基于Super-Twisting算法的内燃机车永磁同步发电系统策略研究

为了使内燃机车永磁同步发电系统在内燃机全速范围内和突变性负载条件下均能稳定控制中间直流环节电压且减小电压的脉振,采用Super-Twisting高阶滑模算法对电压外环进行控制得到给定转矩,与传统PI外环控制相比,中间直流环节电压开始的超调减小,且电压跟随性、稳定性得到提升。同时,为了提高发电系统变流器容量利用率,在矢量控制的基础上,提出改进的功率因数控制策略对电机进行控制。仿真试验表明,所提发电系统在内燃机宽转速范围、突变性负载条件下,可以得到平稳且能够快速恢复的中间直流电压。同时,发电系统在切换转矩内无功功率基本能稳定在零附近,超过切换转矩后无功功率依旧保持较低水平,提高了变流器容量利用率。     

考虑LVRT能力的风电场联络线距离保护研究

具备低电压穿越(LVRT)能力的风电场能够在系统故障及电网电压跌落期间连续运行,因此,对具备LVRT能力的风电场联络线距离保护配置时,要综合考虑风电场LVRT时间。本文采用卸荷保护电路措施来提高永磁直驱风机(PMSG)的LVRT的能力,通过分析风电场LVRT与风机低电压保护动作时间配合关系,提出风电场联络线的距离保护时间配合的改进方案,最后仿真验证了提出方案的有效性和可行性。     

正阻尼PMSG并网系统限幅间歇饱和引起的次/超同步振荡分析

风电并网所引起的次/超同步振荡研究多集中于小信号模型分析,较少考虑遭受大扰动后限幅等非线性影响。基于单边限幅的描述函数与广义Nyquist判据,对正阻尼直驱式永磁同步发电机(PMSG)限幅环节间歇饱和引起的切换型次/超同步振荡进行分析。首先给出并网PMSG状态空间简化模型并分析其小干扰稳定性;其次发现一种大扰动后并网PMSG因不对称单边d轴电流限幅间歇饱和引起的新型切换型振荡现象;再次结合并网PMSG网侧变流器的频域模型以及单边限幅的描述函数,给出含限幅环节的PMSG系统近似分析模型;最后结合广义Nyquist判据,近似分析不同限幅值和参数下的振荡频率,并解释该种振荡频率随限幅上限降低而增加的现象。     

适用于次同步振荡分析的直驱式风电场等值方法

为解决大规模直驱式风电场阻抗建模困难和数值仿真节点限制的问题,基于阻抗分析法的核心原理,以等值前、后直驱式风电场外阻抗特性相一致为目标,提出了适用于次同步振荡分析的直驱式风电场等值方法。该方法包括基于阻抗灵敏度分析的分群聚合和基于遗传算法的等值降阶2个步骤。分别以风电场含相同型号直驱风机和不同型号直驱风机为例,对等值前、后的直驱式风电场外阻抗特性进行对比分析。结果表明,所提方法能够实现大规模直驱式风电场模型的等值降阶,等值前、后的直驱式风电场外阻抗特性较为接近,其等值误差能够被量化。     

直驱风电场和串补之间的次同步振荡风险

随着电网规模的持续扩大,串补长距离输电系统引发的次同步振荡现象频现。因此,如何探析串补输电系统失稳的深层原因是当前系统稳定性分析发展方向之一。本文基于开环模式谐振理论,提出了一种串补输电线路引发次同步振荡的开环模式谐振分析方法,文章首先建立了直驱风电场外接串补输电线路的小信号模型,并通过开环模式谐振分析方法研究了串补线路和直驱风电场之间的动态交互作用。结果表明串补主导的开环次同步振荡模式与风电场主导的开环次同步振荡模式在复平面靠近时,系统的闭环稳定性将会下降,并运用残差指标成功预测了开环模式谐振条件下闭环模式的位置,而改变风机参数或调整串补度可以规避动态交互的发生。本文通过算例系统验证了上述理论分析的正确性,证明直驱风电场通过串补输电线路进行输电时存在一定的失稳风险,能在一定程度上为串补输电系统的参数整定提供借鉴。     

An imbalance fault detection method based on data normalization and EMD for marine current turbines

This paper proposes an imbalance fault detection method based on data normalization and Empirical Mode Decomposition (EMD) for variable speed direct-drive Marine Current Turbine (MCT) system. The method is based on the MCT stator current under the condition of wave and turbulence. The goal of this method is to extract blade imbalance fault feature, which is concealed by the supply frequency and the environment noise. First, a Generalized Likelihood Ratio Test (GLRT) detector is developed and the monitoring variable is selected by analyzing the relationship between the variables. Then, the selected monitoring variable is converted into a time series through data normalization, which makes the imbalance fault characteristic frequency into a constant. At the end, the monitoring variable is filtered out by EMD method to eliminate the effect of turbulence. The experiments show that the proposed method is robust against turbulence through comparing the different fault severities and the different turbulence intensities. Comparison with other methods, the experimental results indicate the feasibility and efficacy of the proposed method.     

Power conversion system for high altitude wind power generation with medium voltage AC transmission

High Altitude Wind Power (HAWP) generating system provides clean energy at low cost and high capacity factor due to reduced size of the turbine and high speed streamlined wind at high altitude. An air-borne wind turbine (AWT) at high altitude extracts kinetic energy from wind using buoyancy provided by the blimp/aerostat. The generated electrical power is then transmitted to the ground based station (without any power conditioning) using the transmission lines (tether). The power conversion system (PCS) for harnessing HAWP is proposed in this paper. The proposed PCS consists of a three-level neutral point clamped (NPC) rectifier, a three-level NPC DC–DC converter followed by a two-level inverter. Modelling, design and control of the PCS are presented and discussed. The PCS provides generation side maximum power-point tracking (MPPT) using sensorless optimal torque control technique. The DC–DC converter provides electrical isolation as well as voltage step-down functions. A modified proportional resonant (PR) control which can selectively eliminate lower order current harmonics of the grid-connected inverter is also presented. The proposed control scheme of the PCS is evaluated through simulation studies using software programs like PSIM and MATLAB. A scaled-down 1 kW laboratory prototype of the complete PCS is designed, built and tested. The experimental test results obtained validate the proposed control scheme for efficient power generation from high altitude wind and interface to the grid/load.     

Modified predictive control for both normal and LVRT operations of a Quasi-Z-Source Matrix Converter based WECS

A new Wind Energy Conversion System (WECS), a Permanent-Magnet Synchronous Generator (PMSG) fed by a Quasi-Z-Source Matrix Converter (qZSMC), is proposed. At the same time, the paper proposes a Modified Predictive Control (MPC) for both normal and Low Voltage Ride-Through (LVRT) operations of the proposed WECS. First, the qZSMC comprised of a Three-Phase Quasi-Z-Source Network (TPQZSN) and a Matrix Converter (MC) is analyzed in both time and frequency domains. The TPQZSN is modeled using state–space averaging method and its transfer functions are derived. The transfer functions are then analyzed using Bode plot, and eventually a guide to select the proper passive components of the qZSMC is rendered. A MPC is proposed to control grid-side quantities while the generator speed is controlled by shoot-through adjustment. Unlike the Traditional Predictive Control (TPC), the proposed MPC can be applied to z-source converters, while considerably reducing output current ripples. The proposed control system is further adapted to enhance LVRT capability of the proposed WECS. The performance of the proposed WECS is evaluated under both normal and abnormal working conditions, comparing it with the Traditional MC-based PMSG-WECS (TMC-WECS).     

风电场等值建模研究综述

随着风电场规模的不断增大,对风电场中每台风机建模将造成计算量过大,不利于大型风电场的研究,需要对风电场进行等值化简.对双馈感应风机和直驱永磁同步风机两种当前热门机型的建模进行概述,同时介绍了潮流计算中风电场的处理方法,并对风电系统的等值进行了综述,包括风速的等值、风电场的分群、同群风机的等值方法、常用的参数优化算法及其对等值的影响.最后综述了含单一主流机型风电场通常采用的等值方法,并指出随着不同机型并存的大型混合风电场的增多,混合风电场等值建模研究的必要性及研究趋势.     

永磁直驱风电系统低电压运行特性的分析

通过构建永磁直驱风电系统的仿真模型,实现网侧变换器输出有功和无功功率的解耦控制,增加卸荷负载以提高其应对电压跌落等故障的穿越能力,对风电系统运行在单位功率因数、超前和滞后功率因数情况下的跌落特性进行了仿真分析,讨论了电压跌落期间风电系统对电网的无功支持.仿真结果表明,直驱式永磁同步电机风电系统具有较强的低电压穿越能力,可以安全运行在不同功率因数下,同时能在电网电压故障期间对系统提供一定的无功支持.