A Three-Level Hysteresis Function Approach to the Sliding-Mode Control of Single-Phase UPS Inverters

A new approach to the sliding-mode control ofsingle-phase uninterruptible-power-supply inverters is introduced in continuous time. A three-level hysteresis sliding function is used to directly control the inverter switches, with the result that a transistor is switched during a half-cycle while it remains either on or off during the other cycle. An expression is derived for the predicted switching frequency. The performance of the proposed control method has been tested through computer simulations and experiments under different loads (a resistive load and a diode bridge rectifier load). Simulation and experimental results verify the correct operation of the proposed control strategy. In addition, the switching frequency prediction is seen to be quite accurate.