Low-Voltage Ride-Through Techniques for Two-Stage Photovoltaic System under Unbalanced Grid Voltage Sag Conditions

Xiangyang Lin, Yang Han, Ping Yang, Congling Wang, Jingqi Xiong
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引用次数: 6

Abstract

This paper proposes a low voltage ride through (LVRT) control strategy for two-stage photovoltaic power generation system (PVPGS) during unbalanced grid faults, where the two-stage PVPGS is composed of PV arrays, the frond-end Boost converter, and the rear-end three-phase inverter. Discharging circuit is added at the dc-link of the twostage PVPGS, and the positive sequence and negative sequence vector current control in the double synchronous reference frame (DSRF) is employed for rear-end three-phase grid-connected inverter. The reference current calculation method considering current limitation is introduced, and the dual-loop control in DSRF is utilized for rear-end inverter, where the outer voltage loop is used for maintaining dc-link voltage, the positive sequence inner current loop is applied to improve dynamic response for current tracking, and the negative sequence inner current loop is designed for eliminating current overshoot. Moreover, a separate DC voltage loop is adopted in discharging circuit for the LVRT operation. A 500kVA twostage PVPGS model is built in the PSCAD/EMTDC platform, the performance of proposed control strategy is evaluated by simulations under asymmetric conditions including single-phase and two-phase ground fault, and two-phase short-circuit fault.
电网电压暂降不平衡条件下两级光伏系统的低压穿越技术
针对电网不平衡故障时两级光伏发电系统(PVPGS)由光伏阵列、前端升压变换器和后端三相逆变器组成的情况,提出了一种低电压穿越(LVRT)控制策略。在两级PVPGS直流环节增加放电电路,对后端三相并网逆变器采用双同步参考系(DSRF)中的正序和负序矢量电流控制。引入了考虑电流限制的参考电流计算方法,将DSRF中的双环控制应用于后端逆变器,其中电压外环用于维持直流电压,正序电流内环用于改善电流跟踪的动态响应,负序电流内环用于消除电流超调。此外,LVRT的放电电路采用了单独的直流电压环路。在PSCAD/EMTDC平台上建立了500kVA两级PVPGS模型,通过单相、两相接地故障和两相短路故障等非对称条件下的仿真,对所提出的控制策略进行了性能评估。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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