FEASIBILITY STUDY FOR THE USE OF ASYNCHRONOUS GENERATORS IN WIND POWER PLANTS

ABSTRACT

World population growth drives energy demand. Electricity from conventional energy sources can no longer cover existing consumption. Therefore, the development of renewable energy sources, especially wind power, is a modern requirement. The production of electricity in wind turbines is mainly carried out by synchronous generators. However, recent studies have shown that the use of asynchronous generators in wind turbines is technically and economically beneficial. The article analyzes the technical issues of electricity production using asynchronous generators in wind power plants.

АННОТАЦИЯ

Рост мирового населения стимулирует спрос на энергию. Электроэнергия из обычных источников энергии больше не может покрывать существующее потребление. Поэтому развитие возобновляемых источников энергии, особенно энергии ветра, является современным требованием. Производство электроэнергии в ветряных турбинах в основном осуществляется синхронными генераторами. Однако недавние исследования показали, что использование асинхронных генераторов в ветряных турбинах технически и экономически выгодно. В статье анализируются технические вопросы производства электроэнергии с использованием асинхронных генераторов на ветроэнергетических установках.

Keywords: wind turbine, asynchronous generator, wind power plant, energy sources, analyzing the technical issues.

Ключевые слова: ветряная турбина, асинхронный генератор, ветряная электростанция, источники энергии, анализ технических вопросов.

Introduction

The use of non-traditional and alternative energy sources is currently one of the most common tasks, both in terms of creating energy resources and in terms of their consumption. Particular interest in such energy sources comes from the population located in areas remote from the central power supply, in other words, in areas without electrification. Energy received during operation alternative energy sources can be used both for constant power supply and for backup power supply, which is especially convenient for cottage settlements, small settlements or strategic sites. The wind turbines that were originally designed for use in rural areas were directly connected to the generators, that is, the generator and turbine had the same revolution per minute. In modern systems, the turbine is connected to the generator via a gearbox that allows variable generator speeds, up to 4 to 5 times the speed of the turbine, or even more.  For example, if the turbine rotates at 100 rpm, the generator can have a 400 rpm speed. While this reduces the generating cost, it increases the weight (and costs) of the wind converter and its tower, and has a one-time procurement and annual maintenance costs of the gearbox.

Analysis of asynchronous generators

In comparison to light weight systems, heavier wind converters cause further difficulties in crane hauling and installation on the tower top. One of the advantages of direct connection of the turbine and the generator is elimination of the gearbox and its maintenance requirements [1].

The operation of any asynchronous machine in generator mode requires a reactive power source. The value of the capacitance required to excite the generator at a given frequency:

                                           (1)

where  L₁ and L_m - the inductance of the stator winding and the magnetizing circuit of the generator, Hz. In general, the capacitance required to obtain the voltage across the generator at the load value is is determined by:

                              (2)

Where

                                                 (3)

                                          (4)

It is reasonable to use autonomous AG  at values

                                                    (5)

When   lower, the required capacity increases rapidly and the generator is almost completely loaded with a reactive current. AG in contrast to synchronous generators (SG), which require strict synchronization of the speed when connected in parallel, in turn, they can be configured for a fairly simple parallel operation.

Have parallel operating AG, the rotational speed may differ, while in the common circuit of stator windings a current of such a frequency is created that corresponds to resonance in a complete equivalent circuit, including, in addition to load and capacitor bank circuits, circuits of combined stator and rotor windings of generators with corresponding active and reactance resistances. AGs find little use in relatively weak current sources in autonomous power plants. Observing certain conditions, it is allowed to operate in the AG mode of powerful turbine generators. Perspectives improvement of AG and their wider implementation are associated with the ongoing development high efficiency lightweight capacitors  [2].

Comparison of asynchronous and synchronous generators

SGs of classical design with electromagnetic excitation are mounted on installations either small, or very high power. Manufacturing technology and experience in calculating such machines allows you to install powerful gearless plants (up to 2 MW) with good structural performance, high efficiency and the ability to regulate the voltage over a wide range by changing the excitation current [3]. The SG has a rigid dependence of the frequency of the generated EMF on the speed of the shaft. If the wind is gusty, then the generator generates high values ​​of the variable components in the operating parameters and together with the network the performance of such generators deteriorates. This limits, and in regions with sharp variable winds makes impossible, the use of SG for direct connection to the network. With this kind of work between the generator and the mains install a semiconductor frequency converter. Asynchronous synchronous generators (ASG) are more under development than under industrial applications. In the ASG, to a magnetically symmetric rotor, through three rings, to a three-phase (sometimes two-phase) excitation winding is supplied with voltage, the magnitude and phase of which changes proportional to slip. The excitation voltage is regulated by a converter frequency.

Conclusion

The above analysis shows that the use of asynchronous generators in small wind turbines is technically and economically efficient. Since the amount of load connected to small wind turbines is also small, there is no need to increase the power or voltage in them. It follows that low-power wind turbines are used for pre-calculated loads. In this case, the load increase will be ignored. Synchronous generators are commonly used in high power wind turbines. The advantage of generators of this type is that they have the ability to change the voltage even with increasing load. However, due to the complex design of the structure, the use of generators of this type in wind turbines is associated with a number of difficulties.

References:

1. Mohammad Taghi Ameli, Saeid Moslehpour, Amin Mirzaie “Feasibility Study for Replacing Asynchronous Generators with Synchronous Generators in Wind Farm Power Stations” Proceedings of The 2008 IAJC-IJME  International Conference.
2. Bubenchikova T., Molodikh V., Rudenok A., Danilov D., Shevchenko D. “SELECTION OF ELECTRICAL GENERATORS FOR WIND TURBINES”, International Research Journal ▪ No12 (54) Part 3, December.
3. Gaber El Saady , El-Nobi A.Ibrahim,  Hamdy Ziedan ,Mohammed M.Soliman “Analysis of Wind Turbine Driven Permanent Magnet Synchronous Generator under Different Loading Conditions”, Innovative Systems Design and Engineering  Vol.4, No.14, 2013.