【作者】 蔚兰；

【导师】 陈国呈；

【作者基本信息】 上海大学 ， 电力电子与电力传动， 2011， 博士

【摘要】 随着能源枯竭和环境污染的日趋严重,风能、太阳能等可再生能源的分布式发电(Distributed Generation, DG)技术在世界各国得到迅猛发展,将分布式发电融入集中式发电,并建立混合型发电体系已成为供电系统发展的必然趋势。众所周知,构成分布式发电系统的风力发电、太阳能发电等机组单机容量小,易受大电网的影响。当电网发生故障时,分布式发电系统可能出现大规模从电网解列的情况,为此世界各国对分布式发电系统并网制定了入网规则,其中对低电压穿越技术(Low Voltage Ride Though, LVRT)的要求备受关注。本文对分布式并网发电系统低电压穿越的若干关键技术,如变速恒频双馈感应风力发电机(Doubly-Fed Induction Generator, DFIG)稳态控制策略、转子侧变换器低电压穿越控制策略、网侧变换器低电压穿越控制策略、全功率变换器低电压穿越控制策略等进行了深入研究。论文主要工作如下:根据双馈感应风力发电机的运行特点,以矢量控制(Vector Control, VC)理论为基础,研究了电网电压定向的DFIG稳态控制策略及空载并网控制策略,对空载并网及稳态运行分别进行了实验研究,在变速条件下实现无冲击电流并网及输出有功、无功功率的解耦控制。为了提高双馈风力发电系统在电网发生故障时的动态响应速度,研究了一种电网电压定向的DFIG直接功率控制(Direct Power Control, DPC)策略,建立了相应的空载并网及稳态运行控制模型,进行了相关的实验研究。结果表明DPC实现了与VC相同的无冲击并网、解列、有功/无功功率解耦控制等功能;而在电网故障时,DPC能提高双馈感应风力发电系统的动态性能,增强系统的低电压穿越能力。在分析了电网电压跌落时双馈感应发电机定子磁链暂态变化过程的基础上,研究了电网故障发生时刻及故障程度对转子励磁变换器的影响,得出了电网发生故障时双馈发电机各个物理量之间的量化关系,找到了转子过电压、过电流的根本原因。提出了一种电网故障时消除定子磁链直流分量及负序分量的转子侧变换器低电压穿越控制策略,实验结果验证了所提控制策略在电网电压跌落时,减小了双馈发电机的定、转子过电流,提高了低电压穿越能力。深入分析了电网故障时双馈发电机处于不同运行状态下,网侧变换器的动态过程及直流母线电压波动的原因。根据电网故障发生及排除时网侧变换器的响应特性,提出了一种通过改变调制电压信号实现网侧变换器低电压穿越的控制策略。实验结果验证了所提的控制策略能快速调节直流母线电压,使之趋于平稳,并在电网故障时将双馈发电机转子电能快速回馈到电网。在深入研究了电网故障时双馈感应发电机转子电压、电流暂态变化过程的基础上,得出了单靠改进转子励磁变换器控制算法实现低电压穿越的条件;当无法满足该条件时,研究了一种改进转子侧变换器控制策略和硬件保护技术相结合的LVRT控制方法。实验结果验证了所提方法在电网严重故障时,限制了定、转子电流,保护了转子励磁变换器,同时提高了为电网提供功率支持的快速性。对全功率并网变换器低电压穿越控制技术进行了研究,以三相光伏并网发电系统为研究对象,对其稳态控制及低电压穿越控制进行了研究,提出了一种电网发生对称故障时,通过调节前馈补偿量实现LVRT的控制策略;研究了电网发生不对称故障时,采用正、负序控制器分别控制输出电流的正、负序分量以实现LVRT的控制方法,并对上述控制策略进行了仿真和实验验证。建立了以TMS320F2407A为核心的双PWM变换器硬件实验平台,在该实验平台上完成了上述双馈感应风力发电机矢量控制、直接功率控制、转子侧变换器及网侧变换器低电压穿越实验验证,及改进转子侧变换器控制策略与硬件保护相结合的双馈感应发电机低电压穿越实验验证,三相光伏全功率变换器稳态控制实验及低电压穿越实验验证。更多还原

【Abstract】 With the increase of global environmental pollution and serious energy crisis, Distributed Generation(DG) technologies using renewable resources like wind energy and photovoltaic (PV) energy are developed quickly around the world. As we all know, the DG unit capacity is small and they are easily interrupted by the grid fluctuation. When the grid fault happens, DG may disconnect from the grid, so some countries presented the grid codes for DG. Low Voltage Ride Through(LVRT) requirement is one of the most important research topics. In this paper some key DG LVRT technologies, such as variable speed constant frequency wind power generation of doubly-fed induction generator (DFIG) flexible cutting-in and steady state operation control methods, rotor side converter(RSC) LVRT control strategy, grid side converter(GSC) LVRT control strategy, three phase PV full power converter LVRT control strategy are studied deeply, the contributions of this dissertation are as follows:According to characteristic of DFIG, the gird voltage orientated Vector control(VC) strategy is studied. Idle-load cutting-in and steady state operation are studied by experiments. Flexible cutting-in, decoupling control of active power and reactive power are obtained when the rotor speed changes.To improve the dynamic response, a DFIG Direct Power Control(DPC) is studied. The cutting-in and steady state operation DPC modes are established and studied by experiments. The experimental results show that using DPC achieves the same purpose with VC and DPC improves the LVRT ability during grid fault.Based on analysis of DFIG stator flux transient period, how the DFIG rotor excited converter is affected by the voltage sag moment and percent during the grid fault is researched. The cause of stator and rotor overcurrent and the relationship of DFIG physical values are found. This paper proposed a DFIG RSC LVRT control method by reducing the DC flux and negative flux. The experimental results prove that the mentioned control method prevents the stator and rotor overcurrent and improves the LVRT ability.GSC dynamic process of different running state during grid fault is analyzed. A GSC LVRT control method is proposed based on GSC response. The method modifies the modulation voltage signal during grid fault to control AC current and stabilize the DC-link voltage. The experimental results prove that the GSC LVRT control method make DC-link voltage stable and transfer rotor power to the grid quickly.Based on analysis of transient period of DFIG rotor voltage and current, the LVRT limiting condition using RSC control strategy to achieve LVRT is found. A DFIG LVRT method combining the improved control stragety with hardware protect is studied when the limiting condition is not met. The experimental results prove that the method limit the stator and rotor overcurrent, protect the rotor converter and provide power to the grid quickly during serious grid fault.The full power converter is studied. The steady state operation and LVRT control of a 3-phase PV converter is studied. A LVRT control strategy is proposed by regulating the forward compensation voltage during symmetric grid fault. The positive and negative controllers are used to control positive and negative current to achieve LVRT when asymmetric grid fault happened.A double PWM converter experimental system is established based on the TMS320F2407A. The DFIG VC and DPC steady state control, cutting-in control, the RSC and GSC LVRT control, RSC control method combined with Crowbar circute protect control experiments are made based on the system. The PV converter steady state control and LVRT control experiments are made based on the system also.更多还原