Patent Description:
A phase converter converting a three phase current into a two phase current is known from <CIT>.

Using balanced three-phase power transformers such as scott power transformer in two-phase power connections and in rail distribution networks leading to some harmonics cancellation is known from DOI <NUM>. <NUM>/YEF-ECE.

Document SPI <NUM><NUM><NUM> A1 discloses a three phase converter with three phase legs that are interconnected in a star-configuration. Each phase leg comprises switching cells each comprising semi-conductor switches to selectively provide a connection to a corresponding energy storage element. The three phase converter further includes a controller that monitors the DC voltage of the energy storage elements and controls the switching of each switching cell. Each phase leg of the three phase converter, comprises two parallel branches of switching cells connected to a closed circuit. The voltage levels of each of the energy storage elements are monitored and balanced, wherein the balancing includes circulating a current within the two branches of each phase leg of the multilevel converter.

It is object of the invention to improve application of phase converters in the field of catenary systems.

Advantageous embodiments are subject of the dependent claims.

According to an aspect of the invention, in a method for symmetrising or balancing a three phase current that is converted via a phase converter into a two phase current being composed of a first phase current flowing through a first electrical load and a second phase current flowing through a second electrical load being electrically separated from the first electrical load, at least one of the electrical loads comprises an electric energy storage device in a train for storing electric energy to supply an electric motor in the train, wherein the first and second phase current are set in that a difference between the the absolute value of the first phase current and the absolute value of the second phase current falls below a predefined reliability value.

The invention is based on the thought that currently available electric power cars can be extended by an accumulator to bridge unelectrified sections of rail tracks. The accumulator can be charged during passing electrified sections of the rail tracks or when standing for example at a terminus of a line. The bridgeable distance with currently available accumulators is between <NUM> and <NUM>. Such electric power cars equipped with an accumulator will most probably be used on rail tracks in the country side, where the rail operator will be forced to take the electric energy from the medium-voltage power grid.

However, the charging power of a single accumulator train set during standstill is between <NUM> MVA and <NUM> MVA. This electric power will be doubled in case of a double traction train and can thus not be symmetrically taken from the medium-voltage power grid as a single phase load without violating reliability values for an unsymmetrie or unbalance in the medium-voltage power grid e.g. according to EN <NUM> or IEC <NUM>-<NUM>-x.

In order to establish a balanced energy extraction from the medium-voltage power grid as best as possible, it is proposed with the provided method to convert the three phase current into a two phase current and to balance the two phases against each other. By that means, it is secured that the energy extraction by the train operator complies with a reliability value, that is at least given by the power grid operator. Therefore, the predefined reliability value should be dependent on a threshold value for an unsymmetrie balance in an electric power supply network providing the three phase current in one embodiment of the provided method.

In a further embodiment of the provided method, the step setting the first and/or second phase current includes the step limiting one of the phase currents based on the other phase current. By that means, it is secured that the energy extraction from the power grid does not result into the need of an unnecessary energy extraction.

In another embodiment of the provided method, the step setting the first and/or second phase current include guiding at least a part of one of the phase currents through an auxiliary load, if the other phase current increases the one of the phase currents. This auxiliary load can preferably be an accumulator. This means allows the extraction of a required electrical energy via one phase current. Surplus electrical energy taken via the other phase current can for example be intermediately stored in the accumulator and used at a later time. Alternatively the auxiliary load can be a further phase converter feeding the electric energy to the primary side of the above mentioned phase converter back into the power grid.

According to another aspect of the invention, a control device is adapted to execute a method according to one of the preceding claims.

In a further embodiment, the control device includes a memory and a processor. Therein, the provided method is stored in the memory as computer program, wherein the processor is adapted to execute the method, when the computer program is loaded from the memory into the processor.

According to another aspect of the invention, a computer program comprises program code means to perform all steps of the provided method, when the computer program is executed on an electrical device or in one of the provided control devices.

According to another aspect of the invention, a computer program product includes a program code that is stored on a computer readable data carrier and that executes the provided method, when it is executed on a data processing system.

According to another embodiment of the invention, a train which is adapted to receive a first phase current from a phase converter that converts a three phase electric current into a two phase electric current with the first phase current and a second phase current, comprises an electric motor; an electric energy storage device that is adapted to receive the first phase current and to supply the electric motor with electric energy; a communication device that is adapted to receive an information about the second phase current; and a provided control device.

According to another aspect of the invention, a catenary system for providing electric energy to electrically driven trains, includes a first catenary section, a second catenary section that is electrically separated or insulated from the first catenary section and a phase converter that is adapted to receive a three phase current from a electric power supply network, to transform the three phase current into a two phase current with a first phase current and a second phase current and to provide the first current to the first catenary section and the second phase current to the second catenary section.

In a further embodiment of the provided catenary system, the phase converter is a Scott transformator.

In a another embodiment, the provided catenary system includes a provided controller.

In an additional embodiment, the provided catenary system includes an electric energy storage device coupled to one of the two catenary sections.

The above described characteristics, features and advantages of this invention as well as the manner and way how they are achieved will get further comprehensive based on following description of the embodiments that will be explained in further detail in connection with the figures.

In the figures, equal technical elements will be provided with equal reference signs and described only one time. The figures are only of schematic nature and does in particular not disclose any real geometric dimension.

Reference is made to <FIG> that shows in a schematic view a catenary system <NUM> that supplies a train <NUM> with electrical energy.

The train <NUM> that is guided on a rail track <NUM> is driven by a first electric motor <NUM> and a second electric motor <NUM>. The first electric motor <NUM> can be supplied with electric energy by a first accumulator <NUM>, while the second electric motor <NUM> can supplied with electric energy by a second accumulator <NUM>. The first accumulator <NUM> is loaded with electric energy via a first pantograph <NUM>, while the second accumulator <NUM> is loaded via a second pantograph <NUM>.

Usually, while the train <NUM> is on the track <NUM>, both pantographs <NUM>, <NUM> can get the electric energy to be charged into the accumulators <NUM>, <NUM> from a catenary <NUM>. In some application scenarios, the catenary <NUM> is divided into two or more catenary sections <NUM>, <NUM> that are each electrically separated via a section insulator <NUM>. In such an application scenario, if the first pantograph <NUM> is positioned below the first catenary section <NUM> and the second patograph <NUM> is positioned below the second catenary section <NUM> as shown in <FIG>, the first accumulator <NUM> will be charged via the first catenary section <NUM>, while the second accumulator <NUM> will be charged via the second catenary section <NUM>. Such a scenario can be kept uphold for a comparably long time, like at a terminus of a line, when the train <NUM> is waiting for its next mission.

The thought behind the present embodiment is to use the before described scenario to symmetrically take electric energy from a three phase power grid <NUM> when charging the first and the second accumulator <NUM>, <NUM>. This idea shall be described in further detail hereinafter:
The three phase power grid <NUM> provides a three phase current <NUM> feeding a phase converter <NUM>. The phase converter <NUM> is exemplary embodied as Scott transformer and transforms the three phase current <NUM> into a two phase current <NUM> that itself supplies the catenary <NUM>.

The three phase current <NUM> that is input into the phase converter <NUM> includes a first phase input current <NUM>, a second phase input current <NUM> and a third phase input current <NUM>, while the phase converter <NUM> outputs a first phase output current <NUM> and a second phase output current <NUM>. To convert the three phase current <NUM> into the two phase current <NUM>, the phase converter <NUM> includes a first transformator <NUM> with a first input inductance <NUM> and a first output inductance <NUM> and further a second transformator <NUM> with a second input inductance <NUM> and a second output inductance <NUM>. All inductances <NUM> to <NUM> are electrotechnically equal and wound with an equal inductance winding amount.

The first phase input current <NUM> is input into the first input inductance <NUM> at a first center tap <NUM> that is located at an winding amount of √<NUM>/<NUM> of the complete winding amount of the first input inductance <NUM>. The side opposite of the first center tap <NUM> of the first input inductance <NUM> is connected to a second center tap <NUM> in the middle of the second input inductance <NUM>. The first output inductances <NUM> is connected between the first catenary <NUM> and ground <NUM>, whereas the second output inductances <NUM> is connected between the second catenary <NUM> and ground <NUM> in such a way, that both output inductances <NUM>, <NUM> are connected to each other in a starshape way.

To realize the above mentioned idea to symmetrically take energy from the three phase power grid <NUM>, the train <NUM> includes a control device <NUM>, which structure is shown in <FIG>. This structure is only provided as example and should not limit the basic idea behind the invention in any way.

The control device <NUM> measures the converted two phase current <NUM> and determines, whether the converted two phase current <NUM> results from an unsymmetric three phase current <NUM>. In case, the converted two phase current <NUM> results from an unsymmetric three phase current <NUM>, the control device <NUM> amends the two phase current <NUM> to symmetrise the three phase current <NUM>.

In the present embodiment, the control device <NUM> therefore includes a first measuring equipment <NUM> for measuring the first phase output current <NUM> and a second measuring equipment <NUM> for measuring the second phase output current <NUM>. The first measuring equipment <NUM> outputs a first current value <NUM> that reflects a measuring value for the first phase output current <NUM>. The first current value <NUM> can reflect the first phase output current <NUM> in an arbitrary way, like as mean value over a predefined time, as effective value over a predefined time, as instantaneous value, etc. Analogously to the first measuring equipment <NUM>, the second measuring equipment <NUM> outputs a second current value <NUM> that reflects a measuring value for the second phase output current <NUM>.

The control device <NUM> further includes a comparison equipment <NUM> that is adapted to compare measured current values <NUM>, <NUM> and to output a first adjustment signal <NUM> or a second adjustment signal <NUM> that controls the above mentioned symmetrisation. For outputting the adjustment signals <NUM>, <NUM>, the comparison equipment <NUM> includes a comparison element <NUM> that is embodied as subtraction element in <FIG>. The output of the comparison element is a comparison value <NUM> that indicates with its sign, which of the measured current values <NUM>, <NUM> is larger and based on its absolute value the difference between the measured current values <NUM>, <NUM>. The comparison equipment <NUM> further includes a determination element <NUM> that defines based on a reliability value <NUM>. In the present embodiment, the reliability value <NUM> is a limit for the before mentioned absolute value of the comparison value <NUM>, that is between the measured current values <NUM>, <NUM>, upon which an unsymmetrie in the three phase current <NUM> raises for example security criteria of the provider of the three phase current <NUM>. In contrast, the sign in the comparison value <NUM> indicates whether the the first measured current value <NUM> or the second measured current value <NUM> is too high to keep within the security criteria of the provider of the three phase current <NUM>. Based on this information, the determination element <NUM> outputs either the first adjustment signal <NUM> or the second adjustment signal <NUM>.

The control device <NUM> further includes a first control element <NUM> in the path of the first phase output current <NUM> and a second control element <NUM> in the path of the second phase output current <NUM>. These control elements <NUM>, <NUM> can be exemplary embodied as current limiters that limit the respective phase output current <NUM>, <NUM> based on the first or second adjustment signal <NUM>, <NUM> in a way, that the security criteria of the provider of the three phase current <NUM> is kept. In detail, if the comparison value <NUM> indicates that the first phase output current <NUM> is too high, the comparison equipment <NUM> controls with the first adjustment signal <NUM> the first control element <NUM> to limit the first phase output current <NUM> to a current value <NUM> that is within the security criteria or technical connection condition of the provider of the three phase current <NUM>. If in contrast the comparison value <NUM> indicates that the second phase output current <NUM> is too high, the comparison equipment <NUM> controls with the second adjustment signal <NUM> the second control element <NUM> to limit the second phase output current <NUM> to a current value <NUM> that is within the security criteria of the provider of the three phase current <NUM>.

By that means, the accumulators <NUM>, <NUM> in the train <NUM> can be charged with a symmetric current drain from the three phase power grid <NUM>, if rectified.

The disadvantage of the control device <NUM> of <FIG> is that an unbalanced current drain from the three phase power grid <NUM> will usually occur, if either the first accumulator <NUM> or the second accumulator <NUM> is fully charged, such that the charging current of the respectively other accumulator <NUM>, <NUM> must be limited in order to respect the technical connection conditions. To fully charge both accumulators <NUM>, <NUM>, an alternative control device <NUM>' is proposed in <FIG>.

This alternative control device <NUM>' includes instead of current limiters switches as control elements <NUM>, <NUM> that guide the output phase current <NUM>, <NUM> that is too high according to the before mentioned criteria to an auxiliary load <NUM>. The auxiliary load <NUM> can be a third accumulator or any other electric energy consumer that is able to adsorb the exceeding electric energy.

By that means, it is ensured that both, the first accumulator <NUM> as well as the second accumulator <NUM> can be fully charged.

In <FIG> and <FIG>, it is assumed that the described control devices <NUM> are located in one single railcar of the train <NUM>. However, the invention can also be practiced on different railcars of the train <NUM> or even on different trains. To describe this possibility in further detail, the first measuring equipment <NUM> and the first control element <NUM> forms a first current control equipment <NUM>, whereas the second measuring equipment <NUM> and the second control element <NUM> forms a second current control equipment <NUM>.

An embodiment to implement the invention on different railcars of the train <NUM> is shown in <FIG>.

Therein, the comparison equipment <NUM> and the first current control equipment <NUM> can be located in a first railcar <NUM> of the train <NUM> with the first pantograph <NUM>. In a second railcar <NUM> of the train <NUM> with the second panthograph <NUM>, the second current control equipment <NUM> can be located.

To facilitate the invention, in the above described way, it is only required to establish an information connection or communication link between the first railcar <NUM> and the second railcar <NUM> to exchange the second measured current value <NUM> and the second adjustment signal <NUM>.

The auxiliary load <NUM> according to <FIG> can be provided either in one of the railcars <NUM>, <NUM> or stationary regarded to the train <NUM>. An electric power line between the railcars <NUM>, <NUM> and the auxiliary load <NUM> must be installed in an application dependent way.

Analogously to <FIG>, the the first current control equipment <NUM> can be located in the train <NUM> with the first pantograph <NUM>, wherein the second current control equipment <NUM> can be located in another train <NUM>' with the second pantograph <NUM> that is located on another track <NUM>' and takes electric energy from another catenary <NUM>'. The section insulator <NUM> will thus be the air between the two catenaries <NUM>, <NUM>'.

Indeed, the comparison equipment <NUM> can be located in one of the trains <NUM>, <NUM>', it is also possible to locate the comparison equipment <NUM> at a common coordination center. As described in line with <FIG>, the auxiliary load <NUM> can also be located in one of the trains <NUM>, <NUM>' or stationary to all trains <NUM>, <NUM>'.

Locating the comparison equipment <NUM> at a common coordination center allows further controlling the symmetric current drain from the three phase power grid <NUM> even for running trains <NUM>, <NUM>' by guiding surplus electric current to other trains running on a same track. This should be explained in fore detail by referring to <FIG>.

Claim 1:
Method for symmetrising a three phase current (<NUM>) that is converted via a phase converter (<NUM>) into a two phase current (<NUM>) composed of a first phase current (<NUM>) flowing through a first electrical load (<NUM>, <NUM>) and a second phase current (<NUM>) flowing through a second electrical load (<NUM>, <NUM>) electrically separated from the first electrical load (<NUM>, <NUM>), wherein at least one of the electrical loads (<NUM>, <NUM>; <NUM>, <NUM>) comprises an electric energy storage device (<NUM>, <NUM>) in a train (<NUM>, <NUM>') for storing electric energy to supply an electric motor (<NUM>, <NUM>) in the train (<NUM>, <NUM>'), and characterised in that at least one of the first and second phase current (<NUM>, <NUM>) is set (<NUM>, <NUM>) in that a difference (<NUM>) between the absolute value of the first phase current (<NUM>) and the absolute value of the second phase current (<NUM>) falls below a predefined reliability value (<NUM>).