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With the increasing use of VSC-HVDC links, voltage stability control has become a vital issue in AC/DC power systems. This paper proposes an optimal coordinated control (OCC) method in AC/DC systems incorporating VSC-HVDC to exploit the ability of VSC-HVDC to enhance steady-state voltage stability. First, this paper extends L-index to AC/DC systems incorporating VSC-HVDC. Then based on this, two kinds of optimal coordinated control are proposed respectively for voltage deviation correction and voltage stability enhancement. The optimal coordinated control is modelled as a linearly constrained quadratic programming problem based on sensitivity, which can get a solution quickly. The model considers characteristics of different controllable variables so it can coordinate the controllable resources of a power system. Furthermore, based on the proposed optimal coordinated control, a control strategy is designed which can jointly ensure voltage stability margin and maintain voltage magnitude in a reasonable range. In this way, the ability of VSC-HVDC systems participating in voltage stability control is fully exploited. The result of the simulation on modified New England 39-bus power system shows that the proposed method can comprehensively coordinate control variables and effectively enhance voltage stability.
Inspec keywords: quadratic programming; voltage-source convertors; HVDC power convertors; AC-DC power convertors; power system stability; voltage control; voltage regulators; control system synthesis; optimal control
Subjects: Control system analysis and synthesis methods; Voltage control; Optimisation techniques; Stability in control theory; Power system control; Power electronics, supply and supervisory circuits; Optimal control; Control of electric power systems; Optimisation techniques; AC-DC power convertors (rectifiers)