Model predictive direct voltage control strategy with hybrid cost function and loss observer for 3P-2L-VSC converter system

Abstract

3P-2L-VSC converter system suffers from complex control structure, cumbersome parameter design and slow system dynamic response under conventional double-loop scheme. In this paper, model predictive direct voltage control strategy with hybrid cost function and loss observer is designed to improve system performance and simplify system control structure. First, a model predictive direct voltage control strategy is proposed based on Euler discrete differential and integral method to enhance system dynamic response, which eliminates the cascaded intermediate link and achieves direct targets control. Second, a system power loss observer is designed based on Lyapunov function to improve prediction accuracy for FCS-MPC and system steady performance. Third, an improved hybrid cost function with targets and intermediate state is designed to track targets and reduce intermediate state fluctuation, which overcomes the lack of inner current loop. Finally, the advantages of the proposed strategy are verified in simulation and experiment, where the maximum RMSEs of steady state V_dc, i_q and i_d are 0.045, 0.81 and 0.58 at rated power respectively, and the recovery time of DC voltage is reduced by about 30 ms and 35 ms compared with PI-MPC when DC load and DC voltage change.