Feasibilty, Stability, and Voltage Collapse in Weak Back-to-Back HVDC Links

The problem of the weak back-to-back HVDC link is investigated by quasi-steady-state analysis and small perturbation linearized stability analysis. The large ac line impedances on either sides of the HVDC link present severe constraints so that there may be no feasible steady-state solutions unless α and γ are co-ordinated with load demands. Formulae of steady-state stability limits, hunting frequencies, and voltage collapse are derived. One scenario for voltage collapse instability is discovered. A Composite Phasor Diagram is presented.