The Model Predictive Control Research Of Three-phase Voltage Source PWM Rectifier

With the development of industrial technology,the requirements of power conversion technology are gradually improved,and the rectifier is gradually becoming more and more widely used in modern industry.Therefore,it is necessary to study the high-performance rectifier.Due to the VSR has the advantages of sinusoidal electric current,work under unit power factor easily,and lower voltage fluctuation in DC side,it can be very well qualified for the application demand of the existing industrial products.Therefore,increasing the control accuracy of the existing PWM rectifier,ensuring smaller switching losses and obtaining lower harmonic content have been continuously emphasized.The Model Predictive Control method is a technique which can improve the control accuracy,reduce the harmonic content,and has a significant effect on obtaining smaller voltage and current fluctuations.In this paper,a detailed and in-depth study was conducted for MPC by Three Voltage Vector.The Model Predictive Control is a control strategy which sampled at each control cycle,according to the obtained current measurement information,solve a finite time domain open loop optimization problem online,and the first element of the obtained control sequence is applied to the controlled object.At the next moment,repeat the above process:refresh the optimization with a new measurement and re-solve.From the predictive control content,it can be concluded that the predictive control can refract the online optimization problem into the PWM rectifier,which is obviously different from the traditional control,that is,the optimal switching sequence is solved online.We can find that the switching sequence obtained by the Model Predictive Control much better than the former in comparison with the previous SVPWM control.Therefore,it is theoretically proved that the predictive control can meet the more precise control requirements.Firstly,constructing the mathematical model for a VSR,and enumerating its voltage-current relationship,power relationship,and switching function relationship.Using active power and reactive power as a control target establish a predictive control structure,that is,collecting the AC side voltage and current information,using the instantaneous reactive power theory calculate the reference power as the basis for prediction,by using the rectifier mathematical model calculate the next moment predicted power,to construct the objective function of the difference between the reference power value and the predicted power value as the control target,calculate the objective function values under the action of all the switching sequences in sequence in the control cycle and compare them.Find the minimum objective function value and establish the corresponding switch sequence as the switch sequence output at the next time.Second,due to the earlier predictive control was to have only one set of switching sequences in each cycle,the control accuracy was poor.Therefore,based on the above-mentioned theoretical support,a three-vector predictive control is constructed to increase the number of switching actions in a single cycle and ensure that the predicted power is closer to a given power,that is,the three groups of switch sequences are divided into three steps in each predictive control period,and the combined effect is to obtain the predicted power at the next moment.It can be found that compared with the conventional SVPWM control,the predictive control improves the response speed,reduces the power and DC-side output voltage fluctuations,and reduces the harmonic content of the AC-side input current.But at the same time,because the three vectors predictive control has three sets of switching sequences in each cycle,the single sequence effect is not controlled during the period,and the calculation amount is too large,which will cause the calculation time and implementation control time to be unbalanced and weaken the effect.Finally,an improved three vector prediction algorithm is proposed.That is,optimizing the objective function firstly,split the three-step actions within a single cycle,optimally control each step to ensure that each set of switching sequences in a single cycle precisely reaches the optimum,and adjust the switching sequences within the cycle,has reduced the switching frequency effectively.At the same time,based on the above method built simulation in Matlab/Simulink to validate the feasibility of the control strategy.Also give out all the simulation structure figure and conclusion.Showing the feasibility of the control strategy.