模块化多电平换流器柔性直流输电系统控制策略研究
发布时间：2018-09-10 19:16
【摘要】：模块化多电平换流器柔性直流(Modular Multilevel Converter-High Voltage Direct Current,MMC-HVDC)输电系统具有模块化程度高、输出波形质量好、独立调节有功功率和无功功率等优点,因其能够适应高电压、大功率传输要求,具有很好的应用前景,已有诸多实际工程投运。本文以MMC-HVDC系统为研究对象,针对系统正常运行和桥臂不对称运行存在环流、子模块电容电压不平衡等问题进行研究。研究了MMC-HVDC系统模型预测控制,将比例-积分控制器与模型预测控制相结合,依据交流电流跟踪目标函数、子模块电容电压均衡目标函数以及相应的权重系数建立综合目标函数,根据环流抑制补偿电平调节开关状态,在保持子模块电容电压均衡的同时,实现了对环流的有效抑制。分析了MMC-HVDC系统上下桥臂阻抗不对称运行时桥臂电流成分,指出桥臂阻抗不对称所在桥臂不均分交流侧电流,会造成环流成分不仅含有二倍频分量,还存在基频分量,引起直流侧电流波动。提出了一种桥臂阻抗不对称时模型预测控制策略,该策略结合预测时刻子模块电容电压排序,根据综合目标函数和环流抑制目标函数,选择最优开关状态,实现了桥臂阻抗不对称运行时环流的抑制,减小了直流侧电流波动。对于存在冗余子模块的MMC-HVDC系统,建立了模块化多电平换流器冗余容错数学模型,提出了一种冗余容错模型预测控制策略,根据正常运行子模块数量设定子模块电容电压均衡目标函数,依据环流抑制目标函数调整桥臂最优子模块开通状态,在实现交流电流跟踪、子模块电容电压均衡的同时,可以实现子模块数目不对称时对环流基频成分和二倍频成分的抑制。基于MATLAB/SIMULINK搭建MMC-HVDC系统仿真模型,分别对系统正常运行、上下桥臂阻抗不对称运行、上下桥臂子模块数目不对称运行三种情况进行仿真分析,仿真结果验证了所提控制策略的可行性和有效性。
[Abstract]:Modularized multilevel converter flexible direct current (Modular Multilevel Converter-High Voltage Direct Current,MMC-HVDC) transmission system has the advantages of high modularization, good quality of output waveform, independent regulation of active and reactive power, etc., because it can meet the requirements of high voltage and high power transmission. It has a good prospect of application, and many practical projects have been put into operation. In this paper, MMC-HVDC system is taken as the research object. The problems of circulating current and capacitor voltage unbalance in the normal operation and asymmetric operation of the bridge arm are studied in this paper. The model predictive control of MMC-HVDC system is studied. The integrated objective function is established according to the objective function of AC current tracking, the objective function of capacitance voltage equalization of submodule and the corresponding weight coefficient, by combining the proportional and integral controller with the model predictive control. According to the switching state of the current suppression compensation level, the effective suppression of the circulation is realized while maintaining the capacitor voltage equalization of the submodule. In this paper, the current components of the upper and lower arm of the MMC-HVDC system are analyzed when the impedance of the upper and lower leg is asymmetrical. It is pointed out that the current of the bridge arm in which the impedance of the bridge arm is asymmetrical is not only divided equally into the AC side current, but also the basic frequency component is found in the circulation component. Cause DC side current fluctuation. In this paper, a predictive control strategy for bridge arm impedance asymmetry is proposed. The optimal switching state is selected according to the integrated objective function and the circulation suppression objective function, combined with the capacitor voltage order of the predictive time submodule. The current fluctuation of DC side is reduced by suppressing the circulation when the bridge arm impedance is asymmetrical. For the MMC-HVDC system with redundant sub-modules, a mathematical model of modularized multilevel converter redundancy fault tolerance is established, and a redundant fault-tolerant model predictive control strategy is proposed. According to the number of submodules in normal operation, the objective function of capacitor voltage equalization of sub-modules is set, and the opening state of the optimal submodule of the bridge arm is adjusted according to the objective function of circulation suppression. The AC current tracking and capacitor voltage equalization of sub-modules are realized at the same time. The fundamental and double frequency components of the circulation can be suppressed when the number of submodules is asymmetric. The simulation model of MMC-HVDC system based on MATLAB/SIMULINK is built. The simulation analysis is carried out for the normal operation of the system, the asymmetric operation of the upper and lower arm impedance, and the asymmetric operation of the upper and lower arm submodules. Simulation results verify the feasibility and effectiveness of the proposed 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】：TM721.1
本文编号：2235374
[Abstract]:Modularized multilevel converter flexible direct current (Modular Multilevel Converter-High Voltage Direct Current,MMC-HVDC) transmission system has the advantages of high modularization, good quality of output waveform, independent regulation of active and reactive power, etc., because it can meet the requirements of high voltage and high power transmission. It has a good prospect of application, and many practical projects have been put into operation. In this paper, MMC-HVDC system is taken as the research object. The problems of circulating current and capacitor voltage unbalance in the normal operation and asymmetric operation of the bridge arm are studied in this paper. The model predictive control of MMC-HVDC system is studied. The integrated objective function is established according to the objective function of AC current tracking, the objective function of capacitance voltage equalization of submodule and the corresponding weight coefficient, by combining the proportional and integral controller with the model predictive control. According to the switching state of the current suppression compensation level, the effective suppression of the circulation is realized while maintaining the capacitor voltage equalization of the submodule. In this paper, the current components of the upper and lower arm of the MMC-HVDC system are analyzed when the impedance of the upper and lower leg is asymmetrical. It is pointed out that the current of the bridge arm in which the impedance of the bridge arm is asymmetrical is not only divided equally into the AC side current, but also the basic frequency component is found in the circulation component. Cause DC side current fluctuation. In this paper, a predictive control strategy for bridge arm impedance asymmetry is proposed. The optimal switching state is selected according to the integrated objective function and the circulation suppression objective function, combined with the capacitor voltage order of the predictive time submodule. The current fluctuation of DC side is reduced by suppressing the circulation when the bridge arm impedance is asymmetrical. For the MMC-HVDC system with redundant sub-modules, a mathematical model of modularized multilevel converter redundancy fault tolerance is established, and a redundant fault-tolerant model predictive control strategy is proposed. According to the number of submodules in normal operation, the objective function of capacitor voltage equalization of sub-modules is set, and the opening state of the optimal submodule of the bridge arm is adjusted according to the objective function of circulation suppression. The AC current tracking and capacitor voltage equalization of sub-modules are realized at the same time. The fundamental and double frequency components of the circulation can be suppressed when the number of submodules is asymmetric. The simulation model of MMC-HVDC system based on MATLAB/SIMULINK is built. The simulation analysis is carried out for the normal operation of the system, the asymmetric operation of the upper and lower arm impedance, and the asymmetric operation of the upper and lower arm submodules. Simulation results verify the feasibility and effectiveness of the proposed 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】：TM721.1
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