【作者】 李芬；

【导师】 邹云屏；

【作者基本信息】 华中科技大学 ， 电气工程， 2010， 博士

【摘要】 各种电力电子变换电源,如不间断供电电源(UPS)、交流电机驱动器等,出厂时需要进行严格的老化和相关的稳态、动态特性考核试验,以保证出厂电源的优良品质。针对传统能耗型电源试验方式存在能源浪费、调节不便等缺点,采用电力电子器件组成的绿色节能试验系统可以满足对被试电源老化筛选考核日益增长的节能、环保需求。本文针对单相背靠背绿色试验系统,展开深入的研究工作。基于单相背靠背系统的基本组成电路及其工作原理,根据稳态矢量三角关系,阐明稳态下交流电网和单相PWM变流器之间有功、无功交换机理,研究了PWM变流器作为可控电流源运行的实质,并建立了PWM变流器的状态平均空间数学模型。根据瞬时能量平衡,分析出单相系统瞬时输入功率存在二倍频脉动是导致母线电压存在二次谐波的根源。研究了母线电压二次谐波对输入交流电流的影响,推导出双环控制电压控制器增益(带宽)与输入交流电流THD之间的矛盾关系,得出了通过对电压闭环带宽的限制可以改善稳态输入电流质量的结论。对改善输入电流质量的低通滤波器和100Hz陷波器性能进行了比较。本文建立L滤波的并网变换器小信号模型,研究了变换器运行工况(整流或回馈)、主电路参数母线电容变化对电压闭环极点分布的影响,分析变换器在回馈状态下可能存在的稳定性问题。同时根据结构框图,直观分析各种扰动输入对母线电压动态响应的影响,为全面提高并网变换器动态特性和扰动能力的控制策略提供指导。以负载电流扰动为主验证系统特性,定义了并网变换器直流侧等效输出阻抗的概念。针对双环控制下电压闭环带宽的限制,采用负载电流前馈的策略,并根据不同控制下输出阻抗波特图,比较了直接负载电流前馈和完全的负载电流前馈控制的区别。针对单相系统负载电流观测器数字化实现存在的问题,提出通过瞬时输入功率计算母线电流的方法,避免负载电流观测过程中采样频率有限引起的失真和引入母线电流高频开关分量,而为抑制负载观测电流、母线电压的二次低频谐波的影响,设计一种新型滤波器。本文采用LCL滤波器代替原来交流侧L滤波器并网,可以解决L滤波器对高频谐波衰减不足的问题。通过对LCL滤波器物理模型、PWM调制谐波电压理论、入网谐波标准的研究,根据需要满足的约束条件(谐波抑制、稳态特性等),提出了完整、参数相互协调的LCL滤波器设计原则。针对LCL滤波器自身谐振,研究了一种易于实现且不会增加损耗的有源阻尼方法,分析了电流环控制参数变化时闭环系统的稳定性特性,并提出控制参数需满足的约束条件。针对直接由公共耦合端(PCC)电压波形获得并网指令电流波形模式,将控制器参数和物理模型结合建立了LCL滤波并网变换器的闭环高频输入阻抗模型,详细地研究其在不同功率等级时整流工况、有源逆变工况下的频率特性；并比较两种工况下PCC电压前馈对输入阻抗特性的影响。本文针对背靠背系统的关键技术,从整体角度建模,揭示直流母线电压动态波动的本质以及稳态下母线电压谐波成分与两侧交流电参数间的物理关系(尤其当被试电源频率不同于电网频率时,结合瞬时功率理论和互调理论,推导出直流母线电压谐波成分(包括互调产物)表达式,分析并网输出电流谐波和间谐波产生机理)。根据上述物理关系,从稳态谐波和动态能量突变电压波动两方面给出了详细的母线电容的设计原则。提出一种基于工频陷波器的新型滤波器设计,减小输出并网电流的间谐波。根据交流电子负载功率流动的方向,考虑到电流环的延时,提出了采用输入电流指令前馈的功率前馈控制,解决直流母线电压大范围波动与瞬变能量动态平衡的难题。本文根据实际电网存在可能谐振、PCC并联谐波负载下PCC电压畸变的情况,引入谐波阻尼思想,为背靠背试验系统并网变换器提出一种新的并网指令电流策略。该算法使并网变换器在回馈能量的同时,实现对畸变的PCC电压特定次的谐波电压(电网谐振频率处)呈现一定正值的谐波电阻,对提高绿色节能试验系统工作的电网适应性,具有重要的实用意义。通过仿真,对比研究了传统纯正弦指令电流模式、直接由PCC电压波形获取指令电流波形以及本文提出的特定频率的谐波阻尼算法三种模式下的效果,验证了该算法抑制PCC电压畸变的有效性。更多还原

【Abstract】 AC power electronic products, such as Uninterruptible Power Supply (UPS), AC motor drives, etc., are widely used in industrial, commercial and residential applications for high power quality requirements. However, before these AC sources can be used in practice, they must be tested for reliability and stability. Traditionally, the method of consumption load is in common. In this way, not only the tested power is wasted but also the operation is inconvenient. To meet the requirements of energy-saving and environmentally friendly features for AC power source burn-in test, green recovery-energy-based system composed by power switches is proposed. This paper focuses on the single-phase back-to-back green recovery-energy-based system, and the in-depth work is organized as follows:According to the steady-state vector relationship, the principle on the exchange of active and reactive power between the single-phase PWM rectifier and AC source is analyzed, the reason that PWM rectifier can be operated as controllable current source is also point out and the average state space mathematical model is established for control. Based on the instantaneous energy balance, for single-phase system, the instantaneous ac input power fluctuates at the twice frequency of AC source, which leads to the fluctuation of DC bus voltage at the twice frequency of AC source, unfortunately, causing the input ac current distortion. The relationship between Total Harmonic Distortion (THD) of input ac current and voltage-loop bandwidth is revealed. That offers limits for voltage controller design. The low-pass filter and notch filter for improving the current quality are compared.The linearized small-signal mathematical of PWM rectifier is set up for discussing the effect of operation of PWM rectifier under consumer mode and the power feedback mode, and circuit parameters on the closed-loop poles. The stability problem under power feedback operation is also discussed. At the same time, the influence of all kinds of disturbance on the dynamics of DC bus voltage is analyzed for the improved control. The dynamics test is mainly for the load transient, and the concept of the equivalent out impedance for DC bus is given. Due to the limitation of voltage-loop bandwidth, the load current feed forward control is proposed. The difference between full load current feed forward control and direct load current feed forward control is investaged by the output impedance bode. To overcome the defects of digital realization of observer such as aliasing due to the limited sampling frequency and DC bus current PWM harmonics, the method to estimate DC bus current by instantaneous input power is presented. Also a novel filter is proposed for reducing the impact of twice harmonics of DC bus voltage and current.Due to better attenuating current harmonics around switching frequency injected to the grid, L-filter is substituted by LCL-filter in grid connection of PWM rectifier. The transfer functions models of LCL-filter, the pulse-width-modulation theory and the harmonics requirements for input current of grid-connect converter are described. According to the restrictions such as harmonics suppression, steady-state characteristics etc., the throughout LCL-filter parameters design is analyzed. Because of the resonance phenomenon of LCL-filter, it may bring stability problems in the current loop. In order to overcome them, a control strategy applying the filter-capacitor current feedback in the current loop is proposed to achieve the function of damping resistor, and stability conditions for controller parameters are also analyzed. Then, the input impedance integrated the controller with the LCL-filter parameters in high frequency region is modeled and analyzed by the frequency responses of the transfer functions models, including the consumer mode and the power feedback mode. Also, the influence of the disturbance of Point of Common Coupling (PCC) voltage is studied.Both the essence of DC bus voltage fluctuation and the harmonics relationship in steady state between the AC side and the DC side of AC/DC converter and DC/AC converter will be revealed by the integrated modeling. Especially, when the frequency of AC tested source is different from that of the grid, the harmonics and inter-modulation production in the DC bus is analyzed in detail, and the generation of the output current harmonics and inter-harmonics injected to the grid is revealed, by means of instantaneous power theory and inter-modulation theory. Considering the steady-state harmonics and transient DC bus voltage fluctuation, a whole design for the critical storage component-DC bus capacitor is presented. To suppress the output current harmonics and inter-harmonics injected into the grid, a novel filter is given. Also, the difficulty of a wide range of DC bus voltage fluctuation and the balance of transient energy during dynamic is overcame by a feed forward control of the input current reference RMS.Under real grid-connected conditions, the PCC voltage is distorted in the distribution network due to the resonant and other nonlinear loads connected to the same PCC. Applying the harmonic damping concept, a novel grid-connected current reference strategy is proposed. This strategy makes the grid-connected converter of back-to-back system behaves as a positive resistance for the specific harmonic (at the resonant frequency) of PCC voltage to damp the possible resonance and suppress the harmonics of the PCC voltage, independent of a negative resistance for fundamental component to realize power feedback. This study provides theoretical and experimental basis for promoting the process of green recovery-energy-based system to a practical application. Three current reference algorithm (the sinusoidal grid-connected current reference, grid-connected current reference produced by PCC voltage directly, and the proposed method) are compared.更多还原