Research On Control Method Of Three Phase Three Level Reversible PWM Converter

Traditional power electronic rectifiers mainly use diode uncontrolled rectifier or thyristor phase controlled rectifier,these rectifiers make a lot of harmonic and reactive power injected into the power grid,resulting in the "pollution" of the power grid,which does not meet the environmental requirements of green energy conservation.In the field of motor control,frequency converter is the most widely used motor controller.Frequency converter usually has the structure of AC-DC-AC power conversion.The former stage uses the rectifier device to realize the rectification of the AC grid,but in the process of motor braking,the traditional rectifier device can not realize the reversible feedback of energy,so it will also cause a lot of power loss.PWM converter has the characteristics of high power factor,low harmonic distortion and reversible two-way flow of energy,which can effectively solve the problems of power grid "pollution" and energy loss.Therefore,in recent years,PWM converter has become a research hotspot in the field of motor control.In this paper,the reversible three-phase three-level PWM converter is studied.The main circuit topology of diode neutral point clamping is adopted.Through the relationship between switching function and DC output level,the mathematical model of PWM converter is established in three-phase static ABC coordinate system,and then the model is transformed into two-phase static α β coordinate system and synchronous rotating dq coordinate system The equivalent circuit model of corresponding coordinate system is established.In the synchronous rotating dq coordinate system,the traditional double closed-loop control method of PWM converter is studied.The current decoupling is used to realize the independent control of DQ axis equation.The design methods of current inner loop and voltage outer loop are analyzed,and the parameters of closed-loop controller are calculated.This paper studies the single fuzzy PI control method of PWM converter voltage outer loop.On this basis,aiming at the traditional single fuzzy PI controller can not adapt to the wide AC and wide DC voltage application conditions,this paper proposes a double fuzzy PI controller of voltage outer loop,takes the traditional single fuzzy PI controller of voltage outer loop as the main fuzzy controller,and a sub fuzzy controller based on AC side voltage variation and DC side given voltage variation is designed.The output of the sub fuzzy controller is a group of auxiliary correction of PI parameters in the outer voltage loop.The sub fuzzy controller and the main fuzzy controller constitute the double fuzzy controller.The final correction of PI controller parameters in voltage outer loop is the sum of the output of main fuzzy controller and the output of sub fuzzy controller.In this paper,the design method of double fuzzy controller is given.Through PSIM simulation software,the dynamic and static characteristics of traditional PI controller,traditional single fuzzy PI controller and double fuzzy PI controller in wide voltage range are compared and verified.The results show that the double fuzzy PI controller is used in PWM converter voltage outer loop under wide AC and DC voltage conditions It can obtain better dynamic and static performance.Aiming at the suppression of low-order current harmonics in AC side,this paper proposes a method of integration of harmonic detection and harmonic compensation based on resonant controller,gives the digital design method of discrete resonant controller,and calculates the coefficient of resonant controller under specific harmonic frequency.The parallel resonant controller structure is adopted.By extracting and compensating the 6th,12th and 18th harmonics in the fundamental rotating coordinate system,the low order harmonics 5th,7th,11th,13th,17th and 19th harmonics are compensated.The effectiveness of harmonic compensation is verified by PSIM simulation.When the grid voltage is unbalanced,the secondary harmonic of voltage will be generated in the DC side of the PWM converter.At the same time,the lower harmonics of the grid side current will become larger When the voltage is unbalanced seriously,the performance of the PWM converter will be affected.Therefore,this paper studies the compensation method of positive and negative sequence feedforward under unbalanced grid voltage.Through an all pass filter,the positive and negative sequence components of grid voltage are decomposed,and the feedforward of positive and negative sequence components of grid voltage is realized in forward channel.In this paper,the software design method of phase locking using positive sequence component of grid voltage and voltage feedforward is given,and the effectiveness of the positive and negative sequence feedforward strategy for the suppression of second harmonic of DC side voltage and low harmonic of AC side current is verified by PSIM simulationA prototype of reversible three-phase three-level NPC-I PWM converter is developed.The design and selection methods of main energy storage devices and power switching devices are given.According to the requirement of DC side reliability,the detection method of DC side insulation resistance of PWM converter is studied.Finally,the correctness of the PWM converter control method and design is verified by experiments.