电气专业毕设英文文献(格式已修改)

本科毕业设计
外文文献及译文
文献题目：Direct Torque Control of Induction Motors
Utilizing Three-Level Voltage Source Inverters 文献作者： Xavier del Toro Garcia, Antoni Arias, Marcel G.
Jayne and Phil A. Witting
文献来源： IEEE Trans. Ind. Electron, vol. 51，No. 4，pp.
744–757
发表日期：2004年8月
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翻译日期：
英文原文：
Direct Torque Control of Induction Motors Utilizing Three-Level Voltage Source Inverters Xavier del Toro Garcia, Antoni Arias, Marcel G. Jayne,
and Phil A. Witting
Abstract—A new control strategy for induction motors based on direct torque control is presented which employs a three-level inverter instead of the standard two-level inverter. The controller is designed to achieve a torque ripple reduction by taking advantage of the increase in the number of inverter states available in a three-level inverter. The harmonic distortion in the stator currents and the switching frequency of the semi-conductor devices are also reduced in the new control system presented.
Index Terms—Induction motor drives, three-level converter, torque control.
I. INTRODUCTION
The standard voltage source inverter (VSI) traditionally used in electrical drive systems is the two-level VSI, which unfortunately has a number of inherent limitations. For example, the maximum voltage that can be supported by the semiconductor switching devices in the VSI limits the maximum value of dc-link voltage. Furthermore, the output voltages and currents from the VSI can contain high harmonic distortion.
The output voltage waveforms can also contain large values of dV/dt, which contribute to the degradation of the machine windings insulation and bearings, and also produce considerable electromag-netic interference during operation. New multilevel VSI topologies,however, can considerably reduce many of these limitations [1].
The most commonly used multilevel topology is the three-level neutral point clamped (NPC) VSI[2]. This type of VSI has advantages over the standard two-level VSI, such as a greater number of levels in the output voltage waveforms, less harmonic distortion, and lower switching frequencies.
Direct torque control (DTC) has emerged to become a possible alternative to the well-known vector control strategies for induction motor control systems [3], [4]. Although considerable research has been made into the two-level topologies associated with this method of control, the amount of research carried out to date into DTC systems employing multilevel topologies is still rather limited. The major advantage of the three-level VSI topology when applied to DTC is the increase in the number of voltage vectors available. This means the number of possibilities in the vector selection process is greatly increased and leads to a more accurate control system, which can result in a reduction of the torque and flux ripples. This is of course achieved at the expense of an increase in the complexity of the vector selection process. Although several authors have recently proposed the implementation of DTC utilizing this higher-level topology, their approaches are based on the use of more complex vector selection tables combined with modulation techniques based on analytical methods which have machine parameter dependency[5] [6]. A different approach is a selection table based on the concept of virtual vectors [7]. These new methods considerably increase
the complexity of the control strategy when compared to the classical DTC system[3], and they cannot be extended to different multilevel topologies with a higher number of levels because of the table selection method adopted.
Fig. 1. Schematic diagram of the new controller.
This paper describes a controller based on DTC that can be applied to different multilevel VSI topologies. It avoids the use of hysteresis comparators and look-up tables, and it does not require the knowledge of the motor model in the control system except for the inherent estimator as in the classical DTC system.
II. NEW CONTROLLER
The general structure of the new controller is shown in Fig. 1. This novel controller generates a reference stator voltage vector (u∗s) in α–βcoordinates (usα,usβ) according to the DTC basic principle, rather than
using the VSI state look-up table as used in classical DTC. This approach adopted is close to the DTC with space vector modulation scheme with closed-loop flux and torque control, and stator flux oriented control [4]. More recently, other similar methods based on the predictive torque control concept have appeared [8] [9].
The inputs to the controller are the stator flux error (eψs),the torque error (eΓe) and, additionally, the stator flux angular speed (ωB),which is obtained to incorporate the back electromotive force (BEMF) term to improve the torque response at different operating points. The reference voltage vector calculated by the controller can be synthesized using different techniques with different degrees of complexity, such as choosing the nearest vector available or using modulation techniques [9]–[11]. This controller can be applied to any topology because the type of VSI only affects the way the reference voltage vector has to be synthesized.
The controller is based on the principle that the desired decoupled control of the stator flux modulus and torque is achieved by the controller acting on the respective radial and tangential components of the stator flux vector (ψB). The variation of the stator flux vector is approximately proportional to the voltage vector applied to the motor. Therefore, when calculating the reference voltage vector (in x–y coordinates fixed to the stator flux vector), the tangential component (u∗sy) will depend on the torque error (eΓe), whereas the radial component (u∗sx) will depend on the stator flux error (eψB). As can be seen in Fig. 1, two closed-loop proportional controllers are employed to generate the components of the reference voltage vector. Kψs and KΓe are the proportional gains of these controllers and have been tuned experimentally to achieve a minimum torque and flux ripple. Their initial values can be set to approximately the
ratio between nominal stator voltage and nominal stator flux modulus for Kψs, and the ratio between nominal stator voltage and nominal stator flux
Fig. 2. Torque response characteristics for classical DTC with a two-level VSI. Operating point: Γ=7.4 Nm. ωm = 200 r/min.
modulus for Kψs, and the ratio between nominal stator voltage and nominal torque for KΓe.
It can be seen in Fig. 1 that a feedforward action that compensates the BEMF term is added to the output of the torque controller to calculate the tangential component of the reference voltage vector. The BEMF term is obtained by multiplying the nominal stator flux modulus (ψsn) and the stator flux angular speed (ωs), which is previously filtered by means of a low-pass filter.
The reference vector in x–y coordinates is then transformed to α–β fixed coordinates. The novel controller developed synthesizes the reference voltage by choosing the nearest VSI vector to the reference voltage vector. The nearest vector is found by means of calculating the minimum distance of the voltage vectors that can be delivered by the VSI
to the reference voltage vector. This calculation involves evaluating the modulus of the difference between vectors. The complexity of the system presented is increased when compared to classical DTC due to the use of proportional controllers instead of hysteresis comparators, the x–y to α–β coordinate transformation and the method to find the nearest vector. Finally, it should be noted that the balance of the neutral point voltage is one of the main issues associated with the control of the three-level NPC VSI [11]. In the novel controller the balance is achieved by selecting the appropriate configuration among the redundant possibilities that exist for some of the vectors delivered by the VSI.
III. EXPERIMENTAL RESULTS
The practical implementation of the new controller is based on a dSpace DS1103 board that performs the control tasks. This board contains a PowerPC and a DSP. A three-level NPC VSI utilizing IGBT devices is used to supply a 380/220-V four-pole 1.1-kW cage-rotor induction motor. The dc-link voltage employed is 200 V. Figs. 2 and3 show the steady-state torque responses at 200 r/min and nominal torque conditions (7.4 Nm) for the classical DTC strategy with a two-level VSI and the new control system employing a three-level VSI described in this paper, respectively. The sample time used was 100 µs in both systems.
To assess the performance of both systems, the torque standard deviation (σΓe) is calculated for the torque ripple. Additionally, the flux standard deviation (σψs), the total harmonic distortion (THD) of the stator current THD_iS, and the mean switching frequency in the semiconductor devices (FSw) are calculated for both systems. From the experimental
results shown in Figs. 2 and 3, it is apparent that the torque ripple for the new system utilizing a three-level VSI is considerably reduced. The result
Fig. 3. Torque response characteristics for the new controller with a three-level VSI. Operating point: Γ=7.4 Nm. ωm = 200 r/min.
of the VSI switches in the proposed system are both reduced by more than 50%. The switching frequency is reduced due to the utilization of a three-level VSI. In this type of VSI, some transitions between the three possible states of a leg do not involve the commutation of all the switches.
IV. CONCLUSION
A new controller based on the DTC principle is presented, and it is shown that the controller can be easily implemented in a three-level VSI drive system. The new controller does not involve the use of any motor model parameters, as in classical DTC, and therefore, the control system
is more robust compared to other methods that incorporate motor parameters. The experimental results obtained for the new DTC scheme employing a three-level VSI illustrate a considerable reduction in torque ripple, flux ripple, harmonic distortion in the stato currents,and switching frequency when compared to existing classic DTCsystems utilizing the two-level VSI.
REFERENCES
[1] J. Rodriguez, J. Lai, and F. Z. Peng, “Multilevel inverters: A survey of topologies, controls, and applications,” IEEE Trans. Ind. Electron.,vol. 49, no. 4, pp. 724–738, Aug. 2002.
[2] A. Nabae, I. Takahashi, and H. Akagi, “A new neutral-point-clamped PWM inv erter,” IEEE Trans. Ind. Appl., vol. IA-17, no. 5, pp. 518–523,Sep./Oct. 1981.
[3] I. Takahashi and T. Noguchi, “A new quick-response and high-efficiency control strategy of an induction motor,” IEEE Trans. Ind. Appl.,vol. IA-22, no. 5, pp. 820–827, Sep./Oct. 1986.
[4] G. Buja and M. P. Kazmierkowski, “Direct torque control of PWM inverter-fed AC motors—A survey,” IEEE Trans. Ind. Electron., vol. 51,no. 4, pp. 744–757, Aug. 2004.
[5] K.-B. Lee, J.-H. Song, I. Choy, and J.-Y. Yoo, “Torque ripple reduction in DTC of induction motor driven by three-level inverter with low switching frequency,” IEEE Trans. Power Electron., vol. 17, no. 2, pp. 255–264,Mar. 2002.
[6] G. Brando and R. Rizzo, “An optimized algorithm for torque oscillation reduction in DTC-induction motor drives using 3-level NPC inverter,” in Proc. IEEE ISIE, Ajaccio, France, Jun. 2004, pp. 1215–1220.
[7] Z. Tan, Y. Li, and M. Li, “A direct torque control of induction motor based on three-level NPC inverter,” in Proc. IEEE PESC, Vancouver, BC, Canada, Jun. 2001, pp. 1435–1439.
[8] P. Correa, M. Pacas, and J. Rodríguez, “Predictive torque control for inverter-fed induction machines,” IEEE Trans. Ind. Electron., vol. 54,no. 2, pp. 1073–1079, Apr. 2007.
[9] M. Nemec, D. Nedeljkovic, and V. Ambroic, “Predictive torque control of induction machines using immediate flux control,” IEEE Trans. Ind. Electron., vol. 54, no. 4, pp. 2009–2017, Aug. 2007.
[10] A. K. Gupta and A. M. Khambadkone, “A space vector PWM scheme for multilevel inverters based on two-l evel space vector PWM,” IEEE Trans. Ind. Electron., vol. 53, no. 5, pp. 1631–1639, Oct. 2006.
[11] J. Pou et al., “Fast-processing modulation strategy for the neutral-point-clamped converter with total elimination of low-frequency voltage oscillations in t he neutral point,” IEEE Trans. Ind. Electron., vol. 54, no. 4, pp. 2288–2294, Aug. 2007.
中文译文：
基于三电平电压型逆变器的异步电机的直接
转矩控制
摘要：一种基于直接转矩控制的电动机的新型控制方式，其采用了三电平逆变器，而非标准的两个电平逆变器。

这种控制系统通过增加逆变器的数量亦即采用三电平逆变器，从而实现降低转矩波动的目的。

在新的控制系统中，定子电流的高次谐波失真现象和半导体开关器件的开关频率也相应减少。

关键词：异步电机驱动，三电平变换器，转矩控制。

一绪论
标准电压源逆变器（VSI），传统上用在电机驱动系统的是双电平VSI，但是不幸的是其具有一些固有的局限性。

举例来说，因为其最大电压即是半导体开关器件所能承受的最大电压，从而影响了其直流输出电压的品质。

此外，从VSI输出的电压和电流，可能包含高次谐波，从而产生失真现象。

而且输出的电压波形，还可能包含较大的dv/dt，即电压波动较大，这加速了电机绕组绝缘破坏和轴承的磨损，同时在操作中也会产生相当大的电磁干扰。

本文所介绍的这种新型多层次的VSI的拓扑结构，可以很大程度上弥补这方面的不足。

最常用的多层次拓扑结构，是三个级别中性点钳位（NPC）VSI。

这种类型的VSI比标准的两个级别VSI更具有优势，如在控制输出电压波形，减少谐波失真等方面，同时在降低开关频率方面具有更好的表现。

直接转矩控制（ DTC ）的出现已经可能替代著名的矢量控制策略成为新的主流感应电机控制系统。

虽然在两个层次的拓扑结构及
与此相关联的方法控制上已经有相当多的研究。

大量的研究表明，迄今为止所研究的DTC系统，在运用于多层次的拓扑结构方面仍相当有限。

利用3个级别的VSI拓扑结构的先进性在于，它适用于接受数目增加的电压矢量。

这意味着，在载体的选择程序中有多种可能性，并且极大地增加控制系统的准确性。

当然，这是在牺牲在复杂的载体选择过程减少扭矩和通量中抖动的增加。

虽然经过几次的改进，最近作者又提出了利用这种更高层次的拓扑结构实施对接受数目增加的电压矢量，其办法是基于使用更复杂的载体选型表合并与调制技术为基础的分析方法，其中有机参数的依赖。

图 1新型控制器示意图
本文介绍了一种基于直接转矩控制的控制器，可以适用于不同的多电平逆变器拓扑。

它避免了滞环比较器和查找表的使用，它不需要电机模型的知识控制系统中除了固有的估计在传统直接转矩控制系统。

二 新型控制器
一般结构的新型控制器如图.1所示 ，这新型控制器生成一个参考定子电压矢量（ s *）在α - β坐标系( us us ,)根据有关DTC 的基本原则， 而不是使用国家标准的查找表中使用的经典DTC 。

采用的这方法是对空间矢量接近 DTC 有关闭-环流出和转力矩控制的调音方案和固定子流出定向控制。

最近，其他类似根据预测转矩控制的方法已经出现。

控制器的输入是定子流出误差 (e e ), 转力矩误差 (e e ) 和定子熔化角速度 (s ),用以获得合并后面的电动势 (BEMF)在不同的营运点来改善转力矩回应。

参考电压矢量计算像是选择最接近的载体提供或使用调制技术，由控制器可合成采用不同技术与不同程度的复杂性。

参考电压矢量计算 。

控制器可应用于任何拓扑，因为所有类型仅仅影响参考电压矢量要合成。

控制器根据以下原则，即理想的解耦控制定子磁场模量和扭矩达到了控制器代理对各自的径向和切向组件定子磁通矢量（s ）。

由图. 2可知变异的定子磁通矢量与电压矢量近似成正比。

力矩响应特性，为经典特性与DTC 的两个层面均具有。

图2 传统两级VSI 直接转矩控制转矩响应特性
运行条件：Γ= 7.4 nm 。

ωm = 200r/min
因此，在计算参考电压矢量（X-Y 坐标定子磁通矢量）和切组件（ U*sy ）将在很大程度上依赖于扭矩误差（e e ） ，而径向分量（ U*sx ）将在很大程度上依赖于定子磁场误差（Eψs ） 。

由图. 1 可以看出，两个闭合回路比例控制器控制生成组件的参考电压矢量。

s 和e 是这些控制器的比例因子，并已通过实验调试，以达到最起码的扭矩和磁通纹波。

其初始值，可设定为定子电压和额定定子磁场模量对s ，及比例与定子额定电压和额定转矩对e 的比率。

由图. 1可以看出，用反馈来弥补BEMF 是增加控制器的输出的扭矩切向组成部分的参考电压矢量。

对BEMF 来说，通过一个低通滤波器过滤得到了成倍的定子磁场模（sn ）和定子磁场角速度（ωs ）。

在X -Y 坐标参考向量转化为α – β修正固定坐标。

新型控制器的发展，参考电压选择最接近所有向量切向参考电压矢量。

用最接近的矢量方式计算最小距离的电压矢量可由所有电压矢量作为参考，这种计算涉及模量之间的差额。

最近提出了系统的复杂度相比传统直接转矩控制的而不是由于迟滞比较器的比例控制器的使用增加，X –Yα–β坐标变换和fi和最近的向量法。

最后，应该指出的是，中性点电压的平衡是一个随着三电平VSI [ 11 ]控制有关的主要问题。

在所有新型控制器中，选择适当配置使之存在的多余的可能，从而使结构矢量达成平衡来实现VSI 的 递送。

三实验结果
新的控制器的实现是基于一个执行控制任务的dSPACE的DS1103板。

这板包含一个PowerPC单元和DSP单元。

三电平逆变器采用IGBT器件，其作用使是供给380／220V四极1.1-kw笼型转子感应电动机。

直流电压是200 V的稳压直流单元。

图2和图3分别显示稳态转矩响应在200 r/min和额定转矩的条件下（7.4 nm），文中所描述的经典的直接转矩控制两电平VSI和新的采用三电平逆变器控制系统的不同转矩状态。

所有系统使用的采样时间均100µs。

采用扭矩标准偏差（σΓE）来计算转矩脉动，从而评估系统的性能。

此外，FLUX的标准偏差（σψS），总谐波失真（THD）的定子电流和thd_is，平均开关频率在半导体器件（FSW）计算系统。

从图2和图3所示的实验结果可以看出，利用三电平逆变器的新系统的电机电磁转矩波动明显大为降低。

图3 新型三电平逆变器控制器的转矩响应特性。

运行条件：Γ= 7.4 nm。

ωm = 200r/min
在该推荐系统中，逆变器中电子器件开关频率均减少50%以上。

随着三电平逆变器利用率的降低，开关频率也随之降低。

这种类型的逆变器中，一条支路的三种可能的状态之间的过渡不不需要所有换向开关都动作。

四结论
基于直接转矩控制原理，这里提出了一种的新型控制系统理论，而且实验表明，该控制系统可以通过一个三电平逆变器驱动系统从而比较容易的实现。

类似传统的直接转矩控制，新的控制器不涉及任何电机模型参数的使用，因此，与其他使用电机参数模型的方法相比，该系统具有较强的鲁棒性。