A small-scale standalone wind energy conversion system featuring SCIG, CSI and a novel storage integration scheme

doi:10.1016/j.renene.2015.12.041

Renewable Energy

Volume 89, April 2016, Pages 360-370

https://doi.org/10.1016/j.renene.2015.12.041 Get rights and content

Highlights

•
A comparison between PWM-CSI and PWM-VSI for small-scale standalone wind energy conversion system (WECS) is conducted.
•
A CSI-based SCIG WECS with a novel scheme for integration of a battery-based energy storage system is proposed.
•
A systematic approach for the dc-link inductor design is presented.
•
The performance of the proposed system under variable wind and load conditions are demonstrated through simulation.

Abstract

In this paper, a small-scale standalone wind energy conversion system composed of a squirrel-cage induction generator, a buck converter and a current-source inverter is proposed, as an attractive renewable energy solution for off-grid communities. Geared squirrel-cage induction generators are well-known for their robustness, simplicity, light weight and low cost. Current-source inverters, even though mainly used in medium-voltage, high power applications, and proposed for megawatt-level grid-connected wind energy conversion systems, offer potential benefits in small-scale off-grid wind energy conversion systems that are yet to be investigated and evaluated against those of commonly-used voltage-source inverters. In the proposed system, the generator's shaft speed is controlled by a buck converter to extract maximum available wind power in normal mode of operation, and the wind power is dumped when it is not possible to absorb maximum available power by the storage system and the load. A novel scheme for integration of a battery energy storage system is proposed and an effective power management algorithm is employed to maintain the supply-demand power balance through direct control of dc-link current. A systematic approach for the dc-link inductor design is presented. The feasibility of the proposed system and its performance under variable wind and load conditions are analyzed and demonstrated through simulation.

Introduction

Small-scale, standalone wind turbines, equipped with a properly-sized energy storage system, offer a promising renewable energy-based solution for electricity needs of off-grid communities.

Although permanent-magnet synchronous generator (PMSG) is the dominant generator type in off-grid small-scale variable-speed wind turbine systems, the issues of high cost and insecurity of future supply of rare-earth material used in magnets remain to be resolved [1]. On the contrary, squirrel-cage induction generator (SCIG) has been highly recommended as a robust, low-cost and low-maintenance machine for small-scale standalone wind energy conversion system (WECS) [1].

In a variable-speed wind turbine system, the time-varying generated ac power is rectified to dc and then inverted to ac power with regulated voltage and frequency, as required by the load. A three-phase diode bridge rectifier offers the simplest and most economical rectifier structure. The inversion is traditionally performed by a pulse-width modulated voltage-source inverter (PWM-VSI). Due to voltage step-down nature of VSI, a dc/dc booster is usually employed to keep the dc-link voltage high enough to allow generation of the desired ac output voltage [2], [3]. To date, VSI is the dominant topology in both large- and small-scale WECS [4]. The potential of an impedance-source inverter, as a replacement for the conventional VSI-dc booster combination in standalone WECS, has been demonstrated in Ref. [5]. Current-source inverter (CSI), on the other hand, has been adopted mainly in medium-voltage, high-power applications. To date, different configurations of CSI-based power electronic converters have been proposed and validated for megawatt-level on-grid WECS [6], [7]. The advantageous features reported in the literature for CSI, when substantiated, can make CSI a promising option and possibly a preferred choice for small-scale standalone WECS.

This paper focuses on developing a CSI-based small-scale standalone WECS and attempts to verify the feasibility of the proposed system by addressing the challenges associated with maximum power tracking, energy storage integration, power management and dc-link inductor design.

The paper is organized as follows. The advantages of CSI over VSI, relevant to the work presented in this paper, are highlighted in Section 2. Section 3 introduces the proposed system including the proposed energy storage system integration scheme. The approach to dc-link inductor design is described in Section 4. Section 5 gives the control scheme details. Simulation results are presented in Section 6. Finally, Section 7 concludes the paper.

Section snippets

PWM-CSI versus PWM-VSI for standalone WECS

This section conducts a comparison based on reliability, cost, efficiency, and protection requirements, between PWM-CSI and PWM-VSI for small-scale standalone WECS, assuming that the inverters use six IGBT switches with six antiparallel diodes (VSI) or series diodes (CSI), feed the same three-phase R-L load at the same voltage and frequency, have comparable ratings and operate at the same switching frequency and under the same environmental conditions.

System description

Fig. 1 shows the proposed wind energy conversion system. The system consists of the rotor blades, a geared-drive self-excited squirrel-cage induction generator, a three-phase diode bridge rectifier, a dc/dc buck converter, a dc-Link inductor, a three-phase PWM IGBT current-source inverter, a capacitor filter, a delta/star (Δ/Yn) transformer, a Y-connected three-phase R-L load, a battery-based energy storage system integrated with the dc-link via a full-bridge dc/dc converter with reduced number

Design of DC-link inductor

A standalone WECS, employing a diode rectifier, a dc/dc boost converter, a VSI and a bidirectional buck-boost dc/dc converter as the interface of the storage battery with the system requires two inductors (one for the boost converter and one for the buck-boost converter), and a dc-link capacitor. In the proposed WECS, in contrast, the dc-link inductor (L_dc) is shared by the buck converter, reduced H-bridge and CSI, resulting in reduction of the system size, weight and cost. L_dc is sized

Control strategies

The controller blocks, shown in Fig. 1, are designed to achieve the following tasks:

Simulation results and discussion

To evaluate the performance of the proposed system, a 20 kW standalone WECS using a 460 Vrms SCIG and feeding a three-phase R-L load requiring a regulated voltage of 380 V/220 Vrms at 60 Hz, is modeled in Matlab/Simulink environment. The system's parameters are given in Appendix B. The performance of the system is examined under variable wind speed and unbalanced three-phase R-L load, according to the wind speed and load profiles given in Table 3. The rated values for the unbalanced load are

Conclusion

A small-scale standalone WECS based on self-excited SCIG and a CSI was proposed. A dc/dc buck converter was used to extract maximum power from wind. A novel storage integration scheme was implemented inspired by the duality of CSI and VSI. The dc-link inductor, shared by three converters, was systematically designed. A novel control algorithm was developed to regulate the dc-link current through power management among battery bank and dump load. The proposed system was examined under both

Acknowledgments

The authors would like to acknowledge the financial support received from the Royal Commission for Jubail & Yanbu (RCJY) in the Kingdom of Saudi Arabia through the Saudi culture bureau in Canada.

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View full text

A small-scale standalone wind energy conversion system featuring SCIG, CSI and a novel storage integration scheme

Highlights

Abstract

Introduction

Section snippets

PWM-CSI versus PWM-VSI for standalone WECS

System description

Design of DC-link inductor

Control strategies

Simulation results and discussion

Conclusion

Acknowledgments

Renew. Sustain. Energy Rev. (Elsevier)

Electr. Power Energy Syst. (Elsevier)

Microelectron. Reliab.

J. Microelectron. Reliab. Elsevier

Permanent magnet synchronous generator-based standalone wind energy supply system

IEEE Trans. Sustain. Energy

Power electronics converters for wind turbine systems

IEEE Trans. Ind. Appl.

Standalone SCIG-based wind energy conversion system using Z-source inverter with energy storage integration

A novel converter configuration for wind applications using PWM CSI with diode rectifier and buck converter

Current Source Converters for Megawatt Wind Energy Conversion Systems

Toward reliable power electronics – challenges, design tools and opportunities

IEEE Ind. Electron. Mag.

Examples for Failures in Power Electronics Systems

An industry-based survey of reliability in power electronic converters

IEEE Trans. Ind. Appl.

A smart gate drive with self-diagnosis for power MOSFETs and IGBTs

A new fault detection technique for IGBT based on gate voltage monitoring

Freewheeling diode reverse-recovery failure modes in IGBT applications

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