Automatic synthetic loading of induction motors based on phase modulation using fuzzy PI controllers

This paper describes an automatic equivalent loading method for ac machines based on phase modulation technique. In this scheme , the test motor is supplied by a variable voltage magnitude variable frequency voltage source that is generated by a wound rotor induction machine. A wound rotor induction machine is employed as a three phase synchronous generator with two quadrature rotor field windings. The rotor direct axis excitation winding is fed by a single-phase PWM inverter while the rotor quadrature axis field winding is supplied by a three-phase rectifier. The test motor RMS voltage and current are automatically maintained on their nominal values , using the current and voltage fuzzy PI regulators. The above method can also be applied to a double system test motors so that no power is fed back to the power supply. The proposed control scheme is verified by some simulations. Computer simulation results obtained confirm the feasibility and effectiveness of the automatic synthetic loading method so that the test motor nominal losses can be measured without the need for attaching mechanical load to the shaft. These results also show that the proposed closed loop control system is robust and stable subject to the system parameter uncertainties.