Abstract
A method of rapidly demarcating the critical commutation failure (CF) region of a multi-infeed high-voltage direct-current (HVDC) system is proposed. Based on the nodal impedance matrix and nodal voltage interaction factor, for different AC fault conditions—both balanced and unbalanced—a method of calculating the extinction angles of converters in multi-infeed HVDC systems is deduced in detail. First, the extinction angles of convertor stations under single-phase, double-phase, and three-phase ground faults and line-to-line faults occurring at any bus in an AC system are calculated. The minimum extinction angle serves as a CF criterion. If the calculated extinction angle for a certain bus is smaller than the minimum extinction angle, then a fault at that bus will cause CF of the HVDC system and put that bus into a failed bus set. The critical failure impedance boundaries of the topology diagram can therefore be demarcated by examining every bus in the AC system. The validity and accuracy of the proposed index and the method were verified by calculation results based on the three-infeed HVDC system model of the IEEE 39-bus system. Finally, the critical failure impedance boundary was demarcated in the IEEE 118-bus system to demonstrate the application in a wider range of systems.
Highlights
In multi-infeed high-voltage direct-current (HVDC) systems, an AC system failure may cause commutation failure (CF) at the convertor station near a fault location or even CF of the multi-DC transmission lines at the same time or in succession [1,2,3]
A great deal of research and operational experience have proved that when there is a fault in the AC system, a decrease in the extinction angle of the inverter is the primary cause of CF of the converter valve group [5, 7,8,9]
If only AC system faults are considered, a converter bus (CB) voltage drop is the major cause of CF because the extinction angle is smaller than the inherent limit extinction angle of the valve
Summary
In multi-infeed high-voltage direct-current (HVDC) systems, an AC system failure may cause commutation failure (CF) at the convertor station near a fault location or even CF of the multi-DC transmission lines at the same time or in succession [1,2,3]. If only AC system faults are considered, a converter bus (CB) voltage drop is the major cause of CF because the extinction angle is smaller than the inherent limit extinction angle of the valve. At the moment of the AC fault, the inverter extinction angle decreases, along with a decline in the commutation voltage; CF occurs when the extinction angle becomes smaller than the critical extinction angle. Erefore, at the moment of the fault, the advance firing angle and ratio remain unchanged; the extinction angle decreases, along with a stepping down of the CB voltage. When an unbalanced fault occurs in an AC system, the voltage variation of the CB could lead to CF
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