Compensation filter and method for activating a compensation filter

Abstract

A compensation filter and a method for activating a compensation filter are disclosed. In an embodiment a compensation filter includes an operational amplifier, a capacitive element, a first and a second resistive element and a current converter. The compensation filter is configured to attenuate a common mode interference in a critical frequency range.

Claims

1. A compensation filter comprising: a first port; a second port; a power line between the first port and the second port; an operational amplifier with an input and an output; a capacitive element coupled between the first port and the output of the operational amplifier, wherein the capacitive element has a capacitance value; a first resistive element coupled between the capacitive element and the output of the operational amplifier, wherein the first resistive element has a first resistance value; a current converter coupled in parallel with the capacitive element, wherein the current converter couples the power line to the input of the operational amplifier; a second resistive element coupled between the capacitive element and the input of the operational amplifier, wherein the second resistive element has a second resistance value; and a power supply connection separate from the power line, wherein a critical frequency range starts above a mains frequency, wherein the capacitance value is sufficiently large so that leakage currents below 1 kHz are compensated for, and wherein the compensation filter is configured to attenuate a common mode interference in the critical frequency range.

2. The compensation filter according to claim 1, wherein the compensation filter is configured to transmit a compensation signal with the same frequency, the same amplitude and an inverse arithmetic sign to the power line when the common mode interference in the power line occurs.

3. The compensation filter according claim 1, wherein the common mode interference contains a leakage current.

4. The compensation filter according to claim 1, wherein the current converter comprises magnetically coupled inductive elements.

5. The compensation filter according to claim 1, wherein the power line comprises conductors for one, two or three phases.

6. The compensation filter according to claim 1, wherein the power line comprises conductors for three phases, wherein the conductors are coupled via a neutral point to the operational amplifier, wherein the neutral point is coupled to a respective conductor for each phase through a parallel interconnection of a capacitive element and a resistive element.

7. A method for activating the compensation filter according to claim 1 with a power supply connection, the method comprising: connecting the power supply connection to an energy source before the compensation filter is connected between a consuming unit and the energy source.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Important aspects and details of concrete forms of embodiment are explained in more detail with reference to the schematic figures.

(2) FIG. 1 shows an equivalent circuit diagram that explains the mode of operation of the compensation filter;

(3) FIG. 2 shows a preferred frequency characteristic of the compensation filter;

(4) FIG. 3 shows the coupling to a three-phase line;

(5) FIG. 4 shows an equivalent circuit diagram for determining an appropriate magnitude of the coupling capacitance;

(6) FIG. 5 shows a form of embodiment of the compensation filter with an external power supply connection; and

(7) FIG. 6 shows the effect of a delayed connection between an energy source and a consuming unit.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

(8) FIG. 1 shows an equivalent circuit diagram of a possible circuit topology of the compensation filter KF. The compensation filter KF has a first port P1 and a second port P2. A power line SL is connected between the first port P1 and the second port P2. The compensation filter further has an operational amplifier OPV. The operational amplifier has an input E and an output A. The coupling capacitance, i.e., the capacitive element with the capacitance C.sub.o, is connected between the power line SL and the output A of the operational amplifier. The first resistive element R.sub.o is connected between the coupling capacitance and the output A of the operational amplifier OPV. A current converter SW is connected in parallel with the coupling capacitance C.sub.o. The current converter SW has a first inductive element SW1 and a second inductive element SW2. The first inductive element SW1 is arranged at the primary side of the current converter SW and is connected in the power line SL or at least coupled with the power line SL. The second inductive element SW2 of the current converter SW is arranged at the secondary side of the current converter SW and is coupled to the input E of the operational amplifier. The second inductive element SW2 of the current converter SW is connected in parallel with the second resistive element R.sub.B. The second resistive element R.sub.E is connected in series between the coupling capacitance C.sub.o and the input E of the operational amplifier OPV.

(9) I.sub.N represents the complete interference, e.g. the complete leakage current. I.sub.o is the compensation current that is determined by the operational amplifier OPV and the additional circuit elements C.sub.o, R.sub.E and R.sub.o. The arithmetic sign, frequency and the amplitude of the compensation current I.sub.o are preferably selected such that a current path provided by the amplifier is generated, so that preferably no leakage current, or at most a small, residual leakage current IR can be detected at the first port P.sub.1. The compensation filter can be connected to an external energy source or to a fault current circuit breaker between the energy source and the compensation filter via the first port P1. The compensation filter can be connected to an electric consuming unit via the second port P2.

(10) FIG. 2 shows a preferred frequency characteristic FG of the compensation filter. The critical frequency range is, for example, defined such that attenuation values of 10 dB specify the lower and upper limits of the frequency range.

(11) FIG. 2 correspondingly shows a critical frequency range from 150 hertz up to 30 kilohertz. The overshoot at frequencies just under 100 hertz effectively represent a signal amplification. This is not, however, problematic, and does not present either a functional or a technical safety problem.

(12) FIG. 3 illustrates how a coupling to a power line with three phases is possible. The symmetry point of the three phases is obtained at the neutral point SP. The neutral point SP is connected in each case by a parallel circuit of a capacitive element CE and a resistive element R.sub.B to the respective conductor L1, L2, L3 and the power line SL. The neutral point SP is connected at the output through a parallel interconnection comprising the coupling inductance Co and the second resistive element R.sub.B to the rest of the compensation circuit (not shown here).

(13) The interference to be compensated for here is a common mode interference. This means an interference that acts additively on the amplitude, frequency and phase of all the conductors L1, L2, L3 of the power line SL. It is therefore enough to have the electronics of the compensation filter act on the neutral point SP of the power line SL.

(14) FIG. 4 shows an equivalent circuit diagram that advantageously helps to determine the value of the coupling capacitance C.sub.o. The mains connection is realized through the one coupling capacitor or a plurality of coupling capacitors. A voltage drop occurs at the capacitors when a leakage current is compensated for and thus flows through the one coupling capacitor or a plurality of coupling capacitors. So that the compensation current I.sub.o always remains correct, the operational amplifier must also take the associated voltage drop at the coupling capacitor into account in the control of the output voltage. In order to be able to compensate also for leakage currents with a frequency below one kilohertz, coupling capacitors with a greater capacitance than is usually known are necessary in order to obtain a lower impedance and thus a smaller voltage drop.

(15) FIG. 5 illustrates the possibility of supplying the electronic circuit components ELC, e.g. the operational amplifier OPV, with electric energy via an external power supply connection VA. Electric energy is here strictly not taken from the power line. Through this it is possible to supply the electronic circuit components ELC with electrical energy and to wait for transient response processes before the compensation filter KF starts its work, i.e., before the compensation filter connects an electric consuming unit to an external energy source.

(16) The temporal sequence associated with this is shown in FIG. 6. The upper curve VSUP represents the temporal sequence of the supply voltage of the electric circuit components ELC of the compensation filter KF. The lower curve VOPV shows the output signal of the operational amplifier. The electronic circuit components are supplied with energy at the time T.sub.o. It takes a certain time ΔT here until the supply voltage has reached the correct value. The operational amplifier takes up its type as soon as a supply voltage is made available to it. It does, however, only achieve its greatest effectiveness at the time point T.sub.o plus ΔT at which the supply voltage VSUP has reached its intended value.

(17) If the compensation filter were required before the operation filter is working in the desired manner, it is possible that leakage currents or other interference signals would not be fully compensated for, and an unintentional actuation of a fault current circuit breaker can be the result.

(18) Because the compensation filter receives its own supply voltage at the power supply connection VA, preferably in such a way that this occurs before functioning of the filter is wanted, transient response processes can take place. As soon as the compensation filter is working as desired, it can be connected to the first and to the second port between an energy source and a consuming unit.

(19) The time delay ΔT can here lie in the order of magnitude of 100 milliseconds.

(20) The compensation filter and the method for activating a compensation filter are here not restricted to the technical details that are illustrated and described. The compensation filter can comprise further circuit components such as for example further coupling capacitors and further electronic circuit components. The method can comprise additional steps e.g. in relation to the connection to the external energy source or the connection to the consuming unit.