基于自适应虚拟阻抗的多并联构网型变流器无功功率分配策略

Reactive Power Sharing Strategy for Multiple Parallel Grid-forming Converters Based on Adaptive Virtual Impedance

由于变流器出口线路阻抗的不匹配,采用传统下垂控制策略的多并联构网型变流器难以实现无功功率的精确分配。为了提高无功功率分配精度,文中分析了并联变流器的功率分配机理,提出了一种将变流器的无功功率分配误差和输出电压相结合的自适应虚拟阻抗设计方法。基于该方法的无功功率分配策略在实际线路阻抗未知且分布式单元之间无互联通信的工况下,可实现无功功率高精度分配。该策略还可以改善引入虚拟阻抗存在的无功功率分配精度与输出电压跌落之间的矛盾,抑制变流器间的环流。此外,对变流器进行小信号稳定性分析以合理设计控制参数。硬件在环仿真的结果验证了所提控制策略的有效性。

Due to the mismatch of the line impedance of each converter,it is difficult to realize the accurate reactive power sharing for multiple parallel grid-forming converters under the traditional droop control strategy.In order to improve the reactive power sharing accuracy,this paper analyzes the power sharing mechanism of the parallel converters and proposes an adaptive virtual impedance design method that combines the reactive power sharing error and the output voltage of the converter.Under the operation condition where the actual line impedance is unknown and there is no interconnection communication between distributed units,the reactive power sharing strategy based on the proposed method can achieve high reactive power sharing accuracy.It also improves the contradiction between the reactive power sharing accuracy and the output voltage drop that exists when the virtual impedance is introduced.And the circulating current between converters is suppressed.In addition,the small-signal stability analysis of the converter is performed to rationally design the control parameters.The hardware-in-loop simulation results verify the effectiveness of the proposed control strategy.