Stability Improvement of Current Control by Voltage Feedforward considering a Large Synchronous Inductance of Diesel Generator

This paper analyzes an effect of voltage feed forward control in order to improve stability of BESS which is connected to diesel generator in stand-alone microgrid. In the stand-alone microgrid, BESS can be charged from the diesel generator when SOC of battery bank is insufficient, where BESS operates as CC-CV control. In this case, although LCL filter is designed to put a resonance point greater than one sixth of sampling frequency, resonant frequency is forced to move to a lower frequency region due to a large synchronous inductance. Therefore, current control of BESS may become unstable. As a solution of this problem without additional passive or active damping, it is possible to improve the stability of BESS by appropriately adjusting the gain of voltage feedforward term which is applied for eliminating the back ground harmonic of voltage. PI + Resonant controller in the synchronous reference frame regulates a current, and system delay of 1.5T(s) is considered for the analysis. The effect of synchronous inductance and feedforward path on stability of BESS is analyzed in s-domain and z-domain. feedforward gain for stable BESS operation is selected to 0.4. The demonstration site is constructed and stability is verified through simulation and experiment, and THD of current is improved to 3.1%.