This book deals exclusively with the power-flow modelling of HVDC transmission systems. Different types of HVDC transmission systems, their configurations/connections and control techniques are covered in detail. Power-Flow modelling of both LCC- and VSC-based HVDC systems is covered in this book. Both the unified and the sequential power-flow methods are addressed. DC grid power-flow controllers and renewable energy resources like offshore wind farms (OWFs) are also incorporated into the power-flow models of VSC-HVDC systems. The effects of the different power-flow methods and HVDC control strategies on the power-flow convergence are detailed along with their implementation. Features: Introduces the power-flow concept and develops the power-flow models of integrated AC/DC systems. Different types of converter control are modelled into the integrated AC/DC power-flow models developed. Both unified and the sequential power-flow methods are addressed. DC grid power-flow controllers like the IDCPFC and renewable energy resources like offshore wind farms (OWFs) are introduced and subsequently modelled into the power-flow algorithms. Integrated AC/DC power-flow models developed are validated by implementation in the IEEE 300-bus and European 1354-bus test networks incorporating different HVDC grids. This book aims at researchers and graduate students in Electrical Engineering, Power Systems, and HVDC Transmission.