面向构网型逆变器的改进下垂控制方法及其在多VSC系统中的实现

Improved Droop Control Method for Grid-Forming Inverters and Its Implementation in Multiple-VSC Systems

摘要: 针对构网型逆变器在电压支撑与多机协同运行中的控制需求，提出一种面向电压指令量精确跟踪的改进下垂控制方法，并进一步将其推广到多电压源变流器(VSC)并联系统。该方法以传统下垂控制为基础，围绕VSC控制中关键电压指令量Vod的跟踪误差展开改进：首先构造基于输出误差反馈的改进下垂控制结构，在此基础上进一步引入PID环节以提升指令电压跟踪精度和动态支撑能力。基于MATLAB/Simulink与Simscape平台建立单VSC与多VSC仿真模型，对传统下垂控制、无PID改进下垂控制和带PID改进下垂控制进行了对比分析。结果表明：在单VSC场景下，所提方法可使Vod对参考电压Vodref的跟踪误差由传统下垂控制下约0.7 V减小到约0.4 V，并在引入PID后实现近似无静差跟踪；在三VSC并联系统中，所提方法在负荷切换工况下仍能保持较好的电压支撑效果，使各VSC输出电压幅值更准确地跟踪指定值。进一步讨论表明，由于该方法仅在传统下垂控制外增加一个误差反馈PID环节，不需要额外通信链路，因此在数字控制硬件上具有较好的工程可实现性。

Abstract: To improve voltage-support performance and multi-converter coordination of grid-forming inverters, an improved droop control method oriented to accurate tracking of the key voltage command Vod is presented and further extended to multiple voltage source converters (VSCs). On the basis of conventional droop control, the proposed method improves the tracking performance of the key voltage command Vod in VSC control. Specifically, an improved droop control structure based on output error feedback is first constructed, and a PID link is further introduced to enhance the tracking accuracy of the command voltage and the dynamic support capability. Single-VSC and multi-VSC simulation models are established in MATLAB/Simulink and Simscape to compare conventional droop control, the modified droop control without PID, and the modified droop control with PID. Results show that, in the single-VSC case, the tracking error of Vod with respect to Vodref is reduced from about 0.7 V under conventional droop control to about 0.4 V after error-feedback compensation, and nearly zero steady-state error is achieved after introducing PID. In the three-VSC parallel system, the proposed method still maintains good voltage support under load-switching conditions, and the output voltage amplitudes of each VSC can track their specified values more accurately. Further discussion indicates that, since the proposed method only adds an error-feedback PID link outside the conventional droop control and does not require additional communication links, it has good engineering implementability on digital control hardware.