CA2381148A1

CA2381148A1 - Demagnetization-protected permanent magnet ship propulsion system

Info

Publication number: CA2381148A1
Application number: CA002381148A
Authority: CA
Inventors: Ingo Schuring; Reinhard Vogel; Wolfgang Rzadki
Original assignee: Individual
Current assignee: Siemens AG
Priority date: 1999-08-03
Filing date: 2000-08-02
Publication date: 2001-02-08
Also published as: WO2001010001A2; CN1372715A; KR20020025210A; NO20020443L; EP1208632A2; JP2003506998A; NO20020443D0; WO2001010001A3

Abstract

Electrical propulsion system for high power levels, for example for power levels above 500 kW, with high availability and long life, in particular for an ocean-going ship, with the propulsion system having a permanent-magnet electric motor, which interacts with at least one rotating power load in particular a ship's propeller, and at least one power converter for supplying power to the electric motor, as well as a control, regulating and monitoring device for the system, wherein the electric motor is designed to operate reliably over a long time period and, in particular, is designed to be protected against total or partial demagnetization, with this being achieved by supplementary design and operating measures, for example circuitry and control measures, with respect to the motor and the power converter.

Description

Description Demagnetization protected permanent-magnet ship propulsion system The invention relates to an electrical propulsion system for high power levels, for example for power levels above 500 kW, with high availability and long life, in particular for an ocean-going ship, with the propulsion system having a permanent-magnet electric motor, which interacts with at least one rotating power load in particular a ship's propeller, and at least one power converter for supplying power to the electric motor, as well as a control, regulating and monitoring device for the system.
Permanent-magnet electric motors have been known in widely differing physical forms for a very long time.
various physical forms for permanent-magnet electric motors are described, for example, in the article in the Siemens Journal 49, 1975, Issue 6, Pages 368 to 374. The power levels which could be achieved at that time were up to 500 kW. For a long time, this was the power limit for permanent-magnet electrical machines, and even larger machines, for example up to 30 MW, have been developed only recently. For machines such as these, which represent a considerable investment, a long life is required with high availability, in order to justify the investment costs. In general, ships have a life of 25 to 30 years, so that the same life is therefore required for their propulsion systems. Until now, it has not been possible to guarantee such a life for large permanent-magnet electric motors. One object of the invention is to specify a system by means of which such a long life is reliably achieved by large permanent-magnet electric motors.

The object is achieved in that the electric motor is designed to operate reliably over a long time period and, in particular, is designed to be protected against total or partial demagnetization, with this being achieved by supplementary design and operating measures, for example circuitry and control measures, with respect to the motor and the power converter. The life of the permanent magnets is the major criterion for the life of a [lacuna] designed in accordance with the design rules for long life. The critical factor governing the life of a propulsion system, which operates with permanent magnets, for ships or for other large electrically operated systems - a ship may also be regarded as an industrial system - is the life of the magnetic components. Demagnetization can occur, for example, due to overheating or due to large internal magnetic fields. Furthermore, the magnets may corrode, and demagnetization due to aging is also possible. It is also possible for the magnet to migrate, or the like, on the rotor of the electric motor, for example if large circumferential accelerations occur in the event of a defect. The propulsion system according to the invention takes account, in a way which is novel to date, of life-reducing factors described above.
Analyses relating to the demagnetization of permanent-magnet electric motors can also be found in the Diploma Thesis by Ville Nahkuri entitled "Large Power Permanent Magnet Propulsion Motors", 24.02.1998, Helsinki University of Technology, Faculty of Electrical and Communications Engineering. The Diploma thesis shows that the temperatures within the electric motor are below the critical values, but that the magnetic field can form a risk for the permanent magnets in the event of malfunctions in the electrical system. The Diploma Thesis does not indicate any solution to this problem which can not be achieved without adversely affecting the other system components.
The refinement of the invention provides that the propulsion system has permanent magnets composed of a magnetically aging-resistant magnetic alloy, for example based on sintered and heat-treated neodymium-iron-boron, which is attached, in particular in an interlocking manner, to the rotor of the electric motor. Appropriate magnetic alloys have been known for some time from small electrical drive systems, for example for actuating drives. Their long-term behavior has been sufficiently investigated in practice and theoretically. The investigations have indicated a life which, when they are used correctly, is considerably greater than the required time of 25 to 30 years. This is dependent on the magnets being in a constant position and orientation, and they must not migrate.
A further refinement of the invention provides for the electric motor to be designed without cooling by means of a coolant with closed-circuit cooling and, especially when used has a steering propeller motor, in a motor pod, to have external wall cooling. This advantageous refinement provides the greatest possible confidence with respect to overheating. If there is no coolant circulation system, it cannot fail, either.
External wall cooling operates satisfactorily in all conditions, in particular for a ship's pod propulsion system. When the ship is in motion, cooling is ensured by the movement of the propulsion system through water.
The cooling effect increases as the vessel speed increases, that is to say with the amount of power consumed in the propulsion system. This automatically results in cooling which reacts as a function of the power.

A further refinement of the invention provides for the magnetic circuit of the propulsion system to be designed such that any short-circuit current at the rating point is automatically limited to non-critical values. The short-circuit current - for example caused by short-circuiting the terminals - results in 1.7 times the rated current, in a typical application. This value is not critical since the magnet system according to the invention is designed, for example, for 2.2 times the current without the magnetic field produced by the overcurrent damaging the permanent magnets.
Since this interacts with current limiting in the power converter, for example to 110 ~ to 120 of the design current, which is configurable, this results in the current flowing through the motor being reliably limited to non-critical values at all points. To achieve this, the invention provides for the power converter to have maximum current limiting, which is configurable, for its individual branches, for example to a value which reliably prevents demagnetization due to overcurrent. Since the individual branches of the power converter, and not just this power converter as a unit, are included in the monitoring, this results in the current flowing in the motor being limited to non-critical values at all points, even in improbable situations.
One particular advantage in this case is the use of current limiters which switch off very quickly, for example in less than one millisecond, on the basis of the physical effect, for example HTS current limiters.
HTS (High Temperature Superconducting) current limiters operate at about 77 K, that is to say cooled by liquid nitrogen. If the critical current density is exceeded, this immediately results in a relatively large finite resistance, that is to say it results in primary 199903518 - 4a.-disconnection. Secondary disconnection, for example by means of a circuit breaker, is then required a short time later.

Appropriate current limiters have already been proposed in the public domain, for example for a size of 1 MVA
by the applicant. The switching element is a YBCO layer on a ceramic plate conductor.
Limiting is possible in specific form for the various power semiconductors used, depending on the configuration of the power converter, that is to say, for example, for GTOs, for IBGTs or for thyristors. The corresponding power semiconductors are advantageously also monitored individually, in order to detect short-circuited semiconductors immediately, in order that they can be replaced. Even the short-circuiting of the power semiconductors that are used, which can never be completely precluded, can thus not damage the magnet system.
In order to monitor the propulsion system, the invention furthermore provides for the system to have measurement devices between the power converter and the electric motor, as well as between the power converter and the transformer, both overall and for individual power branches . Faults in the power converter can thus be identified and rectified quickly. Appropriate, known measurement devices are provided for identification.
Current limiting as a function of the motor rotation speed is of particular importance. This takes account of the fact that the internal magnetic field depends on the motor rotation speed.
As further safety measures, the system has a ground fault indication and protection device, for ships and the like, a cable discontinuity monitoring device, a phase balance monitoring device and further monitoring and protection circuit components, in particular for overcurrents and excess heat. It is thus possible to take account of all conceivable faults in the entire system which could lead to overheating of the motor.
A further refinement of the invention provides for the system according to the invention to have a multiple winding system in the motor with two power converters, which each feed the windings, and for operation with two electric propulsion motors each having a power converter, and with three winding sections of the power converter in each case being interconnected to form a three-phase system. Overall, this results in relatively small sub units, which can each be monitored and switched off individually. Once again, this ensures that no damaging overcurrents can occur in the propulsion motor.
A remote diagnosis device is also provided in this case, which covers, in particular, the ship operating system and the power converter with its components.
Such a remote diagnosis device which operates, for example, for ships with satellite communication allows the manufacturer's specialists to report to the ship engineer which components he should replace, and which components could fail in the near future. This also further improves the safety with regard to demagnetization and operational safety.
In order to ensure the life of the permanent magnets, the invention provides for them to be composed of a magnetically aging-resistant and, in particular, corrosion-resistant magnetic alloy, for example based on sintered and heat-treated neodymium-cobalt-copper-iron-boron, for example the Vac-quality Vacodynm 677HR.
The invention furthermore provides for the permanent magnets to be long-term coated or varnished, and to have a smooth surface. The shape is, for example, cuboid. This thus results not only in the corrosion-resistant base material, but also in a corrosion-protected overall design. In the conditions that occur in the electric motor, there is no loss of material in the permanent magnets, and they do not lose their magnetic force either, over the required life.
The magnet blocks are advantageously fixed on their base by means of adhesive bonding, in particular by means of a fully crosslinked silicone adhesive in the form of a single-component adhesive. The magnet blocks must be fixed on their base for installation. The use of a fully crosslinked silicone adhesive in the form of a single-component adhesive in this case advantageously prevents the possibility of corrosion centers forming at the junction between the magnet and the pole shoe.
In order to monitor the electric motor, the invention provides for the stator windings to have temperature sensors, in particular temperature sensors with measurement evaluation and/or initiation of a warning function. In this case, it is also advantageously possible to provide for the temperature sensors to be connected to the regulating part of the system, in order to reliably prevent overheating of the windings and of the magnets. This results in an additional monitoring capability, which allows, in particular, damaging trends relating to the heating of the electric motor to be counteracted.
The attraction forces of the individual magnet blocks are very high. One advantageous refinement of the motor provides for the diameter and the maximum operating rotation speed of the electric motor to be designed such that, even at the maximum rotation speed, a resi-dual force remains between the magnet cuboid and its contact surface (automatic permanent magnet adhesion).

the magnet blocks are also fixed in an interlocking manner and with a force fit on their base by means of a binding in conjunction with the geometric configuration of the pole shoes, this interlocking and force-fitting adhesion is further assisted by automatic permanent magnet adhesion. The magnet cuboids are positioned reliably without adversely affecting the life, and even if extreme forces occur, for example in the event of a defect. The binding may be composed of either fiber-reinforced plastic or else of a non-magnetic material.
Fiber-reinforced plastic allows the binding to be designed to be particularly thin, however, so that the motor can be designed with a particularly narrow air gap.
The end windings of the stator windings are advantageously designed to be encapsulated, and are connected to the external wall via fixed thermally conductive links. This results in a failure-resistant design, which is undoubtedly far superior to forced circulating cooling, with closed-circuit cooling.
Designing the electric motor with an encapsulated outer housing without any openings also has the same aim.
This ensures that no foreign bodies can enter, or can be introduced, into the electric motor from the outside, for example during repairs or the like.
Therefore, this results in the electric motor requiring no maintenance, being in an encapsulated form, and having a very long life. There is therefore advantageously no need for any accessible shaft between the ship and the pod, as is known for pod propulsion systems using permanent magnets and with closed-circuit cooling. There is thus no need for motor repairs during the routine docking of ships every five years, and all that need be done is to inspect, and if necessary to replace, parts which are subject to wear such as sails and bearings.

Finally, the invention also provides for magnetic field sensors to be arranged in the motor in order to improve reliability, which can be switched on, in particular, periodically or under event control. Furthermore, a computation unit is provided, which determines the electrical and magnetic state of the motor continuously from measurement data, for example from individual currents in the electric motor, from the motor temperature, from the emitted power and from the rotation speed, and possibly from other characterizing influencing variables, and emits a warning when critical magnitudes are approached, preferably also initiating countermeasures. A permanent [lacuna] is advantageously reached, in order, in particular for the remote diagnosis, to provide continuous monitoring of the propulsion motor taking account of the interactions between the individual influencing variables.
The invention will be explained in more detail with reference to drawings, from which further details, which are also significant to the invention, will become evident, in the same way as from the dependent claims.
In detail, in the figures:
Figures l, 2, 3 and 4 show the individual circuits provided for the system Figure 5 shows a typical magnetic flow pattern for the permanent magnets, Figure 6 shows a temperature curve over the length of the rotor, Figure 7 shows the profile of the magnetic force, and Figure 8 shows the magnetic force profile of a neodymium-iron-boron magnet plotted against time The drawings, in conjunction with the teaching in the patent claims, together with the detailed statement contained in them and the description, are self-explanatory to those skilled in the art.
Figures 1 to 4 use the conventional symbols from electrical engineering for transformers, power converters and electric motors. As can be seen, the three-phase machine shown in Figure 1 and having a 6-pulse converter has the minimum number of phases to be monitored and of half-power semiconductors. Individual monitoring of the phase and power semiconductors is thus advantageously chosen in this case.
In Figure 2, which shows the circuit diagram of a three-phase machine with a 12-pulse power converter, the number of power branches in the power converter is doubled, and the monitoring can be simplified here, to the extent that it relates to the power converter. In Figure 3, the monitoring in the electric motor can also be reduced. The circuit of a 6-phase machine shown in Figure 4 with two 12-pulse power converters, results in the optimum configuration with regard to reliability.
The magnetic profiles which are shown in Figure 5 and are illustrated in an idealized form are distinguished in particular by their symmetry. It is thus possible to avoid particular flux concentrations.
Figure 6 shows the stator temperature as a function of the length of the electric motor. The rotor temperature is approximately 10° below the stator temperature, so that there is advantageously no need to monitor the rotor temperature separately. It is evident that the air gap temperature is the highest on the field side of the electric motor, this is where the thermocouples for monitoring are thus advantageously concentrated.

The motor temperature can be monitored easily and reliably by means of densely concentrated thermocouples on the magnet side of the electric motor, with the thermocouples advantageously being firmly connected to the stator winding.
Finally, Figure 7 shows the magnetic force on no load, at the rated load and in the event of a short-circuit.
As can be seen, the magnetic force is in each case within the reversible part of the characteristic profile, even for the short-circuit case. Protection against demagnetization is thus provided, even in the event of a short-circuit.
Finally, Figure 8 uses a logarithmic representation to show the irreversible polarization losses found in detailed investigations for various coefficients B/~,OH
at 130°c. 130°c is considerably greater than the highest temperatures, as shown in Figure 6, in the electric motor according to the invention, that is to say, with regard to over temperature, there is a safety margin against demagnetization, which is so high that it can be assumed that the magnets will have a long-term life even beyond the required 25 to 30 years.
The required life of 25 to 30 years for permanent-magnet propulsion systems for pod motors for ships can be ensured on the basis of the transformer resins that are used, which have been proven over many years, with a long-term temperature resistance of more than 150°
(more than 20 years of operational experience is likewise already available here), relating to the long-term magnetic force of 130° and the maximum temperature that occurs of around 90 ° in the area of the permanent magnets, and since overcurrents are reliably avoided in the windings of the electric motor. The encapsulated configuration with direct external wall cooling, which is fail-safe, makes a not inconsiderable contribution

Claims

claims

1. An electrical propulsion system for high power levels, for example for power levels above 500 kW, with high availability and long life, in particular for an ocean-going ship, with the propulsion system having a permanent-magnet electric motor, which interacts with at least one rotating power load in particular a ship's propeller, and at least one power converter for supplying power to the electric motor, as well as a control, regulating and monitoring device for the system, characterized in that the electric motor is designed to operate reliably over a long time period and, in particular, is designed to be protected against total or partial demagnetization, with this being achieved by supplementary design and operating measures, for example circuitry and control measures, with respect to the motor and the power converter.

2. The propulsion system as claimed in claim 1, characterized in that said propulsion system has permanent magnets composed of a magnetically aging-resistant magnetic alloy, for example based on sintered and heat-treated neodymium-iron-boron, which is attached, in particular in an interlocking manner, to the rotor of the electric motor.

3. The propulsion system as claimed in claim 1 or 2, characterized in that the electric motor is designed to operate without cooling, by means of a coolant with closed-circuit cooling and, in particular, has pod external wall cooling when used as the steering propeller motor.

4. The propulsion system as claimed in claim 1 or 2 or 3, characterized in that the magnetic circuit is designed such that any short-circuit current at the rating point is automatically limited to non-critical values.

5. The propulsion system as claimed in one or more of the preceding claims, characterized in that the current in the windings of the electric motor is limited by the power converter, which is configurable, for example to 110% to 120% of the design current.

6. The propulsion system as claimed in one or more of the preceding claims, characterized in that the power converter has maximum current limiting, which is configurable, for its individual branches, for example limiting to a value which reliably prevents demagnetization due to overcurrent.

7. The propulsion system as claimed in one or more of the preceding claims 1 to 6, characterized in that said propulsion system has current limiters which, by virtue of a physical effect, switch off very quickly, for example in less than 1 millisecond, in particular HTS
current limiters.

8. The propulsion system as claimed in one or more of claims 1 to 6, characterized in that said propulsion system has IGBT power semiconductors with an automatic fast switch-off mechanism in the event of a malfunction.

9. The propulsion system as claimed in one or more of claims 1 to 6, characterized in that said propulsion system has thyristors whose operation is monitored.

10. The propulsion system as claimed in one or more of the preceding claims, characterized in that said propulsion system has measurement devices for the individual phase currents between the power converter and the electric motor.

11. The propulsion system as claimed in one or more of the preceding claims, characterized in that said propulsion system has measurement devices for the phase currents between its power converter transformer and the power converter.

12. The propulsion system as claimed in one or more of the preceding claims, characterized in that said propulsion system has current limits which can be configured as a function of the motor rotation speed and, possibly, of the motor torque.

13. The propulsion system as claimed in one or more of the preceding claims, characterized in that said propulsion system has a circuit breaker, which can also be switched when on load, between its supply network and the power converter transformer.

14. The propulsion system as claimed in one or more of the preceding claims, characterized in that said propulsion system has a ground fault indication and protection device, for ships or the like.

15. The propulsion system as claimed in one or more of the preceding claims, characterized in that said propulsion system has a cable discontinuity monitoring device.

16. The propulsion system as claimed in one or more of the preceding claims, characterized in that said propulsion system has a phase balance monitoring device.

17. The propulsion system as claimed in one or more of claims 5 to 16, characterized in that said propulsion system has further monitoring and protection circuit components, regulation devices and control devices, in particular for overcurrents and excess heat.

18. The propulsion system as claimed in one or more of the preceding claims, characterized in that said propulsion system has a multiple winding system in the motor with two power converters, which each feed the windings, and with three winding sections in each case being interconnected to form a three-phase system.

19. The propulsion system as claimed in one or more of the preceding claims, characterized in that said propulsion system has a remote diagnosis device which, in particular, covers the ship operating system and the power converter with its components.

20. The propulsion system, in particular as claimed in claim 2, characterized in that said propulsion system has permanent magnets composed of a magnetically aging-resistant and especially corrosion-resistant magnetic alloy, for example based on sintered and heat-treated neodymium-cobalt-copper-iron-boron.

21. The propulsion system as claimed in one or more of the preceding claims, characterized in that said propulsion system has, as permanent magnets, long-term coated or varnished magnet blocks, in particular long-term coated or varnished magnet blocks with a cuboid shape.

22. The propulsion system as claimed in claim 21, characterized in that the magnet cuboids are fixed on their base by adhesive bonding, in particular by a fully crosslinked silicone adhesive in the form of a single-component adhesive.

23. The propulsion system as claimed in one or more of the preceding claims, characterized in that the stator windings have temperature sensors, in particular temperature sensors with measurement evaluation and/or initiation of a warning function.

24. The propulsion system as claimed in claim 23, characterized in that the temperature sensors are connected to the control section of the system, in order to prevent overheating of the windings and/or field magnets.

25. The propulsion system as claimed in one or more of the preceding claims, characterized in that the diameter and maximum rotation speed of the electric motor are designed such that, even at the maximum rotation speed, a residual force remains between a magnet cuboid and its contact surface (automatic permanent magnet adhesion).

26. The propulsion system, in particular as claimed in claim 3, characterized in that the stator of the electric motor is shrunk, together with its windings, into its housing and, in its end winding region, has fixed, heat-dissipating links, in particular composed of filled plastic, for example composed of filled epoxy resin, with the end windings themselves being encapsulated using insulation resin.

27. The propulsion system as claimed in one or more of the preceding claims, characterized in that the field magnets are preferably in the form of cuboids, are arranged on pole shoes with a polygonal surface, and are fixed from the outside by means of a binding on the polygonal surfaces.

28. The propulsion system as claimed in claim 7, characterized in that the binding is composed of fiber-reinforced plastic, in particular of a plastic reinforced with glass fibers, carbon fibers, or Kerlar, with the binding preferably having fibers, which are not impregnated in advance, in strip form.

29. The propulsion system as claimed in claim 28, characterized in that the plastic is a Class F
insulation plastic, in particular a filled transformer resin.

30. The propulsion system as claimed in one or more of claims 1 to 27, characterized in that the field magnets have a binding composed of a non-magnetic material, for example of a stainless steel strip.

31. The propulsion system as claimed in one or more of the preceding claims, characterized in that the electric motor has an encapsulated outer housing without any openings.

32. The propulsion system as claimed in one or more of the preceding claims, characterized in that said propulsion system has magnetic field sensors in the electric motor, in particular magnetic field sensors which can be switched on periodically or under event control.

33. The propulsion system as claimed in one or more of the preceding claims, characterized in that said propulsion system has a computation unit which continuously determines the electrical and magnetic state of the motor by calculation, taking account of individual variables, for example of individual currents in the electric motor, the winding temperature, the emitted power and the rotation speed, and possibly other influencing variables, and emits a warning when critical magnitudes are approached, preferably also initiating countermeasures.