Control of Three-Phase Electric Springs Used in Microgrids under Ideal and Non-Ideal Conditions

A control scheme is proposed for the three-phase electric springs (TPESs), based on the recently introduced d control and an improved phase locked loop (PLL). The scheme utilizes three independent d controls, one for each phase, to stabilize the voltages across the critical loads (CLs) while handing over imbalance and distortion of the microgrid voltages, in addition to their fluctuations, to the non-critical loads (NCLs). Instrumental in achieving this outcome is the operation of the improved PLL that separates the fundamental component of the positive sequence of the microgrid voltages from the other sequences and harmonics. The scheme is also able to stabilize the CL voltages under imbalance of CLs and NCLs. Simulation results obtained under various conditions of imbalance of the microgrid voltages and/ or the loads, and of distortion of the microgrid voltages, taken individually and together, show the effectiveness of the proposed control scheme of TPESs.