【作者】 余蜜；

【导师】 康勇； 张宇；

【作者基本信息】 华中科技大学 ， 电气工程， 2009， 博士

【摘要】 随着人类对能源的需求日益增加，光伏发电技术成为研究与开发的热点。本文致力于对光伏发电系统的能量变换部分中的并网电流控制技术和逆变并联均流控制技术进行研究。光伏并网逆变器可通过L滤波器或LCL滤波器两种结构并网运行，本文先对L型并网电流控制研究，然后研究LCL型并网控制存在的特殊问题。针对标准对并网电流谐波畸变率、功率因数以及对参考电流跟踪误差的要求，本文推导了这些指标与闭环根频率f_n（闭环特征根的固有频率）的关系，由此提出了以闭环根频率f_n为控制系统设计的唯一量化指标的研究方法。以常用的PI控制为例，本文首次给出并网指标与闭环根频率的定量关系。在L型并网中，针对离散化可能引起的系统稳定性下降的问题，本文分析并获得了PI控制离散化系统稳定范围时闭环根临界频率f_nmax与采样频率f_s之间的定量关系，针对离散化可能引起系统稳态特性下降的问题，对比分析了PI控制离散化前后的频域特性，综合考虑并网指标、稳定性要求和离散化对稳态特性影响三个主要因素，推导了离散化PI控制对最低采样频率的量化要求。在L型并网中，考虑到离散化控制存在滞后一拍的问题时，本文分析并获得了离散PI控制系统稳定范围时闭环根临界频率f_nmax和采样频率f_s之间的定量关系；针对存在滞后一拍可能引起系统稳态特性下降的问题，分析了PI控制滞后一拍对频域特性造成的影响，综合考虑并网指标、稳定性要求和离散化对稳态特性影响三个主要因素，推导了存在滞后一拍的离散化PI控制对最低采样频率的量化要求。在LCL并网中，针对LCL滤波器是否满足开关纹波电流抑制特性要求的问题，本文研究并获得了LCL滤波器所适用开关频率范围。针对LCL滤波器的谐振可能引起系统稳定性下降的问题，在连续域中分析了内电感电流反馈控制的稳定性，得出了闭环控制的稳定性不受LCL滤波器谐振的影响的结论。在LCL型并网电流控制中，针对内电感电流反馈控制的稳态特性可能满足不了并网电流要求的问题，本文分析了电流跟踪特性、抗干扰特性等特性，获得并网指标对闭环根频率及LCL滤波参数的要求。在LCL型并网中，针对离散化可能引起的系统稳定性下降问题，本文分析并获得了离散化PI控制系统稳定时闭环根临界频率f_nmax与采样频率f_s间的定量关系。考虑到离散化控制存在滞后一拍问题，本文分析并获得了系统稳定时闭环根临界频率f_nmax与采样频率f_s间的定量关系。在分散逻辑均流控制中，均流控制策略需要明确参考电压调节量与环流之间的关系，为了描述该关系，本文首次提出了虚拟环流阻抗概念，并获得了虚拟环流阻抗的数学模型。针对电压瞬时反馈控制可能对均流控制带来负面影响，分析了虚拟环流阻抗数学模型，获得的结论为：增加电压瞬时反馈控制后，并联系统的虚拟环流阻抗值大幅减小，同时阻抗特性也发生改变。在均值均流控制中，为解决参考电压的幅值控制与相位控制存在耦合关系导致均流控制的响应速度变慢的问题，本文采用了利用虚拟环流阻抗解耦的均流控制策略。为进一步加快均流控制的动态响应速度，本文提出了基于虚拟环流阻抗调节器的瞬时均流控制策略。针对滤波参数不一致可能降低该瞬时均流控制策略的均流性能的问题，本文分析了滤波参数不一致时具有该策略的并联系统环流的数学模型，得出的结论为：该均流控制策略具有很好的鲁棒性。仿真与实验结果也表明该均流控制策略具有优异的动态及稳态特性。更多还原

【Abstract】 While the world’s power demand is increasing,photovoltaic power distributedgenerating system is gaining more and more visibility.This dissertation is focused on theresearch of grid-on current control and current-sharing control,which are the keytechniques in power conversion ofphotovoltaic energy.The grid-on inverter is connected with power system via L filter or LCL filter.Thecommom problem of current control is researched with L filter first,then the specialproblem in LCL grid-on current control is researched.The technical requirements forgrid-on PV system are the total harmonic distortion,power factor and current trackingerror of grid current.The relationship between these requirements and the naturalfrequency of the close-loop characteristic roots(FCCR)is analyzed in the paper.Then atheory in which FCCR is used to quantize the technical requirements is proposed in thepaper.Taking PI control algorithm for example,the quantitative relationship is presented.As the system stability may fall down in grid-on inverter with a L filter while thecontroller is discreted,the quantitative relationship between critical FCCR and samplingfrequency is analyzed.As the system steady performance may fall down while thecontroller is discreted,the steady performance of discrete control system is compared tothat of continues control system.Considering the technical requirements,the stability andthe steady performance,the quantitative requirement for sampling frequency is present indiscrete control system.Considering that there is a step delay in discrete control in grid on inverter with a Lfilter,the quantitative relationship between critical FCCR and sampling frequency isanalyzed,and the steady performance is analyzed.Considering the technical requirements,the stability and the steady performance,the quantitative requirement for samplingfrequency is present in discrete control system with a step delay.As LCL filter may not satisfy the engineering requirements for some switchingfrequency in grid-on inverter,the range of switching frequency is analyzed.As thestability may fall down because of resonance of LCL filter,the stability of current controlsystem in continues time is analyzed,and the conclusion is that the stability is not affected by the resonance.As the performance may not satisfy the technical requirements in grid-on inverterwith inner inductor current feedback control,the current tracking performance andanti-interference performance are analyzed,and requirements for FCCR and parameter ofLCL filter are obtained.As the stability may fall down in grid-on inverter with a LCL filter while thecontroller is discreted,the quantitative relationship between critical FCCR and samplingfrequency is analyzed and obtained.When discrete control is with a step delay,thequantitative relationship between critical FCCR and sampling frequency is analyzed andobtained.As the relationship between regulated reference voltage quantity and circulatingcurrent need to definite clearly in distributed logic current-sharing control,the concept ofvirtual circulating impedance is proposed,and its mathematical model is obtained.As thevoltage feedback control may affect the current-sharing control performance,themathematical model is analyzed.The conclusion is obtained,that the magnitude ofcirculating impedance is decreased sharp and the characteristic is changed by voltagefeedback control.As the magnitude control and phase control are coupled in roots mean square(RMS)current-sharing control,the respond speed of current-sharing control becomesslower.To solve the problem,a novel decoupled strategy based on virtual circulatingimpedance is proposed in the paper.To further accelerate respond speed,a novel instantaneous current-sharing controlstrategy based on virtual circulating impedance controller is proposed in the paper.As thedifference in inverter modules’ parameters may decrease the current-sharing performance,the mathematical model of circulating current in parallel system with the instantaneouscurrent-sharing control strategy is analyzed,and the conclusion is obtained,that thestrategy is robust.The results of experiment and simulation verify that the current-sharingcontrol strategy has very good performance.更多还原