Research On Unified Control Strategy Of T-type Three-level Grid-connected Inverter Based On Finite Set Model Predictive Control

Distributed power sources in microgrids are affected by objective factors such as wind power,day and night alternation,the grid connected inverter is often in idle state,which limits the utilization rate of microgrid-connected equipment.in addition,its impact on grid power quality is becoming increasingly prominent.For this reason,a unified control strategy for power grid connection and power quality management of microgrid-connected inverters is studied,and the control functions of the two are combined to enable the system to achieve power grid connection without changing the main circuit topology.And dual functions of power quality management,effectively improving system equipment utilization.In this thesis,a T-type three-level grid-connected inverter is used as the research object.Finite Control Set Model Predictive Control(FCS-MPC)is adopted without the need of Space Vector Pulse Width Modulation(SVPWM)for its current control,the following studies have been carried out:(1)Based on the topology of the T-type three-level grid-connected inverter,its mathematical model in the two-phase stationary coordinate system(??)is derived.Combined with the FCS-MPC design idea of power electronic converter,the design method of the predictive controller for T-type three-level grid-connected inverter finite set model is given.The cost function is designed to comprehensively evaluate the three key performance indicators of reference current tracking error,DC-point midpoint balance,and switching loss.Based on the priority difference of the performance indicators,an analytic hierarchy process(AHP)is used to find the replacement price function weight factor.Finally,two-step predictive control is used to compensate for the delay of this control strategy.(2)Aiming at the shortcomings of too many prediction times and rolling optimization times in the three-level T-type grid-connected inverter FCS-MPC application,referring to the idea of deadbeat predictive control,an improved FCS-MPC with fast vector selection The control strategy reduces the number of predictions and rolling optimizations from 27 times of traditional FCS-MPC to 10-7 times,greatly reducing the amount of calculations,and establishes a photovoltaic grid-connected model in MATLAB/Simulink.The feasibility of the improved FCS-MPC was verified.(3)Based on the FCS-MPC current tracking control,PQ control is used to realize decoupling of active power and reactive power,and an improved current detection method based on CPT theory is used for power quality management current detection.A unified control strategy of power grid connection and power quality management of grid-connected inverter is proposed,which has three working modes: full power grid connection mode,full power quality management mode and unified work mode of power grid connection and power quality management,and a method of optimal power quality management based on the residual capacity of grid connected inverter is proposed.Finally,in Matlab / Simulink,the unified control strategy of power grid connection and power quality management of grid connected inverter is simulated and verified.