TITLE: NOTCH FILTER, AND FILTER AND ELECTRICAL SYSTEM COMPRISING SUCH NOTCH FILTER

[0001] The present invention relates to a notch filter, as well as a filter and an electrical system comprising such a notch filter.

[0002] It is known to use a notch filter comprising a notch inductance and a notch capacitance defining a notch resonance frequency.

[0003] Such prior art notch filter has an attenuation comprising a notch (i.e. a quick increase of the attenuation) around the notch resonance frequency and that goes near zero away from the notch resonance frequency.

[0004] A goal of the invention is to propose a notch filter allowing to control the attenuation.

[0005] An object of the invention is therefore a notch filter comprising a notch inductance and a notch capacitance defining a notch resonance frequency, characterized in that it further comprises an attenuation control resistance in parallel with the notch inductance if the notch inductance and the notch capacitance are in series or in series with the notch capacitance if the notch inductance and the notch capacitance are in parallel.

[0006] Thanks to the invention, the value of the attenuation control resistance allows to control the attenuation above the notch resonance frequency.

[0007] Optionally, the notch resistance is a frequency dependent resistance.

[0008] Optionally, the notch inductance and the notch capacitance are in series, and the attenuation control resistance is in parallel with the notch inductance.

[0009] Optionally, the attenuation control resistance has a resistance value that decreases with frequency starting from the notch frequency.

[0010] Optionally, it further comprises a capacitance in parallel with the notch inductance and the attenuation control resistance.

[0011] Optionally, it further comprises a capacitance in series with the attenuation control resistance. [0012] Optionally, the notch inductance and the notch capacitance are in parallel, and the attenuation control resistance is in series with the notch capacitance.

[0013] Optionally, the attenuation control resistance has a resistance value that increases with frequency starting from the notch frequency.

[0014] Optionally, it further comprises an inductance in series with the notch capacitance and the attenuation control resistance.

[0015] Optionally, the attenuation control resistance has a resistance value that increases with frequency until at least a frequency greater than the notch resonance frequency.

[0016] Another object of the invention is a filter comprising: a low-pass filter; and a notch filter according to the invention, wherein one amongst the notch inductance and the notch capacitance is also part of the low-pass filter.

[0017] Another object of the invention is an electrical system comprising: a power source; a load; and a notch filter according to the invention or a filter according to the invention, through which the load is connected to the power source.

[0018] The invention will be better understood using the description which follows, given solely by way of example and made with reference to the appended drawings in which:

[0019] [Fig. 1] figure 1 is a circuit diagram of an electrical system comprising an electromagnetic compatibility filter according to prior art,

[0020] [Fig. 2] figure 2 is a circuit diagram of an electrical system comprising an electromagnetic compatibility filter according to prior art,

[0021] [Fig. 3] figure 3 is a frequency analysis comparing the attenuation of the electrical systems of figures 1 and 2,

[0022] [Fig. 4] figure 4 is a circuit diagram of an electrical system comprising an electromagnetic compatibility filter according to a first embodiment of the invention, [0023] [Fig. 5] figure 5 is a frequency analysis comparing the attenuation of the electrical systems of figures 2 and 4,

[0024] [Fig. 6] figure 6 is a circuit diagram of an electrical system comprising an electromagnetic compatibility filter according to a second embodiment of the invention,

[0025] [Fig. 7] figure 7 is a frequency analysis comparing the attenuation of the electrical systems of figures 4 and 6,

[0026] [Fig. 8] figure 8 is a circuit diagram of an electrical system comprising an electromagnetic compatibility filter according to a third embodiment of the invention,

[0027] [Fig. 9] figure 9 is a frequency analysis comparing the attenuation of the electrical systems of figures 6 and 8,

[0028] [Fig. 10] figure 10 is a circuit diagram of an electrical system comprising an electromagnetic compatibility filter according to a fourth embodiment of the invention,

[0029] [Fig. 11] figure 1 1 is graph illustrating the variation of resistance with frequency of a frequency dependent resistance,

[0030] [Fig. 12] figure 12 is a circuit diagram of an electrical system comprising an electromagnetic compatibility filter according to prior art,

[0031 ] [Fig. 13] figure 13 is a circuit diagram of an electrical system comprising an electromagnetic compatibility filter according to a fifth embodiment of the invention,

[0032] [Fig. 14] figure 14 is a circuit diagram of an electrical system comprising an electromagnetic compatibility filter according to a sixth embodiment of the invention,

[0033] [Fig. 15] figure 15 is a frequency analysis comparing the attenuation of the electrical systems of figures 12, 13 and 14,

[0034] [Fig. 16] figure 16 is a circuit diagram of an electrical system comprising an electromagnetic compatibility filter according to a seventh embodiment of the invention, and

[0035] [Fig. 17] figure 17 is a frequency analysis comparing the attenuation of different configurations of the electrical system of figure 16.

[0036] Referring to figure 18, a notch filter 1800 according to the invention will now be described. [0037] Notch filter 1800 comprises a notch inductance L _N and a notch capacitance CN in series defining a notch resonance frequency. Notch filter 1800 further comprises an attenuation control resistance RN in parallel with notch inductance L _N .

[0038] Referring to figure 19, attenuation with respect to the frequency for notch filter 1800 is illustrated, as attenuation control resistance RN increases.

[0039] Referring to figure 20, a notch filter 2000 according to the invention will now be described.

[0040] Notch filter 2000 comprises a notch inductance L _N and a notch capacitance CN in parallel defining a notch resonance frequency. Notch filter 2000 further comprises an attenuation control resistance RN in series with notch capacitance CN.

[0041 ] Referring to figure 21 , attenuation with respect to the frequency for notch filter 2000 is illustrated, as attenuation control resistance RN increases.

[0042] Referring to figure 1 , an example 100 of electrical system according to prior art will now be described.

[0043] In this example, electrical system 100 comprises a DC power source 102, an electromagnetic compatibility (EMC) filter 104 and a load 106 connected to DC power source 102 through EMC filter 104. Load 106 represents for example an electronic equipment and exhibits a load resistance RL. More precisely, electrical system 100 comprises first and second power electrical branches 108, 1 10 connecting together DC power source 102 to load 106. First power electrical branch 108 usually has a high potential and conveys current to load 106, while second power electrical branch 1 10 has a low potential and conveys current back to DC power source 102. Second power electrical branch 110 may be connected to a ground of electrical system 100.

[0044] In other examples, the power source 102 could be an AC power source.

[0045] Preferably, in the described example, the electrical system 100 is a “high power” electrical system, which means for example that the current between DC power source 102 and load 106 exceeds 1 A. In particular, electrical components placed on the first power electrical branch 108 must be designed for this level of current.

[0046] EMC filter 104 comprises a pi filter 1 12, which is a low-pass filter having a cutoff frequency F p (i.e. a low-pass resonance frequency). Pi filter 108 comprises a first shunt capacitance C located on a first shunt branch 114 connecting together power electrical branches 108, 110 and being in parallel with DC power source 102. Pi filter 108 further comprises a second shunt capacitance C2 located on a second shunt branch 116 also connecting together power electrical branches 108, 110 and being in parallel with load 106. Pi filter 108 further comprises a series inductance Ln located on first power electrical branch 108, between the two shunt electrical branches 114, 1 16.

[0047] Voltage noise v _n caused by a noise source 118 such as power electronics, switched circuits or other circuits generating unwanted voltage ripples across branches 108, 1 10, may appear in electrical system 100. This noise voltage v _n leads in turn to a noise current i _n circulating in power electrical branches 108, 1 10, between DC power source 102 and load 106. If noise voltage v _n is too high, the electronic equipment represented by load 106 may malfunction.

[0048] EMC filter 104 is designed for filtering noise voltage v _n . This noise voltage v _n comprises, in the frequency domain, several harmonics. In the case of differential mode noise, these harmonics have rapidly decreasing amplitudes after the first harmonic. In the case of common mode noise, the first harmonics have essentially constant amplitudes (equal to the amplitude of the first harmonic) and the following harmonics have decreasing amplitudes. The decreasing is due to the fact that the frequency either starts to be impacted by load 106 or to get close to the rise time of the noise source. Therefore, if the emission requirements are constant, EMC filter 104 is designed to provide a required attenuation at a required frequency generally taken equal to the first harmonic frequency, and above this required frequency.

[0049] The higher is the required attenuation T, the lower is the needed cutoff frequency F _P . For getting a low cutoff frequency F _P , inductance L and capacitances Cl n, C2TT need to have high value, which increases their size. Furthermore, inductance L has to transfer low frequency and DC signal.

[0050] Referring to figure 2, an electrical system 200 according to prior art will now be described.

[0051 ] Electrical system 200 is similar to electrical system 100, except for the EMC filter, now referenced 202. EMC filter 202 comprises the pi filter 112 of figure 1 and a notch filter 204. In the described example, notch filter 204 comprises capacitance C2TT of pi filter 112 and, in addition, a notch inductance L _N located on second shunt branch 1 16, in series with capacitance C2TT. [0052] In the described example, the notch filter 204 has a notch resonance frequency F _N higher than low-pass frequency F p.

[0053] Referring to figure 3, as an example, attenuation below a threshold T for frequencies above a frequency F (150 kHz in the illustrated example) is sought.

[0054] Curve C100 illustrates the attenuation with respect to the frequency for electrical system 100. The values of the electrical components are: C = C2 = 10 nF and Ln = 1 mH. As illustrated, curve C100 passes below threshold T at frequency F and stays below at higher frequencies.

[0055] Curve C200 illustrates the attenuation with respect to the frequency for the electrical system 200. The values of the electrical components are: C = C2 = 10 nF, Ln = 0,470 mH and LN is 112.7 pH. Therefore, the value of inductance L has been lowered with respect to electrical system 100. However, curve C200 comprises an attenuation notch N around notch resonant frequency F _N , which is chosen very close to frequency F, for example between 5% of frequency F. Thanks to this attenuation notch N, curve C200 still passes below threshold T at frequency F and stays below at higher frequencies, despite the lowered inductance L _N .

[0056] As illustrated, inductance L _N cannot be further lowered because of a bump B located just after the attenuation notch N.

[0057] Referring to figure 4, an electrical system 400 according to the invention will now be described.

[0058] Electrical system 400 is similar to electrical system 200, except for the EMC filter, now referenced 402. More particularly, the notch filter, now referenced 404, further comprises a notch resistance RN in parallel with inductance L _N . Resistance RN can have any value depending on the filter.

[0059] Referring to figure 5, curve C400 illustrates the attenuation with respect to the frequency for electrical system 400. The values of the electrical components are: C = C2 = 10 nF, L = 0,450 mH, L _N = 112.7 pH and RD = 400 Q. The value of inductance L _H has therefore been further lowered with respect to electrical system 200. This has been possible thanks to resistance RN which dampens bump B. Curve C400 still passes below threshold T at frequency F and stays below at higher frequencies, despite the lowered inductance L _N .

[0060] Alternatively, the notch filter could be used to dampen the low frequency peak p of the low-pass filter. [0061] Referring to figure 6, another electrical system 600 according to the invention will now be described.

[0062] Electrical system 600 is similar to electrical system 400, except for the EMC filter, now referenced 602. More particularly, the notch filter, now referenced 604, further comprises a high frequency capacitance CHF placed in parallel with inductance L _N . Capacitance CHF allows improving the attenuation at high frequencies, with almost no impact around required frequency F. This will be further illustrated on the following figure.

[0063] Referring to figure 7, curve C600 illustrates the attenuation with respect to the frequency for electrical system 600. The values of the electrical components are: C = C2TT = 10 nF, Ln = 0,482 mH, RD = 400 Q and CHF = 1 nF. The value of inductance Ln has therefore been slightly increased. However, in return, attenuation is improved for high frequencies. This is noticeable in the illustrated example starting from 1 MHz.

[0064] Referring to figure 8, another electrical system 800 according to the invention will now be described.

[0065] Electrical system 800 is similar to electrical system 600, except for the EMC filter, now referenced 802. More particularly the notch filter, now referenced 804, further comprises a capacitance CN2 in series with resistance R _N , both being in parallel with inductance L _N . Capacitance CN2 creates an auxiliary notch filter 806 with inductance L _N . Preferably, notch filter 806 has a resonance frequency close to resonance frequency F _N of notch filter 804, for example between 5% of resonance frequency F _N . To this end, capacitance CN2 is substantially equal to capacitance C2 , for example between 5% of capacitance C2 .

[0066] Adding capacitance CN2 allows to decrease inductance L _N . The reduction may go for example up to 50%. A smaller inductance L _N has the advantage to have often less resistance which means better notch behavior leading to improved performance. This will be further illustrated on the following figure. The smaller inductance LN may also have a reduced size.

[0067] Referring to figure 9, curve C800 illustrates the attenuation with respect to the frequency for electrical system 800. The values of the electrical components are: C = C2TT = 10 nF, Ln = 0,482 mH, L _N = 98 pH, RD = 400 Q, CHF = 1 nF and CN2 = 10 nF. The value of inductance L _N has therefore been decreased. However, curve C800 still passes below threshold T at frequency F and stays below at higher frequencies, despite the lowered inductance L _N . There is even a distance between curve C800 and threshold T at frequency F, which can be used to further decrease inductance Ln.

[0068] Referring to figure 10, another electrical system 1000 according to the invention will now be described.

[0069] Electrical system 1000 is identical to electrical system 800, except for the EMC filter, now referenced 1002, and more particularly the notch filter, now referenced 1004, which does not comprise capacitance CHF. This allows to further decrease inductance L , at the expense of slightly less attenuation at high frequencies.

[0070] In other embodiments, in order to improve attenuation at high frequencies, resistance RN (of figure 4, 6, 8 or 10) is preferably a frequency dependent resistance having a resistance value that decreases with frequency starting from the notch resonance frequency. For example, resistance RN comprises one of the following: an inductor above complex permeability, an operational amplifier circuit with feedback like a gyrator circuit and an equivalent series resistance of capacitance CN of figure 8 or 10. An inductor above complex permeability is an inductor operating at high frequency where core loss dominates the component which then is again a resistance. As frequency increases the choke turns from being an inductor to a resistor due to more and more energy is being used to change the internal inductors magnetic domains.

[0071 ] Referring to figure 11 , an example of evolution of resistance RN with respect to the frequency is illustrated. Resistance RN decreases until a frequency of about 2 MHz. In particular, resistance RN decreases from the notch frequency F to 2 MHz. In addition, for example, resistance RN comprises a capacitor operating in the Electrical Series Resistance (ESR) area with an ESR decreasing with frequency, due for example to dielectric.

[0072] Referring to figure 12, an electrical system 1200 according to prior art will now be described.

[0073] Electrical system 1200 is similar to electrical system 100, except for the EMC filter, now referenced 1202. In electrical system 1200, EMC filter 1202 comprises a parallel LC filter 1204, which is a low-pass filter having a cutoff frequency F p (i.e. a low-pass resonance frequency). Parallel LC filter 1204 comprises a first shunt capacitance CLC placed on shunt branch 114 and a series inductance LLC placed on first power electrical branch 108, between shunt electrical branch 114 and load 106.

[0074] Referring to figure 13, another electrical system 1300 according to the invention will now be described.

[0075] Electrical system 1300 is similar to electrical system 1200 except for the EMC filter, now referenced 1302, which comprises a notch filter 1304 in addition to parallel LC filter 1204. Notch filter 1304 comprises inductance LLC of parallel LC filter 1204, a notch capacitance CN and a notch resistance RN in series with capacitance CN, both being in parallel with inductance LLC-

[0076] Referring to figure 14, another electrical system 1400 according to the invention will now be described.

[0077] Electrical system 1400 is similar to the electrical system 1300, except for the EMC filter, now referenced 1402, and more particularly the notch filter, now referenced 1404, which further comprises an inductance LN in series with capacitance CN and resistance RN, all three being in parallel with inductance LLC-

[0078] Referring to figure 15, curve C1200 illustrates the attenuation with respect to the frequency for electrical system 1200. The values of the electrical components for curve C1200 are: CLC = 10 nF and LLC = 1 mH.

[0079] In this example, attenuation T is required starting from a frequency F of 160 kHz. As illustrated, curve C1200 passes below threshold T at frequency F and stays below at higher frequencies.

[0080] Curve C1300 illustrates the attenuation with respect to the frequency for the electrical system 1300. The values of the electrical components are: CLC = 4.9 nF, LLC = 1 mH, CN = 1 nF and RD = 600 Q. The value of inductance CLC has therefore been lowered with respect to electrical system 1200, thanks to resistance RN which allows to control the attenuation above notch resonant frequency F _N ; similarly to what was described previously in reference to figures 1 to 11 .

[0081] In order to improve attenuation at high frequencies, resistance RN (of figure 13) is preferably a frequency dependent resistance having a resistance value that increases with frequency starting from the notch resonance frequency. For example, we can use the increasing resistance of an inductor in its complex permeability area. [0082] Curve C1400 illustrates the attenuation with respect to the frequency for the electrical system 1400. The values of the electrical components are: CLC = 5.9 nF, LLC = 1 mH, CN = 1 nF, RD = 600 Q and LHF = 100 pH. Adding inductance LHF allows to increase the attenuation at high frequencies, at the cost of a slight increase of CLC- Inductance LHF can be used in addition to a frequency dependent resistance RN.

[0083] Referring to figure 16, another electrical system 1600 according to the invention will now be described.

[0084] In electrical system 1600, the EMC filter, now referenced 1602 first comprises a second order low-pass filter 1604 having a cutoff frequency F p. Second order low- pass filter 1604 comprises a series inductance LLC located on first power electrical branch 108, between DC power source 102 and first shunt electrical branch 1 14. Second order low-pass filter 1604 further comprises a first shunt capacitance C1 LC located on first shunt branch 114 and second and third shunt capacitances C2 c, C3LC located in series on second shunt branch 116. Second order low-pass filter 1604 further comprises a dampening resistance RLC located on second shunt branch 116, in series with capacitances C2 c, C3LC.

[0085] EMC filter 1602 further comprises a notch filter 1606 having a notch resonance frequency close to cutoff frequency F p, for example between 5% of cutoff frequency F p. Notch filter 1606 comprises capacitances C2 c, C3LC and a notch inductance L _N located on second shunt branch 116, in series with capacitances C2 c, C3LC. Notch filter 1606 further comprises a control resistance RN in parallel with inductance L _N .

[0086] In other examples, capacitance C2 c and resistance RLC could be removed.

[0087] Referring to figure 17, curve C1604 illustrates the attenuation with respect to the frequency for the second order low-pass filter 1604 in an ideal case (i.e. of electrical system 1600 without inductance L _N and resistance RN, and with RLC = 0 Q). The values of the electrical components are: LLC = 300 nH, C1 LC = 1 pF, and C2LC = C3LC = 2 pF. As illustrated, curve C1604 comprises a peak P at cutoff frequency F p.

[0088] Curve C1604’ illustrates the attenuation with respect to the frequency for the second order low-pass filter 1604 for resistance RLC = 860 mil. As illustrated, peak P is dampened thanks to resistance RLC-

[0089] Curve C1600 illustrates the attenuation with respect to the frequency for the electrical system 1600. The values of the electrical components are: LLC = 300 nH, C1 LC = 1 nF, C2LC = C3LC = 1 pF, RLC = 500mQ, L _N = 900n and RN = 225 Q. Adding inductance L _N and resistance RN therefore allows to reduce capacitance C2LC, C3LC and resistance RLC- In fact, because notch resonance frequency F _N is close to cutoff frequency FLP, the attenuation notch of notch filter 1606 compensates at least in part peak P of second order low-pass filter 1604, so as to dampen peak P.

[0090] It is clear that a notch filter like the ones described above allows to control the attenuation above the notch resonance frequency.

[0091] The invention is not limited to the embodiments described above. It will appear to those skilled in the art that various modifications can be made to the embodiments described above, in the light of the teaching which has just been disclosed to them.

[0092] In particular, although the described examples use a DC power source, the invention could be used for AC power source, for example between each of the three lines of a three-phase system and the ground.

[0093] The invention could also be used in low power systems.

[0094] In the detailed presentation of the invention which has been made previously, the terms used should not be interpreted as limiting the invention to the embodiments set out in this description, but must be interpreted to include all the equivalents the prediction of which is within the reach of the skilled person by applying their general knowledge to the implementation of the teaching which has just been disclosed to them.