A large amount of distributed generation is connected to the grid, reducing the rotational inertia of the power system. Based on the Static Synchronous Generator Model, this paperSintroduces a inertia controller on the outer voltage control loop to enhance the grid inertia. The developed inertia controller can generate the inertial current superposed in the conventional current reference. The inertial current can be adjusted arbitrarily, consequently realizing the equivalent simulation of inverter inertia on the basis of the conventional double-loop control. In addition, the physical mechanism of the developed inertia controller is investigated. The experimental results show that the presented method can adjust the inertia of grid-tied inverters flexibly and can enhance the system stability.