基于LCL滤波的级联STATCOM控制策略及应用研究

发布时间：2017-12-27 00:13

本文关键词：基于LCL滤波的级联STATCOM控制策略及应用研究　出处：《中国矿业大学》2016年博士论文　论文类型：学位论文

【摘要】：近年来,随着工业设备现代化的不断发展,各种非线性、频繁波动及不平衡负荷的使用日益增多,由此导致出现了低功率因数、线损增大、严重谐波污染、三相不平衡及电压波动等严重危害电网电能质量的问题,于是补偿无功、治理谐波及解决三相不平衡技术成为当前研究的热点。相比常规无功补偿装置,静止同步补偿器(Static Synchronous Compensator,简称STATCOM,又称SVG)由其具备的动态无功调节、实时谐波补偿及解决三相负载不平衡的突出性能,成为电网稳定性调节技术的潮流及发展方向,因此本文对基于LCL滤波的级联STATCOM关键控制技术及其应用的研究具有重要理论研究与应用价值。星型结构6k V、10k V中压配电网中性点通常采用不直接接地的保护方式,而级联STATCOM装置中性点采用不接地的方式,于是在针对LCL滤波的级联STATCOM分析建模过程中需要考虑系统中性点与装置中性点之间的电压。本文依据开关函数,在考虑电网中性点与STATCOM装置中性点之间电压的基础上,建立了基于LCL滤波级联STATCOM在a-b-c与d-q坐标下的精确数学分析模型。针对LCL滤波的级联STATCOM系统在d-q坐标下的电流控制模型中出现的高阶、非线性、强耦合特性,本文提出一种针对无源阻尼LCL滤波的状态反馈精确线性化电流解耦方法,实现了d-q坐标下基于特征谐波补偿的有功及无功输出变量的解耦控制。本文采用带无源阻尼的LCL滤波器来实现STATCOM低频补偿带宽内低输出阻抗,高频滤除带宽高输出阻抗的电流快速跟踪控制。由于LCL滤波存在三阶不稳定特性,其关键参数的选择会对其谐振频率、各次电流衰减性能和阻尼损耗等造成影响,于是本文从各次补偿电流的衰减性能及其引起阻尼损耗的角度详细讨论了滤波器的优化设计方案,以此提出了一种在保证滤波性能及稳定性基础上,基于特定次谐波补偿的复合有功损耗控制策略。为了进一步增强无源阻尼LCL滤波的稳定控制性能与改善低频段补偿带宽,建立了基于LCL滤波、比例积分(Proportion-Integral,PI)控制、二阶低通滤波及积分校正环节的控制内环设计,实现无源阻尼LCL补偿带宽控制的稳定。在三相电压不平衡及电网频率波动状态下,本文提出一种基于d-q坐标变换及改进型递归离散傅立叶变换(Discrete Fourier Transform,DFT)相结合的锁相环设计,及与之相适应的无功、谐波指令电流全补偿与选择性补偿检测算法。结合锁相环的瞬时无功及谐波电流全补偿检测算法,实现对非理想电网中存在波动的无功及谐波实时检测。针对非理想电网频率下DFT算法进行选择性谐波电流检测时出现的较大幅值与相位延时误差问题,基于d-q坐标变换及与锁相环相适应的改进型DFT特定次谐波动态检测策略只需要1/2工频周期即可完成对含有不平衡分量指令电流的动态检测跟踪,而不考虑不平衡分量时其检测时间只有传统DFT检测的1/6,避免因检测延时而负载变化后造成谐波注入问题。针对基波及谐波电流快速变化特性及电网频率波动时电流环高精度补偿的稳态误差问题,本文提出了d-q坐标下与锁相环相结合的两种改进型复合控制器设计。由于理想比例谐振控制(Proportional Resonant,PR)在谐振点稳定带宽较窄,且存在不稳定的虚轴开环极点,本文改进的比例积分谐振(Proportional-Integral Resonant,PIR)复合控制器通过PI校正低频、串联校正环节拓展高频、与之对应的稳定校正环节改善稳定性来保证电流控制环的稳定及补偿电流的控制精度。针对重复控制器存在控制周期响应延迟问题,本文基于d-q坐标变换与改进的1/2或1/6重复周期相结合建立了以PI控制为内环、改进型重复控制器为外环的双环电流跟踪控制结构。通过PI控制器、二阶低通滤波器及相应校正环节实现指令电流快速跟踪响应,改进型重复控制外环对控制内环的跟踪误差进行进一步调整,有效改善了补偿带宽内指令电流的跟踪精度与动态响应性能。同时,本文中的锁相环保证了控制器对于波动频率的自适应性,实现了两种复合控制在电网频率波动时的高精度补偿控制。针对星型结构STATCOM相间直流侧电压不平衡问题,本文建立了基于零序及负序电压注入的有功交换数学模型。通过对比其调节能力及适应性,在此基础上提出一种基于d-q-0坐标系与改进型递归DFT相结合的零序电压注入的相间电压平衡控制方法。同时建立了与之对应的基于整体、相间与相内电压动态分层控制模型,实现对装置电容电压的均衡控制。基于二倍频谐波电压PI外环校正来调节直流侧整体电压平衡控制中总体有功的注入。针对相内电压均衡控制,本文采用基于载波移相调制的链节电压独立平衡控制策略与单极性载波层叠调制的调制波分配控制策略。为解决H桥内开关器件均衡损耗问题,论文通过一种基于占空比脉冲调制的H桥内损耗平均控制策略来均衡桥内IGBT器件的动作。本文在6k V±6Mvar LCL滤波级联STATCOM的关键控制技术基础上,开发出实验样机,并给出了样机中软、硬件设计方案。通过搭建的实验样机平台,对包括基波及前20次特定谐波的综合补偿效果进行了实验验证,实验表明了本文研究的基于LCL滤波级联STATCOM控制策略的有效性。
[Abstract]:In recent years, with the continuous development of modern industrial equipment, various nonlinear, frequent fluctuations and unbalanced load increasing use, thus resulting in low power factor, line loss increase, serious harmonic pollution, three-phase unbalance and the voltage fluctuation and other serious harm to the power quality problems, so the reactive power compensation and harmonic control and to solve the unbalanced technology has become a research hotspot. Compared with the conventional reactive power compensation device, static synchronous compensator (Static Synchronous Compensator, referred to as STATCOM, also known as SVG) by dynamic have no prominent performance of reactive power regulation and real-time harmonic compensation and three-phase load imbalance, become the trend and direction of development of power grid stability control technology, this paper researches on LCL filter cascade STATCOM the key control technology and its application based on has important theory research and application value. 6K V 10K, star of V medium voltage distribution network neutral point protection usually do not directly grounded, and cascade STATCOM device neutral grounding mode, so the analysis considers the voltage between the neutral and neutral system device needs in the process of modeling in cascaded STATCOM filter for LCL. Based on switching function, considering the voltage between neutral point and neutral point of STATCOM device, an accurate mathematical analysis model based on LCL filter cascade STATCOM in a-b-c and d-q coordinates is established. According to the cascade STATCOM system LCL filter current in d-q coordinate control of high order, nonlinear and strong coupling characteristics in the model, this paper proposes a LCL filter for passive damping state feedback linearization decoupling method, realizes the active harmonic compensation based on characteristic and reactive power decoupling control of the output variable d-q coordinate. In this paper, the LCL filter with passive damping is used to achieve STATCOM low frequency compensation, low output impedance within the bandwidth, and fast current tracking control with high bandwidth and high output impedance. The LCL filter has three order unstable characteristics, the selection of key parameters will affect the resonant frequency, the current attenuation performance and damping loss, so this paper from the compensation current attenuation performance and damping loss caused by the angle of optimization design of filter is discussed in detail, which presents a ensure the filtering performance and stability. The specific harmonic compensation control strategy based on composite power loss. In order to further enhance the performance and improve the low-frequency compensation bandwidth stability control of passive damping LCL filter, LCL filter, proportional integral is established based on (Proportion-Integral, PI) control, two order correction low-pass filter and integral control loop design, implement passive damping LCL compensation bandwidth control stability. In the three-phase unbalance voltage and frequency fluctuation condition, this paper presents a d-q based on the coordinate transformation and the improved recursive discrete Fu Liye transform (Discrete Fourier Transform, DFT) design of phase locked loop, and the corresponding reactive power compensation, and selective harmonic current compensation instruction detection algorithm. Combined with the instantaneous reactive power and harmonic current compensation detection algorithm of phase-locked loop, the real-time detection of reactive power and harmonics in the non ideal power grid is realized. Large amplitude and phase delay errors of selective harmonic current detection based on DFT algorithm under non ideal grid frequency, improved DFT specific harmonic dynamic detection strategy d-q and PLL based on coordinate transformation and adaptation needs only 1/2 power cycle can be completed with unbalanced tracking dynamic detection component command current, and without considering the unbalanced weight when the detection time only the traditional DFT detection 1/6, avoid detection delay and load changes caused by harmonic injection. Aiming at the steady-state error of high-precision compensation of current loop, the fast and variable characteristics of fundamental and harmonic currents, and the design of two improved composite controllers based on d-q coordinates and phase-locked loops are proposed. Because the ideal proportional resonant control (Proportional Resonant, PR) in the resonance frequency stability with narrow bandwidth, and the imaginary axis unstable open-loop poles, this paper improved proportional integral resonant (Proportional-Integral Resonant, PIR) PI composite controller through the correction of low frequency and high frequency link cascade compensator is extended, and the corresponding correction link to improve stability to ensure the stability of control accuracy and stability and current compensation current control loop. In view of the existence of control period response delay in repetitive controller, based on d-q coordinate transformation and improved 1/2 or 1/6 repeat cycle, a dual loop current tracking control structure with PI control as internal loop and improved repetitive controller as outer loop is established. Through a PI controller, two order low-pass filter and the corresponding correction link to achieve fast tracking the instruction current response, improved repetitive control to further adjust the loop tracking error on the control loop, effectively improve the tracking precision and dynamic instruction current compensation within the bandwidth response performance. At the same time, the phase-locked environment protection in this paper proves the adaptability of the controller to the frequency of fluctuation, and realizes the two kinds of compound control of high precision compensation control in the frequency fluctuation of power grid. In this paper, a mathematical model of active switching based on zero sequence and negative sequence voltage injection is established to solve the problem of unbalanced DC voltage in the star shaped structure of STATCOM. By comparing its adjustment ability and adaptability, a phase voltage balancing control method based on d-q-0 coordinate system and improved recursive DFT is proposed. At the same time, a dynamic hierarchical control model based on the whole, phase and phase voltage is set up to realize the balanced control of the capacitance voltage of the device. Control of DC side overall voltage balance control based on two frequency harmonic voltage PI external loop correction
【学位授予单位】：中国矿业大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TM761

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