Control system for a magnetic bearing and associated method

Abstract

A control system (1) for a magnetic bearing (3, 4) is proposed. The control system (1) comprises a control loop (BR1) for the magnetic bearing, the control loop having a master control node (5) and at least two slave control nodes (6, 7) connected in series by a first bidirectional data bus (8) of said system, and a second bidirectional data bus (9) connecting the control nodes (6, 7) located at the ends of the control loop. The master control node includes transmitting means (10). Figure 1

Description

Title of the invention: Magnetic bearing control system and associated method Technical field of the invention

[0001] The present invention relates to the control of magnetic bearings.

[0002] The present invention relates more particularly to a system for controlling a magnetic bearing comprising control nodes and a method for controlling the magnetic bearing. State of the prior art

[0003] A magnetic bearing control system may be based on a distributed type architecture comprising a “master” control module and “slave” control modules connected to the “master” control module by data buses to form a magnetic bearing control loop clocked by the “master” control module.

[0004] Each “slave” control node independently controls a power converter controlling a different servo axis of the bearing, in particular from data generated by sensors of the magnetic bearing.

[0005] A first data bus connects the “master” control module and the “slave” control modules in series to each other, and a second data bus connects the “master” control module to the “slave” control module located at the end of the control loop.

[0006] However, when a bus fails, for example when the bus wires are cut between two adjacent slave control nodes, the data passing over said bus is no longer routed to all of the slave control nodes, resulting for example in desynchronization of the slave control nodes likely to degrade the operation of the magnetic bearing.

[0007] It is therefore proposed to overcome all or part of these drawbacks by improving the reliability of the magnetic bearing control system. Summary of the invention

[0008] In view of the above, the invention proposes a method for controlling a magnetic bearing by a control loop comprising a first bidirectional data bus connecting in series a master control node and at least two slave control nodes, and a second bidirectional data bus connecting said control nodes located at the ends of the control loop, each slave control node controlling a different servo axis of the magnetic bearing.

[0009] The method comprises:

[0010] • the transmission of a first data frame by the master control node to through the first data bus; and

[0011] • the transmission of a second data frame by the master control node to across the second data bus, the first and second frames being identical.

[0012] By "bearing servo axis" is meant the axis which is defined by two diametrically opposed coils of the magnetic bearing stator.

[0013] Despite the failure of one of the first or second bidirectional data buses, the magnetic bearing is controlled by the control loop.

[0014] Preferably, each data frame comprises as many predetermined locations as there are slave and master control nodes, each predetermined location being associated with a slave or master control node such that each slave or master control node knows the address of the predetermined location associated with said node, each frame comprising a succession of bits, the transmission of the first frame comprising the successive transmission of the bits of said frame and the transmission of the second frame comprising the successive transmission of the bits of said frame.

[0015] Advantageously, the method further comprises, for each slave and master node, writing data of said node in the bits associated with the predetermined location of said node in the first and second frames.

[0016] Preferably, each data frame comprises servo data of the slave control nodes.

[0017] Advantageously, the first data bus and the second data bus are synchronous buses.

[0018] There is also provided a system for controlling a magnetic bearing comprising a control loop of the magnetic bearing, the control loop comprising a master control node and at least two slave control nodes connected in series by a first bidirectional data bus of said system, and a second bidirectional data bus connecting together the control nodes located at the ends of the control loop.

[0019] The master control node comprises transmission means configured to:

[0020] • transmit a first data frame through the first data bus, and.

[0021] • transmit a second data frame through the second data bus.

[0022] Advantageously, each data frame comprises as many predetermined locations as there are slave and master control nodes, each predetermined location being associated with a slave or master control node so that each slave or master control node knows the address of the predetermined location associated with said node, each frame comprising a succession of bits, the transmission means being configured to successively transmit the bits of the first frame through the first data bus and to successively transmit the bits of the second frame through the first data bus.

[0023] Preferably, each slave and master control node comprises writing means configured to write data of said node into the bits associated with the predetermined location of said node in the first and second frames.

[0024] Advantageously, the master control node comprises a slave control node.

[0025] Preferably, each slave control node is configured to drive said magnetic bearing independently of other slave control nodes. Brief description of the figures

[0026] Other aims, characteristics and advantages of the invention will appear on reading the following description, given solely by way of non-limiting example, and made with reference to the appended drawings in which:

[0027] [Fig.l]

[0028] illustrates an example of a distributed type magnetic bearing control system according to the invention; and

[0029] [Fig.2]

[0030] illustrates an example of implementation of the control system of a magnetic bearing following the detection of a failure according to the invention. Detailed description of the invention

[0031] Reference is made to [Fig.l] which illustrates an example of a control system 1 of a magnetic bearing controlling a device 2 comprising magnetic bearings.

[0032] In a manner known per se, the device 2 comprises a stator 2a and a rotor 2b placed in the stator 2a.

[0033] The stator 2a comprises two magnetic bearings 3, 4 arranged at the ends of the stator 2a.

[0034] Each magnetic bearing 3, 4 comprises coils distributed uniformly in the circumferential direction on the inner side of the stator 2a, two diametrically opposed coils being connected to each other so as to be powered simultaneously by an electrical power converter.

[0035] Two diametrically opposed stator coils define a control axis of the magnetic bearing and allow this axis to be controlled.

[0036] The distributed type control system 1 comprises a BRI control loop comprising a master control node 5, a first slave control node 6 connected to the master control node 5 and a second slave control node 7 connected to the first slave control node 5.

[0037] The master control node 5 may for example be located at one end of the BRI control loop.

[0038] Alternatively, the master control node 5 may be located elsewhere in the BRI control loop.

[0039] The master control node 5 may comprise a slave control node.

[0040] The master 5 and slave 6, 7 control nodes are connected to each other by a first 8 bidirectional data bus.

[0041] A second bidirectional data bus 9 connects the master control node 5 and the second slave control node 7.

[0042] The slave control nodes 6, 7 are clocked by the master control node 5.

[0043] The first and second data buses 8, 9 form a communication ring.

[0044] The first data bus 8 and the second data bus 9 are for example synchronous buses.

[0045] The master control node 5 comprises transmission means 10, writing means 11 and reading means 12.

[0046] Each slave control node 6, 7 is connected to the first data bus 6 and to the second data bus 7.

[0047] The first slave control node 6 is capable of controlling a first magnetic bearing 3 and the second slave control node 7 is capable of controlling the second magnetic bearing 3.

[0048] The first slave control node 6 is connected to the coils of the first magnetic bearing 3 and the second slave control node 7 is connected to the coils of the second magnetic bearing 3.

[0049] Each slave control node 6, 7 comprises reading means 13, 14, writing means 15, 16 and transmission means 17, 18.

[0050] Of course, the system 1 can comprise more than two slave control nodes to control the device 2. It is sufficient to add an additional slave control node per magnetic bearing, the additional node being connected in series to an adjacent node.

[0051] When neither of the first nor second data buses 8, 9 is faulty, the transmission means 10 of the master control node 5 transmit a first TRI data frame through the first data bus 8 and a second TR2 data frame through the second data bus 9, the first and second TRI, TR2 frames being identical.

[0052] The first and second frames TRI, TR2 are transmitted simultaneously or sequentially.

[0053] Each TRI, TR2 frame comprises a succession of bits emitted successively by the means of emission 10.

[0054] Each TRI, TR2 data frame comprises as many predetermined locations as there are slave control nodes 6, 7 and master node 5.

[0055] Each predetermined location is associated with a slave control node 6, 7 such that each slave control node 6, 7 knows the address of the predetermined location associated with said node 6, 7.

[0056] In this case, each TRI, TR2 frame comprises three locations.

[0057] It is assumed that a first location of each TRI frame, TR2 is intended to contain data from the master node 5, a second location of each TRI frame, TR2 is intended to contain data from the first slave control node 6 and a third location of each TRI frame, TR2 is intended to contain data from the second slave control node 7.

[0058] The data of the slave control nodes 6, 7 comprises servo data of said nodes.

[0059] When each TRI, TR2 frame is sent, the writing means 11 of the master node 5 write the data of the master node 5 in the first location of each TRI, TR2 frame.

[0060] When the first slave control node 6 receives the first TRI frame, the reading means 13 of the first slave control node 6 can read the data of the master node 5 stored in the first location of the first TRI frame and the writing means 15 of the first slave control node 6 write the data of the first slave control node 6 in the second location of the first TRI frame.

[0061] When the second location of the first TRI frame is completed, the transmission means 17 of the first slave control node 6 transmit the first TRI frame through the first bus 8.

[0062] When the second slave control node 7 receives the first TRI frame, the reading means 14 of the second slave control node 7 can read the data of the master node 5 and the data of the first slave control node 6 stored in the first and second locations of the first TRI frame and the writing means 16 of the second slave control node 7 write the data of the second slave control node 7 in the third location of the first TRI frame.

[0063] When the third location of the first TRI frame is completed, the transmission means 18 of the second slave control node 7 transmit the first TRI frame through the second bus 9.

[0064] The first TRI frame comprising the three locations storing the data of nodes 5, 6, 7 is received by the master node 5 and read by the reading means 12 from master control node 5.

[0065] When the second slave control node 7 receives the second frame TR2, the reading means 14 of the second slave control node 7 can read the data of the master node 5 stored in the first location of the second frame TR2 and the writing means 15 of the second slave control node 7 write the data of the second slave control node 7 in the third location of the second frame TR2.

[0066] When the third location of the second frame TR2 is completed, the transmission means 18 of the second slave control node 7 transmit the second frame TR2 through the first bus 8.

[0067] When the first slave control node 6 receives the second frame TR2, the reading means 13 of the first slave control node 8 can read the data of the master node 5 and the data of the second slave control node 7 stored in the first and third locations of the second frame TR2 and the writing means 15 of the first slave control node 6 write the data of the first slave control node 6 in the second location of the second frame TR2.

[0068] When the second location of the second frame TR2 is completed, the transmission means 17 of the second slave control node 6 transmit the second frame TR2 through the first bus 8.

[0069] The second frame TR2 comprising the three locations completed by nodes 5, 6, 7 is received by master node 5.

[0070] The two frames TRI, TR2 received by each node 5, 6, 7 make it possible to quickly share all the data from said nodes to each node of the system 1.

[0071] [Fig.2] illustrates an example of implementation of system 1 following detection of a failure of one of the data buses 8, 9.

[0072] It is assumed that the wires of the first bus 6 are cut (represented by a cross) between the first and second slave control nodes 6, 7.

[0073] The first TRI frame completed by the writing means 11 of the master control node 5 and transmitted by the means 10 of said node is received by the first slave control node 6.

[0074] The reading means 13 of the first slave control node 6 can read the data of the master node 5 stored in the first location of the first TRI frame and the writing means 15 of the first slave control node 6 write the data of the first slave control node 6 in the second location of the first TRI frame.

[0075] The transmission means 17 of the first slave control node 6 transmit the first TRI frame completed on the first bus 8.

[0076] As the first bus 8 is cut between the first and second slave control nodes 6, 7, the first completed TRI frame is received by the master control node 5, read by the reading means 12 of the master control node 5 and transmitted by the transmission means 10 of the master control node 5 on the second bus 9.

[0077] The reading means 14 of the second slave control node 7 can read the data of the first slave control node 6 and of the master control node 5.

[0078] The second frame TR2 completed by the writing means 11 of the master control node 5 and transmitted by the means 10 of said node is received by the second slave control node 7.

[0079] The reading means 14 of the second slave control node 7 can read the data of the master node 5 stored in the first location of the second frame TR2 and the writing means 16 of the second slave control node 7 write the data of the second slave control node 7 in the third location of the second frame TR2.

[0080] As the first bus 8 is cut between the first and second slave control nodes 6, 7, the transmission means 18 of the second slave control node 7 transmit the second completed frame TR2 on the second bus 9.

[0081] The second completed frame TR2 is received by the master control node 5, read by the reading means 12 of the master control node 5 and transmitted on the first bus 8.

[0082] The reading means 13 of the first slave control node 6 can read the data of the second slave control node 7 and of the master control node 5.

[0083] The master control node 5, and the first and second slave control nodes 6, 7 receive all of the data transmitted by the BRI control loop despite the failure of the first bus 8, so that all of the master 5 and slave 6, 7 control nodes control the magnetic bearing.

[0084] Despite the failure of the BRI control loop, the magnetic bearings 3, 4 continue to operate.

[0085] The first and second frames TRI, TR2 are transmitted simultaneously or sequentially.

Claims

Claims

1. Method for controlling a magnetic bearing (3, 4) by a control loop (BRI) comprising a first bidirectional data bus (8) connecting in series a master control node (5) and at least two slave control nodes (6, 7), and a second bidirectional data bus (9) connecting said control nodes (5, 7) located at the ends of the control loop, each slave control node (6, 7) controlling a different servo axis of the magnetic bearing, characterized in that the method comprises: • the transmission of a first data frame (TRI) by the master control node (5) through the first data bus (8); and • the transmission of a second data frame (TR2) by the master control node (5) through the second data bus (9), the first and second frames being identical.

2. A method according to claim 1, wherein each data frame comprises as many predetermined locations as there are slave and master control nodes (5, 6, 7), each predetermined location being associated with a slave or master control node such that each slave or master control node knows the address of the predetermined location associated with said node, each frame comprising a succession of bits, the transmission of the first frame (TRI) comprising the successive transmission of the bits of said frame and the transmission of the second frame (TR2) comprising the successive transmission of the bits of said frame.

3. The method of claim 2, further comprising for each slave and master node (5, 6, 7), writing data of said node into the bits associated with the predetermined location of said node in the first and second frames (TRI, TR2).

4. Method according to one of the preceding claims, in which each frame (TRI, TR2) of data comprises servo data of the slave control nodes (6, 7).

5. Method according to one of the preceding claims, wherein the first data bus (8) and the second data bus (9) are synchronous buses.

6. Control system (1) of a magnetic bearing (3, 4) comprising a control loop (BRI) of the magnetic bearing, the control loop comprising a master control node (5) and at least two slave control nodes (6, 7) connected in series by a first bidirectional data bus (8) of said system, and a second bidirectional data bus (9) connecting together the control nodes (6, 7) located at the ends of the control loop, characterized in that the master control node comprises transmission means (10) configured to: • transmit a first data frame (TRI) through the first data bus (8), and • transmit a second data frame (TR2) through the second data bus (9).

7. System according to claim 6, in which each data frame (TRI, TR2) comprises as many predetermined locations as there are slave and master control nodes (5, 6, 7), each predetermined location being associated with a slave or master control node so that each slave or master control node knows the address of the predetermined location associated with said node, each frame comprising a succession of bits, the transmission means being configured to successively transmit the bits of the first frame through the first data bus (8) and to successively transmit the bits of the second frame through the first data bus (8).

8. System according to claim 7, wherein each slave and master control node (5, 6, 7) comprises writing means (11, 15, 16) configured to write data of said node into the bits associated with the predetermined location of said node in the first and second frames (TRI, TR2).

9. System according to one of claims 6 to 8, wherein the master control node (5) comprises a slave control node.

10. System according to one of claims 6 to 9, wherein each slave control node (6, 7) is configured to drive said magnetic bearing (3, 4) independently of other slave control nodes.

Images