电网不平衡时采用串联网侧变换器的DFIG风电系统协调控制

针对采用串联网侧变换器的双馈感应发电机(doubly fed induction generators, DFIG)风电系统,详细分析电网电压不平衡条件下该系统的运行情况,从抑制不平衡定子电压及维持系统有功功率平衡的角度出发,分别提出电网不平衡时串联网侧变换器和并联网侧变换器的控制策略.与电网不平衡下DFIG系统的传统运行控制方案相比,所提系统协调控制策略无需改变电网不平衡下转子侧变换器的控制策略,简化转子侧变换器的控制并有效提高其运行可靠性;所提方案在实现DFIG系统电磁转矩、直流链电压及系统总输出有功功率无二倍频波动的同时,实现电网不平衡下DFIG定、转子三相电流平衡,进一步提高了DFIG系统运行的稳定性和可靠性.通过对电网不平衡下采用串联网侧变换器的DFIG风电系统和采用传统控制策略的DFIG系统进行了仿真计算和对比分析,验证所提协调控制策略的正确性和有效性.     

Fault ride-through capability improvement in a DFIG-based wind turbine using modified ADRC

In this paper, an overview of several strategies for fault ride-through (FRT) capability improvement of a doubly-fed induction generator (DFIG)-based wind turbine is presented. Uncertainties and parameter variations have adverse effects on the performance of these strategies. It is desirable to use a control method that is robust to such disturbances. Auto disturbance rejection control (ADRC) is one of the most common methods for eliminating the effects of disturbances. To improve the performance of the conventional ADRC, a modified ADRC is introduced that is more robust to disturbances and offers better responses. The non-derivability of the fal function used in the conventional ADRC degrades its efficiency, so the modified ADRC uses alternative functions that are derivable at all points, i.e., the odd trigonometric and hyperbolic functions (arcsinh, arctan, and tanh). To improve the efficiency of the proposed ADRC, fuzzy logic and fractional-order functions are used simultaneously. In fuzzy fractional-order ADRC (FFOADRC), all disturbances are evaluated using a nonlinear fractional-order extended state observer (NFESO). The performance of the suggested structure is investigated in MATLAB/Simulink. The simulation results show that during disturbances such as network voltage sag/swell, using the modified ADRCs leads to smaller fluctuations in stator flux amplitude and DC-link voltage, lower variations in DFIG velocity, and lower total harmonic distortion (THD) of the stator current. This demonstrates the superiority over conventional ADRC and a proportional-integral (PI) controller. Also, by changing the crowbar resistance and using the modified ADRCs, the peak values of the waveforms (torque and currents) can be controlled at the moment of fault occurrence with no significant distortion.     

不平衡电网电压下风力发电机网侧变流器控制研究

针对电网电压不平衡下风力发电机网侧变流器的控制问题,提出一种基于比例积分谐振(proportional integrate resonant,PIR)控制器的矢量控制方法。以双馈风力发电机为研究对象,建立了它及其网侧变流器在不平衡电网电压条件下的数学模型,并分析了其工作原理和相关控制关系。介绍了谐振控制器的工作原理,建立数学模型,进行参数设计,并在MATLAB中进行验证。在MATLAB仿真平台中搭建了一台6MW的双馈电机模型,验证了谐振控制器能够准确的控制网侧变流器跟踪电网电压,有助于双馈电机的平稳运行。     

Improved rotor current control of wind turbine driven doubly-fed induction generators during network voltage unbalance

This paper investigates an improved control and operation of a doubly-fed induction generator (DFIG) system under unbalanced network conditions. A new rotor current control scheme is presented, which consists of a main controller and an auxiliary compensator. The main controller is constructed in the same way as the conventional vector control design without involving sequential-component decomposition in order to guarantee system stability and high transient response. While the auxiliary controller is specially designed to control the negative sequence current taking into account the impact of the main controller on negative sequence components. Simulated results on a commercial 1.5-MW DFIG system and experimental tests on a 1.5-kW DFIG prototype are provided and compared with those of conventional vector control and dual PI current control schemes to demonstrate the effectiveness of the proposed control strategy during steady-state and transient conditions when the network voltage is unbalanced.     

Battery energy storage-based system damping controller for alleviating sub-synchronous oscillations in a DFIG-based wind power plant

This paper presents the issue of the Sub-synchronous resonance (SSR) phenomenon in a series compensated DFIGbased wind power plant and its alleviation using a Battery Energy Storage-based Damping Controller (BESSDCL). A supplementary damping signal is developed considering the angular speed deviation and is incorporated into the BESS control system. Wide-area Measurement System data is used to determine the angular speed deviation. A linearized system model is developed to perform eigenvalue analysis, and to detect and examine unstable SSR modes. The variation of wind speed and three-phase fault are also taken into consideration to validate the robustness of the controller. To further verify the efcacy of the proposed damping controller, time-domain simulations are performed using MATLAB/Simulink. The application of the proposed BESSDCL stabilizes all the unstable system modes efectively at wind speeds of 7 m/s, 9 m/s, and 11 m/s, and at 40%, 50%, and 60% series compensation levels, as well three-phase fault conditions.     

A SCR crowbar commutated with power converter for DFIG-based wind turbines

This paper presents an active crowbar, constructed with silicon controlled rectifiers (SCRs), for doubly fed induction generator (DFIG)-based wind turbines to fulfill low-voltage ride-through (LVRT) requirements demanded by grid codes. By this design, not only the active deactivation of the costly IGBT crowbar, replacing the passive crowbar for this ability, can be achieved with the more cost-effective SCRs, but also the reliability of the circuit is strengthened thanking to the high surge capability of SCR. In this topology, three back-to-back SCR switches are connected in delta form and further engaged with the rotor circuit of DFIG through power dissipation resistors, working as the main circuit of crowbar, while the rotor side converter (RSC) is used to commutate the SCRs at the desired deactivation moment to disconnect the crowbar, allowing for resumption of the feedback control to DFIG. By this topology the harmonics introduced into the rotor circuit by the diode bride in the IGBT crowbar are got rid of and by this commutation method the overvoltage risk at turning off the IGBT is eliminated. With the simulative results on a 2 MW DFIG, the comparison with the IGBT crowbar is made. The feasibility of the proposed crowbar technique is further demonstrated with experiments on a laboratory-scale test rig.     

Advanced control of a doubly-fed induction generator for wind energy conversion

The aim of this paper is to propose a control method for a doubly-fed induction generator used in wind energy conversion systems. First, stator active and reactive powers are regulated by controlling the machine inverter with three different controllers: proportional–integral, polynomial RST based on pole placement theory and Linear Quadratic Gaussian. The machine is tested in association with a wind-turbine emulator. Secondly a control strategy for the grid-converter is proposed. Simulations results are presented and discussed for each converter control and for the whole system.     

基于扩张状态观测器的DFIG网侧变换器滑模控制

针对双馈风力发电机网侧变换器因负载变化和滤波参数摄动导致控制效果不佳的问题,提出一种扩张状态观测器（extended state observer, ESO）与滑模控制相结合的网侧变换器双闭环控制策略。内环采用以功率为状态变量的基于ESO的滑模直接功率控制,外环采用以电压平方为状态变量的基于ESO的滑模控制;应用ESO对系统状态变量与包含系统未建模动态、负载变化和滤波参数摄动等集总不确定项进行估计,即可无需系统的精确数学模型设计滑模控制方法,实现网侧变换器在复杂环境下的鲁棒控制,理论分析了ESO和滑模控制的稳定性。此外引入功率差前馈环节,减小负载变化时外环滑模控制非线性带来的冲击。最后通过负载变化和滤波参数摄动两个算例仿真,结果表明,与传统矢量控制和滑模控制相比,所提控制策略在复杂环境下具有更强的鲁棒性。     

电网电压不平衡下采用串联网侧变换器的双馈感应风电系统改进控制

为进一步提高电网电压不平衡下采用串联网侧变换器的双馈感应发电机(doubly fed induction generator,DFIG)风电系统的运行性能,研究了适用于该系统的改进运行控制策略。提出电网电压不平衡下采用串联网侧变换器的DFIG系统的3种可选运行方案,以此为基础提出串联网侧变换器与并联网侧变换器的协调控制策略,并建立了在双同步dq旋转坐标轴系下两者的控制模型。所提系统协调控制方案无需改变电网电压不平衡下转子侧变换器的控制策略,在实现发电机输出功率无二倍频波动、电磁转矩无二倍频波动以及定、转子三相电流平衡的同时,可实现电网电压不平衡下整个系统或总输出有功功率无二倍频波动(同时可实现直流链电压无二倍频波动)或总输出无功功率无二倍频波动或整个系统无负序电流注入电网的不同运行功能,进一步增强了不平衡电压下DFIG风电系统的运行能力。对一台采用串联网侧变换器的DFIG风电模拟系统在不平衡电压条件下的运行进行了相关实验,实验结果验证了该文所提改进控制策略的可行性。     

不平衡电网电压下基于串联网侧变换器的DFIG控制策略

电网电压不平衡会导致双馈感应发电机组(DFIG)定、转子电流出现较大不平衡,使发电机功率和电磁转矩发生振荡,从而恶化机组运行状况.分析了串联网侧变换器抑制不平衡电网电压对DFIG系统影响的机理,利用并联网侧变换器的控制及静止坐标系下的比例谐振控制器,提出了基于串联网侧变换器的DFIG在不平衡电网电压条件下的控制策略;在实现DFIG电磁转矩、直流母线电压及系统总输出有功功率无2倍频波动的同时,使DFIG定、转子三相电流平衡.所述方法具有不改变转子侧变换器的控制策略、无需求解复杂高阶矩阵的特点.对一台基于串联网侧变换器的2 MW DFIG系统进行了仿真,验证了所提出控制策略的正确性和有效性.     

Comparative study of three types ofcontrollers for DFIG in wind energyconversion system

This paper presents an enhanced control strategy for Wind Energy Conversion System (WECS) using Doubly-Fed Induction Generator (DFIG). A robust Super-Twisting (STW) sliding mode control for variable speed wind turbine is developed to produce the optimal aerodynamic torque and improve the dynamic performance of the WECS. The electromagnetic torque of the DFIG is directly tracked using the proposed control to achieve maximum power extraction. The performance and the effectiveness of the STW control strategy are compared to conventional Sliding Mode (SM) and Proportional-Integral (PI) controllers. The proposed STW algorithm shows interesting features in terms of chattering reduction, finite convergence time and robustness against parameters variations and system disturbances.     

Dynamic modeling and control of DFIG-based wind turbines under balanced network conditions

The performance of wind power station is researched by utilizing a detailed model which includes a wind turbine (WT), doubly fed induction generator (DFIG) and power electronic devices. In the initial stage, a comprehensive review and definition of each part of this system are presented. Then dynamic modeling and simulation of a sample power system are carried out. The operation of a DFIG coupled with WT under balanced condition of a power grid is investigated and stationary reference frame is utilized for analysis of a wind energy conversion system. At the second step, a wind power station is connected to the power grid in order to test the performances of the wind power station controller. The control plan utilizes stator flux oriented control and grid voltage vector control for the rotor and the grid side converter, respectively. MATLAB simulations clearly confirm the effectiveness of the control strategies.     

电网谐波条件下双馈感应风电系统改进控制

为提高电网谐波条件下双馈感应发电机DFIG(doubly-fed induction generator)的安全稳定运行性能及系统并网电能质量,利用基于串联网侧变换器的双馈风电系统具有定子机端电压灵活可控的特性,在对含有5、7次谐波电网电压条件下该系统运行行为分析的基础上提出了电网谐波条件下适用于该系统的改进控制策略;在实现发电机电流无畸变,且其输出功率、电磁转矩无波动的同时,亦可实现系统输出功率无6倍频波动或输出电流无畸变2种可选的运行功能;最后,对1台2 MW基于串联网侧变换器的DFIG系统在电网谐波条件下的仿真分析,验证了所提改进控制策略的有效性。     

直驱型永磁风电机组并网控制系统的研究

对直驱型永磁风电机组并网控制系统工作结构与原理进行讨论,并研究变流器电机侧与电网侧的并网控制电路与控制策略。应用并联多变流器的方法,采取电网电压定向的电流、电压双闭环矢量控制模式,设计逆变并网控制。基于对交-直-交背靠背双PWM变流器的控制,运行软件仿真了690 V/2.5 MW直驱型永磁风电机组的变流器并网过程。实验结果表明,控制电路与策略正确有效,并网变流器能进行双向的能量传递,并且具有良好的静动态特性。     

LCL滤波的风力发电网侧变流器不同控制结构下的性能研究

风力发电系统中LCL滤波器的电网侧电流反馈和变流器侧电流反馈都可用作电流闭环控制,但不同的电流反馈控制结构会对变流器产生不同的影响.分别在理想电网无阻尼电阻、非理想电网无阻尼电阻和理想电网有阻尼电阻3种情况下对风力发电网侧变流器进行了分析.建立了电网电压定向的同步旋转dq坐标系下的风力发电网侧变流器数学控制模型,其中PI控制器被用于补偿被控电流的误差.根据推导出的不同电流控制结构下的闭环传递函数,对其进行了根轨迹分析.通过分析及仿真发现变流器侧电流反馈控制结构相对于电网侧电流反馈控制结构控制算法较复杂,但是系统稳定性好,电网电流的谐波畸变率较低,而电网侧电流反馈控制结构尽管抗电网扰动性较强,但调节器参数受到很大限制,系统动态响应速度较慢,稳态精度较低.     

基于Crowbar保护的双馈风力发电机低电压控制策略研究

针对双馈风力发电机在电压大幅骤降时投入Crowbar电路后引起直流侧过电压和动态无功补偿的问题,基于反馈线性化理论,提出了对网侧变频器进行非线性控制策略。通过协调控制STATCOM对电网进行动态无功补偿。仿真表明:网侧非线性控制器在电压骤降过程中能很好地抑制直流侧过电压;通过引入STATCOM补偿装置,很好地满足系统无功需求,证实了所提出控制策略的正确性,提高了系统的低电压穿越能力。     

基于矩阵变换器双馈风力发电系统矢量解耦控制

本文结合矩阵变换器、双馈感应电机(DFIG)风力发电系统的优点,导出了双馈电机风力发电系统在同步旋转dq坐标轴下的矢量控制数学模型;针对常规矢量控制中存在电流耦合情况,设计一种新型、简易的电流前馈解耦控制方案.在此基础上,建立基于矩阵变换器交流励磁磁场定向电流解耦矢量控制策略.MATLAB仿真结果表明,当有功、无功功率变化时,电流解耦控制具有良好动态性能.本文设计了11kW风力发电试验装置并进行离、并网实验,当双馈电机处于亚同步、超同步状态时,双馈电机定子电压和频率均能保持稳定,实现变速恒频运行.实验结果表明,基于矩阵变换器交流励磁双馈风力发电系统是可行的,并具有一定的实用价值.     

DFIG rotor voltage control for system dynamic performance enhancement

This article develops a model of a doubly fed induction generator system including the detailed dynamics of the converter circuitry. The order of the converter controls in terms of providing damping to the system is identified through residue principles. Supplementary damping controller has been incorporated so as to compensate for the phase lag introduced by the rotor voltage input, which was observed to have the largest residue contribution at the lightly damped mode. The improvement in damping profile was verified by simulating the system for a number of disturbance conditions. While the power oscillation damping (POD) controller was observed to enhance the system damping generally, it was also able to ride through low voltage conditions arising out of severe fault conditions thus averting total system collapse.     

Modeling and control of PMSG-based variable-speed wind turbine

This paper presents a control scheme of a variable-speed wind turbine with a permanent-magnetic synchronous generator (PMSG) and full-scale back-to-back voltage source converter. A comprehensive dynamical model of the PMSG wind turbine and its control scheme is presented. The control scheme comprises both the wind-turbine control itself and the power-converter control. In addition, since the PMSG wind turbine is able to support actively the grid due to its capability to control independently active and reactive power production to the imposed set-values with taking into account its operating state and limits, this paper presents the supervisory reactive power control scheme in order to regulate/contribute the voltage at a remote location. The ability of the control scheme is assessed and discussed by means of simulations, based on a candidate site of the offshore wind farm in Jeju, Korea.     

Speed control of grid-connected switched reluctance generator driven by variable speed wind turbine using adaptive neural network controller

In wind energy conversion system, variable speed operation is becoming popular nowadays, where conventional synchronous generators, permanent magnet synchronous generators, and doubly fed induction generators are commercially used as wind generators. Along with the existing and classical solutions of the aforementioned machines used in wind power applications, the switched reluctance generator (SRG) can also be considered as a wind generator due to its inherent characteristics such as simple construction, robustness, low manufacturing cost, etc. This paper presents a novel speed control of switched reluctance generator by using adaptive neural network (ANN) controller. The SRG is driven by variable speed wind turbine and it is connected to the grid through an asymmetric half bridge converter, DC-link, and DC-AC inverter system. Speed control is very important for variable speed operation of SRG to ensure maximum power delivery to the grid for any particular wind speed. Detailed modeling and control strategies of SRG as well as other individual components including wind turbine, converter, and inverter systems are presented. The effectiveness of the proposed system is verified with simulation results using the real wind speed data measured at Hokkaido Island, Japan. The dynamic simulation study is carried out using PSCAD/EMTDC.