摘要
为保证并网逆变器的并网电流与电网电压同步,通常采用锁相环获取电网电压相位信息.同时,为提高并网电流质量,常考虑在回路中加入电网电压前馈.然而,当逆变器工作在弱电网下时,它们均有可能对系统的稳定性带来负面影响.该文以单相LCL型并网逆变器为例,旨在研究弱电网下锁相环和电网电压前馈造成系统不稳定的原因并进行优化.针对2个不稳定因素存在的情况,该文提出一种导纳合成相量法来分析多个导纳共同作用时的影响机理.考虑到带通滤波器可以衰减不稳定因素的影响,文中加入带通环节对系统的鲁棒性进行优化.结合上述导纳合成相量法的分析结果,确定带通环节的设计目标,并进一步给出带通环节参数的具体设计过程.结果表明,并网逆变器加入优化设计的带通环节后,即使在电网阻抗变化范围较大的情况下,系统仍能稳定工作.
Abstract
For grid-connected inverter,phase-locked loop(PLL)is generally adopted to obtain the voltage phase information in order to make the grid current be synchronized with the grid voltage.In the meantime,the grid voltage feedforward scheme is usually employed to improve the grid current quality.However,both of these two factors may cause negative impacts on the stability in weak grid.This paper focuses on the single-phase LCL-type grid-connected inverter,aiming to explore the causes of instability and optimize its performance accordingly.In view of the existence of dual unstable factors,a synthesis-admittance-phasor scheme is proposed to analyze the influence mechanism.Considering the attenuation effect of the band-pass filter(BPF),the design goal of the band-pass link is determined according to the analysis results of the synthesis-admittance-phasor scheme,and the specific design process of the parameters is further given.The results show that the grid-connected inverter with the optimally designed band-pass link can still work stably even when it is against the wide grid-impedance variation.
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