Modeling and stability analysis of a DC power system with solid state power controllers

A solid state power controller (SSPC) has become a popular element of a large-scale DC power system. An SSPC has a unique capability to limit short term overcurrent through the power device (MOSFET) operation in the active region. The device is controlled by a current feedback loop whose characteristics are shown to be strongly dependent on the SSPC load. The interaction between an SSPC control loop and a load converter can cause the instability, which was observed on the NASA Space Station hardware. The instability origin is revealed by the proposed small-signal SSPC model in the current limiting mode of operation. The MOSFET parasitic capacitances were demonstrated to play a crucial role in the influence of the load impedance on the SSPC dynamic behavior. Several design measures to decrease the SSPC loop sensitivity to the load are recommended. Small-signal analysis results are compared with the experimental data.