| The integrated charger uses the hardware of electric vehicle motor drive system to realize charging,which is expected to solve the two problems of slow charging speed and hard to find at the same time.Z-source converter is widely used in motor drive because of its fewer active devices and higher reliability.In order to realize integrated charging,it is necessary to study Z-source rectifier.The integrated charging system reuses the hardware of the electric drive system,and the main circuit hardware is not designed according to the charging function.The charging mode is not the optimal efficiency,so it is necessary to improve the efficiency.The research object of this paper is a three-phase quasi-z-source rectifier which works under the condition of discontinuous inductance current to achieve soft switching.In order to make the three-phase soft switching quasi-z-source rectifier operate under a certain working condition,the model is reasonably simplified,and the mathematical model is established by using the switching average method.The average model explains the factors that determine the output voltage,which provides the basis for the regulation of the output voltage.The small signal model describes the dynamic characteristics of the system at a certain working point,which provides a theoretical basis for the design of the control system.Then the accuracy of the small signal model is verified by software frequency sweep and step response.Finally,PI parameters are adjusted based on the small signal model to realize the double closedloop control of grid side current and voltage and the closed-loop control of DC side voltage.The soft switch operation of the system is studied.Firstly,the operating mode of the system is analyzed,and the conditions of forming soft switch are obtained.On this basis,a new modulation method is proposed to make the system still form soft switch at the sector boundary.Finally,a method to select the inductance value of quasi-z-source network is proposed.The suitable inductance value can be found through equality and inequality constraints,which can predict the variation range of output resistance forming soft switch.Based on the average model of the system and the operating conditions of the soft switch,a constant current and voltage control strategy is proposed,which can maintain the soft switch by changing the system parameters when the output resistance changes.In order to meet the thd requirements of grid side current,the composite control method of proportional repetitive control is used to suppress the low order harmonics,and the carrier phase shifting method is used to suppress the high order harmonics based on the segmented three-phase motor.Based on the parallel carrier phase-shifting method of three quasi-z-source networks,a method of eliminating one or two quasi-z-source networks is proposed to realize the inductance grading adjustment of quasi-z-source networks,so as to expand the output resistance range of soft switching.Finally,the theory and method are verified according to the sequence of model in the loop test,software in the loop test,hardware in the loop test and experiment.Through the experiment,it is found that there are voltage spikes on the grid side.Then,according to the causes of voltage spikes,some kinds of voltage spikes are classified,and the suppression schemes are proposed to improve the efficiency of the system. |
