EMI Suppression Components

Abstract

An EMI suppression assembly (10) is provided that includes a piezoelectric element (12) configured to provide a low impedance propagation path for electromagnetic disturbances at a resonant frequency of the piezoelectric element (12).

Description

Technical Field

[0001] The present disclosure relates to electromagnetic interference suppression assemblies. In particular, the present disclosure relates to electromagnetic interference suppression assemblies having piezoelectric elements. Background Art

[0002] Electromagnetic interference (EMI) may be caused by electromagnetic disturbances generated by electrical devices and may adversely affect the performance of other electrical devices. To reduce the emission of electromagnetic disturbances, active or passive EMI suppression components may be used. Summary of the invention

[0003] The present disclosure is directed to an EMI suppression assembly that includes a piezoelectric element configured to provide a low impedance propagation path for electromagnetic disturbances at a resonant frequency of the piezoelectric element.

[0004] It is worth noting that the term "EMI suppression component" as used throughout the description refers in particular to a (passive) electrical component, such as a capacitor, which can be used to suppress the propagation of electromagnetic disturbances. Furthermore, the term "electromagnetic disturbance" as used throughout the description refers in particular to "any electromagnetic phenomenon (IEC, 1989) that can degrade the performance of a device, equipment or system or adversely affect active or inert materials" [Goedbloed: Electromagnetic Compatibility, P.4, (1993)].

[0005] Furthermore, the term "piezoelectric element" as used throughout the description refers in particular to a transducer that mechanically deforms (due to the inverse piezoelectric effect) upon application of an electric field. Additionally, the term "resonant frequency" as used throughout the description refers in particular to an excitation frequency at which the electrical impedance is at a local minimum. For example, by measuring the current and voltage while sweeping a range of electrical excitation frequencies, and calculating the electrical impedance, it is possible to determine the local minimum of the corresponding electrical impedance diagram (see Figure 1a ) to derive the resonant frequency.

[0006] Providing a low impedance propagation path for electromagnetic disturbances at the resonant frequency of the piezoelectric element allows for selective attenuation of peaks of the disturbance spectrum. Thus, by tuning the piezoelectric element to (the peaks of) the disturbance spectrum, attenuation can be improved compared to (conventional) capacitors which would (by themselves) not allow for selective attenuation of said peaks. Furthermore, many piezoelectric materials present advantageous properties with respect to insulation and breakdown voltage, which makes EMI suppression components applicable to a wide range of scenarios.

[0007] The EMI suppression component may be included in the power filter. For example, the terminals of the EMI suppression component may be (directly) connected (via wires) to the poles of a two-wire single-phase, three-wire single-phase, three-wire two-phase, three-wire three-phase or four-wire three-phase power distribution network / system.

[0008] The EMI suppression component may be included in a circuit configured to operate at a fixed switching or clock frequency to induce an electromagnetic disturbance having a spectrum with a peak, wherein the resonant frequency of the piezoelectric element matches the peak frequency.

[0009] Thus, an EMI suppression component can suppress the propagation of electromagnetic disturbances over a relatively large frequency band (like a "conventional" capacitor), while also providing higher suppression over a relatively smaller frequency band around the resonant frequency.

[0010] The frequency spectrum of the electromagnetic disturbance may have another peak at another resonance frequency of the piezoelectric element.

[0011] For example, the piezoelectric material and dimensions of the piezoelectric element can be selected during the design phase so that the piezoelectric element has several resonant frequencies that match the peaks of the spectrum of the electromagnetic disturbance. Thus, not only one peak can be suppressed, but two (or more) peaks can be suppressed by using a single EMI suppression component.

[0012] EMI suppression components can act as Y capacitors.

[0013] For example, one terminal of the EMI suppression component may be connected to a safety ground, and the other terminal of the EMI suppression component may be connected to line, neutral, to a DC plus or DC minus of an intermediate circuit (dc link) of a fixed frequency pulse width or phase shift controlled converter, or to any other suitable potential of the converter. During the circuit design phase, the EMI suppression component may replace or supplement one or more Y capacitors. In this regard, it should be noted that the local impedance minimum caused by the resonance of the EMI suppression component may allow for better peak disturbance attenuation than a Y capacitor with the same capacitance ( Figure 1a ). Due to existing restrictions on the capacitance value resulting from the allowed leakage current, this makes the EMI suppression component particularly useful when acting as a Y-capacitor.

[0014] EMI suppression components can act as X-capacitors.

[0015] For example, one terminal of the EMI suppression component may be connected to the line and the other terminal of the EMI suppression component may be connected to the neutral line, or one terminal of the EMI suppression component may be connected to the DC plus and the other terminal of the EMI suppression component may be connected to the DC minus of the intermediate circuit (dc link) of a fixed frequency pulse width or phase shift controlled converter, or to any other suitable potential of the converter, thereby attenuating differential mode disturbances. Therefore, at the circuit design stage, the EMI suppression component may be envisioned to replace or supplement one or more (or even all) X capacitors within a given circuit design.

[0016] The EMI suppression components may be arranged between the galvanically isolated primary and secondary sides of the converter. The converter may be a power supply operating at a fixed switching frequency. For example, the converter may be a flyback converter, an active clamp flyback converter, a forward converter, an active clamp forward converter, an asymmetric half bridge, a phase shifted full bridge, or a dual active bridge.

[0017] The circuit may further comprise another electromagnetic interference suppression component, wherein the another electromagnetic interference suppression component acts as a line filter.

[0018] The circuit may further include a capacitor and / or another EMI suppression component connected in parallel to the electromagnetic interference suppression component.

[0019] By connecting capacitors and EMI suppression components in parallel, attenuation can be improved over a relatively large frequency band. By connecting multiple EMI suppression components in parallel, multiple different peaks of the electromagnetic disturbance spectrum can be attenuated or the attenuation of a single peak can be improved.

[0020] The circuit may further comprise a ceramic oscillator, wherein the ceramic oscillator comprises a piezoelectric resonator. The piezoelectric resonator may have the same piezoelectric material as the piezoelectric element and / or may have the same temperature dependence of one or more resonant frequencies as the piezoelectric element (in the operating range of the ceramic oscillator).

[0021] Therefore, if a temperature change occurs, the oscillator frequency and the resonant frequency may experience the same frequency shift, so that both the oscillator frequency and the resonant frequency remain equal or at least well aligned. Therefore, the drift of the resonant frequency may not adversely affect EMI suppression.

[0022] In another example, the piezoelectric element may function as a piezoelectric resonator of a ceramic oscillator.

[0023] For example, a piezoelectric element may have three or four terminals, wherein a first pair of terminals (ports) is used in connection with EMI suppression, and a second pair of terminals (different from the first pair of terminals) is used in connection with a ceramic oscillator.

[0024] The circuit may further include an oscillator, wherein the oscillator operates at the resonant frequency of the piezoelectric element. In addition, the piezoelectric element can be used within the oscillator to directly derive the operating frequency of the electronic device. This derivation can deliver a frequency different from the resonant frequency, such as half the resonant frequency, one third of the resonant frequency, etc.

[0025] The piezoelectric element may be sandwiched between walls of the housing of the EMI suppression assembly or between a wall of the housing of the EMI suppression assembly and another piezoelectric element.

[0026] By clamping (sandwiching) the piezoelectric element, the resonance frequency can be adapted.

[0027] The circuit may be included in an apparatus further comprising an integrated circuit configured to control a switching or clock frequency of the circuit to achieve an effect that the switching or clock frequency or a harmonic of the switching or clock frequency matches the resonant frequency of the piezoelectric element. The integrated circuit may be connected to the piezoelectric resonator.

[0028] The circuit may be included in a device and be, for example, a switching power supply, a digital circuit, a motor, a motor driver, or an electronic circuit (eg, a power electronic circuit).

[0029] Thus, EMI suppression components may be employed in any circuit operating at a substantially constant frequency that produces electromagnetic disturbances having a frequency spectrum with different peaks.

[0030] The resonant frequency of the piezoelectric element may be tuned to a fixed switching or clock frequency or a harmonic of a fixed switching or clock frequency, wherein the fixed switching or clock frequency or a harmonic of the fixed switching or clock frequency falls under applicable EMI regulations.

[0031] For example, if only electromagnetic disturbances having frequencies at or above 150 kHz are dropped under applicable EMI regulations, the fixed switching or clock frequency can be at or above 150 kHz, where the resonant frequency of the piezoelectric element can be tuned to the fixed switching or clock frequency, or the fixed switching or clock frequency can be below 150 kHz, where the resonant frequency of the piezoelectric element can be tuned to a harmonic of the fixed switching or clock frequency, where the harmonic has a frequency above 150 kHz.

[0032] More specifically, circuits such as switching power supplies, motor drives or other power electronic circuits often operate in a frequency band that allows to advantageously exploit the fact that EMI regulations must be met starting at a certain frequency (e.g., for many applications, EMI requirements are met starting at 150 kHz). Therefore, frequencies slightly below 150 kHz, 75 kHz, 50 kHz, etc. are preferred, since then only the second, third, fourth harmonics, etc. must be suppressed. For these applications, the EMI suppression components can be tuned to those different frequencies above 150 kHz that exhibit high disturbance levels.

[0033] The starting frequency for meeting EMI regulations usually results in a frequency gap where possible improvements due to higher frequencies cannot be achieved due to the requirements of meeting said EMI regulations. The proposed EMI suppression components allow operation in these frequency bands, since the EMI can be sufficiently suppressed by tuning the resonance to the (fundamental) operating frequency of the circuit.

[0034] Manufacturing the EMI suppression component may include determining a peak in a frequency spectrum of electromagnetic disturbances generated by the circuit, and determining a piezoelectric material and dimensions of a piezoelectric element of the EMI suppression component, wherein the piezoelectric element of the EMI suppression component has a resonant frequency that matches the peak frequency of the frequency spectrum.

[0035] That is, EMI suppression components can be fitted to a given circuit during the design phase.

[0036] Manufacturing the electrical device may include selecting an EMI suppression component, and adapting an operating frequency of a circuit of the electrical device so that the adapted circuit generates an electromagnetic disturbance having a spectrum with a peak, wherein the peak frequency matches a resonant frequency of a piezoelectric element of the selected EMI suppression component.

[0037] That is, the circuit can also be adapted to available EMI suppression components. For example, EMI suppression components may be available at a variety of given resonant frequencies, and the EMI suppression component requiring the least amount of adaptation work can be selected in view of a given circuit design.

[0038] It should be appreciated that the features and attendant advantages of the disclosed EMI suppression components / circuits / devices may be achieved by the disclosed methods, and vice versa. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] The foregoing aspects and many of the attendant advantages will be more readily understood by reference to the following detailed description when taken in conjunction with the accompanying drawings, wherein like reference numerals refer to like parts throughout the various views unless otherwise specified.

[0040] Figure 1 shows a schematic cross-sectional view of an EMI suppression assembly according to an example;

[0041] Figure 1a Demonstrating (conventional) capacitors and Figure 1 Comparison between the impedances of the EMI suppression components illustrated in;

[0042] Figure 2a Demonstrating the first example Figure 1 A schematic top view of an EMI suppression component;

[0043] Figure 2b Demonstrating the second example Figure 1 A schematic top view of an EMI suppression component;

[0044] Figure 2c A schematic cross-sectional view showing a piezoelectric element according to a first example;

[0045] Figure 2d A schematic top view showing a piezoelectric element according to a second example;

[0046] Figure 2eshows a schematic cross-sectional view of an EMI suppression assembly according to another example;

[0047] Figure 2f A clamped piezoelectric element is shown;

[0048] FIG3a shows a block diagram of a prior art circuit;

[0049] Figure 3b A block diagram showing a circuit according to the present invention;

[0050] Figure 3c Show Figure 3b Modification of the circuit;

[0051] Figure 3d Show Figure 3c possible implementation plans for the modification;

[0052] Figure 4a and Figure 4b shows the attenuation of the peak of the electromagnetic disturbance spectrum;

[0053] Figure 5 A flow chart showing a method of manufacturing an EMI suppression assembly; and

[0054] Figure 6 A flow chart showing a method of manufacturing an electrical device.

[0055] It is worth noting that the drawings are not drawn to scale, and unless otherwise indicated, they are intended only to conceptually illustrate the structures and procedures described herein. In addition, it should be understood that the drawings and the following detailed description relate to examples, and should not be interpreted as limiting the inventive concept to any one of the physical configurations shown. DETAILED DESCRIPTION

[0056] Figure 1 A schematic cross-sectional view of an exemplary EMI suppression component 10 is shown. The EMI suppression component 10 includes a piezoelectric element 12, i.e., a structure made of a piezoelectric material (e.g., lead zirconate titanate, barium titanate, lithium niobate, etc.). The EMI suppression component 10 has a port 22 having a first terminal 24 electrically connected to a conductive material layer 28 (a first electrode) disposed on a first side of the piezoelectric element 12, and a second terminal 26 electrically connected to a conductive material layer 30 (a second electrode) disposed on a second side of the piezoelectric element 12. Figure 1 As shown in , the conductive material layers 28, 30 (electrodes) may be (directly) adhered to the piezoelectric element 12 and form a plate capacitor.

[0057] When a (non-zero) voltage is applied to the terminals 24, 26, the electromagnetic field generated between the layers of conductive material 28, 30 induces mechanical stress in the piezoelectric element 12 due to the inverse piezoelectric effect (to which the piezoelectric material of the piezoelectric element 12 is susceptible). As a result, the piezoelectric element 12 changes its shape. If the electromagnetic field changes periodically, the piezoelectric element 12 oscillates around its initial position.

[0058] Figure 1a A (conventional) capacitor (i.e. a capacitor having a dielectric material between electrodes that are not susceptible to the piezoelectric effect) and a Figure 1 The impedance of the EMI suppression component 10 is shown in FIG. Figure 1a As can be seen in FIG. 1 , if the voltage applied to terminals 24, 26 is alternating at the resonant frequency of piezoelectric element 12, the impedance of EMI suppression assembly 10 is at a local minimum. Thus, EMI suppression assembly 10 provides a low impedance propagation path ("short circuit") for electromagnetic disturbances at the resonant frequency. At other frequencies, EMI suppression assembly 10 behaves like a "conventional" capacitor.

[0059] like Figure 2a to Figure 2d As shown in FIG, the piezoelectric element 12 may be provided in various forms. For example, the piezoelectric element 12 may be shaped as a (single) disk ( Figure 2a ) or a single sheet / beam ( Figure 2b ). However, the piezoelectric element 12 may also take a more "complex" form and comprise several disks / plates / beams (of different sizes), such as Figure 2c and Figure 2d In addition, Figure 2e As shown in FIG. 1 , the EMI suppression assembly 10 may include multiple (separate) piezoelectric elements 12 (of different sizes / shapes), wherein the electrodes 28, 30 (arranged at the sides) of the piezoelectric elements 12 may be connected in parallel. Figure 2f As shown in , piezoelectric element 12 may be, for example, sandwiched (clamped) between walls of a housing of EMI suppression assembly 10 .

[0060] FIG. 3a shows a switching power supply 32a (flyback converter) and a power supply filter 34a according to the state of the art. The switching power supply 32a is controlled via a control circuit 38 connected to an oscillator 36a (RC circuit). Figure 3bAs shown in , any (conventional) capacitor within the power filter 34a (which increases the filtering of electromagnetic disturbances) can be replaced or supplemented by the EMI suppression component 10. That is, the power filter 34 can include one or more EMI suppression components 10 acting as X capacitors and one or more EMI suppression components 10 acting as Y capacitors. Therefore, when the EMI suppression components 10 are adopted, common-mode and differential-mode disturbances can be filtered. The dashed components can still be used instead of being replaced, however, due to the adoption of the EMI suppression components 10, the capacitance, inductance, number, size and / or cost of the components can be reduced.

[0061] Furthermore, due to the favorable properties of available piezoelectric materials with respect to insulation and breakdown voltage, both (galvanically separated) sides of a fixed frequency converter, such as a flyback converter, a forward converter, an asymmetric half-bridge, a phase-shifted full-bridge, a dual active bridge, etc., can be connected to the EMI suppression component 10 (acting as a Y-capacitor). Furthermore, the EMI suppression component 10 can be used in place of or in parallel to any (conventional) capacitor in an electronic device for reducing EMI by providing a "high frequency short circuit".

[0062] In addition, if Figure 3c As shown in FIG. 1 , oscillator 36a may be replaced by a ceramic oscillator 36. The piezoelectric material of the ceramic oscillator 36 may be similar to or the same as the piezoelectric material of one or more piezoelectric elements 12 of the EMI suppression assembly 10 within the circuit, so that temperature-induced shifts in the resonant frequency do not cause frequency misalignment. For example, Figure 3d As shown in , the ceramic oscillator 36 may even share the piezoelectric element 12 with the EMI suppression assembly 10 .

[0063] Figure 4a An exemplary disturbance spectrum 40 is shown. To reduce the disturbance intensity at peak 42 of spectrum 40, piezoelectric element 12 and / or electrodes 28 and 30 of EMI suppression assembly 10 may be selected so that the resonant frequency of piezoelectric element 12 (see Figure 1a ) corresponds roughly to the frequency of peak 42. Figure 4b As shown in FIG. 1 , the EMI suppression assembly 10 allows for an improved (narrowband) attenuation of the peak 42' compared to the use of (conventional) capacitors. By further adapting the piezoelectric element 12, the electrodes 28 and 30 or by connecting a plurality of piezoelectric elements 12 / EMI suppression assemblies 10 in parallel, one or more additional peaks of the spectrum 40 may be attenuated. Thus, each piezoelectric element 12 may attenuate one or more disturbance peaks 42.

[0064] Figure 5A flow chart is shown of a method of making an EMI suppression assembly 10. The method may begin at step 44 of determining a peak 42 of a frequency spectrum 40 of electromagnetic disturbances generated by a circuit. The process may then proceed to step 46 of determining a piezoelectric material and dimensions of a piezoelectric element 12 and a size / shape of electrodes 28 and 30 of the EMI suppression assembly 10, wherein the piezoelectric element 12 of the EMI suppression assembly 10 has a resonant frequency that matches the peak frequency of the frequency spectrum 40.

[0065] Furthermore, instead of tailoring the EMI suppression component 10 to the circuit, the circuit can also be designed to fit an available EMI suppression component 10, such as Figure 6 is shown in the flow chart. Figure 6 The method shown in the flowchart of FIG. 1 begins at step 48 by selecting an EMI suppression component 10. After the EMI suppression component 10 has been selected, the method continues at step 50 by adapting the operating frequency of the circuit so that the adapted circuit generates an electromagnetic disturbance whose frequency spectrum has a peak, wherein the peak frequency matches the resonant frequency of the piezoelectric element 12 of the selected EMI suppression component 10.

[0066] Description of Reference Numerals

[0067] 10 EMI Suppression Components

[0068] 12 Piezoelectric element

[0069] 12a Disc

[0070] 12b Sheet / Beam

[0071] Port 22

[0072] 24 First terminal

[0073] 26 Second terminal

[0074] 28 Conductive material (layer)

[0075] 28a Conductive material (layer)

[0076] 30 Conductive material (layer)

[0077] 30a Conductive material (layer)

[0078] 32 Switching Power Supply

[0079] 32a Switching Power Supply

[0080] 34 Power filter

[0081] 34a Power filter

[0082] 36 Oscillator

[0083] 36a Oscillator

[0084] 38 Control Circuit

[0085] 40 Spectrum (perturbation)

[0086] 42 Peak

[0087] 44 Process Steps

[0088] 46 Process Steps

[0089] 48 Process Steps

[0090] 50 process steps

Claims

1. A circuit comprising an electromagnetic interference suppression component (10), wherein: The circuit is configured to operate at a fixed switching or clock frequency that causes an electromagnetic disturbance having a spectrum (40) with a peak (42), The electromagnetic interference suppression component (10) comprises a piezoelectric element (12), wherein the piezoelectric element is configured to provide a low impedance propagation path for electromagnetic disturbances at a resonant frequency of the piezoelectric element (12). The resonant frequency of the piezoelectric element (12) matches the peak frequency, and is characterized in that: The electromagnetic interference suppression component (10) is arranged between a galvanically isolated primary side and a secondary side of a converter.

2. The circuit of claim 1, wherein the converter is a power supply.

3. The circuit according to claim 1, wherein the frequency spectrum (40) of the electromagnetic disturbance has another peak (42) at another resonance frequency of the piezoelectric element (12).

4. The circuit according to claim 1 or 3, wherein the electromagnetic interference suppression component (10) acts as a Y capacitor or an X capacitor.

5. The circuit of claim 1, further comprising a power supply filter (34), the power supply filter 34 comprising the electromagnetic interference suppression component (10).

6. The circuit of any one of claims 1 to 5, wherein the converter is one of: Flyback converter; forward converter; Asymmetric half bridge; Phase-shifted full bridge; and Dual active bridge.

7. The circuit of claim 6, wherein the flyback converter is an active clamp flyback converter and the forward converter is an active clamp forward converter.

8. The circuit according to any one of claims 1 to 7, wherein the further electromagnetic interference suppression component (10) acts as a line filter.

9. The circuit according to any one of claims 1 to 8, further comprising a capacitor and / or a further electromagnetic interference suppression component (10) connected in parallel to the electromagnetic interference suppression component (10).

10. The circuit according to any one of claims 1 to 9, further comprising a ceramic oscillator (36), wherein the ceramic oscillator (36) comprises a piezoelectric resonator as follows: Having the same piezoelectric material as the piezoelectric element (12); and / or The ceramic oscillator (36) has the same temperature dependence of the one or more resonant frequencies as the piezoelectric element (12) within the operating range of the ceramic oscillator (36).

11. The circuit according to any one of claims 1 to 10, further comprising a ceramic oscillator (36), wherein the piezoelectric element (12) acts as a piezoelectric resonator of the ceramic oscillator (36).

12. The circuit according to any one of claims 1 to 11, wherein the piezoelectric element (12) is clamped between walls of a housing of the electromagnetic interference suppression component (10) or between a wall of the housing of the electromagnetic interference suppression component (10) and another piezoelectric element.

13. A device comprising a circuit according to claim 10 or 11, and an integrated circuit, the integrated circuit being configured to control the switching or clock frequency of the circuit to achieve the effect of matching the switching or clock frequency or a harmonic of the switching or clock frequency with the resonant frequency of the piezoelectric element (12), wherein the integrated circuit is connected to the piezoelectric resonator.

14. A device comprising a circuit according to any one of claims 1 to 12, wherein the circuit is one of: Switching power supply; Digital circuits; Motor; Motor drivers; and Electronic circuits.

15. The apparatus of claim 14, wherein the resonant frequency of the piezoelectric element (12) is tuned to the fixed switching or clock frequency or a harmonic of the fixed switching or clock frequency, wherein the fixed switching or clock frequency or the harmonic of the fixed switching or clock frequency falls under applicable EMI regulations.

16. The apparatus of claim 14 or 15, wherein the fixed switching or clock frequency: at or above 150 kHz, wherein the resonant frequency of the piezoelectric element (12) is tuned to the fixed switching or clock frequency; or Below 150 kHz, wherein the resonant frequency of the piezoelectric element (12) is tuned to a harmonic of the fixed switching or clock frequency, wherein the harmonic has a frequency above 150 kHz.

17. A method for manufacturing an electromagnetic interference suppression component (10) included in the circuit according to claim 1, the method comprising: determining a peak value (42) of a frequency spectrum of an electromagnetic disturbance generated by the circuit; as well as The piezoelectric material and size of the piezoelectric element (12) of the electromagnetic interference suppression assembly (10) are determined, wherein the piezoelectric element (12) of the electromagnetic interference suppression assembly (10) has a resonant frequency that matches a peak (42) of the frequency spectrum (40).

18. A method of manufacturing an electrical device, the method comprising: selecting (48) an electromagnetic interference suppression component (10) included in the circuit according to claim 1; as well as An operating frequency of a circuit of the electrical device is adapted, wherein the adapted circuit generates an electromagnetic disturbance having a spectrum (40) with a peak (42) matching a selected resonant frequency of the piezoelectric element (12) of the electromagnetic interference suppression assembly (10).

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