IET Renewable Power Generation
Volume 10, Issue 2, February 2016
Volumes & issues:
Volume 10, Issue 2
February 2016
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- Author(s): Chih-Chiang Hua ; Yi-Hsiung Fang ; Wei-Tze Chen
- Source: IET Renewable Power Generation, Volume 10, Issue 2, p. 127 –132
- DOI: 10.1049/iet-rpg.2014.0403
- Type: Article
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127
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A hybrid maximum power point tracking (MPPT) method with variable step size for photovoltaic (PV) systems is proposed. The proposed MPPT method combines a new modified fractional open-circuit voltage (FOCV) method and the current sensorless method with auto-modulation (CSAM) to achieve fast and accurate tracking. This method not only has fast tracking but also automatically adjusts the step size according to the conditions of PV array. A modified FOCV is designed to move the operating points fast to approach the maximum power points. Afterwards, the CSAM is used for fine tuning, thus the PV system with the proposed MPPT can produce a stable and maximum possible output power. The theoretical analysis of the proposed MPPT is provided, and the laboratory prototype was constructed based on a boost converter with only a single voltage sensor. The simulation and experimental results are presented to verify the system performance.
- Author(s): Mohammed Ali Elgendy ; David John Atkinson ; Bashar Zahawi
- Source: IET Renewable Power Generation, Volume 10, Issue 2, p. 133 –139
- DOI: 10.1049/iet-rpg.2015.0132
- Type: Article
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133
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One of the most commonly utilised maximum power point tracking (MPPT) algorithms for photovoltaic (PV) generators is the incremental conductance (INC) algorithm. Yet, the operating characteristics of this algorithm at high perturbation frequencies, when the system response to MPPT perturbations is never allowed to settle, have not been addressed in the literature. This study characterises system behaviour in this operating mode experimentally for a standalone PV system with a dc motor–pump load. Results show that the INC algorithm operating at a high perturbation rate offers higher energy utilisation efficiency and better system performance despite the resulting non-periodic waveforms of the system.
- Author(s): Rajasekharareddy Chilipi ; Naji Al Sayari ; Khalifa Al Hosani ; Abdul Rahiman Beig
- Source: IET Renewable Power Generation, Volume 10, Issue 2, p. 140 –149
- DOI: 10.1049/iet-rpg.2015.0095
- Type: Article
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140
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This study proposes a control scheme with a new fundamental sequence components extractor for grid interfaced distributed generation inverter under polluted grid conditions. The proposed sequence extractor is realised using third-order sinusoidal signal integrator-based frequency adaptive filters. It has an excellent ability to decompose the three-phase voltage and current signals into positive and negative sequence components under distorted grid scenario. The proposed control scheme is immune to frequency variations and is capable of providing power quality ancillary services such as reactive power compensation and harmonics rejection in addition to basic power injection. The performance of the proposed system under various grid disturbances and loading conditions is evaluated through simulation and experimental studies.
- Author(s): Md Maruf Hossain and Mohd. Hasan Ali
- Source: IET Renewable Power Generation, Volume 10, Issue 2, p. 150 –157
- DOI: 10.1049/iet-rpg.2015.0150
- Type: Article
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p.
150
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Currently, the doubly fed induction generator (DFIG) is getting wider popularity due to its ability to adapt with variable wind speed and to capture more wind energy. According to the grid code, transient stability enhancement of the DFIG system is very important. Though DFIG has a salient feature of the fault ride through capability, this is not sufficient to preserve the necessity of the grid code when the DFIG system is connected with the grid. To accomplish this goal, a DC resistive superconducting fault current limiter (SFCL) is proposed, as it reduces the system power losses during stable operation of the network with improved system efficiency, in comparison with the conventional SFCL. To verify the performance of the transient stability of the DFIG based wind power system with the DC resistive SFCL, both the symmetrical and asymmetrical faults are considered. The performance of the DC resistive SFCL is compared with that of the series dynamic braking resistor (SDBR) and the crowbar system. Simulations are carried out by using the Matlab/Simulink software. Simulation results clearly indicate that the proposed DC resistive SFCL improves the transient stability of DFIG based variable speed wind generator well. Moreover, the overall performance of the proposed method is better than that of the SDBR, as well as the crowbar system.
- Author(s): Marios Charilaos Sousounis ; Jonathan K.H. Shek ; Markus A. Mueller
- Source: IET Renewable Power Generation, Volume 10, Issue 2, p. 158 –165
- DOI: 10.1049/iet-rpg.2014.0331
- Type: Article
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158
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To optimise a tidal energy conversion system, the operation, maintenance and power generation aspects have to be taken into account. As a result the key focus of this study is to propose and investigate an alternative method of implementing a tidal energy conversion system using a pitch-regulated turbine and a variable-speed squirrel cage induction generator with long distance converters. The generator power output can be optimised by utilising variable-speed control strategies allowing the system to operate at maximum power coefficient while availability can be increased by reducing the components installed offshore by using long three-phase cables between the generator and onshore voltage source converters. The tidal current energy conversion system is investigated by developing a full resource-to-grid model in MATLAB/SIMULINK and by performing system analysis regarding the effects of harmonics in the long subsea cables. Simulation results show that optimised filter design and the choice of suitable operating frequency for the generator controller can minimise the overvoltages associated with the harmonics and the reflecting voltage waves in the cables.
- Author(s): Yong-Won Cho ; Woo-Jun Cha ; Jung-Min Kwon ; Bong-Hwan Kwon
- Source: IET Renewable Power Generation, Volume 10, Issue 2, p. 166 –174
- DOI: 10.1049/iet-rpg.2015.0139
- Type: Article
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166
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This study proposes an improved single-phase transformerless inverter with high power density and high efficiency for grid-connected photovoltaic systems. The proposed inverter is comprised of the dual-paralleled-buck inverter and two auxiliary circuits for the zero-current switching turn-off of the diodes. The dual-paralleled-buck inverter and auxiliary circuits are joined by two coupled inductors. To achieve high power density, the proposed inverter operates at high switching frequency of 40 kHz. This leads to lower filter inductors and lower conduction losses of the filter inductors than conventional full-bridge inverters. Moreover, two auxiliary circuits reduce the switching losses caused by high switching frequency operation. Furthermore, the proposed inverter provides the low common-mode leakage current, which satisfies the criteria given by VDE-0126-1-1. Thus, the proposed inverter achieves the maximum efficiency of 99%. The operation principle of the proposed inverter is analysed and verified. Experimental results for a 1 kW prototype are obtained to show the performance of the proposed inverter.
- Author(s): Peng Hou ; Weihao Hu ; Cong Chen ; Zhe Chen
- Source: IET Renewable Power Generation, Volume 10, Issue 2, p. 175 –183
- DOI: 10.1049/iet-rpg.2015.0052
- Type: Article
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175
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The approach in this study has been developed to optimise the cable connection layout of large-scale offshore wind farms. The objective is to minimise the levelised production cost (LPC) of an offshore wind farm by optimising the cable connection configuration. On the basis of the minimum spanning tree (MST) algorithm, an improved algorithm, the dynamic MST algorithm is proposed. The current carrying capacity of the cable is considered to be the main constraint and the cable sectional area is changed dynamically. An irregular shaped wind farm is chosen as the studied case and the results are compared with the layout obtained by a traditional MST algorithm. Simulation results show that the proposed method is an effective way for offshore wind farm collection system layout design.
- Author(s): Ibrahim Abdelsalam ; Grain Philip Adam ; Derrick Holliday ; Barry W. Williams
- Source: IET Renewable Power Generation, Volume 10, Issue 2, p. 184 –193
- DOI: 10.1049/iet-rpg.2015.0136
- Type: Article
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p.
184
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This study proposes three topologies based on single-stage three-phase ac–dc buck-boost converters suitable for medium-voltage high-power applications. The first two topologies are based on a dual three-phase buck–boost converter, with a three-winding phase-shifted transformer to achieve sinusoidal input currents, with relatively small ac filters. The limitation of these two topologies is the switching devices are exposed either to a high voltage beyond that tolerable by a single device. The third topology is based on three single-phase buck–boost converters; with their dc output terminals connected in series to generate high voltage. By using this approach, voltage stresses on the switching devices are greatly reduced, and sinusoidal input currents with nearly unity power factor is achieved over the entire operating range when using small ac filters. Analysis, PSCAD/EMTDC simulations and experimentation are used to assess the feasibility of the proposed topologies during normal operation. Major findings of this study are discussed and summarised as a comparison between the three topologies.
- Author(s): Joonmin Lee and Young-Seok Kim
- Source: IET Renewable Power Generation, Volume 10, Issue 2, p. 194 –202
- DOI: 10.1049/iet-rpg.2015.0250
- Type: Article
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p.
194
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This study proposes a sensorless maximum power point tracking (MPPT) control using an improved variable-speed small-scale wind power generation system (WPGS) with a permanent magnet synchronous generator. The passive elements of a small-scale WPGS that use a conventional boost converter suffer from disadvantages that result in power losses, increased costs, and increased system size. Therefore, to eliminate the passive elements, the proposed system performs MPPT control to vary the duty ratio of a switched-mode rectifier. To evaluate the MPPT algorithms, a comparison was made between a fuzzy-logic-based perturb-and-observe (P&O) control with variable step size and a conventional P&O control with fixed-step size. A wind turbine model is investigated using a squirrel-cage induction motor, and the variable torque is controlled by varying the generator speed. The presented system and algorithm are verified by the simulations and experiments.
- Author(s): Sumei Liu ; Tianshu Bi ; Ke Jia ; Qixun Yang
- Source: IET Renewable Power Generation, Volume 10, Issue 2, p. 203 –211
- DOI: 10.1049/iet-rpg.2015.0003
- Type: Article
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p.
203
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With the fault ride through (FRT) requirement of grid codes, wind generators must stay connected and provide the reactive and active power support during and after the grid faults. The doubly fed induction generators (DFIGs) usually employ an active rotor crowbar to ride-through the faults. The solution works well to protect the DFIG itself, but it has shortcomings in the power support. In the paper, a coordinated FRT control strategy is investigated to improve the power support capability of the DFIGs under the fault conditions. In this strategy, a seamless switch is designed to resume the power control mode after the short-term crowbar interruption. Additional compensation terms are inserted into the converter’s control loops to relieve the side-effect of rotor transient current. The coordinated control of dc-chopper circuit and rotor-side converters is proposed to keep the dc-link voltage within its acceptable range. Moreover, a novel voltage limiter is designed with consideration of the conflicting effect of rotor transient current, converter’s rating constraints and desired power goals. Compared with the conventional crowbar-based strategies, the proposed strategy can fully utilise the DFIG’s potential to generate reactive and active power effectively. These performances have been demonstrated through the simulation and experimental tests.
- Author(s): Ting Ren ; Shi Liu ; Gaocheng Yan ; Huaiping Mu
- Source: IET Renewable Power Generation, Volume 10, Issue 2, p. 212 –220
- DOI: 10.1049/iet-rpg.2015.0065
- Type: Article
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212
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The collector tubes in a receiver play a vital role in the solar power tower system, and directly influence the cost of the power generation. Fast forecast of the temperatures of the collector tubes from the limited number of the temperature measurement data is important. Different from the common computational fluid dynamics prediction method, in this study a back-propagation neural network method is developed to fast acquire the temperature of the receiver, such as the peak temperatures of the inner and outer surfaces, and the outlet mean temperature and the outlet highest temperature of the molten salt. The numerical simulations are implemented to validate the feasibility and effectiveness of the proposed method. Moreover, in the proposed method the temperatures of the tube wall and the molten salt can be fast forecasted without the thermal physical parameters of materials, the boundary conditions or the initial conditions, and the solution of the complicated governing equations.
- Author(s): Ying-Yi Hong ; Faa-Jeng Lin ; Ti-Hsuan Yu
- Source: IET Renewable Power Generation, Volume 10, Issue 2, p. 221 –227
- DOI: 10.1049/iet-rpg.2015.0196
- Type: Article
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221
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Load flow studies are crucial in investigations of operation and planning problems in the power systems. Traditional methods for determining load flow are based on deterministic approaches. However, the parameters of a power system (such as load and renewable power generation) may be uncertain. An exact probabilistic load flow (PLF) study requires a long CPU time due to many convolution computations involving probability density functions. This paper proposes a novel PLF method that is based on Taguchi's orthogonal arrays. The proposed method utilises a few deterministic load flow solutions that are obtained using Taguchi's method to estimate the means and standard deviations of bus voltages, phase angles, line flows, and other metrics. A load flow calculation corresponds to an experiment in Taguchi's method. An optimal experiment is also specified by considering the largest deviation from the nominal load flow solution. A 25-bus standalone power system and a modified Institute of Electrical and Electronics Engineers (IEEE) 118-bus system are tested. The simulation results show that the proposed method not only requires fewer deterministic load flow solutions to perform PLF analysis than the traditional point-estimate method but also yields accurate means and standard deviations of bus voltages and line flows.
- Author(s): Karan Sareen ; Bhavesh R. Bhalja ; Rudra Prakash Maheshwari
- Source: IET Renewable Power Generation, Volume 10, Issue 2, p. 228 –237
- DOI: 10.1049/iet-rpg.2015.0157
- Type: Article
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228
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This study presents a universal islanding detection technique for distribution network containing synchronous, induction and inverter-based distributed generations (DGs). The proposed scheme is based on rate of change of sequence components of current signals acquired at the point of common coupling of the targeted DG. Various non-islanding events along with islanding conditions have been simulated by modelling IEEE 34 bus system using PSCAD/EMTDC software package. Utilising three-phase current samples for full cycle duration of each simulation case of islanding/non-islanding conditions, robust performance of the proposed scheme is achieved. The simulation results indicate that the proposed scheme is capable to detect islanding condition rapidly even with zero active and reactive power mismatches for both synchronous and inverter-based DGs. Further, it eliminates non-detection zone completely, works perfectly for multiple DG systems and avoids nuisance tripping during various non-islanding events. Moreover, the performance of the proposed scheme is not affected by change in capacity of DG, location of DG and length of distribution line. Comparative evaluation of the proposed scheme with the existing scheme clearly indicates the superiority of the proposed scheme.
- Author(s): Sayed Abulanwar ; Weihao Hu ; Zhe Chen ; Florin Iov
- Source: IET Renewable Power Generation, Volume 10, Issue 2, p. 238 –249
- DOI: 10.1049/iet-rpg.2015.0239
- Type: Article
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238
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Significant voltage fluctuations and power quality issues pose considerable constraints on the efficient integration of remotely located wind turbines into weak networks. Besides, 3p oscillations arising from the wind shear and tower shadow effects induce further voltage perturbations during continuous operation. This study investigates and analyses the repercussions raised by integrating a doubly-fed induction generator wind turbine into an ac network of different parameters and very weak conditions. An adaptive voltage control (AVC) strategy is proposed to retain voltage constancy and smoothness at the point of connection (POC) in order to maximise the wind power penetration into such networks. Intensive simulation case studies under different network topology and wind speed ranges reveal the effectiveness of the AVC scheme to effectively suppress the POC voltage variations particularly at very weak grid conditions during normal operation.
- Author(s): Milad Fooladi and Asghar Akbari Foroud
- Source: IET Renewable Power Generation, Volume 10, Issue 2, p. 250 –259
- DOI: 10.1049/iet-rpg.2014.0419
- Type: Article
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250
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Similar to other distributed generation sources, wind turbines cause power quality disturbances (PQDs) issues in power systems. One of the most important PQDs that has bad effects on sensitive loads is flicker. In this study, an algorithm is presented for assessment and recognition of different factors causing flicker of wind turbines. Some aerodynamic factors (wind shear and tower shadow) and some mechanical factors (blade pitching errors, gearbox tooth crash and turbine blade break down) are modelled using fixed speed wind turbines. Then, wavelet transform and S-transform are used to extract some dominant features voltage. Then, in order to avoid large dimension of feature vector, Relieff feature selection method is applied to extracted features. The probabilistic neural network (PNN) is used to classify above-mentioned factors. The only adjusted parameter of the PNN classifier is determined by using the particle swarm optimisation technique. Moreover, the short-term severity of flicker (Pst) is calculated for each type of fault as extra features to increase the severability of extracted features. Results show that the classifier can detect different causes of flicker event with high detection accuracy.
Hybrid maximum power point tracking method with variable step size for photovoltaic systems
Experimental investigation of the incremental conductance maximum power point tracking algorithm at high perturbation rates
Control scheme for grid-tied distributed generation inverter under unbalanced and distorted utility conditions with power quality ancillary services
Transient stability improvement of doubly fed induction generator based variable speed wind generator using DC resistive fault current limiter
Modelling, control and frequency domain analysis of a tidal current conversion system with onshore converters
Improved single-phase transformerless inverter with high power density and high efficiency for grid-connected photovoltaic systems
Optimisation of offshore wind farm cable connection layout considering levelised production cost using dynamic minimum spanning tree algorithm
Single-stage ac–dc buck–boost converter for medium-voltage high-power applications
Sensorless fuzzy-logic-based maximum power point tracking control for a small-scale wind power generation systems with a switched-mode rectifier
Coordinated fault-ride-through strategy for doubly-fed induction generators with enhanced reactive and active power support
Temperature prediction of the molten salt collector tube using BP neural network
Taguchi method-based probabilistic load flow studies considering uncertain renewables and loads
Universal islanding detection technique based on rate of change of sequence components of currents for distributed generations
Adaptive voltage control strategy for variable-speed wind turbine connected to a weak network
Recognition and assessment of different factors which affect flicker in wind turbines
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- Author(s): Davide Barater ; Emilio Lorenzani ; Carlo Concari ; Giovanni Franceschini ; Giampaolo Buticchi
- Source: IET Renewable Power Generation, Volume 10, Issue 2, p. 260 –273
- DOI: 10.1049/iet-rpg.2015.0101
- Type: Article
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Photovoltaic (PV) power systems have been in the spotlight of scientific research for years. However, this technology is still undergoing developments, and several new architectures are proposed each year. This study describes the main challenges facing grid-connected PV systems without galvanic isolation, then carries out a review of the state-of-the-art of single-phase systems. The converter topology review is focused on the match between the different types of converters and the different PV panel technologies, determined by the common-mode voltage between the PV string terminals and the ground. The ground leakage current, due to time variations of this voltage, is a source of electric safety and electromagnetic interference (EMI)-related problems, and its amplitude is constrained by international standards. The basic principles of operation of the different solutions are described, along with their strengths and drawbacks. Conversion efficiency is evaluated qualitatively comparing the semiconductor power losses. Finally, the future trends regarding semiconductor devices, PV panels and international regulations for single-phase grid-connected equipment are discussed, and indications on how these might steer future research efforts in PV converters are inferred.
Recent advances in single-phase transformerless photovoltaic inverters
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