异步化高压发电机失磁故障分析

针对以新型电缆绕组构成的异步化高压发电机的失磁过程进行研究,首先建立该电机场路耦合模型,利用耦合模型分析异步化高压发电机在不同转差率下转子发生对称短路失磁和不对称短路失磁故障的磁场进行分析,探索当转子绕组发生不同类型的短路故障时,定子铁心和转子铁心的磁通密度变化规律,为电机和系统故障分析提供数据基础.然后分析了异步化高...     

Direct field orientation controller using the stator phase voltagethird harmonic

This paper presents the development and implementation of a direct field orientation controller (DFOC) for induction machines based on determination of the spatial position of the air gap flux from the third harmonic component of the stator phase voltages. The control utilizes spatial saturation harmonic components rotating at synchronous frequency that are generated in the air gap flux when the machine operates in a saturated condition. When the machine is wye connected, the sum of the three phase voltages results in a signal dominated by the third harmonic and a high frequency component due to the rotor slot ripple. It is shown that the third harmonic voltage component can be effectively used to estimate both amplitude and position of the air gap flux. Two methods for estimation of the air gap flux from the third harmonic voltage are discussed in the paper. A complete induction motor direct field orientation control is designed and implemented in the laboratory. Extensive experimental results showing the DFOC drive system performance are presented and discussed     

A simple and robust adaptive controller for detuning correction infield-oriented induction machines

A novel adaptive controller for correcting the rotor time constant estimate used in the slip frequency calculator of indirect field-oriented controllers (IFOCs) is presented. The controller possesses near digital deadbeat performance and simultaneously maintains its correctness down to zero speed. The robust controller dynamics are based on an operating-point form of digital deadbeat control. The correctness down to zero rotor speed is based on the determination of the rotor flux from an accurate air-gap flux estimate obtained from the third harmonic stator phase voltage component introduced by the saturation of the machine stator teeth. The proposed controller is implemented using a digital signal processor, and the experimental results demonstrate its excellent performance for a wide range of rotor speeds, including locked rotor conditions     

Harmonic field analysis for slip-ring motors including generalrotor asymmetry

A field analysis is presented for slip-ring induction motors with general external impedance asymmetry. The method is based upon a rotating-field theory approach including spatial MMF (magnetomotive force) harmonics. It is shown that a series of nonmains frequency voltages are induced in the stator winding for both balanced and unbalanced rotors. The method is also used to derive the harmonic equivalent circuit for a balanced three-phase slip-ring motor with a skewed rotor. The analysis is verified by comparing predicted torque and current characteristics with measured values obtained from a machine with a balanced rotor and with a rotor connected to asymmetrical external resistances. The influence of MMF harmonics on the phase equivalent circuit and the motor performance is demonstrated. Operation with an unbalanced rotor results in a loss of steady torque and the introduction of large oscillating torques     

Analysis techniques for detection of IM broken rotor bars after supply disconnection

This paper presents some analysis techniques of the space vector of voltages induced in the stator windings after supply disconnection, to detect broken rotor bars in squirrel-cage induction machines. When the motor is disconnected from the supply no currents flow in the stator windings and the voltages measurable at its terminals are due to flux produced by rotor currents. When the rotor is healthy, the voltages measured at motor terminals are almost sinusoidal because of the symmetry of rotor windings. When there are broken rotor bars, the magnetomotive force generated by rotor windings is distorted, and some particular harmonics, contained in the voltages induced in the stator windings, increase their amplitudes. The diagnostic technique is based on monitoring these voltage harmonics and analyzing the space vector of the voltages induced in the stator windings via MUSIC pseudospectrum and short-time MUSIC (STMUSIC) time-frequency pseudorepresentation. The MUSIC algorithm is based on the eigen analysis of the autocorrelation matrix, and permits us to evidence the principal harmonic frequencies of the signal and decrease the noise influence, thus allowing a better detection of the broken rotor bars. The results obtained using MUSIC and STMUSIC algorithm have been compared experimentally with those obtained by fast Fourier transform (FFT) and short-time FFT, respectively, and two different sized induction motors have been tested, to demonstrate the superiority of the former approach. Differently from most of the diagnostic techniques already proposed in the technical literature, the proposed approach is effective regardless of the load condition of the machine, source characteristics, and iron saturation.     

电网谐波电压对同步调相机转子损耗的影响

高压直流输电系统单极大地回线运行会使得附近变压器产生直流偏磁现象,增加变压器副边电压的谐波含量。当变压器与为换流站提供无功支撑的同步调相机连接时,谐波电压会影响同步调相机的转子损耗。本文针对不同谐波电压下,同步调相机转子损耗的变化展开研究。采用时步有限元法计算了同步调相机空载、进相以及迟相运行条件下,谐波电压对转子铁心和槽楔损耗的影响,对比分析了转子各部分损耗大小随电压谐波次数的变化规律。研究结果为同步调相机的安全可靠运行提供了理论基础。     

Analysis of rotor slotting saliency in induction motor sensorless control

This paper deals with induction machines study by Finite Element Analysis (FEA) for position sensorless control drives based on rotating voltage carrier injection. It focuses the analysis of the rotor slotting saliency, under the variations of: (1) supply of the machine (both the high frequency rotating voltage carrier and the fundamental frequency supply), (2) reference flux of the drive, (3) load torque, and (4) rotor geometry design. The relative spatial harmonic of the stator inductance space-vector responsible for the rotor slotting effect has been chosen as an index for evaluating the response to the high frequency carrier. A methodology for retrieving the stator inductance space-vector from a FEA is proposed as well. Results of the variation of the rotor slotting spatial harmonic of the stator inductance with the carrier frequency, the rotor flux linkage, the load torque and the rotor geometry are presented.     

A new self-excitation scheme for three-phase synchronous generators

A new self-excitation scheme has been developed for three-phase synchronous generators. The generator that uses this scheme behaves as a flat-compound machine without automatic voltage regulators. The stator of the generator is provided with an armature winding that generates the fundamental and 2nd-harmonic mmfs. The rotor is equipped with a field winding and a harmonic winding. The harmonic winding is magnetically coupled to the 2nd-harmonic mmf produced by the armature winding. The current flows in the stator armature winding by way of a three-phase set of capacitors connected across its three-phase terminals and the ac voltage is induced in the rotor harmonic winding due to the armature 2nd-harmonic mmf. By connecting the harmonic winding to the field winding through a rectifier circuit, self-excitation of the generator is obtained. This excitation scheme is both self-excited and brushless, and no exciter is required. Additionally, voltage regulation due to load variation can be improved by connecting suitable capacitors. In this paper the operating principle and circuit configuration of the generator are explained and the experimental results using a 1-kVA prototype machine are shown. The generator characteristics are theoretically clarified by approximate analysis, and appropriateness of the theory and the usefulness of the proposed scheme are experimentally confirmed.     

铸铜转子双三相异步电动机设计与优化

以新型电动车用驱动电机为设计目标,利用有限元软件建立铸铜转子双三相异步电动机二维电磁仿真模型,计算电机的峰值输出转矩和功率。对比分析铸铜转子与铸铝转子在效率方面的差异,进一步计算电机的效率分布,通过调节定子和转子槽型来优化电机的效率分布,使电机的最高效区域分布在电动车的常用工况区;对比分析对称电压供电情况下,双三相定子绕组与三相定子绕组在一相忽然断路时对电机转矩的影响,并给出双三相电机缺相运行时的控制策略。以电机的实测数据来验证仿真计算的正确性,电机输出特性满足电动汽车需求。     

基于转子平均瞬时功率的双馈异步发电机定子绕组匝间短路故障诊断

由于双馈异步发电机转子参数的可测性,提出一种基于转子平均瞬时功率的定子绕组匝间短路故障诊断方法。首先推导出计及高次谐波的双馈异步发电机正常及发生定子绕组匝间短路故障时的转子平均瞬时功率的表达式,然后建立了双馈异步发电机的多回路数学模型,并对其正常和不同程度匝间短路故障时的转子平均瞬时功率进行仿真计算。对仿真结果进行频谱分析,得到定子绕组匝间短路故障前后转子平均瞬时功率谐波分量的变化规律,并验证了理论分析的正确性。分析结果表明转子平均瞬时功率谱直观简洁,其2倍频分量不受转差率影响,高次谐波分量对定子绕组匝间短路故障有较强的灵敏性。     

浅谈1.5MW双馈风力发电机定、转子槽型的选择

发电机定、转子槽口形状直接影响到发电机感应电势中的谐波含量,同时影响到整个电机生产制造工艺及电机运行的可靠性。通过对1.5MW变速恒频双馈感应发电机定、转子各种槽型下的谐波分析,可找出在结合生产制造工艺方法及生产设备的基础上,适合的定、转子槽口形状。     

Compensation for parameter variation of induction motor improved torque control characteristics in low- and high-speed regions

In the vector control system using the slip frequency control method, the rotor resistance of an induction motor is used to calculate a slip frequency. Thus the change in temperature of the rotor resistance causes the deterioration of the torque control characteristic. This paper presents a new method of compensating for the rotor resistance change which is robust for the stator resistance change. A current control loop is composed of the λ-δ axes in which the λ axis is coincident to the stator current. In this method, the stator voltage error on the δ axis which is directly obtainable from this current control loop was used. The change in the stator voltage was able to be detected accurately, therefore the torque control accuracy was improved, particularly in the low-speed region. The experimental results of the current response and the compensation for the rotor resistance deviation also are shown. Moreover, although the mutual inductance has been treated as an invariable value, the value does change by a frequency and an exciting command. In this control method, an initial tuning of the equivalent mutual inductance was achieved by detecting the deviation component of the stator voltage on the δ axis at the no-load running condition. Furthermore, in the region with the constant power where the field weakening control was achieved, the excellent experimental results of the compensation for the deviation of the equivalent mutual inductance are shown.     

变速恒频双馈风力发电机投切控制策略

对几种变速恒频双馈风力发电投切控制策略进行深入的研究。基于电压开环控制的投切控制策略，虽具有较好的稳定性，但空载定子电压的控制精度受到限制；基于电压有效值闭环的投切控制策略，虽能提高定子空载电压的控制精 度，但在定子电压的三相对称性及定子电压幅值的波动方面仍存在欠缺；基于空间电压矢量闭环控制的投切控制策略，若采用特定的调节器设计，不仅能确保电压控制精度，而且可以有效抑制定子电压幅值的波动。针对基于空间电压矢量闭环控制的这一投切方案，在PI调节器控制的基础上提出了自适应谐振调节器与PI调节器并行控制的控制策略，有效抑制了定子电压幅值的波动，使定子电压具有较好的控制响应，进而实现了双馈风力发电机零电流切入电网的目的。仿真与试验验证了理论分析及方案设计的正确性。     

异步电机按定子磁场定向的转差频率控制

在分析现有转差频率控制方案优缺点的基础上，提出一种按定子磁场定向的转差频率控制方案。利用坐标变换和磁场定向原理，建立按定子磁场定向的异步电机数学模型。新系统通过定子电压直轴分量直接控制定子磁链的变化率；在转速通道中，电流调节器的输出作为转差频率，继承了标量型转差频率控制方案的优点。新系统的动态控制算法不依赖于转子电阻和电感参数。结果表明，新系统具有良好的静、动态性能和鲁性棒。     

双速异步风力发电机电磁场谐波分析及槽配合选择

根据南亚丘陵地带高、低风季节稳定切换的特点,设计了符合变速恒频发电技术的双速异步发电机。定子采用两套独立绕组,转子采用鼠笼结构。根据电机学原理和傅里叶级数理论,将异步电机旋转磁场分离出基波和各次谐波,并建立了谐波分析的数学模型。通过模型计算,选择了恰当的槽配合和定子节距,使得两个极数方案下基波绕组系数尽量大,同时各次谐波绕组系数尽量小。最终确定了此风力发电机的恰当定转子槽配合为72/82。     

基于转子瞬时功率谱的双馈风力发电机定子绕组故障诊断

提出一种基于转子瞬时功率谱分析的双馈风力发电机定子绕组故障的在线监测与诊断新方法。理论分析表明,与常见的电流或电压谱诊断方法相比,转子瞬时功率谱法既具有无需外加传感器与硬件设备的优点,又由于其特征频率不受转差的影响,当转差存在一定的跟踪或计算误差时,特征频率不会改变,具有很强的抗干扰能力。在PSCAD软件中建立了双馈风力发电机并网模型,对正常及故障状态进行仿真分析,得出转子瞬时功率谱法在双馈风力发电机定子绕组故障诊断中更具敏感性的结论。在动模实验室建立了定子绕组故障诊断的实验平台,进一步证明了转子瞬时功率谱法在双馈风力发电机定子绕组故障诊断中的可行性。     

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.     

非正弦供电十五相感应电机定子漏抗计算

为获得非正弦供电十五相感应电机基波和3次谐波等值电路中的定子漏抗参数,提出了基波和3次谐波定子槽漏抗、谐波漏抗和端部漏抗的分析方法并进行了计算。从槽比漏磁导公式出发求出了基波与3次谐波下的定子槽漏抗。考虑了十五相感应电机定子绕组基波电流与3次谐波电流产生磁势之不同特点,由各自谐波比漏磁导求出相应的谐波漏抗。通过引入气隙电流和镜像电流,用数值法计算线圈间端部电感作为求取基波和3次谐波端部漏抗的基础。分析计算表明,定子整距集中绕组的3次谐波槽漏抗为基波槽漏抗的3倍,但对谐波漏抗和端部漏抗无此比例关系成立。在基波电压下对十五相感应电机样机进行了堵转实验,短路电抗实测值与定转子漏抗计算值相互吻合,间接验证了该文所用计算方法的正确性。     

Analysis of three-phase wound motors under unbalanced conditions

The analysis of three-phase wound motors with unbalanced supply voltages and unbalanced rotor-phase impedances is presented. The rotating field theory and coupling impedances approach are used in modelling the motor in the steady state. The effect of rotor skewing is considered. The relationships between stator and rotor quantities, in a general form, are obtained. The analysis is verified by comparison with the conventional equations for currents and torque.     

磁性槽楔对永磁电机转子损耗及温度场影响

针对实心转子高压永磁电机定子铁心开槽会导致气隙磁导不均匀,气隙中谐波磁场引起电机转子温度升高,影响永磁体的电磁性能的问题,以一台315 k W,6 k V实心转子高压永磁电机为例,建立了样机的二维电磁场时步有限元模型及三维全域流体与固体耦合传热数学模型,给出了求解域及边界条件,通过求解计算模型,将计算数据与实验数据进行了对比,验证了所建模型的正确性。在此基础上研究了槽楔相对磁导率分别为3、5、7、9时对转子表面涡流损耗的影响,分析了磁性槽楔相对磁导率为不同值时电机转子及定子各部分的温度分布,计算结果表明定子槽楔相对磁导率数值的增加,电机的起动转矩降低,转子铁心涡流损耗逐渐减小,电机定子各部分温度先减小后趋于稳定。