A Reduced <i>RLC</i> Impedance Model for Dynamic Stability Analysis of PI-Controller-Based DC Voltage Control of Generic Source-Load Two-Terminal DC Systems

Abstract

For the dynamic stability analysis of PI-controller-based dc voltage control of generic source-load two-terminal dc systems, a simpler <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RLC</i> parallel impedance model has been proposed. First, by ignoring fast inner current control, the output impedance model of the dc voltage control system can be represented as a parallel <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RLC</i> circuit, which gives an intuitive insight into the physical sense of parameters in the dc voltage PI controller. Then, a dynamic impedance ratio is introduced to represent the impact of dc voltage droop control and line impedance on the dc voltage control system. With this ratio, a generalized <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RLC</i> parallel impedance model appropriate for dynamic stability analysis of the considered dc system has been obtained. By simplifying the higher order dynamic impedance ratio model to a first-order high-pass filter in the dc voltage control timescale, a typical second-order model of the total impedance expression can be obtained, by which the dynamic stability of dc voltage control can be investigated in an analytical way. Furthermore, even including low dynamics of the inner current control of the dc voltage control unit and the constant power load (CPL)-side converter, the generic <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RLC</i> model can still be retained. It should be noted that the proposed <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RLC</i> model can be extended to more complex dc systems. Finally, power system computer aided design (PSCAD)/electromagnetic transients including dc (EMTDC)-based simulation verifications and a small-scale hardware-platform-based experimental validations have been provided.