Robust Distributed Secondary Control for DC Microgrids Enhancing Stability and Communication Delay Tolerance

Accurate power sharing and global voltage recovery are common secondary control objectives in DC microgrids (DCMGs). Distributed control outperforms centralized as it allows for plug-and-play capability and operates effectively with low-bandwidth communication. However, it remains sensitive to communication delays, compromising DCMG stability. This paper proposes an enhanced DCMG control architecture, improving its endurance against delays. Secondary control modifies droop nominal voltage to achieve its objectives through a PI controller. The PI gains have direct influences on stability and delay toleration. However, scheduling PI gains to counteract the delay comes with sluggish convergence. The proposed control hierarchy introduces derivative controllers in its structure to increase its degree of freedom. By broadening the PI gains range, communication delays are effectively addressed, thus offering more ample tuning choices that accelerate convergence. The small-signal linearized model is derived and the direct frequency domain method is used to accurately obtain the delay margin characterizing DCMG stability. Due to the transcendental delay terms in the characteristic equation, the roots' damping cannot be obtained. Thus, Pade approximation is engaged in obtaining a manageable number of roots facilitating dominant roots assessment. The proposed control hierarchy has been verified through a Controller-in-the-Loop (CIL) setup via the OPAL-RT environment.