AC-common bus Microgrid system can overcome several weaknesses of DC microgrid system by interconnecting DC/AC inverters for renewable energy with AC network. Nevertheless, unbalanced loads in island and small community electric power system can make performances of AC microgrid system getting worse. These are because of limited voltage regulation capability and mixed power flow in voltage source inverter. In other to overcome the unbalanced load condition, this paper proposes voltage and current control algorithm of 4-LEG inverter based on single phase d-q control method, and also proposes the modeling of voltage controller using Matlab/Simulink S/W. From the S/W simulation and experiment of 250kW proto-type inverter, it is confirmed that the proposed algorithm is useful tool for design and operation of AC microgrid system.