CONVERTER ASSEMBLY AND TEST STAND HAVING A CONVERTER ASSEMBLY

Abstract

The invention relates to a converter assembly comprising a DC voltage intermediate circuit (1) for providing a DC voltage V.sub.DC, comprising a positive terminal and a negative terminal, and at least one machine converter (2) for converting the DC voltage V.sub.DC into a multi-phase AC voltage, wherein at least one energy storage capacitor (3, 3′) is arranged in the DC voltage intermediate circuit (1), and wherein a frequency-dependent resistor (4) which has a higher electrical resistance at high frequencies than at low frequencies is arranged in series with the energy storage capacitor (3, 3′).

Claims

1. Converter assembly, comprising a. a DC voltage intermediate circuit for providing a DC voltage V.sub.DC, comprising a positive terminal and a negative terminal, and b. at least one converter, in particular a machine converter, for converting the DC voltage V.sub.DC into an AC voltage or into another DC voltage, 1. wherein at least one energy storage capacitor is arranged in the DC voltage intermediate circuit between the positive terminal and the negative terminal, wherein a frequency-dependent resistor which has a higher electrical resistance at high frequencies than at low frequencies is connected in series with the energy storage capacitor, characterised in that at high frequencies, in particular at frequencies above 10 kHz, the frequency-dependent resistor has an electrical resistance which is higher by a multiple, preferably by at least a factor of 10 or a factor of 12, than at low frequencies, in particular at frequencies below 500 Hz.

2. Converter assembly according to claim 1, wherein the energy storage capacitor is a particularly high-storage capacitor with a capacitance of over 1 mF, preferably 6 mF, for example an electrolytic capacitor.

3. Converter assembly according to claim 1, wherein a first energy storage capacitor and a second energy storage capacitor, connected in series, are provided, wherein the frequency-dependent resistor is arranged in series between the first energy storage capacitor and the second energy storage capacitor.

4. Converter assembly according to claim 1, wherein one or more particularly alternating-load-resistant intermediate circuit capacitors are arranged parallel to the energy storage capacitor, wherein the ratio of the capacitance of the energy storage capacitor to the capacitance of the intermediate circuit capacitors is preferably greater than 5, particularly preferably greater than 10.

5. Converter assembly according to claim 4, wherein the intermediate circuit capacitors are designed in the form of film capacitors and/or ceramic capacitors.

6. Converter assembly according to claim 4, wherein the intermediate circuit capacitors are realised through the parallel and series connection of individual capacitors.

7. Converter assembly according to claim 4, wherein first intermediate circuit capacitors are designed as film capacitors with a cut-off frequency of around 100 kHz.

8. Converter assembly according to claim 5, wherein second intermediate circuit capacitors are designed as ceramic capacitors with a cut-off frequency of 1 MHz and above.

9. Converter assembly according to claim 1, wherein the capacitors are designed for a DC voltage of over 350V, preferably over 500V, more preferably around 850 V or around 1400 V.

10. Converter assembly according to claim 3, wherein the two energy storage capacitors are arranged on a circuit board or another carrier and the frequency-dependent resistor is arranged on the underside of this circuit board or the carrier.

11. Converter assembly according to claim 1, wherein the frequency-dependent resistor is substantially cylindrical in form with a longitudinal extension L and a diameter D.

12. Converter assembly according to claim 11, wherein the diameter D varies periodically along the longitudinal extension L by an average value D.sub.0+/−ΔD, wherein D.sub.0 is preferably around 10 mm and ΔD preferably around 1 mm.

13. Converter assembly according to claim 1, wherein a DC voltage source providing the DC voltage V.sub.DC is provided, for example a battery or a line converter, which is designed to convert a multiphase supply voltage into a DC voltage.

14. Test stand for a vehicle or a drive, comprising a line converter, a converter assembly according to claim 1 and an electric machine driven by the AC voltage.

15. Powertrain for a vehicle with an electric motor and a converter assembly according to claim 1.

Description

[0030] The invention is explained in more detail below on the basis of a non-exclusive exemplary embodiment, whereby:

[0031] FIG. 1a: shows a schematic circuit diagram of a converter assembly according to the invention;

[0032] FIG. 1b: shows a schematic cross-section through an embodiment of a frequency-dependent resistor according to the invention;

[0033] FIG. 1c: shows a detail from FIG. 1b.

[0034] FIG. 1a shows a schematic circuit diagram of a converter assembly according to the invention for use in a test stand for vehicles. The converter assembly includes a DC voltage intermediate circuit 1 with a DC voltage of around 850 V which is provided by a line converter 7.

[0035] The DC voltage intermediate circuit 1 supplies a machine converter 2, which is operated as a switched inverter. This provides an AC voltage for the operation of an electric load machine for the test stand, for example an electric motor.

[0036] The DC voltage intermediate circuit has a positive terminal and a negative terminal. Two energy storage capacitors 3.3′ are arranged in series connection between the positive terminal and the negative terminal, whereby a frequency-dependent resistor 4 is arranged between the two energy storage capacitors 3.3′. In this exemplary embodiment, the energy storage capacitors 3, 3′ are electrolytic capacitors with a capacitance of around 1 mF. Intermediate circuit capacitors 5, 5′ are arranged in parallel with the energy storage capacitors 3, 3′. These have a lower capacitance, for example in the range of 180 μF, and serve to dissipate high-frequency interference.

[0037] Both the energy storage capacitors 3, 3′, and the intermediate circuit capacitors 5, 5′ are located in the immediate vicinity of the switched converters, namely the line converter 7 and the machine converter 2. In the present embodiment, two types of intermediate circuit capacitors are used, on the one hand ceramic CeraLink capacitors for very fast currents up to a cut-off frequency of 1 MHz, and on the other hand film capacitors for currents up to a cut-off frequency of around 100 kHz. The intermediate circuit capacitors 5, 5′ are in each case designed for a voltage of 850 V and are connected directly to the intermediate circuit with low inductance, i.e. avoiding long connecting cables.

[0038] In this exemplary embodiment, the energy storage capacitors 3, 3′ are also directly connected to the intermediate circuit, so that only low line inductances occur. In order to keep the ripple current load of the energy storage capacitors 3.3′ low, while still making possible test samples with high-frequency current changes of up to around 1000 Hz, a frequency-dependent resistor 4 is connected in series with the energy storage capacitors 3, 3′.

[0039] In an exemplary embodiment which is not illustrated, several parallel branches with energy storage capacitors and frequency-dependent resistors are provided to increase the overall storage capacity of the converter.

[0040] The frequency-dependent resistor 4 is relatively low-impedance for frequencies below 1000 Hz, and relatively high-impedance for switching-frequency-proportional currents, i.e. currents with a frequency of 16 kHz or above. In this exemplary embodiment, the ratio between the electrical resistance at frequencies of 16 kHz and 500 Hz is around 12. This prevents the energy storage capacitors 3,3′, which are coupled with low inductance, from being unduly loaded with the high switching frequency. Consequently, no excessive heating of the energy storage capacitors 3, 3′ occurs, and these can be utilised more efficiently.

[0041] FIG. 1b shows a schematic cross-section through an embodiment of a frequency-dependent resistor 4 according to the invention. In this embodiment, the frequency-dependent resistor 4 is designed in such a way that the electrical skin effect is exploited: at high electrical frequencies, the electric current is displaced to the outer surface of the resistor; the outer surface area is increased through a periodic variation of the diameter, resulting in an increased electrical resistance. This property of the skin effect is used here, advantageously, to make use of a nonlinear ohmic resistance to protect the already-mentioned energy storage capacitor from high-frequency currents. The advantage of such an embodiment is that the frequency-dependent resistor 4 according to the invention is designed, as protection for the energy storage capacitor 3, as a nonlinear and non-oscillating resistor 4 and does not require oscillating components such as an impedance or a capacitance. Thus, the capacitance of the energy storage capacitor 3 is freely selectable and not coupled to a frequency, as is for example the case with an oscillating circuit.

[0042] A schematically indicated first energy storage capacitor 3 and a second energy storage capacitor 3′, connected in series, are provided, wherein the frequency-dependent resistor 4 is arranged in series between the first energy storage capacitor 3 and the second energy storage capacitor 3′. The two energy storage capacitors 3, 3′ are arranged on a circuit board 6, and the frequency-dependent resistor 4 is arranged on the underside of this circuit board 6.

[0043] FIG. 1c shows a detail from FIG. 1b, namely the shape of the frequency-dependent resistor 4. The frequency-dependent resistor 4 is substantially cylindrical in form with a longitudinal extension L and a diameter D. The diameter D varies along the longitudinal extension L by an average value D.sub.0+/−ΔD periodically, wherein D.sub.0 is around 10 mm and ΔD around 1 mm.

[0044] An exemplary embodiment of the invention, not illustrated, comprises a test stand for a vehicle with a line converter 7, a converter assembly according to the invention and an electric machine driven by the generated AC voltage.

[0045] However, the invention is not limited to the present exemplary embodiments, but includes all devices within the framework of the following claims.

[0046] Terms used herein such as converter, line converter or machine converter should not be interpreted too narrowly. A converter according to the invention, be it a machine converter or a line converter, can be understood as any controlled electrical and/or electronic circuit that converts one DC voltage into another DC voltage or AC voltage, or converts an AC voltage into another AC voltage or DC voltage. Such a circuit may for example, but not exclusively, be a direct converter, a matrix converter, an AC voltage converter, a DC voltage converter, a switched bridge inverter, a switched bridge rectifier or the like. The concrete realisation of the converter in terms of circuitry is not critical. Converters provided according to the invention can also feature internal galvanic isolation and can be intended for high electrical powers, for example powers in the region of 100 kW at a DC voltage of 850 V or 300 kVA alternating current power.

LIST OF REFERENCE SYMBOLS

[0047] 1 DC voltage intermediate circuit [0048] 2 machine converter [0049] 3, 3′ energy storage capacitor [0050] 4 resistor [0051] 5, 5′ intermediate circuit capacitor [0052] 6 circuit board [0053] 7 line converter