TRANSMITTING UNIT AND METHOD FOR INTEGRING AN ELECTRICAL TRANSMITTING SIGNAL INTO A DC VOLTAGE LINE

Abstract

The application relates to a transmitter unit (10) for coupling a transmission signal into a DC line (26.1, 26.2) with two output terminals (20) between which the transmission signal is present and which are provided for connection to a coupling device (21) in the DC line (26.1, 26.2), wherein the transmitter unit (10) has an amplifier circuit (12) with a clocked amplifier and the amplitude of the transmission signal is proportional to a supply voltage (Vcc) of the clocked amplifier. The transmitter unit (10) includes a compensation circuit (14) which is configured to detect the amplitude of the transmission signal via a differential voltage measurement at the output terminals (20) and to adjust the supply voltage (Vcc) of the clocked amplifier as a function of the amplitude of the transmission signal.The application further relates to a photovoltaic inverter (30) with a transmitter unit (10) and a method for coupling a transmission signal into a DC line (26.1, 26.2).

Description

TECHNICAL FIELDThe application relates to a transmitting unit for coupling an electrical transmission signal into a DC voltage line, and to a photovoltaic inverter having such a transmitting unit. The application further relates to a method for coupling an electrical transmission signal into a DC voltage line.PRIOR ARTElectrical transmission signals can be impressed, transmitted and decoupled in DC voltage lines of an electrical installation, for example of an energy generation installation, in particular for power line communication between various devices connected to the DC voltage lines. In the case of a photovoltaic system, for example, the so-called SunSpec specification of the SunSpec Alliance defines requirements for power line communication (power line communication PLC) between photovoltaic inverters and electronic units at or in the photovoltaic generators. Photovoltaic installations in particular therefore generally comprise a transmitting unit in the inverter, which generates a defined electrical transmission signal and couples it to the DC voltage lines.TASKThe object of the application is to improve such a transmitter unit and such a method for coupling a transmission signal into a DC voltage line.SOLUTIONThe object is achieved by a transmitting unit having the features of claim 1 and a method having the features of claim 17. Embodiments are set out in the dependent claims.DESCRIPTION OF THE INVENTIONA transmitting unit couples an electrical transmission signal into a DC voltage line. For the coupling-in, two output connections are provided, between which the transmission signal is present. The output connections are provided for connection to a coupling means in the DC voltage line. The transmitting unit has an amplifier circuit with a clocked amplifier. The amplitude of the transmission signal is proportional to a supply voltage of the clocked amplifier, wherein the transmission unit comprises a compensation circuit which is configured to record the amplitude of the transmission signal via a differential voltage measurement at the output connections and to set the supply voltage of the clocked amplifier as a function of the amplitude of the transmission signal.The electrical transmission signal is thus generated by the transmission unit, output via the output connections and coupled into the DC voltage line via the coupling-in means. The coupling can in principle be inductive or capacitive, wherein the coupling means can in particular comprise a coil for inductive coupling. The clocked amplifier of the amplifier circuit can have, for example, a bridge circuit with switches which are controlled in a clocked manner.The compensation circuit can in particular have an analog circuit part for differential voltage measurement. The differential voltage measurement has the advantage that the amplitude of the transmission signal can be detected even if the output connections between which the transmission signal is present do not have a defined ground reference. Optionally, the compensation circuit can perform rectification and smoothing of the measurement signal.By means of a transmitting unit according to the application, it is possible to automatically set the transmission signal to a desired amplitude value and possibly to compensate for deviations therefrom, which can be caused, for example, by component tolerances, changes in the ambient conditions or changes in the DC units connected to the DC voltage lines. This improves the quality of the electrical transmission signal and thus of the data transmission without a manual intervention in the transmission unit being required, for example after the transmission unit or the inverter has been mounted or after changes to the photovoltaic system.In a development of the transmitting unit, the compensation circuit is configured to output a compensation signal depending on the amplitude of the transmission signal in order to set the supply voltage of the clocked amplifier. By means of such a compensation signal depending on the amplitude of the transmission signal, the real amplitude of the transmission signal at the output terminals can be taken into account in the setting of the supply voltage of the clocked amplifier, even if the supply voltage is generated separately, i.e. not by the compensation circuit itself but by a separate voltage supply. The transmitter unit is in turn configured such that the amplitude of the transmission signal is proportional to the supply voltage of the clocked amplifier, so that the amplitude can be set to the desired value by the described embodiment of the compensation circuit.In one embodiment of the transmitter unit, a nominal DC supply voltage is provided, wherein the supply voltage of the clocked amplifier is adjustable in a range between half the nominal DC supply voltage of a voltage supply and twice the nominal DC supply voltage depending on the nominal DC supply voltage and on the compensation signal. The nominal DC supply voltage can be, in particular, a nominal output voltage of a voltage supply of the clocked amplifier, which can be manipulated by means of the compensation signal. Depending on the compensation signal, the supply voltage of the clocked amplifier and thus the amplitude of the transmission signal can then be varied in the range between half and twice a nominal value. As a result, a feedback of the real amplitude of the transmission signal can be realized in order to ensure a transmission signal with a sufficient amplitude. The supply voltage of the clocked amplifier can be adjusted in particular in a range from approximately 4 volts to approximately 10 volts.In one embodiment, the transmitting unit has a DC / DC converter which is configured to generate the supply voltage of the clocked amplifier from a superordinate vehicle electrical system voltage as a function of the amplitude of the transmission signal or as a function of the compensation signal. The DC / DC converter can receive either the amplitude of the transmission signal or a variable dependent thereon from the compensation circuit in order to generate the supply voltage. Alternatively, the DC / DC converter may receive the compensation signal from the compensation circuit to thereby generate or scale the supply voltage. The compensation signal can be either analog or digital.In one embodiment, the transmitting unit has a processor which is configured to generate the compensation signal in digital form as a clock sequence with a duty cycle and to transmit it to the compensation circuit, wherein the duty cycle is set by the processor as a function of the amplitude of the transmission signal. This embodiment has the advantage that the digital signal processing can take place in the processor separately from the compensation circuit, which can be designed as an analog circuit.In one embodiment of the transmitter unit, the compensation circuit outputs the clock sequence as a compensation signal in digital form as a drive signal for semiconductor switches of the DC / DC converter. In this embodiment, the compensation circuit can then directly drive the semiconductor switches of the DC / DC converter, which allows a fast reaction of the DC / DC converter and thus a fast drive of the generation of the supply voltage. The semiconductor switches of the DC / DC converter can be controlled alternatively or additionally to the semiconductor switches being controlled by a control unit of the DC / DC converter.In one embodiment of the transmitter unit, the compensation circuit has a filter which generates the compensation signal as a voltage level in analog form from the clock sequence and outputs it to a control input of the DC / DC converter. In this embodiment, the analog compensation signal acts as a control signal on the generation of the supply voltage, in particular by scaling a nominal output voltage of the DC / DC converter by means of the analog compensation signal.In one embodiment of the transmission unit, two transmission channels can be coupled in via the transmission signal. The transmitting unit can be switched over between the two transmitting channels. The supply voltage of the clocked amplifier or the compensation signal can be alternately switched over between a first and a second supply voltage or between a first and a second compensation signal depending on the transmission channel. This embodiment thus enables dual-channel operation of the transmitter unit, in which the amplitude of the transmission signal for each channel can be well adjusted independently of the respective other channel.In one embodiment of the transmitter unit, the compensation circuit has a temperature sensor for temperature detection. The supply voltage of the clocked amplifier or the compensation signal depends on the detected temperature. This makes it possible to compensate for temperature dependencies, which further improves the quality of the transmission signal.In one embodiment of the transmitting unit, the amplifier circuit is configured to generate a modulation of the transmission signal as a function of a binary predefined signal. The amplifier unit can thus convert a binary predefined signal into a modulated transmission signal, which can then be coupled into the DC voltage line. For this purpose, the binary predefined signal can be generated from a desired continuous signal shape, for example, by means of pulse width modulation or delta-sigma modulation. The transmission signal can be frequency-modulated with a fixed predefined amplitude and can have a plurality of frequencies, in particular two alternatively used frequencies.In one embodiment, the clocked amplifier may comprise a half bridge circuit with semiconductor switches which are driven in a clocked manner. The amplification of the amplifier circuit depends directly on the supply voltage, and the transmission signal is generated by suitable clocking of the semiconductor switches of the half bridge.In one embodiment of the transmitting unit, the amplifier circuit has a class D amplifier circuit. The class D amplifier circuit includes a class D amplifier. A class D amplifier is a switching amplifier that can be used as a power amplifier. The class D amplifier operates to amplify a binary signal in switching operation. Semiconductor power switches, e.g. transistors, of the bridge circuit of the class D amplifier are operated in two discrete states, either conducting or insulating. As a result, the class D amplifier has little power loss.A photovoltaic inverter has the transmitting unit according to the application. The transmitting unit is provided for coupling the transmission signal into the DC voltage lines of the DC bus. The DC bus connects the inverter to at least one photovoltaic generator for the electrical power exchange. The inverter is enabled by the described transmitting unit to communicate via the DC bus with receivers connected thereto. In order to control the amplitude of the transmission signal by the transmission unit, it is also optionally possible to use components which are in any case installed in the inverter. This makes it possible to keep down the additional effort for influencing the amplitude of the transmission signal. For example, the vehicle electrical system voltage of the inverter can be used to generate the supply voltage of the amplifier circuit. In addition, a DC / DC converter provided in the inverter can be used, for example, in addition to generating the supply voltage of the amplifier circuit from the vehicle electrical system voltage. This reduces the cost and complexity of the transmitter unit and / or the inverter.A photovoltaic system may have the described inverter. The photovoltaic installation can also have the at least one photovoltaic generator and the DC bus. The DC bus connects the inverter to the photovoltaic generator for electrical power transfer. The transmitting unit then enables data communication between the inverter and receivers assigned to the photovoltaic generator.In a method for coupling a transmission signal into a DC voltage line, the transmission signal is present between two output connections which are connected to a coupling means in the DC voltage line. An amplifier circuit having a clocked amplifier generates the transmit signal with an amplitude proportional to a supply voltage of the clocked amplifier. A compensation circuit detects the amplitude of the transmit signal via a differential voltage measurement at the output terminals and suitably adjusts the supply voltage of the clocked amplifier.BRIEF DESCRIPTION OF THE FIGURESThe application is explained and described below with reference to exemplary embodiments shown in the figures. FIG. 1 schematically shows a first exemplary embodiment of a transmission unit. FIG. 2 schematically shows a second exemplary embodiment of a transmission unit. FIG. 3 schematically shows an exemplary embodiment of a photovoltaic system. FIG. 4 schematically shows a method for coupling in a transmission signal. FIG. 5 schematically illustrates two-channel operation. FIG. 6 schematically shows a method for voltage adjustment for two-channel operation.The same reference numerals are used in the figures for the same or similar elements. The representations in the figures may not be to scale.FIGURE DESCRIPTIONFIG. 1 shows a first exemplary embodiment of a transmitting unit 10. The DC bus 26 has two DC voltage lines 26.1, 26.2. The output terminals 20 of the transmitter unit 10 are connected to the one DC voltage line 26.1 of the DC bus 26. An electrical transmission signal present between the output connections 20 can be coupled to the DC voltage line 26.1 via a coupling means 21, for example an inductance. The transmitting unit 10 is used for transmitting information encoded in the transmission signal via the DC bus 26 by means of power line communication. The transmission unit 10 can be, for example, a power line transmitter which is basically compatible with the SunSpec standard and / or with similar relevant standards for communication, in particular in a photovoltaic installation.An amplifier circuit 12 of the transmitting unit 10 has a clocked amplifier, which can have, in particular, a half bridge with semiconductor switches. The amplification of the amplifier is effected by suitably clocked switching of a supply voltage Vcc by means of the semiconductor switches. The amplifier thus amplifies a binary predefined signal TX 0 and generates the electrical transmission signal, which is then present between the output terminals 20. The amplifier circuit is configured such that an amplitude of the transmission signal is proportional to a supply voltage Vcc of the clocked amplifier, and may for this purpose comprise a class D amplifier, for example.A signal generator 18 is supplied by a signal generator supply voltage VS. The signal generator 18 outputs a binary predefined signal TX 0, which can be generated by means of coding from a signal profile which is continuously predefined per se. The predefined signal profile can correspond in particular qualitatively to the profile of the desired transmission signal. Suitable encodings of the desired transmission signal or of the continuous signal profile are, for example, delta sigma modulation or pulse width modulation. An input signal 22 may be stored in the signal generator 18, e.g., via a programming interface in a flash memory. The input signal 22 can be identical to the binary predefined signal TX 0, which is output continuously as a transmission signal, for example for the single-channel transmission unit 10 illustrated in FIG. 1.The input signal TX0 is preferably derived from a continuous signal which has, for example, a desired signal profile with different fixed frequencies, each having a fixed amplitude. The amplifier 10 converts the input signal TX0 back into an analog electrical transmission signal from the encoded binary form by suitable clocking and filtering, which is applied to the coupling-in means 21. The amplitude of the transmission signal at the coupling means 21 is proportional to the supply voltage Vcc of the clocked amplifier on the one hand and can have a dispersion on the other hand due to tolerances of components of the amplifier circuit and vary depending on ambient conditions or on the DC units connected to the DC bus 26. Accurate detection, monitoring and setting of the amplitude of the transmission signal is therefore advantageous for the quality of the data transmission via the DC bus.In this case, a dispersion or undesired variation of the amplitude of the transmission signal can be compensated according to the application. The dispersion can occur, for example, due to component tolerances, and a variation of the amplitude of the transmission signal can occur, for example, due to aging of ceramic capacitors and / or due to temperature-related dependencies and / or depending on electrical parameters of a connected PV generator 36.The transmitting unit 10 has a compensation circuit 14, which is supplied with electrical power from an on-board power supply voltage VB and supplies the clocked amplifier with the supply voltage Vcc. Optionally, the supply voltage Vcc of the clocked amplifier can be generated by the compensation circuit 14 itself from the vehicle electrical system voltage VB.The compensation circuit 14 also detects the electrical transmission signal at the output terminals 20 via a differential voltage measurement. The compensation circuit is configured to adjust the supply voltage Vcc of the clocked amplifier depending on the amplitude of the transmission signal. This has the advantage that the actual, real amplitude of the transmission signal can be detected at the output terminals 20 and the supply voltage Vcc of the clocked amplifier can be adjusted accordingly in order to adjust the amplitude to the setpoint value.The detection of the amplitude of the transmission signal and the setting of the supply voltage Vcc of the clocked amplifier can be effected by means of an analog circuit arrangement of the compensation circuit 14.Optionally, information dependent on the detected amplitude of the transmission signal can be transferred via the compensation circuit 14 to a processor 16. The processor 16 can generate a digital compensation signal depending on this information, which can be transmitted from the processor 16 to the compensation circuit 14, for example, as a clock sequence with a duty cycle. In this case, the duty cycle of the digital compensation signal can be adjusted by the processor 16 as a function of the amplitude of the transmission signal, for example by means of a proportional controller and / or a proportional controller, in each case optionally with a characteristic curve. The supply voltage Vcc of the clocked amplifier can then be adjusted by the compensation circuit 14 as a function of the digital compensation signal received from the processor 16, in particular by clocked switching of the vehicle electrical system voltage VB in accordance with the clock sequence of the digital compensation signal received from the processor 16. In a basic embodiment, the compensation circuit 14 can comprise, in addition to the differential voltage detection, the analog signal processing of the measured signals to the processor 16 and of the clocked compensation signal from the processor 16 by filters or the like.FIG. 2 shows a second exemplary embodiment of the transmission unit 10. In contrast to FIG. 1, the transmitting unit 10 in this exemplary embodiment has a DC / DC converter 24. The DC / DC converter 24 is, for example, of clocked design and has controllable semiconductor switches. The DC / DC converter 24 generates the supply voltage Vcc for the amplifier circuit 12 from the on-board power supply voltage VB in accordance with a compensation signal SFB received from the compensation circuit 14. In this exemplary embodiment, too, the compensation circuit 14 itself can be supplied with electrical energy by the vehicle electrical system voltage VB.The compensation circuit 14 generates the compensation signal SFB depending on the amplitude of the transmission signal. The amplitude of the transmission signal can be detected in an analogous manner as in the transmission unit 10 of FIG. 1. The measured amplitude or an information proportional thereto can be forwarded to a processor 16, which can generate a digital compensation signal by means of a controller and / or a characteristic curve as a function of this information and return it to the compensation circuit 14.In this exemplary embodiment, the compensation circuit 14 can output a compensation signal SFB, which is suitable in digital form as a drive signal for semiconductor switches of the DC / DC converter 24. The compensation circuit 14 can then directly drive the semiconductor switches of the DC / DC converter 24, for example, in particular if the digital compensation signal generated by the processor 16 is used as the compensation signal SFB directly or after suitable filtering.The compensation circuit 14 can also have a filter which generates a voltage level in analog form from the digital compensation signal received from the processor 16 and outputs this voltage level as compensation signal SFB to a control input of the DC / DC converter. The compensation signal SFBcan then directly specify the supply voltage Vccto be output by the DC / DC converter 24 or modify a nominal DC supply voltage of the DC / DC converter 24, i.e. bring about a scaling of the supply voltage Vcc. Alternatively, it would be possible to use the compensation signal SFBdirectly as a supply voltage of the DC / DC converter 24, i.e. instead of the vehicle electrical system voltage VB(not shown here).The transmission unit 10 is designed for two-channel transmission, so that the transmission unit can be switched between at least two transmission channels, the respective transmission signal being able to be coupled into different DC buses via the at least two transmission channels. The channel currently used can be selected via a channel selection signal SEL. The signal generator 18 can alternately output two binary predefined signals TX 0, TX 1, wherein the first predefined signal TX 0 is output via the amplifier circuit 12 to the output connections 20 at a supply voltage Vcc having a first value, while the second predefined signal TX 1 is output via a second amplifier circuit, not shown, at the output connections thereof at a supply voltage Vcc having a second value, which differs from the first, and is coupled into a second DC bus, not shown. The input signal 22 can be identical to the respective binary predefined signal TX 0, TX 1, which can be output continuously in alternation. The compensation signal SFB can be alternately switched between a first and a second compensation signal SFB as a function of the transmission channel, wherein the first compensation signal SFB is generated as a function of the amplitude of the transmission signal at the coupling means 21 and the second compensation signal SFB is generated as a function of the amplitude of the transmission signal at a further coupling means, not shown, in a DC line of the second DC bus, not shown here. This makes it possible to use at least the components compensation circuit 14, processor, signal generator 18 and DC / DC converter 24 multiple times for generating PLC signals on different DC buses with any assignment of DC units deviating from one another.FIG. 3 schematically shows a photovoltaic installation 40 having an inverter 30, a DC bus having the DC voltage lines 26.1 and 26.2, a PV generator 36 and an isolation circuit 32. In the case of a plurality of PV generators 36, which can be connected in series to the one DC bus or in parallel via a plurality of DC buses to the inverter 30, a respective isolation circuit 32 per DC bus or per PV generator 36 can be provided.The inverter 30 has an inverter bridge 28 and at least one coupling means 21 for each connected DC bus. The coupling-in means 21 is provided in order to couple the transmission signal present between the output terminals 20 of the transmission unit 10 into a DC voltage line 26.1 of the DC bus 26.The separation circuit 32 represents, by way of example, a receiver for the transmission signal and has a receiving unit 34, which is configured to receive the transmission signal transmitted by the transmitting unit 10. Depending on the received transmission signal, the isolation circuit 21 may isolate the PV generator 36 from the inverter 30 by, for example, opening an electronic DC switch or may connect it to the inverter 30 by closing the electronic DC switch.Such an isolation circuit 32 with the receiving unit 34 for communication via the DC bus allows, for example, a failsafe switch-on and switch-off device for PV generators to be realized. An advantage of communicating over the DC bus 26 is that no additional cabling or radio interfaces need to be installed. The transmission signal is generated and coupled in for the communication via the DC bus, as described, for example, by the transmission unit 10 in the inverter, wherein an adequate signal quality of the transmission signal is ensured by the compensation circuit according to the application.In order to ensure a single-fault safety of the PV system 40, a specific signal can be transmitted, for example, during normal operation of the PV system 40 by the transmission unit 10 on a second clock cycle. The separation circuit 32 evaluates the signal received via the receiving unit 34 and, upon detection of the correct bit stream, switches the DC voltage of the PV generator 36 through to the DC bus. If, for example, the DC bus 26 is now interrupted or the inverter 30 has a defect or the PV system 40 is switched off for other reasons, so that the signal no longer reaches the PV generator 36, the isolation circuit 32 can automatically switch off the PV generator 36. Thus, the entire PV system 40 can be reliably switched to zero voltage if necessary.FIG. 4 schematically shows a method for coupling the transmission signal into the DC voltage line 26.1. The transmission signal is present between the two output terminals 20 which are connected to the coupling means 21 in the DC voltage line 26.1.In 301, the compensation circuit 14 detects the amplitude of the transmission signal via a differential voltage measurement at the output terminals 20, which are connected to the coupling means 21. In 302, the compensation circuit 14 rectify the detected voltage of the transmission signal, for example, by a diode. In 303, the compensation circuit 14 smoothes the detected rectified voltage. The smoothing can be effected, for example, by a type of peaking by integration of the rectified voltage. In 304, the compensation circuit 14 adjusts the supply voltage Vcc of the clocked amplifier. The adjusting in 304 can be effected, for example, by directly adjusting the supply voltage Vcc by the compensation circuit 14 (compare FIG. 1 ) or by outputting the compensation signal SFBto a DC / DC converter 24 (compare FIG. 2 ).FIG. 5 schematically illustrates two-channel operation. In FIG. 5 e), those periods are denoted by 400 for a first channel in which the supply voltage Vcc for the clocked amplifier connected to a first DC bus is optimized by feedback of the amplitude of the transmission signal on this first DC bus, and 401 are denoted by those periods for a second channel in which the supply voltage Vcc for the clocked amplifier connected to a second DC bus is optimized by feedback of the amplitude of the transmission signal on this first DC bus. In FIG. 5 a), the reference numeral 402 denotes the time period in which the transmission signal of the first channel is active, while the regulation of the supply voltage Vcc is active on the basis of the measured amplitude of the transmission signal on the first channel substantially simultaneously in the time period 404. After the switching of the supply voltage Vcc to the second channel, the activity of the second channel then begins at 403, and correspondingly the regulation of the supply voltage Vcc takes place during 405 as a function of the measured amplitude of the transmission signal on the second channel. FIG. 5 shows that the channels each transmit during the transmission pause of the other channel. The regulation of the supply voltage Vcc is started in a predictive manner already before the activity of the transmission signal of the respective channel.The realization of the two-channel operation is possible by the alternating mode of operation. Two independent control processes are defined for this purpose by software. As a result of the predictive voltage changeover, a seamless change between the channels is possible.FIG. 6 schematically shows a method for voltage adjustment for two-channel operation. The method according to FIG. 6 can run, for example, in the processor 16. At 501, which channel is active is received. At 502, the digitized smoothed amplitude values of the active channel transmit signal are received. In 503, the mean value is formed via the values received in 502 for interference suppression. In 504, the control algorithm for amplitude adjustment is performed. In 505, the compensation signal SFB, e.g. in the form of a duty cycle or an analog voltage level, is generated and used for adjusting the supply voltage Vcc. In 506, the respective currently active channel is switched off, and in 507 the regulation of the supply voltage Vcc is switched over to the dependence on the amplitude of the transmission signal of the other channel. In 508, the temperature of the transmission unit 10 is optionally measured in order to be able to perform an optional additional temperature compensation.By using the active control, the amplitude of the transmission signal can be kept with very close tolerances at the required amplitude. The deviations which arise, for example, as a result of component tolerances can be reliably corrected. By using the averaged measured value in the control, it is possible to work with the entire output signal as a controlled variable instead of with the individual oscillation of the amplitude as a controlled variable. As a result, the control is robust with respect to disturbances, such as harmonics from the inverter 30.LIST OF REFERENCE CHARACTERS10 Transmitting unit 12 amplifier circuit 14 compensation circuit 16 processor 18 signal generator 20 output terminals 21 coupling means 22 input signal 24 DC / DC converter 26 DC bus 26.1, 26.2 DC lines 28 inverter bridge 30 inverter 32 isolation circuit 34 receiving unit 36 photovoltaic (PV) generator 40 photovoltaic (PV) system VB on-board power supply voltage Vcc supply voltage VS signal generator supply voltage SEL channel selection SFB compensation signal TX 0 binary predefined signal first transmission channel TX 1 binary predefined signal second transmission channel 400, 401 voltage setting transmission channels 402, 404 activity transmission channels 403, 405 activity regulation transmission channels 301- 304, 501- 508 method steps

Claims

Transmitting unit (10) for coupling an electrical transmission signal into a DC voltage line (26.1, 26.2) having two output connections (20), between which the transmission signal is present and which are provided for connection to a coupling means (21) in the DC voltage line (26.1, 26.2), wherein the transmitting unit (10) has an amplifier circuit (12) with a clocked amplifier and the amplitude of the transmission signal is proportional to a supply voltage (Vcc) of the clocked amplifier, wherein the transmitting unit (10) comprises a compensation circuit (14) which is configured to record the amplitude of the transmission signal via a differential voltage measurement at the output connections (20) and to set the supply voltage (Vcc) of the clocked amplifier as a function of the amplitude of the transmission signal.Transmitter unit (10) according to claim 1, wherein the compensation circuit (14) is configured to output a compensation signal (SFB) depending on the amplitude of the transmission signal in order to adjust the supply voltage (Vcc) of the clocked amplifier.Transmitter unit (10) according to claim 2, wherein a nominal DC supply voltage is provided, wherein the supply voltage (Vcc) of the clocked amplifier is adjustable in a range between half the nominal DC supply voltage and twice the nominal DC supply voltage depending on the nominal DC supply voltage and on the compensation signal (SFB).Transmitting unit (10) according to claim 3, wherein it is provided that the supply voltage (Vcc) is adjustable in a range from approximately 4 volts to approximately 10 volts.Transmitting unit (10) according to one of the preceding claims, having a DC / DC converter (24) which is configured to generate the supply voltage (Vcc) from a superordinate vehicle electrical system voltage (VB) as a function of the amplitude of the transmission signal or as a function of the compensation signal (SFB).Transmitting unit (10) according to one of the preceding claims, wherein the compensation signal (SFB) output by the compensation circuit (14) is analog or digital.Transmitting unit (10) according to one of Claims 2 to 6, wherein the transmitting unit (10) has a processor (16) which is configured to generate the compensation signal (SFB) in digital form as a clock sequence with a duty cycle and to transmit it to the compensation circuit (14), wherein the duty cycle is set by the processor (16) as a function of the amplitude of the transmission signal.Transmitting unit (10) according to Claim 7, wherein the compensation circuit (14) outputs the clock sequence as a compensation signal (SFB) in digital form as a drive signal for semiconductor switches of the DC / DC converter (24).Transmitting unit (10) according to Claim 7, wherein the compensation circuit (14) has a filter which generates the compensation signal (SFB) as a voltage level in analog form from the clock sequence and outputs it to a control input of the DC / DC converter (24).Transmission unit (10) according to one of the preceding claims, wherein two transmission channels can be coupled in via the transmission signal, wherein the transmission unit (10) can be switched over between the two transmission channels, and wherein the supply voltage (Vcc) of the clocked amplifier or the compensation signal can be switched over alternately between a first and a second supply voltage or between a first and a second compensation signal (SFB) depending on the transmission channel.Transmitter unit (10) according to one of the preceding claims, wherein the compensation circuit (14) has a temperature sensor for temperature detection (508), and wherein the supply voltage (Vcc) of the clocked amplifier or the compensation signal (SFB) depends on the detected temperature.Transmitting unit (10) according to one of the preceding claims, wherein the amplifier circuit (12) is configured to generate a modulation of the transmission signal as a function of a binary predefined signal (TX0, TX1).The transmitter unit (10) according to any of the preceding claims, wherein the clocked amplifier comprises a half bridge circuit with semiconductor power switches.The transmitter unit (10) of any preceding claim, wherein the amplifier circuit (12) comprises a class D amplifier circuit.Photovoltaic inverter (30) having a transmitter unit (10) according to one of the preceding claims, wherein the transmitter unit (10) is provided for coupling the transmission signal into the DC voltage line (26.1, 26.2), wherein a DC bus (26) has the DC voltage line (26.1, 26.2), and the DC bus (26) connects the inverter (30) to at least one photovoltaic generator (36) for the electrical power exchange.Photovoltaic installation (40) having an inverter (30) according to Claim 15, the at least one photovoltaic generator (36) and the DC bus (26) for electrical power transfer.Method for coupling a transmission signal into a DC voltage line (26.1, 26.2), wherein the transmission signal is present between two output terminals (20) which are connected to a coupling means (21) in the DC voltage line (26.1, 26.2), wherein an amplifier circuit (12) with a clocked amplifier generates the transmission signal with an amplitude proportional to a supply voltage (Vcc) of the clocked amplifier, wherein a compensation circuit (14) detects the amplitude of the transmission signal via a differential voltage measurement at the output terminals (20) and sets the supply voltage (Vcc) of the clocked amplifier.

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