NL1010800C2 - Method and device for converting a fluid flow of varying strength into electric energy. - Google Patents

Description

Method and device for converting a fluid flow of varying strength into electric energy

The invention relates to a method according to the preamble of claim 1. Such a method is known, inter alia, from US 4695736, Doman. The drawback of the known method is that complicated measuring and control equipment is necessary to calculate and subsequently realize the torque to be exerted by the generator. As a result, errors can occur quickly in the method or failure can occur quickly, which is a drawback.

The object of the invention is to avoid the above-mentioned drawback, and to that end the method takes place according to the feature of claim 1. By letting the frequency converter settings depend solely on the rotation speed of the turbine, a simple control is obtained.

In accordance with an improvement, the method is carried out according to claim 2. This ensures in a simple manner that the turbine always works as efficiently as possible.

According to a further improvement, the method is carried out according to claim 3. As a result, the difference between the theoretically best setting of the frequency converter and the actual setting is relatively small, so that the influence on the acceleration and deceleration of the rotation speed is comparable to the influence of changes in airflow speed.

According to a further improvement, the method is carried out according to claim 4. The power to be supplied by the generator is hereby adapted in a simple manner.

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In accordance with a further improvement, the method is carried out according to claim 5. This makes it possible to optimize the quality of the power supplied to the network.

In accordance with a further improvement, the method is carried out according to claim 6. This allows precise control.

In accordance with a further improvement, the method is carried out according to claim 7. As a result, the quality of the current supplied can be kept as optimal as possible via precise control.

In accordance with a further improvement, the method is carried out according to claim 8. As a result, the setting of the frequency converter is adapted to any changing conditions such as machine properties or duty cycle, so that the turbine can always work as optimally as possible.

In addition, the invention includes devices for performing any of the aforementioned methods.

The invention is explained below with reference to the following. of some embodiments with the aid of a drawing. In the drawing figure 1 shows a schematic diagram of a first embodiment of a windmill, figure 2 a diagram of the power supplied by the generator of a first embodiment of the windmill according to figure 1 depending on the speed, figure 3 a diagram of the power supplied by the generator of an improved embodiment of the windmill according to figure 1, depending on the speed, and figure 4 a schematic diagram of an improved embodiment of the frequency converter shown in figure 1, and figure 5 a schematic diagram of a second embodiment example of a windmill.

In the various figures corresponding parts are always indicated with the same reference numerals as much as possible.

Fig. 1 schematically shows a known windmill with a mill shaft 3 which runs horizontally and on which blades 1 are mounted. The windmill is provided in known manner with means for directing the windmill shaft 3. The angle of the blades 1 is adjustable 10 with an adjusting device 2. The windmill shaft 3 is coupled to the shaft of a generator 4, where a rotor 5 is applied. The rotor 5 can generate a rotating magnetic field in the manner indicated below. The rotor 5 is mounted in a manner not shown and can rotate in a stator 15 6 with a rotation speed n. The stator 6 comprises a number of coils with windings in which a changing magnetic field is created as a result of the rotation of the rotor 5, as a result of which an alternating electric current is generated in the windings.

The coils of the stator 6 are connected to a rectifier 8 in which the alternating electric current is converted into a direct current with a direct voltage Va. Via a DC voltage line 11 in which a choke coil 14 is included, the generated current flows to an inverter 9 in which a DC voltage VB is converted into AC voltage with a frequency and voltage corresponding to a mains connection 10, to which inverter 9 is connected. The DC voltage VA is approximately equal to the DC voltage VB because the choke 14 has the function of reducing current variations, but does not cause changes in the DC voltage. A control 12 is connected to the inverter 9. The control 12 adjusts the transmission of electric current from the choke 14 to the mains connection 10 so that the direct voltages VA and VB have an adjustable value, which value will be discussed below. depends on the rotational speed n. As a result, when electric current is generated in the stator 6, an electric current will flow via the rectifier 8, the choke 14 and the inverter 9 to the mains connection 10. The alternating current generated in the generator 4 with alternating electric voltage, the frequency of which varies with the rotational speed n of the mill shaft 3, is converted in the above-described manner into electric current with a constant voltage and frequency, inter alia from the rectifier 8 and Inverter 9 existing frequency converter 7. In accordance with the known state of the art, diodes 15 include, among others, diodes and thyristors 19 are included in inverter 9.

The generator 4 is designed as an asynchronous generator with rotor windings without an applied field, the magnetic field in the rotor 5 being made self-generating with capacitors in a known manner. The rotor 5 may optionally be provided with permanent magnets for generating the magnetic field or field windings may be provided in a known manner.

The rotational speed n of the mill shaft 3 is measured with a rotational speed meter 13, which is coupled to the mill shaft 3 and is connected to the controller 12. Optionally, the rotational speed can also be determined in other ways, for instance by the frequency of the voltage fluctuations in the coils of the stator 6.

The blades 1 also have an adjustable pitch angle for which the adjusting device 2 is arranged in a known manner. The adjusting device 2 is controlled by the controller 12. Above a maximum permissible rotational speed πμαχ of the mill shaft 3, which mainly depends on the diameter of the blades 1, the controller 12, in cooperation with the adjusting device 2, ensures that the the pitch angle of the blades 1 is changed. The change is such that the efficiency of the blades 1 decreases and the torque exerted on the reel shaft 3 by the blades 1 decreases. As a result, the rotational speed n of the mill shaft 3 does not rise, or only slightly, above the maximum permissible rotational speed ηΜΑχ.

Figure 2 shows a diagram in which the power P to be supplied by the generator 4 is shown as a function of the rotational speed n, the power supplied by the generator 4 being dependent on the DC voltage VA in the frequency converter 7. Above a mi-15 minimum rotational speed n0, the DC voltage VA in the frequency converter 7 is set to DC1. If, due to the wind, the rotational speed n rises above a rotational speed ni, the DC voltage VA is set to DCh. The power 20 supplied by the generator 4 increases with increasing rotation speed n to a maximum value Ph, which depends on the properties of the generator 4. With the double-drawn lines w, in the diagram it is due to the settings of the frequency converter 7 by power to be supplied to the generator at the various rotational speeds n indicated.

Above the maximum permissible rotational speed πμαχ, due to the technical limitations of the generator 4, the power supplied by the generator 4 and taken from the mill shaft 3 remains more or less constant, so that the power to be delivered by the 30 blades 1 may not increase further with an increasing wind speed. because otherwise the spindle 3 will rotate too fast and the grinder could break down. As discussed above, the adjusting device 2 adjusts the blades 1 so that the torque supplied by the blades 1 decreases and the rotational speed n will not increase, or only to a limited extent, into the hatched area.

By making use of changes in the value of the DC voltage VA, the power characteristic 5 of the generator 4 is affected and the windmill can supply power over a wide speed range, the generator 4 providing more power as the wind speed increases. Particularly at low wind speed, commuting and / or continuous switching on and off are prevented.

Figure 3 shows a diagram of an improved embodiment, wherein the number of DC voltage levels VA set in the frequency converter 7 is greater than two. At each level of DC voltage VA, a rotational speed range is associated. In the diagram the DC voltage levels DCi to DC7 are shown, however preferably ten to twenty DC voltage levels and associated rotational speed ranges are maintained. This makes more efficient use of the available wind-20 energy. Also, due to the large number of rotational speed regions, the acceleration and deceleration of the rotation due to differences between the power generated by the blades 1 and the power consumed by the generator 4 will be similar to accelerating and decelerating due to fluctuations in wind speed.

Figure 3 shows a line 1 which indicates the power P to be supplied by the blades 1 at a given wind speed, depending on the rotation speed n. The influence of the blade adjustment 2 is indicated by line 1 '. As shown, there is a rotational speed for each wind speed at which the delivered power is maximum. In that area, the rotational speed and wind speed are best attuned to each other and 01 03 00¾ 7 results in as little loss as possible. The line m is the set of these maxima, thus indicating for which combinations of power and rotational speed the efficiency of the blades 1 is as great as possible. The line m is characteristic 5 for a given mill and ends at the maximum rotational speed nMAx because there the blades 1 are adjusted by the adjusting device 2 with further increasing rotational speed n.

By adjusting the DC voltage VA such that the power taken off by the generator 4 from the mill shaft 3 more or less corresponds to the power to be supplied optimally by the blades 1 at that rotation speed n, the rotation speed n of the mill shaft 3 is achieved. will adjust to a value at which the efficiency 15 of the blades 1 is optimal at the prevailing wind speed. As a result, as much of the energy present in the wind is converted into electricity. This is indicated in figure 3 because in the range for each subsequent rotational speed range, from n0 to n1, from n1 to n2, etc., a determined setting of the power P to be supplied by the generator 4 is determined by recording the DC voltage on the values DCi, DC2, etc. The value of the rotational speed n is measured with a frequency of, for example, 10-20 Hz, so that the power to be supplied by the generator is also determined with that frequency. The double lines w indicate the power P delivered by the generator as a function of the rotational speed n. Owing to the great inertia of the blades 1, the differences in the rotational speed n will slowly occur in the event of differences between the power supplied by blades 1 and the power absorbed by generator 4. By setting five to ten rotational speed ranges, the power to be supplied by the generator 4 already corresponds reasonably with the power to be supplied by the blades 1 at a determined rotational speed n. By setting ten to twenty rotational speed ranges, this is further improved.

In another embodiment, the controller 125 contains a hundred or more speed ranges, whereby the characteristic of the generator 4 is influenced such that the power P worked up by the generator 4 at a certain rotational speed n corresponds to the power P generated by the blades 1 at that rotational speed to be delivered optimally.

Figure 4 shows an improved embodiment of the frequency converter 7 from Figure 1. A thyristor 19 and a capacitor 20 are placed between the choke coil 14 and the inverter 9 and a diode 21 is placed between the thyristor 19 and a capacitor 20. The thyristor 19 cooperates with the choke 14 and will be able to run a short-circuit current through the choke 14 under control of the control 12 for a short period of time. By interrupting this short-circuit current, the choke 14 will charge the capacitor 20. The diode 21 prevents the capacitor 20 from draining while the short-circuit current is running. The thyristor 19 is operated by the control 12 in such a way that the DC voltage VB maintains a more or less constant high value 25, the DC voltage VA being adjustable for changing the characteristic of the generator 4. The inverter 9 is now powered by a more or less constant DC voltage VB, which is chosen in such a way that it is possible to supply the power at the mains connection 10 with a cos φ which remains more or less equal to one and which can be adjusted by the controller 12.

Figure 5 shows a second embodiment of a windmill. In this embodiment, the mill shaft 3 Y._ 9 is driven in a similar manner as described above by the adjustable blades 1. The generator 4 is designed as a synchronous generator with rotor field control. A rotor field is applied in the rotor 5 by a field-5 control 18, the field being determined in dependence on the rotational speed n of the mill shaft 3. This ensures that losses occurring in the generator 4 are limited as much as possible because the generator 4 is brought to its most favorable operating point for each rotational speed n.

The current generated in the stator 6 goes via the frequency converter 7 to the mains connection 10. The stator 6 in the frequency converter 7 is coupled to a first pulse width modulation inverter 15 and the mains connection 10 15 is connected to a second pulse width modulation inverter 16. Both pulse width modulation inverters 15 and 16 are connected by the DC voltage line 11, the DC voltage line 11 is provided with a capacitor 14 over which DC voltages VA and VB are present. The pulse width 20 modulation inverters 15 and 16 are equipped with IGBTs (Integrated Bistable Thyristors).

In the second pulse-width modulation inverter 16, the direct voltage VB is converted into an alternating voltage corresponding to the mains connection 10. In this case, a current pulse is applied to the various phases of the current by means of switches present in the pulse-width modulation inverter 16 with a frequency which varies, for example, between 1,000 and 4,000 Hz. just let through. In the second pulse width modulation inverter 16 there is a control which varies the length and frequency of the pulses such that the DC voltage VB remains more or less constant. As a result, the delivery of electric power to the network adapts to the power supplied by the generator 4. By keeping the DC voltage VB at a constant high value even with variable output 10 of the generator 4, it is possible to supply the power to the mains connection 10 with a cos φ that remains more or less equal to one or is adjustable by the control 12.

In the first pulse width modulation inverter 15, which is designed more or less in the same way but inversely as the second pulse width modulation inverter 16, the power generated by the generator 4, which has an alternating frequency and an alternating voltage, is converted into direct current of constant voltage. To this end, the windings of the stator 6 are connected to the DC voltage line 11 by switches present in the first pulse-width modulation inverter 15 with a frequency of approximately 1,000 to 4,000 Hz. The windings of the stator 6 are optionally used as choke, or a choke (not shown) may be provided so that the voltage can be increased and the capacitor 14 also charged when the rectified voltage VA generated in stator 6 is less than the DC voltage VB. The settings and the circuits of these choke coil (s) depend on the shape of the energy supplied by the generator 4 and may possibly depend on the settings of the field control 18 and thus on the rotation speed n. In the first pulse width modulation inverter 15, this data is known or can be derived from the properties of voltage or current coming from the stator 6, so that the first pulse width modulation inverter 15 can optimally adjust itself.

In the first pulse width modulation inverter 15 there is a control which controls the power drawn from the generator 4, inter alia by varying the frequency and duration of the pulses. The power 12 is set by the control 12 on the basis of the rotational speed n of the mill shaft 3. By making the power to be supplied by the generator 4 dependent on the rotational speed n, as before discussed, the energy present in the wind is most efficiently converted into electrical energy because the rotational speed n of the blades 1 is tuned to the wind speed. In the controller 12, for example, ten to twenty rotational speed ranges are included, with the associated settings of the value of the power to be generated by the generator 4. Optionally, the number of steps can be increased to a few hundred so that the characteristic of the generator 4 closely follows that of the blades 1.

In order to achieve that the power indicated by the control 12 is indeed taken from the generator 4 by the first pulse width-15 modulation inverter 15, the power delivered to the mains connection 10 is measured with a power meter 17. It has been found that operation of, for example, the generator 4 is not always constant and depends, for example, on the machine 20 properties such as, for example, the gap between rotor 5 and stator 6. As a result, there could be a difference, for example, during the day and at night or shortly after switching on and power decreased after prolonged use of the generator 4 in that this gap width varies with temperature. This is undesirable and therefore the actual power taken off is measured with the power meter 17 and optionally compared over a longer period of time, for example with a frequency of 0.1 - 1 Hz and at various rotation speeds n, with the values set by the control 12. . Then the setting of the pulse width and / or frequency is adjusted accordingly.

Preferably, the adjustment takes place in the controller 12, if necessary, the power measurement can also take place in another way.

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The invention has been illustrated above with reference to a few exemplary embodiments with a windmill, in which the details known to those skilled in the art are not shown. Naturally, other combinations of the different parts are also possible, to which the invention can also be applied.

The invention can also be applied in, for example, hydropower installations in which energy is generated in a turbine and the turbine is placed between 10 water basins of different levels, whereby the level difference can vary. In that situation, the turbine may optionally be designed without an adjusting mechanism, because the maximum level difference and thus the maximum energy supply to the turbine is limited by the situation by other means, such as an overflow.

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Claims (9)

Method for converting a fluid flow of varying speed such as wind into electric energy, wherein the fluid flow through a turbine provided with blades (1) 5 is converted into a rotary movement with a rotation speed (n) which is controlled by a control (12) measured, the rotary movement through a generator (4) is converted into electric current of varying frequency and / or voltage and the electric current of varying frequency and / or voltage through a frequency converter (7) is converted into electric current of constant frequency and voltage delivered to a power grid (10) and where the increase in the rotational speed (n) of the blades (1) above a first rotational speed (πμαχ) is limited by, for example, adjusting the blades (1) with the characteristic that for a rotational speed (n) less than the first rotational speed (πμαχ) two or more at a closed rotational speed regions (no-nx, nx-n2 ,. ..) are included in the controller (12) and the frequency converter (7) is automatically set in each rotation speed range by an appropriate setting by the controller (12). Method according to claim 1, characterized in that in each rotation speed range (no-nx, nx-n2, ...) the frequency converter (7) is set by the control (12) such that it is passed by the generator (4) absorbed power more or less corresponds to the power to be optimally supplied by the turbine at said rotational speed (s). Method according to claim 1 or 2, characterized in that at least ten to twenty rotational speed ranges (n0-ni, ni-n2 / ...) are included in the control (12). > Ά Method according to claim 1, 2 or 3, wherein the electric current of varying frequency and / or voltage in the frequency converter (7) is converted into direct current with a rectifier (8) with a first DC voltage (VA), characterized that the rotational speed dependent settings of the frequency converter (7) are changed by changing the first DC voltage (VA). Method according to claim 4, characterized in that in the frequency converter (7) the first adjustable direct voltage (VA) is converted into a second predominantly constant direct voltage (VB). Method according to any one of the preceding claims, characterized in that in the frequency converter (7) the current generated by the generator (4) is converted into a direct current by a first pulse width modulation inverter (15), the rotation speed (s) depending on the frequency converter (7) are changed by changing the settings 20 of the first pulse width modulation inverter (15). Method according to any one of the preceding claims, characterized in that in the frequency converter (7), direct current is converted by AC converting means (16) into alternating current of constant frequency and voltage for supply to the electricity network (10), the inverter -setting means keep the DC voltage (VB) at a more or less constant and possibly adjustable value. Method according to any one of claims 2-7, characterized in that the power supplied by the frequency converter (7) to the electricity grid (10) at a rotation speed (n) is measured, which measured value is compared with the power for that rotation speed (n). (n) power setting and the frequency converter settings (7) are corrected for differences detected over a long period of time and at different rotational speeds (n). 9. Device for performing one of the aforementioned methods.