Probability Distributions.- Linear Models for Regression.- Linear Models for Classification.- Neural Networks.- Kernel Methods.- Sparse Kernel Machines.- Graphical Models.- Mixture Models and EM.- Approximate Inference.- Sampling Methods.- Continuous Latent Variables.- Sequential Data.- Combining Models.

Pattern Recognition and Machine Learning

The wind power generation is a rapidly growing grid integrated renewable energy (RE) technology with an installed capacity of 539.291 GW. The capability of the wind energy conversion system (WECS) to remain integrated into the utility network in the case of low voltage events is called low-voltage ride-through (LVRT) capability. This paper offers a comprehensive overview of improvement techniques of the LVRT capability in WECS to increase the wind energy penetration level in the utility grid. Exhibited portrait manifests a broad spectrum of 1) wind turbines, 2) electrical generators used for wind power applications, 3) international grid codes applicable for grid integration of WECS, 4) LVRT fundamentals in WECS, 5) wind turbines LVRT methods by doubly fed induction generator (DFIG), 6) wind turbines LVRT methods by permanent magnet synchronous generators (PMSG), and 7) LVRT methods of wind turbines using squirrel cage induction generator (SCIG). This ready-reckoner paper critically reviews and classifies more than 190 research papers on LVRT issues, practices, and available technologies for grid integration in wind energy systems, and it aims to be a quick reference for the researchers, designers, manufacturers, and engineers working in the same field.

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Comprehensive Overview of Low Voltage Ride Through Methods of Grid Integrated Wind Generator

Fault-ride-through (FRT) is an imperative capability in wind turbines (WTs) to ensure grid security and transient stability. However, doubly fed induction generator-based WTs (DFIG-WTs) are susceptible to disturbances in grid voltage, and therefore require supplementary protection to ensure nominal operation. The recent amendments in grid code requirements to ensure FRT capability has compelled this study of various FRT solutions. Therefore, for improving FRT capability in pre-installed WTs, re-configuration using external retrofit-based solutions is more suitable and generally adapted. The most relevant external solutions based on retrofitting available are classified as (a) protection circuit and storage-based methods and (b) flexible alternating current transmission system-based reactive power injection methods. However, for new DFIG-WT installations, internal control modification of rotor-side converter (RSC) and grid-side converter (GSC) controls are generally preferred. The solutions based on modifications in RSC and GSC control of DFIG-WT are classified as (a) traditional control techniques and (b) advanced control techniques. This study ensures to curate and compare the FRT solutions available based on external retrofitting-based solutions and internal control modifications. Also, the future trends in FRT augmentation of DFIG-WTs are discussed in this study.

https://ietresearch.onlinelibrary.wiley.com/doi/pdf/10.1049/iet-rpg.2018.5249

Review on FRT solutions for improving transient stability in DFIG-WTs

This paper investigates the fault ride through (FRT) capability improvement of a doubly fed induction generator (DFIG)-based wind turbine using a dynamic voltage restorer (DVR). Series compensation of terminal voltage during fault conditions using DVR is carried out by injecting voltage at the point of common coupling to the grid voltage to maintain constant DFIG stator voltage. However, the control of the DVR is crucial in order to improve the FRT capability in the DFIG-based wind turbines. The combined feed-forward and feedback (CFFFB)-based voltage control of the DVR verifies good transient and steady-state responses. The improvement in performance of the DVR using CFFFB control compared with the conventional feed-forward control is observed in terms of voltage sag mitigation capability, active and reactive power support without tripping, dc-link voltage balancing, and fault current control. The advantage of utilizing this combined control is verified through MATLAB/Simulink-based simulation results using a 1.5-MW grid connected DFIG-based wind turbine. The results show good transient and steady-state response and good reactive power support during both balanced and unbalanced fault conditions.

http://dspace.uniten.edu.my/jspui/bitstream/123456789/11383/1/Improved%20Fault%20Ride%20Through%20Capability%20in%20DFIG.pdf

Improved Fault Ride Through Capability in DFIG Based Wind Turbines Using Dynamic Voltage Restorer With Combined Feed-Forward and Feed-Back Control

Having a reduced number of switches and isolated DC sources yet generating a higher number of voltage levels has been always the challenge when selecting the appropriate Multilevel Inverter (MLI) topology. Nowadays, Single-DC-Source Multilevel Inverter (SDCS-MLI) topologies are being considered as more suitable for many power system applications such as Renewable Energy (RE) conversion systems and electrified transportations compared to the Multiple-DC-Source MLIs (MDCS-MLIs). Moreover, increasing the power rating and minimizing the switching frequency while maintaining reasonable power quality using a SDCS-MLI is an important requirement and a persistent challenge for the industry. Thus, this paper presents a general review on the available SDCS-MLI topologies and future trends. Existing solutions are discussed and analyzed based on their topologies, number of output voltage levels, number of active/passive components, advantages/limitations, maturity, and industrial applications. Furthermore, recommendations for future research and development are suggested in this paper.

/pdf/review-on-single-dc-source-multilevel-inverters-topologies-472h4ethlc.pdf

Review on Single-DC-Source Multilevel Inverters: Topologies, Challenges, Industrial Applications, and Recommendations

A comprehensive review of dynamic voltage restorers

Optimal allocation of D-STATCOM in distribution networks including correlated renewable energy sources

Design and implementation of a new high step‐up DC‐DC converter for renewable applications

This paper presents a single DC source five-level photovoltaic inverter topology for a stand-alone photovoltaic (PV) system. The proposed PV converter system consists of a five-level inverter and a buck DC-DC converter. The DC-DC converter that embedded in the inverter structure is used to realize the maximum power point tracking (MPPT) in various environmental conditions (temperature and irradiation). Also, as the studied system is stand-alone PV system, a battery energy storage system (BESS) is also included which consists of a bidirectional buck/boost DC-DC converter and a battery energy storage. The BESS is connected to a branch of the DC-link and controls the DC-link voltage while managing the battery energy. One of the main advantages of the proposed converter is that the buck DC-DC converter which is in-charge of MPPT, deals with partial power of the PV and hence the system efficiency would be improved. The simulation results using MATLAB/ SIMULINK confirm the performance of the proposed topology in different scenarios.

A Single DC-Source Five-Level Inverter Applied in Stand-Alone Photovoltaic Systems Considering MPPT Capability

Multilevel inverters are useful because of their benefits such as high output voltage quality and lower losses. The multilevel inverters can produce output voltage with low total harmonic distortion (THD) by PWM techniques. The characteristics of inverter output voltage depend on voltage levels of the inverter so that as the number of voltage levels increases, the quality of inverter output voltage improves. Most of the previously presented topologies of multilevel inverters require multiple DC sources to produce multilevel output voltage which have their own specific problems. This paper proposes and analyses a 5-level inverter topology with a single DC source and a buck DC-DC converter in order to reduce the number of independent DC voltage sources. In the proposed topology, the specific input DC voltage is supplied through a single DC and a single-input single-output DC-DC converter. As the proposed topology uses a buck stage, one of the capacitors voltage, which is supplied by DC-DC converter, can be controlled. It is important to emphasize that the DC-DC converter used in the proposed topology is a partial-scale converter reducing its cost and size in comparison with the full-scale ones. The performance of presented topology is demonstrated by the simulation studies using MATLAB/SIMULINK under various conditions.

Mohammad Farhadi-Kangarlu

Papers

A comprehensive review of dynamic voltage restorers

Optimal allocation of D-STATCOM in distribution networks including correlated renewable energy sources

Design and implementation of a new high step‐up DC‐DC converter for renewable applications

A Single DC-Source Five-Level Inverter Applied in Stand-Alone Photovoltaic Systems Considering MPPT Capability

Five-Level Single-DC Source Inverter with Adjustable DC-Link Voltage