模块化多电平VSC-HVDC换流器的优化控制研究

发布时间：2019-06-16 18:47

【摘要】：电压源型换流器高压直流输电(Voltage Sourced Converter based HVDC VSC-HVDC)技术是一种新型的直流输电技术,已有的工程运行经验表明,其非常适合孤岛供电、新能源并网和城市配电网增容等领域应用。近年来围绕VSC-HVDC技术的研究取得了一系列的突破,其中最引人注目的是模块化多电平换流器(Modular Multi-level Converter, MMC)在直流输电工程上的成功应用。 MMC自身储能单元能量的有效控制是保证系统暂稳态运行性能的基础和关键。然而,随着输送容量和直流电压等级的提升,MMC所需储能单元急剧增加,对控制系统提出了更高的要求。再者,拓扑结构和工作机理的不同使得MMC在某些工况下的暂态特性相比于传统两电平、三电平换流器有较大区别。本文以MMC-HVDC换流器能量平衡控制机理为出发点,对换流器在对称以及桥臂子模块数和电网电压两种非对称工况下的暂稳态特性及其优化控制策略进行了研究。 1、研究了计及各桥臂子模块数量差异的MMC-HVDC数学模型。建立了完整的MMC开关周期平均模型,推导了桥臂交流小信号模型；考虑子模块电容电压之和与直流电压的差异,建立了系统对称和两种典型非对称工况下MMC的低频等效模型。 2、研究了MMC-HVDC换流器能量平衡控制策略及功率运行区间的优化方法。分析了桥臂分段电容电压平衡机理,提出了两种段间电容电压平衡控制策略；分析了MMC开关频率的影响因素,提出了以满足周期内最值控制要求为目标的段内电容电压优化控制策略,有效降低了器件的等效开关频率；分析了上下桥臂、相间以及总的子模块能量平衡控制机理,讨论了不同站级有功类控制方式下总的子模块电容电压控制的实现方式；提出了基于三倍频调制电压注入和子模块基值调整的MMC-HVDC换流器功率运行区间优化方法。 3、研究了基于分桥臂电流控制的子模块故障非对称容错控制策略。分析了故障子模块旁路退出对MMC内部及输出特性特性的影响,讨论了保证系统持续运行的子模块故障数量上限；提出了改进的分桥臂电流控制策略,结合两种子模块电容电压控制目标,改善了MMC的子模块故障非对称容错控制效果。 4、研究了基于子模块电容电压和环流预估的非对称电网故障穿越优化控制策略。基于瞬时功率平衡理论,提出了子模块电容电压在线预估实现方案；讨论了非对称电网电压下各序分量对MMC内部及直流侧变量的影响；明确了暂态期间子模块电容电压和桥臂环流等内部变量的预期控制目标；提出了基于子模块电容电压预估调制和桥臂环流预估控制的复合控制策略；结合具体的站级控制策略,仿真分析了复合控制策略对改善系统暂态运行性能的控制效果。 5、开展了401电平MMC-HVDC动模系统相关控制策略的试验研究。介绍了401电平物理动模、混合实时仿真平台的系统架构和主要功能,基于两种试验系统分别进行了分段电容电压平衡和非对称电网故障穿越优化控制动模试验,试验结果验证了相关理论分析和所提出的控制策略的正确性。
[Abstract]:The voltage source type converter high-voltage direct current transmission (VSC-HVDC) technology is a new type of DC power transmission technology. The existing engineering operation experience shows that it is very suitable for island power supply, new energy and network and city distribution network capacity-increasing. In recent years, a series of breakthroughs have been made in the research of VSC-HVDC technology, one of which is the successful application of Modular Multi-level Converter (MMC) in DC power transmission engineering. The effective control of the energy of the self-energy storage unit of the MMC is the basis and the close of the system's temporary steady-state operation. The key. However, with the increase of the transfer capacity and the DC voltage level, the energy storage unit required by the MMC is rapidly increased, and a higher demand for the control system In addition, the difference of the topological structure and the working mechanism is that the transient characteristics of the MMC in some working conditions are compared with the traditional two-level, and the three-level converter has a large area. Based on the energy balance control mechanism of the MMC-HVDC converter, the transient stability and the optimal control strategy of the converter under the conditions of symmetry and the number of submodules of the bridge and the voltage of the grid are studied in this paper. ............................................................ In this paper, a complete MMC switch cycle average model is established, and a small signal model of the bridge arm is derived. Considering the difference between the sum of the capacitor voltage and the DC voltage of the sub-module, the system symmetry and the low frequency of the MMC under two typical non-symmetrical conditions are established. The energy balance control strategy and the power operation interval of the MMC-HVDC converter are studied in this paper. In this paper, the mechanism of the voltage balance of the segment capacitance of the bridge arm is analyzed, and the control strategy of the voltage balance between the two segments is put forward. The influencing factors of the frequency of the MMC switch are analyzed. The control strategy is used to effectively reduce the equivalent switching frequency of the device, and the energy balance control mechanism of the upper and lower arm, the interphase and the total sub-module is analyzed, and the total sub-module capacitance voltage control in different station-level active-class control modes is discussed. The invention provides an MMC-HVDC converter power operation area based on a three-frequency-multiplication modulation voltage injection and a sub-module base value adjustment, 3. The fault of sub-module based on the current control of the bridge arm is studied in this paper. The fault-tolerant control strategy is called fault-tolerant control strategy. The influence of the bypass of the fault sub-module on the internal and output characteristics of the MMC is analyzed, the upper limit of the number of sub-modules in the system's continuous operation is discussed, the improved control strategy of the split-arm current is proposed, and the two sub-modules are combined The control target of the capacitance is improved, and the fault of the sub-module of the MMC is improved. The fault-tolerant control effect is called fault-tolerant control. In this paper, on the basis of the instantaneous power balance theory, the realization of the on-line estimation of the capacitor voltage of the sub-module is put forward, and the inside of the MMC is discussed in this paper. and a composite control strategy based on the sub-module capacitance voltage prediction modulation and the bridge arm circulation estimation control is proposed; and the combined control strategy The specific station-level control strategy and the simulation and analysis of the composite control strategy to improve the transient state of the system Control effect of operation performance.5. A 401-level MMC-HVDC dynamic system is implemented. The experimental research of the related control strategy is introduced. The system architecture and main function of the 401-level physical and dynamic simulation platform are introduced, and the voltage balance of the section and the asymmetric power grid are respectively carried out based on the two test systems. The test of the dynamic simulation of the obstacle crossing optimization control and the test results verify the relevant theoretical analysis and the related theoretical analysis.
【学位授予单位】：中国电力科学研究院
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TM721.1

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