SYNCHRONOUS ELECTRICAL MACHINE AND BOAT COMPRISING SUCH A MACHINE

Provided is a synchronous electrical machine that includes a stator and a wounded rotor, the stator having a plurality of phases, each phase comprising coils connected together and magnetic stator poles cores fixed on a stator frame and evenly distributed along a stator diameter, each coil being wounded around a different magnetic stator pole core to form a magnetic stator pole, each phase comprising a same number of magnetic stator poles, the magnetic stator poles of each phase being disposed in the stator frame to form a concentric winding stator. The rotor includes a plurality of magnetic rotor pole cores evenly distributed around the rotor and rotor coils, each rotor coil being wounded around a different magnetic rotor pole core to form a magnetic rotor pole.

I. CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to European Patent Application Serial Number 22174105.1, filed May 18, 2022, which is herein incorporated by reference.

II. FIELD OF INVENTION

The present invention concerns electrical rotating machines and relates more particularly to a synchronous electrical machine comprising a wounded rotor.

The present invention also relates to a boat comprising such a synchronous electrical machine.

In this description, “boat” shall mean any type of motorized floating vessel or vehicle designed to be sailed.

A boat may comprise a main electrical propulsion system comprising a diesel engine, electrical generators supplying board network and electrical motors for propulsion. Additional electrical machines are also used between the main electrical motor for propulsion and the propeller to add propulsive power to the turbine and/or to add electrical power to the network. The additional electrical machines may reach up to 10 MW at 50-100 rpm.

The additional electrical machines are generally synchronous machines made of either permanent magnet rotors or wounded rotors.

As the additional electrical machines are implemented in the boat, the space reserved for each machine is limited and torque mass ratio of each machine is an important point as well as reliability, continuity of service and efficiency.

Transporting, manufacturing, assembling or repairing a permanent magnet rotor can be very complex and requires non-magnetic tools.

Further, due to the permanent magnets of the rotor, the assembly of the rotor in the stator of the synchronous electrical machine requires specific assembly procedures which are time costly.

Such machines mostly implement an axial cooling to cool the stators. A cooling fluid is passing only between adjacent coils of the stators generating hotspots in the stators and limiting therefore the torque density.

It is known that wounded rotor synchronous machines are less performant than permanent magnet synchronous machines. Wounded rotor synchronous machines generate higher thermal losses due to the current circulating in the rotor winding. It is therefore proposed to remedy the disadvantages related to synchronous electrical machines according to the prior art.

IV. SUMMARY OF INVENTION

In view of the foregoing the invention proposes a synchronous electrical machine comprising a stator and a wounded rotor, the stator comprising a plurality of phases, each phase comprising coils connected together and magnetic stator poles cores fixed on a stator frame and evenly distributed along a stator diameter, each coil being wounded around a different magnetic stator pole core to form a magnetic stator pole, each phase comprising a same number of magnetic stator poles, the magnetic stator poles of each phase being disposed in the stator frame to form a concentric winding stator.

The rotor comprises a plurality of magnetic rotor pole cores evenly distributed around the rotor and rotor coils, each rotor coil being wounded around a different magnetic rotor pole core to form a magnetic rotor pole.

Advantageously, the magnetic stator pole cores are fixed on the stator frame with first removable fasting means and the magnetic rotor pole cores are fixed on a rotor shaft with second removable fasting means.

Preferably, the first removable fasting means comprise first screws passing through holes evenly disposed on a longitudinal direction of the stator frame and tapered retaining means incorporated in each magnetic stator pole core, the first screws being engaged in the tapered retaining means, and the second removable fasting means comprising second screws passing through holes evenly disposed on a longitudinal direction of the magnetic rotor pole core, the rotor shaft comprising tapered holes in which the second screws are engaged.

Advantageously, a non-magnetic shim can be interposed between each magnetic stator poles and the stator frame.

The non-magnetic shim avoids Eddy-induced losses in the frame.

Preferably, each magnetic stator pole core extending in a longitudinal direction of the stator comprises at least one cooling groove on a surface of the said magnetic stator pole core in contact with the stator frame and extending along the longitudinal direction so that the groove and the contact surface of the stator frame form a cooling channel.

The cooling channel improves the cooling of the machine and also permits to reduce Eddy-currents losses induced in the frame.

Advantageously, each magnetic stator pole core comprises a plurality of magnetic elements, two adjacent magnetic elements being separated by an air gap forming a radial cooling duct.

Preferably, the stator frame comprises openings on the lateral surface of the stator frame so that a cooling fluid circulating in cooling ducts escapes from the stator through the openings.

Advantageously, the stator frame comprises an opening at each of end so that a cooling fluid circulating in cooling ducts escapes from the stator through the openings.

Advantageously, each magnetic stator pole core comprises at least one tie rod and one end plate at each end of the magnetic stator pole core, the tie rods passing through the magnetic stator pole cores to connect the two end plates fixed on the stator frame.

Preferably, tierods and end plates are made of non-magnetic steel to avoid additional losses.

Tierods's numbers and shapes can be optimized to maximise mechanical stiffness of the whole pole as well as magnetic reluctant circuit.

Advantageously, the wounded rotor is lodged in the stator or the stator is lodged in the wounded rotor.

Preferably, the rotor comprises commutation means configured to supply all of the rotor coils or a part of the rotor coils to vary the rotation speed of the rotor when the coils of the stator are supplied with a supply signal having a constant predetermined frequency.

Advantageously, the rotor comprises a first slip ring and a second slip ring having each a different electric potential, the stator comprising two brushes, each brush cooperating with a different slip ring to supply the commutation means.

Preferably, the rotor comprises three slips and the stator comprises three brushes, each brush cooperating with a different slip ring, each slip ring having a different electric potential, a first set of rotor coils being supplied with a first and a second slip rings, and a second set of rotor coils being supplied with the first and the third slip rings, the second set of rotor coils forming compensation poles, the sum of the first and second set of coils being equal to the number of rotor coils.

Another object of the invention relates to a boat comprising a synchronous electrical machine as defined above.

VI. DETAILED DESCRIPTION OF THE INVENTION

FIG.1illustrates an example of a boat1comprising a propulsion unit2for propelling the boat1, a power supply network NET supplying the propulsion unit2, with electrical power.

The propulsion unit2comprises a propulsion motor3, a power converter4and a propeller5driven by the propulsion motor3through a shaft6.

The power controller4supplies the propulsion motor3from the power supply network NET delivering an alternative voltage.

The propulsion unit2further comprises a booster unit7.

The booster unit7comprises a synchronous electrical machine8comprising a stator9and a rotor10comprising a rotor shaft10a, the rotor shaft10abeing connected at each end to the shaft6between the propulsion motor3and the propeller3, and a reversible power converter11to supply the synchronous electrical machine8.

The synchronous electrical machine8operates in a motor mode or in a generator mode.

In the motor mode, the synchronous electrical machine8supplied by the reversible power converter11generates a torque on the shaft6to assist the propulsion motor3.

In the generator mode, the rotor10is driven by the shaft6so that the synchronous electrical machine8generates electrical energy supplying the reversible power converter11.

The power converter11supplies for example the power supply network NET with the electrical energy power generated by the synchronous electrical machine8in generator mode.

The boat1may comprise more than one network NET.

The power converters4and11are made from semiconductors, for example diodes, thyristors or piloted interrupters.

FIGS.2and3illustrate a view and a radial cross section of an example of the synchronous electrical machine8.

The stator9comprising a stator frame11, magnetic stator pole cores12fixed on the stator frame19and extending along a longitudinal direction of the stator, and coils13.

The magnetic stator pole cores12are favourably evenly distributed along a stator diameter.

Each coil13is wounded around a different magnetic stator pole core12having approximatively a length equal to the length of the stator9.

Each magnetic stator pole core12and coil13wounded around the said stator pole core13form a magnetic stator pole.

The stator9comprises for example eighteen magnetic stator poles.

The coils13are disposed in the stator frame9and connected together to form a plurality of phases each phase comprising a same number of magnetic stator poles.

For example, the stator9comprises three phases, each phase comprising six stator magnetic poles.

The magnetic stator poles of each phase are disposed in the stator frame9to form a concentric winding stator.

The concentric winding stator reduces the Joule losses comparing to a distributed winding stator due to the fact their coil's head is shorter.

Moreover, the machine8has a higher torque density compared to synchronous machines comprising a distributed winding stator.

The rotor10comprises a plurality of magnetic rotor pole cores14evenly distributed around the rotor10and fixed on the rotor shaft10a, and rotor coils15.

Each rotor coil15is wounded around a different magnetic rotor pole core14forming a magnetic rotor pole, the poles of the rotor being identical.

The rotor10is lodged in the stator9and rotates around a central axis A1.

In another embodiment, the stator9is lodged in the rotor10.

In this example, it is assumed that the rotor10comprises twenty-four magnetic rotor poles P1to P24.

The rotor poles P1to P24are disposed in the rotor10so that the rotor pole Pn+1 is between the rotor pole Pn et Pn+2, n being an integer between 1 and 22, the rotor poles P1and P24being adjacent.

The rotor10further comprises a first slip ring and a second slip ring (not represented) cooperating with two brushes (not represented) of the stator9, each brush cooperating with a different slip ring to supply the rotor coils15as explained in the following.

The reversible power converter11supplies the stator9and the rotor10of the machine8respectively with alternative voltage and continuous voltage.

In another embodiment, the booster unit7comprises a continuous voltage source to supply the rotor10and alternative voltage source to supply the stator9, both sources being independent.

The rotor coils15are supplied through the brushes and the slip rings.

Alternatively, the slip rings may be supplied with an exciter.

FIG.4illustrates a view of a first example of the magnetic stator pole core12and an example of the magnetic rotor pole core14defining an air gap16of the machine8.

The shape of the magnetic rotor pole core14can be adjusted to limit air gap flux density harmonics and their consequences on vibration, noise and losses.

The magnetic stator core12and magnetic rotor pole core14are made for example of magnetic laminations to reduce Eddy-currents losses in the pole cores.

The magnetic stator core12further comprises two holes21,22extending in the longitudinal direction.

The two holes21,22have different shapes designed to optimize the magnetic flux circulating in the core12.

Each hole21,22lodges a tie rod23,24to maintain compacted the magnetic laminations of the core12.

Preferably, the tie rods23,24are made of non-magnetic steel to avoid Eddy-current losses in the frame11.

FIG.5illustrates a radial cross section of a part of the stator9comprising the first example of the magnetic stator pole core12illustrates atFIG.4and a rotor coil15.

The magnetic stator pole core12is fixed on the stator frame11with first removable fasting means so that the magnetic stator pole core12is in contact with the frame11.

The first removable fasting means permit to easily assemble and disassemble the stator pole comprising the magnetic stator pole core12and the coil15, for example when the coil15is in fault.

The first removable fasting means may comprise first screws17passing through holes18evenly disposed on a longitudinal direction of the stator frame11and tapered retaining means incorporated in the stator magnetic pole core12.

The passing through holes18and the retaining means are arranged in the stator9so that each first screw17is engaged in tapered retaining means to fix the magnetic stator pole core12on the stator frame11.

The tapered retaining means comprise for example nuts19arranged in a fixing groove20of the stator magnetic pole core12.

A non-magnetic shim25may be interposed between the magnetic stator pole core12and the stator frame11to reduce Eddy-currents losses in the frame11in order to limit warming of the stator9.

The non-magnetic shim25is for example made of laminate material or stainless steel if thermal exchange with frame is needed.

FIG.6illustrates a radial cross section of a part of the rotor10comprising an example of the magnetic rotor pole P1comprising the magnetic rotor pole core14and the rotor coil15.

The rotor magnetic pole core14is fixed on the rotor shaft10awith second removable fasting means so that the rotor magnetic core14is in contact with the rotor shaft25.

The second removable fasting means permits to easily assemble and disassemble the rotor set comprising the magnetic rotor pole core14and the associated rotor coil15, for example when the rotor coil15is in fault.

As the rotor10is wounded and does not comprise permanent magnets, manufacturing and repairing the rotor10do not require non-magnetic tools compared to permanent magnets rotors.

Further the assembling of the rotor in the stator is easier as well as transportation.

The second removable fasting means may comprise second screws26passing through holes27evenly disposed on a longitudinal direction of the magnetic rotor pole core14, and tapered holes28disposed in the rotor shaft10aand arranged in the rotor shaft10aso that each second screw26is engaged in a different tapered hole28.

The rotor poles P1to P24are modular poles easy to arrange on a pre-existing rotor shaft design.

Their shapes, including the face in the air gap, can be optimized to maximise performances. Assembling can also be done using dove tails and keys bars.

FIG.7illustrates a radial cross section of a part of the stator9comprising a second example of the magnetic stator pole core12.

The stator pole core12comprises three cooling grooves29on the surface30of the stator pole core12in contact with the stator frame11.

The stator pole core12may comprise more than three cooling grooves29.

The cooling grooves29extend along the longitudinal direction of the stator9so that the cooling grooves29and the surface of the stator frame11in contact with the surface30of the stator pole core12form cooling channels31.

The cooling channels31and a cooling fluid flowing in the channels may form a bilateral cooling scheme.

The stator9further comprises one end plate at each end of the magnetic stator pole core12fixed on the stator frame11and connected by the tie rods21,24.

The tie rods21,24engaged in the end plates fix the stator pole cores12in the frame11with or without obstructing the cooling channels34if an open or closed frame is used as shown in the following onFIGS.9and10.

The stator pole core12further comprises on a first circumferential side a groove32and on the second circumferential side a lug33so that the lug33of a first stator pole core is engaged in the groove32of the second stator pole core to maintain the stator pole core12in the stator9.

The first example of the magnetic stator pole core12illustrated inFIG.5may also be provided with the groove32and the lug33.

FIG.8illustrates a view of a third example of the magnetic stator pole core12and the example of the magnetic rotor pole core14.

The magnetic stator pole core12comprises a plurality of magnetic elements34arranged according to the longitudinal direction of the stator9and having a radial section identical to the radial section of the second example of the magnetic stator pole core12illustrated onFIG.7.

Each element34comprises cooling grooves35cooperating with the stator frame11to define cooling channels as explain above.

Each magnetic element34comprises for example a stack of magnetic laminations.

Two adjacent magnetic elements34are separated by an air gap forming a radial cooling duct36.

The magnetic elements34are fixed in the stator9by the tie rods23,24passing through the magnetic elements34and connected to end plates37,38of the stator pole core12.

Spacers or pins may be inserted between two adjacent magnetic elements34to from the radial cooling duct36.

The longitudinal length of the magnetic element34and the radial cooling duct36are determined so that the length of the plurality of magnetic element34and ducts36is equal to the length of the stator9.

Cooling fluid flows in the air gap defined between the magnetic rotor pole core14and the magnetic elements34at each end of the stator pole core12as represented by arrows F1, F2, flows in the air ducts36(arrows F3), and escapes the stator9by flowing in the cooling channels (arrows F4) defined by the cooling grooves35and the stator frame11.

As the cooling fluid flows in the pole core12, the exchange surface between the stator pole core12comprising the radial cooling ducts36is increased so that the cooling of the stator set is enhanced and the torque density is significantly increased.

In this way, a bilateral cooling may be obtained. As the size of the machine8is closely related to the cooling design capacity, bilateral cooling described before allows to reach much higher torque density compared to a machine known of the prior art.

FIG.9illustrates a first example of the stator frame11.

The stator frame9comprises openings39on the lateral surface of the frame11so that the cooling fluid circulating in the cooling ducts36escapes from the stator9through the openings39.

FIG.10illustrates a second example of the stator frame11. The stator frame11comprises an opening40at each end of the stator frame so that the cooling fluid circulating in cooling ducts36escapes from the stator through the openings40.

FIG.11illustrates a first example of an electrical circuit of the rotor10.

In this example, the rotor shaft10acomprises the first slip ring41and the second slip ring42, and the rotor frame11comprises a first brush43in contact with the first slip ring41and the second brush44in contact with the second slip ring42, the first brush43and the second brush44being respectively supplied by two different electric potentials of the converter11.

The rotor10further comprises commutation means45connected to the slip rings41,42and supplying all of the rotor coils15of the rotor poles P1to P24or a part of the rotor coils15to vary the rotation speed of the rotor10.

The commutation means45permit to allow speed variation of the rotor10without modifying the frequency of the supply signals generated by the converter11to supply the machine8and without any changes in the stator coils12.

The rotation direction of the rotor10is easily adjusted by modifying the control of supply signal generated by the converter11.

Each rotor coil15comprise a first extremity15aand a second extremity15b.

The control circuit46may comprise a processing unit located on the rotor10to communicate with the switches K1, K2, K3, K4, K5.

A first extremity of a first switch K1, a first extremity of a fifth switch K5, the first extremity15aof the coil15of the poles P1, P5, P9, P13, P17, P21, and the second extremity15bof the winding15of the poles P2, P4, P6, P8, P10, P12, P14, P16, P18, P20, P22, P24are connected to the first slip ring41.

The second extremity of the first switch K1, a first extremity of a second switch K2and the first extremity15aof the coil15of the poles P3, P7, P11, P15, P19and P23are connected together.

The second extremity of the second switch K2, a first extremity of a third switch K3, and the second extremity15bof the coil15of the poles P1, P5, P9, P13, P17and P21are connected to the second slip ring40.

The second extremity of the fifth switch K5, the second extremity of a third switch K3, a first extremity of the fourth switch K4, and the second extremity15bof the coil15of the poles P3, P7, P11, P15, P19and P23are connected together.

In the following, a closed switch is understood as a switch in which current flow through, and an open switch is understood as a switch in which no current flow through.

When the first switch K1, third switch K3and fourth switch K4are closed, and the second switch K2and the fifth switch K5are open by the control circuit46, the poles P1to P24of the rotor10are supplied with a current delivered by the converter11.

When the first switch K1, third switch K3and fourth switch K4are open, and the second switch K2and the fifth switch K5are closed by the control circuit46, one on two poles is supplied by the converter11, namely the poles P1, P3, P5, P7, P9, P11, P13,15, P17, P19, P21and P23are supplied with a current delivered by the converter11.

As the rotation speed of the rotor10is determined by the number of supplied poles P1to P24, the arrangement of the poles P1to P24and the supply frequency of the converter11, the commutation means allow to modify easily the rotation speed of the rotor10of the machine8without modifying the frequency of the supply signal delivered by the power converter11or modifying the stator coils.

The rotation direction of the rotor10is easily adjusted by modifying the control of supply signal generated by the converter11.

The switching means comprising five switches K1to K5allow to choose the rotor speed between a first rotation speed when all the poles P1to P24supplied by the converter11, and a second rotation speed when one on two poles P1to P24are supplied by the converter11, the first speed being half as high as the second speed when the frequency of the supply signal is equal to a constant predetermined value.

The synchronous machine8comprising the concentric winding topology in the stator9and the wounded rotor10as described below allows to achieve the speed variation of the rotor10without modifying the supply signal generated by the converter11and without modifying the stator coils arrangement.

In another embodiment, the switching means are designed to choose between more than two different rotation speeds by supplying less than one pole out of two poles, for example one pole out of four poles.

FIG.12illustrates a second example of an electrical circuit of the rotor10.

In this example, the rotor shaft10A comprises the first slip ring41, the second slip ring42, a third slip ring48, and the rotor frame11comprises the first brush43in contact with the first slip ring41, the second brush44in contact with the second slip ring42a third brush47in contact with the third slip ring48, the first brush43, the second brush44and the third brush47being respectively supplied by three different electric potentials of the converter11.

The second extremity15bof the coil15of the poles P4, P8, P12, P16, P20, P24is connected to the third slip ring48.

A first set of the rotor coils15of the poles P1, P2, P3, P5, P6, P7, P9, P10, P11, P13, P14, P15, P17, P18, P19, P21, P22, P23, are supplied with the first and second slip rings41,42, and a second set of the rotor coils15of the poles P4, P8, P12, P16, P20, P24are supplied with the first and third slip rings41,48.

The sum of the first and second set of coils15is equal to the number of rotor coils15.

The second set of rotor coils15form compensation poles of the rotor10to reduce the distortion of the magnetic flux in the air gap16leading to less losses, ripples, vibrations, or noise. In addition, this can also help to enhance the torque-speed capabilities of the proposed machine.

FIG.13illustrates another example of the synchronous electrical machine8.

The machine8comprises a stator49lodged in a wounded rotor50, the stator49and the rotor50having the same architecture as the stator9and the rotor10.