Asynchronous generator

In electrical power engineering, asynchronous generators are asynchronous machines that are operated as a generator . Among other things, they are used in decentralized small power plants for economic reasons instead of synchronous generators to generate electricity. Asynchronous generators are also used as so-called additional or auxiliary generators.

Basics

Asynchronous generator simplified equivalent circuit diagram

Every asynchronous machine can be used both as a motor and as a generator . For use as a generator, the asynchronous machine must be magnetically excited and mechanically driven. If asynchronous motors are driven faster than the rotational frequency of the rotating field , then they work as a generator and feed real power into the network. This can e.g. B. occur when descending passenger elevators , conveyors or cranes . This effect is known as regenerative braking . In the case of pole-changing machines with switching from high speed to low speed (or vice versa) there are additional requirements so that no inadmissible peaks related to current or mechanical load can occur. The goal remains to feed the braking energy into the grid in generator mode. If asynchronous motors are operated via a drive control (frequency converter), this must be capable of feedback. This means that the frequency converter must allow real four-quadrant operation.

Layout and function

Principle drawing of a squirrel cage
(without sheet iron packages )

Three-phase asynchronous machines with squirrel cage rotors are used as classic asynchronous generators . They have a much simpler structure than other asynchronous generators. The most common asynchronous generators have 4 poles. As a result, the rotating field speed is only 1500 min ⁻¹ . In order to achieve a speed graduation and thus a smoother network coupling, stator with pole-changing windings are used in certain areas. As a result, the asynchronous generator achieves optimum energy yield across the entire power range. The runner is designed as a round bar runner. In addition to the use of normal industrial motors, special asynchronous machines are also built for generator use. These asynchronous generators have rotor bars made of copper in order to achieve a higher degree of efficiency. In addition, due to the better sheet quality (low-loss magnetic sheets for stator and rotor), they are specially designed and optimized for use as a generator.

The dependence of the torque M on the speed n is decisive for the operating behavior of the asynchronous machine . This dependency can be read from the torque-speed characteristic of the asynchronous machine. If additional forces act on the generator shaft, the slip increases , which in turn increases the electrical power output. The difference between full load speed and idle speed is very small in practice. The difference to the synchronous speed is given in percent and referred to as generator slip, it is around 1 percent. This means for a four pole machine, that it in full-load operation with 1515 min ^-1 running.

Since asynchronous machines can be operated both subsynchronously and oversynchronously, the following relationship applies to a four-pole machine:

Subsynchronous operation: slip s> 0 → motor operation n _N = 1480 min ⁻¹
Oversynchronous operation: slip s <0 → generator operation n _N = 1515 min ⁻¹

Because the rotor speed is higher than the rotating field speed in oversynchronous operation, the rotor frequency is also higher than the rotating field frequency. A voltage is thus induced in each of the bars of the rotor. Since the bars are spatially offset from one another, there is also a phase shift between the respective voltages of the individual bars. This means that a multi-phase voltage is effective in the rotor . Has the runner z. B. 25 rods, 25 phase-shifted AC voltages are effective. Since the rotor bars are connected to the front sides of the rotor via short-circuit rings, a multi-phase alternating current flows. With 25 bars, a 25-phase alternating current flows . Around the rotor , the multi-phase alternating current causes a rotor rotating field that has exactly the same number of poles as the exciting stator rotating field, since the squirrel cage rotor automatically adapts to the number of poles on the stator. For this reason, this rotor can be used for a large number of poles. The rotor rotating field is offset by the load angle λ compared to the stator rotating field and rotates in the direction of rotation of the rotor, lagging behind the rotor by the amount of slip because the rotor (oversynchronously) rotates faster than the stator rotating field. However, the prerequisite is that the drive power remains the same. The rotor field induces a voltage in the stator winding .

Efficiency

Losses in the asynchronous generator

For generators that are operated with a long duty cycle, the efficiency of the machine is of great importance. The efficiency of the generator is essentially influenced by three factors, the copper losses , the iron losses and the friction losses . In the case of generators that are operated in partial load operation for a long time, good partial load efficiency is also important. The load-dependent additional losses are generally 0.5 percent of the rated power output. The efficiency η of the generator can be optimized by constructive measures . Depending on the performance, this optimum is up to 90 percent for asynchronous generators, and even higher for larger generators.

Power factor

The power factor cos φ in the asynchronous generator is load-dependent. This is particularly important when the machine has a small overturning moment . The power factor is a measure of the machine quality. This means that as the reactive power requirement increases at a given operating point of the generator, the machine current also increases. The greater machine current in turn leads to greater losses. In the partial load range, a deterioration in the power factor leads to a relative deterioration in the loss balance of the machine. Therefore, when designing the machine, it is important to ensure in advance whether the generator has to work in the extreme partial load range for a long time. The magnetization requirements of the machine can be better adapted through power switchable stator windings. With this measure, the required reactive power requirement is already matched on the generator side to the active power actually delivered. The optimal machine-side power factor for modern asynchronous generators is 0.87.

Magnetic excitation

The three-phase asynchronous generator does not require a permanently connected direct current source for magnetic excitation . However, it is also unable to magnetically excite itself. This is due to the fact that the direction of the inductive reactive component remains unchanged between motor and generator operation. For this reason it is not possible for the asynchronous generator to feed into a network that is only loaded with inductive or ohmic resistances. Ohmic and inductive resistances cannot supply the required inductive current, which in this case serves as magnetizing current. The necessary excitation of the asynchronous generator can take place by external excitation or by capacitor excitation. The external excitation occurs through connection to a network fed by synchronous generators; the synchronous generators can supply the necessary inductive reactive current. This circuit is then called a line-excited asynchronous generator. The capacitor is excited by connecting capacitors in parallel to the stator winding. This circuit is then called a capacitor-excited or self-excited asynchronous generator.

Line-excited asynchronous generator

In line-excited asynchronous generators, the stator draws the reactive power required to build up the magnetic field from the supply network . For this it is necessary that other generators work as phase shifters and deliver the required reactive power. If the rotor is driven oversynchronously, this is called a negative slip. The primary voltage is created in the rotor - U ₀₂ . The rotor current flows - I ₂ . This rotor current in turn causes the rotor field which, due to the negative slip, runs counter to the mechanical direction of rotation. The result is that the asynchronous machine feeds real power into the grid. The active power fed into the network increases with the increase in the oversynchronous speed. The network frequency is determined by the connected synchronous generators . ${\ displaystyle \ Phi _ {2}}$

Capacitor-excited asynchronous generator

In a capacitor-excited asynchronous generator, the parallel connection of stator winding and capacitor forms an oscillating circuit . In addition, some residual magnetism must still be present in the rotor iron . If there is no longer any remanence , the rotor iron must be pre- magnetized using a battery . Corresponding power electronics are required for this. With the help of the resonant circuit, the magnetic flux is built up in the stator circuit. If the capacitors are dimensioned accordingly, the desired original voltage is generated. The asynchronous generator works without a reactive power supply from the network. The capacitors can be connected in both star and delta . However, it has proven itself in practice that the capacitors are connected in a triangle. However, the capacitors must not be connected directly to the generator terminals, as this would result in undesirable self-excitation. To avoid this, the capacitors must be connected at the end of the line. Since the frequency of the asynchronous generator is not influenced very much, another parameter, in this case the voltage, has to be kept constant. With asynchronous generators, the voltage is speed-dependent and must be kept constant by means of a control. This is done by regulating the speed. To keep the voltage constant, it must be possible to change the speed between idle and full load. Any frequency fluctuations that may occur are of no practical importance.

business

If the rotor is driven, the resonant circuit consisting of the main winding and capacitor is excited by the remanence of the rotor core until a stable operating point is established. When loaded, the asynchronous generator requires additional reactive power. The increasing reactive current component of the stator current must also be provided from the capacitor reactive power. The reactive power of the capacitors is often insufficient in the case of a higher load to cover the demand of the asynchronous generator for magnetizing reactive power . In this case the generator de-energizes. This load dependency of the terminal voltage is greater with ohmic-inductive load than with pure active load. This is because with an ohmic-inductive load, the available magnetizing current is reduced by the inductive reactive current requirement of the load. To reduce the load-dependent voltage drop , instead of fixed capacitors, exciter capacitances can be used, which can be adjusted in stages. However, this can lead to voltage peaks when switching the capacitors. Another good variant to improve the voltage constancy is the use of saturation reactors. Choke coils are connected in parallel to the capacitors. The iron core of the choke coils is designed in such a way that it is saturated even at a low magnetic flux density . These saturable chokes partially bypass the capacitors if the induced voltage rises to an impermissibly high level. As a result, they weaken the excitement and thus also the tension. Another variant, for generators up to a maximum of 100 kilowatts, is the use of a voltage-influenced speed controller. By changing the speed, the voltage can be regulated within a certain range. As a result, the voltage remains constant despite the unchanged capacitor. However, the frequency fluctuates by around ten percent.

Network connection

An asynchronous generator can be connected to an existing network very easily. In contrast to the synchronous generator, synchronization is problem-free with the asynchronous generator. There are two ways of connecting to the grid , direct grid coupling and inverter coupling.

Direct network coupling

Asynchronous generators can be connected to the grid without any special precautions; this is called direct or rigid grid coupling. This connection can take place either at standstill or at any speed. The asynchronous machine automatically pulls the entire machine set “into step”. Due to the slip, there is a softer coupling to the network. However, this only applies to asynchronous generators with lower power, which have a relatively high slip. In the case of machines with a higher output, a network surge occurs when connecting to the network. To avoid this, larger asynchronous generators are not connected directly to the grid. In addition, fluctuations in the driving machine, e.g. B. in wind turbines, wind fluctuations, transferred as load fluctuations into the network. This leads to flicker and voltage fluctuations in the network . If the asynchronous generator is left connected to the mains when the prime mover fails, it continues to run as a motor and consumes energy from the mains (reverse power). The effect is z with some asynchronous generators. B. used in block-type thermal power stations or in certain early wind turbines as a starting aid. This variant of the network coupling was z. B. in wind turbines of the so-called "Danish concept", which due to its simplicity in the 1980s and z. T. the 1990s were often used, widespread. The direct network coupling is hardly used any more due to the disadvantages for the network.

Converter coupling

It is advantageous if the asynchronous generator is connected to the network via a converter . Two converter types are used for asynchronous generators, the direct converter and the converter with intermediate circuit.

Direct converter

With this type of converter, the input and output are directly connected without an intermediate circuit by means of semiconductor valves, e.g. B. thyristors , interconnected. From the three voltages of the three-phase network, three approximately sinusoidal voltages are generated. Although the output frequency is variable, it is smaller than the input frequency. Due to the extensive power section, direct converters require a complicated control. For this reason, despite their high degree of efficiency, they are only rarely used in asynchronous generators.

Inverter with intermediate circuit

Converter-coupled asynchronous generator

When connecting to the network with a DC link converter, a pulse converter, namely an IGBT converter, is connected between the asynchronous generator and the network . The stator winding of the asynchronous generator is connected to the converter system. The output of the inverter feeds into the three-phase network via an LC filter. The converter system consists of:

LC filter
Pulse rectifier
DC voltage intermediate circuit
Pulse inverter.

A fourth pulse inverter bridge branch makes it possible to create a four-wire network with a neutral wire . The inverter is regulated in such a way that the phase voltages form a symmetrical three-phase system. A microcontroller- controlled IGBT converter allows the system's operating range to be expanded on the network. In addition, high-quality island operation can also be achieved.

Additional reactive power compensation

Reactive power compensation system (75 kvar): saturation chokes in the middle, metal-paper capacitors at the bottom

Since line-excited asynchronous generators place a heavy load on the network due to the required reactive power, it is often necessary to generate additional reactive power compensation using capacitors. The generator reactive power is compensated to 90% by a capacitor bank connected in parallel, this corresponds to a cos φ of 0.96. A larger compensation is difficult to carry out with simple capacitors, since the resonance frequency of the resonant circuit can lead to harmonics when it approaches the mains frequency , which in turn would result in mechanical oscillations . In addition, a high proportion of harmonics has a disadvantageous effect on connected electronic loads.

It should also be noted that the self-excitation limit can be exceeded. This means that the generator generates a voltage despite the network being switched off. This self-excitation occurs when the capacitors are too large. Without a load, the frequency at the generator terminals increases with increasing voltage. Another problem arises when the generator excites itself when the idling speed increases, although the compensation capacitors are dimensioned in such a way that the self-excitation limit is not reached during nominal operation. In order to prevent possible damage to compensated systems, these systems are provided with additional protective devices, these are:

Frequency monitoring (today ± 1 Hertz possible)
Voltage monitor
Phase error angle measurement
Interlocking the circuit breaker with the compensation system
Automatic compensation system

Furthermore, the compensation system must be locked so that it is only switched to the grid together with the generator.

Island operation

With asynchronous generators alone, isolated operation (without mains connection), e.g. B. can be achieved as an emergency generator. The "self-excited asynchronous generator" represents one possibility for island operation. Without connection to an external three-phase network that is able to provide inductive reactive power for magnetization, the reactive power can be made available by a parallel-connected capacitor battery, which itself requires capacitive reactive power and thus emits inductive. In isolated operation, the frequency is given constant by the converter. The voltage amplitude is regulated taking into account the maximum phase current amplitude. In the event of an overload, the voltage amplitude is reduced if necessary. This task cannot be accomplished with a simple capacitor-excited asynchronous generator. High-quality island operation using an asynchronous generator can only be carried out with precise control electronics. Problems with island operation result from single-phase loading. This single-phase load disturbs the symmetry in the stand-alone grid. Precise regulation is required to compensate for these disturbances. The control electronics ensure that only the active power that is currently required is supplied so that the generator voltage does not become too high. Furthermore, the control electronics ensure that there are no dangerous excess voltages in the lightly loaded outer conductor.

Advantages and disadvantages

advantages

Robust
Low maintenance
Soft network coupling
No synchronization required
Speed elastic
Inexpensive

Source:

disadvantage

Reactive power demand from the grid
No cos φ regulation
Capacitor battery required for isolated operation
Not suitable as a phase shifter

Areas of application

Asynchronous generators with squirrel cage rotors are mainly used in decentralized small power plants with outputs of up to 1500 kilowatts .

Application examples

Statutory provisions and other regulations

EN 60 034 Part 1 General provisions for rotating electrical machines
EN 60 034 part 8 Terminal designations and direction of rotation for electrical machines
DIN IEC 34 Part 7 Types of rotating electrical machines
EN 60034-5 Degrees of protection of rotating electrical machines
EN 60034-6 Types of cooling, rotating electrical machines

literature

Gregor D. Häberle, Heinz O. Häberle: Transformers and electrical machines in power engineering systems. 2nd edition, Verlag Europa-Lehrmittel, Haan-Gruiten, 1990, ISBN 3-8085-5002-3
Ernst Hörnemann, Heinrich Hübscher: Electrical engineering specialist training in industrial electronics. 1st edition. Westermann Schulbuchverlag GmbH, Braunschweig, 1998, ISBN 3-14-221730-4
Gert Hagmann: Power electronics. 3rd edition, AULA-Verlag GmbH, Wiebelsheim, 2006, ISBN 978-3-89104-700-2

Individual evidence

↑ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k Andreas Kremser: Electrical machines and drives, fundamentals, motors and applications. 2nd edition, Teubner Verlag, Stuttgart, 2004, ISBN 3-519-16188-5 , pp. 121-124.

^ A. Senner: Electrical engineering. 4th edition. Verlag Europa-Lehrmittel, 1965.

↑ ^a ^b ^c ^d Günter Boy, Horst Flachmann, Otto Mai: The master's examination in electrical machines and control technology. 4th edition, Vogel Buchverlag, Würzburg, 1983, ISBN 3-8023-0725-9 .

↑ ^a ^b ^c Clarence Feldmann: Asynchronous generators for single and multi-phase alternating currents . Your theory and mode of action, published by Julius Springer, Berlin 1903, pp. 23–35.

↑ ^a ^b ^c ^d ^e Rolf Fischer: Electrical machines . 12th edition, Carl Hanser Verlag, Munich and Vienna, 2004, ISBN 3-446-22693-1 .

↑ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ Franz Moeller, Paul Vaske (ed.): Electrical machines and converters. Part 1 structure, mode of operation and operating behavior, 11th revised edition, BG Teubner, Stuttgart 1970.

^ Klaus Fuest, Peter Döring: Electrical machines and drives. 6th edition, Friedrich Vieweg Sohn Verlag / GWV Fachverlage GmbH, Wiesbaden 2004, ISBN 3-528-54076-1 .

↑ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k ^l ^m ⁿ Erich Hau: Wind power plants, basics, technology, use, economy. 4th completely revised edition, Springer Verlag, Berlin Heidelberg 2003, ISBN 978-3-540-72150-5 .

↑ Heinz M. Hiersig (Ed.): VDI-Lexikon Maschinenbau. VDI-Verlag GmbH, Düsseldorf 1995, ISBN 9783540621331 .

↑ Herbert Kindler, Klaus-Dieter Haim: Basic connections in electrical engineering, charge-field networks . Vieweg technical books, 1st edition, Friedrich Vieweg & Sohn Verlag, Wiesbaden 2006, ISBN 3-8348-0158-5 , p. 290.

↑ ^a ^b ^c Eckhard Spring: Electrical Machines - An Introduction, . 3rd edition, Springer Verlag Heidelberg-Dordrecht-London-New York, Berlin Heidelberg 2009, ISBN 978-3-642-00884-9 , pp. 225-238.

↑ ^a ^b Siegfried Heier : Wind power plants, system design, network integration and control. 5th edition, Vieweg + Teubner, Wiesbaden 2009, ISBN 978-3-8351-0142-5 , pp. 158-167.

^ ^A ^b Ekbert Hering, Rolf Martin, Jürgen Gutekunst, Joachim Kempkes: Electrical engineering and electronics for mechanical engineers. 2nd edition, Springer Verlag Heidelberg-Dordrecht-London-New York, Berlin Heidelberg 2012, ISBN 978-3-642-12880-6 , pp. 399-407.

↑ ^a ^b A. Königswerther (Ed.), W. Winkelmann: Floor plan of electrical engineering. V. tape, transformers and asynchronous motors; Their mode of operation, calculation and construction, Verlagbuchhandlung Dr. Max Jänecke, Hanover 1907, pp. 124–128.

↑ ^a ^b ^c Helmut Schaefer: Electrical power plant technology. Fundamentals, machines and devices, protection, control and automation technology, Springer Verlag Berlin - Heidelberg, Berlin Heidelberg 1979, ISBN 978-3-540-08865-3 , pp. 56-57.

↑ ^a ^b ^c ^d ^e Th. Buchhold, H. Happoldt: Electrical power plants and networks. Second edition, Springer Verlag Berlin - Heidelberg GmbH, Berlin Heidelberg 1952, pp. 101-124.

^ Siegfried Heier: Use of wind energy. 3rd completely revised edition, Druck Verlag TÜV Rheinland GmbH, Cologne 1996, ISBN 3-8249-0242-7 , pp. 38, 39.

↑ ^a ^b ^c ^d ^e Hans Kurt Köthe: Power supply with wind generators. Franzis-Verlag GmbH & Co. KG, Munich 1992, ISBN 3-7723-4491-7 .

↑ Carlos Ferrer Moncada: The self-excitation of asynchronous generators . Doctoral thesis at the Swiss Federal Institute of Technology in Zurich, printed by Thomas & Hubert, Weida in Thuringia 1935.

^ F. Blaabjerg, Z. Chen, R. Teodorescu, F. Iov: Power Electronics in Wind Turbine Systems . Online (accessed March 23, 2012; PDF; 579 kB).

↑ Thomas Fladerer: The asynchronous generator in the small power plant . Loher GmbH, Ruhstorf / Rott 2004 Online ( Memento from July 16, 2012 in the Internet Archive ).

↑ ^a ^b ^c Klaus Heuck, Klaus-Dieter Dettmann, Detlef Schulz: Electrical energy supply. 9th edition, Springer Vieweg, Wiesbaden 2013, ISBN 978-3-8348-1699-3 , pp. 342–355.

↑ ^a ^b ^c ^d ^e ^f Martin Kaltschmitt, Wolfgang Streicher, Andreas Wiese (eds.): Renewable energies - system technology, economic efficiency, environmental aspects. Springer Fachmedien Wiesbaden, pp. 488–496.

↑ Asynchronous generators Danish concept (accessed via Waybackmachine on May 9, 2019).

↑ ^a ^b ^c Yulong Huang, Hartmut Mrugowski: Control procedure for grid and island operation of a small hydropower plant with asynchronous generator . Rostock University, Institute for Electrical Power Engineering.

↑ Yulong Huang, Hartmut Mrugowski: Small hydropower plant with asynchronous generator and converter control strategy for island operation . Rostock University, Institute for Electrical Power Engineering. ISBN 9783832502508 .

↑ TÜV Süddeutschland (Ed.): Special features when using power generating sets . Online (accessed March 23, 2012).

↑ Patent specification: Method for exciting an asynchronous machine for island operation and device. Document identification DE102007043123A1, April 2, 2009. Online (accessed March 23, 2012).

↑ Metallwarenfabrik Gemmingen GmbH: GEKO power generator systems . Gemmingen 2013, pp. 4–8.

^ Jürgen Staab: Renewable energies in municipalities. 2nd revised and expanded edition, Springer Fachmedien Wiesbaden, Wiesbaden 2013, ISBN 978-3-8349-4403-0 , pp. 77-79.

↑ Solar Atlas Leipzig Hydroelectric Power Plants Generators (accessed via Waybackmachine on May 9, 2019).

Web links

Comparison of asynchronous generator / synchronous generator (last accessed on February 5, 2015)
Grid perturbations from wind turbines in wind parks. Online (accessed March 23, 2012; PDF; 192 kB)
Grid perturbations caused by the operation of wind turbines on the grid [1] (accessed on March 23, 2012; PDF; 517 kB)
Michael Häusler: Power electronics for connecting large offshore wind farms to the network [2] (accessed on March 23, 2012; PDF; 109 kB)

[Quelle_25-1] ↑ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k Andreas Kremser: Electrical machines and drives, fundamentals, motors and applications. 2nd edition, Teubner Verlag, Stuttgart, 2004, ISBN 3-519-16188-5 , pp. 121-124.

[Quelle_5-2] A. Senner: Electrical engineering. 4th edition. Verlag Europa-Lehrmittel, 1965.

[Quelle_4-3] Günter Boy, Horst Flachmann, Otto Mai: The master's examination in electrical machines and control technology. 4th edition, Vogel Buchverlag, Würzburg, 1983, ISBN 3-8023-0725-9 .

[Quelle_20-4] Clarence Feldmann: Asynchronous generators for single and multi-phase alternating currents . Your theory and mode of action, published by Julius Springer, Berlin 1903, pp. 23–35.

[Quelle_1-5] Rolf Fischer: Electrical machines . 12th edition, Carl Hanser Verlag, Munich and Vienna, 2004, ISBN 3-446-22693-1 .

[Quelle_2-6] ↑ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ Franz Moeller, Paul Vaske (ed.): Electrical machines and converters. Part 1 structure, mode of operation and operating behavior, 11th revised edition, BG Teubner, Stuttgart 1970.

[Quelle_7-7] Klaus Fuest, Peter Döring: Electrical machines and drives. 6th edition, Friedrich Vieweg Sohn Verlag / GWV Fachverlage GmbH, Wiesbaden 2004, ISBN 3-528-54076-1 .

[Quelle_3-8] ↑ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k ^l ^m ⁿ Erich Hau: Wind power plants, basics, technology, use, economy. 4th completely revised edition, Springer Verlag, Berlin Heidelberg 2003, ISBN 978-3-540-72150-5 .

[Quelle_8-9] Heinz M. Hiersig (Ed.): VDI-Lexikon Maschinenbau. VDI-Verlag GmbH, Düsseldorf 1995, ISBN 9783540621331 .

[Quelle_21-10] Herbert Kindler, Klaus-Dieter Haim: Basic connections in electrical engineering, charge-field networks . Vieweg technical books, 1st edition, Friedrich Vieweg & Sohn Verlag, Wiesbaden 2006, ISBN 3-8348-0158-5 , p. 290.

[Quelle_23-11] Eckhard Spring: Electrical Machines - An Introduction, . 3rd edition, Springer Verlag Heidelberg-Dordrecht-London-New York, Berlin Heidelberg 2009, ISBN 978-3-642-00884-9 , pp. 225-238.

[Quelle_29-12] Siegfried Heier : Wind power plants, system design, network integration and control. 5th edition, Vieweg + Teubner, Wiesbaden 2009, ISBN 978-3-8351-0142-5 , pp. 158-167.

[Quelle_22-13] A ^b Ekbert Hering, Rolf Martin, Jürgen Gutekunst, Joachim Kempkes: Electrical engineering and electronics for mechanical engineers. 2nd edition, Springer Verlag Heidelberg-Dordrecht-London-New York, Berlin Heidelberg 2012, ISBN 978-3-642-12880-6 , pp. 399-407.

[Quelle_31-14] A. Königswerther (Ed.), W. Winkelmann: Floor plan of electrical engineering. V. tape, transformers and asynchronous motors; Their mode of operation, calculation and construction, Verlagbuchhandlung Dr. Max Jänecke, Hanover 1907, pp. 124–128.

[Quelle_24-15] Helmut Schaefer: Electrical power plant technology. Fundamentals, machines and devices, protection, control and automation technology, Springer Verlag Berlin - Heidelberg, Berlin Heidelberg 1979, ISBN 978-3-540-08865-3 , pp. 56-57.

[Quelle_26-16] Th. Buchhold, H. Happoldt: Electrical power plants and networks. Second edition, Springer Verlag Berlin - Heidelberg GmbH, Berlin Heidelberg 1952, pp. 101-124.

[Quelle_9-17] Siegfried Heier: Use of wind energy. 3rd completely revised edition, Druck Verlag TÜV Rheinland GmbH, Cologne 1996, ISBN 3-8249-0242-7 , pp. 38, 39.

[Quelle_6-18] Hans Kurt Köthe: Power supply with wind generators. Franzis-Verlag GmbH & Co. KG, Munich 1992, ISBN 3-7723-4491-7 .

[Quelle_10-19] Carlos Ferrer Moncada: The self-excitation of asynchronous generators . Doctoral thesis at the Swiss Federal Institute of Technology in Zurich, printed by Thomas & Hubert, Weida in Thuringia 1935.

[Quelle_11-20] F. Blaabjerg, Z. Chen, R. Teodorescu, F. Iov: Power Electronics in Wind Turbine Systems . Online (accessed March 23, 2012; PDF; 579 kB).

[Quelle_12-21] Thomas Fladerer: The asynchronous generator in the small power plant . Loher GmbH, Ruhstorf / Rott 2004 Online ( Memento from July 16, 2012 in the Internet Archive ).

[Quelle_30-22] Klaus Heuck, Klaus-Dieter Dettmann, Detlef Schulz: Electrical energy supply. 9th edition, Springer Vieweg, Wiesbaden 2013, ISBN 978-3-8348-1699-3 , pp. 342–355.

[Quelle_28-23] ↑ ^a ^b ^c ^d ^e ^f Martin Kaltschmitt, Wolfgang Streicher, Andreas Wiese (eds.): Renewable energies - system technology, economic efficiency, environmental aspects. Springer Fachmedien Wiesbaden, pp. 488–496.

[Quelle_13-24] Asynchronous generators Danish concept (accessed via Waybackmachine on May 9, 2019).

[Quelle_14-25] Yulong Huang, Hartmut Mrugowski: Control procedure for grid and island operation of a small hydropower plant with asynchronous generator . Rostock University, Institute for Electrical Power Engineering.

[Quelle_15-26] Yulong Huang, Hartmut Mrugowski: Small hydropower plant with asynchronous generator and converter control strategy for island operation . Rostock University, Institute for Electrical Power Engineering. ISBN 9783832502508 .

[Quelle_16-27] TÜV Süddeutschland (Ed.): Special features when using power generating sets . Online (accessed March 23, 2012).

[Quelle_17-28] Patent specification: Method for exciting an asynchronous machine for island operation and device. Document identification DE102007043123A1, April 2, 2009. Online (accessed March 23, 2012).

[Quelle_19-29] Metallwarenfabrik Gemmingen GmbH: GEKO power generator systems . Gemmingen 2013, pp. 4–8.

[Quelle_27-30] Jürgen Staab: Renewable energies in municipalities. 2nd revised and expanded edition, Springer Fachmedien Wiesbaden, Wiesbaden 2013, ISBN 978-3-8349-4403-0 , pp. 77-79.