High Voltage Transfer Ratio Modulation And Low-frequency Harmonic Analysis Of Ultra Spare Matrix Converter

Matrix Converter?MC?received much attention in the process of the motor drive and new energy power generation due to their advantages like high power density and conversion efficiency.However,the MC always suffers the problems of low voltage transfer ratio,the high harmonic components in overmodulation mode and imperfect of the low-frequency harmonics analysis theory.To solve above problems,this paper are intensively studied.The maximum voltage vector trajectory under double active synthetic modulation of UMSC is derived,and the characteristics analyzed.Based on the above conclusion,the relationship among MLO-VTR of USMC,initial phase of output voltage,output/input frequency ratios and input power factor are established and calculating the limit value of MLO-VTR.The theoretical analysis results show that MLO-VTR for USMC can break 0.866 by changing the initial phase of the output voltage,which is an important complement to the MLO-VTR theory of MC.By analyzing the three limit voltage vectors under different space vector modulation methods in the inverter stage,a double mode space vector overmodulation strategy for USMC based on the maximum output voltage vector is proposed.The over-modulation mode I and mode II are re-divided,The overmodulation strategies in both modes are realized respectively by the linear superimposed principle of upper and lower.output vectors.The proposed overmodulation strategy not only obtains the reference output voltage accurately,at the same time also can extends VTR with a small harmonic distortion rate to 0.954 while the maximum VTR of USMC remains 1.By analyzing the two modulation methods in the rectifier and the three modulation methods in the inverters,a multi-mode space vector overmodulation strategy for USMC with improved VTR is proposed.The three modes are divied according limit current and limit voltage vectors.The proposed strategies are realized by using different modulation methods of the rectifier and inverter in each mode,respectively,which can not only reach the maximum VTR to 1.05,but also can achieve reduce the output voltage low frequency harmonic components less than 3%when the VTR of USMC is less than 1.Based on the structural characteristics of USMC,The low-frequency harmonics analysis method based on Double Fourier integral transform is proposed.The proposed harmonics analysis method analyzed the harmonic characteristics of output voltage and input current in overmodulation mode and linear mode.It is shown that the main low-frenquency harmonic frequencies of the output voltage in the overmodulation mode are 6z₂±1|f_out and|6z₁f_in±f_out|,the main low-frenquency harmonic frequencies of the input current in the overmodulation mode are|6z₁±1|f_inn and|6z₂f_out±f_in|.The prototype of USMC is built to investigate the maximum linear VTR under different working conditions and two proposed overmodulation strategies.The experiment results verified the effectiveness of the proposed strategies and correctness of theoretical analysis.