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The phase-locked loop (PLL) is the main controller element for the fast and accurate synchronisation and operation of grid-connected renewable energy systems (RESs). It is used to extract the grid voltage information such as the phase angle, the frequency and amplitude. Subsequently, this information is used in the control system of the grid-side converter of the RES. The performance of the PLL is critical under abnormal grid conditions such as in the event of balanced and/or unbalanced faults, frequency and phase variations, the presence of harmonics, interharmonics and DC offset. This study sets out with a benchmarking study of the four latest state-of-the-art PLLs. The PLLs compared are the decoupled dual synchronous reference frame PLL, the decoupling network designed in αβ- frame PLL, the enhanced pre-filtering moving average filter type-2 PLL and the harmonic-interharmonic DC-offset PLL. The PLLs are analysed and compared based on their performance, their dynamic response and their computational complexity. The benchmarking concludes with a PLL selection guide depending on the application and other system constraints. Experiments and simulation results are presented to compare and analyse the performance of the selected PLLs.

Diversifying the role of grid-side converters (GSCs) associated with distributed generation (DG) may have a technical and economic impact. The increasing number of residential photovoltaic systems can be exploited by distribution network (DN) operators in order to support and improve the power quality of the grid without considerable further capital investment. The GSC can support the grid during abnormal conditions but may also be used to improve the DN power quality by balancing out asymmetries and alleviating the grid from undesired harmonics. The proposed advanced control technique demonstrates through simulation and experimental results that the role of GSC can be upgraded to improve the power quality of the grid. Furthermore, the proposed control scheme is validated on a realistic low-voltage DN using data from the Electricity Authority of Cyprus. Consequently, conventional practices by DN operators for improving the power quality can be reassessed as the necessary power electronics hardware for mitigating grid problems is already present within the GSCs of DG systems.

Ports have been key elements in Europe's economic development. This situation is even more relevant on islands, which are highly dependent on the maritime sector. Consequently, over the years, ports with diverse functionalities have been established both in mainland Europe and on its outlying islands. This article discusses the environmental impact of leisure marinas on European islands, especially as they are closely linked to economic development through tourism. The aim is to study the environmental impact of these infrastructures by determining the carbon and water footprints of marinas on European islands in the Atlantic and the Mediterranean. The results obtained enable the authors to make recommendations in order to reduce the overall environmental footprint of marinas on islands, considering that these territories are much more vulnerable to climate change than mainland locations in Europe.

The application of Photovoltaic (PV) in the distributed generation system is acquiring more consideration with the developments in power electronics technology and global environmental concerns. Solar PV is playing a key role in consuming the solar energy for the generation of electric power. The use of solar PV is growing exponentially due to its clean, pollution-free, abundant, and inexhaustible nature. In grid-connected PV systems, significant attention is required in the design and operation of the inverter to achieve high efficiency for diverse power structures. The requirements for the grid-connected inverter include; low total harmonic distortion of the currents injected into the grid, maximum power point tracking, high efficiency, and controlled power injected into the grid. The performance of the inverters connected to the grid depends mainly on the control scheme applied. In this review, the global status of the PV market, classification of the PV system, configurations of the grid-connected PV inverter, classification of various inverter types, and topologies are discussed, described and presented in a schematic manner. A concise summary of the control methods for single- and three-phase inverters has also been presented. In addition, various controllers applied to grid-tied inverter are thoroughly reviewed and compared. Finally, the criteria for the selection of inverters and the future trends are comprehensively presented.

Recently, Asynchronous Motors are extensively used as workhorse in a multitude of industrial and high-performance applications. Induction Motors (IM) have wide applications in today’s industry because of their robustness and low maintenance. A smart and fast speed control system, however, is in most cases a prerequisite for most applications. This work presents a smart control system for IM using an Adaptive Fuzzy Logic Controller (AFLC) based on the Levenberg–Marquardt algorithm. A synchronously rotating reference frame is used to model IM. To achieve maximum efficiency and torque of the IM, speed control was found to be one of the most challenging issues. Indirect Field-Oriented Control (IFOC) or Indirect Vector Control techniques with robust AFLC offer remarkable speed control with high dynamic response. Computer simulation results using $$\hbox {MATLAB/Simulink}^{{\textregistered }}$$ Toolbox are described and examined in this study for conventional PI and AFLC. AFLC presents robustness as regards overshoot, undershoot, rise time, fall time, and transient oscillation for speed variation of IFOC IM drive in comparison with classical PI. Moreover, load disturbance rejection capability for the designed control scheme is also verified with the AFL controller.

The increasing penetration of distributed renewable energy sources (RES) requires appropriate control techniques in order to remain interconnected and contribute in a proper way to the overall grid stability, whenever disturbances occur. In addition, the disconnection of RES due to synchronization problems must be avoided as this may result in penalties and loss of energy generation to RES operators. The control of RES mainly depends on the synchronization algorithm, which should be fast and accurately detect the grid voltage status (e.g., phase, amplitude, and frequency). Typically, phase-locked loop (PLL) synchronization techniques are used for the grid voltage monitoring. The design and performance of PLL directly affect the dynamics of the RES grid side converter (GSC). This paper presents the characteristics, design guidelines and features of advanced state-of-the-art PLL-based synchronization algorithms under normal, abnormal and harmonically-distorted grid conditions. Experimental tests on the selected PLL methods under different grid conditions are presented, followed by a comparative benchmarking and selection guide. Finally, corresponding PLL tuning procedures are discussed.

The large scale integration of Renewable Energy Sources (RES) requires sophisticated control techniques for efficient power transfer under faults and/or off-nominal grid conditions. A RES is efficiently integrated to the grid via proper control of the Grid Side Converter (GSC) by accurately estimating the grid voltage phase angle. Moving Average Filter (MAF) based Phase Lock Loop (PLL) techniques provide reduced complexity, however, they present disadvantages under specific grid fault conditions. The most recent MAF based technique is the EPMAFPLL, which provides improved dynamic response and reduces the phase error under off-nominal grid frequencies. However, the EPMAFPLL presents high phase and frequency overshoot at the time of fault. Furthermore, inaccurate harmonic mitigation under off-nominal grid frequencies was not investigated in EPMAFPLL. A modified EPMAFPLL (EPMAFPLL Type 2) is proposed in this paper. The modified EPMAFPLL accurately compensates the offset errors under off-nominal grid frequencies, offers lower frequency overshoot and faster dynamics under faults. In addition, it provides accurate compensation of grid voltage harmonics under off-nominal grid frequencies.

The increased penetration of RES requires the development of advanced control techniques that can work accurately with improved performance and less computational resources under unbalanced and harmonically distorted grid conditions. The paper sets out with a benchmarking study of two existing current control techniques developed for compensating the harmonics and gird voltage unbalance. The techniques are analyzed in terms of their performance and computational complexity. Both techniques can work satisfactory under abnormal grid scenarios, but these techniques are computationally complex and the performance of one under unbalanced conditions is not accurate. The proposed controller (Type 1) presented, eliminates oscillations under unbalanced voltage conditions. Furthermore, it enhances the quality of the injected current and works efficiently with improved performance (low overshoot and less oscillation) at the time of fault. However, it slightly increases the computational complexity something that motivated the development of a further controller (Type 2) that can work with less computational resources and improved performance under such conditions.

This work presents current and voltage waveform data recorded from Ayia Anna wind farm in Cyprus and the subsequent analysis in Matlab using Fast Fourier Transform (FFT) algorithms. The analysis aims to investigate whether the harmonic content, is within acceptable IEEE standard limits. Recorded data were arranged in descending order with respect to output power generation. Total harmonic distortion (THD) for voltage and current were analyzed by classifying the measured data in three categories depending on the output power so that the harmonic distortion is correlated with the output power generated.

Electricity grid regulations are frequently revised in order to accommodate the ever-increasing penetration of distributed renewable energy systems (RES). Interconnected RES are required to operate conditionally under normal and abnormal grid conditions. Furthermore, RES are required to have fault ride through (FRT) capability so that they can provide voltage and frequency support to the grid. The FRT operation may necessitate the injection of positive, negative or both sequence components of current. Therefore, appropriate control techniques are needed that can perform under all grid conditions (faults and harmonics) without violating the grid codes. A benchmarking comparison between two existing current control techniques motivated the proposal of a new current controller with an improved performance and lower computational complexity. The proposed controller allows accurate injection of pure sinusoidal positive, negative or both sequences currents under normal and abnormal grid scenarios. The proposed control strategy can work with considerably lower computational complexity and with improved response as compared to the two existing controllers.

Two and three level VSC inverters are the building blocks of most of inverter applications necessitating the employment of appropriate switching techniques that result in harmonic free sinusoidal output. The paper presents the generalized method for harmonic elimination in two and three level voltage sourced converter. The technique used for suppression of selective low-ordered harmonics form the inverter's output voltage waveform is Selective harmonic elimination (SHE). The inverter's output voltage waveform is mathematically modeled using Fourier series that results in the system of nonlinear equations. The non-linear equations are solved for eliminating the specific low order harmonics. The main objective in calculating appropriate switching angle is to minimize the value of Total Harmonic Distortion (THD). To solve the system of non-linear equations numerical method Newton Raphson is applied and appropriate switching angles are calculated. The remaining uneliminated higher order harmonics are eliminated by connecting appropriate value of filter at the output stage of VSC inverter. The model of two level VSC is simulated in SimPowerSystem Matlab tool bar together with the algorithm of Newton Raphson technique. The time domain plot and frequency spectrum of inverter's output waveform is presented in the results section. The results of two and three level VSC inverters are analyzed and debated together with the comparative analysis on the basis of THD. Moreover, a comparison is presented on the basis of IEEE standard Std. 519 and EN 50160.

The paper presents the estimation of an unknown non-linear system in ARX form. The estimated model is used in Adaptive self-tuning regulator to regulate the output of plant at desired reference input using Minimum Degree Pole Placement Controller (MDPP). Most of the literature includes the conventional RLS algorithm to estimate the system parameters. The estimation technique addressed here is Fuzzy Logic Identifier (FLI). The proposed estimator approximates the system using a linear model at each operating point. The linear identification of model necessitates the use of linear control strategy. Therefore, the design of MDPP controller based on linear identified system is also presented. The consequents of FLI are updated using Levenberg-Marqardt (LM) algorithm. MATLAB/Simulink is used for the implementation of proposed estimation techniques. The effectiveness of the proposed estimators and control strategy is tested on a non-linear plant. The results are presented and debated together with a comparative analysis of RLS and FLI. Superiority in performance is found for FLI in estimating and controlling the non-linear using MDPP. The performance indices Mean Square Error (MSE), Mean Absolute Error (MAE) and Mean Time-Weighted Error validate the effectiveness of proposed FLI.

This paper presents the performance analysis of six-pulse line commutated converter (LCC) and advanced control strategy Fuzzy Logic Control (FLC) for speed control of a dc motor. The speed of motor is maintained at the desired reference value by adjusting the value of armature current. The armature current is varied by controlling the firing angle of LCC. The desired value of reference current is obtained from the corresponding speed value and is fed to the controller. The controller takes the measured and reference value of armature current as an input. The output of the controller is firing angle. To maintain the motor speed at the desired value two controllers the FLC and the conventional Proportional Integral Derivative (PID) controllers are employed and their performance is compared. The proposed controllers and power system is implemented in Control System and SimPowerSystem toolbox of MATLAB. Results of Computer simulation are described and debated together with a comparative analysis of the different control schemes. The simulation results show that the proposed FLC has tracking ability with better steady state error and transient response than conventional PID controller. Moreover, the deleterious effects of converter on input current and power factor are also discussed.

In this paper, the drift-diffusion numerical technique is discussed for the simulation of photovoltaic applications. The necessary differential equations, which are the Poisson and electron and hole charged particle continuity equations are explained, and the coupling between the above equations is discussed. Thereafter, the different physical processes involved in the simulation of thin film silicon photovoltaics are exploited. Then, all the transport properties related specifically to silicon and at a material temperature of 300 K such as the mobilities and diffusion coefficients for electrons and holes, the intrinsic silicon concentration, and generation and recombination mechanisms are identified from the literature. Finally, the formulation of the drift-diffusion model using finite elements in two-dimensional Cartesian and two-dimensional cylindrical axisymmetric coordinates is deployed to be used in the simulation of thin film photovoltaic applications. (7 pages)

Cyprus is required to increase its share of renewable energies to 13% by 2020 according to the 2009 EU directive. The slow growth of renewables necessitated new grant schemes in the sector by the government Amongst other, the ability to invest in photovoltaic parks up to 150 kilowattpeak (kWp) has finally become a reality in 2009. This paper, presents results related to the performance yield of such a Photovoltaic (PV) park in a specific area in Cyprus and an economic feasibility study of the investment. The performance was evaluated using the meteorological data for the area under examination in conjunction with PVSYST. The economic feasibility study was carried out using a tool designed by the Cyprus Institute of Energy. The results suggest that such an investment, is currently very attractive, with the IRR ranging between 10 to 13 % over a 35 year period. (4 pages)

The presence of direct current (DC) offset and harmonics–interharmonics (HIHs) in grid voltage input signal of phase-locked loop (PLL) results in inaccurate controller response. The inaccuracies are due to the low- and high-frequency oscillations that appear in the PLL estimated phase, amplitude and frequency. The suppression of fundamental frequency oscillations caused by DC offset (DO) in the input voltage signal must be carried out without compromising the dynamic response of the system. The use of low-pass filters, for example, results in undesirable, slow response. This study proposes an accurate and fast decoupling of fundamental frequency oscillations using a mathematic-cancellation decoupling cell. Higher-frequency oscillations generated by HIHs are eliminated by a different harmonic compensation network (HCN) that is also proposed in this study. The performance of conventional techniques is limited because they eliminate only specifically selected harmonics. The proposed PLL, however, eliminates any number of HIHs present in the grid with the least computational complexity and without any prior knowledge. Furthermore, its advanced features provide accurate synchronisation under any abnormal grid condition at the lowest computational complexity when compared with the existing state-of-the-art PLLs. The advanced performance of the proposed HIHDO-PLL is verified through simulation and experimental results.