Method for generating an alternating current by means of an inverter of a wind turbine

Abstract

Provided is a method for generating a multiphase electrical alternating current having a sinusoidal fundamental wave in each phase by a multiphase inverter of a wind power installation. The multiphase inverter is controlled by a tolerance band method which respectively has an upper and a lower band limit for each of the phases of the inverter. The inverter has, for each phase, an upper switch for generating a positive sine half-wave of the alternating current of the phase and a lower switch for generating a negative sine half-wave of the alternating current of the phase. The method includes generating the positive sine half-wave by the upper switch and generating the negative sine half-wave by the lower switch based on the band limits of the phase, and changing at least one of the band limits such that a signal component superimposed on the respective sinusoidal fundamental wave is reduced.

Claims

1. A method, comprising: generating a multiphase electrical alternating current having a sinusoidal fundamental wave in each phase of a plurality of phases using a multiphase inverter of a wind power installation, wherein the multiphase inverter is controlled using a tolerance band method which has an upper band limit and a lower band limit for each phase of the plurality of phases of the multiphase inverter, respectively, and wherein the multiphase inverter has, for each phase of the plurality of phases, an upper switch for generating a positive sine half-wave of the alternating current of the phase and a lower switch for generating a negative sine half-wave of the alternating current of the phase; generating, for each phase of the plurality of phases, the positive sine half-wave by the upper switch based on the upper and lower band limits for the alternating current of the phase; generating, for each phase of the plurality of phases, the negative sine half-wave by the lower switch based on the upper and lower band limits for the alternating current of the phase; and changing at least one of the upper and lower band limits such that a signal component superimposed on the respective sinusoidal fundamental wave is reduced.

2. The method as claimed in claim 1, comprising: capturing a DC component as the superimposed signal component.

3. The method as claimed in claim 1, comprising: changing the at least one of the upper and lower band limits such that at least one switching frequency of the upper switch or the lower switch is changed.

4. The method as claimed in claim 1, comprising: capturing the superimposed signal component by capturing a switching frequency of the upper switch and capturing a switching frequency of the lower switch and comparing the switching frequencies of the upper switch and of the lower switch.

5. The method as claimed in claim 1, comprising: changing one of the upper band limit or the lower band limit such a that the superimposed signal component is reduced, wherein another one of the lower band limit or alternatively the upper band limit remains unchanged.

6. The method as claimed in claim 1, comprising: changing at least one of the upper band limit or the lower band limit such that a difference between a switching frequency of the upper switch and a switching frequency of the lower switch is minimized.

7. The method as claimed in claim 1, comprising: changing at least one of the upper band limit or the lower band limit such that a switching frequency of the upper switch or a switching frequency of the lower switch is reduced.

8. The method as claimed in claim 1, comprising: changing at least one of the upper band limit or the lower band limit with a time constant that is a multiple of a duration of a fundamental oscillation of the alternating current of the phase.

9. The method as claimed in claim 1, comprising: determining switching frequencies of the upper and lower switches over a half-wave of a fundamental oscillation.

10. The method as claimed claim 1, comprising: changing the upper and lower band limits by applying a correction value to the upper and lower band limits.

11. The method as claimed claim 10, wherein the correction value is a variable correction value and changing the upper and lower band limits is made by a PI controller based on a DC offset.

12. The method as claimed in claim 1, wherein the upper and lower switches each have at least one IGBT for generating the positive and negative sine half-waves.

13. The method as claimed in claim 1, wherein the tolerance band method uses a desired current value, and the multiphase inverter is controlled based on the desired current value.

14. The method as claimed in claim 1, comprising: changing the upper and lower band limits based on a desired current value.

15. A wind power installation, comprising: at least one multiphase inverter configured to generate multiphase electrical alternating current having a sinusoidal fundamental wave in each phase of a plurality of phases, wherein the at least one multiphase inverter is controlled using a tolerance band method which respectively has an upper band limit and a lower band limit for each phase of the plurality of phases of the at least one multiphase inverter, and wherein the at least one mulitphase inverter includes: for each phase of the plurality of phases, at least one upper switch configured to generate a positive sine half-wave of the alternating current of the phase; and for each phase of the plurality of phases, at least one lower switch configured to generate a negative sine half-wave of the alternating current of the phase, wherein the wind power installation is configured to: change at least one of the upper and lower band limits such that a signal component superimposed on the respective sinusoidal fundamental wave is reduced.

16. The wind power installation as claimed in claim 15, wherein the upper and lower switches each have at least one IGBT for generating the positive and negative sine half-waves.

17. The wind power installation as claimed in claim 15, comprising: a PI controller configured to change the upper and lower band limits by a correction value based on a DC offset.

18. A method for feeding a multiphase electrical alternating current into an electrical supply network with a nominal system voltage by a wind power installation connected to the electrical supply network and has at least one multiphase inverter that is a full converter, comprising: generating the multiphase electrical alternating current having a sinusoidal fundamental wave in each phase of a plurality of phases using the at least one multiphase inverter of the wind power installation, wherein the at least one multiphase inverter is controlled using a tolerance band method which has an upper band limit and a lower band limit for each phase of the plurality of phases of the at least one multiphase inverter, respectively, and wherein the at least one multiphase inverter has, for each phase of the plurality of phases, an upper switch for generating a positive sine half-wave of the alternating current of the phase and a lower switch for generating a negative sine half-wave of the alternating current of the phase; generating, for each phase of the plurality of phases, the positive sine half-wave by the upper switch based on the upper and lower band limits for the alternating current of the phase; generating, for each phase of the plurality of phases, the negative sine half-wave by the lower switch based on the upper and lower band limits for the alternating current of the phase; changing at least one of the upper and lower band limits such that a signal component superimposed on the respective sinusoidal fundamental wave is reduced; and feeding, into the electrical supply network, in the alternating current by the full converter.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

(1) The present invention is now explained in more detail, by way of example, below on the basis of exemplary embodiments with reference to the accompanying figures.

(2) FIG. 1 shows a schematic view of a wind power installation according to one embodiment.

(3) FIG. 2 shows a schematic structure of an electrical section of a wind power installation for feeding in an electrical alternating current according to one embodiment.

(4) FIG. 3 schematically shows the structure of a generator apparatus for generating an electrical three-phase alternating current by means of a tolerance band method according to one embodiment.

(5) FIG. 4 shows a schematic structure of a part of the method, namely for generating a single-phase electrical alternating current of a phase having a sinusoidal fundamental wave according to one embodiment.

(6) FIG. 5 illustrates a method sequence for changing a band limit for reducing a DC component of a phase according to one embodiment.

DETAILED DESCRIPTION

(7) FIG. 1 shows a wind power installation 100 for generating a multiphase electrical alternating current having a sinusoidal fundamental wave in each phase.

(8) For this purpose, the wind power installation 100 has a tower 102 and a nacelle 104. An aerodynamic rotor 106 having three rotor blades 108 and a spinner 110 is arranged on the nacelle 104. The rotor 106 is caused to rotate by the wind during operation and thereby drives a generator in the nacelle 104, wherein the generator is preferably in the form of a six-phase ring generator.

(9) FIG. 2 shows, in a simplified manner, an electrical section 200 of a wind power installation shown in FIG. 1.

(10) The electrical section 200 has a six-phase ring generator 210 which is caused to rotate by the wind via a mechanical drive train of the wind power installation in order to generate a six-phase electrical alternating current. The six-phase electrical alternating current is transferred, by the generator 210, to the rectifier 220 which is connected to the three-phase inverter 240 via a DC voltage intermediate circuit 230. The six-phase ring generator 210 which is in the form of a synchronous generator is electrically excited in this case via the excitation 250 from the DC voltage intermediate circuit 230.

(11) The electrical section 200 therefore has a full converter concept in which the network 270 is fed by means of the three-phase inverter 240 via the wind power installation transformer 260. This network 270 is usually a wind farm network which feeds an electrical supply network via a wind farm transformer. However, feeding directly into the electrical supply network instead of the farm network 270 also comes into consideration.

(12) In order to generate the three-phase current I1, I2, I3 for each of the phases U, V, W, the inverter 240 is controlled with a tolerance band method. In this case, the control is effected via the controller 242 which captures each of the three currents I1, I2, I3 generated by the inverter 240 by means of a current capture unit 244. The controller is therefore set up to individually control each phase of the inverter by means of the current capture unit 244. For this purpose, the controller 242 can specify a desired current value Isoll, on the basis of which the currents I1, I2, I3 are controlled. The desired current value Isoll is preferably individually calculated and specified for each phase U, V, W inside the installation.

(13) FIG. 3 schematically shows the structure of a generator apparatus 300 for generating an electrical three-phase alternating current by means of a tolerance band method. In particular, FIG. 3 shows a part which may be a part of the inverter shown in FIG. 2.

(14) The generator apparatus 300 has a DC voltage intermediate circuit 330 which is connected to the generator of a wind power installation via a rectifier. The DC voltage intermediate circuit 330 has a first potential Udc+ and a second potential Udc with a center tap M which is set up to be connected to a filter device in order to lead a filter connected at the output 346 of the inverter, for example, back to the DC voltage intermediate circuit 330. In addition, a capacitor having the capacitance C1, C2 is respectively arranged between the center tap M and the two potentials Udc+, Udc in order to store energy in the DC voltage intermediate circuit 330 and to accordingly smooth the DC voltage 2Udc.

(15) The inverter 340 which is connected to the DC voltage intermediate circuit 330 respectively generates a separate current I1, I2, I3 at the output 346 of the inverter 340 for each of the three phases U, V, W. For this purpose, the inverter 340 respectively has an upper switch T1, T3, T5 and a lower switch T2, T4, T6 for each of the three phases U, V, W, wherein the upper and lower switches T1, T2, T3, T4, T5, T6 are controlled by means of a tolerance band method, in particular via the controller 342.

(16) The controller 342 itself operates with a current-controlled tolerance band method. For this purpose, the controller 342 captures the currents I1, I2, I3 generated by the inverter 340 at the output 346 of the inverter 340 by means of a current capture unit 344. The currents I1, I2, I3 captured in this manner are compared with a desired value Isoll in order to determine the band limits OB12, UB12, OB34, UB34, OB56, UB56 for upper and lower switches T1, T2, T3, T4, T5, T6. The controller 342 also captures the switching frequencies f1, f2, f3, f4, f5, f6 of the individual upper and lower switches T1, T2, T3, T4, T5, T6 in order to respectively change a corresponding band limit OB12, UB12, OB34, UB34, OB56, UB56, by comparing the frequencies f1, f3, f5 of the corresponding upper switches T1, T3, T5 and the frequencies f2, f4, f6 of the corresponding lower switches T2, T4, T6, in such a manner that the difference between the switching frequencies f1, f2, f3, f4, f5, f6 of the respective upper switches T1, T3, T5 and of the respective lower switches T2, T4, T6 is minimized, in particular in such a manner that a signal component of the respective phase U, V, W superimposed on the respective sinusoidal fundamental wave is reduced.

(17) The indices of the band limits OB12, UB12, OB34, UB34, OB56, UB56 and of the switching frequencies f1, f2, f3, f4, f5, f6 each relate to the indices of the upper and lower switches T1, T2, T3, T4, T5, T6. Details of the band limits and switching frequencies are also explained, by way of example, for a first phase U in FIG. 5.

(18) FIG. 4 shows the schematic structure 400 of a part of the method, in particular for generating a single-phase electrical alternating current I1 of a phase U having a sinusoidal fundamental wave.

(19) The reference variable Isoll, that is to say the desired current value for the inverter, is passed to the tolerance block 480. The tolerance block 480 uses this to determine the corresponding band limits OB12, UB12 for the upper switch T1 and the lower switch T2 of the phase U. The upper switch T1 and the lower switch T2, which are represented by the block 484, then generate the single-phase electrical alternating current I1 of the phase U having a sinusoidal fundamental wave according to the band limits OB12, UB12, wherein the switches T1, T2 themselves have the actual switching frequencies fos, fus or are operated at said frequencies.

(20) The actual switching frequencies fos, fus of the upper and lower switches T1, T2 are captured and are passed to a frequency block 486 which determines a frequency difference f from said frequencies, that is to say the difference in the switching frequencies between the upper switch T1 and the lower switch T2. The frequency difference f itself is fed back to the band limits OB12, UB12 via a PI controller 482 in order to accordingly adapt the actual switching frequency fos, fus of the switches T1, T2.

(21) In addition, the single-phase alternating current I1 generated is determined by means of a current capture unit and is fed back to the switches T1, T2 in order to control the switches or the inverter on the basis of the current.

(22) FIG. 5 illustrates a method sequence 500 for changing a band limit for the purpose of reducing a DC component of a phase according to one embodiment.

(23) The upper and lower switches T1, T2 are controlled by means of a tolerance band method 590 and operate within the band limits OB12, UB12 which run around an optimum sine sin. The upper switch T1 operates at a first switching frequency fT1 and the lower switch T2 operates at a second switching frequency fT2. As a result, a DC component I1G is established in the phase U.

(24) The switching frequencies fT1, fT2 are captured by a controller in a first step 591 and are compared with one another in a second step 592. The frequency difference f resulting from the comparison is passed, just like the switching frequencies f1, f2, to the tolerance block 593 which uses it to determine a change in a band limit in such a manner that the signal component I1G superimposed on the respective sinusoidal fundamental wave sin is minimized.

(25) By way of example and in a highly simplified manner, the tolerance block 593 has determined a shift of the lower band limit 594 downward for the purpose of minimizing the DC component I1G because the values 2 and 3 were measured for the switching frequencies fT1, fT2 and a frequency difference f of 1 was therefore determined. This is transmitted to the upper and lower switches T1, T2.

(26) In a next step 595, the upper and lower switches T1, T2 now operate within the band limits OB12, UB12* which run around the optimum sine sin, that is to say the sinusoidal fundamental wave. The lower band limit UB12* was therefore changed. The upper switch T1 continues to operate at the switching frequency fT1 and the lower switch operates at the new switching frequency fT2*, wherein these switching frequencies fT1, fT2* are substantially the same, namely are both 2 in the simplified example, with the result that a DC component I1G*, assumed to be 0 here, is established in the phase U but is considerably smaller than the DC component I1G. The lower band limit UB12* modified here by way of example can retain its modified value even in the case of complete correction of the DC component by using a PI controller.

(27) In a next step 596, these switching frequencies fT1, fT2* can be captured again by the controller and can then be optimized further if necessary.