| Parallel-connected full bridge multipulse rectifier(MPR)system has the advantages of high reliability,high durability and strong overload capacity,and is widely used in high-power occasions.However,due to the nonlinearity of rectification devices and the commutation overlap,the current harmonics and voltage notch will lead to serious power harmonic pollution.Using passive or active methods,effective harmonic reduction can be carried out from the DC side,and has a stronger targeting effect.However,passive harmonic reduction methods can not eliminate high order harmonics,and the conversion capacity of active harmonic methods is still larger.Therefore,for the parallel-connected full bridge MPR based on the interphase rector at DC side,this paper carries out the research on the uncontrolled passive,controllable passive,active converting and their hybrid harmonic reduction methods and rectification system design methods,in order to improve the harmonic reduction ability of the rectification system under the condition of local limited grid capacity.In order to select a more reasonable hybrid harmonic reduction circuit configuration and implementation method,passive and active harmonic reduction mechanism at DC side of parallel-connected full bridge MPR is studied firstly.For the unconventional interphase reactor(UIPR)with double-tapped,secondary wingding rectification and secondary winding current injection respectively,according to the corresponding relationship between the input current at AC side and the modulation current of the auxiliary circuit at DC side,the necessary conditions and operation modes of the passive and active harmonic reduction circuits are studied.Mathematical models between the parameters of harmonic suppression circuit and the input current at AC side are established.The variation laws of input current and output load voltage under different harmonic reduction methods are analyzed.The above research contents lay a foundation for the subsequent research on hybrid harmonic reduction methods.Based on the analysis of passive harmonic reduction mechanism,a dual passive harmonic reduction method at DC side is proposed,which increases the step number of input current and pulse number of output voltage of rectifier to 36.The harmonic reduction method of conventional TIPR is compared and analyzed.The working conditions and modes of dual passive harmonic reduction circuit are studied.From the two perspectives of the minimum the total harmonic distortion(THD)value of the input current and the minimum ripple coefficient of the output load voltage,the optimal parameters of dual passive harmonic reduction circuit are deduced.The input current and output voltage characteristics of both 36-pulse rectifiers are analyzed.In addition,the conduction loss and the kilovoltampere(KVA)rating of magnetic element in harmonic reduction circuit are studied.Through simulation and experiment,the harmonic reduction effects of both 36-pulse rectifiers under optimal conditions,load changes and input voltage fluctuations are compared.This method can reduce the complexity of harmonic reduction circuit and realize that the harmonic of input current is close to IEEE-519 harmonic standard.In order to simultaneously increase the input current step number and output load voltage pulse number of MPR to 48,and further improve the current harmonic reduction ability,a controllable hybrid harmonic reduction method at DC side based on unconventional triple-tapped interphase reactor(UTIPR)is proposed.Firstly,the topology of the traditional triple-tapped IPR with switching device is changed,and the working conditions and modes of the controllable hybrid harmonic reduction circuit are studied.Secondly,according to the premise that the step number of input current and the pulse number of output voltage are 48,the optimal conduction sequence of the switch devices is determined.Thirdly,the parameters of controllable hybrid harmonic circuit are optimally designed from the perspective of the minimum THD of the input line current.Furthermore,the input current and output voltage characteristics of the 48-pulse rectifier using this method are analyzed,and the KVA ratings of magnetic elements are calculated.Finally,the harmonic reduction effect of the 48-pulse rectifier is experimentally studied when the load changes and the input voltage fluctuate.Under the condition of optimal parameters,the input current of the 48-pulse rectifier is approximately sine wave,which meets the IEEE-519 harmonic standard.The dual passive and controllable hybrid harmonic reduction methods at DC side can only suppress some characteristic harmonics.In order to suppress the high order harmonics of MPR and reduce the output voltage ripple simultaneously,a hybrid harmonic reduction method at DC side based on current injection technology is proposed.The structure of the hybrid harmonic reduction circuit is determined by studying the modulation current matching strategy.The primary winding of UIPR is connected to DIPR,and the secondary winding is connected to the single-phase bridge PWM rectifier.Based on the output load voltage ripple,KVA rating of active auxiliary circuit and input current THD value,the optimal parameters of UIPR are derived to optimize the design of active injection current waveform.The main circuit and control circuit parameters of single-phase bridge PWM rectifier are designed.The influence of the height and width of the active injection current waveform on the harmonic reduction effect of the MPR is studied experimentally,which verified the correctness of the proposed method.Compared with the active harmonic reduction method,the KVA of active auxiliary circuit is reduced.Compared with the passive harmonic reduction method,the proposed method can effectively suppress the high order harmonics of input current and improve the harmonic reduction ability.According to the actual current harmonic reduction effect on the AC side of the parallel-connected full bridge MPR,the hybrid harmonic reduction methods at DC side provide a variety of solutions for applications that meet different harmonic requirements. |
PDF Full Text Request