An auto-disturbance rejection controller for STATCOM based on cascaded multilevel inverters

The static synchronous compensator (STATCOM) is a flexible ac transmission system(FACTS) device which can be used to generate reactive power in long distance ac power transmission. Cascade multilevel STATCOM is a so strongly coupled and nonlinear system that conventional linear control cannot assure a satisfactory behavior. In order to achieve high dynamic performance and robustness of control system, a new control strategy for cascade multilevel STATCOM is presented by using auto-disturbance rejection controller (ADRC). ADRC is a kind of nonlinear robust control techniques, which is independent of the model of the controlled object. Extended states observer (ESO) in ADRC can provide the estimate of the real action of the system internal (including the unmeasured and coupled state) and external unknown disturbances, as well as compensates the action. Then the active and reactive current can be controlled with decoupled auto-disturbance rejection controllers. The simulation and experimental results show that ADRC scheme has outstanding robustness and adaptability against modeling uncertainties and external disturbances, and produces good dynamic performance.