Method for feeding in an electrical alternating current

Abstract

A wind power installation and a method for feeding a filtered alternating current into an electrical supply grid by the wind power installation are provided. The wind power installation includes at least one inverter having an inverter output for providing an inverter current. The at least one inverter is coupled at its inverter output to an active filter. The active filter filters the inverter current provided at the inverter output and provides the filtered alternating current for feeding into the electrical supply grid. The method includes providing the inverter current at the inverter output by switching at least one switch of the inverter, sensing the switching, and controlling the active filter based on the sensed switching to filter the inverter current provided at the inverter output and produce the filtered alternating current.

Claims

1. A method for feeding a filtered alternating current into an electrical supply grid by a wind power installation, comprising: providing, at an inverter output of an inverter of the wind power installation, an inverter current by switching at least one switch of the inverter; sensing a switching state of the at least one switch of the inverter; and controlling an active filter, coupled to the inverter output, based on the sensed switching state to filter the inverter current provided at the inverter output and producing the filtered alternating current for feeding into the electrical supply grid.

2. The method for feeding the filtered alternating current as claimed in claim 1, wherein controlling the active filter includes: reducing a harmonic component of the filtered alternating current compared with the inverter current.

3. The method for feeding the filtered alternating current as claimed in claim 1, comprising: switching the at least one switch according to a switching frequency; and sensing the switching state of the at least one switch according to a sampling frequency that is at least twice the switching frequency.

4. The method for feeding the filtered alternating current as claimed in claim 1, comprising: controlling the active filter based on an activation signal initiating the switching of the at least one switch; or controlling of the active filter based on a control voltage initiating the switching of the at least one switch.

5. The method for feeding the filtered alternating current as claimed in claim 1, comprising: activating the inverter using a tolerance band method to provide the inverter current at the inverter output, wherein the active filter filters the inverter current based on the switching state of the at least one switch by the tolerance band method.

6. The method for feeding the filtered alternating current as claimed in claim 1, further comprising: switching the at least one switch using a tolerance band method that is based on the inverter current provided at the inverter output; and controlling the active filter based on the sensed switching state without taking into account the inverter current provided at the inverter output.

7. The method for feeding the filtered alternating current as claimed in claim 1, comprising: controlling of the active filter based on the sensed switching state to reduce at least one harmonic component of the inverter current, minimize a current harmonic component of the inverter current, or reduce a current harmonic component of one of a 1st current harmonic to a 60th current harmonic.

8. The method for feeding the filtered alternating current as claimed in claim 1, wherein: the inverter includes a plurality of inverter modules having a respective plurality of inverter module outputs for providing a plurality of inverter module currents, respectively, and the plurality of inverter module outputs are interconnected such that their respectively plurality of inverter module currents are superposed to form the inverter current; and a collective evaluation device senses and evaluates a plurality of activation signals of the plurality of inverter modules, respectively, and the collective evaluation device activates the active filter for filtering the inverter current.

9. The method for feeding the filtered alternating current as claimed in claim 1, comprising: controlling the active filter based on at least one direct current (DC) link voltage of the inverter or a current setpoint value for the inverter.

10. A wind power installation, comprising: an inverter with an inverter output for providing an inverter current; and an active filter, coupled to the inverter output, for filtering the inverter current to produce a filtered alternating current for feeding into an electrical supply grid, the active filter being configured to be controlled based on sensed switching state of at least one switch of the inverter to filter the inverter current and thereby produce the filtered alternating current.

11. The wind power installation as claimed in claim 10, comprising: a controller for controlling the inverter to provide, at the inverter output, the inverter current by switching the at least one switch.

12. The wind power installation as claimed in claim 10, wherein the inverter has at least six switches, and wherein two switches including an upper switch and a lower switch are switched to provide a current for each phase of the inverter current.

13. The wind power installation as claimed in claim 10, wherein the at least one switch of the inverter is an insulated-gate bipolar transistor (IGBT) or a metal oxide semiconductor field-effect transistor (MOSFET).

14. The wind power installation as claimed in claim 10, wherein the inverter is activated using a tolerance band method and the active filter filters the inverter current based on the switching state of the at least one switch generated by the tolerance band method.

15. The wind power installation as claimed in claim 10, comprising: a full power converter including the inverter as an inverter portion of the full power converter.

16. The wind power installation as claimed in claim 10, wherein the active filter has at least one active component that is at least one IGBT or one MOSFET configured to operate with a clocking frequency that is greater than a switching frequency of the at least one switch or greater than a switching frequency of multiple switches multiplied by a number of inverter modules of the inverter.

17. The wind power installation as claimed in claim 10, wherein: the inverter includes a plurality of inverter modules having a respective plurality of inverter module outputs for delivering a plurality of inverter module currents, respectively and the plurality of inverter module outputs are interconnected in such that the plurality of inverter module currents are superposed to form the inverter current; and the wind power installation includes a collective evaluation device configured to sense and evaluate activation signals of the plurality of inverter modules and activate the active filter for filtering the inverter current.

18. The wind power installation as claimed in claim 10, wherein the active filter has an output coupled to the inverter output, and wherein the active filter operates on the inverter output to reduce at least one current harmonic of the inverter current.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

(1) The present invention is now explained in more detail below, by way of example, 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 construction 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 construction of an inverter for providing an inverter current by means of a tolerance band method,

(5) FIG. 4 schematically shows the coupling of the active filter to the switches of a number of inverter modules and

(6) FIG. 5 schematically shows a control table of a collective evaluation device.

DETAILED DESCRIPTION

(7) FIG. 1 shows a wind power installation 100 for feeding electrical alternating current into an electrical supply grid.

(8) For this purpose, the wind power installation 100 has a tower 102 and a nacelle 104. An aerodynamic rotor 106 with 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, the generator preferably being in the form of a 6-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 6-phase ring generator 210, which is caused to rotate by the wind by way of a mechanical drive train of the wind power installation in order to generate a 6-phase electrical alternating current.

(11) The 6-phase electrical alternating current is transferred from the generator 210 to the rectifier 220, which is interconnected with the 3-phase inverter 240 by way of a DC voltage link 230.

(12) The 6-phase ring generator 210, which is in the form of a synchronous generator, is electrically excited in this case by way of the excitation 250 from the DC voltage link 230.

(13) The electrical section 200 consequently has a full converter concept, in which the grid 270 is fed by means of the 3-phase inverter 240. This grid 270 is usually a wind farm grid, which feeds into an electrical supply grid by way of a wind farm transformer. However, feeding directly into the electrical supply grid instead of the farm grid 270 also comes into consideration.

(14) Furthermore, a transformer may also be provided for feeding into the grid 270.

(15) To generate the three-phase current I.sub.1, I.sub.2, I.sub.3 for each of the phases U, V, W, the inverter 240 is controlled with a tolerance band method. In this case, the control takes place by way of the controller 242, which senses each of the three currents I.sub.1, I.sub.2, I.sub.3 provided or generated by the inverter 240 at the inverter output 246 by means of a current sensor 244.

(16) The controller is consequently designed to control each phase of the inverter individually by means of the current sensor 244. For this purpose, the controller 242 may prescribe a current setpoint value Isoll, in dependence on which the currents I.sub.1, I.sub.2, I.sub.3 are controlled. The current setpoint value Isoll is preferably individually calculated and prescribed for each phase U, V, W internally in the installation. The currents I.sub.1, I.sub.2, I.sub.3 thus generated are also referred to as an inverter current or inverter currents.

(17) The inverter 240 is also coupled at its inverter output 246 to an active filter 260, in order to filter the inverter current I.sub.1, I.sub.2, I.sub.3 provided at the inverter output 241 and thereby provide a filtered alternating current I*.sub.1, I*.sub.2, I*.sub.3 for feeding into the electrical supply grid.

(18) For this, the active filter 260 is controlled in dependence on the sensed switching actions of the switches of the inverter 240. That the active filter 260 is controlled in dependence on these switching actions is indicated by the signal line 262, which transfers the activation signals of the controller 242 to the switches of the inverter 240 also to the active filter 260.

(19) Also provided is a collective evaluation device 264, which is designed to sense the activation signals by means of the signal line 262 and further signal AS, such as, for example, the DC link voltage U.sub.DC and the current setpoint value I.sub.soll, and evaluate them. The collective evaluation device 264 then activates the active filter 260 in dependence on the activation signals thus sensed and evaluated and further signals AS.

(20) In order in particular to filter current harmonics up to the 60th order, the active filter 260 has low-pass characteristics, the active filter 260 being controlled by means of the activation signals for the switches of the inverter 240.

(21) FIG. 3 schematically shows the construction 300 of an inverter for providing an inverter current by means of a tolerance band method. In particular, FIG. 3 shows part of the electrical section that is shown in FIG. 2.

(22) The construction 300 has a DC voltage link 330 which is connected by way of a rectifier to the generator of a wind power installation. The DC voltage link 330 has a first potential U.sub.DC+ and a second potential U.sub.DC− with a center tap M. Also respectively arranged between the center tap M and the two potentials U.sub.DC+, U.sub.DC− is a capacitor with the capacitance C.sub.1, C.sub.2, in order to store energy in the DC voltage link 330 and smooth the DC voltage 2U.sub.DC correspondingly.

(23) The inverter 340, which is interconnected with the DC voltage link 330, generates respectively for each of the three phases U, V, W a separate current I.sub.1, I.sub.2, I.sub.3 at the output 346 of the inverter 340. The inverter 340 respectively has for this, for each of the three phases U, V, W, an upper switch T.sub.1, T.sub.3, T.sub.5 and a lower switch T.sub.2, T.sub.4, T.sub.6, the upper and lower switches T.sub.1, T.sub.2, T.sub.3, T.sub.4, T.sub.5, T.sub.6 being activated in particular by way of the controller 342 by means of a tolerance band method.

(24) The controller 342 itself operates with a current-controlled tolerance band method. For this, the controller 342 senses the currents I.sub.1, I.sub.2, I.sub.3 generated or provided by the inverter 340 at the output 346 of the inverter 340 by means of a current sensor 344. The currents I.sub.1, I.sub.2, I.sub.3 thus sensed are compared with a setpoint value Isoll, in order to determine the activation signals OB.sub.11, UB.sub.11, OB.sub.12, UB.sub.12, OB.sub.13, UB.sub.13 for upper and lower switches T.sub.1, T.sub.2, T.sub.3, T.sub.4, T.sub.5, T.sub.6.

(25) FIG. 4 schematically shows the coupling 400 of the active filter 460 to the switches OB.sub.11, UB.sub.11, OB.sub.21, UB.sub.21, OB.sub.31, UB.sub.31 of a number of inverter modules 410, 420, 430, the inverter module currents I.sub.11, I.sub.12, I.sub.13 of which are superposed to form the inverter current I.sub.1 of the phase U. FIG. 4 therefore shows a single-phase view of the phase U of a three-phase system, comprising the phases U, V and W.

(26) The inverter modules 410, 420, 430 are respectively connected on the DC side to a DC voltage link, which is indicated by the clamping voltage U.sub.DC+, U.sub.DC−.

(27) For providing the inverter module currents I.sub.11, I.sub.12, I.sub.13, the individual inverter modules 410, 420, 430 are activated by means of the activation signals A.sub.11, A.sub.21, A.sub.31. The activation signals A.sub.11, A.sub.21, A.sub.31 in this case prescribe a corresponding switching state to the upper switches OB.sub.11, OB.sub.21, OB.sub.31 and the lower switches UB.sub.11, UB.sub.21, UB.sub.31.

(28) The inverter module 410 is in this case the switching state +1, i.e., the upper switch OB.sub.11 is active and the lower switch UB.sub.11 is inactive.

(29) The inverter module 420 has in this case the switching state −1, i.e., the upper switch OB.sub.21 is inactive and the lower switch UB.sub.21 is active.

(30) The inverter module 430 has in this case the switching state −1, i.e., the upper switch OB.sub.31 is inactive and the lower switch UB.sub.31 is active.

(31) The activation signals A.sub.11, A.sub.21, A.sub.31 and also the DC link voltage U.sub.DC and the current setpoint value I.sub.soll for the inverter modules 410, 420, 430 are fed to the collective evaluation device 464, which transfers them to the control unit 468 of the active filter 460. The activation signals A.sub.11, A.sub.21, A.sub.31 are transferred to the collective evaluation device 464 as switching states, to be specific in the instantaneous state that is given by way of example as the three switching states +1, −1 and −1.

(32) The collective evaluation 464 is preferably designed for reproducing both the individual switching states of the individual inverter modules 410, 420, 430 and a collective switching state Σ of all of the inverters 410, 420, 430.

(33) In the present case, in the instantaneous state that is given by way of example the collective switching state Σ is −1. On the basis of the collective switching state Σ, the control unit 468 of the active filter can then determine the rise of the corresponding flanks of the tolerance band method of the inverter modules 410, 420, 430 and correspondingly activate the switches of the active filter by means of the activation signal S.sub.F in such a way that the filtered alternating current I.sub.C has less harmonics than the inverter current I.sub.1.

(34) For this, the control unit 468 controls the switches IG.sub.11, IG.sub.12 of the active filter 460 in dependence on the three switching states +1, −1 and −1 and also the DC link voltage U.sub.DC and the current setpoint value Isoll by the activation signal SF, which likewise prescribes a switching state +1 for the switches IG.sub.11, IG.sub.12 of the active filter 460. The active filter 460 generates from this by means of a DC voltage source C.sub.F a filter current I.sub.F, which is superposed with the inverter current I.sub.1 to form a filtered alternating current I*.sub.1.

(35) The control of the switches IG.sub.11, IG.sub.12 of the active filter 460 may take place, for example, by means of a look-up table, in which the switching states of the switches IG.sub.11, IG.sub.12 of the active filter 460 in dependence on the switching states of the upper and lower switches OB.sub.11, OB.sub.21, OB.sub.31, UB.sub.11, UB.sub.21, UB.sub.31 of the inverter modules 410, 420, 430 are stored.

(36) The look-up table may in this case be stored either in the collective evaluation device 464 or in the control unit 468 of the active filter 460. Such a look-up table, which is also referred to as a control table, is represented by way of example below in FIG. 5. The collective evaluation device 464 may be digital logic or a digital circuit, an analog circuit, a controller, a microcontroller or a microprocessor, among others. The collective evaluation device 464 may include memory for data storage and well as one or more analog or digital comparators. The collective evaluation device 464 may receive data, process the data according to a truth table and output data based on the processing. The control unit 468 may be a controller, a microcontroller or a microprocessor, among others.

(37) FIG. 5 schematically shows a control table 500 of a collective evaluation device. In particular, FIG. 5 shows here a control table of the collective evaluation device 464 shown in FIG. 4.

(38) Entered in the top row 510 are the activation signals A.sub.11, A.sub.21, A.sub.31 of the upper and lower switches, the collective switching state Σ and the activation signal S.sub.F of the active filter.

(39) The individual columns 520, 530, 540, 560 also have the corresponding switching states of the activation signals A.sub.11, A.sub.21, A.sub.31, S.sub.F. The column 550 reproduces the corresponding collective switching state Σ.

(40) Corresponding to FIG. 4, the row 570 shows that the activation signals A.sub.11, A.sub.21, A.sub.31, which comprise the switching states +1, −1 and −1, have the effect that the switching state +1 is transmitted to the switches of the active filter.

(41) For a simplified representation, it has been assumed here that the DC link voltage U.sub.DC and the current setpoint value I.sub.soll are constant and have no influence on the values of the table. In a preferred embodiment, however, they are taken into account, which is indicated by S.sub.F(U.sub.DC, I.sub.soll). The control table would then have to be correspondingly supplemented by adding the columns for the DC link voltage U.sub.DC and the current setpoint value I.sub.soll.