【作者】 高鹏飞；

【导师】 高强；

【作者基本信息】 哈尔滨工业大学 ， 电气工程， 2010， 硕士

【摘要】 作为钢铁、冶金、采矿、水利等行业生产中的关键设备,高压大功率同步电动机由于其转矩和功率因数可调,对电网波动不敏感,效率高的优点,广泛用于拖动大型鼓风机、水泵、压缩机等负载。随着电力电子变换技术和微控制器技术的发展,现普遍认为自控变频起动是高压大功率同步电机的最佳起动方式。本文针对自控变频式同步电动机无冲击并网这一技术难点,进行了较为深入的分析和研究,提出了基于全数字锁相环的调频锁相方法和基于励磁电流闭环控制的调压策略。首先,对自控变频式同步电机无冲击并网原理进行了理论分析,结合无冲击并网应遵循的三个基本条件,详细描述了并网过程中的控制方法。在并网前,采用断续换流法起动,在电机转速升至额定转速的8%后,切换至负载换流法直到将同步电动机拉至同步转速附近。当转速达到95%额定转速时即可认为进入并网过程。其次,为实现励磁电流的闭环控制,设计了一套并网硬件平台,包括电网侧和电机侧电压幅值、过零点检测调理电路,励磁电流检测及调节电路以及与主控制器通讯电路。根据维持直流母线电流连续及抑制直流母线电流波动两方面的要求选取了直流平波电抗器的电感值。起动时根据负载需求,给定并保持恒定的励磁电流,进入并网过程后闭环控制励磁电流,使电机反电势跟踪电网电压,具有很高的稳态精度。最后,提出了采用检测电网线电压和电机反电势过零点鉴相、锁相环与带死区的速度环协同调节的双模控制方式。从根本上解决了锁相捕捉频率带宽窄,容易失锁的问题,具有暂态过程平稳,稳态无静差的特点。在实验样机环境下,以额定参数为3kW/380V/1500r/min同步电机为控制对象进行实验,并网控制阶段末期,同步电机定子端电压与电网电压的频率差小于0.25Hz,电压差小于电机额定电压5%,相位差几乎为零,完全满足工程中无冲击并网条件。更多还原

【Abstract】 As the key equipment in iron and steel enterprises, metallurgy, mining or hydro-electric industries, high-voltage and high-power synchronous motor was generally used to drive large blowers, pumps, compressors, for its advantage of adjustable torque and power factor, being insensitive to grid fluctuation and very high efficiency. It is commonly considered that the self-controlled soft-start method is the best mode to start this kind of motors. To solve the difficulty of electrical grid connection technology without impact, in this paper, analysis and research are presented. It gives digital Phase-Locked-Loop to adjust motor frequency and phase, and closed-loop excitation plot to regulate Back-EMF.In the beginning of this paper, it derived from some basic mathematical relationships and working principles of this technology. Combined with three conditions, holistic approach of entire process of grid-connection was introduced. When the start process begins, under 8% of rated speed of the motor, break commutate mode is adapted. At medium and high speed, zero-crossing detection of Back-EMF is used until it approximately rises to the synchronous speed, almost the 95% of rated speed. After that, grid-connection segment activates.Secondly, to implement the closed-loop control of excitation current, a series of circuits is designed to acquire grid voltage, Back-EMF and their zero-crossing points, also to adjust excitation current and communicate with main controller. Smoothing reactor was determined based on DC bus’s continuity and fluctuation condition. When starting, excitation current will be able to adjust manually and control automatic. The excitation controller has satisfactory steady state precision.At last, software PLL algorithm applies the zero-crossing-point phase-detector to compute the phase difference of grid and motor. It coordinates with speed-loop and electricity-loop and has solved PLL’s narrow bandwidth problem. The PLL algorithm has smooth steady state and has no static error.A 3kW/380V/1500r/min synchronous motor is used as control plant in the experiment platform. At the end of grid-connection process, the difference of grid voltage and Back-EMF meets the following conditions: frequency difference less than 0.25Hz; voltage difference less than 5% EMF; phase difference approaches to zero. It is a very satisfactory result to realize grid-connection without impact.更多还原