Small signal stability analysis for thyristor converters on weak power systems

The phase controlled thyristor converter supplied from a weak power system is modeled in the time domain. A state variable formulation is used for the discrete nonlinear model. Local linerization is performed about an equilibrium state to obtain a small signal steady state model for such a thyristor converter system. The stability constraints for the digital controller parameters are also obtained for a fast closed loop control. As an illustration, the small signal steady state stability analysis is shown for a six-pulse controlled thyristor dc drive having a fast control loop, weak bus, current harmonic filter, power factor correcting capacitor and transformer leakage reactance.