EP4639750A1 - Prevention of magnet demagnetization in a rotor - Google Patents

Prevention of magnet demagnetization in a rotor

Info

Publication number
EP4639750A1
EP4639750A1 EP24733162.2A EP24733162A EP4639750A1 EP 4639750 A1 EP4639750 A1 EP 4639750A1 EP 24733162 A EP24733162 A EP 24733162A EP 4639750 A1 EP4639750 A1 EP 4639750A1
Authority
EP
European Patent Office
Prior art keywords
generator
phase
current
phase angle
magnet
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
EP24733162.2A
Other languages
German (de)
French (fr)
Inventor
Ziad Azar
Nima Madani
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Siemens Gamesa Renewable Energy AS
Original Assignee
Siemens Gamesa Renewable Energy AS
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Siemens Gamesa Renewable Energy AS filed Critical Siemens Gamesa Renewable Energy AS
Publication of EP4639750A1 publication Critical patent/EP4639750A1/en
Pending legal-status Critical Current

Links

Classifications

    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
    • H02P9/00—Arrangements for controlling electric generators for the purpose of obtaining a desired output
    • H02P9/006—Means for protecting the generator by using control
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
    • H02P29/00—Arrangements for regulating or controlling electric motors, appropriate for both AC and DC motors
    • H02P29/60—Controlling or determining the temperature of the motor or of the drive
    • H02P29/66—Controlling or determining the temperature of the rotor
    • H02P29/662—Controlling or determining the temperature of the rotor the rotor having permanent magnets
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
    • H02P9/00—Arrangements for controlling electric generators for the purpose of obtaining a desired output
    • H02P9/10—Control effected upon generator excitation circuit to reduce harmful effects of overloads or transients, e.g. sudden application of load, sudden removal of load, sudden change of load
    • H02P9/12—Control effected upon generator excitation circuit to reduce harmful effects of overloads or transients, e.g. sudden application of load, sudden removal of load, sudden change of load for demagnetising; for reducing effects of remanence; for preventing pole reversal
    • H02P9/123—Control effected upon generator excitation circuit to reduce harmful effects of overloads or transients, e.g. sudden application of load, sudden removal of load, sudden change of load for demagnetising; for reducing effects of remanence; for preventing pole reversal for demagnetising; for reducing effects of remanence
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
    • H02P2207/00—Indexing scheme relating to controlling arrangements characterised by the type of motor
    • H02P2207/05—Synchronous machines, e.g. with permanent magnets or DC excitation
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/70—Wind energy
    • Y02E10/72—Wind turbines with rotation axis in wind direction

Definitions

  • the present invention relates to a method and to a corresponding controller of controlling an electrical generator system in particular for prevention and or minimisation of magnet demagnetization . Furthermore , the present invention relates to an electrical generator system comprising the controller and further relate s to a wind turbine comprising the electrical generator system .
  • An electrical generator may comprise plural permanent magnets mounted to a rotor house which is rotatably supported relative to a stator .
  • the permanent magnet may be at ris k to get irreversibly fully or partially demagnetized .
  • a short-circuit in one of the stator windings may occur or may be expected to occur at lea st once during the turbine lifetime or the generator lifetime . Therefore , the permanent magnets are conventionally designed to withstand such fault as worst operations , i . e . , highest allowed magnet temperature .
  • Thi s may conventionally be mitigated in the design by requiring a larger amount of magnet material leading to higher costs , higher weight and/or power derating at a lower ambient temperature meaning los s of energy production .
  • the generator may be stopped and in particular a wind turbine needs to be stopped and the generator need to be equipped with newly non-demagnetized permanent magnets . This come s at additional costs , i . e . crane , new magnets , los s of supply to the customer .
  • a method of controlling an electrical, in particular synchronous, generator system comprising a generator including a stator having at least one set (or multiple sets, e.g. 2, 3, 4, 5, 6, or a larger number of sets) of stator windings and a rotor having plural permanent magnets, in particular of a wind turbine, the method comprising: monitoring when a magnet temperature indicates a critical condition; in case of the critical condition, entering a magnet preventive protection control mode including to shift of the phase angle of the generator current of at least one phase (or all phases) of the at least one winding set.
  • the method may for example be implemented in software and/or hardware and/or may be performed by a portion of a controller, in particular a wind turbine controller.
  • the stator may be configured as a segmented stator comprising plural stator segments or may be provided as a non-segmented stator covering the entire circumference.
  • the stator windings may be provided in a concentrated winding topology or distributed wind- ing topology. If the generator system comprises plural winding sets, to each of the winding sets, embodiments of the present invention may be employed or performed, including to shift the phase of the generator current of any of the winding sets.
  • the magnet temperature may relate to a measured or estimated or derived temperature of one or more of the permanent magnets .
  • the magnet temperature may be measured by one or more temperature sensors installed at the rotor for example for measuring the magnet temperature of one or more of the permanent magnets.
  • the critical condition may be indicated. Thereby, all permanent magnets may be protected from demagnetization.
  • the generator currents may have (previous to the occurrence of the critical condition) a particular electrical phase relative to a reference, in particular the voltage (of the same phase, e.g. A-phase) of the considered winding set.
  • the method may then include to shift the phase angle or angles of the generator current/s (in particular for each of the plural phases, for example three phases) to be different from the condition before the critical condition has been indicated.
  • the phase-shift e.g. for each electrical phase of the winding set
  • phase angle of the generator current When the phase angle of the generator current is shifted, in particular prior to a fault condition, a current peak value occurring later due to a fault, such as a short-circuit, may be reduced so that demagnetization of the permanent magnets may be avoided.
  • the critical condition may be indicated in ca se that a magnet temperature satisf ies one or more criteria , a s will be explained below .
  • the magnet preventive protection control mode may be considered as a particular control mode of the generator system which is aimed at protecting the permanent magnets from demagnetization .
  • the magnet preventive protection control mode may be characterized for example still by a reference active power and/or reference reactive power , reference voltage , reference and/or winding temperature and/or reference ambient temperature .
  • a reference active power and/or reactive power may or may not be met , e . g . in favour of more ef ficiently or effectively protecting the permanent magnets .
  • the shift of the phase of the generator may in particular performed prior to the occurrence of a short-circuit in one of the stator windings or in the single stator winding set , depending on the construction of the stator .
  • embodiment s of the present invention provide methods and controllers to prevent a permanent generator ( turbine ) performance los s , i . e . , permanently lower power output , due to magnet irreversible demagnetization which is for example caused by short-circuit faults which might occur once the magnet temperature reaches a certain level .
  • a s the generator system may be designed for optimal performance per magnet volume with no need for extra material to prevent irreversible demagneti zation .
  • embodiments of the present invention may allow to delay the power de-rating which might have been applied in conventional methods .
  • the magnet preventive protection control mode includes , in particu- lar for each set of stator winding present, controlling the electrical generator system in order to shift the phase (angle) of the generator current (e.g. for each phase, e.g. A- phase, B-phase, C-phase) relative to a phase (angle) of a generator voltage or a q-axis or a d-axis .
  • the phase (angle) of the generator voltage (for a considered electrical phase and a considered winding set) may be given or determined by the position of the rotating rotor relative to the stator due to the fact that the permanent magnets induce voltages in the stator windings.
  • a dq-synchronously rotating coordinate frame rotates synchronously with the rotor.
  • the zero crossing, where the stator winding voltage increases, may correspond to the location of the q-axis.
  • the maximum voltage at the electrical angle of 90° may correspond to the position of the d-axis of the dq-coordinate system.
  • the phase (angle) of the generator current may be shifted relative to the voltage phase (angle) which may also be expressed as to be shifted relative to the q-axis.
  • the phase (angle) of the generator current may be more negative than the phase (angle) of the generator voltage, for example by an amount of 5° to 40° less than the voltage phase (angle) .
  • a controller for controlling the electrical generator system, a controller according to an embodiment of the present invention may be employed.
  • the stator winding voltage may for example form a substantially a sinusoidal curve having the crossing zero at the electrical angle zero and having the maximum at the electrical angle of 90°.
  • the generator current is then shifted according to the control method such that a graph of the current is right shifted relative to the stator voltage by an amount of for example between 10° and 30°.
  • the right shift of the generator current corresponds to a negative relative phase (angle) between the current and voltage or corresponds to the condition, where the generator current has a more negative electrical phase (angle) than the generator voltage.
  • the relative angle may be changed such that the current electrical angle is smaller than the current electrical angle before entering the magnet preventive protection control mode and such that in particular the current electrical angle i s smaller than the voltage electrical angle .
  • the above-des cribed embodiments regarding the shifting of the phase of the generator current may allow high f lexibility and adaptation of the method according to the requirement s .
  • the magnet temperature relate s to or compri ses at least one of : a temperature of at least one of the permanent magnets , in particular a mea sured temperature ; a mean temperature of the plural permanent magnets ; a maximum temperature of the plural permanent magnets , or a derived magnet temperature based on measured flux linkage or phase voltage or rated power and current .
  • triggering the magnet preventive protection control mode based on the magnet temperature may allow to shift the generator current phase ( angle ) prior to the actual occurrence of the short-circuit .
  • the converter may comprise a generator side converter portion , a DC link and a utility grid converter portion .
  • the generator side converter portion may be controlled .
  • Each of the generator converter portions may comprise plural controllable switches , such a s high-power transi stors , which may be supplied with respective gate control signals for defining desired electrical output quantities .
  • One quantity which might be controllable by the ( generator s ide ) converter portion may be the relative electrical phase angle of the generator current relative to the generator voltage .
  • the generator current i s to be understood as the current flowing in the one or more winding sets of the generator .
  • the relative electrical angle of the generator current relative to the generator voltage may relate to the relative electrical angle of one of the phase s of the multiple phases of the generator currents flowing in the set of stator windings . For each phase of the windings the shift of the generator current phase angle may be applied .
  • the controlling the electrical generator system is further performed in order to change an amplitude of the generator current , in particular in dependence of the magnet temperature and/or an amount of the shift of the generator current phase angle and/or a power demand or reference value .
  • the amplitude of the generator cur- rent / s may be controlled or changed when the magnet preventive protection control mode is entered .
  • the phase ( angle ) of the generator current relative to the generator voltage is set , such that the current phase ( angle ) is more negative than the voltage phase ( angle )
  • the amplitude of the current may either be increased or decreased, for example to substantially maintain an active power output .
  • the amplitude of the current may be controlled according to the particular application .
  • controlling the electrical generator system is performed in order to change the ( relative ) phase ( angle ) and the amplitude of the generator current in combination, such that a power output of the generator system complies with a power reference or is substantially unchanged.
  • power output performance may be maintained while at the same time, demagnetization of the permanent magnets may be prohibited or avoided.
  • the phase angle is shifted before the occurrence of a fault or fault condition of the generator system.
  • a fault of the generator system may have the consequence that shortly after the fault, such as being 10 ms and 50 ms later, relatively high current peak is expected or observed in the stator windings. This relatively high current peak would conventionally demagnetize permanently the permanent magnets. Wherein, however, the phase angle is shifted before the occurrence of the fault, the amplitude of the high current peak may be reduced, potentially prohibiting demagnetization of the magnets.
  • the fault or fault condition is present if at least one of the following occurs or holds: a short circuit related to the stator, in particular in at least one stator winding; a fault in at least one portion of the converter; a fault in a breaker; a fault in a DC-link between converter portions.
  • a peak current occurs after the fault and after shifting the (relative) phase angle and before a breaker opens, wherein a peak current amplitude is below a current threshold above which demagnetization of at least one permanent magnet would be caused .
  • the peak current may for example occur between 10 ms and 40 ms after the occurrence of the fault, in particular short- circuit.
  • the phase (angle) of the generator current may, how- ever , have been shifted before the occurrence of the fault .
  • the occurrence of the short-circuit current peak value may be too early quick for a circuit breaker to open .
  • embodiment s of the present invention may enable to achieve that the peak current amplitude stays below the current threshold above which demagnetization of a permanent magnet would be caused .
  • the critical condition is detected if at least one of the following criterium is satis fied : the magnet temperature is above a first threshold, in particular for at lea st a first threshold time period; the magnet temperature is below a second threshold, in particular for les s than a second threshold time period , wherein a temperature above the second threshold would cause demagnetization of the magnet ; a rate of increase of the magnet temperature is above a threshold rate , in particular for at least a third threshold time period; a combination of the above criteria .
  • a controller for controlling an electrical , in particular synchronous , generator system comprising a generator including a stator having stator windings and a rotor having plural permanent magnets , in particular of a wind turbine , the arrangement compri sing : an input port adapted to receive an indication signal when a magnet temperature indicates a critical condition ; the controller being adapted, to , in ca se of the critical condition , enter a magnet preventive protection control mode including to shift a phase of a generator current , in particular adapted to carry out or control a method according to any one of the preceding claims .
  • the controller may be implemented in software and/or hardware .
  • the controller may be a portion of a generator controller or a wind turbine controller .
  • the controller may further comprise one or more temperature measurement sensors which are installed to measure the temperature of one or more of the permanent magnets .
  • the controller may compri se arithmetic/ logical circuitry, in particular a ( semiconductor ) proce s sor .
  • the controller i s adapted to generate and output a control signal caus ing the generator system to shift the pha se angle of the generator current relative to a generator voltage .
  • the control s ignal may for example be configured a s a converter control signal supplying one or more reference value s to a converter or a converter controller .
  • the control system or a control signal generated by the converter controller may include gate driver signal s for the one or more controllable switches comprised in the converter , in particular in the generator side converter portion .
  • an electrical , in particular synchronous , generator system comprising : a generator including a stator having stator windings and a rotor having plural permanent magnets ; in particular a converter electrically connected to the stator windings of the generator ; and a controller according to one of the two preceding claims connected to control the system, in particular the converter .
  • a wind turbine including : an electrical generator system according to the preceding claim; a hub at which plural rotor blades are connected and which is mechanically coupled to the rotor of the generator .
  • FIG. 1 schematically illustrate s a wind turbine according to an embodiment of the present invention compri sing an electrical generator system according to an embodiment of the present invention which includes a controller according to an embodiment of the present invention ;
  • Fig . 2 illustrates curves of a generator current and generator voltage a s set according to embodiments of the pre sent invention
  • Fig . 3 illustrates curves repre senting short-circuit current peak values for different relative electrical phase angles between current and voltage ;
  • Fig . 4 illustrates curves of phase currents having dif ferent electrical phase angle s as applied according to embodiments of the present invention ;
  • Fig . 5 illustrates curves of a generator current having dif ferent phase angle s and al so different amplitudes as applied according to embodiments of the present invention .
  • the wind turbine 1 schematically illustrated in Fig . 1 comprises a wind turbine tower 2 on top of which a nacelle 3 i s mounted .
  • the nacelle 3 harbours an electrical generator sys tem 4 according to an embodiment of the present invention .
  • the generator system 4 is mechanically coupled to a hub 5 at which plural rotor blades 6 are mounted .
  • the electrical generator system 4 comprises a generator 7 including a stator 8 having stator windings and a rotor 9 having plural permanent magnets 10 .
  • the generator system 4 further comprise s a converter 11 which is electrically connected to the stator windings of the generator 7 .
  • the generator system 4 compri ses a controller 12 for controlling the electrical generator system 4 which is connected to control the system .
  • the converter 11 comprises a generator side converter portion 13 , a DC link 14 and a utility grid converter portion 15 which is via one or more optional transformers connected or connectable to a utility grid 16 to provide in particular three-pha se electrical power to the utility grid 16 .
  • the controller 12 comprise s an input port 13 adapted to receive an indication signal (e . g . temperature signal ) 14 when a magnet temperature indicates a critical condition .
  • the indication signal 14 may for example be or comprise a tempera- ture measurement signal of a temperature sensor 17 which is mounted at the rotor 9 to measure the temperature of one or more of the permanent magnets 10.
  • the indication signals 14 may be a binary signal which may for example be derived by logic/arithmetic unit defining whether the critical condition is present, in particular based on the temperature of one or more of the magnets 10.
  • the controller 12 is adapted to, in case of the critical condition, enter a magnet preventive protection control mode, including to shift a phase (angle) of a generator current.
  • the controller is configured to generate and output a control signal 18 to the generator side portion 13 of the converter 11 which controls the generator 7 such that the phase (angle) of the generator current is shifted relative to a generator voltage phase (angle) .
  • the controller 4 in particular together with the temperature sensor 17 is adapted or configured to carry out a method of controlling the electrical machine of the electrical generator system 4.
  • a magnet temperature is monitored (for example via the temperature sensor 17) and it is checked whether the temperature indicates a critical condition.
  • a magnet preventive protection control mode is entered including to shift the phase of the generator current.
  • Fig. 2 illustrates a curve in a coordinate system having as an abscissa the electrical rotor position and having as an ordinate a magnitude of electrical quantities.
  • the curve 20 represents the generator voltage and the curve 21 represents a generator current (of one phase, for example the A-phase) , when a magnet preventive protection control mode has been entered.
  • the prevention protection control mode includes to shift the phase (angle) of the generator current 21 relative to a phase (angle) of the generator voltage 20.
  • the phase shift is labelled with refer- ence sign cp.
  • the current 21 is advanced relative to the generator voltage 20.
  • the voltage U(t) and the current I (t) may be given according to the following equations :
  • I (t) 10 * sin(w*t - cp) , where w is the electrical rotational speed.
  • phase of the generator current I (t) is smaller than the phase of the generator voltage U (t) .
  • the value of -cp may change between -10 and -30°, for example, or may have even different values.
  • the generator system 4 comprises the converter 11 and controlling the electrical generator system 4 includes to control the converter 11, in particular the generator side portion 13 by supplying the control signal 18 indicative of a (relative) electrical phase angle of the generator current.
  • the control signal 18 may either directly indicate the phase-shift angle or may for example indicate a reference of active power and/or voltage.
  • Fig. 3 illustrates curves in a coordinate system having as an abscissa the time and having as an ordinate the phase current.
  • a magnet preventive protection control mode has already been entered including to shift the generator current relative to the generator voltage.
  • the curves 22a, ..., f indicate the short-circuit current peak values, when the generator current is -10 electrical degrees, -15, -20, -25, -30, or -35 electrical degrees relative to the generator voltage. It can be appreciated that the larger the negative phase-shift of the generator current, the lower the short-circuit current peak value. Thereby, demagnetization of permanent magnets after a fault which happened at a point in time tl may be avoided.
  • a short-circuit may have occurred in one or more phases of the one or more stator windings .
  • Figs. 4 and 5 illustrate embodiments how to shift a phase (angle) of a generator current and/or change an amplitude of a generator current in a magnet preventive protection control mode according to embodiments of the present invention.
  • the abscissas in Figs. 4 and 5 indicate the electrical rotor position and the ordinates represent the phase currents.
  • the curves 20 in Figs. 4 and 5 again illustrate the generator voltage.
  • the curves 23, 24, 25 indicate the phase currents when the phase-shift is -10°, -20° or -30° relative to the generator voltage 20 and has the same amplitude, for example as prior to the indication of the critical condition.
  • the curves 26, 27, 28 in Fig. 5 illustrate the generator currents where the phase-shift is -10, -20 or -30 electrical angles and further having different amplitudes (than before the indication of the occurrence of the critical condition) .
  • Embodiments of the present invention provide a magnet preventive protection control mode, wherein the generator phase current angle is advanced by the generator converter, via setting a control mode that is activated when the magnet temperature reaches a certain level. Therefore, in case of a fault occurrence (see for example time point tl in Fig. 3) , the permanent magnets (for example 10 in Fig. 1) (and the generator) may be protected, since the fault currents will be lower as has been illustrated in Fig. 3 compared to the condition, where the phase current value is not advanced.
  • the current angle advancing level (i.e. , the shift of the generator current relative to the generator voltage) may be for example a function of a magnet temperature.
  • Sensors for example temperature sensors 17 in Fig. 1
  • the proposed technique may be cost-free and no additional hardware may be required .
  • Fig. 3 it is confirmed by calculation and measurements that the value of the short-circuit current peak during the fault is determined by the phase current angle prior to the fault. The more advanced the phase current angle is, the less the value of the short-circuit current peak is, as can be seen in Fig. 3.
  • the table illustrates the variation of the permanent performance loss due to short-circuit faults as a function of the phase current angle set prior to the fault.
  • the Fig. 4 demonstrates an example of phase current waveforms for different current angles, i.e. , at a fixed current amplitude. It is also possible, that the current amplitude can be varied, as needed by the power demand, when the current angle is advanced, as is illustrated in the Fig. 5.

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Control Of Eletrric Generators (AREA)

Abstract

It is described a method of controlling an electrical, in particular synchronous, generator system (4) comprising a generator (7) including a stator (8) having stator windings and a rotor (9) having plural permanent magnets (10), in particular of a wind turbine, the method comprising: monitoring when a magnet temperature indicates a critical condition; in case of the critical condition, entering a magnet preventive protection control mode including to shift a phase of a generator current/s (21).

Description

DESCRIPTION
Prevention of magnet demagnetization in a rotor
Field of invention
The present invention relates to a method and to a corresponding controller of controlling an electrical generator system in particular for prevention and or minimisation of magnet demagnetization . Furthermore , the present invention relates to an electrical generator system comprising the controller and further relate s to a wind turbine comprising the electrical generator system .
Art Background
An electrical generator may comprise plural permanent magnets mounted to a rotor house which is rotatably supported relative to a stator . In case of unwanted or unde sired high temperature or high stator current s , the permanent magnet may be at ris k to get irreversibly fully or partially demagnetized . A short-circuit in one of the stator windings may occur or may be expected to occur at lea st once during the turbine lifetime or the generator lifetime . Therefore , the permanent magnets are conventionally designed to withstand such fault as worst operations , i . e . , highest allowed magnet temperature . Thi s may conventionally be mitigated in the design by requiring a larger amount of magnet material leading to higher costs , higher weight and/or power derating at a lower ambient temperature meaning los s of energy production . In case of full or partial irreversible demagneti zation faults of the permanent magnets , the generator may be stopped and in particular a wind turbine needs to be stopped and the generator need to be equipped with newly non-demagnetized permanent magnets . This come s at additional costs , i . e . crane , new magnets , los s of supply to the customer . Thus, there may be a need for a method and a corresponding controller of controlling an electrical generator system comprising permanent magnets wherein the risk of demagnetization of the magnets or the risk of generally damage of the permanent magnets is reduced. Further, there may be a need for an electrical generator system capable of in particular prevention of demagnetization or reduction of the risk of demagnetization of the permanent magnets and there may be further a need for a wind turbine comprising the generator system.
Summary of the Invention
This need may be met by the subject matter according to the independent claims . Advantageous embodiments of the present invention are described by the dependent claims.
According to an embodiment of the present invention it is provided a method of controlling an electrical, in particular synchronous, generator system comprising a generator including a stator having at least one set (or multiple sets, e.g. 2, 3, 4, 5, 6, or a larger number of sets) of stator windings and a rotor having plural permanent magnets, in particular of a wind turbine, the method comprising: monitoring when a magnet temperature indicates a critical condition; in case of the critical condition, entering a magnet preventive protection control mode including to shift of the phase angle of the generator current of at least one phase (or all phases) of the at least one winding set.
The method may for example be implemented in software and/or hardware and/or may be performed by a portion of a controller, in particular a wind turbine controller. The stator may be configured as a segmented stator comprising plural stator segments or may be provided as a non-segmented stator covering the entire circumference. The stator windings may be provided in a concentrated winding topology or distributed wind- ing topology. If the generator system comprises plural winding sets, to each of the winding sets, embodiments of the present invention may be employed or performed, including to shift the phase of the generator current of any of the winding sets.
The magnet temperature may relate to a measured or estimated or derived temperature of one or more of the permanent magnets . The magnet temperature may be measured by one or more temperature sensors installed at the rotor for example for measuring the magnet temperature of one or more of the permanent magnets. In particular, if at least one of the measured or derived temperatures relating to one or more of the magnets indicates a dangerous or critical condition, for example when the temperature reaches a threshold, then the critical condition may be indicated. Thereby, all permanent magnets may be protected from demagnetization.
The generator currents (e.g. A-phase, of a particular one of a considered winding set) may have (previous to the occurrence of the critical condition) a particular electrical phase relative to a reference, in particular the voltage (of the same phase, e.g. A-phase) of the considered winding set. The method may then include to shift the phase angle or angles of the generator current/s (in particular for each of the plural phases, for example three phases) to be different from the condition before the critical condition has been indicated. The phase-shift (e.g. for each electrical phase of the winding set) may be for example between ±5 electrical degrees to ±40 electrical degrees (e.g. relative to the respective voltage for each respective electrical phase of the winding set) .
When the phase angle of the generator current is shifted, in particular prior to a fault condition, a current peak value occurring later due to a fault, such as a short-circuit, may be reduced so that demagnetization of the permanent magnets may be avoided. The critical condition may be indicated in ca se that a magnet temperature satisf ies one or more criteria , a s will be explained below .
The magnet preventive protection control mode may be considered as a particular control mode of the generator system which is aimed at protecting the permanent magnets from demagnetization . The magnet preventive protection control mode may be characterized for example still by a reference active power and/or reference reactive power , reference voltage , reference and/or winding temperature and/or reference ambient temperature . According to embodiments of the present invention , a reference active power and/or reactive power may or may not be met , e . g . in favour of more ef ficiently or effectively protecting the permanent magnets .
The shift of the phase of the generator may in particular performed prior to the occurrence of a short-circuit in one of the stator windings or in the single stator winding set , depending on the construction of the stator . Thereby, embodiment s of the present invention provide methods and controllers to prevent a permanent generator ( turbine ) performance los s , i . e . , permanently lower power output , due to magnet irreversible demagnetization which is for example caused by short-circuit faults which might occur once the magnet temperature reaches a certain level .
According to embodiments of the present invention , better magnet material utilization may be enabled, a s the generator system may be designed for optimal performance per magnet volume with no need for extra material to prevent irreversible demagneti zation . Furthermore , embodiments of the present invention may allow to delay the power de-rating which might have been applied in conventional methods .
According to an embodiment of the present invention , the magnet preventive protection control mode includes , in particu- lar for each set of stator winding present, controlling the electrical generator system in order to shift the phase (angle) of the generator current (e.g. for each phase, e.g. A- phase, B-phase, C-phase) relative to a phase (angle) of a generator voltage or a q-axis or a d-axis .
The phase (angle) of the generator voltage (for a considered electrical phase and a considered winding set) may be given or determined by the position of the rotating rotor relative to the stator due to the fact that the permanent magnets induce voltages in the stator windings. A dq-synchronously rotating coordinate frame rotates synchronously with the rotor. The zero crossing, where the stator winding voltage increases, may correspond to the location of the q-axis. The maximum voltage at the electrical angle of 90° may correspond to the position of the d-axis of the dq-coordinate system. During the method, the phase (angle) of the generator current may be shifted relative to the voltage phase (angle) which may also be expressed as to be shifted relative to the q-axis. The phase (angle) of the generator current may be more negative than the phase (angle) of the generator voltage, for example by an amount of 5° to 40° less than the voltage phase (angle) .
For controlling the electrical generator system, a controller according to an embodiment of the present invention may be employed. In a coordinate system having as an abscissa an electrical angle and having as an ordinate an amplitude of the voltage or current, the stator winding voltage may for example form a substantially a sinusoidal curve having the crossing zero at the electrical angle zero and having the maximum at the electrical angle of 90°. The generator current is then shifted according to the control method such that a graph of the current is right shifted relative to the stator voltage by an amount of for example between 10° and 30°. The right shift of the generator current corresponds to a negative relative phase (angle) between the current and voltage or corresponds to the condition, where the generator current has a more negative electrical phase (angle) than the generator voltage. Thereby, high current peaks which might occur after a fault condition, such as a short-circuit, may be reduced, in order to avoid irreversible demagnetization of the permanent magnets.
According to an embodiment of the present invention, shifting the phase (angle) of a generator current includes at least one of: advancing the phase (angle) of the generator current relative to a previous phase (angle) of the generator current; advancing the phase (angle) of the generator current relative to the phase (angle) of the generator voltage or a q-axis ; setting the phase (angle) of the generator current to be different than the phase (angle) of the generator voltage or a q-axis; setting the phase (angle) of the generator current to be smaller than the phase (angle) of the generator voltage or a q-axis; setting the phase (angle) of the generator current to be different than the phase (angle) of the generator voltage or a q-axis such that a difference phase depends on the magnet temperature; setting the phase (angle) of the generator current to be by between 40° and 5°, in particular 30° and 10°, smaller than the phase (angle) of the generator voltage or a q-axis; dynamically adjusting a relative phase (angle) between generator current and voltage or a q-axis based on the magnet temperature.
Advancing the phase (angle) of the generator current may mean to right shift a current graph relative to a voltage graph. Before entering the magnet preventive protection control mode, the relative electrical phase angle between the generator current and the generator voltage may be zero or may be different from zero depending on the desired performance or reference for example reactive power. The relative angle of zero may correspond to the maximum torque generation by the generator which may lead to the maximum power output or active power output, or maximum torque per amber, or maximum voltage. However, in some productive operational modes, the relative electrical angle may be set to be different from ze- ro . When entering the magnet preventive protection control mode , however , the relative angle may be changed such that the current electrical angle is smaller than the current electrical angle before entering the magnet preventive protection control mode and such that in particular the current electrical angle i s smaller than the voltage electrical angle . The above-des cribed embodiments regarding the shifting of the phase of the generator current may allow high f lexibility and adaptation of the method according to the requirement s .
According to an embodiment of the present invention , the magnet temperature relate s to or compri ses at least one of : a temperature of at least one of the permanent magnets , in particular a mea sured temperature ; a mean temperature of the plural permanent magnets ; a maximum temperature of the plural permanent magnets , or a derived magnet temperature based on measured flux linkage or phase voltage or rated power and current .
It might have been observed that prior to a short-circuit in the stator windings , the temperature of the magnet may already increase . Thus , triggering the magnet preventive protection control mode based on the magnet temperature may allow to shift the generator current phase ( angle ) prior to the actual occurrence of the short-circuit .
According to an embodiment of the present invention , the electrical generator system comprise s at least one converter connected to the stator windings , wherein controlling the electrical generator system includes to control the converter by supplying a control signal indicative of a ( relative ) electrical phase angle of the generator currents .
The converter may comprise a generator side converter portion , a DC link and a utility grid converter portion . In particular , according to embodiments of the present invention , the generator side converter portion may be controlled . Each of the generator converter portions may comprise plural controllable switches , such a s high-power transi stors , which may be supplied with respective gate control signals for defining desired electrical output quantities . One quantity which might be controllable by the ( generator s ide ) converter portion may be the relative electrical phase angle of the generator current relative to the generator voltage . The generator current i s to be understood as the current flowing in the one or more winding sets of the generator . The relative electrical angle of the generator current relative to the generator voltage may relate to the relative electrical angle of one of the phase s of the multiple phases of the generator currents flowing in the set of stator windings . For each phase of the windings the shift of the generator current phase angle may be applied .
According to an embodiment of the present invention , the controlling the electrical generator system is further performed in order to change an amplitude of the generator current , in particular in dependence of the magnet temperature and/or an amount of the shift of the generator current phase angle and/or a power demand or reference value .
Alternatively or additionally to the phase ( angle ) of the generator current/ s , also the amplitude of the generator cur- rent / s may be controlled or changed when the magnet preventive protection control mode is entered . For example , when the phase ( angle ) of the generator current relative to the generator voltage is set , such that the current phase ( angle ) is more negative than the voltage phase ( angle ) , the amplitude of the current may either be increased or decreased, for example to substantially maintain an active power output . The amplitude of the current may be controlled according to the particular application .
According to an embodiment of the present invention , controlling the electrical generator system is performed in order to change the ( relative ) phase ( angle ) and the amplitude of the generator current in combination, such that a power output of the generator system complies with a power reference or is substantially unchanged. Thereby, power output performance may be maintained while at the same time, demagnetization of the permanent magnets may be prohibited or avoided.
According to an embodiment of the present invention, the phase angle is shifted before the occurrence of a fault or fault condition of the generator system.
A fault of the generator system may have the consequence that shortly after the fault, such as being 10 ms and 50 ms later, relatively high current peak is expected or observed in the stator windings. This relatively high current peak would conventionally demagnetize permanently the permanent magnets. Wherein, however, the phase angle is shifted before the occurrence of the fault, the amplitude of the high current peak may be reduced, potentially prohibiting demagnetization of the magnets.
According to an embodiment of the present invention, the fault or fault condition is present if at least one of the following occurs or holds: a short circuit related to the stator, in particular in at least one stator winding; a fault in at least one portion of the converter; a fault in a breaker; a fault in a DC-link between converter portions. Thereby, a great variety of potential faults may be supported.
According to an embodiment of the present invention, a peak current occurs after the fault and after shifting the (relative) phase angle and before a breaker opens, wherein a peak current amplitude is below a current threshold above which demagnetization of at least one permanent magnet would be caused .
The peak current may for example occur between 10 ms and 40 ms after the occurrence of the fault, in particular short- circuit. The phase (angle) of the generator current may, how- ever , have been shifted before the occurrence of the fault . The occurrence of the short-circuit current peak value may be too early quick for a circuit breaker to open . Thus , embodiment s of the present invention may enable to achieve that the peak current amplitude stays below the current threshold above which demagnetization of a permanent magnet would be caused .
According to an embodiment of the present invention , the critical condition is detected if at least one of the following criterium is satis fied : the magnet temperature is above a first threshold, in particular for at lea st a first threshold time period; the magnet temperature is below a second threshold, in particular for les s than a second threshold time period , wherein a temperature above the second threshold would cause demagnetization of the magnet ; a rate of increase of the magnet temperature is above a threshold rate , in particular for at least a third threshold time period; a combination of the above criteria .
Thereby, great flexibility is provided to adapt the method according to the particular requirements or the application .
It may allow the use of magnets with lower coercivity, or the use of le s s magnet volume .
It should be understood, that features , individually or in any combination , disclosed , des cribed, applied or employed for a method of controlling an electrical generator system may also , individually or in any combination , applied or provided for a controller for controlling an electrical generator system according to embodiments of the present invention and vice versa .
According to an embodiment of the present invention , it is provided a controller for controlling an electrical , in particular synchronous , generator system compris ing a generator including a stator having stator windings and a rotor having plural permanent magnets , in particular of a wind turbine , the arrangement compri sing : an input port adapted to receive an indication signal when a magnet temperature indicates a critical condition ; the controller being adapted, to , in ca se of the critical condition , enter a magnet preventive protection control mode including to shift a phase of a generator current , in particular adapted to carry out or control a method according to any one of the preceding claims .
The controller may be implemented in software and/or hardware . The controller may be a portion of a generator controller or a wind turbine controller . In embodiments of the present invention , the controller may further comprise one or more temperature measurement sensors which are installed to measure the temperature of one or more of the permanent magnets . The controller may compri se arithmetic/ logical circuitry, in particular a ( semiconductor ) proce s sor .
According to an embodiment of the present invention , the controller i s adapted to generate and output a control signal caus ing the generator system to shift the pha se angle of the generator current relative to a generator voltage .
The control s ignal may for example be configured a s a converter control signal supplying one or more reference value s to a converter or a converter controller . The control system or a control signal generated by the converter controller may include gate driver signal s for the one or more controllable switches comprised in the converter , in particular in the generator side converter portion .
According to an embodiment of the present invention it is provided an electrical , in particular synchronous , generator system, comprising : a generator including a stator having stator windings and a rotor having plural permanent magnets ; in particular a converter electrically connected to the stator windings of the generator ; and a controller according to one of the two preceding claims connected to control the system, in particular the converter .
Furthermore , it is provided a wind turbine , including : an electrical generator system according to the preceding claim; a hub at which plural rotor blades are connected and which is mechanically coupled to the rotor of the generator .
The aspects defined above and further aspects of the present invention are apparent from the examples of embodiment to be described hereinafter and are explained with reference to the examples of embodiment . The invention will be described in more detail hereinafter with reference to examples of embodiment but to which the invention is not limited .
Brief Des cription of the Drawings
Embodiments of the pre sent invention are now described with reference to the accompanying drawings . The invention is not restricted to the illustrated or des cribed embodiments .
Fig . 1 schematically illustrate s a wind turbine according to an embodiment of the present invention compri sing an electrical generator system according to an embodiment of the present invention which includes a controller according to an embodiment of the present invention ;
Fig . 2 illustrates curves of a generator current and generator voltage a s set according to embodiments of the pre sent invention ;
Fig . 3 illustrates curves repre senting short-circuit current peak values for different relative electrical phase angles between current and voltage ; Fig . 4 illustrates curves of phase currents having dif ferent electrical phase angle s as applied according to embodiments of the present invention ; and
Fig . 5 illustrates curves of a generator current having dif ferent phase angle s and al so different amplitudes as applied according to embodiments of the present invention .
Detailed Description
The wind turbine 1 schematically illustrated in Fig . 1 comprises a wind turbine tower 2 on top of which a nacelle 3 i s mounted . The nacelle 3 harbours an electrical generator sys tem 4 according to an embodiment of the present invention . The generator system 4 is mechanically coupled to a hub 5 at which plural rotor blades 6 are mounted .
The electrical generator system 4 comprises a generator 7 including a stator 8 having stator windings and a rotor 9 having plural permanent magnets 10 . The generator system 4 further comprise s a converter 11 which is electrically connected to the stator windings of the generator 7 . Further , the generator system 4 compri ses a controller 12 for controlling the electrical generator system 4 which is connected to control the system .
In the embodiment illustrated in Fig . 1 , the converter 11 comprises a generator side converter portion 13 , a DC link 14 and a utility grid converter portion 15 which is via one or more optional transformers connected or connectable to a utility grid 16 to provide in particular three-pha se electrical power to the utility grid 16 .
The controller 12 comprise s an input port 13 adapted to receive an indication signal ( e . g . temperature signal ) 14 when a magnet temperature indicates a critical condition . The indication signal 14 may for example be or comprise a tempera- ture measurement signal of a temperature sensor 17 which is mounted at the rotor 9 to measure the temperature of one or more of the permanent magnets 10. In other embodiments, the indication signals 14 may be a binary signal which may for example be derived by logic/arithmetic unit defining whether the critical condition is present, in particular based on the temperature of one or more of the magnets 10.
The controller 12 is adapted to, in case of the critical condition, enter a magnet preventive protection control mode, including to shift a phase (angle) of a generator current. In the embodiment illustrated in Fig. 1, the controller is configured to generate and output a control signal 18 to the generator side portion 13 of the converter 11 which controls the generator 7 such that the phase (angle) of the generator current is shifted relative to a generator voltage phase (angle) .
The controller 4 in particular together with the temperature sensor 17 is adapted or configured to carry out a method of controlling the electrical machine of the electrical generator system 4. Thereby, a magnet temperature is monitored (for example via the temperature sensor 17) and it is checked whether the temperature indicates a critical condition. In case of the critical condition, a magnet preventive protection control mode is entered including to shift the phase of the generator current.
Fig. 2 illustrates a curve in a coordinate system having as an abscissa the electrical rotor position and having as an ordinate a magnitude of electrical quantities. The curve 20 represents the generator voltage and the curve 21 represents a generator current (of one phase, for example the A-phase) , when a magnet preventive protection control mode has been entered. As can be appreciated from Fig. 2, the prevention protection control mode includes to shift the phase (angle) of the generator current 21 relative to a phase (angle) of the generator voltage 20. The phase shift is labelled with refer- ence sign cp. The current 21 is advanced relative to the generator voltage 20. The voltage U(t) and the current I (t) may be given according to the following equations :
U (t) = U0 * sin (w*t)
I (t) = 10 * sin(w*t - cp) , where w is the electrical rotational speed.
Thus, the phase of the generator current I (t) is smaller than the phase of the generator voltage U (t) . The value of -cp may change between -10 and -30°, for example, or may have even different values.
In the embodiment illustrated in Fig. 1, the generator system 4 comprises the converter 11 and controlling the electrical generator system 4 includes to control the converter 11, in particular the generator side portion 13 by supplying the control signal 18 indicative of a (relative) electrical phase angle of the generator current. The control signal 18 may either directly indicate the phase-shift angle or may for example indicate a reference of active power and/or voltage.
Fig. 3 illustrates curves in a coordinate system having as an abscissa the time and having as an ordinate the phase current. At a point in time which is earlier than the illustrated curves, a magnet preventive protection control mode has already been entered including to shift the generator current relative to the generator voltage. The curves 22a, ..., f indicate the short-circuit current peak values, when the generator current is -10 electrical degrees, -15, -20, -25, -30, or -35 electrical degrees relative to the generator voltage. It can be appreciated that the larger the negative phase-shift of the generator current, the lower the short-circuit current peak value. Thereby, demagnetization of permanent magnets after a fault which happened at a point in time tl may be avoided. At the time tl, for example, a short-circuit may have occurred in one or more phases of the one or more stator windings . Figs. 4 and 5 illustrate embodiments how to shift a phase (angle) of a generator current and/or change an amplitude of a generator current in a magnet preventive protection control mode according to embodiments of the present invention. Thereby, the abscissas in Figs. 4 and 5 indicate the electrical rotor position and the ordinates represent the phase currents. The curves 20 in Figs. 4 and 5 again illustrate the generator voltage. The curves 23, 24, 25 indicate the phase currents when the phase-shift is -10°, -20° or -30° relative to the generator voltage 20 and has the same amplitude, for example as prior to the indication of the critical condition.
The curves 26, 27, 28 in Fig. 5 illustrate the generator currents where the phase-shift is -10, -20 or -30 electrical angles and further having different amplitudes (than before the indication of the occurrence of the critical condition) .
Embodiments of the present invention provide a magnet preventive protection control mode, wherein the generator phase current angle is advanced by the generator converter, via setting a control mode that is activated when the magnet temperature reaches a certain level. Therefore, in case of a fault occurrence (see for example time point tl in Fig. 3) , the permanent magnets (for example 10 in Fig. 1) (and the generator) may be protected, since the fault currents will be lower as has been illustrated in Fig. 3 compared to the condition, where the phase current value is not advanced.
The current angle advancing level (i.e. , the shift of the generator current relative to the generator voltage) may be for example a function of a magnet temperature. Sensors (for example temperature sensors 17 in Fig. 1) may be conventionally installed in a generator system. Therefore, the proposed technique may be cost-free and no additional hardware may be required . As can be appreciated from Fig. 3, it is confirmed by calculation and measurements that the value of the short-circuit current peak during the fault is determined by the phase current angle prior to the fault. The more advanced the phase current angle is, the less the value of the short-circuit current peak is, as can be seen in Fig. 3.
The following table 1 shows the permanent performance loss due to short-circuit faults vs. phase current angle:
Table 1 :
The table illustrates the variation of the permanent performance loss due to short-circuit faults as a function of the phase current angle set prior to the fault.
The Fig. 4 demonstrates an example of phase current waveforms for different current angles, i.e. , at a fixed current amplitude. It is also possible, that the current amplitude can be varied, as needed by the power demand, when the current angle is advanced, as is illustrated in the Fig. 5.
The embodiments of the present invention may provide the one or more of the following advantages:
- Lower generation cost, as less magnet material may be required . - Higher energy output, as power derating vs. ambient temperature can be delayed.
It should be noted that the term "comprising" does not ex- elude other elements or steps and "a" or "an" does not exclude a plurality. Also elements described in association with different embodiments may be combined. It should also be noted that reference signs in the claims should not be construed as limiting the scope of the claims.

Claims

CLAIMS :
1. Method of controlling an electrical, in particular synchronous, generator system (4) comprising a generator (7) including a stator (8) having at least one set of stator windings and a rotor (9) having plural permanent magnets (10) , in particular of a wind turbine, the method comprising: monitoring when a magnet temperature indicates a critical condition in case of the critical condition, entering a magnet preventive protection control mode including to shift a phase angle of a generator current (21) .
2. Method according to the preceding claim, wherein the magnet preventive protection control mode includes: controlling the electrical generator system (4) in order to shift the phase angle of the generator current (21) of at least one phase, in particular all phases, of the at least set of stator windings relative to a phase angle of a generator voltage (10) or a q-axis (20a) .
3. Method according to any one of the preceding claims, wherein shifting the phase angle of a generator current in particular of all phases of one or more sets of stator windings, includes at least one of: advancing the phase angle of the generator current (21) relative to a previous phase of the generator current; advancing the phase angle of the generator current (21) relative to the phase of the generator voltage (20) or a q- axis (20a) ; setting the phase angle of the generator current (21) to be different than the phase of the generator voltage (20) or a q-axis (20a) ; setting the phase angle of the generator current (21) to be smaller than the phase angle of the generator voltage or a q-axis (20a) ; setting the phase angle of the generator current (21) to be different than the phase angle of the generator voltage (20) or a q-axis (0a) such that a difference angle phase (4>) depends on the magnet temperature; setting the phase angle of the generator current (21) to be by between 40° and 5°, in particular 30° and 10°, in reference to the phase angle of the generator voltage (20) or a q-axis (20a) ; dynamically adjusting a relative phase angle (4>) between generator current (21) and voltage (20) or a q-axis (20a) based on the magnet temperature and/or magnet temperature variations .
4. Method according to any one of the preceding claims, wherein the magnet temperature relates to or comprises at least one of: a temperature of at least one of the permanent magnets (10) , in particular a measured temperature; a mean temperature of the plural permanent magnets (10) ; a mean temperature of one or more specific permanent magnets ; a maximum temperature of one or more specific permanent magnets ; a maximum temperature of the plural permanent magnets (10) .
5. Method according to any one of the preceding claims, wherein the electrical generator system (4) comprises at least one converter (11) connected to the stator windings, wherein controlling the electrical generator system (4) includes to control the converter (11, 13) by supplying a control signal (18) indicative of a electrical phase angle of the generator current (21) .
6. Method according to any one of the preceding claims, wherein the controlling the electrical generator system (4) is further performed in order to change an amplitude of the generator current (26, 27, 28) , in particular in dependence of the magnet temperature and/or an amount of the shift of the generator current phase angle and/or a power demand or reference value.
7. Method according to any one of the preceding claims, wherein controlling the electrical generator system (4) is performed in order to change the phase and the amplitude of the generator current (26, 27, 28) in combination, such that a power output of the generator system complies with a power reference or is substantially unchanged.
8. Method according to any one of the preceding claims, wherein the phase angle is shifted before occurrence of a fault or fault condition of the generator system (4) .
9. Method according to any one of the preceding claims, wherein the fault or fault condition is present if at least one of the following occurs or holds : a short circuit related to the stator, in particular in at least one stator winding; a fault in at least one portion of the converter; a fault in a breaker; a fault in a DC-link between converter portions.
10. Method according to any one of the preceding claims, wherein a peak current (22a, ... , f) occurs after the fault and after shifting the phase angle and before a breaker opens, wherein a peak current amplitude is below a current threshold above which demagnetization of at least one permanent magnet would be caused.
11. Method according to any one of the preceding claims, wherein the critical condition is detected if at least one of the following criterium is satisfied: the magnet temperature is above a first threshold, in particular for at least a first threshold time period; the magnet temperature is below a second threshold, in particular for less than a second threshold time period, wherein a temperature above the second threshold would cause demagnetization of the magnet; a rate of increase of the magnet temperature is above a threshold rate, in particular for at least a third threshold time period; a combination of the above criteria.
12. Controller (12) for controlling an electrical, in particular synchronous, generator system (4) comprising a generator (7) including a stator (8) having at least one set of stator windings and a rotor (9) having plural permanent magnets
(10) , in particular of a wind turbine (1) , the arrangement comprising : an input port (18) adapted to receive an indication signal when a magnet temperature indicates a critical condition; the controller (12) being adapted, to, in case of the critical condition, enter a magnet preventive protection control mode including to shift a phase angle of a generator current (21) of at least one phase of the at least one set of stator windings, in particular adapted to carry out or control a method according to any one of the preceding claims.
13. Controller (12) according to the preceding claim, wherein the controller is adapted to generate and output a control signal (18) causing the generator system (4) to, for at least one phase of the at least one set of stator windings, shift the phase angle of the respective generator current (21) relative to a respective generator voltage (20) .
14. Electrical, in particular synchronous, generator system (4) , comprising: a generator (7) including a stator (8) having at least one set of stator windings and a rotor (9) having plural permanent magnets (10) ; in particular, in particular for each set of stator windings, a converter (11, 13) electrically connected to the respective set of stator windings of the generator; and a controller (12) according to one of the two preceding claims connected to control the system, in particular the converter (11, 13) .
15. Wind turbine (1) , including: an electrical generator system (4) according to the preceding claim; a hub (5) at which plural rotor blades (6) are connected and which is mechanically coupled to the rotor (9) of the generator (7) .
EP24733162.2A 2023-07-10 2024-06-13 Prevention of magnet demagnetization in a rotor Pending EP4639750A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
EP23184490.3A EP4492672A1 (en) 2023-07-10 2023-07-10 Prevention of magnet demagnetization in a rotor
PCT/EP2024/066420 WO2025011866A1 (en) 2023-07-10 2024-06-13 Prevention of magnet demagnetization in a rotor

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EP24733162.2A Pending EP4639750A1 (en) 2023-07-10 2024-06-13 Prevention of magnet demagnetization in a rotor

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CN103034261A (en) * 2012-12-07 2013-04-10 无锡风电设计研究院有限公司 Permanent magnet generator temperature control system
JP6218976B2 (en) * 2015-02-02 2017-10-25 三菱電機株式会社 Synchronous machine control device and permanent magnet temperature estimation method for synchronous machine
EP3125418B8 (en) * 2015-07-27 2019-06-12 Siemens Gamesa Renewable Energy A/S A method to detect or monitor the demagnetization of a magnet
DK3522362T3 (en) * 2018-02-01 2024-03-04 Siemens Gamesa Renewable Energy As CONTROL OF AN ELECTRIC PERMANENT MAGNET MACHINE WITH MULTIWINDING SET

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