【作者】 刘钊；

【导师】 康勇； 段善旭；

【作者基本信息】 华中科技大学 ， 电气工程， 2010， 博士

【摘要】 由于风力发电的随机性,风电场接入到电网会对接入地区电网的电压稳定性带来影响；同时电网电压的稳定性又会影响到风电场的接入,进一步恶化电网电压的稳定性。在风电穿透功率较大的电网中,其电网电压的稳定性尤为重要,静止同步补偿器(STATCOM)能有效的提高电力系统暂态电压稳定性。本文以±1.8Mvar链式STATCOM的研制为背景,对三角形连接的链式STATCOM的主电路进行建模分析和参数设计,并针对直流电容电压平衡控制、系统电压不平衡控制、并网电流波形控制以及锁相环等关键技术作了系统深入的研究。主电路分析是研究链式STATCOM的基础。论文基于三角形连接的链式STATCOM可以等效为三个单相链式STATCOM,建立了链式STATCOM的数学模型,推导了其稳态表达式,在此基础上,对±1.8Mvar链式STATCOM主电路进行了参数设计,并分析了电容、电感、开关频率等参数对装置性能的影响。针对链式STATCOM中的锁相环问题进行了分析。对比分析了三种常用的锁相环方法,分析了锁相环的动态性能和稳态精度对链式STATCOM输出性能的影响,给出了几种系统相位发生突变时链式STATCOM仍能维持稳定工作的方法。直流电容电压平衡控制是链式STATCOM中的关键问题之一。论文通过功率平衡的方法分析了造成链式STATCOM直流电容电压不平衡的原因在于各链节吸收和消耗的有功不一致,因此提出了基于有功电压矢量叠加的平衡控制方法,该方法通过在链节输出电压中叠加有功分量从而改变其吸收的有功来实现直流电容电压平衡。此外提出了矢量分析的方法,通过该方法可以对各种平衡控制策略的稳定性及调控能力进行分析。为了找出最合适的平衡控制策略,仍然通过矢量分析将所提方法同另外两种常用的平衡控制方法进行对比,通过对比可知所提的控制策略具有稳定性好、调控能力强的优点,仿真验证了对比分析的正确性。系统电压不平衡下的控制是链式STATCOM中另一个关键问题。论文通过分析在系统电压不平衡下链式STATCOM的控制方法指出链式STATCOM需要同时输出正序、负序及零序分量其各相才能输出任意可控大小的无功电流,并提出了分相瞬时电流控制策略,在此基础上研究了链式STATCOM在不平衡电压下的补偿模式,提出了无功补偿模式和电压控制模式两种改进型补偿模式。通过分相瞬时电流控制能够维持链式STATCOM在不平衡电压下的正常工作,通过两种改进型补偿模式使链式STATCOM能够有效的对不平衡系统进行补偿。仿真结果表明,所提出的不平衡电压控制策略有效地增强了链式STATCOM在不平衡电压下的安全运行能力,并按照所设计的工作模式能有效地补偿系统中的无功。针对链式STATCOM并网中低次谐波电流问题进行了分析,传统的PI控制器无法对正弦指令电流无静差跟踪,而且其带宽有限,谐波抑制能力不足,因此提出了比例控制器与重复控制器并联的复合控制器结构,对复合控制器进行了详细的设计,并与比例控制器作对比,复合控制器具有足够的频率带宽,可以对基波电流无静差跟踪以及谐波抑制能力良好。仿真结果表明,所设计复合控制显著的增强了链式STATCOM的电流跟踪能力和谐波抑制能力。搭建了链式STATCOM实验样机,并在样机上实现了文中所设计的直流电容电压平衡控制、分相瞬时电流跟踪控制、系统电压不平衡控制,并进行了大量的实验研究,实验结果进一步验证了上述控制策略是正确有效的；此外所有控制策略均在燕山石化6kV/±1.8Mvar以及吉林风电场6kV/±8Mvar的链式STATCOM工业产品上得到验证。更多还原

【Abstract】 For the randomness of wind power, the access of wind farm to the grid will impact the regional voltage stability; at the same time, the stability of power system would affect the access of wind farm, which will further deteriorate the grid voltage stability. The voltage stability is particularly important in the grid with large wind power penetration; static synchronous compensator (STATCOM) can improve the transient voltage stability of power system. In this paper, it takes the±1.8Mvar cascade multilevel STATCOM as the background, from which the the modeling is analyzed and the parameters are designed for the main circuit of delta-connected cascade multilevel STATCOM, furthermore, the key technologies of DC capacitor voltage balance control, system voltage unbalance control, grid current waveform control and phase-locked loop are all detailedly studied.Main circuit analysis is the research foundation of cascade multilevel STATCOM. A mathematical model of cascade multilevel STATCOM is established that the delta-connected cascade multilevel STATCOM can be equivalent into three single-phase chains, and its steady-state expressions are deduced. On this basis, the parameters of main circuit for±1.8Mvar cascade multilevel STATCOM have been designed, while the effections of capacitor, inductor and switching frequency on device performance have been discussed and analyzed.The methods of phase-locked-loop (PLL) for cascade multilevel STATCOM are analyzed. A comparison is given among three types of commonly used phase-locked loop method, whose dynamic performance and steady-state precision are analyzed based on the effection to output characteristics of STATCOM, and several ways against of system phase mutation for cascade multilevel STATCOM are shown.DC capacitor voltage balance control is one of the key problems for cascade multilevel STATCOM. Considering that the imbalance of DC capacitor voltage is caused by the inconsistency of active power absorbed and consumed by chain, a balance control strategy based on active voltage vector superposition is proposed, in which an active voltage component is superposed to chain’s output voltage to change its absorbed active power. A general analytical method based on vector analysis is also presented, by which the performance of balance control strategy can be analyzed, including stability and regulation capacity. To find out the most appropriate balance control strategy, a comparison still based on vector analysis among the proposed and other two commonly used methods is provided, from which it can be known that the proposed balance control strategy has the advantage of good stability and strong regulation capacity, and simulations are performed to prove it.System voltage imbalance control is another key issue of cascade multilevel STATCOM. The control method has been analyzed for cascade multilevel STATCOM under unbalanced system voltage in the paper, from which it can be known that STATCOM needs to output positive sequence, negative sequence and zero sequence components at the same time to output any controlled reactive current, based on which the individual pahse instantaneous current control strategy has been proposed, and two modified compensation modes are studied:reactive control mode and voltage control mode. The cascade multilevel STATCOM can maintain normal operation under unbalanced voltage by using the individual phase instantaneous current control strategy and the unbalanced system can be effectively compensated by the two modified compensation modes. Simulation results show that the operation capability of cascade multilevel STATCOM under unbalanced voltage can be effectively enhanced by the proposed control strategy and it can compensate system reactive power in accordance with the designed compensation mode.The problem of low-order harmonic current for delta-connected cascade multilevel STATCOM has been studied. Traditional PI controller can not track sinusoidal command current without steady-state error, and has insufficient harmonic suppression ability for its limited bandwidth. A novel low-order harmonic suppression method based on hybrid controller is proposed, which is composed by proportional controller and repetitive controller. The hybrid controller has been detailedly designed; compared to the proportional controller, it can track sinusoidal command current without steady-state error and has good harmonic suppression ability for its sufficient bandwidth. A comparison of simulation is given between hybrid controller and proportional controller, from which the effectiveness and feasibility of proposed method has been proved.A prototype of cascade multilevel STATCOM has been built. The proposed control strategies including DC capacitor voltage balance control, individual phase instantaneous current control and system voltage imbalance control are all implemented in the prototype, and many experimental researches have been made, from which the effectiveness and feasibility of proposed methods have been proved. In addition, all control strategies have been verified by the industrial products of Yanshan petrochemical 6kV/±1.8Mvar and Jilin wind farm 6kV/±8Mvar cascade multilevel STATCOM.更多还原