System for contactless energy transmission and method for operating such a system

Abstract

The invention relates to a system for contactless energy transmission, comprising a power supply device which applies an intermediate frequency alternating current into a primary conductor, at least one secondary coil which is inductively coupled to the primary conductor for supplying at least one load, the power supply device having a current sensor for detecting the alternating current, the feed device has means for determining a fluctuation value of a peak value of the alternating current, which means are connected to monitoring means that monitor whether the fluctuation value exceeds a permissible deviation range from a threshold value.

Description

TECHNICAL FIELD

[0001] The invention relates to a system for contactless energy transmission and to a method for operating such a system. BACKGROUND

[0002] A system for contactless energy transmission is known from DE 100 53 373 and especially from its Figure 1 The system has a feeding device which applies an intermediate-frequency alternating current into an elongate primary conductor. A mobile load can be moved along the primary conductor and has a secondary coil which is inductively coupled to the primary conductor and by means of which energy can be extracted. In industrial applications, high currents are generated, as a result of which the primary conductor must be designed for such high currents with a correspondingly large cross section, but this leads to high costs. Furthermore, high ohmic losses are generated.

[0003] Intermediate-frequency alternating current is understood here as meaning an alternating current with a frequency of between 10 kHz and 1 MHz.

[0004] It is known from WO 2006 / 005 930 A1 that, by means of pulsed operation of a system for contactless energy transmission, arcing is prevented with pulse interruptions, however, the maximum power which can be transmitted from the feeding device to the mobile load is thereby reduced.

[0005] As the closest prior art, a method for inductively transmitting electrical power is known from DE 10 2022 004 254 A1, in which the time derivative of the current is monitored and evaluated. SUMMARY

[0006] It is therefore an object of the invention to improve environmental protection.

[0007] According to the invention, this object is achieved by a system according to the features given in claim 1 and by a method according to the features given in claim 14.

[0008] In the case of the system, the main feature of the invention is that the system is set up for contactless energy transmission and

[0009] comprises a feeding device which applies an intermediate-frequency alternating current into a primary conductor, at least one secondary coil which is inductively coupled to the primary conductor for supplying at least one load,

[0010] wherein the feeding device has a current sensor for detecting the alternating current,

[0011] wherein the feeding device has a means for determining the value of the fluctuation / unruhe, especially the fluctuation rate, of the peak value, especially the amplitude, of the alternating current,

[0012] wherein the device is connected to a monitoring component, which monitors whether the value exceeds an allowed deviation range relative to a threshold value,

[0013] In particular, the monitoring component is embodied in a suitable manner to display, forward an alert message and / or to switch off or to switch into a pulse operation of the feeding device at least for a certain period of time, depending on the monitoring result.

[0014] The advantage here is that, when an arc occurs, for example due to a cable break, this dangerous state is recognized by the increased fluctuation and thus also the safety-oriented switching off or pulse operation can be carried out. In the pulse operation, the arc is extinguished because the energy supply to the arc is interrupted intermittently. The increase in the fluctuation is recognized by monitoring the value. Here, the difference between the maximum and the minimum of the peaks of the alternating current can be used as the value. The low-pass filtering reduces the probability of false alarms.

[0015] Preferably, the alternating current is detected by the current sensor in such a way that the current sensor provides an analog value. After conversion into a digital value, the respective peaks are determined and subsequently the maximum and / or the minimum is obtained by time-sliding low-pass filtering. In this way, the fluctuation value can be determined as the difference between the low-pass filtered maximum and minimum determined in a time-sliding manner, and it can be monitored whether the fluctuation value exceeds an allowed deviation range relative to a preset threshold value. In this way, when an arc occurs, the large difference between the maximum and the minimum peak can be recognized simply and quickly, so that safety measures can be activated.

[0016] The advantage according to the invention is that the time derivative of the current does not have to be calculated, so that the required effort is low and nevertheless a reliable recognition of the arc is achieved. Because according to the invention, the respective peak is determined in each cycle of the alternating current and the fluctuation or the fluctuation rate of the sequence of peaks thus determined over time is evaluated. That is, neither the time derivative is evaluated nor is it monitored whether the time derivative exceeds a threshold value. Alternatively, such a step, i.e. the calculation of the time derivative and the monitoring of whether the time derivative of the current exceeds a threshold value, can also be added to the above-mentioned subject matter of the invention.

[0017] In an advantageous design, the threshold value is constant. The advantage here is that the system can be implemented without large outlay.

[0018] In an alternative embodiment, the threshold value has different values depending on the operating state of the system,

[0019] In particular, the preset threshold value at a first point in time is greater than at a second point in time, in particular at a later point in time,

[0020] In particular, the preset threshold value is greater in a time phase / interval in which the feeding device is switched on, in particular in which the feeding device starts to be supplied with power by the public AC power grid, than during later operation, in particular continuous operation, of the feeding device. The advantage here is that false alarms can be reduced. Since in operating states in which the current changes greatly, an arc can be falsely assumed to be present. The adjustment of the threshold value thus enables the system to be operated more stably.

[0021] In an advantageous design, the fluctuation value is a fluctuation range of the peak value, in particular of the amplitude, of the AC current, determined in a time- sliding manner. The advantage here is that a simple and fast calculation method can be used.

[0022] In an alternative embodiment, the fluctuation value is determined as the difference between a PT1 filtered and / or low-pass filtered maximum value, in particular determined in a time- sliding manner, and a PT1 filtered and / or low-pass filtered minimum value, in particular determined in a time- sliding manner, of the peak value. The advantage here is that individual outliers can be suppressed by means of low-pass filtering.

[0023] In an advantageous design, the current sensor has an analog-digital converter to provide the detected current value as digital current data. The advantage here is that

[0024] In an advantageous design, the fluctuation value is determined as the difference between a maximum value and a minimum value for each time step,

[0025] wherein, in each time step, the respective newly updated maximum value Î_LastMaxFilter is assigned the value of the peak value, in particular of the amplitude, of the AC current, if the peak value, in particular the amplitude, of the AC current is greater than or equal to the value Î_LastMaxFilterPT1; otherwise, the respective newly updated maximum value Î_LastMaxFilter is assigned the value Î_LastMaxFilterPT1, which is determined in each time step by adding the product of the difference between the peak value, in particular the amplitude, and the value Î_LastMaxFilter of the previous time step multiplied by the factor K_T to the value Î_LastMaxFilter of the previous time step,

[0026] In particular, the factor K_T is chosen to be much less than 1, in particular less than a tenth. The advantage here is that the maximum value is determined in a low-pass filtered manner, so that the influence of individual outliers is negligible.

[0027] In an advantageous design, in each time step, if the peak value, in particular the amplitude, of the alternating current is less than or equal to the value Î_LastMinFilterPT1, the corresponding newly updated minimum value Î_LastMinFilter is assigned the value of the peak value; otherwise, the corresponding newly updated minimum value Î_LastMinFilter is assigned the value Î_LastMinFilterPT1, which is determined in each time step by adding the product of the difference between the peak value, in particular the amplitude, and the value Î_LastMinFilter of the previous time step multiplied by the factor K_T to the value of the previous time step. The advantage here is that the minimum value is determined in a low-pass filtered manner, so that the influence of individual outliers is negligible.

[0028] In an advantageous design, for the case of exceeding the permissible deviation range relative to the preset threshold value, the feeding device and the subsequent pulse operation are implemented such that the pulse width and / or the amplitude variation of the alternating current is presettable, controllable or adjustable. The advantage here is that the environmental protection is improved and the costs are reduced, since the ohmic losses are reduced and thus the electrical energy is better utilized. In addition, the pulse operation is advantageous, since a continuous generation of an electric arc is avoided. Namely, if a component or an electrical connection is broken in the event of a fault or failure, an electric arc is generated, which can persist as long as there is a current. However, by setting the pulse width, i.e. without a continuous supply of current, the electric arc will experience a short power outage. This interruption lasts, for example, a few milliseconds, preferably more than 4 milliseconds. When the current supply is switched on again, i.e. the next current pulse is generated in the primary conductor, the electric arc cannot reignite, since the distance between the breaking points is too large for the voltage present. Thus, the safety of the device is additionally increased by the pulse operation mode.

[0029] Advantageously, the total energy consumption of the load can be transmitted from the primary conductor by inductive transmission. The information can be transmitted separately or can be transmitted by modulating a higher frequency current component onto the primary conductor. Here, too, the information transmission takes place as required, even when the primary current is zero. In an advantageous design, the information transmission is additionally synchronized with the zero crossings of the primary current in the time range in which the primary current is not zero.

[0030] In an advantageous design, the primary conductor is designed to extend in length, in particular wherein the load is arranged to be movable along the primary conductor. The advantage here is that a rail vehicle or a vehicle equipped with a rail guide antenna can be supplied contactlessly.

[0031] In an advantageous design, the primary conductor is arranged such that the load is arranged to be rotatable relative to the primary conductor. This has the advantage that rotating tables or other rotary axes in devices or machines, such as for example robots or machine tools, can be supplied with power.

[0032] In an advantageous design, the intermediate frequency is between 9 kHz and 100 kHz. This has the advantage that electronic power semiconductors, such as IGBTs or MOSFETs, can be used to switch the primary conductor's high currents at low losses. A high efficiency can thus be achieved.

[0033] In an advantageous design, the pulse width, the pulse duration and / or the characteristic time, such as the amplitude modulation period, in the amplitude modulation is greater than the period of the intermediate frequency current, in particular ten times or more than ten times the period of the intermediate frequency current. This has the advantage that the average amount of primary current available can be adapted to the requirements of the inductively powered load even in the case of high line inductances.

[0034] In an advantageous design, the duty cycle is coordinated with the energy buffer and the power consumption of the load. This has the advantage that the current flowing is less than the maximum possible current and thus the ohmic losses are low.

[0035] In an advantageous design, the load with the associated secondary coil is arranged to be movable along the primary conductor. This has the advantage that a contactless supply can be provided even in the case of a movable load.

[0036] In an advantageous design, an interval controller is associated with the primary conductor or with individual sections of the primary conductor. This has the advantage that each interval section can be precisely controlled, regulated and / or monitored.

[0037] In an advantageous design, means for data exchange are included in the feeding device, in the interval controller and / or in a load or loads. This has the advantage that data can be transmitted to the feeding device, which can then be taken into account by the feeding device. In this way, the current in the primary conductor can be adapted to the actual requirements.

[0038] In an advantageous design, the pulse width, the duty cycle and / or the amplitude variation of the feeding device can be preset in dependence on data, such as the number of loads in an interval section, the size of the energy in the energy buffer of the load, the respective power requirement of the load. This has the advantage that it is possible to feed as little current as possible into the primary conductor. In this way, the ohmic losses can be limited to a minimum.

[0039] A method for operating a system for contactless energy transmission

[0040] In this method, the essential feature of the application is that the intermediate-frequency alternating current is applied by the feeding device to the elongate primary conductor, at least one secondary coil is inductively coupled to the primary conductor for supplying at least one load, wherein the current is fed in such a way that the ohmic losses are as small or minimal as possible. As a result, the efficiency of the system is improved and cables with a smaller cross section can be used as primary conductor.

[0041] In particular, the pulse width, the duty cycle and / or the amplitude variation process is preset, controlled or regulated when the current is fed in. At this point, advantageously, various information can be taken into account, such as the number of loads in a section, the size of the energy in the energy buffer of the load and / or the respective power requirement of the load.

[0042] In an advantageous design, the power requirement of the load and / or the time variation process of the power requirement is predetermined, in particular before the power requirement occurs. As a result, it is advantageously possible to exceed the critical value, since the current variation process and thus the exact thermal loading of the primary conductor and other components can be determined. As a result, the maximum permissible temperature can always be taken into account.

[0043] In an advantageous design, the time variation process of the current in the primary conductor is set in such a way that a critical value of the current is exceeded over a period of time, wherein the critical value is the maximum current value permissible for the primary conductor in the case of a constant current value in the primary conductor, and the period of time is so short that the current variation process expected over this period of time does not damage the primary conductor. Advantageously, the critical current value is reached when a constant current value, in particular an effective alternating current value, is permanently present. At this point, the temperature occurring is important. At the critical value, a critical temperature is reached, which can lead to damage to the primary conductor when this critical temperature is exceeded.

[0044] Further advantages emerge from the dependent claims. BRIEF DESCRIPTION OF DRAWINGS

[0045] The application is now explained in more detail on the basis of the drawings:

[0046] Figure 1 A method for determining a fluctuation value of a primary conductor current is schematically depicted. DETAILED DESCRIPTION

[0047] The system for contactless energy transmission according to the application has a feeding device which feeds an intermediate-frequency alternating current into an elongate primary conductor of the system. Mobile loads of the system can be moved along the primary conductor and have a secondary coil which is inductively coupled to the primary conductor, by means of which energy can be extracted. In industrial applications, high currents occur, for which the primary conductor must then be designed with a correspondingly large cross section, but this leads to high costs. Furthermore, high ohmic losses occur.

[0048] In order to identify a non-regular operating state of the system, in particular in which an electric arc maintained by the primary conductor current can be identified as a result of a damage to the compensation element or as a result of a breakage of the primary conductor, in particular of the line conductor, a fluctuation value of the primary conductor current is calculated from the detected primary conductor current value in such a way that, as a fluctuation value of the primary conductor current, the difference between a slidingly determined, in particular low-pass filtered, maximum value and a slidingly determined, in particular low-pass filtered, minimum value is determined, and it is monitored whether the value thus determined exceeds an allowed deviation range with respect to a pre-set threshold value.

[0049] That is, if the fluctuation value of the primary conductor current exceeds a critical value, in particular a threshold value, in terms of magnitude, a warning message is displayed and / or forwarded or the power feeding device is switched off.

[0050] Thus, a pulsed operation is not required, and according to the application, a power loss associated therewith can also be avoided.

[0051] The fluctuation value of the primary conductor current I Last is determined according to the calculation rule in Figure 2 as the difference between the respective updated maximum value I LastMaxFilter and the minimum value I LastMinFilter of the primary conductor current at the respective time step n:

[0052] Maximum filter:

[0053]

[0054]

[0055] Minimum filter:

[0056]

[0057]

[0058] Here, n denotes the time step, and K T determines the time constant of the low-pass filter. Thus, the fluctuation value is low-pass filtered and expresses a fluctuation rate.

[0059] Therefore, for each time step, if the peak value, in particular the amplitude, of the primary conductor current is greater than or equal to the value Î_LastMaxFilterPT1, the updated new maximum value Î_LastMaxFilter is assigned the value of this peak value; otherwise, the updated new maximum value Î_LastMaxFilter is assigned the value Î_LastMaxFilterPT1, which is determined in each time step by the sum of the value Î_LastMaxFilter of the preceding time step and the difference between the peak value, in particular the amplitude, and the value Î_LastMaxFilter of the preceding time step, multiplied by the factor K_T.

[0060] In a corresponding manner, for each time step, if the peak value, in particular the amplitude, of the primary conductor current is less than or equal to the value Î_LastMinFilterPT1, the updated new minimum value Î_LastMinFilter is assigned the value of this peak value; otherwise, the updated new minimum value Î_LastMinFilter is assigned the value Î_LastMinFilterPT1, which is determined in each time step by the sum of the value Î_LastMinFilter of the preceding time step and the difference between the peak value, in particular the amplitude, and the value Î_LastMinFilter of the preceding time step, multiplied by the factor K_T.

[0061] In particular, the factor K_T is chosen to be much smaller than 1, in particular less than 0.1.

[0062] However, instead of determining the fluctuation degree value in this way, it is also possible to monitor whether the fluctuation range, which is determined in a sliding manner, exceeds an allowed deviation range with respect to a preset threshold value.

[0063] In all cases, the threshold value is either preset as a constant value or, alternatively, can vary depending on the operating state. In the latter case, for example, a greater value is specified as the threshold value when starting the system, i.e. when switching on the feed device of the system, and a smaller value is specified as the threshold value in the continuous operation which follows.

[0064] When switching on the feed device, the rectifier is connected to the public AC network and, as a result, the DC voltage supply of the terminal stage is established. In this way, a greater load current change can be caused, but no arc due to a cable breakage is generated. Therefore, the threshold value varying over time enables an adaptation to the respective operating state of the system, thus reducing the probability of triggering false alarms.

[0065] But in an improved embodiment of the application, in the case of an exceeding of the permissible deviation range, a pulsed operation can also be carried out instead of a de-energization, so that a continued operation of the system with an increased safety can be achieved. That is, if the arc is only triggered accidentally, for example, due to a temporary maintenance or work operation, the system is first brought to a pulsed operation, so that a continuous formation of an arc is avoided, and subsequently, after a defined time period, the normal operation, i.e. the continuous operation, can be switched back again.

[0066] The overall advantage of the control or regulation of the pulse width of the terminal stage of the inverter is that, in terms of the lifetime or operating time of the device, a smaller current occurs, and thus less ohmic losses are generated.

[0067] The terminal stage has at least two series circuits which are connected in parallel to one another, wherein the parallel circuits are supplied with a direct voltage from a direct voltage source. Preferably, the direct voltage source is a rectifier which is supplied with power from the power grid and which provides a direct voltage on the output side.

[0068] Each of the series circuits has two semiconductor switches, in particular MOSFETs or IGBTs, which are connected in series to one another and which are operated in a pulse width modulated manner, wherein the pulse width modulation duration is a period T and the pulse width modulation frequency is preferably in the range of 10 kHz to 1 MHz. The primary conductor is supplied with power from a tap in the middle of the series circuit.

[0069] By repeatedly connecting and disconnecting the terminal stage in time, a pulsed operation can be achieved which extinguishes the generated arc, since the pulse duration of the pulsed operation is preferably in the range of 1 ms or more. The pulsed operation can also be operated in a pulse width modulated manner, wherein the duty cycle corresponds to the ratio of the on time T_E to the off time T_A.

[0070] The period of the pulsed operation is T_P. This period is much greater than the period T of the intermediate frequency current. The latter corresponds to a frequency of approximately 10 kHz to 25 kHz. But frequencies of up to 50 kHz or even 1000 kHz can also be used.

[0071] The load comprises an energy buffer which is fed by the secondary coil, like for example a smoothing capacitor connected downstream of the rectifier or a capacitor in parallel to the secondary coil, the capacity of which is designed in such a way that, together with the secondary coil, a resonant circuit is formed, the resonant frequency of which is the same as the average frequency of the current in the primary conductor. Other or further energy buffers can also be used. The invention makes use of the energy capacity of the energy buffer. Since, in the time T_A, the energy buffer supplies the load. In the time T_E, the feeding device supplies the load and additionally replenishes the energy buffer.

[0072] For the pulsed operation, various embodiments are possible:

[0073] A first variant provides that the feed circuit comprises means for detecting the current and / or the voltage, the measured values of which are used to determine the theoretical power value.

[0074] For example, if the power requirement of the load increases, this is identified by a change in the current measurement and / or the voltage measurement, and can be counteracted by increasing the duty ratio or the peak value of the primary conductor current. The current detection means can be installed directly on the primary conductor. The voltage detection means can be installed on a rotary transformer contained in the feed circuit. In this case, the rotary transformer is shown in DE 100 53 373, the features of the system for contactless energy transmission disclosed in the description of which are likewise contained in the present application. Figure 1

[0075] In a second variant, the primary conductor has at least one section section in the entire device, but can also have a plurality of section sections, which are each equipped with a section controller, the section controller comprising an electronic circuit and being capable of data exchange with the feed circuit. It is thus possible to transmit the number of loads to be supplied individually in the section section and other data, like for example their required power and the existing energy capacity in the energy buffer, to the feed circuit. The feed circuit can then determine the required power therefrom and thus also the pulse width modulation ratio / duty ratio and / or the course of the current peak value in the primary conductor, and apply the current accordingly.

[0076] In a third variant, the system even has loads which are connected to the feed circuit for data exchange, either directly or via a corresponding section controller. It is thus possible for the loads to transmit their current required power and / or their existing energy size in the energy buffer, and for the feed circuit to adjust the primary conductor current accordingly, wherein the pulse width modulation ratio and / or the course of the primary conductor current peak value is dependent on the transmitted information.

[0077] For the transmission of data, in the stationary region, a bus system of the prior art can be used. For the transmission of data to or from loads which are arranged movably, transmission by radio waves, infrared waves, other electromagnetic waves or ultrasound waves is advantageous. If the mobile part moves a correspondingly suitable antenna along a slot of the coaxial conductor, a slotted coaxial conductor laid along the primary conductor can also be used. Advantageously, for the transmission of data it is also possible to implement that information is modulated onto the primary conductor current using frequencies above the medium frequency.

[0078] ​In a fourth variant, the secondary winding is connected to a current-voltage converter, the output of which supplies the rectifier. The resulting DC voltage can be used as intermediate circuit voltage for the frequency converter which supplies the electric motor. The current-voltage converter is formed here from passive electronic components, such as inductors, capacitors and resistors. Since the supply circuit on the primary side applies a current of intermediate frequency, i.e. essentially a current source, the DC voltage supplied by the rectifier arranged on the secondary side is constant. This is because the output of the rectifier is connected to a capacitor which acts as an energy buffer for the DC voltage. That is, if the current peak I in the primary conductor now decreases, the DC voltage, i.e. the intermediate circuit voltage, decreases accordingly, for example also in the same proportion as the current peak I in the primary conductor. But since the current in the primary conductor is set to the full current peak I in the present application, the rectified voltage also always remains at its corresponding high value. The energy buffer is designed in such a way that it buffers the voltage during the off time T_A, i.e. the voltage only decreases negligibly.

[0079] In another embodiment according to the application, the current-voltage converter is designed for higher powers. That is, the current-voltage converter can also be used in systems in which the current in the primary conductor continuously has its peak value. But the same current-voltage converter can also be used in systems in which the pulse width modulation ratio is less than 100%. In this way, the variety of current-voltage converters can be limited. The costs of the overall system family can thus be reduced.

[0080] The drive of a mobile load, i.e. a vehicle, is exemplary here and comprises a frequency converter for supplying an electric motor which in turn drives a shaft of the vehicle or a machine. By means of information transfer, the drive, in particular the frequency converter, is informed that it should start the vehicle from the time t_0. At this time, it is also known that the vehicle should reach a predetermined theoretical speed. The frequency converter can thus preset the maximum torque, i.e. also the possible maximum acceleration, from the time t_0. After a first time period which can be determined by the frequency converter or a computer, the theoretical speed is reached and only a low torque has to be applied to overcome the rolling and / or sliding friction.

[0081] As already mentioned above, the drive is supplied in a contactless manner by the primary conductor. Here, only a critical maximum continuous current value is allowed to exist in the primary conductor. If this critical maximum continuous current value is continuously exceeded, the risk of component damage, such as for example melting of the insulation of the primary conductor or melting of the copper conductor, increases.

[0082] When the vehicle is started, it is also necessary for the idealized electrical power P time curve shown in Figure 2 to be supplied by the primary conductor to the drive.

[0083] In the pulsed mode, the frequency converter is able to allow a temporary, i.e. during a first time period, exceeding of the critical current value due to a sharp increase in the power requirement. For this purpose, the frequency converter predicts the power requirement and thus also the current change process in the primary conductor and determines a time period during which the exceeding of the critical current value is allowed.

[0084] The predicted, i.e. already determined, power requirement is reported to the feeding device, which subsequently takes this into account accordingly, i.e. feeds a correspondingly too high current into the primary conductor.

[0085] In another embodiment according to the application, only one load is provided. The determined consumption can thus be assigned exactly to this load and the load current is determined to be exceeded.

[0086] In another embodiment according to the application, a plurality of loads are provided, each of which reports its predicted current requirement to the feeding device, which subsequently feeds the total required current.

[0087] List of reference signs:

[0088] 1 analog-digital converter

[0089] 2 maximum filter

[0090] 3 minimum filter

[0091] Î_Last load current, in particular primary conductor current

[0092] Î_LastMaxFilter maximum value

[0093] Î_LastMinFilter minimum value

[0094] Î_Last_Unruhe measure for the volatility or fluctuation of the load current Î_Last.

Claims

1. System for contactless energy transmission, the system comprising a feeding device which applies an intermediate-frequency alternating current into a primary conductor, at least one secondary coil being inductively coupled with the primary conductor to supply at least one load, the feeding device having a current sensor for detecting the alternating current, characterized in that the feeding device has means for determining a fluctuation value of the peak value, in particular of the amplitude, of the alternating current, in particular a fluctuation rate, the means being connected with a monitoring component which monitors whether the fluctuation value exceeds an allowed deviation range with respect to a threshold value, in particular wherein the monitoring component is implemented in a suitable manner to display, forward an alert message and / or switch off or at least temporarily switch into a pulsed mode of operation of the feeding device depending on the monitoring result.

2. System according to claim 1, characterized in that the threshold value is constant, or the threshold value has different values depending on the operating state of the system, in particular wherein a preset threshold value at a first point in time is greater than at a second, in particular later, point in time, in particular wherein the preset threshold value is greater during a time phase in which the feeding device is switched on, in particular in which the feeding device starts to be supplied with power from a public alternating current network, than during a later, in particular continuous, operation of the feeding device.

3. System according to at least one of the preceding claims, characterized in that the fluctuation value is a fluctuation range of the peak value, in particular of the amplitude, of the alternating current, determined in a time- sliding manner, or the fluctuation value is determined as the difference between a PT1 filtered and / or low-pass filtered maximum value of the peak value, in particular determined in a time-sliding manner, and a PT1 filtered and / or low-pass filtered minimum value of the peak value, in particular determined in a time-sliding manner. The current sensor has an analog-digital converter for providing the detected current value as a digital data stream.

4. System according to at least one of the preceding claims, characterized in that 5. System according to at least one of the preceding claims, characterized in that the fluctuation value is determined as the difference between the maximum value and the minimum value for each time step, wherein in each time step the value of the peak value, in particular of the amplitude, of the alternating current is assigned to the correspondingly updated new maximum value Î_LastMaxFilterPT1 if the peak value, in particular of the amplitude, of the alternating current is greater than or equal to the value Î_LastMaxFilterPT1; otherwise the correspondingly updated new maximum value Î_LastMaxFilterPT1 is assigned the value Î_LastMaxFilterPT1 which is determined in each time step by determining the sum of the value Î_LastMaxFilterPT1 of the previous time step and the difference between the peak value, in particular of the amplitude, and the value Î_LastMaxFilterPT1 of the previous time step multiplied by a factor K_T, in particular wherein the factor K_T is chosen to be much smaller than 1, in particular smaller than 0.

1. ​ 6. System according to at least one of the preceding claims, characterized in that In each time step, if the peak value, in particular the amplitude, of the alternating current is less than or equal to the value Î_LastMinFilterPT1, the respective updated new minimum value Î_LastMinFilter is assigned the value of the peak value; otherwise, the respective updated new minimum value Î_LastMinFilter is assigned the value Î_LastMinFilterPT1, which is determined in each time step by the sum of the value Î_LastMinFilterPT1 of the previous time step and the difference between the peak value, in particular the amplitude, and the value Î_LastMinFilterPT1 of the previous time step multiplied by the factor K_T.

7. System according to at least one of the preceding claims, characterized in that The feeding device is implemented so as to be suitable for pulse operation, in which the pulse width, the duty cycle and / or the amplitude variation of the alternating current is predefinable, controllable or adjustable, in particular after exceeding an allowed deviation range relative to a threshold value.

8. System according to at least one of the preceding claims, characterized in that The primary conductor is arranged to be laid in an elongate manner, in particular on the ground, in particular wherein the load is arranged to be movable along the primary conductor.

9. System according to at least one of the preceding claims, characterized in that the intermediate frequency is between 10 kHz and 1000 kHz, and / or the pulse width, the pulse duration and / or the characteristic time, such as the amplitude modulation period, in the case of amplitude modulation, is greater than the period of the intermediate frequency current, in particular ten times or more than ten times the period of the intermediate frequency current, and / or the duty cycle is matched to the energy buffer and the power consumption of the load.

10. System according to at least one of the preceding claims, characterized in that the secondary coil is fastened to the load, the load with the secondary coil is arranged to be movable along the primary conductor, in particular wherein the primary conductor is arranged in such a way that the load is arranged to be rotatable relative to the primary conductor.

11. System according to at least one of the preceding claims, characterized in that a section controller is assigned to the primary conductor or to a section of the primary conductor, respectively, and / or the feeding device, the section controller and / or the load comprise means for data exchange.

12. System according to at least one of the preceding claims, characterized in that The pulse width, the duty cycle and / or the amplitude variation of the feeding device can be predefinable from data, such as the number of loads in the section, the amount of energy in the energy buffer of the load, the respective power requirement of the load.

13. System according to at least one of the preceding claims, characterized in that the load comprises means for determining the time variation of its power requirement or current requirement, and / or the load comprises means for transmitting information about the time variation of its power requirement or current requirement to the feeding device or to a computer connected to the feeding device for transmitting signals or information.

14. Method for operating a system for contactless energy transmission, - applying an alternating current of intermediate frequency into a long-stretched primary conductor by means of a feeding device, at least one secondary coil being inductively coupled to the primary conductor for supplying at least one load, - detecting the alternating current, - characterized in that - a fluctuation value of the peak value, in particular of the amplitude, of the alternating current is determined, in particular a fluctuation rate, and it is monitored whether the fluctuation value exceeds an allowed deviation range with respect to a threshold value, - in particular wherein, depending on the monitoring result, an alarm message is displayed and / or forwarded or the feeding device is switched off or is brought into a pulsed operation at least for a certain period of time.

15. The method according to the preceding claim, characterized in that - the fed-in current is such that ohmic losses are as little or minimal as possible, and / or - the pulse width, the duty cycle and / or the amplitude variation are preset, controlled or regulated when the current is fed in, and / or - information, such as the number of loads in the section, how much energy is in the energy buffer of the loads and / or the respective power requirement of the loads, is taken into account, and / or - the power requirement of the loads and / or the time variation of the power requirement is predetermined, in particular before the power requirement occurs, and / or - the time variation of the current in the primary conductor is set such that a critical value of the current is exceeded over a period of time, which critical value is the maximum current value allowed for the primary conductor in the case of a constant continuous current value in the primary conductor, the period of time being so short that the variation of the current in this period of time is not expected to damage the primary conductor.

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