Power Quality Enhancement in Electricity Grids with Wind Energy Using Multicell Converters and Energy Storage

In recent years, the wind power industry is experiencing a rapid growth and more wind farms with larger size wind turbines are being connected to the power system. While this contributes to the overall security of electricity supply, large-scale deployment of wind energy into the grid also presents many technical challenges. Most of these challenges are one way or another, related to the variability and intermittent nature of wind and affect the power quality of the distribution grid. Power quality relates to factors that cause variations in the voltage level and frequency as well as distortion in the voltage and current waveforms due to wind variability which produces both harmonics and inter-harmonics. The main motivation behind work is to propose a new topology of the static AC/DC/AC multicell converter to improve the power quality in grid-connected wind energy conversion systems. Serial switching cells have the ability to achieve a high power with lower-size components and improve the voltage waveforms at the input and output of the converter by increasing the number of cells. Furthermore, a battery energy storage system is included and a power management strategy is designed to ensure the continuity of power supply and consequently the autonomy of the proposed system. The simulation results are presented for a 149.2 kW wind turbine induction generator system and the results obtained demonstrate the reduced harmonics, improved transient response, and reference tracking of the voltage output of the wind energy conversion system.Peer reviewedFinal Accepted Versio

An Investigation of the Influences of the Voltage Sag on the Doubly Fed Induction Generator using Tuned PI Controllers

The paper presents dynamic and transient behavior of the doubly fed induction generator (DFIG) in the wind farms in the normal and faulted grid respectively. When Voltage sag or any fault occurs in the network, the variables in the Doubly Fed Induction Generators are varying severely. If a voltage sag occurs, active and reactive power generated by the DFIG start to oscillate. The DC-link voltage will be bigger and will have fluctuation, and the rotor current will increase. In this paper, proportional integral (PI) controllers are used to control the DFIG in the wind farms for driving of the electronic devices including Rotor Side Converter (RSC) and Grid Side Converter (GSC) and controlling the active and reactive power of DFIG. PI parameters are tuned by particle swarm optimization algorithm (PSO). Whereas the model of DFIGs and electronic device in the paper are nonlinear so PI controllers cannot protect and control the DFIG as well. Hence, effect of PI parameters is investigated on the DFIG with simulating in MATLAB software. Also, low voltage ride through (LVRT) feature for DFIG is explored in presence of PI controllers. The results of the simulation present DC-link over voltage and rotor and stator over current in the DFIG. In addition, it will explore the effect of proportional integral controllers when three-phase short circuit fault occurs

Voltage Stability Enhancement of Wind Generator System Using Superconducting Fault Current Limiter

Wind generator systems have stability problems during network faults. The superconducting fault current limiter (SFCL) has the ability to prevent the magnitude of short-circuit current from increasing. This work proposes the SFCL device to enhance the voltage stability of a fixed-speed wind generator system.In this work the performance of SFCL is compared to that of the thyristor switched capacitor (TSC) method and the pitch control method. The comparison is done in terms of voltage stability enhancement, controller complexity and cost. The effectiveness of the proposed methodology is tested considering permanent and temporary, balanced and unbalanced faults in the power system model consisting of a wind generator and a synchronous generator.From the simulation results it is evident that performance of SFCL is better. On comparison it can be concluded that SFCL performs better when compared to TSC or pitch control method. Simulations are performed through Matlab/Simulink software

Fault Ride-Through Capacity Enhancement of Fixed Speed Wind Generator by A Modified Bridge-type Fault Current Limiter

Fault Ride-Through (FRT) is a common requirement to abide by grid code all over the world. In this work, to enhance the fault ride-through capability of a fixed speed wind generator system, a modified configuration of Bridge-Type Fault Current Limiter (BFCL) is proposed. To check the effectiveness of the proposed BFCL, its performance is compared with that of the Series Dynamic Braking Resistor (SDBR). A harmonic performance improvement by the proposed method is also analyzed. Three-line-to-ground (3LG), line-to-line (LL) and single-line-to-ground (1LG) faults were applied to one of the double circuit transmission lines connected to the wind generator system. Simulations were carried out using Matlab/Simulink software. Simulation results show that the proposed BFCL is very effective device to achieve the FRT and suppress fault current that eliminates the need for circuit breaker replacement. Also, the BFCL improves the harmonic performance and helps follow harmonic grid code. Moreover, it was found that the BFCL works better than the SDBR, and has some distinct advantages over the SDBR

Offshore Wind Farm-Grid Integration: A Review on Infrastructure, Challenges, and Grid Solutions

Recently, the penetration of renewable energy sources (RESs) into electrical power systems is witnessing a large attention due to their inexhaustibility, environmental benefits, storage capabilities, lower maintenance and stronger economy, etc. Among these RESs, offshore wind power plants (OWPP) are ones of the most widespread power plants that have emerged with regard to being competitive with other energy technologies. However, the application of power electronic converters (PECs), offshore transmission lines and large substation transformers result in considerable power quality (PQ) issues in grid connected OWPP. Moreover, due to the installation of filters for each OWPP, some other challenges such as voltage and frequency stability arise. In this regard, various customs power devices along with integration control methodologies have been implemented to deal with stated issues. Furthermore, for a smooth and reliable operation of the system, each country established various grid codes. Although various mitigation schemes and related standards for OWPP are documented separately, a comprehensive review covering these aspects has not yet addressed in the literature. The objective of this study is to compare and relate prior as well as latest developments on PQ and stability challenges and their solutions. Low voltage ride through (LVRT) schemes and associated grid codes prevalent for the interconnection of OWPP based power grid have been deliberated. In addition, various PQ issues and mitigation options such as FACTS based filters, DFIG based adaptive and conventional control algorithms, ESS based methods and LVRT requirements have been summarized and compared. Finally, recommendations and future trends for PQ improvement are highlighted at the end

Low Voltage Ride through Enhancement for Wind Turbines Equipped With DFIG under Symmetrical Grid Faults

In modern power systems with significant penetration of wind-turbines (WTs), improvement of low voltage ride through (LVRT) capability of WTs equipped with doubly-fed induction generators (DFIGs) is an important issue. Thus, this paper proposes a low voltage ride through (LVRT) strategy, which comprise of a capacitor connected in series with an inductor both connected in parallel to a resistor. The configuration is then connected to a small series resistor via a pair of antiparallel-Thyristors. The circuit and its switching control scheme of the proposed LVRT circuit are designed to: minimize the transition times, maintain the RSC connection to the rotor-windings, and reduce oscillations of dc-link voltage. In this case, the capacitor is entitled to eliminate ripples generated in the rotor voltage while the inductor reduces the ripple in rotor current. Different fault conditions were studied to validate the performance of the proposed scheme using MATLAB/Simulink platform. Comparative results and analysis are presented with conventional LVRT strategies

Combining Multi-Band Power System Stabilizers and Hybrid Power Flow Controllers to Support Electricity Grids with High Penetration of Distributed Renewable Generation

The paper demonstrates the application of a new power flow configuration consisting of a Hybrid Power Flow Controller (HPFC) and a Multi-Band Power System Stabilizers (MB-PSS) to enhance the performance of a multi-machine power network in the presence of solar photovoltaic (PV) and wind energy sources. The HPFC is a new type of FACTS (Flexible AC Transmission Systems) device, which has been introduced to address inter-area congestion problems by controlling the real power flow and providing voltage regulation. The MB-PSS, on the other hand, is a power system stabilizer based on different frequency modes of electromechanical oscillations, where the discontinuities caused by the faults in the grid are taken in consideration, for multiple fault clearing times.The multi-machine power network with PV and wind distributed generation and the proposed power flow configuration are simulated using Matlab/ SimPowerSystems Toolbox and analyzed under three phase to ground short-circuits faults occurring in the middle of transmission line

Artificial Intelligence-based Control Techniques for HVDC Systems

The electrical energy industry depends, among other things, on the ability of networks to deal with uncertainties from several directions. Smart-grid systems in high-voltage direct current (HVDC) networks, being an application of artificial intelligence (AI), are a reliable way to achieve this goal as they solve complex problems in power system engineering using AI algorithms. Due to their distinctive characteristics, they are usually effective approaches for optimization problems. They have been successfully applied to HVDC systems. This paper presents a number of issues in HVDC transmission systems. It reviews AI applications such as HVDC transmission system controllers and power flow control within DC grids in multi-terminal HVDC systems. Advancements in HVDC systems enable better performance under varying conditions to obtain the optimal dynamic response in practical settings. However, they also pose difficulties in mathematical modeling as they are non-linear and complex. ANN-based controllers have replaced traditional PI controllers in the rectifier of the HVDC link. Moreover, the combination of ANN and fuzzy logic has proven to be a powerful strategy for controlling excessively non-linear loads. Future research can focus on developing AI algorithms for an advanced control scheme for UPFC devices. Also, there is a need for a comprehensive analysis of power fluctuations or steady-state errors that can be eliminated by the quick response of this control scheme. This survey was informed by the need to develop adaptive AI controllers to enhance the performance of HVDC systems based on their promising results in the control of power systems. Doi: 10.28991/ESJ-2023-07-02-024 Full Text: PD

Partitioning And Interface Requirements Between System And Application Control For Power Electronic Converter Systems

Applications of power electronics in power systems are growing very rapidly and changing the power system infrastructure in terms of operation speed and control. Even though applications of power electronics are wide spread, the cost and reliability of power electronics are the issues that could hinder their penetration in the utility and industrial systems. The demand for efficient and reliable converter controllers gave rise to modularized converter and controller design. The objective of this dissertation is to determine the appropriate partitioning and interface requirements between the system and application control layers for power electronic converters so that the minimum set of system layer to application layer control interfaces is compatible across all power electronic controllers. Previous work, using the Open System Architecture (OSA) concept has shown that there is a set of common functions shared by different converters at the low-level control layers. It has also shown that, depending on the application, there is a variation in control functions in application/middle control layers. This functional variation makes it difficult to define system functionality of power converters at upper control layers and further complicates the investigation into the partition requirements of system to application control layer. However, by analyzing the current or voltage affected by a converter in terms of orthogonal components, where each component or group of components is associated with a power-converter application, and the amount of required DC bus energy storage, a common functionality can be observed at the application control layer. Therefore, by establishing common functionality in terms of affected current or voltage components, a flexibility of operation can be realized at upper control layers that will be a major contribution towards standardizing the open system architecture. In order to a construct functional flexible power converter control architecture, the interface requirements to the system control layer and the partitioning between the system control layer and application control layer need to be explored. This will provide flexibility of system design methodology by reducing the number of constraints and enabling system designers to explore possible system architectures much more effectively