The kinetic energy stored in the rotating mass of wind turbine generators can provide the effective power quality solution to the inertia-free stand-alone (IFSA) microgrid by improving its stability. In conventional power systems, the power released from the inertia of synchronous generators regulates the system frequency. However, the frequency does not vary much even when the large disturbance or load change occurs in the IFSA microgrid with the only converter-based-generators (CBGs). This paper proposes the new inertia control method of type-4 permanent magnet synchronous generator (PMSG) wind turbine system in the IFSA microgrid by utilizing the measurement of DC-link voltage of converter and its derivatives, not by system frequency. Several case studies are carried out to evaluate the performance of proposed inertia control in the IFSA microgrid with the electromagnetic transients program (EMTP) based simulation. Also, its effectiveness is verified with the experimental results from the hardware-in-the-loop (HIL) test implemented by the controller interface with the digital signal processor (DSP), which is connected to the real-time digital simulator (RTDS).