Research On Current Source PWM Rectifier Control Technology

Current source PWM rectifier has the characteristics of small input-line current harmonic distortion,adjustable dc current and low buck chopper.It is widely used in superconducting magnetic energy storage,active power filter,power battery charger,induction heating and so on.With the development of superconducting magnetic energy storage,the efficiency problem of three-phase current PWM rectifier system could be solved,which makes that it has more competitive strength and influence in market application.In the paper,it has been researched the load driving characteristics of current source rectifier(CSR),constant dc current for current source rectifier under distorted and unbalanced conditions the harmonics,and circulating current restraining method control of multilevel current source rectifier(MCSR).The main innovatory points and contributions include the following aspects:First,this paper includes a comparative analysis of the power topology,the switching mode and system loss aspect on the traditional three-phase voltage PWM rectifier and three-phase current PWM rectifier.Researching on what current inner loops are used with proportional resonant(PR)control with voltage source rectifier(VSR)and CSR as the research object in this paper.Basing on outer loop control with dc voltage square of VSR,and deduce the improvement with dc current square of CSR.This paper analyzes two systems of the closed loop transfer function and mathematical forms.Functional relationship and change trend are studied in the optimal damping coefficient with nature surge frequency and loaded as well as regulator parameters of PI.Two systems are adaptive with the load with the optimal goal of steady and dynamic.What the selections are based on topology and methods is given in the design of system.This theory simplifys design flow,and shorten adjustment period.Second,according to dc current has larger low-order harmonics with current source PWM rectifier under distorted and unbalanced condition,traditional control strategy need complex separating positive and negative sequence components,rotating transition of coordinate and decoupling control.Constant dc current control strategy is put forward without PLL with Current Source PWM Rectifier in this paper.By using derived power outer-loop control with dc current square,constant dc current control substitute traditional PI control.In current inner-loop using proportion resonant and harmonic compensation realize grid current no error following.That control algorithms are based on the stationary frame simplify control without complex separating positive and negative sequence components,rotating transition of coordinate and decoupling control.Final,according to the larger low-order harmonics of input-line current on the MCSR that is based on LC filter,a method of virtual resistor in parallel with capacitor of improvement indirect current control is proposed.And determination method of virtual resistor is given.The improvement of the control of current indirect reduce system complexity and easily to achieve.Simulation shows this improvement algorithm feasibility.According to circulation phenomenon of dc side of the traditional MCSR,a method of current-balancing control of dc side is put forward.This strategy reduces circulating current effect of bridge legs.The simulation results verify the credibility of proposed method.