Electromagnetic interference filter having controlled impedance magnitude

1. An electromagnetic interference (EMI) 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 passive 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 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.

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

3. 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.

4. 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.

5. An EMI filter according to claim 1 ,

wherein the active filter bandwidth is between 10 kHz and 10 MHz.

6. 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.

7. An EMI filter according to claim 6 ,

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.

8. 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.

9. An electromagnetic interference (EMI) 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 passive 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 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, wherein the passive source circuit includes a n-order passive filter; and wherein n is 2 or greater.

10. An EMI filter according to claim 9 ,

wherein the passive source circuit comprises a C-L circuit including at least a source capacitance, a source inductance and a source damping resistor.

11. An EMI filter according to claim 10 ,

wherein the source damping resistor is equal or smaller than 3Ω.

12. An EMI filter according to claim 10 ,

wherein the passive source circuit comprises a source capacitance of about 1 nF and a source inductance of about 7 μH.

13. An electromagnetic interference (EMI) 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 passive 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 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, wherein the passive load circuit includes at least a single passive component and a load damping resistor.

14. An EMI filter according to claim 13 ,

wherein the passive load circuit includes a load capacitance of about 20 nF and a load damping resistor of about 1Ω.