Three-phase VSCF induction generator synchronised by a single-phase supply through a passive single-element phase converter

Abstract

A passive single-element phase converter connected between phases of a 3-phase cage-induction machine and a single-phase supply connected to the combination sets up a synchronously rotating field in the machine airgap. The rotor is driven supersynchronously by a prime mover and balanced 3-phase power is generated. For small slips the machine is a variable-speed constant-frequency (VSCF) generator. In remote areas capacitor self-excited stand-alone induction generators are often used. Where single-phase supply is available, the system presented eliminates the need for capacitors, and the torque on the turbine is maintained constant by dissipation in the resistive element of the phase converter. Variation of the phase-converter parameters as a function of slip maintains output phase balance. Symmetrical component analysis gives the power balance of the generating system. The range of possible supersynchronous operation is defined by the operational range of the phase converter. It is shown that, for certain operating slips, no dissipation occurs in the phase converter. Verification of operation is presented by MATHCAD simulation and laboratory experimentation with a resistive load. A simple nonvoltage-distorting 3-phase output VSCF generating system with single-phase synchronising source and passive phase conversion at small negative slips is presented.