Method and test device for testing power amplifiers for broadband high-frequency powerline communication

Abstract

Method for testing power amplifiers (545), in particular of electric vehicles or charging stations, for broadband high-frequency powerline communication via cables (300, 310, 320), comprising the steps: a) connecting the power amplifier (545) to be tested and a test device with one of the cables (310), b) Determine a termination impedance of the cable on or in the test fixture c) sampling a broadband radio-frequency signal transmitted on one of the cables (310) from the output stage to be tested, which is generated with a constant spectral power density in each frequency range (3050) of the broadband radio-frequency signal used for radio-frequency communication, according to the Nyquist-Shannon sampling theorem at the end of one of the cables (310) associated with the test device (100) and detecting at least one time transient, both during the transmission of the broadband radio-frequency signal, d) determining a spectral power density spectrum (3100) associated with one of the cables (310) and the specified termination impedance based on the at least one time transient detected using the one of the cables (310) for the specified termination impedance e) evaluating the one or more frequency ranges (3050) of the spectral power density spectrum used for communication, f) wherein in step b) the termination impedance is set to a value which is adapted to an impedance of the cable (300) and in step e) during the evaluation it is checked whether deviations occur in one or more areas of the spectral power density spectrum compared to a spectral power density spectrum which is expected or detected during communication with an output stage which is correctly adapted with regard to the impedance, and g) outputting a result of the evaluation which comprises at least one indication of the correctness or incorrectness of the impedance matching of the output stage (545) to be tested.

Description

[0001] The invention relates to testing devices and methods for testing an output stage, in particular of electric vehicles or charging stations, for broadband high-frequency powerline communication via different, in particular pluggable, cables.

[0002] Electric vehicles typically have at least one electrical storage device in the form of a battery, which stores electrical energy to power the electric vehicle's electric drive motor. To recharge this storage device, the electric vehicle is connected to the charging station using a charging cable. The charging cable, at least on the electric vehicle side, is usually equipped with a charging cable plug that plugs into a charging cable port, also known as a charging cable socket.

[0003] Since electric vehicles (EV) and charging stations (EVSE - electric vehicle supply equipment) are designed differently, for example with regard to the charging current that the charging stations can provide and with which the electric vehicles can be charged, communication between the electric vehicle and the charging station is carried out on a pair of wires of the charging cable.

[0004] For charging cables with so-called TYPE 2 plugs, for example, the cables labeled control pilot (CP - control pilot) and protective earth (PE - protective earth) are used.

[0005] It is known, for example, to carry out pulse width modulation with a square-wave voltage signal in order to signal a maximum charging current with which the electric storage device of the electric vehicle can be charged.

[0006] To enable the exchange of other data, and especially more data, such as automated charging current billing, powerline communication with a broadband radio-frequency signal is also carried out on the same wire pair. The radio-frequency signal is modulated, for example, using an orthogonal frequency division multiplexing (OFDM) technique.

[0007] The information is transmitted via a large number of frequency channels of the broadband radio frequency signal.

[0008] In order for powerline communication to run smoothly in the frequency range from 1.8 megahertz to 30 megahertz, for example, it is necessary that the power amplifiers and the cable used for transmission, the charging cable, are matched to each other in terms of their impedances over the frequency range used.

[0009] In general, the following complex relationship applies to the required termination impedance ZE of a power amplifier to be tested: ZE=ZA⋅((coshγ⋅l+ZLZA⋅sinhγ⋅l))((coshγ⋅l+ZAZL⋅sinhγ⋅l)) where ZL is a line impedance, ZL is a load impedance, y is the wave propagation constant of the line, l is the line length.

[0010] If the line impedance and the terminating impedance of the power amplifier are matched for the useful frequency range, ZE = ZA applies in this range.

[0011] If impedance matching is not correct in an output stage, reflections will occur for individual or multiple frequencies or frequency ranges. These reflections can lead to resonances and cancellations on individual or multiple frequency channels. Information transmission on these frequency channels is then disrupted. This interference can lead, for example, to a charging process not being able to begin or being aborted prematurely.

[0012] Typically, OFDM-modulated broadband powerline communication takes place on the charging cable's pair of wires in the frequency range from 1.8 MHz to 30 MHz at 1.2 volts peak-to-peak (Vpp), using 1,150 channels spaced at 24.124 kHz (kilohertz). This high-frequency signal is superimposed on a pulse-width modulated (PWM) square wave signal with a frequency of 1 kHz and voltages ranging from plus 12 V (volts) to minus 12 V.

[0013] The methods known from the state of the art for checking the correct impedance matching over the relevant frequency range fail due to the two different transmission methods used simultaneously.

[0014] DE 101 00 181 A1 describes a method for evaluating interference voltage in a power line communication (PLC) system. An impedance stabilization network is connected to a coupling agent, and a measurement signal is measured at the coupling agent's output. Thus, a measurement signal to be measured is specifically introduced into the system.

[0015] DE 10 2011 105 392 B4 describes a method for adapting the transmission characteristics of a signal to be transmitted via a PLC, whereby a measuring signal to be coupled in is also used, the impedance of which is determined.

[0016] From DE 10 2013 214 825 A1 a method is known for determining the physical properties of a signal to be transmitted via a PLC, in which the spectral distribution of the energy density of the signal is measured.

[0017] US 2022 / 0 163 603 A1 proposes the use of an impedance network, which is integrated, for example, into a charging cable connector, which attenuates a specific frequency. The document proposes testing the correct connection to the charging cable by determining whether this specific frequency is correctly attenuated.

[0018] US 2016 / 0 112 135 A1 proposes a transmission device for reducing transmission losses, comprising a transmitter that generates a first electromagnetic wave for data transmission. A coupler couples the first electromagnetic wave to a single-wire transmission medium having an outer surface to form a second electromagnetic wave that is guided to propagate along the outer surface of the single-wire transmission medium via at least one guided wave mode comprising an asymmetric or non-fundamental mode with a lower cutoff frequency.A carrier frequency of the second electromagnetic wave is chosen to be within a limited range of the lower cutoff frequency so as to concentrate a majority of the electric field within a distance from the outer surface that is less than half the largest cross-sectional dimension of the single-wire transmission medium and / or to reduce propagation losses.

[0019] US 2017 / 0 018 830 A1 describes a system that performs method steps that detect signal degradation of guided electromagnetic waves that are bound to a transmission medium without using an electrical return path, wherein the guided electromagnetic waves have a non-optical frequency range, and comprising adjusting an alignment of at least a portion of the fields of the guided electromagnetic waves to mitigate the signal degradation.

[0020] The invention is based on the technical object of specifying an improved method and a device as well as a system with which an output stage, in particular a remote output stage connected or to be connected via a cable, can be checked for correct impedance matching for signal transmission.

[0021] The object is achieved according to the invention by a method having the features of patent claim 1, a testing device having the features of patent claim 9, and a system having the features of patent claim 14. Advantageous embodiments of the invention emerge from the subclaims.

[0022] The invention is based on the idea of ​​evaluating a broadband high-frequency signal, such as that used in powerline communication, which is typically generated at the beginning of a powerline communication and transmitted via a cable from the power amplifier to be tested. The transmitted signal is sampled to detect at least one time transient. Based on this at least one time transient, a power spectral density spectrum is determined, which is also referred to as power spectral density (PSD) in the prior art. The power spectral density spectrum is the spectral power density of the transmitted signal plotted against frequency, which is transmitted per frequency bandwidth. By definition, the frequency bandwidth here must be selected to be infinitesimal.In practice, however, a power density spectrum is usually specified with values ​​related to a preselected finite bandwidth, a resolution bandwidth (RBW). The spectral power density can also be mathematically understood as the Fourier transform of the autocorrelation function of a time-dependent transmitted signal. Therefore, the spectral power density spectrum is also referred to as the autopower spectrum. By evaluating individual frequency ranges of the spectral power density spectrum, i.e., the PSD spectrum, it can be determined whether or not interference due to reflections that disrupt communication occurs in these sections.

[0023] In particular, a method for testing power amplifiers, in particular of electric vehicles or charging stations, for broadband high-frequency powerline communication via cable is created, comprising the steps: a) Connect the power amplifier to be tested and a test device with one of the cables, b) Determine a termination impedance of the cable on or in the test fixture c) sampling a broadband radio-frequency signal transmitted on one of the cables from the power amplifier to be tested, which is generated with a constant spectral power density in each frequency range of the broadband radio-frequency signal used for radio-frequency communication, in accordance with the Nyquist-Shannon sampling theorem at the end of one of the cables associated with the test device and detecting at least one time transient, both during the transmission of the broadband radio-frequency signal, d) Determining a spectral power density spectrum associated with one of the cables and the specified termination impedance based on the at least one time transient acquired using the one of the cables for the specified termination impedance e) evaluating the one or more frequency ranges of the spectral power density spectrum used for communication, f) wherein in step b) the termination impedance is set to a value that is adapted to an impedance of the cable and in step e) during the evaluation it is checked whether deviations occur in one or more areas of the spectral power density spectrum compared to a spectral power density spectrum that is expected or detected during communication with a correctly impedance-adapted output stage, and g) Outputting a result of the evaluation which includes at least an indication of the correctness or incorrectness of the impedance matching of the power amplifier to be tested.

[0024] If an increase and / or decrease in the spectral power density is detected in the frequency ranges used for transmitting information in powerline communication compared to the expected spectral power density (possibly based on a bandwidth resolution), it can be concluded that a mismatch exists. If the spectral power density decreases too sharply in more than 40% of the entire transmission spectrum, it can be assumed that communication cannot proceed without interference. In areas of excessive increase, electromagnetic compatibility regulations may be violated.

[0025] Accordingly, a test device for testing power amplifiers, in particular of electric vehicles or charging stations, for broadband high-frequency powerline communication via cable, comprising: a cable connector for connecting one end of one of the cables, which is connected at another end to the power amplifier under test; a cable termination device connected to the cable connection, for determining a termination impedance of the line connected to the cable connection on or in the testing device; a sampling device connected to the cable connection for sampling the broadband radio frequency signal transmitted on one of the cables according to the Nyquist-Shannon sampling theorem and detecting at least one time transient, both during the transmission of the broadband radio frequency signal; a calculation unit for determining a spectral power density spectrum associated with one of the cables based on the at least one time transient detected using one of the cables, and an evaluation device for evaluating one or more frequency ranges of the spectral power density spectrum, wherein during the evaluation it is checked whether deviations occur in one or more frequency ranges of the spectral power density spectrum compared to a spectral power density spectrum which is expected or detected during communication with an output stage which is correctly matched with regard to impedance, and an output device which outputs a result of the evaluation which outputs at least one indication about the correctness or incorrectness of the impedance matching of the output stage to be tested.

[0026] A system comprises an embodiment of the described test device and a set of cables of different lengths.

[0027] The result of the test is a statement as to whether the power amplifier to be tested offers a guarantee that, when used with a cable that normally corresponds to the state of the art, it will enable undisturbed communication due to correct impedance matching or whether operational disturbances are to be expected due to incorrect impedance matching.

[0028] The evaluation can be carried out without concrete knowledge of a spectral power density spectrum of a powerline communication with output stages correctly matched in terms of impedance. Fluctuations above a threshold value do not occur with correctly matched output stages. In one embodiment, it is therefore provided that the checking in method step e) whether deviations occur in one or more areas of the spectral power density spectrum compared to a spectral power density spectrum that is expected or detected during communication with an output stage correctly matched in terms of impedance comprises checking whether fluctuations in the spectral power density above a threshold value occur in a determined spectral power density spectra.

[0029] Since the occurrence of reflections and resonances depends on the length of the cable used, a preferred development provides that the transmission of the high-frequency signal, its sampling, and determination of the spectral power density spectrum assigned to the cable is also carried out for another cable that has a different length than the one initially selected. If the power amplifier is correctly matched in terms of impedance, there are no differences in the spectral power density spectrum that depend on the respective assigned cable length. This means that the spectral power density spectra for the different cable lengths used are the same within the framework of statistical variations. The evaluation can thus be carried out by checking whether the spectral power density spectra determined for the different cable lengths show deviations at least in individual frequency ranges.Ideally, the difference is zero within tolerance limits over the entire frequency range used for broadband powerline communication, taking into account the change in attenuation caused by the known attenuation of the cable.

[0030] In one embodiment, it can therefore be concluded that the impedance has been correctly adapted if the determined difference between the spectral power density spectra for cables of different lengths is zero or if the spectral power density spectra are not different at least within a tolerance limit.

[0031] The evaluation can be simplified by evaluating mean values ​​of the spectral power density spectra.

[0032] One embodiment therefore provides that steps a) to d) are additionally carried out using at least one other of the cables, wherein the at least one other of the cables has a length that differs from the at least one of the cables, and the terminating impedance in step b) is set identically to when steps a) to d) are carried out for the at least one of the cables, and that the evaluation of step e) comprises calculating an average spectral power density for each of the determined spectral power density spectra over the frequency ranges used for the power line communication, comparing the average values ​​pairwise for spectral power density spectra that are recorded for different cable lengths but the same terminating impedance, and classifying the power amplifier to be tested as incorrectly tuned if deviations above an average threshold value occur.

[0033] One embodiment provides that steps a) to d) are additionally carried out using at least one other of the cables, wherein the at least one other of the cables has a length that differs from the at least one of the cables, and the terminating impedance in step b) is set identically to when steps a) to d) are carried out for the at least one of the cables, and that the evaluation of step e) comprises calculating an average spectral power density over the frequency ranges used for the power line communication for each of the determined spectral power density spectra, comparing the average values ​​pairwise for spectral power density spectra that are recorded for different cable lengths but the same terminating impedance, and classifying the power amplifier to be tested as incorrectly tuned if deviations above an average threshold value occur.

[0034] By extending the method, even the impedance of the power amplifier under test, which is not correctly tuned, can be estimated. For this purpose, it is advantageous to perform the sampling and evaluation not only for different cable lengths with the same termination on or in the test fixture, but also for different terminations of the line. This means that both the cable length and the termination impedance of the line are varied. Transmissions from the power amplifier under test are sampled and evaluated for different cable lengths for at least two different terminations of the line on or in the test fixture with regard to impedance.In this process, a single transmission is sampled and evaluated, transmitting a broadband high-frequency signal exclusively from the power amplifier under test, whose spectral power is evenly distributed across the frequency range used for powerline communication. It turns out that the difference in the mean values ​​attributable to the change in cable length is essentially independent of the selected line termination in or on the test device. This difference, which is determined from mean values ​​for different cable lengths but the same line termination, is a measure of the impedance of the incorrectly matched power amplifier under test, at least if it is equal to a difference determined for a different line termination in terms of impedance.

[0035] If a difference, which is calculated from two average values ​​of the spectral power density for different cable lengths but the same line termination, occurs above a predefined tolerance threshold, it has been shown that, to a good approximation, the impedance of the output stage Z E for the respective frequency is given by the following equation: ZE=Difference×ZA where the difference from the physical unit dBm / Hz is to be converted into a factor and Z A the impedance of the cable used.

[0036] According to a preferred embodiment of the method, method steps a) to d) are therefore carried out for a plurality of cables with a different length, wherein steps a) to d) are carried out at least twice for each of the plurality of cables, wherein in method step b) different terminating impedances are determined, and during the evaluation in method step e) the differences in the mean spectral power densities of the spectral power density spectra determined for different cable lengths but identical terminating impedances are compared for at least two of the differently determined terminating impedances, and if these differences in the mean values ​​are equal within a tolerance but different from zero, the terminating impedance of the power amplifier to be tested is estimated on the basis of the difference by converting the difference into a factor and multiplying it by the impedance of the cables.

[0037] In a preferred embodiment, the terminating impedance is set to a value that is adapted to an impedance of the cable by terminating a line connected to the corresponding one of the cables in or on the test device via an ohmic terminating resistor whose value corresponds to the impedance of the line of the cable, or by connecting the corresponding one of the cables via the line to another output stage circuit of a high-frequency transmitting and receiving unit that is correctly tuned with regard to the impedance over the entire frequency range used for power line communication and is attenuated with regard to its own transmission during reception of the high-power signal of the output stage to be tested.

[0038] The cables used preferably comprise a two-wire cable for powerline communication. A preferred embodiment of the system thus provides for the cables to be provided with two-wire cables for powerline communication, with an impedance of 100 ohms. Accordingly, a 100 ohm resistor is preferably used as a termination resistor matched to the cable impedance.

[0039] One embodiment of the test device provides that the cable termination device comprises an ohmic terminating resistor which corresponds to the impedance of the cable.

[0040] If different termination impedances are required, a termination impedance matched to the cable impedance is preferably used. A different impedance is preferably selected with a large impedance difference compared to the cable impedance. An infinite or nearly infinite impedance is preferred. This can be adjusted and determined by interrupting, i.e., opening, the line connected to the corresponding cable in the test fixture in or on the test fixture. For example, a connection can be established with an open line.

[0041] A preferred embodiment therefore provides that the different impedances determined in method step b) comprise an infinite impedance, which is determined by opening the line connected to the corresponding one of the cables in or on the test device.

[0042] In one embodiment of the testing device, the cable termination device may comprise a switching device for terminating the line in or on the testing device via the terminating resistor corresponding to the impedance of the cable, or for switching it to an open state to simulate an infinite impedance, or for connecting it to a correctly impedance-matched output stage of a radio-frequency transmitting and receiving unit of a powerline communication device in order to achieve an optimal adaptation of the cable termination.

[0043] Embodiments can only include two of the three possibilities presented here.

[0044] For example, you can switch between an ohmic terminating resistor and an open line.

[0045] The reliability of the determined result can be further increased by providing, in one embodiment, that the iterated method steps are carried out for more than two cables, each of which has a different length.

[0046] Likewise, further reliability improvement can be achieved if the iterated process steps are performed for at least three termination impedances. Preferably, an ohmic termination resistor matched to the cable impedance, an open line for infinite resistance, and a connection to a correctly matched powerline communication device's output stage are used as three different termination impedances.

[0047] An optimal test is possible if the sampling and evaluation is carried out for a termination of the cable which is formed via a correctly impedance-matched output stage of a powerline communication device by connecting this to the line which is connected to the cable in the test device and to which the sampling device is coupled.

[0048] The evaluation device is adapted accordingly to carry out these improved evaluation procedures.

[0049] It should be emphasized here that the broadband high-frequency signal required for the test from the power amplifier under test, which is generated and transmitted with a constant spectral power density, is usually generated as part of a powerline communication protocol. Many charging stations transmit such a broadband high-frequency signal, usually for a limited time, at regular intervals to facilitate the initiation of powerline communication.

[0050] In other embodiments, it may be provided that a signal, which may also be referred to as an initiation signal, is transmitted to the output stage to be tested for a broadband high-frequency powerline communication in order to trigger the transmission of the broadband high-frequency signal, which is generated with a constant spectral power density in each frequency range of the broadband high-frequency signal used for the high-frequency communication.

[0051] In a preferred embodiment of the device, the test device is provided as part of a powerline communication device. The initiation signal can then be simply generated by the powerline communication device. To avoid interfering with the measurement of the response of the power amplifier under test, the power amplifier emitting the initiation signal is subsequently attenuated, i.e., this prevents it from generating high-frequency signals and feeding them onto the line and, via this, onto the corresponding cable through which the connection to the power amplifier under test is established.

[0052] The powerline communication device and the test fixture can be stand-alone units or an integrated one-piece unit. If the test fixture is part of a powerline communication device, it can also be implemented in an electric vehicle or charging station.

[0053] The signal with uniform spectral power density required for sampling can be generated by transmitting suitable information that ensures the most uniform distribution of the spectral power density possible over the entire broadband radio frequency range.

[0054] An orthogonal frequency division multiplexing method is particularly preferred as the modulation method. In this method, the information is transmitted on equally spaced frequency channels that are evenly distributed across the frequency range used for communication.

[0055] In another embodiment, the high-frequency signal is generated with a uniformly distributed spectral power density within a resolution bandwidth used to calculate the spectral power density spectrum according to method step d). This means that the same transmission power is emitted in the transmission signal in frequency sections whose width corresponds to the resolution bandwidth for generating the spectral power density spectrum.

[0056] This is achieved, for example, in an orthogonally frequency-division modulated signal when the same information is transmitted in each of the equally spaced frequency channels used, which corresponds to a maximum radiated transmission power in the corresponding frequency channel.

[0057] The output device can, for example, be a display or an acoustic device that emits an acoustic signal indicating correct or incorrect matching. If the deviation in the impedance matching is determined based on the difference between the determined spectral power density, the output device preferably comprises a digital display device or an analog display device. In other embodiments, the output device can alternatively and / or additionally be designed as an interface via which a digital and / or optical signal is output in which the result of the evaluation is encoded. In particular, this can be a network interface, for example for wireless communication via WLAN or Bluetooth.

[0058] A testing device, together with one, preferably several, cables of different lengths, forms a system. This results in a system for testing power amplifiers, particularly those of electric vehicles or charging stations for broadband, high-frequency powerline communication, with regard to their impedance matching.

[0059] The invention is explained in more detail below with reference to a drawing. Herein: Fig. 1 a schematic representation of a test device for testing an output stage for its impedance matching; Fig. 2 a schematic flow diagram of a method for testing an output stage for powerline communication with regard to impedance matching; Fig. 3 a schematic representation of a power density spectrum of a correctly matched power amplifier; Fig. 4 a spectral power density spectrum of a correctly tuned power amplifier, where transmission is possible over a cable twice as long as in the embodiment according to Fig. 3 is used; Fig. 5 a spectral power density spectrum corresponding to that of the Fig. 3, which is recorded with a correctly tuned power amplifier, but with an “open” termination resistor on or in the test fixture; Fig. 6 a spectral power density spectrum corresponding to that of the Fig. 4, which is recorded with a correctly tuned power amplifier, but with an “open” termination resistor on or in the test fixture; Fig. 7 a spectral power density spectra analogous to that of the Fig. 3, where the power amplifier under test is not correctly matched in terms of impedance, but the cable is correctly terminated on the test fixture; Fig. 8 a spectral power density spectra analogous to that of the Fig. 4, where the power amplifier to be tested is not correctly matched with regard to impedance, but the cable is correctly terminated on the test device and the cable is twice as long as in the Fig. 3, Fig. 5 and Fig. 7 is; Fig. 9 a spectral power density spectra analogous to that of the Fig. 5, where the power amplifier under test is not correctly matched in terms of impedance and the cable is open on or in the test fixture; and Fig. 10 a spectral power density spectra analogous to that of the Fig. 6, where the power amplifier to be tested is not correctly matched with regard to impedance and the cable is open on or in the test device, the cable being twice as long as in the Fig. 3, Fig. 5, Fig. 7 and Fig. 9 is.

[0060] In Fig. 1 schematically illustrates a test device 100 for testing an output stage 545 with regard to impedance matching for powerline communication. The test device can, for example, be a separate test device or also be part of an electric vehicle 10 or another device. In the example shown, the device 100 is part of an electric vehicle 10. The output stage 545 to be tested of a powerline communication device 530 is part of a radio-frequency transmitting and receiving unit 540. This is designed to carry out powerline communication with a broadband radio-frequency signal. For example, the powerline communication is carried out in the frequency range from 1.8 MHz (megahertz) to 30 MHz and with an orthogonal frequency division multiplex modulation (OFDM) method. Frequency bands in this range can be omitted.

[0061] The powerline communication device 530 is in turn part of a communication device 520, via which, in addition to the powerline communication, a low-frequency communication with pulse width modulation is also carried out.

[0062] The power amplifier 545 to be tested could also be part of another communication device of an electric vehicle or another device that is part of a charging infrastructure for electric vehicles, for example.

[0063] The test device 100 and the power amplifier 545 are connected to one another via a charging cable 310 of several charging cables 300 of different lengths. The cables 300 preferably comprise a two-wire line 305 for powerline communication as well as low-frequency communication. The cables may comprise additional lines for charging. Here, for example, the charging cables 300 are all designed for the same impedance, for example, 100 Ω, and have an attenuation of approximately -0.33 dB / m.

[0064] The test device 100 comprises a cable connection 110 to which the charging cable 310 is terminated.

[0065] To check whether the output stage 545 is correctly tuned in terms of impedance, the test device 100 has a sampling device 150. For this purpose, the sampling device 150 is coupled to a line 120 connected to the cable connector 110. The sampling device 150 is capable of sampling the broadband radio-frequency signal of the radio-frequency transmitting and receiving unit 40 transmitted via the charging cable 310 while the broadband radio-frequency signal is being transmitted via the charging cable 310. Sampling is performed at a sampling rate that is at least twice as high as the highest frequency occurring in the broadband radio-frequency signal for information transmission. During sampling, a time transient is detected.

[0066] Whether reflections occur on the cable 310, for example, the two-wire line 305 of the cable 310, depends on the tuning of the output stage 545 under test and the termination of the cable 310 or the line 120 connected thereto in the test device 100. For this purpose, the test device has a cable termination device 130 to determine the termination impedance in or on the test device. In the illustrated embodiment, the cable termination device 130 comprises an ohmic termination resistor 145. This is matched to the line impedance of the cable 300. If these each comprise a two-wire line 305 for communication, which has a line impedance of 100 ohms, an ohmic termination resistor 145 of 100 ohms is matched to the line impedance.

[0067] If the cable 310 is terminated with the ohmic terminating resistor 145 during the measurement in the test device 100, adjusted to the impedance of the line impedance, no reflections may occur on the cable 310 if the output stage 545 to be tested is correctly adjusted with regard to the impedance.

[0068] The time transient data obtained during sampling are used in a calculation unit 170 to calculate a spectral power density spectrum. Typically, the calculation is performed based on a specified frequency bandwidth, a resolution bandwidth (RWB). For example, if the powerline communication uses frequencies in the range of 1.8 MHz to 30 MHz, a resolution bandwidth of 10 kHz is selected for the evaluation.

[0069] The powerline communication of the electric vehicle charging infrastructure uses an orthogonal frequency division multiplexing (OFDM) method, which uses 1,150 carriers spaced at 24.124 kHz. These are distributed across the frequency range from 1.8 MHz to 30 MHz. The voltage capacitively coupled to the charging cable 310 is nominally 1.2 volts peak-to-peak (Vpp). In addition, low-frequency communication is carried out via the charging cable with a pulse-width modulated signal, which uses a square wave of 1 kHz with a voltage of + / -12 V. The components involved and required for this are not shown separately here for the sake of simplicity.

[0070] If no interference occurs due to incorrect impedance matching of the 545 power amplifier, the spectral power density spectrum 3100-1 has a nearly uniformly constant value over a frequency range 3040 used for high-frequency communication. Such a power density spectrum is Fig. 3 is shown schematically. The power spectral density 3010 in dBm / Hz is plotted against the frequency 3020. The power spectral density (PSD) is constant across the frequency ranges 3050 used for powerline communication. The visible gaps 3060 are omitted in the frequency range, as these are reserved for other communication not carried out on the cable. For powerline communication of the type described above, in which 250 nW of radio frequency power is used per carrier, for example, determining the power density spectrum based on a resolution bandwidth (RBW) of 10 kilohertz (kHz) results in a value of approximately -35 dBm RBW 10 kHz.

[0071] The test device 100 comprises an evaluation device 200, in which the thus determined spectral power density spectrum is evaluated. The power amplifier 545 to be tested is considered to be correctly matched with regard to impedance if the spectral power density spectrum corresponds to the expected spectral power density spectrum. For this purpose, it can be compared, for example, with a spectral power density spectrum stored in a memory 210 of the evaluation device 200. Alternatively or additionally, peaks and / or valleys / dips in the spectral power density spectrum can be determined.

[0072] If peaks or dips occur in the spectral power density spectrum, this indicates that the power amplifier 545 being tested is not correctly tuned in terms of impedance. The result of the evaluation is output via an output device 280.

[0073] The output device 280 can be a display in digital or analog form. Alternatively, an acoustic output can also be provided. This can be provided in addition to a graphical or visual output. The output device can also be an interface for transmitting the evaluation result to another device. Any known interfaces, both wired and wireless, are suitable for this purpose.

[0074] To rule out the possibility that the evaluation is dependent on a specific cable length of the charging cable 310, in a preferred embodiment, the cable 310 with one length is replaced by another cable 320 with a different length, which differs from the one length. A high-frequency signal is again transmitted from the high-frequency transmitting and receiving unit 540 to the output stage 545 under test, and during this time, a sample is taken by the sampling device 150, and another time transient is recorded. A further spectral power density spectrum is determined by the calculation unit 170.

[0075] Fig. 4 shows a spectral power density spectrum 3100-2, which is also transmitted from a correctly tuned power amplifier 545, via a cable 320 that is twice as long as the cable 300, which is also terminated in the test device via the ohmic terminating resistor.

[0076] This spectral power density spectrum 3100-2 also shows no pronounced peaks or dips in the spectral power density 3010.

[0077] In contrast, the spectral power density spectra 3100-3 of the Fig. 5 and 3100-4 of the Fig. 6 significant fluctuations 3070 of the power spectral density 3010 in the frequency ranges used for communication 3050. The power spectral density spectrum 3100-3 of the Fig. 5 corresponds to the spectral power density spectrum 3100-1 of the Fig. 3. The spectral power density spectrum 3100-4 of the Fig. 6 corresponds to the spectral power density spectrum 3100-2 of the Fig. 4. All these spectral power density spectra 3100-1 to 3100-4 are generated with a correctly tuned 545 power amplifier.

[0078] In contrast to the power spectral density spectra 3100-1 and 3100-2, which are each recorded with a termination resistor correctly adapted to the impedance of the respective cable 310, whose lengths, however, differ, the power spectral density spectra 3100-3 and 3100-4 are recorded with an “open end” of the cable.

[0079] For this purpose, the cable termination device 130 comprises a switching device 140. This can optionally connect the line to the ohmic termination resistor 145 or to an open line end 146. Alternatively, the switching device 140 can be switched to an open state to open the line 120.

[0080] In Fig. 5 and Fig. 6, peaks 3080 due to reflections and overall strong fluctuations 3070 of the spectral power density are visible.

[0081] However, it turns out that the power density spectra 3100-1, 3100-2 and 3100-3, 3100-4 recorded with the same cable terminations each have the same mean value of the power density. For example, the power density spectra 3100-1, 3100-2 have a mean value of -52 dBm and the power density spectra 3100-3, 3100-4 have a mean value of -43 dBm.

[0082] Fig. 7 to 10 show the comparable spectral power density spectra 3100-5 to 3100-8, which result from a power amplifier 545 under test that is not correctly matched with regard to impedance.

[0083] It can be seen that in the spectral power density spectra 3100-5 and 3100-6, which are recorded with an ohmic terminating resistor 145 in the test device 100, significant fluctuations 3070 of the spectral power density 3010 occur. Also visible are peaks due to reflections 3080. The mean value of the spectral power density spectrum 3100-5, for example -43 dBm, differs from the mean value of the spectral power density spectrum 3100-6, which is recorded with twice the cable length, for example -46 dBm, by 3 dBm.

[0084] The two analog spectral power density spectra 3100-7 and 3100-8, each recorded with an open cable 310, ie the open line 120 in the test device 100, also show, as expected, strong fluctuations 3070, but also the same difference of 3 dBm between the mean values ​​-37 dBm and -40 dBm.

[0085] Based on this difference, the impedance deviation of the 545 power amplifier under test can be determined. The impedance of the 545 power amplifier is the product of the difference, specified in dBm / Hz, converted into a factor multiplied by the impedance of the charging cable used. The conversion of the decibel value into a factor F is performed as is usual for converting energy or power quantities: F=10D10, where D is the difference in dBm / Hz and 0 dBm / Hz is associated with the factor 1.

[0086] The deviation of 3dBm corresponds to a factor of 2. Thus, it can be estimated: Z E =2·Z A , where Z A = 100 Ohm. The incorrectly tuned power amplifier to be tested therefore has an estimated impedance of about 200 Ohm, Z E = 2·100 Ohm = 200 Ohm.

[0087] Additionally, via the switching device 140 of the cable termination device 130, the line 120 can also be connected to another powerline communication device 40's output stage 45, correctly matched in terms of impedance. This termination of the cable 310 thus represents a third termination option. With this termination, corresponding spectral power density spectra can also be acquired. However, it is necessary to operate the other output stage 45 in such a way that it does not emit a high-frequency signal itself during the sampling of the high-frequency signal of the output stage 545 under test and is correspondingly attenuated.

[0088] The further powerline communication device 30 is part of a further communication device 20 which is arranged, for example, in an electric vehicle 10.

[0089] Terminating line 120 and cable 310 via the other correctly tuned power amplifier 45 can be advantageous for initiating transmission of the high-frequency signal from the power amplifier 454 under test. Transmissions are typically used at the beginning of a transmission according to a transmission protocol. In this case, a broadband high-frequency signal is transmitted, often iteratively, whose spectral power density is constant across the entire frequency range used, i.e., often across several spaced frequency ranges.

[0090] In Fig.2, the method 1000 for testing an output stage with respect to impedance matching is shown schematically again. First, one of the cables, which are preferably charging cables, is selected 1010. A cable with a certain length is selected. Subsequently, the output stage to be tested is connected 1020 to the device for testing the output stage. A terminating impedance for the cable is set 1030 in or on a test device. Preferably, initially, this is set to a value that corresponds to the cable's line resistance. A broadband high-frequency signal generated by the high-frequency transmitting and receiving unit of the powerline communication device and coupled to the charging cable by the output stage to be tested is sampled 1040 during transmission via the charging cable. This is done in accordance with the Nyquist-Shannon sampling theorem. A time transient is detected 1050.

[0091] From the time transient recorded for one cable with one length, a power spectral density spectrum (PSD spectrum) is determined 1060.

[0092] In the simplest embodiment, an evaluation is performed 1100. The spectral power density spectrum determined from the time transient is examined 1120 for deviations from an expected spectral power density spectrum in at least one frequency range, preferably in several frequency ranges. If, for example, peaks or dips are detected in a specific frequency range, the power amplifier under test is classified as incorrectly tuned. If, however, the spectral power density spectrum corresponds to expectations in the one or more frequency ranges examined, the power amplifier is classified as correctly tuned with regard to impedance. The result is output 1200.

[0093] In an improved embodiment, after detecting the time transient and determining the spectral power density spectrum for one charging cable with one length, a check is made to determine whether another charging cable with a different length is present 1070. If this is the case, the already determined spectral power density spectrum is saved for later evaluation 1080. Then, when one of the cables 1010 is selected again, another of the charging cables with a different length is selected. The method steps of connecting the power amplifier to be tested to the device for testing with the other charging cable 1020, defining the cable termination 1030, sampling the high-frequency signal 1040, and detecting the time transient 1050 are then carried out again for the other charging cable with the different length. The cable termination is defined identically to the first cable.The corresponding spectral power density spectrum is then calculated for the second time transient now recorded (1060). During the subsequent evaluation, this spectral power density spectrum is also checked for any peaks or dips. Additionally or alternatively, an average value is determined for each of the two determined spectral power density spectra (1130). These are compared (1140). If these are equal, it can be assumed that the power amplifier under test is correctly tuned.

[0094] The evaluation can be improved even further by carrying out method steps 1010 to 1080 for several cable lengths, in particular two cable lengths, and also for several different cable terminations in the test device. In one embodiment, this is checked in method step 1065. Here, it is checked whether, for the cable measured so far, at least two different, preferably three different cable terminations have already been used with regard to the impedance to determine a spectral power density spectrum. If this is not the case, the method steps of storing the last determined power density spectrum 1080, determining the termination impedance 1030, sampling the high-frequency signal 1040 of the power stage to be tested and detecting a time transient 1050 as well as determining the spectral power density spectrum 1060 are iterated.Evaluation steps 11xx can also be carried out after the acquisition of one or more of the spectral power density spectra or at the end of the procedure.

[0095] In one of the described variants of the method, if multiple cable lengths and terminations are used, the spectra for the various cable terminations are first recorded and determined, and then the cable is replaced. However, it can also be performed in a different order.

[0096] If differences are detected during the mean value evaluation for different cable lengths but the same cable termination, the impedance of the power amplifier under test can be estimated. 1150. This evaluation is preferably verified by checking whether the mean value differences for each pair of cables are equal within a specified tolerance for two different cable terminations, using different cables. If this is the case, the impedance estimate of the power amplifier under test can be considered reliable.

[0097] In some embodiments, the estimated impedance is only determined or output if the mean differences for at least one cable pair with cables of different lengths for two different cable terminations, i.e., termination impedances in or on the test device, are equal to each other within the specified tolerance. Preferably, one termination impedance is selected as infinite, which is achieved by an open line 146. The other impedance is preferably selected to match the cable impedance and is implemented by terminating via an ohmic termination resistor. Alternatively, a tuned output stage of a powerline communication device can be used.

[0098] The calculation unit and the evaluation device are preferably implemented as a program-controlled processing unit. Alternatively, electronic circuits can be used, which, in particular, calculate the spectral power density spectrum.

[0099] It will be understood by those skilled in the art that only exemplary embodiments are described here. The features of the various embodiments can be used in any combination to form other embodiments. List of reference symbols 10 electric vehicles 20 Communication device 30 Powerline communication device 40 High-frequency transmitting and receiving unit 45 power amplifier 100 Test device for testing a power amplifier 110 Cable termination 120 line 130 Cable termination device 140 switching device 145 ohmic termination resistor 146 open line 150 scanning device 170 Calculation unit 200 evaluation device 210 storage 220 Comparison device 280 Output device 300 cables 305 Two-wire cable 310 a cable of a length 320 other cable of different length 500 charging stations 520 Communication device 530 Powerline communication device 540 high-frequency transmitting and receiving unit 545 power amplifier 1000 methods for testing power amplifiers 1010 Select one of the cables or another of the cables with a different length 1020 Connecting the power amplifier to the testing device 1030 Setting the termination impedance 1040 Sampling of the transmitted high-frequency signal 1050 Capturing a time transient 1060 Determining a spectral power density spectrum 1065 Has the currently connected cable been used with different impedance terminations? 1070 Check if cables of different length are present 1080 Saving the determined spectral power density spectrum 1100 Evaluation of the spectral power density spectra 1120 Checking for deviations from an expected / correct power spectral density spectrum 1130 Determine the mean value of the spectral power density spectra 1140 Compare means / calculate differences 1150 Calculate the estimated impedance of the power amplifier to be tested 1200 Output of the result(s) of the evaluation 3010 spectral power density 3020 frequency 3040 frequency range 3050 used frequency ranges 3060 gaps 3070 fluctuations 3100, 3100-x spectral power density spectrum ,-x counting index

Claims

[1] Method for testing power amplifiers (545), in particular of electric vehicles or charging stations, for broadband high-frequency powerline communication via cable (300, 310, 320), comprising the steps: a) connecting the power amplifier (545) to be tested and a test device with one of the cables (310), b) Determine a termination impedance of the cable on or in the test fixture c) sampling a broadband radio-frequency signal transmitted on one of the cables (310) from the output stage to be tested, which is generated with a constant spectral power density in each frequency range (3050) of the broadband radio-frequency signal used for radio-frequency communication, according to the Nyquist-Shannon sampling theorem at the end of one of the cables (310) associated with the test device (100) and detecting at least one time transient, both during the transmission of the broadband radio-frequency signal, d) determining a spectral power density spectrum (3100) associated with one of the cables (310) and the specified termination impedance based on the at least one time transient detected using the one of the cables (310) for the specified termination impedance e) evaluating the one or more frequency ranges (3050) of the spectral power density spectrum used for communication, f) wherein in step b) the termination impedance is set to a value which is adapted to an impedance of the cable (300) and in step e) during the evaluation it is checked whether deviations occur in one or more areas of the spectral power density spectrum compared to a spectral power density spectrum which is expected or detected during communication with an output stage which is correctly adapted with regard to the impedance, and g) outputting a result of the evaluation which comprises at least one indication of the correctness or incorrectness of the impedance matching of the output stage (545) to be tested. [2] Method according to claim 1, characterized by that the checking in method step e) as to whether deviations occur in one or more areas (3050) of the spectral power density spectrum (3100-x) compared to a spectral power density spectrum which is expected or detected during communication with an output stage correctly matched with regard to impedance, comprises checking whether fluctuations in the spectral power density above a threshold value occur in a spectral power density spectrum determined for a terminating impedance matched to the impedance of the cable. [3] Method according to claim 1 or 2, characterized bythat steps a) to d) are additionally carried out using at least one other of the cables (320), wherein the at least one other of the cables (320) has a length that differs from the at least one of the cables (310), and the terminating impedance in step b) is set identically to when steps a) to d) are carried out for the at least one of the cables, and that the evaluation of step e) comprises calculating an average spectral power density over the frequency ranges (3050) used for the power line communication for each of the determined spectral power density spectra, comparing the average values ​​in pairs for spectral power density spectra (3100-x) that are recorded for different cable lengths but the same terminating impedance, and classifying the power amplifier to be tested as incorrectly tuned if deviations above an average threshold value occur. [4] Method according to claim 3, characterized by that the method steps a) to d) are carried out for several of the cables with a different length, wherein the steps a) to d) are carried out at least twice for each of the plurality of cables (300), wherein in method step b) different terminating impedances are determined, and during the evaluation in method step e) the differences in the mean spectral power densities of the spectral power density spectra determined for different cable lengths but identical terminating impedances are compared for at least two of the differently determined terminating impedances, and if these differences in the mean values ​​are equal within a tolerance but different from zero, the terminating impedance of the output stage to be tested is estimated on the basis of the difference by converting the difference into a factor and multiplying it by the impedance of the cables. [5] Method according to one of the preceding claims, characterized by that the setting of the terminating impedance to a value that is adapted to an impedance of the cables is carried out by terminating a line connected to the corresponding one of the cables in or on the test device via an ohmic terminating resistor whose impedance corresponds to a line impedance of the cables, or by connecting the corresponding one of the cables in or on the test device to the output stage circuit of a high-frequency transmitting and receiving unit (40) that is correctly tuned with regard to the impedance over the entire frequency range used for power line communication and is attenuated with regard to its own transmission during reception of the high-power signal of the output stage (545) to be tested. [6] Method according to one of the preceding claims, characterized bythat the different impedances determined in method step b) comprise an infinite impedance which is determined by opening the line (120) connected to the corresponding one of the cables (300) in or on the test device. [7] Method according to one of the preceding claims, characterized by that the cables (300) are provided with two-wire lines (305) for powerline communication and that the impedance of the cables (300) is 100 ohms each. [8] Method according to one of the preceding claims, characterized by that a signal is transmitted to the output stage (545) to be tested for broadband high-frequency powerline communication in order to trigger the transmission of the broadband high-frequency signal, which is generated with a constant spectral power density in each frequency range of the broadband high-frequency signal used for the high-frequency communication. [9] Test device (100) for testing power amplifiers (545), in particular of electric vehicles or charging stations (500), for broadband high-frequency powerline communication via cable (300), comprising: a cable connector (110) for connecting one end of one of the cables (310) which is connected at another end to the output stage (545) to be tested; a cable termination device (120) connected to the cable connection (110) for defining a termination resistance of the line (120) connected to the cable connection (110) on or in the test device; a sampling device (150) connected to the cable connection (110) for sampling the broadband radio frequency signal transmitted on one of the cables (310) according to the Nyquist-Shannon sampling theorem and detecting at least one time transient, both during the transmission of the broadband radio frequency signal; a calculation unit (170) for determining a spectral power density spectrum associated with one of the cables (310) based on the at least one time transient detected using one of the cables (310), and an evaluation device (200) for evaluating one or more frequency ranges (3050) of the spectral power density spectrum (3100-x), wherein during the evaluation it is checked whether deviations occur in one or more frequency ranges (3050) of the spectral power density spectrum (3100-x) compared to a spectral power density spectrum that is expected or detected during communication with an output stage that is correctly matched with regard to impedance, and an output device (280) which outputs a result of the evaluation, which outputs at least one indication about a correctness or incorrectness of the impedance matching of the output stage (545) to be tested. [10] Test device (100) according to claim 9 characterized by that the cable termination device (130) comprises an ohmic terminating resistor (145) which corresponds to the impedance of the cables. [11] Test device (100) according to claim 10, characterized by in that the cable termination device comprises a switching device for terminating the line in or on the device for testing via the terminating resistor which corresponds to the impedance of the cable (300), or for switching it to an open state in order to simulate an infinite impedance, or for connecting it to an output stage of a high-frequency transmitting and receiving unit (40) of a power line communication device (30) which is correctly matched with regard to the impedance in order to produce an optimal adaptation of the cable termination. [12] Test device (100) according to one of claims 9 to 11, characterized by that the test device is part of a powerline communication device (30). [13] Test device (100) according to one of claims 9 to 12, characterized by that it is designed to carry out the method according to claims 1 to 7. [14] System (500) for testing output stages (545), in particular of electric vehicles or charging stations (500), for broadband high-frequency powerline communication with regard to their impedance matching, comprising the testing device (100) according to one of claims 9 to 13 and at least one cable (300) adapted with regard to impedance to the high-frequency transmitting and receiving unit (40) of the device (100), preferably a plurality of cables (300, 310, 320) of different lengths, for powerline communication for connecting to one of the output stages (545) to be tested.

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