DE3922573A1 - Wind power plant with induction generator overload protection - responds quickly to increase in wind speed adjustment of turbine blades to stabilise generator torque - Google Patents

Abstract

The wind (10) drives a twin-bladed rotor (11) on a shaft (12) geared (13) to the generator (15) which is transformer coupled (17) to an electrical network, energy store or load (18). The angular setting (21) of the rotor blades (22) is adjusted by a controller (20) in accordance with either the generator output or shaft speed. The reversing torque of the machine (15) in generation mode is between 1.2 and 1.5 times the rated torque for more rapid response of the control to gusts of wind. ADVANTAGE - Power control is achievable with inexpensively mfd. parts and without noteworthy detriment to efficiency.

Description

The invention relates to a wind turbine with which the wind energy via a rotor to an asynchronous generator is transmitted, with a constant Power the rotor blade angles are adjustable.

In systems for converting wind energy into electrical One strives for energy, the performance of the system on one To keep the nominal torque constant, especially a power to avoid rising above the nominal torque. This is through Limiting the power consumption of the rotor to an ent speaking nominal power achieved by the rotor blade angle is adjusted according to the wind speed. The inertia of this rotor power control makes it particularly Especially in large systems, the regulation of Blade angle adjustment through further regulations base to unwanted effects of sudden wind to avoid speed changes.

There are numerous procedures for the supporting regulation known in the book by Erich Hau "Windkraftanlagen", Springerverlag 1988, pp. 262-273, 286-319, together are summarized. These procedures are essentially based on that the increase in wind energy initially leads to an increase in Rotor speed is implemented under - as far as possible - Keeping the driving rotor or gear torque constant tes until the blade angle setting to reduce the Power consumption of the rotor intervenes.  

For the additional control either the rotor shaft (e.g. torsionally elastic shaft) or the transmission (for example Superimposition gearbox with limited output speed) or the generator (e.g. as a synchronous generator) is used or by inserting couplings (e.g. hydro dynamic coupling) or by converters.

In the case of a system of the type mentioned at the beginning, this will be Performance control problem as proposed by the book cited above, pp. 302, 303, that the asynchronous generator with increased slip is interpreted. This ensures that the torque of the Generator when the rotor speed increases experiences less increase and the torque in the period not the tilting moment until the blade angles are set reached. However, this solution comes at the expense of effectiveness degree, especially with the increase of the slip of the effects degree of the generator drops.

The invention has for its object a system type mentioned so that a performance control with little technical effort and is possible without significant loss of efficiency.

The object is achieved with the features of Claim 1 solved.  

The low tilting moment ensures that despite high wind acceleration no high generator torque occurs, that could affect the gearbox output shaft. The Gearbox is not exposed to high loads, if you have to adapt it to rapid changes in wind power Send blade angle adjustment is not done quickly enough. At the same time it is achieved that the power fluctuations have a small bandwidth at the output of the generator, by brief voltage peaks due to the low tipping turn out relatively flat at the moment.

The well-known design for a soft system by lifting the slip can be in the embodiment of the invention can also be considered by the slip is raised slightly to about 1.5 to 3.5%. Thereby the tipping moment shifts to higher speeds, so that the overturning moment in the operation of the wind turbine is only extremely is rarely achieved.

With the invention it is possible to have gusts of wind Intercept asynchronous generator so that neither a burden of the transmission is done, the need for a special one designed and technically complicated gear or readjustment of the electrical energy generated to see.

The invention is illustrated schematically in the drawing illustrated embodiments explained in more detail.  

Show it:

Fig. 1 is a block diagram of the mechanical-electrical chain of effects of a wind turbine and

Fig. 2 is a diagram of the torque characteristic of an asynchronous generator.

Fig. 1 shows the drive train of a wind power plant, consisting of an operable wind-10 rotor 11, which is connected via a drive shaft 12, a gearbox 13 and a transmission output shaft 14 to a generator 15 whose output 16 through a transformer 17 with a power to be supplied network 18 (or electrical storage or consumer) is connected. The wind turbine is equipped with a controller 20 which, depending on the electrical power of the generator 15 or depending on the speed of the drive shaft 12, adjusts the angular position 21 of the rotor blades 22 of the rotor 11 in accordance with the wind power.

As a rule, a wind energy installation must be designed and designed in such a way that a constant power is present by an automatic control at the output 16 of the generator and that overloads on the installation are avoided. Due to the inertia of the rotor blades 22 and the actuators, the regulation lags behind a change in wind speed, so that the system is temporarily exposed to additional loads which the system has to endure.

Taking this into account, an asynchronous generator is used as the generator 15 , the torque characteristic of which is shown in FIG. 2. The left side of the diagram shows the curve in engine operation, which is not dealt with here. On the right side of the diagram, which represents the generator operation, the dash-dotted curve shows the curve of the torque M depending on the ratio of the speed n to the target speed n _{s of} the generator. The curve reaches a maximum value over a relatively steep ascent 25 , the so-called tilting moment M _k . This curve represents the characteristic for a conventional asynchronous motor in which the ratio of the overturning moment M _k to the nominal torque M _{N is} approximately 2.5.

When using such a generator a gust of wind until the intervention of the control device 20 , 21 raise the speed n of the generator 15 such that a sharp increase in the torque M and thus the output power of the generator 15 takes place.

In order to avoid these consequences, the increase in power at the rotor 11 must either be absorbed by a complicated gear 13 , or an expensive converter must be connected downstream of the generator, with which the increase in electrical power is processed.

According to the prior art mentioned at the outset, the slip of the asynchronous generator has been increased. The curve of the torque characteristic for a generator with increased slip corresponds to the dashed curve in FIG. 2.

After this curve, the moment M becomes when the wind energy changes or speed changes do not increase as quickly as it can however, at very high speeds, torque is still high achieve values.

According to the invention, however, a design of the asyn chron generator is chosen in which the ratio between overturning moment M _k to the nominal moment M _{N is} between 1.1 and 1.8, preferably between 1.2 and 1.5. The torque characteristic of such a generator takes the course of the solid curve 30 . Here, an increased torque M is suppressed from the outset by the low tilting moment, so that the risk of overload in the periods between wind energy fluctuation and rotor blade angle adjustment no longer occurs.

This design eliminates the need for other measures - in particular on the transmission 13 and on the electrical converter 17 - for absorbing excess wind or electrical power.

The reduction of the generator overturning torque is known With a special shape of the rotor bars, e.g. achieved as a double rod. With the reduction of Generator tilting moment is the reactive power of the Generator increases, but this can be done in a known manner be compensated by capacitors.  

The desired effect described above can be supported by increasing the slip, thereby shifting the overturning torque to higher speeds and consequently further braking the increase in torque M when the wind power increases. The torque characteristic assumes the curve shape identified by the number 31 in FIG. 2.

Claims (3)

1. Wind power plant with which the wind energy is transmitted via a rotor to an asynchronous generator, a controller for adjusting the rotor blades being provided, characterized in that an asynchronous generator ( 15 ) is used, the tilting moment (M _k ) of which is 1.1 is up to 1.8 times the nominal torque (M _N ). 2. Plant according to claim 1, characterized in that the ratio between the breakdown torque (M _k ) and nominal torque (M _N ) of the asynchronous generator ( 15 ) is between 1.2 and 1.5. 3. Plant according to claim 1 or 2, characterized in that the asynchronous generator ( 15 ) is designed with a slightly increased slip.