模块化多电平变换器的优化控制策略研究

发布时间：2018-05-19 15:03

本文选题：模块化多电平变换器 + 电容均压　；参考：《中国矿业大学》2016年硕士论文

【摘要】：随着电力电子技术在无功补偿、有源电力滤波器、高压直流输电等领域的应用,高压大功率电力电子设备成为研究热点。多电平变换器因其开关器件承受电压低、电压谐波含量低等优点,是目前解决高压大功率变换最有效的方案之一。本文以模块化多电平变换器(modular multilevel converter,MMC)为研究对象,围绕调制策略、子模块电容均压控制策略及其优化控制策略进行了研究。本文对MMC拓扑结构和工作原理进行了介绍,并推导了MMC数学模型。分析了基于闭环均压的载波移相调制策略和基于排序均压的最近电平逼近调制策略,并进行了仿真验证。根据理论计算和仿真验证,从输出谐波含量、基波特性以及动态特性等方面进行对比分析,指出相应调制策略的优缺点和适用范围。为了减少最近电平逼近调制在电平数较少的低次谐波含量,采用统一脉宽调制进行优化。然而该方法仍采用传统的排序均压算法并未考虑降低开关频率和控制器的负担。为进一步优化算法,采用了基于统一脉宽调制的优化均压策略,该方法不需要对子模块电容电压进行排序,还通过设置子模块电容电压阈值,从而避免频繁地投切开关器件,使其适用于子模块数较多的场合。为保证电容均压和抑制环流,常规控制方法一般与PI调节器结合,导致控制系统出现参数整定困难、控制滞后等缺点。本文介绍了模型预测控制(model predictive control,MPC),该方法具有响应速度快、跟踪性能好、多变量控制等优点。然而存在计算量大的问题,现有的处理器很难满足实时计算的要求。为此本文采用了优化模型预测控制,通过对子模块电容电压排序以及电流方向来确定可能的开关状态组合,有效降低了可能的开关状态组合,大大降低系统的运算量。这两种方法都需要进行复杂的加权系数整定过程,因此本文提出了基于MMC的满意优化预测控制(satisfying-optimized predictive control,SOPC)。仿真验证了SOPC具有良好的稳态和动态特性。最后在MMC实验样机对本文所采用的优化控制策略进行实验验证,结果验证了本文所用方法是有效的。
[Abstract]:With the application of power electronics technology in reactive power compensation, active power filter, HVDC transmission and other fields, high-voltage high-power electronic equipment has become a research hotspot. Multilevel converter is one of the most effective solutions to high voltage and high power conversion because of its advantages of low voltage and low voltage harmonic content. In this paper, the modularized multilevel converter (Modular multilevel convertor MMC) is studied, and the modulation strategy, submodule capacitive voltage equalizing control strategy and its optimal control strategy are studied. This paper introduces the topology and working principle of MMC, and deduces the mathematical model of MMC. The carrier phase shift modulation strategy based on closed loop voltage sharing and the nearest level approach modulation strategy based on sorting voltage are analyzed and verified by simulation. According to theoretical calculation and simulation verification, this paper compares and analyzes the output harmonic content, fundamental wave characteristics and dynamic characteristics, and points out the advantages and disadvantages and applicable range of the corresponding modulation strategy. In order to reduce the low order harmonic content of the nearest level approximation modulation, the unified pulse width modulation is used to optimize it. However, the traditional equalization algorithm is not used to reduce the switching frequency and the burden of the controller. In order to further optimize the algorithm, an optimal voltage sharing strategy based on uniform pulse width modulation is adopted. The method does not need to sort the capacitance voltage of the submodule, and by setting the threshold of the capacitor voltage of the submodule, the device is avoided to be cut off frequently. Make it suitable for the situation where the number of submodules is more. In order to ensure capacitor voltage equalization and restrain circulation, the conventional control method is usually combined with Pi regulator, which leads to the difficulty of parameter setting and the control lag of the control system. This paper introduces the model predictive control (MPC), which has the advantages of fast response, good tracking performance and multivariable control. However, the existing processors are difficult to meet the requirements of real-time computing because of the large amount of computation. In this paper, the optimal model predictive control is used to determine the possible switch state combination by ordering the capacitor voltage and the current direction of the sub-module, which can effectively reduce the possible switching state combination and greatly reduce the system operation. Both of these two methods need to perform complex weighting coefficient tuning process. Therefore, a satisfactory optimal predictive control based on MMC is proposed in this paper, which is satisfied with fying-optimized predictive control. Simulation results show that SOPC has good steady-state and dynamic characteristics. Finally, the optimal control strategy used in this paper is verified by the MMC experimental prototype, and the results show that the proposed method is effective.
【学位授予单位】：中国矿业大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TM46

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