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Article
Publication date: 1 January 2012

Grzegorz Iwanski and Gonzalo Abad

Doubly fed induction generator DFIG applied in over 50 percent of modern variable speed wind power systems and interesting also for adjustable speed diesel generation sets…

Abstract

Purpose

Doubly fed induction generator DFIG applied in over 50 percent of modern variable speed wind power systems and interesting also for adjustable speed diesel generation sets or multi‐megawatt water turbines is troublesome in the mean of maintenance of slip‐rings and brushes. Especially, it concerns isolated power systems and offshore wind turbines. Application of brushless DFIG in such cases eliminates the mentioned problem. Constructions of the machine and consequently the model and mathematical description is more complicated than classical slip‐ring DFIG, therefore it is still developed in several scientific institutions to obtain adequate performance. The following work is dedicated to mathematical description, modelling and implementation of the control method for autonomous operation in the laboratory model of brushless DFIG.

Design/methodology/approach

Analysis and simulation of the machine model and laboratory tests on a small scale prototype of brushless DFIG.

Findings

It has been proven that sensorless direct voltage control of DFIG can be applied for both slip‐ring and brushless machines, as it does not require machine parameters.

Research limitations/implications

Brushless DFIG development is far from the performance needed by industrial implementation. Lower efficiency and higher reactive power needed by the machine, in comparison to classical DFIG of the same power range, result from double air gap seen by magnetic flux. However, the constructions of prototype machines are better and better, and their capabilities become closer to DFIG.

Practical implications

Variable and adjustable speed generation systems such as wind turbines, diesel generation sets, water turbines.

Originality/value

Standalone power systems with DFIG described in several papers require quite complicated control methods based on the mathematical equations of the machine model. Thus, these methods have to be significantly modified for the brushless version of this machine type, due to the fact of a much more complicated model. The proposed sensorless method of the output voltage control requires only redesign (tuning) of the PI controllers responsible for control of the rotor current, stator voltage amplitude and frequency.

Details

COMPEL - The international journal for computation and mathematics in electrical and electronic engineering, vol. 31 no. 1
Type: Research Article
ISSN: 0332-1649

Keywords

Article
Publication date: 26 August 2014

Grzegorz Iwanski, Piotr Pura, Tomasz Łuszczyk and Mateusz Szypulski

Doubly fed induction generator (DFIG) is widely used in wind energy conversion systems and it can operate with other primary movers. The purpose of this paper is to focus…

Abstract

Purpose

Doubly fed induction generator (DFIG) is widely used in wind energy conversion systems and it can operate with other primary movers. The purpose of this paper is to focus on the standalone operation of DFIG which may expand the area of possible applications and increase capabilities of the generation system in terms of power quality.

Design/methodology/approach

Synthesis of the control method was preceded by analysis of mathematical model of the machine. The control method based on the negative sequence and high harmonics extraction has been developed and verified in the laboratory unit. Control of the fundamental frequency component uses neither rotor speed nor position sensors.

Findings

The original method allows to compensate negative sequence and high harmonics of the generated voltage. At the same time, due to the active filtering capability of the grid side converter, the stator phase current shape is close to sine wave. Thus, it is seen by the machine as a linear load, what eliminates the electromagnetic torque ripples.

Practical implications

The system and control method can be applied in variable speed generation systems, e.g. wind turbines or diesel engines operating in the standalone mode.

Originality/value

Although the selective compensation of negative sequence and harmonics are known in the literature, until now the methods have been verified for the system with a rotor position sensor. Moreover, the stator current feed-forward improving the transient properties, as well as results of transient states caused by the load step change, have not been proposed in publications.

Details

COMPEL: The International Journal for Computation and Mathematics in Electrical and Electronic Engineering, vol. 33 no. 5
Type: Research Article
ISSN: 0332-1649

Keywords

Article
Publication date: 1 January 2012

Łukasz Drązikowski and Grzegorz Iwański

This paper presents control strategy of VSC connected to the unbalanced grid in stationary coordinates system. The algorithm shown in the paper can be applied to typical…

Abstract

Purpose

This paper presents control strategy of VSC connected to the unbalanced grid in stationary coordinates system. The algorithm shown in the paper can be applied to typical inverter to reduce or even eliminate oscillation of DC‐link voltage under unbalanced operation. That has a direct influence on constant flow of p component of power which is essential for drives system for reducing torque ripples.

Design/methodology/approach

The presented strategy of control assumes that orientation of grid voltage and line current vectors hodographs have to be opposite. Mathematical analysis and simulation has been done. Laboratory tests on low power has also been carried out.

Findings

This method leads to fixed p component of power flow and fixed DC bus voltage. The presented idea of control may cause reduction of voltages asymmetry in three‐phase network with significant impedance (local grid, microgrid, isolated grid).

Research limitations/implications

For 50 Hz power system, the presented control strategy has at least 5 ms response time because calculations are based on current and 5 ms delayed values of grid voltage. The paper presents only a simple steady state laboratory test that has been done in low scale of voltage and current.

Practical implications

The paper shows an example of implementation of the method with simple dead‐beat current controller based on DSP microprocessor. The algorithm can be easy applied in a DC/AC converter for elimination DC‐link oscillations under unbalanced working conditions.

Originality/value

Control methods presented in many other papers always provide sinusoidal, symmetrical three‐phase currents irrespective of grid voltage symmetry. The presented idea of control causes reduction of DC‐Link voltage and p, q components of power oscillations due to grid voltage asymmetry.

Details

COMPEL - The international journal for computation and mathematics in electrical and electronic engineering, vol. 31 no. 1
Type: Research Article
ISSN: 0332-1649

Keywords

Article
Publication date: 4 January 2011

Grzegorz Iwanski

Wind‐diesel sets offered as a reliable hybrid isolated power systems with reduction of fuel consumption, consists of variable speed wind turbines and fixed speed diesel…

Abstract

Purpose

Wind‐diesel sets offered as a reliable hybrid isolated power systems with reduction of fuel consumption, consists of variable speed wind turbines and fixed speed diesel engines. Load and wind energy variations cause, that the load power of the diesel genset is varied in wide range. Fixed speed generation set operates with the best efficiency only in a narrow range of the load, therefore implementation of a load adaptive, adjustable speed genset may additionally reduce fuel consumption.

Design/methodology/approach

Analysis of the system components model, simulation and laboratory tests on a small‐scale model.

Findings

Topology and output voltage control method of four‐wire adjustable speed autonomous wind‐diesel system dedicated for isolated power plants with high wind penetration.

Research limitations/implications

The paper presents only part of the work which has to be done for the complete system. Load and energy management has to be applied in standalone system, as not in each operating point of proposed wind‐diesel system, can rated load be supplied. To fully prove the proposed system and control concept, tests of megawatt range system are advisable. To evaluate the fuel saving, a real wind and load profile in a selected isolated place is needed.

Practical implications

Every adjustable speed generation systems can save fuel. However, proposed topology in main part consists of known and implemented solutions, therefore costs of the new installation will not be increased significantly.

Originality/value

Proposed costs effective topology of adjustable speed wind‐diesel generation system has not been presented by any other authors. Standalone operation of doubly fed induction generator system is rarely reported in the papers.

Details

COMPEL - The international journal for computation and mathematics in electrical and electronic engineering, vol. 30 no. 1
Type: Research Article
ISSN: 0332-1649

Keywords

Article
Publication date: 4 January 2011

Abdou Tankari Mahamadou, Bailo Camara Mamadou, Dakyo Brayima and Nichita Cristian

The wind speed is very fluctuant and contains a significant energy. Taking into account the turbulent component in the energy management would increase the profitability…

Abstract

Purpose

The wind speed is very fluctuant and contains a significant energy. Taking into account the turbulent component in the energy management would increase the profitability of the wind‐diesel hybrid system. Sometimes, a diesel generator is used to compensate the requested energy but the storage devices are required to prevent disturbances induced by the wind generator current on the DCbus. The purpose of this paper is to show how the battery and flywheel (or ultracapacitors (UCs)) are used to mitigate the fluctuations of the wind generator current. The proposed method is based on the filtering of the wind generator current. The high power density sources (flywheel and UCs) are used in aims to improve the batteries' lifetime, which is estimated, in this paper, by using the rainflow cycles counting method. Spectral studies are made and the simulation and experimental results are analyzed.

Design/methodology/approach

This study is organized according to the following main and sub‐topics: wind speed characteristics, hybrid system energy management, behavioral simulations results, spectral analysis and batteries' lifetime estimation and experimental setup and results.

Findings

The simulations results highlight the interest in using a second‐order filter. The experimental results show that the fluctuations induced by the wind generator current are effectively mitigated by the storage devices.

Originality/value

The spectral analysis of the current for different filters parameters is realized and the application of the rainflow cycles counting method, in this context, is presented. This paper is interesting for the experimental hybrid system design according to the method proposed to control the DCDC converters.

Details

COMPEL - The international journal for computation and mathematics in electrical and electronic engineering, vol. 30 no. 1
Type: Research Article
ISSN: 0332-1649

Keywords

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