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Generalized Theory of Boundary Control for Single-phase Multilevel Inverter using Second-order Switching Surface

The concept and derivation of second-order switching surface in boundary control is extended to multilevel inverters in this paper. The second-order switching surface is set close to the trajectory that passing through the target operating point, which accelerates the trajectory moving towards the target operating point after a hypothesized switching action. Three topologies of single-phase multilevel inverters are investigated in this paper; they are full-bridge three-level diode-clamped inverter, cascaded five-level inverter and hybrid seven-level inverter. The second-order switching surface is derived in each voltage region, and the controller is verified with circuit simulations as well as low-power prototypes. The dynamic responses of the three inverters with different loads, including resistive load, inductive load and nonlinear load are examined. The simulation and experimental results show that the output voltage of the multilevel inverters using the proposed boundary controller can achieve a near optimal response to a large-signal load disturbance and an output reference voltage change.