ELECTROMAGNETIC INTERFERENCE FILTER HAVING CONTROLLED IMPEDANCE MAGNITUDE

Abstract

Electromagnetic interference filter for suppressing interferences in DC network, the network comprising a source device powering a load device via a bus connectable to the source device at an input side and to the load device at an output side.

The EMI filter being connected to the bus and comprising an active filter circuit having an active filter bandwidth and being configured to sense a noise component superimposed in the bus and inject a cancelling noise in the bus to suppress said noise component. The EMI filter further comprises a passive circuit including a source circuit connected to the bus at the input side and a passive load circuit to the bus connected at the output side, the passive circuit being configured to provide, at least at a cutoff frequency of the active filter bandwidth, a source impedance at the input side that differs from a load impedance at the output side by a factor of at least two.

Claims

1. Electromagnetic interference filter for suppressing interferences in a DC network, the network comprising a source device powering a load device via a bus; connectable to the source device at an input side and to the load device at an output side; the EMI filter being connected to the bus and comprising an active filter circuit having an active filter bandwidth and being configured to sense a noise component superimposed in the bus at the input side traveling towards the output side and inject a cancelling noise in the bus to suppress said noise component; wherein the EMI filter further comprises a passive circuit including a source circuit connected to the bus at the input side and a passive load circuit connected to the bus at the output side, the passive circuit being configured to provide, at least at a cutoff frequency of the active filter bandwidth, a source impedance at the input side that differs from a load impedance at the output side by a factor of at least two.

2. An EMI filter according to claim 1, wherein the passive circuit being configured to provide, at each frequency of the active filter bandwidth, a source impedance at the input side that differs from a load impedance at the output side by a factor of at least two.

3. An EMI filter according to claim 1, wherein the passive source circuit includes a n-order passive filter; and wherein n is 2 or greater.

4. An EMI filter according to claim 3, wherein the passive source circuit comprises a C-L circuit including at least a source capacitance, a source inductance and a source damping resistor.

5. An EMI filter according to claim 4, wherein the source damping resistor is equal or smaller than 3Ω.

6. An EMI filter according to claim 1, wherein the passive load circuit includes at least a single passive component and a load damping resistor.

7. An EMI filter according to claim 1, wherein the active filter circuit is a current-sensing current-injecting active filter; and wherein the passive circuit is configured such that, the source impedance is at least 10 times greater than the load impedance.

8. An EMI filter according to claim 4, wherein the passive source circuit comprises a source capacitance of about 1 nF and a source inductance of about 7 μH.

9. An EMI filter according to claim 1, wherein the active filter circuit is a voltage-sensing voltage-injecting active filter; and wherein the passive circuit is configured such that the load impedance is at least 10 times greater than the source impedance.

10. An EMI filter according to claim 6, wherein the passive load circuit includes a load capacitance of about 20 nF and a load damping resistor of about 1Ω.

11. An EMI filter according to claim 1, wherein the active filter bandwidth is between 10 kHz and 10 MHz.

12. An EMI filter according to claim 1, wherein the passive source circuit is configured to adjust the current/voltage compensation capabilities of the active filter circuit.

13. An EMI filter according to claim 12, wherein the passive source circuit is configured to adjust the magnitude of the noise component such that a peak-to-peak voltage of the noise component between the passive source circuit and the active filter circuit is smaller than a maximum output voltage and/or current capability of the active filter circuit.

14. An EMI filter according to claim 1, wherein the bus comprises a first power conductor and a second power conductor; and wherein at least one capacitance is provided between the first and second power conductors between the input side and the EMI filter, such as to equalize the impedance seen from each power conductors to ground.

15. An EMI filter according to claim 1, connected to a bus that is a DC bus or an AC bus.

Description

SHORT DESCRIPTION OF THE DRAWINGS

[0020] Exemplar embodiments of the invention are disclosed in the description and illustrated by the drawings in which:

[0021] FIG. 1 shows the working principle of an active filter;

[0022] FIG. 2 shows an active filter circuit representation implemented as a feedback current-sensing current-injecting circuit;

[0023] FIG. 3 illustrates an EMI filter comprising a passive circuit, according to an embodiment;

[0024] FIG. 4 illustrates a possible configuration of the passive circuit, according to an embodiment;

[0025] FIG. 5 shows a graph of the source impedance and the load impedance plotted as a function of the working frequency of the active filter circuit of FIG. 4;

[0026] FIG. 6 illustrates a possible configuration of the passive circuit, according to another embodiment;

[0027] FIG. 7 shows a graph of the source impedance and the load impedance plotted as a function of the working frequency of the active filter circuit of FIG. 6; and

[0028] FIG. 8 illustrates the EMI filter, according to another embodiment.

EXAMPLES OF EMBODIMENTS

[0029] With reference to FIG. 3, an EMI filter 22 is shown according to an embodiment. The EMI filter 23 is destined to cooperate with a DC network comprising a source device 20 powering a load device 21 via a DC bus 15. The DC bus 15 is connected to the source device 20 at an input side 23. Here, the term “input” substantially means “at the side of the source device 20”. The DC bus 15 is further connected to the load device 21 at an output side 24. Here, the term “output” substantially means “at the side of the load device 21”. The EMI filter 22 is connected to the DC bus 15 and/or is forming a part of the DC bus 15. The EMI filter 22 comprises an active filter circuit 220 having an active filter bandwidth and configured to sense a noise component superimposed in the DC bus 15 at the input side 23 and inject a cancelling noise in the DC bus 15 to suppress said noise component. The noise component travels from the input side 23 towards the output side 24.

[0030] The EMI filter 22 further comprises a passive circuit 221, 222 including a passive source circuit 221 connected at the input 23 and a passive load circuit 222 connected at the output side 24. The passive circuit 221, 222 is configured to provide, at least at a cutoff frequency F.sub.C of the active filter bandwidth, a source impedance Z.sub.S at the input side 23 that differs from a load impedance Z.sub.L at the output side 24 by a factor of at least two, more preferably of at least 10. Alternatively, or in addition the passive circuit 221, 222 is configured to provide, at each working frequency F.sub.W of the active filter bandwidth, a source impedance Z.sub.S at the input side 23 that differs from a load impedance Z.sub.L at the output side 24 by a factor of at least two, more preferably of at least 10.

[0031] The active filter bandwidth is between 10 kHz and 10 MHz.

[0032] The passive source circuit 221 can be further configured to adjust the magnitude of the noise component such as to avoid saturation of the active filter circuit 220. For this sake the passive source circuit 221 is configured to adjust the magnitude of the noise component such that a peak-to-peak voltage of the noise component between the passive source circuit 221 and the active filter circuit 220 is smaller than a maximum output voltage and/or capability of the active filter circuit 220.

[0033] In one aspect, the passive source circuit 221 is configured to adjust the magnitude of the noise component below 300 mA. More generally, knowing the noise disturbance coming from the source device 20 and the maximum current/voltage capabilities of the active filter circuit 220, the passive source circuit 221 can be configured to adjust the current/voltage compensation capabilities of the active filter circuit 220, in other words, such that the noise disturbance is reduced in amplitude to fulfil the maximum capabilities of the active filter circuit 220. For example, the passive source circuit 221 can be configured to adjust the magnitude of the noise component by a factor of at least five times. In particular, if the noise coming from the source device 20 has current peaks of 5 A and the active filter circuit 220 can source/sink maximum 1 A, the passive source circuit 221 is designed to reduce the current peaks at least to 1 A.

[0034] In an embodiment, the active filter circuit 220 comprises a current-sensing current-injecting active filter. The passive circuit 221, 222 is configured such that, at least at a cutoff frequency F.sub.C the source impedance Z.sub.S is at least two times, more preferably at least 10 times greater than the load impedance Z.sub.L. Alternatively, or in addition, the passive circuit 221, 222 is configured such that at each working frequency F.sub.W of the active filter bandwidth, the source impedance Z.sub.S is at least two times, more preferably at least 10 times greater than the load impedance Z.sub.L.

[0035] In one aspect, the passive source circuit 221 can include a n-order passive filter, wherein n is 2 or greater.

[0036] FIG. 4 illustrates a possible configuration of the passive circuit 221, 222 including the source circuit 221 connected at the input side 23 and the passive load circuit 222 connected at the output side 24, according to an embodiment. As shown if FIG. 4, the passive source circuit 221 can comprise a C-L circuit including at least a source capacitance C.sub.S, a source inductance L.sub.S and a source damping resistor R.sub.s. For example, the passive source circuit 221 can comprise a C-L circuit including at least a source capacitance C.sub.S, a source inductance L.sub.S and a source damping resistor R.sub.s connected to the DC bus 15.

[0037] As shown in FIG. 4, the DC bus 15 can comprise a first power conductor 11 and a second power conductor 12. In such configuration, the C-L circuit including at least a source capacitance C.sub.S, a source inductance L.sub.S and a source damping resistor R.sub.s can be connected to each of the first and second power conductors 11, 12.

[0038] In one aspect, the source damping resistor R.sub.s is equal or smaller than 3).

[0039] In one aspect, the passive source circuit 221 can comprise a source capacitance C.sub.S of about 1 nF and a source inductance L.sub.S of about 7 μH.

[0040] The passive load circuit 222 can include at least a single passive component C.sub.L, L.sub.L and a load damping resistor R.sub.L. For example, the passive load circuit 222 can include at least a single passive component C.sub.L, L.sub.L and a load damping resistor R.sub.L connected to the DC bus 15. As shown in FIG. 4, the DC bus 15 can comprise a first power conductor 11 and a second power conductor 12. In such configuration, the passive load circuit 222 can be connected to each of the first and second power conductors 11, 12.

[0041] In one aspect, the passive load circuit 222 can include at a load capacitance C.sub.L of about 20 nF and a load damping resistor R.sub.L of about 1Ω.

[0042] The elements or components as described before might be formed/lumped by the individual electric elements or components, as illustrated in FIG. 4.

[0043] FIG. 5 shows a graph of the source impedance Z.sub.S and the load impedance Z.sub.L plotted as a function of the working frequency F.sub.W of the active filter circuit 220 of FIG. 4. The active filter bandwidth is indicated by the grey area on the graph, whereas the cutoff frequency F.sub.C is not shown. The active filter circuit 220 may be arranged with multiple cutoff frequencies F.sub.C.

[0044] In another embodiment, the active filter circuit 220 comprises a voltage-sensing voltage-injecting active filter. The passive load circuit 222 can be configured such that, at least at a cutoff frequency F.sub.C a load impedance Z.sub.L is at least two times, more preferably at least 10 times greater than the source impedance Z.sub.S. Alternatively, or in addition, the passive circuit 221, 222 is configured such that at each frequency of the active filter bandwidth, a load impedance Z.sub.L is at least two times more preferably at least 10 times greater than the source impedance Z.sub.S.

[0045] FIG. 6 schematically shows an example of such an active filter circuit 220 comprising a voltage-sensing voltage-injecting active filter including a passive source circuit 221 connected at the input side 23 and a passive load circuit 222 connected at the output side 24. The general description of the circuit is the same as for the current-sensing current-injecting of FIG. 4, i.e., a second or higher order filter at source side and a single component filter at load side. For example, the passive source circuit 221 can comprise a C-L circuit including a source capacitance C.sub.S (for example being about 3.3 uF), a source inductance L.sub.S (for example being about 100 nH) and a damping resistor R.sub.s smaller than 1 Ohm. The passive load circuit 222 can include a single inductance, e.g., 30 uH. The configuration of the EMI filter 22 shown in FIG. 6 allows for achieving load impedance Z.sub.L is at least two times, more preferably at least 10 times greater than the source impedance Z.sub.S. at least at a cutoff frequency F.sub.C and/or in the working frequency of the active filter, i.e., 10 kHz-10 MHz.

[0046] The elements or components as described before might be formed/lumped by the individual electric elements or components, as illustrated in FIG. 6.

[0047] FIG. 7 shows a graph of the source impedance Z.sub.S and the load impedance Z.sub.L plotted as a function of the working frequency F.sub.W of the active filter circuit 220 of FIG. 6, whereas the cutoff frequency F.sub.C is not shown. The active filter circuit 220 may be arranged with multiple cutoff frequencies F.sub.C.

[0048] The passive circuit 221, 222 is configured to provide, at a cutoff frequency F.sub.C of the active filter bandwidth, a source impedance Z.sub.S that differs from a load impedance Z.sub.L by a factor of at least two, more preferably of at least ten. Alternatively, or in addition the passive circuit 221, 222 is configured to provide, at each frequency of the active filter bandwidth, a source impedance Z.sub.S that differs from a load impedance Z.sub.L by a factor of at least two, more preferably of at least ten. The passive circuit 221, 222 is arranged to adjust the magnitude of the noise component such as to avoid saturation of the active filter circuit 220, regardless of the configuration of the active filter 220. For this sake the passive source circuit 221 is configured to adjust the magnitude of the noise component such that a peak-to-peak voltage of the noise component between the passive source circuit 221 and the active filter circuit 220 is smaller than a maximum output voltage and/or current capability of the active filter circuit 220.

[0049] For example, the active filter 220 can comprises a current-sensing current-injecting active filter, a voltage-sensing current-injecting active filter, a current-sensing voltage-injecting or a voltage-sensing voltage-injecting active filter.

[0050] In yet another embodiment, at least one capacitance can be provided between the first and second power conductors 11, 12 between the source device 20 and the EMI filter 22, such as to equalize the impedance seen from each power conductors 11, 12 to ground. In the EMI filter 22 illustrated in FIG. 8, a capacitance C.sub.2 is added between the two power conductors 11, 12 on the side of the passive source circuit 221. Here, the passive source circuit 221 and the passive load circuit 222 are similar to the ones shown in FIG. 4.

[0051] The elements or components as described before might be formed/lumped by the individual electric elements or components, as illustrated in FIG. 8.

[0052] The EMI filter 22 can be placed in a motor drive unit on a DC power bus or on the AC side, in an electric vehicle, although this is not the only application of the present disclosure. The same inventive filter structure is suitable for suppressing interferences in DC networks as well as for suppressing interferences in AC networks. Other applications of the EMI filter 22 can include input or output of DC/DC converters and on-board chargers, for example in a vehicle.

REFERENCE NUMERAL USED IN THE FIGURES

[0053] 11 first power conductor [0054] 12 second power conductor [0055] 15 DC bus, bus [0056] 20 source device [0057] 21 load device [0058] 22 electromagnetic interference (EMI) filter [0059] 220 active filter circuit [0060] 221 passive source circuit [0061] 222 passive load circuit [0062] 23 input side [0063] 24 output side [0064] A filter gain [0065] B.sub.F active filter bandwidth [0066] C.sub.L load capacitance [0067] C.sub.S source capacitance [0068] C.sub.2 capacitance [0069] F.sub.C cutoff frequency [0070] F.sub.W working frequency [0071] IL insertion Loss [0072] L.sub.L load inductance [0073] L.sub.S source inductance [0074] R.sub.L load damping resistor [0075] R.sub.S source damping resistor [0076] Z.sub.S source impedance [0077] Z.sub.L load impedance