Voltage Stability Analysis Of HVDC Systems

With the increased use of HVDC transmission systems in power systems, situations have arisen and will be even more frequent in the future, where sigle-infeed HVDC system with a parallel AC line and several HVDC systems are located in close of each other. It is evident that interactions between the different HVDC systems will occur in such configurations, and it is of importance to analyze such systems in a systematic way to ensure that there are no risks of adverse interactions. A method based on the eigenvalue decomposition technique, known as modal analysis of multi-infeed HVDC systems. In this method, not only the critical eigenvalues are useful in evaluating the voltage stability of the system, but their associated eigenvectors also contain information on the most severe disturbances to the system.In this paper, the use of these modal information for such analysis id further exploited. The elements of the Reduced-Jacobian Matrix are functions of some parameters of the system. For example, Effective Short Ratio , Power Base Ratio , Coupling Impedance and Load Flow of the system. For single-infeed HVDC system with a parallel AC line, Computer simulations using Power System Analysis Software Package (PSASP) were performed. For multi-infeed HVDC systems, when the minimum eigenvalue of the system becomes zero, the voltage stability graph can be plotted Effective Short Circuit Ratio as function of coupling impedance. Using the voltage stability graph, the voltage stability margin can be known. The bus participation factors can be computed from the left and right eigenvectors associatedwith the minimum eigenvalues. The AC commutation bus with the largest participation factors is the critical bus, meaning that it has the largest involvement in the voltage instability. Consequently, it is also the most effective system location for implementing remedial measures.The significant influence of system parameters on the voltage stability are also investigated. A change in converter control mode from constant-power to constant-current always improve system voltage stability.