Research On High Power Density And Large Current Rectifier Using Autotransformer

Large current rectifiers are widely used in metal smelting,electrowinning,ship propulsion system and other industrial fields.Large current rectifiers also play an important role in the development of social economy,and become popular for researchers.The performance indicators for the large current rectifiers contain power density,energy conversion efficiency,power quality of AC and DC side.Therefore,a novel large current rectifier using autotransformer and two parallel-connected three-phase half-wave rectifiers is proposed,and the aforementioned performance indicators are taken into consideration for the proposed rectifier.In order to improve the power density and cut down the weight of large current rectifier,an optimal design method for phase-shift transformer is proposed.For the goal of reducing output voltage ripple,the phase shifting angle of autotransformer is obtained.By using position coefficients,the phasor diagram of autotransformer is analyzed and the winding configurations under different position coefficients are obtained.From the voltages across and currents through the windings of autotransformer,the relationship between kilovoltampere(kVA)rating of autotransformer and position coefficient k1 is obtained.From the relation curve between kVA rating and position coefficient k1,the minimal kVA rating of autotransformer is 95.03% and there are only three windings in a core limb when k1 is equal to zero.In order to analyze the effect of disturbance on the input current and load voltage of large current rectifiers,a new frequency domain model using double Fourier series method is proposed.The switching function contains disturbance is obtained by double Fourier analysis when the input voltage contains positive sequence disturbance or negative sequence disturbance.Then the frequency domain model is obtained from the model of switching function.The theoretical and simulation results show that,comparing with traditional switching function,the switching function which considers disturbance can describe the real state of rectification devices accurately,and it can be used to analyze the effect of disturbance on the input current and output voltage ripple of large current rectifiers.In order to reduce the volume of the rectification system,an optimal design method for the inductance of inter-phase reactor(IPR)is proposed.From the field current through the IPR,the minimal inductance which can make circuit work is obtained.On this foundation,the relation curve between total harmonic distortion(THD)value of input current and inductance of IPR is obtained by Simulink.Then the critical inductance is obtained which can result in the minimal THD value of input current.From the simulation results,the proposed method can improve the power quality of large current rectifier and reduce the inductance of IPR.In order to suppress the harmonic of input current,a method for harmonic elimination of DC side using active IPR is proposed.With the help of switching function,the input current and load voltage are analyzed.Then the circulating current is derived when the input currents are sinusoidal.A full-bridge PWM rectifier,connected with IPR,is used to extract the harmonic energy and feedback the harmonic energy to the load.As the experimental results show,the THD value of rectification system is decreased from 27.01% to 3.73%,so the rectification system has good performance in harmonic suppression.