Research On The Control Strategy Of Multilevel Current Source PWM Rectifier

The current source multi-level PWM rectifier has the advantages of high output power,low switching frequency,low grid current harmonics,and DC voltage lower than the grid voltage peak,the contradictory relationship between the power level and switch frequency of the power electronics is solved,which has unique advantages in high-power occasions such as electric vehicle charging piles,induction heating,etc.In addition,with the continuous development of superconducting energy storage technology in recent years,the issue of inductive energy storage has been solved,so current source multilevel PWM rectifiers have broad application prospects.Combining the above advantages,a three-phase current source five-level PWM rectifier is mainly discussed and analyzed in this thesis.The main research contents of this thesis are as follows,Firstly,the topology and working principle of the three-phase current source five-level PWM rectifier are analyzed,the mathematical model and the principle of space vector modulation(SVPWM)based on the 60 ° coordinate system are deeply studied.Aiming at the problem of average current inductor current imbalance,a method to distribute reasonably the action time and switching sequence of the redundant switch combination is proposed to ensure the DC current balance of each rectifier unit.Then,in view of the dynamic performance and robustness of the three-phase current source five-level PWM rectifier control system and the resonance spikes of the grid side LC filter,the control strategy is studied deeply.The method that current inner loop adopts the combination of predictive current control and active damping is proposed,and the DC power square adjustable power factor is adopted for the outer loop.The active damping can suppress the current distortion and oscillation by LC filter without generating additional power losses,and the grid-side current distortion is suppressed effectively.The dynamic response speed and stability are improved significantly.The control algorithm proposed in this thesis is compared with the traditional PI double closed-loop by Matlab/Simulink which verifies the excellent control effect of the composite control.Finally,a PC/104 industrial control board and FPGA are used to build a three-phase current sourece five-level PWM rectifier experimental platform.The communication between the PC/104 industrial control board and the peripheral chip and the experimental hardware circuit design are completed.The IGBT drive signal is generated by FPGA hardware program.The correctness of the modulation strategy and the superiority of the control strategy are verified.