A sliding mode based direct power control of three-phase grid-connected multilevel inverter
This paper presents an approach to Direct Power Control (DPC) of a three-phase grid connected three level neutral-point clamped inverter. The presented approach can be extended to other topologies of multilevel inverters. The proposed DPC strategy is based on the Sliding Mode Control (SMC). The active and reactive power are directly controlled by three-level inverter switching states using the value of the delivered power error calculated from previous samples of three phase voltages and currents. An optimal control vector defined in dq reference frame minimizing the ripple is obtained using predicted values of three phase currents. An appropriate switching sequence is generated for each optimal vector using direct and indirect way. In the direct way the switching vector the nearest to the optimal control vector, and the direct way uses space vector modulation. The proposed strategy is robust to system parameters variations. The major advantage of proposed approach is its simple analog/digital control implementation. Moreover, PID controllers, look-up tables, and pulse-width modulators are not necessary. The designed control system is tested on a simulation model of a three-level neutral-point clamped multilevel inverter. Simulation results of a three-level neutral-point clamped multilevel inverter topology confirm the design aims.