Optimization of the Gas Generator in Composite Power System with Tip-Jet Rotor

The key and bottleneck of research on the tip-jet rotor compound helicopter lies in the power system. Computational Fluid Dynamics (CFD) was used to numerically simulate the gas generator and rotor inner passage of the tip-jet rotor composite power system, studying the effects of intake mode, inner cavity structure, propellant components, and injection amount on the characteristics of the composite power system. The results show that when a single high-temperature exhaust gas enters, the gas generator outlet fluid is uneven and asymmetric;when two-way high-temperature exhaust gas enters, the outlet temperature of the gas generator with a tilted inlet is more uniform than that with a vertical inlet;adding an inner cavity improves the temperature and velocity distribution of the gas generator's internal flow field;increasing the energy of the propellant is beneficial for improving the available moment.

Design and dynamic characteristic prediction of air-powered twin-rotor piston engine

A novel air-powered twin-rotor piston engine(ATPE) utilizing a differential velocity driving mechanism to achieve a high output torque was proposed.The ATPE had eight separated rotary cylinders which can dynamically enlarge the engine displacement as a result of the special driving mechanism,which was named dynamic volume expansion.The mathematical model of ATPE comprising a dynamic model and a thermodynamic model was established under the assumption of no mechanical friction.The model was numerically simulated in Matlab.The results show that shortage of low output torque confusing traditional air-powered engines can be overcome.The average output torque sharply increases to 100 N·m,which is about three times that of traditional air-powered engines with equal cylinder displacement under the pressure of 0.6 MPa at 480 r/min.ATPE can be used to drive vehicles directly without transmission box,therefore the energy transfer efficiency of ATPE can be increased.Furthermore,benefitting from the novel gas distribution system,the engine shows an ability in self-adjusting under different loads.The arrangements of air ports automatically adjust the open interval of air ports according to the load,which may simplify the speed control system.

Theoretical and Empirical Limits: Reexamining Betz’s Upper Limit towards a Practical Power Coefficients in Wind Turbines*

The aspiration of all wind turbine designers is to attain Betz’s upper limit, which represents the highest efficiency in wind energy extraction. Majority of working turbines operate slightly below this limit with an exception of a few operating in wind tunnels. This study proposes for a comprehensive reevaluation of Betz’s derivation, aiming to establish the gap between a theoretical power limit and a practical limit for realization. There are two common expressions for power coefficient giving the same optimal value of 59%, but they generate different power-coefficient curves when plotted against velocity ratios. This paper presents a new method being referred as “Direct Multiplication Fractional Change” (DMFC) for deriving power-coefficient curves in wind energy, and compares its generated curve with established models. Discrepancies in power-coefficient expressions are identified and harmonized. Three approaches, namely EVAM, LVM, and DMFCM, were used for the numerical derivation of cp in the study, with their evaluation summarized in a table. The study collaborates its findings with a formulated velocity-distance curve, commonly presented as a hypothetical velocity profile in some publications. The results from DMFCM indicate two distinct maxima for the power coefficient. On the front side of the disc, a maximum of 0.5 is achievable in practice, although it is not the highest theoretically. On the rear side, a theoretical maximum of 0.59 is observed, but this value is not attainable in practice. These maxima are separated by their positions along the line of flow relative to the disc. However, this approximation is limited to a streamlined flow model of the rotor disc.

基于锥角控制的下风向风力机功率调节策略

针对中小型下风向风力机开展了功率调节策略研究.首先,对100 W下风向风力机进行了仿真计算和风洞实验,探究了下风向风力机的气动性能;然后,分析了风轮锥角对风力机输出功率和叶根载荷的影响机制,归纳出输出功率与锥角余弦值的三次方正相关,叶根载荷与锥角余弦值的平方正相关;最后,形成了一套基于锥角控制的下风向风力机功率主/被动调节策略.研究结果表明:采用主动调节策略可在超额定风速运行时有效控制风轮输出功率,并可使叶根载荷极值降低14.2%;较控制前,采用被动调节策略可使得在超额定风速运行时,输出功率与额定功率的平均偏差减小20.84 W.两种调节策略皆可实现超额定风速运行时下风向风力机输出功率的有效控制.

Design and Analysis of Different Types of Rotors for Pico-Turbine

Small-scale vertical axis wind turbine (VAWT) rotor is developed for use in areas lacking adequate energy infrastructure. The materials and methods of construction are selected to minimize cost as much as possible. The paper describes the design of different kinds of vertical axis wind turbine rotors having different number of blades and twist angle. The aim of the work is to study the influence of the different designs on rotational speed and power of rotor in different wind speed.

无润滑电磁轴承保护轴承跌落过程摩擦发热分析

为在设计阶段预测电磁轴承保护轴承的寿命,计算跌落过程中保护轴承的发热功率非常重要。很多场合下保护轴承无润滑或只有固体润滑,因此选择局部法,重点分析球与滚道之间的滚动弹性滞后、球自旋、差动滑动等机制引起的发热,推导了差动滑动发热功率解析公式。开展实际电磁轴承高速电机无制动自由跌落实验,实测轴心轨迹和保护轴承冲击力,利用实验数据计算了保护轴承发热功率,并与实测转子动能变化率对比。研究发现,在确定了保护轴承安装预紧力情况下,局部法计算的保护轴承发热功率与转子动能变化率在量级上相当,证明了理论计算可行性;球自旋发热最多,其次是球与滚道差动滑动发热,两者之和占总发热的主要部分,球与滚道弹性滞后发热较少。

新型沙漏形隔磁结构的主副齿式永磁游标电机的设计与分析

基于传统交替极双定子分裂齿式永磁游标电机的拓扑结构提出一种新型沙漏形隔磁结构的主副齿式永磁游标电机,旨在进一步提高电机转矩密度和解决永磁体极间漏磁的问题。依据磁场调制原理,首先对定子主齿和副齿的结构参数进行优化设计,主齿的调节作用使低速旋转永磁体磁场和高速旋转电枢磁场进行耦合,副齿对气隙磁场进一步调节产生其他次有效谐波增加电机的同步转矩分量。在永磁体两侧引入沙漏形隔磁结构,该结构不仅抑制极间泄漏,而且大大降低永磁体径向应力和径向形变;并探究永磁体极弧系数对转矩及功率因数的影响,确定优化设计后的模型参数。最后用有限元仿真结果验证了沙漏形隔磁结构的主副齿式永磁游标电机的优越性,相较于传统的分裂齿式永磁游标电机,该电机具有更大的转矩和更小的转矩脉动。

Impact of interconnections and renewable energy integration on the Philippine-Sabah Power Grid systems

This study presents a comprehensive impact analysis of the rotor angle stability of a proposed international connection between the Philippines and Sabah,Malaysia,as part of the Association of Southeast Asian Nations(ASEAN)Power Grid.This study focuses on modeling and evaluating the dynamic performance of the interconnected system,considering the high penetration of renewable sources.Power flow,small signal stability,and transient stability analyses were conducted to assess the ability of the proposed linked power system models to withstand small and large disturbances,utilizing the Power Systems Analysis Toolbox(PSAT)software in MATLAB.All components used in the model are documented in the PSAT library.Currently,there is a lack of publicly available studies regarding the implementation of this specific system.Additionally,the study investigates the behavior of a system with a high penetration of renewable energy sources.Based on the findings,this study concludes that a system is generally stable when interconnection is realized,given its appropriate location and dynamic component parameters.Furthermore,the critical eigenvalues of the system also exhibited improvement as the renewable energy sources were augmented.

Power Factor Correction Rectifier with a Variable Frequency Voltage Source in Vehicular Application

This paper presents a PFCVF (Power Factor Correction) rectifier that uses a variable frequency source for alternators for electric and hybrid vehicles application. In such application, the frequency of the signal in the alternator changes according to the vehicle speed, more over the loading effect on the alternator introduces harmonic currents and increases the alternator apparent power requirements. To overcome these problems and aiming more stability and better design of the alternator, a new third harmonic injection technique is proposed. This technique allows to preserve a good THD (Total Harmonic Distortion) of the input source at any frequency and to decrease losses in semiconductors switches, thereby allowing more stability and reducing the apparent power requirements. A comparative study between the standard and the new technique is made and highlights the effectiveness of the new design. A detailed analysis of the proposed topology is presented and simulations as well as experimental results are shown.

抑制风机超速脱网的永磁风电场经柔直系统并网的受端交流故障穿越控制策略

永磁风电场经柔直外送的系统发生受端交流电压跌落时,利用转子储能进行风机减载控制的策略可能存在超速脱网问题。对此,提出一种抑制转子超速脱网的风电场减载控制策略。该策略通过转子转速与风机有功功率的关系,对风电机组减载期间的最小有功功率整定,确定风电场的最小有功输出,尽可能地减小直流两侧不平衡功率。严重故障时与直流卸荷电阻配合,快速减载的同时减小卸荷电阻承担的容量。搭建了基于某型号的永磁风电机组构成的风电场经柔直外送的仿真模型,对所提控制策略与传统控制策略进行仿真对比分析,验证了所提控制策略的有效性。

基于灰色关联机理组合模型的压缩机电功率预测

为了精确获得压缩机电功率,通过变频滚动转子制冷系统实验台,根据灰色关联(GRM(1,m))预测模型样本需求量少、预测精度高与机理(Mechanism)模型能够反映系统本质特性的特点,利用Matlab语言编程建立GRM(1,m)-Mechanism组合预测模型。通过3种模型对压缩机电功率进行预测,结果表明:GRM(1,m)-Mechanism组合模型的预测精确性和适用性更好,其最大相对误差、平均相对误差分别为4.05%,1.71%;比机理模型分别降低了1.29%,1.09%;比灰色关联(GRM(1,m))预测模型降低了1.02%,2.19%。最后,通过压缩机变转速试验验证组合模型预测平均相对误差在1.9%以内,进一步证明GRM(1,m)-Mechanism组合模型的精确性和适用性。

CDR风力发电机多领域耦合动态建模及全工况分层协同控制

针对一种串列式双叶轮(CDR)风力发电机,基于自由涡尾迹理论提出前后叶轮串列式布局下后叶轮入流风速建模方法,首次建立了包含前后叶轮、传动轴系和塔筒等关键子系统的“气动-传动-电气-支撑件”多领域耦合动态模型;考虑CDR风力发电机结构及特性,以风力机安全运行和最大出力为目标,设计整机分层协同控制架构;采用Fortran语言开发适用于不同容量等级CDR风力发电机的精细化仿真软件,结合高性能服务器搭建仿真实验平台。为验证方案有效性,配置某典型2.7 MW CDR风力发电机设计参数,依据国际电工委员会(IEC)标准开展全工况载荷分析及性能验证。结果表明:所建立的整机模型可准确反映风力机各子系统间的耦合动态特性,所提出的分层协同控制方法在安全载荷范围内具有良好的最优功率曲线跟踪性能。

新型双定子无刷双馈风力发电机直接功率控制

新型双定子无刷双馈发电机包括内外功率绕组和内外控制绕组,二者分别通过中间带隔磁环的背靠背笼障转子进行磁场耦合。针对该新型双定子无刷双馈风力发电机提出一种直接功率控制方法,内外功率绕组及内外控制绕组分别串联以保持各自同相绕组的电磁一致性,将功率绕组有功和无功功率滞环比较器输出值及控制绕组磁链扇区号综合,采用查找表得到控制绕组机侧变流器所需输出的电压空间矢量。通过定量对比研究12/8极50 kW样机控制系统阶跃信号作用下的特性仿真与实验结果,验证了所提双定子无刷双馈风力发电机直接功率控制在亚同步~超同步速度变化范围内变速恒频发电、最大功率跟踪、无功功率与单位功率因数控制等方面的正确性、可行性和有效性。

基于磁热耦合法的高功率密度永磁电机永磁体温度分布特性与试验研究

具有高效率、结构简单等优点的永磁同步电机(PMSM)在高功率密度需求的驱动应用场景中得到广泛应用。然而,该类型电机通常不设置转子冷却措施,设计不当将出现转子温升偏高,引起转子结构变形、永磁体(PM)不可逆失磁等风险。结合电动汽车用高功率密度永磁电机的发热和冷却过程,建立计及材料特性随温度变化的磁热耦合计算模型,以一台115 kW-8极的外水套冷却方式永磁电机为例,采用电机实测电流数据作为电磁分析的输入条件,通过电磁与传热的双向耦合计算,获得准确的电机永磁体损耗与温度分布。为进一步验证电机永磁体的温度分布特性,搭建转子内部零部件在线测温系统,获得负载状态下电机转子永磁体完整的温度数据和分布规律,验证了磁热耦合分析方法的准确性,为该类型电机转子永磁体的温升抑制及防退磁设计提供参考。

基于桨距角控制的永磁风电机组高电压穿越控制策略

为解决传统永磁风电机组高电压穿越控制策略存在超速脱网风险问题,提出一种基于桨距角控制的高电压穿越控制策略。高电压穿越期间,首先,按照并网要求向电网提供无功支撑;其次,考虑转子转速限制,当转子转速达到参考值时启动桨距角控制,抑制转子转速上升;最后,通过仿真试验,验证了所提控制策略的有效性。基于桨距角控制的永磁风电机组高电压穿越控制策略,既能向电网提供无功支撑,又能避免超速脱网。

一种系留多旋翼无人机备用电源设计

针对系留多旋翼无人机在地面电源异常断电时的安全降落需求,以提高系留多旋翼无人机的定位稳定性为目的,设计一种基于超级电容器的国产化备用电源。该备用电源由主控单元、充电单元、放电单元、均衡单元和超级电容器组构成,主控单元实时监控超级电容器组的运行状态,充电、放电和均衡单元分别控制超级电容器组充电、放电和均衡过程。结果表明:该备用电源具有宽温度适应性、免维护、结构简单和国产化率较高等特点,能有效地应用于系留多旋翼无人机装备中。

励磁系统交流侧接地对转子接地保护的影响

励磁系统交流侧接地将引起注入式转子接地保护、乒乓切换式转子接地保护误动作。本文介绍了一起相关案例,并对引起误动的基本原理进行了深入分析和定量计算,总结了励磁系统交流侧接地引起采样数据变化的典型特征,提出了关于缩小转子接地保护定位范围的思考。当转子一点接地保护动作后,应首先根据采样数据的变化,对故障点位于励磁系统交流侧还是直流侧做出初步判断,缩小故障定位范围,为快速查找故障提供决策依据。

微小无人机旋翼动力系统性能测试实验教学平台开发

为了满足高等院校交通运输类专业无人机系统教学需求,设计并开发了微小无人机旋翼动力系统性能测试实验教学平台,主要由主体台架系统、控制和数据采集系统、数据显示和分析系统组成。依托该实验教学平台,进行了悬停和前飞状态的旋翼性能测试实验。实验结果表明:配合风洞系统,利用该实验教学平台能够实时获取旋翼动力系统主要性能参数;气动拉力和扭矩直接测量误差均低于0.5%,电流电压直接测量误差为0.2%,桨力效和系统力效间接测量误差均低于5%。该实验教学平台可应用于小型无人机旋翼动力系统性能分析的实验教学。

高风电渗透率下考虑系统风电备用容量的储能配置

风电的高比例渗透削弱了电力系统的惯性与调频容量,储能凭借响应迅速、出力稳定等特点被广泛应用于电网的惯量支撑及频率调节工作。首先以双馈风机额定转速与有功出力为约束条件,基于转子超速控制设置最适功率预留系数,划分风机参与系统调频的风速范围。在此基础上,考虑系统频率支撑能力,提出一种风电机组与储能协调配合的调频方法。通过对储能有功出力与系统稳态恢复过程的分析,刻画了虚拟同步机控制策略下储能系统的动态频率调节特性,由此实现储能在应对系统不同工况与不同支撑需求下控制参数的最优配置。仿真结果表明,所提方法能够在保证系统调频需求的同时充分利用风电自身的调频容量,优化储能系统参数的配置结果,实现储能出力的平滑输出,提高系统的频率支撑能力。