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This study explores the optimization of dynamic voltage restorers (DVRs) within hydro turbine systems using the Bee Optimization Algorithm (BOA), focusing on enhancing power system stability and quality through advanced control strategies. Emphasizing total harmonic distortion (THD) minimization, the research addresses power quality challenges prevalent in hydroelectric power generation. Detailed simulations demonstrate how BOA effectively reduces THD, optimizing DVR performance in response to grid disturbances typical in renewable energy integrations. Findings validate the BOA's efficacy in improving voltage stability and underscore the potential of bio-inspired algorithms for smart grid applications in hydro settings. This approach not only supports the reliability of hydroelectric power systems but also opens new avenues for employing multi-objective optimization techniques to advance DVR functionality, contributing to the sustainable management of energy infrastructures. [ABSTRACT FROM AUTHOR]

This paper describes research on the harmonic-distortion capacity of a single-stage photovoltaic (PV) 3.68 kWp generator in a microgrid configuration. An overview of various harmonic compensator methods used in PV generators is presented to evaluate their advantages and disadvantages. Proportional-resonant (PR) structures with harmonic compensators (HCs) are designed, modeled, and validated through real-time tests. The modeling of harmonic compensation structures for a photovoltaic inverter using MATLAB/SIMULINK R2022a is explained in detail. The harmonic compensation capacity of a PV generator inverter is studied under voltage harmonics, grid frequency variation, and voltage unbalance. The contributions of this work are, firstly a bibliographic analysis of various strategies currently used for harmonic compensation in grid-connected inverters and secondly, a detailed explanation of the modeling of harmonic compensation structures using MATLAB/SIMULINK. Finally, a demonstration of the improvement in energy quality that results from using harmonic compensation techniques in photovoltaic generators in microgrid configurations affected by grid disturbances is performed. The obtained results show that harmonic compensation strategies based on resonant filters are a good alternative for the reduction of harmonic voltage distortion in the presence of grid disturbances such as frequency variation and voltage unbalance. [ABSTRACT FROM AUTHOR]

This paper describes research on the harmonic-distortion capacity of a single-stage photovoltaic (PV) 3.68 kWp generator in a microgrid configuration. An overview of various harmonic compensator methods used in PV generators is presented to evaluate their advantages and disadvantages. Proportional-resonant (PR) structures with harmonic compensators (HCs) are designed, modeled, and validated through real-time tests. The modeling of harmonic compensation structures for a photovoltaic inverter using MATLAB/SIMULINK R2022a is explained in detail. The harmonic compensation capacity of a PV generator inverter is studied under voltage harmonics, grid frequency variation, and voltage unbalance. The contributions of this work are, firstly a bibliographic analysis of various strategies currently used for harmonic compensation in grid-connected inverters and secondly, a detailed explanation of the modeling of harmonic compensation structures using MATLAB/SIMULINK. Finally, a demonstration of the improvement in energy quality that results from using harmonic compensation techniques in photovoltaic generators in microgrid configurations affected by grid disturbances is performed. The obtained results show that harmonic compensation strategies based on resonant filters are a good alternative for the reduction of harmonic voltage distortion in the presence of grid disturbances such as frequency variation and voltage unbalance.

This paper presents the novel islanding detection technique that depends on the piezoelectric sensors for distributed generation sources (DGs) in the grid-integrated operation mode. The islanding detection method employs a piezoelectric sensor for the detection of the frequency variations during grid disruptions. The designed diaphragm-based sensor has a natural frequency as that of the fundamental frequency of the system frequency signal. Any further deviations from the natural frequency due to the disturbances will be sensed by the sensor and a control signal is being sent to the associated circuit breaker for suitable action. The sensor structure is modeled using the finite element method and implemented in the Phase-Locked Loop (PLL) of the grid-integrated DGs. The proposed circular diaphragm-based sensor structure will have the bandwidth in the range of natural frequency with the tolerance rate of ±1% and uses the input signal received from the PLL controller outer loop. The proposed islanding detection technique's performance and reliability for grid-integrated DG are validated using the real-time hardware in the loop test-bed platform. The HIL virtual simulated responses show that the method can be proposed effectively for islanding detection in the event of frequency variations in the grid-integrated DG systems. [ABSTRACT FROM AUTHOR]

Solar generation has increased rapidly worldwide in recent years and it is projected to continue to grow exponentially. A problem exists in that the increase in solar energy generation will increase the probability of grid disturbances. This study focuses on analyzing the grid disturbances caused by the massive integration to the transmission line of utility-scale solar energy loaded to the balancing authority high-voltage transmission lines in four regions of the United States electrical system: (1) California, (2) Southwest, (3) New England, and (4) New York. Statistical analysis of equality of means was carried out to detect changes in the energy balance and peak power. Results show that when comparing the difference between hourly net generation and demand, energy imbalance occurs in the regions with the highest solar generation: California and Southwest. No significant difference was found in any of the four regions in relation to the energy peaks. The results imply that regions with greater utility-level solar energy adoption must conduct greater energy exchanges with other regions to reduce potential disturbances to the grid. It is essential to bear in mind that as the installed solar generation capacity increases, the potential energy imbalances created in the grid increase.

The major concern for the single-phase grid-connected inverter system is the phase and frequency error of the phase-locked loop (PLL) under various grid disturbances. This paper employs an effective cascaded band pass filter (CBPF) to eliminate the effects of the DC offset and harmonics present in the grid voltage. However, the presence of a prefilter slowed the dynamic performance of all-pass filter (APF) based PLL, implied to generate the orthogonal signal in the single-phase system. To improve the dynamic performance along with the harmonics filtering capability, a nonlinear loop filter (LF) based PLL with CBPF is proposed. The nonlinear LF contains a nonlinear function applied in proportional-integral control to improve the dynamic response of the PLL. Under various grid disturbances, the proposed controller has a faster dynamic response with less overshoot. Furthermore, the proposed PLL is capable of eliminating the effects of DC offset and subharmonics. The proposed PLL is compared with different state-of-the-art PLLs to assess the performance under various grid disturbances. The efficacy is validated experimentally as well as through simulation results. [ABSTRACT FROM AUTHOR]

A unified active power control scheme is devised for the grid-integrated permanent magnet synchronous generator-based wind power system (WPS) to follow the Indian electricity grid code requirements. The objective of this paper is to propose control schemes to ensure the continuous integration of WPS into the grid even during a higher percentage of voltage dip. In this context, primarily a constructive reactive power reference is formulated to raise and equalize the point of common coupling (PCC) potential during symmetrical and asymmetrical faults, respectively. A simple active power reference is also proposed to inject a consistent percentage of generated power even during faults without violating system ratings. Eventually, the efficacy of the proposed scheme is demonstrated in terms of PCC voltage enhancement, DC-link potential, grid real, and reactive power oscillation minimization using the PSCAD/ EMTDC software. [ABSTRACT FROM AUTHOR]

This paper presents a direct analytical method to predetermine the steady-state values of a permanent magnet synchronous generator (PMSG) based wind power system (WPS) at each stage of power flow. A generalized structured is developed with two independent equivalent circuits, that is, PMSG and grid side. To effectively determine the converters performance numerals despite grid disturbances, steady-state model is structured with positive sequence components of grid voltage. The advantage of the proposed model is that the methods evade the requirements of d-q modeling and a dedicated controller to evaluate the system performance. Using the proposed steady-state model, the entire WPS components ratings is predicted evading time domain simulation with complicated controller design. Also, the simple controller design is proposed to aid in optimal power flow supplement with FRT requirements under all possible system operating conditions. Ultimately, validation of predetermined values with the simulated PSCAD/EMTDC response including the proposed controller is investigated. [ABSTRACT FROM AUTHOR]

Solar generation has increased rapidly worldwide in recent years and it is projected to continue to grow exponentially. A problem exists in that the increase in solar energy generation will increase the probability of grid disturbances. This study focuses on analyzing the grid disturbances caused by the massive integration to the transmission line of utility-scale solar energy loaded to the balancing authority high-voltage transmission lines in four regions of the United States electrical system: (1) California, (2) Southwest, (3) New England, and (4) New York. Statistical analysis of equality of means was carried out to detect changes in the energy balance and peak power. Results show that when comparing the difference between hourly net generation and demand, energy imbalance occurs in the regions with the highest solar generation: California and Southwest. No significant difference was found in any of the four regions in relation to the energy peaks. The results imply that regions with greater utility-level solar energy adoption must conduct greater energy exchanges with other regions to reduce potential disturbances to the grid. It is essential to bear in mind that as the installed solar generation capacity increases, the potential energy imbalances created in the grid increase. [ABSTRACT FROM AUTHOR]

The smart transformer (ST) is a key component for the continuously evolving smart grid applications. It is a very promising alternative to the conventional transformer owing to its numerous advantages. For instance, it allows instantaneous voltage regulation, bidirectional power control as well as the integration of renewable energy systems and electric vehicles into the distribution grid. Among the different existing ST topologies, the three-stage topology is considered as the most robust and efficient when coupled to the smart grid. In conjunction with an appropriate control strategy, it guarantees improved performance as compared to its counterparts. Several controllers were proposed for the three-stage based-ST, such as linear quadratic regulator, proportional integral, sliding mode control (SMC). However, these controllers require an exact value of ST system parameters, which is not guaranteed with the integration of renewable energies due to the abrupt changes in the atmospheric conditions. To overcome these limitations, a modified controller is proposed in this paper, namely the backstepping-sliding mode control (BS-SMC). The BS-SMC approach combines the advantages of the SMC and the BS to achieve the highest performance of the ST. The overall mathematical and numerical model of the proposed controller is provided. For a fair comparison, the SMC is also developed. Moreover, different sets of simulations were performed under normal and disturbed operating conditions. The obtained results prove the good robustness of the proposed BS-SMC and flexibility towards different electrical disturbances. [ABSTRACT FROM AUTHOR]

This article proposes a harmonic compensation method using an open-end winding interior permanent magnet synchronous motor driven by an electrolytic capacitorless dual inverter under grid disturbances. In a conventional electrolytic capacitorless single inverter, harmonic currents are superimposed on the output current of the inverter owing to the increase in the dc-link voltage ripple caused by grid disturbances. Consequently, the reliability of the motor drive system is reduced, and the torque ripple causes mechanical vibrations. The proposed harmonic compensation method estimates the harmonic voltage and outputs it using a compensating inverter. The experimental results show that peak-to-peak of the motor current and the 150 Hz component of the shaft torque are reduced by 10.3 and 92.4%, respectively, compared to the conventional system under unbalanced input voltage. Therefore, the improvement of reliability of a motor drive system and reduction of the torque ripple are achieved without an energy buffer under grid disturbances. [ABSTRACT FROM AUTHOR]

DC-link dynamic is one of the most important issues for current source converters (CSC). In practice, the dc-link voltage suffers from the slow dynamic due to grid disturbances, which will affect the quality of output waveform and damage the converter. Many solutions have been presented to cope with it, but none of them achieve the zero dynamic dc-link voltage control. In order to fill the technical gap, a novel solution is proposed in this article. First, the impact of grid disturbances on the CSC is discussed with instantaneous power theory and small-signal model analysis. Second, a new solution is presented to eliminate the adverse impacts of grid disturbances, so as to achieve the zero dynamic dc-link control concept. Meanwhile, the power quality of grid current is improved. Finally, the experiments for the proposed solution under grid disturbances are carried out with TMS320F28335 DSP + XC3400 FPGA digital control hardware platform. The experimental results verify the effectiveness of the proposed solution. [ABSTRACT FROM AUTHOR]

The continuous growth of Renewable Energy (RE) in the grid reduces system inertia and damping, impacting the overall stability of power systems. To alleviate this issue, “virtual” inertia can be provided by power electronics converters. Under this functionality they are controlled to emulate the behavior of rotating machines, operating as Virtual Synchronous Generators (VSGs). However, grid-connected inverters are susceptible to voltage and frequency disturbances which negatively affect their performance. Therefore, this paper introduces a Unified Power Flow Controller (UPFC) with VSG functionality that can compensate for voltage variations at the point of common coupling and provide a constant voltage reference for the connection of remote RE systems. The detailed controlled strategy together with the small-signal analysis are also developed in this work. The UPFC-VSG is compared with an equivalent Static Synchronous Compensator (STATCOM) with centralized energy storage also under VSG control to illustrate the major benefits of the UPFC-VSG. Validation of the analysis and the proposed control method is provided through simulation of a UPFC-VSG and a STATCOM-VSG supporting the grid-connection of a 100-MVA RE system.

Summary: This article deals with the improvement of maximum efficiency schemes of doubly fed induction generator–based wind turbines (DFIG‐WTs) through controlling their rotor current. The nonlinearity characteristics, parameters uncertainty, and grid disturbances in the DFIG‐WTs may affect the tracking performance and the energy conversion efficiency. The magnetizing inductance has the highest value, compared to the other DFIG parameters. Also, its value varies during grid disturbances due to main flux saturation. Therefore, improper setting of its value in the controller can result in significant performance distortion. Active disturbance rejection controller (ADRC) is a simple and robust control technique that can deal with the system's internal and external disturbances. Besides, ADRC does not strongly depend on the accurate mathematical model of the system. For further improvement of the response speed of the traditional ADRC, a novel control strategy based on a model‐assisted ADRC (MA‐ADRC), considering the variation of the magnetizing inductance, is proposed to regulate the rotor current. Furthermore, a new tuning approach is suggested to evaluate the parameters of the MA‐ADRC. Response of the presented strategy is assessed on a 1.5 MW DFIG‐WTs using MATLAB/Simulink package. The proposed MA‐ADRC is compared with the traditional proportional‐integral (PI) controller and existing ADRCs strategies under various scenarios. The simulation results validate the precise tracking performance of the suggested strategy and its robustness against grid disturbances and wind speed variations. [ABSTRACT FROM AUTHOR]

A unified active power control scheme is devised for the grid-integrated permanent magnet synchronous generator-based wind power system (WPS) to follow the Indian electricity grid code requirements. The objective of this paper is to propose control schemes to ensure the continuous integration of WPS into the grid even during a higher percentage of voltage dip. In this context, primarily a constructive reactive power reference is formulated to raise and equalize the point of common coupling (PCC) potential during symmetrical and asymmetrical faults, respectively. A simple active power reference is also proposed to inject a consistent percentage of generated power even during faults without violating system ratings. Eventually, the efficacy of the proposed scheme is demonstrated in terms of PCC voltage enhancement, DC-link potential, grid real, and reactive power oscillation minimization using the PSCAD/ EMTDC software.

The Low-Voltage Ride-Through (LVRT) capacity of the Doubly Fed Induction Generator (DFIG) is one of the important requirements to ensure power systems stability, incorporating wind energy. While traditional control schemes present inappropriate performances under disturbances, this paper introduces a novel Neural Inverse Optimal Control (N-IOC) scheme for LVRT capacity enhancing. The developed controller is synthesized using recurrent high order neural network, which is utilized to build-up the DFIG and the DC-link dynamics. Based on such identifier, the proposed N-IOC is synthesized. This controller is experimentally validated on 1 ∕ 4 HP DFIG prototype considering various grid disturbances. Results illustrate the proposed controller effectiveness for LVRT enhancement without required decomposition process and/or any additional device. [ABSTRACT FROM AUTHOR]

The control of power converter devices is one of the main research lines in interfaced renewable energy sources, such as solar cells and wind turbines. Therefore, suitable control algorithms should be designed in order to regulate power or current properly and attain a good power quality for some disturbances, such as voltage sag/swell, voltage unbalances and fluctuations, long interruptions, and harmonics. Various synchronisation techniques based control strategies are implemented for the hybrid power system applications under unbalanced conditions in literature studies. In this paper, synchronisation algorithms based Proportional-Resonant (PR) power/current controller is applied to the hybrid power system (solar cell + wind turbine + grid), and Dual Second Order Generalized Integrator-Phase Locked Loop (DSOGI-PLL) based PR controller in stationary reference frame provides a solution to overcome these problems. The influence of various cases, such as unbalance, and harmonic conditions, is examined, analysed and compared to the PR controllers based on DSOGI-PLL and SRF-PLL. The results verify the effectiveness and correctness of the proposed DSOGI-PLL based power control method.

The large‐scale wind energy conversion systems (WECSs) based on doubly‐fed induction generators (DFIGs) are very popular in recent years due to the numerous technical and economic benefits. With the increasing penetration level of wind energy, the latest grid codes require the DFIG‐based WECSs to remain connected to the grid under grid fault scenarios and deliver the required reactive power into the grid. However, the direct connection of the stator of the DFIG to the grid makes it prone to grid disturbances, especially to voltage sag. This study proposes a modified demagnetisation control strategy to enhance the low‐voltage ride‐through (LVRT) capability of the DFIG under grid faults. The proposed control strategy is implemented in a coordinated approach by using the existing demagnetisation control and the addition of an external resistance in the stator side of the DFIG. The demagnetisation control damps the direct current component of the stator flux and the external resistance accelerates the damping of the transient flux by decreasing the time constant and hence, enhancing the LVRT capability of DFIG. The effectiveness of the proposed control strategy is demonstrated under both symmetrical and asymmetrical grid faults simulated system through MATLAB/Simulink®. The comparative results justify the merits of the proposed methodology. [ABSTRACT FROM AUTHOR]

In this Letter, a demodulation based pre-filtering technique is proposed for fast detection of the single-phase grid variables. The estimation of grid voltage parameters is achieved through a Type-I synchronous reference frame phase-locked loop (PLL). The modified bandpass filter in the pre-filtering stage ensure a better rejection of the DC-offset and harmonics. Thus, the grid variables are estimated rapidly with the help of a simple proportional controller. Consequently, in-loop filtering burden and the effort required to tune the PLL is minimal. However, steady errors are witnessed in the fundamental amplitude and the phase information which are mitigated by a curve fitting technique. Importantly, the proposed PLL scheme has improved the dynamic performance under off-nominal frequency conditions with immunity against grid disturbances. The robustness of the proposed algorithm is experimentally verified vis-à-vis existing literature. [ABSTRACT FROM AUTHOR]

A systematized active power control scheme has been proposed in this paper to address the most crucial wind specific control functions of permanent magnet synchronous generator based wind-driven generator. The control strategies are targeted to reform the conventional control scheme of the back–back voltage source converters evading additional chopper circuit, dual current control, and compensation loops. Primarily, the torsional mode oscillation damping control is actively incorporated with the dc-link voltage control loop of the machine-side converter. Simultaneously, power regulation associated to fault ride through compliance and oscillation damping pertaining to grid disturbances are amended on grid-side converter active power control loop. The proposed control schemes were studied using PSCAD/EMTDC simulations and the results proved to have better consistency over the conventional schemes under different operating conditions. [ABSTRACT FROM AUTHOR]

Recently, the use of distributed power generation systems (DPGSs) based on renewable energy resources is increasingly being pursued as a supplement and a reliable alternative to the large traditional energy sources. For it, power-electronic interface technologies and control have also emerged as the most important key elements in the area of energy management and integrating DPGSs. The specification of a power-electronic interface is subject to several requirements that are related not only to the DPGS itself but also to its interactions with the power system especially where the utility grid is subject to events that can potentially lead to large-scale disturbances or even to its collapse if it operates near its capacity without fault margin. This study deals, first, with an optimized energy management strategy and, second, with a newly-conceived control strategy called symmetrical components control algorithm (SCCA) that was proposed for four-leg three-phase grid-connected voltage source inverter (VSI) used for DPGSs with wind–solar–battery sources. A mechanism of negative and zero sequences injection based on the control of (d , q) current coordinates has been introduced. The performance of entire control system, to enhance the unbalanced fault ride-through capability of DPGSs, has been evaluated by time domain simulations with MATLAB/Simulink. Advantages of the combined active–reactive control ensuring both current and voltage controls have been achieved compared to the majority of already published strategies. The distinct features of the proposed SCCA strategy prove that it allows to meet the requirements for grid interconnection and the new stricter standards with respect to power quality, safe running, and islanding protection. [ABSTRACT FROM AUTHOR]

This work introduces a novel damped fifth‐order generalized integrator (DFOGI) based control algorithm for grid‐integrated solar photovoltaic (PV) system. Moreover, for GMPPT (Global Maximum Power Point Tracking), HPO (Human Psychology Optimisation) algorithm is used. Here, a three‐phase three wire, single‐stage topology of grid‐integrated partially shaded PV array is implemented. Global maximum power peak searching behavior of HPO algorithm is very rapid and accurate, which gives a satisfactory steady‐state and dynamic performances, even in rapid solar irradiance change condition. The prime objective of proposed DFOGI control is to accurately transfer the solar power to the grid at unity power factor, even when grid suffers from abnormal and adverse conditions. During these conditions, on the grid side, the power quality is maintained, where the proposed control technique provides power factor correction, and harmonics mitigation. The proposed techniques are modeled, and their performances are verified experimentally on a developed prototype, in solar insolation variation conditions, as well as in different grid disturbances such as over and under‐voltage, phase imbalance, harmonics distortion in the grid voltage etc. Test results have met the objectives of the proposed work and parameters are under the permissible limit, according to the IEEE‐519 standard. [ABSTRACT FROM AUTHOR]

This study proposes a real‐time sliding mode field oriented control for a doubly‐fed induction generator (DFIG)‐based wind turbine prototype connected to the grid. The proposed controller is used to track the desired direct current (DC) voltage reference at the output of the DC link, to maintain constant the grid power factor at the step‐up transformer terminals controlled by the grid side converter, and to force independently the stator active and reactive power to track desired values through the rotor currents controlled by the rotor side converter. This control scheme is based on a recurrent high‐order neural network (RHONN) identifier trained on‐line by an extended Kalman filter. The RHONN is used to approximate the DC link and the DFIG mathematical models. The adequate approximation helps to calculate the exact equivalent control part of the sliding mode controller and to eliminate the effects of disturbances and unknown dynamics appearing in the grid, which improves the robustness of the control scheme. This controller is experimentally validated on a 1/4 HP DFIG prototype and tested for variable wind speed to track a time‐varying power reference and to extract the maximum power from the wind, under both balanced and unbalanced grid conditions. [ABSTRACT FROM AUTHOR]

Abstract This paper proposes a Neural Input–Output Feedback Linearization (N-IOFL) controller for a Doubly Fed Induction Generator (DFIG) prototype connected to the grid. Under unbalanced grid voltages, the existing control strategies need to be modified, becoming very complicated. By using an identifier based on Recurrent High Order Neural Network (RHONN), trained on-line with an Extended Kalman Filter (EKF), an adequate model of the DFIG and of the DC-link can be obtained, which helps the control law based on feedback linearization to reject grid disturbances appearing under non-ideal grid conditions without decomposition process. Based on such identification, the proposed controller is used to track a desired Direct Current (DC) voltage reference at the output of DC-link, to maintain constant the electric power factor controlled by the Grid Side Converter (GSC), and to force independently the rotor currents to track a specified reference defined from the required stator powers, controlled by the Rotor Side Converter (RSC), under both balanced and unbalanced grid conditions. Real-time results illustrate the effectiveness of the proposed controller even in presence of non-ideal grid conditions. Highlights • Investigating the Doubly Fed Induction Generator connected with the grid in presence of grid disturbances. • Implementing an identifier based on Recurrent High Order Neural Networks. • Using Extended Kalman filter to train online the proposed neural identifier. • Linearizing the controlled system using the neural Input–Output Feedback Linearization control. • Implementing in real-time the proposed control scheme and testing it under grid disturbances. [ABSTRACT FROM AUTHOR]

Wind energy systems based on doubly fed induction generators (DFIG) are very sensitive to grid disturbances, mainly voltage sags, which can cause rotor and stator overcurrents and rotor overvoltage, resulting in turbines shutdown or even damage to the converter connected to the rotor. Besides, the transmission system operators have been issuing strict grid codes, which require the wind energy conversion system (WECS) to keep operating during grid disturbances and supplying reactive power to the system, if necessary. Due to difficulties to access the offshore DFIGs, avoiding damages and shutdowns in these WECS is paramount. In order to overcome this problem, this article proposes the control of the generator stator flux through a series voltage compensator (SVC) with minimised components. The proposed SVC draws power from the grid through a transformer with a single turn in the primary side (single turn primary transformer) and injects power in the system through an LC filter, without any series transformer. The control of the generator stator flux reduces considerably the stator and rotor current as well as the rotor voltage, allowing the generator to ride‐through the grid disturbances. [ABSTRACT FROM AUTHOR]

The ability of riding through the grid disturbances can increase the integration of microgrids into the distribution system. Consequently, a grid‐connected microgrid should provide ancillary services such as low voltage ride‐through (LVRT) capability and reactive power support to sustain the power system operations during abnormal grid conditions. The objective of this paper is to propose an LVRT scheme that improves the power quality of the entire microgrid. The developed method is implemented as the controller of the interface voltage‐sourced converter (VSC) of a distributed energy resource and consists of primary and secondary control levels. The former includes the cascaded voltage and current control loops and the droop controller, while the latter controls the reactive power injection during the balanced/unbalanced voltage sags/swells. The proposed scheme is developed based on the independent control of each phase and does not require calculation of symmetrical components. Moreover, it can be employed in the VSC control systems with various reference frames and is effective for droop‐based grid‐connected microgrids with both single‐phase and three‐phase four‐wire configurations. The proposed strategy is implemented using the hierarchical control system and preserves the plug and play capability. Several case studies are presented to verify the effectiveness of the proposed strategy. [ABSTRACT FROM AUTHOR]

This paper emphasizes the development of a simplified active power control scheme for enhanced operation of grid integrated permanent magnet synchronous generator based wind-driven generators (WGs). An active power reference generation scheme is proposed for the machine side converter (MSC) to inject active power into the grid even under grid disturbances, without violating system components rating. In this scheme, the controller employed for MSC adjusts the active power captured proportionate to the drop in the grid voltage upon considering wind speed and rotor speed. Furthermore, unlike dual vector control scheme, the grid side converter controller is implemented in a positive synchronous frame with the proposed current oscillation cancellation scheme to suppress the oscillations in dc-link voltage, active and reactive power of the grid and to obtain symmetrical sinusoidal grid current. Extensive analytical simulation has been carried out in PSCAD/ EMTDC to validate the superiority of proposed control scheme over the conventional schemes when WG is subjected to various grid disturbances. The reduced percentage of oscillation in the system parameters such as dc-link voltage and grid active power confirms the efficacy of the proposed method when compared with the conventional control techniques. [ABSTRACT FROM PUBLISHER]

The control of power converter devices is one of the main research lines in interfaced renewable energy sources, such as solar cells and wind turbines. Therefore, suitable control algorithms should be designed in order to regulate power or current properly and attain a good power quality for some disturbances, such as voltage sag/swell, voltage unbalances and fluctuations, long interruptions, and harmonics. Various synchronisation techniques based control strategies are implemented for the hybrid power system applications under unbalanced conditions in literature studies. In this paper, synchronisation algorithms based Proportional-Resonant (PR) power/current controller is applied to the hybrid power system (solar cell + wind turbine + grid), and Dual Second Order Generalized Integrator-Phase Locked Loop (DSOGI-PLL) based PR controller in stationary reference frame provides a solution to overcome these problems. The influence of various cases, such as unbalance, and harmonic conditions, is examined, analysed and compared to the PR controllers based on DSOGI-PLL and SRF-PLL. The results verify the effectiveness and correctness of the proposed DSOGI-PLL based power control method. [ABSTRACT FROM AUTHOR]

To maximise functional efficacy and reliability of distributed generations (DGs), this study leads to modelling, control, stability analysis, and hardware validation of a new adaptive current controller in the application of an on‐grid voltage source converter (VSC) system. For effective mitigation of power system hindrances without affecting the power quality (PQ), self‐tuning of weights associated with the proposed variable leaky adaptive step‐size‐least mean square (VLAS‐LMS) control algorithm based on artificial neural network (ANN) is updated in natural frame and felicitous shaping of VSC outputs are witnessed. The selection of a constant step‐size associated with proposed controller usually yields updating of same weights by all the sampling periods and hardly takes care of rate of convergence factor, which decides the stability of the controller. It can no longer avoid wavering of weights during grid disturbances, resulting in high‐filtering gains. Again, a constant leaky factor may lead to over‐ or under‐parameterisation of regularisation component. These disputes can be overcome in the proposed algorithm by the introduction of an adaptive step size along with a variable leaky factor. Furthermore, PQ is maintained as trade‐off by the inclusion of detuned LC filter. Experimental outcome ensures the validation and effectiveness of the proposed controller. [ABSTRACT FROM AUTHOR]

Isolated electrical systems lack electrical interconnection to other networks and are usually placed in geographically isolated areas—mainly islands or locations in developing countries. Until recently, only diesel generators were able to assure a safe and reliable supply in exchange for very high costs for fuel transportation and system operation. Transmission system operators (TSOs) are increasingly seeking to replace traditional energy models based on large groups of conventional generation units with mixed solutions where diesel groups are held as backup generation and important advantages are provided by renewable energy sources. The grid codes determine the technical requirements to be fulfilled by the generators connected in any electrical network, but regulations applied to isolated grids are more demanding. In technical literature it is rather easy to find and compare grid codes for interconnected electrical systems. However, the existing literature is incomplete and sparse regarding isolated grids. This paper aims to review the current state of isolated systems and grid codes applicable to them, specifying points of comparison and defining the guidelines to be followed by the upcoming regulations.

Almost all synchronization methods that can be found in the literature are based on a fixed sampling period approach and implemented by the addition of filter stages to the conventional Synchronous Reference Frame Phase Locked Loop (SRF-PLL) structure. A less common approach is the variable sampling period (VSP), used in methods like VSP-PLL. These methods allow implementing a synchronous sampling period which automatically adapts the monitoring and control systems to the grid voltage and current, improving their processing performance. Notwithstanding the advantages of the synchronous sampling period approach, this operation principle is not commonly adopted in the literature since a proper design is required to avoid implementation problems and possible conflicts with other modules. This manuscript reviews the advantages of VSP approach, unveils similarities between VSP-PLL and SRF-PLL that allow improving the understanding of the former by comparing it to the latter, and provides guidelines for a proper implementation of a synchronous sampling method. In addition, a Hybrid Sampling Period (HSP) approach that combines the advantages of SRF-PLL and VSP-PLL is proposed. The three approaches are compared, the advantages of hybrid methods are discussed and the methodology for adopting the VSP and HSP approach in most fixed sampling period method is presented. Finally, the proposal is verified by experimental implementation. [ABSTRACT FROM AUTHOR]

Conventional band-pass filter (BPF)-based damper is commonly employed to damp the vibrations in the drive train caused by turbulent winds. However, for the case of grid disturbances or faults resultant torsional vibrations, the performance of the BPF-based damper can be compromised because of the potential low-frequency vibration modes from grid side. To overcome this shortcoming, low-pass filter (LPF)-based torsional damper was proposed in this study. The theoretical analysis of the two torsional damper was assessed in frequency domain. Performance comparison of the two dampers was conducted through simulations and the proposed LPF-based torsional damper outperformed the conventional one in the presence of unexpected low-frequency vibrations. Results also showed that retuning the BPF by decreasing the quality factor can restore the intended performance of torsional damper.

In this paper, an uncertainty and disturbance estimator (UDE)-based robust power flow control is developed for grid-connected inverters to achieve accurate power delivery to the grid. The model of power delivering with both frequency dynamics and voltage dynamics is derived at first. The UDE method is introduced into the controller design to deal with model uncertainties (e.g., output impedance and power angle), coupling effects, and external disturbances (e.g., the fluctuation of the dc-link voltage, the variation of output impedance/line impedance, and the variations of both frequency and amplitude in the grid voltage). Also, this controller does not need a voltage regulator or a current regulator and is easy for the implementation and parameter tuning through the design of the desired tracking error dynamics and the UDE filters. Experimental results are provided to show the effectiveness of the proposed method for different disturbance rejection scenarios, the low-voltage fault-ride through capability, and the weak grid operation capability. The good robustness of the UDE-based control is also demonstrated through the comparison with two other controllers: the proportional–integral controller and the active disturbance rejection controller. [ABSTRACT FROM AUTHOR]

For a multimegawatts doubly-fed induction generator (DFIG), the grid voltage disturbances may affect the stator flux and induce the transient stator flux, due to the direct connection of the stator and the grid. The accumulation of the transient stator flux caused by the variations of the stator voltage may introduce harmful power and torque oscillations to the DFIG, and even lead to rotor overcurrent. For the conventional field-oriented vector control strategy, the design of the controller is based on the steady-state model of the DFIG, which neglects the dynamic of the stator flux, and, therefore, it cannot work well during the transient state to decay the transient flux and to suppress the flux accumulation. In this paper, a dual-loop control strategy, which includes the conventional current loop and an additional flux loop, is proposed to not only control the active and reactive power, but also decay the stator transient flux, and avoid the accumulation of the stator transient flux. Moreover, the proposed strategy can obtain nearly constant stator active power and electromagnetic torque, which may prolong the lifetime of the drive train. A case study on a typical 2-MW DFIG-based wind turbine demonstrating the effectiveness of the proposed control methods is verified with simulations in MATLAB/Simulink. The proposed control methods are also experimentally validated using a scaled-down 7.5-kW DFIG. The simulation and experimental results clearly validate the effectiveness and feasibility of the proposed strategy, and show the improved dynamic performances of the DFIG. [ABSTRACT FROM PUBLISHER]

This paper presents a grid current control technique on the power converter level. The submitted analysis deals with a control method of positive and negative current sequences in a grid-connected converter during voltage sags. The control method should assure the proper exchange of active and reactive powers without power ripple, the mitigation of harmonic distortion of grid currents, and should also enable the control of grid current peaks. A simple expression is determined, which allows estimation of maximum active and reactive powers exchanged between the grid and the converter without exceeding the admissible converter current. Some simulation and experimental results are reported to validate the theoretically predicted performance of the control strategy. [ABSTRACT FROM PUBLISHER]

• Investigation of the power converter topologies used in the input stage of the smart transformer, including two-level and multi-level rectifiers. • The sliding mode controller has been implemented for the studied configurations of the smart transformer. • Evaluation of the proposed configurations under grid disturbances, namely voltage drop, overvoltage and harmonic injection. This paper presents a comprehensive investigation of several configurations and control strategies adopted for Smart Transformer (ST). The ST structure is composed of three stages, namely, input stage, isolation stage, and output stage. The latter are implemented using different power conversion topologies. These topologies operate under variant voltage and current levels, which leads to the generation of high conduction and switching power losses. To overcome these issues, multilevel converters are proposed in this paper for the input stage. Particularly, the cascaded H-bridge (CHB), and neutral point clamped converters are used. Furthermore, the ST's dynamic performance is considered and a Sliding Mode Controller is introduced. Numerical simulations of the proposed structures are performed using Matlab/Simulink under disturbed operating modes. A comparative evaluation of the different topologies is, then, established. The obtained results show that the CHB is the most adequate configuration and the improved performance of the proposed controller are verified. [Display omitted] [ABSTRACT FROM AUTHOR]

Isolated electrical systems lack electrical interconnection to other networks and are usually placed in geographically isolated areas—mainly islands or locations in developing countries. Until recently, only diesel generators were able to assure a safe and reliable supply in exchange for very high costs for fuel transportation and system operation. Transmission system operators (TSOs) are increasingly seeking to replace traditional energy models based on large groups of conventional generation units with mixed solutions where diesel groups are held as backup generation and important advantages are provided by renewable energy sources. The grid codes determine the technical requirements to be fulfilled by the generators connected in any electrical network, but regulations applied to isolated grids are more demanding. In technical literature it is rather easy to find and compare grid codes for interconnected electrical systems. However, the existing literature is incomplete and sparse regarding isolated grids. This paper aims to review the current state of isolated systems and grid codes applicable to them, specifying points of comparison and defining the guidelines to be followed by the upcoming regulations. [ABSTRACT FROM AUTHOR]

The objective of this paper is to provide an assessment on voltage profiles in residential neighborhoods in the presence of photovoltaic (PV) systems. The network was modeled in PSCAD using common feeder characteristics that Canadian system planners use in suburban residential regions. A simulation study was performed to investigate potential voltage rise issues in the network up to 11.25% total PV penetration in the feeder and LV transformer capacity penetration up to 75%. Results indicate that the PV penetration level should not adversely impact the voltage on the grid when the distributed PV resources do not exceed 2.5 kW per household on average on a typical distribution grid. Moreover, the role of feeder impedance, feeder length, and the transformer short circuit resistance in the determination of the voltage rise is quantified. [ABSTRACT FROM PUBLISHER]

This paper describes the connected photovoltaic (PV) power generation system's grid overvoltage protection function and summarizes the occurrence of the output power loss due to the grid voltage rise. Power injection from the PV system will raise the voltage at the power distribution line. A power conditioning subsystem (PCS) needs to regulate its output if the voltage becomes higher than the upper limit in order to avoid the overvoltage at the power grid. Thus, a PV system cannot generate electricity under the high grid voltage. There are 553 residential PV systems installed in Ota, Japan, for the demonstration research project of clustered PV systems. Measurement data of these 2.1-MW grid-connected PV systems are used for the analysis. Only the limited number of PV systems experienced a significant amount of output energy loss due to the high grid voltage in a particular day, whereas the other system's outputs also raise the grid voltage. The causes of this maldistribution of the output energy loss are the difference of the line impedance, the difference of the starting voltage of the PCS's grid overvoltage protection function, and the imbalance of the load in single-phase three-wire power distribution systems. The present control of the PCS successfully avoids the overvoltage on the grid but cannot share the loss. [ABSTRACT FROM AUTHOR]

Renewable energy sources like wind, sun, and hydro are seen as a reliable alternative to the traditional energy sources such as oil, natural gas, or coal. Distributed power generation systems (DPGSs) based on renewable energy sources experience a large development worldwide, with Germany, Denmark, Japan, and USA as leaders in the development in this field. Due to the increasing number of DPGSs connected to the utility network, new and stricter standards in respect to power quality, safe running, and islanding protection are issued. As a consequence, the control of distributed generation systems should be improved to meet the requirements for grid interconnection. This paper gives an overview of the structures for the DPGS based on fuel cell, photovoltaic, and wind turbines. In addition, control structures of the grid-side converter are presented, and the possibility of compensation for low-order harmonics is also discussed. Moreover, control strategies when running on grid faults are treated. This paper ends up with an overview of synchronization methods and a discussion about their importance in the control. [ABSTRACT FROM AUTHOR]