Adjustable speed three-phase AC motor drives are now preferred over DC motor systems, for many industrial drives, and battery-powered cars. This is because static inverters, with adjustable frequency and voltage, are reliable and economical. Induction motors provide brushless operation, but they have slip and a relatively low lagging power factor. Synchronous motors have better power factor and no slip and are also better for vector control and good dynamic performance. But brushless, exciterless, synchronous motors have permanent magnet rotors and lack easy adjustability of flux and power factor.The feasibility research is being done on an AC motor drive, for which a U.S. Patent has been obtained. The machine is synchronous, but brushless and does not need exciter or permanent magnets. The stator creates an auxiliary rotating field, besides the main field. The auxiliary field rotates at a different rpm and serves to induce AC currents in the rotor circuit. This AC is rectified by means of rotor mounted diodes, to provide DC excitation, for synchronous running with respect to the main field. The field is adjustable from the stator side. The project covers the fabrication of both the motor and the matching inverter.Commercial Applications:The project introduces adjustable speed drive systems using inverter-fed brushless AC motors, which can provide performance benefits over existing ones. They have Applications potential in all types of industrial adjustable speed AC motor drive systems, both present and future, including battery powered cars.
