METHOD AND DEVICE FOR DETERMINING THE VOLTAGE LEVEL OF A CHARGE CONTROL SIGNAL

Abstract

Method (100) for determining the voltage level of a charging control signal (110) for charging systems of electric vehicles, wherein the charging control signal (110) is a pulse width modulated PWM signal with adjustable pulse width (120), wherein the method (100) comprises the following: Acquisition (101) of measured values ​​of the charging control signal (110) in a time range specified by a measurement window (130); Detecting (102) a falling edge (111) of the charging control signal (110) and a corresponding time (112) of the falling edge (111) based on the charging control signal (110) and a predefined threshold (140); and upon detection (102) of the falling edge (111) of the charging control signal (110), determining (103) a voltage level (113) of the charging control signal (110) based on at least a first part (115) of the measured values ​​of the charging control signal (110) acquired in the measurement window (130), which were acquired before the time (112) of the falling edge (111) of the charging control signal (110).

Description

Technical area

[0001] The present invention relates to a method and a device for determining the voltage level of a charging control signal, in particular for charging systems of electric vehicles. The invention further relates to an optimized voltage measurement of a charging control signal. State of the art

[0002] The pulse-width modulated (PWM) charging control signal for Type 1 / CCS 1, Type 2 / CCS 2, and Megawatt Charging (MCS) systems must be precisely evaluated for the charging process. Among other things, the magnitude of the positive voltage signal level must be determined. However, due to parasitic impedances, i.e., capacitances and inductances in the signal path, as well as external interference, this signal is often highly noisy and therefore cannot be measured reliably and accurately.

[0003] Known solutions to this problem include heavy filtering of the PWM signal, continuous sampling with subsequent averaging via software, and acquiring multiple measured values ​​after a rising edge has been detected. However, these solutions require significant processor processing time to achieve satisfactory measurement accuracy. Furthermore, the memory requirements for continuous sampling are not negligible.

[0004] The document DE 101 50 050 A1 relates to a method for detecting a signal, in particular a voltage, for example a battery voltage, and to a corresponding device.

[0005] The document DE 10 2014 202 678 A1 relates to a method for detecting a short circuit in a PWM driver circuit and a corresponding device for detecting a short circuit in a PWM driver circuit. Description of the invention

[0006] An object of the invention is therefore to provide an improved voltage level determination of the charging control signal, which enables an accurate measurement of the voltage level while reducing the interference influence of parasitic impedances.

[0007] The object is achieved by the subject matter of the independent claims. Advantageous developments of the invention are specified in the dependent claims, the description, and the accompanying figures.

[0008] The invention described below enables the precise measurement of the voltage level while reducing the interference of parasitic impedances.

[0009] The inventive solution is based on the idea of ​​deliberately measuring the voltage shortly before the falling edge, rather than in the initial range of the high level, i.e., after the rising edge. This is made possible by continuously sampling the voltage signal and signaling the voltage evaluation via the falling edge of the PWM signal.

[0010] The invention described below combines the possibilities of precise voltage measurement through continuous, rapid sampling of the PWM signal for charge control with the efficiency and memory-optimized evaluation of a limited number of measured values ​​at a specific trigger time. By placing the measurement window at the end of the voltage plateau, the maximum steady state of the PWM signal is utilized, thus enabling the greatest possible independence from the signal's transient response.

[0011] According to a first aspect, the above-described object is achieved by a method for determining the voltage level of a charging control signal for charging systems of electric vehicles, wherein the charging control signal is a pulse-width modulated (PWM) signal with an adjustable pulse width, the method comprising the following: detecting measured values ​​of the charging control signal in a time range predetermined by a measurement window; detecting a falling edge of the charging control signal and a corresponding time of the falling edge based on the charging control signal and a predetermined threshold value; and upon detecting the falling edge of the charging control signal, determining a voltage level of the charging control signal based on at least a first portion of the measured values ​​of the charging control signal detected in the measurement window, which were detected before the time of the falling edge of the charging control signal.

[0012] Such a method leads to an improved voltage level determination of the charging control signal, in which an accurate measurement of the voltage level is realized while reducing the interference influence of parasitic impedances.

[0013] By placing the measurement window before the falling edge of the PWM signal, the maximum steady state of the PWM signal is utilized, thus enabling the greatest possible independence from the signal's transient response. The measurement window is optimally adapted to the steady state of the PWM signal, allowing for resource-efficient storage of the measured values, as only measured values ​​in the steady state are considered to determine the voltage level.

[0014] According to an exemplary embodiment of the method, the detection of the falling edge of the charging control signal is based on a comparison of the charging control signal or a signal derived from the charging control signal with the predetermined threshold value.

[0015] The technical advantage of such a method is that the falling edge can be easily detected based on a threshold comparison. For example, a simple comparator can be used to detect the specified threshold.

[0016] According to an exemplary embodiment of the method, the measurement window is set such that several measured values ​​can be detected within a part of the pulse width of the PWM signal.

[0017] The technical advantage of such a method is that the multiple measured values ​​allow for a more precise determination of the voltage level than if only a single measured value or a few measured values ​​were used. Averaging these multiple measured values ​​is therefore more accurate than evaluating only one or a few measured values.

[0018] According to an exemplary embodiment of the method, the measurement window is set to be at least 16 µs long. It can be set so that multiple measured values ​​can be captured within a portion of a minimum pulse width of the PWM signal according to the IEC 61851-1 standard.

[0019] The technical advantage of such a method is that all current intensities of the charging current, which are signaled via the pulse width of the PWM signal, can be reliably detected.

[0020] According to an exemplary embodiment of the method, the voltage level is determined without a second part of the measured values ​​acquired in the measurement window, which were acquired immediately before the time of the falling edge.

[0021] The technical advantage of such a method is that measured values ​​already acquired at the time of the falling edge are not included in the voltage level determination, as they would otherwise falsify the voltage level determination. This guarantees a very high degree of accuracy in the voltage level determination. The time of the falling edge refers to a recorded point in time, which was determined, in particular, by a comparator through a threshold comparison. The actual physical point in time at which the charge control signal begins to drop may differ from this.

[0022] For the threshold comparison, a threshold can be used that is sufficiently far from the actual positive voltage level of the charge control signal for fault-tolerant detection. This can result in a delay, i.e., the detected time of the falling edge occurs later than the actual drop in the voltage level of the charge control signal. By omitting the second part of the measured values ​​acquired in the measurement window, measured values ​​that do not belong to the positive voltage level and that were stored due to this delay can be disregarded when calculating the value of the voltage level of the charge control signal.

[0023] The length of the second part can be determined based on simulation or empirical values. The length of the second part can comprise a dynamically adjusted number of stored measured values ​​or a predetermined fixed number of stored measured values. For example, the most recent measured value before the time of the falling edge or a different number of measured values ​​before the time of the falling edge are discarded, i.e., these discarded measured values ​​are not taken into account when determining the voltage level of the charge control signal.

[0024] A dynamic test phase is also conceivable, particularly when commissioning the charging system, in which different lengths of the second part are tried out one after the other, whereby the length of the second part is set after the test phase to the value that resulted in the highest voltage level in the test phase and / or has the smallest variance of the voltage level.

[0025] According to an exemplary embodiment of the method, the voltage level is determined based on an averaging of at least the first part of the measured values ​​acquired in the measuring window.

[0026] The technical advantage of such a method is that only the measured values ​​shortly before the falling edge, which were acquired in the steady state of the PWM signal, are used for averaging. This eliminates outliers, which would otherwise distort the result. The measurement accuracy of the voltage level determination is thus very high.

[0027] According to an exemplary embodiment of the method, the method comprises filtering the charging control signal before acquiring the measured values. The filtering is performed using an analog filter designed to suppress signal overlays in the charging control signal caused by an interference signal, for example, originating from a power line signal. The analog filter can be a low-pass filter, for example.

[0028] The technical advantage of such a method is that high-frequency oscillations due to an influence of the charging control signal by power line communication are filtered out beforehand and thus cannot distort the determination of the voltage level.

[0029] According to an exemplary embodiment of the method, the method comprises sampling the filtered charge control signal with an analog-to-digital converter to obtain the measured values ​​of the charge control signal; and storing the sampled measured values ​​in a buffer memory, wherein a size of the buffer memory corresponds to the time range specified by the measurement window.

[0030] The technical advantage of such a method is that such a buffer memory is efficiently adapted to the measurement window and can therefore store the acquired measured values ​​very resource-efficiently. The buffer memory can overwrite previously acquired measured values ​​with new measured values, so that at the time of the falling edge, only the measured values ​​acquired during the steady state of the PWM signal are present in the memory. The time at which the falling edge begins and the time at which the falling edge is acquired can usually differ from one another, so that the buffer memory already contains measured values ​​acquired during the falling edge. However, these few measured values ​​can be efficiently detected and excluded from the determination of the voltage level.

[0031] According to an exemplary embodiment of the method, the detection of the falling edge is based on a comparison of the filtered charging control signal with the predetermined threshold value; wherein the predetermined threshold value corresponds to a signal level between a positive voltage level and a negative voltage level of the charging control signal.

[0032] The technical advantage of such a method is that the threshold value can be efficiently adjusted with knowledge of the positive voltage level and the negative voltage level; for example, it can be set in the middle between the positive and negative voltage levels.

[0033] According to a second aspect, the above-described object is achieved by a device for determining the voltage level of a charging control signal for charging systems of electric vehicles, wherein the charging control signal is a pulse-width modulated (PWM) signal with an adjustable pulse width, the device comprising: an analog-to-digital converter for acquiring measured values ​​of the charging control signal; a buffer memory for storing the acquired measured values ​​over a predetermined time range; a comparator for detecting a falling edge of the charging control signal based on the charging control signal and a predetermined threshold value; and a processor configured, upon detecting the falling edge of the charging control signal, to determine a voltage level of the charging control signal based on at least a first portion of the measured values ​​stored in the buffer memory, which were acquired before the falling edge of the charging control signal.

[0034] The technical advantage of such a device is that it enables improved voltage level determination of the charging control signal, allowing accurate measurement of the voltage level while reducing the interference influence of parasitic impedances.

[0035] As already described above for the corresponding method according to the first aspect, by placing the measurement window before the falling edge of the PWM signal, the maximum steady state of the PWM signal is utilized, thus enabling the greatest possible independence from the signal's transient response. The measurement window is optimally adapted to the steady state of the PWM signal, and the measured values ​​can thus be stored in a resource-efficient manner, because only measured values ​​in the steady state are considered to determine the voltage level.

[0036] According to a third aspect, the above-described object is achieved by a computer program product comprising instructions which, when the program is executed by a computer, cause the computer to carry out the method according to the first aspect.

[0037] According to a fourth aspect, the above-described object is achieved by a computer-readable storage medium comprising instructions which, when executed by a computer, cause the computer to carry out the method according to the first aspect. Short character description

[0038] The invention is described in more detail below using exemplary embodiments and the figures. They show: Fig. 1a shows an exemplary representation of a Control Pilot (CP) signal 110 with parasitic signal components, which represents a charging control signal for a charging system; Fig. 1b an exemplary representation of the CP signal 110 from Fig. 1a after filtering with an analog filter; Fig. 2a shows a schematic representation of a method 100 according to the invention for determining the voltage level of a charging control signal; Fig. 2b an exemplary representation of the CP signals 110 from the Fig. 1a and Fig. 1b for use in the method 100 according to the invention from Fig. 2a; Fig. 3 shows a schematic representation of an inventive method 200 for determining the voltage level of a charging control signal according to an exemplary embodiment; Fig. 4 is a schematic representation of a buffer memory 203 for use in the Fig. 3 method 200; and Fig. 5 a schematic representation of an inventive device 300 for determining the voltage level of a charging control signal.

[0039] The figures are merely schematic representations and serve only to illustrate the invention. Identical or equivalent elements are provided with the same reference numerals throughout.

[0040] In the following detailed description, reference is made to the accompanying drawings, which form a part hereof, and in which is shown by way of illustration specific embodiments in which the invention may be practiced. It is understood that other embodiments may be utilized and structural or logical changes may be made without departing from the scope of the present invention. The following detailed description, therefore, is not to be taken in a limiting sense. Further, it is to be understood that the features of the various embodiments described herein may be combined with one another unless specifically indicated otherwise.

[0041] The aspects and embodiments are described with reference to the drawings, where like reference numerals generally refer to like elements. In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of one or more aspects of the invention. However, it may be apparent to one skilled in the art that one or more aspects or embodiments may be practiced with a lesser level of specific detail. In other instances, well-known structures and elements are shown in schematic form to facilitate describing one or more aspects or embodiments. It is understood that other embodiments may be utilized and structural or logical changes may be made without departing from the concept of the present invention.

[0042] Fig. 1a shows an exemplary representation of a Control Pilot (CP) signal 110 with parasitic signal components, which represents a charging control signal for a charging system.

[0043] The Control Pilot Signal or charging control signal 110 conveys, for example, the available AC charging current, i.e. the current that, for example, an AC wallbox can provide.

[0044] The request for digital communication is also initially encoded by the duty cycle (i.e., the pulse width 120) of the PWM signal 110 and is required for all DC charging processes in Type 1, Type 2, and MCS charging systems. For this purpose, a PWM signal with +12V / -12V and a frequency of 1kHz is generated. To evaluate the signal, the most accurate transmission of the signal shape is necessary, which is, however, complicated by parasitic effects in the signal path, as described in Fig. 1a can be seen.

[0045] Parasitic impedances, i.e., capacitances or inductances, cannot be completely avoided in any electrical signal path, but they play a particularly important role in charging systems with long charging cables. The long cable lengths cause, for example, superimposed sinusoidal components 117 on the originally rectangular PWM signal 110, as shown in Fig. 1a. These are particularly pronounced when a new voltage level is being applied, ie, after a rising 116 or falling 111 edge of the original signal.

[0046] These sinusoidal components 117 appear as damped oscillations superimposed on the square-wave signal. A measurement of the applied voltage level during this first time period after a voltage edge 116, 111 is very inaccurate unless the oscillations 117 are specifically filtered out.

[0047] Fig. 1b shows an exemplary representation of the CP signal 110 from Fig. 1a after filtering with an analog filter.

[0048] Excessive filtering of the signal or a very large parasitic capacitance component, on the other hand, results in a strongly smoothed edge 116 at the beginning of the voltage plateau, as in Fig. 1b. Here, too, the measurement of the original signal level is severely impaired.

[0049] To obtain the most accurate measurement result possible, it is necessary to wait for the signal to reach steady state. The optimal measurement window 130 (the dashed area in the graphics) is therefore located shortly before the next signal change, i.e., shortly before the falling edge 111 of the PWM signal 110.

[0050] Common solutions, for example, use the rising edge 116 of the signal to start an ADC measurement with one or more measurement points. Since it's unclear exactly when the falling edge 111 will occur without knowing the duty cycle 120, it's difficult to determine this point in time (relative to the rising edge 116).

[0051] Thus, there are two approaches: a fixed dead time between the rising edge 116 and the start of the measurement or a continuous measurement with subsequent determination of the optimal measurement time for the voltage evaluation.

[0052] In the first case, the challenge is to maintain sufficient distance from the interference signals immediately following the rising edge 116 and at the same time not to mistakenly measure beyond the time of the falling edge 111.

[0053] In the second case, the memory requirements for the measurement points to be acquired are very large. Since the signal waveform only repeats after 1 ms, it is advisable to store all measured values ​​in a buffer for this period and then select and evaluate the appropriate measurement window using software.

[0054] The sampling rate is a key factor in measurement quality. The faster and more frequently the signal is sampled, the less impact any interference or noisy signal components have, as these can be filtered out by averaging. However, fast sampling requires a lot of memory, as many data points must be recorded and buffered.

[0055] The memory requirement can be reduced by maintaining only a limited time window 130 in the buffer memory and evaluating these measurement points at a suitable time. The optimal time is marked by the falling edge 111 of the PWM signal 110 to be measured.

[0056] In the following, a method 100 according to the invention is described which uses such a limited time window 130 to record the measured values.

[0057] Fig. 2a shows a schematic representation of a method 100 according to the invention for determining the voltage level of a charging control signal and Fig. Figure 2b shows an exemplary representation of the CP signals 110 from the Fig. 1a and Fig. 1b with characteristic parameters for use in the method 100 according to the invention from Fig. 2a.

[0058] The charging control signal 110 is, for example, a pulse-width modulated signal, i.e. PWM signal, with adjustable pulse width 120, which is used in charging systems of electric vehicles, for example according to the IEC 61851-1 standard or other common standards.

[0059] The method 100 includes the following steps: Acquiring 101 measured values ​​of the charging control signal 110 in a time range specified by a measuring window 130; Detecting 102 a falling edge 111 of the charging control signal 110 and a corresponding time 112 of the falling edge 111 based on the charging control signal 110 and a predetermined threshold value 140; and Upon detection of the falling edge 111 of the charging control signal 110: determining a voltage level 113 of the charging control signal 110 based on at least a first part 115 of the measured values ​​of the charging control signal 110 acquired in the measuring window 130, which were acquired before the time 112 of the falling edge 111 of the charging control signal 110.

[0060] The detection 102 of the falling edge 111 of the charging control signal 110 can be carried out, for example, based on a comparison of the charging control signal 110 or a signal derived from the charging control signal 110, for example a time average of the measured values ​​of the charging control signal, with the predetermined threshold value 140.

[0061] The measurement window 130 can advantageously be set so that several measured values ​​can be detected within a part of the pulse width 120 of the PWM signal 110.

[0062] For example, the measurement window 130 can be set so that several measured values ​​can be captured within a part of a minimum occurring pulse width 120 of the PWM signal 110 according to the IEC 61851-1 standard.

[0063] The voltage level 113 can be determined, for example, without a second part 114 of the measured values ​​acquired in the measurement window 130, which were acquired immediately before the time 112 of the falling edge 111. As in Fig. As shown in Figure 2b, the second part 114 is the measured values ​​that were already recorded with the onset of the falling edge 111, but the threshold comparison with the threshold 140 has not yet been triggered.

[0064] The voltage level 113 can be determined, for example, based on an averaging of at least the first part 115 of the measured values ​​acquired in the measurement window 130. This first part 115 is the adjusted measured values, which do not include the second part 114, which were acquired at the onset of the falling edge 111.

[0065] The method 100 may further comprise filtering the charging control signal 110 prior to the acquisition 101 of the measured values. The filtering may be performed using an analog filter configured to suppress signal overlays in the charging control signal 110, for example, caused by an interference signal, such as a powerline signal or another high-frequency interference signal. The analog filter may, for example, be a low-pass filter configured to allow the high frequencies of the PWM signal 110 to pass through, but no longer the high frequencies of the powerline signal.

[0066] The method 100 may further include the following steps: Sampling the filtered charge control signal with an analog-to-digital converter to obtain the measured values ​​of the charge control signal 110; and Saving the sampled measured values ​​in a buffer memory. The size of the buffer memory can correspond to the time range specified by the measurement window 130, as in Fig. 2b.

[0067] The detection 102 of the falling edge 111 can be based on a comparison of the filtered charging control signal with the predetermined threshold value 140.

[0068] The predetermined threshold value 140 may, for example, correspond to a signal level between a positive voltage level 110a and a negative voltage level 110b of the charging control signal 110, as in Fig. 2b.

[0069] Fig. 3 shows a schematic representation of an inventive method 200 for determining the voltage level of a charging control signal according to an exemplary embodiment.

[0070] The method 200 has two paths, a first path with blocks 201, 202 and 203 and a second path with blocks 211, 212, 213, 214 and 215, the second path being influenced by the first path.

[0071] The first path starts with sampling 201 of the PWM signal, which is the one described above. Fig. 1a to 2b described PWM signals 110 or charging control signals 110.

[0072] The sampled value is then written 202 into a buffer memory and at the next sampling time, another sampled value of the PWM signal is sampled 201 and written 202 into the buffer memory again.

[0073] After a certain repetition of sampling 201 and writing 202, the buffer memory finally has a number of n+x digits or samples of the PWM signal.

[0074] The second path starts with a check 211 of the PWM signal for a falling edge. If a falling edge is detected in step 212, the buffer memory evaluation is initiated 213, as in step 203. Otherwise, the PWM signal is checked again 211 for a falling edge.

[0075] When evaluating the buffer, the last x buffer values ​​are discarded in step 214. This means that the length of the second part 114 of the buffer values ​​corresponds to the number of x discarded buffer values.

[0076] In the subsequent step 215, the remaining n measured values ​​are averaged. After averaging 215, a voltage level of the PWM signal is obtained.

[0077] The PWM signal is then checked again 211 for a falling edge.

[0078] The method 200 is a specific embodiment of the method described above for Fig. 2a and Fig. 2b described method 100.

[0079] The acquisition 101 of measured values ​​of the charging control signal 110 in a time range specified by a measurement window 130 corresponds to steps 201, 202 and 203, wherein these acquired measured values ​​are present in the buffer memory in step 203.

[0080] The detection 102 of a falling edge 111 of the charging control signal 110 and a corresponding time 112 of the falling edge 111 corresponds to steps 211 and 212.

[0081] Determining 103 a voltage level 113 of the charging control signal 110 corresponds to steps 213, 214 and 215.

[0082] Fig. 4 shows a schematic representation of a buffer memory 203 for use in the Fig. 3 presented procedure 200.

[0083] The buffer memory 203 is opened according to step 203 of the Fig. 2 is used. After each sampling 201 of the PWM signal 110, a measured value or sample value of the PWM signal 110 is available, which is written into the buffer memory 203. The writing direction 226 of the buffer memory 203 is, for example, clockwise, as in Fig. 4. The next sample value for the next sample is written one position further clockwise into the buffer memory 203.

[0084] In step 203 according to Fig. 2, a number of n+x samples are written as storage values ​​into the buffer memory 203, of which n samples 115 are relevant, namely those that were written into the buffer memory before the onset of the falling edge 111, and x samples, corresponding to the second part 114, are irrelevant and are to be discarded, namely those that were still written into the buffer memory during or after the onset of the falling edge 111. The last relevant storage value 224 corresponds to the last sample of the n samples 115, while the last written storage value 225 corresponds to the last sample of the x samples in the second part 114.

[0085] The above Fig. 2a and Fig. 2b thus comprises all n+x sample values ​​that fit into the buffer memory 203. The first part 115 of the measured values ​​acquired in the measurement window 130 according to the Fig. 2a and Fig. 2b comprises the n relevant samples 115, while the second part 114 of the measured values ​​acquired in the measurement window 130 according to the Fig. 2a and Fig. 2b comprises the x samples 114 to be discarded, which were still stored in the buffer memory 203, ie the length of the second part 114 is x.

[0086] Fig. 5 shows a schematic representation of an inventive device 300 for determining the voltage level of a charging control signal.

[0087] The device 300 is analogous to the one described above for the Fig. 2a and Fig. 2b described method 100.

[0088] The device 300 is used to determine the voltage level of a charging control signal 110 for charging systems of electric vehicles, wherein the charging control signal 110 is a pulse width modulated, PWM, signal with adjustable pulse width 120.

[0089] The device 300 comprises an analog-digital converter 303 for detecting 101 measured values ​​304 of the charging control signal 110, for example as described above for the Fig. 2a and Fig. 2b and 3.

[0090] The device 300 comprises a buffer memory 203 for storing the acquired measured values ​​over a predetermined time range, for example as described above for the Fig. 3 and Fig. 4 described in more detail.

[0091] The device 300 comprises a comparator 305 for detecting 102 a falling edge 111 of the charging control signal 110 based on the charging control signal 110 and a predetermined threshold value 140, for example as described above for the Fig. 2a, Fig. 2b, Fig. 3 and Fig. 4 described.

[0092] The device 300 comprises a processor 307 which is designed, upon detection of the falling edge 111 of the charging control signal 110, to determine a voltage level 113 of the charging control signal 110 based on at least a first part 115 of the measured values ​​304 stored in the buffer memory 203, which were acquired before the falling edge 111 of the charging control signal 110, for example as described above for the Fig. 2a, Fig. 2b, Fig. 3 and Fig. 4 described.

[0093] Optionally, the device 300 may comprise an analog filter 301 configured to filter the PWM signal before it is supplied as a filtered signal 302 to the AD converter 303 and the comparator 305.

[0094] The filter 301 can be configured to filter the charging control signal 110 before the measured values ​​are acquired 101. The analog filter 301 can be configured to suppress signal interference in the charging control signal 110 caused by an interference signal, for example, by a power line signal.

[0095] The analog-to-digital converter 303 may be configured to sample the filtered charge control signal 302 to obtain the measured values ​​of the charge control signal 110.

[0096] Buffer memory 203 can be configured to store the sampled measured values. The size of buffer memory 203 can correspond to the time range specified by measurement window 130.

[0097] An embodiment of the device 300 is described in more detail below.

[0098] An advantageous technical solution is that a microcontroller performs a continuous, high-frequency sampling of the PWM signal 110, with the individual sample values ​​304 being written directly into a buffer memory 203. The provided memory area with n + x positions is smaller than would be necessary for recording a complete period of the PWM signal 110 (approximately 1 ms). The time range covered by the buffer memory 203 is, for example, denoted by t buffer designated.

[0099] If the end of the designated memory area is reached, the oldest measured values ​​are to be discarded and replaced by new samples (First In First Out / FIFO memory or also called ring buffer). To determine when the optimal signal portion is located in the buffer memory 203, the falling edge 111 of the PWM signal 110 at time t interrupt 112 (see Fig. 2b) an interrupt is generated in the microcontroller and the contents of the buffer memory 203 are processed.

[0100] It may be advantageous to discard a number x of the most recent measured values ​​114 (as in Fig. 4), since the beginning of the falling edge 111 may have been measured and should not be included in the evaluation. The relevant time portion of the signal to be evaluated is denoted by t rel and contains n measured values ​​115 (as in Fig. 4). The n measured values ​​115 are averaged, and the positive voltage level 110a of the PWM signal 110 is calculated from them.

[0101] The signal flow can effectively be divided into two paths: - An analog signal flow leads via the ADC 303 into the buffer memory 203; - A digital signal flow leads via a comparator 305 as a trigger directly into the processor 307.

[0102] To write the ADC measurement values ​​304 directly to the buffer memory 203, it is advantageous to use a microcontroller with DMA functionality. This keeps the processor load for capturing and storing the individual measurement points 304 as low as possible.

[0103] The optimum size of the measurement window 130 can be derived from the minimum duty cycle 120 of the PWM signal 110 to be recorded. According to current standards (e.g. IEC 61851-1), a minimum duty cycle of 3% at a maximum frequency of 1020 Hz should still be able to be accurately recorded. This results in a positive pulse width of a good 29 µs. Taking into account the maximum permissible settling time (i.e. the time until 95% of the signal level is reached) of 3 µs, this results in a minimum pulse width of approximately 26 µs in an undisturbed system. If a further 10 µs are taken into account for the transient response of the signal disturbed by parasitic impedances, this results in a minimum suitable measurement window of 16 µs. At a sampling rate of 1 MHz, this corresponds to 16 measured values ​​within the measurement window.

[0104] To rule out the possibility that the falling edge 111 of signal 110 was also measured, the last two measured values ​​can be discarded, which corresponds to the maximum permissible fall time of 2 µs. Thus, the voltage level can be determined by averaging the remaining 14 measured values.

[0105] The times listed above are only examples. Faster or slower sampling, as well as different assumptions for the optimal measurement window 130, may result in different values ​​for the measurement window size and the values ​​to be recorded. LIST OF REFERENCE SYMBOLS 100 methods for determining voltage levels 101 first procedural step: recording 102 second process step: recognition 103 third process step: Determine 110 Charging control signal, PWM signal 110a positive signal level of the PWM signal 110b negative signal level of the PWM signal 111 falling edge of the PWM signal 112 Time of falling edge, t interrupt 113 voltage level of the charge control signal to be determined 114 second part 115 first part 116 rising edge of the PWM signal 117 sinusoidal noise components 120 Pulse width of the PWM signal, Duty Cycle 130 measuring windows 140 threshold, threshold voltage level 200 methods for determining voltage levels 201 first block in the first path: scanning 202 second block in the first path: Write 203 third block in the first path: buffer memory with n+x places 211 first block in the second path: Check 212 second block in the second path: Recognize 213 third block in the second path: Evaluate 214 fourth block in the second path: discard 215 fifth block in the second path: averaging 224 last relevant memory value 225 last written memory value 226 Write direction buffer memory 300 Device for determining voltage levels 301 (analog) filter 302 filtered PWM signal 303 analog-to-digital converter 304 single measured value 305 Comparator 307 processor

Claims

[1] Method (100) for determining the voltage level of a charging control signal (110) for charging systems of electric vehicles, wherein the charging control signal (110) is a pulse-width modulated PWM signal with an adjustable pulse width (120), the method (100) comprising: detecting (101) measured values ​​of the charging control signal (110) in a time range predetermined by a measuring window (130); Detecting (102) a falling edge (111) of the charging control signal (110) and a corresponding time (112) of the falling edge (111) based on the charging control signal (110) and a predetermined threshold value (140); and upon detection (102) of the falling edge (111) of the charging control signal (110), determining (103) a voltage level (113) of the charging control signal (110) based on at least a first part (115) of the measured values ​​of the charging control signal (110) detected in the measurement window (130), which were detected before the time (112) of the falling edge (111) of the charging control signal (110). [2] Method (100) according to claim 1, wherein the detection (102) of the falling edge (111) of the charging control signal (110) is based on a comparison of the charging control signal (110) or a signal (302) derived from the charging control signal (110) with the predetermined threshold value (140). [3] Method (100) according to claim 1 or 2, wherein the measurement window (130) is set such that a plurality of measurement values ​​can be detected within a part of the pulse width (120) of the PWM signal (110). [4] Method (100) according to one of the preceding claims, wherein the measurement window (130) is at least 16 µs long. [5] Method (100) according to one of the preceding claims, wherein the voltage level (113) is determined without a second part (114) of the measured values ​​acquired in the measuring window (130) which were acquired immediately before the time (112) of the falling edge (111). [6] Method (100) according to one of the preceding claims, wherein the determination of the voltage level (113) is based on an averaging of at least the first part (115) of the measured values ​​acquired in the measuring window (130). [7] Method (100) according to one of the preceding claims, comprising: Filtering the charging control signal (110) before detecting (101) the measured values, wherein the filtering is carried out with an analog filter which is designed to suppress signal superpositions in the charging control signal (110) caused by an interference signal, in particular a power line signal. [8] Method (100) according to claim 7, comprising: Sampling the filtered charge control signal (302) with an analog-to-digital converter to obtain the measured values ​​of the charge control signal (110); and Storing the sampled measured values ​​in a buffer memory (203), wherein a size of the buffer memory (203) corresponds to the time range specified by the measurement window (130). [9] Method (100) according to claim 7 or 8, wherein the detection (102) of the falling edge (111) is based on a comparison of the filtered charging control signal (302) with the predetermined threshold value (140); wherein the predetermined threshold value (140) corresponds to a signal level between a positive voltage level (110a) and a negative voltage level (110b) of the charging control signal (110). [10] Device (300) for determining the voltage level of a charging control signal (110) for charging systems of electric vehicles, wherein the charging control signal (110) is a pulse-width modulated PWM signal with an adjustable pulse width (120), the device (300) comprising: an analog-to-digital converter (303) for detecting (101) measured values ​​(304) of the charging control signal (110); a buffer memory (203) for storing the acquired measured values ​​over a predetermined time range; a comparator (305) for detecting (102) a falling edge (111) of the charging control signal (110) based on the charging control signal (110) and a predetermined threshold value (140); and a processor (307) which is designed, upon detection (102) of the falling edge (111) of the charging control signal (110), to determine (103) a voltage level (113) of the charging control signal (110) based on at least a first part (115) of the measured values ​​(304) stored in the buffer memory (203) which were acquired before the falling edge (111) of the charging control signal (110).

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