Strategy based on passivity theory for nonlinear control of STATCOM with cascaded H-bridges

Aiming at the poor transient stability of traditional linear control method for STATCOM in the conditions of high voltage and large power, a nonlinear control strategy based on the passivity theory is proposed for the STATCOM with cascaded H-bridges, which guarantees the Lyapunov function stability of the system. The mathematical model and operating principle of STATCOM system are analyzed, based on which, its Euler-Lagrange system model is built. In order to reduce the number of expected stable equilibrium points, the DC capacitor voltage of power unit is kept stable by controlling the active current on d-axis. The amount of damping injected into the system to accelerate the system energy dissipation for faster convergency is analyzed. In order to eliminate the influence of one-sampling-period delay, a discrete state observer is constructed to predict the reference current. Simulative and experimental results show that, the control strategy has better dynamic performance and robustness, effectively reducing the harmonic component of STATCOM output current.