Research On Control Strategy Of Parallel Interleaved Multilevel Converter

Parallel interleaved multilevel converter(PIMC)is a new high-power conversion topology developed on the basis of multi-converter parallel structure.PIMC realizes high-power electric energy conversion by increasing the current rating of the converter due to parallel multiple bridge arms,which is suitable for high-power applications where the voltage level is not high.This paper takes parallel interleaved multilevel converter as the research object,and its basic working principle,modulation strategy,leg current balancing strategy and grid-tie inverter control strategy are studied.The basic structure and circuit switching state of PIMC circuit with two-level half bridge leg in parallel are analyzed in depth,and the mathematical model of PIMC circuit is established.Two mathematical model is established for the PIMC using separate leg inductors and coupled leg inductors.By comparing and analyzing the multi-level basic modulation strategy and combining the characteristics of PIMC circuit,a single-carrier multi-level modulation algorithm is realized.The algorithm has the advantages of simple design,strong scalability,and less controller resources.According to the PIMC mathematical model,a leg current balancing control algorithm based on carrier phase-shift modulation is implemented,which has the advantage of not increasing the switching frequency.Aiming at the single-carrier multilevel modulation algorithm,a leg current sorting balancing method is proposed.However,this sorting balancing algorithm has the disadvantage of high switching frequency.Aiming at this problem,a current sorting balancing algorithm based on switching frequency optimization is proposed by analyzing the timing diagram of control.The algorithm limits the number of times the leg open during a switching cycle.Under the premise of retaining good current balancing results,the switching frequency of the leg is greatly reduced.This improves the efficiency of the system.A mathematical model of the grid-tie system is established for the three-phase parallel interleaved multilevel inverter.Dead-beat control is used in the current inner loop design?The method has the advantages of good control precision,no complicated parameter setting,and good output harmonic characteristics.Designed the power outer loop of the grid-tie inverter,the correctness and effectiveness of power-current double closed-loop control system of PIMC grid-tie inverter design are verified by simulation.Finally,the PIMC modulation strategy experiment,the leg current sorting balancing algorithm experiment,the switching frequency optimization leg sorting balancing experiment,and the grid-tie inverter control strategy experiment are completed.Finally,the experimental results were analyzed.