The invention relates to a rail vehicle and a method of operating a rail vehicle. The rail vehicle comprises a plurality of current collectors, wherein each current collector electrically connects the rail vehicle with an energy supply network during operation.

However, there are time intervals during operation of the rail vehicle, and especially while the rail vehicle is driving on rails, when no electric energy is supplied from the energy supply network through at least one of the current collectors: Energy supply networks like networks that comprise overhead electric lines or electric lines in the form of live rails (often called: third rails) comprise section points where consecutive sections of the electric lines are electrically separated from each other. At a section point, there is a gap between the consecutive sections. This means that there is no electric connection between the consecutive sections. A current collector, such as a pantograph for contacting an overhead electric line or a contact shoe for contacting the third rail, therefore loses electric contact to the energy supply network for a short period of time when the rail vehicle passes the section points. Since the rail vehicle comprises a plurality of current collectors, electric energy can still be supplied to the rail vehicle during this short period of time.

There are different kinds of devices within rail vehicles that require electric energy for operation. One kind of devices belongs to the traction system, such as traction motors, current converters, their electrical connections and electric components that are electrically connected to these devices. Another kind of devices is called auxiliary devices and belongs to the auxiliary system of the rail vehicle. The auxiliary devices support the operation of the rail vehicle, but are not part of the traction system. Examples are cooling devices for cooling current converters and traction motors and control devices for controlling the operation of devices of the traction system. At least some of the auxiliary devices are required for propulsion and braking of the rail vehicle. For example if the control device of the traction converter that provides at least one traction motor with electric energy would stop operation, the traction converter cannot provide energy to the traction motor anymore and cannot be operated in dynamic braking mode anymore.

Failure of cooling devices for cooling the current converters of the traction system or for cooling the traction motors might not stop propulsion immediately, but in the long term. A further kind of devices, such as electric lights and heating, provides comfort to passengers or allows the handling of freight.

Although not restricted to this purpose, the present invention especially relates to the supply of electric energy to auxiliary devices.

Typically, electric devices within rail vehicles are provided with electric energy by an alternating current that is produced by a current converter, in short: “converter”. The alternating current line to the electric devices is connected to the “output side” or “alternating current side” of the converter. The “input side” or “direct current side” of the converter is connected to a direct current circuit, which is often called “intermediate circuit” or “DC bus”. In case of a direct current (DC) energy supply network of the railway on which the rail vehicle travels, the electric energy is typically supplied from the supply network through one of the current collectors and through an inductance of the direct current circuit to the input side of the current converter. In case of an alternating current (AC) energy supply network of the railway, the electric energy is supplied typically from the supply network through one of the current collectors and through a transformer to a line converter to the direct current circuit. The line converter rectifies the alternating current on the secondary side of the transformer into a direct current of the direct current circuit.

Especially with regard to the energy supply to the auxiliary devices, there can be a plurality of current converters, namely auxiliary system current converters, wherein each of the auxiliary system current converters converts the direct current from in each case one direct current circuit into an alternating current on its output side. Each direct current circuit is separately connected to one of the current collectors of the rail vehicle, i.e. the energy supply from the energy supply network to each direct current circuit individually depends on the electric connection of the corresponding current collector to the energy supply network. When one of the current collectors arrives at a section point, its electric connection to the energy supply network is interrupted while the electric connection of at least one other of the plurality of current collectors of the rail vehicle to the energy supply network is maintained. However, the at least one other of the plurality of current collectors will also arrive at the section point. In order to allow for continuous energy supply to the auxiliary devices, there is an alternating current line of the rail vehicle to which all or a plurality of the output sides of the auxiliary system current collectors are connected. As long as at least one of the auxiliary system current collectors feeds an alternating current into the alternating current line, the auxiliary devices can be provided with electric energy, although the supply power might significantly drop while one of the current collector passes a section point.

Typically, a current converter converts the DC current into an AC current by repeatedly switching on and off converter switches. For example in case of a three-phase DC to AC converter, there are at least six switches, typically semiconductor switches, such as IGBTs (insulated gate bipolar transistors). More generally speaking there are typically at least two switches per phase. There is typically a connection point of the output side (the AC side) of the converter in between the two switches of the phase. However, there can be more switches per phase, in particular if a plurality of switches is arranged parallel to each other in order to increase the maximum allowed current.

When the current collector, that has passed a section point, has established an electric connection to the line section after the section point, the energy supply from the energy supply network through the current collector to the assigned current converter is re established. However, the different current converters that are connected with their output sides to the alternating current line must produce alternating currents that are in phase, i.e. phase shifts of the produced alternating currents must be avoided during most of the operation time. Phase shifts may occur only over short time intervals. There are two options to achieve the requirement that the alternating currents are in phase when the energy supply through the assigned current collector to the current converter is re established after a section point.

According to a first option, the input sides of the different current converters may be connected to each other by an electric line for supplying electric energy from a different current collector to the current converter. Therefore, the current converter may continue producing an AC current on its output side while the assigned current collector passes the section point. However, this electric line on the input sides of the current converters increases time and effort for manufacturing the rail vehicle significantly.

According to a second option, the converter control device of the current converter may synchronize controlling the converter switches with another current converter as soon as the energy supply through the assigned current collector to the input side of the current converter has been re-established. However, this requires some time so that the time gap of suspended AC current production is larger than the interruption time interval in which the electric connection through the assigned current collector to the energy supply network is interrupted.

It is an object of the present invention to provide a solution to a method of operating a rail vehicle under the circumstances mentioned above and for a rail vehicle with the features mentioned above which provides for a small time gap of suspended AC current production at section points and requires little constructional effort. It is a further object of the present invention to provide a corresponding rail vehicle.

It is proposed, with respect to a method and a rail vehicle with the features mentioned before, to continue processing phase information about the phase position of the alternating voltage and/or alternating current on the output side of the current converter during an interruption time interval during which the energy supply from the energy supply network through the assigned current collector to the input side of the current converter is interrupted. Therefore, electric lines connecting the input sides of different current collectors are not required and an alternating current on the output side of the converter, that is synchronized with other alternating currents fed to the alternating current line, can be produced immediately after re-establishment of the energy supply from the energy supply network through the assigned current collector to the input side of the current converter.

In particular, the following is proposed:

A method of operating a rail vehicle, the rail vehicle comprising:

- a plurality of current collectors, each current collector electrically connecting the rail vehicle with an energy supply network,

- a plurality of converters, including a first converter and a second converter, each converter being assigned to an assigned current collector of the plurality of current collectors and converting a direct current on an input side of the converter to an alternating current on an output side of the converter by repeatedly switching on and off converter switches based on phase information about a phase position of an alternating voltage and/or phase current on the output side of the converter,

- an alternating current line, electrically connecting the output sides of the converters, wherein, when the rail vehicle passes a section point of the energy supply network, so that an interruption of energy supply from the energy supply network to the input side of the first converter through the assigned current collector of the first converter occurs, a) the interruption is detected, b) converting a direct current on the input side of the first converter to an alternating current on the output side of the first converter is stopped, c) processing of the phase information about the phase position of the alternating voltage and/or alternating current on the output side of the first converter is continued during a time interval of the interruption, d) a return of the energy supply from the energy supply network to the input side of the first converter is detected and e) processing results of the continued processing of the phase information during the time interval of the interruption are used for a restart of converting a direct current on the input side of the first converter to an alternating current on the output side of the first converter.

Furthermore, a rail vehicle is proposed, comprising

- a plurality of current collectors, each current collector (such as a pantograph or an electric contact shoe) being adapted to electrically connect the rail vehicle with an energy supply network,

- a plurality of converters, including a first converter and a second converter, each converter being assigned to an assigned current collector of the plurality of current collectors and each converter being adapted to convert a direct current on an input side of the converter to an alternating current on an output side of the converter by repeatedly switching on and off converter switches based on phase information about a phase position of an alternating voltage and/or alternating current on the output side of the converter,

- an alternating current line, being adapted to electrically connect the output sides of the converters,

- a supply presence sensor or supply presence sensors, the supply presence sensor, each supply presence or the supply presence sensors being adapted to generate sensor signals indicating the presence or non-presence of electric energy supply from the energy supply network to the input side of the first converter through the assigned current collector of the first converter,

- a first converter control device adapted to control operation of the first converter, wherein the rail vehicle is adapted, when the rail vehicle passes a section point of the energy supply network, so that an interruption of energy supply from the energy supply network to the input side of the first converter through the assigned current collector of the first converter occurs, a) to detect the interruption based on the sensor signals of the supply presence sensor or of the supply presence sensors, b) to stop converting a direct current on the input side of the first converter to an alternating current on the output side of the first converter, c) to continue, during a time interval of the interruption, with processing the phase information about the phase position of the alternating voltage and/or alternating current on the output side of the first converter, d) to detect a return of the energy supply from the energy supply network to the input side of the first converter based on the sensor signals of the supply presence sensor or of the supply presence sensors, e) to use processing results of the continued processing of the phase information during the time interval of the interruption for a restart of converting a direct current on the input side of the first converter to an alternating current on the output side of the first converter.

In the following, embodiments of the method and of the rail vehicle are described. For each embodiment of the method, there is a corresponding embodiment of the rail vehicle and vice versa.

Each converter of the plurality of converters may electrically be connected or may electrically be connectable (e.g. by closing a switch) to the assigned current collector.

There may be more than two current converters connected with their output sides to the alternating current line. A train may comprise, for example, three or more current collectors, wherein each of the current collector is electrically connected or electrically connectable (e.g. by closing a switch) to the input side of one current converter and the output sides of these current converters are electrically connected or electrically connectable (e.g. by closing a switch) to the alternating current line, which may extend through the train from the current converter closest to the front of the train to the current converter closest to the back of the train. The phase position, often called “phasing”, of the alternating voltage and/or alternating current on the output side of the converter comprises information about the times when the alternating voltage and/or alternating current reaches its maximum values, minimum values or the value zero. For example in case of a three-phase current, there is typically a phase-shift of 120° between each pair of phases and the same applies to the corresponding alternating voltage. According to the basic knowledge of the skilled person, there is also a phase shift between the alternating current and the alternating voltage of each phase, this phase shift depending on the inductances and capacitances involved. However, knowledge about the phase position of the alternating voltage or alternating current on the output side of the converter is sufficient to control the converter switches in a manner that results in the production of an alternating current on the output side of the converter that is in phase with the alternating current(s) of (an)other converter(s) that is/are connected to the same alternating current line with its/their output side(s).

There are at least two approaches how to continue processing phase information about the phase position of the alternating voltage and/or alternating current on the output side of the current converter during the interruption time interval.

According to a first approach, the alternating voltage and/or alternating current on the output side of the converter is measured as a function of time, i.e. the alternating voltage and/or alternating current is repeatedly measured, and this measurement continues during the interruption time interval. Corresponding sensors for measuring at least one phase voltage of an alternating voltage and/or phase current of an alternating current are well known in the art and converter control devices typically process the phase information received with the sensor signals of such a sensor. For example, there are two alternating current sensors on the output side of the converter that are arranged and adapted in each case to measure the alternating current in one of three phase lines of the alternating current line. In particular, the phase current of the third phase line of the alternating current line can be calculated based on the assumption that the electric current through the three phase lines comprise a phase shift of 120° between each pair of phases lines. In addition, there may be a single voltage sensor that is adapted and arranged to measure the voltage between two of the three-phase lines. However, the invention is not limited to this specific example of two current sensors and one voltage sensor on the output side of the converter. For example, there may be three current sensors and/or two voltage sensors.

In any case, it is preferred that the sensor/sensors on the output side of the converter is/are arranged and adapted to measure the voltage and/or current of the alternating current line at a location beyond any line switch in the alternating current line (see below) that can be controlled to open and close an electric connection between the output side of the converter and the alternating current line. Thereby, the sensor/sensors can continuously provide sensor signals, even when the line switch is open.

The sensor signals are processed, for example by a control device adapted to control the first converter and the control device performs the control taking into account the sensor signals. The control results in a switching pattern (i.e. sequences of switching the converter switches on and off over time) of the converter switches. In particular, the process that is performed by the control device in order to control the switching of the converter switches may be performed before the assigned current collector arrives at the section point and may continue during the interruption time interval. It should be noted however, that the length of the interruption time interval is not necessary equal to the length of the time gap between energy supply from the energy supply network to the input side of the first converter before the assigned current collector arrives at the section point and the energy supply after re-establishment of the energy supply after passing the section point. In other words, the converter control device does not necessarily continue with processing the sensor signals over the complete time gap while there is no energy supply to the input side of the converter. It is sufficient, for example, if the converter control device only continues with processing the sensor signals shortly before the time gap is over. The minimum length of the time gap may be known to the converter control device, so that the converter control device can start with continued processing soon enough. However, it is preferred that processing the sensor signals is continued all over the time gap, i.e. there is no interruption of the sensor signal processing, and thereby processing of the phase information, at a section point at all. In any case, processing of the phase information may result in calculating the switching patterns during the interruption time interval or during the complete time gap. Corresponding control signals that cause the switching patterns may be output to the converter switches by the converter control device, so that the converter switches are actually switched, or may not be output to the converter switches during the interruption time interval. According to a second approach, the processing of the phase information during the interruption time interval does not depend on sensor signals or may not completely depend on sensor signals. The advantage is that less processing power is required and the phase information does not depend on the alternating current on the output side of the first converter during the interruption time interval. Although the output side of the first converter may be connected to the alternating current line during the interruption time interval, the alternating current in the alternating current line nearby the first converter may not be suitable for obtaining the phase information. According to the second approach, it is assumed that the phasing of the alternating voltage and/or alternating current in the alternating current line does not alter at the beginning and over the time gap of interrupted energy supply from the energy supply network to the input side of the first converter at the section point. For example, the processing of the phase information during the interruption time interval may comprise continuously or repeatedly receiving time signals (such as from an internal clock of the converter control device) and calculating a state of the phase position / the phasing at least when it has been detected that the energy supply from the energy supply network to the input side of the first converter has returned. Optionally, the phase position / the phasing may be calculated continuously or repeatedly based on the time signals.

In particular, the time interval of interruption (i.e. the interruption time interval) may end when the assigned current collector of the first converter has already been connected electrically to the energy supply network after passing the section point, but the operation of the first converter has not restarted yet. In any case, it is preferred that the time interval of interruption starts while there is no electric connection between the assigned current collector of the first converter and the energy supply network, e.g. there is no electric contact between the assigned current collector and the overhead electric line or the third rail. In addition or alternatively it is preferred that processing of the phase information about the phase position of the alternating voltage and/or alternating current on the output side of the first converter continues while there is no electric connection between the assigned current collector of the first converter and the energy supply network.

The alternating current line may extend through the rail vehicle in or along the direction of travel at least from the position of the first converter to the position of the second converter. Typically, the first converter and the second converter are positioned in different sections of the rail vehicle, such as different cars of a train.

The supply presence sensor or supply presence sensors are in particular located on the input side of the first converter at any location within the electric circuit between the first converter and it is assigned current collector. Typically, a first sensor is located in the electrical connection between the assigned current collector and the main transformer (in case of an AC supply network) or the main inductance (in case of a DC supply network), and a second sensor is located in the direct current circuit on the input side. The first sensor may measure the voltage of the current at the electrical connection and the second sensor may measure the voltage of the direct current circuit. If there are more than one supply presence sensor, the non-presence of energy supply may be indicated by sensor signals of one of the sensors after arrival at the section point and the return (i.e. the presence) of the energy supply may be indicated by sensor signals of another one of the sensors. For example the sensor signals of the second sensor may be used to detect the non-presence, since this allows for a short delay of stopping the alternating current production by the first converter, thereby reducing the time interval while there is no alternating current production. On the other hand, the return of the energy supply from the energy supply network may be indicated best by the sensor signals of the first sensor, since this sensor is located closer to the current collector and the sensor signals may be used to detect the return by the converter control device.

However, according to a particularly reliable solution, it is preferred that at least the signal of a voltage sensor in the direct current circuit (i.e. an embodiment of the second sensor mentioned before) is used to detect - on arrival at the section point - non-presence of electric energy supply from the energy supply network to the input side of the first converter through the assigned current collector of the first converter and to detect - having passed the section point - the return of the electric energy supply. Soon after arrival at the section point, the voltage in the direct current circuit drops, and this can be detected if the condition is fulfilled that the voltage has decreased by a predetermined voltage difference and/or to a predetermined voltage value. When the electric energy supply has returned, this can be detected if the condition is fulfilled that the voltage has increased by a predetermined voltage difference and/or to a predetermined voltage value. In all these cases, for example the converter control device of the first converter may detect the interruption of energy supply to the input side of the first converter by evaluating the sensor signals of the supply presence sensor or of the supply presence sensors.

Although the rail vehicle and the method of operating a rail vehicle have been described and will be described especially with regard to the first converter, the same may apply to the second converter or any further converter that is connected or can be connected to the alternating current line. In particular, the current collector that is assigned to the second converter or to any further converter will arrive later or earlier than the current collector assigned to the first converter at the section point. Consequently, all solutions and embodiments described with reference to the first converter may also apply to the second converter or to any further converter.

In particular, the rail vehicle comprises a line switch, wherein the lines which is controlled/ controllable (e.g. by the control device of the first converter or by another control device of the rail vehicle) to open and close an electric connection between the output side of the first converter and the alternating current line. Therefore, the line switch has an open state and a closed state. In the open state, the first converter is disconnected from the output sides of the second converter and any further converter that is/are connected or can be connected to the alternating current line.

It is preferred that, when the interruption is detected, the line switch is maintained in the closed state so that the electric connection between the output side of the first converter and the alternating current line is maintained. The rail vehicle may be adapted correspondingly. There are at least the following advantages related to this embodiment. An alternating current produced by another converter that is connected to the alternating current line can be used to transfer electric energy to the first converter which may rectify the alternating current and may therefore deliver electric energy to the direct current circuit on its input side. This electric energy may be used for different purposes, such as maintaining the voltage of the direct current circuit at a high level and/or to provide electric energy to any other device connected to the direct current circuit.

However, under certain circumstances, the line switch may be opened while there is no energy supply from the energy supply network through the assigned current collector to the input side of the first converter. For example if there is a high alternating current (e.g. a current exceeding a predetermined threshold value) in the alternating current line to the first converter, the lines which is opened.

In particular, the converters may be auxiliary converters that are adapted to supply auxiliary devices of the rail vehicle with electric energy via the alternating current line. As mentioned above, the auxiliary devices are adapted to support operation of the rail vehicle, but do not belong to the traction system of the rail vehicle, although they may support operation of devices of the traction system.

A control device of the first converter may use (or may be adapted to use) the processing results of processing the phase information to synchronise repeatedly switching on and off converter switches of the first converter with the phase position of the alternating voltage and/or alternating current on the output side of the first converter. Thereby, the operation of different converters that are connected to the alternating current line on their output sides is optimised.

For example as described above, the rail vehicle may comprise at least one alternating current line sensor adapted to sense the alternating voltage and/or alternating current on the output side of the first converter, wherein the phase information about the phase position of the alternating voltage and/or alternating current on the output side of the first converter is obtained from sensor signals of the at least one alternating current line sensor. The rail vehicle may be adapted correspondingly.

When the energy is supplied from the energy supply network through the assigned current collector to the input side of the first converter has returned, the production of the alternating current by the first converter can be re-started. However, caused by inductances and capacitances, the produced alternating current that is fed into the alternating current line may not immediately be in phase with the alternating current or alternating current produced by the second converter or any further converters that are connected to the alternating current line. Therefore, it is preferred that, during a time interval after the restart of converting a direct current on the input side of the first converter to an alternating current on the output side of the first converter, the phase information about the phase position of the alternating voltage and/or alternating current on the output side of the first converter for controlling repeatedly switching on and off converter switches of the first converter is disregarded. In particular, the first converter control device may be adapted correspondingly.

There are different ways how the information about the phase position may be disregarded. One option is not to continue processing the sensor signals of a sensor that measures the alternating voltage and/or alternating current in the alternating current line, since the sensor signals represent the produced alternating current that is affected by the inductances and capacitances, or the sensor signals are at least influenced by the inductances and capacitances. Instead, the control of the converter switches may be performed during this time interval after the restart of the first converter operation on the basis of the phase information process before the restart the converter control device may be adapted correspondingly. Another option is to filter the repeatedly and/or continuously received phase information, which may be produced by a sensor that measures of the alternating voltage and/or alternating current in the alternating current line. For example, a filter may be used that produces a “gliding mean values” of the received phase information, i.e. that considers in each point in time the most recent received phase information and to the phase information received during a time interval of set length towards the past.

Examples and embodiments of the present invention will be described with reference to the attached figures. The figures show:

Fig. 1 schematically a rail vehicle traveling on an electrified route with an overhead electric supply line which comprises a section point, wherein the rail vehicle is approaching the section point,

Fig. 2 the arrangement of Fig. 1 a short period of time later, when a first current collector of the rail vehicle has arrived at the section point,

Fig. 3 the arrangement of Fig. 2 a short period of time later, when the first current collector of the rail vehicle has passed the section point and is now in contact with another section of the overhead electric line,

Fig. 4 schematically an example of electric devices and circuits of the rail vehicle shown in Fig. 1 to 3 for the situation shown in Fig. 1, Fig. 5 schematically an example of electric devices and circuits of the rail vehicle shown in Fig. 1 to 3 for the situation shown in Fig. 2,

Fig. 6 schematically an example of electric devices and circuits of the rail vehicle shown in Fig. 1 to 3 for the situation shown in Fig. 3,

Fig. 7 details of an embodiment of electric circuits and of one of the converters shown in Fig. 4 to 6,

Fig. 8 a flowchart illustrating the operation of a rail vehicle that passes a section point of sections of an energy supply network and

Fig. 9 a diagram of the alternating current produced by a current converter as a function of time for a time interval while a rail vehicle is passing a section point of sections of an energy supply network.

Fig. 1 shows a rail vehicle 1 while driving on rails of a railway 5. The railway vehicle 1 comprises two current collectors 3a, 3b which electrically contact overhead line sections 6a, 6b of an energy supply network 6. In the situation shown in Fig. 1 (and Fig. 4, as will be explained later) both current collectors 3a, 3b are in electric contact with a first section 6a of the energy supply network 6. Therefore, energy is supplied from the energy supply network 6 through both current collectors 3a, 3b to the rail vehicle 1.

In the situation shown in Fig. 2 (and Fig. 5, as will be explained later), the first current collector 3a has arrived at a section point 7 of the energy supply network. There is a gap between the first overhead line section 6a and the second overhead line section 6b at the section point 7. Therefore, the first current collector 3a is electrically disconnected from the energy supply network 6 and energy is supplied from the energy supply network 6 only through the second current collector 3b to the rail vehicle 1 , or possibly through other current collectors not shown in the figures.

In the situation shown in Fig. 3 (and Fig. 6, as will be explained later), the first current collector 3a has passed the section point 7 of the energy supply network and is now in electric contact with the second overhead line section 6b. The second current collectors 3b is still in electric contact with the first section 6a of the energy supply network 6. Therefore, energy is supplied from the energy supply network 6 through both current collectors 3a, 3b to the rail vehicle 1.

The energy supply network 6 may be a direct current (DC) or an alternating current (AC) network. Furthermore, the energy supply network may not comprise overhead electric lines, but, for example, third rails. With reference to Fig. 4 to 6, an example of the operation of the rail vehicle 1 shown in Fig. 1 to 3 will be described.

As schematically shown in Fig. 4 to 6, the rail vehicle 1 may comprise two current converters 11a, 11b. Each current converter 11a, 11b is connected on its input side to a direct current circuit 14a, 14b and on its output side to an alternating current line 15 via an alternating current line switch 12a, 12b. There may be a capacitance in each direct current circuit 14a, 14b, as schematically indicated in Fig. 4 to 6. Electric loads (not shown) are connected to the alternating current line 15. The alternating current line switches (in short: line switches) 12a, 12b are controllable by a control device, which may be the current control device 16a, 16b that also controls the operation of a respective one of the current converters 11a, 11b or may be any further control device (not shown) that controls at least one switch and/or device of the arrangement shown. The converter control device 16b of the second current converter 11b is shown in Fig. 4, but not in Fig. 5 and 6.

The current collectors 3a, 3b are electrically connected to in each case one of the direct current circuits 14a, 14b via a main inductance 13a, 13b. If the energy supply network is an AC network, the main inductance 13a, 13b replaced by a main transformer for transforming the voltage of the energy supply network to a lower voltage and by a line converter for rectifying the alternating current from the current collector 3a, 3b to a direct current.

In particular, the current converters 11a, 11b may be auxiliary system current converters for providing alternating current electric energy via the alternating current line 15 to auxiliary devices (not shown). Alternatively, the current converters 11a, 11b may be traction converters for providing traction energy to at least one electric traction motor (not shown). The converter control device 16a of the first current converter 11a is connected to a direct current circuit sensor 17a and is connected to an alternating current line sensor 18a. The direct current circuit sensor 17a is adapted to repeatedly or continuously measure the voltage in the direct current circuit 14a. The alternating current line sensor 18a is adapted to measure the alternating voltage and/or the alternating current in the alternating current line, and viewed from the first current converter 11a, the alternating current line sensor 18a is located at a position beyond the line switch 12a in the alternating current line. In particular, the alternating current line may be a 3-phase alternating current line, as indicated by three diagonal lines. The converter control device 16a repeatedly or continuously receives, during operation of the rail vehicle 1, the sensor signals of the direct current circuit sensor 17a and of the alternating current line sensor 18a. Furthermore, the converter control device 16a processes the sensor signals and performs the control of the first current converter 11a based on the sensor signals.

In the situation shown in Fig. 1 and Fig. 4, electric energy is supplied from the energy supply network through the current collectors 3a, 3b to the current converters 11a, 11b which convert a direct current on their input side (the side of the respective direct current circuit 14a, 14b) to an alternating current on their output side (the side of the alternating current line 15). This converting operation is an inverting operation. Other than shown in Fig. 4, the line switches 12a, 12b are closed so that the alternating currents flow through the alternating current line 15 to the device connected to the alternating current line 15.

In the situation shown in Fig. 2 and Fig. 5, electric energy is supplied from the energy supply network continuously through the second current collector 3b to the second current converter 11b which converts a direct current on its input side to an alternating current on its output side. When the first current collector 3a arrives at the section point 7 and loses electric contact to the energy supply network, the voltage in the first direct current circuit 14a drops, while the first current converter 11a continues converting a direct current from the first direct current circuit 14a to an alternating current that is fed into the alternating current line 15. For example when a predetermined voltage or voltage drop in the first direct current circuit 14a is sensed by the direct current circuit sensor 17a, and the corresponding sensor signals arrives at the first converter control device 16a, the first converter control device 16a stops operating the current inverting operation. Then, the electric energy is supplied from the energy supply network only through the second current collector 3b to the second current converter 11b which produces an alternating current that is fed into the alternating current line 15. Especially in case of the converter configuration that will be described with reference to the example shown in Fig. 7, the first current converter 11a comprises diodes so that the alternating current from the alternating current line 15 is rectified and a direct current is fed into the first direct current circuit 14a. The corresponding energy flow is indicated in Fig. 5 by arrows. Consequently, the capacitance of the first direct current circuit 14a remains charged and a certain voltage level can be maintained.

In the situation shown in Fig. 3 and Fig. 6, the first current collector 3a has passed the section point 7 and has now electric contact with the second overhead line section 6b of the energy supply network 6. The first current converter control device 16a senses the return of the energy supply to the first direct current circuit 14a using the sensor signals of the direct current circuit sensor 17a, since the energy supply through the first current collector 3a and the main inductance 13a increases the voltage of the first direct current circuit 14a. For example when a predetermined voltage or voltage rise in the first direct current circuit 14a is sensed, the first current converter control device 16a starts controlling switching actions of the converter switches of the first current converter 11a.

After the operation of converting a direct current into an alternating current has stopped (in the situation shown in Fig. 2 and Fig. 5) and before the operation has restarted (in the situation shown in Fig. 3 and Fig. 6), processing of the phase information about the phase position of the alternating voltage and/or alternating current on the output side of the first converter continues. Therefore, the first current converter control device 16a is prepared, before its inverting operation is restarted, to control the switching operations of the converter switches of the first current converter 11a in a manner that produces an alternating current that is in phase with the alternating current in the alternating current line 15 or in a manner so that the alternating voltage on its output side is in phase with the alternating voltage in alternating voltage line 15.

The phase information in the interruption time interval can be obtained by the first converter control device 16a from the sensor signals of the alternating current line sensor 18a. The first line switch 12a remains closed during the interruption time interval. Another option to obtain the phase information, especially if the first line switch 12a is opened for example due to a high alternating current in the alternating current line 15, is to extrapolate the periodic behaviour of the alternating current and/or alternating voltage in the alternating current line 15 over the course of time. This means that the sensor signals of the alternating current line sensor 18a may be stored in a data storage of the first converter control device 16a which may access the stored data if required for extrapolation.

The arrangement shown in Fig. 7 shows details of a specific embodiment. The direct current source 20 on the left-hand side of the figure may represent at least the energy supply network and the assigned current collector of the first current converter. A direct current circuit 21 is connected to the direct current source 20. The direct current circuit 21 comprises a switch 22 for disconnecting the direct current circuit 21 from the direct current source 20, and inductance 23 and a switchable resistance 24.

A converter circuit 30 is connected to the direct current circuit 21. The converter circuit 30 comprises a capacitance 29 that may be considered being part of the direct current circuit, since it stabilizes the voltage of the direct current circuit furthermore, the converter circuit 30 comprises the current converter with three parallel branches of connections between the opposite poles of the direct current circuit. Each branch comprises two controllable converter switches 25a, 25b; 25c, 25d; 25e, 25f. The operation of the converter switches 25 is controlled by the converter control device (not shown in Fig. 7). There is a diode 26a, 26b; 26c, 26d; 26e, 26f antiparallel to each converter switch 25, so that the current converter may operate as a passive rectifier. For many operational states of the current converter, the diodes 26 are also involved in the process of inverting a direct current from the direct current circuit 21.

There are three alternating current phase lines on the output side of the current converter. Each of these phase lines is connected to a connection point of one of the branches in between the two converters switches 25 of the branch. The phase lines connect the current converter with a primary side of a transformer 28, which is preferably an electrically insulating transformer. There is a capacitor circuit 27 connected to the secondary side of the transformer 28. The alternating current line switch 12 is adapted to disconnect the converter circuit 30 from an alternating current line that is not shown in Fig. 7. This alternating current line may be the alternating current line 15 shown in Fig. 4 to 6. An example of a method of operating a rail vehicle of the kind indicated before will be described with reference to Fig. 8: In a first step S1 , the assigned current converter of the first converter arrives at a section point. In a following step S2, the converter control device of the first converter detects that the energy supply through the assigned current converter has been stopped, for example in the manner described with reference to Fig. 5. In a following step S3, the control device stops operating the converter switches of the current converter. In particular, all converter switches remain in their open states.

In a following step S4, phase currents in the alternating current line (e.g. line 15 of Fig. 5) on the output side of the first converter are measured and the corresponding sensor results are evaluated to check if high current occur, for example high currents that indicate regenerative braking of the rail vehicle. As shown by three arrows on the right hand side of the block representing step S4 in Fig. 8, this process is repeatedly performed while energy flow from the energy supply network to the input side of the first converter is interrupted. If the converter control device detects in step S4 that high currents occur, the line switch on the output side of the first converter is opened in step S4a. Depending on the continued monitoring of the alternating current in step S4, the lines which may remain open or maybe closed again. While the lines which is open, energy may flow from the output side of the first converter to its input side, i.e. an alternating current on the output side is rectified to a direct current on the input side, as indicated by step S5.

In parallel to steps S4, S4a and S5, the step S6 is performed in which processing of phase information about the phase position of the alternating voltage and/or alternating current on the output side of the first converter is continued during the time interval of interrupted energy flow from the assigned current collector to the input side of the first converter. In the following step S8, the return of the energy flow is detected, for example as described before with reference to Fig. 6, and the inverting operation of the first converter is restarted.

Fig. 9 shows the current I in the alternating current line (e.g. alternating current line 15 of Fig. 4 to 6) before, during and after the assigned current collector of the first converter passes a section point. The current I is shown as a function of time t. It is periodic until the converting (inverting) operation of the first converter, i.e. the production of an alternating current on its output side, is stopped at time to. Immediately after time to, the current decreases to zero. At time t1 , the converting operation re-starts. In the following time interval until time t2, the produced alternating current is not yet periodically stable, due to inductances and capacitances involved. During the time interval from time t1 to time t2, the converter control device preferably disregards the phase information, since phase information acquired during this time interval may be distorted depending on the location of the source of information, such as in case of the sensor position of the alternating current line sensor 18a of Fig. 4 to 6.

List of reference signs

1 rail vehicle

3a, 3b current collector

5 railway

6 energy supply network

6a, 6b overhead line sections of energy supply network 7 section point of energy supply network with gap between sections

11a, 11b currents converters 12a, 12b alternating current line switches 13a, 13b main inductances 14a, 14b direct current circuits 15 alternating current line 16a converter control devices 17a direct current circuit sensor 18a alternating current line sensor 20 direct current source 21 direct current circuit 22 switch

23 inductance

24 switchable resistance

25a to 25f converter switches 26a to 26f diodes

27 capacitor circuit

28 transformer

29 capacitor

30 converter circuit