An integrated control approach for standalone operation of a hybridised wind turbine generating system with maximum power extraction capability
Highlights
► novel remote area power supply (RAPS) configuration. ► power flow control and control strategies. ► maximum power extraction.
Introduction
Renewable energy schemes are becoming popular among regional and remote communities as a viable method of supplying power [1], [2]. Selection of suitable energy sources to form a hybrid RAPS system depends entirely on the availability of resources within the locality. Among all renewable energy options, wind power has gained the momentum as one of the most widespread and commercially viable renewable energy generation technologies [3]. However, one of the major challenges associated with wind based power generating schemes is their intermittency [4], [5]. To overcome this issue, hybrid remote area power supply (RAPS) schemes can be formed to supply reliable power to the customers [6]. Although hybrid RAPS systems offer attractive advantages and solutions for rural electrification, the design, control and operational aspects involved with such power systems are still challenging [7].
Doubly-fed induction and permanent magnet synchronous machines are more popular and widely used and dominant variable speed wind turbine generator technologies [8]. They offer many advantages over other types of wind turbine systems1 including variable speed operation, maximum power extraction capability, active and reactive power control capabilities and ability to suppress the mechanical stresses [9]. However, the involvement of power electronic devices such as inverters in variable speed wind generators represents significant cost factor in their over-all arrangement and complexity in operation.
Due to the variable nature (i.e. intermittency) of wind, a wind turbine generator alone cannot supply power to meet the load demand continuously. To make it dispatchable, similar to other conventional generation units such as a diesel generator, the generated power has to be regulated at a desired level [10]. With rapid development currently taking place on energy storage devices, their application in wind energy systems is seen to provide a promising opportunity to mitigate the issues associated with wind power fluctuations. Typically, battery storage systems are widely advocated for such remote application owing to high energy density levels [11], [12].
In recent studies, the hybrid operation of standalone variable speed wind turbine generators has been explained predominantly with other types of RAPS components such as energy storage system and diesel generators. The hybrid operation of a standalone power supply system consisting of a battery storage integrated with a DFIG and a PMSG based wind turbine generator is explained in [13], [14] respectively. Furthermore, the modelling aspects associated with the standalone operation of DFIG and PMSG are demonstrated in [15], [16] respectively. However, the hybridised wind energy system consisting of a DFIG and a PMSG together with a battery storage system has not received any research attention and forms the basis of this paper.
The proposed novel wind energy conversion system shown in Fig. 1, consists of a DFIG and a PMSG where the latter is connected to the DC bus of the DFIG. Such an arrangement of two wind turbine generators essentially avoids the necessity of having an inverter for the PMSG compared to the situations where PMSG alone serves AC loads. In addition, the battery storage is used to meet the demand-generation mismatch during over-generation and under-generation situations. The main objectives of this research work are to address the followings: (a) development of a power management methodology, (b) development of individual controllers for each system component, and (c) extraction of the maximum power from the two types of wind turbine generators (i.e. DFIG and PMSG).
Section snippets
Design considerations of the hybridised wind energy system
If the DFIG and PMSG based wind turbines are operated independently, PMSG requires an additional inverter to satisfy the customer demand (i.e. AC loads). In addition, PMSG based wind turbine generating system needs an additional battery storage system and DC link capacitor. With the proposed arrangement shown in Fig. 1, the PMSG can be operated by sharing the components with DFIG such as an inverter (i.e. LSC), a battery storage system and a DC capacitor. However, there are some limitations
DFIG and associated control
The DFIG performs as the main source of energy in the proposed RAPS system. Therefore, the main contribution towards the load side voltage and frequency regulation has to be realised using the converter control associated with the DFIG. In this regard, RSC is used to achieve the voltage and frequency regulation, whereas the DC bus voltage regulation is achieved via the LSC. To achieve these objectives, vector control scheme has been employed for the RSC and LSC. Stator indirect flux orientation
Maximum power extraction from wind
The optimal RAPS operation can be achieved by operating both DFIG and PMSG at their maximum power extraction modes. In the existing literature, several methods have been discussed to extract maximum power from wind. In general, the maximum power extraction from wind can be obtained using (19), (20), (21), (22) [18], [19] .where Pa is aero dynamic power, Pm is power output of the turbine, Cp is power coefficient of
PMSG and associated control
When a PMSG alone supplies power to the remote loads, usually it requires a back-to-back converter. However, in the proposed topology, the PMSG is connected to an uncontrolled three-phase diode bridge rectifier11 and it is interfaced to the DC bus of the DFIG via a DC/DC converter as shown in Fig. 4. Considering the voltage constant
Battery storage and associated control
Nickel–Cadmium battery model given in [20] is employed in this paper. Due to limited availability of RAPS system components, it is assumed that battery storage system is able to supply power without having any difficulties. Therefore, as in real life applications, the state of charge detection of the battery storage system has not been implemented within the converter control.
A bi-directional buck-boost converter is used to interface the battery storage with the DC bus of the back-to-back
Simulation results
The suitability of the proposed RAPS system has been investigated in relation to the ability of regulating the voltage and frequency on the load side and also the maximum power extraction capability of the two types of wind turbine generators (i.e. DFIG and PMSG). The RAPS system parameters are listed in Appendix B.
The entire RAPS system has been simulated under fluctuating wind and load conditions. Fig. 8 shows the system response and Fig. 9 illustrates the power sharing among different system
Conclusions
This paper has proposed a novel hybrid wind generating system which can be used to supply power to remote area customers. The overall operation of the RAPS system is enhanced by considering its power-electronic arrangements and by extracting maximum power from wind. These objectives have been realised by avoiding, the deployment of an inverter for the PMSG and developing the control strategies for DFIG, PMSG and battery storage system. In addition, the primary voltage and frequency control have
Acknowledgements
This work is supported by the Australian Research Council (ARC) and Hydro Tasmania Linkage Grant, LP0669245. The authors gratefully acknowledge the support and their cooperation.
References (20)
- et al.
Rural electrification in India and feasibility of photovoltaic home systems
Int J Electr Power Energy Syst
(2011) Modelling and simulation of a high penetration wind diesel system with battery energy storage
Int J Electr Power Energy Syst
(2011)- et al.
Comparative evaluation of different power management strategies of a standalone PV/Wind/PEMFC hybrid power system
Int J Electr Power Energy Syst
(2012) - et al.
Improvement performances for wind energy conversion systems
Int J Electr Power Energy Syst
(2010) - Mendis N, Muttaqi K, Sayeef S, Perera S. Power generation in isolated and regional communities: application of a...
- Zhou Y, Ferreira JA, Bauer P. How new technology developments will lower wind energy costs. In: Integration of...
- et al.
A mighty wind
IEEE Power Energy Mag
(2009) - Haruni AMO, Gargoom A, Haque ME, Negnevitsky M. Dynamic operation and control of a hybrid wind-diesel standalone power...
Wind power in power systems
(2005)- Cheng KWE, Lin JK, Bao YJ, Xue XD. Review of the wind energy generating system. In: International conference on...
Cited by (13)
Coordinated and adaptive power management of AC microgrid system comprising wind and diesel generation sources and AC stand-alone load
2021, Electric Power Systems ResearchCitation Excerpt :Once wind generators and renewable energy sources (RESs) are employed in islanded microgrids, dispatchable energy sources and energy storage systems should be used alongside RESs to improve the system reliability [17,18]. In [19-21], to supply the time varying power demand and keep balance of power, at least an energy storage unit is used. The integration of RESs, ESSs and other dispatchable energy sources in DC or AC microgrids have been discussed in several papers [22-28].
Terminal voltage build-up and control of a DFIG based stand-alone wind energy conversion system
2016, Renewable EnergyCitation Excerpt :The application of isolated DFIG systems in embedded aircraft grid, micro hydro power systems, and diesel generators has also been reported [12–15]. In order to achieve constant voltage and frequency, irrespective of the rotational speed and the loading conditions, most of the authors have suggested the field oriented control strategy [7–15]. The stator voltage is regulated indirectly by controlling the magnetizing current of the machine, while the stator frequency is kept constant by impressing proper slip frequency currents from rotor terminals.
A new synchronous generator based wind energy conversion system feeding an isolated load through variable frequency transformer
2015, Renewable EnergyCitation Excerpt :These power electronics converters are costly, require sophisticated control system, cause harmonic distortion and thereby deteriorate the power quality. Moreover, they require suitable compensation in order to meet the standards for harmonic pollution which further increases the cost and complexity of the system [9–11]. The main challenge faced in a synchronous generator (SG) based SWECS is the power quality.
A novel quasi-oppositional harmony search algorithm and fuzzy logic controller for frequency stabilization of an isolated hybrid power system
2015, International Journal of Electrical Power and Energy SystemsCitation Excerpt :In past, some research works have, successfully, been proposed in the literature with regard to control design methodologies of pitch controller in wind side and governor controller in the diesel side in order to damp out the f and P fluctuations. Controller management researches such as optimization of controller parameters [7–10], proportional–integral (PI) controllers [11–14], variable structure control [15–20], and energy storage controller [21,22] have been reported in the literature. Nevertheless, under sudden change in load demands and intermittent wind power, input to the pitch controller of the wind side and the governor control of the diesel side may no longer be able to control effectively the system f and P due to their slow responses.
Effective utilization of excess energy in standalone hybrid renewable energy systems for improving comfort ability and reducing cost of energy: A review and analysis
2015, Renewable and Sustainable Energy ReviewsCitation Excerpt :Recently, utilization of renewable sources has become more attractive, cost effective, and significant. However, because renewable sources are variable and intermittent, a need for a storage system and/or backup source arises to ensure continuity in supplying the load [7–9]. Hybrid energy systems are systems that combine two or more energy conversion sources (electricity/heat generation and/or storage devices), and when combined, will overcome any inherent limitations [10–14].
Direct driven wind energy conversion system connected to load using variable frequency transformer
2021, International Journal of Electrical Engineering and Education