Grid-connected inverter for wind power generation system

In wind power generation system the grid-connected inverter is an important section for energy conversion and transmission, of which the performance has a direct influence on the entire wind power generation system. The mathematical model of the grid-connected inverter is deduced firstly. Then, the space vector pulse width modulation （SVPWM） is analyzed. The power factor can be controlled close to unity, leading or lagging, which is realized based on H-type current controller and grid voltage vector-oriented control. The control strategy is verified by the simulation and experimental results with a good sinusoidal current, a small harmonic component and a fast dynamic response.

A Simulation Research on the Grid-Connected Control Technology of Single-Phase Inverters Based on MATLAB

This paper primarily discusses the main circuit of single-phase inverter circuits.It begins by introducing the research context and the significance of the subject,then discusses the topology of grid-connected single-phase inverter circuits,continues by discussing the control strategy for grid-connected single-phase inverter circuits,realizes a sinusoidal pulse width modulation(SPWM)signal generation circuit and an inverse control algorithm program,and finally ensures good output waveform and fast dynamic response.In view of the hysteresis feature of the grid voltage’s synchronous signal sampling circuit,the acquisition function in digital signal processing(DSP)control chips is applied,and the reasons for the hysteresis phenomenon are thoroughly investigated.The reliability of the SPWM control algorithm is revealed through the results.

Two-stage ADMM-based distributed optimal reactive power control method for wind farms considering wake effects

Since the connection of small-scale wind farms to distribution networks,power grid voltage stability has been reduced with increasing wind penetration in recent years,owing to the variable reactive power consumption of wind generators.In this study,a two-stage reactive power optimization method based on the alternating direction method of multipliers(ADMM)algorithm is proposed for achieving optimal reactive power dispatch in wind farm-integrated distribution systems.Unlike existing optimal reactive power control methods,the proposed method enables distributed reactive power flow optimization with a two-stage optimization structure.Furthermore,under the partition concept,the consensus protocol is not needed to solve the optimization problems.In this method,the influence of the wake effect of each wind turbine is also considered in the control design.Simulation results for a mid-voltage distribution system based on MATLAB verified the effectiveness of the proposed method.

A Novel Asymmetrical Single-Phase Multilevel Inverter Suitable for Hybrid Renewable Energy Sources

This paper introduces a novel single-phase asymmetrical multilevel inverter suitable for hybrid renewable energy sources. The proposed inverter consists of two isolated DC sources and six power semiconductor controlled switches. The suggested inverter is capable of generating seven-level output when the input DC voltage is taken in the ratio of 1:2. The higher magnitude DC source is fed from Photo Voltaic (PV) panels, whereas the lower magnitude DC source is fed from Wind Turbine (WT) driven Permanent Magnet DC (PMDC) generator. Both the renewable energy sources are connected to the inverter via two DC-DC boost converters connected in cascade (i.e. one for maximum power point tracking and another for DC-link voltage control). The proposed hybrid renewable energy source inverter is connected to single-phase grid via proper control systems. The complete system is simulated using MATLAB/SIMULINK and the results are presented in detail.

Improved three-vector based dead-beat model predictive direct power control strategy for grid-connected inverters

Since only one inverter voltage vector is applied during each duty cycle, traditional model predictive direct power control(MPDPC) for grid-connected inverters(GCIs) results in serious harmonics in current and power. Moreover, a high sampling frequency is needed to ensure satisfactory steady-state performance, which is contradictory to its long execution time due to the iterative prediction calculations. To solve these problems, a novel dead-beat MPDPC strategy is proposed, using two active inverter voltage vectors and one zero inverter voltage vector during each duty cycle. Adoption of three inverter vectors ensures a constant switching frequency. Thus, smooth steady-state performance of both current and power can be obtained. Unlike the traditional three-vector based MPDPC strategy, the proposed three vectors are selected based on the power errors rather than the sector where the grid voltage vector is located, which ensures that the duration times of the selected vectors are positive all the time. Iterative calculations of the cost function in traditional predictive control are also removed, which makes the proposed strategy easy to implement on digital signal processors(DSPs) for industrial applications. Results of experiments based on a 1 kW inverter setup validate the feasibility of the proposed three-vector based dead-beat MPDPC strategy.

Active and Reactive Power Decoupling Control of Grid-Connected Inverters in Stationary Reference Frame

Proportion resonant(PR)controllers are able to achieve zero steady-state error for AC input signals and are widely used for simplifying control systems in the stationary reference frame.However,power decoupling in the stationary reference frame with a PR controller has not been investigated thoroughly.Based on the complex vector model of a grid-connected inverter(GCI),this paper deduces theoretically the power coupling relationship of GCI with the traditional PR current controller.A modified PR controller is provided for achieving the power decoupling,and the design method of the controller is presented.Simulation and experimental results verify that there is coupling between active and reactive power using the traditional PR controller and the proposed method can realize the power decoupling.

适应于逆变型风电接入系统的改进故障序分量选相方法

针对传统故障序分量选相元件在逆变型风电接入系统中可靠性较低的问题,提出了一种改进的故障序分量选相方法。首先,分析在最新风电场低电压穿越策略下,风电侧的故障序阻抗特性及传统故障序分量选相元件的适应性。然后,利用负正序、负零序阻抗相位差等效正负序、零负序电流分支系数相位差,以补偿传统序分量选相判据的相角误差。最后,采用补偿后的故障序电流相位差作为选相判据,实现了故障相的判别。同时通过调整零负序选相分区,使其具有较好的耐过渡电阻能力。仿真实验表明,在不同故障类型、故障位置和过渡电阻下改进选相方法均能可靠地选出故障相。

基于边界圆限定的风电并网逆变器模型预测功率控制

随着风电机组单机容量不断增长,要求风电并网逆变器的开关频率较低以降低损耗,为此提出一种新型单边界圆限定模型预测功率控制策略。该策略根据当前时刻功率误差与预设边界圆的位置关系决定下一时刻最优矢量的选择原则,无需复杂的坐标变换即可将功率误差限制在系统允许范围内,同时通过选取合适的边界圆半径减小了风电并网逆变器的平均开关频率。最后,在Matlab/Simulink仿真软件中验证了该策略的有效性和正确性。

Wind Energy Conversion System from Electrical Perspective—A Survey

This paper focuses on the wind energy conversion system (WECS) with the three main electrical aspects: 1) wind turbine generators (WTGs), 2) power electronics converters (PECs) and 3) grid-connection issues. The current state of wind turbine generators are discussed and compared in some criteria along with the trends in the current WECS market, which are ‘Variable Speed’, ‘Multi-MW’ and ‘Offshore’. In addition, the other crucial component in the WECS, PECs will be discussed with its topologies available in the current WECS market along with their modulation strategies. Moreover, three main issues of the WECS associating with the grid-connection, fault-ride through (FRT) capability, harmonics/interharmonics emission and flicker, which are the power quality issues, will be discussed due to the increasing responsibility of WECS as utility power station. Some key findings from the review such as the attractiveness of BDFRG are presented in the conclusion of this paper.

弱电网下海上低频风电系统网侧控制和稳定性分析研究

低频交流输电技术广泛应用于海洋风电的输送,但其送出的电流质量和系统稳定性会受到网侧变流器和弱电网线路阻抗的影响。文章针对海上低频风电系统的网侧控制,研究了αβ坐标系下基于虚拟同步机(Virtual Synchronous Generator,VSG)控制方法,并引入虚拟阻抗环节实现VSG的功率解耦,使得网侧变流器能在电网频率突变时自发调频,提高了其并网电能质量和弱电网下的稳定性。考虑到VSG并网系统与弱电网之间的交互作用,利用谐波线性化方法建立了αβ坐标系下VSG并网系统的序阻抗模型,结合阻抗分析法和Nquist稳定判据分析了并网系统在弱电网下的稳定性。最后,通过仿真验证了分析的正确性。

柔性直流送出系统交流线路的自适应距离保护方法

柔性直流系统接入使得电网故障特征发生明显改变,传统距离保护应用于柔性直流送出系统交流线路时存在不正确动作风险。针对该问题,指出了基于正序电压极化的距离保护动作特性受柔性直流系统控制策略影响的规律,阐明了柔性直流近端或电网侧背后发生相间故障时拒动或误动的机理。在此基础上,提出了结合暂态信息的自适应距离保护方法,利用故障初瞬自然响应阶段时域信息,构建快速方向判别元件,再结合方向判别结果自适应调整距离保护动作范围,保证距离保护正确动作。实时数字仿真试验结果验证了所提方法的有效性。

考虑风-储-直参与调频的电力系统频率特征定量分析

以风电、储能、柔性直流输电为代表的高比例可再生能源和大量电力电子设备的并网,使得电网中传统火电的比例下降,这将在一定程度上影响电力系统的频率稳定性。为定量分析风电、储能、柔性直流输电系统参与调频下电力系统的频率特征,首先提出多种调频资源参与调频下的电网频率特征定量分析总体思路,建立风-储-直调频频率响应模型。然后基于频率特性传递函数对电力系统稳态频率偏差、初始频率变化率、最大频率偏差和频率安全裕度进行理论推导;且定量分析了稳态频率偏差变化规律以及惯性时间常数、辅助调频单元控制比例系数对频率稳定性的影响,并计算稳态频率偏差与功率扰动的关系。最后,基于仿真软件验证了所提分析方法的可行性和有效性。仿真表明所提方法可有效定量分析电力系统频率特征,可为双高电力系统下电网频率安全稳定运行与控制提供指导依据。

基于降阶线性扩张状态观测器的风电并网逆变器线性自抗扰控制

针对风电并网逆变器直流母线电压易受电网电压波动和负载扰动影响的问题,提出了一种电压外环改进型线性自抗扰控制(LADRC)。建立了风电并网逆变器在d-q旋转坐标系下的数学模型,在此基础上,设计了基于降阶线性扩张状态观测器的线性自抗扰控制,减小了观测器的相位滞后,提高了系统的扰动观测精度;在观测器总扰动通道上增加了一个超前滞后的校正环节以减弱观测器的噪声放大效应;文章对改进型LADRC控制策略进行了频域特性分析。仿真结果表明,相比于传统LADRC控制策略,所提的控制策略对并网逆变器直流母线电压具有更好的控制效果。

High performance decoupled active and reactive power control for three-phase grid-tied inverters using model predictive control

Finite control set-model predictive control (FCS-MPC) is employed in this paper to control the operation of a three-phase grid-connected string inverter based on a direct PQ control scheme. The main objective is to achieve high-performance decoupled control of the active and reactive powers injected to the grid from distributed energy resources (DER).The FCS-MPC scheme instantaneously searches for and applies the optimum inverter switching state that can achieve certain goals, such as minimum deviation between reference and actual power;so that both power components (P and Q) are well controlled to their reference values.In addition, an effective method to attenuate undesired cross coupling between the P and Q control loops, which occurs only during transient operation, is investigated. The proposed method is based on the variation of the weight factors of the terms of the FCS-MPC cost function, so a higher weight factor is assigned to the cost function term that is exposed to greater disturbance. Empirical formulae of optimum weight factors as functions of the reference active and reactive power signals are proposed and mathematically derived. The investigated FCS-MPC control scheme is incorporated with the LVRT function to support the grid voltage in fulfilling and accomplishing the up-to-date grid codes. The LVRT algorithm is based on a modification of the references of active and reactive powers as functions of the instantaneous grid voltage such that suitable values of P and Q are injected to the grid during voltage sag.The performance of the elaborated FCS-MPC PQ scheme is studied under various operating scenarios, including steady-state and transient conditions. Results demonstrate the validity and effectiveness of the proposed scheme with regard to the achievement of high-performance operation and quick response of grid-tied inverters during normal and fault modes.

Model predictive control of grid-connected PV power generation system considering optimal MPPT control of PV modules

Because of system constraints caused by the external environment and grid faults,the conventional maximum power point tracking(MPPT)and inverter control methods of a PV power generation system cannot achieve optimal power output.They can also lead to misjudgments and poor dynamic performance.To address these issues,this paper proposes a new MPPT method of PV modules based on model predictive control(MPC)and a finite control set model predictive current control(FCS-MPCC)of an inverter.Using the identification model of PV arrays,the module-based MPC controller is designed,and maximum output power is achieved by coordinating the optimal combination of spectral wavelength and module temperature.An FCS-MPCC algorithm is then designed to predict the inverter current under different voltage vectors,the optimal voltage vector is selected according to the optimal value function,and the corresponding optimal switching state is applied to power semiconductor devices of the inverter.The MPPT performance of the MPC controller and the responses of the inverter under different constraints are verified,and the steady-state and dynamic control effects of the inverter using FCS-MPCC are compared with the traditional feedforward decoupling PI control in Matlab/Simulink.The results show that MPC has better tracking performance under constraints,and the system has faster and more accurate dynamic response and flexibility than conventional PI control.

Novel Wind Power Grid-connection System Using Inductive Filtering Technology

Herein,a novel wind power grid-connection system based on inductive filtering is proposed to improve grid-connection compatibility,and is implemented in a 50-MW real system.First,the topology and wiring configuration of the proposed system are discussed.Thereafter,an equivalent circuit and mathematical model are established to reveal the filtering characteristics and resonance damping mechanism of the proposed system.Finally,a 50-MW wind farm-based experimental study,which is conducted to validate the effectiveness and availability of the system is discussed.The experimental results show that the main harmonics,power factor,voltage fluctuation,and flicker satisfy national standards.

双馈风电变流器IGBT模块功率循环能力的分析

阐述不同风况条件下的双馈分电机组变流器运行可靠性评定特点,探讨一种以变流器IGBT模块运行功率为基础,对循环能力进行评定的方式,同时说明风速会对功率循环水平造成的不同影响。

基于双向变流器的风光互补系统在通信电源中的应用研究

文章概述了风能发电系统和光伏发电系统的原理和工作方式。针对传统通信电源的局限性,引入了基于双向变流器的风光互补系统,并探讨了双向变流器的原理、拓扑结构,进一步研究了风光互补系统与通信电源需求的匹配性。

风光互补技术及应用新进展

简要回顾国内外风电、光伏技术与应用发展态势,结合风光互补系统应用,分析、介绍了风光互补LED路灯照明系统、智能控制器设计、分布式供电电源、风光互补水泵系统,并着重分析生物质能、风能和太阳能互补分布式能源梯级系统原理,涉及的技术关键等。研究表明,风能、光伏发电应用需要实现低成本、规模化,风光互补技术应用前景广阔。

基于变平滑时间常数的电池储能系统优化控制方法

在风力发电系统中配备一定的储能系统将会起到平滑功率波动的作用。以储能并网逆变器及其优化控制为研究对象,从兼顾并网功率平滑度和延长储能系统使用寿命出发,提出一种基于变平滑时间常数和功率限幅的优化控制方法,通过实时调整平滑时间常数和功率限幅来实现对电池储能系统的保护。逆变器的底层实现采用可切换模式的改进双环控制算法,避免电池欠压或过压运行。实验结果验证了所提优化控制方法的有效性和可行性,能避免电池储能系统的过充、过放和过载状态。