DE102020215055A1 - Circuit arrangement for reducing common-mode interference in a power electronic device - Google Patents

Abstract

The invention relates to a circuit arrangement (110) for reducing common-mode interference in a power electronic device (130), which has input connections (131, 132) and output connections (135, 136, 137), and which represents a common-mode interference source during operation, with a transformer (160 ) and a plurality of capacitors (181, 182, 185, 186, 187), a first connection (161) of the transformer (160) being connected via a respective capacitor (181, 182) to a respective input connection (131, 132) of the electronic power device ( 130) is to be connected, with a second connection (162, 163) of the transformer (160) being connected via a respective capacitor (130) to an output connection (135, 136, 137) of the electronic power device (130), and with two more Terminals of the transformer (160) are to be connected to ground (154), and use thereof, a power electronic system (100) with such a circuit arrangement, and a vehicle with such a power electronic system (100).

Description

The present invention relates to a circuit arrangement for reducing common-mode interference in a power electronic device, a power electronic system with a power electronic device and such a circuit arrangement, a vehicle with such a power electronic system and the use of such a circuit arrangement.

Background of the Invention

When operating power electronic devices, such as voltage converters or converters, common-mode interference occurs, which leads to electromagnetic emissions. These must always be minimized when operating electrical systems so that these systems do not influence other systems in the environment. Various solutions are known for electromagnetic filtering of individual current-carrying lines.

the WO 2020/114653 A1 discloses, for example, the use of common-mode chokes at the input and/or output of a power converter and a short-circuited additional line. This allows common-mode interference to be reduced.

Disclosure of Invention

According to the invention, a circuit arrangement, a power electronic system, a vehicle and a use of such a circuit arrangement with the features of the independent patent claims are proposed. Advantageous configurations are the subject of the dependent claims and the following description.

The invention is concerned with reducing common-mode interference in a power electronic device that has input terminals and output terminals and that represents a source of common-mode interference during operation. Such a power electronic device is, for example, a power converter (e.g. a pulse-controlled inverter, rectifier and the like) or a voltage converter (DC-DC converter or DC-AC converter). Input and output connections—or generally also input and output—are to be understood as meaning the connections that are supplied with voltage or are acted upon. For example, a DC-DC converter has two input and two output terminals. On the other hand, a DC-AC converter, for example, has two input terminals and output terminals according to the number of AC phases.

Common-mode interference is based on common-mode currents and is the main source of EMC problems (EMC stands for "Electromagnetic Compatibility") in, for example, drive systems that are used in different areas. These common-mode currents affect the interference voltages generated by a power electronic device. A power converter or converter is a typical source of common mode noise.

On one side, this source can be coupled to ground, for example, through stray capacitances of a motor cable and the motor. On the other side, the common-mode currents close e.g. through the mains cable or flow into the mains. If a network simulation is set up between the power grid and the drive system, then there is a possibility of being able to measure these currents. Other electronic and electrical devices that are connected to the same power supply can be adversely affected by common mode interference.

A line impedance stabilization network (LISN) is an electrotechnical device that is used to measure line-bound interference emissions as part of measurements and tests for EMC as a simulation of supply networks.

Various technical solutions can be used to reduce the emitted common-mode interference voltage spectrum in a power electronic device. These can be, for example, common-mode chokes, as already mentioned, or Y-capacitors (so-called Y-capacitors are to be understood as meaning capacitors that are connected between the phase or neutral conductor and a touchable, protectively earthed apparatus housing and thus bridge the basic insulation). Passive EMC filters in general, possibly with a different number of stages, can also be considered, an optimized design of the load capacity (motor, cable, mains, etc.), specialized PWM methods for minimizing the common-mode voltages and optimized switching processes of the semiconductors.

A very effective EMC measure is the use of passive EMC filters. Y-capacitors are typically required in the structure of the filter for efficient attenuation of common-mode interference. However, the use of Y-capacitors increases the proportion of leakage currents. Leakage currents have a harmful effect on the human body, so they are limited by law. Therefore, the size of Y-capacitors is limited in most cases, and the use of Y-capacitors is sometimes also prohibited. When the desired EMC filter attenuation is reached, the proportion of leakage currents often increases so much that RC switches (residual current switches) can trip undesirably. Around To solve these problems, alternative filter topologies can be applied.

A power electronic device regularly represents a source of common-mode interference during operation. Common-mode interference can propagate through stray capacitances in the system (stray capacitances are inherently undesirable capacitances that are present in many components such as cables). To avoid this propagation it is possible to short circuit the source of common mode noise. In this case the effect of common mode noise on the power supply side (and those measured on the network) is much smaller. However, it is also conceivable to connect additional components such as resistors (component) and/or capacitors to the path of the common-mode currents. In addition, both the common-mode noise source and the power supply network can be isolated with high-impedance components. Additional components can also provide an alternative low-impedance path for common-mode currents for better filtering.

As part of the invention, a circuit arrangement for reducing common-mode interference in a power electronic device is now proposed, which has a transformer and a plurality of capacitors. In this case, the transformer has in particular two coils, each with two connections, so the transformer has a total of four connections.

A first connection of the transformer is to be connected to the input connections of the electronic power device via a respective capacitor, and a second connection of the transformer is to be connected to the output connections of the electronic power device via a respective capacitor. The input terminals are connected to each other via capacitors, likewise the output terminals are connected to each other via capacitors. Two further connections of the transformer - i.e. the two remaining connections - are to be connected to ground or to be placed on ground.

There are two preferred variants of how the transformer can be specifically connected. In the first variant, the first connection and the second connection of the transformer are assigned to a common coil of the transformer. The two coils are then wound in particular in opposite directions. The transformer then serves to couple high-frequency common-mode currents caused by the power electronic device to ground. In addition, the already mentioned common-mode chokes can also be provided for the input connections and/or output connections. However, due to the effect of the transformer, these can be designed to be less effective or even omitted. In addition, this principle ensures galvanic isolation between the power supply (input connections) and the further path (output connections) from the common-mode current.

The circuit arrangement advantageously also has a resistor (component) which is connected at the first connection or at the second connection of the transformer between the relevant connection and the capacitors connected to it. A resistor can also be provided, which is to be connected between one of the two other terminals of the transformer and ground. In other words, the direct current path can be supported with damping resistors, which serves to reduce common-mode currents even better by converting them into thermal energy. This also reduces losses in the transformer and in the capacitors. A particular advantage of this principle is that the capacitance of the Y-capacitors already mentioned can be reduced, in some cases the Y-capacitors can even be dispensed with entirely.

In the second variant, the first connection and the second connection of the transformer are assigned to two different coils of the transformer. This then also means that the two other connections and thus both coils must be connected to ground on one side. The two coils are then wound in particular in the same direction. In this case, the transformer acts as a galvanic decoupling between the input and output terminals of the power electronic device, e.g. between the primary and secondary side of a power converter. Depending on the high-frequency material properties of the core of the transformer, high-frequency components of the common-mode current are attenuated in the transformer. Common-mode currents on the input and output terminals of the power electronic device are mutually compensated. A particular advantage of this variant is that the leakage currents from lines to ground are limited by the leakage inductance of the transformer. The already mentioned common-mode chokes can also be provided in this variant.

In summary, it can be seen that the proposed circuit arrangement allows the construction of an EMC filter either without Y-capacitors or with Y-capacitors with a significantly lower capacitance while the damping effect remains the same. For example, in a stationary Drive system, secured with a residual current circuit breaker, Y-capacitors lead to false tripping of the switch. In the proposed concept, leakage currents in the Y-capacitors are avoided or reduced. For applications in the automotive industry, ie in particular in a vehicle, the capacitance of the Y capacitors is limited for safety reasons. In the case of e-vehicles (i.e. vehicles in which an electric motor is used as the (single) drive), the total energy that can be stored in all Y-capacitors is limited to approx. 0.2 J in a HV circuit . With the proposed circuit arrangement, this can be maintained much more easily.

The subject matter of the invention is also a use of the proposed circuit arrangement for reducing common-mode interference in a power electronic device which has input connections and output connections and which represents a common-mode interference source during operation. The circuit arrangement must be appropriate for this purpose, i.e. connected to the input and output terminals and to ground.

The subject matter of the invention is also a power electronic system with a power electronic device and a correspondingly connected circuit arrangement, as explained above. The output connections can be used in particular to supply an electrical machine, in particular in a vehicle.

The subject matter of the invention is also a vehicle with an electric machine and a power electronic system connected to it, as mentioned above.

With regard to the advantages and further configurations of the electronic power system and the vehicle, to avoid repetition, reference is made to the above explanations, which apply accordingly here.

Further advantages and refinements of the invention result from the description and the attached drawing.

The invention is shown schematically in the drawing using exemplary embodiments and is described below with reference to the drawing.

character list

• 1 shows schematically a power electronic system according to the invention in a preferred embodiment.
• 2 shows schematically a power electronic system according to the invention in a further preferred embodiment.

embodiment(s) of the invention

In 1 a power electronic system 100 according to the invention is shown schematically in a preferred embodiment. The electronic power system 100 has an electronic power device 130 , for example a DC-AC converter or power converter, and a circuit arrangement 110 .

The power converter 130 in turn has two input terminals 131, 132 and three output terminals 135, 136, 137. The input connections are connected, for example, to a network simulation 120 whose housing is in turn connected to ground 154 . This artificial network 120 (also referred to as LISN) is typically only used for measurement purposes, in practice, i.e. in the vehicle, an energy source such as a battery is usually provided instead. The output terminals are connected to a load 140, which is, for example, an electric machine or an electric motor, represented by unspecified windings and capacitances. The housing of the load 140 is also grounded 154. The electric motor 140 can be used, for example, to drive a vehicle.

A common-mode choke 150 or 152 is provided both at the input terminals 131, 132 or their connecting lines to the network simulation 120 and at the output terminals 135, 136, 137 or their connecting lines to the load 140.

A common mode choke (CMC, or current-compensated choke) typically has several identical windings through which an operating current flows in opposite directions, so that their magnetic fields cancel out in the core of the choke. Such interference currents typically occur in the same direction in the forward and return lines (these are, for example, the two connecting lines between the network simulation 120 and the power converter 130)). The common-mode choke forms a very high inductance for this common-mode interference, since these interference currents do not compensate in it. Common-mode chokes can be made, for example, from one-piece, closed ferrite cores in ring shape, E-shape, frame shape or so-called D-shape by winding wires be threaded through toroidal cores and wound onto bobbins for other core shapes.

The circuit arrangement 110 also has a transformer 160 and five capacitors 181, 182, 185, 186, 187. The transformer 160 has two coils 166, 167, which are wound in opposite directions, and four connections 161, 162, 163, 164. The two connections 161, 162 are assigned to the coil 166, while the two connections 163, 164 are assigned to the coil 167 Terminal 161 is now connected through capacitor 181 to input terminal 131, and through capacitor 182 to input terminal 132. Similarly, terminal 162 with an intervening resistor 170 is connected through capacitor 185 to output terminal 135, through capacitor 186 to the output terminal 136, and via the capacitor 187 to the output terminal 137. The two terminals 163, 164 are connected to ground 154, with a resistor 172 being interposed at the terminal 164.

In this case, the transformer 160 serves to couple high-frequency common-mode currents caused by the converter 130 to ground 154 . The primary common-mode current flows from the output terminals 135, 136, 137 via the associated capacitors 185, 186, 187 via the coil 166 and the capacitors 181, 182 to the input terminals 131, 132, or vice versa. A secondary common-mode current, which flows via ground 154, then results in the coil 167. This principle provides galvanic isolation between the power supply (input terminals) and the further path (output terminals) from the common mode current. As already mentioned, the common-mode chokes can be designed to be less effective or even omitted entirely.

In 2 a power electronic system 200 according to the invention is shown schematically in a further preferred embodiment. The electronic power system 200 basically corresponds to the electronic power system 100 1 , with the difference of a differently designed circuit arrangement 210. The circuit arrangement 210 in turn corresponds to the circuit arrangement 110 from FIG 1 , but the transformer 160 is connected differently and the ohmic resistances are not present, as will be explained below. Otherwise, refer to the description 1 referenced, the same components are provided with the same reference numerals.

Here, too, the transformer 160 has two coils 166, 167, which are wound in the same direction, and four connections 161, 162, 163, 164. The two connections 161, 162 are assigned to the coil 166, while the two connections 163, 164 are assigned of the coil 167. The terminal 161 is also connected here via the capacitor 181 to the input terminal 131, and via the capacitor 182 to the input terminal 132. However, the terminal 163 is connected via the capacitor 185 to the output terminal 135, via the capacitor 186 to the Output terminal 136, and via the capacitor 187 to the output terminal 137. The two terminals 162, 164 are connected to ground 154 and are also connected to one another via this.

In this case, the transformer 160 acts as a galvanic decoupling between the input and output terminals or between the primary and secondary side of the power converter 130. The common-mode current flows from the output terminals 135, 136, 137 via the associated capacitors 185, 186, 187 and via the coil 167 to ground 154, from there then again via the coil 166 and the capacitors 181, 182 to the input terminals 131, 132, or vice versa. A particular advantage of this variant is that the leakage currents from lines to ground 154 are limited by the leakage inductance of the transformer 160 .

QUOTES INCLUDED IN DESCRIPTION

This list of the documents cited by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent Literature Cited

• WO 2020/114653 A1 [0003]

Claims (12)

Circuit arrangement (110, 210) for reducing common-mode interference in a power electronic device (130), which has input connections (131, 132) and output connections (135, 136, 137), and which represents a common-mode interference source during operation, with a transformer (160) and several capacitors (181, 182, 185, 186, 187), wherein a first connection (161) of the transformer (160) is to be connected to the input connections (131, 132) of the electronic power device (130) via a respective capacitor (181, 182), wherein a second terminal (162, 163) of the transformer (160) is to be connected to the output terminals (135, 136, 137) of the electronic power device (130) via a respective capacitor (185, 186, 187), and wherein two further terminals of the Transformer (160) are to be connected to ground (154). Circuit arrangement (110) after claim 1 , The first connection (161) and the second connection (162) of the transformer (160) being associated with a common coil (166) of the transformer (160). Circuit arrangement (110) after claim 2 , further comprising a resistor (170) connected between the first terminal or second terminal (162) of the transformer (160) and the capacitors connected thereto. Circuit arrangement (110) after claim 2 or 3 , further comprising a resistor (172) to be connected between one (164) of the two other terminals of the transformer (160) and ground (154). Circuit arrangement (210) after claim 1 , wherein the first connection (161) and the second connection (163) of the transformer are assigned to two different coils (166, 167) of the transformer (160). Circuit arrangement (110, 210) according to one of the preceding claims, wherein a common-mode choke (150, 152) is provided at the input connections (131, 132) and/or at the output connections (135, 136, 137) of the electronic power device (130). . Circuit arrangement (110, 210) according to one of the preceding claims, wherein the electronic power device (130) is designed as a power converter. Use of a circuit arrangement (110, 210) according to one of the preceding claims for reducing common-mode interference in a power electronic device (130) which has input connections (131, 132) and output connections (135, 136, 137) and which represents a common-mode interference source during operation. Electronic power system (100, 200), with an electronic power device (130) and a connected circuit arrangement (110, 210) according to one of Claims 1 until 7 . Power electronic system (100, 200) after claim 9 , wherein the power electronic device (130) is designed as a power converter. Power electronic system (100, 200) after claim 9 or 10 , wherein the output connections (135, 136, 137) are used to supply an electrical machine (140), in particular in a vehicle. Vehicle with an electric machine (130) and a power electronic system (100, 200) connected to it claim 11 .

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