Stability Analysis, Chaos Control of Fractional Order Vallis and El-Nino Systems and Their Synchronization

In this article the authors have studied the stability analysis and chaos control of the fractional order Vallis and El-Nino systems. The chaos control of these systems is studied using nonlinear control method with the help of a new lemma for Caputo derivative and Lyapunov stability theory.The synchronization between the systems for different fractional order cases and numerical simulation through graphical plots for different particular cases clearly exhibit that the method is easy to implement and reliable for synchronization of fractional order chaotic systems. The comparison of time of synchronization when the systems pair approaches from standard order to fractional order is the key feature of the article.

Stability Analysis of q-axis Rotor Flux Based Model Reference Adaptive System Updating Rotor Time Constant in Induction Motor Drives

q-axis rotor flux can be chosen to form a model reference adaptive system(MRAS)updating rotor time constant online in induction motor drives.This paper presents a stability analysis of such a system with Popov’s hyperstability concept and small-signal linearization technique.At first,the stability of q-axis rotor flux based MRAS is proven with Popov’s Hyperstability theory.Then,to find out the guidelines for optimally designing the coefficients in the PI controller,acting as the adaption mechanism in the MRAS,small-signal model of the estimation system is developed.The obtained linearization model not only allows the stability to be verified further through Routh criterion,but also reveals the distribution of the characteristic roots,which leads to the clue to optimal PI gains.The theoretical analysis and the resultant design guidelines of the adaptation PI gains are verified through simulation and experiments.

Small-signal Stability Criteria in Power Electronics-dominated Power Systems:A Comparative Review

To tackle emerging power system small-signal stability problems such as wideband oscillations induced by the large-scale integration of renewable energy and power electronics,it is crucial to review and compare existing small-signal stability analysis methods.On this basis,guidance can be provided on determining suitable analysis methods to solve relevant small-signal stability problems in power electronics-dominated power systems(PEDPSs).Various mature methods have been developed to analyze the small-signal stability of PEDPSs,including eigenvalue-based methods,Routh stability criterion,Nyquist/Bode plot based methods,passivity-based methods,positive-net-damping method,lumped impedance-based methods,bifurcation-based methods,etc.In this paper,the application conditions,advantages,and limitations of these criteria in identifying oscillation frequencies and stability margins are reviewed and compared to reveal and explain connections and discrepancies among them.Especially,efforts are devoted to mathematically proving the equivalence between these small-signal stability criteria.Finally,the performance of these criteria is demonstrated and compared in a 4-machine 2-area power system with a wind farm and an IEEE 39-bus power system with 3 wind farms.

Small Signal Stability of Three-phase and Six-phase Synchronous Motors:A Comparative Analysis

Small signal stability analysis is conducted for an asymmetrical six-phase synchronous motor in comparison with its equivalent three-phase counterpart.For this purpose,a linearized model of the six-phase synchronous motor is developed using the dq0 approach,which is used in eigenvalue criteria to determine absolute stability in comparison with its equivalent three-phase counterpart.The analysis includes a comparison of the variation in evaluated eigenvalues associated with the stator and rotor sides according to changes in both the three and six-phase machine parameters and working conditions.Key analytical results are experimentally investigated and validated on a test rig.

Distributed Control Framework and Scalable Small-signal Stability Analysis for Dynamic Microgrids

As a growing number of microgrids(MGs)has been integrated into the modern power grids,the interconnection and applicable cooperation among multiple MGs motivate the development of networked MGs.Dynamic MGs,as an advanced networked MGs structure,can not only integrate multiple MGs into the distribution system but also fulfill the requested system network reconfiguration with improved flexibility.A general distributed control approach for networked MGs is reviewed.A distributed control framework for dynamic MGs operation is developed,along with an extensible architecture with considerations of large-scale distributed energy resources(DERs)integration.A scalable small-signal stability analysis is conducted per the proposed distributed control strategies and the conditions under which the system is exponentially stable are derived.At last,the effectiveness of the proposed control framework and stability analysis are verified using a 6-bus test feeder.

Analysis of Transforming dq Impedances of Different Converters to A Common Reference Frame in Complex Converter Networks

DQ impedance-based method has been widely used to study the stability of three-phase converter systems.As the dq impedance model of each converter depends on its local dq reference frame,the dq impedance modeling of complex converter networks gets complicated.Because the reference frames of different converters might not fully align,depending on the structure.Thus,in order to find an accurate impedance model of a complex network for stability analysis,converting the impedances of different converters into a common reference frame is required.This paper presents a comprehensive investigation on the transformation of dq impedances to a common reference frame in complex converter networks.Four different methods are introduced and analyzed in a systematic way.Moreover,a rigorous comparison among these approaches is carried out,where the method with the simplest transformation procedure is finally suggested for the modeling of complex converter networks.The performed analysis is verified by injecting two independent small-signal perturbations into the d and the q axis,and doing a point-by-point impedance measurement.

跟网型变换器的小扰动同步稳定机理分析与致稳控制

弱电网下,跟网型变换器易出现因阻尼不足导致的小扰动同步失稳问题。为此,该文借鉴复转矩分析理论,计及复杂控制耦合,建立跟网型变换器的复转矩模型。量化多环控制耦合、线路阻抗、控制参数等因素对系统阻尼转矩的影响,从阻尼的角度揭示跟网型变换器的小扰动同步失稳机理。根据理论分析,提出一种基于相位补偿的锁相环阻尼重塑控制策略,通过补偿多环控制耦合引入的负阻尼,增强变换器的小扰动同步稳定性。最后,开展相应的仿真与实验,验证理论分析的正确性与改进控制策略的有效性。

基于虚拟电力系统稳定器的低频振荡抑制策略

基于虚拟同步发电机(VSG)控制的新能源机组虽可增强电网惯量及频率稳定性,但可能继承与同步机类似的低频振荡问题。针对该问题,首先基于单台VSG并网的线性化模型,构建了适用于VSG的Phillips-Heffron模型,借助阻尼转矩法挖掘了VSG低频振荡的诱发机理。进一步提出一种附加于VSG无功环节的虚拟电力系统稳定器(VPSS),并给出了控制结构及基于相位补偿法的参数设计过程。研究结果表明:VSG发生低频振荡是由于系统受扰后,虚拟功角的振荡信号经过虚拟励磁调节器对VSG机电振荡回路产生了负阻尼转矩。将所提VPSS接入系统可在几乎不影响振荡频率的前提下,实现0.1~3 Hz下VSG低频振荡的有效抑制。

考虑频率耦合特性的D-PMSG复数域阻抗建模及其特征分析

阻抗分析法因其简单有效被广泛用于含电力电子变换器的互联系统稳定性研究。然而,采用传统方法对频域序阻抗建模时,需通过非线性变换(Park变换及其反变换)进行坐标系转换,这会导致不同周期分量的卷积运算及相应的频移,其过程较为烦琐。针对上述问题,基于复向量时域微分算子,提出了永磁直驱同步发电机(D-PMSG)等效阻抗建模方法。该方法在时域周期系统稳定运行轨迹的邻域内直接进行小信号线性化,并采用指数旋转因子灵活反映系统受扰后的时变特性,结合时域微分算子等效表征互联系统控制环节的动态特性,避免了频域阻抗建模时坐标系的反复变换,大幅降低了解析建模的复杂度。此外,所提方法能够更加清晰地阐释互联系统受到扰动时D-PMSG并网逆变器产生频率耦合现象的物理意义;同时,能够说明基频电压初始相位对耦合分量相频特性的影响。最后,利用仿真验证了所提算法的有效性。

Small signal stability analysis of a synchronized control-based microgrid under multiple operating conditions

In this paper,a synchronized control strategy of double fed induction generator that can provide reserve capability and primary frequency support for microgrid is firstly developed.The microgrid based small signal stability performance is investigated under multiple operating conditions.The effect of three categories of key controller parameters on dominant eigenvalues is studied by sensitivity analysis,including:1)active power drooping coefficient;2)reactive power drooping coefficient;3)parameters of outer loop excitation current control.Finally,some constructive suggestions on how to tune controller parameters to improve microgrid’s small signal stability performance are discussed.

计及电压动态特性的虚拟同步机暂态稳定性分析

针对仅考虑摇摆方程可能导致虚拟同步机暂态稳定性分析误判的问题,首先考虑公共耦合点处电压变化对系统暂态行为的影响,建立了计及电压动态特性的虚拟同步机暂态模型,实现对虚拟同步机动态特性的全面精准刻画。在此基础上提出了一种直接求解极限切除角和极限切除时间的快速迭代求解算法,并分析了虚拟同步机核心控制参数改变对系统暂态稳定性的影响机理。最后,搭建了典型结构虚拟同步机的电磁仿真模型,验证了理论分析和关键暂态指标求解算法的正确性,结果表明相比于仅考虑摇摆方程的暂态模型,所提模型能更精准地刻画虚拟同步机暂态特性。

并联永磁同步风电机组小干扰稳定性分析

采用平均磁链定向控制多台永磁同步风电机组进而构造分频发电系统是未来陆上尤其是海上风电的汇集方案之一,但对该模式下多台风电机组间稳定性的研究鲜有文献涉及。针对此问题,基于特征值分析法,研究了平均磁链定向控制的永磁同步风电机组之间的小干扰稳定性。首先,基于高压大容量直驱式永磁同步风电机组的分频集电系统拓扑结构,建立了适用于小干扰稳定分析的风电系统的数学模型;其次,通过辨识振荡模态并分析模态参与因子确定了影响系统振荡的主控因素,通过绘制根轨迹分析了主控因素参数变化对系统振荡的影响,并发现系统振荡受发电机电感、电阻和直流电容参数的影响最大;最后,通过时域仿真验证了研究结论的正确性。

基于级联线性-非线性自抗扰控制器的永磁直线同步电机速度控制策略研究

为了提升永磁直线同步电机(permanent magnet linear synchronous motor,PMLSM)在负载变化、参数摄动和其他不确定因素下的抗扰性能和速度跟踪性能,提出一种基于级联线性-非线性自抗扰控制器的PMLSM速度控制策略。首先,建立考虑负载扰动和参数失配的PMLSM数学模型;其次,设计级联线性-非线性扩张状态观测器来实时估计和补偿系统所受的不确定扰动,前级线性扩张状态观测器保证系统在大扰动下保持稳定,后级非线性扩张状态观测器利用非线性机制进一步提高系统对扰动的估计精度,从而将线性自抗扰控制和非线性自抗扰控制的优势相结合,以此提升系统的速度跟踪性能和抗扰动能力;并且,对所提控制器提出基于劳斯判据的稳定性分析方法,并对系统的抗扰性能和噪声抑制性能进行了频域分析;最后,对基于PI控制、级联线性自抗扰控制、非线性自抗扰控制和级联线性-非线性自抗扰控制的永磁直线同步电机系统进行仿真和实验对比,验证所提方法的优越性。

基于虚拟同步发电机的多机逆变系统稳定性分析

为解决新能源并网逆变系统给电网惯量和阻尼特性带来的问题,虚拟同步发电机技术(VSG)得到广泛应用,但VSG的引入也可能对系统的稳定性带来影响。对此,首先在单机逆变系统小信号模型的基础上建立多机逆变系统小信号模型;然后,分析系统关键参数特征根轨迹,从参数异步变化角度研究目标参数对多机系统整体和各VSG之间高、中、低频稳定性的影响,揭示了多机系统参数的多频段稳定性影响规律,确定了多机系统部分结构和控制参数的稳定裕度。最后,通过仿真试验验证了理论分析的结论。

基于等效同步功率的孤岛并联构网变流器系统暂态稳定性分析

随着构网变流器在微电网中应用的增长,其对微电网暂态稳定的影响受到了广泛关注。不同于单机无穷大系统,孤岛并联构网变流器系统的频率和功角差相互耦合,暂态响应特性更为复杂。为精准分析孤岛并联构网变流器系统的暂态响应,文中基于功角耦合运动方程建立双机频率和功角差的三阶暂态同步模型,并且分析了双机出力差异和下垂系数对于暂态稳定的影响特征。为揭示出力和下垂系数对于暂态稳定的耦合机理,对双机系统进行等效同步功率分析,并且提出一种基于构网变流器出力的自适应下垂系数优化策略,可以根据出力差异自适应提升双机系统的等效同步功率,进而提升系统暂态稳定性。最后,采用实时仿真验证了三阶暂态模型的正确性和所提控制策略的有效性。

基于连续可导ESO的虚拟同步机控制策略

在高比例新能源接入的电网中,虚拟同步机技术被广泛应用,但当面对系统扰动时其稳定性较差,可能会存在电压过限、频率波动等问题。因此,为了提高电能质量,将扩张状态观测器引入虚拟同步机控制技术中,对扰动进行观测、估计与补偿,提高系统稳定性,从而在新能源电源波动及大功率负荷投切时得到更稳定的母线电压及系统频率。此外,进一步对扩张状态观测器中的分段函数fal进行矫正,提出一种连续可导的扩张状态观测器控制算法,免去运算过程中的判断环节,突出了“小误差大增益”的特点,并对算法进行稳定性分析和确定参数选择范围。仿真与实验结果验证了所提策略的有效性与可行性。

新能源经柔性直流孤岛送出系统小信号同步稳定机理

为满足绿色低碳发展的需要,我国正大力推进大规模新能源基地的开发,大规模新能源经柔性直流孤岛送出系统受到越来越多的关注。该系统中新能源设备通常采用常见的跟网型控制,为支撑系统稳定运行,柔性直流设备需采用构网型控制。然而目前对于这样一个高比例甚至100%电力电子系统的同步稳定机理尚不完善。针对锁相环和虚拟同步环在系统同步过程中的作用,建立了跟网型新能源和构网型柔性直流设备的同步模型。然后分析了系统小信号稳定性,推导出系统保证稳定的运行区域,分别针对新能源和柔性直流设备提出了存在失稳风险的运行状态。最后在PSCAD仿真中验证所提结论。

Synchronization Stability of Interconnected Microgrids with Fully Inverter-based Distributed Energy Resources

In this paper,the synchronization stability challenges of same-rated frequency interconnected microgrids(IMGs)with fully inverter-based generation units are studied.In this type of weak power grid with low X/R ratios and low line impedances,no strong source with a high-inertia rating exists with which other generation units can be synchronized.Two IMGs controlled using a pinning consensus-based control architecture are considered.The inrush power flow at the beginning of the interconnection process is modeled and analyzed.This power flow is affected by the voltage/phase/frequency difference of the IMG points of common coupling.A small-signal model of the IMGs is obtained that includes a synchronization control unit,and small-signal stability is analyzed based on sensitivity analysis of the most important control and operational parameters.In addition,the transient stability of a nonlinear model of the IMGs under study as implemented in Sim Power Systems/MATLAB is investigated.Stable synchronization is more challenging than the synchronization of multi-area strong power grids and grid-connected MGs.However,synchronization can still be performed by selecting more limited ranges for the control gains and threshold values of the synchronization algorithm.Nevertheless,different disturbances such as high load conditions can cause synchronization instability.

基于自适应参数整定的微电网虚拟同步发电机运行控制

针对在并联微电网系统中可能出现的有功功率振荡的问题,提出了一种自适应虚拟同步发电机参数调节控制方法。构建了转动惯量与角频率变化率、阻尼系数与角频率增量的函数关系。通过仿真试验验证了该方法的有效性。

同步回转压缩机排水采气工艺在丛式气井中的适应性分析

针对L井区丛式气井存在积液减产停产问题,采用并联的方式将多口备选气井接入同步回转压缩机,逐口对积液单井抽吸降压,通过降低井口流压的方式降低井底流压,增大生产压差进而提高气产量,保证井底积液顺利排出,恢复气井产能。结合气井井筒压降模型、气井流入流出曲线以及临界携液流量的理论,研究了同步回转压缩机对降压、排液以及增产的影响。经Y2井场7口井成功应用,结果显示单井井口流压从1.3~1.6 MPa降低至0.1~0.58 MPa,降压效果明显;单井增气量为0.56×10^(4)~2.76×10^(4) m^(3)/d不等,排水采气增产稳产效果好;同步回转压缩机降压增产工艺成本低,利润率高。该研究丰富了积液气井恢复生产的方法和理论,提供了排水采气的良好思路,为该项工艺的后期应用和气井负压开采提供了工艺技术支撑。