A Direct Power Controlled and Series Compensated EHV Transmission Line

This paper presents the design and analysis of a compensation method with application to a 345 kV 480 MVA three-phase transmission line. The compensator system includes a series injected voltage source converter that minimizes the resonance effects of capacitor line reactance. This creates an ability to compensate for the effects of subsynchronous resonance and thereby increase line loadability and control real and reactive power flows. The granularity of power flow control and simultaneous stabilization is achieved by the method of direct decoupled power control (DPC). The design process is detailed with respect to optimal response characteristics considering variations of line parameters, realistic transformer impedances, and maximum ramp response rates. Line effects are demonstrated in a PLECS model in MATLAB, and compensation control system functionality is verified. A case study is provided of a 345 kV transmission line from an EMTP simulation in PSCAD that accounts for distributed parameter effects that are encountered in physical EHV transmission lines. This demonstrates the improvement in stability to power system transients as well as damping of power system oscillations.