Abstract
In the Korean power system, growing power loads have recently created the problems of voltage instability and fault current in the Seoul Capital Area (SCA). Accordingly, the back-to-back (BTB) voltage source converter (VSC) high-voltage direct-current (HVDC) system is emerging to resolve such problems with grid segmentation. However, non-convergence problems occur in this metropolitan area, due to the large change of power flow in some contingencies. Therefore, this paper proposes two kinds of AC transmission emulation control (ATEC) strategies to improve the metropolitan transient stability, and to resolve the non-convergence problem. The proposed ATEC strategies are able to mitigate possible overloading of adjacent AC transmission, and maintain power balance between metropolitan regions. The first ATEC strategy uses a monitoring system that permits the reverse power flow of AC transmission, and thus effectively improves the grid stability based on the power transfer equation. The second ATEC strategy emulates AC transmission with DC link capacitors in a permissible DC-link voltage range according to angle difference, and securely improves the gird stability, without requiring grid operator schedule decisions. This paper compares two kinds of ATEC schemes: it demonstrates the first ATEC strategy with specific fault scenario with PSS/E (Power Transmission System Planning Software), and evaluates the second ATEC strategy with internal controller performance with PSCAD/EMTDC (Power System Electromagnetic Transients Simulation Software).
Highlights
In Korea, the Korea Electric Power Corporation (KEPCO) is planning to install the back-to-back (BTB) voltage source converter (VSC)-high-voltage direct-current (HVDC) system in place of AC transmission in the metropolitan area of Seoul and its surrounding cities
VSC-HVDC control strategy is needed in the metropolitan area, and the proposed AC transmission emulation control (ATEC) strategies can help grid stabilization under various disturbances, prevent cascading outages, and counter power oscillations
The size of the DC capacitor is characterized by a capacitor time constant τ, and it can be expressed by the electrostatic energy E stored in DC capacitors, and the VSC converter rated power capability, SVSC, where N is the total number of capacitors in the VSC-HVDC system, and C is the capacitance of a DC capacitor [18]: τ=
Summary
In Korea, the Korea Electric Power Corporation (KEPCO) is planning to install the back-to-back (BTB) voltage source converter (VSC)-HVDC system in place of AC transmission in the metropolitan area of Seoul and its surrounding cities. To increase system flexibility, the use of a wide area measurement system (WAMS) method that collects voltage and current phasor information at geographically disperse locations is proposed [17]. These monitoring control schemes, which are for point-to-point HVDC systems, can effectively cope with disturbances such as power oscillations, and provide auxiliary control to the AC grid. A monitoring control scheme for a point-to-point HVDC system naturally generates a communication time delay between distant regions, and affects short-term control in a transient situation To resolve this problem, the grid operator should use a real-time synchronized communication device, such as a phasor measurement unit (PMU).
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