Power Injection Models of HVDC and UPFC: A Comparison

This paper solves the power flow problem based on Newton Raphson (NR) method with integration a developed model of High Voltage Direct Current Transmission (HVDC) in multi control modes. Modeling of the HVDC is not an easy task where, in the voltage source model (VSM), the converters are represented as two voltage sources connected in shunt at the HVDC terminal, however this model is efficient but it needs difficult modifications inclusion of the control parameters in Jacbian matrix as state variables. Thus in the developed model, the HVDC is presented as injected loads at its terminals to avoid the modifications of Jacbian matrix where the injected loads are derived in terms of the specified control variables and updated with iterative process of NR power flow. In addition of that tin this model, the HVDC can work with different control modes to control the bus voltage magnitude, active and reactive powers flow through the transmission line separately or continuously. A unified power flow controller (UPFC) is an effective controller that consists of two converters (series and shunt converters) where the coordination of these converters provides the control ability in power system parameters similar to the control modes of the HVDC. In this paper, a simplified power injection model of the UPFC is used for direct incorporation into in Newton Raphson (NR) power flow. The models are tested with standard IEEE system to verify the effectiveness of the models and show performance of the HVDC and UPFC with multi-control modes.