Research On Modulation Strategy And Control Of Single-Stage High Frequency Link Inverter

High-frequency-link inverters are widely used in photovoltaic and other new energy gridconnected occasions.Among them,the cycle-conversion high-frequency link inverter has the advantages of single-stage power conversion,two-way energy flow,electrical isolation,etc,but there are safety commutation problems that affect the cycle converter Reliability.How to use a suitable modulation strategy to solve the commutation problem is a guarantee for the stable operation of the inverter and the improvement of power quality.Based on the above problems,this paper proposes a new switching modulation strategy,which can realize the soft switching of the power switch tube and the soft commutation of the output filter inductance and the leakage inductance of the transformer.The main research contents are as follows:Firstly,the modulation strategy of the single-stage high-frequency link inverter is studied,and a new type of modulation strategy is proposed for the problem of inductor current commutation.Under the new modulation strategy,the working mode of the circuit in a switching cycle is deeply analyzed.Through the circuit modal analysis,the leakage inductance current of the transformer between the converters naturally drops to zero,and the secondary switch tube ZCS is turned off,thus realizing the safe soft commutation of the cycloconverter.By simplifying the working mode under the new modulation strategy,the equivalent model and external characteristics of the circuit are obtained,and the realization conditions of the soft switching and soft commutation principle of the circuit are analyzed.Secondly,through the principle analysis of the high-frequency chain of the single-stage high-frequency-link inverter,the mathematical models of the front-stage full-bridge converter and the subsequent-stage cycloconverter are established.The Fourier series expansion of the output voltage proves the correctness of the high-frequency link transmission theory under the new modulation strategy.Then,each chain of the single-stage high-frequency link inverter system is equivalent,and the small signal model of the system is established by the state space averaging method,and the open-loop transfer function of the system is obtained.Through the analysis of the open-loop characteristics of the system,the dual closed-loop controllers of single voltage loop and current inner loop and voltage outer loop are compared,and the controller parameters are designed,and the superiority of the dual-loop controller is verified through simulation.Finally,the hardware and software of the circuit are designed,and an experimental prototype of a 600W single-stage high-frequency link inverter is developed.Aiming at the above research content,the correctness of the proposed modulation strategy is verified through experiments.