Discrete-Time distributed secondary control of DC microgrids with communication delays

This paper addresses the challenge of achieving accurate convergence in distributed secondary controls (DSC) under heterogeneous communication delays. Existing control schemes, based on traditional dynamic consensus protocols, often fail to attain precise convergence, leading to undesired system operating points. In response, we propose a discrete-time averaging algorithm that treats clock lags and heterogeneous communication delays as a graph connectivity problem. Under such conditions, we show that the distributed averaging algorithm can achieve convergence to the exact mean value over a directed graph that is not consistently connected. Furthermore, we employ this algorithm to develop a discrete-time DSC (DTDSC) tailored for voltage restoration and state-of-charge (SOC) balancing in energy storage systems (ESSs) within DC microgrids with enhanced precision against time delays. The effectiveness and stability of the proposed controller are investigated through eigenvalue assessments and steady-state analysis. Lastly, hardware-in-the-loop results are provided which demonstrate and verify the resilient performance of the proposed DTDSC under clock lags and heterogeneous delays.