Wind power plant for feeding electrical power by means of full converters

Abstract

The invention relates to a method for feeding electrical power into an electrical supply grid. The method includes rectifying a first AC voltage of an electrical power, produced by a generator, into a first DC voltage and increasing the first DC voltage to a second DC voltage such that the second DC voltage has a step-up ratio in relation to the first DC voltage. Alternatively, the method includes rectifying the first AC voltage into the second DC voltage without producing the first DC voltage. The method includes inverting the second DC voltage into a second AC voltage for feeding electrical power into the electrical supply grid depending on an feed setpoint value and setting the second DC voltage depending on the feed setpoint value and actual value. The second DC voltage is increased depending on an increase in the feed setpoint voltage or actual value.

Claims

1. A method, comprising: generating a first DC voltage from a first AC voltage of generated electrical power generated by a generator, wherein generating the first DC voltage comprises: passive rectifying the first AC voltage into a second DC voltage and stepping up the second DC voltage to the first DC voltage so that the first DC voltage has a step-up ratio relative to the second DC voltage, inverting the first DC voltage into a second AC voltage for feeding the electrical power into an electrical supply grid depending on a feed set point value; wherein the first DC voltage depends on the feed set point value and on a current passing through a power choke, wherein the first DC voltage is increased when the feed set point value increases; and feeding the electrical power into the electrical supply grid via the power choke.

2. The method as claimed in claim 1, wherein: the setting the step-up ratio of the first DC voltage to the second DC voltage depends on the feed set point value; or the passively rectifying the first AC voltage into the first DC voltage depends on the feed set point value.

3. The method as claimed in claim 2, wherein the generating the first DC voltage comprises the passive rectifying, and wherein the step-up ratio is greater than 1 and less than 6.

4. The method as claimed in claim 2, wherein the step-up ratio is less than 4.

5. The method as claimed in claim 2, wherein the step-up ratio is set depending on the second DC voltage.

6. The method as claimed in claim 1, wherein the inverting the first DC voltage into the second AC voltage comprises using a tolerance band method.

7. The method as claimed in claim 1, wherein the first DC voltage depends on power received from the electrical supply grid.

8. The method as claimed in claim 7, wherein the power received from the electrical supply grid is reactive power.

9. The method as claimed in claim 1, wherein: the generator has an operating point depending on a prevailing wind or depending on a specification, and the first DC voltage additionally depends on the operating point.

10. The method as claimed in claim 1, wherein: a step-up converter is used for the stepping up the second DC voltage to the first DC voltage, and the step-up converter is controlled depending on at least one criterion from a list including: a harmonic content of a fed-in current; an operating point of a feed-in; a number of inverters used for inverting; an operating point of the generator; a reactive power set point value or an actual value of the reactive power; a detected line voltage of the electrical supply grid; a grid condition of the electrical supply grid; a positive sequence component of the fed-in current; a negative sequence component of the fed-in current; an impedance of a power choke; an excitation power of the generator when the generator is a separately excited synchronous generator; a specification of a grid operator; and grid sensitivity of the electrical supply grid.

11. The method as claimed in claim 1, comprising: determining the second DC voltage by directly measuring the second DC voltage or by detecting the generated electrical power generated by the generator, wherein the second DC voltage is higher than 100 V and lower than 800 V.

12. The method as claimed in claim 11, wherein the second DC voltage is lower than 400 V.

13. A method, comprising: generating a first DC voltage from a first AC voltage of generated electrical power generated by a generator, wherein generating the first DC voltage comprises: rectifying the first AC voltage into a second DC voltage and stepping up the second DC voltage to the first DC voltage so that the first DC voltage has a step-up ratio relative to the second DC voltage; inverting the first DC voltage into a second AC voltage for feeding the electrical power into an electrical supply grid depending on a feed set point value; wherein the first DC voltage depends on the feed set point value, wherein the first DC voltage is increased when the feed set point value increases; wherein: the step-up ratio sets the first DC voltage to be between 400 V and 1200 V; or the rectifying the first AC voltage into the first DC voltage sets the first DC voltage to be between 400 V and 1200 V, wherein: the feed set point value is a reactive power set point value; or the first DC voltage is set depending on a reactive current component of the electrical power fed into the electrical supply grid.

14. A wind power plant for feeding electrical power into an electrical supply grid, comprising: a generator configured to generate electrical power and for outputting a first AC voltage; a first rectifier configured to rectify the first AC voltage into a first DC voltage, and at least one step-up converter configured to step up the first DC voltage to a second DC voltage with a step-up ratio of the second DC voltage relative to the first DC voltage; a controller configured to set the second DC voltage depending on a feed set point value, wherein the feed set point value depends on an electrical characteristic of the supply grid, wherein the second DC voltage is increased depending on an increase in the feed set point value; at least one inverter configured to invert the second DC voltage into a second AC voltage for feeding the electrical power into the electrical supply grid depending on the feed set point value; and a power choke connected downstream of the at least one inverter.

15. A wind park with a plurality of wind power plants including the wind power plant as claimed in claim 14.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

(1) The invention is explained in greater detail hereinafter by way of example using embodiments with reference to the accompanying figures.

(2) FIG. 1 shows a perspective representation of a wind power plant.

(3) FIG. 2 shows a schematic representation of a wind park.

(4) FIG. 3 schematically shows a generator of a wind power plant and its connection to an electrical supply grid according to an embodiment.

(5) FIG. 4 shows a generator of a wind power plant and its connection to an electrical supply grid according to a further embodiment.

DETAILED DESCRIPTION

(6) FIG. 1 shows a wind power plant 100 with a tower 102 and a nacelle 104. A rotor 106 with three rotor blades 108 and a spinner 110 is arranged on the nacelle 104. During operation, the rotor 106 is transferred into a rotational movement by the wind and thus drives a generator in the nacelle 104.

(7) FIG. 2 shows a wind park 112 with three wind power plants 100 by way of example, which can be identical or different. The three wind power plants 100 thus represent essentially any number of wind power plants of a wind park 112. The wind power plants 100 provide their power, namely the generated current in particular, via an electrical park grid 114. In this case, the respectively generated currents or power from the individual wind power plants 100 are added up and a transformer 116 is usually provided which boosts the voltage in the park in order to then feed into the supply grid 120 at the feed-in point 118, which is also generally described as PCC. FIG. 2 is merely a simplified representation of a wind park 112, which does not show a control system, for example, although a control system is present, of course. The park grid 114 can also be configured in a different manner, for example, to name just one other example, wherein a transformer is also present at the output of each wind power plant 100, for example.

(8) FIG. 3 schematically shows a generator 300, which feeds into or is intended to feed into an electrical supply grid 302. The generator 300 is formed as a separately excited synchronous generator and has an armature 304 and a stator 306. The armature 304, which can also be described as a rotor but here is described as an armature, in order to avoid any confusion with an aerodynamic rotor of the wind power plant, rotates relative to the stator 306.

(9) The generator 300 shown is a separately excited synchronous machine here and in addition the armature 304 receives an exciting current I.sub.exc from an excitation converter 308.

(10) The generator 300 emits a stator voltage from the stator 306, which stator voltage forms the first AC voltage V.sub.AC1 here. This first AC voltage V.sub.AC1 is represented in three phases here. Preferably, provision can also be made for two three-phase AC voltages to be emitted which correspondingly form a six-phase AC voltage, which applies to all embodiments.

(11) This first AC voltage V.sub.AC1 is then rectified into the first DC voltage V.sub.DC1 by means of a first rectifying device which is formed as a passive rectifier 310 here.

(12) The first DC voltage V.sub.DC1 is stepped up to the second DC voltage V.sub.DC2 by means of the step-up converter 312. This second DC voltage V.sub.DC2 can also serve as a source for the excitation converter 308 which, however, is only one of a plurality of possibilities for supplying the excitation converter 308.

(13) The second DC voltage V.sub.DC2 is then converted into the second AC voltage V.sub.AC2 by means of the inverter 314. For this purpose, a tolerance band method is preferably proposed here which recirculates the resulting current and attempts to maintain it within a tolerance band by way of corresponding switching operations. However, details regarding this are not reproduced here. Depending on this second AC voltage V.sub.AC2, a current then arises which flows through the power choke 316 and then continues to flow into the electrical supply grid 302, i.e., is fed in there. In principle, the feed-in can take place via a transformer which can provide a boost to the second AC voltage V.sub.AC2 or the AC voltage at the output of the power choke, depending on the voltage level in the electrical supply grid 302. However, in this case, this boost is not important, such that a transformer of this type has been omitted for the sake of simplicity.

(14) It is now proposed that the second DC voltage V.sub.DC2 is increased or reduced as required. This can take place by way of the step-up converter 312 and/or the inverter 314. For this purpose, a measuring and control block 318 is provided which generates a corresponding set point value V.sub.DC2S and correspondingly provides it to the step-up converter 312 or the inverter 314. FIG. 3 shows both specifications, i.e., to the step-up converter 312 and to the inverter 314, however provision can alternatively be made for only one of the two possibilities to be used.

(15) For this purpose, the measuring and control block 318 receives at least one feed set point value which is illustrated here as P.sub.sp and Q.sub.sp. Preferably, the set point of the active power and/or set point of the reactive power is actually used, however other variables, and in particular also additional variables, are also possible.

(16) Using P.sub.sp and/or Q.sub.sp is thus using the corresponding feed set point value. In this respect, P.sub.sp or Q.sub.sp describes the active power which is to be fed in or reactive power which is to be fed in, and these are thus each feed set point values. These feed set point values are also specified to the inverter 314, since said inverter is intended to control the corresponding feed-in. It should be considered that FIG. 3 is illustrative in this respect and it is also possible that the inverter 314 inherently specifies its set point values to the measuring and control block 318, for example. It is also possible that the functionality of the symbolically represented measuring and control block 318 is accommodated in a common process computer which controls at least the inverter 314 and/or the step-up converter 312.

(17) For implementation, the step-up converter 312 can then implement a step-up ratio of the first DC voltage relative to the second DC voltage V.sub.DC1, V.sub.DC2, in particular by way of a duty cycle. The inverter 314, for which the second DC voltage V.sub.DC2 can also form its intermediate circuit voltage, can implement control of this second DC voltage V.sub.DC2 by feeding in more or less power. However, in this case, minor changes can be sufficient so that the specification of the set point values P.sub.sp and Q.sub.sp can still be substantially maintained. However, it is also possible to control the second DC voltage via the specification of P.sub.sp, at least partially.

(18) Setting the second DC voltage V.sub.DC2 can also take further input variables into account, which is illustrated here as the consideration of further input variables by the measuring and control block 318, wherein, however, it is actually also a variant that a measuring and control block 318 of this type is provided as an independent element.

(19) In this respect, FIG. 3 nevertheless illustrates that an excitation power or an exciting current I.sub.exc is taken into account. Such a current which is generated by the excitation converter 308 can be detected for this purpose, which is symbolized by FIG. 3. However, the excitation converter 308 can alternatively also emit corresponding information.

(20) Output values of the generator 300 can also be used, and in this case its operating point can also be used and in order to demonstrate this, values are recorded between the generator 300 and the passive rectifier 310 which are illustrated in a simplified manner as generator voltage V.sub.G, generator power P.sub.G and generator current I.sub.G.

(21) It is also possible to take into account the current which is fed in I.sub.E and it is also possible to take into account the line voltage V.sub.N. In principle, all of these considerations can also be combined. Better and more differentiated bases for setting the second DC voltage V.sub.DC2 are the result of combinations.

(22) A time progression for the first AC voltage V.sub.AC1, the first DC voltage V.sub.DC1, the second DC voltage V.sub.DC2 and the second AC voltage V.sub.AC2 is additionally represented in FIG. 3 by four schematic diagrams, namely in each case above the area of the structure shown in which they are encountered. It can be recognized therefrom, which is an idealized representation, that the first AC voltage V.sub.AC1 is rectified into the first DC voltage V.sub.DC1 and it is then increased to the voltage level of the second DC voltage V.sub.DC2. In the diagram of the second DC voltage V.sub.DC2, two arrows indicate that the voltage level can be increased or reduced. The second DC voltage V.sub.DC2 is then inverted into the second AC voltage V.sub.AC2.

(23) FIG. 4 corresponds substantially to FIG. 3, with the difference being that an active rectifier 413 is provided instead of the passive rectifier 310 and the step-up converter 312. This active rectifier 413 rectifies the first AC voltage V.sub.AC1 directly into the second DC voltage V.sub.DC2.

(24) Although this can also have different effects on the first AC voltage V.sub.AC1, which in turn can also have an influence on the operation of the generator 300, identical or at least similar elements are still described in a simplified manner in FIG. 4 with the same reference numbers in comparison to the structure of FIG. 3. These can actually be identical, are at least similar in their mode of operation. In this respect, for explanation, reference is also made to the explanation for FIG. 3.

(25) In this case, the structure of FIG. 4 is such that the second DC voltage V.sub.DC2 can be set by the active rectifier 413 and/or by the inverter 314. A combination is also possible in this case.

(26) In order for the active rectifier 413 to set the second DC voltage V.sub.DC2, this active rectifier 413 can correspondingly control its rectifying device. Controllable rectifying devices of this type can be controllable thyristors or IGBTs, for example.

(27) In comparison to FIG. 3, only three voltage diagrams are thus represented in FIG. 4, which voltage diagrams schematically show the respective voltage and in the representation in FIG. 4 are also each drawn above the respective point of the structure where the corresponding voltage is encountered.

(28) Correspondingly, the three diagrams initially show the first AC voltage V.sub.AC1 which is rectified into the second DC voltage V.sub.DC2 by means of the active rectifier and from which the second AC voltage V.sub.AC2 is then generated by inversion. The diagram also indicates here that the level of the second DC voltage V.sub.DC2 can be changed.