Filter Monitoring

Abstract

Provided is an apparatus for delivering electrical power, in particular for delivering regeneratively produced electrical power, which has at least one converter and at least one filter for matching the delivery of power by the converter to a load impedance. Also provided is a method for operating the apparatus for delivering electrical power which allows improved monitoring of the functioning of the filters or mains filters and which uses means for determining at least one filter current in at least one filter, which means are designed in such a manner that said means make it possible to determine the at least one filter current during operation of the apparatus. Comparison means are provided and generate an error information signal using the desired value and actual value of the filter current and a predefinable error criterion.

Claims

1. An apparatus for delivering electrical power, in particular for delivering regeneratively produced electrical power to a load impedance, having at least one converter and at least one filter, characterised in that means for determining at least one filter current of at least one filter are provided, which are designed to allow a determination of the at least one filter current during operation of the apparatus, wherein comparison means are provided, which using the desired value and actual value of the filter current and a predefinable error criterion generate an error information signal, wherein as means for determining the at least one filter current a current sensor for measuring the current in only one phase or at least one current sensor for measuring the current in only two phases of the at least one filter are provided.

2. The apparatus according to claim 1, characterised in that at least one current sensor is provided, configured to measure the differential filter current between two phases of at least one filter.

3. The apparatus according to claim 1, characterised in that at least one filter group is provided and the means for determining the filter currents are designed to at least to some extent allow a determination of the filter currents or differential filter currents of the individual filter groups.

4. The apparatus according to claim 1, characterised in that the apparatus for delivering electrical power has a mains connection (3) and at least one mains filter (9, 14) is provided.

5. The apparatus according to claim 1, characterised in that the apparatus for delivering electrical power is a wind turbine with a double-fed asynchronous generator or a wind turbine with a synchronous generator.

6. The apparatus according to claim 1, characterised in that the at least one filter is configured as an absorption circuit, high-pass, low-pass or RC filter or as a higher-order filter.

7. The apparatus according to claim 1, characterised in that means for changing the operation of the apparatus, means for deactivating at least one filter or a filter group, or means for changing the switching frequency as a function of the error information signal, are provided.

8. A method for operating an apparatus for delivering electrical power, in particular for delivering regeneratively produced electrical power to a load impedance, according to claim 1, wherein the apparatus has at least one converter and at least one filter, characterised in that during operation of the apparatus for delivering electrical power at least one filter current in the least one filter is determined and the at least one filter is monitored dependent on the determined filter current, wherein comparison means are provided, which using the desired value and the actual value of the filter current and a predefinable error criterion generate an error information signal.

9. The method according to claim 8, characterised in that using at least one current sensor the filter current in at least one phase of the at least one filter or a differential filter current of two phases of the at least one filter is measured.

10. The method according to claim 8, characterised in that comparison means generate an error information signal using the at least one filter current of at least one phase of at least one filter or at least one differential filter current of two phases of at least one filter and the measured voltage values at the at least one filter and a predefinable error criterion.

11. The method according to claim 8, characterised in that the filter current is measured in each case in at least one phase or in each case the differential filter current of two phases of at least one filter group and at least to some extent the individual filter groups are monitored dependent on the determined filter currents or differential filter currents.

12. The method according to claim 8, characterised in that the error information signal is calculated from a comparison between the desired and actual values of at least one filter current or from a comparison of the desired and actual values of at least one variable calculated using the determined filter current and at least one predefinable error criterion.

13. The method according to claim 8, characterised in that the at least one predefinable error criterion is selected dependent on the characteristic to be monitored of the least one filter.

14. The method according to claim 8, characterised in that the determination of the at least one filter current or of the at least one differential filter current is carried out for predefined frequencies, in particular for the fundamental oscillation or a harmonic.

15. The method according to claim 8, characterised in that dependent on the error information signal, the operation of the apparatus is changed, at least one filter is deactivated, and/or the switching frequency of the converter is changed.

16. A computer program product, during the execution of which by means of a computer a method according to claim 8 is carried out and the monitoring of the at least one filter takes place by evaluation of the error information signal of the associated filter.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

[0035] The intention of the following is to further explain the invention using exemplary embodiments in conjunction with the drawing. The drawing shows in:

[0036] FIG. 1 shows a schematically sketched circuit diagram of an exemplary embodiment of an apparatus for delivering electrical power with a double-fed asynchronous generator;

[0037] FIG. 2 shows a further exemplary embodiment of an apparatus for delivering electrical power with a synchronous generator;

[0038] FIG. 3 shows a schematic circuit diagram of an exemplary embodiment of a first filter topology;

[0039] FIG. 4 shows a schematic circuit diagram of an exemplary embodiment of a second filter topology;

[0040] FIG. 5 shows a schematic circuit diagram of an exemplary embodiment of a third filter topology;

[0041] FIG. 6 shows a flow diagram of exemplary embodiments of the method according to the invention for filter monitoring;

[0042] FIG. 7 shows an exemplary embodiment with a current transformer for determining a filter current phase of a filter in a star connection;

[0043] FIG. 8 shows a sketched circuit diagram of an exemplary embodiment with a current sensor for measuring the differential currents of two phases of a filter in a delta connection;

[0044] FIG. 9 shows a schematic flow diagram of an exemplary embodiment of the method according to the invention during measurement of just one filter current phase;

[0045] FIG. 10 shows a space vector diagram in the αβ system of coordinates; and

[0046] FIG. 11 shows a schematic flow diagram of a further exemplary embodiment of the method according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0047] FIGS. 1 and 2 show two exemplary embodiments of apparatus for delivering electrical power, as normally used in wind turbines. The apparatus in FIG. 1 comprises a generator 1, the stator 2 of which is directly connected with an electricity grid 3 which, for example represents the load impedance. The rotor 4 of the generator 1 is connected via a machine-side converter 5, a direct voltage intermediate circuit 10 and a grid-side converter 6 to the electricity grid 3. The generator is configured as an asynchronous generator and represents a double-fed asynchronous generator, as often used for wind turbines. The two converters 5 and 6 can be operated with differing switching frequencies, for which reason it may be advantageous to use separate filters 7 and 8. It is also possible, however, to use just one filter or one filter group 9. The filters 7, 8, 9 shown can thus all be considered as optional and in practice will be selected according to the intended purpose.

[0048] In the present exemplary embodiment, these are shown as filter groups 7, 8 and 9, since these are in each case configured in relation to the individual systems to be damped. Thus, the stator filter 7 must damp the effect of the stator 2 on the grid 3. The filter 8 on the other hand must match the effect of the converter 6 on the grid. The filter 9, in turn, is intended to damp the entire system comprising the grid-side converter and the stator and its repercussions on the grid 3. In the exemplary embodiment from FIG. 1 a plurality of filters are directly available, but these must be selected according to the intended purpose and thus considered as optional. The generator 1 in FIG. 1 in the form of an asynchronous generator can for example be coupled with a rotor of a wind turbine, in order in this way to convert the mechanical energy of the wind into electrical energy.

[0049] In each filter 7, 8 and 9, in the exemplary embodiment from FIG. 1, in each case means 7′, 8′ and 9′ are provided, with which the filter currents can be determined in the respective filters 7, 8 and 9.

[0050] FIG. 2 shows an exemplary embodiment of an apparatus according to the invention with a generator 1′, the stator 2 of which is connected via a machine-side converter 11, a direct voltage intermediate circuit 13 and a grid-side converter 12 to the grid 3. The generator 1′ can for example have a permanently excited rotor, so that unlike the configuration in FIG. 1 the entire power output takes place via the converter 12 on the grid 3. Here the mains filters 14 is intended to adjust the effect of the converter 12 to the grid. The filter 14 must in this regard also be configured for delivering high powers and can for example be configured to increase the filter performance of a plurality of identically built filters for the same frequency, not shown here. These filters can also be combined to form individual filter groups. Additionally, a filter 14a can be provided, to damp the effects of the converter 11 on the generator 1′ and vice versa. This filter also contains means for determining at least one filter current 14a′.

[0051] In general, however, instead of the generator 1 or 1′ an apparatus for delivering electrical power can also have other means for providing electrical energy, for example a photovoltaic system, providing a direct current, delivered via converters 6, 12 into an electricity grid.

[0052] According to the invention, in the apparatus according to FIG. 1 and FIG. 2 means for determining at least one filter current 7′, 8′, 9′ or 14′ are provided, configured such that these allow a determination of the at least one filter current of the at least one filter 7, 8, 9 or 14 during operation of the apparatus. In at least one of the filters 7, 8, 9 or 14 used, preferably means for direct measurement of filter currents can be provided. The determined or directly measured filter currents serve for monitoring the individual filters and ensure that the correct functioning of the filters during operation of the apparatus is known. With the apparatus for delivering electrical power shown in FIG. 1 and FIG. 2 it is thus possible, using the filter current determination during operation to monitor the functioning of the filters and to intervene directly in the event of ageing, defective structure or a defect.

[0053] The means 7′, 8′, 9′, 14′ or 14a′ optionally have means for deactivating the filter or isolating the filter in order, for example in the event of a defect, to be able to isolate this from the apparatus.

[0054] The specific structure of typically used filter topologies are shown by the schematic circuit diagrams of FIG. 3, FIG. 4 and FIG. 5. FIG. 3 shows what is known as an absorption circuit in a delta connection. The three filter phases L1, L2, L3 in each case contain an inductance 15, a resistor 16 and a capacitor 17. The three phases L1, L2 and L3 of the absorption circuit from FIG. 3 are in each case connected via a capacitor 17, so that a delta connection is formed. With the exemplary embodiment of a filter shown as an absorption circuit in a star connection in FIG. 4, the three filter phases L1, L2, L3 are interconnected at a central point 18. The star point 18 can also have zero potential. In turn, the individual phases comprise an inductance 15, a resistor 16 and a capacitor 17.

[0055] FIG. 5 shows a star-shaped circuit having an RC filter formed merely of one resistor 16 and one capacitor 17 per phase. Here also, the filter phases L1, L2 and L3 are joined at the star point 18.

[0056] The filter topologies shown in FIG. 3-FIG. 5 represent only a small sample of the possible filter types, however. Also, the filters can be designed as a high-pass, low-pass, absorption circuit or RC filter or also a higher order filter. Irrespective of their design, however, all filters have connections for all three phases L1, L2 and L3, suitable for measuring filter currents. Furthermore, all filters usually have a symmetrical design in relation to the individual phases L1, L2 and L3.

[0057] FIG. 6 then shows a flow diagram for exemplary embodiments of the method according to the invention in single-phase, two-phase or three-phase current measurement.

[0058] In the exemplary embodiment with single-phase current measurement, at least one filter current is determined, for example the filter current i.sub.F,L1 of phase L1. The voltage values at the filter up of phases L1, L2 and L3 are available, since as can be seen from FIG. 1 and FIG. 2, these correspond to the mains voltage and a measurement of this voltage is in any case needed for controlling the converter.

[0059] From the voltage values for the phases L1, L2 and L3, in step 20 via a αβ0 transformation, the components in the αβ0 system of the voltage are determined. The following equation is used for this purpose:

[00003]$\begin{array}{cc}\left[\begin{array}{c}{u\left(t\right)}_{F,\alpha }\\ {u\left(t\right)}_{F,\beta }\\ {u\left(t\right)}_{F,0}\end{array}\right]=\frac{1}{3}.Math.\left[\begin{array}{ccc}2& -1& -1\\ 0& \sqrt{3}& -\sqrt{3}\\ 1& 1& 1\end{array}\right].Math.\left[\begin{array}{c}{u\left(t\right)}_{F,L.Math..Math.1}\\ {u\left(t\right)}_{F,L.Math..Math.2}\\ {u\left(t\right)}_{F,L.Math..Math.3}\end{array}\right]& \left(3\right)\end{array}$

[0060] A filter 22 then determines the values of the αβ0 components of the voltage but also of the measured filter current i.sub.F,L1 for a predefined frequency, for example the fundamental oscillation or the first harmonic of the switching frequency.

[0061] Taking into consideration the fixed angular relationship between the phases L1, L2 and L3 in the αβ0 system, taking into consideration for example Δφ from the measured voltage values, a reference filter current value i.sub.F,ref,L1 for phase L1 is calculated. The respective phase angle Δφ to be taken into consideration is dependent as follows on the respectively measured phase for the filter current or the differential filter current:

TABLE-US-00001 TABLE 1 Measurement i.sub.F,L1 i.sub.F,L2 i.sub.F,L3 i.sub.F,L1-i.sub.F,L2 i.sub.F,L2-i.sub.F,L3 i.sub.F,L3-i.sub.F,L1 Δφ 0 [00004]$\frac{2.Math..Math.\pi }{3}$ [00005]$\frac{-2.Math..Math.\pi }{3}$ [00006]$\frac{-\pi }{6}$ [00007]$\frac{\pi }{2}$ [00008]$\frac{-5.Math..Math.\pi }{6}$

[0062] The reference current i.sub.F,ref,L1 is, for example, calculated by means of the characteristic values for the parts used, thus the known inductances, resistors and capacitors in the aαβ0.

[0063] If, for example, an absorption circuit in a star connection, as shown in FIG. 7, is used as a filter and if via a current sensor 30, for example in the form of an inductive current transformer the phase L1 is measured, then for example when taking into account the fundamental oscillation ω in the αβ system of coordinates rotating at mains frequency the αβ components of the filter voltage u.sub.F are given by the following:

u.sub.Fαβ0=u.sub.F,α+j.Math.u.sub.F,β=u.sub.F.Math.e.sup.j.Math.(ωt+φ.sup.u.sup.)=u.sub.F.Math.((Cos(ωt+φ.sub.u)+j.Math.sin(ωt+φ.sub.u))  (4)

and through multiplication by e.sup.−jωt

u.sub.F=u.sub.Fαβ0.Math.e.sup.−j.Math.ωt=u.sub.F.Math.(Cos(φ.sub.u)+j.Math.Sin(φ.sub.u))  (4a)

[0064] The calculation of the two αβ components of the reference current i.sub.F,ref is then performed from

[00009]$\begin{array}{cc}{\underset{\_}{i}}_{F,\mathrm{ref}}=i_{F,\mathrm{ref},\alpha }+j.Math.i_{F,\mathrm{ref},\beta }=\frac{{\underset{\_}{u}}_F}{{\underset{\_}{z}}_F}& \left(5\right)\end{array}$

where:

Z.sub.F=R.sub.F(ω)+j.Math.X.sub.F(ω)  (6)

[0065] In this way the two components are obtained for the reference value of the filter current, which is dependent merely on the known reference values for the impedance and the respectively measured filter voltages:

[00010]$\begin{array}{cc}{\underset{\_}{i}}_{F,\mathrm{ref},\alpha }=\frac{u_{F,\alpha }.Math.R_F\left(\omega \right)+u_{F,\beta }.Math.X_F\left(\omega \right)}{\sqrt{{R_F\left(\omega \right)}^2+{X_F\left(\omega \right)}^2}}.Math..Math.{\underset{\_}{i}}_{F,\mathrm{ref},\beta }=\frac{-u_{F,\alpha }.Math.X_F\left(\omega \right)+u_{F,\beta }.Math.R_F\left(\omega \right)}{\sqrt{{R_F\left(\omega \right)}^2+{X_F\left(\omega \right)}^2}}& \left(7\right)\end{array}$

[0066] In order to obtain the single-phase reference current i.sub.F,ref,L1, the vector must still be projected onto the axis of the actual measured current with the angle Δφ from Table 1 given by the embodiment of the measurement. This is obtained by the following equation:

i.sub.F,ref,L1=Re{i.sub.F,ref.Math.e.sup.−j.Math.Δφ}=i.sub.F,ref,α.Math.Cos(Δφ)+i.sub.F,ref,β.Math.Sin(Δφ)  (8)

[0067] In FIG. 10 the associated space vectors are shown, giving the projections when using the individual phases L1, L2 or L3, in particular also when taking into consideration differential current measurements, and therefore corresponds to a representation of the difference angle from Table 1 in the αβ system of coordinates rotating at mains frequency.

[0068] According to a further exemplary embodiment, as shown in FIG. 8, using a current sensor 31 a filter current difference, for example a filter current difference between phases L1 and L2 can be measured. In this case, for the calculation of the reference current another difference angle Δφ is used. As can be seen from the table, an angle of −π/6 must then be used.

[0069] In the comparison means 25 shown in FIG. 6 for example the difference between measured phase current i.sub.F,L1 and the actual value 28, can then be determined in the filter with the reference filter current i.sub.F,ref,L1 of phase L1, thus the desired value 27. Preferably here a time mean value of the difference is formed to minimise possible measurement uncertainties and measurement fluctuations, i.e. measurement errors. The mean value of the difference is given by

[00011]$\begin{array}{cc}\Delta .Math..Math.i_{F,L.Math..Math.1,\mathrm{MW}}\left(t\right)=\frac{1}{T}.Math.{\int }_t^{t+T}.Math.\left(i_{F,\mathrm{ref},L.Math..Math.1}\left(\tau \right)-i_{F,L.Math..Math.1}\left(\tau \right)\right).Math.d.Math..Math.\tau & \left(9\right)\end{array}$

[0070] The time mean value of the desired value is given by

[00012]$\begin{array}{cc}{i}_{F,\mathrm{ref},L.Math..Math.1,\mathrm{MW}}\left(t\right)=\frac{1}{T}.Math.{\int }_t^{t+T}.Math.i_{F,\mathrm{ref},L.Math..Math.1}\left(\tau \right).Math.d.Math..Math.\tau & \left(10\right)\end{array}$

[0071] Via the comparison means 25 by means of an error criterion, an error information signal S can then be generated, if the following equation is satisfied:

Δi.sub.F,L1,MW(t)>i.sub.F,ref,L1,MW(t).Math.limit.sub.F,rel  (11)

limit.sub.F,rel is the error criterion and a predefined value which, for example, is between 10% and 15% for the monitoring of a filter defect and gives the width of the permitted deviations relative to the reference filter current. This value can be freely selected. The error information signal S can then be further evaluated. Depending on the characteristic to be monitored of the filter, so e.g. the structure, ageing or defect, various error criteria can be selected, the values of which are matched to the corresponding application.

[0072] Furthermore, FIG. 6 shows two further embodiments, in which two phases, for example phases L1 and L2 or also all three phases L1, L2, L3 are measured using current sensors.

[0073] When measuring two current phases L1 and L2, these can be transformed via the following transformation 21 in an αβ system:

[00013]$\begin{array}{cc}\left[\begin{array}{c}{i\left(t\right)}_{F,\alpha }\\ {i\left(t\right)}_{F,\beta }\end{array}\right]=\left[\begin{array}{cc}1& 0\\ \frac{1}{\sqrt{3}}& \frac{2}{\sqrt{3}}\end{array}\right].Math.\left[\begin{array}{c}{i\left(t\right)}_{F,L.Math..Math.1}\\ {i\left(t\right)}_{F,L.Math..Math.2}\end{array}\right]& \left(12\right)\end{array}$

[0074] When measuring all three filter current phases the transformation 20 of the filter currents in the αβ0 system is given by the equation (1).

[00014]$\begin{array}{cc}\left[\begin{array}{c}{i\left(t\right)}_{F,\alpha }\\ {i\left(t\right)}_{F,\beta }\\ {i\left(t\right)}_{F,0}\end{array}\right]=\frac{1}{3}.Math.\left[\begin{array}{ccc}2& -1& -1\\ 0& \sqrt{3}& -\sqrt{3}\\ 1& 1& 1\end{array}\right].Math.\left[\begin{array}{c}{i\left(t\right)}_{F,L.Math..Math.1}\\ {i\left(t\right)}_{F,L.Math..Math.2}\\ {i\left(t\right)}_{F,L.Math..Math.3}\end{array}\right]& \left(13\right)\end{array}$

[0075] Following a filter 22 at the frequency to be considered, in the αβ0 or αβ system of coordinates the components according to step 23′ or 23″ of the reference filter currents are calculated and compared with the αβ components or αβ0 components of the measured filter currents for determination of an error criterion.

[0076] FIG. 7 and FIG. 8 show exemplary embodiments of filter current measurements or differential filter current measurements. In FIG. 7 in phase L1 a current sensor 30, for example a Rogowski current transformer or a current transformer with a Hall sensor is arranged which measures the magnetic flow generated by the current flow to determine the current flow. These current transformers 30 demonstrate good accuracy and a robust measurement behaviour and their measurement range can be precisely matched to the filter currents, allowing optimum resolution of measured values to be achieved. As can be seen from FIG. 8, with a single current sensor 31 a differential current can be measured directly by an arrangement of the phases L1 and L2 counter to one another in the current sensor 31.

[0077] By measuring the filter currents also in just one phase of the filter it is possible to identify a change in the impedance of the filter early. Table 2 shows the different kinds of errors that can be detected during single-phase, two-phase or three-phase measurement.

[0078] As can be seen, even with a single-phase filter current measurement, so with particularly low measurement effort, in a star connection of the filters both a supply line breakage and deviation from the rated value of a component of the filter can be detected. For a filter in a delta connection to this end the measurement of a differential phase current Δi must be performed. In Table 2 n/a=not applicable, x=identification possible, ---=identification not possible, I=single-phase current measurement, Δi=differential current measurement of two phases.

TABLE-US-00002 TABLE 2 Measurement 3-phase 2-phase 1-phase Error type Star Star-N Delta Star Star-N Delta Star Star-N Delta N open n/a x n/a n/a — n/a n/a — n/a Supply line x x x x x x x x x interruption Deviation from x x x x x x i i Δi component rated value

[0079] Monitoring of the filter currents is in particular advantageous in apparatus for delivering electrical power, which can only be accessed with difficulty, for example offshore systems, since the filter monitoring takes place electronically and ageing processes, which are particularly important in capacitors, can be identified in advance. Furthermore, there are particular advantages in the continued operation of the systems being enabled by deactivating individual filter groups using corresponding means for isolating the filter groups.

[0080] With reference to FIG. 9 a further exemplary embodiment is to be specified, in which a direct comparison between the αβ components of the filter current I.sub.F,L1 measured in one phase is carried out.

[0081] To this end, initially in step 32 the filter current measured in phase L1, taking into consideration the available voltage values 33 and 34, U.sub.f,alpha and u.sub.f,beta, in the αβ0 system of coordinates, the components of the measured filter current i.sub.F are calculated in the αβ system rotating at mains frequency in step 35. Then a difference is calculated between the respective αβ components 36, 37 of the filter currents measured in step 36′, 37′ and the reference values of the filter current of the αβ components 38, 39. From the difference vector having difference values 40, 41 in the αβ system of coordinates according to step 42 the absolute value is found and fed to a comparison step 44. In the comparison step 44 the absolute value of the difference vector in the αβ system is compared with the absolute value of the filter current reference vector I.sub.F,ref,αβ and for example a quotient is formed and compared with an error criterion in p.u. From this an error information signal S can then be generated.

[0082] A further exemplary embodiment is shown in FIG. 11, representing a simplification of the exemplary embodiment from FIG. 9. Assuming that the voltage component lies in the β axis and the filter current component lies in the α axis, the method according to the invention can insofar be simplified, in that a difference calculation only has to be carried out in one of the αβ components 36, 37. This is, for example, the case for a capacitive filter with sufficient accuracy.

[0083] Similarly to FIG. 9 in FIG. 11 initially in step 35, from the filter current 32 measured in phase L1 taking into consideration the available voltage values U.sub.Falpha, 33 and U.sub.F,beta, 34 in the αβ0 system of coordinates, the components of the measured filter current I.sub.F,α, 36 and I.sub.F,β, 37 are calculated in the αβ system of coordinates rotating at mains frequency. The difference is then formed only between the α component 36 and the reference value of the α component of the filter current 39 to give difference value 40. In step 42, from the α component 40 and the β component 37 the vector magnitude is formed. This value can then be compared in the comparison step 44 with a predefinable error criterion. This can, for example, be formed by considering the desired value of the α component of the filter current 39. From the comparison, an error information signal S can then be generated and, for example, cause a change in the operating state of the apparatus for delivering electrical energy. Similarly to the α component 36, it is also conceivable to use the corresponding β component 37 for the comparison with the reference variable, provided the condition that the component of the filter currents lies in this axis is met.

[0084] All references, including publications, patent applications, and patents cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein.

[0085] The use of the terms “a” and “an” and “the” and similar referents in the context of describing the invention (especially in the context of the following claims) is to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to,”) unless otherwise noted. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.

[0086] Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations of those preferred embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.