Tightly regulated power converters behave as constant power loads which may introduce instability in power systems. Prior to this work, the design-oriented stability criteria of DC and three-phase AC systems has been extensively studied, while the stability of single-phase AC power systems has received less attention. In this research, the modeling and stability analysis of single-phase AC power systems is studied. In particular, this research focuses on a system architecture where loads are connected in series and powered by a current source. Based on the proposed current source and load power electronic based topologies, which are typically used in airfield lighting systems, three types of system characterization are developed: waveform-level model, average-value <i>qd</i> model, and <i>qd</i> impedance/admittance measurement. Each approach has its own advantages and drawbacks, but the result - a frequency-domain (s-domain) representation of the system, is identical. Applying the generalized Nyquist stability criterion, the small-signal stability criteria of the system is developed. It is shown that the predictions of the system stability using these three approaches are consistent.