Comparative study of power converter topologies and control strategies for the harmonic performance of variable-speed wind turbine generator systems

Power converters play a vital role in the integration of wind power into the electrical grid. Variable-speed wind turbine generator systems have a considerable interest of application for grid connection at constant frequency. In this paper, comprehensive simulation studies are carried out with three power converter topologies: matrix, two-level and multilevel. A fractional-order control strategy is studied for the variable-speed operation of wind turbine generator systems. The studies are in order to compare power converter topologies and control strategies. The studies reveal that the multilevel converter and the proposed fractional-order control strategy enable an improvement in the power quality, in comparison with the other power converters using a classical integer-order control strategy.     

Blade pitch control malfunction simulation in a wind energy conversion system with MPC five-level converter

This paper is on a wind energy conversion system simulation of a transient analysis due to a blade pitch control malfunction. The aim of the transient analysis is the study of the behavior of a back-to-back multiple point clamped five-level full-power converter implemented in a wind energy conversion system equipped with a permanent magnet synchronous generator. An alternate current link connects the system to the grid. The drive train is modeled by a three-mass model in order to simulate the dynamic effect of the wind on the tower. The control strategy is based on fractional-order control. Unbalance voltages in the DC-link capacitors are lessen due to the control strategy, balancing the capacitor banks voltages by a selection of the output voltage vectors. Simulation studies are carried out to evaluate not only the system behavior, but also the quality of the energy injected into the electric grid.     

Modelling, control and simulation of an overall wind energy conversion system

More and more conversion systems have been proposed to capture wind energy in order to produce electrical power. In this paper, an energetic macroscopic representation is used to describe such systems composed of very different parts. This representation yields the simulation model of the overall system based on energetic considerations. Moreover, a control structure can be deduced from this representation by simple inversion rules. Hence, the different strategies of wind turbine management can be shown by the theoretical control structure. In order to illustrate this modelling and control methodology a 750 kW wind energy conversion system is studied and simulated.     

An adaptive feedback linearization strategy for variable speed wind energy conversion systems

This paper presents a control strategy based on adaptive feedback linearization intended for variable speed grid‐connected wind energy conversion systems (WECS). The proposed adaptive control law accomplishes energy capture maximization by tracking the wind speed fluctuations. In addition, it linearizes the system even in the presence of turbine model uncertainties, allowing the closed‐loop dynamic behaviour to be determined by a simple tuning of the controller parameters. Particularly, the attention is focused on WECS with slip power recovery, which use a power conversion stage as a rotor‐controlled double‐output induction generator. However, the concepts behind the proposed control strategy are general and can be easily extended to other WECS configurations. Copyright © 2000 John Wiley & Sons, Ltd.     

Integrated strategy for real-time wind power fluctuation mitigation and energy storage system control

To address the impact of wind-power fluctuations on the stability of power systems, we propose a comprehensive approach that integrates multiple strategies and methods to enhance the efficiency and reliability of a system. First, we employ a strategy that restricts long-and short-term power output deviations to smoothen wind power fluctuations in real time. Second, we adopt the sliding window instantaneous complete ensemble empirical mode decomposition with adaptive noise(SW-ICEEMDAN) strategy t...     

垂直轴永磁直驱风力发电系统全风速功率控制

垂直轴风力机(VAWT)发电系统是一种应用潜力良好的新型风力发电系统。为了提高机组的风能转化效率,研究了全风速运行范围内的功率控制策略。建立了整机系统的数学模型,讨论了VAWT的气动机械特性及其4种工作模式;在此基础上,分析了机组在额定风速以内MPPT运行模式下,基于最佳叶尖速比(TSR)跟踪原理的最大风功率吸收控制策略;针对在额定风速以上的恒功率运行模式,设计了基于二阶扩张状态观测(ESO)方法的实时气动转矩估计器以及基于恒额定功率发电的最佳角速度控制策略;最后给出了全风速功率控制的系统结构。通过仿真试验,验证了该功率控制策略在全风速运行范围内实现整机高风能转化效率的良好效果。     

Power conversion in renewable energy systems: A review advances in wind and PV system

Grid‐connected photo voltaic (PV) systems are being developed very fast and systems from a few kW to tenths of a MW are now in operation. As an important source of distributed generation (DS) the PV systems need to comply with a series of standard requirements in order to ensure the safety and the seamless transfer of the electrical energy to the grid. Multilevel voltage source converters (VSC) is a heart of the PV system and are emerging as an important power converter options for low, medium, and high‐power applications. These VSCs have bought numerous advantages, especially in renewable energy systems such as PV and wind energy systems. In this article, several topologies of VSCs, which brings together some concepts from traditional converters and multi‐level converters, are presented. Also, several control strategies for controlling current, voltage, active power and reactive power have also been reviewed. Various topologies with their technical aspects have been reviewed and the best suitable topology and control scheme for grid connected PV and wind energy systems has been suggested. Copyright © 2016 John Wiley & Sons, Ltd.     

用于风电功率平抑的飞轮储能阵列功率协调控制策略

风电输出功率存在随机性和波动性的问题,使得电网调频难度加大.采用飞轮储能匹配风电的形式可以减小其功率波动,提高并网能力.以交流母线并联的飞轮储能阵列为研究对象,首先针对现有功率分配策略中存在的问题,提出一种考虑功率分配上限和能使各单元荷电状态(SOC)趋于一致的功率协调控制策略.同时为保证功率控制精度和储能系统的响应速...     

Disturbance observer‐based integral sliding mode control for wind energy conversion systems

Recently, wind power production has been under the focus in generating power and became one of the main sources of alternative energy. Generating of maximum power from wind energy conversion system (WECS) requires accurate estimation of aerodynamic torque and uncertainties presented in the system. The current paper proposed the generalized high‐order disturbance observer (GHODO) with integral sliding mode control (ISMC) for extraction of maximum power via variable speed wind turbine by accurate estimation of wind speed. The assumption in previous works that considers the aerodynamic torque as slow‐varying is not applicable for the real system. Therefore, the high‐order disturbance observers were designed for precise estimation of uncertainties with fast‐changing behavior. A robust control system was designed to control the speed of the rotor at the optimal speed ratio. The obtained simulation results have shown the better performance characteristics than conventional linear quadratic regulator (LQR) approach. The stability of the proposed algorithm was proven by Lyapunov stability anaysis. Simulations results were obtained in Matlab/Simulink environment.     

Effect of intermittent voltage source converter faults on the overall performance of wind energy conversion system

The doubly fed induction generator (DFIG) is interfaced to the AC network through voltage source converters (VSCs) which are considered to be the core of the DFIG system. This paper investigates the impact of different intermittent VSC faults on the overall performance of a DFIG-based wind energy conversion system (WECS). The fault ride through capability of the DFIG under various VSC faults is also investigated. Faults such as open circuit and short circuit across the switches, when they occur within the grid side converter (GSC) and rotor side converter (RSC), are considered and compared in this paper. Short circuit and open circuit across the DC-link capacitor are also considered in this study as common VSC problems. Simulation results indicate that the short circuit faults have a severe impact on the overall performance of the DFIG, especially when they occur within the GSC. This is attributed to the fact that the GSC directly regulates the point of common coupling voltage. The open circuit faults have less impact on the performance of the DFIG-based WECS. A proper controller along with flexible AC transmission device should be available to compensate the required active and reactive power during these faults. A protection technique is necessary to detect these faults in advance to protect the VSC switches and the machine winding from any catastrophic failure.     

Five-leg converter topology for wind energy conversion system with doubly fed induction generator

In this paper, application of a five-leg converter in Doubly Fed Induction Generator (DFIG) for Wind Energy Conversion Systems (WECS) is investigated. The five-leg structure and its PWM control are studied and performances are compared with the classical six-leg topology. The main drawback of five-leg converter with respect to the six-leg back-to-back converter is the need to increase the dc-link voltage for the same operation point, i.e. the same powers in case of WECS. So, different methods for the reduction of the required dc-link voltage in the five-leg case are studied. The five-leg converter is used to replace the conventional six-leg one, with the same ability. For the performance evaluation of this structure and its fully digital controller in a more realistic and experimental manner, Hardware in the Loop experiments is carried out. It is shown that efficient control of active and reactive powers and dc-link voltage is performed. Hardware in the Loop results demonstrate the high performance of the proposed fully digital control which is implemented on an Altera FPGA target.     

Energy and reliability benefits of wind energy conversion systems

The electrical energy production and reliability benefits of a wind energy conversion system (WECS) at a specific site depend on many factors, including the statistical characteristics of the site wind speed and the design characteristics of the wind turbine generator (WTG) itself, particularly the cut-in, rated and cut-out wind speed parameters. In general, the higher the degree of the wind site matching with a WECS is, the more are the energy and reliability benefits. An electrical energy production and reliability benefit index designated as the Equivalent Capacity Ratio (ECR) is introduced in this paper. This index can be used to indicate the electrical energy production, the annual equivalent utilization time and the credit of a WECS, and quantify the degree of wind site matching with a WECS. The equivalent capacity of a WECS is modeled as the expected value of the power output random variable with the probability density function of the site wind speed. The analytical formulation of the ECR is based on a mathematical derivation with high accuracy. Twelve WTG types and two test systems are used to demonstrate the effectiveness of the proposed model. The results show that the ECR provides a useful index for a WTG to evaluate the energy production and the relative reliability performance in a power system, and can be used to assist in the determination of the optimal WTG type for a specific wind site.     

风电氢联产系统功率平滑控制仿真研究

风能的随机性会引起风力发电出力不平稳,与此同时,电网电压跌落会给风电机组带来脱网运行的风险。针对该问题,文章将电解槽-储氢罐-质子交换膜燃料电池循环系统作为储能装置,接入风力发电系统背靠背变换器直流侧,构成了风电氢联产系统。在风电过剩时,系统通过电解水制氢储存多余电能;在风能不足时,消耗氢气产生电能,补偿不足的有功功率。文章在分析系统构成及运行方式的基础上,设计了各组成单元协调控制策略。MATLAB仿真结果表明:在文章提出的控制策略作用下,系统可以有效地抑制风速随机变化引起的输出功率的波动;配电网电压跌落时,系统具有较强的抵御风机脱网的能力。     

Multivariable control algorithm for laboratory experiments in wind energy conversion

Advanced experimentation with wind energy conversion systems is described. The real time multivariable control of a wind turbine is designed for investigation of theoretical concepts and their physical implementation. The control system includes a speed controller and a disturbance estimator for enhanced robustness of the control system. In order to provide students with deeper understanding of wind energy and energy extraction, a maximum power point tracking algorithm is developed and integrated into the control system. The multivariable control system is implemented in a small wind turbine laboratory system. A power electronic interface is based on two DC–DC converters: a buck converter for control of the speed and a boost converter controlling the load voltage. Experimental results demonstrate effectiveness of the multivariable control system for a wind turbine providing maximum power extraction. The experiment can be reconfigured for teaching various control concepts to both undergraduate and graduate students.     

适用于微网中储能变换器的并网开关控制策略

本文针对微网中储能变换器的并网开关控制问题进行了深入研究,深入分析了可控硅整流器(silicon controlled rectifier,SCR)开关的过零关断特性造成的关断延迟对本地负荷造成的影响.为保证本地负荷供电稳定、可靠,本文利用现有条件,提出SCR强制关断控制策略,该策略仅通过软件控制策略迫使流过SCR的电...     

Modeling and simulation of grid-connected photovoltaic energy conversion systems

Solar power generation using PV (photovoltaic) technology is a key but still evolving technology with the fastest growing renewable-based market worldwide in the last decade. In this sector with tremendous potential for energy security and economic development, grid-connected PV systems are becoming today the most important application of solar PV generation. Based on this trend, PV system designers require an accurate and reliable tool in order to predict the dynamic performance of grid-tied PV systems at any operating conditions. This will allow evaluating the impact of PV generation on the electricity grids. This paper presents a detailed characterization of the performance and dynamic behavior of a grid-connected PV energy conversion system. To this aim, a flexible and accurate PV simulation and evaluation tool (called PVSET 1.0) is developed. The PV system is modeled, simulated and validated under the MATLAB/Simulink environment. The accuracy of simulation results has been verified using a 250 Wp PV experimental set-up.     

Dynamic model of wind energy conversion systems with variable speed synchronous generator and full-size power converter for large-scale power system stability studies

This paper presents a dynamic model for variable speed wind energy conversion systems, equipped with a variable pitch wind turbine, a synchronous electrical generator, and a full power converter, specially developed for its use in power system stability studies involving large networks, with a high number of buses and a high level of wind generation penetration. The validity of the necessary simplifications has been contrasted against a detailed model that allows a thorough insight into the mechanical and electrical behavior of the system, and its interaction with the grid. The developed dynamic model has been implemented in a widely used power system dynamics simulation software, PSS/E, and its performance has been tested in a well-documented test power network.     

A variable speed wind energy conversion scheme for connection toweak AC systems

A three level control system for a variable speed wind energy conversion scheme (VSWECS) supplying a weak AC power system is presented. The objective of the control strategy is to maximize energy capture and simultaneously to support the voltage of the bus where the VSWECS is connected. Using an insulated gate bipolar transistor (IGBT) inverter, both control of active and reactive power supplied to the grid and reduction of harmonic distortion can be achieved. The response of the proposed scheme has been tested and evaluated in a test system using a developed computer program simulating in detail the system operation