并网变流器全工作区间的稳定性分析方法研究

Study on the Stability Analysis Method of Grid-connected Converters in Full Operating Range

并网变流器作为分布式新能源发电的核心装备,其全工作区间运行稳定性研究的理论与实践价值巨大。目前,针对并网变流器的稳定性研究主要采用阻抗法和状态空间法,多以额定工况下的分析结果指导整个静态工作区的控制器设计。而实际并网变流器在不同功率段往往表现出不同的运行特性,如在青海省某光伏电站输出功率达到额定值65%左右时,公共连接点处更易出现电压、电流波形畸变。因此,进行并网变流器全工作区间运行特性的研究意义显著。然而,现有阻抗法和状态空间法等典型稳定性分析方法通常只在单一工作点进行建模,如何将其简单、直观地推广到全工作域的相关研究还较少。为分析并网变流器系统在全工作区间内稳定性,提出一种稳定域构建方法。首先,利用dq轴之间的多重耦合效应和锁相环的动态特性,将变工作点因子引入建模过程中;接着,构建一个含工作点变量的变流器单输入单输出传递函数模型。基于所提出的模型,能够直观分析系统的稳定工作域,进而能够研究系统参数对稳定域的影响规律。仿真与实验结果验证了该模型和理论分析的有效性。

The research on operation stability of grid-connected converter(GCC),the core equipment of distributed new energy power generation,in full working range has important theoretical and practical value.At present,impedance-based method and state-space based method are commonly used in the stability study of GCC;while analysis results under rated operating conditions are widely used to guide the design of the controller in the whole static operating area.However,GCCs often show different operating characteristics in different power ranges.For example,in a photovoltaic plant in Qinghai Province,the voltage and current at the point of common coupling(PCC)tend to have waveform distortion when the output power reaches about 65%of its rated value.Therefore,it is of great significance to study the operation characteristics of GCC in full operating range.However,existing typical stability analysis methods,including impedance-based method and state-space method,are only used when modeling at a single working point.There are less researches related to extend the existing methods to the full operating range.This paper proposes a stability region-based method to analyze the stability of GCC in full operating range.First,the operating point is introduced into the modeling process as a variable through the multiple coupling effect between dq axes and the dynamic characteristics of phase locked loop(PLL).Then,a single-input single-output(SISO)transfer function model of the converter is constructed,which includes the operating point variables.Based on the proposed model,the stable working domain of the system can be analyzed intuitively,as well as the influence mechanisms of system parameters on stable domain.The simulation and experimental results verify the validity of the model and the theoretical analysis.