Hybrid Harmonic Reduction Methods At DC Link Of Parallel-Connected Multi-Pulse Rectifier

Multi-pulse rectifier is the interface of most high-power power electronic devices and AC grid,and is widely applied in practice.The common 12-pulse rectifier has the advantages of low complexity,high reliability,and high conversion efficiency.However,the harmonic reduction ability of 12-pulse rectifier is limited.In this paper,based on the parallel-connected multi-pulse rectifier,a single passive harmonic reduction method at DC link,a dual passive harmonic reduction method at DC link,a current harmonic direct injection method at DC link,and a hybrid harmonic reduction method at DC link are studied,which can effectively improve the harmonic reduction ability of parallel-connected multi-pulse rectifier.In order to improve the harmonic reduction ability of the rectifier and reduce the complexity of harmonic reduction circuit,a single passive harmonic reduction method at DC link is proposed.The working modes of single passive harmonic reduction circuit is analyzed.From the perspective of minimum THD of input current,the interphase reactor is optimized.And the influence of single passive harmonic reduction circuit on the capacity of magnetic devices is analyzed.The simulation and experimental results show that the single passive harmonic reduction method can double the pulse number of output voltage and the ladder number of input current at the same time,and reduce the harmonic content to half of the original.Therefore,this method effectively improves the power quality of parallel-connected multi-pulse rectifier.In order to further improve the power quality of 12-pulse rectifier and double star rectifier,a dual passive harmonic reduction method at DC link is proposed.The dual passive harmonic reduction circuit is composed of a two-tap converter and a single passive harmonic reduction circuit.The working modes of dual passive harmonic reduction circuit is analyzed.From the perspective of minimum THD of input current,the multi-winding interphase reactor is optimized.And the influence of dual passive harmonic reduction circuit on load voltage ripple and magnetic devices capacity is analyzed.The simulation and experimental results show that the pulse number of output voltage and the ladder number of input current both increase to three times the original after using the dual passive harmonic reduction method,and the harmonic content is reduced to one third of the original.In order to reduce the complexity of active harmonic reduction method,a current harmonic direct injection method at DC link is proposed.In this method,the circulating current generated by single-phase full-bridge inverter is directly injected into the input ends of interphase reactor,and no secondary winding is used.With the target of no harmonics in input current,the circulating current is quantitatively analyzed,and the influence of the circulating current on the capacity of magnetic devices is analyzed.The simulation and experimental results show that when this method is applied to a high current rectifier,the THD value of input current is reduced from 22.21% to 3.82%,and the harmonic reduction effect is remarkable.In order to reduce the low order and high order harmonics of input current and suppress the load voltage ripple,a hybrid harmonic reduction method at DC link is proposed.With the multi-winding active tap reactor as the medium,this method combines the tap converter and the single-phase full-bridge inverter.From the perspective of minimum THD of input current,the multi-winding active tap reactor is optimized.With the target of no harmonics in input current,the compensating current generated by single-phase full-bridge inverter is analyzed.And the circuit parameters of main circuit and control circuit of the rectifier is designed.The simulation and experimental results show that when this method is applied to a double star rectifier,the load voltage is 12 pulse,the ripple is reduced,the input current is approximately sinusoidal,and the THD value is reduced to less than 5%.