DC link capacitor unit with EMC filter effect

Abstract

Intermediate circuit capacitor unit with EMC filter effect (ZKKEMF), for arrangement in the current path between a DC voltage source, in particular a high-voltage battery (HVB) and a power electronic unit (LE), comprising two busbars (S), each connectable at a first end to a DC voltage source and at a second end to a power electronic unit (LE); and at least two intermediate circuit capacitors (C) arranged between the busbars (S); wherein on each busbar (S) at least one magnetic core (MK) is arranged between two intermediate circuit capacitors (C) for damping differential mode interference; at least one pair of Y capacitors (Cy); wherein each of the Y-capacitors (Cy) of a pair of Y-capacitors (Cy) connects a respective busbar (S) to the electrical ground (GND); and at least one common mode choke (CMC) enclosing both busbars (S); wherein the common mode choke (CMC) is designed to attenuate common mode interference; characterized in that at least one pair of Y capacitors (Cy) is designed to attenuate common-mode interference; at least one magnetic core (MK) is arranged between adjacent intermediate circuit capacitors (C) on each busbar (S); the number n of intermediate circuit capacitors (C) is 1 greater than the number of magnetic core pairs between adjacent intermediate circuit capacitors (C); the intermediate circuit capacitors (C) due to their arrangement between the magnetic cores (MK) serve not only to store energy but also to dampen differential mode interference; the total capacitance of the intermediate circuit capacitors (C) is dimensioned such that power fluctuations caused by switching operations in the power electronic unit (LE) can be compensated; and wherein the at least one pair of Y capacitors (Cy), the at least one common mode choke (CMC), the at least two intermediate circuit capacitors (C) and the at least one magnetic core (MK) are arranged one after the other in the direction from the first end to the second end of the busbars (S); or wherein the at least one common-mode choke (CMC), the at least one pair of Y capacitors (Cy), the at least two intermediate circuit capacitors (C) and the at least one magnetic core (MK) are arranged one after the other in the direction from the first end to the second end of the busbars (S); and wherein at least a majority of the two busbars (S), as well as all electrical elements (Cy, CMC, C, MK) of the intermediate circuit capacitor unit (ZKKEMF), namely the at least one pair of Y capacitors (Cy), the at least one common-mode choke (CMC), the intermediate circuit capacitors (C) and the magnetic cores (MK) arranged between each two intermediate circuit capacitors (C), are arranged in a common housing; and wherein the last electrical element before the second end of the busbars (S) is an intermediate circuit capacitor (C).

Description

[0001] The present invention relates to an intermediate circuit capacitor unit with EMC filter effect

[0002] In electric and hybrid vehicles, power electronics are used to convert direct current into alternating current and vice versa. Electronic switches, for example, transform the direct current signal into a sinusoidal signal using pulse-width modulation. Such power electronics are highly efficient, which leads to a high switching edge steepness and a high switching frequency. The switching processes ensure a discontinuous energy flow between the alternating current and direct current circuits, and the voltage in the direct current circuit, in particular, is subject to large fluctuations. To minimize the voltage fluctuation in the direct current circuit, a suitable energy storage device is desirable.

[0003] The high frequency and steepness of the signal edge also lead to harmonics in the signals. Electromagnetic coupling can lead to electromagnetic compatibility problems. To prevent impacts on the vehicle and the environment, the CISPR 25 standard, for example, specifies frequency-dependent limits for interference emissions. To comply with these limits, the DC signal must be filtered using an electromagnetic compatibility filter (EMC filter). The filtering and attenuation effect of conventional EMC filters is often unsatisfactory, especially in certain operating situations.

[0004] In addition, conventional filter and energy storage units are expensive and require a relatively large installation space.

[0005] It is therefore an object of the present invention to provide an intermediate circuit capacitor unit with EMC filtering effect, which enables a reliable filtering and damping effect between the DC voltage source and the power electronics in all operating situations and avoids damage, and which is cost-effective to manufacture and requires little installation space.

[0006] Furthermore, a reliable drive train for an electric or hybrid vehicle and a reliable method for operating such a drive train are to be specified.

[0007] These problems are solved by the subject matter of the independent claims. Advantageous further developments arise from the dependent claims.

[0008] An intermediate circuit capacitor unit according to the invention with EMC filter effect for arrangement in the current path between a DC voltage source, in particular a high-voltage battery and a power electronic unit, comprises two busbars, each connectable at a first end to a DC voltage source and at a second end to power electronics; and at least two intermediate circuit capacitors arranged between the busbars; wherein on each busbar at least one magnetic core is arranged between two intermediate circuit capacitors for damping differential mode interference; at least one pair of Y capacitors; wherein each of the Y capacitors of a pair of Y capacitors connects a respective bus bar to the electrical ground; and at least one common mode choke enclosing both busbars; wherein the at least one pair of Y capacitors and the common mode choke are configured to attenuate common mode noise.

[0009] According to a basic concept of the present invention, the DC link capacitor unit with EMC filtering combines all electrical elements necessary for temporary energy storage and for damping differential and common-mode interference in a single unit. The DC link capacitor unit with EMC filtering can thus be manufactured more cost-effectively and with a smaller installation space, which is a major advantage, especially in electric and hybrid vehicles, where space is often limited in the drivetrain.

[0010] The at least one pair of Y capacitors and the at least one common-mode choke reliably attenuate common-mode interference on the busbars between the DC voltage source and the power electronics unit, and prevent excessive current flow of the common-mode interference to the DC voltage source. This reliably prevents electromagnetic radiation that could interfere with other devices.

[0011] The presence of at least one pair of magnetic cores on the busbars between two intermediate capacitors and the intermediate circuit capacitors reliably dampens differential mode interference and prevents excessive current flow back to the DC voltage source. This also reliably prevents electromagnetic radiation that could interfere with other devices.

[0012] The at least one pair of magnetic cores on the busbars between two intermediate capacitors may also be formed as a common core, with a first region surrounding the first busbar and with a second region surrounding the second busbar.

[0013] The DC link capacitors are used for reliable energy storage, especially for short-term energy storage. This prevents high-frequency voltage fluctuations in the DC link, preventing damage to the DC voltage source and maximizing the efficiency of the drive train.

[0014] Their capacity corresponds approximately to the capacity of conceivable intermediate capacitors, which are arranged, for example, in a separate branch.

[0015] According to a further basic concept of the invention, all of the aforementioned electrical elements are arranged directly on the busbars or electrically connected to them via one or more circuit boards, and combined in a single unit, which increases the quality of attenuation of common-mode and differential-mode interference and the compensation of current ripples by temporarily storing energy. This is particularly advantageous compared to a conceivable solution in which some of these elements are arranged in one or more separate branches and / or in parallel without the interposition of magnetic cores. The intermediate circuit capacitor unit with EMC filtering effect according to the invention thus combines the functions of energy storage for stabilizing the voltage level in the DC intermediate circuit and of an EMC filter.

[0016] Unlike a conceivable arrangement of intermediate circuit capacitors connected in parallel in a branch to the busbars, according to the invention the intermediate circuit capacitors are arranged one after the other between the two busbars, with a respective interposition of a pair of magnetic cores.

[0017] In particular, the function of short-term intermediate storage of energy corresponds according to the invention to that in a conceivable solution in which one or more intermediate circuit capacitors are arranged in a branch to the busbars.

[0018] The electromagnetic filter effect is also significantly improved by the intermediate circuit capacitor unit with EMC filter effect according to the invention compared to other conceivable solutions, in particular compared to solutions in which intermediate circuit capacitors are arranged in a branch to the busbars.

[0019] The electrical characteristics of the intermediate circuit capacitors, the magnetic core pairs, the at least one pair of Y capacitors and the at least one common mode choke can have varying sizes in order to fulfill the desired damping and energy buffering functions depending on the application.

[0020] In the smallest embodiment, the inventive DC link capacitor unit with EMC filtering action comprises a pair of Y capacitors, a common-mode choke, and two DC link capacitors with a pair of magnetic cores arranged between them. However, the number of these electrical elements can be expanded upwards.

[0021] The busbars between the DC voltage source, in particular the high-voltage battery, and the power electronics unit are DC busbars. The busbars between the power electronics unit and the electric machine or motor, however, are AC busbars.

[0022] In one embodiment, the at least one pair of Y capacitors and the at least one CMC can be arranged on the busbars spatially separated from the other components.

[0023] According to a first embodiment, at least a large portion of the two busbars, as well as the at least one pair of Y capacitors, the at least one common-mode choke, and the magnetic cores arranged between two intermediate circuit capacitors, are arranged in a common housing. Housing these electrical elements in a common housing offers a cost and space advantage over separate construction or housing in separate housings.

[0024] According to a further embodiment, the total capacitance of the intermediate circuit capacitors is dimensioned such that power fluctuations caused by switching operations in the power electronics can be compensated.

[0025] According to a further embodiment, the total capacitance is 200 to 1000 µF.

[0026] This allows power fluctuations to be reliably compensated and electrical energy to be stored particularly effectively.

[0027] The capacitance of the individual DC link capacitors and the total capacitance of all DC link capacitors corresponds approximately to the capacitance of a conceivable arrangement of DC link capacitors in a branch to the busbars.

[0028] According to a further embodiment, two magnetic cores form a push-pull choke at corresponding positions of the busbars between two intermediate circuit capacitors.

[0029] According to a further embodiment, the push-pull choke comprises a pair of cores made of magnetizable material with at least one winding, each of which is arranged around a busbar and each has an inductance of in particular 10 - 1000 nH.

[0030] This allows differential mode interference to be damped particularly reliably, and in addition, such a differential mode choke can also temporarily store electrical energy.

[0031] According to a further embodiment, the intermediate circuit capacitors, due to their arrangement between the magnetic cores, serve not only to store energy but also to dampen differential mode interference.

[0032] According to a further embodiment, the at least one pair of Y capacitors, the at least one common-mode choke, the at least two intermediate-link capacitors, and the at least one magnetic core are arranged one after the other in the direction from the first end to the second end of the busbars. Thus, at least one pair of Y capacitors can be provided as the first electrical element of the intermediate-link capacitor unit with EMC filtering effect, followed by at least one common-mode choke and the at least two intermediate-link capacitors, each with a core pair arranged between them.

[0033] Alternatively, the at least one common-mode choke, the at least one pair of Y-capacitors, the at least two intermediate circuit capacitors, and the at least one magnetic core can be arranged one after the other in the direction from the first end to the second end of the busbars. Thus, the first electrical element of the intermediate circuit capacitor unit with EMC filtering effect can be at least one common-mode choke, followed by at least one pair of Y-capacitors and at least two intermediate circuit capacitors, each with a core pair arranged between them.

[0034] According to a further embodiment, at least one magnetic core is arranged between adjacent intermediate circuit capacitors on each busbar.

[0035] According to a further embodiment, the number n of intermediate circuit capacitors is 1 greater than the number of magnetic core pairs between adjacent intermediate circuit capacitors.

[0036] Two to six intermediate circuit capacitors can be provided.

[0037] Such an arrangement of the intermediate circuit capacitors and magnetic cores allows a particularly reliable energy storage and differential mode noise damping function to be achieved.

[0038] According to a further embodiment, the last element before the second end of the busbars is an intermediate circuit capacitor.

[0039] According to a further embodiment, the Y capacitor is a pair of a first capacitor between the first bus bar and ground and a second capacitor between the second bus bar and ground, which in total have a capacitance of 20 - 50 nF.

[0040] According to a further embodiment, the at least one common-mode choke has a core made of magnetizable material which surrounds both busbars, and one or more windings through which current flows in opposite directions, apart from any common-mode interference, so that their magnetic fields cancel each other out in the core.

[0041] According to a further embodiment, at least one common mode choke has an inductance of 20 - 80 µH.

[0042] With such at least one pair of Y capacitors and with such at least one common-mode choke, common-mode interference can be dampened particularly reliably.

[0043] According to a further embodiment, a low-ohmic resistor is connected in series upstream or downstream of at least one of the at least one Y capacitor and one of the intermediate circuit capacitors, in order to dampen undesirably occurring resonances caused by the mutual interaction of the elements of the ZKKEMF or by the interaction between elements of the ZKKEMF and adjacent components of the DC intermediate circuit, in particular the high-voltage battery HVB or the power electronics unit LE.

[0044] The low-ohm resistor can in particular have a resistance of 0.05 to 1 ohm.

[0045] By means of such a low-ohm resistor, unwanted resonances can be reliably dampened.

[0046] The invention also relates to an electric drive, in particular a drive train for an electric or hybrid vehicle, comprising: a direct voltage source, in particular a high-voltage battery; a power electronic unit; and an intermediate circuit capacitor unit with EMC filtering effect of the type described here, which is arranged in the current path between the DC voltage source and the power electronic unit; wherein the first ends of the busbars are each connected to an output of the DC voltage source and the second ends of the busbars are each connected to an input of the power electronic unit, without the interposition of one or more further energy buffer elements, in particular intermediate circuit capacitors.

[0047] The advantages and embodiments stated above with reference to the intermediate circuit capacitor unit with EMC filtering effect apply equally to the electric drive according to the invention and the electric drive train according to the invention with such an intermediate circuit capacitor unit with EMC filtering effect, which is arranged in the current path, in particular a direct current path, between the direct voltage source and the power electronics unit. These advantages and embodiments will not be repeated here.

[0048] According to one embodiment, the power electronic unit is a power electronics unit for a direct or alternating voltage circuit, for example for a battery, in particular a traction battery or an electric motor, or a power electronics unit for connecting high-voltage and low-voltage vehicle electrical systems, or a power electronics unit for supplying auxiliary units.

[0049] According to a further embodiment, the drive train further comprises a direct or alternating voltage circuit, for example a battery, in particular a traction battery, or an electric motor, or an auxiliary unit, or a high-voltage and low-voltage electrical system, which is connected to the power electronic unit.

[0050] A method for operating the drive train of the type described here comprises the following method steps: (a) generating a current flow across the busbars from the DC voltage source to the power electronic unit and compensating for current ripples resulting from non-constant power consumption by temporarily storing electrical energy in the intermediate circuit capacitors; and / or (b) damping of differential mode interference, caused for example by switching pulses in the power electronics unit, by the intermediate circuit capacitors arranged between the magnetic cores; and / or (c) Attenuation of common-mode interference, caused for example by switching pulses in the power electronic unit, by the at least one pair of Y capacitors and by the at least one common-mode choke.

[0051] The advantages and embodiments stated above with reference to the intermediate circuit capacitor unit with EMC filtering effect apply equally to the method according to the invention for operating the drive train. These advantages and embodiments will not be repeated here.

[0052] The present invention is explained in more detail below using exemplary embodiments with reference to the accompanying figures. Fig. 1 shows a schematic representation of a drive train A for an electric or hybrid vehicle with an intermediate circuit capacitor unit with EMC filtering effect, according to an embodiment of the present invention; Fig. 2 shows a schematic representation of the drive train with intermediate circuit capacitor unit with EMC filter effect according to Fig. 1, during regular engine operation with current flow from the high-voltage battery to the power electronics; Fig. 3 shows a schematic representation of the drive train with DC link capacitor unit with EMC filter effect from Fig. 1 when current ripples occur; Fig. 4 shows a schematic representation of the drive train with intermediate circuit capacitor unit with EMC filter effect from Fig. 1 when differential mode interference occurs; Fig. 5 shows a schematic representation of the drive train with intermediate circuit capacitor unit with EMC filter effect from Fig. 1 when common mode interference occurs; Fig. 6 shows a schematic representation of the drive train with DC link capacitor unit with EMC filter effect from Fig. 1, with concrete, purely exemplary characteristics of the electrical elements of the intermediate circuit capacitor unit with EMC filter effect.

[0053] The Fig. 1, the drive train A of an electric or hybrid vehicle shown by way of example comprises a high-voltage battery HVB, which represents a direct voltage source and which is connected to a power electronic unit LE via two busbars S, in particular direct voltage busbars.

[0054] The power electronic unit LE can be power electronics for a direct or alternating voltage circuit, for example a battery, in particular a traction battery, or power electronics for an electric motor, or power electronics for supplying auxiliary units, or power electronics for connecting high-voltage and low-voltage vehicle electrical systems.

[0055] The power electronic unit LE is connected to the electrical machine EM in a suitable manner, in particular via three-phase AC busbars. The electrical machine EM can be designed, for example, as a synchronous or asynchronous machine.

[0056] A DC link capacitor unit with EMC filtering effect ZKKEMF is arranged on the busbars S between the high-voltage battery HVB and the power electronics unit LE. The DC link capacitor unit with EMC filtering effect ZKKEMF is also referred to below as the DC link capacitor unit ZKKEMF.

[0057] The Fig. 1 left shown first ends of the busbars S each with an output of the high-voltage battery HVB and the Fig. 1 The second ends of the busbars S shown on the right are each connected to an input of the power electronic unit LE.

[0058] The first ends of the busbars S are directly connected to the Fig. 1 input of the intermediate circuit capacitor unit ZKKEMF shown on the left or with its first electrical element, the Y capacitor Cy.

[0059] Likewise, the second ends of the busbars S are directly connected to the output of the intermediate circuit capacitor unit ZKKEMF, in particular to its last electrical element, namely the last intermediate circuit capacitor C, without one or more further energy buffer elements being arranged in the sections of the busbars S between the high-voltage battery HVB and the intermediate circuit capacitor unit ZKKEMF or in the sections of the busbars S between the intermediate circuit capacitor unit ZKKEMF and the power electronics unit LE.

[0060] The high-voltage battery HVB, the power electronics unit LE and the electric machine EM are each provided with at least one connection to the common electrical ground.

[0061] The intermediate circuit capacitor unit ZKKEMF has, viewed from the first, left end to the second, right end of the busbars 2, a Cy capacitor, a common mode choke CMC (Common Mode Choke), four intermediate circuit capacitors C and a first pair of magnetic cores MK on the busbars S between the first and second intermediate circuit capacitors C, a second pair of magnetic cores MK on the busbars S between the second and third intermediate circuit capacitors C, and a third pair of magnetic cores MK on the busbars S between the third and fourth intermediate circuit capacitors C.

[0062] When the electric machine EM is in drive mode, direct current flows from the high-voltage battery HVB via the intermediate circuit capacitor ZKKEMF to the power electronics unit LE. This unit converts direct current into alternating current using a number of transistors (e.g., six transistors), thus driving the electric machine EM.

[0063] In recuperation mode (not shown), the electric machine EM generates alternating current or alternating voltage in generator mode, the power electronics unit LE converts the alternating voltage into direct voltage, and direct current flows through the intermediate circuit capacitor unit ZKKEMF to the high-voltage battery HVB.

[0064] During operation of the drive train A, voltage ripples occur at the input and output of the power electronics unit LE due to the way the power electronics unit LE functions, particularly due to discrete switching operations of the transistors and the resulting discontinuous current flow. One reason for this is that the DC voltage circuit has an unavoidable, geometry-dependent electrical capacitance. A switching operation in the power electronics unit LE and the resulting high current consumption lead to the discharge of the DC voltage circuit. The high-voltage battery HVB cannot supply current quickly enough, resulting in a voltage drop.

[0065] As explained in more detail below, the purpose of the intermediate circuit capacitor ZKKEMF is to increase the capacitance of the DC voltage circuit and reduce the amplitude of such voltage ripple. The intermediate circuit capacitor ZKKEMF thus acts as an energy buffer. The DC voltage circuit is the DC voltage circuit formed between the high-voltage battery HVB and the power electronics unit LE by the busbars S.

[0066] Conventional power electronic units are highly efficient and require high switching frequencies and steep switching edges. During operation, the DC signal / DC flow is superimposed on a high-frequency AC signal / AC flow. However, this superposition is undesirable and is considered interference; it can, for example, disrupt other electrical systems. Such interference is divided into common-mode interference and differential-mode interference.

[0067] As will be explained in detail below, the intermediate circuit capacitor unit ZKKEMF according to the invention dampens both differential mode and common mode interference.

[0068] The inventive DC link capacitor unit with EMC filtering effect (ZKKEMF) combines the functions of intermediate energy storage and damping of differential-mode and common-mode interference in a single technical unit. It thus acts as an energy storage / intermediate energy storage device and as an EMC filter. All of these electrical elements of the DC link capacitor unit are preferably enclosed in a common housing.

[0069] In other words, three pairs of magnetic cores MK are arranged on the busbars S between two intermediate circuit capacitors C. These magnetic cores MK serve to dampen differential mode interference.

[0070] In the examples of the intermediate circuit capacitor units ZKKEMF of the Fig. 1-4, the first element located on the far left in the direction of the high-voltage battery HVB is a Y-capacitor Cy, followed by a common-mode choke CMC.

[0071] In the examples of the intermediate circuit capacitor units ZKKEMF of the Fig. 5 and Fig. 6 their arrangement is the other way round: First, on the far left in the direction of the high-voltage battery HVB, there is a common-mode choke CMC, followed by a Y-capacitor Cy.

[0072] In the present embodiments, the Y capacitor Cy is designed as a pair of Y capacitors Cy, in particular as a pair of a first capacitor between the first bus bar S and ground GND and a second capacitor Cy between the second bus bar S and ground GND, which in total typically have a capacitance of 20-50 nF.

[0073] The common mode choke CMC encloses both busbars S.

[0074] The intermediate circuit capacitors C are each arranged between the busbars S. The total capacitance of the intermediate circuit capacitors C is dimensioned such that power fluctuations and voltage ripples caused by switching operations in the power electronic unit LE can be compensated; their capacitance is typically 200 to 1000 µF.

[0075] The two magnetic cores MK at corresponding positions on the busbars S, each between two intermediate circuit capacitors C, form a differential mode choke DMC (differential mode choke). In addition to the pair of cores MK made of magnetizable material, this choke comprises windings arranged around the respective busbar S, each with an inductance of, in particular, 10 to 1000 nH.

[0076] Due to their arrangement between the magnetic cores MK, the intermediate circuit capacitors C have, in addition to their function of energy storage, also the function of damping differential mode interference.

[0077] The common mode choke CMC is a core made of magnetizable material that surrounds both busbars S and has windings through which current flows in opposite directions, so that their fields cancel each other out in the core.

[0078] The common mode choke CMC has an inductance of 20 - 80 µH.

[0079] The combination of all these electrical elements and all these functions in a common DC link capacitor unit ZKKKEMF and in one housing reduces costs and space.

[0080] In the embodiment of the present invention, which will now be described with reference to Fig. 2 to 6, the electrical machine EM is a drive converter of an electric motor of a motor vehicle.

[0081] In Fig. 2 this is in motor operation, a voltage of 800 V is applied, alternatively a voltage of 400 V or 48 V could be applied.

[0082] The assumed power from the power electronics unit LE and the electric machine EM is approximately 160 kW. The current flow from the high-voltage battery HVB through the busbars to the power electronics unit LE is indicated by arrows and is approximately 200 A. This is pure direct current, without interference.

[0083] These current and power values apply to all subsequent Fig. 2 to 5 explained operating states and will not be repeated again.

[0084] It is clearly visible that the current flows via the upper, first busbar S from its left end to its right end to the power electronics unit LE, and the current flows similarly on the second, lower busbar S back from the power electronics unit LE to the high-voltage battery HVB, both of which are indicated by arrows. The current thus flows through the magnetic cores MK of the common-mode choke CMC and through the magnetic cores MK between the intermediate circuit capacitors C. In the case of direct current, the magnetic cores MK act as a short circuit; the magnetic cores MK therefore have no effect. No current flows through the intermediate circuit capacitors C themselves, and likewise, no current flows through the Y capacitors Cy of the pair of Y capacitors Cy to ground GND.

[0085] In Fig. 3, current ripples now occur, caused by a non-constant power consumption, for example, of 5 A by the power electronics unit LE. These current ripples are compensated by the intermediate circuit capacitors C, which serve to temporarily store energy.

[0086] In Fig. 3 and the following figures, the length of the arrows qualitatively represents the amount of current flowing.

[0087] It can be seen that the strength of the flowing current on the first, upper busbar S increases from left to right, and that the strength of the flowing current on the second, lower busbar S decreases from right to left.

[0088] The strong current ripples caused by the power electronics unit LE, recognizable by the long arrow directly at the lower output of the power electronics unit LE, are passed on to the high-voltage battery HVB to a greatly reduced extent, as is illustrated by the decrease in the length of the arrows on the lower busbar S from right to left.

[0089] A current now flows through the intermediate circuit capacitors C from the lower busbar S to the upper busbar S. Accordingly, the current flow on the second busbar S from the high-voltage battery HVB to the power electronics unit LE increases, as is illustrated by the increase in the length of the arrows on the upper busbar S from left to right.

[0090] The strong current flow at the lower output of the power electronics unit LE, indicated by the long arrow pointing to the left, is dampened by the magnetic cores MK and the intermediate circuit capacitors C and reflected back to the power electronics unit LE by the intermediate circuit capacitors C. This is indicated by the upward-pointing arrows through the intermediate circuit capacitors C and by the extension of the arrows on the upper busbar S to the right toward the power electronics unit LE.

[0091] The intermediate circuit capacitors C take over the function of intermediate energy storage, while the magnetic cores MK reduce the further propagation of the ripple in the direction of the DC voltage circuit due to their electrical behavior.

[0092] In Fig. 4, differential mode interference now occurs, caused by switching pulses from the power electronic unit LE and, to a lesser extent, from the electrical machine EM, for example, at a level of 3A.

[0093] This differential mode interference is damped and reflected by the intermediate circuit capacitors C and is passed on to the high-voltage battery HVB to a much reduced extent.

[0094] Again, the length of the arrows qualitatively represents the amount of current flowing.

[0095] On the upper busbar S, a current now flows from the right, namely from the power electronics unit LE to the left to the high-voltage battery HVB, and likewise on the lower busbar S, a current flows from the high-voltage battery HVB to the power electronics unit LE.

[0096] The strong current flow at the upper output of the power electronics unit LE, recognizable by the long arrow exiting to the left, is dampened by the magnetic cores MK and the intermediate circuit capacitors C and reflected by the intermediate circuit capacitors C in particular back to the power electronics unit LE, recognizable by the downward-pointing arrows through the intermediate circuit capacitors C and by the extension of the arrows on the lower busbar S in a right-hand direction towards the power electronics unit LE.

[0097] Based on Fig. 5 explains the occurrence and treatment of common-mode interference by the ZKKEMF intermediate circuit capacitor unit.

[0098] The common-mode interference is in turn caused by switching pulses in the power electronic unit LE and, to a lesser extent, by the electrical machine EM and has, for example, a value of 2A.

[0099] This common-mode interference is attenuated by the Y capacitor Cy or the pair of Y capacitors Cy and the common-mode choke CMC, and is passed on to the high-voltage battery HVB only to a greatly reduced extent. In addition, the differential-mode chokes DMC also attenuate the common-mode interference to a small extent.

[0100] In the common mode interference shown, a current flows on both busbars S from the right, the power electronics unit LE to the high-voltage battery HVB to the left.

[0101] The attenuation is visualized by the current flowing towards ground GND through the up and down arrows of the Y capacitor Cy or the pair of Y capacitors Cy and by the arrows, which are greatly reduced in length, after the common mode choke CMC.

[0102] In the Fig. 5 and Fig. 6 the arrangement of the Y-capacitor Cy and the common mode choke CMC is reversed compared to the previous figures: In the Fig. 5 and Fig. 6, the first element of the intermediate circuit capacitor unit ZKKEMF from the left is the common mode choke CMC and the second element is the Y capacitor Cy or the pair of Y capacitors Cy.

[0103] In Fig. 6 now shows typical characteristics for the common mode choke CMC: 50 pH, for the pair of Y capacitors Cy: 30 nF each, for the first intermediate circuit capacitor C: 80 µF, for the first pair of magnetic cores MK: 100 nH each, for the second intermediate circuit capacitor C: 150 µF, for the second pair of magnetic cores MK: 15 nH, for the third intermediate circuit capacitor C: 100 µF, for the third pair of magnetic cores MK: 10 nH each and for the fourth and last intermediate circuit capacitor C: 200 µF.

[0104] These characteristic values of the electrical components are only examples. In particular, the values presented do not allow for a general ordering of ascending or descending values of the elements connected in series.

[0105] Due to their dual function of temporarily storing energy and damping differential mode interference, the intermediate circuit capacitors C have a larger capacitance than conventional capacitors in an electromagnetic filter. In these cases, they typically have electrical characteristics of a maximum of 20 µF; in this case, the smallest, first intermediate circuit capacitor C already has an electrical characteristic of 80 µF.

[0106] The characteristics of electrical elements with the same function can, but do not have to, be identical. In the present embodiment, for example, the electrical characteristics of the intermediate circuit capacitors C are different from one another.

[0107] Furthermore, all capacitors can be connected in series with a low-ohm resistor, which is not shown here. List of reference symbols A drivetrain HVB high-voltage battery ZKKEMF DC link capacitor unit with EMC filter effect S busbars LE Power Electronics EM electric machine CMC common mode choke MK Magnetic Core DMC push-pull choke (differential mode choke) C DC link capacitor (between the busbars) Cy Y capacitor (between each power rail and ground) GND electrical ground

Claims

[1] Intermediate circuit capacitor unit with EMC filter effect (ZKKEMF), for arrangement in the current path between a DC voltage source, in particular a high-voltage battery (HVB) and a power electronic unit (LE), comprising two busbars (S), each connectable at a first end to a DC voltage source and at a second end to a power electronic unit (LE); and at least two intermediate circuit capacitors (C) arranged between the busbars (S); wherein on each busbar (S) at least one magnetic core (MK) is arranged between two intermediate circuit capacitors (C) for damping differential mode interference; at least one pair of Y capacitors (Cy); wherein each of the Y-capacitors (Cy) of a pair of Y-capacitors (Cy) connects a respective busbar (S) to the electrical ground (GND); and at least one common mode choke (CMC) enclosing both busbars (S); wherein the common mode choke (CMC) is designed to attenuate common mode interference; characterized by , that at least one pair of Y capacitors (Cy) is designed to attenuate common-mode interference; at least one magnetic core (MK) is arranged between adjacent intermediate circuit capacitors (C) on each busbar (S); the number n of intermediate circuit capacitors (C) is 1 greater than the number of magnetic core pairs between adjacent intermediate circuit capacitors (C); the intermediate circuit capacitors (C) due to their arrangement between the magnetic cores (MK) serve not only to store energy but also to dampen differential mode interference; the total capacitance of the intermediate circuit capacitors (C) is dimensioned such that power fluctuations caused by switching operations in the power electronic unit (LE) can be compensated; and wherein the at least one pair of Y capacitors (Cy), the at least one common mode choke (CMC), the at least two intermediate circuit capacitors (C) and the at least one magnetic core (MK) are arranged one after the other in the direction from the first end to the second end of the busbars (S); or wherein the at least one common-mode choke (CMC), the at least one pair of Y capacitors (Cy), the at least two intermediate circuit capacitors (C) and the at least one magnetic core (MK) are arranged one after the other in the direction from the first end to the second end of the busbars (S); and wherein at least a majority of the two busbars (S), as well as all electrical elements (Cy, CMC, C, MK) of the intermediate circuit capacitor unit (ZKKEMF), namely the at least one pair of Y capacitors (Cy), the at least one common-mode choke (CMC), the intermediate circuit capacitors (C) and the magnetic cores (MK) arranged between each two intermediate circuit capacitors (C), are arranged in a common housing; and wherein the last electrical element before the second end of the busbars (S) is an intermediate circuit capacitor (C). [2] The intermediate circuit capacitor unit with EMC filtering effect (ZKKEMF) according to claim 1, wherein the total capacitance is 200 to 1000 µF. [3] Intermediate circuit capacitor unit with EMC filter effect (ZKKEMF) according to one of the preceding claims, wherein two magnetic cores (MK) form a push-pull choke (DMC) at corresponding positions of the busbars (S) between two intermediate circuit capacitors (C); and / or wherein the push-pull choke (DMC) comprises a pair of cores made of magnetizable material with at least one winding, each arranged around a busbar (S) and each having an inductance of in particular 10 - 1000 nH. [4] Intermediate circuit capacitor unit with EMC filter effect (ZKKEMF) according to one of the preceding claims, wherein two to six intermediate circuit capacitors (C) are provided. [5] Intermediate circuit capacitor unit with EMC filter effect (ZKKEMF) according to one of the preceding claims, wherein the Y capacitor CY is a pair of a first capacitor between the first busbar (S) and ground and a second capacitor between the second busbar (S) and ground, which in total have a capacitance of 20 - 50 nF. [6] Intermediate circuit capacitor unit with EMC filter effect (ZKKEMF) according to one of the preceding claims, wherein the at least one common-mode choke (CMC) has a core made of magnetizable material surrounding both busbars (S), and a plurality of identical windings through which current flows in opposite directions, so that their magnetic fields cancel each other out in the core, and where at least one common mode choke (CMC) has an inductance of 20 - 80 µH. [7] Intermediate circuit capacitor unit with EMC filter effect (ZKKEMF) according to one of the preceding claims, wherein a low-ohmic resistor is connected in series upstream or downstream of at least one of the at least one Y capacitor (Cy) and one of the intermediate circuit capacitors (C), for damping undesirably occurring resonances; wherein the low-ohm resistor in particular has a resistance of 0.05 to 1 ohm. [8] Electric drive, in particular drive train (A) for an electric or hybrid vehicle, comprising: a direct voltage source, in particular a high-voltage battery (HVB); a power electronic unit (LE); and an intermediate circuit capacitor unit with EMC filter effect (ZKKEMF) according to one of the preceding claims, which is arranged in the current path between the DC voltage source and the power electronic unit (LE); wherein the first ends of the busbars (S) are each connected to an output of the DC voltage source and the second ends of the busbars (S) are each connected to an input of the power electronic unit (LE), without the interposition of one or more further energy buffer elements, in particular intermediate circuit capacitors. [9] Electric drive according to claim 8, wherein the power electronic unit (LE) is a power electronics unit for a direct or alternating voltage circuit, for example for a battery, in particular a traction battery, or a power electronics unit for an electric motor, or a power electronics unit for supplying auxiliary units, or a power electronics unit for connecting high-voltage and low-voltage vehicle electrical systems; and wherein the drive train (A) further comprises a direct or alternating voltage circuit, for example a battery, in particular a traction battery, or an electric motor, or an auxiliary unit, or a high-voltage and low-voltage vehicle electrical system, which is connected to the power electronic unit (LE).

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