A Multiterminal HVDC Load-Flow with Flexible Control Specifications

This paper presents a sequential ac-dc load-flow method for parallel multiterminal dc networks. P.u.-expressed dc 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 powers 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 dc 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.