组网型变流器离散域双闭环控制研究

Research on Dual-loop Controlled Grid-forming Converter in the Discrete-time Domain

高性能组网型变流器在微电网、轨道交通、航空地面电源等场合具有重要的应用前景。传统基于连续域分析方法将数字控制一拍延时进行近似,无法确定电流内环最优增益,且电压环高频补偿能力弱,容易引发电压振荡问题。为此,建立了组网型变流器的离散域数学模型,通过根轨迹分析提出了电流内环最优增益,获得了最大有源阻尼并抑制了滤波器谐振。针对电压环,提出了延时补偿方法提高系统稳定性,通过谐振控制器实现对各频次电压的无静差跟踪,避免了输出电压振荡,抑制了死区、母线电压波动以及非线性负载对输出电压的影响。仿真与实验结果验证了所提方法的有效性与实用性。

High-performance grid-forming converters have important application prospects in micro grids,rail transit,aviation ground power supply and other applications.The traditional double-loop control implemented in the continuous-time domain approximates the one-sampling delay.The optimal gain of the inner-current controller cannot be determined.The high-frequency harmonic compensation frequency of the voltage loop is highly limited.To solve these issues,the discrete-time domain model of the grid-forming converter is established,and the optimal gain of the innercurrent loop is developed through root locus analysis.In this manner,the maximum active damping is obtained,and the filter resonance is suppressed.Regarding the outer-voltage loop,the proportional resonant controller achieves the tracking of selected-frequency voltage without static-state error,and a delay compensation technique is proposed to improve the stability.Also,the adverse effects of the dead time,bus voltage fluctuations and nonlinear load imposed on the output voltage is suppressed.Simulation and experimental results have verified the correctness and effectiveness the proposed method.