GB2482201A

GB2482201A - Inductive energy receiver for rail vehicle

Info

Publication number: GB2482201A
Application number: GB1012460.0A
Authority: GB
Inventors: Ja Rgen Meins; Faical Turki; Harry Seiffert
Original assignee: Bombardier Transportation GmbH
Current assignee: Alstom Transportation Germany GmbH
Priority date: 2010-07-23
Filing date: 2010-07-23
Publication date: 2012-01-25
Also published as: WO2012010649A2; WO2012010649A8; GB201012460D0; WO2012010649A3

Abstract

An arrangement adapted for receiving an electromagnetic field, for producing electric energy from the electromagnetic field by induction and for providing a load 205, particularly a rail vehicle, with the electric energy. The arrangement comprises at least one phase line 1a, 2a, 3a comprising an inductance L71, L72, L73 and a capacitance C71, C72, C73 and a rectifier 203 connected to the at least one phase line. The capacitance is arranged and used to optimize a phase shift between the voltage induced by the electromagnetic field and the current produced by the voltage while electric energy is transferred to the load. The capacitance comprises at least two capacitors 371, 381, 382, 383, 384 and at least one of the capacitors is switchable and is connected to the phase line via a switch 385, 383, 387, 388. A control device 397 is provided, connected to the switch and adapted to switch on or switch off the at least one switchable capacitor so that the capacitance, and thereby the phase shift is modified.

Description

Operating an inductive energy receiver The invention relates to an arrangement for receiving an electromagnetic field, for producing electric energy from the electromagnetic field by induction and for providing a load with the electric energy, in particular for providing a rail vehicle (e.g. a tram) or a road vehicle with energy. Furthermore, the invention relates to a method of operating such an arrangement.

Track bound vehicles, in particular vehicles for public passenger transport, usually comprise a contactor for mechanically and electrically contacting a line conductor along the track, such as an electric rail or an overhead line. Typically, at least one propulsion motor on board the vehicles is fed with the electrical power from the external track or line and produces mechanic propulsion energy. In addition or alternatively, the transferred energy can be used for operating auxiliary systems of the vehicle. Such auxiliary systems, which do not produce traction of the vehicle, are, for example, lighting systems, heating and/or air conditioning system, the air ventilation and passenger information systems.

Trams and other local or regional trains are operated usually via overhead lines within . cities. However, especially in historic parts of cities, overhead lines are undesirable. On the other hand, conductor rails in the ground or near the ground cause safety problems.

The present invention in particular relates to inductively transferring energy from an arrangement of electrical conductors, which is arranged along the track, to the vehicle while the vehicle is travelling along the track. There is no electrical contact between the *:::* vehicle and the conductor arrangement. The conductor arrangement carries an alternating current which generates a corresponding alternating electromagnetic field and the electromagnetic field is used to transfer the electrical energy to the vehicle.

For receiving the electromagnetic field and for producing electric energy by induction, the receiving arrangement comprises at least one inductor. The electric voltage which is induced is an alternating voltage corresponding to the frequency of the electromagnetic field, If a load is provided with electric energy from the receiving arrangement, the resulting alternating current is rectified, either by a controlled rectifier or by an uncontrolled rectifier. The efficiency of the rectifier depends on the phase shift of the alternating voltage and the alternating current on the input side of the rectifier. Voltage and current should be in phase, i.e. the phase shift should be zero. Therefore, each phase line of the receiving arrangement is provided with a capacitance. If the capacitance of the phase line is chosen so that the impedance is zero, voltage and current are in phase.

However, it is difficult to choose the capacitance, since the inductance may vary.

It is an object of the present invention to provide an arrangement for receiving an electromagnetic field and for producing electric energy from the field by induction in order to provide a load with the electric energy, wherein the losses caused by a phase shift between the alternating voltage and the alternating current are reduced. In particular, the long-term mean value of the losses shall be minimized.

The invention is based on the following considerations: The inductance and the capacitance of each of the phase lines of the receiving may vary due to different effects.

The inductance which is effective for the impedance is influenced by any inductance of other phase lines of the receiving arrangement. Furthermore, the effective inductance depends on the coupling to the conductor or conductors which produce the electromagnetic field. In particular, the distance to these primary side conductor or conductors influences the effective inductance on the secondary side of the system.

The term "phase line" also includes the case that the capacitance is parallel to the *...

* inductance in contrast to the preferred case in which the capacitance is in series to the * inductance. *

...: Preferably, the primary side conductor arrangement may be arranged along a track of a * rail vehicle or of a road vehicle. The secondary side is the side of the receiving *:::* arrangement which produces the electric energy by induction. It might be possible to find a capacitance which is optimized for the average coupling between the primary side and the secondary side and which takes the influences of the inductivities of the other phase lines of the receiving arrangements into account. However, even such an optimized capacitance is subject to variation. One important factor which influences the capacitance is the temperature. More generally speaking the ambience of the receiving arrangement may influence the capacitance (and also the inductance). In addition, the capacitor or capacitors which constitute the capacitance may change due to ageing.

In order to reduce or eliminate the effect of the ambient temperature, the temperature can be controlled for example by using a cooling device. However, the aging effect cannot be eliminated by controlling the temperature.

Alternatively, the capacitance can be realized by a combination of different capacitors, wherein some of the capacitors have a positive temperature coefficient and the other capacitors have a negative temperature coefficient. This might reduce the influence of the temperature on the capacitance, but -again -does not eliminate the aging effect.

Therefore, it is a basic idea of the present invention to provide at least one capacitor which can be switched on and switched off. Switching on the at least one capacitor means that the total capacitance of the phase line includes the switchable capacitor or capacitors.

On the other hand, the switchable capacitor or capacitors do not influence the total capacitance if it/they is/are switched off. In particular, each phase line may comprise one or more than one capacitors which is/are not switchable. In addition, at least one switchable capacitor may be connected in parallel to the non-switchable capacitor/s.

One possibility to choose the optimal capacitance is to observe from time to time the efficiency of the rectifier. This efficiency may be observed indirectly or directly. For example, the efficiency may be observed indirectly if the energy which is transferred to the load is measured over a period of time. In case of a rail vehicle, for example, the period of time may be one day of operation. If the energy which is provided to the battery system of the rail vehicle is larger for a specific capacitance than for another capacitance, this S...

specific capacitance is used for further operation.

S..... * .

Alternatively, direct measurement of the efficiency of the rectifier can be performed by 1...: measuring electric quantities directly at the input and/or output of the rectifier. According * to a preferred embodiment, the output voltage (the rectified direct voltage) of the rectifier *::: is measured, and optionally the direct current at the output of the rectifier is also * measured.

Preferably, the switching state of the at least one switchable capacitor is automatically controlled by a control device. The control device is adapted to control the switch or switches for switching on and off the at least one switchable capacitor. As a result, the capacitance is modified, thereby, the phase shift between the voltage and the current is reduced and, thereby, an efficiency of the arrangement is increased (in particular an impedance of the arrangement is reduced). There are several approaches how the control device can make sure that the efficiency of the arrangement is actually increased by modifying the capacitance. These approaches will be described in the following. However, in any case, it is preferred that the arrangement comprises: -at least one phase line comprising an inductance and a capacitance, wherein the capacitance is arranged and used to optimize a phase shift between the voltage which is induced by the electromagnetic field and the current which is produced by the voltage while electric energy is transferred to the load, -a rectifier which is connected to the at least one phase, and wherein: -the capacitance comprises at least two capacitors, -at least one of the capacitors is switchable and is connected to the phase line via a switch and -wherein the arrangement comprises a control device which is connected to the switch and which is adapted to switch on or switch off the at least one switchable capacitor so that the capacitance is modified, thereby the phase shift is modified and thereby an efficiency of the arrangement is improved, in particular an impedance of the arrangement is reduced.

Preferably, the control performed by the control device is performed periodically, i.e. it is periodically checked if the capacitance is to be modified. A corresponding closed control loop uses at least one measurement value, preferably a voltage and/or a current on the input side and/or output side of the rectifier. This at least one measurement value forms the basis for calculating whether the capacitance is to be modified or not, and, if yes, in I...

* which manner the capacitance is to be modified.

* .* *** * S The load which is to be provided with electric energy by the arrangement may be any * electric load within a vehicle, such as a rail vehicle or a road vehicle. In case of a rail 55.5.

* vehicle, the load may be the traction system for generating traction of the vehicle and/or *:::* anyauxiliarydevice which is used during operation of the vehicle, butdoes not produce * traction. S..

In particular, the arrangement may comprise a voltage sensor adapted and arranged to measure a voltage which is or depends on the voltage that is induced by the electromagnetic field and/or may comprise a current sensor adapted and arranged to measure a current in the phase line or a load current produced by the voltage and wherein the control device is adapted to control the at least one switch depending on the measured voltage and/or on the measured current.

One way to perform the control is to switch on or off at least one of the capacitors in order to increase or decrease the capacitance, to evaluate a resulting modification of the measured voltage and/or measured current, to decide whether the increased or decreased capacitance results in an improved efficiency (in particular a reduced impedance) of the arrangement and to reverse the switching state of the capacitors and/or to switch off or on at least another one of the capacitors if the increased or decreased capacitance has not resulted in an improved efficiency (in particular a reduced impedance) of the arrangement.

This way of performing the control has the advantage that the control is independent of the specific features of the receiving arrangement. Therefore, the same control can be performed for different types of receiving arrangements. In addition, since the calculations which are to be performed by the control device are simple, the control is fast and, therefore, can be performed at very high frequencies. As a result, fast changes of the induced voltage, for example due to fast changes of the coupling between the primary side and the secondary side (see above), can be compensated by this type of control.

According to a possible embodiment of this type of control, the increase or decrease of the capacitance is performed as a test in order to find out if the increased or decreased capacitance results in a reduced impedance and this test is repeatedly performed, for example periodically at a predetermined repetition frequency. This means, for example, that an optimized capacitance may have been found after performing the test, but the test * is repeated an,way to find out if the optimized value of the capacitance is still optimal. * *

Another way of performing the control isto repeatedly evaluate the measured voltage * and/or the measured current, to repeatedly calculate the efficiency (in particular *1***S * impedance) of the arrangement from the measured values and to control the at least one switch so that the efficiency is maximized (in particular the impedance is minimized).

* Preferably, the calculation of the efficiency of the arrangement from the measured values a.

* is based on a calculation model of the receiving arrangement. It is not necessary that the model is a complete model of the receiving arrangement. For example, considering the timing and delays of the receiving arrangement is one way of modelling the behaviour of the arrangement. Delay" means that the result of a modification of the capacitance cannot be measured immediately after the modification. Rather, the electric current through the respective phase line will react faster to the modification of the capacitance then the electric voltage which is induced.

The impedance of the receiving arrangement is a preferred physical quantity for use in the control of switching on or off the capacitor or capacitors. The impedance can easily be determined from the quotient of the voltage and the current on the output side (direct current side) of the rectifier. Observing the voltage and the current on the output side of the rectifier has the advantage that these electric quantities can easily be measured. In case of a receiving arrangement having more than one phase (e.g. three phases and therefore having three phase lines) the voltage and current on the output side depend on the capacitance of all phase lines.

If the control is performed at high frequencies (for example 1 Hz or higher) which are higher then the fluctuations of the induced voltage effective inductance due to changes in the ambience and/or changes of the coupling between the primary side and the secondary side, it may be sufficient to measure only the current or the voltage, in particular on the output side of the rectifier. Therefore, especially the first type of control which comprises the test mentioned above can be performed using just one electric quantity as input to the control.

The second type of control which uses a model of the receiving arrangement has the advantage that the switching of the switchable capacitor or capacitors can be performed at lower frequencies. This reduces switching losses.

If a model is used forthe control, itis preferred thatthe derivative of the impedance of the S...

* receiving arrangement with respect to a variation of the capacitance is calculated and is q ** *5* * controlled to be zero. The idea behind this way of performing the control is that the * capacitance is optimal if this derivative is zero since both an increased and a decreased S.....

* capacitance would lead to an increased impedance. S**S

S

In case that a model of the receiving arrangement is used for the control, it is preferred * that measurement values of the voltage and of the current, preferable on the output side of the rectifier, are collected over a period of time. Usually, the current varies over this period of time, since the load is varying. In addition, the induced voltage may also vary. As a result, several pairs of measurement values, each consisting of a voltage value and a current value, are obtained and increase the reliability of the determination of the impedance. If the impedance is also varying, this will typically take place as fluctuation due to fluctuating ambience conditions and/or coupling to the primary side. Therefore, the result for the impedance obtained from the collected measurement values is a mean value. For the control, such a mean value is preferred compared to fluctuating values, since the control becomes more stable. In case of a rail vehicle, a time interval for the collection of measurement values of about one second is appropriate.

In particular, the switching time for switching the switchable capacitor(s) on or off is a point in time when the alternating voltage which is induced by the electromagnetic field is zero or is smaller than a predetermined threshold value. Therefore, only a small electric current flows during the switching process. The time-dependent voltage can be measured or the control device, which controls the switching of the capacitors, is coupled to the rectifier which enables the switching only if the voltage is (nearly) zero.

In case that the receiving arrangement comprises more than one phase line, each of the phase lines comprises an inductance and a capacitance. Furthermore, each of the capacitances comprises at least on switchable capacitor so that the impedance of each phase line can be minimized separately by switching on and off the at least one switchable capacitor. Preferably, the separate control processes for controlling the switching off the capacitors of the different phase lines use the measured voltage and/or current on the output side (direct current side) of the rectifier as measured input variables.

The electric variables on the output side of the rectifier depend on the capacitance in every phase line. Measuring the electric quantities on the output side of the rectifier reduces the number of measurements needed compared to measuring the individual quantities in the phase lines on the input side of the rectifier. Furthermore, as mentioned above, the quotient of the voltage and the current on the output side of the rectifier, i.e. the S..

impedance of the receiving arrangement, including all phase lines, directly indicates the *.. SI.

efficiency of the receiving arrangement and a complicated measurement of the time behaviour of the voltage and current in order to compute the phase shift on the input side of the rectifier can be omitted.

s.d...

I

For example, the control of the different phase lines can be performed periodically, * wherein several cycles of the control process for an individual phase line are performed * and then several cycles of the control process for another phase line are performed and so on, so that all phase lines are controlled in sequential order one after the other.

Preferably, each cycle of each control process includes the measurement of the corresponding input variables (in particular voltage and/or current).

The present invention also provides a method of operating an arrangement for receiving an electromagnetic field, for producing electric energy from the electromagnetic field by induction and for providing a load with the electric energy, wherein: -at least one capacitor of the arrangement is switched on or off so that a capacitance of the arrangement is modified, -the switching is performed in a manner so that an impedance of the arrangement is reduced.

In particular, the method may be performed to operate an arrangement according to one of the embodiments described in this description. Modifications and embodiments of the method have been described or follow from the description of the arrangement.

Examples and further embodiments of the invention will be described with reference to the attached drawing in the following. The figures of the drawing show: Fig. 1 a tram travelling on a track which comprises a conductor arrangement for

producing an electromagnetic field,

Fig. 2 a receiving arrangement having three phases for receiving an electromagnetic field, for example the electromagnetic field produced by the conductor arrangement shown in Fig. 1, wherein the receiving arrangement comprises a rectifier which is connected to the three phase lines of the receiving arrangement and wherein a load is connected to the output side of the rectifier, Fig. 3 schematically the control of four switchable capacitors which are connected in parallel to each other and in parallel to a non-switchable capacitor, Fig. 4 a diagram showing the voltage on the output side of a rectifier, for example the rectifier of the arrangement shown in Fig. 2, as a function of the direct current on S.. SSS * the output side of the rectifier for two different values of the capacitance, Fig. 5 the capacitance as a function of time fora control which performs switching steps * in order to find out if a modified capacitance would result in an improved S. SSS* * impedance of a receiving arrangement, and Fig. 6 a control loop which uses a model of the receiving arrangement for minimizing * the impedance of a receiving arrangement. * S.

S

Fig. 1 shows a vehicle 162, e.g. a tram, which is provided with energy by induction. The track of the vehicle 162, which is not shown in detail (for example the rails are not shown) comprises a conductor arrangement 157 for producing an electromagnetic field. In this particular embodiment, the conductor arrangement 157 is divided in consecutive segments 157a, 157b, 157c, 157d, 157e, 157f which can be operated separatelyand independent of the other segments. Each segment I 57a -1 57f comprises electrical conductors which carry an alternating current while operated. Consequently, an electromagnetic field is produced which is received by the receiving arrangement 161 of vehicle 162. In particular, the electric energy which is produced by the receiving arrangement 161 is used to charge energy storages 163a, 163b. Alternatively, the electric energy may directly be used for traction or auxiliary devices.

In the specific embodiment shown in Fig. 1, the conductors of the segments 1 57a -I 57f are provided with electric energy via direct current lines 141 a, 141 b and respective inverters 1 52a, 1 52b, 1 52c, 1 52d, 1 52e for inverting the direct current into an alternating current through the conductors. The operation of the segments 1 57a -1 57f may be controlled by a control device 151 which directly controls one of the inverters 152c.

Control signals to the other inverters 1 52a, I 52b, 1 52d, 1 52e are transferred from the inverter 152c via a control line arrangement 158. These control signals may be start and stop signals for starting and stopping the operation of the respective inverter 152.

Fig. 2 shows a receiving arrangement having three phases. Each phase comprises an inductance L71, L72, L73 and a capacitance C71, C72, C73. The inductance and the capacitance can be realized in each case by a plurality of elements. The inductance may be realized, for example, by one or more than one windings of an electrical conductor.

The inductance is connected with the capacitance, wherein the capacitance may be formed by capacitors which are connected in parallel to each other. This means that the S..... current which is produced by the inductance by induction flows to one pole of the capacitance and the other pole of the capacitance is connected to the input side of a rectifier. Furthermore, the inductivities of the different phase lines are connected to a common star point 71.

S *.... * S

The number of different phase lines of the receiving arrangement is not restricted to three.

**.:.. Any other number of phase lines, including one, can be used. The electric voltages and currents which are produced by the phase lines are not in phase, i.e. there is a phase shift, provided that the different phase lines are located at a distance to each other and that the different locations of the phase lines are met by different flux lines of the electromagnetic field. For example, in case of the vehicle shown in Fig. 1 which travels along a track, the different phase lines are located at a distance to each other in the direction of travel. The phase shift between the phase lines depends on the distance and

on the electromagnetic field.

In Fig. 2 the phase lines are denoted by reference numerals la, 2a, 3a. During operation, while a load is connected to the rectifier 203, an alternating current Isla, ls2a, Is3a is produced by the phase lines la, 2a, 3a.

The arrangement shown in Fig. 2 comprises a non-controlled rectifier 203. Alternatively, a controlled rectifier may be connected to the phase lines la, 2a, 3a. In the example shown in Fig. 2, each phase line 1 a, 2a, 3a is connected to a branch of the rectifier 203, wherein each branch comprises two diodes 211a, 211b; 212a, 212b; 213a, 213b which are connected in series to each other. The phase lines Ia, 2a, 3a are connected to a point in between the respective series connection of diodes 211, 212, 213 of the branch. The branches are parallel to each other and are connected to direct current lines 76a, 76b.

During operation, the direct current line 76b is at lower electric potential than direct current line 76a.

A capacitance 204 which may have the capacitance value C7d may be connected in parallel to the branches of the rectifier 203 in order to flatten fluctuations of the output voltage of the rectifier 203. The output voltage is the difference of the electric potentials of direct current lines 76a, 76b. The output voltage Ud is drawn on the right hand side of Fig. 2 as a voltage across a load 205 which may have the resistance RL.

Alternatively to the circuit diagram shown in Fig. 2, a delta circuit may be used instead of the star point circuit shown and/or the capacitance may be in parallel to the inductance instead of in series to the inductance. * *

Fig. 3 shows an arrangement of capacitors 371, 381, 382, 383, 384 which form a capacitance of a single phase line of a receiving arrangement for receiving an electromagnetic field. Preferably, each of the phase lines of the receiving arrangement *:::* comprises such an arrangement of capacitors. Four of the capacitors 381, 382, 383, 384 * are connected in series with a switch 385, 386, 387, 388 so that they are switchable independently of the other capacitors. If the corresponding switch 385, 386, 387, 388 is closed, the capacitor 381, 382, 383, 384 contributes to the total capacitance. If the corresponding switch 385, 386, 387, 388 is open, the capacitor 381, 382, 383, 384 does not contribute to the total capacitance. The vertical line 1 a below and above the capacitor 371 can be interpreted as a section of one of the phase lines of the arrangement in Fig. 2.

In this case, the horizontal lines 351, 354 in Fig. 3 are the electric connections from the capacitors 381, 382, 383, 384 to the phase line Ia.

The total capacitance influences the efficiency of the receiving arrangement which is schematically shown in block 395. The efficiency can be determined by measuring the voltage and the current, in particular on the output side of the rectifier of the receiving arrangement. Optionally, the measured values of the voltage and the current may be collected over a time interval of predetermined length. The measurement values are input to a efficiency calculation device 396 which is part of the closed control loop and may be realized by a computer program or by an electric and/or electronic circuit. The calculation may be performed in different manner and different quantities can be calculated as measure of the efficiency. The calculation of one of the possible measures is sufficient for each implementation of the control loop. In the example shown in Fig. 3, the measure is the angle q between the phases of the current and voltage in one of the phase lines. In this case, the angle is the phase difference which could also be denoted by ip.

An alternative measure of the efficiency is the impedance of the receiving arrangement, including the rectifier, which can be calculated by dividing the voltage on the output side of the rectifier by the current on the output side of the rectifier. Alternatively, if the cycle of performing the control loop is fast compared to the time constant of the voltage (which is preferred), it is also possible to measure the increase or decrease of the current as a reaction to the increase or decrease of the capacitance performed in a preceding cycle of the control loop. I..

The calculation of the impedance or the phase difference between the voltage and the current on the input side of the rectifier is not necessarily based on a model of the receiving arrangement, since these measures of the efficiency are measures which characterize any type of receiving arrangement. However, this does not exclude the possibility that these or other measures of the efficiency are calculated using a model of the receiving arrangement. An example of a control loop which uses a model of the *:*::* receiving arrangement will be described with reference to Fig. 6.

S

The control loop shown in Fig. 3 also comprises a calculation device 397, which may also be implemented using a computer program or an electric and/or electronic circuit, for calculating the desired capacitance or for calculating the desired modification of the presence capacitance. The calculation device 397 outputs a corresponding signal in order to modify the capacitance. In the example shown in Fig. 3, the output signal is transferred to an AND logic device 390, 391, 392, 393 which is connected to the respective switch 385, 386, 387, 388 of the capacitor 381, 382, 383, 384 to be switched on or off. The AND logic device 390, 391, 392, 393 comprises a second input which is connected to a detecting device 398 for detecting if the voltage of the phase line on the input side of the rectifier is zero or if the absolute value of the voltage is smaller than a predetermined threshold value. This ensures that the capacitor is only switched on or off while the voltage is nearly zero. The corresponding AND logic device 390, 391, 392, 393 outputs a switch command or enabling signal to the switch 385, 386, 387, 388 only if the signals at both inputs of the logic device 390, 391, 392, 393 indicate that the respective switch 385, 386, 387, 388 is to be switched.

With reference to Fig. 4, a first way of performing the control will be described. The basic principle of this way of performing the control is the test mentioned above, wherein the capacitance is varied and the response of the receiving device is evaluated in order to find out if the per-formed variation of the capacitance has increased or decreased the efficiency. This test may be performed periodically as will be described with reference to Fig. 5.

Fig. 4 shows a diagram of the dependency of the voltage on the output side of the rectifier DC-U on the current on the output side of the rectifier DC-I. "DC" means "direct current" which indicates that the respective quantity is to be measured on the output side of the rectifier. Two curves showing the dependency are visible in Fig. 4. The upper curve is denoted by Ti and is, for example, the curve for the highest possible efficiency of the receiving arrangement, i.e. the voltage and the current on the input side of the rectifier are in phase. The lower curve is denoted by T2 and corresponds to a lower efficiency of the receiving arrangement. The two curves comprise a section where the slope of the nearly linear dependency is larger and comprise a section where the slope of the linear dependency is smaller. The region with the larger slope is the region for small values of the current DC-I, i.e. there is nearly no load current. During operation of the load, the section with the smaller slope is valid. Therefore, the control may be performed only while a load is provided with electric energy from the receiving arrangement.

Since the curve with the optimal efficiency corresponds to a specific value of the capacitance and since any variation of the capacitance regardless whether the capacitance is increased or decreased results in a reduced efficiency, it cannot be decided by only using the information about the reduced efficiency whether the capacitance is to be increased or decreased. Additional information is needed. This additional information is obtained by varying the capacitance and evaluating if the efficiency is increased or decreased.

Fig. 5 shows the total switchable capacitance of one phase line as a function of time.

While time passes, the control is periodically performed. Starting at time zero, when the total switchable capacitance is zero, this capacitance is continuously increased by switching on the capacitors step by step until the efficiency is no longer increased by switching on additional capacitors. Then, the switchable capacitors are switched off again step by step until the efficiency is decreased. Afterwards, the efficiency is again increased by switching on capacitors step by step until the efficiency is decreased. This procedure is continued as shown in Fig. 5 by the zig-zag behaviour of the curve. While this type of control is performed, the optimal capacitance may change (not shown in Fig. 5), for example due to a temperature change. Immediately after this change, the curve would not show the regular zig-zag behaviour, but one or more than one of the linearly increasing or decreasing sections of the curve would be longer than the other sections, but would nearly have the same slope as the zig-zag sections shown in Fig. 5. As a result, the total switchable capacitance would fluctuate around the changed optimal switchable capacitance.

In case that the receiving arrangement comprises more than one phase line, the procedure which has been described before will be performed during a time interval for one of the phase lines and the corresponding switchable capacitance of this phase line.

When a predetermined time has elapsed or when the optimal capacitance has been reached at least one time or, preferably, several times, the control of the switchable *...

capacitance of this phase line is interrupted and a control of the capacitanceof another phase line is started. Again, after elapse of a predetermined time or when the optimal capacitance has been reached at least once, the control of this phase line is stopped and the control of another phase line is started. This procedure is continued so that all phase lines are controlled from time to time.

A second type of control will be described with reference to Fig. 6. This closed loop control may be realized using an electric and/or electronic circuit comprising logic elements, for example, but is preferably performed by a computer program. "0" in the top left region of Fig. 6 indicates that a set value of zero is to be achieved. A value denoted by D which will be explained in more detail is subtracted from this set value by subtraction unit 618. The corresponding difference is input to a first open loop control unit 601, which is preferably a control unit showing a proportional (P) or a proportional and integral (P1) behaviour of the output variable. According to the example shown, the output value corresponds to a difference of the capacitance tC which should be applied to the total capacitance of the phase line in order to reduce or eliminate the control deviation. This output value is input to a first modelling unit 602 and to a first differentiating unit 604. The first modelling unit 602 models the behaviour of the receiving arrangement in such a manner that the response of the measured current I which forms a basis for calculating the efficiency of the receiving arrangement is output. For example, the first modelling unit 602 may take into account measured values of the voltage and the current of the receiving arrangement, preferably on the output side of the rectifier. If values collected over a time interval of predetermined length are taken into account by unit 602, the information about the efficiency, in particular about the impedance, of the receiving arrangement is used as the basis for calculating the output value I. In practice, the first modelling unit 602 may be realized as a low pass or delay unit of the type PT1.

The output value of the first modelling unit 602 is input to a second modelling unit 603 and to a second differentiating unit 607. Similarly to the first modelling unit 602, the second modelling unit 603 models the behaviour of the receiving arrangement, but outputs the voltage which corresponds to the variation of the capacitance tC which is output by the unit 601 and which causes the current I on the output side of unit 602. The second modelling unit 603 may also use measurement values of the current and of the voltage in the same manner as the first modelling unit 602, but takes into account the different behaviour of the voltage compared to the current. For example, the second modelling unit 603 may be implemented as a low pass or delay unit, for example of the type P11. The output of the second modelling unit 603 is input to a third differentiating unit 610 which calculates the derivative of the voltage with respect to time t. This is indicated in Fig. 6 by quotientX.

The second differentiating unit 607 calculates the derivative of the current I with respect to time t and outputs this derivative, which is denoted by Y in Fig. 6, to an inverting unit 608.

This unit 608 calculates the reciprocal value of the derivate. The output of the inverting * unit 608 and the output X of the third differentiating unit 610 are input to a multiplying unit 612 which multiplies the input value and outputs the corresponding product Z which is the variation of the voltage U divided by the variation of the current I. In other words, the output of unit 612 is the derivative of the voltage with respect to the current. This result is input to a fourth differentiating unit 614 which calculates the derivative of the input value with respect to time. The output value is denoted by K in Fig. 6.

Furthermore, the first differentiating unit 604 calculates the derivative of the variation of the capacitance LC with respect to time. This derivative is denoted by L in Fig. 6 and is input to a second inverting unit 605 which calculates the reciprocal value and outputs the reciprocal value to a second multiplying unit 616. In addition, the output value K of the fourth differentiating unit 614 is also input to the multiplying unit 616 as second input factor. The multiplying unit 616 calculates the product of the two input variables and outputs the product which is denoted by reference sign D. This product is the derivative of the voltage U with respect to the current I and with respect to the variation of the capacitance tIC. Since the derivative of the voltage U with respect to the current I (variable Z in Fig. 6) can be interpreted as the impedance of the receiving arrangement if U is the voltage on the output side of the rectifier and if I is the current on the output side of the rectifier, variable D can be interpreted as the derivative of the impedance with respect to the variation of the capacitance C. Therefore, the variable D should be zero, since this derivative is a condition for the presence of a maximum of the impedance.

Therefore, the set value 0" is input to the subtracting unit 618, as mentioned above.

If there is more than one phase line, the control of the different phase lines can be performed one after the other in the same manner as described above with respect to the other type of control. * . *

*.***. * * *

****** * * * S..... * * * .* * S * * ** * *

S

Claims

Claims An arrangement adapted for receiving an electromagnetic field, for producing electric energy from the electromagnetic field by induction and for providing a load (205) with the electric energy, in particular for providing a rail vehicle with energy, wherein the arrangement corn prises: -at least one phase line (la, 2a, 3a) comprising an inductance (L71, L72, L73) and a capacitance (C71, C72, C73), wherein the capacitance (C71, C72, C73) is arranged and used to optimize a phase shift between the voltage which is induced by the electromagnetic field and the current which is produced by the voltage while electric energy is transferred to the load (205), -a rectifier (203) which is connected to the at least one phase line (la, 2a, 3a), and wherein: -the capacitance (C71, C72, C73) comprises at least two capacitors (371, 381, 382, 383, 384) -at least one (381, 382, 383, 384) of the capacitors (371, 381, 382, 383, 384) is switchable and is connected to the phase line (la, 2a, 3a) via a switch (385, 386, 387, 388) and -wherein the arrangement comprises a control device (397) which is connected to the switch (385, 386, 387, 388) and which is adapted to switch on or switch off the at least one switchable capacitor (381, 382, 383, 384) so that the capacitance is modified, thereby the phase shift is modified and thereby an efficiency of the arrangement is improved. aa.....

*
2. The arrangement of the preceding claim, wherein the arrangement comprises a voltage sensor adapted and arranged to measure a voltage which is or depends on the voltage that is induced by the electromagnetic field and/or comprises a current sensor adapted and arranged to measure a current in the phase line (la, * 2a, 3a) or a load current produced by the voltage and wherein the control device (397) is adapted to control the at least one switch (385, 386, 387, 388) depending on the measured voltage and/or on the measured current.
3. The arrangement of the preceding claim, wherein the control device (397) is adapted to switch on or off at least one of the capacitors (381, 382, 383, 384) in order to increase or decrease the capacitance, is adapted to evaluate a resulting modification of the measured voltage and/or measured current, is adapted to decide whether the increased or decreased capacitance results in an improved efficiency of the arrangement and is adapted to reverse the switching state of the capacitors and/or to switch off or on at least another one (381, 382, 383, 384) of the capacitors if the increased or decreased capacitance has not resulted in an improved efficiency of the arrangement.
4. The arrangement of claim 2, wherein the control device (397) is adapted to repeatedly evaluate the measured voltage and/or the measured current, is adapted to repeatedly calculate the impedance of the arrangement from the measured values and is adapted to control the at least one switch (385, 386, 387, 388) so that the efficiency is maximized.
5. The arrangement of one of the preceding claims, wherein the arrangement further comprises a primary side conductor arrangement (157) adapted to produce the electromagnetic field which induces the voltage in the at least one phase line (la, 2a, 3a).
6. The arrangement of the preceding claim, wherein the primary side conductor arrangement (157) is arranged along a track of a rail vehicle (162) and wherein the at least one phase line (la, 2a, 3a) and the control device (397) are arranged in and/or on a rail vehicle (162).
7. A method of operating an arrangement for receiving an electromagnetic field, for producing electric energy from the electromagnetic field by induction and for providing a load (205) with the electric energy, in particular of operating the arrangement of one of the preceding claims, wherein: -at least one capacitor (381, 382, 383, 384) of the arrangement is switched on or off so that a capacitance of the arrangement is modified, -the switching is performed in a manner so that an efficiency of the arrangement is increased. S..
8. The method of the preceding claim, wherein a process of switching on or off at least one capacitor (381, 382, 383, 384) of the arrangement is performed in order to find out whether the corresponding increased or decreased capacitance results in an increased efficiency of the arrangement and, if the increased or decreased capacitance has not resulted in an increased efficiency of the arrangement, the switching state of the capacitors (381, 382, 383, 384) is reversed and/or at least another one of the capacitors (381, 382, 383, 384) is switched off or on.
9. The method of claim 7, wherein the switching is performed as a result of a control loop adapted to repeatedly evaluate a measured voltage and/or current of the arrangement and adapted to repeatedly calculate the efficiency of the arrangement from the measured values, wherein an output of the control loop is used to control the at least one switch so that the efficiency is maximized. * S ****S..... * .SS..... * SSS..... * . * *S * . S * **S