电压型高压直流输电控制策略的研究

发布时间：2018-09-03 13:54

【摘要】：随着各种大规模可再生能源接入电网，传统的电力装备、结构和运行技术等在接纳超大规模可再生能源方面越来越难以适应，因此必须采用新技术来满足。而基于电压源型换流器的直流输电技术是解决这一问题的有效技术手段之一。为此本文针对电压源型换流器进行了深入研究。本文首先对换流器的数学模型进行了研究，构建了换流器及其并联的数学模型，并针对其数学模型设计了电流与电压控制器。此外，利用PSCAD对双端两电平HVDC与双端MMCVSC-HVDC进行了故障时的仿真。针对电网含有谐波及不平衡下的并网电流畸变问题，本文提出了在两相静止坐标系下的准比例谐振与重复控制组成的复合电流控制策略。重复控制器与准谐振控制相结合，既能解决重复控制无法无静差跟随工频电流问题，又能消除准谐振控制器的相位误差，抑制单一控制器所存在的缺陷。此后，设计了一种基于二阶广义积分的锁相环。理论、仿真及实验表明：在电网不平衡及谐波时，复合控制策略能够有效改善电流波形，降低并网电流THD；同时基于二阶广义积分的的锁相环可以在电网不平衡和含谐波时对正序电压及相位进行快速准确的检测。由于不使用陷波器进行电网正负序分离，，锁相速度快。利用此锁相环可以更好的对电流进行控制。多换流器并联可以提高系统的功率与可靠性，降低成本，但会产生环流。环流会增加系统损耗，降低系统效率。针对环流问题，提出了基于无差拍控制的环抑制策略，同时提出了一种虚拟换流器的概念，通过调节控制环节中SVPWM的零矢量实现N模块环流的抑制。理论、仿真及实验表明：无论给定电流及交流侧滤波电感是否相等，此方法能将各个功率模块零序环流的大小控制在同一水平，实现各模块“均流”，动态相应快，环流抑制效果较好。最后，开发研制了一套30kW的高压直流输电实验平台，实验平台主要由6台换流器组成。首先独立设计了全部控制电路，对实验平台进行硬件调试，并对一次回路进行了改进。在此基础上，对软件进行编程，进行了定矢量电压控制、电流环复合控制算法以及并联换流器环流抑制等实验。
[Abstract]:With a variety of large-scale renewable energy connected to the grid, the traditional power equipment, structure and operation technology are becoming more and more difficult to adapt to accept super-large scale renewable energy, so new technologies must be adopted to meet the needs. The DC transmission technology based on voltage source converter is one of the effective methods to solve this problem. Therefore, the voltage source converter is studied in this paper. In this paper, the mathematical model of the converter is studied, and the mathematical model of the converter and its parallel connection is constructed, and the current and voltage controller is designed for the mathematical model. In addition, two-terminal two-level HVDC and two-terminal MMCVSC-HVDC are simulated by PSCAD. In order to solve the problem of grid-connected current distortion with harmonics and unbalance, a compound current control strategy consisting of quasi-proportional resonance and repetitive control in two-phase stationary coordinate system is proposed in this paper. The combination of repetitive controller and quasi-resonant control can not only solve the problem that repetitive control can not only follow the power frequency current without static error, but also eliminate the phase error of the quasi-resonant controller and restrain the defects of the single controller. Then, a phase locked loop based on the second order generalized integral is designed. The theory, simulation and experiment show that the compound control strategy can effectively improve the current waveform and reduce the THD; of grid-connected current when the power network is unbalanced and harmonic. At the same time, the phase-locked loop based on the second order generalized integral can detect the positive sequence voltage and phase quickly and accurately when the power system is unbalanced and contains harmonics. Because no notch filter is used to separate the positive and negative sequence of the power system, the phase locking speed is fast. Using this PLL, the current can be controlled better. Parallel multi-converter can improve the power and reliability of the system, reduce the cost, but will produce circulation. The circulation will increase the system loss and reduce the system efficiency. Aiming at the circulation problem, a loop suppression strategy based on deadbeat control is proposed, and a concept of virtual converter is proposed, which can suppress the circulation of N module by adjusting the zero vector of SVPWM in the control link. Theoretical, simulation and experimental results show that this method can control the size of zero sequence circulation of each power module at the same level regardless of whether the current and AC side filter inductance are equal or not, and realize the "current sharing" of each module. The effect of circulation inhibition is better. Finally, a high voltage DC transmission experimental platform of 30kW is developed, which is mainly composed of 6 converters. First, all the control circuits are designed independently, the hardware of the experimental platform is debugged, and the primary circuit is improved. On this basis, the software is programmed, and experiments are carried out, such as constant vector voltage control, current loop compound control algorithm and parallel converter circulation suppression.
【学位授予单位】：哈尔滨工业大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TM721.1

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