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EP-4741842-A1 - METHOD FOR DETERMINING A CAPACITANCE VALUE OF A CAPACITOR OF A RC CIRCUIT ON A DC LINK OF A VEHICLE

EP4741842A1EP 4741842 A1EP4741842 A1EP 4741842A1EP-4741842-A1

Abstract

It is proposed a method for determining a capacitance value (C) of a capacitor (CA) of a RC circuit on a DC link (DCL) of a vehicle, wherein the RC circuit comprises a charging resistor (RE) or a discharging resistor (RD), the method comprising the following steps: a) measuring a sequence of values (U0-U20; U0-new-U20-new) of a charging voltage (Ut) or a discharging voltage (Ud) of the capacitor (CA) over an evaluation time interval (T1), b) determining - a value or - a definite integral with respect to time of a first time derivative of the sequence of values (U0-U20; U0-new-U20-new) of the charging voltage (Ut) or the discharging voltage (Ud) in the evaluation time interval (T1), c) determining - a value or - a definite integral with respect to time of a second time derivative of the sequence of values (U0-U20; U0-new-U20-new) of the charging voltage (Ut) or the discharging voltage (Ud) in the evaluation time interval (T1), d) determining the capacitance value (C) of the capacitor (CA) by using one of the following relations: - the negative quotient of the value of the first time derivative and the value of the second time derivative, wherein the negative quotient is divided by a known resistance value (R) of the charging resistor (RE) or the discharging resistor (RD), gives the capacitance value (C), or - the negative quotient of the definite integral of the first time derivative and the definite integral of the second time derivative, wherein the negative quotient is divided by a known resistance value (R) of the charging resistor (RE) or the discharging resistor (RD), gives the capacitance value (C). Furthermore, a corresponding system and a vehicle comprising the system are proposed.

Inventors

  • NEUGEBAUER, ANDREAS

Assignees

  • ALSTOM Holdings

Dates

Publication Date
20260513
Application Date
20241106

Claims (7)

  1. A method for determining a capacitance value (C) of a capacitor (CA) of a RC circuit on a DC link (DCL) of a vehicle, wherein the RC circuit comprises a charging resistor (RE) or a discharging resistor (RD), the method comprising the following steps: a) measuring a sequence of values (U0-U20; U0-new-U20-new) of a charging voltage (Ut) or a discharging voltage (Ud) of the capacitor (CA) over an evaluation time interval (T1), b) determining - a value or - a definite integral with respect to time of a first time derivative of the sequence of values (U0-U20; U0-new-U20-new) of the charging voltage (Ut) or the discharging voltage (Ud) in the evaluation time interval (T1), c) determining - a value or - a definite integral with respect to time of a second time derivative of the sequence of values (U0-U20; U0-new-U20-new) of the charging voltage (Ut) or the discharging voltage (Ud) in the evaluation time interval (T1), d) determining the capacitance value (C) of the capacitor (CA) by using one of the following relations: - the negative quotient of the value of the first time derivative and the value of the second time derivative, wherein the negative quotient is divided by a known resistance value (R) of the charging resistor (RE) or the discharging resistor (RD), gives the capacitance value (C), or - the negative quotient of the definite integral of the first time derivative and the definite integral of the second time derivative, wherein the negative quotient is divided by a known resistance value (R) of the charging resistor (RE) or the discharging resistor (RD), gives the capacitance value (C).
  2. The method according to claim 1, characterized in that the value of the first time derivative is determined by using numerical differentiation with regard to - the whole evaluation time interval (T1) or - a first subinterval of the evaluation time interval (T1), wherein the first subinterval comprises at least three values (U0-U20; U0-new-U20-new) of the charging voltage (Ut) or the discharging voltage (Ud), wherein the value of the second time derivative is determined by using numerical differentiation with regard to - the whole evaluation time interval (T1) or - a second subinterval of the evaluation time interval (T1), wherein the second subinterval comprises at least three values (U0-U20; U0-new-U20-new) of the charging voltage (Ut) or the discharging voltage (Ud).
  3. The method according to claim 1 or 2, characterized in that a plurality of capacitance values (C) is determined, wherein the plurality of capacitance values (C) - are qualified as usable if a predefined measure of statistical dispersion of the plurality of capacitance values (C) is not exceeded and/or - are qualified as unusable if a predefined measure of statistical dispersion of the plurality of capacitance values (C) is exceeded.
  4. The method according to any one of claims 1-3, characterized in that the capacitance value (C), and/or, if applicable, the plurality of capacitance values (C), are qualified as unusable, if a change in a supply voltage (US) of the RC circuit is detected in the evaluation time interval (T1).
  5. A system (1, 10) for determining a capacitance value (C) of a capacitor (CA) of a RC circuit on a DC link (DCL) of a vehicle, wherein the RC circuit comprises a charging resistor (RE) or a discharging resistor (RD), wherein the system (1) is configured to perform the method according to any one of claims 1-4, wherein the system (1) comprises: a) a measuring device, configured to measure a sequence of values (U0-U20; U0-new-U20-new) of a charging voltage (Ut) or a discharging voltage (Ud) of the capacitor (CA) over an evaluation time interval (T1), b) a computing device, configured to determine - a value or - a definite integral with respect to time of a first time derivative of the sequence of values (U0-U20; U0-new-U20-new) of the charging voltage (Ut) or the discharging voltage (Ud) in the evaluation time interval (T1) and configured to determine - a value or - a definite integral with respect to time of a second time derivative of the sequence of values (U0-U20; U0-new-U20-new) of the charging voltage (Ut) or the discharging voltage (Ud) in the evaluation time interval (T1) and configured to determine the capacitance value (C) of the capacitor (CA) by using one of the following relations: - the negative quotient of the value of the first time derivative and the value of the second time derivative, wherein the negative quotient is divided by a known resistance value (R) of the charging resistor (RE) or the discharging resistor (RD), gives the capacitance value (C), or - the negative quotient of the definite integral of the first time derivative and the definite integral of the second time derivative, wherein the negative quotient is divided by a known resistance value (R) of the charging resistor (RE) or the discharging resistor (RD), gives the capacitance value (C).
  6. A vehicle comprising the system (1, 10) according to claim 5.
  7. The vehicle according to claim 6, characterized in that the vehicle is a railway vehicle.

Description

The invention relates to a method for determining a capacitance value of a capacitor of a RC circuit on a DC link of a vehicle, a system configured to perform the method and a vehicle comprising the system. Capacitors are commonly used in DC links of traction converters of vehicles, particularly railway vehicles, particularly in RC circuits with a charging resistor and/or a discharging resistor. In this respect, capacitors particularly can serve as filter capacitors. In operation, capacitance values decrease over time as a result of aging. In order to prevent consequential damage, particularly of traction converter components due to reduced filtering capabilities, an accurate capacitance supervision is required. If progressed aging is detected, it can be necessary to replace capacitors. It is known to use measured values of a charging current and measured values of a charging voltage of a capacitor to determine a capacitance value based on the differential equation I = C * dU(t)/dt, rearranged C = I / (dU(t)/dt), wherein I is the charging current, C is the capacitance value, U(t) is the charging voltage, dU(t)/dt is the first derivative with respect to time t of the charging voltage. In practice, this method may be unreliable. The charging resistor reduces the charging current to very low values. These low charging current values can be below accuracy limits of measuring devices, such as current transformers. Furthermore, the resolution of A/D converters being used (such a resolution can be, for example, 1 A) is insufficient for use in low value ranges, for example ranges below 10 A. The resolution characterizes the minimal difference between two current values between which the A/D converters can distinguish. It is an object of the present invention to propose a method for determining a capacitance value of a capacitor of a RC circuit on a DC link of a vehicle with an improved accuracy, wherein the implementation and the utilization of the method should be simple and cost-effective. The object is solved according to the invention by a method according to claim 1, a system according to claim 5 and a vehicle according to claim 6. In particular, it is proposed a method for determining a capacitance value of a capacitor of a RC circuit on a DC link of a vehicle, wherein the RC circuit comprises a charging resistor or a discharging resistor, the method comprising the following steps: a) measuring a sequence of values of a charging voltage or a discharging voltage of the capacitor over an evaluation time interval,b) determining a value ora definite integral with respect to time of a first time derivative of the sequence of values of the charging voltage or the discharging voltage in the evaluation time interval,c) determining a value ora definite integral with respect to time of a second time derivative of the sequence of values of the charging voltage or the discharging voltage in the evaluation time interval,d) determining the capacitance value of the capacitor by using one of the following relations: the negative quotient of the value of the first time derivative and the value of the second time derivative, wherein the negative quotient is divided by a known resistance value of the charging resistor or the discharging resistor, gives the capacitance value, orthe negative quotient of the definite integral of the first time derivative and the definite integral of the second time derivative, wherein the negative quotient is divided by a known resistance value of the charging resistor or the discharging resistor, gives the capacitance value. "At least one" has the same meaning as "one or a plurality". The terms "in part" or "partially" or "at least partially" have the same meaning as "partially or wholly". In the following, features are sometimes described in the singular. Such a description alternatively or additionally includes a corresponding disclosure for a plurality of such features, if applicable, and vice versa. The "definite integral of the first time derivative" is the "definite integral with respect to time of the first time derivative". The "definite integral of the second time derivative" is the "definite integral with respect to time of the second time derivative". The term "evaluation time interval" can generally mean, that all values in it or a part of or parts of the values in it can be used for evaluation purposes and/or further calculations. The vehicle particularly can be a railway vehicle, for example a locomotive or a traction wagon, for example of a tramway or a subway train or a light rail system or a regional train or an interregional train or a long-distance train or a highspeed train. The vehicle comprises the DC link and a traction system, in which electric traction energy is transmitted via the DC link to at least one electric traction engine. Alternatively, the vehicle can be an electric bus, an electric car or any electrically powered road or rail vehicle comprising a DC link. Alter