System and method for operating a system for contactlessly transmitting electrical power

Abstract

The invention relates to a system and to a method for operating a system for contactlessly transmitting electrical power, wherein a movable part of the system has one or more secondary windings from which one or more respective rectifiers are supplied, wherein, by means of one or more switches, a phase of each AC-side connection of each rectifier can be connected to a centre tap of a series circuit which is formed from capacitors (9) and is supplied and / or powered from the DC-side connections of the rectifiers that are connected in parallel, wherein a signal processing unit (4) is designed with a zero-current-detection unit such that the signal processing unit emits a pulse-width-modulated control signal (10) to the switch(es) (7) as a relevant actuation signal (11) only when the input current of each AC-side connection of the rectifiers (8) disappears.

Description

[0001] System and method for operating a system for contactless transmission of electrical power

[0002] Description:

[0003] The invention relates to a system and a method for operating a system for contactless transmission of electrical power.

[0004] It is well known that in such a system a secondary winding is inductively coupled to a primary conductor.

[0005] From DE 102018 105 608 A1, the closest prior art is a charging arrangement for motor vehicles with circuit control on the receiver side.

[0006] A circuit arrangement with adjustable capacitance is known from DE 102018 129 315 A1.

[0007] A charging device for an electric vehicle is known from US 2020 / 0 156491 A1.

[0008] An AC / DC converter is known from US 2011 / 0 019452 A1.

[0009] From DE 102010 022 122 A1 a method for operating an arrangement for inductive energy transmission to an electrical consumer is known.

[0010] DE 102015 005 871 A1 discloses a system for contactless energy transmission from a primary conductor laid in the ground to a vehicle moving on the ground.

[0011] The invention is therefore based on the object of developing a system for the contactless transmission of electrical power, wherein the voltage provided on the secondary side is to be controllable in an electromagnetically compatible manner.

[0012] According to the invention, the object is achieved in the system according to the features specified in claim 1 or 2 and in the method according to the features specified in claim 14. Important features of the invention in the system for contactless transmission of electrical power according to claim 1 are that a mobile part of the system has one or more secondary windings from which one or more respective rectifiers are supplied, wherein by means of one or more switches, one phase of the respective AC-side terminal of the respective rectifier can be connected to a center tap of a series circuit formed by capacitors, which is supplied and / or fed from the parallel-connected DC-side terminals of the rectifiers, wherein a signal processing unit is designed with a zero-current detection unit,that the signal processing unit releases a pulse-width-modulated control signal to the switch(es) as a respective control signal only when the input current at the AC-side terminal of the rectifier or at one of the respective AC-side terminals of the rectifiers disappears, in particular thus feeding it to the switches for their control, in particular wherein the AC voltages applied to the AC-side terminals of the rectifiers are synchronous to one another, in particular time-synchronous, in particular wherein the pulse-width-modulated control signal is asynchronous to the AC voltages applied to the AC-side terminals of the rectifiers, in particular wherein the pulse-width-modulated control signal is the manipulated variable of a controller which is designed such that the manipulated variable is determined such that the voltage applied to the series circuit, which is detected by means of a sensor,especially intermediate circuit voltage, is regulated to a setpoint.

[0013] The advantage here is that the voltage provided on the secondary side can be regulated in an electromagnetically compatible manner. This is because the voltage provided to the series circuit varies depending on the switch position. By controlling the switches with pulse width modulation, this voltage can be regulated to a setpoint using a controller. Although pulse width modulation is carried out asynchronously to the alternating current impressed on the primary conductor, the switches are operated synchronously with each other and synchronously with the zero crossings of the current in the primary conductor. This improves electromagnetic compatibility. The system is therefore subject to less electromagnetic radiation and / or load.

[0014] Important features of the system for contactless transmission of electrical power according to claim 2 are that a mobile part of the system has secondary windings, each of which is inductively coupled to a primary conductor of the system, into which an alternating current is or is impressed, wherein, in particular to form a respective resonant circuit, each of the secondary windings has a respective capacitance connected in parallel or in series, so that the resonance frequency of the respective resonant circuit thus formed is equal to the frequency of the alternating current impressed into the primary conductor, wherein each of the resonant circuits is connected to the AC voltage side terminal of a respective rectifier, wherein the DC voltage side terminals of the rectifiers are connected in parallel and supply a series circuit of in particular two capacitances, in particular to provide an intermediate circuit voltage,in particular, wherein the series circuit is designed as a capacitive voltage divider, wherein in each rectifier a respective controllable switch in its closed state connects a phase of the AC voltage-side connection of the respective rectifier to the center tap of the series circuit, wherein a controller, in particular depending on the deviation between the actual value of the voltage applied to the series circuit, in particular intermediate circuit voltage, and a setpoint value, generates a pulse-width-modulated control signal, which from a signal processing unit - depending on the output signal of a zero-current detection unit - feeds the control signal to the switches, in particular so that the change in state of the control signal is only passed through at or during detected zero current as a control signal for the switches, wherein the zero-current detection unit is connected to current sensors,which detect the respective input currents at the AC-side terminals of the rectifiers, in particular, wherein only the actual current value signal detected by the current sensor whose low-pass filtered, in particular sliding-determined, peak value signal is the largest is used to detect the zero current.

[0015] The advantage here is that the voltage provided on the secondary side can be regulated in an electromagnetically compatible manner. This is because the voltage provided to the series circuit varies depending on the switch position. By controlling the switches with pulse width modulation, this voltage can be regulated to a setpoint using a controller. Although pulse width modulation is carried out asynchronously to the alternating current impressed on the primary conductor, the switches are operated synchronously with each other and synchronously with the zero crossings of the current in the primary conductor. This improves electromagnetic compatibility. The system is therefore subject to less electromagnetic radiation and / or load.

[0016] In an advantageous embodiment, the primary conductor, to which the secondary windings arranged on the mobile part are inductively coupled, is laid out elongatedly in a system, in particular wherein the secondary windings are spaced apart from one another in the direction, in particular the laying direction, of the line conductor, in particular wherein the inductive coupling of the respective secondary windings to the primary conductor has different strengths. It is advantageous in this case that the primary conductor can be arranged along a railway line traversed by the mobile part, so that the mobile part, in particular the traction drive of the mobile part, can be supplied inductively from the primary conductor.

[0017] In an advantageous embodiment, each of the rectifiers is a single-phase bridge rectifier. This has the advantage that a voltage doubler circuit can be easily created by connecting or disconnecting the phase of the AC-side terminal to the center tap. In this way, a voltage between a single and double voltage value can be provided by pulse-modulated control of the switches.

[0018] In an advantageous embodiment, the alternating voltages applied to the AC-side terminals of the rectifiers are synchronous with each other, particularly time-synchronous. It is advantageous that the DC-side terminals of the rectifiers can be connected in parallel.

[0019] In an advantageous embodiment, the pulse-width modulated control signal is asynchronous to the alternating current impressed on the primary conductor and / or to the alternating voltages present at the AC-side terminals of the rectifiers. This is advantageous because the controller only has to consider the control deviation of the intermediate circuit voltage and can thus be independently optimized with respect to its pulse-width modulation frequency.

[0020] In an advantageous embodiment, the capacitors connected in series in the series circuit, in particular two capacitors, have the same capacitance values. It is advantageous in this case that half of the intermediate circuit voltage is available at the center tap. In an advantageous embodiment, the zero-sequence current detection unit is designed such that the input current of the AC-side terminal of the rectifier whose low-pass filtered input voltage at the AC-side terminal of the rectifier or whose low-pass filtered peak value signal of the actual current signal has the greatest value in terms of magnitude is used for zero-sequence current detection. It is advantageous in this case that the actual current signal with the best signal-to-noise ratio is used.

[0021] In an advantageous embodiment, the zero-current detection unit has a multiplexer with a select input for comparing the low-pass filtered, in particular sliding-determined, peak values ​​of the actual current value signals. Depending on the result of the comparison, only the actual current value signal or only the output signal of the comparator with the actual current value signal supplied to its input is passed from the multiplexer to the data input of a D flip-flop whose associated low-pass filtered, in particular sliding-determined, peak values ​​of the actual current value signal are the largest. In particular, the pulse-width modulated control signal is passed to the static input of the D flip-flop. The advantage here is that only the current sensor signal with the best signal-to-noise ratio is used for zero-current detection.

[0022] In an advantageous embodiment, the mobile part is movable along the primary conductor, in particular wherein the mobile part has a traction drive that can be powered by the voltage provided in the series circuit. The advantage here is that the inductive coupling enables contactless power supply to the mobile part.

[0023] In an advantageous embodiment, the current sensor(s) are designed as inductive current transformers. This has the advantage that the actual current signal is galvanically decoupled from the primary conductor.

[0024] In an advantageous embodiment, the comparator(s) are designed with a switching hysteresis. This is advantageous in that the switching edges upon detection of the zero crossing are very steep, and stable operating behavior can be achieved due to the hysteresis. In an advantageous embodiment, a comparator is connected downstream of the multiplexer. This is advantageous in that the switching edge output by the multiplexer has the desired steepness.

[0025] In an advantageous embodiment, each switch is controlled by a respective, in particular uniquely assigned, D flip-flop, wherein each of the data inputs of the D flip-flops is fed from the output of the multiplexer, and wherein the pulse-width-modulated control signal is supplied to each of the static inputs of the D flip-flops, with one of the data inputs being inverted. Advantageously, the switches can be operated synchronously or in a push-pull configuration.

[0026] Important features of the method for operating a system for contactless transmission of electrical power are that one or more secondary windings are inductively coupled to a primary conductor and a respective rectifier is supplied from the respective secondary winding, wherein by means of a respective switch a phase of the respective AC-side terminal of the respective rectifier is connected or not connected to a center tap of a series circuit formed from capacitors depending on the switching state of the respective switch, wherein the series circuit is supplied and / or fed from the DC-side terminals of the rectifiers connected in parallel, wherein a pulse-width modulated control signal is determined such that the voltage applied to the series circuit, in particular the intermediate circuit voltage, is regulated to a setpoint value,wherein only the state of the pulse-width-modulated control signal present at a zero crossing of an actual current value is fed to the switches, in particular as a control signal, wherein the actual current value is the input current at the AC-side terminal of the rectifier whose input current detected at the AC-side terminal has the greatest amplitude after peak value filtering and low-pass filtering.

[0027] The advantage of this is that the switching edge of the pulse-width-modulated control signal is only forwarded to the switches when zero current is present. Furthermore, the current signal with the best signal-to-noise ratio is always used for zero current detection.

[0028] In an advantageous embodiment, the actual current value is fed via a comparator to the data input of a D flip-flop, to whose static input the pulse-width-modulated control signal is fed. The advantage here is that the state of the multiplexer output signal applied to the data input is only available as the output signal of the D flip-flop and thus as a control signal for the switches when the control signal applied to the static input changes.

[0029] Further advantages emerge from the dependent claims. The invention is not limited to the combination of features in the claims. Further possible combinations of claims and / or individual claim features and / or features of the description and / or the figures will become apparent to those skilled in the art, particularly from the problem and / or the problem posed by comparison with the prior art.

[0030] The invention will now be explained in more detail using schematic illustrations:

[0031] Figure 1 schematically shows a system according to the invention for the contactless transmission of electrical power via an inductive coupling.

[0032] Figure 2 schematically shows another system according to the invention for contactless transmission of electrical power via an inductive coupling.

[0033] Figure 3 schematically shows another system according to the invention for contactless transmission of electrical power via an inductive coupling.

[0034] Figure 4 schematically shows another system according to the invention for contactless transmission of electrical power via an inductive coupling.

[0035] Figure 5 schematically shows another system according to the invention for contactless transmission of electrical power via an inductive coupling.

[0036] As shown in Figure 1, the system comprises a primary conductor 1, which is preferably provided in an industrial plant as an elongated line conductor.

[0037] A mobile part arranged to be movable along the primary conductor 1 has secondary windings 2 which are inductively coupled to the primary conductor 1 and thus provide a corresponding alternating voltage when a medium-frequency alternating current is impressed into the primary conductor 1.

[0038] Each of the secondary windings 2 has a respective capacitance connected in parallel and / or in series, which is dimensioned such that the resonant frequency of the resonant circuit formed by the respective capacitance and the respective secondary winding 2 is essentially equal to the frequency of the alternating current impressed into the primary conductor 1. In this way, efficient transmission of electrical power is possible even with weak and fluctuating inductive coupling. Each of the resonant circuits feeds a respective rectifier 8. In particular, the respective resonant circuit feeds the AC-side terminal of the respective rectifier 8.

[0039] The DC voltages provided at the respective DC voltage side connection of the respective rectifiers 8 are supplied via controllable switches 7 to capacitances 9, in particular intermediate circuit capacitances 9, in particular capacitors, wherein depending on the switch position of the switch 7 the two DC voltages are connected in parallel or only half the value of this respective DC voltage is generated and thus depending on the switch position an intermediate circuit voltage of different magnitude is made available, from which consumers can be supplied, such as the traction drive of the mobile part and / or an electronic circuit which is arranged on the mobile part.

[0040] In particular, the DC-side connection of the first rectifier 8 feeds the series circuit formed by the two capacitances, in particular capacitors, and the DC-side connection of the second rectifier 8 feeds the series circuit formed by the two capacitances 9, in particular capacitors.

[0041] By means of the first controllable switch 7, the center tap of the series circuit can be connected to a phase of the AC-side connection of the first rectifier 8, and by means of the second controllable switch 7, the center tap of the series circuit can be connected to a phase of the AC-side connection of the second rectifier 8.

[0042] When the switches 7 are closed, the center tap between the two capacitors 9 is galvanically connected to one of the phases of the AC side connection of the two rectifiers.

[0043] The switches 7 are operated synchronously; the two DC-side terminals of the rectifiers 8 are always connected in parallel.

[0044] In a first switch position of the switches 7, these switches 7 are open.

[0045] In a second switch position of the switch 7, one of the phases of the AC-side terminals of the two rectifiers is galvanically connected to one another and galvanically connected to the center tap between the series-connected capacitors 9, wherein this series connection of the capacitors 9 is supplied from the DC-side terminals of the rectifiers 8 connected in parallel.

[0046] As shown in Figure 1, both rectifiers are designed as single-phase bridge rectifiers.

[0047] In the first switch position, both switches 7 are open, and the lower DC-side potentials of the rectifiers 8 are connected to each other. The upper DC-side potentials of the rectifiers 8 are also connected to each other. Thus, the DC-side terminals of the two rectifiers are connected in parallel.

[0048] In the second switch position, all switches 7 are closed, and thus a first phase of the AC-side terminal of the first rectifier 8 is galvanically connected to the first phase of the AC-side terminal of the second rectifier 8. Furthermore, these two phases are also connected to the center tap between the two capacitors 9, which form a series circuit supplied by the two parallel-connected DC-side terminals of the rectifiers 8.

[0049] The voltage available in the series circuit can be described as intermediate circuit voltage and supplies a consumer not shown in Figure 1, for example an electric motor traction drive of the handset.

[0050] A zero current detection unit is arranged in the signal processing unit 4, wherein the zero current detection unit is designed to detect the zero crossing of the output current of that resonant circuit whose output current supplied to the respective rectifier has a better signal-to-noise ratio and / or whose output current supplied to the respective rectifier has the larger, in particular low-pass filtered, amplitude of the detected current signal.

[0051] To detect the better current sensor signal, in a first embodiment, the voltages applied to the secondary windings 2 are detected, rectified, and low-pass filtered. The two voltage signals thus obtained are low-pass filtered and fed to a comparator, which decides which of the two voltage signals is higher. Depending on the result of this decision, the comparator controls a switch, which, depending on its switching state, passes either the detected value of the output current of the first resonant circuit or the detected value of the output current of the second resonant circuit to the zero-current detection unit.

[0052] To detect the better current sensor signal, in a second embodiment, the respective current signal itself is passed through a peak filter and a low-pass filter and then fed to the comparator, which decides which of the two signals has the larger amplitude. Based on this decision, the corresponding current sensor signal is then selected, and the zero-current detection unit detects the zero crossing of the actual current value.

[0053] The intermediate circuit voltage is detected by a voltage sensor and the actual voltage value thus detected is regulated by a controller 5 to a setpoint value by the controller 5 generating a pulse-width modulated control signal 10 as a manipulated variable.

[0054] The pulse width modulation frequency of the control signal 10 is determined by the controller 5 depending on the difference between the actual voltage value and the voltage setpoint, in particular wherein the controller 5 is a PI controller or a PID controller.

[0055] The control signal 10 is fed to the signal processing unit 4, which determines the control signal 11 of the switches 7.

[0056] In this case, the control signal 10 is linked to the output signal of the zero current detection unit, so that a change in the state of the control signal 11 can only be effected when the zero crossing of the actual current value is detected, in particular when the output current of the associated oscillating circuit disappears.

[0057] Thus, when the output current disappears, the state of the control signal 11 is adjusted to the state of the control signal 10 currently present on the input side of the signal processing unit 4.

[0058] Thus, the switching state change of the switches 7 only occurs synchronously with the alternating current impressed into the primary conductor, whereby the pulse-width-modulated control signal 10 generated by the controller is asynchronous to the alternating current impressed into the primary conductor 1. The secondary windings 2 are spaced apart from one another along the primary conductor 1. The inductive coupling between the primary conductor 1 and the respective secondary winding 2 depends on the structural design of the system and also, for example, on a segmented routing of the primary conductor 1, so that the inductive coupling of each of the secondary windings 2 can be different. However, since the primary conductor 1 is supplied with an alternating current, the voltages induced in the secondary windings 2 are synchronous with one another.

[0059] The pulse width modulation frequency is smaller than the frequency of the alternating current impressed into the primary conductor 1, in particular at least four times smaller.

[0060] For example, the pulse width modulation frequency has a value between 10 kHz and 20 kHz, specifically a value from the frequency range that is not or only barely perceptible to humans. The frequency of the alternating current impressed into primary conductor 1, for example, has a value between 30 kHz and 1 MHz.

[0061] Thus, the respective edge of the control signal 11 is essentially shifted by no time or only by a short time period relative to the respective switching edge of the control signal 10.

[0062] In particular, when switches 7 are permanently closed, the intermediate circuit voltage is twice as high as when switches 7 are open.

[0063] In further embodiments according to the invention, not only two but also additional secondary windings 2 are provided in a corresponding manner, each of which is inductively coupled to the primary conductor and to which further capacitors are connected in parallel and / or in series, so that the resonance frequencies of the respective resonant circuits thus formed are equal to the frequency of the alternating current impressed into the primary conductor.The output current of the resonant circuit flowing from the respective resonant circuit having the respective secondary winding 2 to a respective rectifier 8, which is assigned to the respective secondary winding, is in turn detected and fed to the selection switch, in particular select switch, which is now designed as a selector switch, wherein the selection switch is controlled by the zero current detection unit, which in turn compares the rectified and low-pass filtered current or voltage signals by means of the comparator and determines the signal with the largest magnitude in order to control the selection switch in such a way that the zero crossing of the corresponding output current can be used to enable the change in state of the control signal.

[0064] As shown in Figure 2, the signal processing unit 4 comprises a first comparator 20, to which the actual current value signal detected by the first current sensor is fed, and a second comparator 20, to which the actual current value signal detected by the second current sensor is fed. In this way, a well-defined edge steepness can be provided.

[0065] The output signals of both comparators 20 are fed to a multiplexer 21, whereby only that of the two output signals is passed to the output out of the multiplexer 21 whose associated selection signal is the stronger signal at the select input of the multiplexer 21.

[0066] The selection signal assigned to the first current sensor 3 is generated from the actual current value signal of the first current sensor 3 by feeding it to a peak value filter 22, the output signal of which is fed to a low-pass filter 23, the output signal of which is fed to the first terminal of the select input of the multiplexer 21.

[0067] The selection signal assigned to the second current sensor 3 is generated from the actual current value signal of the second current sensor 3 by also feeding this to a further peak value filter 22, the output signal of which is fed to a further low-pass filter 23, the output signal of which is fed to the second terminal of the select input of the multiplexer 21.

[0068] Since the respective comparator 20 receives the respective actual current value signal directly, an interference-free digital signal is present at the multiplexer.

[0069] The output signal of multiplexer 21 is fed to the data input of a D flip-flop 24. The pulse-width-modulated control signal 10 generated by controller 5 is fed to the static input of D flip-flop 24. The output of D flip-flop 24 provides the control signal for controlling switches 7. These switches 7 are, in turn, controlled synchronously.

[0070] According to the invention, the pulse width modulated control signal of the controller is

[0071] 5, in particular the voltage regulator, is only passed on to the voltage generation unit 6, which includes the rectifiers 8, the switches 7, and the capacitors 9, upon the positive edge of the comparator output, in particular upon a current zero crossing from negative to positive. In other embodiments, however, the D flip-flop 24 reacts to the negative edge or to both edges.

[0072] In the embodiment shown in Figure 3, in contrast to the embodiment shown in Figure 2, two D flip-flops 24 are used, with the control signal of the respective switch 7 being provided by a respective D flip-flop 24, whose statistical inputs are connected in parallel and whose data inputs are inverted to achieve counter-clocked switching of the switches 7 and thus also a different control behavior when controlling the intermediate circuit voltage. In particular, this allows for a further improvement in electromagnetic compatibility.

[0073] In further embodiments according to the invention, several D flip-flops 24 could also be connected in series in order to delay the PWM signal of the controller by several current zero crossings.

[0074] In the embodiment according to Figure 4, in contrast to the embodiment according to Figure 2, the comparators 20 are removed and only a single comparator 20 is arranged on the output side of the multiplexer 21.

[0075] In the embodiment shown in Figure 5, in contrast to the embodiment shown in Figure 2, only a single secondary winding 2 is provided on the mobile part, which is connected in parallel or in series with a capacitor, so that the resonant frequency of the thus formed resonant circuit equals the frequency of the alternating current impressed on the primary conductor 1. The rectifier 8 is fed from the resonant circuit. The input current at the AC-side input of the rectifier 8 is detected by a current sensor 3, in particular the output current of the resonant circuit.

[0076] A series circuit comprising two capacitors 9 is supplied from the DC-side terminal of the rectifier 8, with the center tap of the series circuit being connectable to a phase of the AC-side terminal of the rectifier 8 via a controllable switch 7. A controller 5 regulates the voltage applied to the series circuit, in particular the intermediate circuit voltage, to a setpoint by determining a pulse-width modulated control signal as a manipulated variable, which is fed to the static input of a D flip-flop 24, the output signal of which is used as the control signal for the switch 7.

[0077] The actual current value signal, which is passed through a comparator 20, is fed to the data input of D flip-flop 24. The aforementioned peak filters 24 are preferably discharged with a time constant. For example, these peak filters 24 are implemented as a capacitor that can be fed via a diode, with a high-ohm resistor connected in parallel such that the capacitor is discharged with the specified time constant. In particular, peak filtering is thus implemented in a sliding manner. Furthermore, low-pass filtering integrated into the peak filter is possible.

[0078] List of reference symbols

[0079] 1 primary conductor, in particular elongated line conductor

[0080] 2 Secondary winding, in particular secondary winding designed as a resonant circuit with capacitance

[0081] 3 Current sensor

[0082] 4 Signal processing unit

[0083] 5 controls

[0084] 6 Voltage generation unit

[0085] 7 switches

[0086] 8 rectifiers

[0087] 9 Capacitance, especially intermediate circuit capacitor

[0088] 10 Control signal

[0089] 11 Control signal

[0090] 20 Comparator

[0091] 21 multiplexers

[0092] 22 peak filters

[0093] 23 low-pass filters

[0094] 24 D flip-flop

Claims

Patent claims:

1. System for contactless transmission of electrical power, wherein a mobile part of the system has one or more secondary windings from which one or more respective rectifiers are supplied, wherein by means of one or more switches one phase of the respective AC-side terminal of the respective rectifier can be connected to a center tap of a series circuit formed from capacitors (9), which is supplied and / or fed from the parallel-connected DC-side terminals of the rectifiers, wherein a signal processing unit (4) is designed with a zero-current detection unit,that the signal processing unit releases a pulse-width-modulated control signal (10) to the switch(es) (7) as a respective control signal (11) only when the input current at the AC-side terminal of the rectifier (8) or at one of the respective AC-side terminals of the rectifiers (8) vanishes, in particular thus feeding it to the switches for their control, in particular wherein the AC voltages applied to the AC-side terminals of the rectifiers are synchronous to one another, in particular time-synchronous, in particular wherein the pulse-width-modulated control signal (10) is asynchronous to the AC voltages applied to the AC-side terminals of the rectifiers (8), in particular wherein the pulse-width-modulated control signal is the manipulated variable of a controller which is designed such that the manipulated variable is determined such that the value detected by means of a sensor,the voltage applied to the series circuit, in particular the intermediate circuit voltage, is regulated to a setpoint.

2. System for the contactless transmission of electrical power, wherein a mobile part of the system has secondary windings, each of which is inductively coupled to a primary conductor of the system, into which an alternating current is or is impressed, wherein, in particular to form a respective resonant circuit, each of the secondary windings has a respective capacitance connected in parallel or in series, so that the resonance frequency of the respective resonant circuit thus formed is equal to the frequency of the alternating current impressed into the primary conductor, characterized in that each of the resonant circuits is connected to the AC voltage side terminal of a respective rectifier, wherein the DC voltage side terminals of the rectifiers are connected in parallel and supply a series circuit of in particular two capacitances, in particular to provide an intermediate circuit voltage,in particular wherein the series circuit is designed as a capacitive voltage divider, wherein in each rectifier a respective controllable switch in its closed state connects a phase of the AC voltage side connection of the respective rectifier to the center tap of the series circuit, wherein a controller, in particular depending on the deviation between the actual value of the voltage applied to the series circuit, in particular intermediate circuit voltage, and a setpoint value, generates a pulse width modulated control signal which is supplied by a, Signal processing unit - depending on the output signal of a zero current detection unit - transmits the control signal to the switches, in particular so that the change in state of the control signal is only transmitted at or during detected zero current as a control signal for the switches, wherein the zero current detection unit is connected to current sensors which detect the respective input currents at the AC voltage side terminals of the rectifiers, in particular wherein only the actual current value signal detected by the current sensor whose low-pass filtered, in particular slidingly determined, peak value signal is the largest is used to detect the zero current.

3. System according to claim 1 or 2, characterized in that the primary conductor, to which the secondary windings arranged on the mobile part are inductively coupled, is laid in an elongated manner in a system, in particular wherein the secondary windings are spaced apart from one another in the direction, in particular the laying direction, of the line conductor, in particular wherein the inductive coupling of the respective secondary windings to the primary conductor is of different strengths.

4. System according to one of the preceding claims, characterized in that each of the rectifiers is a single-phase bridge rectifier.

5. System according to one of the preceding claims, characterized in that the alternating voltages applied to the AC-side terminals of the rectifiers are synchronous with one another, in particular time-synchronous, and / or that the pulse-width modulated control signal is asynchronous with the alternating current impressed into the primary conductor and / or with the alternating voltages applied to the AC-side terminals of the rectifiers.

6. System according to one of the preceding claims, characterized in that the capacitors connected in series in the series circuit, in particular two capacitors, have the same capacitance values.

7. System according to one of the preceding claims, characterized in that the zero current detection unit is designed such that the input current of the AC-side terminal of that rectifier is used for zero current detection whose low-pass filtered input voltage at the AC-side terminal of the rectifier or whose low-pass filtered peak value signal of the actual current value signal has the respective largest value in terms of magnitude.

8. System according to one of the preceding claims, characterized in that the zero current detection unit has a multiplexer with a select input for comparing the low-pass filtered, in particular slidingly determined, peak values ​​of the actual current value signals, wherein, depending on the result of the comparison, only that actual current value signal or only the output signal of that comparator with the actual current value signal supplied to its input is passed from the multiplexer to the data input of a D flip-flop whose associated low-pass filtered, in particular slidingly determined, peak values ​​of the actual current value signal are the largest, in particular wherein the pulse-width modulated control signal is passed to the static input of the D flip-flop.

9. System according to one of the preceding claims, characterized in that the mobile part is movable along the primary conductor, in particular wherein the mobile part has a traction drive which can be supplied from the voltage provided at the series circuit.

10. System according to one of the preceding claims, characterized in that the current sensor(s) are designed as inductive current transformers.

11. System according to one of the preceding claims, characterized in that the comparator(s) are designed with a switching hysteresis and / or that the pulse width modulation frequency is smaller than the frequency of the alternating current impressed into the primary conductor (1), in particular at least four times smaller.

12. System according to one of the preceding claims, characterized in that a comparator is connected downstream of the multiplexer.

13. System according to one of the preceding claims, characterized in that each switch is controlled by a respective, in particular uniquely assigned, D flip-flop, wherein each of the data inputs of the D flip-flops is fed from the output of the multiplexer and wherein the pulse-width modulated control signal is supplied to each of the static inputs of the D flip-flops, wherein one of the data inputs is designed to be inverting.

14. A method for operating a system for contactless transmission of electrical power according to one of the preceding claims, wherein one or more secondary windings are inductively coupled to a primary conductor and a respective rectifier is supplied from the respective secondary winding, characterized in that by means of a respective switch, a respective phase of the respective AC-side terminal of the respective rectifier is connected or not connected to a center tap of a series circuit formed from capacitors (9) depending on the switching state of the respective switch, wherein the series circuit is supplied and / or fed from the DC-side terminals of the rectifiers connected in parallel, wherein a pulse-width-modulated control signal is determined such that the voltage applied to the series circuit, in particular the intermediate circuit voltage, is regulated to a desired value,wherein only the state of the pulse-width-modulated control signal present at a zero crossing of an actual current value is fed to the switches, in particular as a control signal, wherein the actual current value is the input current at the AC-side terminal of the rectifier whose input current detected at the AC-side terminal has the greatest amplitude after peak value filtering and low-pass filtering.

15. Method according to one of the preceding claims, characterized in that the actual current value is fed via a comparator to the data input of a D flip-flop, to whose static input the pulse-width modulated control signal is fed.

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