【作者】 王文超；

【导师】 王颖杰；

【作者基本信息】 中国矿业大学 ， 电气工程， 2017， 硕士

【摘要】 在大功率并网变换器系统中,随着功率等级不断提高,为降低系统损耗、提高器件输出能力,系统的开关频率不断降低,但也因此造成电流控制系统性能下降。为此,本文以两电平并网变换器为研究对象,考虑低开关频率下系统延时的影响,对其数学模型和控制策略进行研究。首先,在不同坐标系下建立了并网变换器的常规数学模型,接着在考虑系统延时的情况下,建立了d-q坐标系下低开关频率并网变换器的复矢量和传递函数阵模型,揭示了系统耦合的原因。其次,引入相对增益矩阵(RGA)分析法,分析了不同开关频率下L型并网变换器未解耦系统动、静态耦合程度,尽管PI调节器能够完全消除系统静态耦合,但动态耦合随开关频率的降低愈加严重。加入常规前馈解耦后系统动态耦合程度有所改善,但仍很严重,为此在保留系统主通道特性的前提下,提出了输出反馈解耦策略,通过传递函数阵对角化,实现系统解耦。并通过RGA分析法和多输入多输出(MIMO)根轨迹法对比了不同解耦策略下系统的控制性能和参数敏感性。最后给出了低开关频率下L型并网变换器控制系统的参数设计方法,并通过MATLAB/Simulink对不同的解耦控制策略进行了仿真分析。接着,在低开关频率LCL型并网变换器复矢量模型的基础上,基于复矢量零极点对消思想,提出了无源阻尼串联解耦策略。进一步地,结合陷波器有源阻尼策略,提出了陷波阻尼串联解耦策略,并给出了低开关频率下LCL型并网变换器控制系统的参数设计方法。最后通过系统闭环频率特性和单位阶跃响应,对比了解耦和未解耦系统的控制性能,并通过MATLAB/Simulink对其进行了仿真验证。最后,搭建了L型/LCL型并网变换器实验平台,对低开关频率下两种并网变换器的控制性能进行了实验验证,实验结果验证了本文所提理论分析和所提策略的可行性和正确性。更多还原

【Abstract】 With the increase of the rated power,the switching frequency tends to be lower to reduce system losses and improve device output ability in the high-power grid-connected converter system.However,it also leads to performance degradation in the current control system.Therefore,in this paper,the two-level grid-connected converter is taken as the research object,and its mathematical model and control strategy are studied with considering the influence of time delay at low switching frequency.Firstly,the conventional mathematical model of grid-connected converter is established in different coordinates.Then the complex vector and transfer function matrix model of grid-connected converter are established in d-q coordinate at low switching frequency with explicitly considering the time delay,which reveals the reasons of system coupling.Secondly,the relative gain array(RGA)analysis method is introduced to analyze the static and dynamic coupling degree of L type grid-connected converter system with non-decoupling method at different switching frequency.Although the PI regulator can completely eliminate the static coupling of the system,the dynamic coupling is more serious with the decrease of switching frequency.The dynamic coupling degree of the system is improved,after the traditional feedforward decoupling method is employed,but it is still very serious.Therefore,an output feedback decoupling method is proposed to realize the decoupling of the system in this paper under the premise of keeping the main channel characteristics of the system,which is based on the idea of transfer function matrix diagonalization,where the control performance and parameter sensitivity of the system with different decoupling methods are compared by RGA analysis method and multiple input and multiple output(MIMO)root locus.Finally,the parameter design method of control system for the L type grid-connected converter at low switching frequency is given,and the simulation analysis is conducted in MATLAB/Simulink.Thirdly,on the basis of the complex vector model of LCL type grid-connected converter at low switching frequency,a passive damping series decoupling method is proposed,which is based on the idea of complex vector zero pole cancellation.Further more,a trap damping series decoupling method is proposed based on the active damping method of notch filter,where the parameter design method of the control system for the LCL type grid-connected converter at low switching frequency is given.Finally,the control performance of the coupling system and decoupling system is compared by the frequency characteristics and unit step response of the closed-loop system and it is verified in MATLAB/Simulink simulation.Finally,the experimental platform of L/LCL type grid-connected converter is built to verify the control performances of the two types of grid-connected converter system at low switching frequency.The experimental results verify the feasibility and correctness of the proposed theoretical analysis and method.更多还原