Method of reducing common mode current

Abstract

A method of reducing common mode current that flows between an internal ground of an electrical circuit and an Earth ground, the electrical circuit is supplied by an electrical network delivering an alternating voltage. The method includes applying a voltage by the electrical network between the internal ground of the circuit and the Earth ground and applying an additional voltage between the internal ground of the circuit and the Earth ground using an electronic component interposed between the internal ground of the circuit and Earth ground, this additional voltage opposing the voltage applied by the electrical network between the internal ground and the Earth ground so as to reduce the common mode current at the frequency of the electrical network.

Claims

1. A method of reducing common mode current flowing between an internal ground of an electrical circuit and the Earth ground, said circuit being supplied by an electrical network delivering an alternating voltage, the method comprising: applying a voltage by the electrical network between the internal ground of the circuit and the Earth ground; and applying an additional voltage between the internal ground of the circuit and the Earth ground using an electronic component interposed between the internal ground of the circuit and the Earth ground, this additional voltage opposing the voltage applied by the electrical network between the internal ground and the Earth ground, so as to reduce the common mode current at the frequency of the electrical network.

2. The method according to claim 1, wherein the additional voltage has a sign opposite to that of the voltage applied by the network between the internal ground of the circuit and the Earth ground.

3. The method according to claim 1, wherein the additional voltage is applied in parallel to the parasitic capacitance existing between the internal ground of the circuit and the Earth ground.

4. The method according to claim 1, wherein the 0 dB bandwidth of the electronic component extends between 5 Hz and 1.1 kHz.

5. The method according to claim 1, wherein the additional voltage in absolute value is less than or equal to the value of said voltage applied by the electrical network.

6. The method according to claim 1, wherein the additional voltage is generated at the output of the electronic component which receives as input the common mode current flowing between the internal ground of the circuit and the Earth ground when the circuit is supplied by the electrical network.

7. The method according to claim 6, wherein the common mode current used as input to the electronic component is obtained from a current delivered by the electrical network to the electrical circuit.

8. The method according to claim 6, wherein the electronic component is configured to slave the value of the common mode current which it receives as input, to a predetermined set value.

9. The method according to claim 1, wherein the additional voltage is applied between the internal ground of the circuit and the Earth ground by applying a first voltage between the internal ground of the circuit and the internal ground of the electronic component and by applying a second voltage of opposite sign to that of the first voltage between the Earth ground and the internal ground of the electronic component, so that the difference between the first and the second voltage is equal to the additional voltage.

10. The method according to claim 1, wherein the electrical network delivers an alternating voltage whose frequency is 50 Hz or 60 Hz.

11. The method according to claim 1, wherein the electronic component is without a field effect transistor.

12. The method according to claim 1, wherein the electrical circuit includes a rectification stage for the alternating voltage delivered by the electrical network, this stage having a positive output terminal and a negative output terminal, and the internal ground of the circuit being connected to one of said output terminals.

13. The method according to claim 12, wherein an energy storage unit is connected between the positive and negative output terminals of the rectification stage, the method being implemented during the recharging of the energy storage unit.

14. The method according to claim 13, the electrical circuit forming part of a hybrid or electrically driven vehicle.

15. An assembly, comprising: an electrical circuit, comprising a rectification stage for an alternating voltage, said stage having a positive output terminal and a negative output terminal and the circuit having an internal ground connected to one of said output terminals; a frame; and a component electrically connected first to the internal ground of the circuit and secondly to the frame, the component being configured for applying a voltage between the internal ground of the circuit and the frame, when the electric circuit is supplied by an electrical network, for reducing the current at the frequency of the network flowing between the internal ground and the frame.

16. The assembly according to claim 15, wherein the electrical circuit does not comprise a transformer.

17. A method of reducing common mode current flowing between an internal ground of an electrical circuit and the Earth ground, said circuit being supplied by an electrical network delivering an alternating voltage, the method comprising: applying a voltage by the electrical network between the internal ground of the circuit and the Earth ground; and applying an additional voltage between the internal ground of the circuit and the Earth ground using an electronic component interposed between the internal ground of the circuit and the Earth ground, this additional voltage opposing the voltage applied by the electrical network between the internal ground and the Earth ground, so as to reduce the common mode current at the frequency of the electrical network, wherein the electrical circuit does not comprise a transformer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention may be better understood on reading the following non-restrictive example of its implementation and on examining the accompanying drawings in which:

(2) FIG. 1 schematically shows an assembly within which the invention may be implemented,

(3) FIG. 2 schematically shows a model in common mode equivalent to the assembly in FIG. 1,

(4) FIG. 3 shows the diagram of FIG. 2 in which an example of component according to the invention is introduced,

(5) FIG. 4 shows the assembly from FIG. 1 in which an example of a solution according to the invention is implemented, the component used for this implementation being shown functionally, and

(6) FIG. 5 shows the assembly from FIG. 1 in which an example of a solution according to the invention is implemented, the component used for this implementation being shown structurally.

DETAILED DESCRIPTION

(7) FIG. 1 shows an assembly 1 within which the invention may be implemented.

(8) This assembly 1 is supplied by an electrical network 2 via a connector 3. The electrical network 2 delivers an alternating voltage to an electrical circuit 4 of the assembly 1. In the example considered, the network 2 is three-phase and delivers a voltage with an effective value equal to 230 V. The frequency of the voltage is 50 Hz in the example considered. The neutral N of the electrical network 2 is connected to the Earth ground and a parasitic impedance 6 is interposed between the neutral N and the Earth ground.

(9) The electrical circuit 4 includes inductances, a rectification stage 8 for the alternating voltage delivered by the network 2 and whose output terminals 9 and 10 are traversed by a direct current.

(10) The rectification stage 8 includes, for example, controllable switches such as transistors. Stage 8 is, for example, a PFC component, known to a person skilled in the art for rectifying an alternating voltage, adapting the value of the rectified voltage to the load of the circuit 4 and complying with the standards in force regarding the value of the power factor and the emission of harmonic currents.

(11) A capacitor 11 is fitted between the output terminals 9 and 10 of stage 8. An energy storage unit, e.g. a battery, not shown, may be connected in parallel with this capacitor 11. This battery absorbs an electrical power, e.g. greater than 100 W, e.g. of the order of 3 kW when the electrical network 2 is single-phase, e.g. of the order of 20 kW when the electrical network 2 is three-phase. The assembly 1 further includes a metal frame 12. In the event of a frame Earth ground fault, the frame is potentially connected to the Earth ground via an impedance 16. This impedance 16 corresponds, in the case where the frame forms part of a vehicle, to the body resistance of a user of the vehicle when the latter touches the bodywork on the one hand and the ground on the other.

(12) When the assembly 1 forms, for example, a part of an electric or hybrid vehicle. The inductances 7 then correspond, for example, to the phase windings of the stator of an electric motor for driving an electric motor. The windings 7 can then be connected to the electrical network 2 according to the teaching of patent application WO 2010/057892.

(13) A capacitance 15 models the parasitic impedances and/or actual impedances added for technical reasons, in the form of capacitor-type electronic components, notably between the terminal 10 of the circuit 4 and the frame 12. The terminal 10 of the circuit 4 is here the negative output terminal of the rectification stage 8 and the electrical circuit 4 has an internal ground 13 which is here connected to the terminal 10. Because of the existence of this capacitor 15, a common mode current can flow from the circuit 4 to the frame 12 and flowing through the Earth ground, loop back into the network 2.

(14) In the case where the electrical network 2 delivers a multiphase alternating voltage and during a sequence of operation of the switches of the control stage 8, the terminal 10 is alternately connected to the neutral of the network 2 and to one of the phases of the network 2. In the case of a single-phase network 2, the terminal 10 is selectively connected to the neutral or to the phase of the network 2.

(15) A voltage E is thus applied between the terminal 10 and the frame 12 connected to the Earth ground and, due to this voltage and the capacitor 15, current flows from the terminal 10 to the Earth ground.

(16) The part of the circuit 4 upstream from the terminal 10 and the network 2 can thus be likened to a voltage source 20 alternately applying between the terminal 10 and the frame 12: a zero voltage E, and a voltage E just like that delivered by the network 2 to the circuit 4.

(17) Accordingly, a current i flows through the capacitor 15 and the impedances 16 and 6 before looping back into the network 2. Thus the equivalent common mode model shown in FIG. 2 is obtained.

(18) An example of implementation of the invention will be described with reference to FIG. 3.

(19) As can be seen in FIG. 3, an electronic component 21 is fitted in parallel with the capacitor 15 for reducing the value of the common mode current, or even cancelling this current. The electronic component 21 has a terminal connected to the output terminal 10 of the rectification stage 8 and a terminal connected to the frame 12.

(20) This component 21 is an active filter configured for generating a frequency equal to that of the electrical network 2, this frequency in the example considered being 50 Hz, an additional voltage F opposing the voltage applied by the voltage source 20. The resultant voltage applied to the impedances 6 and 16 is thus reduced, even cancelled, so the current passing through these impedances 6 and 16 is reduced, even cancelled.

(21) The additional voltage E is applied by the electronic component 21 in parallel with the capacitor 15.

(22) In the example considered, the component 21 is associated with a system of measurement 23 of the common mode current i passing through the circuit 4. In the case of a three-phase network, this system of measurement 23 can measure the current in each of the phases, using, for example, a nanocrystalline or other magnetic core and by calculation from these currents, determine the common mode current. Based on this information, the electronic component 21 generates at the terminals of the capacitor 15, in parallel with the latter, a voltage opposing the voltage applied by the source 20 between the terminal 10 and the frame.

(23) An example of component 21 will now be described functionally and structurally with reference to FIGS. 4 and 5.

(24) In the example described, the component 21 includes two amplifier stages 23 and 24. Each of these amplifier stages generates a voltage from the current value determined by the system 23. The two stages 23 and 24 may or may not be identical and may or may not generate the same voltage. The first and second voltage both have, for example, an amplitude of approximately 300 V.

(25) In the example described, the first stage 23 is connected via the intermediary of a decoupling capacitance 28 to the output terminal 10 of the rectification stage 8 and the second stage 24 is connected via the intermediary of another decoupling capacitance 29 to the frame 12.

(26) The second stage 24 includes a unit negative gain 30.

(27) With the two stages 23 and 24 shown in FIG. 4, a first voltage is applied between the output terminal 10 and the internal ground 25 of the electronic component 21 by the first stage 23 whilst a second voltage of opposite sign is applied between the frame 12 and the internal ground 25 of the electronic component 21. The difference between these two voltages corresponds to the voltage applied by the electronic component 21 to the capacitor 15 for reducing the common mode current.

(28) Each amplifier stage 23 or 24 includes a high gain, low-pass filter 33 and a DC voltage component generator 34.

(29) The component 21 further includes, upstream from stages 23 and 24, gains 32 and 35, a zero comparator 36 and a unit 37 forming a PID-type controller.

(30) FIG. 5 shows an example of a structural embodiment of the component 21 whose functional representation is given in FIG. 4. As can be seen, a number of functions are implemented using operational amplifiers supplied by a positive voltage of 5 V and a negative voltage of 5 V.

(31) The values indicated in FIG. 5 give an example of dimensioning of the component 21 for reducing the common mode current passing through the capacitor 15 for a frequency of 50 Hz in generating an additional voltage at the terminals of this capacitor 15.

(32) The invention is not limited to what has just been described.

(33) In another example, not shown, a single stage amplifier may be used for generating the additional voltage.

(34) In a further variant, the effective voltage delivered by the network 2 to the circuit 4 has another value.

(35) The invention may be applied to assemblies 1 other than those forming part of a vehicle.

(36) The expression comprising a should be understood as meaning comprising at least one unless specified otherwise.