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Ac motor drives are becoming increasingly popular in the field of industrial processes and transportation electrification. Currently, many industrial applications are based on induction machines supplied by inverters and controlled with field-oriented control techniques. Such techniques require the knowledge of the machine parameters to ensure the correctness of the torque control both in dynamic and steady-state conditions. In particular, an accurate determination of the induction motor rotor time constant is crucial. Therefore, this article analyses in detail the physical phenomena involved during the flux-decay test used for the rotor time constant determination. The reported analysis has been performed on a 15 kW induction motor. The transient of the machine's back-electromotive force (back-emf) has been critically analyzed during its evolution, finding a link between its evolution in time and the magnetic phenomena that occur both in the stator and the rotor. In particular, the effects due to the lamination saturation, the stator and rotor leakage inductances, and the stator iron losses have been associated with the transient evolution of the machine's back-emf.

The Simplified Virtual Synchronous Compensator (S–VSC) is a Virtual Synchronous Machine (VSM) solution available in the literature, which operates as a virtual compensator. Previous works demonstrated that it can provide grid services (e.g., inertial behavior, grid support during faults) only in grid–following operation. However, the grid–forming capability of the S–VSC (and in general of a virtual compensator) has never been investigated in the literature. Therefore, this article proposes an S–VSC model able to operate both in grid–following and in grid–forming configuration. First, the article validates the small–signal stability of the control algorithm both in grid–mode and island operation through an eigenvalue–based stability analysis. Next, the control algorithm is experimentally validated on a 15 kVA inverter connected to a scaled microgrid. The experimental tests demonstrate that the S–VSC can operate both as grid–following and grid–forming. Moreover, it can seamlessly switch from the grid–connected to the island operation without requiring any communication system. Finally, the grid–forming capability of the S–VSC is experimentally validated even in case of a fault occurrence, thus representing a valid solution for the control of a microgrid.