Showing papers on "Voltage sag published in 2021"

Mitigation of power quality issues in smart grid using levy flight based moth flame optimization algorithm

Abstract: Now a days, energy demand have been increasing due to industrialization factors in the world. The energy demand and environmental problems also increased such as global warming and air pollution. The problems must be solved by introducing renewable energy resources in grid connection. The increasing demand solved by combining renewable energy resources with grid connection which is the smart grid (SG) system. The SG system is affected by the voltage collapses and power quality (PQ) issues such as voltage sag, voltage swell, voltage interruption etc. Because of connection of renewable resources with grid connection. In the SG is consists of renewable energy systems (RES) and power storage devices. The RES are photovoltaic (PV), wind turbine (WT) that are connected with grid through the voltage source inverter (VSI). In the SG system, the power flow, power management and PQ are the main problems which must be solved to maintain stable operation. Thus, in this paper, Levy flight-moth flame optimization (LFMFO) is developed for improving the performance and mitigates the PQ issues in the SG system. To avoid the local optima and improve the global search of MFO, Levy flight is utlized in the SG system. Using the proposed algorithm, improve the performance of the SG with the voltage, droop control based low voltage ride through (LVRT) and damping controls for reduce the PQ issues. The proposed strategy is validated in the MATLAB/Simulink platform and investigated the PV power, wind power, voltage sag, current, voltage swell and voltage interruption. The proposed method shows the ability to mitigate PQ issues in SG system. The proposed methods provide the best optimal results toward to achieve objective of MG system. Under voltage sag, voltage swell and voltage interruption conditions of SG, proposed methods shows best performance to improve stability of the system. The execution of proposed system is shown and compared with the existing techniques of Cuckoo search (CS) algorithm and particle swarm optimization (PSO) algorithm.

A New Method for Fault Location in Distribution Networks Based on Voltage Sag Measurements

Abstract: This paper presents an innovative method for fault location in distribution networks based on classical circuit analyses. Two synchronized and few nonsynchronized pre- and during-fault voltages are required at few buses along with the impedancematrix. A new impedance matrix manipulation procedure is proposed so that the distribution system is investigated in partitions across multiple subsystems. This procedure allows the fault location process to be performed by solving systems of determined equations, making the method more technically accessible. The fault is located by analyzing the voltage sag at the terminal-bus of each subsystem separately. The proposed method is validated on the IEEE 33-bus, 12.66 kV distribution system with/without distributed generation (DG). Simulation results show the robustness and accuracy of the method under several pre- and during-fault scenarios and measurements errors.

Power Quality Enhancement in Grid-Connected PV/Wind/Battery Using UPQC: Atom Search Optimization

Abstract: Nowadays, the integration of hybrid renewable energy system (HRES) in grid connected load system are encouraged to increase reliability and reduce losses. The HRES system is connected to the grid system to meet required load demand and the integrated design creates the power quality (PQ) issues in the system due to non-linear load, critical load and unbalanced load conditions. Hence, in this paper, atom search optimization (ASO) with unified power quality conditioner (UPQC) is designed to solve the PQ issues in HRES system. The main objective of the work is the mitigation of PQ issues and compensate load demand in HRES system. The PQ issue problems are solved with the help of UPQC device in the system. The UPQC performance is increased by introducing fractional order proportional integral derivative (FOPID) with ASO based controller in series and shunt active power filter to mitigate PQ issues of current and voltage. Initially, HRES is designed with photovoltaic (PV) system, wind turbine (WT) and battery energy storage system (BESS) which connected with the load system. To analysis the presentation of the proposed controller structure, the non-linear load is connected with the system to create PQ issues in the system. The PQ issues are mitigated and load demand is reimbursed with the assistance of HRES system. The proposed method is employed in the MATLAB/Simulink platform and performances were analysed. Three different cases are used to validate the performance of the proposed method such as Sag, Swell, and disturbances. Additionally, total harmonic distortion (THD) is analysed. The proposed method is compared with existing methods of proportional integral (PI) controller, gravitational search algorithm (GSA), biogeography based optimisation (BBO), grey wolf optimization (GWO), extended search algorithm (ESA), random forest algorithm (RFA) and genetic algorithm (GA).

Super Twisting Sliding-Mode Control of DVR With Frequency-Adaptive Brockett Oscillator

Abstract: This article presents a super twisting sliding-mode control (ST-SMC) for single-phase dynamic voltage restorers (DVRs). Unlike the conventional first-order sliding-mode controller, the proposed ST-SMC technique eliminates the need for differentiating the compensation voltage in the sliding surface function while keeping the merits of first-order SMC. As a consequence of employing ST-SMC, a continuous control signal is achieved from which the pulsewidth modulation (PWM) signals can be generated. In this case, the inverter operates at a constant switching frequency. The stability analysis of ST-SMC is also presented. The reference compensation voltage needed in ST-SMC is estimated by using Brockett oscillator-based frequency-locked loop. Theoretical considerations are verified through experimental results under ideal and distorted grid voltage conditions. The obtained results show that the ST-SMC has good dynamic performance and can maintain the load voltage at a desired level under voltage sag, swell, and harmonically distorted grid voltages.

A Novel Solar Photovoltaic Fed TransZSI-DVR for Power Quality Improvement of Grid-Connected PV Systems

Abstract: In this article, a new solar PV fed Dynamic Voltage Restorer (DVR) based on Trans-Z-source Inverter (TransZSI) is proposed to improve the power quality of on-grid Photovoltaic (PV) systems. DVR is a power electronic compensator using for injecting the desired voltage to the Point of Common Coupling (PCC) as per the voltage disturbance. In the proposed DVR, in place of traditional VSI, TransZSI with outstanding merits of buck/boost, a broader range of voltage boost gain, fewer passive components, and lower voltage stress, is put forth. For efficient detection, accurate voltage disturbances mitigation, and also lessening the injected voltage harmonics, a hybrid Unit Vector Template with Maximum Constant Boost Control (UVT-MCBC) method is proposed for TransZSI-DVR. The performance of the proposed TransZSI-DVR with UVT-MCBC has been analyzed under severe sag, slight sag with harmonics, swell, and interruption. The comparative studies and simulation results have shown the effectiveness of the proposed TransZSI-DVR, as opposed to traditional ZSI-DVR and VSI-DVR. The TransZSI-DVR in the PV system has mitigated voltage sag/swell/interruption. It has also improved the power quality of both the injected voltage to the PCC and PV system’s output voltage.

Dynamic Voltage Support for Low-Voltage Ride-Through Operation in Single-Phase Grid-Connected Photovoltaic Systems

Abstract: This article presents a dynamic voltage support (DVS) scheme for achieving low-voltage ride-through (LVRT) with a grid-connected photovoltaic (PV) inverter during the voltage sag fault. The DVS scheme is achieved by formulating an additional reactive active current control mode which is developed from a conventional reactive current control approach. This provides stable operation of the system and achieves higher effectiveness due to the lower X / R ratio at the point of common coupling in low-voltage networks. Further, the performance of the proposed controller is assessed by simulating a 4 kW system for voltage sag faults. Further, the proposed controller tested with the real-time simulations and experimental setup for voltage sag conditions. The results presented demonstrate that the active and reactive power is regulated in concordance with grid code requirements. The controller achieves LVRT within the time limits of grid standard during symmetrical faults, which makes it appropriate for fast transient events. This operates the PV system under its nominal capacity, avoiding unwanted grid disconnection events.

Optimal Placement and Sizing of Wind Turbine Generators and Superconducting Magnetic Energy Storages in a Distribution System

Abstract: High penetration of intermittent wind-turbine generation (WTG) into electric distribution system along with large variations of load demand introduce many problems to the system such as high power losses, voltage sag, and low voltage stability. To mitigate such problems, the distribution system is supported by superconducting magnetic energy storages (SMESs). This paper is aimed at determining the optimal placement and sizing of WTGs and SMESs in a distribution system using a proposed multi-objective-function based optimization method. The method is a hybrid one being based on an efficient algorithm called Equilibrium Optimizer (EO) along with loss sensitivity factor (LSF). The weighted-sum multi-objective function (IMO) is formulated for simultaneous minimization of energy-loss and voltage-deviation as well as enhancement of voltage-stability as indices characterizing the distribution system performance. The weight factors are no longer assumed or left open to the preferences of the decision maker. They are computed while optimizing the indices of the IMO in order to determine the optimal placement and sizing of WTGs and SMESs. The proposed method for optimal placement and sizing of WTGs and SMESs is tested and validated on the standard IEEE 33-bus distribution system with time-varying voltage-dependent load models including residential, industrial, commercial, and mixed loads as well as variable wind-speed. The results obtained using EO algorithm are compared with those obtained by particle swarm optimization (PSO) and genetic algorithm (GA) to validate the effectiveness of EO. The numerical results and simulations imply that the combination of WTGs and SMESs can successfully achieve minimization of energy-loss and voltage-deviation as well as enhancement of voltage-stability, and thereby significantly improve the performance of distribution system.

Phase-Locked Loop Independent Second-Order Generalized Integrator for Single-Phase Grid Synchronization

Abstract: Second-order generalized integrator (SOGI) requires fast and accurate grid voltage frequency information for quadrature signal generation (QSG) in single-phase systems. Conventionally, synchronous reference frame phase-locked loop (PLL) (SRFPLL) is used in a cascade manner and provides frequency feedback to SOGI. PLL is a non-linear closed-loop control system that requires adequate gain parameter design trade-off to provide accurate grid synchronization. Additionally, it creates interdependent loops while estimating the grid frequency and phase-angle. This results in unwanted frequency disturbances during grid transients, such as voltage sag and phase-angle jumps (PAJs) which are fed back to the SOGI as well. Thus, this article proposes two PLL independent frequency-feeding approaches for SOGI: Type-A and -B. The frequency is estimated using the normalized single-phase grid voltage signal in both types. In Type-A, the normalization is done using cascaded recursive discrete-Fourier transform (RDFT) and inverse RDFT (IRDFT). On the other hand, in Type-B, SOGI outputs are used for normalization. The grid voltage amplitude is estimated using the absolute value of the in-phase and in-quadrature components of the proposed frequency-adaptive SOGI. Furthermore, the third-order polynomial approximation of the arctangent function is implemented for phase-angle estimation in both types. The performance of both the types during transients and steady-state grid voltage disturbances (dc offset and harmonics) are compared with SOGIPLL using both simulations and experiments.

Performance of DVR Using Optimized PI Controller Based Gradient Adaptive Variable Step LMS Control Algorithm

Abstract: A custom power device known as dynamic voltage restorer (DVR) has been investigated to operate a distribution system at its desired performance. The distribution system with voltage-related power quality issues in the supply side has been addressed through this article using DVR. Four different grid disturbances, such as voltage sag, swell, unbalances, and distortions, have been taken into account while testing the DVR capability. DVR has been controlled using optimized proportional and integral (PI) gains integrated with gradient adaptive variable learning rate least mean square control algorithm. Adaptiveness of variable step-size in LMS makes the control robust in case of dynamics in the system, which assures better performance. Also, the other major contribution of this article is the implementation of optimization-based self-tuning PI gains in the proposed control. The evaluation of optimizer in estimating the PI gains is presented in terms of the response of dc-link voltage DVR. The simulation work of proposed control algorithms on DVR has been done and satisfactory results are found. For the experimental validation, d-SPACE made Micro Lab Box is used as control processor, and both dynamic and steady-state results are discussed for its effectiveness.

A Sensitive Industrial Process Model for Financial Losses Assessment Due to Voltage Sag and Short Interruptions

Abstract: The financial loss assessment of industrial users due to voltage sag and short interruptions is important for distribution network performance evaluation and power quality enhancement scheme design Existing assessment models are highly dependent on complete industrial process information, which is difficult to obtain To solve this problem, a new sensitive industrial process model needs limited industrial processes information is proposed In the proposed model, the sensitive equipment is modeled by voltage tolerance curves (VTC), and the truth table is used to characterize the logical relationship As the industrial process information is limited, the boundary value of VTC and partial logical function values of the truth table are uncertain To determine the model's uncertain parameters objectively, an optimization model with the goal of minimizing the deviation of the assessment loss is constructed, and the details of the algorithm are also given out An example based on some investigation data is given to verify the effectiveness of the model and show how to use it

An Improved Bipolar-Type AC–AC Converter Topology Based on Nondifferential Dual-Buck PWM AC Choppers

Abstract: A novel single-phase pulsewidth modulation (PWM) direct ac–ac converter based on two-level nondifferential dual-buck ac chopper legs with inverting and noninverting operations is first proposed in this article. It has the ability to resolve both voltage sag and swell problems at the same time when used as distributed flexible voltage conditioner. Compared to the traditional ac–ac converter, it has much enhanced system reliability thanks to no shoot-through problems even when all switches of each ac chopper legs are turned on , and therefore, the PWM dead time is not needed leading to improve the utilization of the duty cycles. Only half of the switches in the proposed converter is switched at high frequency during a switching period at most, which significantly reduces the total switching loss. In particularly, the converter has two greatest advantages that it retains the common sharing ground of the input and output and has the same buck/boost operation process for noninverting and inverting modes. In order to fully testify the performance of the proposed converter, a 500-W experimental prototype is built and tested at different conditions.

Improved Fundamental Frequency Estimator for Three-Phase Application

Abstract: This letter reports a digital signal processing based frequency estimation technique that relies on the storage of fundamental three-phase grid voltage samples. Unlike phase-locked loop algorithms, the proposed algorithm does not require the phase error information when estimating the grid frequency. Moreover, only four consecutive samples of the fundamental orthogonal components are required in order to estimate the deviation in the grid frequency. The proposed scheme is facilitated with an inherent nonadaptive comb filtering behavior in order to reject the dc offset and harmonics while attaining a good immunity to voltage sag and the fundamental negative sequence component. Additionally, the off-nominal harmonic rejection capability of the proposed frequency estimator is enhanced by using a postfiltering method. The experimental validations reported in this study demonstrate that the proposed frequency estimator is suitable for three-phase grid applications.

A finite control set model predictive control scheme for single-phase grid-connected inverters

Abstract: The present article investigates a control scheme for single-phase grid-connected inverter based on the finite control set model predictive control (FCS-MPC) approach. The proposed grid integration scheme provides direct control of the active and reactive power (PQ) injected to the grid from distributed energy resources (DER) composed of a photovoltaic (PV) array as a renewable resource integrated with a battery bank as energy storage. The direct PQ control scheme includes also low voltage ride through (LVRT) capability of the inverter during voltage sag. The optimum inverter switching state is indicated via the employed FCS-MPC algorithm instantaneously such that the actual PQ, injected to the grid, will track the corresponding reference values. During normal operation, the active power, injected to the grid, is set to the maximum possible value, while the reactive power is nil. Under voltage sag, the PQ will be injected to the grid as a function of the percentage of voltage sag based on the existing grid codes and regulations. In single-phase systems, successful application of direct PQ control depends on accurately creating the fictitious orthogonal components of grid current and voltage required for instantaneous power computations. Therefore, the following three different orthogonal signal generation (OSG) methods are utilized in this study in order to create such virtual (quadrature) components: second-order generalized integrator (SOGI), all-pass filter (APF), and quarter cycle phase delay (QCPD). In addition, qualitative and quantitative analyses of the obtained results are involved in this study of the FCS-MPC PQ system in order to compare the three adopted OSG methods. The PSIM® software was utilized in this study for modeling and studying the overall FCS-MPC system and the DER grid integration system. According to the results, the investigated FCS-MPC approach is effective in providing quick response and flexible control of PQ injected to the grid through the use of the three OSG methods. Moreover, the investigated FCS-MPC scheme successfully involves the LVRT option in order to improve the dynamic grid voltage support during the permissible duration of voltage sag following the LVRT profiles and grid codes of many countries.

An Enhanced Frequency-Adaptive Single-Phase Grid Synchronization Technique

Abstract: Second-order generalized integrator phase-locked loop (SOGIPLL) relies on the frequency feedback from the PLL estimation. The frequency is used to generate the equivalent in-phase and in-quadrature signals of the single-phase grid voltage. The phase-angle-coupled frequency feedback makes the SOGIPLL structure vulnerable to various grid voltage transients such as voltage sag, phase-angle jumps (PAJs), and frequency variations. This article proposes a PLL independent frequency estimation technique. It estimates the frequency using the simplified teager energy operation on the normalized in-phase voltage component output of the SOGI. The phase-angle is estimated using the third-order polynomial approximated arctangent function on the in-phase and in-quadrature outputs of the proposed frequency-adaptive SOGI. The grid synchronization technique presented in this work avoids the use of any trigonometric operations and PLL gain tuning issues. Additionally, the impact of steady-state grid disturbances, namely, harmonics and dc offset on the proposed synchronization technique is investigated. Finally, its performance robustness is compared with other techniques during both grid transients and steady-state disturbances using both simulation analysis and experimental validation.

Increasing Voltage Support Using Smart Power Converter Based Energy Storage System and Load Control

Abstract: Voltage sag and swell affect the normal operation of loads as well as distributed generating sources and reduce the overall reliability of the system. For improving the voltage at point of common coupling, different grid code requires control of active and reactive powers through power electronic solutions. In this article, a smart power converter (SPC) is introduced in the distribution grid, and different from the existing voltage support solutions, this article utilizes control and coordination capabilities of SPC to provide medium voltage (MV) grid voltage support during voltage sag/swell. The proposed control scheme aims to improve the voltage support capability of SPC in the MV grid by the coordinated operation of SPC MV converter, low voltage converter, and battery energy storage system (BESS). For achieving the same voltage support capability, the proposed method requires lower rated BESS as compared to existing solutions. Simulation and experimental results show the effectiveness of the proposed scheme.

A Multi-Objective Control Strategy for Three Phase Grid-Connected Inverter During Unbalanced Voltage Sag

Abstract: This paper presents a new multi-objective control strategy for inverter-interfaced distributed generation (IIDG) to ensure its safe and continuous operation under unbalanced voltage sags. The proposed control strategy can effectively improve the low voltage ride through (LVRT) capability, reduce active power oscillations, and limit overcurrent simultaneously, which are marked as the most important control objectives of IIDG during unbalanced voltage sags. The advanced voltage support scheme, which utilizes positive sequence component, is firstly proposed to maximize the LVRT capability of IIDG during unbalanced voltage sags. Then, to ensure the safety of IIDG, the active power oscillation suppression and current limitation algorithm are designed individually. Based on the control algorithms of such objectives, the multi-objective control method, including scenario classification and reference current determination, is then presented to achieve such three objectives under various system conditions simultaneously. Finally, case studies and evaluations based on MATLAB/Simulink are carried out to illustrate the effectiveness of the proposed method.

Design and Implementation of Novel Noninverting Buck–Boost AC–AC Converter for DVR Applications

Abstract: This article proposes the new noninverting buck–boost ac–ac converter, which can minimize the reverse recovery loss by disabling the body diodes of switches and using the external fast recovery diodes for its current freewheeling. In particular, the proposed ac–ac converter takes advantages of metal-oxide semiconductor field effect transistors and external fast recovery diodes to achieve the high efficiency. Also, it has the high reliability without the shoot-through and dead-time considerations in the circuit. Moreover, it can be simply implemented without employing the conventional commutation control. This results in decreasing the control complexity. As its proper application, a new type of dynamic voltage restorer (DVR) based on the proposed noninverting buck–boost converter is described. It enables to solve the voltage sag and swell problems by utilizing both positive and negative gains of converter. Then, the hardware prototype of proposed ac–ac converter and DVR are implemented to verify their practical effectiveness.

Positive sequence voltage control, full negative sequence cancellation and current limitation for static compensators

Abstract: This paper presents a control scheme in the stationary reference frame for Static Synchronous Compensators that provides three features: 1) regulation of the positive sequence voltage to the nominal value, 2) full cancellation of the negative sequence voltage, and 3) peak limitation of the injected currents. These features can help improving the performance of these devices under perturbed grid conditions, including low, high and unbalanced voltages. Also, the peak current limiter guarantees both the safe operation of the converter, and a priority-based achievement of the voltage regulation targets, which is of interest during severe perturbations like voltage dips. Experimental results, implementation details and closed-loop analysis are presented to validate the regulation capabilities and to demonstrate the feasibility of the power quality improvement.

Cost of Industrial Process Shutdowns Due to Voltage Sag and Short Interruption

Abstract: The objective of this work is to propose and apply a methodology to obtain the cost of industrial process shutdowns due to voltage sag and short interruption. A field survey, aided by a specific questionnaire, was carried out in several industries connected to medium voltage networks, in the states of Espirito Santo and Sao Paulo in Brazil. The results obtained were the costs per event and the costs per demand in a total of 33 companies in 12 different types of activities. It is noteworthy that this survey brings a relevant technical contribution to the electricity sector, helping to fill, even partially, an existing gap in both national and international literature.

Power quality event classification using optimized Bayesian convolutional neural networks

Abstract: Management of the electrical grid has an importance on the sustainability and reliability of the electrical energy supply. In the process, it is still crucial that power quality (PQ) is evaluated as part of any grid management master plan. This article provides a novel approach for classifying PQ disturbances such as voltage sag, swell, interruption and harmonics. In the proposed method, colorized continuous wavelet transform coefficients of the voltage signals are applied to convolutional neural networks as an image file. Thus, there is no need for extra feature selection and data size reduction steps as in conventional machine learning-based classifiers. Experiments were conducted on a dataset containing 1500 real-life disturbance signals measured from different locations in Turkey by Turkish Electricity Transmission Corporation. With the power of deep learning in image processing, the proposed method provides very high classification accuracy with a value of 99.8%. Comparisons with the other PQ disturbance classification methods, which are using traditional signal processing-based feature extraction and machine learning algorithm, prove that the proposed method has a simple methodology and overcomes the defects of these methods.

Voltage stability enhancement in grid-connected microgrid using enhanced dynamic voltage restorer (EDVR)

Abstract: Microgrid (MG) has extensive properties to overcome common problems of local distribution system. Some of those problems are generation and demand difference, blackout and brownout, environmental concerns due to burning of natural resources in power stations (indirectly), and reliability issues. Research on microgrid is being conducted to enhance its features to mitigate power quality (PQ) problems associated with distribution system. Voltage sag and swell have been major power quality problems for decades, loads in distribution system are heavily affected due to these power quality problems. In the distribution system, microgrid and power quality compensation strategy should be existed in order to ensure reliability and voltage sag/swell mitigation. Dynamic voltage restorer (DVR) is comprehensive power electronics based Flexible Alternating Current Transmission System (FACTS) device, it is third-generation FACTS device as its control scheme selection flexibility and power line coupling approach make it advance when compare to first and second-generation FACTS devices. In this paper, an Enhanced Dynamic Voltage Restorer (EDVR) is presented to efficiently mitigate voltage sag/swell in grid connected microgrid. On the one side, the presence of microgrid structure ensures reliability of distribution system for local loads on the other side, EDVR ensures voltage sag/swell free power supply for loads. The control strategy of EDVR is based on enhanced synchronous reference frame (ESRF) approach and fuzzy technique system. ESRF is specially design for fast and precise operation of EDVR whereas; fuzzy technique system is responsible for standardized voltage supply for local loads. DC link voltage of EDVR is effectively regulated with the help of proposed control scheme at the time of voltage sag/swell compensation. Stability analysis of ESRF control has been done using modeling of VSC and eigenvalue analysis system. Simulation results on MATLAB/Simulink verified the performance of EDVR under presented control approach hence the specific loads in distribution system are more secure under proposed microgrid system with EDVR.

Optimization of DG Units in Distribution Systems for Voltage Sag Minimization Considering Various Load Types

Abstract: The optimum installation of distributed generation (DG) units in distribution systems has always been challenging due to the continually increase of electrical energy demands. However, the improper installation of DG units may have negative impact on the power quality of the distribution system. Voltage sag is one of the most important power quality problems, which has the bad effects on the performances of different loads, especially on sensitive and uninterruptible loads. To mitigate the voltage sag problem in distribution systems, a new formulation is proposed for optimal location and sizing of DG units. Particle swarm optimization algorithm is employed to solve the problem. The minimization of the total power losses, total cost of DG units, improvement of the voltage profile, and the reduction in the voltage sag effect are considered as the main objectives. To involve the voltage sag occurrence in distribution system, a penalty is considered for interruption of each type of available load. Different types of load models such as industrial, residential and commercial loads are considered in the system. For the demonstration of the effectiveness of the proposed algorithm, 34-bus test system is considered as the case study. The proposed method results are shown that there is about 72% reduction in total power losses in the optimal configuration of DG units in the distribution system. It is observed that the total number of disturbed buses decreases to 4, which is equal to 12%, as the number of DG units increases. It can be seen that the total cost of the system is reduced from 36.250 to 31.824 M$, when the optimum number of DG units is increased from 1 to 5. The simulation results show the effectiveness of the proposed algorithm.

The LVRT Control Scheme for PMSG-Based Wind Turbine Generator Based on the Coordinated Control of Rotor Overspeed and Supercapacitor Energy Storage

Abstract: With the increasing penetration level of wind turbine generators (WTGs) integrated into the power system, the WTGs are enforced to aid network and fulfill the low voltage ride through (LVRT) requirements during faults. To enhance LVRT capability of permanent magnet synchronous generator (PMSG)-based WTG connected to the grid, this paper presents a novel coordinated control scheme named overspeed-while-storing control for PMSG-based WTG. The proposed control scheme purely regulates the rotor speed to reduce the input power of the machine-side converter (MSC) during slight voltage sags. Contrarily, when the severe voltage sag occurs, the coordinated control scheme sets the rotor speed at the upper-limit to decrease the input power of the MSC at the greatest extent, while the surplus power is absorbed by the supercapacitor energy storage (SCES) so as to reduce its maximum capacity. Moreover, the specific capacity configuration scheme of SCES is detailed in this paper. The effectiveness of the overspeed-while-storing control in enhancing the LVRT capability is validated under different levels of voltage sags and different fault types in MATLAB/Simulink.

High Gain Non Isolated DC Converter Employed in Single-Phase Grid-Tied Solar Photovoltaic Supply System

Abstract: This article presents a high gain non isolated dc converter (HGNIDC) employed in single-phase grid-tied solar photovoltaic supply system (SPSS). In the proposed power optimized architecture based SPSS, each photovoltaic (PV) module is connected through HGNIDC to the common dc bus. The HGNIDC boosts up the low PV voltage as well as facilitates to harvest the maximum solar energy. For maximum power harvesting, fuzzy logic control (FLC) is used. The FLC enables high conversion efficiency at different weather conditions, fast dynamic response, reduced PV voltage oscillation, and does not require system specifications. For delivering the power to the ac grid from the common dc bus, an H-bridge voltage source converter (VSC) is used. The synchronization of VSC with the utility grid is carried out using an enhanced third-order generalized integrator (ETOGI). The ETOGI is able to extract fundamental grid voltage even under grid polluted conditions such as voltage sag, swell, higher dc-offsets, and harmonics. The performance of the proposed control approaches is validated using MATLAB/Simulink platform. The real time implementation is obtained using DSP board TMS320F28379D on the developed laboratory prototype.

A Voltage Sag Detection Method Based on Modified S Transform With Digital Prolate Spheroidal Window

Abstract: Voltage sag is one of the most prominent power quality problems in the electric power system. Accurate estimation of voltage sag parameters is an important reference for electric utilities and users to evaluate power quality. In this paper, a novel algorithm based on modified S transform with digital prolate spheroidal window (DPSW) is proposed to achieve accurate detection of voltage sag. The DPSW and its time-frequency characteristics are firstly detailed. Then, the construction and performance of modified S transform with DPSW are given. Since DPSW has superior time-frequency distribution, characteristics of voltage sag signal, such as sag depth, duration, and phase jump, can be obtained by analyzing the two-dimensional complex matrix after the modified S transform with DPSW. Simulation and experimental results verify the accuracy and validity of the proposed algorithm.