Performance of an inverter-fed self-controlled synchronous motor with series characteristics

The paper describes the operation of a synchronous motor in the self-controlled mode, yielding series characteristics. The drive consists of a single-quadrant transistor chopper and a three-phase transistor inverter feeding the armature of a synchronous machine. The field winding in series with an additional inductor, both clamped with a diode, forms the DC link choke. The switching signals for the inverter are derived from a rotor position encoder in a way to ensure an average orthogonal relationship between the field and the armature MMFs. The field winding in the DC link makes the excitation MMF proportional to the armature current resulting in series characteristics. Analytical treatment for the steady state performance of the drives as well as a digital computer simulation study for the dynamic behaviour of the scheme, under certain justifiable assumptions, is presented. An experimental model using a laboratory type synchronous machine is built and tested. Performance characteristics of the drive determined from the test results and predicted from the analyses resemble those of a DC series motor