A nonlinear control for a BTB STATCOM system with asymmetrically structured converters

This paper describes a new BTB STATCOM system with asymmetrically structured converters and develops its mathematical model. The BTB STATCOM employs a PWM technology for a rectifier station and a multipulse technology for an inverter station. We propose a control strategy for the following three control variables: active and reactive rectifier power and DC voltage. In the rectifier station, input-output linearization via the feedback control law is applied for independent control of the active and reactive power. Conversely, the input-output linearization controller is not applicable for maintaining the DC voltage. We design an alternative indirect damping controller for the reactive current within the inverter station. The proposed controller provides an improved stability margin and a decreased oscillation for DC voltage with a degraded reactive current tracking performance of the inverter. The effectiveness of the proposed controller is validated via the local stability at each operating point and the performance of the time response. Parameter-dependent Lyapunov functions for zero dynamics and the closed-loop system prove the stability of the damped internal dynamics and closed-loop system, respectively.