【作者】 管清伟；

【导师】 马晓春；

【作者基本信息】 北京交通大学 ， 电气工程， 2012， 硕士

【摘要】 近年来随着交流电网的不断扩大,交流输电的局限性愈发明显,而高压直流输电系统直作为一种新兴的输电技术具有明显的优势,直流输电具有响应速度快,系统稳定性较好,能量损耗少等优点,因此在风力发电、分布式发电、海上供电、城市中心配电、远距离输电以及电网互联等方面有着广泛的应用。本文对基于电压源变流器的辐射式并联多端直流输电系统进行了相关的研究,首先为电压源变流器建立了在abc和dq坐标系下的数学模型,并根据建立的数学模型为变流器设计了定直流(交流)电压定有功(无功)功率以及直流电压下降控制器和过电压控制器。本文论述了统一式(单点电压控制)以及电压下降式(多点电压控制)控制策略,在此基础上提出并设计出了一种应用于辐射式并联多端直流输电系统的新型混合式控制策略。该控制策略的可控性和稳定性均较好。并且本文还进行了辐射式并联多端系统的直流功率潮流和变流器直流电压、电流的计算方法的研究。在电磁暂态仿真软件PSCAD/EMTDC中搭建了一个辐射式并联五端直流输电系统,并进行了相应的仿真研究。仿真研究表明,采用新型混合式控制策略的多端系统具有可靠的运行特性和高度的可控制性。新型混合式控制策略在定电压变流器正常运行时,多端系统电压是由定电压变流器决定,此时是单点电压控制,在定电压变流器满载或者因故障被从多端系统中切除时,电压下降变流器承担起控制多端系统直流电压的责任,此时是多点电压控制,因此这种控制策略稳定性以及可控性要优于现有的控制策略,再结合本文提出的直流潮流计算方法,可以方便的预测多端系统的稳定运行状态,或通过逆向运算来控制多端系统的运行方式。更多还原

【Abstract】 In recent years, with power grid expands, the limitation of ac power transmission is obvious. HVDC system, as a new transmission technology, has significant advantage. HVDC transmission has faster response, better system stability and less waste energy. It is in a wide range of applications such as wind power generation, distributed power generation, offshore power supply, urban power distribution, long-distance transmission and interconnection of synchronized AC system.This paper focus on the radial parallel multi-terminal HVDC system based on voltage source converters. In the first place, the mathematical model of VSC is established in different coordinate system. According to the mathematical model, constant voltage controller, constant power controller and voltage droop controller are proposed. This paper introduced the unified and voltage droop type control strategy. Based on this, the new hybrid control strategy is put forward. This new control strategy is better than the old ones in controllability and stability. This paper also carried out the dc power flow calculation method for the radial parallel multi-terminal HVDC system. A Five-terminal HVDC system is built in the electromagnetic transient simulation software PSCAD/EMTDC.The simulation results show that the parallel multi-terminal HVDC system with new hybrid control strategy has excellent reliability and controllability. The new hybrid control strategy can be split into two stages according to the load condition of the voltage regulator. Stage one is when the voltage regulator is in light load condition. System voltage is set by the voltage regulator. Stage two is when the voltage regulator is in full load condition or cut off from the system. The voltage regulator works as a normal power dispatcher. System voltage is set by voltage droop converters. So the reliability and controllability of the new control strategy is superior to the existing control strategies. Combining the proposed dc flow calculation method, it is pretty easy to predict the stable operation of the multi-terminal system. And through the reverse operations, it is also very convenient to control the stable operation of the multi-terminal system.更多还原