Abstract:
A filter for filtering a three-phase electrical power waveform produces a three-phase output power waveform. The filter has an inductor with three sets of first and second coils, each having a capacitor connected in series therewith. Each of the three sets of first and second coils has a tap intermediate the first and second coils where the output waveform is present, each tap capable of being connected to a load. In some embodiments, the inductor is passive adaptive and includes resistors for reducing current in-rush.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation of U.S. patent application Ser. No. 14/249,043, filed Apr. 9, 2014, which claims the benefit of U.S. Provisional Application No. 61/809,963, entitled “Drive Harmonic Mitigation Devices and Methods of Use Thereof,” filed on Apr. 9, 2013, whose disclosures are incorporated herein by reference in their entirety for all purposes. 
    
    
     FIELD 
     The present invention relates to conditioning of an electrical power signal, and more particularly, to apparatus and methods for reshaping an electrical power output waveform generated by a first device and presenting the altered waveform to another device or circuit. 
     BACKGROUND 
     Circuits for altering electrical power waveforms are known. For example, L-R-C (inductor-resistor-capacitor) low pass filters and sine wave filters are known for use in altering a power output from a variable speed drive for an electric motor, e.g., for conditioning a pulse width modulated output in order to supply the motor with a more sinusoidal power waveform. Notwithstanding, improved and/or alternative power conditioning circuits remain desirable. 
     SUMMARY 
     The disclosed subject matter relates to a device for modifying an input electrical waveform generated by a source of electrical power provided on a first conductor. The device includes a first inductor capable of connecting to the first conductor. A second inductor is connected in series to the first inductor distal to the first conductor and a capacitor is connected in series with the second inductor distal to the first inductor. A second conductor is connected between the first inductor and the second inductor, the second conductor capable of presenting an output waveform. 
     In another embodiment of the present disclosure, a relative polarity between the first inductor and the second inductor is additive. 
     In another embodiment of the present disclosure, the input electrical waveform is a first electrical waveform and wherein the source of electrical power produces a plurality of electrical waveforms, each provided on one of a plurality of conductors and further comprising a plurality of devices, each having a first inductor capable of connecting to one of the plurality of conductors, a second inductor connected in series to the first inductor, a capacitor connected in series with the second inductor distal to the first inductor and a plurality of second conductors connected between the first inductor and the second inductor, the plurality of second conductors capable of presenting a multi-phase output waveform. 
     In another embodiment of the present disclosure, the plurality of electrical waveforms is three in number, each having a different phase to provide three-phase electrical power at three second conductors. 
     In another embodiment of the present disclosure, the first inductor and the second inductor are disposed on a common core. 
     In another embodiment of the present disclosure, each of the series connected first inductors and second inductors are disposed on a common core. 
     In another embodiment of the present disclosure, the source of electrical power is an adjustable speed drive. 
     In another embodiment of the present disclosure, the source of electrical power produces the input electrical waveform by pulse-width modulation. 
     In another embodiment of the present disclosure, the output waveform is supplied to an electric motor. 
     In another embodiment of the present disclosure, the device reduces harmonic currents otherwise present absent the second inductor. 
     In another embodiment of the present disclosure, a resistor is interposed between and in series with the second inductor and the capacitor. 
     In another embodiment of the present disclosure, at least one of the first and second inductors is an adaptive passive inductor. 
     In another embodiment of the present disclosure, each of the first and second inductors is an adaptive passive inductor. 
     In another embodiment of the present disclosure, the device has an E-shaped core, each of the first and second inductors being wound about a corresponding leg of the E-shaped core and further comprising an I-shaped core disposed proximate the ends of each leg of the E-shaped core and further comprising a high permeability core gap piece disposed between each leg of the E-shaped core and the I-shaped core. 
     In another embodiment of the present disclosure, a filter for filtering an input electrical power waveform produces an output power waveform. The filter has an inductor having first and second coils and a capacitor connected in series. The filter has a tap terminal intermediate the first and second inductors. A conductor extends from the tap terminal and is capable of being connected to a load. 
     In another embodiment of the present disclosure, the input electrical power is provided by an adjustable speed drive and the load is a motor. 
     In another embodiment of the present disclosure, the inductor is of the passive adaptive type and further comprising a resistor connected in series between the inductor and the capacitor. 
     In another embodiment of the present disclosure, a filter for filtering a three-phase electrical power waveform produces a three-phase output power waveform. The filter has an inductor having three sets of first and second coils, each having a capacitor connected in series therewith. Each of the capacitors are connected in common distal to the series connection with the second coil. Each of the three sets of first and second inductors having a tap intermediate the first and second inductors where the output waveform is present, each tap capable of being connected to a load. 
     In another embodiment of the present disclosure, the inductor is passive adaptive and further comprising a resistor connected in series between the inductor and the capacitor, the load being a three-phase electric motor. 
     In another embodiment of the present disclosure, the inductor is formed on an E-shaped core each of the three sets of coils being wound on a corresponding leg of the E shape. 
     In another embodiment of the present disclosure, the device has a three phase core, each of the first and second inductors being wound about a corresponding portion of the three phase core. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the present disclosure, reference is made to the following detailed description of exemplary embodiments considered in conjunction with the accompanying drawings. 
         FIG. 1  is circuit diagram of a prior art sine wave filter. 
         FIG. 2  is a circuit diagram of a sine wave filter in accordance with a first embodiment of the present disclosure. 
         FIG. 3  is a schematic circuit diagram of an inductor that may be used with a sine wave filter in accordance with another embodiment of the present disclosure. 
         FIG. 4  is a circuit diagram of a sine wave filter in accordance with another embodiment of the present disclosure. 
         FIG. 5  is a graph of frequency response for a sine wave filter in accordance with an embodiment of the present disclosure compared to a prior art filter. 
         FIG. 6  is a rear perspective view of a sine wave filter in accordance with an embodiment of the present disclosure. 
         FIG. 7  is a front perspective view of a sine wave filter in accordance with an embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     An aspect of the present disclosure is the use of the apparatus disclosed herein for drive output filters that provide a nearly sinusoidal output voltage when driven from variable frequency drives or other types of Pulse-width modulation (PWM) inverters with switching frequencies from 2 kHz to 8 kHz. In some embodiments, the apparatus of the present disclosure are utilized to eliminate and/or minimize the problem of motor/cable insulation failures, heating, and/or audible noise. In some embodiments, the apparatus disclosed by the present disclosure are utilized to reduce electromagnetic interference (EMI) by eliminating the high dV/dt associated with inverter output waveforms. In some embodiments, added cable protection and the economy of using standard grade electrical wire is a significant benefit of using the sine wave filters of the present disclosure to protect against long lead drive-to-motor excess voltage problems. 
       FIG. 1  shows a prior art L-R-C (inductor-resistor-capacitor) low pass drive output filter F. Such filters may also be known as Sine wave filters. Prior art Sine wave filters may shunt a high PWM switching frequency (typically 2 kHz to 8 kHz), e.g., from an adjustable speed drive (ASD) through capacitors C 1 , C 2 , C 3  and provides primarily just the fundamental voltage waveform to a motor (typically 10 or 120 Hz). In some instances, a three phase inductor I is tuned with a capacitor(s) C 1 , C 2 , C 3  below the drive switching frequency. In some instances, a resistor or resistors R 1 , R 2 , R 3  may be used to provide damping, to increase filter stability and reduce the initial inrush of current to the filter F when the drive ASD is first turned on. An aspect of the present disclosure is the recognition that prior art approaches may employ a trade-off between inductor size and capacitance value. More particularly, because the inductor is made from copper windings, it is typically the most expensive part of the filter. As a result, there is an incentive to reduce the size of the inductor, but this has the undesirable effect of lowering its inductance. To compensate for the lowered inductance, the capacitance value of the capacitor is increased to maintain the same low pass filter cutoff frequency. This can result in an increase in the harmonic currents through the inductor and the capacitor. Increases in harmonic current increase power losses within the inductor, with the electrical power being converted to waste heat and mechanical vibration. The increased winding losses in the inductor conductors may be due to proximity effects, gap heating, and skin effect heating associated with increased harmonic current. These factors represent a limitation on the reduction of inductor size, in that the inductor size may need to be maintained at a certain minimum to reduce the flux density in the core to reduce power losses to an acceptable level or a more expensive, lower loss core material may need to be used. 
       FIG. 2  shows a filter  10  in accordance with an embodiment of the present disclosure interposed between an adjustable speed drive ASD  12  and a motor  14 . The ASD  12  would receive electrical power from, e.g., a power grid or a generator (not shown). The motor  14  has a three phase input as indicated by lines  16 ,  18 ,  20  and the ASD has a three phase output, as indicated by lines  22 ,  24 ,  26 . An inductor  28  intermediates between the ASD  12  and the motor  14 . The inductor  28  may be of the passive adaptive type, as shown in  FIG. 3  below. The filter  10 , may permit reducing inductor size, while avoiding the above-mentioned issues pertaining to winding losses, harmonic currents, etc., outlined above associated with reducing the size of the typical L-R-C filter. This greater latitude in reducing inductor  28  size is due in part to the arrangement of the coils A, B, C, D, E, F and the connections of the motor lines  16 ,  18 ,  20  to tap terminals  4 ,  5 ,  6  intermediate windings A and D, B and E and C and F, respectively. The inductor  28  is coupled to the ASD at terminals  1 ,  2  and  3  and has a plurality of windings A, B, C, D, E, F, each of which have a variable inductance attributable to the inductor  28  being of a passive adaptive type. Terminals  7 ,  8 ,  9  at the end of windings D, E, and F, respectively, connect to resister-capacitor couples  30  and  32 ,  34  and  36  and  38  and  40 , respectively. The polarity of windings A, B, C with respect to D, E, F are shown by a dot. 
       FIG. 3  shows an inductor  128  that may be utilized in filter  10  of  FIG. 2 . The inductor  128  has an E-shaped core  142  and an I-shaped core element  144 , both of which may be made from core steel. The windings A and D, B and E and C and F are disposed around the three arms  142 A,  142 B and  142 C of the E-shaped core  142 , respectively. The terminals  1 - 9  referred to above in  FIG. 2  are also shown in  FIG. 3 . High permeability core gap pieces, “FAPS”  146 A,  146 B,  146 C, as described in U.S. Patent Publication No. 20120256719, entitled “Harmonic Mitigation Devices and Applications Thereof,” to Shudarek et al., which is incorporated by reference herein for all purposes, may be interposed between each of the arms  142 A,  142 B,  142 C and the I-shaped element  144 . The FAPS have the effect of providing adaptive passive inductance as indicated by the arrow symbols on the coils A, B, C, D, E, F in  FIG. 2 . When an inductor, like inductor  128  of  FIG. 3 , is used in the filter  10  of  FIG. 2 , windings A, B and C are coupled to windings D, E and F with the polarities indicated in  FIG. 2  to increase the inductance tuned with the capacitor. In the embodiment of  FIG. 2 , the capacitors  32 ,  36 ,  40  will only need to be rated for a reduced current as compared to the typical filter (See  FIG. 1 ) with just three coils, e.g., A, B and C. In some embodiments, the D, E and F windings only need to be rated for the capacitor current opposed to the A, B and C windings which have to be rated for the full motor current. In some embodiments, the D, E and F windings add relatively minor cost and size to the filter  10 . In some embodiments, the voltage insertion loss of the filter is also reduced since only windings A, B and C are in series with the motor  14  and not windings D, E and F. While the inductor  28 ,  128  of  FIG. 3  shows a variable inductance by coils A, B, C, D, E, F, attributable to the use of FAPS, an inductor made without FAPS, such as described in U.S. Pat. No. 7,142,081 may be used for some applications. The inductor  28 ,  128  may have a three phase configuration other than an EI configuration as described above relative to  FIG. 3 . For example, the inductor  28 ,  128  may have multiple gaps per leg. 
     Some embodiments, e.g., as illustrated by filter  10  of  FIG. 2 , may require damping e.g., by resistors  30 ,  34 ,  38  to reduce inrush when the filter  10  is first energized to reduce ringing near the resonant frequency of the filter  10  during operation. Alternatively, in some applications, the filter  10  may not require additional damping.  FIG. 4  shows a filter  210  in accordance with an embodiment of the present disclosure without damping resistors like  30 ,  34 ,  38  or the adaptive passive inductor  28  utilized in the embodiment of  FIG. 2 . The inductor  228  of  FIG. 4  is similar to the one shown in  FIGS. 2 and 3  but without the FAPS. The arrangement of the coils A, B, C, D, E, F and the connections of the motor lines  216 ,  218 ,  220  to tap terminals  4 ,  5 ,  6  intermediate windings A and D, B and E and C and F, respectively, is the same as in  FIGS. 2 and 3 . The inductor  228  is coupled to the ASD  212  at terminals  1 ,  2  and  3 . Each individual coil, D, E, and F, displays self-inductance and additional, mutual inductances from the other five coils and may each be tuned with the capacitors  250 ,  252 ,  254 , respectively, to the switching frequency of the ASD drive  212 . 
       FIG. 5  shows the difference in frequency response between a prior art drive output filter, e.g., as shown in  FIG. 1  and the filter  210  shown in  FIG. 4 .  FIG. 5  shows that the prior art filter F exhibits a gradual response, whereas the filter  210  exhibits an optimal attenuation at a specific frequency, in the example shown in  FIG. 4   a,  2 kHz. 
       FIGS. 6 and 7  show a filter  310  in accordance with an embodiment of the present disclosure where additional damping by resistors is omitted consistent with the circuit shown in  FIG. 4 . The filter  310  includes a core  328  and capacitors  350 ,  352 , and  354 . The A, B and C windings of the filter  310  may be constructed from multiple turns, e.g., twelve, of insulated 7.5″×0.035″ copper sheet. The D, E and F windings of the filter  310  may be wound with, e.g., four turns of biflar 0.102″×0.204″ magnet wires. In one embodiment, the filter  310  may be used as a filter for a 480 V motor rated at 415 A, which is connected to the filter  310  via lines  316 ,  318 ,  320 . The present invention is explained with reference to the attached drawings, wherein like structures are referred to by like numerals throughout the several views. The drawings shown are not necessarily to scale, with emphasis instead generally being placed upon illustrating the principles of the present invention. Further, some features may be exaggerated to show details of particular components. 
     The figures constitute a part of this specification, include illustrative embodiments of the present invention and illustrate various objects and features thereof. Further, the figures are not necessarily to scale, in that some features may be exaggerated to show details of particular components. In addition, any measurements, specifications and the like shown in the figures are intended to be illustrative, and not restrictive. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention. 
     Detailed embodiments of the present invention are disclosed herein, however, it is to be understood that the disclosed embodiments are merely illustrative of the invention that may be embodied in various forms. In addition, each of the examples given in connection with the various embodiments of the invention are intended to be illustrative, and not restrictive. Any alterations and further modifications of the inventive feature illustrated herein, and any additional applications of the principles of the invention as illustrated herein, which would normally occur to one skilled in the relevant art and having possession of this disclosure, are to be considered within the scope of the invention. 
     Throughout the specification and claims, the following terms take the meanings explicitly associated herein, unless the context clearly dictates otherwise. The phrases “an embodiment” and “in some embodiments” as used herein do not necessarily refer to the same embodiment(s), though it may. Furthermore, the phrases “another embodiment” and “in some other embodiments” if used herein, do not necessarily refer to a different embodiment, although it may. Various embodiments of the invention may be readily combined, without departing from the scope or spirit of the invention. 
     In addition, as used herein, the term “or” is an inclusive “or” operator, and is equivalent to the term “and/or,” unless the context clearly dictates otherwise. In addition, throughout the specification, the meaning of “a,” “an,” and “the” include plural references. The meaning of “in” includes “in” and “on.” 
     It will be understood that the embodiments described herein are merely exemplary and that a person skilled in the art may make many variations and modifications without departing from the spirit and scope of the claimed subject matter. For example, while an iron/steel core is shown for coils A, B, C, D, E, F in  FIGS. 2-4 , a ferrite core could be used. All such variations and modifications are intended to be included within the scope of the appended claims.