Performance of an SCR-inverter-based commutatorless series motor with load commutation and unaided startup capability

This paper examines the starting and variable-speed performance of a silicon-controlled-rectifier-based commutatorless series motor with special emphasis on the commutating process for the operation of a self-controlled synchronous machine in the load-commutated mode, unassisted by extra components or special techniques, even at very low speeds, including starting. A dynamic simulation of the drive, in which the field winding of the synchronous machine is located in the DC link has been presented, the results of which are validated by comparison with those of an experimental prototype. The influence of the damper windings on the commutation process and in the suppression of the voltage spikes so generated, and in reducing overlap times, has also been studied. A phasor-diagram-based steady-state analysis predicts the parameters of suitable machines for such an operation. The inherent series characteristics of this drive, its high power factor, and self-starting capability will find applications in large-power traction drives, flywheel energy storage systems, centrifugal pumps, etc.