Improvements in direct torque control of induction motors
Improvements in direct torque control of induction motors
复制标题
感应电机直接扭矩控制的改进
DOI：
10.5821/dissertation-2117-93629
复制
发表时间：
2001
影响因子：
6.7
通讯作者：
Antoni Arias Pujol
中科院分区：
文献类型：
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作者：
Antoni Arias Pujol
本文主要研究三相笼型异步电动机的速度控制方法，重点研究了直接转矩控制（DTC）的改进技术。经典的直接转矩控制存在固有的缺点，如：由零状态引起的启动问题，对转矩和磁链估计器的强制要求，以及转矩脉动。在经典的直接转矩异步电动机驱动中，整个周期都施加一个电压矢量，这会导致定子电流和电磁转矩在周期早期超过其参考值，造成高转矩纹波。然后依次进行开关循环，其中应用零开关矢量以将电磁转矩减小到参考值。本文提出了一种基于将所选有功状态施加到逆变器上的技术，使其恰好达到转矩和磁通参考值。剩余的开关时间选择一个几乎不会改变转矩和磁通的零状态。因此，必须确定每次开关时间的占空比。通过改变其极值（0到1）之间的占空比，可以对电机施加任何电压。每采样周期的最佳占空比是电磁转矩误差、定子磁链位置和工作点的非线性函数，由电机转速和电磁转矩决定。显然，由于每个工作点都是不同的非线性函数，因此对这种表达式进行建模是极其困难的。因此，本文的重点是实现基于模糊逻辑的占空比控制器，其中每个切换周期确定最优占空比。此外，该模糊控制器是自适应的，可适用于任何感应电动机。设计了定子磁链参考最优控制器，不仅可以实现较小的转矩脉动，还可以降低主电源驱动的无功功耗。这是通过改变定子磁通参考值，参照相应的转矩参考值来实现的。因此，选取的定子磁链参考值应刚好能产生所需转矩，并给出仿真结果，以比较经典直接转矩控制和基于模糊逻辑的直接转矩控制。控制算法已在基于PC/DSP的电路板上实现，便于在软件设计中使用并行性。设计了一个1.5kW的三相感应电机驱动器，并获得了实验数据，验证了仿真结果。
This thesis is mainly devoted to the investigation of speed control methods for three phase cage induction motors with particular emphasis being given to Direct Torque Control (DTC) improved techniques.Classical Direct Torque Control has inherent disadvantages such as: problems during starting resulting from the null states, the compulsory requirement of torque and flux estimators, and torque ripple. In the classical DTC induction motor drive a voltage vector is applied for the entire period, and this causes the stator current and electromagnetic torque exceeds its reference value early during the cycle, causing a high torque ripple. Switching cycles then follows this, in which the zero switching vectors are applied in order to reduce the electromagnetic torque to reference value. This thesis suggests a technique based on applying to the inverter the selected active states just enough time to achieve the torque and flux references values. The rest of the switching period a null state is selected which won't almost change both the torque and the flux. Therefore, a duty ratio has to be determined each switching time. By means of varying the duty ratio between its extreme values (0 up to 1) it is possible to apply any voltage to the motor. The optimum duty ratio per sampling period is a non-linear function of the electromagnetic torque error, the stator flux position and the working point, which is determined by the motor speed and the electromagnetic torque. It is obvious that it is extremely difficult to model such an expression since it is a different non-linear function per working point. Therefore, this thesis is focused on performing a fuzzy-logic-based duty-ratio controller, where the optimum duty ratio is determined every switching period. Additionally, this Fuzzy Controller is adaptive and may be applied to any induction motor.A stator flux reference optimum controller is also designed, which not only helps to achieve a smaller torque ripple, but also reduces the reactive power consumption of the drive taken from the main supply. This is achieved by changing the stator flux reference value with reference being made to the correspondent torque reference value. Therefore, the stator flux reference value chosen is to be just of sufficient value to produce the desired torque Simulated results are shown in order to compare the classical DTC and the Fuzzy Logic based DTC.The control algorithms have been implemented on a PC/DSP based board that facilitates the use of parallelism in software design. A 1.5kW, three-phase induction motor drive has been designed and experimental data obtained from it in order to verify the results achieved by simulation.