This requirement may be the result of a design tradeoff between the desire to limit thermal losses (tending to reduce the resistance) and reach an acceptable measurement accuracy (tending to increase the resistance). For example, the conductive path may be at least <NUM>%, preferably at least <NUM>%, preferably at least <NUM>%, preferably <NUM> times, preferably <NUM> times or preferably <NUM> times as long as the distance from the input area <NUM> to the output area <NUM>.

<FIG> is a top view of a conductive layer <NUM> in a busbar according an embodiment of the present invention. The conductive layer <NUM> has a machined pattern <NUM> defining four parallel conductive paths as well as connection sites <NUM>, <NUM> allowing the sensing of a voltage drop over the portion of the conductive path that extends between the connection sites <NUM>, <NUM>. From the input area <NUM>, which is common to all four paths, each path passes through a common portion <NUM> followed by a respective meandering portion that ends in a respective one of the four output areas <NUM>. For this purpose, the machined pattern <NUM> not only comprises slots (vertically oriented in <FIG>) in baffle-like arrangements but also slots (horizontally oriented in <FIG>) which delimit one meandering portion of a conductive path from an adjacent one. The common portion <NUM> may be said to be substantially straight in the sense that it allows current to flow substantially along a straight line connecting the input area <NUM> and the beginning of the meandering portion of each conductive path. Each conductive path comprises an upstream <NUM> and a downstream <NUM> connection site, respectively located at the beginning and end of the meandering portion. The voltage drop over the meandering portion can be determined by electrically connecting the poles of a voltmeter or equivalent circuitry between the connection sites <NUM>, <NUM>, as will be discussed with reference to <FIG>.

As exemplified by <FIG>, the section of the conductive path joining the two connection sites <NUM>, <NUM> is approximately <NUM> times as long as the distance between the connection sites <NUM>, <NUM>. In other embodiments, a corresponding section of the conductive path may be at least <NUM> times, preferably <NUM> times, preferably <NUM> times as long as the distance between the connection sites. This is advantageous since the connection leads of the voltmeter can be kept reasonably short.

<FIG> is a top view of a conductive layer <NUM> belonging to a two-layer busbar according a further embodiment of the present invention. The conductive layer <NUM> has a machined pattern <NUM> which defines four parallel conductive paths. For illustration purposes, <FIG> shows a capacitor <NUM> having its two poles connected to the input area <NUM> of the shown conductive layer <NUM> and to an input area <NUM> of a second conductive layer (not shown) of the busbar. The two input areas <NUM>, <NUM> may be suitable for connecting a capacitor <NUM> serving as a direct-current capacitor for intermediate storage of electric energy that may be supplied via conductors and/or for smoothing purposes. <FIG> further shows four semiconductor devices <NUM>, which are connected between a respective output area <NUM> of the shown conductive layer <NUM> and an output area <NUM> of the second conductive layer (not shown). Accordingly, between the poles of the capacitor <NUM>, there are four closed electric circuits, including a first circuit composed of: the input area <NUM> in the first conductive layer <NUM> - the straight portion of the first conductive path - the meandering portion of the first conductive path - the first output area 12a of the first conductive layer <NUM> - the first semiconductor device 402a, the first output area 22a of the second conductive layer (not shown) - a conductive path of the second conductive layer (not shown) - the input area <NUM> of the second conductive layer (not shown).

Unlike the conductive layer shown in <FIG>, the conductive layer <NUM> illustrated in <FIG> comprises a single dedicated connection site <NUM> for each conductive path, namely, the upstream connection site. The respective output areas <NUM> are used additionally as downstream conductive site, that is, for connecting one pole of the measurement equipment. In other words, the downstream conductive site coincides with the output area <NUM>. <FIG> further shows a first example current monitoring arrangement comprising resistors Rin, Rf and an operational amplifier <NUM> configured to perform non-inverting amplification of the voltage drop between the first upstream connection site 15a and the first output area 12a. A theoretical gain factor may be equal to <NUM> + Rf/Rin. The current monitoring arrangement further comprises a sensor <NUM> for reading the amplified output of the operational amplifier <NUM>. Clearly, similar current monitoring arrangements may be provided at the second, third and fourth conductive paths on the first conductive layer <NUM>.

The current monitoring arrangements may be used to monitor derived electric quantities as well. In particular, the value of a capacitor connected to the busbar <NUM>, such as the capacitor <NUM>, may be monitored on the basis of the measured current.

The inventors furthermore envisage a second example current monitoring arrangement, which may replace the first example current monitoring arrangement but otherwise be connected in the same manner, to the upstream connection site <NUM> and the output area <NUM>. On a general functional level, the second example current monitoring arrangement is configured to separate low-frequency and high-frequency components of the measured voltage drop into separate branches of circuitry. This may be achieved by letting measurements on the low-frequency components primarily rely on the resistive properties of the conductive layer <NUM>, whereas measurements on the high-frequency components may be based on inductive phenomena. The two signals picked up in this manner may undergo low-pass and high-pass filtering, respectively, and optional gain calibration before they are summed together, to form a complete frequency representation of the voltage drop signal. The second example current monitoring arrangement may be more sophisticated to implement but may provide greater accuracy and a more even output over the studied frequency range.

<FIG> illustrates, in accordance with a further embodiment, a machined pattern <NUM> on a conductive layer <NUM> of a busbar for providing a meandering conductive path. The machined pattern <NUM>, which comprises three vertical slots, defines a conductive path with two segments where the current is conveyed in a direction differing from an imaginary straight line between the input area <NUM> and output area <NUM>.

In accordance with a still further embodiment, <FIG> shows a conductive layer <NUM> with a machined pattern <NUM> having a mere two vertical slots. The slots of the machined pattern <NUM> define a conductive path that is not only slightly longer than an imaginary straight line between the input area <NUM> and output area <NUM>, but also significantly narrower in its central segment. Connection sites <NUM> and <NUM> are provided to allow connection of measurement circuitry for monitoring the voltage drop along the central segment.

Finally, <FIG> shows a machined pattern <NUM> on a conductive layer <NUM> of a busbar for providing a meandering conductive path that includes at least one retrograde segment. More precisely, the conductive path between the input area <NUM> and the output area <NUM> comprises a meandering portion which begins at the upstream connection site <NUM> and ends at the downstream connection site <NUM>. Between these sites <NUM>, <NUM>, the conductive path comprises a first segment oriented in an approximate northwest direction in the plane of <FIG>, i.e., one where the flowing current approaches the input area <NUM> again. The first segment is follows by a second segment, in which the current flows in an approximate south-southeast direction, and a third segment that is vertically oriented. The conductive pattern continues through on the right-hand half of the conductive pattern <NUM>, where a vertical fourth segment is follows by a north-northeast fifth segment, a southeast sixth segment. In the sixth segment, again, current will be forced geometrically closer to the input area <NUM> and away from the output area <NUM>, that is, away from the general direction of travel. For this reason, the first and sixth segments may be referred to as retrograde segments. Machined patterns which define one or more retrograde segments are advantageous since the connection sites <NUM>, <NUM> can be placed with a small geometric separation even though they are joined by a long portion of the conductive path. This is space-saving and/or helps reduce the length of the connection lines towards the measurement circuitry.

In one example, a busbar according to any of the described embodiments has a nominal current of at least <NUM> A, such as at least <NUM> A. The resistance of the busbar may range from <NUM> to <NUM><NUM>µΩ, such as <NUM> to <NUM><NUM>µΩ, or preferably <NUM> to <NUM>µΩ. In cases where multiple parallel conductive paths are provided, the resistance values apply for one conductive path.

In another example, the busbar has a nominal current of at least <NUM> A and a resistance of <NUM> to <NUM>µΩ, preferably <NUM> to <NUM>µΩ, for one conductive path. Even for the highest resistance values, the losses due to current monitoring is of the order of tens of watts.

By way of quantitative comparison in an example case, the resistance and inductance of a conductive busbar layer without and with a machined pattern <NUM> of the type shown in <FIG> have been simulated by finite-element modeling using Ansys™ software. The simulation parameters and results are summarized in Table <NUM>.

In the notation introduced above, the simulation provides kR ≈ <NUM>, kL ≈ <NUM> per path. Accordingly, the provision of the machined pattern increases the resistance much more than it increases the inductance.

Claim 1:
Power electronics circuitry, comprising:
a busbar (<NUM>) comprising a first conductive layer (<NUM>) with an input area (<NUM>) and an output area (<NUM>),
wherein the conductive layer has a machined pattern (<NUM>) defining a meandering conductive path between the input area and the output area; and
wherein the power electronics circuitry further comprises: a current monitoring arrangement (<NUM>,<NUM>) adapted to sense a voltage drop over said meandering conductive path; the power electronics circuitry being characterised by a direct-current capacitor (<NUM>) connected at the input area of the busbar;
a semiconductor device (<NUM>) connected at the output area of the busbar.