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Improved Model Predictive Control for Three-Level T-type Inverter under imbalanced Neutral Point Voltage Condition

The three-level T-type inverter 3LT2 I is widely adopted in photovoltaic (PV) systems. To improve separate maximum power point tracking (MPPT), the voltages of the top and bottom side capacitor are controlled to be unequal in PV modules. However, in terms of the deformation of space vector diagram, the current is distorted when applying the conventional model predictive control (CMPC) method. To overcome the limitation and mitigate current ripples under imbalanced neutral point (NP) voltage condition, an improved model predictive control (IMPC) based on asymmetric voltage vector diagram is proposed in this paper. Firstly, the imbalanced mechanism is analyzed in detail. Secondly, the imbalanced capacitor voltages are introduced to 3LT2 I model to generate the predictive output voltage. Finally, the current ripple is mitigated by penalizing the error produced in the cost function with IMPC. Moreover, the fast response has been obtained by the proposed method. To verify the practicability of the proposed method, the conventional and proposed method have been compared in simulation.