Assessment of energy management technique for achieving the sustainable voltage level during grid outage of hydro generator interfaced DC Micro-Grid

Abstract

An appropriate energy management scheme is needed for the reliable and sustainable operation of DC microgrid. The energy management scheme of DC microgrid (MG) is mainly controlled by main energy resource of MG. Main energy resource needs to be dispatchable unit for forming the reference voltage within DC MG. In this work, a micro hydro generator (MHG) is considered as a dispatchable source for forming the sustainable voltage level of DC MG operating under the abnormal condition. In this work, the abnormality refers to the outage of solar PV due to intermittency during fluctuating load condition. But, due to mechanical time constant of MHG and rate of charging/discharging current limit of energy storage system, the fluctuating load cannot get compensated. The uncompensated fluctuating load results in unsustainable voltage control of DC MG. The CEMS proposed in this work, maintains sustainable voltage level of DC MG during the load power fluctuation through a coordination of mechanical control loop (MCL)-electrical control loop (ECL). The coordination targets sustainable voltage control of MG with optimal power extraction of micro hydro generation. To ensure the optimal power from MHG during load power fluctuation, CEMS operates it in the variable speed mode through pre-set load controller (PSLC) and proportional predictive controller. Depending on the type of load power fluctuation, the proportional predictive controller generates a reference torque to MCL based on the predicted speed change set by PSLC. PSLC predicts the load power and speed change on iteration basis. MCL sets proportional mechanical power to the permanent magnet synchronous generator through hydro turbine. Then, MHG is going to dispatch the proportional DC power to the load through voltage-oriented control scheme of active rectifier. ECL balances the mismatched power flow between the output power of MHG and fluctuating load through a battery-SC based energy storage system. In this work, the proposed CEMS assessed against slow rate fluctuating (t ≥ 9secs) and fast rate fluctuating (t < 3secs) load patterns. Moreover, the proposed CEMS is validated in MATLAB/Simulink as well as OPAL-RT real time simulator.