Method of air turbine operation and air turbine for performing this method

A method of operating a wind turbine and a wind turbine for performing the method

Technical field

The invention relates to a method of operating a wind turbine in which the rotor windings of an asynchronous generator comprising stator coils connected to a grid voltage supplied or supplied by rotor currents by a power supply or supply unit are driven by a wind turbine rotor. wherein the frequencies of the supply or supply rotor currents are controlled as a function of the rotational speed of the rotor, and the supply unit is electrically disconnected from the rotor windings in the event of predetermined variations in the voltage distribution network. The invention further relates to a wind turbine for carrying out this method.

BACKGROUND OF THE INVENTION

Wind power plants experience extreme and short-term fluctuations in primary energy supply due to wind gusts. For this reason, variable speed generators are used for generating electricity by wind turbines, since by using such generators wind energy is not immediately supplied to the distribution network, but accumulates in the centrifugal masses of the wind turbine by changing the rotational speed. In this way, the mechanical loads of the wind power plant can be substantially reduced compared to fixed speed power plants, and the mechanical parts can be designed and constructed to be light in weight and cost-effective. Asynchronous generators typically use asynchronous 4 generators in which their stator coils are directly connected to the grid and whose rotor windings are driven by the rotor of the wind power plant and fed by rotor currents using suitable converters. That is, the frequencies of the supplied rotor currents are controlled in such a way that the sum of the rotor rotation frequency and the rotor current frequency is constantly equal to the grid distribution frequency. Rectifier converters connected to the grid can be used to power the rotor windings, as well as auxiliary voltage circuit converters with a grid converter and a rotor power converter connected thereto via inductive and / or capacitive reactive resistance.

When using rectifier converters and using auxiliary voltage circuit converters, there is a problem that large voltage differences occur between the distribution network and the stator coils due to changes in the supply voltage amplitudes caused by the distribution network, such as short connections. These differences in turn cause large currents to occur in the stator coils directly connected to the distribution network. These high currents are generated in the stator coils because the asynchronous generator is usually fully excited by changing the amplitude of the distribution grid frequency and the mechanical power is permanently supplied by the rotor. The occurrence of large currents in the stator coils due to changes in the supply voltage leads to high induced voltages in the rotor windings, which in turn can damage the inverters used to supply the rotor current. When using an auxiliary voltage circuit converter, the inverse diodes of the rotor power converter can be completely destroyed due to high currents caused by voltages induced in the rotor windings. For this reason, in the known operation of an asynchronous generator wind power plant, the power supply unit used to supply the rotor currents due to voltage variations of the auxiliary circuit is usually disconnected from the rotor windings, especially when the voltage drops are caused by short connections. ·························

9 · · · · · · · · · · · · · · · · · ·. In this way to prevent damage to the power supply unit or converter due to voltages or currents induced in the rotor windings. After the supply voltage has stabilized, in the known methods the rotor current supply is restored to drive the asynchronous generator and re-synchronize with the distribution network. These methods are described, for example, in "Siemens - Energietechnik 5" (1983) Vol. 6, p. 364-367: 'Einsatz einer doppelt gespeisten Asynchronmaschine in der Grossen Windenergieanlage Grovian'. The contents of this document relating to the disconnection of the converter from the rotor windings are explicitly incorporated herein by reference. The duration of the interruption of the operation of the asynchronous generator between the drop in the supply voltage, which can lead to a drop in the supply voltage amplitude up to 15% of the setpoint, and a recovery of the supply voltage to e.g. 80% of the setpoint can usually be only a few seconds wind power efficiency.

Increasing the number of uses of regenerative energy sources, such as wind turbines, for generating electricity, has the problem that the duration of the supply voltage drop is considerably prolonged because insufficient energy is available to quickly stabilize the supply voltage after a voltage drop.

SUMMARY OF THE INVENTION

In light of these problems in the known embodiments, it is an object of the present invention to improve the known methods of operation of a wind power plant, which improvement should be used to stabilize the supply voltage after voltage drops without jeopardizing the electrical components of the wind power plant. such ways.

According to a first aspect, the object is solved by improving the known methods of operation of a wind power plant, the method of operation of a wind turbine, in which the rotor windings of an asynchronous generator comprising stator coils connected to grid voltage are supplied or fed by rotor currents. Wind turbines wherein the frequencies of the supply or supply rotor currents are controlled as a function of the rotational speed of the rotor and the supply unit is electrically disconnected from the rotor windings according to the invention in the event of predetermined voltage amplitude variations of the distribution network. caused by a change in the amplitude of the voltage, it recovers when the currents generated in the rotor windings by this change fall to a predetermined value.

This improvement relates to the finding that the high currents induced in the rotor windings when the supply voltage drops, will decrease and / or disappear after disconnecting the inverters that are used to supply the rotor currents, for example by shorting the rotor windings over a resistor having a low impedance of 50 up to 150 ms, so that the rotor current supply can be restored after this short time without endangering the inverters. In addition, taking into account the fact that even if the supply voltage drops to 15% of the setpoint, reliable detection of phase position and zero passages is possible, the regulated power supply of the wind power to the distribution grid can be restored by correspondingly controlling the amplitude and phase position of the supplied of the rotor currents immediately after reducing the currents induced in the rotor windings. In this way, the wind power plant contributes to stabilizing the supply voltage, which can remain at about 15% of the supply voltage for a time period of 500 ms, so that after the induced currents are reduced and / or disappeared in the rotor. · 'S. ····. ·· ····

J · ♦ ··· ♦ ·· ···· · ·· ·· ·· winding time period longer than 300 ms. During this time period, the wind turbine can contribute to stabilizing the supply voltage before the supply voltage increases again and cause a new increase in the currents induced in the rotor windings, which may make it necessary to disconnect the power supply unit or converters from the rotor windings again. .

During this time period, a multiple of the rated current of the power plant can be fed to either the distribution network or the short circuit, causing a drop in the supply voltage.

In principle, recovery of the rotor current supply can be achieved provided that the predetermined time is constant. From the standpoint of increasing plant safety, it has proven particularly advantageous when the rotor current supply is restored when the rotor current is sensed as a two or three-phase signal or when the rectified current is sensed as a single-phase signal and the current that is sensed drops to a predetermined value. Transformers (for example, compensated current transformers) can be used to sense currents.

Consideration should also be given to increasing the amplitude of the supply voltage to a desired value within less than one millisecond of supply voltage recovery. Therefore, a DC voltage and an AC voltage of 50 Hz can be induced in the rotor, so that it may be necessary to disconnect the rotor windings from the power supply unit again, for example by shorting the rotor windings. The generator is partially disconnected from the voltage by quasi-short-circuited rotor windings. As a result, depending on the actual rotational frequency, the DC component decreases and the 50 Hz AC component becomes effective. If at the time of the supply voltage drop (undervoltage occurring in the distribution network), φφ φφφφ φ φ · φ φ · · φ

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ΦΦΦ Wind speed in the subsynchronous range, restoring the supply voltage leads to an attempt to short-circuit the motor to jump to the synchronous speed in motor mode. This means that when the supply voltage returns, the wind turbine can obtain current. If the wind speed of the wind turbine was in the above-synchronous range at the time of the voltage drop (grid undervoltage occurrence), repeating the supply voltage causes the motor to jump to the synchronous rotation frequency in generator mode. This means that when the supply voltage returns, the wind turbine supplies power. When the amplitude of the rotor current drops sufficiently below 100 to 200 ms, the rotor current supply can be restored in the method of the invention when the supply voltage is restored.

As already explained above, it may be particularly advantageous within the scope of the invention that the rotor windings are short-circuited to disconnect from the supply or supply unit, so that the currents induced in the rotor windings can be reduced particularly quickly. Therefore, a so-called "lever" can be used, which short-circuits the rotor windings through a low impedance resistor, in particular through impedance, and reduces motor excitation. This so-called lever can be realized, for example, in the form of a partially regulated bridge B6. When an auxiliary voltage circuit converter is used, the rotor current converter can be locked at the same time, since the grid converter remains connected to the grid and provides apparent power. As explained above, in this case, the rotor current and the starting current fall within a time span of 50 to 150 ms depending on the resistance.

According to a preferred embodiment of the invention, the control device is designed to control the amplitude and / or phase position of the currents induced in the rotor windings. Active power and reactive power • to ··· · to · · · to · to · to · to · to · ♦ · to * · · · The asynchronous generator can be regulated depending on each other by changing the phase position.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in more detail with reference to the drawings, to which reference is made explicitly for any detail that may be relevant to the invention but is not explained in detail in the description. In the drawings, Fig. 1 shows a schematic diagram of a wind power circuit according to the invention with an asynchronous dual-power generator and a converter in the rotor circuit; Fig. 2 shows a typical change in voltage drop over time; .

DETAILED DESCRIPTION OF THE INVENTION

According to Fig. 1, a wind turbine according to the present invention comprises a rotor 10 which is rotatably arranged about a substantially horizontal axis and which is connected via an transmission 20 to an asynchronous generator 30. The asynchronous generator 30 comprises stator coils 32 connected to a grid and rotor windings 34 connected via gearbox 20 to rotor 10 ..

Rotor frequency is sensed by sensor 40. Rotor currents are fed to the rotor windings via transducer 50. Transducer 50 comprises a mains-side inverter 52 and a rotor inverter 54 connected thereto via DC. · · · · · · · · · · ·

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Next, a short-circuiting element 60, which is designed as a so-called "lever", is used, whereby the windings of the rotor 34 can be short-circuited by a low impedance resistor. A sensor 40 detecting the rotational speed of the rotor 34 is coupled to the rotor converter 54 on the rotor side to allow regulation of the frequency of the currents fed in the rotor windings as a function of the rotational speed of the rotor. Further, a rotor filter 70 formed as a low-pass filter is provided between the shorting element 60 and the rotor converter 54. A network filter 71 is further provided between the network converter 52 and the distribution network. In addition, a synchronization switch 72 is used to synchronize the wind turbine with the distribution network.

According to FIG. 2, the voltage drop has three phases. In the first phase, the amplitude of the supply voltage drops very quickly in less than one millisecond to a value of about 15% of the desired value. In the second phase, which lasts up to 3 seconds, the supply voltage amplitude remains at this low value. Finally, in a third phase having a duration of 50-150 ms, the supply voltage returns to a value of about 80% or more of the desired value.

During a drop in the supply voltage in the first phase, the converter 50, in particular the rotor converter 54 on the rotor side, must be protected from damage by currents induced in the rotor windings. For this reason, an emergency unit is used in the embodiment of the wind power plant according to the invention. The emergency unit may be operated to electrically disconnect the power supply unit, i.e. the converter 50, from the rotor windings 34. For this purpose, the emergency unit comprises a shorting element 60. Therefore, in an emergency, i.e. when a voltage drop occurs in the distribution network, the rotor windings are short-circuited by the shorting element 60 in this first phase and the rotor converter 54 is blocked. After the induced currents have disappeared in the rotor windings within 50 to 150 ms, the shorting element 60 has been disconnected. 9999 9999 9999

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999 ("Levers") and unlocking the rotor drive 54 restores the rotor current to the rotor side 54 via the rotor drive. To this end, the wind power plant according to this embodiment of the present invention comprises an unlocking arrangement for unlocking the rotor current supply after disconnection. When the currents generated in the rotor windings 34 and causing the converter 50 to disconnect from the rotor windings to a predetermined value, the unlocking arrangement unlocks the rotor current supply. Then the rotor current supply is restored. In the embodiment according to the invention, this unlocking arrangement consists of a shorting element 60 .. When the supply voltage is restored during the third phase, the drive can be disconnected from the rotor windings again, if necessary, to prevent damage to the drive due to currents induced in the rotor windings when the supply voltage is restored.

As shown in FIG. 3, the shorting element 60 (&amp; quot; lever &amp; quot;) can be implemented as a bridge B6. In this case, the dissipation of the rectified rotor currents can be achieved by the current transformer resistor 62 in the bridge B6. When the voltage of the auxiliary circuit in the converter 50 exceeds a predetermined value due to excessively high rotor currents, a lever formed as a bridge B6 is actuated. The same procedure is then used as in the case of short-circuiting the distribution network. If an excessively high current appeared in the rotor due to the short-term undervoltage of the grid, the turbine would actually act as if the grid was short-circuited. Then, when the current drops to a predetermined value, the bridge thyristors B6 are blocked and the short-circuiting of the rotor windings 34 is terminated. The rotor current supply is then restored. As a result, the thyristors form an unblocking arrangement of an embodiment of the invention.