Implementation of Multiple-Slack-Terminal DC Microgrids for Smooth Transitions Between Grid-Tied and Islanded States

Abstract

Bidirectional interlinking converter (BIC) is normally configured as the slack terminal to regulate system bus voltage for dc microgrid operation in grid-tied state. In case of utility grid fault, BIC is disabled and the system changes to operate in islanded state. Localized battery energy storage (BES) voltage regulation mode (VRM) operation is activated to maintain system power balance. Operating mode changes of BES and BIC during islanding and reconnection might result in system voltage fluctuations and undesirable inrush current. Detailed transition procedure, which is crucial, has seldom been discussed in literature. In this paper, multiple-slack-terminal dc microgrid, in which both BIC and BES operate in VRM with droop control, is implemented to ensure smooth transitions between grid-tied and islanded states. BES operating mode change is eliminated, and thus, system bus voltage is actively regulated throughout the transitions. Contactor is installed at BIC dc side to decouple BIC operating mode change and grid connection. A counter is used to ensure bus voltages at both sides of contactor have been matched stably to minimize inrush current. To enhance system control accuracy, multilevel energy management system is carried out. A lab-scale dc microgrid has been developed for experimental verifications.

Voltage and frequency control strategies of hybrid AC/DC microgrid: a review

“…Various signal processing techniques such as wavelet analysis and S-transform are also used for islanding detection [64][65][66]. A control strategy for transition mode of a DC microgrid with utility grid is presented in [67] with BESS. Voltage regulation in transition mode is provided by BESS operating in droop voltage control mode.…”

Review of the DC voltage coordinated control strategies for multi‐terminal VSC‐MVDC distribution network

“…When in normal network operating condition, the power balance is regulated entirely by the master terminal. However, when an outage occurs on the master and/or the network communication fails, the other terminals take over the DC voltage control; hence, the power balance achieves high stability and reliability in MTDC grid operation [33, 67–69].…”

Autonomous Control Strategy for Microgrid Operating Modes Smooth Transition

“…current transformer, voltage transformer, relay, etc.) need sufficient time to detect the fault, acquire data and broadcast new operational assignments, which leads to a blackhole for the microgrid being uncontrolled [9]. To compensate for deteriorated dynamic performances, some researches elaborated designs to optimally reduce total harmonic distortion (THD) [10], the output error between parallel-aligned controllers [11] and small-disturbance response [12], to name just a few.…”