A device, system, and method for controlling a rotational arrangement, and use of such device and system

Abstract

A device 10 for controlling a rotational arrangement 5 comprising a first 20a, second 20b and third 20c shafts arranged concentrically. The device comprises rotor assembly 30, first stator assembly 40

Description

The present invention relates to a device for controlling a rotational arrangement comprising a first shaft, a second shaft and a third shaft, which shafts are arranged concentrically. The device comprises a rotor assembly and a first stator assembly. The rotor assembly comprises means for generating a magnetic field, which means are configured to be arranged at the first shaft. The first stator assembly comprises a first stator winding configured to be arranged at the second shaft, which first stator winding is configured to interact with the rotor assembly at the first shaft. The present invention also relates to a system and a method for controlling a rotational arrangement, and use of the device and the system. Rotational arrangement comprising three concentrical shaft are used in various application, hydroelectric power units, steam turbines, aircraft engines and automotive transmissions. There is a desire to be able to control the rotation of the three shafts, for example with the purpose of assuring rotational stability of the rotational arrangement, such as to enable the first and the second shaft to rotate with same or essentially the same torque. It is also desired to control the rotation of the rotational arrangement such that possible resonant rotation resulting in intense vibration or wobbling is avoided. An object of the present invention is to provide an improved device for controlling a rotational arrangement comprising a first shaft, a second shaft and a third shaft, which shafts are arranged concentrically. In particular, an object of the invention is to control the rotational arrangement such that resonant rotation is avoided. A further object of the invention is to control the torque between the three shafts. Yet another object of the invention is to control the angular velocity of the three shafts. These objects are obtained by means of a device for controlling a rotational arrangement comprising a first shaft, a second shaft and a third shaft, which shafts are arranged concentrically. The device comprises a rotor assembly comprising means for generating a magnetic field, which means are configured to be arranged at the first shaft, a first stator assembly comprising a first stator winding configured to be arranged at the second shaft, which first stator winding is configured to interact with the rotor assembly at the first shaft, and a second stator assembly comprising a second stator winding configured to be arranged at the third shaft, which second stator winding is configured to interact with the rotor assembly at the first shaft, and a control unit configured to receive information on torque or the entity dependent on the torque of the first shaft, the second shaft and the third shaft, wherein the control unit is configured to control the first stator winding and the second stator winding based on the information such that a respective difference in torque or angular velocity between the first shaft and the second shaft, between the first shaft and the third shaft, and between the second and the third shaft, are controlled. The control unit is configured to control the torque of the first shaft, the second shaft and the third shaft by controllably exciting the first stator winding and the second stator winding based on the information on the torque or the entity dependent on the torque of the first shaft, the second shaft and the third shaft. The rotational arrangement is an arrangement comprising the concentrically arranged first, second and third shaft, which generally are configured such that the first shaft is rotating in a first direction and the second and the third shaft are rotating in a second direction opposite to the first direction. The first, second and third shaft are as such configured rotating independent of each other. The second and the third shaft are configured to rotate in the same direction, however, independent from each other. The first stator winding and the second stator winding are configured to be connected to a power network or a load. Thereby, currents that are induced in the first stator winding and the second stator winding create an electromagnetic drag, which opposes the motion of the first shaft, the second shaft and the third shaft. In the case when the control unit excites the first stator winding, the induced current in the first stator winding is opposed and accordingly the electromagnetic drag, which opposes the relative motion between the first shaft and the second shaft is reduced. Correspondingly, in the case when the control unit excites the second stator winding, the induced current in the second stator winding is opposed and accordingly the electromagnetic drag, which opposes the relative motion between the first shaft and the third shaft is reduced. Regarding the first stator winding, the control unit is configured to controllably excite the first stator winding through the manipulation of the stator current including at least one of voltage, frequency and phase, such that a control torque on the first shaft is generated. In that the first shaft and the second shaft both are rotatable and coupled in terms of the first stator winding and the means for generating a magnetic field at the rotor assembly, such control of the first stator winding also results in a generated torque on the second shaft that is opposite to the generated torque on the first shaft. Regarding the second stator winding, the control unit is configured to control the second stator winding correspondingly to the first stator winding. The control unit is configured to controllably excite the second stator winding through the manipulation of the stator current including at least one of voltage, frequency and phase, such that a further control torque on the first shaft is generated. Thereby, the torque of the first shaft is controlled by the control of the second stator winding. In that the first shaft and the third shaft both are rotatable and coupled in terms of the second stator winding and the means for generating a magnetic field at the rotor assembly, such control of the second stator winding results a further generated torque on the third shaft that is opposite to the further generated torque on the first shaft. The device has the advantage of enabling the torque of the first shaft, the second shaft and the third shaft to be controlled. The control unit is configured to receive information on the torque or the entity dependent on the torque of the first shaft, the second shaft and the third shaft. Based on the information, the control unit is configured to control the torque of the first shaft, the second shaft and the third shaft by controlling the controllably excite the first stator winding and the second stator winding. The expression ‘means for generating a magnetic field are configured to be arranged at the first shaft’ is to be interpreted as the means are operational connected to the first shaft. Correspondingly, ‘the first stator winding configured to be arranged at the second shaft’ is to be interpreted as the first stator winding is operational connected to the second shaft. Correspondingly, ‘the second stator winding configured to be arranged at the third shaft’ is to be interpreted as the second stator winding is operational connected to the third shaft. According to an embodiment of the invention, the control unit is configured to control the rotational arrangement such that the absolute value of the torque of the first shaft and the second shaft are the same or approximately the same. Thereby, the rotational arrangement may be controlled such that resonant rotation is avoided. According to an embodiment of the invention, the rotational arrangement is arranged such that the first shaft and the second shaft are rotating in opposite directions, and wherein the control unit is configured to control the rotational arrangement such that the first shaft and the second shaft are rotating with the same or approximately the same angular velocity in the opposite direction. Thereby, the rotational arrangement may be controlled such that resonant rotation is avoided. According to an embodiment of the invention, the control unit is configured to control the rotational arrangement based on a relative angular velocity between the first shaft and the second shaft, and between the first shaft and the third shaft, such that the relative angular velocity is maintained. According to an embodiment of the invention, the entity dependent on the torque is at least one of angular velocity of the shaft and a phase angle of a generated current from the first stator winding, or a combination of the angular velocity and the phase angle. The angular velocity of the shaft or the phase angle, or both, is / are used in determining the torque of the first, second and third shaft. The determined torque is used by the control unit to control the first stator winding and the second stator winding. According to an embodiment of the invention, the device comprises a power arrangement connected to the first stator winding and the second stator winding, wherein the power arrangement is configured to be controlled by the control unit such that electric current is controllably provided to the first stator winding and the second stator winding. The power arrangement is used for exciting the first and second stator winding. According to an embodiment of the invention, the means for generating a magnetic field comprises one of field winding, conductive bars and one or more permanent magnets, or a combination of these. An advantage of using permanent magnets is that the permanent magnets add weight to the rotor assembly and thereby improves the rotational stability of the rotational arrangement as a whole. According to an embodiment of the invention, the means for generating a magnetic field comprises field winding, and the power arrangement is connected to the field windings, wherein the power arrangement is configured to be controlled by the control unit such that electric current is controllably provided to the field winding. By means of the control of the field windings of the rotor assembly, the field winding may be used to control the torque of the second shaft and the third shaft. The control of the field winding is corresponding to the control of the first stator winding and the second stator winding. The control unit is configured to controllably excite the field winding through the manipulation of a field current including at least one of voltage, frequency and phase, such that a control torque on at least one of the second shaft and the third shaft are generated. According to an embodiment of the invention, the means for generating a magnetic field comprises conductive bars arranged internally short circuited such that a magnetic field is generated by currents induced in the conductive bars. According to an embodiment of the invention, the power arrangement comprises a power source and a power converter device, wherein the power converter device is configured to receive electric power from the power source and controllably convert the electric power to electric current that is controllably provided to the first stator winding and the second stator winding based on the information. According to an embodiment of the invention, power converter device is configured to be controlled by the control unit such that at least one of voltage, frequency and phase is controlled, such that a control torque on at least one of the second shaft and the third shaft are generated. According to an embodiment of the invention, the power source comprises an energy storage configured to controllably provide power to the power converter device. According to an embodiment of the invention, the power converter device is configured to be connected to the power network, and wherein the power converter device is configured to receive electric power from the power network. According to an embodiment of the invention, the device comprises a power transferring module configured to be connected to the first stator winding for transferring generated power away from the device. According to an embodiment of the invention, the power transferring module comprises a power cable configured to be connected to a power network. The power network act as a load that create an electromagnetic drag, which opposes the motion of the first shaft, the second shaft and the third shaft. According to an embodiment of the invention, the device comprises a further rotor assembly comprising further means for generating a magnetic field. According to an embodiment of the invention, the further means for generating a magnetic field mainly is magnetically coupled to the second stator winding. According to an embodiment of the invention, the further means for generating a magnetic field comprises one of further field winding, further conductive bars and one or more further permanent magnets, ora combination of these. According to an embodiment of the invention, the further means for generating a magnetic field comprises further field winding, and the power arrangement is connected to the further field windings, wherein the power arrangement is configured to be controlled by the control unit such that electric current is controllably provided to the further field winding. According to an embodiment of the invention, the further means for generating a magnetic field comprises further conductive bars arranged internally short circuited such that a magnetic field is generated by currents induced in the further conductive bars. The above objectives are further obtained by means of a system comprising system comprising the device according to any of above embodiment and a rotational arrangement comprising a first shaft, a second shaft and a third shaft, which shafts are arranged concentrically. According to an embodiment of the invention, the rotor assembly is arranged surrounding the first stator assembly. According to an embodiment of the invention, the rotor assembly is arranged surrounding the second stator assembly. According to an embodiment of the invention, the further rotor assembly is arranged surrounding the second stator assembly. According to an embodiment of the invention, the first shaft comprises a flywheel arrangement. The flywheel arrangement is configured to add mass to the first shaft for the purpose of increasing the rotational stability of the first shaft. According to an embodiment of the invention, the second shaft comprises a flywheel arrangement. The flywheel arrangement is configured to add mass to the second shaft for the purpose of increasing the rotational stability of the second shaft. According to an embodiment of the invention, the third shaft comprises a flywheel arrangement. The flywheel arrangement is configured to add mass to the third shaft for the purpose of increasing the rotational stability of the third shaft. According to an embodiment of the invention, the rotational arrangement is comprised by a contra-rotating wind turbine. According to an embodiment of the invention, the first shaft corresponds to an outer shaft of the contra-rotating wind turbine and the second shaft corresponds to an inner shaft of the contra-rotating wind turbine. According to an embodiment of the invention, the rotational arrangement is comprised by a contra-rotating propeller of an aircraft or a hydrodynamic vehicle. According to an embodiment of the invention, the rotational arrangement is comprised by a rolling mill for metalworking. According to an embodiment of the invention, a first vertical axis wind turbine is connected to the first shaft. According to an embodiment of the invention, a second vertical axis wind turbine is connected to the second shaft. According to an embodiment of the invention, the rotational arrangement further comprise a sensor arrangement configured to detect torque or an entity dependent on the torque of the first shaft, the second shaft and the third shaft. According to an embodiment of the invention, the entity dependent on the torque is at least one of angular velocity of the shaft and a phase angle of a generated current from the first stator winding, or a combination of the angular velocity and the phase angle. According to an embodiment of the invention, the sensor arrangement comprises an angular velocity sensor, such as MEMS Gyroscopes. According to an embodiment of the invention, the sensor arrangement comprises the sensor arrangement comprises as sensor for detecting phase angle of the generated current, such as one of a current transformer, a voltage transformer, a hall effect sensor, a resistive voltage divider circuit, a digital phase meters and a microcontroller or a digital signal processor. The above objectives are further obtained by means of a method for controlling a rotational arrangement comprising a first shaft, a second shaft and a third shaft, which shafts are arranged concentrically. The method comprises the steps of receiving information on torque or an entity dependent on the torque of the first shaft, the second shaft and the third shaft, determining control parameters for the first stator winding and the second stator winding based on said information, and providing electric current to the first stator winding and the second stator winding according to the determined control parameters. According to an embodiment of the invention, the step of providing electric current to the first stator winding and the second stator winding according to the determined control parameters comprises controlling at least one of voltage, frequency and phase, such that a control torque and / or a further control torque on the first shaft is generated. According to an embodiment of the invention, the method comprises determining the control parameters such that the torque of the first shaft and the second shaft are the same or approximately the same. According to an embodiment of the invention, the method comprises determining the control parameters such that the first shaft and the second shaft are rotating with the same or approximately the same angular velocity in the opposite direction. According to an embodiment of the invention, the method comprises receiving information on at least one of at least one of angular velocity of the shaft and a phase angle of a generated current from the first stator winding, or a combination of the angular velocity and the phase angle. According to an embodiment of the invention, the method comprises, calculating the torque of the first shaft and second shaft based on at least one of angular velocity of the shafts and phase angle of a generated current from the first stator winding, and calculating control parameters based on the calculated torque of the first shaft and second shaft. The above objectives are further obtained by means of use of the device according to any of the above embodiments. The above objectives are further obtained by means of use of the system according to any of the above embodiments. Embodiments of the present invention will now be described, by way of example only, with reference to the following figures, wherein: Fig. 1 discloses a system comprising a rotational arrangement and a device for controlling a rotational arrangement according to an embodiment of the invention; Fig. 2a-c discloses a system according to a further embodiment of the invention; Fig. 3 discloses a system according to an embodiment of the invention, where the rotational arrangement is a vertical-axis wind turbine; and Fig. 4 discloses a flow chart of a method for controlling a rotational arrangement. In Fig. 1 is a system 1 according to an embodiment of the invention disclosed. The system 1 comprises a rotational arrangement 5 and a device 10 for controlling the rotational arrangement 5. The rotational arrangement 5 comprising a first shaft 20a, a second shaft 20b and a third shaft 20c, which shafts 20a-c are arranged concentrically. The rotational arrangement 5 is for example part of a wind turbine generator, a hydroelectric power unit, a steam turbine, an aircraft engine, or an automotive transmission. According to a preferable embodiment, the rotational arrangement is comprised by a contrarotating wind turbine or alternatively a contra-rotating propeller of an aircraft or a hydrodynamic vehicle. According to an alternative embodiment, the rotational arrangement is comprised by a rolling mill for metalworking, such as a rolling mill for steel. In the disclosed embodiment in fig. 1, the first shaft 20a and the second shaft 20b are extending from a first direction and the third shaft 20c is extending from a second direction opposite to the first direction. The device 10 for controlling the rotational arrangement 5 comprises a rotor assembly 30 comprising means for generating a magnetic field 32, which means are arranged at the first shaft 20a. According to a preferable embodiment of the invention, the rotor assembly 30 further comprises a flywheel arrangement 34 configured to improve the rotational stability of the rotor assembly 30. The device 10 further comprises a first stator assembly 40 comprising a first stator winding 42 arranged at the second shaft 20b. The first stator winding 42 is configured to interact with the means for generating a magnetic field 32 of the rotor assembly 30 at the first shaft 20a. Accordingly, there is an electromagnetic coupling between the first stator assembly 40 and the rotor assembly 30. The device 10 further comprises a second stator assembly 50 comprising a second stator winding 52 arranged at the third shaft 20c. The second stator winding 52 is configured to interact with the means for generating a magnetic field 32 of the rotor assembly 30 at the first shaft 20a. Accordingly, there is an electromagnetic coupling between the second stator assembly 50 and the rotor assembly 30. In the embodiment in fig. 1, the system 1 is arranged such that the rotor assembly 30 is arranged surrounding the first stator assembly 40. Furthermore, the rotor assembly 30 is arranged surrounding the second stator assembly 50. In the case where the rotational arrangement 5 is a vertical-axis wind turbine (VAWT), the first shaft 20a may be connected to a lower turbine 22a, the second shaft 20b may be connected to an upper turbine 22b, and the third shaft 20c may be a shaft of a fundament 24 holding the device 10 rotatable arranged in respect to the fundament 24, see fig. 3. The device 10 further comprises a control unit 60 configured to receive information on the torque or the entity dependent on the torque of the first shaft 20a the second shaft 20b and the third shaft 20c. The control unit 60 is configured to controllably excite the first stator winding 42 and the second stator winding 52 based on the information on the torque of entity dependent on the torque. The control unit 60 is configured to control the excitation of the first stator winding 42 and the second stator winding 52 such that a torque or an angular velocity the first shaft 20a, the second shaft 20b and the third shaft 20c are controlled. In particular, the control unit 60 is configured to control the first stator winding 42 and the second stator winding 52 such that a respective difference torque between the first shaft 20a and the second shaft 20b, and between the first shaft 20a and the third shaft 20c, are controlled. According to a preferable embodiment, the control unit 60 is configured to control the first stator winding 42 and the second stator winding 52 such that the absolute value of the torque of the first shaft 20a and the second shaft 20b are the same or approximately the same. According to a preferable embodiment, the rotational arrangement 5 is configured such that the first shaft 20a and the second shaft 20b are rotating in opposite directions, and the control unit 60 is configured to control the first stator winding 42 and the second stator winding 52 such that the first shaft 20a and the second shaft 20b are rotating with the same or approximately the same angular velocity in the opposite direction. The information on the torque or the entity dependent on the torque of the first shaft 20a the second shaft 20b and the third shaft 20c is for example an angular velocity of the shafts 20a-c or a phase angle of a generated current from the first stator winding 42, or a combination of both. According to an embodiment of the invention, the system 1 comprises a sensor arrangement 70 configured to detect torque or an entity dependent on the torque of the first shaft 20a, the second shaft 20b and the third shaft 20c. The sensor arrangement 70 is configured to provide the information to the control unit 60. The sensor arrangement 70 comprises for example an angular velocity sensor, such as a MEMS Gyroscope. The sensor arrangement 70 also or alternatively comprises a sensor for detecting phase angle of the generated current, such as one of a current transformer, a voltage transformer, a hall effect sensor, a resistive voltage divider circuit, a digital phase meters and a microcontroller or a digital signal processor. The sensor arrangement 70 is preferably comprised by the rotational arrangement 5. The information may be used for other purposes of controlling the rotational arrangement 5. The device 10 further comprises a power arrangement 80 connected to the first stator winding 42 and the second stator winding 52. The power arrangement 80 is configured to be controlled by the control unit 60 such that electric current is controllably provided to the first stator winding 42 and the second stator winding 52. Thereby, the first stator winding 42 and the second stator winding 52 are controllably excited such that the torque or the angular velocity the first shaft 20a, the second shaft 20b and the third shaft 20c are controlled. The power arrangement 80 comprises a power source and a power converter device. The power source may be a power network or an energy storage, or the combination of both. The power source is configured to be controlled by the control unit 60 such that the power source controllably provide power to the power converter device. The power converter device is configured to receive electric power from the power source and controllably convert the electric power according to the desired control and excitement of the first stator winding 42 and the second stator winding 52 for the purpose of controlling the torque or the angular velocity the first shaft 20a, the second shaft 20b and the third shaft 20c. The device 10 further comprises a power transferring module 90 configured to be connected to the first stator winding 42 for transferring generated power away from the device 10. The power transferring module 90 is preferably connected to a power network. The power transferring module 90 preferably comprises a power cable configured to be connected to the power network. The means for generating a magnetic field 32 of the rotor assembly 30 comprises one of field winding, conductive bars and one or more permanent magnets, or a combination of these. In the case where field winding is used as the means for generating a magnetic field 32, the control unit 60 is configured to control the excitement of the field winding corresponding to the control of the first stator winding 42 and the second stator winding 52. In the case where conductive bars are used as the means for generating a magnetic field 32, the conductive bars are connected in a closed loop with no external electrical connections, such in a so called a squirrel-cage configuration. The currents induced in the conductive bars create a secondary magnetic field within the rotor assembly 30, which interacts a primary rotating magnetic field from the first stator winding 42 and the second stator winding 52. In the case where permanent magnets are used as the means for generating a magnetic field 32, the magnetic field of the permanent magnets are coupled with the magnetic field from the first stator winding 42 and the second stator winding 52. In fig. 2a-c is the system 1 according to a further embodiment of the invention disclosed. The embodiment in fig. 2a-c differs from the embodiment in fig. 1, in that the device 10 further comprises a further rotor assembly 90 comprising further means for generating a magnetic field 92. The further means for generating a magnetic field 92 is mainly magnetically coupled to the second stator winding 52. The further means for generating a magnetic field 92 comprises one of a further field winding, further conductive bars and one or more further permanent magnets, or a combination of these. According to a preferable embodiment of the invention, means for generating a magnetic field 32 of the rotor assembly 30 comprises permanent magnets, while the further means for generating a magnetic field 92 of the further rotor assembly 90 comprises conductive bars. Permanent magnets add weight to the further rotor assembly 90 and thereby improves the rotational stability of the rotational arrangement 5 as a whole. In the case when the further means for generating a magnetic field 92 comprises further field winding, the control unit 60 is configured to control the excitement of the further field windings. Corresponding to the first stator winding 42 and the second stator winding 52, the power arrangement 80 is connected to the further field windings and the control unit 60 is configured to control the power arrangement 80 such that the difference torque or angular velocity between the first shaft 20a and the second shaft 20b, and between the first shaft 20a and the third shaft 20c, are controlled. In the case when the further means for generating a magnetic field 92 comprises further conductive bars, the conductive bars are arranged internally short circuited such that a magnetic field is generated by currents induced in the further conductive bars. According to a preferable embodiment of the invention, the device 10 comprises a housing 100 that is configured to contain and protect the components of the device 10. In the embodiment in fig. 2a, the system 1 is arranged such that device 10 for controlling the rotational arrangement 5 comprises the rotor assembly 30 comprising means for generating a magnetic field 32, which means are arranged at the first shaft 20a. The first stator assembly 40 comprising the first stator winding 42 is arranged at the second shaft 20b. The first stator winding 42 is configured to interact with the means for generating a magnetic field 32 of the rotor assembly 30 at the first shaft 20a. Accordingly, there is an electromagnetic coupling between the first stator assembly 40 and the rotor assembly 30. The device 10 further comprises the further rotor assembly 90 comprising the further means for generating a magnetic field 92. In fig. 2a, the further rotor assembly 90 is arranged at the first shaft 20a adjacent to the rotor assembly 30. The first rotor assembly 30 and the further rotor assembly 90 are electrically isolated from each other. The second stator assembly 50 comprising the second stator winding 52 is arranged at the third shaft 20c. The second stator winding 52 is configured to interact with the further means for generating a magnetic field 92 of the further rotor assembly 90 at the first shaft 20a. Accordingly, there is an electromagnetic coupling between the second stator assembly 50 and the further rotor assembly 90. Corresponding to the embodiment in fig. 1, in fig. fig. 2a, the first shaft 20a and the second shaft 20b are extending from a first direction and the third shaft 20c is extending from a second direction opposite to the first direction. Fig. 2b differs from the embodiment in fig. 2a in that the first shaft 20a, the second shaft 20b and the third shaft 20c are all extending from the same direction. Also, in fig. 2c, the first shaft 20a, the second shaft 20b and the third shaft 20c are all extending from the same direction. The embodiment in fig. 2c differs from the embodiment in fig. 2a and 2b, in that further rotor assembly 90 is arranged on the second shaft 20b. Accordingly, there is an electromagnetic coupling between the second stator assembly 50 and the further rotor assembly 90. Thereby, the second shaft 20b and the third shaft 20c are electromagnetic coupled by means of the further rotor assembly 90 and the second stator assembly 50. In the disclosed embodiment in fig. 2c, the further rotor assembly 90 arranged on the first stator assembly 40. However, it shall be understood that correspondingly to the embodiment in fig. 2a, the further rotor assembly 90 may be arranged in vicinity to the first stator assembly 42 on the second shaft 20b. In fig. 4 is a flow chart of a method for controlling a rotational arrangement 5 according to an embodiment of the invention. The method is based on the device 10 according to any of above embodiments. In a step 110, the method is initiated by receiving information on torque or an entity dependent on the torque of the first shaft 20a, the second shaft 20b and the third shaft 20c. The information may be received from a control system of the rotational arrangement 5 or a sensor arrangement 70. According to a preferable embodiment of the invention, step 110 comprises receiving information on at least one of at least one of angular velocity of the shafts 20a-c and a phase angle of a generated current from the first stator winding 42, or a combination of the angular velocity and the phase angle. In a step 120, the method comprises determining control parameters for the first stator winding 42 and the second stator winding 52 based on the received information. The control parameters are determined such that a respective difference in torque or angular velocity between the first shaft 20a and the second shaft 20b, and between the first shaft 20a and the third shaft 20c, are controlled. In the case where the means for generating a magnetic field 32 of the rotor assembly 30 comprises field winding 32, according to an embodiment, the method further comprises determining control parameters for the field winding 32. According to a preferable embodiment of the invention, step 120 comprises calculating the torque of the first shaft 20a and second shaft 20b based on at least one of angular velocity of the shafts 20a-c and phase angle of a generated current from the first stator winding 42, and calculating control parameters based on the calculated torque of the first shaft 20a and second shaft 20b. In a step 130, the method comprises providing electric current to the first stator winding 42 and the second stator winding 52 according to the determined control parameters. By means of providing electric current to the first stator winding 42 and the second stator winding 52, the first stator winding 42 and the second stator winding 52 are controllably excited such the torque or angular velocity between the first shaft 20a and the second shaft 20b, and between the first shaft 20a and the third shaft 20c, are controlled. The method is preferably iterated continuously during to operation of the rotational assembly. Accordingly, the sequence of the steps 110, 120 and 130 are continuously repeated. In the case where the means for generating a magnetic field 32 of the rotor assembly 30 comprises field winding 32, according to an embodiment, the method further comprises providing electric current to the field winding 32 according to the determined control parameters. Regarding step 120, in the case where the device 10 comprises a further rotor assembly 90 comprising further field winding, in an embodiment of the invention, the method further comprises determining control parameters for the further field winding. Regarding step 130, in the case where the device 10 comprises a further rotor assembly 90 comprising further field winding, in an embodiment of the invention, the method further comprises providing electric current to the further field winding. According to an embodiment of the invention, the step 120, comprises determining the control parameters such that the torque of the first shaft 20a and the second shaft 20b are the same or approximately the same. According to an embodiment of the invention, the step 120, comprises determining the control parameters such that the first shaft 20a and the second shaft 20b are rotating with the same or approximately the same angular velocity in the opposite direction. It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. 08 10 25

Claims

1. A device (10) for controlling a rotational arrangement (5) comprising a first shaft (20a), a second shaft (20b), and a third shaft (20c), which shafts are arranged concentrically, 5 wherein the device (10) comprises:a rotor assembly (30) comprising means for generating a magnetic field (32), which means are configured to be arranged at the first shaft (20a); anda first stator assembly (40) comprising a first stator winding (42) configured to be arranged at the second shaft (20b), which first stator winding (42) is configured to interact10 with the rotor assembly (30) at the first shaft (20a);characterized in that the device (10) further comprises:a second stator assembly (50) comprising a second stator winding (52) configured to be arranged at the third shaft (20c), which second stator winding (52) is configured to interact with the rotor assembly (30) at the first shaft (20a); and15 a control unit (60) configured to receive information on torque or an entity dependenton the torque of the first shaft (20a), the second shaft (20b) and the third shaft (20c), wherein the control unit (60) is configured to control the first stator winding (42) and the second stator winding (52) based on said information such that a respective difference in torque or angular velocity between the first shaft (20a) and the second shaft (20b), and between the first shaft20 (20a) and the third shaft (20c), are controlled.

2. The device (10) according to claim 1, wherein the control unit (60) is configured to control the rotational arrangement (5) such that the absolute value of the torque of the first shaft (20a) and the second shaft (20b) are the same or approximately the same.

253. The device (10) according to claim 1, wherein the rotational arrangement (5) is arranged such that the first shaft (20a) and the second shaft (20b) are rotating in opposite directions, and wherein the control unit (60) is configured to control the rotational arrangement (5) such that the first shaft (20a) and the second shaft (20b) are rotating with30 the same or approximately the same angular velocity in the opposite direction.

4. The device (10) according to claim 1, wherein the control unit (60) is configured to control the rotational arrangement (5) based on a relative angular velocity between the first shaft (20a) and the second shaft (20b), and between the first shaft (20a) and the third shaft08 10 25(20c), such that the relative angular velocity is maintained.

5. The device (10) according to any of the previous claims, wherein said entity dependent on the torque is at least one of angular velocity of the shafts (20a-c) and a phase 5 angle of a generated current from the first stator winding (42), or a combination of theangular velocity and the phase angle.

6. The device (10) according to any of the previous claims, wherein the device (10) comprises a power arrangement (80) connected to the first stator winding (42) and the 10 second stator winding (52), wherein the power arrangement (80) is configured to becontrolled by the control unit (60) such that electric current is controllably provided to the first stator winding (42) and the second stator winding (52).

7. The device (10) according to any of the previous claims, where the means for 15 generating a magnetic field (32) comprises one of field winding, conductive bars and one or more permanent magnets, or a combination of these.

8. The device (10) according to an of claim 1-6, wherein the means for generating a magnetic field (32) comprises field winding, and the power arrangement (80) is connected to 20 the field winding, wherein the power arrangement (80) is configured to be controlled by the control unit (60) such that electric current is controllably provided to the field winding.

9. The device (10) according to any of the previous claims, wherein the means for generating a magnetic field (32) comprises conductive bars arranged internally short 25 circuited such that a magnetic field is generated by currents induced in the conductive bars.

10. The device (10) according to any of the previous claims, wherein the power arrangement (80) comprises a power source and a power converter device, wherein the power converter device is configured to receive electric power from the power source and 30 controllably convert the electric power io electric current that is controllably provided to the first stator winding (42) and the second stator winding (52) based on said information.

11. The device (10) according to claim 10, wherein the power source comprises an energy storage configured to controllably provide power to the power converter device.08 10 2512. The device (10) according to any of the previous claims, wherein the device (10) comprises a power transferring module configured to be connected to the first stator winding (42) for transferring generated power away from the device (10).5 13. The device (10) according to claim 12, wherein the power transferring modulecomprises a power cable configured to be connected to a power network.

14. The device (10) according to any of the previous claims, wherein the device (10) comprises a further rotor assembly (90) comprising further means for generating a magnetic 10 field (92), wherein the further means for generating a magnetic field (92) mainly is magnetically coupled to the second stator winding ¢52).

15. The device (10) according to claim 14, wherein the further means for generating a magnetic field (92) comprises one of further field winding, further conductive bars and one or 15 more further permanent magnets, or a combination of these.

16. The device (10) according to claim 14, wherein the further means for generating a magnetic field (92) comprises further field winding, and the power arrangement (80) is connected to the further field windings, wherein the power arrangement (80) is configured to 20 be controlled by the control unit (60) such that electric current is controllably provided to the further field winding.

17. The device (10) according to any of the previous claims, wherein the further means for generating a magnetic field (92) comprises further conductive bars arranged internally 25 short circuited such that a magnetic field is generated by currents induced in the further conductive bars.

18. A system (1) comprising the device (10) according to any of claim 1-17 and a rotational arrangement (5) comprising the first shaft (20a), the second shaft (20b), and the 30 third shaft (20c), which shafts (20a-c) are arranged concentrically.

19. The system (1) according to claim 18, wherein the rotor assembly (30) is arranged surrounding the first stator assembly (40).08 10 2520. The system (1) according to any of claim 18-19, wherein the rotor assembly (30) is arranged surrounding the second stator assembly (50).

21. The system (1) according to any of claim 18-20, wherein a further rotor assembly (90) 5 is arranged surrounding the second stator assembly (50).

22. The system (1) according to any of claim 18-21, wherein the first shaft (20a) comprises a flywheel arrangement (34).10 23. The system (1) according to any of claim 18-22, wherein the rotational arrangement(5) is comprised by a contra-rotating wind turbine.

24. The system (1) according to any of claim 23, wherein the first shaft (20a) corresponds to an outer shaft of the contra-rotating wind turbine and the second shaft (20b) corresponds 15 to an inner shaft of the contra-rotating wind turbine.

25. The system (1) according to any of claim 18-22, wherein the rotational arrangement (5) is comprised by a contra-rotating propeller of an aircraft or a hydrodynamic vehicle.20 26. The system (1) according to any of claim 18-22, wherein the rotational arrangement(5) is comprised by a rolling mill for metalworking.

27. The system (1) according to any of claim 18-26, wherein the rotational arrangement (5) further comprise a sensor arrangement (70) configured to detect torque or an entity 25 dependent on the torque of the first shaft (20a), the second shaft (20b), and the third shaft(20c).

28. The system (1) according to any of claim 18-27, wherein said entity dependent on the torque is at least one of angular velocity of the shaft and a phase angle of a generated30 current from the first stator winding (42), or a combination of the angular velocity and the phase angle.

29. A method for controlling a rotational arrangement (5) comprising a first shaft (20a), a second shaft (20b), and a third shaft (20c), which shafts are arranged concentrically, using a 35 device (10);08 10 25wherein the device (10) comprises:a rotor assembly (30) comprising means for generating a magnetic field (32), which means are configured to be arranged at the first shaft (20a);a first stator assembly (40) comprising a first stator winding (42) configured to be5 arranged at the second shaft (20b), which first stator winding (42) is configured to interact with the rotor assembly (30) at the first shaft (20a);a second stator assembly (50) comprising a second stator winding (52) configured to be arranged at the third shaft (20c), which second stator winding (52) is configured to interact with the rotor assembly (30) at the first shaft (20a); and10 a control unit (60);wherein the method comprises the steps of:receiving, by the control unit (60), information on torque or an entity dependent on the torque of the first shaft (20a), the second shaft (20b) and the third shaft (20c);determining, by the control unit (60), control parameters for the first stator winding15 (42) and the second stator winding (52) based on said information; andproviding electric current to the first stator winding (42) and the second stator winding(52) according to the determined control parameters, such that a respective difference in torque or angular velocity between the first shaft (20a) and the second shaft (20b), and between the first shaft (20a) and the third shaft (20c), are controlled.2030. The method according to claim 29, wherein the method comprises determining the control parameters such that the torque of the first shaft (20a) and the second shaft (20b) are the same or approximately the same.25 31. The method according to claim 29, wherein the method comprises determining thecontrol parameters such that the first shaft (20a) and the second shaft (20b) are rotating with the same or approximately the same angular velocity in the opposite direction.

32. The method according to any of claim 29-31, wherein the method comprises30 receiving information on at least one of at least one of angular velocity of the shaft and a phase angle of a generated current from the first stator winding (42), or a combination of the angular velocity and the phase angle.

33. The method according to claim 32, wherein the method comprises:35 calculating the torque of the first shaft (20a) and second shaft (20b) based on at leastone of angular velocity of the shafts and phase angle of a generated current from the first stator winding (42); andcalculating control parameters based on the calculated torque of the first shaft (20a) and second shaft (20b).LO CXIi— co

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