Method for operating a wind park

Description of the invention

The invention relates to a wind farm control system comprising at least two wind farms.

Initially, wind installations (wind farms) were built as single devices and only in recent years, due to administrative and construction regulations, wind installations are installed in wind farms. The smallest unit of a wind farm therefore comprises a system of at least two wind farms, but most often of a much larger number. As an example, we can mention the wind farm called Holtriem (East Frisia), where more than 50 wind installations have been installed in a combined system. It is expected that in the coming years the number of units as well as the size of the installed capacity of wind farms will increase significantly. In most cases, the potential of wind installations is greatest in regions with low-short-circuit power grids and low population density. It is there that the technical limits for connecting wind installations are quickly achieved by wind installations, as a result of which it is no longer possible to install further wind installations in such places.

A conventional wind farm is connected, for example, to a 50 MW transformer, so its total power may be up to 50 MW, i.e. 50 installations, each with 1 MW of nominal power.

The wind farms are not continuously operating at their rated operating point and therefore the entire wind farm does not continuously reach the maximum power values. If the rated power of the wind farm corresponds to the maximum value of all possible feed-in power, it means that the wind farm is not set for optimal use.

In the description of the patent application PCT / EP00 / 06493 (WO0125630 A1) a method of operating a wind farm is presented, according to which the total output power of the wind farm is greater than the maximum possible power of the grid feed. Applying this solution to the example above requires increasing the power to a value in excess of 50 MW, for example 53 MW. At wind speeds high enough to reach the power cap of 50 MW, the wind farm's control system - when the entire maximum capacity is exceeded - turns on the regulation to reduce the capacity of individual installations or the entire wind farm, so that the output power is constantly under control. This means that at a wind speed above the rated value (wind speed where the power of the plant reaches its rated value), at least one or all of the power plants are running at a (slightly) throttled output (e.g. 940 kW instead of 1 MW).

According to the aforementioned PCT / EP00 / 06493 description, all components of the power network (network components are, for example, transformers and lines) can be used optimally or they can be load balanced in an optimal way (using them up to thermal limitation is also a possibility). In this way, the existing wind farm can be better used by installing the maximum possible number of wind farms. Therefore, the number of wind installations is not (so strictly) limited by the existing grid capacity.

According to the cited description, the control / regulation of the wind power plant has a data input with which the electric power can be set in the range of 0 to 100% (rated power). For example, if on this data input the reference power value is 350 kW, then the maximum output power of this wind installation will not exceed the reference value of 350 kW. The reference power value can be any value from 0 to the rated value (for example, from 0 to 1 MW). This data input is used directly for power limiting purposes. It is also possible to regulate the generator output power with a regulator, depending on the grid voltage (wind farm grid or power grid).

Assuming that the wind farm contains 10 wind farms, each of which has a rated output power of 600 kW, thanks to the capacitive reactance of the grid components (line capacitance) or the limited reactance of the transformer, it was assumed that the maximum power to be delivered (power limitation) is 5200 kW. It is possible to limit the power of all wind installations to a maximum of 520 kW by means of a reference value (at the input). This ensures that the required power limit is always met. Another possibility is not to allow the maximum power to be exceeded as the sum of the power of all installations while producing the maximum amount of energy (kilowatt hours (operation)).

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In the range of low to moderate wind speeds, it is not uncommon for wind farms to be located on the favorable side of the farm (that is, the side that the wind first encounters in the wind farm) to receive a fairly strong gust of wind. And if all wind installations are simultaneously controlled to reduce their power to their throttled values ​​(for example all down to 520 kW), this generated power is actually achieved by some wind installations situated on the good side of the farm, while other wind installations, which although "overshadowed by the wind relative to these well positioned wind installations (second and third rows)) receive less wind and consequently operate with less power for example only 460 kW and do not reach a maximum throttled power of 520 kW. Thus, the entire power output of the wind farm is significantly lower than the allowed limit output of 5200 kW.

In such a case, the regulation of the power of the wind farm according to the cited patent is that the power of the individual wind farms is regulated in such a way as to obtain the maximum possible energy production. Thus, the total electricity capacity of the wind farm increases. Wind farm power regulation assumes regulation of individual wind installations in such a way as not to exceed the maximum allowable connection power, and at the same time to obtain the maximum value of the work produced (kWh).

Management of a wind farm according to the cited patent description allows it to be easily adapted to the situation that has arisen. Thus, for example, it is easy to implement different power throttling of individual installations when a single installation or multiple installations of a wind farm are (must) be removed from the grid when, due to maintenance or other reasons, a single installation or multiple installations have to be temporarily shut down.

In order to control / regulate a wind farm or individual wind installations, it is possible to use a data processing device or a control device connected to the data inputs of individual installations and which, based on the wind speed data at each of these installations, determine an appropriately favorable power throttling value for each installation. wind farm or for the entire wind farm.

The discussed patent specification PCT / EP00 / 06493 includes the drawing shown in this specification as: Pos. 1, which is a block diagram of a wind farm control system, and Pos. 2 which shows a wind farm;

Pos. 1 is a block diagram of a wind farm control system with a μΡ microprocessor connected to an inverter (PWR) with which the polyphase AC can supply power to the utility grid. The microprocessor has a power P input, a power factor (cos φ) input as well as a power gradient input (dP / dt).

An inverter device comprising a rectifier, a DC intermediate circuit and a frequency converter is connected to the generator of the wind power plant and receives therefrom the energy produced by the generator with a variable rotational speed, i.e. depending on the rotational speed of the wind power plant.

The solution in this figure is used to illustrate how the power supplied by the wind turbine can be limited to the maximum possible value of the mains feed.

Pos. 2 shows a wind farm comprising three wind farms 1, 2 and 3, two of which, viewed from the direction of the wind, two are next to each other and the third is located behind them. Since each of the individual wind installations has a power input for the power setting of the respective installation (Fig. 1), the power level of an individual wind installation can be set to the desired value by means of a data processing device with which the entire wind farm is controlled. In fig. The 2 advantages of positioning wind farms are those that the wind encounters first, i.e. plants 1 and 2.

In the case of a low-power power grid (island), if a relatively large consumer is disconnected from the electrical grid, the frequency increases very quickly (impact). Drives such as diesel engines, water wheels and the like take some time to lower their power (mechanical and electrical). During this time, these generators produce more energy than they take from the electricity grid. This energy is then used to speed up the generators. This means that the speed of rotation and therefore the frequency of the grid increases.

However, many electrical devices, such as computers, servomotors and the like, that are connected to the utility grid, are not designed to operate on fluctuating or rapidly changing frequency networks, which can damage these electrical devices to their destruction.

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The patent description of Polish application No. 358384 (which is based on the international application PCT / EP / 003705, publication No. WO01 / 86143 A1) deals with the elimination of problems related to frequency and voltage fluctuations at a given point of the network. Frequency stability is achieved in that the power supplied to the grid by the wind farm is regulated or set depending on the frequency of the power grid, the power of the wind power plant is reduced when the grid frequency is higher or lower, preferably by about 3%, and more preferably 6% from its set point. The state of the art according to this patent specification is illustrated in the drawings in which:

Pos. 3 is a graph of frequency / power versus time for a wind farm;

Pos. 4 is a side view of the wind power plant;

Pos. 5 is a block diagram of a microprocessor controlled wind turbine inverter;

Pos. 6 shows a regulating device for a wind plant;

Pos. 7 shows the connection of the wind farm to the electricity grid;

Pos. 8 shows an alternative diagram to that of FIG. 3.

When wind power installations operate with grids of such low power, their (mechanical and) electrical power is controlled depending on the increase in grid frequency. This is to prevent a further increase in the grid frequency or to achieve a reduction in the grid frequency.

Pos. 3 illustrates the need to reduce the output power P of a wind farm (wind farm) depending on the grid frequency f. In this case, the value of 100% corresponds to the reference or target frequency (50 Hz, 60 Hz) of the electrical network. The values ​​of 100.6% or 102% correspond to the higher values ​​of the frequency f of the network.

The electric capacity of the wind farm (or wind farm) is not yet reduced, for example when the frequency increases by 0.6% (i.e. up to 100.6%). If the grid frequency continues to increase, the electricity capacity of the wind turbine is reduced. In the illustrated example, the electrical power of the wind power plant is reduced to zero when the grid frequency increases to 102%.

Pos. 5 shows an embodiment of a wind installation that meets these requirements. This wind turbine has adjustable rotor blades (blade angle adjustment) so that the mechanical power of the wind turbine can be reduced. For example, if the angle of attack of the rotor blades is set in dependence on the wind, the force of the rotor blades can be reduced to the required value. The alternating current from a generator (not shown) connected to the rotor which is provided with rotor blades is rectified with a rectifier 2 and smoothed with a capacitor 3. The inverter 4 converts the direct current into alternating current which is supplied to the grid L1, L2, L3 . The frequency of this output current is determined by the network. A control device 5 comprising a microprocessor measures the mains frequency and controls the power switches of the frequency converter such that the output frequency corresponds to the mains voltage (mains frequency). If - as described above - the grid frequency increases, the electric power is reduced as shown in Fig. 3.

Shown schematically in Fig. 5, the rotor 4 of the wind plant is coupled to a generator G, which supplies electric power depending on the wind speed, and therefore on the wind power. The alternating current produced by the generator G is first rectified by a frequency converter and then converted into alternating current with a frequency corresponding to the mains frequency. The grid voltage at the grid feed-in point is determined by the grid frequency detector. As soon as the grid frequency exceeds the set value - see Pos. 3 - the output electrical power is reduced to counteract the increase in network frequency. Thus, by means of the regulating device, the frequency of the network is regulated to the required value or at least a further increase in frequency is prevented.

This method of supply control with the power supplied by the wind installation allows for avoiding or significantly reducing the fluctuations in the grid frequency.

Pos. 7 shows the connection of the wind installation to the electricity grid, where the electricity generated by the wind installation is supplied to the grid at the feed-in point. Numerous recipients are connected to the network, presented in the example schematically in the form of houses.

Pos. 8 shows the more important components of the control and regulation device in a slightly different way than Fig. 3. The control and regulation system has a rectifier in which the alternating current generated in the generator is rectified. An inverter connected to a rectifier converts the direct current, initially converted in the intermediate circuit, into alternating current that feeds the grid in the form of electricity

PL 212 009 B1 by means of lines L1, L2 and L3. The inverter is controlled by a microprocessor, which is part of the entire control device. For this purpose, the microprocessor is connected to the inverter. The input parameters for the voltage control with which the available electric power of the wind installation 2 feeds the network are the instantaneous value of the network voltage, the network frequency f, the electric power P of the generator, the power factor cos φ, as well as the power gradient dP / dt. In the microprocessor, regulation of the supply voltage with a given network frequency is performed.

The present invention relates to a wind farm comprising at least two wind installations, each having an electric generator driven by a rotor and supplying electricity to an electricity grid, and in particular to consumers connected thereto.

In known wind power plants producing electricity, the generator works in parallel with the energy consumer, often the power grid. During operation of a wind plant, the active electrical power produced by the generator can vary depending on the prevailing winds. As a result, the grid voltage (magnitude and phase) may also vary, for example at the feed point, depending on the currently prevailing wind speed. The same also applies to the supply current.

However, in a situation requiring the supply of electricity produced for the utility grid, for example the public utility grid, fluctuations in the grid voltage may occur. However, in the interest of the reliable operation of the connected consumers, such fluctuations are only allowed to a narrow extent.

Relatively large deviations from the reference value regarding the mains voltage, in particular for medium voltages, can be compensated for, for example, by switching on switching devices such as regulating transformers, which are triggered when the value exceeds or falls below a predetermined limit value. In this way, within the specified tolerance limits, the grid voltage is kept substantially constant.

The object of the present invention is to obtain a wind installation or a wind farm which, even with fluctuations in the supplied active power, is able to reduce or at least prevent a significant increase in undesirable voltage fluctuations at a given point in the grid, compared to a situation without wind or wind installations.

This objective has been achieved by a wind farm control system consisting of at least two wind farms, characterized in that it has a control device with a frequency meter adapted to throttle the power of at least one or more wind farms, and a suitable voltage meter measuring the voltage in the wind farm. the set measurement point of the grid section for each separately regulated part of the wind farm.

Preferably, the regulating device has a microprocessor, so that digital regulation can be applied. An inverter is preferably coupled to the microprocessor.

The mechanical power of the wind power plant is reduced by adjusting the adjustable rotor blades to the wind.

In the wind farm (s) according to the invention, frequency stability is achieved by changing the phase angle φ of the electric power generated by the wind power plant or wind farms, depending on the measurements in the grid of at least one voltage. This avoids undesirable fluctuations in the voltage supplied to the consumer, in particular the existing voltage in the network, by changing the phase angle of the supplied power depending on the voltage at the consumer or in the network. Thus, it is possible to compensate for undesirable voltage fluctuations that arise as a result of changes in the active power supplied by the wind power installation or wind installations and / or the power drawn from the grid by the consumers.

It is particularly advantageous to alter the phase angle such that the voltage at at least one predetermined point in the network remains substantially constant. In such a case, in order to obtain the required control parameter, the voltage is measured in at least one point of the network. In particular, this point may not be a power point. Measurements of voltage values ​​and the appropriate change of the phase angle of the electric power supplied by the wind power installation or wind farms allows for a quickly responsive and effective control system.

In a particularly preferred embodiment, the values ​​to be given for adjusting the phase angle are obtained based on the given parameters. These parameters may advantageously be provided in the form of a table in which the preset families of characteristics are presented in the form of discrete values ​​which allow the derivation of the phase angle setting.

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In an advantageous development of the invention, the control system can directly or indirectly cause that when a predetermined limit value of the voltage fluctuations is exceeded, it is brought back to the tolerance range by actuating a switching device in the network, for example a regulating transformer. Simultaneously or in addition, the phase angle is set over a predetermined period to a constant value - preferably an average value, for example zero, in order to be able to compensate for the voltage fluctuations that follow, again by means of an appropriate change of the phase angle.

In a particularly advantageous development of the invention, the respective steps of measuring the voltage and adjusting the phase angle can be performed separately in the electrically separated network sections in order to adjust each section so that the voltage in each of these sections remains substantially constant.

Advantageous development of wind farms provides for voltage measurements for each separately regulated part of the wind farm, so that electrically separated sections of the grid can also be separately regulated such that the voltage in each of these grid sections remains substantially constant.

The subject of the invention in the exemplary embodiments is shown in the drawing, in which:

Fig. 1 shows a simplified representation of a wind power plant feeding the grid,

Fig. 2 shows a regulating device designed to work with a wind power plant;

Fig. 3 shows the relationship between the mains voltage and the phase angle;

Fig. 4 shows the main components of the adjusting device shown in Fig. 2 and

Fig. 5 schematically illustrates the control system of a plurality of wind farms.

The wind power plant 2 shown schematically in Fig. 1 has a rotor 4 and is connected to a grid 6 which may for example be a public main grid. A plurality of consumers 8 are connected to the grid. An electric generator (not shown in Fig. 1) of the wind power plant 2 is connected to a control and regulation device 10 which initially rectifies the alternating current produced in the generator and then converts it into an alternating current whose frequency corresponds to network frequency. The control and regulation device 10 has an adjusting device according to the invention.

A voltage measuring device can be provided at each measuring point 22 of the network 6, measures (in addition to the phase) in particular the value of the network voltage and returns this measured value to the control device 10 as the corresponding adjustable parameter.

Fig. 2 shows a regulating device in a wind farm according to the invention. The schematically illustrated rotor 4 is coupled to a generator 12 which produces an electrical power which may depend on the wind speed. The alternating current produced in the generator 12 may first be rectified and then converted into an alternating current whose frequency corresponds to the frequency of the grid.

The grid voltage is measured at measuring point 22 of the grid 6 with a voltage measuring device (not shown). Depending on the value of the measured mains voltage - possibly by means of a microprocessor shown in Fig. 4 - the optimal phase angle is calculated. The grid voltage U is then regulated to a predetermined value Uref by means of a regulating device.

The electric power supplied by the generator 12 to the network 6 is regulated by changing the phase angle.

Fig. 3 shows the relationship between the line voltage and the phase angle. If the voltage deviates from its setpoint Uref, located between the voltage values ​​Umin and Umax, then according to the characteristic curve of the diagram, the phase angle is changed in such a way that, depending on the sign of the deflection, either inductive or capacitive reactive power is supplied to the network in to stabilize the voltage at the voltage measuring point (measuring point 22 in Fig. 1).

Figure 4 shows the main components of the control and regulation device 10 shown in Figure 1. The control and regulation device 10 has a rectifier 16 in which the alternating current generated in the generator is rectified. An inverter 18 connected to a rectifier 16 converts the pre-rectified direct current into alternating current which feeds the network 6 in the form of three-phase alternating current via lines L1, L2 and L3.

The inverter 18 is controlled by a microprocessor 20 which is part of the entire regulating device. For this purpose, the microprocessor 20 is connected to the inverter 18. The input quantities to the microprocessor 20 are - the current value of the network voltage U, the electric power P of the generator,

The set point of the mains voltage Uref and the power gradient dP / dt. According to the invention, the variation of the power to be delivered is performed in the microprocessor 20.

Fig. 5 shows two wind farms 2 as an example of a wind farm. Depending on the grid situation, the regulation applies to one wind farm 2 or both. The regulating device 10 is connected to each of the wind installations 2, which may also symbolize a plurality of wind installations. The regulation device 10 measures the voltage at the preset measuring points 22, 27 of the network sections 6, 7 and transmits this data via lines 25, 26 to the appropriately assigned regulation devices 10.

The sections 6, 7 of the network can be connected to each other or separated by a switching device 23. Parallel to the switching device 23, a switching device 24 is provided, which enables the connection or disconnection of two regulating devices 10 according to the state of the switching device 23.

Thus, if the two sections 6, 7 of the grid are connected to each other, then the two control devices 10 are also connected to each other, so that the entire grid can be considered as one whole and is fed by the entire wind farm as a whole, the wind farm being uniformly regulated depending on the voltage at test points 22, 27.

Thus, if the two sections 6, 7 of the grid are separated by a disconnecting device 23, the regulating devices 10 are also separated from each other such that a part of the wind farm is monitored at the measurement point 22 by a line 25 and the corresponding part of the wind farm can be suitably regulated from the regulating device 10, and the second section 7 of the network is monitored at point 27 by line 26 and by means of the regulating device 10, properly regulated to stabilize the voltage in section 7 of the network.

The division of the network need not be limited to two sections. It can go further by assigning one installation to one network section.

The central regulation of the wind farm provides that the wind farm not only supplies the power grid with energy, but at the same time can be controlled in such a way that it supports the grid, preferably with the help of the public grid operator (electric utility company). In principle, when in this specification reference is made to a wind farm, this also applies to individual wind installations, and when it is mentioned a plurality of wind installations it is not always the case for a wind farm.

In order to centrally control the wind farm according to the invention, the public utility grid operator not only has control access via a suitable control line (bus system) to the wind farm / wind farms, but also receives wind farm / wind farm data such as e.g. measured wind parameters, data on the condition of the wind farm and also, for example, data on the available power (current power (active power)) of the wind farm.

Such centralized control may also mean, for example, that in certain circumstances the wind farm has been completely disconnected from the grid, for example in a situation where the operator's rules for connection to the wind farm grid cannot be complied with.

The regulation of the wind farm can take place, for example, in all wind installations or in the farm simultaneously or evenly, increasing the power supply with a predetermined power gradient. Of course, alternatively it is possible to assume that for a wind farm with e.g. 10 to 20 installations, first one or two installations (in the correct order relative to the power gradient value) start feeding the grid with full power and then depending on their assumed power gradients, further installations are switched on within the assumed time, until all available wind farm capacities can start feeding the grid.

Another aspect of wind farm regulation is the provision of a reserve capacity of, for example, 10% of the wind farm's currently available capacity, or a fixed value of, for example, 500 kW and 1 MW or more per wind farm. This reserve capacity should not be confused with a wind farm capacity that exceeds the grid connection capacity of the wind farm. This reserve power definitely relates to the reserve power (both active and reactive power) which does not exceed the range of the grid connection power. This standby capacity is recommended by the utility grid operator. This means that when the wind is sufficient from the point of view of the wind farm to supply the grid with the connection power, the energy company may decide, by recommendation being an intervention in the control of the wind farm, that all theoretically possible available capacity will not be used and some of it will remain in reserve character.

The normal bus system as well as the standard bus system can be used to control the wind farm as well as to provide data to the utility plant. There are standard interfaces for such a standard bus system, for example sys8

Profibus, so that the central control of the wind farm can also be implemented by means of appropriate standard control commands.

Additionally, it can also be established that a wind farm with a designed capacity, for example a total output capacity greater than 50 MW, is considered a large-capacity power plant and therefore must meet the conditions required for such a plant. It is therefore established that the wind farm is regulated so that the switching value (switching capacity) is not exceeded. It is important that there are no undesirable effects of grid reverse effects when switching off / on in the wind farm. For example, when switching on / off the wind farm, the current should not be higher than the set value compared to the rated power corresponding to the switching capacity. This value may be in the range of 1.0 and 1.4, for example.

If the frequency of the public utility grid increases, then it is important that, from reaching a given frequency, e.g. from 50.25 Hz (at a nominal frequency of 50 Hz), the supplied active power of the wind farm is automatically reduced until the grid frequency again stabilizes at the value stated above.

Thus, it must always be possible for the wind farm to operate at a lower feed-in power level in order to be able to meet the grid demands. This wind farm power control also means that the power supply (in particular active power) can be reduced to any given value under any operating conditions and from any point.

For example, if the grid voltage fell below the assumed value, the situation would be the same as for the frequency. In other words, when the voltage drops below or exceeds the assumed grid voltage by a certain value, the power supply is reduced first, and when the grid voltage drops below or exceeds the given value limit, the wind installations are completely disconnected from the grid or at least the grid feed power is set to zero. .

It is therefore determined that when a certain grid voltage and / or grid frequency is reached, an attempt is made to shut down the wind farm without supplying power that has already been reduced previously.

However, this also means that with given frequency or voltage deviations, which are within the given range around the grid frequency / voltage, it is not permissible to automatically disconnect the wind farm from the grid.

In order for the switch-off procedure to take place in good time, a protective relay (distance protection) can, for example, be installed in the interconnecting node.

Means should also be provided which, when starting the wind farm, synchronize the grid voltage and the wind farm voltage, because when the wind farm is restarted, the asynchronous voltage severely disrupts the grid and may cause its shutdown.

Power throttling below the wind farm's distribution capacity can be accomplished in various ways.

Thus, for example, the power may be reduced in total on individual installations, such that the total distribution capacity of the wind farm takes on the desired reduced power value. An alternative to this may be to assume that only individual installations are reduced in terms of their feed-in power, so that the total feed-in power of the wind farm again takes the desired value.