Characteristics of three-phase induction motors under unbalanced rotor impedances

An analysis is developed for three-phase induction motors with balanced or unbalanced rotor impedances. The validity of this analysis is verified by comparing its results, under balanced conditions and in the steady state, with those obtained using conventional methods. The method is also verified experimentally for a 7.3 kW, 220 V, four-pole, 50-cycle slip-ring induction motor with balanced or unbalanced rotor impedances. The analysis is then used to study the characteristics of three-phase induction motors under unbalanced rotor impedances.     

Detection of Winding Faults in Wound Rotor Induction Motor Using Loci of Direct and Quadrature Axes of Rotor Currents

In this paper, loci of direct and quadrature axis of rotor currents are used for online detection of winding fault on stator side as well as rotor side in three-phase wound rotor induction motor. The proposed technique is used for detecting load on induction motor and open circuit fault condition on stator side as well as rotor side. Detection of winding fault is affected by unbalanced supply voltage. In order to overcome this problem, FFT of modulus of direct and quadrature axis is used. The experimental results of rotor current analysis are validated with stator current analysis. Research works reported in the literature are based on stator currents analysis. The proposed technique of detecting winding faults and distinguishing between stator winding faults and unbalanced supply voltage using rotor current is not reported in the literature.     

不平衡电压下双馈异步风力发电系统的建模与控制

提出了不平衡电网电压条件下双馈异步发电机(DFIG)在正、反转同步速旋转坐标系中的完整数学模型,推导和分析了不平衡电网电压条件下DFIG定子输出瞬时有功、无功功率组成.在此基础上,提出了小值稳态不平衡电网电压条件下增强DFIG不间断运行能力的4种可供选择的控制方案.讨论了不同不平衡控制目标下转子正、负序电流指令值计算原则,设计了正、反转同步速旋转坐标系中DFIG的双幽转子电流控制器的不平衡控制方案,实现了不平衡电网电压条件下转子正、负序电流的独立跟踪控制,有效地提高了小值稳态不平衡电网条件下风电机组的不间断运行能力.仿真研究验证了理论分析的正确性和所提出的双dq转子电流不平衡控制方案的有效性.     

永磁同步电机转子偏心电磁力和挠度的分析与计算

为了准确计算永磁同步电机(PMSM)转子的挠度,降低电机的生产制造成本,基于理论解析和有限元法,分析与计算了转子偏心电磁力和挠度。推导了PMSM不平衡磁拉力的解析表达式,详细介绍了不平衡磁拉力和转子挠度的有限元计算方法。以355 kW 1 500 r/min PMSM为例,对比了不平衡磁拉力、转子挠度的有限元和解析法的计算结果,验证了有限元法的可靠性,对PMSM转子机械的准确计算和振动噪声分析具有一定的参考意义。     

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     

复合实心转子磁阻电机转子阻抗的解析计算

实心转子阻抗计算是一个三维涡流场问题,在磁阻电机中又由于直轴和交轴磁路不对称,使得问题更为复杂。本文通过必要的合理假设,得到了磁阻电机实心转子电磁场的一维模型,从而导出了转子阻抗的解析表达式。利用此式,可以方便地计算不同结构参数时实心转子的阻抗值,进而可以计算相应的电机起动特性,计算结果与样机实测结果吻合较好。本文结论可以用于计算实心转子磁阻电机的异步特性,在研究实心转子异步电机时也可参考应用。     

同步调相机极限工况下典型磁场不对称故障安全风险

同步调相机典型磁场不对称故障下,由强励所形成的不平衡力和跳机风险升高。首先,分析转子动偏心和转子绕组匝间短路等典型故障对调相机磁场的影响机理;然后,借助气隙磁导法推导得到转子承受的不平衡磁拉力表达式,分析强励对不平衡电磁力的影响规律;最后,在一台大型同步电机上进行有限元电磁暂态仿真,模拟动偏心和转子绕组匝间短路故障,分别在调相正常励磁和强励工况下提取了转子所受不平衡电磁力,评估机组在强励状态下发生跳机的可能性。结果表明,强励状态下,调相机组由动偏心故障产生的不平衡磁拉力不会引起机组的剧烈振动,而转子匝间短路故障产生了较大的不平衡磁拉力,可能导致机组跳机。     

隐极同步发电机转子匝间短路时转子不平衡磁拉力特征分析

考虑到转子匝间短路会在定子回路产生与极对数和定子绕组形式有关的偶数次和分数次不平衡电流分量,首先基于不平衡电流谐波分量产生的各次谐波磁动势,推导了转子在定子直角坐标系中不平衡磁拉力(UMP)的表达式,并根据故障时定、转子磁动势的特点,得到了故障后UMP的频率分量表达形式,形成了一套完整的故障时UMP特征分析方法。用该方法对不同极对数的隐极发电机样机转子匝间短路故障进行了分析,并通过基于ANSOFT软件的场路耦合计算得到了故障中转子电磁力的数值结果。仿真结果符合理论分析的UMP特征,验证了所提出的转子受力分析方法的正确性。理论分析与仿真结果均表明,不同极对数和定子绕组形式的发电机故障时转子UMP的谐波特征不同,为机电信息融合的转子匝间短路故障监测奠定了基础。     

The Application of the Duality of Equivalent Circuits to Modelling Cylindrical Solid-Iron Rotors of Synchronous Machines at Asynchronous

ABSTRACT

By means of the duality of magnetic and electric equivalent circuits, an equivalent circuit is derived for the machine with slotted solid-iron rotor at asynchronous speeds. All impedances are calculated from geometrical data. The saturation, the magnetic field in slots and the impedance of the rotor ends are taken fully into consideration.     

感应电机不对称短路的瞬态

首先建立对称运行和不对称短路时感应电机的瞬态模型,然后利用磁链守恒原则确定感应电机不对称短路时定、转子电流的初值,并用实例进行数值求解。全文为普通和双笼感应电机不对称短路的瞬态分析建立了理论基础。     

大功率空心杯异步电机的参数计算与试验验证

空心杯异步电机虽然存在励磁电流大、功率因数低的不足,但其具有转子结构简单、可靠性高、转子无铁心、转动惯量小的突出优点,因此其在一些特殊要求的应用场合仍具有实用价值和应用前景。为了对空心怀异步电机进行性能分析和优化设计,必须能准确计算电机的参数。给出了空心杯异步电机的参数计算方法,通过解析法推导了转子阻抗的计算公式。在专门的试验电机上进行了参数测量,并将计算结果与测量结果进行了对比,此外还将负载试验测得的端口阻抗与计算参数和测量参数计算得到的端口阻抗进行了对比。对比结果证明了计算和分析的正确性。     

Convergence problem in forward/backward sweep power flow method caused by non-positive-sequence impedance of distributed generators and its solution

A variety of distributed generators (DGs) are integrated in distribution system which is usually operated under three-phase unbalanced conditions. The zero and negative sequence impedances of DGs may vary within a large range. In this paper, the convergence problem caused by the zero and negative sequence impedances of DGs in forward/backward sweep three-phase power flow is found through numerical experiments. The reason of this phenomenon is explained and an impedance compensation method is proposed to solve this problem.     

基于辅助槽的永磁电机不平衡磁拉力抑制

由于磁场不对称,不平衡磁拉力存在于一些特定极槽配合的永磁电机当中,如8极9槽电机。该文首先分析了不平衡磁拉力的模型。然后,基于此模型,提出了不平衡磁拉力的抑制方法——辅助槽。分别研究了定/转子辅助槽尺寸（包括槽位置、槽宽和槽深）对不平衡磁拉力的影响规律。为了进一步抑制不平衡磁拉力,提出了两种辅助槽组合的方法。同时,也研究了电机带载情况下辅助槽对不平衡磁拉力的影响规律。结果表明,在轻载时,由永磁磁场引起的不平磁拉力占主导,此时采用定转子辅助槽组合的方法可将不平衡磁拉力减小87.1%;而在重载时,由电枢磁场引起的不平衡磁拉力占主导,此时采用定子辅助槽可将不平衡磁拉力减小52.9%。     

Modeling of unbalanced three‐phase driving‐point impedance with application to control of grid‐connected power converters

The dq transformation is widely used in the analysis and control of three‐phase symmetrical and balanced systems. The transformation is the real counterpart of the complex transformations derived from the symmetrical component theory. The widespread distributed generation and dynamically connected unbalanced loads in a three‐phase system inherently create unbalanced voltages to the point of common coupling. The unbalanced voltages will always be transformed as coupled positive‐sequence and negative‐sequence components with double‐frequency ripples that can be removed by some filtering algorithms in the dq frame. However, a technique for modeling unbalanced three‐phase impedance between voltages and currents of same sequences or of opposite sequences is still missing. We propose an effective method for modeling unbalanced three‐phase impedance using a decoupled zero‐sequence impedance and two interacting positive‐sequence and negative‐sequence balanced impedances in the dq frame. The proposed method can decompose a system with unbalanced resistance, inductance, or capacitance into a combination of independent reciprocal bases (IRB). Each IRB basis belongs to one of the positive‐sequence, negative‐sequence, or zero‐sequence system components to facilitate further analysis. The effectiveness of this approach is verified with a case study of an unbalanced load and another case study of an unbalanced voltage compensator in a microgrid application. Copyright © 2015 John Wiley & Sons, Ltd.     

Analysis of permanent-magnet machine for sensorless control based on high-frequency signal injection

This paper presents the analysis of a surface-mounted permanent-magnet (SMPM) machine for the sensorless control scheme based on the high-frequency fluctuating voltage signal injection method. A simplified high-frequency model of an SMPM machine in the estimated rotor reference frame is developed and a sensorless rotor position and speed estimation algorithm is described. To support this, the high-frequency impedances of an SMPM machine are analyzed by finite-element analysis (FEA) and compared with measurement results using a pulsewidth-modulation (PWM) inverter system under various injection conditions. The results of the FEA and measurements are coincident with each other with some errors due to the nonlinear behavior of the PWM inverter and the SMPM machine. The analysis results give physical insights into selecting the injection conditions for sensorless operation of the SMPM machine even though adjustments considering nonlinear behaviors of PWM inverters are required in the actual operation for the desired performance. The experimental results of speed and position control using a commercial SMPM machine are presented based on the analysis of the SMPM machine for the sensorless control algorithm.     

Impact of inter-bar currents on the performance of the brushlessdoubly fed motor

The brushless doubly fed machine has been proposed as an alternative adjustable-speed drive because of its potential for reducing the size of the necessary power electronic converter. The motor's economic viability may depend upon the ability to die cast the rotor, bringing the cost of production in line with that of an induction machine. Recent industrial experience has shown that when the rotor is die cast, without any special precautions for insulating the bars from the rotor iron, the performance is degraded with respect to a fabricated rotor with insulated bars. This performance degradation is shown to be caused by the presence of inter-bar rotor currents. This paper presents a coupled-circuit model which is able to simulate the performance of the motor, including the presence of the inter-bar currents. The model describes the physical structure of the windings and the rotor in terms of complex harmonic impedances. Both measured results and predicted results are presented. In addition, this model enables investigation of the decreased performance obtained with varying values of inter-bar resistance     

大型同步调相机转子故障温度场分析

随着特高压交直流输电的发展,同步调相机以其快速动态响应能力重新受到关注,同步调相机的安全运行关乎电网的稳定性。论文以TTS-300-2型双水内冷同步调相机为研究对象,建立了其转子三维模型,计算并分析了转子不同负荷下、同一位置不同水路堵塞程度时的转子三维温度场,转子匝间短路和水路堵塞同时存在时的温度场以及转子水路堵塞时的热应力情况,评估故障产生的影响和同步调相机带病运行能力。结果表明,不同负荷下转子温度场分布相似;转子出现故障会导致温度分布不平衡;单个槽内堵塞匝越多,转子温度场畸变越明显;且随堵塞程度的增加,转子热应力随之增加。     

不平衡电压下双馈感应发电机转子侧变流器的灵活功率控制

针对不平衡电压下双馈感应发电机(DFIG)转子侧变流器的控制,分析定子瞬时有功和无功功率与三相定子电压、转子电流的关系,通过引入连续调节系数得到转子三相电流指令值的通用计算式。进一步地,求得指令电流调节系数、转子电流峰值及DFIG定子有功和无功波动的表达式,分析DFIG控制特性随调节系数、电压不平衡度的变化规律;分析不平衡电压跌落下DFIG的可控性,给出电压跌落后定子电压的临界值和转子侧变流器可控的判断条件;以功率波动设定值为目标,计及转子电流峰值限制,建立DFIG单位功率因数和无功功率支持2种模式下的灵活功率控制策略,通过仿真验证所提方法的可行性。     

叶轮不平衡下的风力机自适应独立变桨控制策略

为减小风电机组叶轮不平衡引起的周期载荷,提出一种自适应独立变桨控制策略。首先,基于叶片旋转坐标系和轮毂静止坐标系之间的关系,揭示了机组在叶轮不平衡情况下的载荷特性及变化规律。其次,考虑不平衡周期载荷的频率随机组转速变化的特点,提出了一种谐振频率自适应于叶轮转速的比例—积分—谐振(PIR)独立变桨控制策略,并阐述了变桨控制器参数设计方法。最后,基于FAST-MATLAB/Simulink风电机组载荷及控制联合仿真平台,仿真比较了机组在叶轮平衡和不平衡两种状况下的载荷特性;并在IEC标准湍流风速下对所提自适应PIR独立变桨控制策略的载荷控制性能进行仿真,且将结果与传统比例—积分和比例—谐振独立变桨控制策略进行比较。结果表明,叶轮不平衡会导致风电机组产生频率变化的不平衡周期载荷,且相对传统控制策略所提自适应PIR独立变桨控制策略能够更有效地减小不平衡周期载荷。     

Modeling and enhanced control of DFIG under unbalanced grid voltage conditions

This paper presents a mathematical model of a doubly fed induction generator (DFIG) based on stator voltage orientation (SVO) in the positive and negative synchronous reference frames under unbalanced grid voltage conditions. The oscillations of the DFIG electromagnetic torque and the stator active and reactive powers are fully described during grid voltage unbalance. A new rotor current controller implemented in the positive synchronous reference frame is proposed. The controller consists of a proportional integral (PI) regulator and a harmonic resonant (R) compensator tuned at twice the grid frequency. Thus, the positive and negative sequence components of DFIG rotor currents are directly regulated by the PI + R controller without the need of involving positive and negative sequence decomposition, which indeed improves the dynamic performance of DFIG-based wind power generation system during small steady-state and relatively larger transient network unbalances. The theoretical analysis and the feasibility of the proposed unbalanced control scheme are validated by simulation studies on a 1.5-MW wind-turbine driven DFIG system. Compared with conventional single PI current control design, the proposed control scheme results in significant elimination of either DFIG power or torque oscillation under unbalanced grid voltage conditions.