DE102016212184A1 - Method for detecting an error in a vehicle electrical system - Google Patents

Abstract

A method and an arrangement for detecting a fault in a vehicle electrical system (70) are presented. In the method, a detected vehicle electrical system voltage is evaluated by subjecting a signal representing a variation of the vehicle electrical system voltage in a time domain to a Fourier transformation and evaluating the spectrum obtained by the Fourier transformation, wherein a failure of one phase of a multiphase DC converter ( 72) is detected by an amplitude at a switching frequency and a normalized sum of all frequencies are evaluated in the spectrum.

Description

The invention relates to a method and a diagnostic device for detecting a fault in a vehicle electrical system. The presented method is used u. a. for monitoring a DC-DC converter, in particular a multi-phase DC-DC converter, which is used, for example, in a multi-voltage vehicle electrical system, and for detecting an arc in the electrical system.

State of the art

A vehicle electrical system is to be understood as the entirety of all electrical components in a vehicle. Especially in multi-voltage electrical system Gelichspannungswandler be used. A DC-DC converter is an electrical circuit that converts a DC voltage applied to its input into a DC voltage with a higher, lower or inverted voltage level. Such DC-DC converters are used, for example, in multi-voltage networks. Vehicle systems used in motor vehicles are in many cases designed as multi-voltage networks, which ensure the electrical supply of the components in the motor vehicle.

Due to the increasing electrification of units and the introduction of new driving functions, the requirement for the reliability of the electrical power supply in the motor vehicle increases.

Non-driving activities are permitted to a limited extent in future highly automated driving. A sensory, regulatory, mechanical and energetic fallback by the driver in this case is limited. Therefore, in a highly automatic driving the electrical supply has a previously unknown in the motor vehicle safety relevance. Errors in electrical wiring systems must therefore be reliably and completely recognized.

A diagnosis of the entire voltage converter is from the document DE 10 2013 212 149 A1 known. In this a voltage converter with an input side and an output side is described, which is controllable via a first control device. This control unit can control the voltage converter in such a way that it generates a changed output voltage compared to a normal operating state, which is detected and evaluated by the control unit.

It should be noted that so far it has only been possible to detect a complete failure of a DC-DC converter. In the event of failure of one of the four phases, for example, the output voltage can still be adjusted, in particular in partial load. However, the remaining, functioning phases are inadmissibly overloaded. These can overheat and eventually fail without notice.

Disclosure of the invention

Against this background, a method according to claim 1 and a diagnostic device with the features of claim 8 are presented. Embodiments emerge from the dependent claims and from the description.

The presented method enables the detection of the failure of a single phase of a multiphase DC-DC converter during operation without the need for additional hardware. For this purpose, the method u. a. the use of a Fourier transform.

Furthermore, the method enables the detection of arcs, in particular in the 48V vehicle electrical system, of a vehicle in an embodiment. Arcs occur when disconnecting lines with medium or high voltage under load. It should be noted that electric arcs can cause vehicle fires and therefore have to be detected.

In the presented method, it is possible that the same diagnostic principle and the same diagnostic device can be used both for the arc detection and for the detection of the phase failure of the DC-DC converter. This diagnosis can be divided into various on-board network components. With the presented diagnostic device both error cases can be detected.

Thus, on the one hand, the failure of the arc can be detected by means of a Fourier transformation, which occurs when a current path, for example, is separated in the 48 volt network under load. This is done by the method described herein. On the other hand, a diagnosis of a multiphase Voltage converter with the aid of the same Fourier transform and further computational steps in the post-processing of measured signals are made.

To detect both error cases, a signal representing a profile of the vehicle electrical system voltage in a time domain is subjected to a Fourier transformation. This time range includes, for example, 10 to 20 switching periods, d. H. depending on the frequency, for example, a range of 100 μs to 10 ms.

The diagnosis of a multi-phase voltage converter thus takes place with the aid of the Fourier transformation and further calculation steps in the post-processing of measured signals. It was recognized that the phase amplitudes in the Fourier analysis at the switching frequency, the highest amplitudes can be seen. In the case of an intact DC-DC converter, however, this is not the case. Furthermore, the normalized sum of all frequencies is greater for a defective DC-DC converter than for an intact DC-DC converter. If both criteria are used, the error case "phase failure" can be reliably detected

The presented method uses an algorithm which makes it possible, if necessary, to monitor all phases of the DC-DC converter and the components installed therein without additional hardware. It should be noted that working on the basis of a signal available throughout the vehicle, namely the vehicle electrical system voltage, whereby the "place of implementation" is irrelevant. Thus, available computing capacity can be used efficiently by implementing the algorithm, for example, in a central diagnostic device, which can also perform the arc detection. An FFT evaluation device may be necessary if this is not already intended for arc detection.

Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawings.

It is understood that the features mentioned above and those yet to be explained below can be used not only in the particular combination indicated, but also in other combinations or in isolation, without departing from the scope of the present invention.

Brief description of the drawings

1 shows a block diagram of a two-channel electrical system according to the prior art.

2 shows a simplified representation of a two-channel electrical system.

3 shows in a block diagram a four-phase up / down switching converter according to the prior art.

4 shows a possible sequence of the presented method.

5 shows in a graph the first 150 normalized periodogram coordinates are based on a Uio measurement.

6 shows in a graph the first 150 normalized periodogram coordinates are based on a defect measurement.

7 shows a diagnostic device for parallel detection of an arc.

The invention is schematically illustrated by means of embodiments in the drawings and will be described in detail below with reference to the drawings.

1 shows a possible embodiment of a dual-channel electrical system according to the prior art, the whole by the reference numeral 10 is designated. This includes an electric machine 12 For example, a starter, a first consumer not relevant to safety 14 , a first battery 16 who has a battery management system 18 is assigned, a DC-DC converter 20 acting as a coupling element between a 48 volt side 22 and a low voltage side 24 , For example. With a voltage level of 14 V, is used, a first electronic power distributor or a first electronic power distribution unit 26 (ePDU: electronic power unit), which is an electronic power distributor with fuse function and voltage and current measurements, a second non-safety relevant consumer 28 , a second battery 30 with associated electronic battery sensor 32 , a second ePDU 34 , a second DC converter 36 acting as a coupling element between the high-voltage side 22 and another low-voltage side 38 , for example, also with a voltage level of 14 V, serves a third battery 40 with associated electronic battery sensor 42 , a first safety-relevant consumer 50 , a second safety-relevant consumer 52 , a third safety-relevant consumer 54 and a fourth security-relevant consumer 56 , The security-relevant consumer 54 and the security consumer 50 are mutually redundant, as are the safety-relevant consumers 52 and 56 , The safety-relevant consumers 52 and 56 are installed in a housing.

The base board network is marked with a border 60 with HV components and 14 V components without safety relevance. In this baseboard network 60 are the first battery 16 and the second battery 30 included, once with high voltage (HV), namely the first battery 16 , as well as with 14 V, namely the second battery 30 ,

To the base board network 60 coupled is a safety-relevant channel 62 with safety-relevant consumers such as brake, steering, etc. A second safety-relevant channel 64 also supplies safety-relevant components with 14 V. Since the safety-relevant components are also supplied from 14 V, these are the second DC-DC converter 36 and the third battery 40 intended.

In 2 is shown the simplified structure of a vehicle electrical system, the whole with the reference number 70 is designated. The illustration shows a DC-DC converter 72 , an ePDU 74 and a consumer 76 , The DC-DC converter 72 is between a 14 volt electrical system 80 and a 48 volt electrical system 82 arranged. Not shown are energy sources and energy storage and necessary elements of the 14 volt electrical system 80 , Through a flash 84 is a phase failure in the DC-DC converter 72 indicated.

In a connection 86 between the DC-DC converter 72 and the ePDU 74 can be a first arc 88 arise when it is disconnected under load. To this connection 86 also includes the connectors on the DC-DC converter 72 and at the ePDU 74 , To the ePDU 74 connected is the consumer 76 which is represented by a resistor. Also in a connection 90 to this consumer 76 An arc can occur, in this case the reference numeral 92 designated second arc. Not shown are other possible consumers and energy storage in the 48 volt electrical system 82 ,

As will be explained below, a phase failure of the converter can be detected by a Fourier transformation. For this purpose, the output voltages must be detected and processed in the indicated microcontroller or similar device. The same measuring and processing equipment can then be used for this, including the first arc 88 to recognize.

The detection of a phase failure of the DC-DC converter 72 can also be done outside. One possible place is the ePDU 74 , In this case, the signal acquisition and processing equipment described below as well as the algorithms described below must be incorporated into the ePDU 74 be recorded. With these facilities can then the ePDU 74 in addition to the defect of the DC-DC converter also the first arc 88 and the second arc 92 detect. One possible construction of a diagnostic device is in 7 played.

In 3 the schematic structure of a switching converter is shown as an embodiment of a track-mounted voltage converter, the total with the reference numeral 100 is designated. On the left side are the high side 102 , usually with voltages in the range of 48 V, followed by a first circuit breaker 104 and a first input filter 106 , This is followed by four-phase high-side and low-side mosfets as switching cell 108 , For voltage conversion continues to be a ferrite module 110 needed for energy storage, which consists of coupled inductors 112 consists.

On the 14 V output side, with KL30 and reference numeral 114 marked, there is a second filter 116 and a circuit breaker 118 , On the output side, the required voltages can be measured: Either U _{output voltage_LV} 120 used directly at the converter _output , alternatively, the voltage U _internLV 122 which is between ferrite module 110 and the second filter 116 is tapped, and thus not through the second filter 116 is damped, used.

On the input side are: U _{input voltage_HV} 124 directly on KL40, marked with reference number 130 , Furthermore, the voltage U _internHV , 126 that is between the switch cell 108 and the first filter 106 is tapped, and thus not by the first filter 106 is damped, used.

• – Fehlerhafte Ansteuerung einer der vier High-Side/Low-Side Treiber
• – Ausfall einer der 4 High-Side/Low-Side Treiber
• – Ausfall der High-Side/Low-Side Mosfets einer Phase
• – Unterbrechung einer Phase

A failure of a phase in the switching converter 100 can have different causes. Among others, these can be:

• - Faulty control of one of the four high-side / low-side drivers
• - Failure of one of the 4 high-side / low-side drivers
• - Failure of the high-side / low-side MOSFETs of a phase
• - interruption of a phase

4 shows a possible sequence of the presented method. This is done in one step 200 the measurement of the voltage curve over several switch periods. In a subsequent step 202 If a DFT is performed, the creation of a periodogram follows. Then follow in a further step 204 the search of the maximum ordinate in the periodogram. Then follows in a subsequent step 206 the search of all ordinates. Finally, in a final step 208 the comparison with stored values.

A periodogram, also referred to as a wave diagram, shows the spectral density of a signal. In this case, the frequency or the period is plotted on the x-axis and, for example, the detected variance component on the y-axis.

5 shows in a graph 300 , on the abscissa 302 the frequencies in Hz and at its ordinate 304 the amplitudes are plotted, the first 150 normalized periodogram coordinates based on a Uio measurement, ie for the error-free case. The sum of all ordinates here is 1.02.

6 shows in a graph 400 , on the abscissa 402 the frequencies in Hz and at its ordinate 404 the amplitudes are plotted, the first 150 normalized periodogram coordinates based on a defect measurement. The sum of all ordinates is 2.1023 for this case.

The error detection algorithm used is explained in detail below by way of example:
The presented method provides the measurement one of the related 3 for a certain period of time. The resolution must be well above the switching frequency due to the so-called Nyquist-Shannon sampling theorem. It must continue to record several periods.

In a second step, a discrete Fourier analysis (DFT) will be carried out for this signal in the embodiment. The procedure is as follows:
Given a finite time-discrete signal. M = {g ₀ , ..., g _N } (1.11)

Since there is no information about the behavior of g outside the time interval [t ₀ , t _N ] anyway, it can be assumed at this point that the signal continues periodically, d, h. P (g) = t _N -t ₀ . Of course, this should also be found a way to represent the given signal as a Fourier series or to determine the associated frequency spectrum. This can be done analogously as in steady case 1.1.2, but then the integral in 1.10 must be given by a sum and the differential dt by the "time interval" of the individual measured values t _i -t _i-1 = Δ ^T , i = 1, ..., N are replaced. It is assumed that this is an equidistant scan.

mit

This results in the discrete case.

With

In this case, f _n : = n / ((N + 1) Δ ^T ) and can again be understood as "oscillations during the considered interval" or during P (g).

und 1.14 damit (N + 1)-periodisch ist.On closer examination of 1.14 it is noticeable that applies

and 1.14 so that (N + 1) -periodic.

wobei z die komplexe Konjugation von z ∊ C bezeichnet.It may even go one step further and be shown to be true

where z denotes the complex conjugation of z ∈ C.

This leads to the so-called aliasing effect. This states that in the reconstruction of a periodic, time-continuous signal, the frequency f _n = n / P (g) as an alias of the frequencies f _n + K, f _n + 2K, ... occurs, and these after digitization no longer from each other to distinguish.

The Nyquist-Shannon sampling theorem states that a periodic signal g (t) can be reconstructed from a corresponding digitization without loss of information if all frequency components of the signal are really smaller than half the sampling frequency f _(T) / 2. Conversely, this means that frequencies equal to half the sampling frequency can not be reproduced correctly in the frequency spectrum of the DFT. Strictly speaking, those frequencies flow into the Fourier coefficients of their respective aliases.

Due to the above-described periodic properties of the Fourier coefficients in the especially finite, discrete case, the infinite sum in (1.22) can be shortened in the following way:

It should be noted that there are already numerous algorithms for calculating DFT based on a discrete, finite set of points. The most efficient and widely used way of Implementation is called Fast Fourier Transform (FFT). Also in Matlab, the FFT is already available as a finished routine. This makes it possible to directly transfer an (N + 1) -dimensional vector into its DFT, which is also a (N + 1) -dimensional, complex vector of the Fourier coefficients C = [C ₀ , ..., C _N ] (1.23) is issued.

The following section describes the preparation of a periodogram:
In the third step, according to the presented method, a periodogram is created as follows:
For a given frequency spectrum C and the set of associated Fourier frequencies M _f , the periodogram is defined as a plot of the following mapping: P: M _f - → R (1.24) f _n 7 - → | C _n |, n = -∞, ..., ∞. (1.25)

In the case of DFT, in (1.25), according to (1.18), it is possible to restrict to n = 0, ..., N and beyond to (1.21) n = 0, ..., d (N + 1) / 2e ,

Against this background, it should be noted that all (available) information is already contained in the first N ⁰ : = d (N + 1) / 2e Fourier coefficients. When graphing the periodogram, it is defined that the X-axis should always be in the unit heart (Hz = 1/8). As already mentioned, in the case of DFT:

Assuming that the sampling frequency is also given in Hz, | C _n | for n = 0,..., K-1 is thus to be assigned to the (n / N) * f ^(T) frequency component.

In the following, the constant component of M which is uninteresting for the fault diagnosis is always eliminated by subtraction of the mean value, therefore C ₀ = 0 always applies.

Furthermore, for reasons of clarity, a scaled version of the Fourier coefficients is always considered, namely C ' _n : = 1 / N + 1C _n ∀n = 0, ..., N' (1.27)

This is followed by the transfer of a discrete, finite set of equidistant measurement points M into the real-valued vector of the absolute values of the frequency spectrum (hereafter periodogram coordinates): C ': = [| C' ₀ |, ..., | C '_N' |] (1.28)

so wird bei

vom normierten Frequenzspektrum bzw. dem normierten Periodogramm gesprochen. Aus Gründen der Übersichtlichkeit wird im folgenden Verlauf ausschließlich das normierte Periodogramm für graphische Darstellungen verwendet.Remark: If C ⁰ (element by element) is multiplied by the factor V _M ^-1 , for

so will be at

spoken by the normalized frequency spectrum or the normalized periodogram. For reasons of clarity, only the normalized periodogram for graphical representations will be used in the following process.

To summarize: The amount of X last sampled values of the vehicle electrical system voltage is considered (for a fixed X, eg X = 1000). By means of discrete Fourier transformation, the associated periodogram is determined. Periodogram can be interpreted as the assignment of individual frequencies and their "share of the signal".

The following criteria can now be used to detect the failure of a phase:

1) Frequency and height of the maximum coordinate in the periodogram

If one phase fails, the switching frequency of the converter can be seen as the maximum ordinate in the periodogram. It will open 5 directed. In the iO case, there is no such pronounced peak, the maximum ordinate is smaller in magnitude and is not at the switching frequency of the converter.

2) Sum over all periodogram coordinates

If one phase fails, the sum of all ordinates is significantly larger than for a converter in a faultless case, as shown in the following table: Measurement x = io x = no Ux (250,36,15) (U _output voltage) 1:02 2.1023 Ux (500,36,15) (U _output voltage) 0.92177 2.2211 Ux (1000,36,15) (U _output voltage) 0.92845 4.1359 Ux (250,48,13.8) (U _output voltage) 0.99826 2.0068 Ux (500,48,13.8) (U _output voltage) 0.97457 2.2857 Ux (1000,48,13.8) (U _output voltage) 0.96912 4.2378 Ux (250,36,15) (U _internal) 1.3386 4.2178 Ux (500,36,15) (U _internal ) 1.3347 4.5079 Ux (1000,36,15) (U _internal ) 1.3051 10.4183 Ux (250,48,13.8) (U _internal ) 1.2908 4.0112 Ux (500,48,13.8) (U _internal ) 1.3448 4751 Ux (1000,48,13.8) (U _internal ) 1405 20.3344 Table 1 (OK: OK, NOK: not OK)

According to the presented method, an error can be detected during operation if the sum suddenly rises above all periodogram coordinates at a certain operating point and at the same time the frequency of the maximum coordinate shifts.

In one embodiment, the selectivity of the diagnosis can be improved when the algorithms described above are first calibrated. This means that the operating point-dependent values must be determined for all desired operating points. This is done on the basis of example measurements on the basis of a demonstrably error-free converter and must be done once prior to commissioning of the algorithms.

Furthermore, alternatively, the converter store the above-mentioned values per operating point during initial operation in the production plant or in the vehicle.

• – U_internLV
• – U_internHV
• – U_wandlerausgangLV
• – U_wandlereingangHV

According to the presented method, the voltage can be detected at one of the following locations. It gets up here 2 directed.

• - U_internLV
• - U_internHV
• - U_transducer output LV
• - U_wandlereingangHV

Furthermore, the diagnosis can be carried out both in the converter itself and in other on-board network components.

7 shows an embodiment of a diagnostic device, in total with the reference numeral 500 is designated. This diagnostic device 500 is, for example, implemented in an ePDU and includes hardware 502 and software 504 , In the hardware 502 is a high pass and aliasing filter 506 provided with a pass frequency range f of 1.5 kHz <f <100 Hz, which serves to scan the current in the respective channel in the 48 volt electrical system. Between the hardware 502 and the software 504 is an analog-to-digital converter 510 provided with 10.5 bit usable resolution in this case. The sampled signal is transmitted through this converter 510 read.

In the software 504 are a buffer 520 , one 522 to prevent the "leak" effect, a block 524 to perform an FFT, a block 526 for the selection of characteristic FFT bins, one block 528 to form the square of an amount and a block 530 which filters the calculated values over multiple passes, also referred to as moving average.

In the case of the converter 510 The signal read in is determined via a window function and the FFT the relevant functions. If a predetermined number of the averaged peaks exceeds a threshold value, an arc is detected and the current path is switched off. For the detection of an arc it is assumed that the resulting periodogram has a very broadband amplitude distribution and the number of peaks that are above the threshold is relatively large over a longer period of time.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102013212149 A1 [0005]

Claims (9)

Method for detecting an error in a vehicle electrical system ( 70 ), in which a detected vehicle electrical system voltage is evaluated by a signal representing a profile of the vehicle electrical system voltage in a time domain is subjected to a Fourier transform and the spectrum obtained by the Fourier transform is evaluated, wherein a failure of a phase of a multi-phase DC-DC converter ( 72 ) is detected by an amplitude at a switching frequency and a normalized sum of all frequencies are evaluated in the spectrum. Method according to claim 1, which is used to produce an arc ( 88 . 92 ) in the electrical system ( 70 ) to recognize. Method according to Claim 1 or 2, in which individual phases of the DC-DC converter ( 70 ) be monitored.  Method according to one of Claims 1 to 3, in which the signal is subjected to a discrete Fourier analysis.  Method according to one of Claims 1 to 4, in which operating point-dependent values are determined for all desired operating points.  Method according to one of claims 1 to 5 in which a periodogram is created whose periodogram are evaluated.  Method according to Claim 6, in which normalized periodogram coordinates are evaluated. Diagnostic device for detecting an error in a vehicle electrical system ( 70 ) arranged to carry out a method according to one of claims 1 to 7. Diagnostic device according to Claim 8, which is located in an electronic power distributor ( 74 ) is implemented.

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