A Multiterminal HVDC Load-Flow with Flexible Control Specifications

This paper presents a sequential ac-dc load-flow method for parallel multiterminal de networks. P.u.-expressed de equations are treated separately from ac equations and an interface is used to check and adjust their mutual convergence. A dc converter acts like a load on its ac bus; when it is a rectifier P and Q power are consumed, and when it is an inverter Q is consumed and P is a negative load, or a generation. This method distinguishes itself by its ability to handle a large variety of converter controls, by its capability to modify established controls to respect angle, transformer tap, voltage and current limits at the converters. The interface between the ac and de equations is designed to increase ac-dc convergence possibilities. Standard characteristics such as fixed tap and discrete tap-steps at the converter transformer are also handled. Numerical examples which demonstrate several features of the described method are presented. The Institut de Recherche d´Hydro-Qu??bec (IREQ) has been active for many years in the area of de simulator studies. The IREQ de simulator can simulate simple back-to-back links up to complex multiterminal HVDC networks imbedded into ac networks. The complexity of the networks studied on the de simulator has increased greatly these last years. The requirement therefore, for effective set-up of the simulator studies, is that it is necessary to have a digital ac-dc load-flow computer program which is flexible and can effectively handle arbitrary configurations of multiterminal HVDC systems.