Two-Layer Discrete-Time Iterative Cooperation for Interconnected DC Microgrids

Discrete-time control for interconnected microgrids (MGs) is critical in promoting the energy flow balance among distributed generations (DGs) and loads due to the converters’ discrete system characteristic. We propose a two-layer discrete-time iterative cooperative (TDIC) framework for multiple dc MGs, in which a two-layer iterative voltage estimator is designed. Based on this, the TDIC strategy allows all slave-DGs’ current outputs and estimated voltage to track that of their respective master-DGs, which are then guided to achieve consensus current output ratio and reference voltage synchronization. As long as the sampling period of the lower-cyber layer is less than that of the upper-cyber layer, all DGs’ weighted average voltages can be regulated to the reference voltage, meanwhile the accurate current sharing can be realized within each MG and among multiple MGs. Compared with most continuous communication approaches, the designed control inputs, supported by intermittent communication across sparse two-layer cyber networks, are merely updated at the end of each round of discrete-time iteration, which can significantly reduce the communication pressure as well as ensure a faster convergence speed.