斜槽电机中绕组电感参数的解析计算方法

采用斜槽可以减小电机的齿谐波电压,且可以大幅降低高频的电磁转矩脉动,从而改善电机的性能.由于采用有限元法分析这类电机性能时,计算过程比较复杂,而且比较耗时.因此,提出一种计算斜槽条件下的绕组电感参数的解析方法,基于二维坐标系中的气隙磁动势和磁导概念,利用空间谐波分析方法,计算出各绕组的气隙电感参数.利用所述方法,对比分析了不同斜槽角度对某台同步电机电感参数的影响,并且在一台定子斜一个槽距的同步发电机上进行了实际测试,实测结果验证了该方法的有效性和准确性.     

交流励磁变速恒频发电机谐波同步消除法

目前大容量的交流励磁变速恒频水轮发电机,仍然采用晶闸管换流的交-交变频器提供励磁.由于这种交-交变频器输出电压中含有大量的谐波,导致发电机输出电压质量无法满足实际需求.本文针对采用余弦交点法控制的交-交变频器,通过对输出电压波形的基本结构进行分析,找出谐波的内在规律.并以有源滤波为基础,提出了谐波同步消除方法,与现有的各种有源滤波方法相比,其算法简单、效果明显,即使为发电机提供直流励磁时,也可以达到明显的滤波效果,从而有效提高了发电机输出的电能质量.     

Reduction of higher harmonic sequences in terminal voltage of an AC exciting synchronous generator using magnetically anisotropic slot wedges

This paper describes relationships between characteristics of a magnetically anisotropic slot wedge and voltage higher harmonics in an ac exciting synchronous generator terminal due to permeance ripple caused by an open-slot-type rotor. From the relationships obtained, practical guidelines were formulated for machine designs applying the magnetically anisotropic slot wedge. The results are as follows.

• 1 (1) Equivalent permeability of the magnetically anisotropic slot wedge became isotropic wedge permeability for air-gap flux ripple.
• 2 (2) Two ways were identified to reduce voltage-higher harmonics by using the slot wedges.
• 3 (3) The level of leakage flux passing through the anisotropic slot wedge was determined only by its permeability in the width direction.
• 4 (4) Effectiveness of the magnetic anisotropic slot wedges inserted into the stator slots was verified from experimental results using a model machine of the open- slot-type rotor.

     

MICROPROCESSOR BASED NONLINEAR EXCITATION CONTROLLER FOR SYNCHRONOUS MACHINES

ABSTRACT

The synchronous machines in power systems have the excitation systems of field winding to improve the transient stability of power systems. The synchronous machines are nonlinear systems, however, the excitation systems have been designed based on linearized systems, because the stability analysis of nonlinear systems is difficult and the generalized control method of nonlinear systems has not been developed yet.

This paper proposes a nonlinear excitation controller for synchronous machines in power systems. For the sake of simplification of the nonlinear state feedback control, this paper considers both the transient stability and the suppression of the rotor swings in transient conditions. The effect of the automatic voltage regulator (AVR) for the synchronous generator is not discussed here. This controller is designed based on Lyapunov's direct method that can directly judge the stability of nonlinear systems. The usefulness and validity of the proposed excitation controller are confirmed by numerical simulations and experiments. The microprocessor based generator excitation system that consists of a nonlinear controller, state variable detector, and PWM inverter, is constructed. The nonlinear excitation controller can improve the transient stability of synchronous machines.     

电网畸变下基于改进DSSOGI-FLL同步信号提取方法

为了满足在不对称、直流分量及谐波畸变等情况下同步信号的提取需求,三相电压需要准确地提取出电压信号的正负序分量、幅值和基波频率。基于DSOGI-FLL的方法可实现电压在不对称和畸变下同步信号的提取。但当电压跌落深大大、直流分量和多次谐波影响下,DSOGI-FLL方法无法实现同步信号的准确提取,使其追踪的波形波动比较大,并降低了追踪速度。文章对SOGI结构进行改进,使其在SOGI的基础上增加求差节点和自适应滤波器,提出了基于改进DSSOGI-FLL的同步信号提取方法,该方法在电压跌落深度大、直流分量和多次谐波影响下能够准确、快速提取出正负序分量、相位和频率等信息。仿真分析验证了改进方法的准确性和有效性。     

Investigation of harmonic currents and power factor on power rectifier circuits with nonequi-PWM and equi-PWM control (inductive load)

Lately, on the power rectifier circuit with semiconductor switching device, PWM control is generally employed for the purposes of reducing the harmonic currents on the dc side and improving the power factor of fundamental wave. In this case, the analysis of the current waveform becomes fairly complex. However, we express the PWM controlled voltage waveform by the step function, and can easily analyze the current waveform. We reported formerly some results of analysis about the waveform and harmonics of the current. In this paper, on the power rectifier circuit to which the nonequi-PWM and equi-PWM control are applied, we exactly calculate the harmonic currents on the dc and ac side, and the power factor by the use of the above analytical results. The characteristics of both control methods are compared on condition that each controlled factor of the load voltage is equal. These results are shown in the calculated charts. The following items can be seen from these charts on the power rectifier circuit: (1) The nonequi-PWM control can let the harmonic currents on the dc side decrease more than the equi-PWM control. But on the contrary, the harmonic currents on the ac side increase. Consequently, when the nonequi-PWM control is applied, the total power factor decreases by the increase of distortion factor of the current on the ac side. (2) The difference between the harmonic currents on the dc and ac side to both of the nonequi-PWM and equi-PWM control increases with the increase of controlled factor of the load voltage. © 1999 Scripta Technica, Electr Eng Jpn, 129(4): 117–125, 1999     

Induced voltage harmonic reduction of PM cylindrical machines

Typically, permanent magnet (PM) machines with surface-mounted magnets have trapezoidal induced voltage waveforms with high harmonic content that can adversely affect torque pulsations, noise, and efficiency. A simple methodology for reducing these harmonics by selecting the appropriate magnet shape and dimensions has been introduced previously by the authors (see IEEE Proc. PES 1989 Summer Mtg.). For illustrative purposes, however, the method used a simplified analytical model of the magnetic circuit, ignoring important factors such as curvature and magnet leakage. The authors presently apply the proposed methodology to cylindrical machines using a more precise model. The results, showing the potential for reducing induced-voltage harmonics by using a double-magnet per pole configuration, have been verified by comparison with results obtained from finite element analysis     

Multipolar permanent-magnet synchronous generators intended for wind power plants

The analytical method of calculating two-dimensional magnetic fields in the active section of permanent-magnet synchronous electrical rotating machines, as applied to their use in the wind energy industry, has been developed. The analytical relationships for calculating distribution of two-dimensional magnetic fields and determining output parameters with due regard for geometry of the active section, the number of pairs of poles, and magnetic characteristics of materials have been obtained. The criteria dependences needed for calculating the electromotive force and main inductive reactance of permanent-magnet synchronous electric machines, with consideration for the geometry of a machine and electrophysical properties of materials being used, have been derived. The procedure of evaluating parameters of permanent-magnet synchronous generators for large-size wind power plants is presented.     

直流入侵三相三柱变压器励磁电流及谐波计算

直流输电系统单极运行时一大地为直流电流的回路,导致大地电位相对于无限远处升高。直流电流通过两个Y0连接的变压器中性点侵入电力系统,故针对三相三柱变压器直流入侵情况建立了直流入侵下的三相三柱变压器的电路模型和相应的方程,结合三柱磁路的麦克斯韦方程和非线性的B—H曲线方程,利用数字迭代法,在MATLAB环境下编程计算了三相三柱变压器直流入侵下的变压器励磁电流和谐波特征。结果表明直流入侵三相三柱变压器下并无磁通的偏移,励磁电流波形亦无畸变,但波形总体沿纵轴方向平移,平移大小为入侵直流电流的大小,励磁电流增加了直流分量,这将增加电路的电阻性热损耗,其它次谐波没有变化,结论为直流入侵三相三柱变压器没有直流偏磁现象。这与文[7]的试验结果完全一致,从计算上验证了试验结果。     

Power system applications for PASC converter systems

This paper shows, using EMTP computer simulations, some preliminary results of applying pulse amplitude synthesis and control (PASC) technology to single-source voltage converter systems. The method can be applied to any single terminal pair source with appropriate modifications in power extraction interface and computer control program to match source and load impedance characteristics. The PASC realization as discussed employs banks of transformers, one bank per phase, in which the primaries are connected in parallel through a switch matrix to the DC source. Two opposite polarity primaries per transformer are pulsed alternatively in time to produce an oscillatory sinusoidal output waveform. PASC conversion system capabilities to produce both leading and lagging power factor power output in single-phase and three-phase Δ or Y configurations are illustrated. EMTP simulations are used to demonstrate the converter capabilities. Also included are discussions regarding harmonics and potential control strategies to adapt the converter to an application or to minimize harmonics     

永磁体内涡流场对同步电机电枢电流的影响

从永磁同步电机结构的实际出发,利用有限元法进行了磁场模拟和计算,分析了在端电压不变的条件下,由于永磁体内涡流产生的磁场和电枢电流产生的变化磁场的相互作用,电枢电流产生非正弦的变化,并且画出了电流的畸变波形。通过简化实验测量出的电流波形证明了计算的正确性。最后分析和讨论了电枢电流变化对电机性能的影响。     

Impact of under-excitation limit control on power system dynamicperformance

Several control functions, in addition to terminal voltage control, are performed by the excitation systems of the synchronous machines in a power plant. The under-excitation limit (UEL) is one of these. In this paper, the authors deal with the effect of such control on the dynamic performance of power systems. Certain simulation results properly characterize UEL action which, depending on the nature and severity of the contingency, can be relatively fast. Their objective is to encourage representation of the under-excitation limit control function in synchronous generator AVR modeling for power system dynamic studies. Essentially, the control acts by precluding excessively binder-excited conditions. In practice, it is applied to prevent both operation beyond the steady-state stability limit and the large magnetic losses produced by leakage fluxes in stator winding end-of-turns during machine operation with very small field circuit excitation     

抑制分数槽永磁电机轴电压定子斜槽法

特定极槽配合的分数槽永磁电机在空载情况下会产生固有轴电压,对轴承有着不可忽视的危害,同时对电机运行的稳定性及安全性也会造成极大的影响。斜槽作为电机性能优化的常用方法,对谐波的削弱也有着很好的效果,故可以采用定子斜槽法来削弱永磁电机空载轴电压的主要谐波。首先,基于磁路原理和法拉第电磁感应定律,推导出考虑斜槽时的分数槽永磁电机空载轴电压的解析模型,分析轴电压的主要谐波成分与斜槽数的关系,给出可使轴电压得到削弱的最佳斜槽数,然后利用二维有限元法分析了不同斜槽度下的4台分数槽永磁电机的空载轴电压,结果证明了解析分析的正确性和有效性。     

Methods of Evaluation of Harmonic Levels in Industrial Plant Distribution Systems

Techniques for analyzing and evaluating the harmonic levels in an industrial facility's electrical distribution system are presented. The various system models and types of harmonic source representation are described. A harmonic evaluation should be performed when a new industrial facility will include sources of harmonics or when the addition of harmonics injecting equipment is being considered. Cogenerators and variable-speed ac induction motor drives are examples of sources of harmonics that are growing in size and number. The methods described utilize a harmonics load flow program based on the direct solution of the impedance matrix at each harmonic frequency. The program includes detailed models of transformers, lines, loads, and generators. It also allows the specification of the harmonic sources by either ac/dc converter parameters or by sampled data of the current or voltage waveform. Results from the analysis of two typical distribution systems in large industrial plants are presented. This analysis illustrates some of the problems that may be encountered and gives recommendations for solutions to these problems.     

Input Power Factor of AC to AC Power Converters

AC to ac power converters are static systems using solid-state switching devices that directly convert ac power of a given frequency to ac power of some desired frequency. They are used to link ac power systems of different frequencies, to provide variable power frequency supplies for ac motor drives, and to generate constant frequency power from the output of variable-speed ac generators. The power conversion process requires the construction of output voltage waveforms, with the required frequency and amplitude, from the ac supply voltages given. The method of output waveform construction determines the input power factor of the ac to ac converter. The practical methods of output waveform construction are summarized and their effects on the input power factor are examined. The relationships between the output and input phase angles for differently controlled ac to ac converters are presented in graphical forms. It is shown that the input power factor of an ac to ac converter can be varied or kept at unity, without the use of passive reactive components, and independently of the output load.     

Identification of machine parameters of a synchronous motor

This paper presents a method for estimating the machine parameters of a synchronous motor. The presented method is equally applicable for a wound field synchronous motor, synchronous reluctance motor, or permanent magnet (PM) synchronous motor, both the interior and surface-mount types. The method works particularly well for machines having a significant amount of space harmonics, such as synchronous reluctance and interior PM (IPM) machines, where the harmonics are predominantly the slot harmonics. It is also well suited for surface PM machines operating under saturation, where the harmonics are saturation-induced. The presence of these harmonics makes the parameter identification difficult. Most of the methods presented so far in the literature have failed to properly identify machine parameters in the presence of space harmonics. In this paper, the machine parameters, identified by using a proposed algorithm, are compared with the finite element and the experimental results to demonstrate the effectiveness of the presented method. Both interior PM and surface PM machines are considered.     

Simplified quasi‐Z source indirect matrix converter

Conventional matrix converters have a limited voltage gain less than 0.866 and also require many power switches and additional input filter that ensures a low input current harmonics to the grid. Quasi‐Z source (qZS) indirect matrix converter can provide high voltage gain and ensure a sinusoidal input current without additional input filter, which requires 12 power switches in rectifier stage. In this paper, a simplified qZS indirect matrix converter is proposed to overcome aforementioned limitations and achieve (1) higher voltage gain than 0.866, (2) less power switches, and (3) LC‐filter function integrated in qZS network to avoid additional filter. The new converter's operating principle and equivalent circuits are analyzed, and the modulation method is presented. The input current closed‐loop control is employed to implement sinusoidal input current waveform even though the proposed converter has less power switches and without extra input filter. A test bench is used to verify the simplified qZS indirect matrix converter and control methods. Simulation and experimental results identically validate the proposed converter system with wide voltage gain range and low input current harmonics. Copyright © 2014 John Wiley & Sons, Ltd.     

交直流同时供电同步发电机的建模

独立交直流同时供电系统被广泛应用在车辆、舰船和飞机等需要同时提供交流电和直流电的场合。在这些电源体积重量受限制的场合, 交直流同时供电同步发电机有特殊的优势。为了提供高品质的电力, 电源的交流电压波形畸变率和直流电压纹波倍受关注, 但其精确计算比较困难。本文使用多回路方法建立了交直流同时供电独立系统的数学模型, 对磁场谐波的作用进行了比较精确的计算。文中对整流桥和自动励磁调节器（ＡＶＲ） 的模型也作了介绍。本文的结果与实验比较, 证明了模型的正确性     

多绕组电机模型的Matlab／SimPowerSystem实现

为满足重量、体积、谐波等方面的特殊要求,独立电力系统常采用交直流多绕组发电机、多相电动机等特种电机。这使得系统的仿真分析与陆用广域电力系统相比差异较大。基于MATLAB/SimPowerSystem,本文提出了一种多绕组发电机的三相发电机等值模型。通过在普通三相发电机基础上增加磁耦合,该模型能够实现多绕组发电机的模拟。与其他实现方法相比,所提出的方法能够充分利用现有仿真算法,可方便地实现独立电力系统的时域仿真。     

交-交变频器谐波消除方法的探讨

随着电力电子技术的发展,交-交变频器的应用愈加广泛。在交-交变频器输出的电压波形中含有大量的谐波,为有效地消除谐波的不利影响,采用余弦交点法控制的交-交变频器,通过对输出电压波形的基本结构进行分析,找出谐波的内在规律,提出了谐波同步消除方法,谐波同步消除方法属于有源滤波,利用其特有的谐波分析方法控制谐波电源的输出补偿电压,补偿电压与谐波同时产生,相位相反,从而达到滤波的目的。与现有的其它方法相比,其算法简单、效果明显,更加适用于输出电压频率频繁变化的场合,即使在变频器直流输出时,也可达到明显的滤波效果。