MT 8020 simulator is used to simulate large power grid. The large grid bus voltage is output to the power amplifier through the analogue port of the simulator, and thus controlling the output voltage of the power amplifier in real time. The power amplifier output is connected to the microgrid AC bus. Current measurement unit collects the current between the microgrid and the power amplifier and then feeds it back to the HIL simulator to correlate the power with the power grid. This forms a  closed-loop  real-time  simulation  structure  which  includes  a    real microgrid and a virtual large power grid.