AU2010291310B2

AU2010291310B2 - Excitation device for an electric machine comprising a superconducting load

Info

Publication number: AU2010291310B2
Application number: AU2010291310A
Authority: AU
Inventors: Ralf Cordes; Sebastian Nielebock
Original assignee: Siemens Energy Global GmbH and Co KG
Current assignee: Siemens Energy Global GmbH and Co KG
Priority date: 2009-09-07
Filing date: 2010-08-31
Publication date: 2013-10-17
Anticipated expiration: 2030-08-31
Also published as: KR20170005153A; EP2476201A2; DE102009040394A1; WO2011026827A2; AU2010291310A1; WO2011026827A3; KR20120048713A

Abstract

The invention relates to an excitation device for an electric machine having a superconducting load, in which a current control device is provided in the static part of the electric machine. A transmitter comprising a primary winding is provided in the static part of the electric machine and a secondary winding is provided in the rotating part of the electric machine. Said current control device comprises a controllable D.C voltage source. Said D.C voltage of the controllable D.C voltage source is transmitted on the secondary side by means of an inverter, the transmitter and a bridge rectifier, said D.C voltage defining the level of the magnetisation current. Using said magnetisation current level which is predefined by the controllable D.C voltage source, the magnetisation current is controlled by the primary side.

Description

PCT/EP2010/062673 / 2009P15504WOAU 1 Description Excitation device for an electric machine comprising a superconducting load The invention relates to an excitation device for an electric machine having a static part and a rotating part and having a superconducting winding in the rotating part. Superconducting windings are used in electric machines, in particular those having a rotating part, since they produce only very low electrical losses. Expediently at least the part of the rotor, in which the superconducting winding is located, is kept at a very low temperature to allow superconductivity. Electrical energy is transmitted from the stator side, i.e. from the static part, to the superconducting load contactlessly, by way of example, by means of a transmitter. A series of problems occurs in this connection. The magnetization current to the superconducting load must therefore be regulated. The purposeful magnetization and demagnetization of the superconducting load must also be facilitated. Finally, there is the problem of still being able to allow damage-free' demagnetization of the superconducting load when the electronic control devices or other components fail. It is the object of the invention to disclose an excitation device which has a simplified construction specifically on the side of the rotor. The problems mentioned above should in particular also be dealt with in the process. This object is achieved by an excitation device having the features of claim 1. The dependent claims relate to advantageous embodiments and developments of the invention.

PCT/EP2010/062673 / 2009P15504WOAU 2 The inventive excitation device is designed to supply a superconducting load in an electric machine with electrical power. The excitation device comprises a first part and a second part, wherein the second part contains the superconducting load and is arranged so as to be rotatable relative to the first part. The first part is expediently arranged on the stator of the electric machine and the second part in the rotor. The excitation device also comprises a transmitter having a primary winding in the first part and a secondary winding in the second part of the excitation device. The transmitter is used for the transmission of electrical energy from the first part into the second part of the excitation device. The magnetization current for the superconducting load is expediently made available contactlessly. A sensor for determining a signal representing the magnetization current to the load is also provided. A voltage across a measuring shunt, by way of example, can be used for this purpose, the measuring shunt being arranged in series with the superconducting load. The measurement can be made in the rotating part of the electric machine. It may also be made in the static part, however. Finally, the excitation device comprises a current control device which sets the magnetization current to a fixable desired value on the basis of the signal representing the magnetization current. The current control device is provided in the first part of the excitation device, expediently on the stator side in an electric machine therefore. By arranging the current control device in the first part of the excitation device, the complexity of the excitation device is advantageously reduced in the second part. The failsafe performance inter alia of the excitation device is improved in PCT/EP2010/062673 / 2009P15504WOAU 3 the second part at least as a result. If the second part is expediently accommodated in the rotor, this failsafe performance significantly aids simplification and the avoidance of maintenance work. It is particularly advantageous if a controllable direct voltage source is provided in the first part. Since the transmission of the electrical energy to the side of the superconducting load via the transmitter requires an alternating voltage, an inverter is expediently provided in the first part. This is connected at the output side to the primary winding of the transmitter. At the input side the inverter is connected to the controllable direct voltage source. A controllable buck converter, by way of example, having a direct voltage source connected upstream, which then does not have to be controllable, can also be provided in addition to a directly controllable direct voltage source. The voltage is advantageously consequently adjusted at the rotating side of the excitation device by the level of the direct voltage, which is applied to the inverter at the input side. Since the sensor delivers a signal representing the magnetization current it is possible to control of the magnetization current from the first part. If the first part of the excitation device is expediently accommodated in the stator of the electric machine, the current is therefore adjusted by the superconducting load from the stator side. A bridge rectifier is preferably provided in the second part. The bridge rectifier provides for a conversion of the alternating current from the secondary winding of the transmitter into a direct voltage to supply the superconducting load. The advantage of the bridge rectifier is that it functions passively and does not require a separate controller therefore. It therefore also has a simpler PCT/EP2010/062673 / 2009P15504WOAU 4 construction than a controllable rectifier. When using a bridge rectifier the transmission of electrical energy via the transmitter functions unidirectionally, namely always from the first part to the second part. In an advantageous embodiment of the invention a freewheeling path is provided parallel to the superconducting load and comprises a diode in series with a resistor. Purposeful demagnetization of the superconducting load can take place via this freewheeling path. Non-purposeful demagnetization, if, by way of example, the controller for the excitation device fails, can also be facilitated via the freewheeling path. A linearization of the demagnetization can advantageously be achieved in the process if a series connection of at least two diodes is used instead of a single diode. For purposeful control of the magnetization and demagnetization it is advantageous if an electronic switch, by way of example a MOSFET, is provided in series with the superconducting load. In a further advantageous embodiment of the invention control signals for the electronic switch are transmitted from the first part to the second part via a second transmitter. The electronic switch can also be supplied with electrical power via this second transmitter. If the sensor for determining the signal, which represents the magnetization current to the load, is provided in the second part of the excitation device, in an advantageous embodiment of the invention the signal may also be transmitted to the first part via the second transmitter. In this case the second transmitter therefore takes over bidirectional data transmission or signal transmission and energy supply. It is particularly advantageous if the bridge rectifier is designed to carry out demagnetization of the superconducting PCT/EP2010/062673 / 2009P15504WOAU 5 load. For this purpose a series connection of at least two diodes respectively, by way of example, can be used in place of the individual diodes of the bridge rectifier. The design of the bridge rectifier is expediently such that sufficient counter voltage is built up for demagnetization of the superconducting load. In the case of the inventive method for operating an excitation device for an electrical machine having a superconducting load in the rotating part of the electrical machine, a magnetization current to the superconducting load is determined. Based on the magnetization current and a desired value for the magnetization current, the voltage in the intermediate circuit on a secondary side of the excitation device is set in the rotating part of the electric machine by adjusting the direct voltage at a primary side of the excitation device in the static part of the electric machine. An excitation device is advantageously used in which electrical energy is transmitted from the static part into the rotating part by transforming a direct voltage in the static part into an alternative voltage. This is passed via a transmitter to the rotating part and is transformed back into a direct voltage via a bridge rectifier. In the case of the inventive method for operating an excitation device for an electric machine having a superconducting load, an excitation device having a first part and a second part is used, with the superconducting part being arranged in the second part. Electrical energy is transmitted from the first part into the second part by means of a transmitter. To supply the transmitter with power a direct voltage with a fixable level is produced in the first part, the direct PCT/EP2010/062673 / 2009P15504WOAU 6 voltage is converted into an alternating voltage, a magnetization current to the superconducting load is determined and, based on the magnetization current and a desired value for the magnetization current, the voltage is set in the second part by adjusting the level of the direct voltage produced in the first part. In other words, the magnetization current through the superconducting load is not set using, by way of example, a switchover of various current paths in the second part or control of an active rectifier in the second part, but by setting the direct voltage in the first part. A controllable direct voltage power pack or any desired direct voltage source is preferably used in connection with a DC/DC converter such as a buck converter for this purpose. A bridge rectifier is preferably used in the second part of the excitation device and the level of the direct voltage produced in the first part is lowered to reduce the magnetization current to the superconducting load. In other words, in a preferred embodiment of the method the bridge rectifier is used to reduce the magnetization current. As a single measure for bringing about a reduction the direct voltage must then be lowered under a threshold to allow current reduction via the diodes of the bridge converter. Preferred, but in no way limiting, exemplary embodiments of the invention will now be described in more detail with reference to the drawings. The features are shown schematized and corresponding features are marked with identical reference numerals. In detail in the figures: Fig. 1 shows a block diagram of a first variant of the excitation device, PCT/EP2010/062673 / 2009P15504WOAU -7 Fig. 2 shows a block diagram of a second variant of the excitation device in which components of the controller and current measurement are illustrated, Fig. 3 shows a block diagram of a third variant of the excitation device in which demagnetization takes place via a bridge rectifier, Fig. 4 shows a block diagram of a fourth variant of the excitation device in which demagnetization is linearized. Fig. 1 shows a block diagram of a first variant of an excitation device 1 for an electric machine having a superconducting load 5. The electrical components are shown in more detail in Fig. 1 than in the other figures in order to illustrate the electrical function. The excitation device 1 is divided into a primary side 3, which is located on the static part of the electric machine (not shown), and a secondary side 4, which is located in the rotating part of the electric machine. The primary side 3 and the secondary side 4 are inductively connected by a transmitter 2. The transmitter 2 comprises a primary winding on the primary side 3 and a secondary winding on the secondary side 4. On the primary side 3 the excitation device 1 comprises a direct voltage source 6. The direct voltage source 6 is a regulated power pack. A capacitor 7 is provided parallel to the direct voltage source 6. The direct voltage source 6 is also connected to an inverter 8. The inverter 8 comprises four IGBTs 9 which are integrated with the inverter 8 in a known manner. The inverter 8 is for its part connected to the primary winding of the transmitter 2. The secondary winding of the transmitter 2 is connected to a bridge rectifier 10 on the secondary side 4 of the excitation PCT/EP2010/062673 / 2009P15504WOAU 8 device 1. The bridge rectifier 10 comprises four didoes in a bridge arrangement in a known manner. The output connections of the bridge rectifier 10 are connected to an intermediate circuit capacitor 11. This is in turn connected in parallel to a diode 12 which is oriented in the same way as the diodes of the bridge rectifier 10. A series connection comprising the superconducting load 5, an electronic switch 13 and a measuring shunt 17 is located parallel hereto. A freewheeling path 14 is provided parallel to the superconducting load 5 and consists of a series connection comprising a resistor 15 and a diode 16. During operation the direct voltage source 6 provides a direct voltage whose level can be controlled. The inverter 8 converts this direct voltage into an alternating voltage. The alternating voltage is supplied to the transmitter 2 on the primary side 3. An alternating voltage is also produced at the secondary dies 4 as a result. This is converted by the bridge rectifier 10 back into a direct voltage. The level of the secondary side direct voltage, which is applied to the intermediate circuit capacitor 11, depends on the level of the direct voltage which is provided by the direct voltage source 6. The direct voltage at the intermediate circuit capacitor 11 in turn determines the size of or change in the magnetization current. The magnetization current for the superconducting load 5 can therefore be set at the stator side. Only the direct voltage source 6 has to be controlled to this end. It is not necessary to control a component on the secondary side 4 of the excitation device 1. During normal controlled operation, i.e. if the magnetization current is controlled, the electronic switch 13 is switched on, i.e. brought into the conducting state. In this case the current circuit is closed from the superconducting load 5 via PCT/EP2010/062673 / 2009P15504WOAU 9 the bridge rectifier 10 back to the superconducting load 5. If the superconducting load 5 is to be purposefully demagnetized, said current circuit is opened. The electronic switch 13 is opened for this purpose, i.e. brought into the non-conducting state. The current flow from the superconducting load 5 then takes the route via the freewheeling path 14. The resistor 15 provided there reduces the current by way of a conversion into heat. The diode 16 in the freewheeling path 14 is switched such that a current flow through the resistor 15 is prevented if an alternating voltage is transmitted via the transmitter 2. The freewheeling path 14 provides for demagnetization even in the event of failure of the controller of the excitation device 1. The prerequisite here is that the electronic switch 13 is opened or remains open if the controller fails. In this case the same situation as in the purposeful demagnetization of the superconducting load results in the event of failure of the controller. The current through the superconducting load 5 then flows via the freewheeling path 14. It is reduced by the resistor 15 in the process. It is therefore advantageously ensured even in the case of total failure of the controller of the excitation device 1 that the magnetization current can be reduced. Destruction of the electric machine is inherently prevented from outside without intervention (fail-safe). A different operating state results if the electronic switch 13 alloys by way of example. In this case the electronic switch 13 can no longer be brought into the non-conducting state. This operating state is apparent only if the electronic switch 13 should actually be switched off, i.e. if demagnetization is provided or the controller of the excitation device 1 fails. Owing to the resistor 15 provided in the freewheeling path 14 the magnetization current of the PCT/EP2010/062673 / 2009P15504WOAU 10 superconducting load 5 does not flow through the freewheeling path 14 in this case. Instead the current is reduced, at least in the beginning, largely across diode 12 provided parallel to the intermediate circuit capacitor 11. Diode 12 therefore also implements an inherent fuse. In addition diode 12 serves to reduce electrical losses in the secondary part 4 of the excitation device 1. For this purpose the diode 12 takes over the magnetization current in the case of no-load operation of the transmitter 2. The magnetization current is measured at the measuring shunt 17 in order to control the regulated power pack 6. The components required for this, as well as further data and control links, are not shown in Fig. 1. Fig. 2 shows a block diagram of a second variant of the excitation device 20. The second variant of the excitation device 20 is modified slightly compared with the first variant of the excitation device 1. In contrast to Fig. 1, Fig. 2 no longer shows the individual electronic components and instead additionally emphasizes the measuring and control connections. The second variant of the excitation device 20 also comprises a primary side 3 and a secondary side 4. A control computer 23 is provided on the primary side 3. This is connected to an electronic control device 24 in the electric machine, by way of example by Ethernet. The electronic control device 24 is connected by an optical fiber to the IGBT inverter 8. The construction of the primary side 3 from the first variant of the excitation device 1 is analogously also present in the second variant of the excitation device 20. A transmission ratio of 5:1 is provided in the case of the transmitter 2. The second variant of the excitation device 20 also comprises a second transmitter 19. This is connected at the primary side 3 to a MOSFET inverter 21. The MOSFET inverter 21 is connected PCT/EP2010/062673 / 2009P15504WOAU 11 at the input side to an alternating voltage power pack. The MOSFET inverter 21 is also connected by optical fibers to the electronic control device 24. The second transmitter 19 has a transmission ratio of 12:1. The electronic control device 24 is finally also connected to a Bluetooth transceiver 25. On the secondary side 4 the excitation device 20 comprises a passive bridge rectifier 10 in connection with transmitter 2. An intermediate circuit capacitor 11, in this case with a capacitance of 500 pF, is situated parallel thereto. The remaining contrition matches that of the secondary side 4 of the first variant of the excitation device 1. An exception is the diode 12 which is not provided in the second variant of the excitation device 20. The resistor 15 of the freewheeling path 14 is selected at 0.98 Ohm in this case. The measuring shunt 17 has a resistance of 100 pOhm. The second variant of the excitation device 20 comprises even more components on the secondary side 4. A passive rectifier 30 is therefore provided on the secondary side of the second transmitter 19 in connection with a buck converter 31. This is in turn connected to a measurement data acquisition 29. A Schmitt trigger control 27 and a Bluetooth transceiver 28 are also provided in connection with the secondary side of the second transmitter 19. The measurement data acquisition 29 is connected to the Bluetooth transceiver 28, the measuring shunt 17, the superconducting load 5 and the intermediate circuit capacitor 11. Fig. 3 shows a third embodiment of the excitation device. Fig. 3 does not show data or signal transmission paths between the primary side 3 and the secondary side 4. The third variant of the excitation device is unchanged on the primary side with respect to the first variant of the excitation device 1. Changes with respect to the first variant of the excitation PCT/EP2010/062673 / 2009P15504WOAU 12 device 1 emerge on the secondary side 4. In this case the superconducting load 5 and the measuring shunt 17 connected in series therewith are present on the secondary side 4. The intermediate circuit capacitor 11 is again parallel thereto. The bridge rectifier 10 is constructed from a series of individual diodes 40 in this case, however. Each of the four diodes of the bridge rectifier 10 constructed in a normal bridge circuit is replaced by a series connection of a plurality of diodes 40. The superconducting load 5 is demagnetized in this case via the diodes 40 of the bridge rectifier 10. The series connection of a sufficient number of diodes 40 means that these build up a sufficient counter voltage to de-energize the superconducting load 5 and consequently reduce the magnetization current. The construction of the secondary side 4 of the excitation device is significantly simplified again thereby since the freewheeling path 14 with its resistor 15 and the diode 16 as well as the electronic switch 13 are omitted. A controller for the electronic switch 13 can also be omitted therefore. One drawback in this connection is the power loss that permanently occurs. The use of the third variant is therefore expedient primarily with low de energizing voltages. In a further variant, not shown in the figures, it is possible to simplify the construction even further. For this purpose the measuring shunt 17 is also omitted. The magnetization current is measured indirectly in this case in that it is measured on the primary side 3. It can be seen that an extremely simple and consequently fail-safe construction variant is therefore advantageously provided. Advantageously, no controller of a switch is required on the secondary side in this construction variant. Current measurement on the PCT/EP2010/062673 / 2009P15504WOAU 13 secondary side is not required either and instead all measuring and control operations are performed on the primary side. Fig. 4 shows a fourth variant of the excitation device. The primary side 3 is unchanged with respect to the third variant. The secondary side 4 is largely constructed like the secondary side 4 in the first variant of the excitation device 1. A bridge rectifier 10, an intermediate circuit capacitor 11, a measuring shunt 17, an electronic switch 13 and the parallel circuit comprising the superconducting load 5 and the freewheeling path 14 with resistor 15 are therefore present. If demagnetization of the superconducting load 5 occurs via the freewheeling path 14, the current flowing through the freewheeling path 14 takes an exponential course. In the excitation device according to the fourth variant demagnetization is linearized. For this purpose the individual diode 16 is replaced in the freewheeling path 14 by a series connection of diodes 16. The resistance of the resistor 15 must be adjusted in this connection.

Claims

1. An excitation device for supplying a superconducting load in an electric machine, comprising: - a first part; - a second part comprising the superconducting load, and the second part arranged so as to be rotatable relative to the first part; - a transmitter having a primary winding in the first part and a secondary winding in the second part; - a sensor for determining a signal representing a magnetization current to the superconducting load; and - a current control device comprising a controllable direct voltage source in the first part which adjusts the magnetization current to a fixable desired value on the basis of the signal.

2. The excitation device as claimed in claim 1, wherein the second part further comprises a bridge rectifier having four diodes.

3. The excitation device as claimed in any one of the preceding claims, further comprising a demagnetization resistor in series with a diode parallel to the superconducting load.

4. The excitation device as claimed in claim 3, wherein the demagnetization resistor is arranged in series with a series connection of at least two diodes.

5. The excitation device as claimed in any one of the preceding claims, further comprising an electronic switch in series with the superconducting load in order to switch between magnetization and demagnetization. 15

6. The excitation device as claimed in claim 2, wherein the bridge rectifier is designed to carry out demagnetization of the superconducting load.

7. The excitation device as claimed in claim 6, wherein in place of each of the four diodes the bridge rectifier comprises one series connection of at least two diodes respectively to establish an adequate counter-voltage to the demagnetization of the superconducting load.

8. The excitation device as claimed in any one of the preceding claims, further comprising a second transmitter, designed for supplying the sensor with electrical power and/or for transmitting a control signal to the electronic switch and/or for transmitting the signal.

9. A method for operating an excitation device for an electric machine having a superconducting load, the excitation device comprising a first part and a second part, and the superconducting load arranged in the second part, the method comprising: - transmitting electrical energy corresponding to an alternating voltage by means of a transmitter from the first part into the second part, the transmitting step further comprising: producing a direct voltage with a fixable level in the first part to supply the transmitter with power, converting the direct voltage into an alternating voltage, determining a magnetization current to the superconducting load, and based on the determined magnetization current and a desired value for the magnetization current, setting the 16 voltage in the second part by adjusting the level of the direct voltage produced in the first part.

10. The method as claimed in claim 9, wherein a bridge rectifier is used in the second part of the excitation device and the level of the direct voltage produced in the first part is lowered to reduce the magnetization current to the superconducting load. SIEMENS AKTIENGESELLSCHAFT Patent Attorneys for the Applicant SPRUSON & FERGUSON