EP2227853A1

EP2227853A1 - Method for operating a wind energy installation

Info

Publication number: EP2227853A1
Application number: EP09700812A
Authority: EP
Inventors: Stephan Engelhardt; Andrzej Geniusz
Original assignee: Woodward SEG GmbH and Co KG
Current assignee: Woodward Kempen GmbH
Priority date: 2008-01-07
Filing date: 2009-01-06
Publication date: 2010-09-15
Also published as: DE102008003299A1; CN101919143B; CN101919143A; US20100277134A1; US8487461B2; WO2009087150A1; DE102008003299B4

Abstract

The invention relates to a method for operating a wind energy installation with a doubly fed asynchronous machine, at least one inverter and at least one control device, wherein electrical energy is at least partly fed into a grid via the inverter, the inverter comprises per phase at least one power semiconductor module with at least two transistor circuits and at least two freewheeling diodes and the inverter is driven at least at certain times by means of pulse width modulation (PWM) using the control device. The object, namely of providing a generic method for operating a wind energy installation in which an improved power output is effected even in the low-noise rotational speed range of the rotors, is achieved by virtue of the fact that, at frequencies of the current to be impressed by the inverter on the machine side of less than 10 Hz, preferably less than 6 Hz, the switched-on duration and/or the switching frequency of the transistor circuits and/or of the freewheeling diodes of the inverter are altered depending on their thermal behaviour by means of the control device.

Description

Method for operating a wind energy plant

The invention relates to a method for operating a wind energy plant with a double-fed asynchronous machine, at least one inverter and at least one control device, wherein over the

Inverter at least partially electrical energy is fed into a network, the inverter per phase at least one power semiconductor module comprising at least two transistor circuits and at least two freewheeling diodes and the inverter using the control device is at least temporarily controlled by a pulse width modulation (PWM). In addition, the invention relates to a computer program and a computer program product for carrying out the method using a processor and a control device of a double-fed asynchronous machine of a wind turbine and a wind turbine.

Wind turbines are becoming increasingly demanding in terms of their efficiency and quietness. Since the noise of the wind turbine increases with increasing rotor speed, a simple way to reduce the noise of a wind turbine, is to reduce their rotor speeds. When reducing the rotor speeds, it may happen that the double-fed asynchronous machine must be operated for a longer time in the synchronous operating range. Usually, in the double-fed induction machine rotor side of the Inverter provided. In the synchronous operating range, currents with very low frequencies in the range of a few hertz are impressed on the rotor side, which are provided via a machine-side inverter. The machine-side inverter is thus dependent on the

Frequency of the rotor side impressed currents operated. The control of the inverter is done conventionally via a pulse width modulation in which the rotor required side currents determined at a high, constant frequency and the power semiconductor modules each phase of the inverter for generating the rotor currents on and off. At very low frequencies, the components of the power semiconductor modules, usually these are a transistor circuit and a freewheeling diode of a corresponding phase, are not uniform in time, but are rather punctually loaded in comparison to their thermal cooling behavior. The components of the

Power semiconductor modules, usually two IGBT modules and two freewheeling diodes per phase, are heated strongly due to the longer duty cycle, without the heat dissipation a

Reduction of the temperature allows. Due to the thermal behavior of the transistor circuits and the freewheeling diodes, these are partially heated to their maximum component temperature. The only option in the synchronous operating range of the double-fed

Asynchronous machine to prevent a corresponding heating, is the reduction of the rotor currents in this rotor speed range. This leads to a significant power loss in these rotor speed ranges. The use of additional gears to avoid this

Speed ranges do not seem practical, as any additional mechanical installation is prone to wear. Another way to avoid the performance dips consists of over-dimensioning the inverter and thus the power semiconductor modules, so that they are not heated too much even in the synchronous operating range. Against this, however, speaks that it is associated with significantly higher investment costs.

Based on this prior art, the present invention has for its object to provide a generic method for operating a wind turbine, in which there is an improved power output even in the low-noise speed range of the rotors.

The above object is achieved according to a first teaching of the present invention by a generic method, characterized in that at frequencies of the machine side einzuprägt by the inverter currents of less than 10 Hz, preferably less than 6 Hz, via the control device, the duty cycle and / or Switching frequency of the transistor circuits and / or the freewheeling diodes of the inverter can be changed depending on their thermal behavior.

In contrast to the conventional control of the power semiconductors via a PWM according to the invention can influence the heating of the power semiconductor modules are taken, so that it is possible to specifically select the heating of the transistor circuits and / or the freewheeling diodes, ie with deviation from the conventional PWM method with constant pulse rate. As a result, it is possible, for example, via the distribution of the current paths to different freewheeling diodes or transistor circuits of the individual phases to achieve improved heat distribution. As a result, the power output of the Wind turbine can not be reduced or not so much, since higher output currents can be generated with the same design.

Is according to a first embodiment of the present

Invention uses a rotor-side inverter, it is possible to dimension the inverter smaller due to its rotor-side arrangement, since the largest part of the electrical power output is fed into the stator on the stator side.

The further improved power output of a wind turbine in the synchronous operating range of the double-fed induction machine can be achieved according to a next embodiment of the method according to the invention characterized in that the duty cycle and / or the switching frequency of the transistor circuits and freewheeling diodes at least depending on the ratio of the respective component temperature to the maximum junction temperature is selected. This refinement of the method according to the invention takes into account that the losses energies of the free-wheeling diodes and the transistor circuits usually designed as IGBT modules are different, so that different component temperatures are present for the same current load of the transistor circuit and the freewheeling diode. By taking into account the different heating behavior, it is possible to exploit additional reserves in the power semiconductor module, without reaching the range of critical junction temperatures of the component temperature.

If the dependence of the duty cycle and / or the switching frequency of the transistor circuits and the freewheeling diode Predetermined from the component temperature by a simulation of the thermal behavior of the components can be estimated in a simple way, the heating of the components and be taken into account at machine side current frequencies of less than 10 Hz, in particular less than 6 Hz.

Cumulatively or alternatively to a simulation of the thermal behavior of the components as a function of the duty cycle or switching frequency, it is possible via sensors to determine the component temperatures. Temperature sensors are usually not placed directly on the components themselves, that is, for example, on the free-wheeling diodes, but in their vicinity, so that the heating of the free-wheeling diode or of the IGBT can be determined via a temperature model. Using the temperature model, the sensor provides a measure of the current component temperature, so that, in particular together with a simulation of the thermal behavior, an even more exact utilization of the component reserves with regard to the maximum component temperature is made possible.

The thermal heating of the components is also determined by power losses, which are generated in particular during the switching on and off operations. If according to a next embodiment of the method according to the invention the number of switching operations in the power semiconductor module is reduced, additional power reserves can therefore be achieved at the same time.

Preferably, to reduce the switching operations, the power semiconductor modules using a

Fiattopverfahrens or via predicted pulse pattern driven. In Fiattopverfahren is instead of a space vector modulation within a predetermined Angle range for the voltage or current to be modulated to leave exactly one output voltage or -ström a component in full scale and thus reduces the number of switching operations. Typical angular ranges of the current or voltage vector, in which the modulation is kept constant, are 30 °, 60 ° and 120 °. In the case of predicted pulse patterns, these are calculated in advance, taking into account various parameters, for example the different power losses and junction temperatures of the transistor circuits and freewheeling diodes, and stored in a table as pulse patterns for entire periods. In operation, the control device outputs only the input variables, for example the rotor currents to be impressed, corresponding pulse patterns for controlling the machine-side inverter. The switching frequency can also be easily reduced in this way, since the operating ranges can be operated with a lower machine-side power frequency with lower switching frequencies.

According to a second teaching of the present invention, the object indicated above is achieved by a computer program with instructions whose execution causes a processor to carry out the method according to the invention. The same applies to a computer program product, the one

Computer program contains commands whose execution causes a processor to perform the inventive method. With regard to the advantages of the computer program or computer program product according to the invention, reference is made to the description of the method according to the invention.

The above object is achieved according to a fourth teaching of the present invention by a control device a double-fed asynchronous machine of a wind turbine solved, wherein the control device controls an inverter of a double-fed asynchronous machine for feeding electrical energy into a network and means are provided for controlling the inverter according to the inventive method. The control device according to the invention allows the operation of a double-fed asynchronous machine of a wind turbine even in the synchronous operating range, without the power output must be significantly reduced.

The same finally applies to a wind turbine comprising a double-fed asynchronous machine, at least one inverter and a control device for carrying out the method according to the invention, wherein the

Wind turbine can be operated in the rotor speed ranges with less noise.

There are now a variety of ways the inventive method, the control device and the wind turbine to design and develop. For this purpose, on the one hand reference is made to the claims subordinate to claim 1 and on the other hand to the description of embodiments in conjunction with the drawings. In the drawing shows

Fig. 1 is a circuit diagram of a

Power semiconductor module from the prior art, as used in wind turbines per current or voltage phase, Fig. 2a) to 2c) typical current-time diagrams of a

Pulse width modulation control of the power semiconductor module of FIG. 1,

Fig. 3a) and 3b) current-time diagrams of

Power semiconductor module of FIG. 1 driven according to a

Embodiment of the method according to the invention,

4 is a circuit diagram of the machine-side, three-phase inverter, as known from the prior art,

Fig. 5 space vector diagram of another

Embodiment of the method according to the invention Fiattopverfahren,

Fig. 6 pulse pattern for controlling the power semiconductor modules of the lines

Ll, L2, L3 according to a further embodiment of the method according to the invention and

Fig. 7 is a schematic representation of a

Embodiment of a wind turbine according to the invention.

Fig. 1 shows first a circuit diagram of a single-phase inverter, as it is known from the prior art. The transistor circuits 1 and 2, which are usually embodied as IGBT modules, together with the freewheeling diodes 3 and 4 connected in parallel, ensure that switching occurs or igniting the IGBT modules 1 and 2 at the output 5, a corresponding current flows with positive or negative signs. For example, the IGBT module 1, together with the free-wheeling diode 4, provides a current flow with a positive sign. The opposite applies to the IGBT module 2 together with the freewheeling diode 3. The IGBT modules 1, 2 and the freewheeling diodes 3, 4 are connected to a voltage source V, which may be, for example, the DC link voltage of the inverter. The voltage-time diagram in FIG. 2a) now shows the profile of a control voltage 6 which is used to control the inverter and the profile of an associated auxiliary voltage 7, as used in conventional pulse-width modulation. At intersections of the auxiliary voltage and the control voltage, the corresponding IGBT modules are switched on or off.

For the positive half cycle of the control voltage 6, the corresponding currents in the IGBT modules 1 Ii and in the freewheeling diode 4 I ₄ are shown in FIGS. 2 b) and 2 c). It can be seen in Fig. 2b) that the IGBT module 1 during the positive

If the control voltage has a sufficiently high frequency, for example mains frequency of 50 to 60 Hz, is due to the slow heat dissipation from the IGBT modules 1, 2 or the Free-wheeling diodes 3, 4 a thermal equilibrium, which leads to a uniform heating of the modules or the freewheeling diodes, wherein the maximum current output of the single-phase inverter shown in Fig. 1 via the constant heating of

Power semiconductor 1, 2, 3, 4 is determined in comparison to the maximum permissible junction temperature of the respective components. In the case of particularly low frequencies of the control voltage, for example less than 10 Hz or 6 Hz, as they occur, for example, in the synchronous operating range of double-fed asynchronous machines, it is easy to imagine that the control voltage 6 assumes the same value over a much longer period. In the present example, this leads to the fact that the IGBT module 1 is actuated significantly longer in relation to the freewheeling diode 4 and is therefore subject to a much greater degree of heating and no equilibrium can be established between heating and heat dissipation.

Moreover, a comparison of Figures 2b) and 2c) shows that, regardless of the thermal properties of the components, i. the IGBT modules 1 and the freewheeling diode 4, the control via the pulse width modulation takes place. It can be clearly seen that the freewheeling diode 4 has significantly shorter switching cycles or current-carrying time cycles.

FIGS. 3a) and 3b) now show a current-time diagram which is generated using the method according to the invention, wherein the on and off phases of the IGBT module 1 and the freewheeling diode 4 are chosen as a departure from the conventional pulse width modulation. The

Duty cycle of the freewheeling diode 4 and the IGBT module 1, for example, advantageously depending on the ratio of the respective component temperature to the maximum junction temperature of the IGBT module or the freewheeling diode can be selected. In the present example, the freewheeling diode 4 has significantly larger reserves in relation to the maximum junction temperature and is driven longer than conventionally. The turn-on of the IGBT module 1 is reduced in order to better distribute the flow of current through both components. Overall, there is an improved distribution of the power losses on both components, IGBT module 1 and freewheeling diode 4. Preferably, the duty cycle is selected so that the component temperatures of the IGBT module 1 and the freewheeling diode 4 with respect to the maximum permissible junction temperature have the same reserves.

In order to explain a further embodiment of the method according to the invention in more detail, a circuit diagram of a three-phase inverter is shown in Fig. 4, in which the IGBT modules as switches 1, 2, 5, 6, 9, 10 are shown. For each IGBT module 1, 2, 5, 6, 9, 10 each freewheeling diodes 3, 4, I ₁ 8, 11, 12 are provided. The power semiconductors 1, 2, 3, 4 supply phase Ll, the power semiconductors 5 to 8 phase L2 and the power semiconductors 9 to 12 phase L3 with power.

The three-phase structure can now be taken into account to the number of switching operations in power semiconductor modules according to a next embodiment of the invention

Reduce the process so that lower power losses occur and thus the heating of the individual power semiconductors is lower.

The space vector diagram in Fig. 5 shows three space pointer areas

13, 14, 15, in which according to the inventive method, a component, for example, Ll is considered maximally controlled. An arbitrary voltage or current space pointer s within the range 13 can then be achieved by a vector addition of the components along the axes Ll, L2 and

Generate L3, wherein, as already stated, in the space vector area 13, the component Ll maximum (= 1) is controlled. The associated vector addition is via the circuit of other power semiconductor modules of the phases L2 and L3, which are denoted here by 16 and 17. In the present embodiment, the solid angle range in which a component is fully controlled is 60 °. The solid angle range can also be chosen differently, for example 30 °. It is clear that the components of the phase Ll, the components 1,2,3,4 are not switched in the selected solid angle range, because they are fully controlled, so that there is a reduction in the number of switching operations in a current path. The reduction of the switching operations in turn leads to a reduction in the heat loss in the power semiconductors, so that their current output can be increased.

Another way to reduce the number of switching operations is achieved by using precalculated pulse patterns to drive the power semiconductors. Corresponding pulse pattern for controlling the power semiconductors of the individual phases Ll, L2 and L3 is shown in FIG. 6. For each angular position αi, c < ₂ , cx ₃ , a specific switching pattern is stored in a table and called up according to the phase position. By optimizing the pulse patterns for low switching frequencies and their thermal effect on the power semiconductors, it is possible to further reduce the number of switching operations. As a result, as in the Fiattopverfahren, less power dissipation generated in the power semiconductors, which leads to an improvement in power reserves.

Finally, FIG. 7 shows a sketch in a sketch

Wind turbine with a propeller 18, which is optionally connected via an unillustrated transmission with the rotor 19 of the double-fed asynchronous machine 20. Of the Stator 21 of the double-fed asynchronous machine 20 is connected via a transformer 22 to a network 23 in the present embodiment. In the present embodiment, a control device 24 determines the rotor speed and compares it with the on the

Measuring points 25 and 26 detected voltages or currents on the stator 21. The control device 24 is connected to the rotor side inverter 27 and controls on the one hand the network side inverter 27 a and on the other hand, the machine provided inverter 27 b. Now reaches the wind turbine due to a reduction in the rotor speed, the synchronous operating range, for example, to reduce the noise, currents are injected with the lower frequency via the rotor. So far, as already stated, at frequencies of less than 10 Hz or less than 6 Hz, the output of the wind turbine significantly reduced in order to protect the power semiconductors from overheating.

On the other hand, the wind turbine according to the invention switches over the inventive control device 24 from the conventional pulse width modulation control of the inverter 27b at current frequencies of less than 10 Hz or 6 Hz to the method according to the invention, which determines the duty cycle and / or the switching frequencies of the

Transistor circuits and freewheeling diodes depending on their thermal behavior changed. By changing the driving method is achieved that the power reduction in the range of synchronism of the double-fed asynchronous machine at constant

Design of the rotor-side inverter does not turn out as strong as usual. As a result, the wind turbine can also operate in low-noise rotor speed ranges be operated without a large loss of performance.

Claims

claims

1. A method for operating a wind turbine with a double-fed asynchronous, at least one inverter and at least one control device, wherein at least partially electrical energy is fed via the inverter into a network, the inverter per phase at least one power semiconductor module comprising at least two transistor circuits and at least two freewheeling diodes and the inverter is driven using the control device at least temporarily via a pulse width modulation (PWM), characterized in that at frequencies of the machine to be impressed by the inverter streams of less than 10 Hz, preferably less than 6 Hz via the control device, the duty cycle and / or Switching frequency of the transistor circuits and / or the freewheeling diodes of the inverter can be changed taking into account their thermal heating.

2. The method of claim 1, wherein a rotor-side inverter is used.

3. The method according to claim 1 or 2, characterized in that the duty cycle and / or the switching frequency of Transistor circuits and / or freewheeling diodes is selected at least in each case depending on the ratio of the respective component temperature to the maximum junction temperature.

4. Method according to one of claims 1 to 3, characterized in that the switch-on duration of the transistor circuits and the freewheeling diodes is selected so that the component temperatures are in each case in the same ratio to the maximum junction temperature of the respective component.

5. The method according to claim 1, wherein the dependence of the switch-on duration and / or the switching frequency of the transistor circuits and the freewheeling diode on the component temperature is predetermined by a simulation of the thermal behavior of the components.

6. Method according to one of claims 1 to 5, characterized in that the component temperatures are determined via sensors.

7. The method of claim 1, wherein the number of switching operations in the power semiconductor module is reduced.

8. The method according to any one of claims 1 to 7, characterized in that to reduce the switching operations the Power semiconductor modules are controlled using a Fiattopverfahrens or precalculated pulse pattern.

A computer program comprising instructions whose execution causes a processor to perform the method of any one of claims 1 to 8.

A computer program product containing a computer program having instructions whose execution causes a processor to perform the method of any one of claims 1 to 8.

11. Control device of a double-fed asynchronous machine of a wind turbine, wherein the Steuerungεvorrichtung controls an inverter of a double-fed asynchronous machine for feeding electrical energy into a network and means are provided for controlling the inverter according to a method of claim 1 to 8.

12. Wind energy plant comprising a double-fed asynchronous machine, at least one inverter and control device for carrying out a method according to one of claims 1 to 8.