Generalized implementations of piecewise linear control characteristics for multiterminal HVDC

Abstract

Large-scale Multi-Terminal (MT) HVDC grids will require decentralized control schemes where the converters can autonomously react to load changes or disturbances in the dc grid without the need for fast actions of a centralized controller. The majority of such proposed schemes are based on assigning a static Piece-Wise Linear (PWL) characteristic to each converter terminal, which defines a functional dependence between the dc voltage and the local current or power references of the converter. Despite evident conceptual similarities, the various schemes and combinations of control characteristics are presented in literature with different implementations. This paper discusses the possibility for generalized controllers that can reproduce these static characteristics within a single implementation by only modifying parametric settings. In particular two alternative implementations are discussed, whereof the first option has been previously presented but without explicitly discussing its potential for implementing a generalized PWL controller. An alternative implementation is then developed and described in detail, based on a state-machine controlling the operation of a dc-voltage controller. The proposed generalized PWL implementation is demonstrated by numerical simulation of a four terminal HVDC system.