三相光伏逆变器的低电压穿越控制策略研究

Study on LVRT Capability of Three-phase PV Grid-connected Inverter

并网逆变器是光伏并网发电系统的核心,出于系统安全考虑,光伏并网系统必须具备一定的低电压穿越能力。目前针对电压平衡跌落故障下并网逆变器的控制已经有了行之有效的措施,但却缺少非对称故障时逆变器行为的分析以及在电压不平衡跌落时保持逆变器稳定运行的有效控制策略。针对这一现状,首先在电网电压平衡跌落时,利用电压电流双闭环控制系统进行分析。接着在研究非对称故障特性的基础上,改进了电压电流双闭环控制系统,分析了功率与直流侧电压波动的原因,并提出了抑制波动现象的控制策略。最后通过一系列试验对逆变器在不同条件下的低电压穿越能力进行了验证,通过分析试验结果可以看出无论是对称还是非对称情况下的控制策略均有良好的控制效果。

The PV inverter is the core of solar power generation.The LVRT capability is required to consider the safe operation of system.The research nowadays focus on the control strategies on the balance fault,while the unbalance fault is not going deeply.This paper analyzes LVRT capability of PV inverter under both balanced and unbalanced grid voltage drop conditions.When grid voltage drop is unbalanced,the design of phase-locked loop is improved based on SOGI-QSG for grid synchronization.Component of the positive and negative sequence of grid voltage and current is seperately detected.New control stratagies are proposed for cancellation of negative-sequence current or DC-link voltage ripple.Furthermore,through a series of experiments,LVRT capability of three-phase PV grid-connected inverter is tested.Good control effect under balanced condition is obtained.