Incorporating HVDC's into monitoring and power system analysis

Abstract

This thesis attempts to study the effect of incorporating HVDC's into monitoring and power system analysis. Power system analysis, including load flow and stability studies, and monitoring defines a complete cycle of the impact of HVDC in a power system network. Load flow calculates the bus voltage magnitude, phase angle, active and reactive power flows based on loads and generations that are already specified. In this regard, our work presents a better way of solving AC - DC load flow equations. In our work, the active and reactive power consumptions of the HVDC link are treated as a function of AC bus voltages and some specified DC parameters. It is then easier to combine the DC part with the AC system. Traditional methods in this regard may encounter convergence problems. We expect that the method used in our work does not encounter convergence problems and is easier to implement. Whereas load flow gives us the solution for bus voltage magnitudes and angles based on certain specified loads and generations, state estimation obtains an estimate of the bus voltage magnitudes and angles based on actual measurements. A state estimator also checks consistency of instrumentation data. In our work with the state estimation, we have presented a new method to design the measurement set of an AC - DC system and explained the choice of the state variables used. The state variables and the measurement set chosen are then used to estimate the state of an AC - DC system. To complete the cycle of the effects of inclusion of a HVDC line in an AC system, we study the impact of HVDC on power system stability in the case of a fault. It should be noted that the power flow through a HVDC link is highly controllable. Accordingly, we can expect the HVDC to improve system stability if it is controlled intelligently. However, if the control measure is not properly designed, HVDC can be detrimental to the system stability. A case has been studied where the HVDC tends to make the system unstable if the setting of the line is not changed during and after a fault. We then propose a control mechanism to strengthen the system stability. Two types of controllers, namely proportional control and proportional - integral control have been studied and compared. Also we have shown their effects on the system stability.