Selection of PI compensator parameters for VSC-HVDC system using decoupled control strategy

Abstract

This paper proposes an approach to the selection and optimization of the parameters of the proportional-integral (PI) compensators in the various control loops of a VSC-HVDC transmission system using a decoupled control strategy. An optimization algorithm based on the simplex method is adopted. The objective is to simultaneously minimize the weighted sum of the "integral of the time absolute-error products" (ITAE) of the power, reactive-power, DC voltage and inner current controllers of the respective VSCs. The initial values of the PI compensator parameters for input to the optimization algorithm are obtained by the application of classical frequency response design methods to simplified linear models of the open-loop transfer functions of VSC-HVDC control system. The optimization process is applied to a detailed electromagnetic transient (EMT) model of the VSC-HVDC system to which a large disturbance is applied. The effectiveness of the optimized PI compensator parameter settings are assessed in terms of rise-time, overshoot, settling times, etc. for a range of disturbances applied to the detailed EMT model. On the basis of these assessments modifications to the weightings of the error signals are found to be necessary to obtain good performance according to the specific control design requirements.