基于变频调速系统的低压穿越性能研究

发布时间：2018-08-09 07:37

【摘要】：近年来,随着电力电子技术的迅猛发展,变频器以其节能降耗的显著优势,在发电厂辅助设备中普遍使用。然而,由于变频器对电网电压波动十分敏感,当电网发生故障引起电压暂降或短时中断,如果该变频器不具备一定的低压穿越能力,将会引发变频器低电压而跳闸,进而威胁发电厂机组的安全,严重影响电网安全稳定运行。因此,对变频调速系统低压穿越性能的研究具有非常重要的实际应用意义。本文首先阐述了低压穿越和双PWM变频器的相关概念,分析现阶段国内外学者专家针对火电厂变频调速系统低压穿越技术问题的研究现状,详细地给出双PWM变频器调制方法的实现和控制系统的设计,进而完成了双PWM变频器的仿真,然后以火电厂变频调速系统为基础,通过现场测试的方式对两种不同型号变频器的低压穿越性能进行评估。本文的主要工作如下:(1)从变频器的基本结构出发,分析了网侧变换器的拓扑结构和工作原理,分别建立了在三相静止坐标系下以及两相旋转坐标系下网侧变换器的数学模型,并根据其拓扑结构和数学模型的推导公式来说明网侧变换器的工作原理。(2)以三电平逆变器主电路结构为基础,着重研究三电平SVPWM(空间矢量脉宽调制)算法,对其稳态工作情况下每相输出时开关状态的变化进行分析,并给出了一种依据最近三矢量原则合成参考电压矢量的算法。通过判断参考电压矢量的位置来适当选取基本矢量,进而得到每个基本矢量的作用时间和相应的作用顺序,再将矢量的作用时间分配给对应的矢量状态,从而有效地控制开关管的导通与关断。(3)完成了对双SVPWM变频器网侧、负载侧变换器控制系统的设计,均采用双闭环控制策略。网侧变换器采用电压外环、电流内环控制,负载侧变换器则采用功率外环、电流内环控制,并由相应的传递函数确定了 PI调节器的参数。通过MATLAB/SIMULINK平台搭建双SVPWM变频器的仿真模型,仿真结果表明了SVPWM算法的有效性和控制系统设计的可行性,输出电压、电流波形的质量较好,提高了整流器和逆变器的转换效率。(4)以安徽某火电厂辅机变频调速系统(给粉机)为例,对不同型号的给粉机变频器随机各选取一台进行低压穿越性能测试,得到辅机变频调速系统低压穿越性能测试结果,分析并得出测试结论。针对不具备低压穿越能力的被试辅机变频器,本文探讨了几种方案以此解决发电厂辅机变频调速系统低压穿越的问题,提高了电网安全稳定运行的可靠性。
[Abstract]:In recent years, with the rapid development of power electronics technology, frequency converter is widely used in auxiliary equipment of power plant because of its remarkable advantage of saving energy and reducing consumption. However, because the inverter is very sensitive to the voltage fluctuation of the power network, if the inverter does not have a certain low voltage traversing capacity, it will cause the converter to trip down at low voltage if the voltage drop or short time interruption is caused by the fault of the power network. Then it threatens the safety of power plant units and seriously affects the safe and stable operation of power grid. Therefore, it is very important to study the low-voltage traversing performance of variable-frequency speed regulation system. In this paper, the concepts of low voltage traversing and double PWM converter are introduced, and the current research status of domestic and foreign scholars and experts on low voltage traversing technology of frequency conversion speed regulating system in thermal power plant is analyzed. The realization of double PWM frequency converter modulation method and the design of control system are given in detail, and then the simulation of double PWM converter is completed, and then based on the frequency conversion speed regulation system of thermal power plant, The low-voltage traversing performance of two different types of inverters is evaluated by field test. The main work of this paper is as follows: (1) starting from the basic structure of the converter, the topology and working principle of the grid-side converter are analyzed, and the mathematical models of the grid-side converter in the three-phase stationary coordinate system and the two-phase rotating coordinate system are established, respectively. The working principle of the grid-side converter is explained according to its topological structure and mathematical model. (2) based on the main circuit structure of three-level inverter, the three-level SVPWM (Space Vector Pulse width Modulation) algorithm is studied emphatically. The change of switching state in each phase output is analyzed, and an algorithm for synthesizing reference voltage vectors based on the principle of the nearest three vectors is presented. By judging the position of the reference voltage vector, the basic vector is properly selected, and then the action time and the corresponding sequence of action of each basic vector are obtained, and then the working time of the vector is allocated to the corresponding vector state. Thus the switch on and off are effectively controlled. (3) the double closed loop control strategy is used to design the control system of double SVPWM converters on the grid side and load side. The voltage outer loop and current inner loop are used in the grid-side converter, while the power outer loop and current inner loop are used in the load-side converter. The parameters of the Pi regulator are determined by the corresponding transfer function. The simulation model of double SVPWM inverter is built on MATLAB/SIMULINK platform. The simulation results show that the SVPWM algorithm is effective and the design of control system is feasible. The quality of output voltage and current waveform is good. The conversion efficiency of rectifier and inverter is improved. (4) taking the frequency conversion speed regulating system of auxiliary machine of a thermal power plant in Anhui province as an example, the low voltage traversing performance test is carried out by selecting one frequency converter of different type power feeder at random. The test results of low voltage traversing performance of frequency conversion speed regulating system of auxiliary machine are obtained, and the test results are obtained. In view of the frequency converter of the auxiliary machine without low voltage traversing ability, this paper discusses several schemes to solve the problem of low voltage crossing of frequency conversion speed regulating system of auxiliary machine in power plant, and improves the reliability of safe and stable operation of power network.
【学位授予单位】：安徽大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TM921.51;TM621

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