基于九开关变换器的双馈风力发电系统研究

发布时间：2018-01-05 05:01

本文关键词：基于九开关变换器的双馈风力发电系统研究　出处：《华中科技大学》2014年硕士论文　论文类型：学位论文

【摘要】：伴随着大规模风电技术的快速发展，风电装机容量在整个电力系统中的比例日益提高，为保证电力系统的安全稳定运行，，电网故障时的低电压穿越运行是风电并网规范对风力发电机组的重要要求之一。目前，双馈型风力发电机组在风力发电市场上占有较大份额，因此提高双馈发电机的低电压穿越能力是一项亟待解决且极具挑战的研究热点。目前，针对双馈风电机组的低电压穿越问题，一种不增加硬件成本、不改变系统结构的方法是通过变流器的励磁控制策略实现的。但是这种方法需要较大的变流器容量，这部分容量在系统正常运行下会造成浪费。典型的双馈风力发电系统通常采用背靠背双PWM变流器。本文提出用新型九开关变换器替代背靠背变流器来实现双馈机组的低电压穿越，并且在正常运行时，九开关变换器的容量又能得到充分利用。九开关变换器是通过开关管复用将背靠背变流器的十二个开关管缩减为九个而组成的新型AC/AC拓扑。该拓扑具有所用开关器件少、结构简洁的特点，通过其特有的SPWM调制，可以实现与背靠背变流器同样的功能。但由于九开关变换器特殊的结构，其直流母线电压将会比背靠背变流器直流侧电压高很多，并且每个开关管的耐压耐流容量也要比背靠背变流器中的高，这是其拓扑结构所固有的缺陷。但这在双馈风力发电应用场合，缺陷能够转化成优势。因为较高的直流侧电压和较大的器件容量使其较容易实现低电压穿越的励磁控制。而在正常工况下，又可以充分利用变换器的九个开关器件，不造成容量的浪费。因此，将九开关变换器作为双馈风电机组的变流器，无论是在稳态运行还是在故障下的穿越运行，都显示出了比背靠背变流器更有优势。本文通过对九开关变换器的调制原理进行深入分析，得出其在双馈发电机组中的端口对外等效形式，从而将基于九开关变换器的双馈风力发电系统等效为网侧等效部分和机侧等效部分，简化了系统的分析。在d轴电网电压定向同步旋转坐标系下，分别对网侧等效变换器和机侧等效变换器进行建模分析，给出其控制策略，结合九开关变换器的调制条件给出了每一部分正常运行的调制控制框图，并通过仿真和实验验证系统控制策略的正确性。对于在电网电压跌落的低电压穿越过程中，本文结合一台典型的兆瓦级双馈发电机分析了九开关变换器在开关器件电流容量和直流母线电压方面相对于背靠背变流器的优势。在一种简单抑制转子侧过流的励磁控制策略下，通过两种系统的电压跌落仿真验证了九开关变换器在双馈机组低电压穿越中的优势。
[Abstract]:With the rapid development of large-scale wind power technology, wind power installed capacity in the power system the proportion is increasing, in order to ensure the safe and stable operation of power system, the low voltage ride through operation of the power grid fault is one of the important requirements specification of wind power of wind turbine. At present, the double fed wind turbine a larger share in wind power market, therefore improve the low voltage ride through capability of DFIG is an urgent and challenging research topic.
At present, the low voltage ride through for doubly fed wind turbine, an increase in the cost of hardware, without changing the structure for system is through the converter excitation control strategy to achieve. But this method requires a large capacity converter capacity, this part will be wasted in the system. Under the normal operation of doubly fed wind power generation system typically, the back-to-back double PWM converter. This paper proposes to use model nine switch converter instead of back-to-back converter to achieve low voltage DFIG across, and during normal operation, the nine switch converter capacity can be fully utilized.
The nine switch converter is twelve switch back-to-back converter tube is reduced to nine and the new AC/AC topology composed by switching multiplexing. This topology has the characteristics of simple structure and less switching devices, and its modulation by SPWM, can be achieved with back-to-back converter with the same function. But because of the structure of nine switching converter is special, the DC bus voltage will be greater than the back-to-back converter DC side voltage is much higher, and each switch of the high flow capacity than back-to-back converter in high, this is the inherent defect of the topology. But the application of doubly fed wind power generation, defects can be transformed into advantages. Because of the high DC voltage and large capacity devices make it easier to achieve low voltage ride through excitation control. In normal working condition, and can make full use of the nine converter switching device, It does not cause waste of capacity. Therefore, the nine switch converter as a converter of doubly fed induction generator (DFIG) is more stable than back-to-back converter whether in steady state operation or under fault crossing operation.
By analyzing the principle of modulating nine switch converter, the double fed generator in the port of foreign equivalent form, which will be the equivalent of double fed wind power generation system of nine switch converter based on network side equivalent parts and machine side equivalent part, simplifies the analysis system. The d axis power grid voltage oriented synchronous rotating coordinate, respectively on the network side equivalent converter and machine side converter equivalent modeling analysis, the control strategy, combined with the modulation conditions of nine converters are modulated every part of the normal operation of the control box, and the correctness of the control strategy simulation and experimental verification of the system.
For the low voltage drop in voltage across the process, combined with a typical MW doubly fed generator of nine switch converter compared with back-to-back converter advantages in switch current capacity and DC voltage. In a simple inhibition excitation control strategy of the rotor over current under voltage by two the drop simulation verify the advantages of the nine switch converter in doubly fed induction generator low voltage ride through.

【学位授予单位】：华中科技大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TM46;TM614

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