| With the continuous development of power electronics technology and semiconductor devices,Neutral Point Clamped(NPC)three-level inverters have gradually become the mainstream choice for high-voltage and high-power places due to their advantages of higher withstand voltage,smaller output harmonics,and more output vectors.However,the neutral point clamped structure will lead to the problem of unbalanced neutral point potential.Aiming at this problem,a model predictive current control scheme is studied in this thesis.At the same time,a parameter increment online compensation scheme is studied for the model prediction mismatch.Firstly,thesis analyzes the structure of permanent magnet synchronous motor,deduces its mathematical model in three coordinate systems,and studies the SVPWM control strategy of three-level inverter.Aiming at the problem of slow dynamic response and excessive overshoot of vector control,a single vector predictive current control scheme is adopted.The single vector model predictive current control only outputs one basic voltage vector in one switching cycle,resulting in large speed fluctuation and current ripple in the motor during steady-state operation.Aiming at the problems of poor dynamic and steady-state performance and low model applicability of single vector model predictive current control,the dual vector model predictive current control is studied and optimized,and the fast vector selection scheme is studied.Aiming at the problem of model mismatch in model predictive control,this thesis studies an online parameter identification method based on position sensorless,which solves the problem of system model mismatch in real time through parameter compensation.Aiming at the problem that the control leads to the reduction of parameter identification accuracy,the maximum torque current ratio control strategy is adopted.The environment of model mismatch is built in MATLAB / Simulink,and the effectiveness of the scheme is verified by designing different parameter mismatch models.The results show that the scheme can correct the system parameters by parameter compensation after the model mismatch occurs,which improves the reliability of the system.Aiming at the neutral point potential imbalance problem of NPC three-level inverter,the reason of neutral point potential imbalance is obtained by analyzing its topology,and a control scheme based on predictive current model is studied.A new partition scheme and vector selection table are designed to balance the neutral point potential and suppress the common mode voltage,and the effectiveness of the scheme is verified by simulation.Finally,through the design experiment,the dynamic performance and steady-state performance of various control algorithms during acceleration and loading are analyzed,and the effectiveness of the proposed scheme for balancing the midpoint potential is verified. |
