Research On Bidirectional AC/DC Matrix Converter

In power system, energy storage system can effectively solve the problem ofimbalance between the renewable power system and power load supply, bidirectionalconverter is indispensable. With the advantage of high power density, adjustable inputpower factor, small current harmonic components, no need of bulky DC component, MatrixAC/DC converter satisfy the demand of energy storage system. Commutation strategy isone of the key technologies for matrix converter. In this paper, the mainly research is basedon matrix AC/DC converter, through the analysis of influence to converter’s output voltagein different current commutation method, choose appropriate commutation method andcontrol strategies to get better system performance.According to the basic theory of matrix converter, this paper introduces the switchingfunction and current space vector modulation. Different switching sequences because ofdistribution of Zero Vectors are concluded. And then investigate the design method of inputfilter, output filter and clamp circuit. By the simulation model established inMatlab/Simulink, the basic function of Matrix AC/DC converter is simulated.Current four-step commutation method is a regular strategy. After the analysis ofnarrow pulse, different distribution of Zero Vector can decrease the appearance of narrowpulse in some degree. In the whole range of voltage modulation ratio we could get goodperformance through the proper use of single Zero Vector, two Zero Vector and three ZeroVector. Because of the time delay of four step commutation, output voltage will increase. Ineach PWM period, through modifying the voltage modulation index, output voltage qualityin low modulation index condition is improved.The optimized current commutation method is investigated, including two-stepcommutation and one-step commutation. The problem in current setup and state switchingof converter is solved, through the combination of current order and value of output currentto decide the current direction. Based on the Analysis of two-step commutation, it figuresout that the influence to output voltage is corresponding with four-step commutation. Inone-step commutation which is directed by input voltage and output current, two-step commutation is utilized to realize the commutation between input phases with clear relativevoltage, and the problem of current distortion in critical intervals is solved.Based on experimental prototype of matrix AC/DC converter, Research includingthree current commutation methods and performance test of converter with battery load arecarried out. The correctness of theoretical analysis is proved by experimental results.