Power Losses Reduction of T-type Grid-Connected Converters Based on Tolerant Sequential Model Predictive Control

Three-level T-type converters (3LT2C) with LCL-filter have high power-quality of grid current particularly in low-voltage system. However, the switching loss and conduction loss degrade the overall efficiency of 3LT2C. The generated heat due to the losses endanger the reliability of the device and shorten its service life. To relieve the power losses as well as maintain high quality current output, a low-loss tolerant sequential model predictive control (LL-TSMPC) is proposed. First, based on the energy loss analysis under switching transitions per commutation, the prediction models of both switching loss and conduction loss are established. Second, the total loss reduction is considered as one control objective in LL-TSMPC. Finally, because multi-objective model predictive control requires selecting appropriate weighting factors, complicating the design to solve this problem, TSMPC based lexicographic optimization is introduced to eliminate the trade-off factors and simplify the MPC controller design. The proposed method is tested on the hardware platform with the rated power of 10-kW prototype. The experimental results show that the LL-TSMPC method can effectively reduce the switching losses while maintaining high power-quality of the grid current.