Emulation of an Induction Machine for Unbalanced Grid Faults

A laboratory power level 5.0 hp induction machine emulation with grid interface for various asymmetric fault transients is implemented in this article. It is done in real time with power-hardware-in-loop (PHIL) technology. The PHIL emulation procedure permits the testing of complex control strategies of an ac microgrid while determining the machine behavior during grid faults. Since asymmetric grid faults generate opposite sequence components in the individual harmonic currents, a novel emulator control strategy with combination of proportional-integral (PI) and proportional resonant (PR) controllers is proposed to mimic the behavior of the real machine under grid faults. A step-by-step procedure for designing the PI and PR controllers is given in detail. An improved induction machine mathematical model with trapezoidal integration is also suggested for precise tracking of the emulator. An emulator laboratory setup is developed with Opal-Rt as the real-time controller and linear amplifier as the emulating device. Simulation and experimental results are provided to validate the tracking capability of the proposed emulator. The results confirm that with the proposed control, emulator currents track the real machine currents.