【作者】 李自成；

【导师】 秦忆； 程善美；

【作者基本信息】 华中科技大学 ， 控制理论与控制工程， 2010， 博士

【摘要】 永磁无刷直流电机因具有结构简单、运行效率高、控制简单和维护方便等优点而得到了广泛应用。传统的无刷直流电机一般采用三相六状态120°导通方式,需要位置传感器在一个电周期内检测到六个关键的转子位置信号以便对三相绕组进行换相控制。然而,位置传感器增大了电机的成本和体积,易受外界信号干扰,降低了系统的可靠性,因此对无位置传感器无刷直流电机控制技术的研究具有重要的理论意义和实用价值。本文以永磁无刷直流电机的无位置传感器控制为研究内容,针对在无位置传感器条件下的无刷直流电机控制的几个关键问题,即转子位置辨识方法、PWM控制策略、电机起动控制方法、转子位置辨识误差及其补偿分析、转矩脉动抑制策略等进行了较为系统和深入的理论分析、仿真和实验研究。反电动势法因原理简单、方法可靠等优点而成为转子位置检测的主要方法。本文在分析传统的反电动势过零检测需要虚拟电机绕组中点方法的基础上,提出了改进的相反电动势转子位置辨识理论。该方法抛弃了传统的反电动势硬件检测原理,只通过检测无刷直流电机任意两路线电压,经软件实时计算后,就可以得到未导通相反电动势的过零点。该方法结构简单、不需要构造虚拟的电机中点和信号深度滤波电路,具有简易性和可靠性等优点。在对无刷直流电机反电动势波形分析的基础上,提出了一种利用线反电动势过零原理来获得转子位置的新方法。该方法通过波形定性分析和傅立叶级数定量推导,均得出线反电动势的过零点就是对应的电子换相点这一结论。对于反电动势波形为任意平顶宽度的梯形波或正弦波,只要三相反电动势波形对称,该方法均适用于转子位置的估算。在此基础上,为减小对电机参数的依赖,提出了一种简化实用的线反电动势法来估算转子位置。该方法只依赖于电机定子电阻,并对定子电阻参数不敏感,无需30°相位延迟和上一次换相信息,具有理论和工程应用价值。分析和比较了无刷直流电机两两导通控制的八种PWM调制方式。通过对各种PWM方式下非换相期间非导通相电流续流情况进行的理论推导,分别得到与上述转子位置辨识方法各自对应的PWM调制方式。电机起动控制问题是无位置传感器控制技术的另一难点。本文基于定子铁心饱和法原理,提出了一种新的起动控制方法:即利用两两导通和三三导通得到的12个电压矢量脉冲施加到定子端,并通过检测各相定子电流峰值来判断定子电感的变化,进而得到转子初始位置所在的30°区间,再通过施加特定的电压矢量将转子精确地定位到换相位置。在此基础上,通过升压升频原理顺序起动电机,一旦检测到线反电动势过零,即可切换到无位置传感器控制方式。研究表明,这种方法电机起动可靠,易于工程实现。详细分析了电机参数变化、电压电流采样误差、滤波电路相位延迟对转子位置辨识误差带来的影响。提出了一种利用最小二乘法原理来拟合线性函数的方法进行相位延迟开环补偿,并根据反电动势波形的对称性提出了一种转子位置误差闭环校正方法。仿真和实验结果表明了该方法的实用性。转矩脉动是无刷直流电机两两导通方式固有的缺点。在无位置传感器控制下,由于转子位置辨识的误差,转矩脉动有可能进一步增大。本文分析了相反电动势平顶宽度、转子位置估算误差和换相期间非换相相电流畸变等因素对转矩脉动的影响后,提出了采用定子电流预测控制方法来抑制无刷直流电机转矩脉动。构建了以dsPIC30F6010为核心的系统实验平台,在此实验平台上进行了无刷直流电机无位置传感器控制系统性能实验,并与有位置传感器控制实验结果进行了对比,实验结果验证了本文提出的无位置传感器控制策略的正确性和可行性。更多还原

【Abstract】 Permanent magnet brushless DC motors (BLDCM) have been widely used due to their simple structure, high efficiency, ease of control, and low maintenance. When using three-phase six-step 120 degree commutation for tranditional BLDCM, position sensors are necessary to sense rotor position information for proper commutation. However, the drawbacks of rotor position sensors in the cost, volume and reliability limit the application of BLDCM. The research on sensorless BLDCM drives has important theoretical significance and practical value. In this thesis, a systematic and in-depth theoretical analysis, simulation and experimental study on several key technologies such as rotor position identification methods, PWM control strategies, motor start-up control algorithms, estimation error compensation, and torque ripple minimization schemes are performed for sensorless BLDCM drives.The method based on back electromotive force (EMF) of BLDCM is one of the major approaches for rotor position estimation because of the advantages of simple and reliable detection. Based on the analysis of traditional zero-crossing of back EMF detection methods requiring a virtual mid-point of motor windings, an improved phase back EMF sensing rotor position method is proposed. The unexcited phase back EMF signal is indirectly obtained from line voltage calculation instead of traditional hardware sensing method. This method is simple and reliable to implement without the need to sense or reconstruct the motor mid-point and depth filter circuits.A novel scheme of zero-crossing of line back EMF sensing rotor position is presented based on the analysis of back EMF waveforms of BLDCM. By qualitative waveform analysis and quantitative calculation, the conclusion that the zero-crossing of line back EMF is actual commutation point is detailedly proved. For arbitrary flat top width of the trapezoidal wave or sine wave, as long as three phase back EMFs are symmetrical, the proposed method is applied to the rotor position estimation. On this basis, in order to reduce dependence on motor parameters, a simplified rotor position emstimation method of line back EMF is also proposed. This method is only dependent on the stator resistance of motor parameters and has some theoretical and engineering application value because of unrequired phase delay by 30°or the last commutation information.Eight kinds of PWM strategies for BLDCM are analyzed and compared. Through the analysis to the diode freewheeling currents in the unexcited phase on non-commutation period, PWM strategies are obtained corresponding to above rotor position identification methods.How to control motor start-up is another difficult problem for sensorless BLDCM drives. Based on principle of stator core saturation, a new start-up control method is proposed. This method employs 12 voltage vectors injecting the stator sides, and the changes of the stator inductance are obtained by detecting the peak stator current of each phase. Therefore, the 30°range of rotor initial position is determined. And then the rotor position is accurately located in the next commutation position through the injection of particular voltage vector. On this basis, motor starting can be completed through the principle of raising voltage raising frequency. Once the zero-crossing of back EMF is detected, operating mode can be switched to sensorless control mode. Studies have shown that this method make the motor start reliably and is easy to implemente practically. The impact of the motor parameters variation, voltage and current sampling error, phase delay from filter circuits on rotor position identification error is detailedly analyzed.The method of fitting a linear function for open loop phase delay compensation based on a least square method is proposed, and a close loop rotor position error correction method is also presented according to the symmetry of back EMF waveforms. Simulation and experimental results show that above methods have practical value. Torque ripple is an inherent shortcoming of BLDCM drives. In sensorless control, torque ripple may be further increased due to rotor position identification errors. The impact of the phase back EMF flat top width, rotor position estimation error, non-commutation phase current distortion on torque ripple is detailedly analyzed. Afterward, a stator current predictive control method is proposed to suppress torque ripple of BLDCM.A system experimental test bed based on a dsPIC30F6010 DSP processor is established for proposed sensorless control schemes of BLDCM. Sensorless control experimental results are compared with test results of position sensor control under the same conditions. Experimental results reveal the effectiveness of the proposed schemes.更多还原