Multi-Vector Based Model Predictive Control for Nested Neutral Point Piloted Converters With Constant Switching Frequency

Abstract

To solve the problem that the switching frequency is not fixed for five-level nested neutral point piloted (NNPP- 5L) converter with classical model predictive control (MPC), an optimized MPC using a multi-vector (MV)-MPC for an NNPP converter with constant switching frequency (CSF) is proposed. First, the mathematical model of NNPP-5L is established, and then a cost function without weighting factors is designed based on the optimized MPC to select the four optimal voltage vectors. Next, the duty time of the four optimal voltage vectors is calculated from the cost function, and the optimal switching sequence with a symmetric seven-segment pulse pattern is generated using a modulator to balance the voltage of capacitors. This strategy offers the advantage of a CSF and computation burden reduced while maintaining the dynamic response of the MPC for NNPP-5L converter. Finally, the effectiveness and feasibility of the proposed MV-MPC for NNPP-5L converter have been validated by simulation analysis and experiment results.