Self-Synchronizing VSM With Seamless Operation During Unintentional Islanding Events

This article proposes a predictive optimal switching vector controlled virtual synchronous machine (VSM) for three-phase microgrid applications, which inherits self-synchronization and islanding detection technique within the controller. A novel synchronization signal is introduced here, to modify the frequency reference in VSMs. This integrates the synchronization and islanding detection within the control loop, thereby resulting in smooth system responses without causing stability issues associated with phase-locked loops. Moreover, it totally eliminates proportional-integral (PI) regulators in the system. The traditional pulsewidth modulation controllers use cascaded internal control loops, and they demand multiple PI regulators and synchronous coordinate transformations. They are associated with finite dynamic response time by PI regulators and necessitate rigorous tuning for practical implementation purposes. The proposed controller, however, estimates the behavior of output voltages and uses a minimization criterion to produce optimal inverter switching sequences. The voltage vectors that cause the overcurrents in the inverter are inherently avoided by the minimization function within the controller. The effectiveness of the proposed control strategy is verified through simulations and experiments validate the performance under different operating conditions.