MMC-STATCOM控制策略的研究

发布时间：2018-01-17 12:37

本文关键词：MMC-STATCOM控制策略的研究　出处：《哈尔滨工业大学》2017年博士论文　论文类型：学位论文

【摘要】：随着电力电子装置在电力系统中的迅速发展,电网的无功危害也日益严重。在多电平变换器应用日益成熟的促使下,高压大容量静止同步补偿器(Static Synchronous Compensator,STATCOM)已成为备受关注的研究热点。模块化多电平变换器(Modular Multilevel Converter,MMC)是实现高压大容量静止无功补偿技术的代表结构之一。本文以MMC-STATCOM为研究对象,分别针对其启动过程、调制技术、控制策略和输出特性进行了深入研究。MMC-STATCOM启动过程是保证补偿器可以正常运行的关键技术之一。本文首先研究了模块电容的取值范围,然后将充电过程分为不可控充电阶段和可控充电阶段。根据不可控充电过程的分析,确定了限流电阻参数选择的方法。不控充电阶段结束后,模块电压低于稳态运行时的电容电压,直接启动会造成交流侧电流出现过冲和畸变。因此,在可控充电环节提出了一种可控启动的控制策略,根据模块投入状态进行分组,使若干模块处于旁路状态,对处于投入状态的模块进行充电,以保证所有模块均能平稳充电至稳态运行电压值,有效降低冲击电流和充电过电压。阶梯波调制可以在相对较低的开关频率下获得较宽的输出范围,具有波形质量高、开关频率低等优点,但阶梯波调制中存在的开关角求解问题。论文针对适用于MMC-STATCOM的阶梯波调制策略进行了深入的研究,提出一种基于共轭梯度法和牛顿迭代法相结合的开关角计算方法,该方法使用共轭梯度法计算非线性方程组的初值,将得到的初值应用牛顿迭代法计算开关角精确解。所提算法综合了共轭梯度法收敛域宽和牛顿迭代法收敛速度快的优点,能够快速得到阶梯波调制法的开关角,结合方波脉冲循环均压方法以实现各个功率模块之间能量均衡。论文研究了MMC-STATCOM的无功控制策略。MMC-STATCOM是一个多变量、强耦合非线性系统,传统线性控制效果不理想。针对这一问题,提出一种基于微分几何法的MMC-STATCOM控制策略。该控制策略首先对目标电流进行序分解,然后基于微分几何理论提出一种状态反馈精确线性化方法,并推导了其反馈控制率,将MMC-STATCOM非线性系统精确线性化,实现对MMC-STATCOM正负序分量的独立控制。该控制策略适用于电网对称及不对称工况,应用范围较广,能够对MMC-STATCOM完全解耦,实现对无功功率的精确控制。最后,论文对MMC-STATCOM交流侧输出电流存在高次谐波的问题展开研究。由于MMC-STATCOM每相桥臂具有桥臂电感,并且输出侧具有滤波电感,可引入滤波电容构成LCL滤波器。针对这一问题,提出一种适用于MMC-STATCOM中的LCL滤波器的设计方法,以逆变器侧电感和网侧电感比、桥臂电感抑制相间环流和限制直流母线故障电流上升率、高频纹波电流抑制、滤波电容与网侧电感分流效果等条件为依据,得到LCL滤波器参数设计方法,有效的降低输出电流中的高次谐波电流。
[Abstract]:With the rapid development of power electronic devices in power system, the reactive power damage of power network is becoming more and more serious, which is promoted by the application of multilevel converters. Static Synchronous Compensator with high voltage and large capacity static synchronous compensator. Statcom has become the focus of research. Modular multilevel converter Modular Multilevel Converter. MMC is one of the representative structures to realize high voltage and large capacity static Var compensation. In this paper, MMC-STATCOM is taken as the research object, aiming at its start-up process and modulation technology respectively. The control strategy and output characteristics are studied deeply. MMC-STATCOM startup process is one of the key technologies to ensure the compensator can run normally. Firstly, the range of module capacitance is studied in this paper. Then the charging process is divided into uncontrollable charging stage and controllable charging stage. According to the analysis of uncontrollable charging process, the method of selecting the parameters of current limiting resistance is determined. The module voltage is lower than the capacitor voltage when the steady state is running, and the direct startup will cause overshoot and distortion of the AC side current. Therefore, a controllable startup control strategy is proposed in the controllable charging link. The modules are grouped according to the input state of the modules, and some modules are in the bypass state. The modules in the input state are charged to ensure that all the modules can be charged smoothly to the steady-state operating voltage. Step wave modulation can obtain a wide output range at relatively low switching frequency, which has the advantages of high waveform quality and low switching frequency. However, there is a problem of solving the switching angle in the step wave modulation. This paper makes a deep research on the step wave modulation strategy suitable for MMC-STATCOM. A new method for calculating the switching angle based on conjugate gradient method and Newton iteration method is proposed. The conjugate gradient method is used to calculate the initial values of nonlinear equations. The exact solution of switching angle is calculated by Newton iterative method. The proposed algorithm combines the advantages of the conjugate gradient method and the fast convergence speed of Newton iteration method, and can quickly obtain the switching angle of step wave modulation method. Combined with the square wave pulse cycle voltage equalization method to achieve the energy balance between the various power modules. The reactive power control strategy of MMC-STATCOM. MMC-STATCOM is a multivariable. In order to solve this problem, the traditional linear control effect is not ideal for strongly coupled nonlinear systems. A MMC-STATCOM control strategy based on differential geometry method is proposed, which firstly decomposes the target current in sequence. Then, based on the differential geometry theory, a state feedback exact linearization method is proposed, and its feedback control rate is derived to linearize the MMC-STATCOM nonlinear system accurately. Independent control of the positive and negative sequence components of MMC-STATCOM is realized. The control strategy is suitable for the symmetrical and asymmetric working conditions of the power network and can be fully decoupled to the MMC-STATCOM in a wide range of applications. To achieve the accurate control of reactive power. Finally. In this paper, the problem of high order harmonics in the output current of MMC-STATCOM AC side is studied. Because of the bridge arm inductance of each phase bridge arm of MMC-STATCOM. And the output side has filter inductance, which can introduce filter capacitance to form LCL filter. In order to solve this problem, a design method of LCL filter suitable for MMC-STATCOM is proposed. Based on the inverter side inductance and grid side inductance ratio, the bridge arm inductance suppresses the interphase circulation and limits the DC busbar fault current rise rate, the high frequency ripple current suppression, the filtering capacitance and the grid side inductance shunt effect and so on. The parameter design method of LCL filter is obtained, which can effectively reduce the high harmonic current in the output current.
【学位授予单位】：哈尔滨工业大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TM761.12

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