US-12627220-B2 - Power converter and method for operating a power converter

US12627220B2US 12627220 B2US12627220 B2US 12627220B2US-12627220-B2

Abstract

The present invention relates to a power converter and to a method for operating same, wherein the power converter is designed to receive two input potentials DC+ and DC−, the power converter comprising a first anti-interference capacitor in order to connect the input potential DC+ capacitively to earth, a second anti-interference capacitor in order to connect the input potential DC− capacitively to earth, a first voltmeter for measuring a first voltage drop Uyp across the first anti-interference capacitor, a second voltmeter for measuring a second voltage drop Uyn across the second anti-interference capacitor, and a calculation unit which is designed to determine a DC link voltage Uzk dropping between the input potential DC+ and the input potential DC− using the first voltage drop Uyp and the second voltage drop Uyn.

Inventors

Marco Bohlländer

Assignees

ROLLS-ROYCE DEUTSCHLAND LTD & CO KG

Dates

Publication Date: 20260512
Application Date: 20211101
Priority Date: 20201120

Claims (16)

1 . A power converter configured to receive an input potential DC+ and an input potential DC−, the power converter comprising: a first interference suppression capacitor configured to connect the input potential DC+ capacitively to ground; a second interference suppression capacitor configured to connect the input potential DC− capacitively to ground; a first voltmeter for measuring a first voltage drop across the first interference suppression capacitor; a second voltmeter for measuring a second voltage drop across the second interference suppression capacitor; and a calculation unit configured to determine, using the first voltage drop and the second voltage drop, a DC-link voltage dropped between the input potential DC+ and the input potential DC−.
2 . The power converter of claim 1 , further comprising a voltage input configured to receive the input potential DC+ and the input potential DC−, wherein the first interference suppression capacitor and the second interference suppression capacitor are arranged in the voltage input and are configured to balance the input potential DC+ and the input potential DC−.
3 . The power converter of claim 2 , further comprising a DC− link capacitor that is connected in the voltage input between the input potential DC+ and the input potential DC−, wherein the DC-link voltage is dropped across the DC-link capacitor.
4 . The power converter of claim 1 , wherein the power converter has a grounded housing, and a potential-ground pick-up for the first voltmeter and the second voltmeter is made at a same geometric point on the grounded housing.
5 . The power converter of claim 1 , wherein the first voltmeter and the second voltmeter each have parasitic capacitances and are configured to connect the power converter capacitively from the input potential DC+ and the input potential DC− to ground.
6 . The power converter of claim 1 , further comprising a controller and an output stage for supplying voltage to an electric motor.
7 . The power converter of claim 6 , wherein the calculation unit is configured to calculate and provide to the controller the DC-link voltage, and wherein the controller is configured to calculate, based on the DC-link voltage, switching of power semiconductors for driving the electric motor.
8 . A method for determining a DC-link voltage in a power converter that is configured to receive an input potential DC+ and an input potential DC−, the power converter comprising a first interference suppression capacitor configured to connect the input potential DC+ capacitively to ground, and a second interference suppression capacitor configured to connect the input potential DC− capacitively to ground, the method comprising: measuring a first voltage that is dropped across the first interference suppression capacitor; measuring a second voltage that is dropped across the second interference suppression capacitor; and determining the DC-link voltage based on the first voltage and the second voltage.
9 . The method of claim 8 , wherein the DC-link voltage is dropped across a DC-link capacitor that is connected in a voltage input of the power converter between the input potential DC+ and the input potential DC−.
10 . The method of claim 8 , wherein the determining of the DC-link voltage is performed according to Kirchhoff's rule, which gives Uzk=−(Uyp+Uyn).
11 . The method of claim 8 , wherein the measuring of the first voltage and the measuring of the second voltage are made on a grounded housing of the power converter, and wherein the first voltage and the second voltage are picked up at a same geometric location on the housing.
12 . The method of claim 8 , wherein the measuring of the first voltage and the measuring of the second voltage are made by a first voltmeter and a second voltmeter, wherein the first voltmeter has a first parasitic capacitance, and the second voltmeter has a second parasitic capacitance, and wherein the method further comprises capacitively connecting the input potential DC+ and the input potential DC− to ground by the first parasitic capacitance and the second parasitic capacitance.
13 . The method of claim 8 , further comprising outputting the DC-link voltage to a controller of the power converter for driving an electric motor; and determining, by the controller, switching of power semiconductors for driving the electric motor based on the DC-link voltage.
14 . The power converter of claim 5 , wherein the first interference suppression capacitor is formed by the parasitic capacitance of the first voltmeter, and wherein the second interference suppression capacitor is formed by the parasitic capacitance of the second voltmeter.
15 . The power converter of claim 7 , wherein the driving is performed via the output stage.
16 . A power converter configured to receive an input potential DC+ and an input potential DC−, the power converter comprising: a first interference suppression capacitor configured to connect the input potential DC+ capacitively to ground; a second interference suppression capacitor configured to connect the input potential DC− capacitively to ground; a first voltmeter for measuring a first voltage drop across the first interference suppression capacitor; a second voltmeter for measuring a second voltage drop across the second interference suppression capacitor; and a calculation unit configured to determine, using the first voltage drop and the second voltage drop, a DC-link voltage dropped between the input potential DC+ and the input potential DC−, wherein the first voltmeter and the second voltmeter each have parasitic capacitances and are configured to connect the power converter capacitively from the input potential DC+ and the input potential DC− to ground, wherein the first interference suppression capacitor is formed by the parasitic capacitance of the first voltmeter, and wherein the second interference suppression capacitor is formed by the parasitic capacitance of the second voltmeter.

Description

This application is the National Stage of International Application No. PCT/EP2021/080262, filed Nov. 1, 2021, which claims the benefit of German Patent Application No. DE 10 2020 214 652.7, filed Nov. 20, 2020. The entire contents of these documents are hereby incorporated herein by reference. FIELD The present embodiments relate to a power converter configured to receive two input potentials, and to a method for operating such a power converter. BACKGROUND Power converters (e.g., inverters) in electrical drives with electric motor are commonly used in low-voltage DC networks (e.g., in IT networks). So that the power converter may drive the motor correctly, various sensors are required in order to determine an electrical actual state (e.g., to calculate and implement on the basis thereof correct switching of the power semiconductors installed in the power converter). A quantity that represents the electrical actual state is the DC-link voltage Uzk. Therefore, power converters usually have a sensor system for ascertaining the DC-link voltage Uzk. Further, inverters in the IT network are connected capacitively by interference suppression capacitors from DC+ and DC− respectively to ground for the purpose of voltage balancing. These capacitors are configured to balance the input potentials DC+ and DC− with respect to ground, and are mostly selected from the class of Y-capacitors. The interference suppression capacitors are configured for the normal situation (e.g., for the situation in which there is no short to ground in the IT network). In a fault situation in which there is a short to ground, these capacitors are placed under an increased load. It is therefore advantageous to be able to identify this fault situation. For the purpose of ascertaining the DC-link voltage Uzk, it has already been proposed to ascertain this voltage via a direct sensor system. This sensor system is configured to pick up at suitable terminals carrying the DC+/− potential the voltage to be measured, to step-down passively the voltage, and then to transfer the value as a raw actual value to a controller in a galvanically isolated manner. This has the disadvantage, however, that fault situations (e.g., shorts to ground) cannot be detected. SUMMARY AND DESCRIPTION The scope of the present invention is defined solely by the appended claims and is not affected to any degree by the statements within this summary. The present embodiments may obviate one or more of the drawbacks or limitations in the related art. For example, a power converter and a method for operating a power converter that at least mitigates the above disadvantage are provided. According to a first aspect of the present embodiments, a power converter includes a first voltmeter for measuring a first voltage drop Uyp across a first interference suppression capacitor, a second voltmeter for measuring a second voltage drop Uyn across a second interference suppression capacitor, and a calculation unit. The calculation unit is configured to determine, using the first voltage drop Uyp and the second voltage drop Uyn, a DC-link voltage Uzk dropped between an input potential DC+ and an input potential DC−. The power converter may be fed from a high-voltage network (e.g., a balanced DC network) or an energy source (e.g., a battery) and may be configured to produce a DC voltage in a low-voltage network (e.g., in an IT network). Unlike conventional power converters, a direct measurement of the DC-link voltage Uzk between the input potentials DC+ and DC− is replaced by a measurement of the voltage Uyp between the ground potential and the input potential DC+, and of the voltage Uyn between the input potential DC− and the ground potential. Using the measured voltages Uyp and Uyn, the DC-link voltage Uzk may be ascertained using Kirchhoff's loop rule equation 0=Uyp+Uzk+Uyn. Solving for the wanted DC-link voltage Uzk yields Uzk (using the passive sign convention) as Uzk=−(Uyp+Uyn). The measurement arrangement according to the present embodiments allows the input potentials with respect to ground to be assessed during operation of the inverter while at the same time replacing the DC-link voltage measurement, thereby keeping the number of sensors (e.g., voltmeters) as small as possible. Further, the DC-link voltage Uzk may be calculated using simple addition of two measured values Uyp and Uyn. The voltages Uyp and Uyn determined by the voltmeters may be used, in addition to calculating the DC-link voltage Uzk, for extended diagnostic purposes (e.g., for identifying a short circuit). For example, slightly or severely increased ripple voltages may be identified, indicating a phase-to-ground short circuit. Whether increased ripple voltages exist may be ascertained by a fast Fourier transform (FFT) or more simply by a min-max value determination. When ascertaining using the FFT, increased ripple voltages may be identified by an increase in the amplitudes of the harmonics. If the min-max value