光伏直流升压汇集系统级联变换器虚拟阻抗控制

Virtual Impedance Control for Cascaded Converters in Photovoltaic DC Boost Collection System

光伏直流升压汇集系统中,光伏侧变流器常采用独立输入、串联输出结构实现直流升压,并依据串联变流器分压情况进行模式切换,以避免串联变流器模块端电压发生越限,但模式切换会引起光伏直流汇集系统稳定性的变化。针对这一问题,建立了光伏侧级联DC/DC变换器在不同工作模式下的等效阻抗模型,应用阻抗匹配稳定性判据对比分析系统稳定性差异;同时,提出了适用于OVR控制模式的电压环虚拟电阻控制和调制环虚拟阻抗控制策略来提高系统稳定性。研究结果表明:调制环虚拟阻抗控制能有效弥补电压环虚拟电阻控制导致光伏DC/DC变换器输出电压跌落的缺陷,并将系统相角裕度提升1.5倍,幅值裕度提升1.2倍,有效的处理模式切换导致的系统稳定性波动问题。最后,在MATLAB/Simulink上搭建仿真模型验证理论分析和所提控制策略的有效性。

In a photovoltaic DC collection system,the photovoltaic side converter usually adopts the structure of independent input and series output to realize DC boost,and the mode switching is carried out according to the voltage distribution of the series converter,so as to avoid the over limit of the module terminal voltage of the series converter.However,the mode switching will cause the stability change of the photovoltaic DC collection system.To solve this problem,taking the photovoltaic power generation DC collection system as the research object,we established an equivalent impedance model of the photovoltaic side cascaded DC/DC converter in different working modes,and adopted the impedance matching stability criterion to compare and analyze the system stability differences.Meanwhile,we proposed a voltage loop virtual resistance control and modulation loop virtual impedance control strategy suitable for OVR control mode to improve system stability.The results show that the modulation loop virtual impedance control can effectively compensate for the defects of the voltage loop virtual resistance control which lead to the falling of the output voltage of the photovoltaic DC/DC converter.In addition,the system phase margin is increased by 1.5 times and amplitude margin is increased by 1.2 times,which can effectively deal with the system stability fluctuation caused by mode switching.Finally,a simulation model is built on the MATLAB/Simulink platform to verify the effectiveness of the analysis and proposed control strategy.