Performance Evaluation of Direct Power Control and Model Predictive Control for Three-Level AC/DC Converters

This paper presents a comparative study of direct power control (DPC) and model predictive control (MPC) for three-level neutral-point-clamped (NPC) AC/DC converters. The operating principle of DPC and MPC are introduced in detail, with focus on vector selection mechanism and suppression of neutral point voltage fluctuation. Special care is given to the avoidance of high voltage jumps in both phase voltages and line voltages. A series of simulation and experimental tests are carried out to evaluate the performance of DPC and MPC in terms of steady state and dynamic performance, control complexity and robustness against load disturbance. The results show that both methods can achieve decoupled control of active power and reactive power, very quick dynamic response and sinusoidal grid currents. However, the MPC presents better stead state performance in terms of lower power ripples, less current harmonics, smaller dc-bus voltage oscillation and neutral-point potential fluctuation. Furthermore, the dynamic response of MPC is even quicker than that of DPC.