Dual-PWM Converter Control Strategy Research And The System Design

Beacause of traditional converter used diode or thyristor as the switching element,who,s uncontrollable or phased controllable,the hamonic current on line side was big and the power factor was low,cause the pollution to grid,and when the motor was working under the braking mode,the power couldn,t return to grid,wasted a lot of electrical energy.To aim at this situation,this paper propose dual-PWM(Pulse Width Modulation) converter.The dual-PWM converter adopt full-controllable element IGBT(Insulated Gate Bipolar Transistor) as the rectfier switching element,and PWM modulation is used,could make the current on line side similar to sine wave,and improve the power fact,make the energy bidirectional flow come true.At first,this paper resereach the topological structure,working modes of the dual-PWM converter,and compare it with the traditional converter,point out advantages of dual-PWM converter.Analyze it as rectifier part and inverter part accroding to topological structure,because the control strategy of inverter was very mature,the control strategy of rectifier is mainly resereached in this paper.The direct power control strategy of power inner loop and voltage outer loop is used in rectifier part,the mathmatic model of three-phase voltage rectifier under abc,αβand dq coordinates are analyzed at first,to aim at the disadvantages of traditional direct power control,such as switching frequency is not fixed and the switching frequency is high,this paper propose Space Vector Method(SVM),in order to improve such disadvantages brought by power loop and switching table; for the traditional direct power control had somemore disadvantages such as the harmonic current on line side was high,and the system was easy interrupted by voltage on line side, to aim at these disadvantages,virtual flux vector is used for directing rotating coordinates,this can eliminate those disadvantages,and lessen the sensors,make costs lower.For the inverter part,this paper adopt vector control based on rotor field orientation.At last,design the hard part and soft part of dual-PWM converter based on DSP, reach decoupling active power and reactive power,and finish system simulation,the simulation result prove that the choosen of PI parameters of voltage outer loop and power inner loop are reasonable,and the whole system is feasible.