【作者】 毛翔；

【导师】 郭育华；

【作者基本信息】 西南交通大学 ， 电力电子与电力传动， 2013， 硕士

【摘要】 风电行业在发展中表现出单机功率不断提升、发展海上风场、直驱式风电机组后来居上等特点。海上永磁直驱风力发电系统作为以上趋势的产物,将会成为未来风电领域的研究热点。传统两电平“背靠背”变流器如果直接用于海上风力发电系统,将会产生开关器件承受的电压、电流应力大；du/dt过大；电磁干扰强等一系列问题。多电平拓扑结构中单个开关器件承压小,输出波形更接近正弦,多电平变流器可以很好地满足大功率中压系统的要求。本文以适用于大功率海上风力发电系统的多电平中压变流器为研究目标,进行拓扑结构选择和研究。通过广泛阅读了解各种多电平结构在风电领域的应用情况。经过对比和分析,将多电平拓扑结构与多相电机相结合,提出了“六相永磁同步发电机+双母线三电平PWM变流器”系统结构方案。使用多相电机可以提升单机功率,符合风力发电单机大型化趋势。双母线制上的每套变流器只分担系统一半的功率,降低了对变流器容量的要求。三电平拓扑结构不仅降低了中压系统对单个开关器件的电压应力,在相同开关频率下比两电平变流器输出电压电流畸变率更小,相应的系统滤波器容量减小。考虑到所选双母线变流器机侧和网侧部分均为三电平PWM整流器,本文建立了三电平PWM整流器在同步旋转坐标系下的数学模型。重点研究了三相三电平变换电路调制方式和中点电位偏移控制方案。在对比分析后选择了三电平SVPWM作为调制方式,并通过调整正负小矢量作用时间有效控制中点电位平衡。SVPWM易于数字实现,且直流母线电压利用率高。选用的中点电位控制方案不增加硬件成本,算法简单,易于实现。为所提出的多电平中压变流器选择合适的控制策略,网侧变流器采用基于电网电压定向的矢量控制,并采用LCL滤波器；机侧变流器通过建立的六相电机单绕组等效模型,将对六相风力发电机的矢量控制等效为对三相永磁同步电机的控制。在Matlab中建立了整个系统模型以验证所提出方案的可行性和正确性本文还针对5MW海上风电变流器进行了主电路器件选取和参数设计,使研究具有一定的实用价值和工程指导意义。更多还原

【Abstract】 Power rising of signal wind turbine, developing of offshore wind farms, direct drive wind generation coming up from behind is shown as characteristics in the development of wind power generation. As the product of the above trend, direct-drive offshore wind power system will become a hot research issue in wind power field in the future. The larger power, higher voltage level and more extreme environments of the offshore wind generation system propose more stringent requirements to the wind power converter. However, the application of traditional two lever back to back in offshore wind power will produce excessive voltage and current stress to the converter, together with higher du/dt and EMS etc. The multilevel topology with smaller stress to single switch and better near-sinusoidal output waveform can meets the requirements of medium voltage system.This paper focuses on the application of multilevel converter topologies in offshore wind power generation system which is characterized by high power and medium voltage to start topology selection and simulation research.After reviewing kinds of multi-level structure used in wind electric field widely. Through compare between different structure, this paper combines multi-level structure and polyphase machine, and propose the scheme that combines six-phase pmsm and duplicate-busbar three-level PWM converter. Using multi-phase machine can promote single-machine capacity, which fit the tendency that wind driven generator is upsizing. Each converter on duplicate-busbar bear half of the system power, which will lower the converter’s sights. Three level structure can not only lower the voltage stress on each switch in medium voltage system, but also reduce the current and voltage distortion and filter capacity of two level converter under the same switching frequency.In consideration of both generator side and power grid side use three level converter, this paper build its math model in synchronous rotating reference frame. Research into three-phase three-level converter’s modulation mode and neutral-point voltage control scheme is conducted. After compare and analysis, three level SVPWM is applied and neutral-point voltage control scheme is through controlling positive and negative vectors’ action time. SVPWM is easy to be realized, and it has high DC use ratio. The applied neutral-point control scheme is simple and save extra hardware cost.The grid side converter is controlled with vector control scheme, and LCL filter is used instead of L filter and LC filter; At the generator side, the vector control of six-phase wind generator is equivalent to the control of three-phase permanent magnet synchronous generator. The whole system model of MATLAB is built to verify the feasibility and validity of the scheme proposed.The paper designs the main circuit and give out the parameter for5MW offshore wind power system, which make the research possess practical value and engineering significance.更多还原