Electromagnetic interference filter
The invention relates to an electromagnetic interference (EMI) filter ( 100 ), having line-side terminals (L 1 -L 3 ) for connecting to an electric supply(S) and load-side terminals (L 1 ′-L 3 ′) for connecting to a load device (L), the EMI filter ( 100 ) comprises a load-side passive EMI filter stage ( 1 ) connected to the load-side terminals (L 1 ′-L 3 ′) and is configured to suppress common-mode and differential-mode noise. The EMI filter ( 100 ) also comprises a line-side active EMI filter stage ( 3 ) connected to the line-side terminals (L 1 -L 3 ) and is configured to suppress differential-mode noise, and at least one intermediate active EMI filter stage ( 2 ) located between the load-side EMI filter stage ( 1 ) and the line-side EMI filter stage ( 3 ), configured to suppress common-mode noise. The invention relates also to a method for manufacturing the EMI filter ( 100 ).
1 . Electromagnetic interference filter, having line-side terminals for a connection to an electric supply and load-side terminals for a connection to a load device, the electromagnetic interference filter comprising:
a load-side passive electromagnetic interference filter stage connected to the load-side terminals and configured to suppress common-mode noise, a line-side electromagnetic interference filter stage connected to the line-side terminals, and configured to suppress differential-mode noise, wherein the load side passive electromagnetic interference filter stage is configured to suppress differential mode noise and the line-side electromagnetic interference filter stage is a line-side active electromagnetic interference filter stage, further comprising an intermediate active electromagnetic interference filter stage between the load-side electromagnetic interference filter stage and the line-side electromagnetic interference filter stage, configured to suppress common-mode noise, in combination with the load device injecting noise with a fundamental frequency onto an electric supply line, wherein the load-side passive electromagnetic interference filter stage exhibits a resonance frequency that is smaller or greater than the fundamental frequency of the noise.
2 . The electromagnetic interference filter of claim 1 , wherein the resonance frequency of the load-side passive electromagnetic interference filter stage is at least two times, preferably five times, smaller or greater than the fundamental frequency of the noise.
3 . The electromagnetic interference filter of claim 1 , wherein the load-side passive electromagnetic interference stage comprises a first inductive filtering element and a second inductive filtering element each being inductively coupled to the electric supply line and each of the inductive filtering elements being configured to suppress common-mode noise, and a capacitive filtering element, electrically connected to the electric supply line and configured to suppress common-mode and differential-mode noise.
4 . The electromagnetic interference filter of claim 1 , wherein the intermediate active electromagnetic interference filter stage includes a common-mode current sensor generating a common-mode signal in relation to a common-mode noise circulating in the electric supply line and a current amplifier receiving the common-mode noise signal and whereas the current amplifier is configured to inject a noise cancellation current into the electric supply line.
5 . The electromagnetic interference filter of claim 1 , wherein the line-side active electromagnetic interference filter stage comprises a voltage amplifier circuit connected to the electric supply line and configured to receive a noise voltage and provide a noise cancellation voltage to the supply line through an actuation transformer inductively coupled to the electric supply line.
6 . The electromagnetic interference filter of claim 5 , wherein the noise cancellation voltage comprises differential-mode and/or common-mode components.
7 . The electromagnetic interference filter of claim 5 , wherein the actuation transformer comprises:
a first and a second magnetic core element, and
a plurality of separate coil elements each being wound around at least one of the magnetic core elements, wherein
the magnetic core elements are arranged to enclose a plurality of conductors of the electric supply line to form a closed magnetic circuit.
8 . The electromagnetic interference filter of claim 7 , wherein the electric supply line is a single-phase or three-phase or multiphase AC line, and the actuation transformer is configured as a single-phase, respectively a three-phase, respectively multiphase transformer with a single magnetic core formed by the first and second magnetic core elements.
9 . Method for manufacturing the electromagnetic interference filter of claim 7 , the method comprising the steps of:
providing the first and the second magnetic core element
uniting the first and the second magnetic core element for providing a closed magnetic circuit
securing the first and the second magnetic core elements
connecting the separate coil elements to the load-side terminals on a first side of the actuation transformer and to the line-side terminals on a second side of the actuation transformer opposed the first side.
10 . The electromagnetic interference filter of claim 1 , wherein
the intermediate active electromagnetic interference filter stage and/or the line-side active electromagnetic interference filter stage include an amplifier circuit with a first control loop and a second control loop, wherein
the first control loop comprises an amplifier module with a transfer function and a gain function for adjusting a gain of the amplifier module, wherein
the second control loop comprises a gain control function configured to adjust the gain function of the first control loop in order to avoid saturation in the amplifier circuit, depending on an input signal.
11 . The electromagnetic interference filter of claim 10 , wherein the gain control function of the second control loop adjusts the gain function of the first control loop following a linear function with an upper end.
12 . The electromagnetic interference filter of claim 11 , wherein the upper end of the linear function corresponds to a peak threshold value setpoint in the gain control function.
13 . The electromagnetic interference filter of claim 10 , wherein the first control loop and the second control loop each is configured to have a time constant, wherein the time constant of the second control loop is greater than the time constant of the first control loop.