Brushless Doubly-Fed Machines:Opportunities and Challenges

The brushless doubly-fed machine(BDFM)is a family of multiport electric machines with two ac electrical ports and a common mechanical port.Different from the conventional singly-fed machines whose synchronous speed is solely determined by a single supply frequency and the actual pole pair number,the BDFM has two supply frequencies and two different pole pair numbers to control the rotor speed.By the two accessible electrical ports,all BDFMs are endowed with more degrees of freedom for speed and power control,inherent fault-tolerant capability and high reliability.The BDFM in its broad sense has been extensively investigated as a promising alternative to the conventional slip-ring doubly-fed induction machine(DFIM)during the past decades,for both limited and wide speed range applications.This paper presents a new theoretical framework of the BDFM within which all topological variants can be closely linked by the similarities in working principle.The individualities of each machine topology are presented first,followed by the commonalities such as the modeling techniques,modes of operation,design considerations and control strategies.The challenges are identified and highlighted based on recent developments and possible opportunities are predicted considering the unique nature of this special AC machine type.

Overview of Research and Development Status of Brushless Doubly-Fed Machine System

The brushless doubly-fed machine(BDFM)has been widely used due to its advantages of robustness,reliable operation,ease of maintenance,adjustable power factor,small converter capacity and low cost.BDFM is attractive for use in many applications such as variable frequency speed regulation systems and variable speed constant frequency generation systems.Hence,there is a rapidly growing interest in design and control of BDFM.In this paper,the origin and development of BDFM are reviewed,the structural characteristics of BDFM are discussed at length,the principles of operation and design are analyzed,and the different control methods used for BDFM are overviewed and compared in detail.Finally,challenges and opportunities of BDFM are concluded.

Brushless Doubly-Fed Induction Machine as a Variable Frequency Transformer

VFT （variable frequency transformer） has been recently used as art alternative to HVDC （high voltage direct current） to control power flow between asynchronous networks. VFT consumes less reactive power than a back-to-back HVDC system, provides faster initial transient recovery, and has better natural damping capability. VFT is simply a DFIM （doubly-fed induction machine） where the machine torque controls the power flow from stator to rotor and vice versa. The main disadvantage of this VFT is the slip rings and brushes required for the rotor circuit, especially in bulk power transmission. The BDFM （brushless doubly-fed machine） with nested cage rotor machine is proved to be a comparable alternative to conventional DFIM in many applications with the advantage that all windings being in the stator frame with fixed output terminals. In this paper, the BDFM is used as a BVFT （brushless variable frequency transformer）. A prototype machine is designed and simulated to verify the system validity.

Performance Description of Brushless Doubly-Fed Induction Machine in Its Asynchronous and Variable Speed Synchronous Modes

Brushless Doubly-Fed Machine has attracted considerable attention in recent years due to its advantages. It has the robustness of the squirrel cage induction machine, and the speed and power factor controllability of the synchronous machine as well as the absence of brushes and slip rings, and using a fractionally rated frequency converter. Hence, there are considerable benefits over the conventional machines, when the machine is applied to applications such as a wind turbine generator or high power adjustable speed drive. However, these benefits are obtained in slightly more complex structure, higher cost and larger dimensions in comparison to the conventional induction machine. This paper presents fundamental aspects of the three modes of operation of brushless doubly fed machine, i.e. simple induction mode, cascade induction mode, and synchronous mode. The investigation is performed by analyzing the spatial harmonic contents of the rotor magnetic flux density. The direct cross couplings between stator and rotor fields as well as, indirect cross coupling between stator fields by the special rotor of this machine is described. Furthermore, loss analysis of the machine in various modes is presented and the torque-speed curves for asynchronous modes are obtained. A 2-D magnetodynamic finite element model based on the D-180 4/8 pole prototype machine is extracted and simulated to verify the results.

Parameter Deviation Effect Study of the Power Generation Unit on a Doubly-Fed Induction Machine-based Shipboard Propulsion System

To lower the difficulty of fault protection,a doubly-fed induction machine based shipboard propulsion system(DFIM-SPS)that is partially power decoupled is presented.In such an intrinsically safe SPS architecture,a synchronous generator(SG)is employed for power generation,and the accuracy of the parameters of power generation unit(PGU)plays an important role in SPS stable operation.In this paper,the PGU parameter deviations are studied to evaluate the effects on system performance.The models of salient-pole SG,type DC1A excitation system(EXS)and DFIM are illustrated first.Besides,the corresponding control scheme is explained.For the 16 important parameters of PGU,up to 40%of parameter deviations are applied to implement parameter sensitivity analysis.Then,simulation studies are carried out to evaluate the parameter deviation effects on system performance in detail.By defining three parameter deviation effect indicators(PDEIs),the effects on the PGU output variables,which are the terminal voltage and output active power,are studied.Moreover,the increasing rates of PDEIs with different degrees of parameter deviations for the key parameters are analyzed.Furthermore,the overall system performance is investigated for the two most influential PGU parameters.This paper provides some vital clues on SG and EXS parameter identification for DFIM-SPS.

Performance Analysis of Nested-loop Secondary Linear Doubly-fed Machine Considering End Effects

Nested-loop secondary linear doubly-fed machine(NLS-LDFM) is a novel linear machine evolved from rotary brushless doubly-fed induction machine, which has a good application prospect in linear metro. In order to analyze the performance of NLS-LDFM, the mechanism and action rules of end effects are investigated in this paper. Firstly, the mechanism of static and dynamic end effects is analyzed in aspect of direct coupling, winding asymmetry and transient secondary current. Furthermore, based on the winding theory for short primary linear machines, the machine parameters are established qualitatively considering pulsating magnetic field of NLS-LDFM. Finally, the NLS-LDFM performance analysis is supplemented by the finite element algorithm(FEA) simulation and experiments under different operating conditions.

Research on Control Strategy of Grid-connected Brushless Doubly-fed Wind Power System Based on Virtual Synchronous Generator Control

The brushless doubly-fed wind power system based on conventional power control strategies lacks ‘inertia’ and the ability to support grid,which leads to the decline of grid stability.Therefore,a control strategy of brushless doubly-fed reluctance generator(BDFRG) based on virtual synchronous generator(VSG) control is proposed to solve the problem in this paper.The output characteristics of BDFRG based on VSG are similar to a synchronous generator(SG),which can support the grid frequency and increase the system ‘inertia’.According to the mathematical model of BDFRG,the inner loop voltage source control of BDFRG is derived.In addition,the specific structure and parameter selection principle of outer loop VSG control are expounded.The voltage source control inner loop of BDFRG is combined with the VSG control outer loop to establish the overall architecture of BDFRG-VSG control strategy.Finally,the effectiveness and feasibility of the proposed strategy are verified in the simulation.

Robust Position Observer for Sensorless Direct Voltage Control of Stand-Alone Ship Shaft Brushless Doubly-Fed Induction Generators

The aim of this paper is to investigate an adaptive sensorless direct voltage control(DVC)strategy for the stand-alone ship shaft brushless doubly-fed induction generators(BDFIGs).The proposed new rotor position observer using the space vector flux relations of BDFIG may achieve the desired voltage control of the power winding(PW)in terms of magnitude and frequency,without any speed/position sensors.The proposed algorithm does not require any additional observers for obtaining the generator speed.The proposed technique can directly achieve the desired DVC based on the estimated rotor position,which may reduce the overall system cost.The stability analysis of the proposed observer is investigated and confirmed with the concept of quadratic Lyapunov function and using the multi-model representation.In addition,the sensitivity analysis of the presented method is confirmed under different issues of parameter uncertainties.Comprehensive results from both simulation and experiments are realized with a prototype wound-rotor BDFIG,which demonstrate the capability and efficacy of the proposed sensorless DVC strategy with good transient behavior under different operating conditions.Furthermore,the analysis confirms the robustness of the proposed observer via the machine parameter changes.

Properties of Brushless DC Machine Induced by Permanent Magnets Applied to a Traction Drive

The paper presents a mathematical model ofbrushless DC machine induced by permanent magnets. Its construction uses the classical model of permanent magnet synchronous machine and induced model of power inverter using the serraphil form. The results of the computer simulation were presented for such states： startup, work under active constant load and the behavior of the machine in terms of exponential and stepping change of the power inverter＇s control angle.

Improvement Torque Performances of Interior Permanent-Magnet Machines

Due to their excellent efficiency,power density and constant power speed region,interior permanent-magnet(IPM)machines are very suitable for electric vehicles(EVs).This paper proposed a new IPM rotor topology,which can offer high reluctance torque,wide constant power speed range and excellent overload capability.Besides,five rotor topologies with integral-slot distributed-windings IPM machines,including four existing IPM topologies and the proposed IPM topology,are designed optimally.Their characteristics,which include d-q axis inductances,saliency ratios,electromagnetic torques,corresponding torque ripples,back-electromotive forces(EMFs),overload capabilities and flux weakening performances are evaluated quantitatively.Finally,a three phase 48s8p hybrid rotor PM machine is built to verify the performances of the proposed IPM machine.This work provides some general concepts for machine developers who are willing to build IPM machines for high-performance EV applications.

Design and analysis of a dual-stator brushless doubly-fed induction machine with a staggered dual-cage rotor

In this paper,a new dual-stator brushless doubly-fed induction machine with a staggered dual cage rotor is proposed,with emphasis on the general interconnection rule of the conductor bars for the staggered dual cage rotor.Since the squirrel cage rotor offers the merits of robustness,reliable structure,high slot filling factor,and low rotor resistance comparing to the wound rotor,it is introduced to the dual-stator brushless doubly-fed induction machine to solve the problems of high copper loss and unreliable rotor structure for the dual-stator brushless doubly-fed induction machine with a wound rotor.The originality of this article is to investigate the interconnection rule of conductor bars between the inner and outer cages.The constraint condition that is supposed to be satisfied is deduced by using the rotating magneto-motive force theory,based on which diverse slot/pole combinations are investigated.The performance comparison between the existing and proposed machines is conducted.Finally,a prototype is designed and fabricated.The experimental results verify the effectiveness of the proposed topology.

无刷双馈电机研究综述与展望

无刷双馈电机具有结构可靠、变频器容量小等优势,非常适合灵活运行于防爆、易燃等特殊或极端工况,近年来受到广泛关注。该文根据无刷双馈电机的基本工作原理,明确了该类电机的命名原则与规范名称;总结了现有定转子方案的结构及性能特点,综合考虑性能指标与结构工艺,提出了转子双套绕组的发展方向;梳理了无刷双馈电机的稳态等效电路模型及基于各类数学模型的优化设计方法,针对现存难以完整考虑不同转速工况性能的不足,阐明了利用新型同步-异步相串联等效电路进行优化设计的思路;对比分析了经典及新近出现的无刷双馈电机控制系统拓扑和控制策略特点,面向典型电动、发电工况建立了完整的电机及控制系统。最后,对无刷双馈电机的上述理论研究问题及工业应用的发展方向进行了总结阐述,为该类电机的深入研究及加快推广应用提供参考和指导。

基于端部绕组模块的定子励磁无刷电机冷却方法

为了提升定子励磁无刷电机的冷却能力,提出了一种基于端部绕组模块的定子励磁无刷电机冷却方法.在电机端部绕组和定子铁芯叠片端部的间隙中插入端部绕组冷却(EWC)模块,以减小定子绕组热点区域和冷却介质之间的间隙,从而提高端部绕组的冷却能力.对非重叠式集中绕组长度计算模型进行改进,评估采用EWC模块前后电机定子电枢绕组长度的变化,分析EWC模块的电导率对电机定子损耗的影响.采用计算流体动力学(CFD)模型,对比EWC模块在不同铜耗和励磁源损耗密度下的冷却性能.结果表明,采用EWC模块可以使端部绕组的稳态温升降低约50%,热态时的绕组电阻降低7.51%,从而改善了定子的冷却条件.

Stability Analysis and Enhanced Virtual Synchronous Control for Brushless Doubly-fed Induction Generator Based Wind Turbines

The brushless doubly-fed induction generator(BDFIG)presents significant potential for application in wind power systems,primarily due to the elimination of slip rings and brushes.The application of virtual synchronous control(VSynC)has been demonstrated to effectively augment the inertia of BDFIG systems.However,the dynamic characteristics and stability of BDFIG under weak grid conditions remain largely unexplored.The critical stabilizing factors for BDFIG-based wind turbines(WTs)are methodically investigated,and an enhanced VSynC method based on linear active disturbance rejection control(LADRC)is proposed.The stability analysis reveals that the proposed method can virtually enhance the stability of the grid-connected system under weak grid conditions.The accuracy of the theoretical analysis and the effectiveness of the proposed method are affirmed through extensive simulations and detailed experiments.

不平衡磁拉力作用下无刷双馈电机的转子振动特性研究

无刷双馈电机长时间运行会出现转轴弯曲、轴承磨损等状况,导致气隙动偏心,并因此产生不平衡磁拉力,影响转子系统动力学特性。为了研究由不平衡磁拉力引起的转子振动特性问题,建立Jeffcott转子动力学模型,得出考虑不平衡磁拉力作用下转子系统的振动微分方程组,并对其自由振动响应进行了计算。以某型号无刷双馈电机的样机尺寸为例,分析气隙动偏心状态下电机气隙长度、转子材料及几何尺寸等对电机振动特性的影响,并利用Runge-Kutta法对振动微分方程组进行分析,结果表明:当转子动偏心率较小时,利用该转子系统的振动微分方程组计算出的解析解与数值计算结果吻合较好,转子的一阶振幅误差仅为0.2%,二阶振幅误差为2%,具有较高的精度且计算较为简便,为电机的高可靠运行提供理论支撑。

不同槽配比下绕线式无刷双馈电机性能对比研究

无刷双馈电机由于结构简单、可靠性高、变频器容量小等优点在恒频变速发电领域受到广泛关注,其定转子的槽数配比对电机性能与振动具有一定程度的影响。为探究这一问题,该文以绕线式无刷双馈电机定转子磁势分析为基础,推导不同槽配合的电磁力波对比以及槽配合对电机性能的影响,给出3种符合要求的槽配比方案,计算出各方案转子绕组谐波,并进行对比分析;利用有限元法对48/36槽、42/36槽与36/30槽3种方案在相同要求下的负载性能进行研究,导出定子齿部电磁力,对电机进行振动响应分析对比;最后,通过样机试验,验证有限元仿真的正确性,同时试验结果也证明所选槽配合下电机具有振动形变量小、转子电流小、系统输出电压和效率高、饱和程度低等优点。

基于自抗扰控制的圆纬机恒张力输纱控制系统设计

针对当前圆纬机积极式送纱方式中存在的纱线张力及输送速度不可任意调节、纱线张力波动大等问题,提出了一种可为圆纬机输送恒定张力纱线的输纱控制系统。构建了以无刷直流电动机速度环为内环、以纱线张力为外环的纱线恒张力双闭环反馈控制系统,通过自抗扰控制技术获取纱线实时动态指标,并对无刷直流电动机目标转速进行调整,最后通过磁场定向控制技术驱动无刷直流电动机。详细阐述了纱线张力的形成机制、纱线恒张力输送控制方案、系统硬件设计及控制算法。输纱测试表明,该控制系统可实现多种类型纱线的恒定张力输送。其中,棉纱张力波动标准差为1.5 cN(300 m/min测试条件),氨纶包芯纱的张力波动标准差为0.33 cN(240 m/min测试条件)。输纱速度的调节范围为0~600 m/min,纱线张力的控制范围为2.0~50.0 cN。

Spiral Vector Modeling of Brushless Doubly-fed Induction Machines with Short-circuited Rotor Windings

A unified spiral vector model is presented that can be used to assist the finite element method-based performance analysis of brushless doubly-fed induction machines with various short-circuited rotor windings.Specifically,magnet-free brushless doubly-fed induction machines working in doubly-fed or singly-fed synchronous mode are investigated.A dynamic model in spiral vector notation is developed,based on which the torque-angle and power-angle characteristics are derived.It is shown that the investigated brushless machines are equivalent to a traditional non-salient-pole synchronous machine with brushes.By introducing a conversion factor,they can also be analyzed with methods similar to the conventional phasor theory.A comparison is made between the brushless doubly-fed induction machine and non-salient-pole wound-field synchronous machine with brushes,revealing that the performance of the brushless machine degrades faster when the laminated core is saturated.A scaled-down prototype is tested to validate the effectiveness of the theoretical analysis.

基于线性自抗扰的无刷双馈电机功率解耦控制策略研究

针对抽水蓄能机组工作环境复杂、温度等扰动较为突出、传统矢量控制对于无刷双馈电机控制精度不足的问题,研究了一种基于线性自抗扰控制的无刷双馈电机功率解耦控制策略,用来降低电机扰动并提高控制精度,提升其运行特性,进而提高其在抽水蓄能系统中的能量转换效率。建立了无刷双馈电机统一坐标系下两相旋转坐标系的数学模型,采用功率绕组定向的方法确定坐标系,推导了功率绕组定向下的电流关系并据此使用控制绕组控制功率绕组的有功和无功,从而实现了功率解耦控制。为提高控制性能,重写转速环和电流环,分析扰动,列写状态方程,设计扩张状态观测器,采用自抗扰技术提升了电机控制性能。进行谐波分析,基于控制绕组电流在同步坐标系下主要谐波为6次谐波的结论,采用重复控制器进行特定频次谐波的抑制。通过Simulink仿真,观察动态响应和d轴绕组电流傅里叶分析,并在电网电压阶跃变化和系统存在白噪声两种状态下与传统PI控制的效果进行对比,验证了所提自抗扰功率解耦控制方法及谐波抑制方法的有效性。

绕线式无刷双馈电机伺服系统的双同步转差型解耦控制研究

针对无刷双馈电机在解耦控制以及整体性能分析方面的不足,首先提出了一种双同步坐标系下无刷双馈电机的转差型解耦控制方案,并分析了该控制实现的必要条件。其次,通过对双同步坐标系下的静态方程求解得到该闭环控制下无刷双馈电机的带载特性。当电机转速和控制电机转子磁链一定时,可求解该工况下电机所能达到的带载边界,通过在负载转矩边界内部取值保证整个伺服系统的稳定运行。最后,通过仿真和实验验证了该控制方案的解耦性能和动态性能,同时也验证了该控制下带载性能分析的正确性和有效性。