【作者】 孙振川；

【导师】 刘锦波；

【作者基本信息】 山东大学 ， 电力电子与电力传动， 2008， 硕士

【摘要】 直接转矩控制技术在电力机车牵引、汽车工业以及家用电器等工业控制领域得到了广泛的应用。在运动控制系统中,直接转矩控制作为一种新型的交流调速技术,其控制思想新颖、控制结构简单、控制手段直接、转矩响应迅速,正在运动控制领域中发挥着巨大的作用。虽然直接转矩控制的优势是矢量控制所不能实现的,但是直接转矩控制依然存在一系列不能忽视的问题。直接转矩控制采用两点式转矩和磁链滞环控制器,使转矩和磁链被控制在给定值的一定范围以内,这种控制方法不可避免地带来电机输出转矩脉动过大和逆变器开关频率不恒定等问题。直接转矩控制采用定子磁链定向,只用便于测量的定子电阻来估计定子磁链,这样在低速运行时会带来磁链估计的误差。虽然在全速范围内估计定子磁链运用低速时采用的电流-转速模型和高速时采用的电压-电流模型的合成模型,即电压-转速模型,然而两种模型的平滑切换又是一个新的问题。直接转矩控制在基频以下调速的理论和应用已经实现,在基频以上的弱磁调速范围内的理论和应用还需要进一步的研究。为了解决这些问题,本文针对异步电动机在两相静止坐标系下的数学模型,对传统直接转矩控制系统和两种改进的直接转矩控制系统进行了研究。在传统直接转矩控制系统中,详细讨论了定子磁链估计的三种基本模型,设计了定子磁链估计的加权模型,使电机在全速运行的范围内都能够得到准确的定子磁链。针对转矩脉动过大和逆变器开关频率不恒定的问题,本文设计了两种改进的直接转矩控制系统。在基于占空比控制的直接转矩控制系统中,通过对一个采样周期内非零电压矢量作用时间占采样周期的占空比的优化,解决了转矩脉动过大的问题;在一个采样周期内,从非零电压矢量到零电压矢量的转换只有一次,实现了开关频率的恒定。在基于滑模变结构的直接转矩控制系统中,本文设计了转矩和磁链滑模变结构控制器代替传统直接转矩控制系统中的转矩和磁链滞环控制器;运用空间矢量脉宽调制技术,实现了开关频率的恒定。本文把传统直接转矩控制系统和两种改进的直接转矩控制系统扩展到基频以上的弱磁范围内的异步电动机调速系统中,对其进行了相关研究。为了验证上述各种控制系统的正确性和有效性,本文采用Matlab/Simulink仿真软件对其进行了仿真验证。针对传统直接转矩控制系统,对定子磁链估计的加权模型进行了仿真验证。仿真结果表明所设计的定子磁链的加权模型能够在电机运行的全速范围内准确地估计定子磁链。针对基于占空比控制的直接转矩控制系统和基于滑模变结构的直接转矩控制系统,本文分别对负载转矩有扰动和无扰动、给定转速为恒定值和不为恒定值四种情况进行了仿真验证,并分别和传统直接转矩控制系统的仿真结果进行了对比。仿真结果表明,两种改进的直接转矩控制系统均能有效的减小转矩脉动和转速的稳态误差。针对电机运行在基频以上的弱磁调速情形,本文运用三种不同的直接转矩控制方法分别进行了仿真验证。仿真结果表明,两种改进的直接转矩控制系统在弱磁调速范围内依然优于传统直接转矩控制系统,依然能够减小转矩脉动和转速的稳态误差。更多还原

【Abstract】 Direct torque control (DTC) technology has been widely used in electrical locomotive, automotive industry, household appliances and other industrial control areas. In the motion control systems direct torque control, as a new strategy of AC drive, is playing an enormous role in the fields of motion control because of its novel idea, simple structure, and fast dynamic response to torque. Although DTC has many advantages over flux-oriented vector control, there are many needful improvements existed in DTC. DTC adopts two torque and flux hysteresis controllers, which serve to control torque and flux within a certain value of given torque and flux respectively. This control strategy inevitably brings some problems such as undesirable torque ripple and unconstant inverter switching frequency. DTC adopts stator flux orientation and uses stator resistance to estimate stator flux, both of which will bring flux error in low-speed operation. While estimating stator flux within full-speed adopts a compound voltage-speed model composed by current-velocity model at low-speed and voltage-current model at high-speed, the smooth handoff between two models is a problem needed to be solved. DTC under base-frequency has been achieved; however, its theory and application can be extended to above base-frequency realm.In order to solve these problems, this paper presents the traditional DTC system and two improved DTC systems aiming at the mathematical model of asynchronous machine on two-phase standstill axis. In the traditional DTC system, three estimation models of the stator flux are discussed in detail and the weighted model is designed, both of which serve to get precise stator flux in full-speed operation. In order to cope with undesirable torque ripple and unconstant switching frequency this paper designs two improved DTC systems. In the DTC system based on duty cycle control, an optimized duty cycle of a non-zero voltage vector is adopted to solve the problem of large torque ripple. There is only one switching opportunity from the non-zero voltage vector to zero one in a total sample cycle, which realizes the constant inverter switching frequency. In the DTC system based on sliding mode control, this paper designs torque and flux sliding mode controllers to replace the traditional ones, and realizes constant switching frequency by handling SVPWM. This paper extends the traditional DTC and two improved DTC methods to above base-frequency realm.In order to verify the effectiveness of the control systems mentioned above, simulations are made using Matlab/Simulink. A stator flux estimated weighted model is constructed in the traditional DTC system. Simulation shows a good result within all speeds. As for the DTC system based on duty cycle control and the DTC system based on sliding mode control, this paper discusses four instances of the load torque with disturbance and no disturbance, the constant and variable assigned rev. Simulation shows that both improved DTC methods can reduce torque ripple and the steady-state error of rev effectively. For the opptunity above base-frequency, three different DTC methods are utilized. Simulation shows that both improved DTC systems are superior to the traditional one in above base-frequency operation.更多还原