Research On Modulation Strategy Of Quasi-Z Source Indirect Matrix Converter

Indirect matrix converter(Indirect matrix converter,IMC)is a compact AC/AC converter without DC components.It has been widely concerned in the field of power conversion due to its superior performance.However,the voltage transfer ratio of traditional IMC is relatively low,the upper limit is only 0.866,which limits the high performance output and practical development of IMC.In order to solve this problem,the Quasi-Z source indirect matrix converter(Quasi-Z Source Indirect Matrix Converter,QZS-IMC)is obtained by introducing the Quasi-Z source network into the AC side of IMC.This kind of converter can not only enlarge the voltage transfer ratio range of the system,but also eliminate the need for additional filters on the input side.In this paper,QZS-IMC is taken as the research object,based on the way that the Quasi-Z source network is located on the AC side,the model of QZS-IMC is set up by using the state space average method.The later IMC outputs effectively in the non-shoot-through state,according to the instantaneous relationship of the output voltage of the Quasi-Z source network,the boost factor of the system and the angle shift between the output voltage of the network and the supply voltage are derived.A more comprehensive boost model is obtained to ensure that the later IMC can achieve accurate modulation,and the voltage transfer ratio of the system is given.Considering that the existence of inductors and capacitors in the Quasi-Z source network will lead to the phase angle discrepancy between the voltage and electrical flow at the grid side,and analyzing the case that the grid side is the unit power factor,it will reduce the reactive power demand of the system structure and improve the power quality.In order to make the IMC output a symmetrical three-phase sinusoidal AC voltage,a space vector pulse width modulation(Space Vector Pulse Width Modulation,SVPWM)strategy is adopted to modulate the QZS-IMC reasonably and accurately.Compared with the power supply voltage,the amplitude of the input voltage of the rectifier stage increases and the waveform has phase change.In the non-shoot-through state,the rectifier stage adopts the SVPWM strategy with zero vector,and the duty cycle formula in the non-shoot-through state is obtained.The inverter stage adopts the classical SVPWM strategy and coordinates with the rectifier to ensure zero current commutation at the rectifier stage.However,the modulation process of SVPWM strategy not only involves complex trigonometric function calculation,but also needs to judge the sectors of rectifier stage and inverter stage respectively.Therefore,a carrier pulse width modulation(Carried Based Pulse Width Modulation,CBPWM)strategy suitable for QZS-IMC is proposed.Substitute the formula obtained by the SVPWM strategy into the carrier formula to obtain two-stage modulation wave formulas.By optimizing and adjusting the order of zero vector and effective vector of inverter stage,the formula of modulating wave can be unified,and then the driving signal controlling each power switch can be obtained by numerical comparison between modulation wave and carrier wave and logical operation.This method can simplify SVPWM strategy to a great extent,and is more conducive to practical implementation.Finally,the model of QZS-IMC is set up by Matlab/Simulink to realize the modulation of QZS-IMC by the two strategies.The simulation consequences first confirm the correctness of the modeling process and formula derivation based on SVPWM strategy,and prove the effectiveness of CBPWM strategy for QZS-IMC,which provides a certain reference and basis for the practical research of QZS-IMC.