Research On Input Current Harmonics Suppression Of Three-phase Half-Bridge Paralleled Rectifier At Dc-sided

The three-phase half-bridge paralleled rectifier,which presents the advantage of single forward voltage drop in the conduction path and lower conduction loss,is commonly used in low-voltage and high-current applications such as electrolysis,electroplating and electric heating,etc.However,the strong nonlinear nature of the rectifier and the commutation overlap produced by the rectifier result in serious harmonic pollution.Seeking a harmonic elimination method with low complexity and high efficiency under the premise of maintaining the original advantages of the three-phase half-bridge paralleled rectifier has become a necessity.Therefore,this paper will research the suppression technique of three-phase half-bridge paralleled rectifier at dc side according to the current relation between ac and dc side,including the new passive pulse multiplication harmonic suppression method,active harmonic elimination method based on the active inter-phase reactor,dc-side suppression ac side harmonic mechanism and rectification system design method.Since diodes are connected in series in the tapped inter-phase reactor,it is not suitable in the low-voltage and high-current fields.Thus,the Secondary-side Full-wave Rectification Inter-phase Reactor(SFRIR)is proposed to produce a novel passive pulse multiplication circuit.The order of the input current and the pulse number of the output voltage are multiplied due to the introduction of SFRIR,which significantly reduce the THD of the input current and the ripple of the output voltage.Through analyzing of the relationship between the output voltage of the rectifier circuit and the output voltage of SFRIR,the necessary condition of SFRIR multiplicative pulse number is provided.Moreover,according the current relationship between the ac side and dc side,the mathematical model between SFRIR turn ratio and the input current THD is established.According to the mathematical model,the optimum ratio of the passive pulse multiplication circuit is derived.Under the optimum ratio condition,the 6k ±1 order harmonic of the input current in double star rectifier or the 12 k ±1 order harmonic of the input current in four star rectifier is completely cancelled because of the SFRIR.However,only some of the characteristic harmonic in the input current can be cancelled by SFRIR.In order to suppress the characteristic harmonic completely,AIPR is introduced into the three-phase half-bridge paralleled rectifier.The type of circulating current which can eliminate current harmonics is analyzed and the waveform parameter is derived.The transfer function of circulating current between the ac side and dc side is built,and the mechanism that triangular circulating current suppress the ac side harmonics is discussed.Namely,when the circulate current generated by AIPR flows through the AC side,the amplitudes of harmonics produced by AIPR and the corresponding harmonics produced by the conventional rectifier are almost equal whereas the phases are opposite.As a result,most of the harmonics are suppressed in the input current.The improving effect of the triangle circulating current on the commutation process is analyzed,which not only significantly reduces the overlap commutation but also completely cancelled the output commutation voltage drop caused by the transformer leakage inductance.The effect of harmonic suppressing at dc side on magnetic device capacity is discussed,and the design method of rectifier with harmonic suppressing at dc side is presented.The output characteristics of rectifier unit is analyzed under the minimized input current harmonic conditions.It is shown that the output voltage and the output current of rectifier unit are both raised by SFRIR.Compared with SFRIR,AIPR will not change the output voltage of rectifier unit but increase the output current of the unit,hence both SFRIR and AIPR will increase capacity of magnetic components.The equivalent capacity of magnetic components(transformers,inter-phase reactor and inter-phase reactor with secondary-side windings)of three-phase half bridge parallel rectifiers with SFRIR or AIPR is analyzed.As a result,SFRIR and AIPR slightly increase the capacity of magnetic component compare with the conventional theme which provide a bright future in high power applications.The experimental prototype(three-phase half-bridge paralleled rectifier with SFRIR or AIPR),is set up to verify the harmonic suppression performance of the proposed theme.The current modulation effect of SFRIR on dc side and the pulse multiplication function of SFRIR is validated.The effect of the input voltage and load variation on harmonics suppression performance is analyzed for the three-phase half-bridge paralleled rectifier with SFRIR.According to the input characteristics of the circulation extracting circuit,the harmonic energy flowing direction in AIPR is presented,and the design and the operational principle of AIPR is provided.In addition,the improvement on the commutation process is verified,and the effect of input voltage and load variation on harmonic suppression performance of the system is studied by experiment.