The description, steady-state analysis, and control design of a microcontroller-based large-scale pulse-width modulated solid-state synchronous condenser (PWM-SSSC) for reactive power compensation is presented. The key feature of the proposed compensator is the low switching frequency of the PWM pattern, which allows the utilization of high-power GTO thyristors. The PWM-SSSC has the additional advantage that large passive magnetic components are substituted with silicon. Closed-loop operation of a high-power PWM-SSSC (having a poor inherent damping) with a PI controller is investigated. Cumbersome z-domain methods for pulse stability analysis are completely avoided by using direct s-domain computations. A systematic approach for tuning the controller parameters is introduced by extending the concept of absolute stability. Selected predicted results are experimentally verified on a scaled-down laboratory prototype. >