Effect of Communication Delay on Steady State Voltage in DC Microgrids

Critical loads in a dc microgrid require the terminal voltages within acceptable limits. Thus secondary controllers are used to attain proportional current sharing and/or good voltage regulation. Depending on the number of communicated variable, the relevant techniques can be broadly categorized as one variable (either current or voltage) and two variable (both current and voltage) per converter communication based control techniques. In any practical network, communication delay is always present which affects both transient and steady state performance of the system. Therefore, to ensure the reliable operation of communication based control techniques, it is imperative to investigate the effect of delay on the system performance. In this work, how the delay in the communication network affects the steady state value of converter terminal voltage is investigated for both one or two variable communication based control techniques. A generalised mathematical expression is derived to establish the relation between the delay and the steady state value of the terminal voltage. Finally, the established mathematical expression is validated in a laboratory scale dc microgrid prototype.