METHOD FOR HEATING A GENERATOR OF A WIND POWER INSTALLATION

Abstract

Provided is a method for heating a generator of a wind power installation during or before starting the installation. The generator is a permanent magnet synchronous generator configured to generate a stator current comprising at least one three-phase current. The installation is configured as a gearless installation and is connected to an electrical supply network for feeding electrical power into the network. The installation comprises a converter, connected to the generator, to control the generator to feed electrical power into the network. The method comprises rotating the rotor with a low rotational speed below a first limit and operating the converter such that the generator generates the stator current and electrical power, and no electrical power is fed into the electrical supply network. At least one portion of the stator current substantially circulates through the generator and the converter to consume power in generator windings to heat the generator.

Claims

1. A method for heating a generator of a wind power installation during or before starting the wind power installation, wherein: the generator is a permanent magnet synchronous generator configured to generate a stator current, wherein the stator current includes at least one three-phase current, the wind power installation is configured as a gearless wind power installation and is coupled to an electrical supply network for feeding electrical power into the electrical supply network, and the wind power installation includes: a rotor having a plurality of rotor blades operable at a variable rotational speed; and a converter coupled to the generator and configured to control the generator, wherein the converter is coupled to the electrical supply network for feeding the electrical power generated by the generator into the electrical supply network, and the method comprises: rotating the rotor using a first rotational speed that is below a first rotational speed limit; operating the converter to cause the generator to generate the stator current and the electrical power; operating the converter to refrain from feeding the electrical power into the electrical supply network; circulating at least a portion of the stator current through the generator and the converter; and consuming power at least in stator windings of the generator to heat the generator.

2. The method as claimed in claim 1, wherein the converter includes: an active rectifier coupled between the generator and a DC voltage link circuit, the active rectifier being configured to control the generator and rectify the stator current into a DC current for feeding into the DC voltage link circuit, wherein the DC voltage link circuit has a link circuit voltage; and an inverter coupled to the DC voltage link circuit and configured to invert energy from the DC voltage link circuit into an AC current for feeding into the electrical supply network, wherein: the inverter is operated such that the DC voltage link circuit is short-circuited at specific time periods, and/or the active rectifier is operated such that phases of the stator current are short-circuited at specific time periods.

3. The method as claimed in claim 1, comprising: controlling, by the converter, the generator using field weakening control for heating the generator, wherein controlling the generator includes controlling a generator torque below a first torque limit value, wherein the first torque limit value is less than a rated torque of the generator, wherein the rated torque is greater than the first torque limit value at least by the factor of 2, and/or controlling the generator by implementing a d/q control, wherein the d/q control sets a d component and a q component in a rotating reference system, wherein the d component is used for controlling a magnetic field of the generator, and the d component is selected such that the d component reduces the magnetic field.

4. The method as claimed in claim 3, wherein the d component is set to a negative value.

5. The method as claimed in claim 1, comprising: in response to the rotor being operated with the first rotational speed, setting a generator voltage to a first value that is lower than a first generator voltage limit value, and/or in response to the rotor being operated with the first rotational speed, operating a DC voltage link circuit to have a first link circuit voltage value that is lower than a first link circuit voltage limit value and greater than a second link circuit voltage limit value.

6. The method as claimed in claim 1, comprising: in response to the rotor continuing to rotate with the first rotational speed, operating a chopper circuit of a DC voltage link circuit and lowering a link circuit voltage to a first link circuit voltage value that is less than a second link circuit voltage limit value.

7. The method as claimed in claim 6, wherein the chopper circuit controls a chopper current from the DC voltage link circuit to a chopper resistor, wherein the chopper circuit uses pulse modulation, in which a pulse duration alternates with a pulse-free time in a period duration, to control the chopper current by setting a pulse ratio, wherein the pulse ratio specifies a ratio of the pulse duration to the period duration, and wherein the pulse ratio is increased to decrease the link circuit voltage.

8. The method as claimed in claim 7, wherein the pulse ratio is increased progressively from 0% to 100%.

9. The method as claimed in claim 1, comprising: in response to the rotor continuing to rotate with the first rotational speed, controlling a link circuit voltage to a zero value using a chopper circuit; and controlling, by the converter, the generator using a field weakening control to cause the generator to generate less power and support controlling the link circuit voltage to the zero value.

10. The method as claimed in claim 1, comprising: in response to the rotor continuing to rotate with the first rotational speed and a link circuit voltage being controlled to a zero value, switching an inverter coupled to a DC voltage link circuit to a zero mode, wherein in the zero mode, both semiconductor switches of at least one semiconductor switch pair are closed to short-circuit the DC voltage link circuit; and in response to the rotor continuing to rotate with the first rotational speed and the link circuit voltage being controlled to the zero value, operating the wind power installation in the zero mode to heat at least the generator.

11. The method as claimed in claim 4, wherein at least one of: the first rotational speed limit is 20 to 50% of a rated rotational speed of the rotor, the first rotational speed limit is 2.5 to 4.5 rotations per minute (rpm), the first rotational speed limit is 3 to 4 rpm, the first generator voltage limit value is 30% to 70% of a rated generator voltage, the first generator voltage limit value is 200 V to 500 V, the first generator voltage limit value is 300 V to 400 V, the first link circuit voltage limit value is 40% to 60% of a rated link circuit voltage, the first link circuit voltage limit value is 400 V to 700 V, the second link circuit voltage limit value is 30% to 40% of the rated link circuit voltage, the second link circuit voltage limit value is 300 V to 400 V, a third link circuit voltage limit value is 5% to 20% of the rated link circuit voltage, the third link circuit voltage limit value is 50 V to 200 V, a zero value is less than the third link circuit voltage limit value, the zero value is less than 2% of the rated link circuit voltage, the zero value is less than 1% of the rated link circuit voltage, the zero value is less than 20 V, or the zero value is less than 10 V.

12. The method as claimed in claim 1, wherein for heating the generator, the wind power installation or the converter is disconnected from the electrical supply network.

13. A wind power installation configured to heat a generator of the wind power installation during or before starting wind power installation, comprising: an installation controller configured to control heating the wind power installation; a permanent magnet synchronous generator configured to generate a stator current, wherein the stator current includes at least one three-phase current, wherein the wind power installation is a gearless wind power installation and is coupled to an electrical supply network, for feeding electrical power into the electrical supply network; a rotor having a plurality of rotor blades operable at a variable rotational speed; and a converter coupled to the generator and configured to control the generator, wherein the converter is coupled to the electrical supply network and configured to feed the electrical power, generated by the generator, into the electrical supply network, wherein the controller is configured to: cause the rotor to rotate with a first rotational speed below a first rotational speed limit; and operate the converter such that the generator generates the stator current and the electrical power, and no electrical power is fed into the electrical supply network, wherein at least a portion of the stator current circulates through the generator and the converter to consume power at least in stator windings of the generator to heat the generator.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0072] The invention is explained in greater detail below by way of example on the basis of embodiments with reference to the accompanying figures.

[0073] FIG. 1 shows a wind power installation in a perspective illustration.

[0074] FIG. 2 shows a converter system with a generator in a schematic illustration.

[0075] FIG. 3 shows a flow diagram for the method for heating the generator.

DETAILED DESCRIPTION

[0076] FIG. 1 shows a schematic illustration of a wind power installation according to the invention. The wind power installation 100 comprises a tower 102 and a nacelle 104 on the tower 102. An aerodynamic rotor 106 comprising three rotor blades 108 and a spinner 110 is provided on the nacelle 104. The aerodynamic rotor 106 is caused to effect a rotational movement by the wind during operation of the wind power installation and thus also rotates an electrodynamic rotor of a generator, which is coupled to the aerodynamic rotor 106 directly or indirectly. The electrical generator is arranged in the nacelle 104 and generates electrical energy. The pitch angles of the rotor blades 108 can be varied by pitch motors on the rotor blade roots 109 of the respective rotor blades 108.

[0077] In this case, the wind power installation 100 comprises an electrical generator 101, indicated in the nacelle 104. Electrical power can be generated by means of the generator 101. For feeding in electrical power, a converter system 105 is provided, which comprises an inverter in order to feed into the electrical supply network at the network connection point PCC, and which comprises an active rectifier connected to the generator 101. It is thus possible to generate a three-phase infeed current and/or a three-phase infeed voltage according to amplitude, frequency and phase, for infeed at a network connection point PCC. That can be effected directly or else jointly with further wind power installations in a wind farm. An installation controller 103 is provided for controlling the wind power installation 100 and also the converter system 105. The installation controller 103 can also acquire predefined values from an external source, in particular from a central farm computer.

[0078] FIG. 2 shows a converter system 200 arranged between a synchronous generator 202 and an electrical supply network 204. The converter system 200 comprises an active rectifier 206 connected to the synchronous generator 202 in order to control a three-phase stator current I.sub.S. For the sake of simplicity, the stator current I.sub.S is depicted only on one phase, but it encompasses all three phases. A current arrow pointing from the synchronous generator 202 in the direction of the active rectifier 206 is depicted in each case. This direction should be understood merely symbolically, however, since the stator current is an AC current, of course. The arrow direction indicates the power flow direction since the synchronous generator 202 is intended to operate as a generator and to output power. In the described method for heating the generator, too, the latter outputs power.

[0079] The active rectifier 206 can convert said three-phase stator current I.sub.S into a DC current and input it into the DC voltage link circuit 208. The resulting DC current is illustrated here as I.sup.+ and I.sup.−. In this case, the active rectifier 206 is illustrated merely schematically by six semiconductor switches S.sub.A to S.sub.F. A complete construction of such an active rectifier also includes, of course, corresponding diodes in parallel with the semiconductor switches, which have been omitted here for the sake of better clarity. The functioning of such an active rectifier, which may also be referred to as a generator-side inverter, is known to a person skilled in the art. The symbols of the semiconductor switches are also greatly simplified.

[0080] A drive unit 210 is provided for driving purposes, which drive unit can be part of an installation controller. The drive unit 210 can drive each of the semiconductor switches S.sub.A to S.sub.F. As a result, the stator current I.sub.S can be controlled and the generator 202 can thus be controlled electrically. For the purpose of driving the generator 202, provision is made for using a d/q control. That is indicated by the symbol d/q in the drive unit 210. Corresponding control lines 212 correspondingly run from the drive unit 210 to the semiconductor switches S.sub.A to S.sub.F.

[0081] The DC voltage link circuit 208 comprises a link circuit capacitor 214, and the DC voltage link circuit 208 and thus the link circuit capacitor 214 have a link circuit voltage V.sub.Z. In the DC voltage link circuit 208, a chopper circuit 216 is additionally provided, in parallel with the link circuit capacitor 214. The chopper circuit 216 comprises a chopper switch 218 and a chopper resistor 220. The chopper switch 218 is likewise configured as a semiconductor switch and can be driven by the drive unit 210 via the chopper control line 222.

[0082] The chopper circuit 216 serves to dissipate power from the DC voltage link circuit 208, if that is necessary. During normal operation that is necessary if the link circuit voltage V.sub.Z becomes too great, namely becomes greater than its rated voltage. The chopper switch 218 can then be driven such that it switches in a pulsed manner in order thereby to control a current through the chopper resistor 220. The chopper resistor 220 usually has a comparatively small resistance, with the result that a high current can flow depending on the driving of the chopper switch 218. Said current is then converted into heat in the chopper resistor 220.

[0083] Furthermore, an inverter 224 is provided, which in principle can be constructed like the active rectifier 206. In particular, it comprises six semiconductor switches S.sub.1 to S.sub.6. Two semiconductor switches in each case form a semiconductor switch pair, namely S.sub.1 and S.sub.2, S.sub.3 and S.sub.4 and also S.sub.5 and S.sub.6. In the case of the inverter 224, too, only a simplified structure is shown, with greatly simplified symbols for the semiconductor switches S.sub.1 to S.sub.6 and also with the omission of diodes correspondingly connected in parallel.

[0084] During normal operation of the wind power installation or of the converter system 200, the inverter 224 generates a three-phase AC current I.sub.N by means of the semiconductor switches S.sub.1 to S.sub.6. Said current is thus generated as a three-phase sinusoidal AC current I.sub.N, for which purpose the three-phase inductor 226 indicated is also required. Said three-phase AC current I.sub.N then flows via a network disconnecting switch 228 into the symbolically indicated electrical supply network 204. The network disconnecting switch 228 is closed, of course, in this normal case. The AC current I.sub.N is indicated by three current arrows in the direction of the electrical supply network 204, but this current is an AC current, of course, and power could also flow from the electrical supply network 204 to the inverter 224.

[0085] For the purpose of driving the six semiconductor switches S.sub.1 to S.sub.6, inverter control lines 230 are provided, via which the drive unit 210 can drive the inverter 224. The drive unit 210 can also drive the network disconnecting switch 228, namely via the disconnecting switch control line 232.

[0086] In a proposed method for heating the generator 202, therefore, the symbolically indicated rotor 234 is rotated with a slow rotational speed by the wind and a generator rotor 236 of the synchronous generator 202 thus rotates with the same rotational speed in the same direction. The synchronous generator 202 is configured here symbolically as internal rotor and thus has its stator 238 on the exterior.

[0087] In any case it is proposed for the method that at the beginning of the method for heating the generator 202, the link circuit voltage V.sub.Z has a medium voltage range, e.g., 400 V if it lies between 1000 and 1200 V during normal operation. The network disconnecting switch 228 is open for this entire method, as is also illustrated in FIG. 2. At the beginning, the inverter 224 is inactive. A voltage is then established very rapidly in the DC voltage link circuit 208 and thus across the link circuit capacitor 214, which specifically is charged by the generator in this case.

[0088] The link circuit voltage is then reduced, however, as a result of the driving of the chopper circuit or the chopper switch 218 thereof. The link circuit voltage V.sub.Z then decreases from the initially medium voltage range into a low voltage range down to close to zero. The generator 206 is then operated with field weakening using a d/q control. The magnetic field of the synchronous generator, at least in the model used to control the synchronous generator, is then reduced to a very great extent. The synchronous generator 202 then generates little current, which at that moment is still generated as three-phase stator current I.sub.S and is converted into the DC current I.sup.+ or I.sup.−. At this moment a chopper current I.sub.C generated by a pulse modulation method then flows through the chopper resistor 220 and through the chopper switch 218. Said chopper current I.sub.C is therefore a pulsed current having an average value greater than the DC current I.sup.+ or I.sup.−, since said DC current is dissipated via said chopper circuit and energy is additionally dissipated from the link circuit capacitor 214.

[0089] If the link circuit voltage V.sub.Z is then zero or almost zero, the inverter 224 is driven such that it carries out a short circuit between the positive busbar 238 and the negative busbar 240. For this purpose, it can simultaneously close and leave closed for example the two semiconductor switches S.sub.1 and S.sub.2 of the corresponding semiconductor switch pair that they form. A short circuit current I.sub.K then flows. The driving of the chopper circuit 216 can then be ended, such that the chopper switch 218 remains open.

[0090] The heating of the generator 202 can then be carried out in this situation, wherein the active rectifier 206 and the inverter 224 will also absorb some heat. Ideally or as a simplification, a steady state is then established in which the stator current I.sub.S is rectified and results in the positive DC current I.sup.+, which flows into the positive busbar 238. From there said current flows further as I.sub.K through the two semiconductor switches S.sub.1 and S.sub.2 of the inverter 224 in the example shown. The short circuit current I.sub.K then corresponds to the positive DC current I.sup.+ in terms of its magnitude. The current then correspondingly flows to the negative busbar 240 and then forms the negative DC current I.sup.−. The latter in this case however is also a result of the control of the stator current I.sub.S by the active rectifier 206. In this respect, a current circulation is formed for the stator current I.sub.S, wherein the stator current in this case partly appears as DC current.

[0091] FIG. 3 illustrates the sequence of the proposed method for heating the generator. In the flow diagram 300 in FIG. 3, firstly the start step 302 is provided. In the start step 302, the wind power installation or its aerodynamic rotor is rotated with low rotational speed. In this case, the converter system has a medium link circuit voltage, as has been described in association with FIG. 2. The flow diagram and thus the start step 302 can be selected for example if the wind power installation has not been operated for a relatively long time and/or if it has fallen below a limit temperature and/or if a corresponding air humidity or even a condensate has been detected. The start step 302 is followed by the chopper step 304. In the chopper step 304, the link circuit voltage V.sub.Z is then slowly reduced and brought as far as possible toward zero or close to zero. That is effected as elucidated in FIG. 2, by means of a chopper circuit such as the chopper circuit 216.

[0092] The field weakening step 306 then follows, although it can also overlap the chopper step 304. In the field weakening step 306, the generator is operated with a field weakening, such that it generates comparatively little power and thus comparatively little current. As a result, bringing the link circuit voltage to zero or close to zero can then be accomplished as well. The zero mode can then commence.

[0093] The zero mode is illustrated in the zero mode step 308. In the latter, the DC voltage link circuit is short-circuited, namely by means of the inverter. That, too, has been described with reference to FIG. 2. The driving of the chopper circuit can then be ended and the method for heating can basically be operated for a relatively long time in the state that was established in the zero mode step 308.

[0094] In order to illustrate this relatively long operation, the zero mode step 308 is followed by an interrogation 310. Said interrogation 310 involves checking whether the heating process was sufficient. For this purpose, a time can be set from experience, or a temperature can be monitored, or the moisture can be monitored directly, to mention some examples. These criteria can also be combined.

[0095] In other words, if a termination condition has not yet been reached, then the interrogation 310 returns to the zero mode step 308. That is merely intended to mean, however, that operation is continued. That is to say that the short-circuiting of the DC voltage link circuit by the inverter is not initialized again, but rather maintained.

[0096] However, if the interrogation 310 reveals that the heating process can be ended, i.e., the interrogation is positive, the method is ended, which is symbolized by the end step 312.

[0097] The various embodiments described above can be combined to provide further embodiments. These and other changes can be made to the embodiments in light of the above-detailed description. In general, in the following claims, the terms used should not be construed to limit the claims to the specific embodiments disclosed in the specification and the claims, but should be construed to include all possible embodiments along with the full scope of equivalents to which such claims are entitled. Accordingly, the claims are not limited by the disclosure.