JP2002510951A - Method and apparatus for limiting current and excess output from AC induction generators - Google Patents

Abstract

The present invention includes a method for limiting the grid connection current and excess output of a wind turbine or similar power generation system for renewable energy utilization, wherein the electric generator of the system comprises: It is an AC induction generator. The generator is connected to the grid by a variable electronically controlled electrical connector of the thyristor-based type. Then, the acceptance angle obtained by adding the phase angle of the generator determines the actual degree of connection. The technique of the present invention relates to grid compatibility, where the generator is subject to a variable, grid independent dump load during the connection process, or during operation when the generator output is higher than desired. Is unique in that This dump load is controlled stepwise or continuously within a relatively wide output range.

Description

DETAILED DESCRIPTION OF THE INVENTION

TECHNICAL FIELD The present invention comprises a method for limiting the grid connection current and excess power of a wind turbine or similar power generation system for renewable energy utilization, the method comprising the steps of claim 1 As noted, it has more special properties. The invention also includes an electronically controllable power diverter (electric brake load) for using this technique.

BACKGROUND ART When an induction motor is driven at a speed higher than a synchronous speed, it functions as a power generator for converting an added mechanical shaft output of a main shaft into electric power. If the prime mover (here, an induction generator) is coupled to an AC grid, the generated current is accepted by the grid. This effect is used, for example, in modern wind turbines and similar energy systems that utilize renewable energy resources. However, it should be noted that induction motors used in generators are specially developed for this purpose.

[0003] Due to the various and unstable nature of the wind, the power generated by the wind turbine naturally changes. Connecting to the power grid presents major technical difficulties. When the turbine is running with almost no load, the connection is usually made while the airflow is increasing. Ideally, it would be possible to control the wind speed as with any other controllable operating parameter. Thereafter, the wind speed can be slowly increased to the exact point where the turbine rotor rotates at the synchronous speed. Once the generator is tuned to the grid, then power surges in the grid, via relays or some similar simple electrical switch mechanism,
Alternatively, the generator can be coupled to the grid without causing torque discontinuities in the wind system. Of course, as a practical matter, this method is not possible because wind speed is not a controlling factor.

[0004] In fact, we must take into account the fact that the speed of the wind, and thus the energy contained therein, can change suddenly. Therefore, the starting point of the turbine is "idle (idle) where the generator is not loaded.
, And assuming that the rotor is also unloaded,
The turbine rotor may suddenly accelerate to a speed faster than the synchronous speed. As soon as the prime mover reaches synchronous speed, coupling of the generator to the grid must occur to prevent the turbine from accelerating or overspeeding. In order to prevent power surges and torque surges in the unwelcome distribution network, the connection to the distribution network needs to be "gently". That is, the power transmission from the generator to the grid during the coupling process must be increased smoothly and uniformly from a minimum power connection to a maximum power connection. To this end, MITA TEKNIK A / S has developed an electronically controllable electrical connector that meets the demand for a fully controllable coupling method. See the specification of Danish Patent Application No. 0758/97.

However, when the dynamic conditions surrounding the wind turbine require severe and fast loading of the rotor, ie when the turbine in the “idling” state is exposed to strong gusts as described above, The desire to have a "calm" connection is in conflict with that demand. Naturally, the reason is that "keep tight control" so that the turbine does not overspeed, so as not to accelerate uncontrolledly during the connection process.
It is necessary. It is precisely during this connection process that we want to gradually increase the load on the generator over a period of time in order to obtain a "gentle" connection to the grid, during which the power to the rotor The braking effect of the machine is reduced as a result. In practice, in a controlled coupling process that takes into account possible effects on the wind turbine structure (gear and rotor shaft torque, bending stress on blades, etc.)
A compromise must be chosen so that the generator is connected to the grid. Regarding grid compatibility, the maximum acceptable grid connection current level must also be taken into account.

[0006] Once the inductive wind turbine is directly connected, the grid frequency and voltage will control the generator and thus the turbine itself. In practice, this means that the speed of the turbine prime mover is determined by the grid frequency. Since the power generated by the turbine depends on the speed of the wind, it is clear that the power distributed to the power grid is constantly changing. Wind systems are designed to produce a certain nominal yield (nominal production) (rated capacity) at a certain wind speed, hereafter referred to as the nominal wind speed. For economic reasons, power grids are usually designed for the same power output (ie, rated capacity). Wind speeds higher than the nominal value (especially between the nominal wind speed and the wind turbine cutout wind speed)
This results in higher electricity output from the generator than the distribution network is designed to accept. In attempting to control the power generated by the wind turbine, two different methods are used. One method is called "stall controlling," which takes advantage of the blade's tendency to stall (lost lift) when the angle of attack of the blade to the airflow exceeds a certain threshold determined by the shape of the blade. Then, fixed pitch blades with specially developed aerodynamic blade shapes are used. Since this control method is not very accurate and requires an oversized gear and generator, the braking torque of the generator on the turbine rotor is sufficient to cause blade stall at the set wind speed. Immediately before the blade stalls, there are often undesirable (and uncontrollable) output surges. This control method is not suitable when the demand for output quality is high.

[0007] The second method uses a variable pitch blade. The required system technically requires that the pitch of the blades be changed quickly enough to follow changes in wind speed, but this is not possible in practice. The result is undesired frequent overloading of the grid and intermittent power loss, as the blades cannot properly follow the changes in wind speed, and thus can potentially generate at a given wind speed. A pitch that does not produce as much output will be occasionally employed.

Another power control method is based on a mechanical auxiliary brake that can be activated for a short time during the grid connection process in order to limit problematic surges in the generated power. Also, so-called "independent" wind systems are used, where the frequency and power are controlled by a variable-load system. As a result of the dump-load (load resistor) being connected or disconnected from the grid depending on the load induced on the grid by the user and the current wind speed, the turbine is set up Satisfies a certain electrical impedance that can rotate only at frequencies. These last two methods are independent of the type of wind system described in this invention.

Regardless of the control method chosen, the “flicker” that often occurs
A phenomenon referred to as "" occurs in connection with wind power generation, i.e., voltage fluctuations typically caused by occasional load changes. One of the signs of this phenomenon is the visual perception of flashing lights, which is, of course, unacceptable. Typically, flicker caused by wind turbines is in the frequency range of 0-8 Hz. The flicker can be caused by blades passing downwind of the windmill tower, periodic turbulence of the wind caused by certain types of terrain, trees growing near the windmill, and so on. Currently, there is no known method to effectively reduce or eliminate flicker from wind turbines.

With respect to wind systems connected to the grid (and similar systems that utilize renewable energy), as wind systems are designed and their numbers increase, the demands on the electrical output quality generated by the wind turbines Will generally be more demanding. In Germany and other countries, wind turbine manufacturers are facing many stricter output quality standards and need to find solutions to the wind quality and power generation issues discussed above. "Grid quality" refers to a set of required standards that a wind system connected to the grid must have (maximum grid connection current, narrow range, etc.) before they can be approved. (Including allowable grid loads, maximum allowable flicker limits, etc.).

It is an object of the present invention to provide a solution to how to meet output quality requirements. More specifically, an object of the present invention is a method of limiting the grid connection current of a wind power generator, and a situation where the power generation by the generator exceeds the nominal power generation, that is, there is flicker, and the wind speed is lower than the nominal operating condition. It is to provide a method for shunting the generated surplus power, usually in the case of high power. It is also an object of the present invention to specify a controllable electric brake load for the technology in the present invention.

DISCLOSURE OF THE INVENTION [0012] The technology of the present invention is useful for the operation of the network during the grid connection process and whenever the power output of the generator is higher than desired, in connection with grid compatibility. The generator is characteristic in that it is loaded by a variable output shunt that is independent of the grid. The output shunt has a stepwise or continuously variable control system over a relatively wide output spectrum. In order to ensure that the generator output does not exceed the nominal grid design criteria, the chosen power section should be wide enough to allow for limiting the power delivered to the grid. This "dump load" technique allows the generation of electricity into the grid without allowing the maximum allowed power to be exceeded, and without unnecessary waste of power that could otherwise be supplied to the grid. Stabilize the machine output at the maximum allowable power generation. Therefore, this technology is not compatible with the requirements of the grid quality.
As in e), the optimal power generation is guaranteed.

Therefore, in the present invention, in an operating condition in which the wind speed mainly changes between the nominal wind speed and the cut-out wind speed of the turbine, the voltage fluctuation (furthermore, a periodic surge exceeding the nominal voltage is generated. In situations where there is (flicker), dump load technology is used. Also, as mentioned above, during the process of connecting the generator to the grid, where the external dump load serves as a supplementary load so that the turbine rotor can be effectively "controlled" during the connection process. Even dump loading technology is used. This means that the turbine will not power surge and without risk of uncontrolled acceleration.
It means that it can be connected to the distribution network.

According to the invention, a dump-loader (dump-loader) consisting of a resistor, a capacitor or an inductor, or of any combination thereof, is stepwise or continuously variable. . That is, they are connected in a stepwise or continuously variable manner through the generator by means of a thyristor switch of a known type, or a similar electrical or electromechanical connection (claim 4). In this way, the dump loader can dump any electrical output from the generator, including capacitive and ineffective outputs. In principle, the dump loader is installed directly on top of the generator and acts as a resistor independent of the grid.

In the present invention, control may be provided to the extent that a dump loader that relies on generator output to provide an indication of generator output and / or other relevant operating parameters is connected.

The control system can follow a preset program, for example, in the form of an algorithm in one system control computer. The program ensures that the dump loader is disconnected when the generator output is less than the nominal output (ie, the grid design capacity). In this way, power quality is taken into account (spikes in output that exceed the nominal output threshold are "burned off" in the dump loader.
)), The utilization of the power generated by the turbine is optimized. In summary, if the output could be distributed to the grid, the dump load technique of the present invention would mean that the grid load could not be exceeded without exceeding the maximum allowable power output and unnecessarily converting the output. This has the effect of stabilizing the generator output to the maximum allowable power generation. In other words, the present technology guarantees an optimal power generation amount while guaranteeing followability with respect to output quality requirements.

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in further detail with reference to the accompanying drawings.

[0018] These figures can be easily understood, but show how dump loading technology is used to control the wind turbine while it is connected to the grid so as not to cause output surges. 1 (FIG. 1) and how it is "adjusted" by the dump load during more normal operating conditions (FIG. 2). The controlled output to the grid is plotted on the curve of FIG. This curve shows how the power quality requirements have been met and the most possible use of turbine power has been achieved.

FIG. 3 shows how the dump-load resistor element of the system can be installed inside the wind turbine tower (1) while the tower is used as a cooling surface. . The tower consists of a curved or cylindrical steel plate (2). The dump load resistor, or at least a component of its electrical resistance, is supplied by an electric heat sink (4) located in a U-profile holder (4).
3). These holders (4) are bolted tight to the inner wall of the tower steel plate.
Heat from the power shunt is released to the tower steel plate and diffuses into the steel plate. That is,
The tower steel plate functions as a cooling element. The radiators are distributed symmetrically along the outside of the tower such that they are equidistant from each other. As a result, the temperature change around the tower is as low as possible.

[Brief description of the drawings]

FIG. 1 is a curve diagram showing operating states before, during, and after a wind power generator is connected to a power distribution network.

FIG. 2 is a curve showing the effect of the dump load technique in an operating state where the generator output exceeds the maximum allowable grid voltage.

FIG. 3 is a cross-sectional view of the wind turbine tower showing the arrangement of the dump load resistor elements.

[Procedural Amendment] Submission of translation of Article 34 Amendment of the Patent Cooperation Treaty

[Submission date] June 7, 2000 (2000.6.7)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claim 1

[Correction method] Change

[Correction contents]

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] Claim 2

[Correction method] Change

[Correction contents]

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H02P 9/48 H02P 9/48 Z (81) Designated countries EP (AT, BE, CH, CY, DE, DK) , ES, FI, FR, GB, GR, IE, IT, LU, MC, NL, PT, SE), OA (BF, BJ, CF, CG, CI, CM, GA, GN, GW, ML, MR) , NE, SN, TD, TG), AP (GH, GM, KE, LS, MW, SD, SL, SZ, UG, ZW), EA (AM, AZ, BY, KG, KZ, MD, RU) , TJ, TM), AL, AM, AT, AU, AZ, BA, BB, BG, BR, BY, CA, CH, CN, CU, CZ, DE, DK, EE, ES, FI, B, GD, GE, GH, GM, HR, HU, ID, IL, IN, IS, JP, KE, KG, KP, KR, KZ, LC, LK, LR, LS, LT, LU, LV, MD , MG, MK, MN, MW, MX, NO, NZ, PL, PT, RO, RU, SD, SE, SG, SI, SK, SL, TJ, TM, TR, TT, UA, UG, US, UZ, VN, YU, ZW [Continuation of summary]

Claims (6)

[Claims] The generator is an AC induction generator (usually a three-phase generator) connected to an AC power distribution network (three-phase AC power distribution network), and the generator is connected to the power distribution network during the connection process. In order to be able to control the voltage and the torque load according to a preset curve and increase it gradually (so-called "gentle start"), its acceptance angle, plus the phase angle of the generator, is the actual angle. Gradual connection to the distribution network (meaning a gradual supply of power to the distribution network) by means of adjustable electronically controlled electrical connector means of the type based on thyristors for determining the degree of connectivity; Connection for wind turbines or renewable energies, especially as the connection with the thyristor is made by adjusting the acceptance angle of the thyristor depending on the instantaneous phase angle of the generator and other relevant operating parameters A method of limiting the grid connection current and surplus power from a power generation system, e.g., operating conditions in which a wind turbine constantly or frequently produces an electrical output higher than the nominal design capacity of the grid, where the wind speed is the nominal wind speed of the turbine and its Regarding grid compatibility, in operating conditions that typically occur when changing between cut-out speeds, as well as in situations where voltage fluctuations (so-called "flicker") occur and occasionally cause output to exceed nominal values, During the connection process, the generator is subjected to a variable dump load during operation where the generator output is otherwise higher than desired, and under all possible operating conditions, i.e. During and in other operating situations, this dump load can be applied to a relatively wide output range that is sufficient to control the output of system power to the grid. A limiting method characterized by being controlled stepwise or continuously. 2. The variable dump load is electronically dependent on the generator output and / or other relevant operating parameters indicative of the generator output, and at the same time the generator output is nominally 2. The method according to claim 1, wherein the method is adjusted according to a preset program for reliably disconnecting the dump loader when the amount of power generation (i.e., the power demand of the power grid) is less than a predetermined value. 3. The dump load is controlled through a computer that collects relevant operating parameters and, based on these parameters, constantly calculates an optimal load for each driving situation with a preset algorithm. 3. The method according to claim 1, wherein the method comprises: 4. A resistor, capacitor, or inductor, or any combination thereof, whose resistance is generated by a thyristor switch or similar electrical or electromechanical switching device of a known type. 4. The method according to claim 1, wherein in its connection through the machine (i.e. in principle independent of the power grid), it is variable stepwise or continuously. Used electric dump loader. 5. The dumper electrical resistance element comprises a radiator mounted inside the tower such that the tower is used to dissipate heat so that it is tightly secured inside the tower wall. An electric dump loader according to claim 4, characterized in that the technique is used for a wind turbine of the type having a steel tower having a closed conical or cylindrical shape. 6. The electric dump loader according to claim 5, wherein the radiators are distributed symmetrically (and equidistant from each other) along a circumference inside the tower wall.