Research On Modulation Strategy Of Dual-output Two-stage Matrix Converter

Since the 21st century,as an efficient converter,the two-stage matrix converter plays an important role in the field of power transformation.However,the two-stage matrix converter can only output a set of three-phase AC voltages.It will be limited in applications in some fields that require dual AC such as wind power generation systems,electric vehicles,and locomotive traction.To solve this problem,a dual output two-stage matrix converter(DOTSMC)based on a nine-switch inverter is proposed in this paper,its inverter stage can realize two groups of three-phase AC outputs with only nine switches.On the topology,because the dual output two-stage matrix converter cannot supply two groups of three-phase symmetrical voltages to two groups of three-phase unbalanced loads,the topology of the dual-output two-stage matrix converter is improved.A phase bridge arm is added in the inverter stage,which forms a four leg dual output two-stage matrix converter(FLDOTSMC)that can control the voltages of two groups of three-phase loads.At the same time,in order to avoid energy waste,the "supplement" idea is proposed,which can realize the output of symmetrical voltage under two groups of three-phase balanced load and two groups of three-phase unbalanced load respectively.In the modulation strategy,firstly,an space vector pulse width modulation strategy(SVPWM)strategy is proposed to modulate the dual output two-stage matrix converter,based on the theory of the above modulation strategy,combined with the carrier formula,a carrier-based pulse width modulation(CBPWM)strategy is proposed to modulate it.Based on this strategy,a modified CBPWM strategy is proposed,which assigns the action time of each inverter according to the proportional coefficient.It can adjust the output voltage range of the two inverters flexibly.Finally,the change of the neutral point voltages of two groups of three-phase loads under unbalanced loads are analyzed,and the expressions of the duty ratio function of the N-phase bridge arm are derived.Combining them with the carrier wave,the modulation wave formula of the N-phase bridge arm Is obtained,the CBPWM strategy of the four-bridge arm dual-output two-stage matrix converter is realized.This method not only avoids the calculation of trigonometric functions without the need for sector judgment,but also simplifies the calculation of three-dimensional space into a two-dimensional plane.It greatly avoids a large number of trigonometric function calculations and makes it easier to achieve modulation in practical applications.Finally,the proposed theory is verified by Matlab/Simulink.First,the SVPWM strategy under balanced load is verified,then the proposed CBPWM strategy under balanced load is simulated,and finally the CBPWM strategy under unbalanced load is verified.Through the above simulation,it can fully prove the scientificity of the proposed SVPWM strategy and CBPWM strategy.