高压变频器长线电缆驱动系统负面效应分析及其对策

发布时间：2018-06-17 06:52

本文选题：高压变频器 + 共模电压　；参考：《西南交通大学》2016年硕士论文

【摘要】：电能的广泛使用,促进了现代社会工业化、信息化的高速发展。电机系统效率的提高,有助于节约电能,与此同时也带来了显著的经济效益。电机主要依靠变频技术来提高电机效率,实现节能。在实际应用中,变频器存在不可忽视的负面效应,主要是变频器产生的共模电压和电机端出现的过电压。目前,变频器主要采用IGBT,这种大功率开关器件上升时间非常短,在如此短的上升时间期间,脉冲电压瞬间从零上升到最高电压或者从最高电压下降到零,由于电机内部高频寄生电容的存在,高频的快速变化的dv/dt作用在电机端时,在电机轴承上会感应出轴电压。当轴电压不断上升,轴承润滑油膜将被击穿,此时会产生放电电流,导致在短时间内电机轴承温度升高,最终损坏,从而破坏整个系统。由于系统中存在着杂散电容,高频的共模电压与电容相互作用,通过电动机机壳、大地和变频器形成共模电流,产生电磁干扰。在石油开采、造纸、采矿业等特殊领域,电动机和变频器由于相距较远,不可避免需在两者之间使用电缆,PWM信号通过电缆输送给电动机,由于PWM高的电压变换率,而且当电缆达到一定长度时,PWM信号可以看成是在电缆上传输的行波,由于电缆的阻抗和电机阻抗不匹配,PWM行波会在电机端发生反射,正向行波和反相行波相互叠加,在电机端出现过电压,此过电压包括加倍的差模电压和共模电压。共模电压的加倍会使电机的负效益成倍增加,差模电压的加倍使得电机的绝缘更容易被破坏。因此,研究变频调速系统在长线电缆传输时所带来的负面效应及对策显得尤为重要。本文首先研究了高压变频驱动系统的理论、拓扑结构,包括整流器、中间直流环节、逆变器,着重分析了高压变频器中的脉波整流器和移相变压器的原理。其次,研究了变频器共模电压产生的机理,得出了逆变器共模电压的产生与其开关状态有关,在此基础上着重研究调制策略对三电平逆变器的共模电压的抑制,研究了三电平逆变器的传统的SPWM、降低共模电压的SPWM和消除共模电压的SPWM,对传统的SVPWM对共模电压的作用进行了研究,提出了消除共模电压改进的策略,并通过仿真验证其正确性。再次,利用传输线理论分析PWM脉冲波在长线电缆上传输的特点,以此分析电机端产生过电压现象的原因,并分析了电缆的分布参数对电机端过电压的影响。最后,研究电机端过电压的抑制措施,研究无源滤波器的设计方法。提出了SHEPWM调制技术和LC滤波器相结合的方法对电机端的过电压进行抑制。研究了SHEPWM的原理、初值的选取、角度的计算。再此基础上利用数学软件MATLAB探讨抑制策略的可行性。
[Abstract]:The wide use of electric energy has promoted the rapid development of modern society industrialization and information technology. The improvement of the efficiency of the motor system helps to save electric energy, and at the same time, it also brings about remarkable economic benefits. The motor mainly depends on the frequency conversion technology to improve the efficiency of the motor and achieve energy saving. In the practical application, the inverter has the negative effect which can not be ignored, mainly the common-mode voltage produced by the inverter and the overvoltage at the motor end. At present, the frequency converter mainly uses IGBT, this kind of high power switch device rise time is very short, in such a short rise time, the pulse voltage instantaneous rise from zero to the maximum voltage, or from the highest voltage to zero, Because of the existence of the high frequency parasitic capacitance in the motor, the high frequency and fast changing dv/dt will induce the shaft voltage on the motor bearing when it acts on the motor end. When the shaft voltage is rising the film of lubricating oil will be broken down and the discharge current will be generated which will cause the motor bearing temperature to rise in a short period of time and eventually damage the whole system. Because of the existence of stray capacitance and the interaction of high frequency common-mode voltage and capacitance, the common-mode current is formed by the motor housing, the earth and the inverter, and the electromagnetic interference is produced. In the special fields of petroleum exploitation, paper making, mining and so on, because of the distance between motor and frequency converter, it is inevitable to use cable PWM signal to transmit to motor through cable between them. Because of the high voltage conversion rate of PWM, Moreover, when the cable reaches a certain length, the PWM signal can be regarded as a traveling wave transmitted on the cable. Because the impedance of the cable does not match the impedance of the motor, the PWM traveling wave will be reflected at the motor end, and the forward traveling wave and the inverse traveling wave will superpose each other. Overvoltage occurs at the motor end, which includes double differential mode voltage and common mode voltage. The double of common-mode voltage will increase the negative benefit of the motor, and the double of the differential mode voltage will make the insulation of the motor more easily destroyed. Therefore, it is very important to study the negative effects and countermeasures of variable-frequency speed control system in long-term cable transmission. In this paper, the theory and topology of high voltage frequency conversion drive system are studied firstly, including rectifier, middle DC link and inverter. The principle of pulse rectifier and phase shift transformer in high voltage converter is analyzed emphatically. Secondly, the mechanism of common-mode voltage generation of inverter is studied, and it is concluded that the common-mode voltage of inverter is related to its switching state. On the basis of this, the suppression of common-mode voltage of three-level inverter by modulation strategy is studied emphatically. The traditional SPWM of three-level inverter, the SPWM of reducing the common-mode voltage and the SPWM of eliminating the common-mode voltage are studied. The effect of the traditional SVPWM on the common-mode voltage is studied, and the strategy of eliminating the improvement of the common-mode voltage is put forward, and its correctness is verified by simulation. Thirdly, the characteristics of PWM pulse wave transmission on long cable are analyzed by using transmission line theory, and the cause of overvoltage at motor end is analyzed, and the influence of cable distribution parameters on over-voltage of motor terminal is analyzed. Finally, the suppression measures of motor overvoltage and the design method of passive filter are studied. A method of combining ShePWM modulation technique with LC filter is proposed to suppress the overvoltage at the motor end. The principle of ShePWM, the selection of initial value and the calculation of angle are studied. On the basis of this, the feasibility of the suppression strategy is discussed by using the mathematical software MATLAB.
【学位授予单位】：西南交通大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TM921.51

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