基于虚拟阻抗的并联VSG改进控制研究

低压微电网在孤岛并联运行时,往往存在功率耦合以及线路阻抗差异等问题,传统的虚拟同步发电机控制很难实现无功功率的精确分配且环流抑制能力较差。为了解决上述问题,本文首先设计了虚拟阻抗使系统等效输出阻抗呈感性,实现了有功和无功的解耦。其次,提出一种改进无功-电压环控制策略,在无功-电压环中引入公共耦合点电压反馈和积分环节,减小公共耦合点电压波动并提高了无功分配精度。考虑到引入虚拟阻抗虽能有效抑制环流,却造成输出电压幅值降落的问题,通过在无功电压环中增加虚拟阻抗压降补偿项,以抬高无功-电压环输出电压幅值,抵消引入阻抗所产生的电压降落。仿真实验结果验证了所提出控制策略的有效性和可行性。

Research on Improved Control of Parallel VSG Based on Virtual Impedance

When low-voltage micro-grid runs in parallel with the island, there are often problems such as power coupling and line impedance difference. The traditional virtual synchronous generator control is very difficult to achieve the accurate allocation of reactive power, and the circulation inhibition ability is poor. In order to solve the above problems, the virtual impedance was designed to make the equivalent output impedance of the system perceptual and realize the decoupling of active and reactive power. Secondly, an improved reactive power voltage loop control strategy was proposed, in which the common point coupling point voltage feedback and integral link were introduced to reduce the voltage fluctuation of the common coupling point and improve the reactive power distribution accuracy. Although the introduction of virtual impedance can effectively suppress the circulating current, it causes the drop of output voltage amplitude. By adding a voltage drop compensation term of virtual impedance in the reactive power voltage loop, the output voltage amplitude of the reactive power voltage loop was increased to offset the voltage drop caused by the introduction of impedance. Simulation results verify the effectiveness and feasibility of the proposed control strategy.