Search Results (3)

The multi-infeed interaction factor (MIIF) is used extensively in indicating the degree of interaction among high-voltage direct current (HVDC) converters and is currently calculated by simulation methods according to the definition, or by using the equivalent impedance ratio method. The first method is an experimental calculation method and the second method does not account for the effects of HVDC control modes. An analytical calculation method for MIIF considering control modes of HVDC links is proposed in this paper. First, the voltage variation of converter bus in the context of small disturbance is equated by using the bus impedance matrix. In this way the equations for the solution of MIIF considering HVDC control mode are obtained. Subsequently, based on two rational assumptions, the practical analytical calculation expression of MIIF is deduced in detail. The MIIF calculation method proposed in this paper is an improvement of the equivalent impedance ratio method and reflects the main influencing factors of voltage interaction including HVDC control modes. Moreover, the derived analytical expression can give a fundamental insight into parameter dependencies of voltage interaction. Finally, the validity and accuracy of the proposed approach are demonstrated in both dual-infeed HVDC system and actual large-scale power grid. Full article

The multi-infeed effective short-circuit ratio (MESCR) is widely used in indicating the strength of multi-infeed AC/DC power systems. However, when the widely used MESCR was adopted to evaluate the stability margin of the Eastern China Grid including three infeed ultra-high-voltage DC (UHVDC) and five high-voltage DC transmission lines in 2016, the MESCR result indicated the system was strong enough but in fact occasionally collapses after the N-1 contingency. To determine the reason for this conflict, this paper theoretically analyzes the limitations of the existing MESCR. The theoretical analysis reveals that when a large amount of capacitor compensations are concentratively installed in the system, the conventional MESCR will not be able to reflect the capacitor compensations’ influence on the system stability, and no matter how many capacitors are installed or where the capacitors are installed, the MESCR almost retains the same value; namely, the MESCR is saturated in such systems. To address the saturation problem of conventional MESCR, this paper proposes an improved multi-infeed effective short-circuit ratio (IMESCR) which considers the influences of all capacitor compensations by converting all capacitors installed throughout the system to virtual capacitors at the DC inverter station. Case studies are carried out based on the New England 39-bus system and the Eastern China Grid, respectively. The simulation results verify the theoretical analysis of the MESCR’s limitations in evaluating the stability of power systems with massive capacitors installed, and proves that the proposed IMESCR could accurately indicate the strength of AC/DC power systems. Therefore, the proposed IMESCR provides a new index for evaluating the stability margin of power systems with massive capacitor compensations installed. Full article

Many of the recent projects for new transmission line have considered the high-voltage direct current (HVDC) system, owing to the many advantages of the direct current (DC) system. The most noteworthy advantage is that a cable can serve as a substitute for the overhead transmission line in residential areas; therefore, the HVDC system application is increasing, and as the number of DC systems in the power system increases, the interaction assessment regarding the HVDC system gains importance. An index named multi-infeed interaction factor (MIIF) is commonly used to estimate the interaction between power converters; however, the HVDC system is composed of two converters and a transmission line. The MIIF represents the interaction between the rectifiers and inverters, but not for the whole system. In this work, a method to assess the interaction of the whole system was therefore studied. To decide on the location of the new HVDC transmission system at the planning stage, in consideration of the interaction of the existing DC system, the line flow change distribution factor, according to the HVDC-transmission capacity change, was examined. Also, a power system transient -stability analysis was performed with different HVDC system locations, depending on the distribution factor. The simulation results indicate that when the factor is higher, two HVDC systems have a stronger interaction and are less stable in the transient state. Full article