Impedance-based stability analysis and design considerations for DC current distribution with long transmission cable

Stability is a major concern for dc distribution systems because the integrated system may become unstable even though the subsystems are stable individually. Significant analysis and design has been applied to dc voltage distribution systems, while stability and related control design are not well studied for dc current distribution systems, especially for the scenarios with long transmission cables. In this paper, impedance expressions for long transmission cables are derived and applied to analyze stability of power converters in dc current distribution systems. The relation between converter closed-loop and open-loop input impedance is discussed by taking a series resonant converter (SRC) with constant current input and regulated output current as an example. Impedance-based stability analysis and design considerations are proposed by employing the Nyquist plot of the system minor loop gain. The stability analysis and design presented are validated through experimental results based on a system with a 1 A current source, a 100 km cable emulator and a 500 W SRC.