The low-harmonic (LOH) voltage of the DC link of three-phase voltage source converter (VSC) requires a large aluminum electrolytic capacitor for suppression under nonlinear AC current. Consequently, this work proposes an active decoupling control method combining DC-link LOH voltage closed loop and LOH current feedforward based on a DC–DC converter. This methodology effectively transfers the DC-link LOH voltage to the smaller-sized decoupling capacitor in the DC–DC converter, thereby reducing the number of capacitors required to stabilize of the VSC DC-link voltage. This work first investigates the relationship between the DC-link LOH voltage and the VSC nonlinear current. Second, a mathematical model for the decoupling capacitor voltage is derived, indicating that its voltage form is complex under nonlinear AC current, making direct voltage control arduous. Subsequently, the principle and design process of the proposed active decoupling control strategy are analyzed in detail. A dedicated fast-response filter structure is also utilized to extract the feedback LOH voltage and feedforward LOH current in the DC link. Meanwhile, a simple control strategy for the DC component of the decoupling capacitor voltage is proposed to improve the utilization of the decoupling capacitor. Finally, the effectiveness and correctness of the method are experimentally verified.

三相电压源换流器（VSC）直流环节的低谐波（LOH）电压需要一个大型铝电解电容器来抑制非线性交流电流。因此，本文提出了一种基于 DC-DC 转换器的、结合直流母线 LOH 电压闭环和 LOH 电流前馈的主动解耦控制方法。这种方法有效地将直流母线 LOH 电压传输到 DC-DC 转换器中较小尺寸的去耦电容器，从而减少稳定 VSC 直流母线电压所需的电容器数量。这项工作首先研究了直流母线 LOH 电压与 VSC 非线性电流之间的关系。其次，推导了去耦电容电压的数学模型，表明其在非线性交流电流下电压形式复杂，导致直接电压控制困难。随后，详细分析了所提出的主动解耦控制策略的原理和设计过程。还利用专用的快速响应滤波器结构来提取直流链路中的反馈LOH电压和前馈LOH电流。同时，提出了一种简单的去耦电容电压直流分量控制策略，以提高去耦电容的利用率。最后通过实验验证了该方法的有效性和正确性。