Tunable LC filter

Abstract

An inductor-capacitor (LC) filter designed to comply with EMC (Electromagnetic Compatibility) standards comprises capacitors; switches for coupling capacitors; differential-mode inductors for coupling capacitors and switches; and common-mode inductors or a combination of differential-mode inductors and common-mode inductors, where an input signal changes the inductance of differential-mode inductors in the LC filter to modify a frequency response of the LC filter. In the LC filter, differential-mode inductors further comprise identical multiple-winding inductors, and the input signal, which biases the plurality of differential-mode inductors, includes a DC signal or a combination of DC and AC signals. A corner-frequency of the LC filter is adjusted and approximated as: fc=1/(2pisqrt(LC)), where fc is the corner-frequency, L is a composite value of inductance, and C is a composite value of capacitance.

Claims

1. An inductor-capacitor (LC) filter comprising: a plurality of capacitors; a plurality of switches for coupling the plurality of capacitors directly; one or more of the plurality of switches are connected in series with one or more of the plurality of capacitors; a plurality of differential-mode inductors for coupling the plurality of capacitors and the plurality of switches directly, wherein an input signal changes an inductance of the plurality of differential-mode inductors in the LC filter to modify a frequency response of the LC filter, wherein the input signal includes a DC (direct current) signal or a combination of DC and AC (alternating current) signals, wherein the LC filter is tuned by the input signal, and a corner-frequency of the LC filter is adjusted to multiple values, where each value imitates a corresponding fixed-corner-frequency filter in the LC filter, and wherein the LC filter is designed to comply with EMC (Electromagnetic Compatibility) standards and reduces and spreads EMC spectral peaks by transferring energy of the EMC spectral peaks to sidebands of the LC filter.

2. The LC filter according to claim 1, wherein the plurality of differential-mode inductors comprises a plurality of identical multiple-winding inductors.

3. The LC filter according to claim 1, wherein the corner-frequency of the LC filter is adjusted and approximated as:
fc=1/(2pisqrt(LC)), wherein fc is the corner-frequency of the LC filter; L is a composite value of inductance of the LC filter; and C is a composite value of capacitance of the LC filter.

4. The LC filter according to claim 1, wherein the input signal biases the plurality of differential-mode inductors.

5. The LC filter according to claim 1, wherein the plurality of differential-mode inductors further function as a plurality of common-mode inductors.

6. An inductor-capacitor (LC) filter comprising: a plurality of capacitors; a plurality of switches for coupling the plurality of capacitors directly; one or more of the plurality of switches are connected in series with one or more of the plurality of capacitors; a plurality of common-mode inductors for coupling the plurality of capacitors and the plurality of switches directly, wherein an input signal changes an inductance of the plurality of common-mode inductors in the LC filter to modify a frequency response of the LC filter, wherein the input signal includes a DC (direct current) signal or a combination of DC and AC (alternating current) signals, wherein the LC filter is tuned by the input signal, and a corner-frequency of the LC filter is adjusted to multiple values, where each value imitates a corresponding fixed-corner-frequency filter in the LC filter, and wherein the LC filter is designed to comply with EMC (Electromagnetic Compatibility) standards and reduces and spreads EMC spectral peaks by transferring energy of the EMC spectral peaks to sidebands of the LC filter.

7. The LC filter according to claim 6, wherein the corner-frequency of the LC filter is adjusted and approximated as:
fc=1/(2pisqrt(LC)), wherein fc is the corner-frequency of the LC filter; L is a composite value of inductance of the LC filter; and C is a composite value of capacitance of the LC filter.

8. The LC filter according to claim 6, wherein the plurality of common-mode inductors further function as a plurality of differential-mode inductors.

9. The LC filter according to claim 6, wherein the plurality of common-mode inductors comprise a 2-winding common-mode inductor or a 3-winding common-mode inductor, wherein the 2-winding common-mode inductor has 2 coils and the 3-winding common-mode inductor has 3 coils.

10. The LC filter according to claim 6, wherein the input signal biases the plurality of common-mode inductors.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) For a better understanding of the aforementioned embodiments of the invention as well as additional embodiments thereof, reference should be made to the Description of Illustrative Embodiments below, in conjunction with the following drawings in which like reference numerals refer to corresponding parts throughout the figures.

(2) FIG. 1 illustrates the use of a common-mode filter between an AC line and a power converter in accordance with some embodiments.

(3) FIG. 2 illustrates a common-mode inductor in accordance with some embodiments.

(4) FIG. 3 illustrates a first order common-mode filter in accordance with some embodiments.

(5) FIG. 4 illustrates a second order common-mode filter in accordance with some embodiments.

(6) FIG. 5 illustrates a third order common-mode filter in accordance with some embodiments.

(7) FIG. 6 illustrates a circuit diagram for a differential-mode choke implementation in accordance with the first embodiment.

(8) FIG. 7 illustrates (a): a 2-winding (2-coil) common-mode inductor (2-circuit common-mode choke) and (b): a 3-winding (3-coil) common-mode inductor (3-circuit common-mode choke) in accordance with some embodiments.

(9) FIG. 8 illustrates a circuit diagram for a tunable LC filter with a 2-winding (2-coil) common-mode inductor in accordance with some embodiments.

(10) FIG. 9 illustrates a circuit diagram for a tunable LC filter with a 3-winding (3-coil) common-mode inductor in accordance with some embodiments.

(11) FIG. 10 illustrates a circuit diagram for a LLC resonant converter having an adjustable series inductance in accordance with some embodiments.

(12) FIG. 11 illustrates a circuit diagram for a LLC resonant converter having an adjustable magnetizing inductance in accordance with some embodiments.

(13) FIG. 12 illustrates a circuit diagram based on FIG. 6 illustrating an Inverter filtering application in accordance with some embodiments.

(14) FIG. 13 illustrates a circuit diagram based on FIG. 6 illustrating a PFC Converter filtering application in accordance with some embodiments.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

(15) Reference will now be made in detail to embodiments, examples of which are illustrated in the accompanying drawings. In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, it will be apparent to one of ordinary skill in the art that the present invention may be practiced without these specific details. In other instances, well-known methods, procedures, components, circuits, and networks have not been described in detail so as not to unnecessarily obscure aspects of the embodiments.

First Embodiment

(16) FIG. 6 illustrates a circuit diagram for a differential-mode choke implementation. This circuit diagram presents two identical multiple-winding inductors. The LC filter in FIG. 6 comprises a half-bridge converter network including series connected capacitors (13) & switches (14), a plurality of differential-mode inductors (15), and a filter capacitor (13a). An input signal (16) changes an inductance of the plurality of differential-mode inductors in the LC filter to modify a frequency response of the LC filter. The plurality of differential-mode inductors further comprises a plurality of identical multiple-winding inductors. The input signal includes a DC signal or a combination of DC and AC signals and biases the plurality of differential-mode inductors. Furthermore, the plurality of differential-mode inductors within the LC filter further function as a plurality of common-mode inductors.

(17) A corner-frequency of the LC filter is adjusted and approximated as:
fc=1/(2pisqrt(LC)),
where fc is the corner-frequency of the LC filter, L is a composite value of inductance of the LC filter, and C is a composite value of capacitance of the LC filter. Here, the composite value of inductance (L) is calculated by adding inductance values of multiple inductors in series. Similarly, the composite value of capacitance (C) is calculated by adding capacitance values of multiple capacitors in parallel. It is noted that practical inductors can have inductances that vary with current through inductor(s) coils, so a series combination needs to address the inductance-versus-current characteristics of each inductor. Other effects such as frequency of the imposed current and core temperature can alter the inductance. Similarly, capacitors can have voltage, frequency, and temperature dependences.

(18) FIGS. 10 and 11 illustrate the application of the adjustable differential inductor to adjust a resonant frequency of a LLC resonant converter for the purpose of reducing power losses in the switches, and/or reducing EMI emissions, and/or compensating for variations in component parameters. 24 in FIG. 10 is a set of differential inductors configured as a current-bias variable inductance. 21 in FIG. 11 is the series inductor, usually denoted L-sub-r (Document 3, Page 1), 22 is the series capacitor, usually denoted C-sub-r, and 23 is the LLC transformer configured to present an adjustable value of inductance via a current bias winding. The inductance imposed by the transformer has been designated L-sub-shunt or L-sub-m in Document 3, Page 1.

(19) FIGS. 12 and 13 illustrate the application of the differential-inductor-based filter toward reducing harmonics and/or carrier components from the output of an Inverter or from being imposed onto the input side of a PFC converter.

Second Embodiment

(20) The LC filter in accordance with the second embodiment comprises a plurality of capacitors; a plurality of switches for coupling the plurality of capacitors; and a plurality of common-mode inductors for coupling the plurality of capacitors and the plurality of switches. Here, an input signal changes an inductance of the plurality of common-mode inductors in the LC filter to modify a frequency response of the LC filter. The plurality of common-mode inductors further comprise a 2-winding common-mode inductor or a 3-winding common-mode inductor. The input signal biases the plurality of common-mode inductors. Furthermore, the LC filter further comprises a plurality of differential-mode inductors or a combination of the plurality of differential-mode inductors and the plurality of common-mode inductors.

(21) The explanation on common components between the first and second embodiments is omitted.

(22) FIG. 7 illustrates (a): a 2-winding (2-coil) common-mode inductor (2-circuit common-mode choke; 17) and (b): a 3-winding (3-coil) common-mode inductor (3-circuit common-mode choke; 18). A common-mode choke is an inductor, where all the relevant conductors are wound together around the same core.

(23) FIG. 8 illustrates a circuit diagram for a tunable LC filter with a 2-winding (2-coil) common-mode inductor. FIG. 8 shows how one of the coils employed in the 2-winding common-mode inductor (19) shares signals between the bias and power circuits. This configuration couples the bias and power circuits electrically, i.e., they are not electrically isolated. The bias and power circuits share a common electrical point, and this lack of isolation may restrict how the bias circuit is constructed and where/how the common-mode coil may be used. But, the 2-winding common-mode inductors are common and thus tend to be more economical due in part to higher volume of usage.

(24) FIG. 9 illustrates a circuit diagram for a tunable LC filter with a 3-winding (3-coil) common-mode inductor. The 3-winding common-mode inductor (20) in FIG. 9 employs 2 windings for power filter and 1 winding for bias. It is less common, thus could be more expensive, but affords flexibility for the bias circuit design and power circuit connections. The 3-winding common-mode inductors have been used in 3-phase systems and provide a starting point for a 3-coil version of the adjustable inductor-based EMC filter.

Advantageous Effects

(25) In some illustrative implementations, the LC filters in the first and second embodiments reduce and spread EMC spectral peaks by transferring some energy to sidebands made from the interaction of the bias signal with the carrier (peak-generating) signal over time. In addition, the LC filters help attenuate EMC signals that respond to variations in loading. Furthermore, the LC filters are capable of using the same bias circuit to monitor for changes in the filters' and filters' load's ground-leakage current. That is, the LC filters can sense ground faults for safety purposes.

(26) The present invention can be extended to include the LC filter is used to stabilize by adding the current bias to the inductors to minimize the effects of temperature and other environmental variations on the performance of the filter.

Broad Scope of the Invention

(27) While illustrative embodiments of the invention have been described herein, the present invention is not limited to the various preferred embodiments described herein, but includes any and all embodiments having equivalent elements, modifications, omissions, combinations (e.g., of aspects across various embodiments), adaptations and/or alterations as would be appreciated by those in the art based on the present disclosure. The limitations in the claims are to be interpreted broadly based on the language employed in the claims and not limited to examples described in the present specification or during the prosecution of the application, which examples are to be construed as non-exclusive. For example, in the present disclosure, the term preferably is non-exclusive and means preferably, but not limited to. In this disclosure and during the prosecution of this application, means-plus-function or step-plus-function limitations will only be employed where for a specific claim limitation all of the following conditions are present in that limitation: a) means for or step for is expressly recited; b) a corresponding function is expressly recited; and c) structure, material or acts that support that structure are not recited. In this disclosure and during the prosecution of this application, the terminology present invention or invention may be used as a reference to one or more aspect within the present disclosure. The language present invention or invention should not be improperly interpreted as an identification of criticality, should not be improperly interpreted as applying across all aspects or embodiments (i.e., it should be understood that the present invention has a number of aspects and embodiments), and should not be improperly interpreted as limiting the scope of the application or claims. In this disclosure and during the prosecution of this application, the terminology embodiment can be used to describe any aspect, feature, process or step, any combination thereof, and/or any portion thereof, etc. In some examples, various embodiments may include overlapping features. In this disclosure, the following abbreviated terminology may be employed: e.g. which means for example.