Research On Five Level Inverter With Coupled Inductor And Its Control Strategy

With the increasingly serious energy problems,the global energy structure is constantly changing,In this context,the fields of new energy power generation,HVDC power transmission,distributed photovoltaic power generation and other fields have developed rapidly.Inverter,as a power conversion device,plays an important role in these fields.Traditional inverters are difficult to perform in high-voltage and high-power applications due to problems such as withstand voltage,while multi-level inverters are widely used due to their unique advantages in withstand voltage level and power quality.This paper takes five-level inverters with coupling inductance as the research object,and studies its control strategy and topology structure with the goal of improving control strategy,improving inverter performance and reducing inverter cost.Firstly,the five-level generation mechanism of the five-level inverter with coupled inductors is analyzed,and the specific working state is introduced.Then,the mathematical model in the two-phase static coordinate system is established,which lays the foundation for the analysis of the subsequent control strategy..Secondly,the problem of inductor current balance in this topology is pointed out,the harm of inductor current imbalance is analyzed,and requirements for subsequent control design are put forward.A traditional finite set model predictive control with inductor current balance is designed by using the basic principles of traditional finite set model predictive current control(FCS-MPC).Aiming at the shortcomings of the traditional model predictive control strategy,such as unstable switching frequency,large amount of calculation,and poor anti-interference performance of the outer loop PI,a sliding-mode model-predictive control(SMMPC)strategy was proposed.The outer loop of the composite control strategy uses sliding mode control instead of traditional PI control.The inner loop improves the traditional model prediction by introducing spatial vector modulation into the target function.The simulation results show that the composite control strategy has the advantages of fixed switch frequency,less computation,inductance current balance and strong disturbance resistance.Then,in order to simplify the control and structure of the single-phase five-level inverter with coupled inductance and reduce the cost of the inverter,a four-tube five-level inverter is proposed by replacing the power switch tube of the third bridge arm with a diode,and designed its control strategy,and completed the simulation verification.In addition,the single-phase inverter is extended to three-phase system,and its feasibility is verified by simulation.Finally,a hardware-in-the-loop simulation platform based on MicroLab is built to verify the effectiveness of the single-phase five-level inverter with coupled inductor and the control strategy proposed in this paper.Experiments and results are carried out for the inverter’s different control strategies,dynamic and static performance and other aspects.The experimental results show that the control strategy proposed in this paper is correct and effective.