逆变器驱动电机系统共模电压抑制方法与实验研究

发布时间：2019-01-23 09:16

【摘要】：随着电力电子技术及器件的不断发展,PWM逆变器以其优越的性能在国民生产的各个领域得到广泛应用。逆变器驱动电机系统作为变频调速领域的典型应用,逆变器的控制技术及其对调速系统的影响是该领域的研究热点。传统的PWM调制方法会导致逆变器驱动系统出现较高的共模电压,在电机内部轴承与机壳之间耦合电容等作用下会在产生轴电流,进一步导致电机轴承绝缘油膜击穿造成电机轴的损坏,甚至会向周围辐射电磁波。因此,从本质上认识共模电压的产生机理及其影响因素,找到抑制共模电压的有效方法,提高逆变器驱动系统的整体性能及运行可靠性对变频调速系统的发展至关重要。首先对逆变器驱动电机系统的发展现状及变频调速系统存在的问题进行介绍,深入分析了三相PWM逆变器数学模型以及共模电压形成原因。最常见的逆变器驱动系统是两电平和三电平逆变器,论文从数学模型入手,分别对两种逆变器工作原理进行研究。分析共模电压的产生路径可知,其是由于调制方法中零矢量的选用而产生的。在对逆变器输出波形进行傅里叶分析后发现,共模电压在载波频率处谐波幅值最大,这对抑制共模电压的滤波器设计提供了理论支持。共模电压的抑制方法大体分为硬件类和软件类,硬件类方法主要是增加滤波器或者改变逆变器拓扑;软件类方法主要是改进调制算法和无零矢量控制。首先分析了前馈有源滤波器、无源滤波器及三相四桥臂逆变器等硬件类抑制共模电压的方法;硬件类方法在抑制共模电压上虽然有一定的作用,并且工程应用较多,但硬件类方法需要增加额外设备和系统控制复杂度。接着对随机变延时PWM、不对称NZPWM等软件类方法进行研究,软件类抑制共模电压的方法虽然不需要增加其他的设备,但是计算量大、对控制器的计算能力要求较高。本文在传统模型预测控制的基础上,结合无零矢量控制提出了能够抑制共模电压的模型预测控制(SCMV-MPC)方法。SCMV-MPC只考虑非零矢量,来实现VSI的控制,同时抑制共模电压。传统的PWM调制方法在一个周期内只采用一个矢量进行控制,而SCMP-MPC方法在一个周期内用两个电压矢量来补偿电压状态数的减少;并且所选取的矢量分别作用,可以有效减小负载电流与参考电流的误差。SCMV-MPC方法在将逆变器驱动电机系统的共模电压限制在±Vdc/6的同时获得令人满意的负载电流波形。最后介绍了系统的仿真及实验平台的设计过程,通过理论研究及实物实验,验证了理论及仿真的有效性。
[Abstract]:With the development of power electronics technology and devices, PWM inverters are widely used in various fields of national production for their superior performance. The inverter drive motor system is a typical application in the field of variable frequency speed regulation. The control technology of inverter and its influence on the speed regulation system are the research hotspot in this field. The traditional PWM modulation method will lead to higher common-mode voltage in the inverter drive system, and the shaft current will be generated under the action of the coupling capacitance between the internal bearing and the housing of the motor. Furthermore, the breakdown of the insulating oil film of the motor bearing causes damage to the motor shaft and even radiates electromagnetic waves to the surrounding area. Therefore, it is very important to understand the mechanism of common-mode voltage and its influencing factors, to find an effective method to restrain common-mode voltage, and to improve the overall performance and reliability of inverter drive system. Firstly, the development status of inverter drive motor system and the problems existing in frequency conversion speed regulation system are introduced, and the mathematical model of three-phase PWM inverter and the common mode voltage forming reason are analyzed in depth. The most common inverter drive system is two-level and three-level inverter. By analyzing the generation path of common-mode voltage, we can see that it is caused by the selection of zero vector in modulation method. After Fourier analysis of the output waveform of the inverter, it is found that the harmonic amplitude of the common-mode voltage is the largest at the carrier frequency, which provides theoretical support for the design of the filter to suppress the common-mode voltage. The common mode voltage suppression methods are generally divided into hardware and software, hardware methods are mainly to increase filters or change the inverter topology, and software methods are mainly to improve modulation algorithm and zero vector control. Firstly, the common mode voltage suppression methods of feedforward active filter, passive filter and three-phase four-leg inverter are analyzed. Although the hardware class method has certain function in suppressing common-mode voltage, and it is widely used in engineering, the hardware class method needs to increase the complexity of additional equipment and system control. Then the random variable delay PWM, asymmetric NZPWM and other software methods are studied. Although the common mode voltage suppression methods do not need to add other equipment, but the calculation is large, the controller's computing power is high. Based on the traditional model predictive control (MPC), a model predictive control (SCMV-MPC) method which can suppress common-mode voltage is proposed in combination with zero-free vector control. SCMV-MPC only considers non-zero vectors to realize the control of VSI. At the same time, the common mode voltage is suppressed. The traditional PWM modulation method uses only one vector in a period, while the SCMP-MPC method uses two voltage vectors in a period to compensate for the reduction of the number of voltage states. The error between the load current and the reference current can be effectively reduced by using the selected vectors respectively. The SCMV-MPC method can obtain a satisfactory load current waveform while limiting the common-mode voltage of the inverter-driven motor system to 卤Vdc/6. Finally, the system simulation and the design process of the experimental platform are introduced. The validity of the theory and simulation is verified by theoretical research and physical experiments.
【学位授予单位】：湘潭大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TM464

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