Dynamic interleaving for dual three phase electric machine and three phase wireless charging system

A method of operating a motor includes providing an electric system coupled with the motor, the electric system including parallel inverter legs; subjecting the motor to a first interleaving angle when the electric system is under a first condition; and subjecting the motor to a second interleaving angle different from the first interleaving angle when the electric system is under a second condition; wherein the steps of subjecting the motor to the first interleaving angle and subjecting the motor to the second interleaving angle occur within continuous operation of the electric system and the motor.

FIELD OF THE INVENTION

One or more embodiments of the present invention relate to a dynamic interleaving method. One or more embodiments of the present invention relate to a dynamic interleaving method for a dual three phase electric machine to reduce the DC-link current ripple. One or more embodiments of the present invention relate to a wireless charging system.

BACKGROUND OF THE INVENTION

Multiphase electric machines are utilized, such as in the automotive sector, due to their high torque density, efficiency, lower torque ripple, and inherent fault tolerance capability. An exemplary multiphase electric machine is a dual three phase electric machine with isolated neutral points between the dual three phases.

Certain dual three phase electric machines have utilized a constant interleaving method. This constant interleaving method purports to reduce the dc-link capacitor current and the dc-link ripple current.

In a certain instance, constant 90° or 180° interleaving angles (φ) were found to be the most appropriate angles of the drive system depending on different modulation strategies that were utilized. In another specific example, when the displacement between the two sets of three-phase windings was 0°, the most appropriate interleaving angle was found to be 180°, and when the displacement between the two sets of three-phase windings was 30°, the most appropriate interleaving angle is found to be 90°.

To the extent these interleaving methods have been proposed, these interleaving methods use a constant value for the interleaving angle within any continuous operation of the machine. However, a constant interleaving angle may not sufficiently reduce the dc-link current ripple. There remains a need in the art for further reduction of the dc-link current ripple, particularly for a dual three-phase permanent magnet synchronous machine (PMSM) drive.

Certain automotive multiphase electric systems include wireless power transfer (WPT) technology for charging an electric vehicle onboard battery. Certain conventional single phase WPT systems, and even certain conventional three-phase WPT systems, can be limited relative to efficiency and power density. There remains a need in the art for improved wireless power transfer technology.

SUMMARY OF THE INVENTION

An embodiment of the present invention provides a method of operating a motor, the method including steps of providing an electric system coupled with the motor, the electric system including parallel inverter legs; subjecting the motor to a first interleaving angle when the electric system is under a first condition; and subjecting the motor to a second interleaving angle different from the first interleaving angle when the electric system is under a second condition; wherein the steps of subjecting the motor to the first interleaving angle and subjecting the motor to the second interleaving angle occur within continuous operation of the electric system and the motor.

Another embodiment of the present invention provides a method of operating a motor, the method including steps of providing an electric system coupled with the motor, the electric system including parallel inverter legs; allowing the motor to experience a first interleaving angle when the electric system is under a first condition; and allowing the motor to experience a second interleaving angle different from the first interleaving angle when the electric system is under a second condition; wherein the steps of allowing the motor to experience the first interleaving angle and allowing the motor to experience the second interleaving angle occur within continuous operation of the electric system and the motor.

A further embodiment of the present invention provides a coil assembly including overlapping windings, the coil assembly including a plurality of phase coils; each of the plurality of phase coils including a first polar half and a second polar half to thereby provide a bi-polar structure; each of the first polar half and the second polar half including a first central linear portion extending from a first outer perimeter arc portion, where the first central linear portion and the first outer perimeter arc portion are at a top layer; a second central linear portion extending from a second outer perimeter arc portion, where the second central linear portion and the second outer perimeter arc portion are at a bottom layer; the first central linear portion and the second central linear portion extending toward a central overlapping portion, the central overlapping portion including an inner first arc portion transitioning to an upper second arc portion, the transitioning including the upper second arc portion partially overlapping the inner first arc portion.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

One or more embodiments of the present invention relate to a dynamic interleaving method. One or more embodiments of the present invention relate to a system implementing a dynamic interleaving method. The dynamic interleaving method may be particularly useful for a dual three-phase electric machine or a coil-integrated inverter system. Advantageously, the dynamic interleaving method serves to significantly reduce DC-link current ripple and RMS current of a capacitor. In the dynamic interleaving method, a phase shift between two inverters is not fixed. In some portions of an electrical cycle, an interleaving angle (φ) is a first angle (e.g. 0 radians (0°)), while in other portions of the electrical cycle, the interleaving angle is a second angle (e.g. π radians (180°)). In this way, interleaving of the dynamic interleaving method is dynamic in behavior and therefore improves performance of a corresponding drive system. One or more embodiments of the dynamic interleaving method are particularly applicable for a discontinuous pulse width modulation (DPWM) method where the duty ratio of the switches is either 1 or 0 for some time of the electrical cycle. An exemplary DPWM method is a discontinuous space vector pulse width modulation (SVPWM) method where switches are clamped to a positive or negative rail of a DC BUS for a certain portion of the electrical cycle.

One or more embodiments of the present invention relate to a coil assembly including overlapping windings. The coil assembly includes a plurality of phase coils. A phase coil includes two polar halves, such that the overall phase coil may be referred to as a bi-polar structure. A polar half includes central linear portions extending from outer perimeter arc portions. A first central linear portion and a first outer perimeter arc portion are at a top layer and a second central linear portion and a second outer perimeter arc portion are at a bottom layer. The first central linear portion and the second central linear portion extend toward a central overlapping portion, which includes a transition from the top layer to the bottom layer. Similarly, there is a transition from the top layer to the bottom layer between the first outer perimeter arc portion and the second outer perimeter arc portion. Taken together, the two polar halves overlap to form the phase coil. In one or more embodiments, that is, for a three-phase, two-layer system, three phase coils can be utilized within the coil assembly. Advantageously, the coil assembly of one or more embodiments of the present invention provides improvements relative to higher power density and lower losses.

With reference toFIGS.1to4,11, and12, one or more embodiments of the present invention relate to a dynamic interleaving method and a system for utilizing the method. The dynamic interleaving method generally includes utilizing a first interleaving angle under a first condition, and utilizing a second interleaving angle different from the first interleaving angle under a second condition.

With reference toFIGS.1to4, a system for utilizing the dynamic interleaving method can include a dual three phase electric machine. The dual three phase electric machine can utilize two parallel interleaved inverters receiving DC current. The two parallel interleaved inverters can utilize an angular displacement angle. An exemplary angular displacement angle is π/6 radians (30°). The two parallel interleaved inverters utilize phase shifting between switching signals of pulse width modulation (PWM). This can be referred to as interleaving, and is generally applied to reduce or eliminate the switching frequency harmonics of the output torque and DC-Link current. Interleaving can also serve to reduce the noise and vibration, the torque ripple, and the DC-link ripple of the electric machine.

A first one of the two parallel interleaved inverters can include three phases (e.g. Phase A, Phase B, Phase C) and a second one of the two parallel interleaved inverters can include three phases (e.g. Phase X, Phase Y, Phase Z). Since the respective sets of three phases are at an angular displacement a first phase of one set of three phases (e.g. Phase A) will be nearby with two phases of the other set of three phases (e.g. Phase X and/or Phase Z).

When a duty ratio in any pair of nearby phases (e.g. Phase A with Phase X and/or Phase A with Phase Z) in a phase sequence diagram (FIG.4) becomes 1 or 0, the dynamic interleaving method utilizes a first interleaving angle (e.g. 180°), which first interleaving angle can be provided to a corresponding motor. For the rest of the time (that is, when the duty ratio in any pair of nearby phases is not 1 or 0), the dynamic interleaving method utilizes a second interleaving angle (e.g. 0°), which second interleaving angle can be provided to a corresponding motor. Since the dynamic interleaving method utilizes a varying interleaving angle, the method includes dynamic interleaving.

With reference toFIGS.11and12, a system for utilizing the dynamic interleaving method can include a coil-integrated inverter system. A coil-integrated inverter system distributed inverter system can be connected to an end-winding of the motor. The coil arrangement for the motor can be any suitable arrangement shown inFIG.11. For a distributed inverter system implemented for a motor, multiple inverter legs are in parallel condition. The distributed inverter system can include a first plurality of inverter legs (e.g. A, B, C) and a second plurality of inverter legs (e.g. X, Y, Z), where the first plurality of inverter legs is at an angular displacement angle relative to the second plurality of inverter legs. An exemplary angular displacement angle is π/6 radians (30°).

The PWM signals for the legs of the inverter can be phase shifted through a combination of fixed and dynamic interleaving angle. InFIG.11, the system is shown with two phase sets—ABC and XYZ. The ABC set has 3 phases: A, B, and C. Each phase within the set has coils, such as A1, A2, and A3. The number of coils within the phases could be more or less depending on any particular design of a machine. So the phase shift between these coils depends on the number of coils within the phase. The phase shift (at PWM frequency) would be 360/number of coils. For the specific example inFIG.11, the number of coils within the phase is 3, so the phase shift is 120° (at PWM frequency). On top of the phase shift between the coils, there is a dynamic phase shift between the two sets. As discussed elsewhere, an exemplary dynamic phase shift between the sets includes the use of two different angles, such as 180° and 0°, at respective different conditions.

For a dynamic interleaving method for the system ofFIG.11, an exemplary logic schematic for the phase shift angle of the inverters is shown inFIG.12. This logic schematic can result in further dc-link current ripple relative to a method without the interleaving method, which reduction can be up to a six times reduction.

Though steps and details of a method of utilizing dynamic interleaving are disclosed elsewhere herein, specific reference is now made to the following one or more steps. A first step can include providing a suitable electric machine, which may also be referred to as an electric system. As mentioned above, exemplary electric machines include a dual three phase electric machine with two parallel interleaved inverters and a coil-integrated inverter system.

A next step can include subjecting a corresponding component to a first interleaving angle when the electric machine is under a first condition, which may also be referred to as being subjected to the first condition. This may also be referred to as allowing the corresponding component to experience the first interleaving angle. An exemplary corresponding component is a motor. An exemplary first interleaving angle is 180°. An exemplary first condition is a duty ratio for any pair of nearby phases being 1 or 0. The nearby phases include a first phase of one set of three phases with the two nearest phases of the other set of three phases.

A further step can include subjecting the corresponding component to a second angle different from the first angle when the electric machine is under a second condition, which may also be referred to as being subjected to the second condition. This may also be referred to as allowing the corresponding component to experience the second interleaving angle. An exemplary second interleaving angle is 0°. An exemplary second condition is the duty ratio for any pair of nearby phases not being 1 or 0.

Though exemplary interleaving angles and conditions are provided herein, it should be readily appreciated that concepts of the present invention can extend to alternative interleaving angles and/or to alternative conditions.

Relative to the first condition and the second condition, a flag signal can be generated based on these conditions. That is, a flag signal can be utilized to give a value of 1 when the first condition indicates the interleaving angle should be the first interleaving angle and to give a value of 0 when the second condition indicates the interleaving angle should be the second interleaving angle.

In one or more embodiments, the dynamic interleaving method is utilized continuously. This reference to continuous utilization may refer to being utilized continuously for a single displacement angle (e.g. π/6 radians (30°)), which may also be referred to as winding displacement or an angular displacement angle. Said another way, the dynamic interleaving method includes utilizing at least two different interleaving angles for a single displacement angle. That is, while the prior art envisions changing an interleaving angle for different displacement angles, these changes occur after the electric system is turned off and the interleaving angle is changed to a different interleaving angle.

As mentioned above, an exemplary angular displacement angle is π/6 radians (30°), which may also be referred to as winding displacement. The most suitable angular displacement angle for any given system may be determined based on a function of operating sectors for the inverters.

With specific reference toFIG.1, a system utilizing a dynamic interleaving method is shown. DC current regulation is applied to two parallel interleaved inverters, which may be referred to as pulse width modulation (PWM) components. The PWM components provide the phase information to an overall inverter. The overall inverter is coupled with a battery and a DC-link capacitor. The overall inverter provides an output, which can be to a dual three-phase permanent magnet synchronous machine (PMSM).

With specific reference toFIG.2, an alternative system utilizing a dynamic interleaving method is shown. DC current is provided to two parallel interleaved inverters, which may be referred to as voltage source inverters. The DC current supply includes a DC-link capacitor. The voltage source inverters provide phases as an output to a motor.

With specific reference toFIG.3, a dynamic interleaving method is shown. Reference is also made toFIG.2and a step of providing a first one of the two parallel interleaved inverters including three phases (Phase A, Phase B, Phase C) and a second one of the two parallel interleaved inverters including three phases (Phase X, Phase Y, Phase Z). A next step can include determining a duty ratio for the phases, which may also be referred to as legs, of the two parallel interleaved inverters. Based on the determined duty ratios, one or more conditions can be analyzed.

With specific reference toFIG.4, a phase sequence diagram of a dual three phase electric machine is shown. From the phase sequence diagram ofFIG.4, any phase has two nearest phases. That is, the nearest phases of Phase A are Phase X and Phase Z. As a result, in-phase conditions can happen for either Phase A with Phase X and/or Phase A with Phase Z. Similarly, the in-phase conditions can occur for any of the following combinations: Phase B with Phase X, Phase B with Phase Y, Phase C with Phase Y, and Phase C with Phase Z. Therefore, a conditional analysis can include determining whether any of the nearby Phases are in-phase. During an in-phase condition, the interleaving angle should be at a first angle (e.g. 180°), while the rest of the time (that is, when any of the nearby Phases are not in-phase), the interleaving angle should be at a second angle (e.g. 0°).

With specific reference toFIG.12, a dynamic interleaving method is shown. Reference is also made toFIG.11and a step of providing a coil-integrated inverter system. A next step can include determining a duty ratio for the phases, which may also be referred to as legs, of the multiple inverter legs. Based on the determined duty ratios, one or more conditions can be analyzed. In a similar manner as above, a conditional analysis can include determining whether any of the nearby Phases are in-phase. During an in-phase condition, the interleaving angle should be at a first angle (e.g. 180°), while the rest of the time (that is, when any of the nearby Phases are not in-phase), the interleaving angle should be at a second angle (e.g. 0°).

One or more embodiments of the dynamic interleaving method may be particularly applicable for a discontinuous pulse width modulation (DPWM) method. In other embodiments, a continuous pulse width modulation (PWM) method may be utilized, though this may lead to less efficient inverter performance. A DPWM method can include the duty ratio of the switches is either 1 or 0 for some time of the electrical cycle. An exemplary DPWM method is a discontinuous space vector pulse width modulation (SVPWM) method where switches are clamped to a positive or negative rail of a DC BUS for a certain portion of the electrical cycle. Several discontinuous SVPWM methods are available for a three-phase system, which can be directly applied to a dual three-phase PMSM system.

Aspects of suitable pulse width modulation (PWM) methods will be generally known to the skilled person, though certain details are disclosed here.

Certain PWM methods are known as 60 degree in-phase discontinuous methods (DPWM1). For DPWM1, in some portion of the electrical cycle, the duty ratio of Phase A and Phase X becomes equal by being 1 or 0. The same event is happening for Phase B and Phase Y, Phase C and Phase Z. This is true for any 60 degree DPWM method. Other examples include 30 degree lagging 60 degree DPWM method (DPWM2) and 30 degree leading 60 degree DPWM method (DPWM3). During those moments DC-link current of the inverters becomes in phase, and the rest of the time, DC-link current is becoming out of phase. During the in-phase conditions, the interleaving angle should be at a first angle (e.g. 180°), while the rest of the time (that is, when not in the in-phase conditions), the interleaving angle should be at a second angle (e.g. 0°).

For the 30 degree DPWM method (DPWM4), Phase A and Phase Z become equal (rather than Phase A and Phase X). A similar thing occurs for Phase B and Phase X, Phase C and Phase Y. The different interleaving angles can be correspondingly applied.

For the 120 degree DPWM methods, where the switch is completely on for one-third of the electrical cycle (DPWMMAX) or completely off for one-third of the electrical cycle (DPWMMIN), sometimes Phase A and Phase X become equal, and sometimes Phase A and Phase Z become equal. During the in-phase condition, DC-link ripple is higher than the out of phase condition. The different interleaving angles can be correspondingly applied.

One or more embodiments of the dynamic interleaving method may be particularly useful for a permanent magnet synchronous machine (PMSM) drive. One or more embodiments of the dynamic interleaving method may be particularly useful for an induction machine.

Turning to certain formulas relative to the dynamic interleaving method, aspects of the system ofFIGS.1to3are further disclosed. Since the two inverters are working in parallel, the total dc-link current of the drive will be the summation of the dc-link currents of the inverters. Dc-link current of the first inverter can be written as the summation of each leg current as in equation (1) below, where Amis the amplitude of the switching harmonics, Anis the amplitude of the phase current harmonic, wcis the carrier frequency, weis the modulating angular frequency, and m and n are respectively the switching and phase current harmonic orders.

Similarly, for the second inverter, the dc-link current can be written as equation (2) below. Here φ is the phase shift angle of the carrier to implement the interleaving and π/6 is the angle due to displacement between the two sets of three-phase windings.

From equation (1) and equation (2), the total phase shift θpsbetween the dc-link currents of the inverters can be written as equation (3) below.

Depending on the value of m and n, an interleaving angle φ can be chosen so that the value of θpswill be π and that specific carrier harmonics can be eliminated through interleaving. This should be contrasted with a constant interleaving angle φ=90° where some of the harmonics will be eliminated (e.g. m=1, n=−2) while the rest of them remain (e.g. m=1, n=2). For the dynamic interleaving method disclosed herein, as the interleaving angle is not constant, depending on the value of m and n, all the harmonics can be canceled.

One or more embodiments of the present invention relate to a developed model and implementation thereof in a control algorithm. Upon implementing a dynamic interleaving method, the dc-link current can be utilized to develop one or more models. These developed models can be utilized for control algorithms for subsequent electric machines. That is, a developed model can be used to predict how a dynamic interleaving method might affect operation of any given electric machine, and this predicted information can be utilized within a control algorithm. Said another way, such model and algorithm and other analysis disclosed herein can be used for developing details (e.g. suitable phase shift) for additional and future phase and control configurations.

With reference toFIGS.5to10, one or more embodiments of the present invention relate to a coil assembly including overlapping windings. The coil assembly10includes a plurality of phase coils12. The phase coil12includes a first polar half12A (FIG.8) and a second polar half12B, such that the overall phase coil12may be referred to as a bi-polar structure.

Each polar half12A,12B includes a first central linear portion14extending from a first outer perimeter arc portion16. First central linear portion14and first outer perimeter arc portion16are at a top layer. Each polar half12A,12B includes a second central linear portion18extending from a second outer perimeter arc portion20. Second central linear portion18and second outer perimeter arc portion20are at a bottom layer.

The first central linear portion14and the second central linear portion18extend toward a central overlapping portion. The central overlapping portion includes an inner first arc portion22, which transitions to an upper second arc portion24. The transition may be the upper second arc portion24slightly overlapping the inner first arc portion22, which may also be referred to as a partial overlap.

Similarly, there is a transition from the top layer to the bottom layer between the first outer perimeter arc portion16and the second outer perimeter arc portion20. The transition may be the upper first outer perimeter arc portion16slightly overlapping the second outer perimeter arc portion20, which may also be referred to as a partial overlap.

As perhaps best seen inFIG.8, each polar half12A,12B is shaped similarly and inner portions thereof are overlapped at the central linear portions. That is, first central linear portion14A of polar half12B overlaps the second central linear portion18of polar half12A, and first central linear portion14of polar half12A overlaps the second central linear portion18A of polar half12B. Taken together, the two polar halves12A,12B overlap to form the phase coil12.

As shown inFIG.5, in one or more embodiments, three phase coils12can be utilized within the coil assembly. The shape of each phase coil12allows for all three to fit within a three phase configuration. A first end of the first outer perimeter arc portion16of a first phase coil12is internal to a second end of the first outer perimeter arc portion16of a second phase coil12. A second end of the first outer perimeter arc portion16of a first phase coil12is external to a first end of the first outer perimeter arc portion16of a third phase coil12. This configuration continues for all phase coils12.

This configuration is similar, yet somewhat reversed, for the central overlapping portions. A first end of the upper second arc portion24of a first phase coil12is external to a second end of the upper second arc portion24of a second phase coil12. A second end of the upper second arc portion24of a first phase coil12is internal to a first end of the upper second arc portion24of a third phase coil12. This configuration continues for all phase coils12.

The embodiment shown inFIG.5may be referred to as a three-phase, two-layer system. Other suitable numbers of phases and layers may be utilized. Other exemplary numbers of phases and layers include four, five, and six, and other suitable numbers. For any number of phases utilized, the coil assembly will utilize an overlapping winding configuration. The specific configuration of the overlap, such as the overlapping angle, can be adjusted based on any particularly utilized numbers of phases and layers.

As an alternative description of the coil assembly10, the overall coil structure of the coil assembly10is generally circular shaped with overlap between the bipolar structures for the phases every 60 degrees towards the center. Coil current will eventually flow clockwise on one half and anti-clockwise on the other half on each phase coil12.

It will be appreciated by the skilled person that the coil assembly structure disclosed inFIGS.5to10is a disclosure of the shapes into which wound wires, which may also be referred to as windings, will be formed into. Other aspects relative to preparing windings, and details and design thereof, will be generally known to the skilled person relative to the disclosure provided herein.

With reference toFIG.6andFIG.10, a wireless charging system50includes two charging pads: a transmitter (Tx)52and a receiver (Rx)54. Transmitter52includes a first coil assembly10. Receiver54includes a second coil assembly10. As shown inFIG.6, the first coil assembly10and the second coil assembly10should face each other in the charging configuration.

The receiver54couples power from the transmitter52through electromagnetic induction. For an automotive use, the transmitter52, which may be referred to as a pad, can be buried in the ground while the receiver54, which may be referred to as a pad, can be attached upside down to a vehicle chassis56. For charging to begin, the first coil assembly10and the second coil assembly10should face each other in generally perfect alignment to transfer power effectively.

As shown inFIG.6, transmitter52and receiver54can each include a relatively highly magnetic permeable ferrite core58and a relatively highly conductive aluminum sheet60. The ferrite core58is layered proximate the coil assembly10such that ferrite core58is between coil assembly10and aluminum sheet60. Since electric vehicle charging wireless power transfer (WPT) systems generally deal with a significantly large airgap between the pads (i.e. pads52,54), the amount of flux leakage may be relatively high. The ferrite core58and aluminum shield60may assist with reducing the leakage and increasing power transfer capability to the vehicle. The ferrite layer58helps orient the flux between the pads52,54in the axial direction. The aluminum shield60also limits the electromagnetic leakage to the surroundings.

An additional aluminum shield (not shown) may be placed in the vehicle in addition to the aluminum shield60attached to receiver54to further reduce emissions inside the vehicle for passenger protection.

Advantageously, the coil assembly10and wireless charging system50of one or more embodiments of the present invention provide improvements relative to higher power density and lower losses.

Examples

A drive system was prepared for analyzing a dynamic interleaving method relative to methods utilizing no interleaving and fixed interleaving. The drive system utilized two inverters in accord with the disclosure relative toFIGS.1to4.

ForFIG.13andFIG.14, a 30 degree lagging 60 degree DPWM method (DPWM2) method was utilized.FIG.13is a graph showing dc-link current for a battery of the drive system for a dynamic interleaving method relative to no interleaving and fixed interleaving. The dynamic interleaving shows significant improvement.FIG.14is a graph showing zoomed fast Fourier transform (FFT) for a dynamic interleaving method relative to no interleaving and fixed interleaving. The harmonics in the switching frequency were reduced significantly while using the dynamic interleaving method. All the sidebands of the switching frequency harmonics were eliminated by using the dynamic interleaving method, while for the fixed interleaving method, some of the sidebands were not eliminated.

ForFIG.15andFIG.16, various DPWM methods were utilized. Specifically, the methods included DPWMMIN, DPWMMAX, DPWM1, DPWM2, DPWM3, and DPWM4, which are discussed above.FIG.15is a graph showing pk to pk DC-link current ripple for the various DPWM methods for a dynamic interleaving method relative to no interleaving and fixed interleaving.FIG.15shows the pk to pk DC-link current ripple was reduced significantly while using the dynamic interleaving method, compared to the no interleaving and fixed interleaving methods.FIG.16is a graph showing DC-link capacitor RMS current for the various DPWM methods for a dynamic interleaving method relative to no interleaving and fixed interleaving.FIG.16shows the DC-link capacitor RMS current was reduced significantly while using the dynamic interleaving method, compared to the no interleaving and fixed interleaving methods.

In light of the foregoing, it should be appreciated that the present invention advances the art by providing an improved dynamic interleaving method and an improved three phase wireless charging system. While particular embodiments of the invention have been disclosed in detail herein, it should be appreciated that the invention is not limited thereto or thereby inasmuch as variations on the invention herein will be readily appreciated by those of ordinary skill in the art. The scope of the invention shall be appreciated from the claims that follow.