电网不平衡条件下的光伏并网发电控制策略

分布式发电系统通常呈现弱电网状态,容易出现电网电压不平衡的情况,此时由于常规控制方案不能处理负序分量,将影响系统内并网逆变器的正常工作。为此,提出了一种解耦双同步坐标系用于获取不平衡电压的正序相位和负序相位;接着分析了不平衡电网下的瞬时功率模型,且通过一个负序分量正序旋转变换矩阵将需要补偿的负序分量注入正序控制坐标系,并引入准谐振控制器对负序分量进行无差跟踪和抑制电网电压谐波的影响;进而实现直流侧电压纹波的抑制,保证最大功率点跟踪精度和较小的并网电流总谐波畸变率。最后,搭建了一个10kW光伏并网逆变器实验平台验证了该方案的正确性和可靠性。

A Control Strategy for Grid-connected Photovoltaic System Under Unbalanced Voltages

Distributed generation systems often appear as a weak-grid, where the voltage is prone to be unbalanced, and the performance of the inverters within the system will be affected as the conventional control scheme cannot deal with the negative sequence (NS) component. A decoupled double synchronous reference frame (DSRF) phase locked loop (PLL) is proposed to obtain the positive sequence (PS) and NS phases of the unbalanced voltage. Meanwhile, an instantaneous power model under the unbalanced grid is analyzed, and then an unbalanced control strategy based on the DSRF-PLL is designed by injecting an NS current into the PS reference current via a negative-sequence-to-positive-sequence (NS-PS) transformation. Quasi-proportional-resonant (QPR) links are introduced to track the PS reference current and suppress the harmonics from the grid so as to suppress the ripples of the DC voltage to guarantee maximum power point tracking (MPPT) accuracy and smaller total harmonic distortion (THD) of the grid-connected current. Finally, the validity and reliability of the proposed scheme is verified via a 10 kW photovoltaic grid-connected inverter.