Patent Description:
Active magnetic bearing comprises a stator comprising electromagnets controlled to keep a rotor in the center of the stator.

The active magnetic bearing comprises at least one axis including two electromagnets diametrically opposed in the stator and supplied by a first and a second power converters controlled by a position controller to maintain the rotor in levitation in the center of the stator. Such a bearing is for instance disclosed in <CIT>.

The position controller generates a control current to control both power controllers.

When a disturbance force appears on the rotor, for example gravity, the electromagnet opposite to the direction of the disturbance must exert a restoring force.

A bias current is added (addition or subtraction) to the control current of the power controller supplying the electromagnet magnet opposite to the direction of the disturbance to maintain equilibrium position of rotor.

When the bias current is added to the control current, the said power controller supplies the said electromagnet with a higher current so that the said power controller generates more heat than the other power controller.

Generally, the first and a second power converters comprise power devices encapsulated in a power supply chip.

<FIG> represents an embodiment of a power supply chip <NUM> comprising a first power controller <NUM> including power devices <NUM> to <NUM> and a second power controller <NUM> including power devices <NUM> to <NUM>.

The power devices of <NUM> to <NUM>, <NUM> to <NUM> of each power controller <NUM>, <NUM> are arranged in line on a side of the chip <NUM>.

When the bias current is added to the control current of the first power controller <NUM>, the power devices of <NUM> to <NUM> of the first power controller <NUM> paced next to each other generate a surplus of heat compared to the power devices of <NUM> to <NUM> of the second power controller <NUM> paced next to each other.

The generated surplus of heat is dissipated by coolers of the chip <NUM>.

As the dissipated surplus of heat is concentrated on a single side of the chip <NUM>, the coolers are design to the dissipated the surplus of heat concentrated on a single side of the chip <NUM>.

An important surface of the chip <NUM> is needed to implemented coolers increasing the size of the chip <NUM>.

Consequently, the present invention intends to overcome these disadvantages by providing a thermally optimized chip.

According to an aspect, a device for controlling a magnetic bearing is proposed.

The magnetic bearing comprises at least an axis including first and second electromagnets diametrically opposed.

The device comprises two power converters per axis of the magnetic bearing, each power converter being configured to supply one different electromagnet of the first and second electromagnets, the device comprising at least eight power devices disposed on a support of the device, the eight power devices being arranged in a first line and a second line, the first line and a second line being parallel, each of the first and second lines comprising at least four power devices, a first set of four power devices of the said at least eight power devices being connected together to form a first power converter, and a second set of four power devices of the said at least eight power devices being connected together to form a second power converter,.

Each of the first and second lines comprises two power devices of the first set and two power devices of the second set, the four power devices of the first and second lines being arranged so that two adjacent power devices belong to different sets and so that the power devices at the extremities of the first line belong to a different set than power devices at the extremities of the second line.

The power devices of the first and second power converts are arranged so that the adjacent power devices of a power device of the first power converter belong to the second power converter.

The generated surplus of heat dissipated by one of the power converters is diffused on the full surface of the device and not concentrated on an area of the surface of the support, reducing the encumbrance of the device.

Preferably, the connection between the power devices of the first set arranged in the first line and the power devices of the first set arranged in the second line crosses the connection between the power devices of the second set arranged in the first line and the power devices of the second set arranged in the second line.

Advantageously, the support of the device comprises coolers, each power devices being disposed on a cooler.

Preferably, each pair of power devices of the first and second sets form a switching cell of the first and second power converters, the first power device and the second power device of each switching cell comprising a commanded power switch and a diode in parallel with the commanded power switch.

Advantageously, each pair of power devices of the first and second sets form a switching cell of the first and second power converters, a first power device of each switching cell comprising a commanded power switch and a diode in parallel with the commanded power switch and the second power devices of each switching cell comprising a passive power switch.

Preferably, the passive power switch comprises a power diode.

Advantageously, the commanded power switch comprises a transistor.

According to another aspect, a system for controlling a magnetic bearing comprising at least an axis is proposed.

The at least one axis includes first and second electromagnets diametrically opposed and a device as defined above, the first power converter supplying the first electromagnet and the second power converter supplying the second electromagnet.

Advantageously, the system further comprises at least one sensor to measure the position of a rotor of the magnetic bearing compared to the first and second electromagnets.

Preferably, the system further comprises a processing unit configured to control commanded power switches of the first and second power converters to supply the electromagnets from measurements delivered the sensor.

The present invention and its advantages will be better understood by studying the detailed description of specific embodiments given by way of non-limiting examples and illustrated by the appended drawings on which:.

Reference is made to <FIG> which represents an example of a system <NUM> for controlling a magnetic bearing, comprising a magnetic bearing <NUM> and a device <NUM> for controlling the magnetic bearing <NUM>.

The magnetic bearing <NUM> comprises an axis including two electromagnets <NUM>, <NUM> diametrically opposed.

A rotor <NUM> is inserted in the magnetic bearing <NUM> between the two electromagnets <NUM>, <NUM>.

The device <NUM> controls the two electromagnets <NUM>, <NUM> so that the rotor <NUM> levitates in a centered position of the magnetic bearing <NUM>.

A first electromagnet <NUM> is connected to a first output <NUM> and a second output <NUM> of the device <NUM>, and a second electromagnet <NUM> is connected to a third output <NUM> and a fourth output <NUM> of the device.

The system <NUM> further comprises a processing unit <NUM> controlling the device <NUM>.

The system <NUM> comprises a sensor <NUM> connected to the processing unit <NUM> and delivering the position of the rotor <NUM> compared to the two electromagnets <NUM>, <NUM>.

<FIG> illustrates an example of the device <NUM>.

The device <NUM> comprises eight power devices <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> disposed on a support <NUM> of the device <NUM>.

Each power device <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> comprises a first connection <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> and a second connection <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>.

The eight power devices <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> are arranged in a first line <NUM> and a second line <NUM> parallel to the first line <NUM>.

The first line <NUM> may be arranged on a first side of the support <NUM> and the second line <NUM> may be arranged on a second side of the support <NUM>.

Each line <NUM>, <NUM> comprises four power devices.

A first set of four power devices <NUM>, <NUM>, <NUM>, <NUM> are connected together to form two switching cells or legs <NUM>, <NUM>.

The first connections <NUM>, <NUM> of a first and second power devices <NUM>, <NUM> are connected together to form a first switching cell <NUM> and the first connections <NUM>, <NUM> of a third and a fourth power devices <NUM>, <NUM> are connected together to form a second switching cell <NUM>.

The two switching cells <NUM>, <NUM> are connected together to form a first power converter.

A second set of four power devices <NUM>, <NUM>, <NUM>, <NUM> are connected together to form two switching cells <NUM>, <NUM>.

The first connections <NUM>, <NUM> of a fifth and a sixth power devices <NUM>, <NUM> are connected together to form a third switching cells <NUM> and the first connections <NUM>, <NUM> of a seventh and an eighth power devices <NUM>, <NUM> are connected together to form a fourth switching cells <NUM>.

The third and fourth switching cells <NUM>, <NUM> are connected together to form a second power converter.

In another embodiment, each of the first and second power converters may comprise more than four power devices implemented to form a multilevel power converter.

The first output <NUM> of the device <NUM> is connected to the first switching cell <NUM> between the first and second power devices <NUM>, <NUM>, and the second output <NUM> of the device <NUM> is connected to the second switching cell <NUM> between the third and fourth power devices <NUM>, <NUM> so that the first power converter supplies the second electromagnet <NUM>.

The third output <NUM> of the device <NUM> is connected to the third switching cell <NUM> between the fifth and sixth power devices <NUM>, <NUM> and the fourth output <NUM> of the device <NUM> is connected to the fourth switching cell <NUM> between the seventh and eighth power devices <NUM>, <NUM> so that the second power converter supplies the first electromagnet <NUM>.

The second connection <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> of each power device <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> is connected to a power supply bus <NUM> of the device <NUM> supplying the device <NUM> with electrical energy.

The second connection <NUM>, <NUM>, <NUM>, <NUM> of each power device <NUM>, <NUM>, <NUM>, <NUM> is connected to a first supply bar <NUM> of the supply bus <NUM> supplying a negative potential.

The second connection <NUM>, <NUM>, <NUM>, <NUM> of each power device <NUM>, <NUM>, <NUM>, <NUM>, <NUM> is connected to a second supply bar <NUM> of the supply bus <NUM> supplying a positive potential.

The first and second power converters convert electrical energy supplied by the power supply bus <NUM> to supply the first and second electromagnets <NUM>, <NUM> with power.

The first line <NUM> comprises the first and third power devices <NUM>, <NUM> of the first set and the fifth and seventh power devices <NUM>, <NUM> of the second set, and the second line <NUM> comprises the second and fourth power devices <NUM>, <NUM> of the first set and the sixth and eighth power devices <NUM>, <NUM> of the second set.

The four power devices of the first and second lines <NUM>, <NUM> are arranged so that two adjacent power devices belong to two different sets and so that the power devices <NUM>, <NUM> at the extremities of the first line <NUM> belong to a different set of four power devices than the power devices <NUM>, <NUM> at the extremities of the second line <NUM>.

The power devices <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> of the first and second power converts are arranged so that the adjacent power devices of a power device <NUM>, <NUM>, <NUM>, <NUM> of the first power converter belong to the second power converter.

When one of the first and second power converters is more in demand, the generated surplus of heat dissipated by the said power converter is diffused on the full surface of the support <NUM> of the device <NUM> and not concentrated on an area of the surface of the support <NUM>.

The power devices <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> may be implemented on coolers <NUM>, <NUM> of the device <NUM> lying on the support <NUM>.

As the generated surplus of heat is dissipated on the full surface of the support <NUM>, the size of the coolers <NUM>, <NUM> is reduced so that the encumbrance of the device <NUM> is reduced.

The thermal mapping of the device <NUM> is homogenize.

As represented on <FIG>, the connection between a power device <NUM>, <NUM> of the first set arranged in the first line <NUM> and a power device <NUM>, <NUM> of the first set arranged in the second line <NUM> crosses the connection between a power device <NUM>, <NUM> of the second set arranged in the first line <NUM> and a power device <NUM>, <NUM> of the second set arranged in the second line <NUM>.

This arrangement of the power devices <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> permits to minimize the routing of the connexions between the power devices comprising for example leads made of cooper reducing even more the encumbrance of the device <NUM>.

The magnetic bearing <NUM> may comprise more than one axis, each axis comprising two electromagnets diametrically opposed, each electromagnet being supplied by a different power converter of the device <NUM>.

The device <NUM> comprises two power converters per axis of the magnetic bearing <NUM> supplying a different electromagnet of the said axis.

<FIG> illustrates schematically a first embodiment of the power devices <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>.

The power device comprises a commanded power switch <NUM> and a diode <NUM> in parallel with the commanded power switch <NUM>.

The commanded power switch <NUM> comprises for example a field effect transistor comprising a gate connected to a third connection <NUM> of the power device <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, a drain connected to the first connection <NUM>, <NUM>, <NUM>, <NUM> and the second connection <NUM>, <NUM>, <NUM>, <NUM> of the power devices <NUM>, <NUM>, <NUM>, <NUM>, and a source connected to the first connection <NUM>, <NUM>, <NUM>, <NUM> and the second connection <NUM>, <NUM>, <NUM>, <NUM> of the power devices <NUM>, <NUM>, <NUM>, <NUM>.

The anode of the diode <NUM> is connected to the source of the transistor <NUM> and the cathode of the diode <NUM> is connected to the drain of the transistor <NUM>.

The processing unit <NUM> controls the commanded power switch <NUM> to supply the electromagnets <NUM>, <NUM> from measurements delivered the sensor <NUM>.

The processing unit <NUM> is connected to third connection <NUM> of the power device <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> to control the gate of the transistor <NUM>.

<FIG> illustrates a second embodiment of the power devices <NUM>, <NUM>, <NUM>, <NUM>.

Each power device <NUM>, <NUM>, <NUM>, <NUM> comprises a passive power switch <NUM> comprising for example a power diode, the cathode of the power diode <NUM> being connected to the first connection <NUM>, <NUM> of the power devices <NUM>, <NUM> and to the second connection <NUM>, <NUM> of the power devices <NUM>, <NUM>, and the anode of the power diode <NUM> being connected to the first connection <NUM>, <NUM> of the power devices <NUM>, <NUM> and to the second connection <NUM>, <NUM> of the power devices <NUM>, <NUM>.

Claim 1:
Device (<NUM>) for controlling a magnetic bearing (<NUM>) comprising at least an axis including first and second electromagnets (<NUM>, <NUM>) diametrically opposed, the device comprising two power converters per axis of the magnetic bearing (<NUM>), each power converter being configured to supply one different electromagnet of the first and second electromagnets (<NUM>, <NUM>), the device comprising at least eight power devices (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) disposed on a support (<NUM>) of the device, the eight power devices being arranged in a first line (<NUM>) and a second line (<NUM>), the first line and a second line being parallel, each of the first and second lines comprising at least four power devices, a first set of four power devices (<NUM>, <NUM>, <NUM>, <NUM>) of the said at least eight power devices being connected together to form a first power converter, and a second set of four power devices (<NUM>, <NUM>, <NUM>, <NUM>) of the said at least eight power devices being connected together to form a second power converter, characterized in that each of the first and second lines (<NUM>, <NUM>) comprises two power devices (<NUM>, <NUM>, <NUM>, <NUM>) of the first set and two power devices (<NUM>, <NUM>, <NUM>, <NUM>) of the second set, the four power devices of the first and second lines being arranged so that two adjacent power devices belong to different sets and so that the power devices at the extremities of the first line belong to a different set than power devices at the extremities of the second line.