Fast terminal sliding mode control for single-phase UPS inverters

A fast terminal sliding mode control (FTSMC) for single-phase UPS inverters is introduced. The conventional terminal sliding mode control (TSMC) exhibits a faster convergence when the system state is close to the equilibrium and a slower convergence rate when it is far away from the equilibrium. The slow convergence rate can be avoided if a linear term is added to the sliding surface function which is referred to the FTSMC. An important consequence of this term is that the system state converges to equilibrium from anywhere in the phase-plane in finite time. The performance of the FTSMC method has been tested by computer simulations and experiments under triac-controlled resistive and diode bridge rectifier loads. The results of the proposed method are compared with a classical TSMC method. It is worth to note that the FTSMC method is capable of shortening the tracking and sliding times resulting in a smaller total harmonic distortion in the output voltage.