Inverter with internal/external ferromagnetic cores

Abstract

An inverter having a first busbar for connection to a positive pole of a battery and a second busbar for connection to a negative pole of the battery and a filter element that includes an annular core surrounding the first and the second busbar and made from a ferromagnetic material. It is proposed that a core made from a further ferromagnetic material to be provided in an intermediate space surrounded by the annular core and formed between the two busbars.

Claims

1. An inverter comprising: a first busbar connected to a positive pole of a battery; a second busbar separately formed and arranged apart from the first busbar, and connected to a negative pole of the battery; and a filter for reducing common-mode and differential-mode interference that includes an annular core surrounding the first and the second busbars and made from a ferromagnetic material, wherein another core made from a further ferromagnetic material is provided between the first and second busbars with a spacing in an intermediate space surrounded by the annular core and the first and second busbars, and the first and second busbars have recesses that point toward one another and that surround the another core in sections.

2. An inverter according to claim 1, wherein the spacing includes a predefined first spacing between the another core and each of inner sides of the annular core facing to each other.

3. An inverter according to claim 1, wherein the spacing includes a predefined second spacing between the another core and each side of the first and second busbars.

4. An inverter according to claim 1, wherein the annular core includes a pass-through surface having a substantial rectangle shape in which the first and second busbars and the another core are arranged, and the first and second busbars are spaced apart from each other and the recesses of the first and second busbars are recessed opposite to each other to form the intermediate space, and the another core is arranged apart from the pass-through surface and the first and second busbars through the spacing.

5. An inverter according to claim 1, wherein at least one of the ferromagnetic or and the further ferromagnetic material has a first relative permeability μ.sub.rl>10.sup.3.

6. An inverter according to claim 1, wherein the another core is held in the annular core by way of a holding device, wherein the holding device is formed from a material having a second relative permeability μ.sub.r2<10.

7. An inverter according to claim 1, wherein a holding device is formed from a plastic.

8. An inverter according to claim 1, wherein the annular core is a toroidal core made from a nanocrystalline ferromagnetic material.

9. An inverter according to claim 1, wherein at least one of the ferromagnetic and the further ferromagnetic material is a ferrimagnetic material.

10. An inverter according to claim 1, wherein the annular core has a circular, oval or substantially rectangular pass-through surface.

11. An inverter according to claim 4, wherein an electric current flows from the positive pole of the battery through the first busbar in one direction and flows toward the negative pole of the battery through the second busbar in another direction opposite to the one direction.

12. An inverter according to claim 1, further comprising a power inverter connected to the filter at a downstream of the filter, and including an intermediate circuit capacitor having an input terminal to which the first busbar is connected, and an output terminal to which the second busbar is connected, and half bridges to which the first and second busbars are connected at a downstream of the intermediate circuit capacitor, each of the half bridges including two power transistors.

Description

(1) Exemplary embodiments of the invention will be explained in more detail below with reference to the drawings. In the figures:

(2) FIG. 1 shows a schematic circuit diagram of an inverter,

(3) FIG. 2 shows a first sectional view through an annular core choke and

(4) FIG. 3 shows a sectional view along the cutting line A-A′ in FIG. 2.

(5) In FIG. 1, the reference sign HV denotes a battery and the reference sign M denotes a three-phase current motor. An inverter, generally denoted by the reference sign I, is connected between the battery HV and the three-phase current motor M. The inverter I comprises a filter stage 1 connected downstream of the battery HV and a power inverter 2 connected downstream of the filter stage 1 and whose outputs are connected to the three-phase current motor M.

(6) The filter stage 1 has a multi-stage design in the present exemplary embodiment. It may also comprise just one stage.

(7) A first busbar is denoted by the reference sign 3 and a second busbar is denoted by the reference sign 4. Each stage of the filter stage 1 may comprise an X-capacitor 5 connected between the first busbar 3 and the second busbar 4 and in each case a Y-capacitor 6 connected against the housing potential by the first busbar 3 and the second busbar 4.

(8) The reference sign 7 generally denotes a filter element for reducing common-mode and differential-mode interference. The filter element 7 comprises an annular core choke 8 surrounding the first busbar 3 and the second busbar 4 and differential-mode chokes 9 formed by the core (not shown here).

(9) The first busbar 3 and the second busbar 4 are connected at output to an intermediate circuit capacitor 10. The reference sign 11 denotes half bridges connected downstream of the intermediate circuit capacitor 10 and that each comprise two power transistors 12. Power transistor groups consisting of a plurality of parallel-connected power transistors may also be provided instead of each of the power transistors 12. The half bridges 11 are driven by way of a controller 13 by way of pulse width-modulated signals, resulting in a three-phase current in the phases u, v and w for operating the three-phase current motor M.

(10) Common-mode and differential-mode interference forms on the first busbar 3 and the second busbar 4 due to the high-frequency switching procedures during operation of the half bridges 11. In order to reduce such interference, according to the invention, the filter element 7 that is described in more detail in FIGS. 2 and 3 is provided, inter alia.

(11) In FIGS. 2 and 3, the reference sign 14 denotes an annular core manufactured from a ferromagnetic material. This may in particular in this case be a toroidal core made from a nanocrystalline ferromagnetic material. In particular in the case of toroidal cores, it is not readily possible to produce any desired geometries in terms of a pass-through surface 15 passing through the toroidal core due to the winding technology required for manufacturing purposes. That is to say, in the case of toroidal cores, the pass-through surface 15 usually has a circular, an oval or roughly rectangular shape.

(12) The reference sign 16 denotes a core manufactured from a further ferromagnetic material and that is formed in an intermediate space Z between the first busbar 3 and the second busbar 4 and the opposing inner sides of the annular core 14. The core 16 has a first spacing A1 from the inner sides of the annular core 14. The reference sign A2 denotes a second spacing that is formed between the core 16 and the busbars 3, 4.

(13) The function of the proposed filter element 7 is as follows:

(14) The core 16, together with the annular core 14, forms a settable inductance that reduces differential-mode interference. The core 16 offers a magnetic path to flux lines F caused by differential-mode interference and thus makes it possible to generate a differential-mode inductance. The magnitude of this differential-mode inductance is able to be set by way of the first spacing 1.

(15) Due to the dimensioning of the core 16 and the inductance generated thereby, the following is stated by way of example:
B=(L i)/A or A=(L i)/B
wherein
B is the induction flux density,
L is the differential-mode inductance,
i is the current through the busbars and
A is the cross-sectional surface area of the core 16.

(16) Assuming that L=2×100 nH and i=200 A, a surface area A=1 cm.sup.2 gives B=0.4 Tesla.

(17) In order to achieve a particularly compact design, the first busbar 3 and the second busbar 4 may each have a recess 17. The recess 17 may for example have a rectangular form in plan view (see FIG. 3).

LIST OF REFERENCE SIGNS

(18) 1 Filter stage 2 Power inverter 3 First busbar 4 Second busbar 5 X-capacitor 6 Y-capacitor 7 Filter element 8 Annular core choke 9 Differential-mode chokes 10 Intermediate circuit capacitor 11 Half bridge 12 Power transistor 13 Controller 14 Annular core 15 Pass-through surface 16 Core 17 Recess A1 First spacing A2 Second spacing F Flux line HV Battery I Inverter M Three-phase current motor u, v, w Phase Z Intermediate space