Power converter incorporating a partial discharge detection circuit

Abstract

The invention relates to a converter (100) comprising a DC filter stage (110) and an inverter (120) connected to the filter stage (110), the filter stage (110) comprising at least common-mode capacitors (C1, C2, C3, C4). The filter stage (110) comprises a detection device (113; 114) for detecting partial discharge currents in the converter, the detection device (113; 114) comprising at least one decoupling capacitor and a current measurement circuit (1134; 1144) for measuring the current in the decoupling capacitor, the decoupling capacitor being formed by at least one of the common-mode capacitors (C1, C2; C3, C4).

Description

[0001] POWER CONVERTER INCORPORATING A PARTIAL DISCHARGE DETECTION CIRCUIT.

[0002] The present invention relates to the field of electronics and more particularly to the measurement of partial discharges in power electronic devices.

[0003] BACKGROUND OF THE INVENTION

[0004] It is recalled that, according to the IEC 60270 standard, a partial discharge is a localized electrical discharge, generated by a high voltage, which partially short-circuits the insulating gap separating two conductors.

[0005] The classic method for measuring partial discharges, recommended by the IEC 60270 standard, consists of connecting the insulation to the terminals of a voltage generator and measuring the thresholds of occurrence of partial discharges through a coupling capacitor associated with a current measurement and processing circuit.

[0006] It was also considered to measure partial discharges in electrical devices during use. The method recommended by the standard is difficult to implement, as it requires an external high-voltage power supply, a decoupling capacitor, and an associated measurement circuit.

[0007] SUBJECT OF THE INVENTION

[0008] The invention aims in particular to enable the measurement of partial discharges in an electronic device connected to an electrical installation.

[0009] SUMMARY OF THE INVENTION

[0010] For this purpose, the invention provides a converter comprising a DC filtering stage and an inverter connected to the filtering stage. The filtering stage includes at least common-mode capacitors and a device for detecting partial discharge currents in the converter. The detection device includes at least one decoupling capacitor and a current measurement circuit in the decoupling capacitor, the decoupling capacitor being formed by at least one of the common-mode capacitors.

[0011] The common-mode capacitors are connected as close as possible to the power supply that could be a source of interference, thus minimizing wiring inductance and having a high cutoff frequency compatible with partial discharge measurement. It is therefore highly advantageous to use at least one of these common-mode capacitors as a decoupling capacitor in a partial discharge current detection device. Partial discharge detection thus does not require any additional capacitors beyond the common-mode capacitors, which are necessary for the converter's operation anyway. The detection device according to the invention enables the detection of partial discharges occurring in the converter and the equipment and cables to which the converter is connected.It is noted that a partial discharge detection device placed on the converter's power supply would not be able to measure the partial discharges detected by the invention because these are greatly attenuated by the converter's filter.

[0012] Depending on optional features, used individually or in whole or in combination:

[0013] - the filtering stage includes at least two damping resistors each in series with one of the common mode capacitors and the measurement circuit is connected to a voltage measuring device arranged to measure a voltage across at least one of the damping resistors;

[0014] - the measurement circuit is connected to the voltage measuring device via a high-pass filter;

[0015] - the detection device is arranged to measure a voltage across the two damping resistors; - the measurement circuit is connected to a current measuring device arranged to measure a current in at least one of the common-mode capacitors;

[0016] - the current measuring device includes at least one Rogowski torus arranged on a conductor connecting the common mode capacitor to ground or the current measuring device includes at least one high frequency current transformer arranged on a conductor connecting the common mode capacitor to ground;

[0017] - the common mode capacitors are mounted on a set of laminated busbars and a printed circuit board extends between the common mode capacitors and the set of laminated busbars and includes a hole for the passage of one leg of one of the common mode capacitors, the current measuring element being printed on the printed circuit board around the hole;

[0018] - the measurement circuit is connected to the current measuring device via a high-pass filter;

[0019] - the detection device is arranged to measure a current in the two common-mode capacitors.

[0020] Other features and advantages of the invention will become apparent from the following description of particular and non-limiting embodiments of the invention.

[0021] BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Reference will be made to the attached drawings, including:

[0023] [Fig. 1] is an electrical diagram of an installation incorporating a power converter;

[0024] [Fig. 2] is an electrical diagram of a part of this power converter incorporating a partial discharge detection device according to a first embodiment of the invention; [Fig. 3] is an electrical diagram of a part of this power converter incorporating a partial discharge detection device according to a second embodiment of the invention;

[0025] [Fig. 4a] is a partial schematic, side view of a power converter according to the invention;

[0026] [Fig. 4b] is a partial schematic, top view of the printed circuit board of this power converter.

[0027] DETAILED DESCRIPTION OF THE INVENTION

[0028] With reference to Figure 1, the power converter according to the invention, generally designated 100, is described here in application to supplying an electrical machine 200 to which the power converter is connected by a cable 300. The electrical machine 200 is here a permanent magnet synchronous machine (PMSM) comprising here three electromagnetic windings.

[0029] The 100 converter includes a 110 DC current filtering stage and a 120 inverter.

[0030] The filtering stage 110 comprises a first line 111 and a second line 112 between which a voltage source establishes a potential difference. Each line has a DC filtering inductance L in common-mode and differential-mode operation and is connected to a set of common-mode capacitors. This set includes:

[0031] - a first common-mode capacitor Cl having one plate connected to the first line 111 and one plate connected to ground,

[0032] - a second common-mode capacitor C2 having one plate connected to the second line 112 and one plate connected to ground,

[0033] - a third common-mode capacitor C3 having one plate connected to the first line 111 and one plate connected to ground via a first damping resistor RI,

[0034] - a fourth common mode capacitor C4 having one plate connected to the second line 112 and one plate connected to ground via a second damping resistor R2.

[0035] Common mode capacitors preferably have a capacitance between a few tens and a few hundred nF.

[0036] The filtering stage 110 further includes a first differential filtering capacitor C5 and a second differential filtering capacitor C6 mounted in parallel between the first line 111 and the second line 112.

[0037] Capacitors are preferably positioned on a printed circuit board or on a set of laminated bars (commonly called "busbar"), depending on the power of the power converter, in order to limit loop inductances.

[0038] The inverter 120 includes a positive terminal 121 and a negative terminal 122 connected respectively to the first line 111 and the second line 112, and three terminals 123, 124, 125, each connected, via cable 300, to one of the windings of the electric machine 200. The inverter 120 also includes three arms of transistors 126 in series connected in parallel to the first terminal 121 and the second terminal 122; each pair of transistors 126 in series having a midpoint connected to one of the terminals 123, 124, 125. The inverter 120 further includes six control inputs 127, one for each of the transistors 126, connected to an electronic control unit (not shown) for cutting the voltage supplied at the output of the filtering stage 110.

[0039] This arrangement of the power converter 100, as shown in Figure 1, is known in itself and will not be detailed further here.

[0040] The power converter 100 further comprises, according to the invention, a device for detecting partial discharge currents in the power converter 100. The detection device comprises at least one decoupling capacitor and a current measurement circuit in the decoupling capacitor, the decoupling capacitor being formed by at least one of the common-mode capacitors.

[0041] In the two embodiments of the invention which will now be described in relation to Figures 2 and 3, the detection device comprises two decoupling capacitors, each formed by one of the common-mode capacitors.

[0042] With reference to Figure 2, and according to the first embodiment of the invention, the detection device, generally designated as 113, comprises two voltage acquisition elements 1131.1, 1131.2 each connected on one side to the terminals of one of the damping resistors RI, R2 and on the other side to an input of a summing 1132 having an output connected to a high-pass filter 1133 connected to the measurement circuit 1134.

[0043] The voltage across the damping resistor RI in series with the common-mode capacitor C3 is representative of the current flowing through the common-mode capacitor C3, and the voltage across the damping resistor R2 in series with the common-mode capacitor C4 is representative of the current flowing through the common-mode capacitor C4. The voltage acquisition devices 1131.1 and 1131.2 are operational amplifier devices.

[0044] The measuring circuit 1134 is arranged to compare the voltage obtained to a threshold and deduce whether a partial discharge current flows in the common mode capacitors C3, C4.

[0045] The 1132 summing amplifier allows the use of measurements of the "positive path" passing through the common-mode capacitor C3 and the damping resistor RI, and the "negative path" passing through the common-mode capacitor C4 and the damping resistor R2. This makes it possible to measure the partial discharges of one phase at the moment of switching (where the maximum overvoltage occurs), regardless of which transistor is conducting. This results in maximum gain and improved accuracy.

[0046] The high-pass filter 1133 allows the suppression of disturbances caused by the switching of transistors 126.

[0047] The detection of a partial discharge in equipment can have several consequences.

[0048] On a test bench, the equipment will be declared non-operational and possibly repaired or modified to remedy this problem.

[0049] On equipment in use, for example in flight for equipment mounted on an aircraft:

[0050] - the equipment is shut down to prevent damage to its insulation; or

[0051] - The values ​​and duration of partial discharges are recorded, without stopping the converter, for subsequent processing to assess the aging of the insulation during a maintenance operation; and / or

[0052] - an alarm indicating that a maintenance operation is required is activated.

[0053] With reference to Figure 3, and according to the second embodiment of the invention, the detection device, generally designated as 114, comprises two Rogowski coils 1141.1, 1141.2 each mounted around the conductor connecting the midpoint to one of the common-mode capacitors C1, C2. The Rogowski coils 1141.1, 1141.2 each have a measurement output connected to an input of a summing junction 1142 having an output connected to a high-pass filter 1143 connected to the measurement circuit 1144.

[0054] The Rogowski toroids 1141.1, 1141.2 measure the current flowing through the common-mode capacitors Cl, C2.

[0055] The 1132 summing junction allows us to exploit the measurements of the "positive path" passing through the common mode capacitor Cl and the "negative path" passing through the common mode capacitor C2, which allows us to measure the partial discharges of a phase at the time of switching (where the maximum overvoltage occurs) regardless of which transistor is conducting.

[0056] The high-pass filter 1143 allows the suppression of disturbances caused by the switching of transistors 126.

[0057] When common-mode capacitors are mounted on a printed circuit board, it is easy to integrate the measurement as close as possible to the components, either by measuring the voltage across the damping resistors RI and R2 or by integrating the Rogowski coils directly onto the PCB. In such an embodiment, one part of each coil is printed on the top side of the PCB, a second part of each coil is printed on the bottom side, and plated-through vias electrically connect the two parts of each coil. The integration of Rogowski coils directly onto the PCB is known, for example, from the following documents:

[0058] - X. Zhao, R. Phukan, C. -. W. Chang, R. Burgos, D. Dong and P. Asfaux, "Design and Optimization of 2x211-kW SiC-Based Aircraft Propulsion Inverter System with High Power Density and High Efficiency", 2023 IEEE Applied Power Electronics Conference and Exposition

[0059] (APEC), Orlando, FL, USA, 2023, pp . 1009-1016, doi 10.1109 / APEC43580 .2023.10131406;

[0060] - B. Bayarkhuu, B. Bat-Ochir, B. Dugarjav, I. Omura Single PCB sensor-based output current reproduction for three-phase inverter systems, www.journals.else- vier . com / power- electronic-de vices -and- component s , 17 décembre 2023, 2772-3704, Elsevier.

[0061] When common mode capacitors are mounted on a 130 laminated bar (see figures 4a and 4b), setting up the detection device is more delicate. A printed circuit board 140 is attached to the laminated busbar 130 to extend between the common-mode capacitors C1, C2 and the laminated busbar 130. The printed circuit board 140 has two holes 141 to allow the passage of the leads of the common-mode capacitors C1, C2, which are fixed to the laminated busbar 130. Each of the holes 141 is surrounded by turns of the Rogowski coil 1141.1, 1141.2, which are printed on the printed circuit board 140 and connected to a connector 142 fixed to the printed circuit board 140 to allow the connection of the Rogowski coils 1141.1, 1141.2 to the measurement circuit 1144 via the high-pass filter 1143. Thus, the Rogowski coils 1141.1, 1141.2 are integrated into the printed circuit board 140.Note that the current measurements are positioned on the terminals of the common mode capacitors Cl, C2 connected to ground: the isolation to be guaranteed by the Rogowski toroids is then minimal.

[0062] Preferably, the printed circuit board 140 is glued to the laminated bar 130 to comply with the mechanical environment constraints of the assembly.

[0063] It should be noted that partial discharges are generated by voltage spikes associated with transistor switching; therefore, they only appear within a time window corresponding to the duration of these spikes (on the order of a few 10 ns to a few 100 ns). Preferably, the detection device is configured to synchronize the measurement of partial discharges with the switching events. It follows that the detection of partial discharges is then advantageously performed within the window corresponding to the duration of the voltage spikes associated with transistor switching.

[0064] It is understood that the key point of the invention is to use a decoupling capacitor as close as possible to the source of partial discharge in order to "short-circuit" these micro-pulses of current in the measurement circuit through the decoupling capacitor. The detection device of the invention uses the common-mode filter capacitor of the converter as its decoupling capacitor, and is thus able to conduct all disturbances downstream (AC side) of the converter, and therefore to measure any partial discharges on these circuits, as indicated in IEC 60270.

[0065] Of course, the invention is not limited to the embodiments described but encompasses any variant falling within the scope of the invention as defined by the claims.

[0066] In particular, the power converter may have a different structure than the one described.

[0067] The converter might not include a damping resistor.

[0068] Alternatively, only one of the common-mode capacitors could be used as the decoupling capacitor. The summing junction could then be omitted, allowing the measurement to be taken only along the path passing through that specific common-mode capacitor. The current measurement can be performed on either one of the common-mode capacitors connected to the positive terminal of the circuit, or on one of the common-mode capacitors connected to the negative terminal. This reduces the number of components, as some of the current can be redirected through the differential-mode capacitors C5 and C6, which have minimal wiring inductance.

[0069] As an alternative to the second embodiment, the Rogowski toroids 1141.1, 1141.2 can be replaced by high-frequency current transformers.

[0070] The connector can be replaced by soldered wires to transmit to the measurement circuit 1144 the measurement signals of the Rogowski toroids 1141.1, 1141.2.

[0071] The power converter according to the invention can be placed in any electrical installation and for example an electrical installation in which the electrical machine is replaced by a transformer.

Claims

DEMANDS 1. Converter (100) comprising a DC filtering stage (110) and an inverter (120) connected to the filtering stage (110), the filtering stage (110) comprising at least common mode capacitors (Cl, C2, C3, C4), characterized in that the filtering stage (110) comprises a partial discharge current detection device (113; 114) in the converter, the detection device (113; 114) comprising at least one decoupling capacitor and a current measurement circuit (1134; 1144) in the decoupling capacitor, the decoupling capacitor being formed by at least one of the common mode capacitors (Cl, C2; C3, C4).

2. Converter according to claim 1, wherein the filtering stage (110) comprises at least two damping resistors (RI, R2) each in series with one of the common mode capacitors (C3, C4) and the measuring circuit (1134) is connected to a voltage measuring device (1131.1, 1131.2) arranged to measure a voltage across at least one of the damping resistors (RI, R2).

3. Converter according to claim 2, wherein the measuring circuit (1134) is connected to the voltage measuring element (1131.1, 1131.2) via a high-pass filter (1133).

4. Converter according to claim 2 or 3, in which the detection device (113) is arranged to measure a voltage across the two damping resistors (RI, R2).

5. Converter according to claim 1, in which the measuring circuit (1144) is connected to a measuring element current (1141.1, 1141.2) arranged to measure a current in at least one of the common mode capacitors (Cl, C2).

6. Converter according to claim 5, wherein the current measuring element (1141.1, 1141.2) comprises at least one Rogowski torus disposed on a conductor connecting the common mode capacitor (Cl, C2) to ground.

7. Converter according to claim 5, wherein the current measuring element (1141.1, 1141.2) comprises at least one high-frequency current transformer disposed on a conductor connecting the common-mode capacitor (Cl, C2) to ground.

8. Converter according to claim 6 or 7, wherein the common mode capacitors (Cl, C2) are mounted on a set of laminated busbars (130) and a printed circuit board (140) extends between the common mode capacitors (Cl, C2) and the set of laminated busbars (130) and includes a hole (141) for the passage of a leg of one of the common mode capacitors (Cl, C2), the current measuring element (1141.1, 1141.2) being printed on the printed circuit board (140) around the hole (141).

9. Converter according to any one of claims 6 to 8, wherein the measuring circuit (1144) is connected to the current measuring element (1141.1, 1141.2) via a high-pass filter (1143).

10. Converter according to any one of claims 5 to 9, wherein the detection device (114) is arranged to measure a current in the two common-mode capacitors (Cl, C2).

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