Model predictive control strategy for NPC grid-connected inverters in unbalanced grids
A model predictive control (MPC) strategy for a three-phase three-level neutral point clamped (NPC) grid-connected inverter is discussed. Conventional two-level inverters are effective when a symmetric fault occurs. But when a three-phase unbalanced fault occurs, they will generate errors and introduce delay in the power system because of the complex design or the neglected negative-sequence component of the grid. To solve this problem, a new method to control a NPC grid-connected inverter is proposed, which combines an MPC strategy with a decoupling double synchronous reference frame phase-locked loop technique. The proposed method reduces the use of PI controllers and enhances the system's response speed. Using simulations and experiments, the proposed MPC strategy for a three-level NPC grid-connected inverter is proven to be accurate and reliable.