Research On Predictive Direct Power Control Strategy Of Three-Phase PWM Rectifier Based On New Grid Voltage Sensorless

Three phase pulse width modulation(PWM)rectifier is widely used in active power filter,renewable energy grid connected power generation,high voltage DC transmission and other industrial fields because of its advantages of sinusoidal current,high power factor,bidirectional energy flow and adjustable DC voltage.Taking the three-phase two-level voltage source PWM rectifier as the research object,this thesis makes an in-depth study on new grid voltage sensorless predictive direct power control(PDPC)strategy.Firstly,the working principle and coordinate transformation relationship of three-phase PWM rectifier are introduced,and the mathematical model based on power control method is established.Aiming at the problems of complex grid voltage sensor sampling process and high additional cost,based on the analysis of the principles of improved second-order generalized integrator(SOGI)and third-order generalized integrator(TOGI),two grid voltage estimation methods that can be applied to three-phase PWM rectifier are proposed,that is,a new grid voltage sensorless algorithm based on improved SOGI and TOGI.Secondly,the traditional PDPC model in coordinate system is introduced,and aiming at the steady-state error of traditional PDPC strategy,the compensation correction method based on internal model principle is introduced to optimize the strategy.Then,the mathematical model based on instantaneous power theory in the case of unbalanced grid voltage is analyzed,and it is clear that the traditional PDPC strategy has the problems of double frequency power fluctuation and high input current harmonic under the situation of unbalanced grid voltage.With the help of extended pq theory,a new grid voltage sensorless PDPC strategy suitable for the case of unbalanced grid voltage is proposed.Finally,MATLAB/Simulink simulation platform is used to verify the feasibility and correctness of the proposed method.The method proposed in this thesis adopts improved SOGI and TOGI respectively,which can directly estimate the grid voltage,avoid the calculation of virtual flux linkage,and is simple to implement.In addition,compared with the instantaneous power theory,the model established by using the extended pq theory does not need the following issues such as the grid voltage phase detection,rotating coordinate transformation and positive and negative sequence extraction of grid voltage and current,which greatly simplifies the control structure.The simulation results show that compared with the traditional PDPC strategy,the proposed method can make the input current in the three-phase PWM rectifier close to the sine wave whether grid voltage is in balance or not,the actual value of instantaneous power changes with the reference value without error,and eliminates the double frequency power fluctuation.