Research On Parallel Control Of High Frequency Link Matrix Three-phase Four-leg Inverter Under Unbalanced Condition

The parallel structure of high frequency link matrix three-phase four-leg inverter is composed of the high frequency inverter,high frequency transformer,back matrix converter of three-phase four-leg inverter and filter.This topology overcomes the disadvantages of the traditional inverter,such as high volume and noise,it has the advantages of electrical isolation and bidirectional flow of energy.The parallel structure of the high frequency link matrix three-phase four-leg inverter can not only expand the capacity of the system,but also can output three-phase balanced voltage under unbalanced conditions.Therefore,the parallel structure of the high frequency link matrix three-phase four-leg inverter has a good prospect.First of all,this paper makes a detailed summary of the research status of the high-frequency link matrix three-phase four-leg inverter and inverter in parallel,understand the research background of the subject,made a good bedding for the research.Secondly,in order to realize the modulation of the matrix converter,the decoupling analysis of the circuit is carried out from the topological structure,this paper introduces two kinds of modulation strategy of high frequency link matrix inverter which are de-re-couple modulation and integration modulation.The relationship between the high frequency link matrix three-phase four-leg inverter and the traditional model of the three-phase four-leg inverter is analyzed based on de-re-couple modulation,the mathematical model of high frequency link matrix three-phase four-leg inverter is analyzed,and the closed loop system is designed.Then,the control of a single high frequency link matrix three-phase four leg inverter is studied,based on the above analysis,the parallel of the high frequency link matrix three-phase four-leg inverter under unbalanced condition is studied.In order to make the positive sequence,negative sequence and zero sequence current of high frequency link matrix three-phase four-leg inverter distribute according to the parallel inverter capacity,this paper puts forward a new control method that the positive sequence current uses a droop control,negative sequence current and the fourth leg current use virtual impedance method respectively to control the positive sequence current,negative sequence current and zero sequence current distribution of the inverter output,and the front three leg and the fourth leg of high frequency link matrix the three-phase four-leg inverter separate control independently.Finally,the output voltage is balanced at the same time the output current and the output power of the parallel system are distributed according to the capacity of the parallel inverter under unbalanced conditions,and the circulation of the system is reduced.Finally,the software and hardware circuit are designed according to the theoretical analysis and simulation of parallel system.The experimental platform of the high frequency link matrix three-phase four leg inverter parallel system is set up,which adopts digital control method of DSP and CPLD cascade.The correctness and feasibility of the theoretical analysis and simulation are verified by experiments.