HYBRID EXCITED ROTARY MACHINE

A vehicle's electrified powertrain includes a battery pack linked to a traction power inverter module (TPIM) converting DC voltage from the battery pack into AC voltage. A rotary electric machine includes a stator energized by the TPIM's AC voltage, enclosing a rotor core capable of rotation. The rotor core contains slots holding conductive bars and permanent magnets, with conductive bars positioned closer to the rotor core's center. The conductive bars and permanent magnets are separated by gaps within each slot. An annular end ring assembly is present at one end of the rotor core, featuring terminal conductors connected to subsets of conductive bars and a secondary coil of a rotary transformer. When the stator is energized, the rotor shaft, connected to the rotor, rotates. The electric machine powers a transmission, which is coupled to the rotor shaft.

INTRODUCTION

The disclosure relates to rotary electric machines. More particularly, the disclosure relates to hybrid excited (HE) rotary machines combining permanent-magnet (PM) excitation and field excitation.

HE machines advantageously provide two sources of rotor magnetic fields. The rotor in such machines may typically include field coils wound from small gauge wires thus limiting the fill factor and adding complexity to rotor manufacturing. HE machines may exhibit relatively high heat and potential for heat induced demagnetization and decreasing field strength of the permanent magnets due in part to the additional copper loss characteristics of field coils.

HE machines having a high fill factor, simpler manufacturing and heat tolerance characteristics are desirable.

SUMMARY

In one exemplary embodiment, an electric machine may include a stator and a rotor core surrounded by the stator and rotatable about an axis, the rotor core having axially opposite ends and a plurality of slots, each slot extending through the rotor core between the axially opposite ends and containing at least one respective electrical conductor and at least one respective permanent magnet, wherein the electrical conductors are radially inboard relative to the permanent magnets and extend beyond the axially opposite ends of the rotor core.

In addition to one or more of the features described herein, the electrical conductors may include conductive bars.

In addition to one or more of the features described herein, the conductive bars may include hairpin conductors.

In addition to one or more of the features described herein, the at least one respective electrical conductor and the at least one respective permanent magnet contained within each slot may be separated by a respective space.

In addition to one or more of the features described herein, the at least one respective permanent magnet contained within each slot may include a stack of permanent magnets.

In addition to one or more of the features described herein, the at least one respective permanent magnet contained within each slot may include a respective first magnet and a respective second magnet, wherein the first magnets are intermediate the second magnets and the electrical conductors, the first magnets have a first temperature rating and the second magnets have a second temperature rating that is less than the first temperature rating.

In addition to one or more of the features described herein, the at least one respective permanent magnet contained within each slot may include a respective first magnet and a respective second magnet, wherein the first magnets are intermediate the second magnets and the electrical conductors, the first magnets have a first coercivity and the second magnets have a second coercivity that is less than the first coercivity.

In addition to one or more of the features described herein, the spaces separating the electrical conductors and the permanent magnets may include cooling passages within the rotor core.

In addition to one or more of the features described herein, the spaces separating the electrical conductors and the permanent magnets may contain a thermal insulator.

In addition to one or more of the features described herein, the conductive bars may be hollow.

In addition to one or more of the features described herein, the slots may be open at a periphery of the rotor core sufficient for radial insertion of the electrical conductors.

In addition to one or more of the features described herein, the electric machine may further include a cylindrical containment sleeve surrounding the rotor core at a periphery of the rotor core.

In addition to one or more of the features described herein, the electric machine may further include an annular end ring assembly at one end of the rotor core containing a first terminal conductor galvanically coupled to a first subset of the conductive bars and a second terminal conductor galvanically coupled to a second subset of the conductive bars.

In addition to one or more of the features described herein, the annular end ring assembly may further contain a secondary coil of a rotary transformer.

In addition to one or more of the features described herein, the annular end ring assembly may radially surround the conductive bars where they extend beyond the one end of the rotor core.

In addition to one or more of the features described herein, the annular end ring assembly may be radially surrounded by the conductive bars where they extend beyond the one end of the rotor core.

In another exemplary embodiment, an electric machine may include a stator, a rotor core surrounded by the stator and rotatable about an axis, the rotor core having axially opposite ends and a plurality of slots, each slot extending through the rotor core between the axially opposite ends and containing at least one respective conductive bar and at least one respective permanent magnet, wherein the conductive bars are radially inboard relative to the permanent magnets and extend beyond the axially opposite ends of the rotor core, and wherein the at least one respective conductive bar and at the least one respective permanent magnet contained within each slot are separated by a respective space, and an annular end ring assembly at one end of the rotor core containing a first terminal conductor galvanically coupled to a first subset of the conductive bars and a second terminal conductor galvanically coupled to a second subset of the conductive bars.

In addition to one or more of the features described herein, the annular end ring assembly may further contain a secondary coil of a rotary transformer.

In addition to one or more of the features described herein, the at least one respective permanent magnet contained within each slot may include a respective first magnet and a respective second magnet, wherein the first magnets are intermediate the second magnets and the conductive bars, the first magnets have a first coercivity and the second magnets have a second coercivity that is less than the first coercivity.

In yet another exemplary embodiment, an electrified powertrain for a vehicle may include a battery pack, a traction power inverter module (“TPIM”) connected to the battery pack, and configured to change a direct current (“DC”) voltage from the battery pack to an alternating current (“AC”) voltage, and a rotary electric machine, including a stator energized by the AC voltage from the TPIM, a rotor core surrounded by the stator and rotatable about an axis, the rotor core having axially opposite ends and a plurality of slots, each slot extending through the rotor core between the axially opposite ends and containing at least one respective conductive bar and at least one respective permanent magnet, wherein the conductive bars are radially inboard relative to the permanent magnets and extend beyond the axially opposite ends of the rotor core, and wherein the at least one respective conductive bar and at the least one respective permanent magnet contained within each slot are separated by a respective space, and an annular end ring assembly at one end of the rotor core containing a first terminal conductor galvanically coupled to a first subset of the conductive bars and a second terminal conductor galvanically coupled to a second subset of the conductive bars, the annular end ring assembly further containing a secondary coil of a rotary transformer for energizing the conductive bars, a rotor shaft connected to the rotor, and configured to rotate about an axis of rotation in conjunction with the rotor when the stator is energized, and a transmission coupled to the rotor shaft and powered by the electric machine.

DETAILED DESCRIPTION

The following description is merely exemplary in nature and is not intended to limit the present disclosure, its application or uses. Throughout the drawings, corresponding reference labels indicate like or corresponding parts and features. Description of parts and features in one drawing is understood to apply to parts and features in other drawings sharing the same reference labels to the extent such parts and features are not otherwise distinguishable through drawing examination by one having ordinary skill in the art or distinguished by additional written description herein.

Referring to the drawings, wherein like reference numbers refer to the same or like components in the several FIGS., an electrified powertrain10is depicted schematically inFIG.1, (e.g., for use aboard an exemplary motor vehicle11.) The powertrain10includes a rotary electric machine12having a rotor12R and a stator12S. The rotor12R may include interior permanent magnets and direct current (DC) field windings as sources of rotor magnetic fields. When the stator12S is energized, the rotor12R supplies motor torque to a transmission20, (e.g., a stepped-gear automatic transmission.) Although omitted for illustrative simplicity, the electrified powertrain10may also include an internal combustion engine configured to generate engine torque. When so equipped, the generated engine torque may be selectively provided to the transmission20, either alone or in conjunction with the motor torque from the electric machine12.

When the vehicle11ofFIG.1is embodied as a hybrid electric vehicle, the electric machine12and/or the engine may power the transmission20. Alternatively, the vehicle11may be a battery electric vehicle, in which case the transmission20may be powered solely by the motor torque from the electric machine12. The disclosed improvements relate to the construction of the electric machine12, and may be realized in hybrid electric vehicle (HEV) and electric vehicle (EV) embodiments of the vehicle11without limitation, as well as in non-vehicular applications such as power plants, hoists, mobile platforms and robots, etc.

With continued reference to the exemplary vehicle11ofFIG.1, the electrified powertrain10may include an alternating current (AC) voltage bus13. The AC voltage bus13may be selectively energized via a traction power inverter module (TPIM)28that is DC coupled to a high-voltage (HV) battery pack24, for instance a lithium ion, lithium sulfur, nickel metal hydride, or other high-energy voltage supply. The AC voltage bus13provides an AC bus voltage (VAC) and conducts AC current to or from the electric machine12. The motor torque from the energized electric machine12, when operating in a drive or motoring mode, is imparted to a rotor shaft125of the rotor12R, with the rotor shaft125journaled, splined, or otherwise connected to the rotor12R. The motor torque is then directed to a coupled load, such as the transmission20and/or one or more road wheels22.

The HV battery pack may be DC coupled to the TPIM28via a relatively high DC voltage bus (e.g., DC link)15at a relatively high DC voltage (VDC). The electrified powertrain10may also include a DC-DC converter26configured to reduce or increase a relatively high DC bus voltage VDC as needed. The DC-DC converter26is connected between the battery pack24and a relatively low DC voltage bus16. In some configurations, an auxiliary battery pack124may be connected to the DC-DC converter26across the relatively low DC voltage bus16. The auxiliary battery pack124may be embodied as a lead-acid battery or a battery constructed of another application-suitable chemistry and configured to store or supply, for example, a 12-15V auxiliary voltage (VAUX) to one or more connected auxiliary devices (not shown).

The rotor12R of the electric machine12is positioned adjacent to the stator12S and separated therefrom by an airgap. The stator12S and the rotor12R may be constructed from a stack-up of thin laminations, (e.g., electrical steel or another ferrous material, with each lamination typically being about 0.2 mm-0.5 mm thick as will be appreciated by those of ordinary skill in the art.) Laminations may be cut to their finished shape by a punch and die or may be cut by a laser, or by wire electrical discharge machining.

The rotor12R shown schematically inFIG.1includes internal rotor slots characterized by voids in the electrical steel of the laminations. Such rotor slots may provide a flux barrier internal to the rotor12R and may contain other rotor features as further described herein. In accordance with certain embodiments, the rotor slots may be partially or completely filled with a combination of permanent magnets (PM) and electrical conductors. The electrical conductors of the rotor12R operate as field windings to strategically produce magnetic fields within the rotor12R. The electrical conductors may be energized by a DC power source, for example from the high DC voltage bus15via a rotary transformer29.

FIG.2depicts an exemplary rotor core201of the rotor12R ofFIG.1in accordance with a hybrid excited (HE) rotary machine. The depiction inFIG.2is representative of one-half of a rotor core201divided through the rotational axis203of the rotor12R for illustrative simplicity and clarity. The rotor core201may be constructed from a stack-up of thin laminations, (e.g., electrical steel or another ferrous material, with each lamination typically being about 0.2 mm-0.5 mm thick as will be appreciated by those of ordinary skill in the art.) Laminations may be cut to their finished shape by a punch and die or may be cut by a laser, or by wire electrical discharge machining. The rotor core201may be alternatively fabricated, for example mold formed from sintered powdered metal and binders under heat and pressure. The stator according to a non-limiting exemplary embodiment is arranged concentrically around the rotor12R such that the rotor12R is surrounded by the stator12S. In such an embodiment, the airgap G is a radial airgap and the electric machine12embodies a radial flux-type machine. However, other embodiments may be realized in which the relative positions of the rotor12R and stator12S are reversed. For illustrative consistency, the embodiment ofFIG.1in which the rotor12R resides radially within the stator12S will be described herein without limiting the construction to such a configuration.

The stator12S ofFIG.1is not illustrated in further detail but may include radially-projecting stator teeth extending inward from a cylindrical stator core. That is, the stator teeth extend toward the rotor12R from the stator core. The inner diameter surface of the stator12S is the radially-innermost surface of the stator teeth facing or opposing the outer peripheral surface205of the rotor12R in spaced adjacency to form the air gap G (seeFIG.1). Adjacent stator teeth are separated from each other by a corresponding stator slot, as will be appreciated by those of ordinary skill in the art. The stator slots enclose electrical conductors, typically copper wires, copper bars, or hairpin conductor. Such conductors collectively form stator windings. A rotating stator magnetic field is generated when the stator windings are sequentially-energized by a polyphase output voltage from the TPIM28ofFIG.1. Stator magnetic poles formed from the resulting rotating stator magnetic field interact with rotor poles to rotate the rotor12R around the rotational axis203.

In the HE rotary machine embodiment ofFIG.2, the rotor core201may include a number of slots207extending axially through the rotor core201between opposite ends209of the rotor core201. The slots may be substantially aligned axially between the opposite ends209of the rotor core though the actual alignment may be skewed as is known in the art. The slots207may be substantially radially aligned though the actual alignment may be offset from a true radial alignment as is known in the art. Reference herein to radial alignment or substantial radial alignment of slots, permanent magnets or electrical conductors is understood to refer to true radial alignment or a skewed radial alignment as known to those skilled in the art. In an embodiment, each slot207may contain an electrical conductor211and a permanent magnet213. The permanent magnets213may be continuous or segmented through the axial length of the slots207. The electrical conductors211are continuous through the axial length of the slots207and may extend axially beyond the opposite ends209of the rotor core201as illustrated at one end209ofFIG.2. The electrical conductors211and the permanent magnets213are arranged within the slots207such that the electrical conductors211are beneath or radially inboard relative to the permanent magnets213.

The permanent magnets213may be collectively referred to herein as rotor magnets and may be constructed, for example, of ferrite, Neodymium-iron-boron, Samarium cobalt, aluminum-nickel-cobalt, etc., or another application-suitable material as may be discussed in further detail herein. The rotor magnets in such embodiment are embedded within respective slots207within the stack of individual steel laminations of the rotor core201. The number, type, position, and/or relative orientation of the rotor magnets ultimately influences the magnitude and distribution of magnetic flux in the ferrous materials of the electric machine12. Also, when viewed axially (e.g.,FIGS.3A and3B) the rotor magnets may be evenly distributed circumferentially. In an embodiment, the poles of the rotor magnets may be axially aligned. In an embodiment, the poles of the rotor magnets may be circumferentially aligned. In an embodiment, the poles of the rotor magnets may be radially aligned.

FIGS.3A and3Bdepict an end view of the rotor core observed along the rotational axis203illustrated inFIG.2.FIGS.3A and3Billustrate a number of diverse embodiments of slot207structures, electrical conductors211and permanent magnets213.FIG.3Aprimarily depicts exemplary embodiments of different electrical conductor211and permanent magnet213arrangements aligned within true radially aligned slots207.FIG.3Bprimarily depicts exemplary embodiments of different radial and skewed-radial slots207and alignments of electrical conductor211and permanent magnet213.

InFIG.3A, slot positions are labeled A through G merely for ease of referencing the diverse exemplary embodiments. Beginning with slot position A, the slot207contains an arrangement of a permanent magnet213and an electrical conductor211radially inboard of the permanent magnet213. A space301separates the permanent magnet213and the electrical conductor211. The electrical conductor211is shown as a single conductive bar. The conductive bar may be any suitable conductor such as, but not limited to, copper, aluminum or brass. Conductive bars may be fabricated using any suitable process including, but not limited to, stamping, rolling, laser cutting, casting, extruding, etc. In the embodiment at slot position A, the conductive bar is solid. The space301may be an air gap, or may be filled with an insulator such as, but not limited to, mineral wool or polyurethane. The space301may also provide a channel for circulating a pressurized coolant such as lubricating oil or air. The slot207at position A is a closed slot having a bridge303of rotor core201material at the outer peripheral surface205of the rotor core201. The bridge303in the embodiment at slot position A may preclude radial insertion of the electrical conductor211and the permanent magnet213, thus limiting rotor core201fabrication to axial insertion.

At slot position B, the slot207contains an arrangement of a permanent magnet213and an electrical conductor211radially inboard of the permanent magnet213. A space301separates the permanent magnet213and the electrical conductor211. The electrical conductor211is shown as a single conductive bar. The conductive bar may be any suitable conductor such as, but not limited to, copper, aluminum or brass. Conductive bars may be fabricated using any suitable process including, but not limited to, stamping, rolling, laser cutting, casting, extruding, etc. In the embodiment at slot position B, the conductive bar is hollow having a central channel305therethrough. The channel may carry a pressurized coolant such as lubricating oil or air. The space301may be an air gap, or may be filled with an insulator such as, but not limited to, mineral wool or polyurethane. The space301may also provide a channel for circulating a coolant such as a lubricating oil. The slot207at position B is an open slot having a break307in the bridge of rotor core201material at the outer peripheral surface205of the rotor core201. The break307in the embodiment at slot position B may be too small for radial insertion of the electrical conductor211and the permanent magnet213, thus limiting rotor core201fabrication to axial insertion.

At slot position C, the slot207contains an arrangement of a permanent magnet213and an electrical conductor211radially inboard of the permanent magnet213. A space301separates the permanent magnet213and the electrical conductor211. The electrical conductor211is shown as a first conductive bar211A and a second conductive bar211B. The conductive bars may be any suitable conductor such as, but not limited to, copper, aluminum or brass. Conductive bars may be fabricated using any suitable process including, but not limited to, stamping, rolling, laser cutting, casting, extruding, etc. In the embodiment at slot position C, the conductive bars are solid. The space301may be an air gap, or may be filled with an insulator such as, but not limited to, mineral wool or polyurethane. The space301may also provide a channel for circulating a coolant such as a lubricating oil. The slot207at position C is an open slot having a break309in the bridge of rotor core201material at the outer peripheral surface205of the rotor core201. The break309in the embodiment at slot position C may be large enough for radial insertion of the electrical conductor211and the permanent magnet213. In an embodiment, a non-magnetic, cylindrical sleeve310may surround the rotor core201when the break309provides no retention features over the permanent magnets213.

At slot position D, the slot207contains an arrangement of a permanent magnet213and an electrical conductor211radially inboard of the permanent magnet213. A space301separates the permanent magnet213and the electrical conductor211. The electrical conductor211is shown as a plurality of electrical conductors211such as hairpin conductors. The hairpin conductors may be any suitable conductor such as, but not limited to, copper, aluminum or brass. Hairpin conductors may be fabricated using any suitable process including, but not limited to, extruding, and shape forming, etc. In the embodiment at slot position D, the hairpin conductors are solid. The space301may be an air gap, or may be filled with an insulator such as, but not limited to, mineral wool or polyurethane. The space301may also provide a channel for circulating a coolant such as a lubricating oil. The hairpin conductors may be radially or axially inserted depending upon the existence and size of any break in the bridge of rotor core201material at the outer peripheral surface205of the rotor core201.

At slot position E, the slot207contains an arrangement of a permanent magnet213and an electrical conductor211radially inboard of the permanent magnet213. A space301separates the permanent magnet213and the electrical conductor211. The electrical conductor211is shown as a single conductive bar. The conductive bar may be any suitable conductor such as, but not limited to, copper, aluminum or brass. Conductive bars may be fabricated using any suitable process including, but not limited to, stamping, rolling, laser cutting, casting, extruding, etc. In the embodiment at slot position E, the conductive bar is solid. A closed channel311is formed in the rotor core201in the space301between the electrical conductor211and the permanent magnet213. The closed channel311may provide a channel for circulating a pressurized coolant such as lubricating oil or air. The conductive bar and permanent magnets213may be radially or axially inserted depending upon the existence and size of any break in the bridge of rotor core201material at the outer peripheral surface205of the rotor core201.

At slot position F, the slot207contains an arrangement of a permanent magnet213and an electrical conductor211radially inboard of the permanent magnet213. A space301separates the permanent magnet213and the electrical conductor211. The electrical conductor211is shown as a single conductive bar. The conductive bar may be any suitable conductor such as, but not limited to, copper, aluminum or brass. Conductive bars may be fabricated using any suitable process including, but not limited to, stamping, rolling, laser cutting, casting, extruding, etc. In the embodiment at slot position F, the conductive bar is solid. A closed channel313is disposed in the rotor core201in the space301between the electrical conductor211and the permanent magnet213. The closed channel313may be a pipe or tube of any suitable cross section. The closed channel313may provide a channel for circulating a pressurized coolant such as lubricating oil or air. The conductive bar and permanent magnets213may be radially or axially inserted depending upon the existence and size of any break in the bridge of rotor core201material at the outer peripheral surface205of the rotor core201.

At slot position G, the slot207contains an arrangement of a permanent magnet213and an electrical conductor211radially inboard of the permanent magnets213. The permanent magnet213is shown as a first permanent magnet213A and a second permanent magnet213B. The first permanent magnet213A is intermediate the second permanent magnet213B and the electrical conductor211. In an embodiment, the first permanent magnet213A may have a first temperature rating that is less than the temperature rating of the second permanent magnet213B. In an embodiment, the first permanent magnet213A may have a first coercivity that is less than the coercivity of the second permanent magnet213B. A space301separates the permanent magnet213and the electrical conductor211. The electrical conductor211is shown as a single conductive bar. The conductive bar may be any suitable conductor such as, but not limited to, copper, aluminum or brass. Conductive bars may be fabricated using any suitable process including, but not limited to, stamping, rolling, laser cutting, casting, extruding, etc. In the embodiment at slot position G, the conductive bar is solid. The space301may be an air gap, or may be filled with an insulator such as, but not limited to, mineral wool or polyurethane. The space301may also provide a channel for circulating a pressurized coolant such as lubricating oil or air. The conductive bar and permanent magnets213may be radially or axially inserted depending upon the existence and size of any break in the bridge of rotor core201material at the outer peripheral surface205of the rotor core201.

InFIG.3B, adjacent sets of magnets213and electrical conductors211are labeled325,335,345and355for ease of referencing the diverse exemplary embodiments. The sets may correspond, for example, to pole pairs as found in interior permanent magnet rotors. The broken lines correspond to radii through the rotor core201corresponding to the general positional distribution of a permanent magnet213and electrical conductor211pair on one side of a set providing a pole pair as described. Slots207are illustrated including a respective space301. Slots may be formed with ledges for support of the permanent magnets213and electrical conductors211as shown in exemplary embodiments of sets325and335. Slots may be formed without ledges for support of the permanent magnets213and electrical conductors211as shown in exemplary embodiments of sets345and355. The set325depicts a pair of magnets213that are radially skewed and a pair of electrical conductors211that are also radially skewed. In the set325, the permanent magnet213and electrical conductor pairs are skewed by an equivalent angle. The set335depicts a pair of magnets213that are truly radially aligned and a pair of electrical conductors211that are radially skewed. The set345depicts a pair of magnets213that are radially skewed and a pair of electrical conductors211that are truly radially aligned. The set355depicts a pair of magnets213that are radially skewed and a pair of electrical conductors211that are also radially skewed. In the set355, the permanent magnets213are skewed at a greater angle than the electrical conductors211.

The HE rotary machine general embodiment ofFIG.2, wherein the electrical conductors211are continuous conductive bars through the axial length of the slots207and extend axially beyond the opposite ends209of the rotor core201, is assumed for the purposes of the following description of the embodiments ofFIG.4. In an embodiment, an annular end ring assembly401may include two or more terminal conductors403for galvanically coupling to respective subsets of the conductive bars211. The terminal conductors403may, for example, be implemented as copper end rings with radially extending features galvanically coupled to subsets of the conductive bars as schematically shown inFIG.4. Such copper end rings may be stacked axially and separated by insulating rings. Permanent connection between the copper end rings and the conductive bars may be by way of soldering, brazing, laser welding, etc. The end ring assembly401is depicted as being radially outward of and surrounding the conductive bars though an alternative placement is illustrated as annular end ring assembly407which is surrounded by the conductive bars. In embodiments wherein the electrical conductors are hairpin conductors, the hairpin conductors may be pre-formed before insertion thus displacing the need for a conductive path end ring at one end of the rotor core. However, an end ring even at the pre-formed side may benefit from structural reinforcement of a non-conductive end ring assembly. In an embodiment, both placements of end ring assemblies401and407may be employed. The end ring assemblies may integrate a secondary coil409of a rotary transformer for providing electrical power to the electrical conductors211to produce a desired magnetic field response to current flow through the electrical conductors211. A stationary primary winding (not shown) may inductively link electrical power to the secondary coil409in one or both of the end ring assemblies. Utilizing the end ring assembly407may advantageously support a more compact rotary transformer wherein the primary coil may be radially inward of the secondary coil409. A similar end ring assembly406may be used on the opposing axial side of the rotor for shorting all electrical conductors211or separate subsets for addition flexibility and degrees of freedom.

FIG.6illustrates an alternate embodiment of a rotor core201resembling a wound salient pole rotor. Slots207are depicted on each side of a separator601and defined between the separator601and the rotor core201. As depicted, the slots207cross section may open up toward the air gap. Thus, to increase the fill factor, the slots207may contain multiple electrical conductors211of various cross sections. The electrical conductors may be bar stock including hairpin conductors or may be wound wire with the separator601providing a winding post. The permanent magnets213may have the poles aligned radially as depicted. The magnetic field in the air gap G may selectively be strengthened or weakened by the current direction through the electrical conductors211. The permanent magnets213may be single piece rectangular cross section as illustrated or may be trapezoidal or multi-piece stacked of differing cross sections like the electrical conductors to improve the fill factor.

All numeric values herein are assumed to be modified by the term “about” whether or not explicitly indicated. For the purposes of the present disclosure, ranges may be expressed as from “about” one particular value to “about” another particular value. The term “about” generally refers to a range of numeric values that one of skill in the art would consider equivalent to the recited numeric value, having the same function or result, or reasonably within manufacturing tolerances of the recited numeric value generally. Similarly, numeric values set forth herein are by way of non-limiting example and may be nominal values, it being understood that actual values may vary from nominal values in accordance with environment, design and manufacturing tolerance, age and other factors.

When an element such as a layer, film, region, or substrate is referred to as being “on” another element, it can be directly on the other element or intervening elements may also be present. In contrast, when an element is referred to as being “directly on” another element, there are no intervening elements present. Therefore, unless explicitly described as being “direct,” when a relationship between first and second elements is described in the above disclosure, that relationship may be a direct relationship where no other intervening elements are present between the first and second elements but may also be an indirect relationship where one or more intervening elements are present (either spatially or functionally) between the first and second elements.

One or more steps within a method may be executed in different order (or concurrently) without altering the principles of the present disclosure. Further, although each of the embodiments is described above as having certain features, any one or more of those features described with respect to any embodiment of the disclosure can be implemented in and/or combined with features of any of the other embodiments, even if that combination is not explicitly described. In other words, the described embodiments are not mutually exclusive, and permutations of one or more embodiments with one another remain within the scope of this disclosure.