Research On Fixed Switching Frequency Method Of VIENNA Rectifier Based On Finite Control Set Model Predictive Control

With the development of power electronics technology,rectifier devices are widely used in industry,and a large number of harmonics are introduced into the power grid at the same time,therefore,the problem of controlling the harmonic pollution of the rectifier device to the power grid has attracted much attention in the field of power electronics technology.The three-phase three-level VIENNA rectifier is a kind of electric energy converter with simple topological structure,the voltage that the switch tube bears is only half of the DC bus voltage,high power factor,and low harmonic content.It has become a research hotspot of power electronic converter control technology.Firstly,this article analyzes the working modes of the VIENNA rectifier in different switching states,the mathematical models in various coordinate systems is established,and a mathematical foundation is used for the research of Finite Control Set Model Predictive Control(FCS-MPC)algorithm in this paper.Secondly,the FCS-MPC is applied to the VIENNA rectifier,the current prediction model is analyzed,and the objective function is established.According to the relationship between the charge and discharge of the upper and lower capacitors of output,the midpoint potential constraint item is introduced into the objective function.The feasibility of the FCS-MPC algorithm and the advantages and disadvantages of the algorithm is analyzed based on the simulation results.Aiming at the problem that the switching frequency of FCS-MPC algorithm is not fixed,the design of filter inductance is difficult,and the quality of input current depends on the size of filter inductance and the level of switching frequency,A method that fixed switching frequency based on Finite Control Set Model Predictive Control with Fixed Switching Frequency(FCS-MPC-FSF)is proposed in this paper.The method obtains the voltage vector minimized the target function as a limited set of optimal voltage vectors by FCS-MPC at first.in order to achieve system fixed switching frequency control,realize the predicted current value can track the given current value thought high-frequency control,so as to achieve deadbeat control,using the finite set of optimal voltage vector and the predicted current value calculation at the next moment The reference voltage vector that acts on the next switching cycle,the finite set of optimal voltage vectors is used as the main vector of the synthesized reference voltage,and two auxiliary voltage vectors are further determined by judging the interval of the reference voltage vector,so as to obtain the three basic voltage vectors required for the synthesized reference voltage vector at second.the Space Vector Pulse Width Modulation(SVPWM)algorithm is used to convert the three basic voltage vectors into corresponding switching signals to act on the rectifier to achieve fixed switching frequency control at final.The FCS-MPC-FSF algorithm combines the advantages of the FCS-MPC algorithm and the SVPWM algorithm,and the problem of switching frequency unfixation and filtering inductance design is solved and the harmonic distortion rate of the input current does not require high switching frequency is reduced by the FCS-MPC-FSF algorithm.The feasibility of the proposed method is proved based on the simulation results.Finally,a completely designing process of experimental parameters,hardware circuit and software program is present in this article.In order to enable 20kHz of the system’s switching frequency,the high-performance processor STM32G474 is used for digital power supply,and a experiment platform of the VIENNA rectifier of 200W with this as the core.the FCS-MPC algorithm and FSC-MPC-FSF algorithm is used in this perform,and the experimental design parameters and the feasibility of using control methods is verified based on experimental results.