一种针对数字控制下光伏并网逆变器的陷波器滞后补偿方法

A Lag Compensation Method Based on Notch Filter for PV Grid-connected Inverter Under Digital Control

由于数字控制中存在着延时环节和零阶保持器环节,使得光伏并网逆变器的运行极易发生不稳定的状况。为了研究数字控制下光伏并网逆变器的稳定性问题,首先针对逆变器建立了z域模型,并推导了其z域传递函数,然后通过严格的数学推证发现当逆变器谐振角频率 w res = π/(3Tsa)时,系统存在的两个开环不稳定极点和一次穿越-π线之间的矛盾导致了逆变器的谐振角频率在此点必不能稳定,同时指出了当逆变器的谐振角频率 w res在π/(3Tsa)附近处时系统亦难以稳定。针对此种情况,提出一种陷波器滞后补偿策略,在讨论了数字控制下陷波器特性和离散方法后,给出了滞后补偿的设计思路和方法。根据前述思路与方法搭建了一台功率为6.6kW的三相光伏并网逆变器,实验结果表明此方法简单有效,能够使逆变器在其谐振角频率 wres位于π/(3Tsa)及其附近处时皆能保持稳定状态,验证了理论分析的准确性。

Due to the existence of time-delay link and zero-order-holder link in digital control,the operation of PV grid-connected inverter is easily unstable.In order to study the stability of PV grid-connected inverter under digital control,the z-domain model was firstly established for the inverter,then the transfer function was derived.It can be found through strict mathematical evidence that whenωres is equal toπ/(3Tsa),the contradiction between two open-loop unstable poles and one pass through-πline leads to a completely unstable case.Besides,the system is easily unstable ifωres is nearπ/(3Tsa).In this case,a lag compensation method based on notch filter was proposed.After studying the characteristic and the discrete method of notch filter,a design idea was given.And based on the design idea,a 6.6kW experimental setup was established.Finally,the correctness of the theoretical analysis is verified by the experiment.