基于MMC的三相四线制STATCOM交流侧控制策略及保护的研究

发布时间：2018-09-06 20:31

【摘要】：配电网中电力电子设备、电气化铁路等非线性负荷的大量增加,导致电流波形发生严重畸变,电能质量问题越来越受到重视。D-STATCOM是有效提高配电网电能质量的装置,针对其补偿容量和耐压水平的限制,本文提出了一种基于模块化多电平变流器(MMC)的三相四线制STATCOM。论文首先对MMC的拓扑结构和工作原理进行了分析,建立了单相MMC数学模型,其功率单元可以实现四象限运行。MMC可以看作一个可控电压源,通过触发脉冲控制开关器件的通断,来控制上下桥臂电压,进而实现对交流侧输出电压的控制。对于脉冲调制技术,主要对CPS-SPWM和CD-SPWM进行了对比,结果表明CPS-SPWM技术能实现有功功率在桥臂上各功率单元间的均衡分配,能有效提高开关等效频率,本文亦采用了CPS-SPWM技术对脉宽进行调制。其次,构建了三相四线制MMC-STATCOM接入系统时的拓扑结构。分析其数学模型和工作原理可知,可以通过控制MMC-STATCOM输出电压的幅值和相位,就可实现容性和感性工况下的转换。对于补偿指令电流的检测,采取基于瞬时无功功率理论的ip-iq法,对于滤波器采用滑动均值滤波算法,计算速度快,占用内存小。还分析了交流侧控制策略中直接电流法和间接电流法的原理,另外为了维持直流侧电压的稳定,对功率单元模块的电容电压采用了均压控制和均衡控制策略。当电力系统在非正常状态下时,为了防止MMC-STATCOM遭受破坏,需要采取一定的保护措施。针对补偿指令过电流情况,提出了截断限流保护和同比例限流保护策略。最后,在Matlab/Simulink上搭建了三相四线制MMC-STATCOM模型,对谐波、无功、不对称综合工况进行了仿真分析,结果表明补偿效果良好,直流侧电压能够稳定在给定值附近,验证了控制策略的有效性。此外,还分析了加装保护措施前后装置输出补偿电流的变化情况,验证了保护措施的可行性。
[Abstract]:D-STATCOM is an effective device to improve the power quality of distribution network. In view of the limitation of its compensation capacity and voltage withstand level, this paper presents a new method based on modularization. Three-phase four-wire STATCOM of level converter (MMC) is presented in this paper. First, the topology and working principle of MMC are analyzed, and the mathematical model of single-phase MMC is established. The power unit of MMC can operate in four quadrants. MMC can be regarded as a controllable voltage source. By triggering the pulse to control the switching device on and off, the upper and lower arm voltage can be controlled. For the pulse modulation technology, the CPS-SPWM and CD-SPWM are compared. The results show that the CPS-SPWM technology can realize the balanced distribution of active power among the power units on the bridge arm, and can effectively improve the switching equivalent frequency. The CPS-SPWM technology is also used to modulate the pulse width. The topological structure of three-phase four-wire MMC-STATCOM is constructed.The mathematical model and working principle are analyzed.It is shown that the capacitive and inductive conversion can be realized by controlling the amplitude and phase of the output voltage of MMC-STATCOM.For the detection of compensating instruction current,the ip-iq method based on instantaneous reactive power theory is adopted. The principle of direct current method and indirect current method in AC side control strategy are also analyzed. In addition, in order to maintain the stability of DC side voltage, voltage sharing control and equalization control strategy are adopted for capacitor voltage of power unit module. In order to prevent the MMC-STATCOM from being destroyed under abnormal conditions, some protective measures should be taken. In view of the overcurrent of compensating instructions, the strategies of cut-off current-limiting protection and proportional current-limiting protection are put forward. Finally, a three-phase four-wire MMC-STATCOM model is built on Matlab/Simulink to simulate the harmonic, reactive and asymmetric conditions. The simulation results show that the compensation effect is good and the DC side voltage can be stabilized near the given value, which verifies the effectiveness of the control strategy.
【学位授予单位】：华北电力大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TM761.12

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