不平衡电网电压下DFIG双SRF控制策略

针对在电网不平衡电压情况下,双馈电机(DFIG)的定子侧有功功率、无功功率以及电磁转矩均出现2次脉动量,提出了一种双同步旋转坐标系(SRF)控制策略,通过对其转子侧电压和电流量进行控制,产生相应的转子电压和电流量,从而实现其不平衡控制目标.运用EMTP-RV仿真软件搭建仿真模型,通过仿真分析对比DFIG在常规定子电压定向矢量控制和考虑电网电压不平衡的DFIG双SRF控制,验证了DFIG的双SRF控制策略可以有效抑制电网电压不平衡情况下引起的电磁转矩、无功功率和总机械功率的2次脉动,实现DFIG的稳定运行.     

不平衡及谐波电压下双馈感应电机谐振滑模控制技术

为提高不平衡及谐波电网下双馈感应电机(doubly fed induction generator,DFIG)的运行性能,该文提出一种静止坐标系下的谐振滑模控制策略;通过在滑模控制切换面方程中加入6倍频谐振项,使系统实现对6倍频交流参考的无静差跟踪;实现了DFIG输出定子电流三相平衡且正弦,或者输出定子有功功率/无功功率平稳无脉动的控制目标,改善了不平衡及谐波电网下DFIG输出的电能质量。对比分析了不平衡及谐波电网下积分滑模控制与谐振滑模控制系统的性能,并证明了所提出控制系统的稳定性和收敛性。最后,构建了1 k W功率等级的DFIG实验平台,对所提控制策略进行了实验验证,证明了其可行性和有效性。     

电网不对称故障下双馈风力发电机组穿越控制的研究

在研究电网电压不对称对双馈感应发电机( DFIG)影响以及DFIG正、负序数学模型的基础上,分析了电网电压不对称条件下DFIG定子输出有功、无功功率和发电机电磁转矩的组成.针对电网电压不对称时负序电流对定子侧有功功率、无功功率、电磁转矩和直流侧电压的影响,提出电流正序分量跟踪控制策略,并在转子侧和网侧变换器的控制中对电网电压的正、负序分量分别处理.转子侧变流器采用正序电流跟踪的滞环控制,实现了电流的无差跟踪.网侧逆变器控制内环采用电流前馈控制,并控制负序电流为零,外环采用电压环稳定直流电压,仿真结果表明,在电网不对称故障时,这种控制策略可以消除负序电流对定子侧有功功率、无功功率、电磁转矩和直流侧电压的影响,实现不对称故障穿越.     

电网不对称故障下双馈风力发电机组穿越控制的研究

在研究电网电压不对称对双馈感应发电机（DFIG）影响以及DFIG正、负序数学模型的基础上,分析了电网电压不对称条件下DFIG定子输出有功、无功功率和发电机电磁转矩的组成。针对电网电压不对称时负序电流对定子侧有功功率、无功功率、电磁转矩和直流侧电压的影响,提出电流正序分量跟踪控制策略,并在转子侧和网侧变换器的控制中对电网电压的正、负序分量分别处理。转子侧变流器采用正序电流跟踪的滞环控制,实现了电流的无差跟踪。网侧逆变器控制内环采用电流前馈控制,并控制负序电流为零,外环采用电压环稳定直流电压。仿真结果表明,在电网不对称故障时,这种控制策略可以消除负序电流对定子侧有功功率、无功功率、电磁转矩和直流侧电压的影响,实现不对称故障穿越。     

不平衡电网电压下双馈电机的协调控制策略

分析了在电网电压不平衡情况下双馈风力发电系统的运行特性。在此基础上,提出了不平衡电网电压下双馈电机的转子侧与网侧变换器协调控制策略,即以电磁转矩、定子侧无功功率以及总输出功率的2倍频脉动量为控制目标,计算出所需的补偿电压,叠加到转子侧与网侧变换器的参考电压中,从而通过补偿控制作用实现对脉动量的抑制。在MATLAB/Simulink中对1.5 MW双馈感应电机(DFIG)接入电压不平衡的电网情况进行了仿真,验证了所提出的控制策略可以有效抑制双馈电机的电磁转矩、无功功率和总输出有功功率脉动。     

具备带不平衡负载功能的虚拟同步机控制策略

当虚拟同步机(VSG)孤岛运行时,不平衡负载的接入会导致其输出电压不平衡。首先分析了不平衡负载条件下VSG输出电压不平衡的机理,提出了基于PR和PI复合控制的VSG电压环路控制方法;其次,考虑到VSG输出电流的d,q轴分量在负载不平衡时含有二倍频波动分量,导致VSG定子电气方程输出电压的d,q轴指令呈现二倍频波动,提出采用电压环PI调节器输出电流指令作为定子电气方程的电流输入;再次,针对不平衡负载条件下有功功率和无功功率含有二倍频分量问题,提出一种采用电压环PI调节器输出电流指令的功率直流分量提取方法;最后,仿真和实验结果证明了所提方案的有效性。     

谐波电网电压下基于矢量谐振控制的双馈异步发电机集成控制策略

通过建立5次、7次谐波电网电压下双馈异步风力发电机(DFIG)的数学模型,分析了DFIG风电机组运行于谐波电网下所产生的性能恶化。为改进DFIG在谐波电网下的运行性能,以DFIG定子电流正弦或定子输出有功/无功功率平稳为谐波控制目标,在转子电流PI闭环调节的基础上,加入定子电流矢量谐振控制或定子功率矢量谐振控制,以达到上述DFIG在谐波电网下的控制目标。为了有效实现控制目标,深入分析和对比了普通谐振控制器和矢量谐振控制器在DFIG运行于谐波电网下的300Hz交流信号调节性能。矢量谐振控制器由于其更为精确的300Hz交流信号调节能力以及充裕的相位裕度以确保闭环工作稳定性,因而更有助于DFIG在谐波电网下控制目标的实现。通过构建的风电机组,实验结果验证了本文所提出的谐波电网电压下的集成控制策略的正确性及有效性。     

不平衡电网电压下虚拟同步发电机模型预测控制

虚拟同步发电机(Virtual Synchronous Generator, VSG)控制算法,可为电网提供惯性并参与电压及频率调节,但在电网电压出现不平衡时会导致并网电流不平衡及有功、无功功率波动的问题,严重影响了并网电能质量。针对此问题,提出了一种不平衡电网下VSG模型预测控制策略,通过基于快速电压矢量选择的模型预测控制策略来控制所重构的正序及负序电流分量,达到有功功率恒定、无功功率恒定及电流平衡的控制目标。此外还引入负序电流调节系数,进而实现这三个目标的协调控制。     

谐波电网下基于重复控制的双馈风力发电机直接功率控制技术

为提高包含更高次谐波电压的电网环境下双馈感应发电机(doubly-fed induction generator,DFIG)的运行性能,改善其馈入电网的电能质量,该文提出了一种基于重复控制调节器的DFIG直接功率控制(direct power control,DPC)策略,分别实现了DFIG定子电流无畸变、有功和无功功率平稳、电磁转矩平稳3个控制目标。进而分析了所提DPC策略在不同控制目标下的稳定运行性能。最后,构建1 k W DFIG实验系统,对所提控制策略的有效性进行了实验验证。     

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。     

A flexible power control strategy for rotor-side converter of DFIG under unbalanced grid voltage sags

Doubly fed induction generator (DFIG) is widely applied in variable-speed wind energy conversion system. The disconnection of a substantial amount of DFIG may arouse the instability problem of power system, thus wind power generators have to remain connected during short-time grid faults. As a result, the voltage sag will lead to overcurrent and overvoltage in the rotor winding of a DFIG, moreover the unbalanced voltage sags will also cause serious fluctuations in its electromagnetic torque and output power. This paper studies the relationship of the stator instantaneous powers with the three-phase stator voltage and rotor current of a DFIG under unbalanced grid voltages. A generalized formula of current reference for the rotor-side converter of DFIG is constructed by introducing continuous adjustment coefficients. Meanwhile, the analytical equations of rotor peak current, stator active and reactive power fluctuations are derived to characterize the operating performance of DFIG. The impacts of adjustment coefficients on DFIG control performance and the feasible region of coefficients restrained by the rotor current constraint are discussed. In consideration of the rotor current limit, the flexible power control strategy for DFIG in unity power factor mode (UPFM) and reactive power supporting mode (RPSM) is presented. The correctness of proposed method is verified by simulation and experiment tests of single-DFIG and multi-DFIG systems.     

Modeling and enhanced control of DFIG under unbalanced grid voltage conditions

This paper presents a mathematical model of a doubly fed induction generator (DFIG) based on stator voltage orientation (SVO) in the positive and negative synchronous reference frames under unbalanced grid voltage conditions. The oscillations of the DFIG electromagnetic torque and the stator active and reactive powers are fully described during grid voltage unbalance. A new rotor current controller implemented in the positive synchronous reference frame is proposed. The controller consists of a proportional integral (PI) regulator and a harmonic resonant (R) compensator tuned at twice the grid frequency. Thus, the positive and negative sequence components of DFIG rotor currents are directly regulated by the PI + R controller without the need of involving positive and negative sequence decomposition, which indeed improves the dynamic performance of DFIG-based wind power generation system during small steady-state and relatively larger transient network unbalances. The theoretical analysis and the feasibility of the proposed unbalanced control scheme are validated by simulation studies on a 1.5-MW wind-turbine driven DFIG system. Compared with conventional single PI current control design, the proposed control scheme results in significant elimination of either DFIG power or torque oscillation under unbalanced grid voltage conditions.     

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.     

负序及谐波畸变电网电压下双馈风力发电系统的改进直接功率控制策略

由于定子直接连接到电网,电网电压中的负序和谐波分量会严重恶化双馈风力发电机(DFIG)系统的运行性能,导致系统输出总电流三相不对称及谐波畸变、总输出有功功率及无功功率波动等,使得DFIG系统无法安全稳定可靠运行,且输出风电质量下降。同时考虑负序和谐波电网下DFIG系统机侧变流器和网侧变流器的运行状态,以改善DFIG系统总输出电流或功率质量为目标,研究基于二阶矢量积分器(SOVI)的DFIG系统网侧和机侧变流器改进直接功率控制(DPC)策略,改善DFIG系统的运行性能。实验结果验证了所提出的负序和谐波畸变电网电压下DPC策略的正确性及有效性。     

双馈电机电压跌落暂态过程分析

为了便于研究并网双馈风力发电机组低电压穿越运行的控制策略,有必要对电压跌落时双馈风电机组的暂态特性进行分析.本文利用双馈发电机定转子磁链的暂态变化机理,推导并提出了双馈风电机组在电网电压骤降时的定子暂态电流和电磁转矩的解析表达式.在此基础上,通过对表达式的分析得到影响电压跌落电磁过渡过程的本质因素.在理论分析基础上,为了验证所提电磁过渡过程的正确性,建立了1.5MW双馈电机低电压穿越控制模型,仿真结果表明:电网电压跌落时,双馈电机定子侧电流和电磁转矩与理论分析基本一致,因而可以说明本文电压跌落的分析方法能够正确地反映电压跌落过程中的电磁现象,可以为双馈电机LVRT控制策略的研究提供足够的理论依据     

Operation and control of a grid-connected DFIG-based wind turbine with series grid-side converter during network unbalance

This paper proposes a control scheme of a grid-connected doubly-fed induction generator (DFIG) wind turbine with series grid-side converter (SGSC) to improve the control and operation performance of DFIG system during network unbalance. The behaviors of DFIG system with SGSC under unbalanced grid voltage conditions are described. The SGSC is controlled to inject voltage in series to balance the stator voltage. Therefore, the adverse effects of voltage unbalance upon the DFIG such as large stator and rotor current unbalances, electromagnetic torque and power pulsations are removed and the conventional vector control strategy for the rotor-side converter (RSC) remains in full force under unbalanced conditions. Meanwhile, three selective control targets for the parallel grid-side converter (PGSC), such as eliminating the oscillations in total active or reactive power, or no negative-sequence current injected to the grid are identified and compared. Besides, the proportional resonant controllers in the stationary reference frame are designed for both the SGSC and PGSC to further improve the dynamic performance of the whole system. Finally, the ratings and losses of the SGSC and the injected transformer are discussed and the effectiveness of the proposed control scheme is verified by the simulation results of a 2 MW DFIG-based wind turbine with SGSC under steady state and small transient grid voltage unbalance.     

基于转子串电阻的DFIG低电压穿越优化控制策略

针对双馈感应风力发电机组(DFIG)的低电压穿越(LVRT)问题,在分析现有转子串电阻电路基础上,考虑限流电阻阻值对低电压穿越期间DFIG瞬态性能的影响,权衡转子电流、转子电压、无功功率、电磁转矩间的关系,对限流电阻阻值的选取原则进行了优化; 转子串电阻电路退出但电网电压未恢复时转子侧变流器的功率协调控制策略得到改善; 在此基础上,利用变流器对DFIG的控制灵活性,提出一种无需定子磁链观测且控制算法简单的换流器改进控制策略。本文所提的LVRT优化控制策略在提高DFIG瞬态性能的同时兼顾了系统暂态稳定性     

An Enhanced LVRT Scheme for DFIG-based WECSs under Both Balanced and Unbalanced Grid Voltage Sags

Due to the latest grid codes, wind energy conversion systems (WECSs) are required to remain connected to grid under grid voltage sags and supply reactive power into the grid. So, this paper proposes an enhanced scheme to improve low-voltage ride through (LVRT) capability of doubly fed induction generator (DFIG)-based WECSs under both balanced and unbalanced grid voltage sags. The proposed scheme is composed of active and passive LVRT compensators. The active compensator is performed by controlling the rotor- and grid-side converters of the DFIG to decrease the stator flux oscillations and inject reactive power into the grid. The passive compensator is based on a three-phase stator damping resistor (SDR) located in series with the stator windings. The proposed scheme decreases the negative effects of grid voltage sags in the DFIG system including the rotor over-currents, electromagnetic torque oscillations, and DC-link over-voltage and also injects reactive power into grid to support the grid voltage. So, the LVRT capability of DFIG is enhanced and new grid code requirements are addressed. Simulation results on a 1.5-MW DFIG-based WECS using MATLAB/Simulink demonstrate the effectiveness of the proposed LVRT scheme under both balanced and unbalanced grid voltage sags.     

电网电压不平衡下双馈型风电场可控运行区域及其控制策略

电网电压不平衡条件下,双馈感应发电机(DFIG)风电机组实现电磁转矩无脉动等不同传统控制目标时所需要的负序电流幅值不同。结合电网电压不平衡条件下电网侧变换器(GSC)与转子侧变换器(RSC)实现各传统控制目标时所需的负序电流幅值,通过详细分析等值DFIG风电场GSC与RSC的输出负序电流能力,得到基于不同电网电压不平衡度和系统有功出力的DFIG风电场可控运行区域。以该可控运行区域为基础,提出电网电压不平衡条件下DFIG风电场的多目标协调控制策略,即根据电网电压不平衡度及系统有功出力选择或切换系统最优控制目标,进而改善不平衡电压下DFIG风电场的运行能力及所并电网的电能质量。仿真与实验结果验证了所提方案的可行性。