Research On Control Strategy Of Bidirectional Isolated AC-DC Matrix Converter

The bidirectional isolated AC-DC matrix converter has the advantages of bidirectional energy flow,electrical isolation of input and output,high power density,etc.It has huge application prospects in energy storage systems.However,due to its complex structure,large number of devices,and coupling of front and back circuits,its control is complicated,and it is difficult to meet the requirements of both the power grid and the load.In view of the above problems,this paper studies the working principle of the bidirectional isolated AC-DC matrix converter,and proposes two new coordinated control strategies.A back-stage single phase-shifting was first proposed.The front-stage 3-1 matrix conversion circuit uses a dual-voltage synthesis modulation strategy,and the back-stage full-bridge circuit uses single-phase shift control.In order to coordinate the front and rear stages,the output voltages of the two stages must be synchronized.This paper analyzes the corresponding relationship between the inductor current and the grid-side current under this control strategy,and the expression of the pulse width is obtained accordingly.The back-stage single phase-shifting control strategy can achieve unit power factor,and the converter has good input and output characteristics under this strategy,and its grid-side current harmonic content is low.Then,a front-stage single phase-shifting control strategy is proposed.The front-stage 3-1 matrix conversion circuit uses phase shift control.The back-stage full-bridge circuit adopts complementary control,and cooperates with the front-stage to adjust the pulse width to carry out segmented proportional proportional coordination control.This paper analyzes the corresponding relationship between the inductor current and the grid-side current under the front-stage single phase-shifting control strategy,and gives the calculation method of the pulse width.The front-stage single phase-shifting control strategy can also achieve better input and output characteristics.In order to obtain the applicable scope and characteristics of the two methods,this paper theoretically analyzes the change trend of the peak-to-peak value of the inductor current and the current stress of the two methods under different working conditions.In the simulation and experiment,by changing the working conditions,the change trend of the peak-to-peak value of the inductor current under different control methods and the working conditions corresponding to the peak-to-peak value of the minimum inductor current are obtained,and then the applicable scope of the two single-phase shift control strategies is obtained.Finally,simulation and experimental results show that these two control strategies can coordinate the front and back circuits,realize the bidirectional flow of energy,and ensure the quality of the grid-side current.The grid-side current is in the same phase as the grid voltage,and a stable DC-side voltage and current can be obtained.Therefore,the correctness and effectiveness of these two methods have been proved.