Abstract: The symmetry and waveform quality of the common AC bus voltage in an islanding microgrid are easily affected by the unbalanced and nonlinear loads. In this paper, the combined three-phase inverter is adopted as the topology of each distributed power supply, and the control strategy to improve the output voltage quality of the inverter is designed. Firstly, the reasons affecting the voltage quality of microgrid with unbalanced and nonlinear loads are analyzed. It is concluded that the balance degree of inverter reference voltage and the reduction of system equivalent impedance are the two elements to improve the voltage quality. Then, a balanced reference voltage control is designed to enable each phase of the inverter to produce symmetrical reference voltages. The proportional resonant voltage controller with self-adjusting frequency and the self-adjusting coefficient strategy under discretization is proposed. At the same time, the output current feedforward control is added. These methods can be adopted to effectively reduce the inverter output impedance at fundamental and each harmonic frequency while improving the open-loop gain, and the imbalance and voltage waveform quality caused by the output impedance voltage drop of the inverter is improved. Finally, the feasibility of the proposed control strategy is verified by simulation and experimental results.