Optimized Autonomous Operation Control to Maintain the Frequency, Voltage and Accurate Power Sharing for DGs in Islanded Systems

Most of the launched power electronics-enabled distributed generators (DGs) adopt phase-locked-loop (PLL) synchronization control. In this paper, we delve into two different autonomous operation control (AOC) strategies to ensure the frequency/voltage profile and accurate power sharing for such DGs in islanded systems. The commonly used AOC is based on the concept of active power-frequency (<inline-formula> <tex-math notation="LaTeX">$P-f$ </tex-math></inline-formula>) and reactive power-voltage magnitude (<inline-formula> <tex-math notation="LaTeX">$Q-V$ </tex-math></inline-formula>) droop and deployed in a decentralized way. It is frequently criticized for inaccurate reactive power sharing between DGs, subject to the mismatch in their output impedances. To cope with this issue, we first design a local AOC using the <inline-formula> <tex-math notation="LaTeX">$P-f$ </tex-math></inline-formula> and <inline-formula> <tex-math notation="LaTeX">$Q-\dot {V}$ </tex-math></inline-formula> (i.e., the time derivate of <inline-formula> <tex-math notation="LaTeX">$V$ </tex-math></inline-formula>) droop concept, where the desired reactive power sharing can be achieved at the expense of a marginal and allowable <inline-formula> <tex-math notation="LaTeX">$V$ </tex-math></inline-formula> excursion. Then, we develop an optimization-based AOC that is implemented through a continuous-time alternating direction method of multipliers (ADMM) algorithm and neighborhood communication. Equilibrium analysis and local asymptotic stability of the proposed AOC strategies are both established using a Lyapunov method. Finally, simulations are carried out in two islanded systems to validate the improvement in power sharing under a wide range of possible system conditions.